Archive for the ‘MECHANICS’ category

Bearing Numbers Explained

September 21, 2012

  • (1) Prefix :
  • (2) Basic Number:
  • (3) Suffix

Prefix

K Cage with roller elements
L Removable bearing ring
R Ring with roller set
S Roll body of stainless steel
W Stainless steel deep groove ball bearing

*Note: Each bearing company may create their own prefixes. e.g. E2. = SKF Energy Efficient bearings

Suffix

2 RS Bearing with rubber seal on both sides. RS provides a better seal but more rolling friction than 2Z.
RS Bearing with rubber seal on one side, one side open.
2 Z / ZZ Bearing with a metal seal on both sides.
Z Bearing with a metal seal on one side, one side open.
E Reinforced Design
P2 Highest precision
K Bearing with taper bore

Bearing Numbers

The example at the header shows a 6001 2RS bearing. So what does the 6001 actually mean?
Lets attempt to break it down.

(6)001

This second number relates the bearing series, which reflects the robustness of the bearing. As you go up the scale below from 9 to 4 the inner and outer race thickness will usually increase along with the ball size, this will be to help cope with extra load.

9 Very thin section
0 Extra light
1 Extra light thrust
2 Light
3 Medium
4 Heavy

60(01)

The 3rd and 4th digits of the bearing number relate to the bore size of the bearing, numbers 00 to 03 have a designated bore size depending on the number.

00 10mm
01 12mm
02 15mm
03 17mm

While numbers over 03 simply have a bore size which is 5 times that of the 3rd and 4th digit.

This first number relates to the bearing type, as shown in the table below type 6 is a deep grooved roller bearing.

1 Self-Aligning Ball BearingThis kind of ball bearing has a spherical outer race, allowing the axis of the bearing to “wander around”. This is important because misalignment is one of the big causes of bearing failure. Self Aligning Ball Bearing
2 Barrel and Spherical Roller Bearings
3 Tapered Roller BearingDesigned to take large axial loads as well as radial loads. double row angular contact ball bearing
4 Deep Groove Double-Row Ball BearingDesigned for heavy radial loads. Double-Row Ball Bearing
5 Axial Deep Groove Ball BearingIntended for exclusively axial loads. Thrust Ball Bearing
6 Deep Groove Ball Bearing(Single row)Typical ball bearing. Handles light axial loads as well as radial loads. Single-Row Deep Groove Ball Bearing
7 Single-Row Angular Contact BearingSpecific geometry of angular contact bearing raceways and shoulders creates ball contact angles that support higher axial loads Angular contact ball bearing
8 Axial Cylindrical Roller BearingsAxial cylindrical roller bearings comprise axial cylindrical roller and cage assemblies and shaft and housing locating washers.
The bearings have particularly small axial section height, have high load carrying capacity and high rigidity and can support axial forces in one direction.

 

Axial Cylindrical Roller Bearings
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Understanding Gears

September 21, 2012

What are gears used for?

Gears play a huge role in much of the technology around today. For example, car engines, drills, lathes, mills, cd/dvd players, printers, mechanical watches, children’s toys, in fact gears are almost everywhere there are motors and engines which produce a rotational movement.

Gears are excellent at keeping the rotation of two axis in sync. Where a belt and pulley system would eventually run out of sync due to a slight inaccuracy in the diameter of pulleys, a geared system will always stay in sync regardless of slight inaccuracies, this is due to the meshing of the gear teeth forcing gears to rotate consistently with one another.

•They are used to reverse direction of rotation, for example when selecting reverse in your car.
•Gears are also used to transfer rotational motion to a different axis.
•Gears are used to alter the speed of rotation which in the same way can be used to alter the end turning force or torque available.

Understanding Gear Ratios

Gear Ratio

The animation above shows two gears in mesh, imagine gear ‘A’ is driving gear ‘B’.

Because gear “A” has 20 teeth and “B” has 40 teeth “A” will travel through two complete turns for every one complete turn of gear “B” this would give a ratio of 1:2. This is because gear “A’s” rotational speed is half that of gear “B”.
If things were the other way around and gear “B” was driving gear “A” then the ratio would become 2:1 as the end rotational speed has been doubled at “A”.

Gear Types

Spur
Spur Gear
Spur gears are a simple gear type, they take the form of a cylinder or disk with their teeth formed around the gears circumference, spur gears can be meshed together on parallel axles.
Bevel
Bevel Gear
Bevel gears have a cone shape which enables them to mesh at various angles except 0 and 180 degrees, that is not to say a single bevel gear can work at multiple angles, the bevel gears must be cut to suit a specific meshing angle. The teeth of a bevel gear can be straight cut, similar to that of a spur gears teeth, or they can be curved along their length with each tooth sitting at an angle (Spiral bevel gear). Zerol bevel gears are too curved along their length but are not angled. Bevel gears are suited best to low speed applications usually sub 5m/s.
Worm drive

Worm Gear

The worm resembles the thread of a screw, and are usually meshed with a worm wheel which looks similar to a typical spur gear. Worm gears are an excellent way to increase torque output while reducing rotational speed. Worm drives have ratios varying from around 10:1 to 500:1, worm gears do have a slight disadvantage in that they are not very efficient, a lot of energy can be wasted due to the sliding action of the gear teeth. The worm itself can have 1 or more teeth, although 1 tooth that follows around the length of the worm several times can look like more than one tooth being present. A worm with one tooth is called a single thread or single start, while a worm with more than one tooth is called a multiple thread or multiple start.
Crown
Crown Gear
Crown gears are a form of bevel gears, the teeth of crown gears project at right angles to the plane of the wheel. Crown gears are usually meshed with another bevel gear, but in some instances are meshed with spur gears.
Helical
Helical Gear

Helical gears have angled teeth which form a curve that resembles a segment of a helix. Helical gears are meshed in parallel or crossed orientations and are used because they offer a more refined operation and run much smoother and quieter than spur gears for example. Helical gears can operate at high speeds and transmit large amounts of torque.

A disadvantage of helical gears is the thrust generated by the curved teeth when under load, this is usually handled by a suitable thrust bearing to help take this load.

Double helical
Double Helical
A double helical gear is similar to 2 separate helical gears joined together but mirrored, this helps eliminate the thrust that a single helical gear would create as in effect there is equal thrust in each direction cancelling each other out.

Dual Fuel System

September 16, 2011
This hydrogen engine takes advantage of the characteristics of Mazda’s unique rotary engine and maintains a natural driving feeling unique to internal combustion engines. It also achieves excellent environmental performance with zero CO2 emissions.

Further, the hydrogen engine ensures performance and reliability equal to that of a gasoline engine. Since the gasoline version requires only a few design changes to allow it to operate on hydrogen, hydrogen-fueled rotary engine vehicles can be realized at low cost. In addition, because the dual-fuel system allows the engine to run on both hydrogen and gasoline, it is highly convenient for long-distance journeys and trips to areas with no hydrogen fuel supply.

01-renesis hydrogen rotary engine-reference exhibit (RE) technology-electronic controlled gas injection-EGR (Exhaust Gas Recirculation)-Dual Fuel system

Technology of the RENESIS Hydrogen Rotary Engine:

The RENESIS hydrogen rotary engine employs direct injection, with electronically-controlled hydrogen gas injectors. This system draws in air from a side port and injects hydrogen directly into the intake chamber with an electronically-controlled hydrogen gas injector installed on the top of the rotor housing. The technology illustrated below takes full advantage of the benefits of the rotary engine in achieving hydrogen combustion.

 

01-hYDROGEN FUELED ROTARY ENGINE CONCEPT-DUAL FUEL SYSTEM-WITH ELECTRONICALLY CONTROLLED HYDROGEN GAS INJECTOR

 

RE Features suited to Hydrogen Combustion

In the practical application of hydrogen internal combustion engines, avoidance of so-called backfiring (premature ignition) is a major issue. Backfiring is ignition caused by the fuel coming in contact with hot engine parts during the intake process. In reciprocal engines, the intake, compression, combustion and exhaust processes take place in the same location—within the cylinders. As a result, the ignition plugs and exhaust valves reach a high temperature due to the heat of combustion and the intake process becomes prone to backfiring.
In contrast, the RE structure has no intake and exhaust valves, and the low-temperature intake chamber and high-temperature combustion chamber are separated. This allows good combustion and helps avoid backfiring.
Further, the RE encourages thorough mixing of hydrogen and air since the flow of the air-fuel mixture is stronger and the duration of the intake process is longer than in reciprocal engines.

01-mazda-hydrogen RE technologies-Dual fuel Car-Hydrogen and gasoline-Hydrogen rotary engine

Combined use of Direct Injection and Premixing

Aiming to achieve a high output in hydrogen fuel mode, a direct injection system is applied by installing an electronically-controlled hydrogen gas injector on the top of the rotor housing. Structurally, the RE has considerable freedom of injector layout, so it is well suited to direct injection.
Further, a gas injector for premixing is installed on the intake pipe enabling the combined use of direct injection and premixing, depending on driving conditions. This produces optimal hydrogen combustion.
When in the gasoline fuel mode, fuel is supplied from the same gasoline injector as in the standard gasoline engine.

 

Adoption of Lean Burn and EGR

Lean burn and exhaust gas recirculation (EGR) are adopted to reduce nitrogen oxide (NOx) emissions. NOx is primarily reduced by lean burn at low engine speeds, and by EGR and a three-way catalyst at high engine speeds. The three-way catalyst is the same as the system used with the standard gasoline engine.
Optimal and appropriate use of lean burn and EGR satisfies both goals of high output and low emissions. The volume of NOx emissions is about 90 percent reduced from the 2005 reference level.

01-EGR System-Exhaust gas Recirculation-layout

Dual Fuel System

When the system runs out of hydrogen fuel, it automatically switches to gasoline fuel. For increased convenience, the driver can also manually shift the fuel from hydrogen to gasoline at the touch of a button.

01-dual fuel system-custom exhaust systems-RX7fp

Idling Stop Technology | i-stop

September 16, 2011

Idle stop systems save fuel by shutting down a vehicle’s engine automatically when the car is stationary and restarting it when the driver resumes driving. Especially in urban areas, drivers often let their car’s engine idle at traffic lights or when stopped in traffic jams. Switching off the engine to stop it idling in these situations enhances fuel economy by about 10% under Japan’s 10-15 mode tests.

Conventional idling stop systems restart a vehicle’s engine with an electric motor using exactly the same process as when the engine is started normally. Mazda’s ”i-stop”, on the other hand, restarts the engine through combustion. Mazda’s system initiates engine restart by injecting fuel directly into a cylinder while the engine is stopped, and igniting it to generate downward piston force. This system not only saves fuel, but also restarts the engine more quickly and quietly than a conventional idle-stop system.

01-i-stop operation-operating principle of the i-stop-idling stop technology-piston position control

  • Piston stop position control and combustion restart technology

In order to restart the engine by combustion, it’s vital for the compression-stroke pistons and expansion-stroke pistons to be stopped at exactly the correct positions to create the right balance of air volumes. Consequently, Mazda’s ”i-stop” effects precise control over the piston positions during engine shutdown. With all the pistons stopped in their optimum position, the system restarts the engine by identifying the initial cylinder to fire, injecting fuel into it, and then igniting it. Even at extremely low rpm, cylinders are continuously selected for ignition, and the engine quickly picks up to idle speed.

Thanks to these technologies, the engine will restart with exactly the same timing every time and will return to idle speed in just 0.35 seconds, roughly half the time of a conventional electric motor idling stop system. As a result, drivers will feel no delay when resuming their drive. With the ”i-stop”, Mazda can offer a comfortable and stress-free ride as well as better fuel economy.

POWER TRANSMISSION

September 13, 2011

GENERAL CONSIDERATIONS

The first decision in designing an engine installation is selection of the coupling and drive method to connect the engine to the driven equipment..
The coupling and drive selection connections are closely related to the proper selection of engine support and mounting. This ensures a successful trouble-free installation from the standpoint of both the engine and driven equipment, as well as the power transmission components. (Refer to Mounting and Alignment section.)

A rigid precision-type mounting system must be provided for both the engine and driven equipment if a solid or nearly solid driveline is utilized.

Drive components which utilize universal joints, drive shafts or belts, and chain-type drives permit slightly greater alignment deviations.

When selecting the power transmission system, the possible need for a complete torsional analysis must be considered. System incompatibility will result in premature and/or avoidable failures.Refer to Mounting and Alignment section

CLUTCHES
General Description and Selection Considerations
Engine starting capability is normally limited and the direct connection of large mass
driven equipment makes starting difficult or impossible, therefore, a type of clutch or
disconnect device may not only be desirable but necessary.

Exceptions, if properly sized to the engine starting capability, may be centrifugal pumps, fans or propellers, and generators which provide a direct connected load with
a low starting torque requirement. Certain compressors which utilize a starting “unloading device” may also be direct connected.

Piston-type pumps, most compressors, belt- and chain-driven equipment, and all mobile vehicles will require an engine disconnect system.

The engine disconnect feature provides an important safety and service function. It permits rotating the engine for service and adjustment, as well as servicing the driven
equipment without disconnecting the drive-train. It also permits engine warm up before applying load — an accepted requirement for extended engine life. On multiple engine installations driving into a common compound or driven machine, it permits operating at less than full power level if desired, as well as at partial power should one engine be down for routine service or because of failure.

Numerous devices are available for connection or engagement of the engine to the driven machine. The device selection will depend on the desired engagement function; however, several general considerations must be made regardless of the
device selected.

The selected device must have adequate capacity to transmit the maximum engine
torque to the driven equipment. With the exception of “dog-type” clutches, which are
generally not acceptable on material handling equipment, clutches rely on friction
for power transmission.
(Dog-type clutches provide a direct mechanical connection and cannot be engaged
during operation nor do they have any modulating [slipping] capability).

Engine-Mounted Enclosed Clutches
These clutches (power takeoffs) will be covered in greater detail under the following
classifications (clutch rating definitions), as well as the specific selection considerations for the type of clutch and application.

Enclosed clutch selection for either rear or front engine mounting must be made in
accordance with the “Horsepower Absorption Capability”.

The following rating definitions are applicable to clutch arrangements offered by
Caterpillar.

Light-Duty (LD)
A light-duty clutch is used primarily to disconnect and pick up light inertia loads, but
does more work during engagement than “cut-off” duty.

A light-duty clutch should engage within two seconds, start the load less than six times per hour, and never heat the pressure plate outer surface above hand holding temperature.

Example: Disconnect clutch between engine and hydraulic torque converter with engine above low idle when engaging clutch, as in power shovel master clutch, generator, or similar drives.

Normal-Duty (ND)
A normal-duty clutch is used to start inertia loads with frequencies up to 30 engagements per hour. More important is that the clutch can start the heaviest inertia load within three seconds, and that the product of seconds of clutch slip per engagement times number of engagements per hour be under 90.

A normal-duty application may raise the outer clutch surface temperature to under
100°F (37.8°C) rise above ambient air temperature.

Example: Power takeoff starting average inertia loads where starting load is 40% of the running load.

Heavy-Duty (HD)
A heavy-duty clutch is used to start inertia loads with frequencies up to 60 engagements per hour. More important is that the clutch can start the heaviest inertia loads within four seconds, and that the product of seconds of clutch slip per engagement times number of engagements per hour be under 180.

Heavy-duty applications may raise the clutch outer surface temperature to a maximum of 150°F (65.6°C) rise above ambient air temperature.

Example: Power takeoff starting average inertia loads whose starting load is 80% of
the running load. Also, rock crusher applications where the clutch is not used to
“break loose” jammed loads.

Extra Heavy-Duty (EHD)
An extra heavy-duty clutch is used to start inertia loads requiring over four seconds to start the heaviest load, with longest slip period per engagement not exceeding 10seconds. Also, when the product of seconds of clutch slip per engagement times number of engagements per hour exceeds 180, it is beyond extra heavy-duty. Contact your Caterpillar dealer for application approval of extra heavy-duty-type service.
Example: Power takeoff starting inertia loads whose starting load approaches or
exceeds the running load.

Typical Light-Duty (LD)
Clutch Applications
A.Agitators — pure liquids.
B.Cookers —cereal.
C.Elevators, bucket — uniform loads,
all types.
D.Feeders — disc-type.
E.Kettle — brew.
F.Line shafts — light-duty.
G. Machines, general — all types with uniform loads, nonreversing.
H.Pumps — centrifugal.

Typical Normal-Duty (ND)
Clutch Applications

A.Agitators — solid or semisolids.
B.Batchers — textile.
C.Blowers and fans — centrifugal andlobe.
D.Bottling machines.
E.Compressors — all centrifugal
andlobe-type.
F.Elevators, bucket — uniformly loaded or fed.
G.Feeders — apron, belt, screw, or vane.
H.Filling machine — can type.
I.Mixers — continuous.
J.Pumps — three or more cylinders; gear- or rotary-type.
K.Conveyor — uniform load.

Typical Heavy-Duty (HD)
Clutch Applications

A.Cranes and hoist — working clutch.
B.Crushers — ore and stone.
C.Drums — braking.
D.Compressors — lobe rotary plus three or more cylinder reciprocating-type.
E.Haulers — car puller and barge-type.
F.Mills — ball-type.
G. Paper mill machinery — except calenders and driers.
H.Presses — brick and clay.
I.Pumps — one- and two-cylinder reciprocating-type.
J.Mud pumps — one- and two-cylinder reciprocating-type.

Typical Extra Heavy-Duty (EHD)
Clutch Applications

A.Compressors — one- and two-cylinder reciprocating-type.
B.Calenders and driers — paper mill.
C.Mills — hammer-type.
D.Shaker — reciprocating-type.

Once all machine parameters have been established, contact your Caterpillar dealer
for selection assistance.

Automotive-Type Clutches
Also known as diaphram or spring-loaded-type clutches, this category is generally a
light-duty classification; it is normally used in strictly mobile applications, such as on-
highway trucks or higher speed mobile machines, which utilize a multi speed transmission. The automotive-type clutch is normally foot-operated for disengagement or is engaged with the friction being generated by spring force acting on an engine-driven plate.

Although this type of clutch is not a Caterpillar price list attachment, on the
smaller engine families, there is offered a selection of flywheels to accommodate the
more common commercial models offered by a number of manufacturers.

If the machine design requires this type of clutch, the package designer and installer
should work very closely with the clutch manufacturer to ensure proper selection.

CAUTION: THIS TYPE OF CLUTCH, DUE TO ITS INHERENT TORQUE CAPACITY LIMITATIONS, SHOULD NOT BE USED WITH THE LARGER 3500 FAMILY CATERPILLAR ENGINES.

Air Clutches
Basically, engagement friction is maintained by air pressure. This feature is particularly advantageous when remote control of the engagement/disengagement functions is required.

Air clutches utilize an expanding air bladder for the clutch element. (See Figure 3).

Air clutches do not normally have side load capability, so if such capability is required, the output shaft must be supported by two support bearings. These bearings must be mounted on a common base with the engine package. Air pressure to operate the clutch is supplied by an air connection through the drilled passage in the output shaft. Clutch alignment tolerances are reduced as air pressure to the clutch increases.

When selecting an air clutch, the package designer/installer must work closely with the clutch manufacturer.

Centrifugal Clutches
The centrifugal clutch accomplishes the engagement/disengagement functions by centrifugal force which is generated by the engine operating speed. It provides a power engagement/disengagement function controlled strictly by the engine governor speed control (throttle).

Centrifugal clutches offer smooth automatic engagement of load without complicated
controls. Typically, a diesel engine with a full load operating speed of 1800 rpm will
be fitted with a centrifugal clutch which effects engagement at a speed of about
1000 engine rpm. Once engaged, most clutches of this type will remain engaged
even if the engine speed is pulled down due to load — as low as the engagement
speed (i.e., 1000 rpm) or lower (e.g., disengagement at 800 rpm). If the load is
such that engine stall speed is approached, the clutch will disengage.

As with the air-type clutches, they have limited or no side load capability and
for other than in-line drive loads, a separately supported output shaft with two support bearings must be provided and must be mounted on a common base with the engine package.

When selecting a centrifugal clutch, the package designer/installer must work closely with the clutch manufacturer.

TRANSMISSIONS
Over the years rapid technological advances have enabled numerous commercial
manufacturers to offer a broad range of transmissions with nearly unlimited features and options.

For this discussion transmissions will be divided into three broad classifications all
of which transmit power through sets of mechanical gears, either spur or helical
types, or planetary designs. Where multi-speed capability is provided, it is accomplished either mechanically or automatically (hydraulically, pneumatically, etc.)

Due to the large number of transmissions commercially available and the fact that
Caterpillar does not offer transmissions (with the exception of marine transmissions —single speed — forward/reverse functions(,the transmission discussion will be restricted to general operating principles and considerations.

When selecting a transmission, the package designer must work closely with the
transmission manufacturer.

CAUTION: REGARDLESS OF THE TYPE OR BRAND OF TRANSMISSION SELECTED,THE DESIGNER MUST ENSURE THAT IT HAS THE CORRECT HORSE-POWER, TORQUE, AND SPEED CAPABILITY TO MATCH THE DIESEL ENGINE PERFORMANCE CHARACTERISTICS.

Mechanical Transmission
The mechanical transmission provides the lowest cost method of providing multiple
output speeds when the driven equipment input speed range or torque requirements
exceed the operating capability of the diesel engine. Mechanical transmissions are usually equipped with some type of clutch assembly to facilitate not only engine starting but also to change gear ratios.

This type of transmission is applicable to both semi mobile and mobile installations
where the momentary loss of power to the driven equipment when gear changes are
effected does not pose operating problems.

Generally, the mechanical transmission is employed when the gear speed change
requirements are not a constant require- ment and the speed shifts do not have to
be executed rapidly.

Today’s modern mechanical transmission, when properly matched to the engine-driven equipment, will provide reliable trouble-free service. Frequent gear changes,
however, will accelerate clutch wear and maintenance costs.

Installation is simplified since mechanical transmissions do not normally require oil
cooling systems as do the automatic type.

Automatic, Semiautomatic, and Preselector-Type Transmissions
As the names imply, these transmission types effect the gear changes either completely automatically or as predetermined by the machine operator.
Engine power engagement/disengagement clutching is normally fully automatic and
does not require the machine operator to physically move a clutch pedal or lever. For
disengagement the operator need only move the selector lever to a neutral position.

As with the mechanical transmission, the automatic type must be carefully matched
to the engine operating horsepower, torque, and speed characteristics. However, with the automatic types, additional match consideration may be required since they normally utilize a torque converter, hydraulic coupling, or other type of non mechanical engagement device for the power engagement/disengagement function.

This is nearly always accomplished hydraulically. The automatic-type transmissions provide operator ease of machine operation, as well as a nearly constant power flow to the driven equipment during gear changes.

A number of commercial manufacturers offer a wide range of automatic-type transmission. The package designer/installer must work closely with the transmission
supplier to ensure the transmission properly matches the machine application and provides the desired operating features.

Some automatic transmission designs utilize a lockup feature. This device, in effect,
turns the transmission into a direct mechanical drive to eliminate the inherent inefficiencies of the hydraulic clutching device.

Generally, the higher cost of an automatic transmission can be justified with a machine requiring high productivity and frequent load cycle changes.

When using automatic-type transmissions, other installation considerations are required since most types require a system to cool the transmission oil. Caterpillar offers jacket water connections to supply cooling water to customer or transmission manufacturer-supplied heat exchangers.

Also offered are complete heat exchanger packages, but care must be exercised to
ensure that the Caterpillar system is capable of handling the transmission heat rejection. The cooling system capacity of the systems offered by Caterpillar can be obtained from your Caterpillar dealer and is in the Owner’s Maintenance Manual.

Speed Increasers/Reducers
These power transmission devices resemble a mechanical transmission in that power is normally transmitted through a mechanical gear set of spur or helical gears. They are used when the engine speed range is not compatible with the driven equipment input speed requirements and when the installation is best suited to an in-line drive arrangement rather than the offset belt of chain drive systems.

Speed increasers/reducers generally utilize a mechanical cutoff clutch for engine starting and are usually of a single-speed, non reversing design, although exceptions
to the above do exist. They seldom exceed two speed ratios.

Speed increasers/reducers are available for either direct engine mounting or for remote mounting. The remote-mounted type should be on a rigid common base with the engine for ease of alignment.
The package designer/installer must work closely with the commercial gear supplier to ensure proper selection and installation.

Compounds
Although infrequently found in material handling/agriculture applications, specific de-signs may require an engine compound.

Basically, a compound is an enclosed gear or chain device which permits several engines to provide input power with the power output coming from one or more shafts.

Compounds providing a single engine input and multiple outputs is most common. An example would be a hydrostatic machine where a single engine provides power to
multiple hydraulic pumps when separate pumps are used for the various functional drives of the machine.

Multiple engine compounds can be used in applications where less than the installed horsepower capability is occasionally called upon for part load operation of the driven machine.

When part load operation is adequate, the excess capability can be removed by
declutching engines, reducing overall operating costs and maintenance.

The package designer/installer must work
closely with the compound manufacturer
to ensure proper selection and installation.

Stub Shafts
Where the application permits, a stub shaft will provide a low cost, simple method of
direct power transmission.

Stub shaft drives must not be used when the starting load of the driven equipment is
sufficient to impair engine starting unless a declutching or unloading device is utilized.
Stub shafts also have limited side load capability.

Hydraulic drive
Hydraulic drive devices generally fall into two major classifications: fluid or hydraulic couplings and torque converters.

The theory involved is similar in all types of hydraulic drives although the internal
design may vary. Basically, the engine output is absorbed by a turbine-type pump.

The oil or fluid in the pump housing is accelerated outward, and the engine power is
transmitted to the outer edge of the pump as kinetic energy in the form of high velocity fluid. This energy is then transferred back towards the center of the output
shaft. This is where the differences occur between a hydraulic or fluid coupling and a
torque converter.

Fluid (Hydraulic) Couplings
In the fluid couplings, the high velocity fluid is directed into a matching turbine located very close to the turbine-type pump which is engine driven. The matching turbine absorbs the energy as the fluid is directed back toward the center of the coupling and the energy is delivered to the output shaft.

The output torque will always equal the input torque less internal friction losses which will be observed as a lower output speed (rpm)than the input speed (engine rpm).

The primary advantage of a hydraulic coupling is the total lack of a mechanical connection between the driving engine and the driven equipment.
This isolates or greatly reduces the transfer of mechanical shocks, vibration, and undesirable torsional effects between the driven load and the engine.

A hydraulic coupling will prevent engine stall under load; however, the engine can be pulled down in speed by varying degrees depending on the hydraulic coupling fluid
cooling capacity. It also permits starting high inertia-driven loads without the use of a cut-off clutch.

The main disadvantages of a hydraulic coupling are the reduced efficiency over a mechanically coupled drive and its inability to generate a torque multiplication as is
possible with a torque converter.

Normally, hydraulic couplings are best suited to applications which are constant speed applications where the slip capability is desirable to compensate for shock loads, overloads, high inertia load startups, and assist in torsional vibration reduction.
Torque Converters
As with hydraulic couplings, torque converters differ considerably in internal construction and refinement but can generally be placed in two classifications: single-stage and multistage. These differences will be expanded later in this section.

The torque converter differs from the hydraulic coupling in that one or more third
members, called stators or turbine reactors, are utilized in addition to the input pump and the output turbine. These stators or reactor members are imposed in the fluid flow path in such a manner as to produce a multiplication of the input torque to the output shaft at reduced output speeds (rpm).

The maximum torque is transmitted to the output shaft (driven equipment) at stall condition (output shaft is not rotating) when it will equal from 1.6 to more than 6.0 times the converter input torque (engine output torquevalue). When operating at full
speed, with the imposed load at a level which permits the output speed to be close to the engine speed, the torque converter acts in principle like a hydraulic coupling.

The necessity of matching a torque converter to the engine cannot be overemphasized. An improperly sized converter, one with the wrong blading or one which operates in a highly inefficient speed range, will prove unsatisfactory. An improperly matched torque converter can result in engine over- load, high inefficiency, high fuel consumption, poor engine response, and other undesirable results.

The torque converter manufacturer generally has computer programs which, when
coupled to the performance characteristics of the engine, can ensure a correct “match” for any installation/application. Most converter manufacturers have performance data on the Caterpillar Diesel Engine models or data can be obtained from your Caterpillar dealer. This data is covered in the Caterpillar Technical Information File (TIF). Performance data for nonstandard ratings is also available from your Caterpillar dealer.

Additionally, cooling of the torque converter fluid is required. Torque converter cooling must be provided for the equivalent of at least 30% of the total engine heat rejection when using a pre combustion chamber-type engine. When using a direct injection-type engine, torque converter cooling must be provided for the equivalent of at least 50% of the total engine heat rejection.
Caterpillar offers, as price list attachments, either jacket water connections for heat
exchanger-type coolers or, on the 3200,3300 and 3400 Series Engines, complete heat exchanger cooling packages. It is imperative that the cooling package be of adequate capacity. The capacity of

Most commercially available converters are also offered with attachment cooling
packages.

If the engine cooling system is used to cool the torque converter, adequate reserve
radiator capacity must be provided.

Single-Stage Torque Converters
This type of converter is normally selected for light-duty applications. It has a decreasing torque absorption curve as the output speed approaches stall condition and will not pull down the engine input speed (lug the engine).

Multistage Torque Converters
Most applications will utilize a multistage converter. They provide a broader usable
range and higher torque multiplication value than single-stage converters.

Torque converter manufacturers provide excellent manuals and assistance in the
selection of the correct converter for a specific application. Consequently, rather than elaborating on selection guidelines in this publication, it is suggested that the package designer/installer counsel with the converter manufacturer for expert advice.
In addition to offering the same benefits as a hydraulic drive, the torque converter also offers a torque multiplication benefit as well as, if properly matched, higher power transmission efficiency. The multistage converter is particularly preferred for variable output speed applications.

As standard price list attachments, Caterpillar offers flywheels to couple to most commercial torque converters and hydraulic drives.

Special Considerations
With the selection of any of the above methods of power transmission, several
general areas must also be given special consideration to ensure a successful
installation.

Side Loading
Excessive side loading is one of the most commonly encountered problems in the
transmission of engine power.

It is impossible to overemphasize the need for accurate evaluation of side load imposition on all types of power transmission devices.

For Caterpillar-supplied attachment power takeoffs, the Caterpillar Industrial Engine
Price List LEKI8162 provides complete instructions and capacity data for side load
evaluation.
For power transmission devices supplied by others, the manufacturer must be consulted for a capability analysis of his equipment.

Overhung Power Transmission Equipment
Power transmission equipment, which is directly mounted to the engine flywheel housing, must be evaluated to ensure that the overhung weight is within the tolerable limits of the engine. If not, adequate additional support must be provided to avoid
damage.

CAUTION: CERTAIN APPLICATIONS, SUCH AS AGRICULTURE MACHINES, DRILLS, OFF-HIGHWAY TRUCK, ETC., REQUIRE CONSIDERATION OF THE EFFECTS OF THE DYNAMIC BENDING
MOMENT IMPOSED DURING NORMAL MACHINE MOVEMENT OR ABRUPT
STARTING AND STOPPING.

The dynamic load limits and the maximum bending moment that can be tolerated by
the flywheel housing can be obtained from your Caterpillar dealer.

For determination of the bending moment of overhung power transmission equipment
installations, see Figure 13.

To compensate for power transmission systems which create a high bending
moment due to overhung load, a third mount is required. Proper design of the
support is essential. Forces and deflections of all components of the mounting
system must be resolved. If the third mount is in the form of a spring, with a vertical rate considerably lower than vertical rate of the rear engine support, the effect
of the mount is in a proper direction to reduce bending forces on the flywheel
housing due to downward gravity forces, but the overall effect may be minor at high
gravity force levels. The use of supports with a vertical rate higher than the engine
rear mount is not recommended since frame bending deflections can subject the
engine power transmission equipment structure to high forces. Another precaution is to design the support so that it provides as little resistance as possible to engine roll.

This also helps to isolate the engine/transmission structure from mounting frame or base deflection.

Wet Flywheel Housings
Certain types of power transmission equipment require a “wet” flywheel housing.
Wet housing equipment requires that the flywheel housing be able to accommodate a degree of flooding by the fluid medium of the power transmission equipment. The standard Caterpillar Diesel Engine does not:

A.Contain sufficient provisions for seal- ing in the area of the rear crankshaft
seal to prevent the transfer of the power transmission fluid into the engine lubricating oil reservoir (pan).

B.Have the capability of evacuating the transmission fluid from the flywheel
housing back to the transmission reservoir to prevent engine crankshaft seal flooding.
COUPLINGS
Unless a belt, chain, or universal joint-type drive is taken directly from the output shaft of the engine-driven power transmission device, the use of some type of mechanical coupling device is recommended.

The coupling must be installed between the power transmission output shaft and
the input drive shaft of the driven machine.

On close-coupled driven equipment, the use of a coupling can be avoided if two basic
criteria are met:
A.Is the torsional compatibility of the driven machine compatible with the engine to the point that lack of a coupling will not cause either engine or driven machine problems?

B.Is the package base sufficiently rigid to avoid any distortion during operation?
Does it contain sufficient alignment control features to successfully retain alignment during operation to preclude the need for the misalignment tolerance capability of a coupling?

Seldom can both of these questions be answered affirmatively.
A large number of commercial coupling designs, are available to the package
designer/installer.

CAUTION: THE COUPLING MUST BE TORSIONALLY COMPATIBLE.

Commercial couplings make use of resilient materials ranging from rubber and tough
fabrics to springs and air-filled tubes and drums in order to absorb minor mechanical misalignment and relative movement between engine and load. It is important to
have the best possible alignment and put a minimum load and reliance on the flexible
coupling. Air clutches are not flexible couplings and imposing misalignment on them
will cause damage.

Four distinct characteristics must be taken into account in the selection of a suitable
coupling:
A. Misalignment Capability
The coupling must be capable of compensating for any misalignment between the engine and equipment to prevent damage to the machine and/or diesel engine crankshaft and bearings.

If single bearing equipment is used, the coupling must be torsionally and radially rigid to transmit the load and support the weight of the driven equipment input shaft.
It must be flexible to compensate for angular misalignment
due to:
1-Thermal growth differences between the diesel engine and driven equipment.
2-Dimensional tolerances between the two units and dynamic conditions, such as torque reaction.
3-Momentary misalignment due to shock or other transient conditions.

B. Stiffness
The coupling must be of proper torsional stiffness to prevent critical orders of torsional vibration from occurring within the operating speed range. For single-bearing driven equipment, a complete torsional analysis is necessary to ensure compatibility. For two-bearing driven equipment, a simpler type of analysis is adequate. A complete torsional vibration analysis can be obtained from your Caterpillar Engine supplier, as can mass-elastic data on the diesel engine to permit
customer analysis.

C. Serviceability
When selecting a coupling, ease of installation and service is an important consideration. If spacers can be used to permit removal and installation of the coupling without disturbing the diesel engine driven machine alignment, time can be saved if service or replacement of the coupling is ever required.

When selecting a coupling, ensure that the design can withstand reasonable misalignment without materially decreasing the service life of the flexible elements.

When coupling design demands extremely close alignment, one of the major purposes for using a coupling is defeated.

D. Coupling Selection
In any installation, the coupling should be the weakest part of the entire power train; the first part to fail.

If failure does occur, the chance of damage to the diesel engine and driven machine is minimized. Safety measures must be considered to prevent major equipment damage should coupling failure occur. The use of a standard, commercially available coupling offers the benefit of parts avail- ability and reduced downtime in case of failure.

AUXILIARY DRIVES
Many applications have a requirement for auxiliary drive capability to power charging
alternators, air compressors, hydraulic steering pumps, etc.
Caterpillar offers, as price list attachments, various auxiliary drive options for all engine models. These attachments provide either mechanical gear or belt drive capability.

Gear Drives
These drives are suitable for direct mounting of air compressors and hydraulic
pumps for power assist steering, etc.

Belt Drives
Several options exist for belt driving various auxiliary attachments. Both of the following methods are available from Caterpillar:

A. Crankshaft Pulleys
Additional stack-on pulleys can be added to the front of the crankshaft.
The number of additional grooves which can be added depends on other belt-driven equipment such as cooling fans and charging alternators and the amount of total side load which will be imposed on the front of the crankshaft.

B. Gear Drive Pulleys
The gear drive auxiliary positions may be equipped with output pulleys.

MECHANICAL GOVERNORS

September 13, 2011

 

Diesel Fuel Systems
Mechanical Governors
This Meeting Guide is the third in a series dealing with the basic
diesel engine fuel system and components. It is about the diesel
governor.
Fig. 01Each Caterpillar diesel engine is equipped with a governor. Why?
Diesel engines can accelerate-increase speed-at the rate of more
than 2000 revolutions per second. Yes, PER SECOND. Without a
governor a diesel engine can quickly destroy itself.
Fig. 02
GOVERNORSNever operate a diesel engine without a governor controlling it. If
you were to move the fuel rack of a diesel engine to the full “ON”
position without a load and with the governor not connected, the
engine speed might climb and exceed safe operating limits before
you could shut it down. One second…two seconds…before you
knew what was happening, the engine may have been seriously
damaged by overspeeding.
This warning – never operate a diesel engine without a governor
controlling it – is concerned with one of the purposes of governors:
to prevent engine overspeeding. Governors also keep the engine at
the desired speed and increase or decrease engine power output to
meet load changes. WARNING

Fig. 03This presentation introduces and explains the mechanical governor.
The mechanical governor is the simplest of the various types of
governors and is basic to their operation.
Besides the mechanical governor, Caterpillar engines use: servomechanical
governors, hydraulic governors and electronic
governors. These governors will be discussed in future
presentations.
MECHANICAL
Fig. 04This tractor is equipped with a mechanical governor. We can see the
governor control lever, the control linkage, the governor and the fuel
injection pump housing.

Fig. 05.
This is a closeup of the governor, mounted on the rear of the fuel
injection pump housing.
Let’s look at the construction and operation of the mechanical
governor using schematic illustrations.
Fig. 06Diesel engine mechanical governors consist of two basic
mechanisms: the speed measuring mechanism and the fuel changing
mechanism.
Fig. 07
The speed measuring mechanism senses engine speed changes, and
the . . . .
Fig. 08. . . fuel changing mechanism increases or decreases the amount of
fuel supplied the engine to correct these changes.
Let’s look at each basic mechanism separately and learn how it
operates.

Fig. 09
The speed measuring mechanism is simple, has few moving parts
and measures engine speed accurately. The main parts are:
1) gear drive from the engine,
2) flyweights, and
3) spring.
Fig. 10The flyweights and “L” shaped ballarms which pivot are mounted
on the governor drive.

Fig. 11
The flyweights are rotated by the engine.
Fig. 12As the flyweights rotate, they exert a centrifugal force outward. The
flyweights move outward pivoting the ballarms upward. The amount
of outward force depends on the speed of rotation.
Centrifugal force is the basic operating principle of the speed
measuring mechanism. Now, what is centrifugal force?

Fig. 13
If we tie a ball on a string . . . .
Fig. 14. . . . . and swing it around and around . . .

Fig. 15
faster and faster, an outward force-centrifugal force- is exerted on
the ball. This centrifugal force swings the ball outward and upward
until the ball is nearly straight out.
And, we can see that the faster we swing it, the greater the pull on
the string and the farther outward it swings.
Fig. 16This force – centrifugal force – is the basic principle used in the
speed measuring operation of the diesel engine governor. Keep
centrifugal force in mind as we discuss the other parts of the speed
measuring mechanism. Remember, the greater the engine speed, the
greater the centrifugal force and, therefore, the greater the
movement of the flyweights and ballarms.

Fig. 17
We need to control this centrifugal force, so we have the governor
spring. The spring acts against the force of the rotating flyweights
and tends to oppose them. The force exerted by the spring depends
on the governor control setting.
Fig. 18
A lever connected to the governor control pushes on or compresses
the spring. The spring force opposes the flyweights to regulate the
desired engine speed setting.
The governor control, shown here as a simple push-pull knob, may
be a hand operated control lever or a foot operated accelerator
pedal.
Fig. 19
As long as the spring force equals the flyweight centrifugal force,
engine speed remains constant.
Fig. 20
The speed measuring mechanism, then, senses and measures engine
speed changes. The fuel changing mechanism links the speed
measuring mechanism with the fuel injection pumps to control
engine.
Fig. 21The fuel changing mechanism consists of the:
1) connecting linkage,
2) rack and
3) the fuel injection pump.
Fig. 22
Flyweight movement – outward in this example – due to engine
speed changes, are transferred through the simple linkage to the
rack and, therefore, to the fuel injection pump plunger.
Fig. 23When the engine load increases – as when a dozer digs in – the
speed decreases. The flyweight force decreases, and the spring
moves the linkage and rack to increase the fuel to the engine. The
increase fuel position is held until the engine speed returns to the
desired setting, and the flyweight force again balances the spring
force.

Fig. 24
When the engine load decreases, the speed increases. The flyweight
force increases, overcoming the spring force, moving the rack to
decrease fuel to the engine. The decrease fuel position is held until
engine speed returns to the governor control setting, and the spring
force again balances the flyweight force.
Fig. 25
In summary, the basic governor consists of the:
drive gears, flyweights, spring, and control lever of the speed
measuring mechanism, and the connecting linkage, rack and fuel
injection pump of the fuel changing mechanism.
Fig. 26
The rack which meshes with the injection pump plunger gear
segments extends from the injection pump housing into the
governor. The rack and fuel injection pumps are parts of the fuel
injection pump housing assembly.
Fig. 27As you recall, Meeting Guide 43, Fuel Systems: Part 2, explained
fuel injection pump operation and how the fuel injected into each
cylinder is increased or decreased.

Fig. 28
In this cutaway governor and fuel injection pump housing, we see
that the rack extends into the governor. Rack movement controls the
amount of fuel injected in each cylinder.
Let’s look at a closer view of our cutaway governor.
Fig. 29In this cutaway section of our housing, see the flyweights, spring,
spring seat and thrust bearing. The thrust bearing (not previously
mentioned) is an anti-friction bearing between the flyweight
ballarms which rotate and the spring seat which, of course, does not
rotate.

Fig. 30
The governor is driven by the lower gear bolted to the fuel injection
pump camshaft.
The control lever has been removed from its shaft in the governor
housing and set in place to show how it is positioned.
Fig. 31Looking closer, we can see (from right to left) the drive gear ,
flyweights , spring, spring seats, control lever and the collar and bolt
which connects to the rack. The purpose of the collar is explained
later.
Fig. 32
This governor cross section illustrates: (1) lever, (2) spring seat, (3)
spring, (4) spring seat and thrust bearing and (5) flyweight
assembly.
The arrows indicate drive gear rotation and rack movement.
Fig. 33Two adjusting screws limit the travel of the governor control lever
between LOW IDLE position and the HIGH IDLE position.
The low idle stop and high idle stop are simply minimum and
maximum engine rpm settings with no load on the engine.

Fig. 34
The high and low idle adjusting screws are located under the cover
on the governor.
Fig. 35
Notice that the holes in the cover are shaped to lock the screws and
prevent them from turning after they are adjusted.
Fig. 36The operators control is positioned at the desired governor setting:
low idle, high idle or fuel off.

Fig. 37
When the lever in the governor is in the LOW IDLE position, a
spring loaded plunger in the lever assembly contacts the low idle
stop of the adjusting screw.
Fig. 38When the lever in the governor is in the HIGH IDLE position, the
lever contacts the high idle adjusting screw.

Fig. 39
To shut the engine down, the governor control is moved full forward
– past . . . .
Fig. 40. . . the low idle stop. It is necessary to force the plunger over the
shoulder on the low idle screw . . .

Fig. 41
. . .to move the rack to the FUEL OFF position.
Fig. 42Looking, again, at the governor cross section see
(1) the high idle adjusting screw and
(2) the low idle adjusting screw. The lever is against the HIGH IDLE screw.
The low idle and high idle screws, then limit minimum and
maximum engine rpm with no load on the engine. What limits
engine power output when the engine is fully loaded?
Fig. 43
A collar and stop bar limit rack travel and, therefore, the power
output. The collar is secured by a bolt connecting the rack linkage.
The stop bar is mounted in the governor housing. With the rack
moved to the FULL LOAD position, the collar just contacts the stop
bar.
Fig. 44
When our engine is operating with the governor at high idle (1) and
picks up a load, the speed decreases, flyweight centrifugal force
lessens, and the spring moves the rack to give the engine more fuel
increasing power. The collar (2) and stop bar (3) limit the distance
the spring can move the rack. As the collar contacts the stop bar,
full load position is reached. This limits the fuel delivered to the
engine so as not to exceed design limitations.
Fig. 45
Returning to the governor cross section, note the location of the:
(1) collar,
(2) stop bar,
(3) bolt and
(4) rack.
Like other diesel engine components, the governor must be
lubricated for long life. Let’s look at a governor lubrication system
schematic.
Fig. 46
The governor is lubricated by the engine lubricating system. Oil
from the diesel engine oil manifold is directed to the governor drive
bearing. All other governor parts are lubricated by splash.
The oil drains from the governor, through the fuel injection pump
housing, back to the engine crankcase.
Fig. 47
In summary, we have discussed the mechanical governor’s primary
components and principle of operation. Remember a governor has
two basic mechanisms: the speed measuring mechanism and the
fuel changing mechanism.
Fig. 48In our cross section we located the lever, spring, spring seats,
flyweights, thrust bearing, drive gears and rack. We also discussed
the high and low idle settings and the full load stop.
At the beginning of this lesson we warned: NEVER OPERATE A
DIESEL ENGINE WITHOUT A GOVERNOR CONTROLLING
IT. Why are governors so important to a diesel engine?
Fig. 49
Note: The instructor should make clear we are not saying
gasoline engines never have a governor. Some
gasoline engines use a governor for the same reasons as
a diesel: to control engine speed and to regulate engine power output.
First, gasoline engines are self-limiting. Engine speed is controlled
by a butterfly valve in the intake manifold which limits the air
supply Limiting the amount of air taken in for combustion, limits
engine speed.
Fig. 50
Diesel engines, however, are not self-limiting. Engine air intake is
not limited, and the cylinders always have more air than is needed
to support combustion. The amount of fuel injected into the
cylinders controls engine speed.
Fig. 51
And, as the fuel is injected directly into the cylinders rather than
into the air intake manifold, engine response is immediate. This,
resulting greater power stroke, adds up to very rapid acceleration.
As we said earlier, diesel engines can accelerate at a rate of more
than 2000 revolutions per second. Because of this rapid
acceleration, manual control is difficult, if not impossible.
Fig. 52NEVER OPERATE A DIESEL ENGINE WITHOUT A
GOVERNOR CONTROLLING IT.

Fig. 53
At this point, we have built up the basic diesel mechanical governor.
This governor works fine on engines whose engine speed is held
fairly constant and the governor is controlled by hand. However, on
other engines, the force needed to compress the governor spring or
to move the rack -just operating the governor – could be very tiring
to the operator.
Fig. 54With the servo-mechanical governor, the work operation of
compressing the governor spring is done with engine oil pressure.

Fig. 55
With the hydraulic governor, the work operation of moving the fuel
injection pump rack is done with engine oil pressure.
These governors are discussed in . . . .
Fig. 56. . . . Meeting Guide 60, “Servo Mechanical Governors.”

Fig. 57

 

TYPES OF GEARS

September 13, 2011

A SPUR GEAR

is cylindrical in shape, with teeth on the outer
circumference that are straight and parallel to the axis (hole).
There are a number of variations of the basic spur gear,
including pinion wire, stem pinions, rack and internal gears.
(See Figure 1.17)

PINION WIRE
is a long wire or rod that has been drawn
through a die so that gear teeth are cut into its surface.
It can be made into small gears with different face widths,
hubs, and bores. Pinion wire is stocked in 4 ft. lengths.
(See Figure 1.18)

STEM PINIONS
are bore-less spur gears with small numbers of
teeth cut on the end of a ground piece of shaft. They are
especially suited as pinions when large reductions are
desired. (See Figure 1.19)

RACK
are yet another type of spur gear. Unlike the basic spur
gear, racks have their teeth cut into the surface of a straight
bar instead of on the surface of a cylindrical blank. Rack is
sold in two, four and six foot lengths, depending on pitch,
which you will learn about starting in chapter 2.
(See Figure 1.20)

INTERNAL GEARS
have their teeth cut parallel to their shafts
like spur gears, but they are cut on the inside of the gear blank.
(See Figure 1.21)

HELICAL GEARS
A helical gear is similar to a spur gear except that the teeth
of a helical gear are cut at an angle (known as the helix
angle) to the axis (or hole). Helical gears are made in both
right and left hand configurations. Opposite hand helical
gears run on parallel shafts. Gears of the same hand operate
with shafts at 90-degrees. (See Figure 1.22, 1.23, 1.24, 1.25)

BEVEL GEARS
A bevel gear is shaped like a section of a cone and usually operates
on shafts at 90-degrees. The teeth of a bevel gear may be straight
or spiral. If they are spiral, the pinion and gear must be of opposite
hand in order for them to run together. Bevel gears, in contrast
to miter gears (see below), provide a ratio (reduce speed) so the
pinion always has fewer teeth. (See Figure 1.26, 1.27)

MITER GEARS
Miter gears are identical to bevel gears except that in a miter
gear set, both gears always have the same number of teeth.
Their ratio, therefore, is always 1 to 1. As a result, miter gears
are not used when an application calls for a change of speed.
(See Figure 1.28, 1.29)

WORMS & WORM GEARS
WORM Worms are a type of gear with one or more cylindrical
threads or “starts” (that resemble screw threads) and a face that
is usually wider than its diameter. A worm gear has a center
hole (bore) for mounting the worm on a shaft. (See Figure 1.30A)

WORM GEARS – like worms – also are usually cylindrical and
have a center hole for mounting on a shaft. The diameter of
a worm gear, however, is usually much greater than the
width of its face. Worm gears differ from spur gears in that
their teeth are somewhat different in shape, and they are
always formed on an angle to the axis to enable them to
mate with worms. (See Figure 1.30B)

Worms and worm gears work in sets, rotating on shafts at right
angles to each other, in order to transmit motion and power
at various speeds and speed ratios. In worm and worm gear sets,
both the worm and worm gear are of the same hand. (Because
right- hand gearing is considered standard, right-hand sets will
always be furnished unless otherwise specified.) (See Figure 1.30)