Archive for the ‘MECHANICS’ category

Bearing Numbers Explained

September 21, 2012

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


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


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.


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


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

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 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 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 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 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.




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.