- Navigation menu
- Final Drives and Differentials
- How it Works: Final Drive Unit
- Around The Corner - How Differential Steering Works (1937)
- Final Drive and Differentials
- Crown Wheel and Pinion
- Complete Guide - Mazda MX-5 Differentials
- US5997425A - Differential steer and final drive configuration - Google Patents
- Final Drives and Differential Basics
- Final drive and differential pdf free
We hope to bring you new and interesting content on our YouTube channel.
Please support us by subscribing. Place An Ad. Site Search.
New to Unique? Learn more about Unique Cars and Parts This website proudly supported by:. Subscribe to RSS.
Volkswagen POA. Lancia POA.
Final Drives and Differentials
Mercedes Ben How it Works: Final Drive Unit. The Propeller Shaft The final drive unit has three functions to perform: it gears down the speed of the propeller shaft to a suitable road wheel speed, it divides the transmitted torque from the engine between the two driving wheels and, except in the case of a transverse engine, it turns the drive through a right angle, transferring it from the propeller shaft to the driving wheels.
The propeller shaft in a conventional front-engined, rear-wheel drive car feeds the engine's torque into the final drive unit. The function of the final drive in this application is to turn the drive through a right angle and divide it into two equal parts which are then delivered to the rear wheels.
A final drive is also needed in a front-wheel drive FWD car but with a transverse engine, as in the British Leyland Mini, there is naturally no need to turn the drive through a right angle. It must still split the drive into equal parts, however, for each driven wheel.
In the earliest days of car design, the driven wheels were joined by a solid axle shaft and turning the drive from the propeller shaft through a right angle was no problem.
How it Works: Final Drive Unit
A bevel gear was attached to the end of the propeller shaft and this meshed in turn with another bevel gear which was attached to the middle of the axle shaft. Since the shaft was solid, it could not help delivering the torque equally to both wheels.
This was all very well but there were considerable disadvantages in having a solid axle. When a car turns a corner, the wheels on the inside of the curve travel a shorter distance than those on the outside and consequently should rotate more slowly. A solid axle assembly forces both wheels to rotate at the same speed, with the result that the inside wheel tends to slip and scuff causing tyre wear, while its resistance to this treatment tends to drive the car forwards instead of leaving it free to travel round the intended curve.
In modern terms it causes understeer which means that more steering lock has to be applied as the car goes round the corner. Understeer and its opposite oversteer are fully described in a later article. Eventually, from the simple pair of bevel gears a more complicated arrangement was developed - the differential.
This allowed the driven wheels to rotate at different speeds while still splitting the torque equally between them. The modern final drive, therefore, consists of two parts: one to turn the drive through a right angle and, incidentally, to gear down the drive according to the needs of the car and the other designed in order to allow differential movement of the wheels. The first need, harking back to the original bevel gear drives, is served by the crown wheel and pinion.
The differential unit, serving the second need, is carried within the crown wheel housing and is attached to the crown wheel.
Around The Corner - How Differential Steering Works (1937)
The drive enters the final drive unit from the propeller shaft or, in the case of a FWD installation, directly from a spur or bevel gear by means of a short input shaft on which the pinion gear is mounted.
The pinion engages with the much larger crown wheel in order to turn the drive into the line of the axle.
Final Drive and Differentials
Crown Wheel and Pinion The earliest crown wheel and pinion arrangements used straight-cut teeth because these were the easiest to make. However, straight-cut teeth mean that the drive is carried by one tooth at a time, which can lead to noise and vibration unless all the teeth are exactly evenly spaced and exactly the same shape. To overcome this problem designers moved to the spiral bevel form in which the teeth of both the crown wheel and the pinion are curved.
With this tooth form, two or possibly even three pairs of teeth are in contact at the same time and smoother running results, together with more even wear.
Crown Wheel and Pinion
A further development was intended to reduce the amount of space taken up in the passenger compartment by the transmission tunnel. This could be achieved if the propeller shaft could be lowered; but as long as the shaft had to meet the final drive at the centre-line height of the rear axle, this could not easily be done.
The answer was to lower the point at which the propeller shaft met the final drive, so that instead of pointing straight at the axle centre line, the axis of the shaft ran some way below. In this way propeller shafts could be lowered by a very useful mm 6ins or more where they ran through the passenger compartment. The penalty was that a new gear tooth form had to be developed to enable the two "out-of-line" gears to mesh.
When the gears are in-line, the teeth are only in rolling contact; but in the out-of-line "hypoid" form, they have to slide as well as roll.
This advance placed new demands on lubrication and these were met by the development of extreme pressure EP oils.
Complete Guide - Mazda MX-5 Differentials
If a non-EP oil is used in a hypoid drive, it breaks down quickly under the stress and gear damage soon follows. One other form of drive also allows the propeller shaft line to be lowered.
This is the worm-and-wheel drive which could almost be considered as an extreme form of hypoid in which all contact is sliding rather than rolling. Peugeot used worm drive for a long time, up to and including the model which was notably quiet in operation but needed an even more specialized lubricant.
The worm-and-wheel drive was used by Peugeot up to the model. It was extremely quiet in operation and alled the propeller shaft to be lowered, thus leaving more room inside the car for passengers.
US5997425A - Differential steer and final drive configuration - Google Patents
The only downside was that it required a specialized lubricant to work effectively over the life of the vehicle. The function of the differential is to split equally the torque and feed it to the road wheels while allowing the wheels to turn at different speeds if necessary.
When entering a bend, the drive shaft gears will rotate at different speeds. They are able to do so because the pinion gears can rotate on their shafts allowing one drive-shaft to turn more quickly than the other.
Final Drives and Differential Basics
When travelling straight ahead, there is no relative movement between the drive-shaft or pinion gears so that they and the differential casing all rotate at the same speed. The earliest crown wheel and pinion units used straight cut teeth to transfer drive. With a curved tooth form, two or three teeth were in contact at the same time.
An offset hypoid bevel arrangement allows the propeller shaft to be lowered.
Final drive and differential pdf free
In the differential lock, a dog-clutch locks the driveshaft gears to the differential housing, forcing them to rotate at the same speed. An alternative design locked the pinion gears.
The multi-plate limited slip differential prevented all torque from being lost if one wheel was unable to find any grip. When there was relative movement between the wheels and their drive-shafts, the rotating pinions would try to puch themselves away from the driveshaft gears; when this happened the multi-plate clutches did not lock the assembly completely but they did provide enough friction to limit the degree of wheelspin so that torque could still be delivered to the "good" wheel.
We are specialized in bumper field,with good quality. Using our products, you needn't care about its I hope our new products finds you in a perfect condition. We are specialized in bumper field,wit Car Parts: Lancia Flaminia P. Make my friend on facebook: Anna Anna Ptt Bumper for more information Site Search New to Unique?
POA Mercedes Ben Place A Free Classified.