LIMITED SLIP DIFFERENTIAL FOR Abarth 500-595 (CHANGE C510) The Abarth 500 (or Abarth 595), like all sports cars with front wheel drive, can suffer from poor traction due to the high torque which is discharged on the wheels. This is manifested especially in the corner exit, where the inner wheel is relieved in part by the weight which insists there for the load shift due to the centrifugal thrust: there is thus found with one of the two wheels which has the ability to discharge to the ground a much lower than the other pair. Recall that a free differential has the characteristic of always and in any case to divide the pair into two equal parts, so the maximum torque that can be discharged to the ground is bound by adherence of the wheel with less load.
The Abarth 500-595 is already fitted as standard with an electronic system called TTC, which SIMULATES a self-locking differential: in practice, when one of the two drive wheels loses traction, the electronic control unit designated to traction control sends a braking impulse to the brake caliper in the wheel slip: the negative torque that is added to the wheel makes it possible to "trick" the normal differential, sending a pair also equal to the wheel with more grip.
The TTC is definitely a valid and secure system, which guarantees a good control of the vehicle, however, we reiterate a limited slip differential is not and does not guarantee the same performance that only a good self-locking can provide. If you usually use your Abarth 500-595in track during track days, or you do not like having to endure the annoying slippage of the inside wheel at each corner exit addressed in a somewhat 'allegro, then a true limited-slip differential can do your case. Our self-locking differential with helical gears, tested on vehicles with more than 30 kgm torque, allows to asymmetrically divide the torque coming from the engine, this means that the wheel with more grip will always receive a torque surplus compared to the more wheel download. The percentage of blocking in shot is about 35%. We chose not to go further since the Abarth 500 is and remains a car road. The differential, with helical gears has a very progressive operation and does not create undesirable effects in normal driving. The percentage of blocking in release is limited to approximately 25%, so as not to affect braking and cornering. A word is very difficult to explain the effect achieved, but the feeling you get to open the throttle after the apex of a curve and not feel the muzzle of a tangent, but pulling inward is a something unknown to a front-wheel drive with differential standards. In addition, the functioning of our differential is compatible with the TTC. How does the limited slip differential? First of all we consider the operation of the normal range front differential. Prometheus slip differential The differential is a device that splits the torque from the gearbox exactly half for each of the two axle shafts, irrespective of the difference of revolutions of the two wheels of the same. Thus, as seen in the figure, called 100 (the units are totally arbitrary) the drive torque to the differential input, on each wheel end a pair of 50. But there is another important parameter to consider: the tire grip on the ground. In fact, the torque can be "downloaded" to the ground up to the limit of adhesion of the wheel; this limit is therefore proportional to the load fraction which acts on the wheel and the coefficient of adhesion, which mainly depends on the consistency of the soil. So if one of the two axle wheel ends in an area smaller adherence (for example on the slippery asphalt), the torque to the ground downloaded from the wheel in question is reduced, since the wheel itself reaches the slip condition. For the differential properties set out above, which is to be a mechanism that divides into equal parts in the input torque, we will have the same torque value even though the other wheel that maintains a good grip. Prometheus slip differential As can be seen from the previous figure, said 30 the value of the torque of the left of the front slip limit, even the right wheel can only download a torque to the ground 30. And then the total of the front axle traction is reduced to the value 60, much lower than the 100 of the previous example. If we assemble the limited slip differential Prometheus instead of the normal differential, traction in these cases improves. Let's see how and by how much.
First of all, in good and homogeneous adhesion conditions, the limited slip differential behaves as an ordinary differential, as shown in the following figure. Prometheus slip differential However, if one wheel loses traction, the other must be a greater torque by approximately 35% compared to what would occur using the normal differential. The total torque discharged to the ground from the front axle is greater than that discharged to the ground by a common differential. The next figure is very explanatory of this mode of operation. Prometheus slip differential The percentage of 35% of locking is the best compromise found through the numerous tests carried out under different conditions. Do not forget that an excessive percentage of locking would make the vehicle too much understeer in normal driving conditions, with consequent problems in the guide. And, on the other hand, a percentage too low clamping, would reduce dell'autobloccante benefits, making it objectively useless. Contact us for any information!