AutoExe original setting.Mechanical type with street vest specifications.

The mechanical (multi-plate clutch) limited slip differential that distributes and transmits effective traction to the left and right drive wheels when cornering or on slippery roads is an AutoExe original that considers usability and comfort based on the proven CUSCO product. I made a setting.
The operation method is 100 Way, which works 50% when the accelerator is ON and 1.5% when the accelerator is OFF.Set the drive side cam angle to 35 to 45 ° and the torque bias ratio to 4.0 to 6.0 on the drive side.The initial torque is 40.8 to 51.0Nm, and a direct working feel and reliable traction are obtained. It is an item that emphasizes the handling that is typical of FR vehicles.Also, in consideration of street driving, the specifications are such that chattering (metal noise when the clutch plate slips) is suppressed as much as possible.Includes designated LSD oil with the product.

The following is an overview of the "aim" and "technology".It's hard to imagine the mechanism because it's a black box diff for most readers, but if you think about diff tuning, you should understand only the principle part.This is because the usability changes greatly depending on the design intent.

First of all, basic knowledge, but in the first place, the differential is for changing the rotation speed of the outer ring and the inner ring that are driven when the vehicle turns.This is because the radius of the trajectory drawn by the inner and outer rings is different when turning at a certain angle as shown in the figure.Naturally, the outer ring must travel a longer distance than the inner ring and must rotate faster.Otherwise (at the same speed), the inner ring will slip and consume excessive rotation, making it impossible to turn smoothly.In short, the differential is a mechanism for giving a difference in rotation to the drive wheels.Therefore, it is translated as "differential device" in Japanese.
Of course, there is no need for differential when going straight, and it is not good to make a differential.This is because if there is a difference in rotation between the drive wheels, the direction of travel will change accordingly.So how does the diff recognize "turning"?The basis of that judgment is the resistance from the road surface.

Let's look at the figure from a different perspective.The fact that the radius of gyration of the inner ring is smaller than that of the outer ring means that the inner ring bends a sharper curve than the outer ring.Therefore, due to the difference in the turning radius, the deviation between the wheel rotation direction and the tire traveling direction becomes large, and the resistance increases accordingly.When turning, there is a difference in the drive resistance of the inner and outer wheels.Therefore, when this difference is detected, the differential function should be activated.Such passive operation is the basis of the differential.Therefore, the problem remains in the actual driving condition.It is OK for practical purposes such as putting it in the garage at low speed, but the "difference in resistance from the road surface" is not necessarily determined only by the turning radius.For example, in high-speed cornering, the load is transferred by the roll, the contact pressure of the inner ring side tire is reduced, and the resistance from the road surface is reduced.On rough roads and icy roads, there may be a difference in the left and right road surface conditions even when going straight, and there may be a difference in resistance.In such a situation, it would be a problem if the differential function of the drive wheels works one by one.At least from the standpoint of enjoying driving, it is not a welcome characteristic.Therefore, LSD was developed to eliminate the differential state.Literally, it's a differential with limited differential functions.

In the actual scene, when trying to run through tight corners at a relatively high speed, the car body gradually rolls outward due to cornering G.As a result, a load is applied to the outer ring of the drive wheel, and the load on the inner ring is reduced.Finally, the resistance on the outer ring side becomes larger.Then, the differential function works in the opposite direction, the rotation speed on the inner ring side increases, and in an extreme case, idling starts.At this time, with a normal differential (open differential) in which the distribution of driving force to the inner and outer rings is the same, the outer ring with high resistance cannot rotate at all.Therefore, even if the accelerator is depressed, the inner drive wheel just spins and does not move forward.There is no traction to move the car forward.

The theory is that LSD is needed there.The mission is to detect fluctuations in the number of revolutions or torque of the inner and outer rings, weaken the differential function, and increase the torque distribution to the outer ring with grip.However, the idling of one wheel is an extreme condition, and in reality, what kind of transient characteristics are tuned from the beginning of the effect is the design intention of each LSD.If you focus only on acceleration in corners like a competition vehicle, you should be aware that some deterioration in maneuverability should be applied "from an earlier stage, stronger", and if you only aim to escape from the emergency, you should do it manually. There is also a switchable diff lock.

Recently, there are various types of LSD, and they are generally classified into "rotation difference sensitive type" and "torque sensitive type".Each is used properly according to the drive system and purpose of use of the vehicle.A typical example of adopting the rotation difference sensitive type is the viscous type (silicon oil is enclosed inside the viscous coupling, and the shear force of the silicon oil is used to perform differential limitation), especially. It is often used in FF vehicles.The purpose is mainly effective when a large rotation difference occurs between the left and right wheels on an extremely low mu road, for example, a snowy road.

The torque-sensitive type is often used in FR cars, and there are various mechanisms, but the one used in FR sports cars generally uses the tooth surface resistance by combining multiple gears. (Super LSD and Torsen type) are the mainstream.

The LSD we adopted this time is a so-called mechanical type with a multi-plate clutch type structure.This type has not been adopted as a mass-produced LSD recently, but it is still active in the front line as a necessity in the world of motor sports.The reason is the "torque bias ratio" by changing the cam angle of the pressure ring according to the application and selecting the number of clutch plates.■This is because the "initial torque" can be set freely, and the response to the generation of differential limitation is excellent. ((■Torque bias ratio = high μ side torque ÷ low μ side torque)

A large torque bias ratio means that the torque distribution ratio to the inner and outer drive wheels can be changed more greatly, and greater traction can be given to the tire with the grip.The torque bias ratio of mass-produced LSD is about 2.0 to 3.0, which is a mild specification for everyone without being aware of the effectiveness of LSD.However, it is not possible to enjoy driving positively.As a result of the evaluation test, we set the torque bias ratio to 4.0-6.0.Furthermore, by setting the initial torque to 40.8 to 51.0 Nm, which is higher than that of mass production, for example, even if one wheel completely loses grip and slips due to the differential gear, the side with grip, that is, The torque corresponding to this initial torque value is transmitted to the tire on the side that is not idling.You can also expect a quick response to the start of differential limiting.There are various methods for setting the initial torque, but by generating it from the inside of the pressure ring with a coil spring, unlike the initial torque due to the reaction force of the cone spring on the outside of the conventional clutch plate, a multi-plate clutch is always applied. By applying pressure, the timing at which the differential limitation occurs is accelerated.
In conclusion, our LSD is not abrupt, it does not drastically change the maneuverability, and you can definitely feel the effect ... Not only the steering operation but also the attitude of the car with aggressive accelerator work. It is tuned to the best transient characteristics of the street that can control.Of course, it goes without saying that it is not a radical specification that pursues only traction performance like the circuit specification.The table below summarizes the comparison with the mass production specifications, so please refer to it.

Finally, for the maniac mecha sect, I will touch on the differential generation principle of our multi-plate clutch type LSD.Four pinion gears are installed on the pinion shaft inside each side gear that is directly connected to the left and right drive shafts.

If there is no torque difference between the left and right side gears, that is, the drive shaft, the pinion gear is free and will not start rotating.On the other hand, when a torque difference occurs on the left and right, a rotation difference occurs in the side gear due to the torque difference, and the four pinion gears start to rotate.At this time, the pinion shaft generates a force in the direction of spreading the cam of the pressure ring according to the torque difference.The pressure ring presses the clutch plate by the force of the thrust generated in the axial direction according to the cam angle, thereby limiting the differential torque difference between the left and right.The larger the angle value of this cam, the larger the thrust force and the larger the torque bias ratio.

The cam specification of our LSD is a 35-way specification with 45 to 15 ° on the drive side and 20 to 1.5 ° on the coast side (when the torque direction is reversed, such as when engine braking).By making the cam angle on the coast side small, the differential limit when entering a corner is kept low, push understeer is suppressed, and the stability of the vehicle is ensured.In addition, as mentioned above, in the multi-plate clutch type LSD, the generation of chattering noise (clutch plate operating noise) tends to be a problem, but on the premise of street use, designated differential oil is used to suppress the generation as much as possible. It is also noteworthy that it comes with.

■ Limited Slip Diff.　Mechanical 1.5WAY type CUSCO designated LSD oil included