1.XDS
a high-performance car need? Strong power, tough suspension, specialty tires, these are obvious, the other not so from the eye but equally important device can not be ignored: differential. Previously, we often mention the differential, but mainly in off-road car, in fact, for high-performance car, the limited slip differential is also essential.
and in the domestic Golf GTI we heard a new term: XDS electronic differential lock. On the official website, so that manufacturers publicize their products: GTI excellent dynamic balance in the corners also benefited from another magic mdash; mdash; dynamic electronic differential lock XDS vehicle, built into the ESP system can be avoided inside the XDS wheel slip, before effectively improve the drive understeer phenomenon; and large-sized brakes provides an extremely excellent braking performance, providing more secure protection for the ultimate speed of the driver. XDS system seems very strong, of course, we need dialectical view manufacturers propaganda Moreover, there may be a lot of people do not understand: Why can avoid wheel slip inside to avoid understeer?
to measure the performance of the merits of a car, in addition to the ability to see straight-line acceleration, the key is performance in the corners, high-performance models equipped with an ordinary differential if so, when will produce a lot of high-speed cornering problem. In everyday driving, we believe that all four wheels are always close to the ground, the grip of the left and right wheels of the difference can be ignored, the power differential distributed equally to left and right wheels. But in the intense driving situation becomes complicated.
Note: the inside of said wheel, the outer wheel is the drive wheel means on both sides, not including the driven wheel.
● One problem: the loss of power
careful drivers will have such a feeling, and that is an important factor affecting vehicle dynamic performance that so-called weight transfer. For example, why the front brake disc brakes after the car than big? Because the vehicle when braking due to inertia leads to a strong bodyForward, most of the body weight to move the front axle, the front wheel braking force must be big, in fact, only the rear axle brakes share a small part of the work.
Similarly, in high-speed cornering of the vehicle will have a great centrifugal force, the centrifugal force and the greater the faster turning, the centrifugal force causes the body weight is transferred to the outer side of the bend, the car members to clearly understand the rejection of outside forces, and we see the manifestation of the body from the outside of the suspension is compressed outside of the bend, and bend the inside of the wheel is almost off the ground, a sharp decline in grip.
At this disadvantage ordinary open differential was exposed, it is always evenly distributed torque around two smaller axle and tends to drag the side. In particular the high-speed cornering of the vehicle, the inner resistance of the drive wheels so small that almost floating effect is greatly reduced when compared with the torque on the side of the axle in a straight line, the lack of grip may even make the wheels begin to slip occurs and the other side of the grip wheel torque obtained great fertility same relatively small, for the driver is equal to the power losses. This is similar to when we do make a wheel to test four-wheel drive system from the ground state: vacant crazy wheel vehicle idling stop there just barely creeping or two, the difference is not necessarily completely away from the wheel in high-speed cornering and the duration is very short. Some people may think that this phenomenon will only last only a few seconds, will not have any effect on the control, but even if a difference of 0.1 seconds each corner may decide victory or defeat in the race against race.
● Second problem: the front-drive understeer
Now we say it oversteer and understeer. The prevailing view is that the former tend to drive understeer then oversteer tends to drive, and this is mainly related to weight distribution front and rear axles, drive the engine and transmission are arranged in front of the front axle, front and rear axle load during static most of the former already allocated nearly top-heavy, so that the forward corners weight front axle load is further increased, which is likely to make the front wheel grip limit break, loss of steering action, are no longer turning body but along the arc of a turn in a predetermined direction the tangential direction of the line pushed out, it is what we usually say Tuitou.
Tuitou to enhance the cornering speed is obviously bad, so can minimize the impact of understeer it? For the first drive, it wants to change the inherent weight distribution is probably more difficult, you canStarting from another angle, that is to create a yaw moment.
What is the yaw moment? For a simple example, we have a bar across the oars of a boat, when we turned to how to do it? If a turn to the left, we must firmly paddle on the right, this will produce a left yaw moment, the ship left turn. The vehicle is turning to the same principle can also be used. There is no observed how the tank is bend? Both sides of the differential track, or even standing around the tank.
back to the car, now we have by applying a yaw moment to enhance the handling of the system, there is the most typical Acura SH-AWD systems, Haldex of the fourth generation of four-wheel drive and Audi, BMW portion of the rear axle four-wheel type equipment like an active torque distribution apparatus. They use the same principle, that is active when the vehicle is allocated to a wheel outside the steering torque to produce a yaw moment of the vehicle to help in cornering the lateral bending.
● XDS electronic differential lock effect of:
XDS electronic differential lock is to solve the above two problems arise. It means an electronic system through simulated brake limited slip differential. It works when the vehicle is to limit fertility status to grip the inside of the drive wheel brake is applied is small. According to the manufacturers say, XDS have the brakes applied braking force 5-15bar, 1bar per square millimeter is 0.1N, square centimeters is equivalent to 10N, which is one kilogram per square centimeter succeed. Wheel brake electronic principles and some of its off-road vehicles of similar aid.
The operation of the brake to the slipping wheel will have two effects:
First, the inside of the slipping wheel such that the resistance increases more torque transmitted from the engine, corresponding to the outer grip good Fertility more wheel torque obtained, to enhance the performance curve of the vehicle;
Second, since the inner wheels and the outer wheels grip the large and small fertility, although it is still evenly distributed torque, but the vehicle is more torque applied to the ground by the outer wheels, resulting in a cross-point bending in the vehicle turning yaw moment assistance, steering is suppressed to some extent.
● XDS really amazing?
Objectively speaking, XDS can really improve vehicle handling, but if by magic to describe it is clearly exaggerated.
First of all, we can see from the official website of the narrative, XDS is a functional extension out of the ESP based on the basis of today’s mainstream ESP system already has a separate function of the brake wheels to four, which means that XDS already have the hardware conditions, the key is to upgrade the software.
Second, XDS system, although smarter than mechanical limited-slip differential, but not on performance and Honda’s SH-AWD and other comparable because its brake force is not too large, it may cause vehicle instability circumstances, I can only say that is an entry-level limited slip devices, can only be used in entry-level performance car.