DESIGNS: ACTIVE AWD DRIVE
It would seem that it is no longer possible to supplement the existing all-wheel drive transmissions with something new. But no wonder they say that there is no limit to perfection; This expression is especially relevant in our time, when many car systems are transformed from passive to active. Recently, Honda reported on the start of production of the SH-AWD (Super Handling All-Wheel Drive system - all-wheel drive system with advanced controllability), which we already reported (ЗР, 2004, No. 6). The novelty seemed so curious to us that we decided to talk about its device in detail.
Unlike all currently known schemes, SH-AWD allows you to distribute torque not only between the rear and front axles, but also between the left and right wheels. Without a doubt, this feature opens a new era in the design of transmissions. It is no secret that four-wheel drive has long ceased to be only a weapon for fighting off-road. Moreover, now this is not about that at all - after all, SH-AWD plan to install on the business class sedans "Honda Legends" and "Acura RL" (the latter still exists as a prototype), which are unlikely to leave the asphalt in their entire lives. All-wheel drive they need to give refined controllability and stability at high speeds and in all weather conditions.
The electronic component of the novelty includes sensors of the angle of rotation, lateral and angular acceleration, wheel speed, engine speed and intake air pressure, gear ratio in the transmission. Information from all sensors enters the computer, which in thousandths of a second calculates the optimal distribution of torque on the wheels. Next, the computer gives the order to the differential control unit: it distributes the moment between the axles and rear wheels in accordance with the immediate need. It transfers from 30 to 70% of the moment to the desired axis, from 0 to 100% to one of the rear wheels. But this is the merit of “iron”, which corresponds, if not surpasses electronics in the amount of know-how.
The main innovations are collected in the rear differential. First of all, these are electromagnetic multi-plate clutches, which were first used in the automotive industry. Each one knows the transmission of the moment to "their" rear wheel, right or left. Built-in electromagnetic coils change the position of the magnet core relative to its body. The electronic brain controls what current is supplied to the magnet - thereby compressing the disk packs and smoothly changing the distribution of torque. Both clutches are able to work independently of each other, but, of course, under the general control of a computer. Clutch modules are supplemented by their own planetary gears.
In tandem with the differential, an accelerator unit works, making the car's behavior in tight corners more reliable. His mission is the forced "twisting" of the rear wheels in turns, which is how he differs from the usual devices.
It is no secret that in a turn, the trajectory of the external rear wheel moves outward relative to the trajectory of the front wheels. The problem is that with the traditional transmission scheme, the rear outer wheel rotates slower than the front ones and thereby prevents full transmission of power. As a result, a deterioration in handling and a risk of skidding. The accelerator unit SH-AWD is designed to solve this problem.
While driving in a straight gear, the planetary gears rotate synchronously with the driveshaft - the speed of the front and rear wheels is the same. As soon as the car enters into a turn, the hydraulic drive, by means of another third clutch module, turns the planetary gear into operation: at the same time, the rear wheel is “spun” from the right side to the optimum speed!
It is noteworthy that the electronics gives orders based on information about driving style. In other words, if the driver enters the car into a turn, keeping his foot on the accelerator pedal, the reaction of the electronics will be completely different in comparison with the situation when the car registers an arc by inertia or when braking. Thus, SH-AWD allows you to change the transmission of torque, eliminating obvious manifestations of understeer or oversteer.
Perhaps, one could put an end here: the above advantages are more than enough to convince the “Honda” bosses to give the novelty a start in life faster. But in order to finally prove the usefulness
SH-AWD, the developers give another argument.