The invention relates to a motor vehicle having a brake system and a drive system, wherein the brake system is composed of: a vehicle movement dynamics controller, an electronic control group for wheel-specific actuation of brakes and a hydraulic unit with pressure medium supply and wheel-specific hydraulic valves, combined to form one assembly, for activating the individual wheel brake cylinders, and wherein the drive system has at least one drive train which has the purpose of driving the wheels and in which a controllable clutch is arranged, which clutch is activated by a clutch controller as a function of operating variables using a clutch actuation means and a hydraulic valve for acting on its hydraulic actuator.
Brake systems with wheel-specific hydraulic valves for activating the individual wheel brake cylinders are a recent development and are particularly suitable for applying modern driving aids such as ABS (anti-lock brake controller), ETC (electronic traction control) and ESP (electronic stability program). They may be, for example, electrohydraulic brake systems (often referred to in specialist literature in abbreviated form as “EHB”), such as is described, for example, in DE 199 23 689 A1.
The drive system may comprise one or more drive trains, corresponding to a vehicle with one or more driven axles. In the first case, the controllable clutch has the purpose of locking the axle differential which is continuously variable in accordance with the requirements of vehicle movement dynamics. In the second case, it can be used for connecting the further driven axle or locking a central differential mechanism (also referred to as inter-axle differential) in a continuously variable fashion, or for controlling the distribution of torque between the two axles.
In the drive systems of this type mentioned above, the clutch, or the clutches, each have a separate functional group with a separate power source and a separate control device which retrieves the operating data of the vehicle from a bus (this is usually a CAN bus) and calculates the necessary clutch position from said data and then correspondingly actuates the clutch. Most of this operating data together with other data, including that from the vehicle movement dynamics controller of the brake system, is used and therefore obtained from the same bus.
Furthermore, in many situations the brake system must be matched to the clutch control. This means that two separate systems have to communicate with one another, the data between the two controllers, which are usually programmed processors, being connected and exchanged via interfaces, coding/decoding means and the bus. This is a source of errors and also requires time which is always critical in vehicle movement dynamics control operations. Furthermore, the expenditure on control and activation is considerable, both in logistical terms and also because the safety requirements which are made of the clutch control require a minimum level of expenditure which exceeds the scope of pure control functions, which is small in itself.
Although DE 37 21 626 discloses a motor vehicle with first-generation four-wheel drive in which the master brake cylinder of a brake device acts on the wheel brakes of the wheels and also the actuating element of a clutch is activated, the brake device is purely hydraulic and therefore does not have any electronically actuated, wheel-specific hydraulic valves. The clutch is only used to disconnect the drive connection during braking and cannot be actuated in a variable fashion.
It is therefore the object of the invention to make the vehicle as a whole cheaper while at the same time improving it functionally.