BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a parking brake system for motor vehicles. The parking brake system has a control for activating a parking brake function, a first control unit for activating a braking device and assigned to a parking brake, and a second control unit for activating the braking device and assigned to a service brake. The second control unit controls brake booster functions that promote traveling comfort and safety.
In addition to a known service brake system (service brake) which is actuated by a foot pedal, legislation requires a parking brake system (parking brake)—frequently also referred to as a handbrake. Such a parking brake is configured so as to be largely independent of the service brake of the motor vehicle and is used, on the one hand, to secure the motor vehicle in a stationary state (static activation) and on the other hand to brake the vehicle while traveling (dynamic activation). Dynamic activation may be necessary when the service brake fails, for example. Conventional vehicles are predominantly equipped with manually activated parking brakes. The parking brake is engaged or released in a metered fashion by a Bowden cable using a brake lever that is usually disposed in the center console. Foot-activated parking brakes that are engaged in a metered fashion by a foot pedal and released instantaneously by a release lever are also known. Metered release of the parking brake is not possible with foot-activated systems.
Both manually activated and foot-activated parking brakes have the disadvantage that the operator of the motor vehicle must apply an appreciable force at least to engage the parking brake. In addition, the brake lever or the foot pedal takes up a large amount of space in the center console or in the pedal region.
In order to overcome this disadvantage, electrical parking brakes—referred to below as electrical parking brakes or EPB for short—are known which are activated with little application of force by controls, for example by switching a key. The controls are advantageously disposed in the dashboard region or steering wheel region. Such an electrical parking brake is known from Published, Non-Prosecuted German Patent Application DE 198 38 886 A1.
When the parking brake is activated dynamically, that is to say the control is activated while the vehicle is traveling, controlled braking of the vehicle must be ensured even when the vehicle is traveling at a high velocity and wheel slip is occurring. The parking brake must therefore by necessity be controlled as a function of the travel situation. For this purpose, in the known parking brake the wheel speeds are transmitted to the control unit of the parking brake and evaluated there. Effective control can be achieved in such a case only by complex algorithms such as are known in anti-lock braking systems. However, this entails high additional costs.
Published, Non-Prosecuted German Patent Application DE 198 26 687 A1 discloses an electrically activated brake system for motor vehicles in which, by activating a parking brake control, the service brake system is activated above a predefined vehicle velocity and the parking brake system is activated below the predefined vehicle velocity.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a parking brake system for motor vehicles which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which controlled braking of the motor vehicle is ensured at low cost when the parking brake is activated dynamically.
With the foregoing and other objects in view there is provided, in accordance with the invention, a parking brake system for a motor vehicle. The parking brake system includes a braking device, a control for activating a parking brake function, a first control unit for activating the braking device and assigned to a parking brake, the first control unit is connected to the control, and a second control unit for activating the braking device and assigned to a service brake. The second control unit is connected to the control and controls brake booster functions which promote traveling comfort and safety. If the control is activated at a vehicle velocity above a predefined minimum velocity and below a predefined maximum velocity, the braking device is activated by the first control unit and by the second control unit. The braking pressures or braking forces are predefined by the second control unit as a function of a braking effect achieved by the first control unit.
In order to achieve continual improvements in safety and to increase the traveling comfort and operating convenience, more and more vehicles are being equipped with brake booster functions such as an electrical stability program (ESP), a traction control system (ASR) or electrical differential lock (EBS) system. Such booster functions can also be used to generate a braking force or a braking pressure at the braking device of the service brake, and thus achieve a braking effect, without activating the service brake pedal. Evaluations, for example of the wheel speeds, which permit the motor vehicle to be braked as a function of a travel situation, are carried out in any case in the control units of such brake booster functions. According to the invention, when the parking brake control is activated while the vehicle is traveling the braking device assigned to the service brake is activated by the control unit of such a brake booster function. In order to do this, the brake actuators which are responsible for generating the braking force or the braking pressure at the brake device are controlled. As a result, the parking brake function is easily assumed by the service brake while the vehicle is traveling. However, in particular the functionality of the control unit of the brake booster function is utilized to control the actuators for the braking device on an individual basis and as a function of a travel situation.
In accordance with an added feature of the invention, the second control unit is programmed to: initiate and control an electrical stability program; initiate and control a traction control function; and initiate and control an electrical differential locking function.
In accordance with an additional feature of the invention, a first signal line connects the control to the first control unit, and a second signal line connects the control to the second control unit.
In accordance with a concomitant feature of the invention, a first signal line connects the control to the first control unit, and a second signal line connects the first control unit to the second control unit. A parking brake request signaled by activating the control is transmitted from the first control unit to the second control unit through the second signal line.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a parking brake system for motor vehicles, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a parking brake system according to the invention. The parking brake system has a control 1 for activating a parking brake function. The control 1 may be embodied, for example, as a single push-button key that merely discriminates between the states “activated” and “not activated”. Likewise, the control 1 may also be embodied as a double push-button key with the states “engage”, “release” and a “home position”. The selection of the control 1 here is mainly dependent, as is its configuration in the interior of the vehicle, on criteria relating to comfort and ergonomics. For safety reasons, the motor vehicle is preferably equipped with a further control (redundancy principle) which is not illustrated. A parking brake request from a driver which is signaled by activating the control 1 is transmitted through a signal line 2 to a first control unit 3 being an electrical parking brake control unit or EPB control unit 3 for short. The parking brake request of the driver is transmitted from the control 1 through a signal line 4 to a second control unit 5 being a brake-booster function-control unit or BAF control unit 5 for short. As an alternative to parallel reading-in of the parking brake request by the EPB control unit 3 and the BAF control unit 5, the parking brake request can also be passed on from the EPB control unit 3 to the BAF control unit 5 via a further signal line 20, for example in the form of a controller area network (CAN) bus shown by the dashed line in FIG. 1.
Brake booster functions which promote safety or comfort, such as for example an electrical stability program and/or a traction control (ASR) and/or an electrical differential lock (EDS), are controlled using the BAF control unit 5. To control such brake booster functions, further signals which characterize the travel situation, for example the wheel speeds, are necessary. This information is transmitted to the BAF control unit 5 from sensors (not illustrated) or other control units via one or more signal lines 6. A variable which characterizes a velocity of the motor vehicle, for example wheel speeds or the actual velocity of the vehicle calculated therefrom, is transmitted from the BAF control unit 5 to the EPB control unit 3 through one or more signal lines 7 (redundancy principle). The BAF control unit 5 controls a service brake actuator 8 by which a desired brake pressure or a desired braking force is set at a braking device 9. When the service brake is a hydraulic one, the service brake actuator 8 is embodied for example as a hydraulic unit via which the hydraulic pressure at the braking device 9 is controlled. The braking device 9 can be embodied here as disc brakes or drum brakes. For reasons of clarity, only a single braking device 9 is illustrated in FIG. 1 by way of example. However, in reality, each wheel of the motor vehicle is preferably assigned its own braking device 9.