Electrical parking brake system for a utility vehicle and operating method

#The invention relates to an electrical parking brake system for a commercial or utility vehicle and to a method for operating the electrical parking brake system.

#In commercial or utility vehicles, electrical parking brake systems, which have to be integrated into the pneumatic brake system of the vehicle, are being used to an increasing degree. The particular feature of electrical parking brake systems is that a handbrake valve is no longer provided to operate them but rather an electrical switch which transmits signals to the electronic control unit of the parking brake system. The electronic control unit then actuates one or more valves as a function of these signals in order to in this way ventilate or vent the spring-type brake cylinders of the parking brake system, that is to say to release or apply the parking brake system.

#With respect to ventilation, that is to say the release of the parking brake system, it is important to comply with certain safety criteria. In particular, the parking brake must never be opened if there is still sufficient pressure in the service brake system to activate the service brake. At least what is referred to as the auxiliary brake pressure must be present, the auxiliary brake pressure being a pressure below the normal service brake pressure which is, however, already sufficient to brake the motor vehicle.

#FIG. 1 is a schematic illustration of components of a first embodiment of an electrical parking brake system according to the invention; and

#FIG. 2 is a schematic illustration of components of a second embodiment of an electrical parking brake system according to the invention.

#FIG. 1 is a schematic illustration of components of a first embodiment of an electrical parking brake system according to the invention. In FIG. 1, continuous lines represent pneumatic lines, while dashed lines indicate electrical lines. A valve device 10 is provided by which compressed air can be applied to a spring-type brake cylinder 12. The spring-type brake cylinder 12 is representative of typical spring-type brake cylinders which can be actuated by the valve device 10. The pressure, which is applied by the valve device 10, is registered by a pressure sensor 28. A signal corresponding to the pressure is output to an electronic control unit 16 by the pressure sensor 28, as a result of which the pressure in the spring-type brake cylinder 12 can be taken into account during the control of the parking brake system, and in particular during the electrical actuation of the valve device 10.

#In addition to the ventilating switched state of the valve device 10, the valve device 10 can vent the spring-type brake cylinder 12. A further pressure sensor 14 is provided, which registers a pressure on the compressed-air-supply side of the valve device 10 and transmits a corresponding signal to the electronic control unit 16. This pressure can, as illustrated, be measured directly upstream of the valve device 10. It can also be measured in the service brake circuits or in a main supply line. It simply has to be characteristic of whether the auxiliary braking effect is already ensured for the operating system. The electronic control unit 16 is connected to other components, specifically and in particular an electrical activation element 18 for the electrical parking brake system which is arranged in the form of a switch or the like in the driver's cab of the vehicle. Furthermore, the electronic control unit 16 can be connected to one or more of the following further components, specifically a seat occupation sensor 20, a brake pedal sensor 22, an accelerator pedal sensor 24 or a seat belt sensor 26. These sensors can supply reliable information as to whether the driver is present in the driver's cab, so that an enabling process takes place within the control unit 16 as a function thereof, and when there is a sufficient pressure measured by the pressure sensor 14, in order to transfer, on this basis, the valve device 10 into a state in which the spring-type brake cylinder 12 is ventilated.

#FIG. 2 is a schematic illustration of components of a second embodiment of an electrical parking brake system according to the invention. According to FIG. 2, the parking brake system corresponds largely to that according to FIG. 1. In contrast to FIG. 1, the valve device 10 is configured as a pilot-controlled valve, with the pilot-controlled solenoid valve 30 and the pilot-controlled piston 32 being represented by their respective switching symbols. As a result, relatively large flow cross sections can easily be made available in the valve region. The pilot-control can be provided by a 3/2 way solenoid valve or, for example, also by two 2/2 way solenoid valves which are connected in parallel. In its energized state, in the latter case one of the solenoid valves connects the supply to a pilot-control chamber, while the other solenoid valve vents the pilot-control chamber in the energized state. In the currentless state, both 2/2 way solenoid valves are switched into the shutoff position by a spring.