Patent Application
20060113835
This application is based on German Patent Application 10 2004 056 661.5 filed Nov. 24, 2004, upon which priority is claimed.
1. Field of the Invention
In modern motor vehicles, electronically regulatable vehicle brake systems are used not only for their actual braking function but also for preventing unstable vehicle travel states. Unstable travel states go hand in hand with the occurrence of wheel slip at least one of the vehicle wheels. Wheel slip can be eliminated by targeted braking of the affected vehicle wheel. In the anti-lock braking mode, blocking of one of the vehicle wheels during a braking event is therefore prevented by modulating the brake pressure, while in the traction control mode, spinning of a driven vehicle wheel is avoided by braking the affected wheel, and in the vehicle stability control mode, skidding of the vehicle is counteracted by purposeful brake engagement. In all these cases, an electronic control unit, with the aid of sensors, serves to detect the braking or travel status of the vehicle and to evaluate the arriving signals as appropriate trigger signals for the components of the vehicle brake system.
2. Description of the Prior Art
Various models of electronically regulatable vehicle brake systems are being manufactured. A distinction is made between conventional systems, in which the brake pressure is generated by the driver by muscle force, and so-called electrohydraulic systems, in which the brake pressure is furnished by external force, by an externally driven pressure generator. Regardless of how the brake pressure is furnished, regulating the brake pressure is done by electronic triggering of electromagnet valves and pressure generators, which are combined into a compact structural unit in a so-called hydraulic unit.
An electronically regulatable vehicle brake system of a conventional, muscle-force-operated design is already known, for instance from German patent disclosure DE 41 38 027 A1. This vehicle brake system has a master cylinder in which a brake pressure is built up by the driver by muscle force. The master cylinder is hydraulically coupled with a hydraulic unit. In the hydraulic unit, among other elements there are electronically triggerable magnet valves, for modulating the brake pressure at a wheel brake. The hydraulic unit furthermore has a triggerable pressure generator. By its intake side, it is connected downstream of the valves for modulating the brake pressure into a hydraulic circuit. Its compression side discharges back into the hydraulic circuit upstream of these valves for modulating the brake pressure. An additional intake line connects the intake side of the pressure generator to the master cylinder. This line connection is controlled by a mechanical blocking valve. The blocking valve operates without a valve spring and prevents a flow of pressure fluid from the intake side of the pressure generator back to the master cylinder, and it opens as soon as an underpressure is present at the intake line. An electromagnet valve connected parallel to the blocking valve controls a pressure fluid communication from the master cylinder to the wheel brakes of a brake circuit. If it is electronically triggered, the electromagnet valve interrupts this pressure fluid communication and thus hydraulically disconnects the master cylinder from the wheel brakes. This is the case in the anti-lock mode, for instance, during which the brake pressure is modulated solely by the pressure generator in cooperation with the magnet valves in the wheel brakes. The pressure generator can aspirate pressure fluid as needed from the master cylinder via the opened blocking valve.
A further electronically regulatable vehicle brake system is known from German patent disclosure DE 197 01 070 A1 which pertains to a so-called electrohydraulic vehicle brake system, in which in the operational state the brake pressure is furnished solely by external force. To that end, there is a motor-driven pressure generator, which communicates via an intake line with a pressure fluid reservoir connected to a master cylinder. The intake line is controlled by a triggerable proportional valve. In this vehicle brake system, the master cylinder serves only to generate a set-point braking valve, which is specified by the driver's actuation of the brake pedal.
A parameter that is definitive for a vehicle brake system defines the dynamics with which the vehicle brake system is capable of reacting to suddenly changing braking conditions. For high dynamics, relatively large control cross sections of the valve devices are advantageous, especially in the case of a valve device for controlling the intake line of the pressure generator. For low ambient temperatures, relatively large control cross sections are also favorable, since in that case, because of the low viscosity of the pressure fluid, the speed with which an increase in the brake pressure in the vehicle brake system occurs necessarily drops. There are technical limits to an arbitrary increase in size of the control cross sections of the valves, because of the associated dimensioning of the magnetic circuit of the valve and the resultant structural size of the valve. In practice, besides valves with suitably large control cross sections, precontrollable hydraulic valves have also proved themselves, among others. These valve models, however, are special models that must be developed specifically for this purpose, and they are therefore disadvantageous because so many parts are needed and because of the handling, design and maintenance costs to the manufacturer of such vehicle brake systems.
By comparison, a vehicle brake system of the invention has the advantage that with relatively little engineering effort and expense, an increased pressure fluid throughput in the intake line of the pressure generator is attained, even at low ambient temperatures. Valves developed specifically for controlling the intake line are no longer necessary, since now a valve structurally identical to the valve for modulating the brake pressure can be used in the intake valve unit. This reduces the number of parts needed and lessens the requisite effort and expense in assembling, developing, and maintaining such vehicle brake systems.
The invention comprises using a 2/2-way magnet valve connected parallel to a mechanical blocking valve, whose blocking valve member, if a pressure threshold in the master cylinder is exceeded, can be moved out of its open basic position into its blocking position counter to the force of a restoring element.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings, in which:
The vehicle brake system 100 shown in
For modulating the brake pressure in the brake circuit 18, magnet valves 22-28, a pressure generator or pump 32 driven by an external motor 30, and a low-pressure reservoir 34 are connected to one another in a hydraulic circuit. These components 22-28, 30, 32 are disposed in a common hydraulic unit, identified by reference numeral 40, which is represented schematically in
An electronic control unit 50 detects input variables 54 measured by sensors 52, 58 and processes them into trigger signals 56 for the magnet valves 22-28 and the motor 30 of the pressure generator 32. The control unit 50 adapts the brake pressure to the slip conditions ascertained at the various vehicle wheels. To that end, a pressure sensor 52 detects the brake pressure prevailing in the master cylinder 10, which represents a set-point value specified by the driver via the pedal 14. Via rpm sensors 58 at the vehicle wheels, the control unit 50 ascertains any danger of wheel locking that might exist. There may also be other sensors, not shown, for instance for detecting the actuation travel or actuation speed of the bake pedal 14, or pressure sensors at various points of the hydraulic circuit, for making additional input variables available to the control unit 50 for the sake of improving the capability of regulating the vehicle brake system 100.
There is one brake pressure buildup valve 22, 28 hydraulically upstream and one brake pressure reduction valve 24, 26 hydraulically downstream of each vehicle wheel. The valves 22-28 are represented by hydraulic switching symbols. Thus these valves 22-28 are electromagnetically actuatable 2/2-way switchover valves, which are kept in their basic position by a restoring device. The pressure buildup valves are open in the basic position, while the pressure reduction valves are blocked in the basic position. A check valve 62 is connected parallel to the pressure buildup valves 22 and 28 in a bypass 60. This check valve opens in the direction from the wheel brake 42, 44 to the master cylinder 10 and thereby makes a fast pressure reduction possible when the brake pressure at the master cylinder 10 is decreasing, or in other words when the driver expresses a wish to lessen the braking.
The pressure generator 32 is connected downstream of the pressure reduction valves 24, 26 and feeds pressure fluid from the wheel brakes 42, 44 back into the hydraulic circuit. In a low-pressure reservoir 34 connected between the wheel brake 42, 44 and the pressure generator 32, pressure fluid can be stored temporarily, so as to assure the supply of pressure fluid to the pressure generator 32 upon startup of the pressure generator. A check valve 64 opening in the direction upstream of the pressure generator 32 prevents pressure fluid from flowing from the pressure generator back into the wheel brake 42, 44.
Besides the aforementioned magnet valves 22-28 for modulating the brake pressure, the brake circuit 18 of the vehicle brake system 100 also has a so-called switchover valve 70. It switches the vehicle brake system 100 over from a muscle-force-actuated normal braking mode to an external-force-actuated traction control mode or a vehicle stability control mode. This switchover valve 70 is a 2/2-way switching valve that can be switched electromagnetically out of its open position into a blocking position, counter to the force of a restoring device. In the blocked state, the communication of the master cylinder 10 with the wheel brakes 42, 44 is interrupted. A muscle-force-actuated brake pressure buildup is not possible then; in other words, in that case a brake pressure buildup is effected solely by means of the external-force-driven pressure generator 32.
A check valve 72 is also connected parallel the switchover valve 70. This check valve blocks in the direction of the master cylinder 10 and opens in the direction of the wheel brake 42, 44. When there is a high pressure upstream of the switchover valve 70, pressure fluid can thus flow into the downstream part of the hydraulic circuit. This situation occurs for instance whenever the driver actuates the brake pedal 14 during a fully active brake pressure regulating operation, for instance during a traction control mode, and the brake pressure thus generated in the master cylinder 10 is higher than the pressure downstream of the switchover valve 70.
An intake line 80 leads from the master cylinder 10 to the intake side of the pressure generator 32, and as a result, the pressure generator can feed pressure fluid as needed to the wheel brakes 42, 44 from the reservoir 16 that is coupled to the master cylinder 10. For controlling this intake line 80, a valve unit 82 is provided according to the invention; it comprises a triggerable electromagnet valve 84 and a mechanical blocking valve 86 connected parallel to the electromagnet valve. The blocking valve 86 has a blocking valve member 88 for controlling a control cross section 92 between an inflow connection 94 and an outflow connection 96. In the pressureless state of the vehicle brake system 100 as shown, the blocking valve member 88 is in its open basic position, while the electromagnet valve 84 is in its blocking position, as long as no electronic triggering by the control unit 50 is taking place.
The electromagnet valve 84 of the valve unit 82 is a 2/2-way valve that can open counter to the force of a restoring element. It is advantageously embodied structurally identically to the pressure reduction valves 24, 26, which reduces the number of different valve models in the vehicle brake system 100 and thus lessens the technical complexity of the vehicle brake system.
Structurally, various valve models are conceivable for the blocking valve 86. A first exemplary embodiment is shown, schematically and highly simplified, in
Instead of a ball valve, a plate or flat-seat valve can be used as the blocking valve 86, as shown in simplified form in
As shown in
In a further variant of a slide valve 86c shown in
As explained above, the mechanical blocking valve 86 is located in a bypass around the electromagnet valve 84 and, up to a certain pressure level in the master cylinder that is dictated by the design of the electromagnet valve, assumes an open position. The blocking valve 86 together with the electromagnet valve 84 thus makes an intake path with especially low flow resistance available to the pressure generator 32, and this allows easy aspiration of pressure fluid from the master cylinder. This goes hand in hand with an increase in pressure buildup dynamics during a fully active pressure buildup of the vehicle brake system 100, as is necessary during the traction control mode or the vehicle stability control mode. In both of these operating modes, even at low ambient temperatures, when the pressure fluid is correspondingly more viscous, pressure fluid in sufficient quantity can be made available to the pressure generator 32 by the valve unit 82 of the invention, and relatively good pressure buildup dynamics can be attained. If the driver actuates the pedal 14 during a fully active pressure buildup, then the pressure buildup in the master cylinder 10 brings about the closing motion of the blocking valve member 86. Together with a lessening of the electronic triggering of the electromagnet valve 84, in these operating modes an unwanted aspiration of pressure fluid from the master cylinder 10 by the external-force-driven pressure generator 32 is then no longer possible.
It is understood that changes and additions to the exemplary embodiments described can be made without departing from the fundamental concept of the invention. In this respect it should be noted once again that the invention is not limited to the muscle-force-actuated vehicle brake system 100 shown in the exemplary embodiment, but instead can be used in vehicle brake systems with an external-force-actuated service brake. In such vehicle brake systems, the master cylinder can be hydraulically decoupled from the brake circuit by disconnection valves and serves solely to detect the driver's wishes in terms of braking. If the external force supply fails, the disconnection valves open and make muscle-force-actuated auxiliary braking possible.
The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 056 661.5 | Nov 2004 | DE | national |
