ELECTRONICALLY SLIP-CONTROLLABLE BRAKING SYSTEM

Abstract

An electronically slip-controllable braking system including an actuatable master brake cylinder, to which at least one wheel brake, associated with a wheel of a front axle and at least one wheel brake, associated with a wheel of a rear axle of a vehicle, are connected. An electronically activatable first actuator system sets and regulates brake pressures different from one another in the wheel brakes as a function of the particular present slip conditions. An electronically activatable second actuator system effectuates the setting and regulating of a uniform brake pressure at the wheel brakes and a third actuator system limits the brake pressure generated by the second actuator system at the wheel brakes associated with the wheels of the rear axle. The third actuator system controls a second pressure medium connection between the associated wheel brake of the rear axle and a pressure medium storage container.

Claims

1. An electronically slip-controllable braking system for a motor vehicle, comprising: an actuatable master brake cylinder, to which at least one wheel brake, which is associated with a wheel of a front axle of the vehicle and at least one wheel brake, which is associated with a wheel of a rear axle of the vehicle, are connected; an electronically activatable first actuator system for setting and regulating brake pressures different from one another in the wheel brakes as a function of the slip conditions present at the particular wheels; an electronically activatable second actuator system for at least indirectly setting and regulating a uniform brake pressure at the wheel brakes of the vehicle braking system; a third actuator system which controls a first pressure medium connection between the wheel brake of the rear axle and the second actuator system; and at least one electronic control unit which controls the electronic activation of at least one of the first, the second, and the third actuator system; wherein the third actuator system controls a second pressure medium connection between the wheel brake of the rear axle and a pressure medium storage container.

2. The electronically slip-controllable braking system as recited in claim 1, wherein the second pressure medium connection connects the associated wheel brake directly to the pressure medium storage container.

3. The electronically slip-controllable braking system as recited in claim 1, wherein the third actuator system is equipped with at least one electronically activatable directional control valve per wheel brake of the rear axle, which is movable from a base position, in which the first pressure medium connection is open and the second pressure medium connection is closed, into at least one first switch position, in which the first pressure medium connection is blocked and the second pressure medium connection is open.

4. The electronically slip-controllable braking system as recited in claim 1, wherein the at least one directional control valve of the third actuator system is movable into a second actuating position, in which the first and the second pressure medium connections are blocked.

5. The electronically slip-controllable braking system as recited in claim 1, wherein the third actuator system is equipped with two directional control valves, which are switchable by electronic activation, per wheel brake of the rear axle, a first directional control valve controlling the first pressure medium connection and a second directional control valve controls the second pressure medium connection.

6. The electronically slip-controllable braking system as recited in claim 1, wherein the pressure medium storage container is one of: (i) connected in a pressure-medium-conducting manner to a reservoir associated with the master brake cylinder of the braking system, or (ii) identical to the reservoir.

Description

BRIEF DESCRIPTION OF EXAMPLE EMBODIMENTS

[0023] An exemplary embodiment of the present invention is shown in the figures and is explained in greater detail below.

[0024] FIG. 1 shows, in schematically simplified form, an electronically slip-controllable braking system on which the present invention is based, including a first actuator system, a second actuator system, and a third actuator system for controlling and regulating the brake pressure in wheel brakes of a front axle and a rear axle of a vehicle.

[0025] FIG. 2 additionally shows the structure according to the present invention of the third actuator system and its fluidic contacting with the remaining vehicle braking system.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0026] Electronically slip-controllable braking system 10 according to FIG. 1 includes, inter alia, an actuating unit 14, which is actuatable by a driver by muscle strength via a pedal 12, for example, and a master brake cylinder 16, acted upon by this actuating unit 14, and which is supplied with pressure medium by a connected reservoir 18. Actuating unit 14 is equipped with an electronically activatable actuator 20, by which the brake force applied by the driver may be boosted via external force. This actuator 20 is, for example, an electronically activatable electric motor including a downstream gear unit. An electronic activation of the electric motor may take place as a function of the actuation of pedal 12 or independently of a pedal actuation. For the first mentioned case, pedal sensors 13 are provided, which detect the actuating force and/or the actuating travel and therefore a braking intention of a driver and whose sensor signals are evaluated by an electronic control unit 22 to compute the activation signals for the electric motor.

[0027] Electronically activatable brake booster or actuating unit 14 form, in operational connection to master brake cylinder 16 and control unit 22 within the vehicle braking system, a so-called second actuator system 24 or secondary actuator system. The latter is capable of applying a uniform brake pressure to wheel brakes 26a through 26d of braking system 10, this application taking place indirectly by way of a first actuator system 30 or primary actuator system situated downstream from second actuator system 24.

[0028] Master brake cylinder 16 supplies two brake circuits separate from one another with pressure medium and is connected for this purpose via two lines 28a, 28b, which are associated with the brake circuits, to mentioned first actuator system 30 or primary actuator system.

[0029] This primary actuator system 30 is the hydraulic assembly of a slip-controllable vehicle braking system well known from the related art, which is also known under the name ABS/ESP braking system. The total of four wheel brakes 26a through 26d are connected in a pressure-medium-conducting manner to this first actuator system or primary actuator system 30. Each two of these wheel brakes 26a, 26b are provided to decelerate wheels 34a, 34b of a front axle 36 or wheels 34c, 34d of a rear axle 38 of the vehicle.

[0030] Primary actuator system 30 is, in contrast to secondary actuator system 24, capable of supplying different brake pressures individually to various wheel brakes 26a through 26d of vehicle braking system 10. For this purpose, this primary actuator system 30 has, inter alia, a pressure generator unit drivable by an electric motor (not shown), and electronically activatable solenoid valves.

[0031] A modulation of the brake pressure by these components is carried out as a function of the slip conditions which prevail at affected wheel 34 and are detected by wheel sensors 35. Their measuring signals represent the particular wheel speeds and are supplied to electronic control unit 22 and further processed into activation signals for the pressure generator or regulating components of first actuator system 30.

[0032] Two brake lines 40c, 40d lead via a third actuator system 42 of vehicle braking system 10 to the two wheel brakes 26c, 26d of rear axle 38. This third actuator system 42 is accordingly situated downstream from primary actuator system 30 and upstream from wheel brakes 26c, 26d of rear axle 38. Primary actuator system 30, third actuator system 42, and wheel brakes 26c, 26d of rear axle 38 are accordingly connected in succession or in series.

[0033] In normal operation of vehicle braking system 10, the required brake pressure is provided by an adapted electronic activation of the second actuator system or secondary actuator system 24 as a function of an actuation of pedal 12 and possibly adapted by electronic activation of the first actuator system or primary actuator system 30 to the slip conditions prevailing at wheels 34a through 34d. The brake pressure buildup or the brake pressure modulation may be carried out with or without driver participation, for example, if the driving condition of the vehicle or the traffic conditions require it, or the vehicle is operated in an autonomous driving mode.

[0034] Despite all technical precautions, malfunctions in such an intended operation of vehicle braking system 10 are not to be precluded entirely. In case of an occurring malfunction at primary actuator system 30, secondary actuator system 24 is capable with the aid of its actuator 20 of independently building up a brake pressure, to finally decelerate the vehicle to a standstill. Primary actuator system 30 and secondary actuator system 24 are accordingly redundant to one another, so that a failure of first actuator system 30 is secured by provided second actuator system 24.

[0035] As explained above, third actuator system 42 is present to lower the brake pressure level at wheel brakes 26c, 26d of rear axle 38 in relation to the brake pressure level at wheel brakes 26a, 26b of front axle 36, if secondary actuator system 24 is active in case of fault of primary actuator system 30 and if the brake pressure provided by secondary actuator system 24 is not convertible in its entirety into brake power by wheel brakes 26c, 26d, i.e., if there is an impending risk of locking at wheels 34c, 34d of rear axle 38.

[0036] Third actuator system 42 is activated in this case by electronic control unit 22 in such a way that the brake pressure at wheel brakes 26c, 26d of rear axle 38 is adapted to a dynamic displacement of the axle load taking place during the braking procedure. Premature locking of wheel brakes 26c, 26d of rear axle 38 and an unstable driving condition of the vehicle which necessarily accompanies this are prevented by such an adaptation of the brake pressure. Furthermore, a lengthening of the vehicle braking distance is counteracted. In other words, third actuator system 42 reduces the brake pressure at wheel brakes 26c, 26d of rear axle 38 enough that wheels 34c, 34d associated with these wheel brakes 26c, 26d do not keep rolling or do not permanently lock in an uncontrolled manner.

[0037] The structure of this third actuator system 42 is illustrated in FIG. 2. Components of FIGS. 1 and 2 corresponding to one another are provided with uniform reference numerals in the following description.

[0038] FIG. 2 shows first actuator system 30, which is supplied with pressure medium under brake pressure via brake lines 28a, 28b, which are associated with the two brake circuits of braking system 10. A total of four wheel brakes 26a through 26d are connected to first actuator system 30 via brake lines 40a through 40d. It is to be presumed that wheel brakes 26a and 26b are located on front axle 36 (FIG. 1) of the vehicle, while wheel brakes 26c and 26d are situated on rear axle 38 (FIG. 1) of the vehicle. Third actuator system 42 is located between first actuator system 30 and wheel brakes 26c, 26d of rear axle 38. The third actuator system includes an actuator housing 50, which is designed separately from first actuator system 30 by way of example and is illustrated on the basis of a dashed outline, and which is contacted via pressure medium connections with brake lines 40c and 40d and with wheel brakes 26c and 26d of rear axle 38.

[0039] One pressure buildup valve 52c, 52d and one pressure reducing valve 54c, 54d are situated on actuator housing 50 per wheel brake 26c, 26d. Furthermore, a pressure medium storage container 56 is provided.

[0040] Furthermore, a pressure-actuated check valve 58c, 58d is connected in parallel to each pressure buildup valve 54c, 54d. This check valve 58c, 58d is situated in the pressure medium circuit in such a way that it blocks a through flow direction from first actuator system 30 to wheel brake 26c, 26d or unblocks the opposite direction thereto, i.e., from wheel brake 26c, 26d to first actuator system 30, if a correspondingly oriented pressure gradient is applied by wheel brake 26c, 26d in the direction of first actuator system 30. Finally, at least one pressure sensor 60 is also present, which measures the instantaneous brake pressure at one of the two wheel brakes 26c, 26d of the rear axle and supplies the corresponding measuring signal to electronic control unit 22.

[0041] As may be inferred from the symbolic illustration in FIG. 2, pressure buildup valves 52c, 52d are preferably electromagnetically actuatable directional control valves having precisely one inflow and one outflow, which are switchable into a blocking position by electronic activation of a valve actuator from a normal open base position, against a force of a restoring means. Pressure buildup valves 52c, 52d control the pressure medium passage of brake lines 40c, 40d and therefore indirectly a first pressure medium connection 46 from second actuator system 24 of braking system 10 to one of wheel brakes 26c, 26d on rear axle 38 of the vehicle.

[0042] The two pressure reducing valves 54c, 54d are also electromagnetically actuatable, but in contrast to explained pressure buildup valves 52c, 52d, they are switchable from a normal closed base position into a passage position against the force of a restoring means. In the passage position, associated wheel brakes 26c, 26d are each coupled via a second pressure medium connection 48 to a shared pressure medium storage container 56. Alternatively, a separate pressure medium storage container 56 could also be associated with each wheel brake 26c, 26d. The at least one pressure medium storage container 56 is suitable for accommodating or storing pressure medium under atmospheric pressure.

[0043] The provided third actuator system 42 is not active in malfunction-free normal operation of vehicle braking system 10, i.e., first actuator system 30 and second actuator system 24 have a pressure-medium-conducting connection to wheel brakes 26c, 26d of the rear axle. Third actuator system 42 is first also activated when a malfunction of primary actuator system 30 has been determined by electronic control unit 22 and in addition the brake pressure provided by secondary actuator system 24, as a result of the axle load displacement occurring during a braking procedure, also cannot be converted in its entirety into a brake power by wheel brakes 26c, 26d of rear axle 38. The latter is detectable by wheel sensors 35 by way of an occurring speed change of wheels 34a through d.

[0044] In the activated state, third actuator system 42 interrupts the pressure medium connection between first actuator 24 and wheel brakes 26c, 26d and thus prevents a further increase of the brake pressure at wheel brakes 26c, 26d of rear axle 38 up to the brake pressure level provided by second actuator system 24. For this purpose, third actuator system 42 blocks brake line 40c, 40d to wheel brakes 26c, 26d of rear axle 38 by electronic activation of pressure buildup valves 52c, 52d.

[0045] Notwithstanding this, in parallel thereto, a further pressure buildup may take place at wheel brakes 26a, 26b of front axle 36 via brake lines 40a, 40b, specifically until these wheel brakes 26a, 26b also reach their locking limit. However, the resulting brake pressure settable at wheel brakes 26a, 26b of front axle 36 is significantly higher than that at rear axle 38, since an additional load of front axle 36 is accompanied by a corresponding relief of rear axle 38 due to the dynamic axle load displacement.

[0046] If the slip conditions at wheels 34c, 34d of rear axle 38 change during a braking procedure controlled by secondary actuator system 24, i.e., in the event of malfunctioning operation of primary actuator system 30, in a direction which makes necessary a reduction of the set brake pressure, this is thus carried out with the aid of electronic activation of pressure reducing valves 54c, 54d of third actuator system 42 by control unit 22. Pressure reducing valves 54c, 54d thereupon switch into their passage position and release second pressure medium connection 48 between wheel brakes 26c, 26d and pressure medium storage container 56. Pressure medium drains out of wheel brakes 26c, 26d via this second pressure medium connection 48 on a direct path to pressure medium storage container 56, until the brake pressure in wheel brakes 26c, 26d is reduced to a lower pressure level, at which a permanent locking hazard of associated wheels 34c, 34d no longer threatens. If this state is achieved, the electronic activation of pressure reducing valves 54c, 54d is canceled, so that pressure reducing valves 54c, 54d are moved by their restoring element back into the base position again, in which second pressure medium connection 48 is interrupted.

[0047] Pressure medium storage container 56 at the end of second pressure medium connection 48 may be connected to reservoir 18 of braking system 10 or may alternatively also be identical to reservoir 18 of master brake cylinder 16. Pressure medium drained from wheel brakes 26c, 26d is thus available again to braking system 10 for a renewed brake pressure buildup or for brake force boosting immediately after a discharge from wheel brakes 26c, 26d.

[0048] Check valves 58c, 58d, which are connected in parallel to pressure buildup valves 52c, 52d, are also used for reducing the brake pressure in wheel brakes 26c, 26d of rear axle 38, but presume correct operation of primary actuator system 30. If such correct operation of primary actuator system 30 is present, the pressure medium may be actively conveyed from wheel brakes 26c, 26d by a pressure generator of primary actuator system 30 to reservoir 56 or 18. Check valves 58c, 58d open in a pressure-controlled manner and thus unblock a bypass around particular pressure buildup valve 52c, 52d. At least a large proportion of the quantity of pressure medium flowing back flows through check valves 58c, 58d and is not obstructed by the narrow through flow cross sections of pressure buildup valves 52c, 52d. The combination of open pressure reducing valves 52c, 52d and check valves 58c, 58d connected in parallel thereto accordingly ensures a preferably unthrottled drainage of the pressure medium from wheel brakes 26c, 26d or opposes the pressure medium flow that is flowing back with an extremely low flow resistance. A brake pressure adaptation accordingly takes place rapidly.

[0049] Of course, modifications or additions to the described exemplary embodiment are possible, without departing from the present invention.

[0050] It is to be noted in this regard that electronic control unit 22 which is mentioned in the description does not necessarily have to be designed as a single control unit, but rather may include multiple individual control units, each may be associated with one or multiple actuator systems 24, 30, 42. However, in particular for reasons of redundancy, at least two control units 22 which are electronically separate from one another are to be provided, of which a first controls first actuator system 30 and/or second actuator system 24, while a second control unit is provided to control third actuator system 42.