Method for Controlling a Hydraulic Brake System

Abstract

In a hydraulic brake system, which includes: a hydraulic pump which is driven by an electric motor and has the purpose of generating a fluid volume flow for the hydraulic brake system; a hydraulic connection for conducting the fluid volume flow between the hydraulic pump and a wheel brake; a reservoir for storing a fluid volume; wherein the reservoir is connected to the hydraulic connection by means of a switching valve, a method includes actuating the switching valve in such a way that by this means a fluid pulsation in the hydraulic connection is counteracted. Furthermore, the method may be implemented with a control unit and a hydraulic brake system.

Claims

1. A method for controlling a hydraulic brake system, said hydraulic brake system including a hydraulic pump which is driven by an electric motor and generates a fluid volume flow for the hydraulic brake system, a hydraulic connection that conducts the fluid volume flow between the hydraulic pump and a wheel brake, and a reservoir that stores a fluid volume, the reservoir being connected to the hydraulic connection by a switching valve, the method comprising: actuating the switching valve in such a way that a fluid pulsation in the hydraulic connection is counteracted.

2. The method according to claim 1, wherein the actuating of the switching valve includes actuating the switching valve so as to attenuate a volume flow gradient from the hydraulic pump to the wheel brake.

3. The method according to claim 1, wherein the actuating of the switching valve includes actuating the switching valve so as to adjust a chronologically varying fluid volume flow loss from the hydraulic pump to the wheel brake.

4. The method according to claim 1, wherein the actuating of the switching valve includes periodically varying a degree of opening of the switching valve.

5. The method according to claim 1, wherein the actuating of the switching valve includes varying a degree of opening of the switching valve during one revolution of the electric motor.

6. The method according to claim 1, wherein the actuating of the switching valve includes taking into account a pump setting.

7. The method according to claim 1, wherein the actuating of the switching valve includes adjusting a degree of opening of the switching valve as a function of a rotor position of the electric motor of the hydraulic pump.

8. The method according to claim 1, further comprising: adapting actuation of the electric motor of the hydraulic pump taking into account the actuation of the switching valve.

9. The method according to claim 1, further comprising at least one of the following steps: defining the fluid volume flow of the hydraulic pump; determining a necessary pressure difference between the hydraulic pump and the wheel brake in order to smooth the fluid pulsation, determining a necessary control flow in order to set a degree of opening of the switching valve, by which a necessary pressure difference is brought about on the basis of an attenuation, formed as a result thereof, of a volume flow gradient; actuating the switching valve with a determined control flow in order to set a corresponding degree of opening of the switching valve; determining a volume flow loss which is brought about, and a necessary increase in rotational speed of the hydraulic pump in order to compensate a volume flow loss; and actuating the hydraulic pump in order to set a necessary increase in rotational speed in order to compensate the volume flow loss.

10. The method of claim 8, wherein the adapting of the actuation of the electric motor includes increasing a rotational speed of the electric motor when the switching valve is opened in order to at least partially compensate the discharge of fluid volume.

11. The method according to claim 1, further comprising: defining the fluid volume flow of the hydraulic pump.

12. The method according to claim 1, further comprising: determining a necessary pressure difference between the hydraulic pump and the wheel brake in order to smooth the fluid pulsation.

13. The method according to claim 1, further comprising: determining a necessary control flow in order to set a degree of opening of the switching valve, by means of which a necessary pressure difference is brought about on the basis of the attenuation, formed as a result thereof, of a volume flow gradient.

14. The method according to claim 1, further comprising: actuating the switching valve with a determined control flow in order to set a corresponding degree of opening of the switching valve.

15. The method according to claim 1, further comprising: determining a volume flow loss which is brought about, and a necessary increase in rotational speed of the hydraulic pump in order to compensate for a volume flow loss.

16. The method according to claim 1, further comprising: actuating the hydraulic pump in order to set a necessary increase in rotational speed in order to compensate a volume flow loss.

17. A control unit of a hydraulic brake system that includes a hydraulic pump which is driven by an electric motor and generates a fluid volume flow for the hydraulic brake system, a hydraulic connection that conducts the fluid volume flow between the hydraulic pump and a wheel brake, and a reservoir that stores a fluid volume, the reservoir being connected to the hydraulic connection by a switching valve, said control unit comprising a processor configured to execute program instructions stored in a memory to: actuate the switching valve in such a way that a fluid pulsation in the hydraulic connection is counteracted.

18. A hydraulic brake system comprising: an electric motor; a hydraulic pump driven by the electric motor so as to generate a fluid volume flow for the hydraulic brake system; a wheel brake; a hydraulic connection that conducts the fluid volume flow between the hydraulic pump and the wheel brake, and a reservoir that stores a fluid volume, a switching valve connecting the reservoir to the hydraulic connection; and a control unit configured to actuating the switching valve in such a way that a fluid pulsation in the hydraulic connection is counteracted, wherein the brake system does not include a static throttle in order to counteract the fluid pulsation in the hydraulic connection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] It is to be noted that the features which are specified individually in the description can be combined with one another in any desired technically appropriate way and indicate further refinements of the disclosure. Further features and the expediency of the disclosure emerge from the description of exemplary embodiments on the basis of the appended figures, of which:

[0040] FIG. 1 shows a brake system of a motor vehicle in a simplified illustration; and

[0041] FIG. 2 shows characteristic curve profiles or pump rattling; and

[0042] FIG. 3 shows characteristic curve profiles or volume flow smoothing.

DETAILED DESCRIPTION

[0043] FIG. 1 shows a simplified illustration of a brake system 1 for a motor vehicle (not illustrated in more detail here). The brake system 1 has a plurality of wheel brakes 2 which can be activated by a driver of the motor vehicle by a brake pedal device 3 as service brakes. The wheel brakes 2 are denoted here by LR, RF, LF and RR, which clarifies their position or assignment on the motor vehicle, where LR stands for left rear, RF stands for right front, LF stands for left front and RR stands for right rear. Two brake circuits 4 and 5 are formed between the brake pedal device 3 and the wheel brakes 2, wherein the brake circuit 4 is assigned to the wheel brakes LF and RR, and the brake circuit 5 is assigned to the wheel brakes LR and RF. The two brake circuits 4 and 5 are of identical design, and the design of the two brake circuits 4, 5 will therefore be explained in more detail below with reference to the brake circuit 4.

[0044] The brake circuit 4 is firstly connected to a master brake cylinder 6 of the brake pedal device 3, wherein the brake pedal device 3 also has a brake pedal 7 which can be activated by the driver and a brake booster 8. The brake booster 8 can be actuated, for example, pneumatically or electromechanically. The brake circuit 4 has a switch-over valve 9 and a high-pressure switching valve 9, which are connected in parallel with one another and follow the master brake cylinder 6. The switch-over valve 9 is designed so as to be open in the currentless state and permits a flow of the hydraulic medium of the brake circuit, that is to say the brake fluid, in both directions. The high-pressure switching valve 9 is designed so as to be closed in the currentless state, and in the energized state it permits a through flow of brake fluid only in the direction of the wheel brakes 2. The switch-over valve 9 is also connected to the two wheel brakes 2 with intermediate connection of in each case an inlet valve 10 which is designed to be opened in both directions in the currentless state. If the two switch-over valves 9 of the brake circuits 4, 5 are closed, the hydraulic pressure remains shut in or maintained in the section of the brake circuits 4, 5 which lies behind, that is to say between, the switch-over valves 9 and the wheel brakes 2, even if the brake pedal 7 is relieved of loading by the driver. If the switch-over valves 9 are opened, a connection of the brake circuits 4, 5 to the reservoir 19 is produced.

[0045] The wheel brakes 2 of the brake circuit 4 are also each assigned an outlet valve 11 which is designed so as to be closed in the currentless state. The outlet valves 11 have a hydraulic pressure accumulator 12 connected downstream of them. The outlet valves 11 are also connected on the outlet sides to a suction side of a pump 13 which is connected to the brake circuit 4 on the pressure side between the switch-over valve 9 and the inlet valves 10. The pump 13 is mechanically coupled to an electric motor 14. There is provision that the electric motor 14 is assigned to the pumps 13 of both brake circuits 4 and 5. Alternatively there can also be provision that each brake circuit 4, 5 has a separate electric motor 14. A control unit 20 controls both the electric motor 14 and the valves 9, 9, 10, 11.

[0046] FIG. 2 shows an illustration of relevant characteristic curve profiles or pump rattling. Opening the switch-over valve at the start of the delivery phase of a pump causes the initial pressure pulse to be partially diverted via the switch-over valve and the volume flow gradient to be attenuated. This reduces the pressure oscillation amplitude in the wheel line. A requirement for this is knowledge of the current rotor position of the motor. The top illustration in FIG. 2 shows the volume flows (as [cm.sup.3/s] plotted against the time [s]) with the disclosed measure implemented, both as V1 at the pump outlet (dashed line), and V2 on the wheel line (continuous line) as well as V3 at the switch-over valve itself (dot-dashed line). In the central illustration, the pressure downstream of the pump is shown (as [bar A] plotted against the time [s]) both as S1 (continuous line) with the disclosed measure implemented, and as S2 (dotted line) without the disclosed measure. In the bottom illustration, the pressure oscillation amplitude downstream of the pump is shown (as [bar] plotted against the time [s]). Here, the reduced pressure oscillation amplitude D1 (continuous line) can be seen with the disclosed measure implemented, in comparison with the normal pressure oscillation amplitude D2 (dashed line) without the disclosed measure.

[0047] FIG. 3 shows characteristic curve profiles relating to the volume flow smoothing. Pump systems with six pistons, referred to as 6c systems, generate a continuous volume flow, but owing to the finite number of pistons this is not constant but rather has fluctuations. The volume flow in the wheel lines can be smoothed by discharging just so much volume flow via the switch-over valve that a constant value is obtained for the wheel line:

Q.sub.USV=Q.sub.PUMPQ.sub.Wheel line

Q.sub.Wheel lineconst.

[0048] FIG. 3 shows here the smoothing of the volume flow of a 6c system in the wheel line by selective discharging of peaks via the switch-over valve. Here, the volume flow is illustrated plotted against the time. The dashed line shows the volume flow of the pump (Q.sub.Pump). The dot-dashed line shows the (flowing-away) volume flow through the switch-over valve (Q.sub.USV). The continuous line shows the resulting smoothed volume flow at the wheel brake (Q.sub.Wheel).

[0049] It is to be noted that the scaling of the X axes and Y axes in the respective illustrations (a=prior art, b=embodiment of the disclosure) is the same. As a result, the differences can be easily determined.