Road vehicle hydraulic service-brake system and activation process

• US 5,342,120 A
• Filed: 10/25/1993
• Issued: 08/30/1994
• Est. Priority Date: 11/24/1990
• Status: Expired due to Fees

• Current Assignee: DaimlerChrysler AG (Mercedes-Benz Group AG)
• Original Assignee: Mercedes-Benz AG (Mercedes-Benz Group AG)
• Inventors: Muller, Armin, Gautsch, Wolfgang, Zimmer, Richard, Freitag, Rainer
• Primary Examiner(s): Oberleitner, Robert J.
• Assistant Examiner(s): Young, Lee W.
• Application Number:
  US08/140,973
• Time in Patent Office: 309 Days
• Field of Search: 303/100, 303/103, 303/93, 303/113.1, 303/113.2, 303/113.4, 303/116.1, 303/116.2, 364/426.02, 364/426.03
• US Class Current: 303/113.2
• CPC Class Codes: B60T 8/32 responsive to a speed condition, e.g. acceleration or deceleration using electrical circuitry or regulation means B60T8/17 ; B60T8/28 takes precedence; electric devices on electrically propelled vehicles indicating the wheel slip B60L3/10; measuring linear or angular speed per se G01P3/00
• CPC Class Codes: B60T 8/4275 Pump-back systems
• CPC Class Codes: B60T 8/4809 Traction control, stability control, using both the wheel brakes and other automatic braking systems
• CPC Class Codes: B60T 8/4881 having priming means

Abstract

A vehicle is equipped both with an anti-lock system working on the return-flow principle and with a drive-slip control device working on the differential brake principle, in which the return pump is utilized as an auxiliary pressure source for loading the driven vehicle wheels with brake pressure. In an operational situation requiring drive-slip control, a pump working at a low pressure level is actuated, even before the control responds, and conveys brake fluid both into the brake circuit of the driven vehicle wheel and into the brake circuit of the non-driven vehicle wheels, which are shut off from the brake unit of the brake system by, on one hand, an ASR-function control valve and, on the other hand, by an isolating valve. The pre-charge pump of the return pump of the brake circuits of the driven vehicle wheels is used as a low-pressure pump. This pressurization of the brake circuits with a moderate brake pressure causes a compensation of the lifting play and is utilized both for the drive-slip control and for normal braking.

Claims

1. A brake system for activating a vehicle hydraulic service-brake system, comprising a vehicle anti-lock system operable in accordance with a return-flow principle, a drive-slip control device operable in accordance with a differential brake principle, wheel brakes of driven vehicle wheels constituting a first brake circuit, wheel brakes of non-driven vehicle wheels constituting a second brake circuit, a return pump operatively arranged in the anti-lock system to function as an auxiliary pressure source for a drive-slip control mode and operatively associated with the first brake circuit of the driven vehicle wheels, a pre-charge pump configured to work at a low outlet-pressure level for supplying an inlet of the return pump with brake fluid from a reservoir of the service-brake system, a brake-light switch configured as a position-sensitive switch member to transmit an output signal as the brake pedal of the brake system is shifted out of a basic position, and an electronic control unit configured and operatively connected with the brake system and with vehicle wheel-speed sensors to detect, via output signals from the sensors, occurrence of at least one of the output signal of the brake-light switch and development and then commencement of a vehicle operational situation requiring the drive-slip control mode, and to trigger an output signal activating the pre-charge pump and controlling a drive-slip control-function control valve into a blocking position, at least for a time period sufficient for generating maximum outlet pressure of the pre-charge pump and corresponding at least to a period of time after which, in the event of a brake actuation taking place with average pedal force and speed of pedal adjustment, the wheel brakes are applied, wherein an isolating valve is operatively arranged for shutting off a portion of a main brake-line of the second brake circuit which leads to a branch point thereof, for at least the time period, from a delivery outlet of a brake unit assigned to the second brake circuit, and a delivery outlet of a low pressure pump is connected to the branch point of the second brake circuit, by way of the portion of the main brake-line connecting the branch point to the isolating valve, via a non-return valve which is loaded in an opening direction by a relatively higher pressure at the delivery outlet of the low-pressure pump than in this portion of the main brake-line.

2. The system according to claim 1, wherein a bypass flow path leading via a non-return valve for the drive-slip control-function control valve is loaded in an opening direction by a relatively higher pressure at an outlet of the brake unit than in a brake-line portion leading from the drive-slip control-function control valve to a branch point of a main brake-line of the first brake circuit of the driven vehicle wheels.

3. The system according to claim 1, wherein the isolating valve is a 2/2-way solenoid valve, of which a basic position is a throughflow position connecting the delivery outlet of the brake unit to the branch point of the main brake-line of the second brake circuit of the non-driven vehicle wheels and configured to be controlled, jointly with the drive-slip control-function control valve, into a blocking energized position by an output signal from the electronic control unit.

4. The system according to claim 3, wherein a bypass flow path leading via a non-return valve for the drive-slip control-function control valve is loaded in an opening direction by a relatively higher pressure at an outlet of the brake unit than in a brake-line portion leading from the drive-slip control-function control valve to a branch point of a main brake-line of the first brake circuit of the driven vehicle wheels.

5. The system according to claim 1, wherein the isolating valve of the first brake circuit of the non-driven vehicle wheels is a hydraulically-controlled 2/2-way valve configured to be controlled out of a blocking basic position into a throughflow position by the outlet pressure of the brake unit.

6. The system according to claim 5, wherein a bypass flow path leading via a non-return valve for the drive-slip control-function control valve is loaded in an opening direction by a relatively higher pressure at an outlet of the brake unit than in a brake-line portion leading from the drive-slip control-function control valve to a branch point of a main brake-line of the first brake circuit of the driven vehicle wheels.

7. The system according to claim 5, wherein a control pressure, at which the isolating valve changes over to the throughflow position, satisfies the relation

8. The system according to claim 7, wherein a bypass flow path leading via a non-return valve for the drive-slip control-function control valve is loaded in an opening direction by a relatively higher pressure at an outlet of the brake unit than in a brake-line portion leading from the drive-slip control-function control valve to a branch point of a main brake-line of the first brake circuit of the driven vehicle wheels.

9. The system according to claim 1, wherein a bypass flow path in arranged parallel to the isolating valve and leads, via a non-return valve which is loaded in an opening direction by a relatively higher pressure at the outlet of the brake unit than in the portion of the main brake-line, from the isolating valve to the branch point of the second brake circuit of the non-driven vehicle wheels.

10. The system according to claim 9, wherein the isolating valve is a 2/2-way solenoid valve, of which a basic position is a throughflow position connecting the delivery outlet of the brake unit to the branch point of the main brake-line of the second brake circuit of the non-driven vehicle wheels and configured to be controlled, jointly with the drive-slip control-function control valve, into a blocking energized position by an output signal from the electronic control unit.

11. The system according to claim 10, wherein the isolating valve of the first brake circuit of the non-driven vehicle wheels is a hydraulically-controlled 2/2-way valve configured to be controlled out of a blocking basic position into a throughflow position by the outlet pressure of the brake unit.

12. The system according to claim 5, wherein a control pressure, at which the isolating valve changes over to the throughflow position, satisfies the relation

13. The system according to claim 1, wherein the isolating valve is a 2/2-way solenoid valve, of which a basic position is a throughflow position connecting the delivery outlet of the brake unit to the branch point of the main brake-line of the second brake circuit of the non-driven vehicle wheels and configured to be controlled, jointly with the drive-slip control-function control valve, into a blocking energized position by an output signal from the electronic control unit.

14. The system according to claim 13, wherein a position transmitter is operatively arranged to monitor the position of the accelerator pedal and to generate an output signal varying continuously in terms of at least one of level and frequency with the operating position of the accelerator pedal, a differentiation stage carries out a time differentiation of the position-transmitter output signal to provide an output signal which is a measure of the speed at which the accelerator pedal is adjusted, and a signal causing the activation of the low-pressure pump and the changeover of at least one of the drive-slip control-function control valve and the isolating valve into a blocking position is already being generated when the speed of the adjustment of the accelerator pedal taking place in reaction to a removal of a driver'"'"'s foot from the pedal exceeds a predetermined threshold value and the vehicle speed is still higher than a relevant threshold value characteristic of continuous travel.

15. The system according to claim 13, wherein a position transmitter is operatively arranged to monitor the position of the accelerator pedal and to generate an output signal varying continuously in terms of at least one of level and frequency with the operating position of the accelerator pedal, a differentiation stage carries out a time differentiation of the position-transmitter output signal to provide an output signal which is a measure of the speed at which the accelerator pedal is adjusted, and a signal causing the activation of the low-pressure pump and the changeover of at least one of the drive-slip control-function control valve and the isolating valve into a blocking position is already being generated when the speed of the adjustment of the accelerator pedal taking place in reaction to a removal of a driver'"'"'s foot from the pedal exceeds a predetermined threshold value and the vehicle speed is still higher than a relevant threshold value characteristic of continuous travel.

17. The system according to claim 1, wherein a decrease of the signal triggered by the removal of a driver'"'"'s foot from the accelerator pedal and controlling at least one of the drive-slip control-function control valve and the isolating valve into a basic position is delayed relative to a decrease of the signal activating the low-pressure pump by a time period generally between about 200 ms and 500 ms.

16. A brake system for activating a vehicle hydraulic service-brake system, comprising a vehicle anti-lock system operable in accordance with a return-flow principle, a drive-slip control device operable in accordance with a differential brake principal, wheel brakes of driven vehicle wheels constituting a first brake circuit, wheel brakes of non-driven vehicle wheels constituting a second brake circuit, a return pump operatively arranged in the anti-lock system to function as an auxiliary pressure source for a drive-slip control mode and operatively associated with the first brake circuit of the driven vehicle wheels, a pre-charge pump configured to work at a low outlet-pressure level for supplying an inlet of the return pump with brake fluid from a reservoir of the service-brake system, a brake-light switch configured as a position-sensitive switch member to transmit an output signal as the brake pedal of the brake system is shifted out of a basic position, and an electronic control unit configured and operatively connected with the brake system and with vehicle wheel-speed sensors to detect, via output signals of the brake-light switch and development and then commencement of a vehicle operational situation requiring the drive-slip control mode, and to trigger an output signal activating the pre-charge pump and controlling a drive-slip control-function control valve into a blocking position, at least for a time period sufficient for generating maximum outlet pressure of the pre-charge pump and corresponding at least to a period of time after which, in the event of a brake actuation taking place with average pedal force and speed of pedal adjustment, the wheel brakes are applied, wherein an isolating valve is operatively arranged for shutting off a portion of a main brake-line of the second brake circuit which leads to a branch point thereof, for at least the time period, from a delivery outlet of a brake unit assigned to the second brake circuit, and a delivery outlet of a low pressure pump is connected to the branch point of the second brake circuit, by way of the portion of the main brake-line connecting the branch point to the isolating valve, via a non-return valve which is loaded in an opening direction by a relatively higher pressure at the delivery outlet of the low-pressure pump than in this portion of the main brake-line wherein a bypass flow path leading via a non-return valve for the drive-slip control-function control valve is loaded in an opening direction by a relatively higher pressure at an outlet of the brake unit than in a brake-line portion leading from the drive-slip control-function control valve to a branch point of a main brake-line of the first brake circuit of the driven vehicle wheels, an isolating valve is operatively arranged for shutting off a portion of a main brake-line of the second brake circuit which leads to a branch point thereof, for at least the time period, from a delivery outlet of a brake unit assigned to the second brake circuit, and a delivery outlet of the low pressure pump is connected to the branch point of the second brake circuit, by way of the portion of the main brake-line connecting the branch point to the isolating valve, via a non-return valve which is loaded in an opening direction by a relatively higher pressure at the delivery outlet of the low-pressure pump than in this portion of the main brake-line.