GB2241030A

GB2241030A - A hydraulic braking system for vehicles

Info

Publication number: GB2241030A
Application number: GB9102558A
Authority: GB
Inventors: Reinhard Gutzeit
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1990-02-07
Filing date: 1991-02-06
Publication date: 1991-08-21
Anticipated expiration: 2011-02-06
Also published as: JPH0752778A; GB2241030B; GB9102558D0; DE4003607A1

Abstract

A braking system (10) has an anti-skid device (45) including a seat valve (19) with a throttle (23, 24) parallel to the valve (20) disposed between the master brake cylinder (12) and a wheel brake (17, 18), the valve being adapted to close in dependence on flow pressure and/or differential pressure, and a return line (27) having an outlet valve (28, 29), a hydraulic pressure accumulator (30) and a return pump (31). Opening of the outlet valve (28, 29) during anti-skid control causes a pressure reduction in the wheel brake (17, 18) which in turn causes closure of the valve (20). On termination of the brake pressure reduction, pressure medium, which continues to flow through the throttle (24) causes the valve (20) to switch into its open position. <IMAGE>

Description

:2:2 -a -10 --3 0 f

DESCRIPTION A HYDRAULIC BRAKING SYSTEM FOR VEHICLES

The present invention relates to a hydraulic braking system for vehicles.

A braking system is already known (EP-A-0 202 845), which has an hydraulically controlled spool valve. In normal braking operation, the spool of the valve permits the flow of pressure medium in a brake line which runs between the master brake cylinder and the wheel brake. The spool is subjected on its one end face to pressure generated by the master brake cylinder. This pressure is transmitted through a longitudinal bore of the spool, which bore is provided with a throttle, into a component chamber of the valve, in which there is seated a pressure spring, which acts on the other end face of the spool. From this component chamber there issues an overflow line, which is connected to the return line for pressure medium, which is connected to the valve. In the return line, which in normal braking operation is closed by the spool, there is an electromagnetically switchable two-port, two-position valve. In the event of threat of one vehicle wheel locking, this valve can be switched into its open position, in which it relieves the component chamber of the hydraulically controlled valve, which chamber accommodates the -2spring, and causes this valve to switch over. In such case, the spool takes up a position in which it interrupts the brake line to the master brake cylinder and connects the wheel brake to the return line. A hydraulic accumulator which is connected to the return line, then receives pressure medium from the wheel brake, which is pumped by a return pump, which is switched on at the same time, back to the master brake cylinder or into the valve, from where it flows through the spool, the throttle and a variable throttle location of the overflow line, which is -formed by the spool position, into the return line. In the event of a subsequent brake pressure build-up phase, the two-port. two-position valve switches into its closing position, while the pressure medium which continues to be delivered by the return pump out of the hydraulic accumulator then flows from the overflow line into the brake line and to the wheel brake. The valve does not switch back into its starting position until there is substantial pressure equality in the master brake cylinder and in the wheel brake. The known braking system requires only one electromagnetically switchable valve; however, the hydraulically switchable valve is relatively expensive because it has both switching and current-control functions. Moreover, a valve of the spool type is i 3necessarily subject to clearance losses. Furthermore. the penetration of solid foreign substances into the gap between the spool and its housing can lead to failure of the valve.

In accordance with the present invention a hydraulic braking system for a vehicle is provided having a master brake cylinder for generating brake pressure in at least one wheel brake and a device for preventing locking of at least one vehicle wheel on braking, said device having a brake line running between the master brake cylinder and the wheel brake, a hydraulically controllable seat valve, which is disposed in the brake line, which switches in dependence on flow pressure and/or differential pressure whilst in its one position permits the flow of pressure medium from the master brake cylinder to the wheel brake, while, during an antiskid operation. in order to reduce brake pressure, it closes off the flow of pressure medium in its other position, a constant throttle connected in parallel to the seat valver which is connected on its inflow side to the master brake cylinder and on its outflow side to the brake line, a return line to the master brake cylinder, a two-port, two-position valve for connecting the return line to a wheel brake; a hydraulic pressure accumulator connected to the return -4line beyond the two-port. two position valve in the direction of flow of the pressure medium, and a pump for delivering pressure medium to the master brake cylinder, disposed in the return line beyond the accumulator in the direction of the flow.

This has the advantage that functional reliability is increased# the seat valve can be manufactured with minimum outlay and the throttle is connected to the brake line independently of the valve.

One embodiment of the invention is described further hereinafter, by way of example only, with reference to the accompanying drawings which is a circuit diagram of a hydraulic braking system having a device for preventing the locking of a vehicle wheel on braking.

The hydraulic braking system 10 shown schematically in the drawing has a master brake cylinder 12, which is actuatable by a brake pedal 11, with a pressure medium reservoir 13. From the master brake cylinder 12 there issues a master brake line 14 for a brake circuit I and a master brake line 14' for a brake circuit II, which is not shown. The construction and function of the brake circuit I will now be described in more detail.

The master brake line 14 divides into two brake -5lines 15 and 16, which lead to wheel brakes 17 and 18 respectively of the wheels (not shown) of the vehicle. In the brake line 15 there is disposed a hydraulically controlled valve 19 and in the brake line 16 there is disposed an identical hydraulically controlled valve 20. Extending parallel with and connected to the brake line 15 is a line 21 having a throttle 23 with a constant cross section. Extending in parallel with and connected to the brake line 16 is a line 22 having a throttle 24 with a constant cross section. Branch lines 25 and 26 of a return line 27, which is connected to the master brake line 14 and extends in parallel with the brake lines 15 and 16, issue from the brake lines 15 and 16, which extend between the respective valve 19 or 20 and the corresponding wheel brake 17 or 18. A two-port. two-position valve 28 and 29 is disposed in the branch lines 25 and 26 respectively. These valves have a springactuatable closed position a and an electromagnetically switchable open position b. Beyond the valves 28 and 29 a hydraulic accumulator 30 is connected to the return line 27. Between the accumulator 30 and the master brake cylinder 12 there is disposed in the return line 27 a return pump 31 having an electric drive motor 32. On the inflow side of the return pump 31 there is disposed in the return line 27 a first -6non-return valve 33; a second non-return valve 34 is disposed on the outflow side of the pump 31 in the return line 27.

The identically formed, hydraulically controllable valves i9 and 20 in the brake lines 15 and 16 have a housing 35 with an inflow opening 36 facing the master brake cylinder 12 and an outflow opening 37, which lies opposite on the wheel brake side. Inside the housing 35 there is a closure member 38, which is formed as a substantially axially symmetrical rotary member. The closure member 38, which is guided with peripheral play in the housing 35, has on the outflow side an annular seal 39. This seal 39 is associated with a valve seat 40 of the housing 35. A spring 41, which is supported on the housing 35 on the outflow side acts on the closure member 38. The spring 41 endeavours to raise the closure member 38 from its valve seat 40. In this open position (shown in the case of valve 19 in the brake line 15), the closure member 38 is supported on the housing 35 at a distance from the inflow opening 36. In the closed position, the closure member 38 acts with its seal 39 on the valve seat 40 of the housing 35 (position of the valve 20 shown in the brake line 16).

Moreover, an electronic control device 42 is - 7provided, to which are connected sensors 43 and 44 which monitor the rotary behaviour of the vehicle wheels associated with the wheel brakes 17 and 18. The control device 42 is also intended for switching the two two-port, two-position valves 28 and 29 as well as the drive motor 32 of the return pump 3 1.

The hydraulic elements located between the master brake cylinder 12 and the wheel brakes 17 and 18 of the braking system 10, and the control device 42 with the associated components form a device 45 for preventing locking of the vehicle wheels on braking. Brake circuit II may be equipped in a corresponding manner. The device 45 has the following function:

In the event of a normal braking operation, which is triggered by the driver putting his foot on the brake pedal 11, pressure medium is displaced out of the master brake cylinder 12 and through the lines 14.15. 16,21 and 22 into the wheel brakes 17 and 18, where the pressure medium generates a brake pressure. The two hydraulically controllable valves 19 and 20, acting as inlet valves, take up their open position (as shown in the case of valve 19), while the twoport. two-position valves 28 and 29, which act as outlet valves for the pressure medium, are in their closed position a.

If, during a braking operation, the control -8device 42 ascertains on the basis of signals, for example from the sensor 44, that there is a risk of locking of the vehicle wheel associated with the wheel brake 18, the control device 42 switches the two-port. two-position valve 29 into its open position b and puts the drive motor 32 of the return pump 31 in-to operation. As a result, pressure medium is withdrawn from the wheel brake 18, which results in a drop in brake pressure, so that the associated wheel of the vehicle can stabilise. The pressure medium taken from the wheel brake 18 flows through the branch line 26 and the return line 27 into the accumulator 30. Pressure medium also flows from the outflow side of the valve 20 and from the throttle 24 in the parallel line 22 through the return line 27 into the accumulator 30. The resulting pressure differential between the inflow side and the outflow side of the valve 20 results temporarily in an intensive flow of pressure medium through the inflow opening 36 into the housing 35, which causes a longitudinal movement of the closure member 38 against the force of the spring 41, such that the valve closes through the action of the seal 39 on the valve seat 40. (In the event of a braking operation with a rapid increase in brake pressure, but without the risk of locking of one of the vehicle wheels, the pressure medium flowing -9through the in-flow opening 36 into the housing 35 of the respective valve 19 or 20 does not however cause the switching of the valve into its closed position. Furthermore. it is necessary for the switching function of the valves 19 and 20 that the cross section of the throttles 23 and 24 and the port cross section of the two-port. two-position valves 28 and 29 must be matched very precisely to one another and to the delivery quantity of the return pump 31. so that there is no over-filling of the accumulator 30 during an anti-skid operation). The pressure medium held in the accumulator 30 is delivered back to the master brake cylinder 12 or some of it flows through the parallel line 22 back to the pressure medium reservoir.

As soon as the control device 42 recognises stabilised rotating behaviour of the vehicle wheel associated with the wheel brake 18, it switches the two-port. two-position valve 29 into its closed position a. Pressure medium from the master brake cylinder 12 flows through the parallel line 22 into the wheel brake 18 and builds up pressure in it and in the branch of the brake line 16 on the outflow side. This pressure is also effective in the interior of the valve 20 between the outflow opening 37 and the valve seat 40. When the pressure forces and the force of the spring 41 on the closure member 38 are in -10equilibrium, the valve 20 switches into its open position. The brake pressure in the wheel brake 18 can then be reduced or increased in an unthrottled manner depending on the wishes of the driver.

11

Claims

-11CLAIMS

1. A hydraulic braking system for a vehicle having a master brake cylinder for generating brake pressure in at least one wheel brake and a device for preventing locking of at least one vehicle wheel on braking, said device having a brake line running. between the master brake cylinder and the wheel brake, a hydraulically controllable seat valve, which is disposed in the brake line, which switches in dependence on flow pressure andlor differential pressure whilst in its one position permits the flow of pressure medium from the master brake cylinder to the wheel brake, while, during an anti-skid operation, in order to reduce brake pressure, it closes off the flow of pressure medium in its other position, a constant throttle connected in parallel to the seat valve, which is connected on its inflow side to the master brake cylinder and on its outflow side to the brake line, a return line to the master brake cylinder, a two-port. two-position valve for connecting the return line to a wheel brake; a hydraulic pressure accumulator connected to the return line beyond the two-port, two position valve in the direction of flow of the pressure medium, and a pump for delivering pressure medium to the master brake cylinder, disposed in the return line beyond the 1.

-12accumulator in the direction of the flow.

2. A braking system as claimed in claim 1, in which the seat valve has a housing with an inlet and an outlet lying opposite to the inlet, in which housing there is disposed a spring and a closure member which is moveable against the valve's seat between the said openings against the force of the spring.

3. A braking system as claimed in claim 2, in which the closure member is an axially symmetrical rotary body, about which pressure medium can flow peripherally and which has a seal on the outflow side by which the closure member is able to act on the valve's seat.

4. A braking system constructed and adapted substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

Published 1991 at Tle Patent Office, State House. 66171 High Holborn. UndonWC1R41P. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point Cwmfelinfach. Cross Keys, Newport- NPI 7HZ. Printed by Multiplex techniques lid. St Mary Cray. Kent.

j