GB2265425A

GB2265425A - Braking systems

Info

Publication number: GB2265425A
Application number: GB9306110A
Authority: GB
Inventors: Guenther Schmidt
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1992-03-25
Filing date: 1993-03-24
Publication date: 1993-09-29
Anticipated expiration: 2013-03-24
Also published as: JPH0624308A; FR2689075B1; GB9306110D0; GB2265425B; DE4209705A1; FR2689075A1

Description

2265425

DESCRIPTION BRAKING SYSTEMS

The invention relates to braking systemst and in particular, but not exclusively, to a braking system having a master cylinder connected to wheel brake cylinders by way of brake lines and connecting lines, wherein solenoid valves and a return pump for an antiskid control are incorporated in the brake lines and connecting lines.

A braking system is known from DE-OS 38 19 812r in which the anti-skid control is coupled to the drive slip control, and comprises a hydraulically driven return pump without low-pressure accumulators, the anti-skid control being provided with three solenoid valves for each brake circuit. A large number of further components, and particularly nonreturn valves, are provided which make this braking system very expensive.

In accordance with the present invention, the individual solenoid valves between the wheel brake cylinder and the master cylinder are by-passed by a by-pass having a non-return valve.

The driver may thereby reduce brake pressures rapidly at any time by releasing the brake pedal, even when the solenoid valves are closed during an antiskid control operation. Upon releasing the brake -2pedal, pressure medium flows from wheel brake cylinders to the master cylinder through a separate return line. This inexpensive circuit arrangement is to be used primarily in vehicles of the lower and medium price range.

In the event of an inadmissible rise in the brake pressure. the controller detects too high a brake slip at least at one wheel and closes the associated solenoid valve. If the brake slip continues to increase despite this measure, a motor for the return pump is started, a solenoid valve is closed towards the master brake cylinder, and the above- mentioned solenoid valve associated with the wheel is opened again. Thus, the master brake cylinder is cut off and the pressure in the wheel brake cylinder is reduced by the return of pressure medium. The pressure in the wheel brake cylinders may now be controlled at the wheel-lock limit by a corresponding control algorithm (not described here) for triggering the three solenoid valves per circuit.

The design of the solenoid valves is also essential in the present embodiment, and particularly the integration of the corresponding nonreturn valves in the solenoid valve. Here, the non-return function is undertaken by a lip seal which surrounds a corresponding valve body and which is fitted in, for -3example, a blind bore of a housing. The lip seal separates an annular space from a chamber and permits brake fluid to flow in only one direction. The lip seal shuts off in the other direction, since its outer lip portion abuts against the inside wall of the blind bore under counter- pressure.

In the case of the solenoid valves which are connected upstream of the wheel brake cylinders and which undertake the actual anti-skid control, the line from the wheel brake cylinder is to open into the annular space and the by-pass is to lead back from the chamber to the brake line or to the master brake cylinder. This means that, upon closing of the solenoid valves, a return flow of brake fluid remains open by way of the nonreturn valve in the form of a lip seal. Of course, in this connection, the chamber should be effectively isolated from the connecting line to the solenoid valve or to the return pump. This is effected in that the connecting line opens into the bottom of the blind bore and this opening is isolated from the chamber by a seal, wherein either the valve body presses axially against this seal by means of a foot or, alternatively, this seal is placed as a radial seal around the foot and is supported against a wall of the blind bore.

Thus, it is clearly shown that, basically, only one embodiment is required or all three valves of a brake circuit and, of course, also has an integrated, electromagnetically operable valve for opening and closing a passage. This valve is located preferably in the valve body and connects the annular space either to the chamber in the case of one solenoid valve directly downstream of the master brake cylinder, or to the connecting line in the case of the solenoid valves connected directly upstream of the wheel brake cylinders. For the sake of simplicity, this valve comprises a valve ball which is mounted on an electromagnetically movable stem and is associated with a corresponding valve seat in an axial bore of the valve body. The stem is supported by way of a spiral spring which ensures that, in the event of failure of the solenoid valve, the valve ball is removed from its valve seat and passage for the flow of brake fluid from the master cylinder to the wheel brake cylinder always remains open. This ensures the required margin of safety of the brake system.

Compared with known brake systems, the advantage resides primarily in the decrease in the number of individual components and in the simplification of the construction of the solenoid valves.

The solenoid valve which is located between the actual solenoid valves connected directly upstream of the wheel brake cylinders and the master brake cylinder, and which combines the two connecting lines leading to the two solenoid valves, may likewise be by-passed by way of a by-pass incorporating a nonreturn valve. This is also a very simple design. In this case, the connecting line opens into the abovementioned annular space, while the by-pass leads from the chamber to the brake line. In the case of increased pressure, the solenoid may thereby be bypassed in the direction of the master brake cylinder even when it is in its shut-off position.

The return pump is connected directly to the connecting lines leading to the two solenoid valves connected upstream of wheel brake cylinders, and, on the other hand, opens into the brake line leading to the master cylinder.

Here, it is sufficient to insert a throttle by which the pulsation, resulting from the return of brake fluid into the master brake cylinder, is reduced. thus increasing the comfort of the brake system. In a very simple embodiment, an additional damping chamber is not provided. Furthermore. an additional accumulator chamber, as in the known brake systems with anti-skid control systems, is not provided.

By way of example only, specific embodiments of the invention will now be described, with reference to the accompanying drawings, in which:- Fig. la is a block circuit diagram of a braking system having a circuit arrangement for a K-split brake circuit (diagonal split); Fig. lb is a block circuit diagram of a braking system having a circuit arrangement for a TT-split brake circuit (front axle-, rear axle split); Fig. 2 is a longitudinal section through a twoport, two-position solenoid valve of Fig.la and Fig.lb illustrated in its working position, constructed in accordance with one embodiment of the invention; Fig. 3 is a longitudinal section through a further embodiment of a two- port, two-position solenoid valve of Fig.la and Fig.lb illustrated in its working position; and Fig. 4 is a block circuit diagram illustrating a by-pass around the solenoid valves of the circuit arrangements of Figs. la and lb.

In a braking system in accordance with the invention shown in Fig. 1, a master cylinder 1 is connected by way of two brake circuits I and II to wheel brake cylinders 2 which are only shown diagrammatically. For the purpose of generating brake pressure, a pedal 3 is connected to a piston rod 4 -7which enters the master cylinder 1 where it pressurizes a brake fluid in the corresponding brake chambers. In the brake circuit 1, this brake fluid may flow, by way of a brake line 5, to the wheel brake cylinder 2. of a left-hand front wheel and of a right-hand rear wheel.

A respective solenoid valve 6 or 7 is connected, as part of the circuit arrangement, upstream of the wheel brake cylinder 2 of the left-hand front wheel and upstream of the wheel brake cylinder 2 of the right-hand rear wheel, wherein the corresponding connecting lines 8 and 9 combine to form the brake line 5 upstream of the solenoid valves 6 and 7. Furthermore, a further solenoid valve 10 is incorporated in the brake line 5.

As indicated in Fig. 4, a by-pass 11 having a non-return valve 12 may also be associated with the solenoid valve 10.

The units comprising the solenoid valve 10 and the solenoid valve 6 or 7 are also each provided with a by-pass 13 or 14 in which are located respective non-return valves 15 and 16 which may be opened in a direction towards the master brake cylinder 1.

The connecting lines 8 and 9 have a further connection line 17, which leads to A return pump 18 whose outlet line 19 opens into the brake line 5 between the solenoid valve 10 and the master brake -8cylinder 1, wherein a damping chamber 20 and a throttle 21 may also be provided upstream of the junction.

Since the brake circuit II is of identical construction to the brake circuit I, it is unnecessary to describe the brake circuit II separately. It only has to be noted that the corresponding return pump 18a of brake circuit II is connected to a motor 22 which also operates the return pump 18 of brake circuit I.

The mode of operation of the braking system in accordance with the invention is as follows:

During a normal braking operation, brake fluid is forced into brake circuit I and brake circuit II by pressure exerted on the pedal 3 and by way of the action of the piston rod 4 in the brake chambers (not shown). In brake circuit I, this brake fluid flows to the wheel brake cylinders 2 by way of the brake line 5 and through the open solenoid valves 10 and 6 or 7. The braking operation is performed by way of the wheel brake cylinders.

If a sensor (not shown) detects locking of, for example, the left-hand front wheel, the circuit arrangement comes into operation. The solenoid valve 6 is closed, so that a further build-up of pressure in the wheel brake cylinder 2 of the left-hand front wheel is not possible, since the connecting line 8 is interrupted towards the brake line 5.

If the brake slip at the left-hand front wheel continues to increase, the motor 2 is started and the return pump 18 is put into operation. The solenoid valve 10 and the solenoid valve 7 are closed, and the solenoid valve 6 is opened again. The master brake cylinder 1 is thereby uncoupled from the wheel brake cylinders 2 of the left-hand front wheel and of the right-hand rear wheel, and the connection between the left-hand front wheel and the right-hand rear wheel is also interrupted.

The excessive brake pressure in the wheel brake cylinder 2 of the lefthand front wheel is reduced by way of the return pump 18, and brake fluid is again returned to the master brake cylinder. This is effected through the damping chamber 20 and the throttle 21, wherein the damping chamber 20 may also be omitted if this loss of comfort is acceptable.

In accordance with the command of a control algorithm not further described here, the solenoid valve 6 is closed again, and the solenoid valves 10 and 7 are opened again, so that a rise in the brake pressure in the wheel brake cylinder 2 of the righthand rear wheel is possible. If the right-hand rear wheel also becomes unstable during the course of the braking operation, anti-skid control similar to that described above with reference to the left-hand front -10wheel is effected. A subsequent build-up of pressure and further modulations are then effected corresponding to the above-described.

It is known that a conventional anti-skid control system has the following elements in the case of a Ksplit brake circuit:

Two return pumps Two accumulator chambers Two damping chambers Four solenoid valves in the case of the wheel brake cylinders and Four solenoid valves in the brake line.

Thus, at least two accumulator chambers are saved in the present case, since the delivery capacity of the return pump alone is adequate for smaller and medium vehicles. Furthermore, it is also possible to omit the damping chambers 20. although this depends upon whether the associated loss of comfort is acceptable. In any case, however, two additional solenoid valves in the brake line are saved.

The separate return line 13 or 14 back to the master brake cylinder is required in order to prevent after-braking after the brakes have been released.

In a TT-split in accordance with Fig. lb, the corresponding circuit arrangement will have the following appearance:

a) An arrangement of elements corresponding to the K-split is chosen for the brake circuit of the front axle (see Fig. lb).

b) A solenoid inlet valve and a solenoid outlet valve are provided in the braking circuit for the rear axle in a conventional manner, although an accumulator chamber is omitted.

In this case, the braking system contains two return pumps, two conventional solenoid valves, a solenoid valve in the brake line and two modified solenoid valves upstream of the wheel brake cylinders. Altogether, this braking system requires only five solenoid valves, and the accumulator chambers may be omitted as well as the damping chambers.

The modified solenoid valves 6 and 7 have to be of special design in order that they may fulfil their function. Two embodiments of such valves are described in Figs. 2 and 3.

The solenoid valve 6/7 is mounted in a housing block 23. For this purpose, a blind bore 24 is provided in the housing block 23. The connecting line 8 branches from the bottom 25 of the blind bore 24 to the return pump 18. In the vicinity of the bottom 25, the by-pass line 13/14 branches laterally to the master cylinder 1. A line 26 to the wheel brake cylinder 2 may be seen above, and spaced from, the bypass line 13/14.

A valve body 27 of the solenoid valve 6/7 is mounted in the blind bore 24 and forms in this blind bore 24 an annular space 28 for mouth of the line 26. This annular space 28 is separated by a lip seal 29 from a chamber 30 from which the by-pass 13/14 opens. Upon an increase in pressure in the line 26, the lip seal 29 enables brake fluid to flow from the wheel brake cylinders back into the chamber 30 by way of the lip seal, or back into the master cylinder 1 by way of the by-pass 13/14. For this reason, the valve body does not abut at least partially against the wall of the blind bore 24, the outer part of the lip seal 29 may yield flexibly and open a space between the lip seal 29 and the wall of the blind bore 24.

On the other side of the lip seal 29, the annular space 28 is sealed by an 0-ring 31.

The valve body 27 presses with a foot 32 against the bottom 25 of the blind bore 24, wherein, in accordance with the invention, an additional seal, particularly a sealing ring 33, is inserted at this location. The chamber 30 and thus the by-pass 13/14 are thereby permanently separated from the connecting line 819. In this manner. the connecting line 8/9 to the return pump only communicates with the line 26 to the wheel brake cylinder 2, when a valve 34 within the valve body 27 has been opened.

A stepped bore 35 is provided in the valve body 27 for the purpose of forming this valve 34. The stepped bore 35 is closed towards the connecting line 8/9 by a filter 36. Following the filter 36, a sleeve 37 having an opening 38 is inserted into the stepped bore 35. This opening 38 forms a valve seat for a valve ball 39 which is supported against a stem 40.

A valve chamber 41 is formed between the stem 40 and the sleeve 37, the stem 40 being supported, in the valve chamber 41, against the sleeve 37 by way of a spiral spring 42.

The valve chamber 41 then in turn communicates with the annular space 28 by way of a transverse bore 43 and a filter cloth 44.

An armature 45, which is mounted in a sealed housing 46 and is surrounded by coil assemblies 47, is contiguous to the stem 40. These coil assemblies 47 may be supplied with current by way of connection tags 48. The coil assemblies 47 cause the stem 40 to move within the stepped bore 35. the valve ball 39 being placed onto the opening 38. On the other hand, if the coil assemblies 47 are not carrying current, the valve ball 39 is removed from its valve seat or the opening 38 by the counter-pressure of the spiral spring 42. Communication between the wheel brake cylinder and the return pump may be closed or opened in this simple manner.

Incidentally, it may be pointed out that the separate arrangement of nonreturn valves 15 and 16 is unnecessary when using a lip seal. This lip seal 29 then acts as a non-return valve, since brake fluid cannot flow through the chamber 30 to the annular space 28 by way of the by-pass 13 or 14.

The embodiment of a solenoid valve 6a17a of Fig.3 differs from that of Fig.2 by the arrangement of a seal 33a as a radial seal and not as an axial seal. For this purpose. the foot 32a of the valve body 27a is lengthened and is located in an additional bore 49. The connecting line 8/9 then opens into the bottom 50 of this bore.

Incidentally. the solenoid valve 10 is also of corresponding construction. In this case, the connecting line 8/9 opens into the annular space 28 as line 26, the by-pass 11 being separated from this annular space 28 by the lip seal 29. Here also, the lip seal 29 acts as non-return valve 12. Finally, the brake line 5 opens into the bottom 25 or 50 of the blind bore 24. The valve arrangement is otherwise the same as that described above.

In the present construction. in accordance with the invention, of a braking system, suitable choice of the algorithm renders possible a control which is comparable to the action of the conventional anti-skid -15control systems, with the single exception that a simultaneous buildup of pressure of one wheel and a reduction in pressure of the other wheel of a brake circuit is not possible. However, it is known that, as a rule, the reduction in pressure has priority, that is, the partner wheel of the same brake circuit is, as a rule, at pressure hold during the reduction in pressure; the same also applies analogously to the build-up of pressure (hydraulic multiplexes). However, anti-skid brake powers of up to 97% of the anti-skid brake powers customary at the present time can be achieved by this method.

A further advantage of the circuit arrangement described is a gradient change-over for the build-up of pressure which becomes effective as soon as the return pump in the circuit delivers. Proof of this may be shown by a calculation with an electrical equivalent-circuit diagram, and, in fact, by the following analogy:

- I I0 V1 R1[ - Y vo V2 R2 Vo Master brake cylinder pressure Io Pump delivery performance A V1 Pressure drop at the solenoid valve 10 V2 Pressure drop at the solenoid valve 6 12 A Volume flow at the left-hand front wheel Rl,,R2 Q Throttle resistances of the valves 10 and 6.

if Vol I01 Rlf R2 (A pressure of the master brake cylinder, delivery performance, throttle resistances) is given, the following value ensues for the volume f low _- 12:

VO - RjIo 12 R 1 + R 2 That is, if the pump is not active ('-! Io = 0), then 12 becomes large, that is, commencement of braking, partial braking.is determined only by the throttles. However, if the return pump is running (ZI Io 0), then the volume flow is reduced; this corresponds to a gradient change-over.

Claims

-17CLAIMS

1. A braking system comprising a master cylinder which is connected to wheel brake cylinders by way of brake lines having at least one solenoid valve and connecting lines having at least one solenoid valve, and a return pump for an anti-skid control. wherein a by-pass with a non-return valve by-passes the lines between the solenoid valve in the connecting lines and the respective wheel brake cylinder towards the brake line or towards the master cylinder and thus by-passes the solenoid valves in the respective connecting line and the brake lines.

2. A braking system as claimed in claim 1, wherein at least one of the solenoid valves in the connecting or brake lines has a valve body which is inserted into a blind bore and which is supported radially against the blind bore by way of a lip seal and at the same time allows a flow of brake fluid from an annular space at one side of the seal to a chamber at the other side of the seal and thus forms the nonreturn valve.

3. A braking system as claimed in claim 2, wherein in the at least one solenoid valve in the connecting lines, the line from the wheel brake cylinder opens into the annular space and the by-pass leads from the chamber back to the brake line or to the master cylinder.

4. A braking system as claimed in claim 3, wherein the chamber on the other side of the lip seal of the at least one solenoid valve in the connecting lines is separated by way of a seal from the connecting line leading to the at least one solenoid valve in the brake line or from the return pump.

5. A braking system as claimed in claim 4, wherein the valve body of the at least one solenoid valve in the connecting lines is supported against the base of the blind bore by way of a foot with an axial seal placed therebelow.

6. A braking system as claimed in claim 4, wherein the valve body of the at least one solenoid valve in the connecting lines engages a bore by means of a foot and is supported laterally against this bore by way of a radial seal.

7. A braking system as claimed in any one of claims 4 to 6, wherein the respective connecting line communicates with the annular space by way of a valve in the valve body.

8. A braking system as claimed in any one of claims 1 to 7, wherein the solenoid valve in the brake line, from which two connecting lines having the solenoid valves branch, is also by-passed by a by-pass incorporating a non-return valve.

9. A braking system as claimed in claim 8, wherein the connecting line opens into the annular space, and the by-pass leads out of the chamber to the brake line.

10. A braking system as claimed in any one of claims 1 to 9, wherein the connecting lines communicate, by way of a connection line, with the return pump whose outlet line leads back to the master cylinder by way of a throttle and/or a damping chamber.

11. A braking system constructed and adapted to operate substantially-as herinbefore described with reference to and as illustrated in the accompanying drawings.