GB1589311A

GB1589311A - Servo amplifier for hydraulic systems especially brake systems

Info

Publication number: GB1589311A
Application number: GB4050577A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1976-10-08
Filing date: 1977-09-29
Publication date: 1981-05-13
Also published as: FR2367206A1; FR2367206B1; DE2645471C2; DE2645471A1; IT1143832B

Description

(54) SERVO AMPLIFIER FOR HYDRAULIC SYSTEMS, ESPECIALLY BRAKE SYSTEMS (71) We, WABCO FAHRZEUGBREMSEN GmbH (Formerly WABCO WESTINGHOUSE GmbH), a German Company of, Am Lindener Hafen 21, 3000 Hannover 91, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a servo amplifier for hydraulic systems, especially brake systems.

It is known, in hydraulic systems, to use a servo amplifier to amplify a specified actuation force, up to a predetermined maximum value, and to utilise this amplified actuation force for the actuation of a working apparatus, for example, in the case of a brake system, a main brake cylinder.

In a known type of servo amplifier, the amplifier mechanism is a cylinder in which there are movably inserted, at one end, an imput member in the form of a ram for the actuation of the servo amplifier and, at the other end, a thrust member for the actuation of the working apparatus, the cylinder bore having an inlet and an outlet for pressure medium.

A servo amplifier of this general type is disclosed in German Auslegeschrift 23 47 282, but has the disadvantage that some of the components described are comparatively expensive to manufacture. Moreover, the amplifier has no outlet which is capable of supplying other hydraulic circuits (i.e. no outlet can be loaded).

German Offenlegungsschrift 23 35 529 discloses a servo amplifier which does have an outlet capable of supplying a load but has the disadvantage that the pressure at this outlet, when the servo ampifier is operated, is dependent on the pressure in an amplifier chamber within the servo amplifier mechanism. Moreover, the amplifier mechanism itself includes a lever arrangement which is complicated and prone to trouble and it is a further disadvantage that the pressure-limiting device, provided to limit the amplification of the actuating force, is dependent purely on the actuation force itself and is thus effective independently of the pressure in the amplifier chamber.

Finally, the particular design proposed for this arrangement occupies too much space, especially for use in vehicle construction.

The present invention provides a servo amplifier for a hydraulic system, comprising a cylinder having a pressure medium inlet connected to an outlet for supplying a load and, at one end, an input member operable to actuate the servo amplifier and, at the other end, a thrust member for actuation by the servo amplifier; an actuating slide valve, cooperable with the thrust member, which connects the inlet to the load-supplying outlet and defines an amplifier chamber within the cylinder, which chamber is connected by way of a flow regulator with a return outlet; and a control slide valve actuable by the input member to connect the inlet to the amplifier chamber, thereby to actuate the thrust member via the actuating slide valve in dependence on operation of the input member actuation of the control slide valve simultaneously adjusting the connection between the inlet and the load-supplying outlet to maintain hydraulic pressure at the load-supplying outlet independent of operation of the input member.

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawing which shows a longitudinal section through a servo amplifier.

The drawing shows the servo amplifier with its cylinder 1 , the cylinder bore 2 of which has a pressure medium inlet 3, an outlet 4 for supplying a load, and closure members 5 and 6 inserted so they are sealed at both ends in the cylinder.

The closure members 5 and 6 have continuous bores set axially to the cylinder bore. In these bores there are disposed, at one end in the closure member 5, an input member, in the form of a ram 7, for the actuation of the servo amplifier and, at the other end in the closure member 6, a thrust member 8 for the actuation of a working apparatus, for example a main brake cylinder. Both the ram and the thrust piece are sealed and arranged so as to slide.

In the cylinder bore 2 there is arranged a slide valve 1 2 which rests against the thrust member 8 under the action of a restoring spring 11 supported against a spring washer 10 lying on the closure member 6 and against a stop 9 provided on the ram 7. The slide valve 12 divides the cylinder bore 2 into a return chamber 13 defined by the slide valve 12 and by the thrust member 8, and an an amplifier chamber 14 defined by the slide valve 12 and the ram 7.

The slide valve 12 has a blind bore 15 arranged axially to the cylinder bore 2 at the end at which the ram is located. The blind bore is connected by way of a transverse bore 16 and an annular groove 17 of the slide valve 12 to the pressure medium inlet 3 and also by way of a further transverse bore 18 and an annulur groove 19 to the outlet 4.

In the blind bore 15 of the slide valve 12 there is arranged a control slide valve 20 that cooperates with the ram 7 and may be displaced against the action of a spring 21 supported against the end of the blind bore 1 5.

The control slide valve 20 has an annular groove 22 connecting the two transverse bores 16 and 18 of the slide valve 12 and thus also the pressure medium inlet 3 and the outlet 4. The control slide valve also has a longitudinal bore 24 connected at one end to the amplifier chamber 14 and at the other end via a throttle 23 to the chamber in which the spring 21 is situated.

Upon actuation of the ram 7, as will be described below, the longitudinal bore 24 may be connected to the pressure medium inlet 3 by way of a transverse bore 25 of the control slide valve 20 and an annular recess 26 of the blind bore 15 of the slide valve 12 and also by way of the annular groove 22 of the control silde valve 20.

At its lateral limitation the annular groove 22 of the control slide valve 20 has control edges 27 and 27', by means of which, when the ram 7 is inoperative as shown in the drawing, the connection between the longitudinal bore 24 and the pressure medium inlet 3 is blocked off and the connection between the outlet 4 and the pressure medium inlet 3 may be fully opened. When the ram 7 is actuated, the edges 27 and 27' open increasingly the connection between the longitudinal bore 24 and the pressure medium inlet 3, thereby admitting pressure medium to the amplifier chamber 14 to actuate the thrust piece 8 as will be described below. At the same time, the edges 27, 27' throttle increasingly the connection between the outlet 4 and the pressure medium inlet 3 thereby to maintain pressure at the outlet 4 independent of actuation of the ram.

The ram 7 has a recess 28 located at the end nearest the slide valve and opening out into the cylinder bore 2. In this recess 28, there is arranged a pressure-limiting device, indicated generally at 29, by way of which the ram 7 cooperates with the control slide valve 20 unless the pressure limiting device 29 is overriden: in this case, as will be described below, the annular end face of the ram 7 is able to cooperate directly with the slide valve 12.

The pressure-limiting device 29 comprises a pressure-responsive member 35 arranged with a certain freedom of movement in the recess 28. At one end the member 35 is guided in a sealed manner with an extension 30 in a longitudinal bore 31, open to the outside of the ram 7, and at its other end using a shoulder 32 it cooperates with the control slide valve 20.

Under the influence of a spring 33 supported against the end wall of the recess 28, the member 35 rest against a stop 34, provided the pressure in the amplifier chamber 14 is below a specified value predetermined by the action of the spring 33. If the pressure in the amplifier chamber 14 reached the specified value, the member 35 may be displaced against the force of the spring 33. The stop 34 against which the member 35 rests is formed by a snap ring located in the recess 28 at the end nearest the slide valve.

The amplifier chamber 14 is connected by way of a bore 36 and a flow regulator 37 to a fluid return outlet 38. The flow regulator 37 is arranged in a cylindrical recess 40 connected at one end by way of the bore 36 to the amplifier chamber 14 and at its other end by way of an annular recess 39 to the return 38. The flow regulator 37 has a sleeve 44 which is inserted into the cylindrical recess 40 so as to slide and which connects the amplifier chamber 14 with the return 38 by way of a throttle 41. The sleeve 44 may be displaced under the influence of the pressure in the amplifier chamber 14 against the influence of a spring 42, and in being so displaced it increasingly blocks off the annular recess 39 joined to the return 38.When the amplifer chamber 14 is without pressure, under the influence of the spring 42 the sleeve rests against a stop 43 provided in the cylindrical recess 40, and in this position opens the annular recess 39 to the cylindrical recess 40.

The return chamber 13 is connected with the return outlet 38 by way of an annular recess 45 set into the end face of the closure member 6, a bore 46 and the annular recess 39.

The manner in which the servo amplifier shown in the drawing operates, is as follows: In the drawing the servo amplifier is shown in its initial position when the ram 7 is inoperative. The pressure medium inlet 3 is connected to the outlet 4 by way of the annular groove 17 and the transverse bore 16 of the slide 12; the annular groove 22 of the control slide valve 20, and the transverse bore 18 and the annular groove 19 of the slide valve 12. The amplifier chamber 14 is without pressure since the control edge 27' of the control slide valve 20 is blocking the connection between the amplifier chamber 14 and the pressure medium inlet 3.

The member 35 of the pressure-limiting device 29 is lying, under the action of the pre-stressed spring 28, against the stop 34. The slide valve 12 is lying, under the action of the spring 21, against the thrust member 8 and the control slide valve 20 is lying, under the action of the spring 21, against the shoulder 32 of the member 35 and is holding the ram 7, assisted by the action of the restoring spring 11, in its ready-to-operate position. Depending on the way in which the servo amplifier has been installed, the path of the control slide valve 20 towards the ram 7 may be limited if required, for example by a stop formed by a snap ring inserted in the blind bore 15 of the slide valve 12.Finally, in the initial position of the servo amplifier, the sleeve 44 of the flow divider 37 lies against the stop 43 under the action of the spring 42, opening the connection from the cylindrical recess 40 to the annular recess 39 connected to the return 38.

When the ram 7 is actuated, it moves under the action of the operating force Fl, with the member 35 of the pressure-limiting device 29 remaining against the stop 34. As the ram 7 moves it takes with it the control slide valve 20 lying against the shoulder 32 of the ram 35, against the action of the spring 21. During this movement, the control slide valve 20 opens, by way of its control edge 27' the connection of the amplifier chamber 14 to the pressure medium inlet 3 by way of the longitudinal bore 24 and the transverse bore 25 of the control slide valve 20; the annular recess 26 of the slide valve 12; the annular groove 22 of the control slide valve 20, and the transverse bore 16 and the annular groove 17 of the slide valve 12.

Simultaneously, the control slide valve increasingly throttles by way of its control edge 27 the connection of the pressure medium inlet 3 to the outlet 4, so that pressure at the outlet 4 is maintained. Thus, the control slide valve causes a build up of pressure in the amplifier chamber 14, which, is independent of any load (i.e. hydraulic circuit) connected to be supplied from the outlet 4. The pressure built up in the amplifier chamber 14 in this manner results in an amplified output force F2 which, is utilised, as required, by way of the thrust member 8 resting against the slide valve 12.

The pressure present in the amplifier chamber 14 is simultaneously applied through the bore 26 to the flow regulator 37. The flow regulator ensures a predetermined maximum flow of for example, 1.5 1/mien., to the return 38 by way of the throttle point 41 of the sleeve 44. As already described, the sleeve 44 moves under the action of the increasing pressure of the amplifier chamber 14 against the action of the spring 42 and, in being so moved, increasingly blocks the annular recess 39 connected to the return outlet 38.

As soon as the pressure in the amplifier chamber 14 reaches the above-mentioned specified value, predetermined by the setting of the pressure-limiting device 29, the member 35 moves against the action of the spring 33, allowing the control slide valve 20 to move under the action of the spring 21. As the control slide valve 20 moves, its control edge 27' increasingly blocks the connection of the pressure medium inlet 3 to the amplifier chamber 14. As a result of this, the pressure rise in the amplifier chamber 14 ceases and the pressure in the amplifier chamber 14 is thus limited to the specified value predetermined by the setting of device 29 and chosesn to be suitable for the design and reliability of the system in which the servo amplifier is to be employed.

As soon as the actuation of the ram 7 ends, the pressure in the amplifier chamber 14 reduces by means of the flow regulator 37 and under the action of the springs with which they are associated, all moving parts of the servo amplifier return to their previously described initial position.

If the fluid pressure fails before or during an actuation of the ram 7, the ram 7 moves under the action of the actuation force F1, against the action of the springs 21 and 33 and also of the restoring spring 11, and finally positions itself with its annular end face against the end face of the slide valve 12 whereupon the actuation force F1 is transformed directly to the thrust member 8 without risk to the moving parts of the servo amplifier.

The advantages that may be obtained using a servo amplifier constructed as described above are, in particular, as follows: The slide valve arrangement 12, 20 provides a simple, space-saving amplifier that can be assembled without difficulty in series production. Owing to its control slide valve 20 which, when the ram 7 is actuated, increasingly opens the correction of pressure medium inlet 3 with the amplifier chamber 14 and increasingly throttles the outlet 4, the servo amplifier has an outlet that may be pressurized independently of the pressure in the amplifier chamber.

Furthermore the pressure-limiting device 29 operates in dependence on the amplifier pressure and may be mechanically overriden when pressure fails. In the case of a pressure failure, the ram 7, the slide valve 12 and the thrust member 8 cooperate mechanically, thus making effective the actuation force of 1:1. Under normal operation, on the other hand, the amplifier pressure can be rapidly reduced when the braking action has ended by means of the flow regulator which ensures a predetermined constant through-flow of pressure medium during the amplifying phase.

The arrangement of the restoring spring 11 produces a supporting effect for the spring 33 acting on the member 35 of the pressurelimiting device 29, on the one hand, and for the spring 21 acting on the slide valve 12 and the control slide valve 20, on the other hand, as a result of which these two springs 33 and 21 can be advantageously designed in an economical manner.

WHAT WE CLAIM IS: 1. A servo amplifier for a hydraulic system, comprising a cylinder having a pressure medium inlet connected to an outlet for supplying a load and, at one end, an input member operable to actuate the servo amplifier and, at the other end, a thrust member for actuation by the servo

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. by the action of the restoring spring 11, in its ready-to-operate position. Depending on the way in which the servo amplifier has been installed, the path of the control slide valve 20 towards the ram 7 may be limited if required, for example by a stop formed by a snap ring inserted in the blind bore 15 of the slide valve 12. Finally, in the initial position of the servo amplifier, the sleeve 44 of the flow divider 37 lies against the stop 43 under the action of the spring 42, opening the connection from the cylindrical recess 40 to the annular recess 39 connected to the return 38. When the ram 7 is actuated, it moves under the action of the operating force Fl, with the member 35 of the pressure-limiting device 29 remaining against the stop 34. As the ram 7 moves it takes with it the control slide valve 20 lying against the shoulder 32 of the ram 35, against the action of the spring 21. During this movement, the control slide valve 20 opens, by way of its control edge 27' the connection of the amplifier chamber 14 to the pressure medium inlet 3 by way of the longitudinal bore 24 and the transverse bore 25 of the control slide valve 20; the annular recess 26 of the slide valve 12; the annular groove 22 of the control slide valve 20, and the transverse bore 16 and the annular groove 17 of the slide valve 12. Simultaneously, the control slide valve increasingly throttles by way of its control edge 27 the connection of the pressure medium inlet 3 to the outlet 4, so that pressure at the outlet 4 is maintained. Thus, the control slide valve causes a build up of pressure in the amplifier chamber 14, which, is independent of any load (i.e. hydraulic circuit) connected to be supplied from the outlet 4. The pressure built up in the amplifier chamber 14 in this manner results in an amplified output force F2 which, is utilised, as required, by way of the thrust member 8 resting against the slide valve 12. The pressure present in the amplifier chamber 14 is simultaneously applied through the bore 26 to the flow regulator 37. The flow regulator ensures a predetermined maximum flow of for example, 1.5 1/mien., to the return 38 by way of the throttle point 41 of the sleeve 44. As already described, the sleeve 44 moves under the action of the increasing pressure of the amplifier chamber 14 against the action of the spring 42 and, in being so moved, increasingly blocks the annular recess 39 connected to the return outlet 38. As soon as the pressure in the amplifier chamber 14 reaches the above-mentioned specified value, predetermined by the setting of the pressure-limiting device 29, the member 35 moves against the action of the spring 33, allowing the control slide valve 20 to move under the action of the spring 21. As the control slide valve 20 moves, its control edge 27' increasingly blocks the connection of the pressure medium inlet 3 to the amplifier chamber 14. As a result of this, the pressure rise in the amplifier chamber 14 ceases and the pressure in the amplifier chamber 14 is thus limited to the specified value predetermined by the setting of device 29 and chosesn to be suitable for the design and reliability of the system in which the servo amplifier is to be employed. As soon as the actuation of the ram 7 ends, the pressure in the amplifier chamber 14 reduces by means of the flow regulator 37 and under the action of the springs with which they are associated, all moving parts of the servo amplifier return to their previously described initial position. If the fluid pressure fails before or during an actuation of the ram 7, the ram 7 moves under the action of the actuation force F1, against the action of the springs 21 and 33 and also of the restoring spring 11, and finally positions itself with its annular end face against the end face of the slide valve 12 whereupon the actuation force F1 is transformed directly to the thrust member 8 without risk to the moving parts of the servo amplifier. The advantages that may be obtained using a servo amplifier constructed as described above are, in particular, as follows: The slide valve arrangement 12, 20 provides a simple, space-saving amplifier that can be assembled without difficulty in series production. Owing to its control slide valve 20 which, when the ram 7 is actuated, increasingly opens the correction of pressure medium inlet 3 with the amplifier chamber 14 and increasingly throttles the outlet 4, the servo amplifier has an outlet that may be pressurized independently of the pressure in the amplifier chamber. Furthermore the pressure-limiting device 29 operates in dependence on the amplifier pressure and may be mechanically overriden when pressure fails. In the case of a pressure failure, the ram 7, the slide valve 12 and the thrust member 8 cooperate mechanically, thus making effective the actuation force of 1:1. Under normal operation, on the other hand, the amplifier pressure can be rapidly reduced when the braking action has ended by means of the flow regulator which ensures a predetermined constant through-flow of pressure medium during the amplifying phase. The arrangement of the restoring spring 11 produces a supporting effect for the spring 33 acting on the member 35 of the pressurelimiting device 29, on the one hand, and for the spring 21 acting on the slide valve 12 and the control slide valve 20, on the other hand, as a result of which these two springs 33 and 21 can be advantageously designed in an economical manner. WHAT WE CLAIM IS:

1. A servo amplifier for a hydraulic system, comprising a cylinder having a pressure medium inlet connected to an outlet for supplying a load and, at one end, an input member operable to actuate the servo amplifier and, at the other end, a thrust member for actuation by the servo

amplifier; an actuating slide valve, cooperable with the thrust member, which connects the inlet to the load-supplying outlet and defines an amplifier chamber within the cylinder, which chamber is connected by way of a flow regulator with a return outlet; and a control slide valve actuable by the input member to connect the inlet to the amplifier chamber, thereby to actuate the thrust member via the actuating slide valve in dependence on operation of the input member actuation of the control slide valve simultaneously adjusting the connection between the inlet and the loadsupplying outlet to maintain hydraulic pressure at the load-supplying outlet independent of operation of the input member.

2. A servo amplifier according to Claim 1, in which the control slide valve is resiliently interconnected with the actuating slide valve.

3. A servo amplifier according to Claim 1 or Claim 2, in which the control slide valve is located in a blind bore in the actuating slide valve and is movable by the input member against a resilient member supported on the floor of the blind bore.

4. A servo amplifier according to Claim 3, in which the connection between the inlet and the load-supplying outlet is provided by an inlet orifice and an outlet orifice in the actuating slide valve, which inlet and outlet orifices connect the pressure medium inlet and the load-supplying outlet, respectively, to the said blind bore, and in which the control slide valve is shaped to interconnect the said orifices within the blind bore.

5. A servo amplifier according to Claim 4, in which the connection between the inlet and the amplifier chamber is provided by a control orifice in the control slide valve, which communicates through a bore in the control slide valve with the amplifier chamber, and the control slide valve being movable by the input member to place the control orifice in communication with the inlet orifice in the actuating slide valve.

6. A servo amplifier according to any one of the preceding claims, in which the control slide valve is shaped to block communication between the inlet and the amplifier chamber when the input member is inoperative.

7. A servo amplifier according to any one of the preceding claims, in which the control slide valve is so shaped that, when the input member is operated, the connection between the inlet and the load-supplying outlet is increasingly throttled as the connection between the inlet and the amplifier chamber is increasingly opened.

8. A servo amplifier according to any one of the preceding claims, in which the input member is cooperable with the control slide valve through a pressure limiting device.

9. A servo amplifier according to Claim 8, in which the pressure limiting device is operable, in response to a predetermined pressure in the amplifier chamber to disconnect the ram from the control slide valve.

10. A servo amplifier according to Claim 8 or Claim 9, in which the pressure limiting device comprises a resiliently-biased pressure-responsive member located in the input member and exposed to the pressure in the amplifier chamber, the pressure responsive member being engageable with the control slide valve when the pressure in the amplifier chamber is below a predetermined value.

11. A servo amplifier according to Claim 10, in which the pressure-responsive member comprises a piston which is positioned in a recess in the input member and is guided by an extension located in a bore in the input member which bore is open to the exterior of the ram.

12. A servo amplifier according to Claim 9, in which the input member, when disconnected from the control slide valve through operation of the pressure limiting device, is cooperable directly with the actuating slide valve.

13. A servo amplifier according to any one of the preceding claims and includes a restoring spring supported, at one end, against the actuating slide valve and, at the other end, against the input member.

14. A servo amplifier according to any one of the preceding claims, in which the flow regulator includes a pressure-responsive member exposed to pressure in the amplifier chamber whereby the fluid return outlet is increasingly throttled as pressure in the amplifer chamber increases.

15. A servo amplifier for a hydraulic system, substantially as described herein wich references to, and as shown in, the accompanying drawings.