GB2071783A

GB2071783A - Hydraulic pressure control system

Info

Publication number: GB2071783A
Application number: GB8102671A
Authority: GB
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co OHG
Priority date: 1980-02-21
Filing date: 1981-01-29
Publication date: 1981-09-23
Also published as: GB2071783B; ES256183Y; FR2476767A1; ES256183U; IT1135584B; DE3006468A1; IT8119914A0; DE3006468C2; JPH0314081B2; FR2476767B1; JPS56134601A

Abstract

A pressure control device for a pressure accumulator, in particular, for automotive vehicles provided with a brake slip control system, has the pressure accumulator fed by disconnectible pump and supplies at least two user components, requiring different minimum feed pressures for correct operation, which are connected to the pressure accumulator. A switching device (2) switches on the pump drive (10) in the evert of a user port (HV) falling below the lowest minimum feed pressure, representing the bottom switching threshold, and this switching device switches off the pump drive (10) upon attainment of a maximum of pressure in the pressure accumulator (3), representing the top switching threshold which is at least equal to the highest minimum feed pressure of the other user component (AS). The bottom switching threshold for switching on the pump drive (10) is increased to the level of the highest minimum feed pressure when the user component (AS) with the highest minimum feed pressure is operated. <IMAGE>

Description

SPECIFICATION Hydraulic pressure control system This invention relates to a hydraulic pressure control system and in particular to a pressure control device for a pressure accumulator especially for automotive vehicles fitted with a brake slip control system. The pressure accumulator is fed by a disconnectible pump and at least two user components are adapted to be connected to the pressure accumulator, which user components require different minimum feed pressures for correct operation.

The problems with such feeding of different pressure fluid user components are that the admissible lowest accumulator pressure has to be determined according to the highest minimum feed pressure of all connectible user components. Consequently, the feed pump will be designed such that the pressure in the pressure accumulator is now allowed to drop under the level of the minimum pressure required. As a result, the feed pump has to be switched on relatively often, although the user component with the highest minimum feed pressure is put into operation only rarely.

Pressure control systems of the aforementioned type are described in the book by Dr.

-Ing. Erwin Samal "Outlines of practical control technology", published by edition R. 01denbourg, 1967. One page 135, a pressure control valve is shown switching on and off the feed pump in dependence on the pressure prevailing in a pressure accumulator. As another example, a water level regulator is shown on page 1 37 controlling the height of a water level by using an electric switching arrangement in such a way that the feed pump is switched on upon attainment of a presettable minimum amount and the water level increases up to a presettable maximum amount, after which the pump is switched off.

Likewise, pressure switches are shown in the handbook "Vickers Handbook of Hydraulics", 1966, in which a hydraulic fluid acts on a piston movable against the force of a spring and actuating a microswitch after having covered a determined travel. However, pressure switches of this kind are only able to be used for switching a unit on or off so that such a switch would have to be available in duplicate, if a greater hysteresis were desired.

Hydraulic switches of the like with adjustable minimum switching pressure and adjustable maximum switching pressure have been described on pages 96 and 97.

The switching elements according to the prior art are not, however, in all cases in a position to solve satisfactorily the problem of pressure control. Particularly in the event of several, different user components being connected to a single pressure accumulator, it is desirable to control the pressure in the pressure accumulator such that in each case only the minimum feed pressures of the connected user components are guaranteed. Especially with regard to brake slip control systems, pressure fluid being pressurised as constantly as possible is required for governing the pressure modulation. At the same time, however, such a pressure accumulator feeds a hydraulic auxiliary force for actuation of the brake unit and maybe further hydraulic user components.As to the hydraulic brake booster, the controlled delivery of pressure is not subjected to such strict conditions of maintaining constant values as is required in the case of pressure fluid serving for control of the pressure modulation for the brake slip control system.

It is, therefore, an object of the present invention to provide a device for pressure control of the type initially referred to, rendering possible the disposition of the required pressure fluid for several user components with different minimum feed pressures by means of a joint pressure accumulator and decreasing the energy necessary for disposition of the accumulator pressure. In addition to this, the device is desired to be safe in its mode of operation and simple in its design.

According to the invention in its broadest aspect there is provided a pressure control device for a pressure accumulator, especially for automotive vehicles fitted with a brake slip control system, the pressure accumulator being fed by a disconnectible pump and at least two user components, requiring different minimum feed pressures for correct operation, being adapted to be connected to the pressure accumulator, characterised in that a switching device is provided which switches on the pump drive in the event of a user port falling below the lowest minimum feed pressure, representing the bottom switching threshold, which switching device switches off the pump drive upon attainment of a maximum pressure in the pressure accumulator, representing the top switching threshold and being at least equal to the highest minimum feed pressure of the other user component, and in that the bottom switching threshold for switching on the pump drive is increased to the level of the highest minimum feed pressure when the user component with the highest minimum feed pressure is operated.

A device in accordance with the present invention may be designed in such a way, for example, that a pressure sensor scans the accumulator pressure and transmits an electric signal to an electronic control device governing the pump drive as a function of electronically established switching thresholds, with at least the bottom switching threshold being adapted to be modified in dependence upon the switched-on user components.

According to a preferred embodiment of the invention, the switching device comprises a first pressure sensor, acted upon by the accumulator pressure, a second pressure sensor, acted upon by the pressure of a return line of a user component, and an electric switch, this switch being jointly controlled by the first and second pressure sensor. In this way, two different pressures are permitted to be scanned by one switching device, and the switch may be actuated corresponding to the pressure conditions. This embodiment is suitable for determination of the hysteresis of the switching device, i.e. the maximum distance between the switching thresholds, the first piston and the second piston are interconnected by a lost motion clutch, and a friction member exists which acts on the second piston.A particularly simple arrangement of the friction member is achieved in that it is located in an opening of the switching device's' housing and is pressed radially against the circumferential surface of the second piston by means of a spring.

To the end that the pump drive is not switched on in the event of sufficient pressure prevailing in the pressure accumulator and the pressure piston of the second pressure sensor being simultaneously pressurised and that the chamber bounded by the pressure piston takes care of an accumulating function from time to time, the actuating member is connected to the pressure piston in such a way that the pressure piston acts on the actuating member via a spring when moving in the sense of the switching-on of the switch and acts on the actuating member directly when moving reversely. When this occurs, the force of the spring is greater than the friction contact between the friction member and the second piston.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing.

In the drawing there is shown a sectional view of housing 1 of a hydraulic-electrical switching device 2 actuating, in response to the pressure in the pressure accumulator 3 and the prevailing pressure of line 4, a microswitch 5, which electrically operates a relay 8 via the electric control lines 6, 7.

When relay 8 is activated and closes contact 9, voltage will be applied via the line 1 3 to the electric motor 10 which has a ground connection 14. The electric motor 10 will drive the pumps 11 and 1 2 through a joint drive, with the pump 11 delivering pressure fluid through the suction connector 1 5 from the pressure fluid reservoir 1 6 via a hydraulic branching member 1 7 to the pressure accumulator 3. Provided in the pressure line 1 8 is a check valve 1 9 opening against the pressure of the pressure accumulator 3 and thus preventing depletion of the pressure accumulator 3 in the event of leakage of pump 11.

To filter out any dirt particles in the pressure fluid, a filter 20 is provided in the suction connector 1 5.

The pressurised fluid of pressure accumulator 3 is led via a pressure line 21 to a pressure chamber 22 of the hydraulic-electrical device 2. As a branch of the pressure line 21, another pressure line 23 leads to the user components HV and AS.

A first piston 24 is located in the pressure chamber 22 whose smallest diameter portion 26 sealingly penetrates an end wall 25 of the pressure chamber. Located between the end wall 25 and the largest diameter portion 27 of the first piston 24, is a spring 28, the force of which has to be overcome by the first piston 24 when moving in the direction of the end wall 25.

The smaller portion 26 of the first piston 24 enters into a chamber 29 and ends in the chamber in a head 30 designed with a greater diameter. Arranged in the chamber 29 is a second piston 31 abutting with its front surface 32 a contact pin 33 of a microswitch 5 recessed into the housing 1.

On the side remote from the front surface 32, the second piston 31 embraces head 30 so that the first piston 24 as well as the second piston 31 abut each other in the rest position shown. The head 30, and consequently the first piston 24, is movable relative to the second piston 31 by an axial clearance x. The connection of the first piston 24 with the second piston 31 in the manner of a lost motion clutch effects a certain hysteresis of the monitoring switching device, as will be described later on. The second piston 31 which is axially movable only within limits between the stops 34 and 35 is loaded by a friction member 36 acting radially thereupon.

The friction member is urged radially in abutment with the piston 31 with a predeterminable force by means of a spring 37 which is disposed in a bore 38 located radially to the second piston 31.

The mode of operation of the parts of the hydraulic-electrical switching device 2 so-far described is as follows: In the rest position shown, the second piston 31 bears against the stop 35, and the microswitch 5 is closed. The relay 8 is activated and the contact 9 is thus closed, i.e.

voltage is applied to the motor 10. The pump 11 delivers pressure fluid from the pressure fluid reservoir 1 6 to the pressure accumulator 3; the pressure prevailing in the pressure accumulator 3 is transmitted to the chamber 22 via the pressure line 21. The pressure in the chamber 25 acts on the first piston 24 and displaces it against the force of the spring 28 in the direction of the microswitch 5. After the axial clearance x towards the second piston 31 is overcome, the second piston 31 will be entrained by the first piston 24 and moved towards the microswitch 5 so that contact pin 33 opens the so-far closed contact of the microswitch. Relay 8 is de-activated due to the break of the relay coil circuit, causing the contact 9 to be opened and the pump feed to be interrupted.Piston 31 will move into abutment with the stop 34 when the maximum pressure is built up, so that the device is now in a left-hand end position in which the pressure accumulator 3 is charged to 90 bar, for instance.

With the pressure slowly dropping below 90 bar, the spring 28 will displace the first piston 24 to the right-hand position so that its end surface 40 will lift from the end surface 41 of the second piston 31. The second piston 31, itself will, however, not move as it is maintained in position by the friction member 36, which has to be designed so as to keep the spring-loaded contact pin 33 in its position.

With pressure continuing to drop, the spring 28 will displace the first piston 24 still further to the right-hand position, so that the head 30 approaches the stop 39 of the second piston 31. When the back rim of the head 30 is in abutment with the stop 39, the spring 28 will displace the entire arrangement comprising the first piston 24 and the second piston 31 to the right-hand position in the event of a further pressure decrease. The contact pin 33 of the microswitch 5 will follow this movement and the pump feed will be switched on again. This might, for instance, happen at an accumulator pressure of approximately 70 bar.

The accumulator will now be charged again up to 90 bar, and the head 30 will finally have to cover the newly developed axial clear ande x from its end surface 40 to the end surface 41 of the second piston 31. Only after this travel has been covered,-the pressure will have been increased to approximately 90 bar until this point of time-will the second piston 31 be able to be displaced again for another switching process.

It is, consequently, the purpose of the lost motion between second piston 31 and head 30 of the first piston 24 to determine the width of the hysteresis, of approximately 20 bar in the shown case, in co-operation with the spring 28 and the friction member 36. It may easily be seen that, once the device is constructed, the hysteresis is achieved by an appropriately chosen spring 28.

Connected in parallel with this portion of the switching device 2 is another portion which engages via a lever 42 in a radial groove 43 of the second piston 31. The lever 42 is pivoted on an axle 44 which is rigidly located in the housing 1. The end portion 45 of the lever 42 in the shape of a ball is so arranged in the second piston 31 that it will move with its centre largely in the plane of the axis of the second piston 31. The other end portion of the lever 42 is in communication with an actuating member 46, which bears via a spring 48 against a pressure piston 47. The actuating member 46 is inserted in the pressure piston 47 in such a manner that the spring 48 keeps the head end portion 49 in the pressure piston 47 in abutment with the stops 50 of the pressure piston.At its end portion acting upon the lever 42, the actuating member 46 includes an oval opening 51, in which a pivot 52 engages which is attached to the end portion of the actuating member 46.

Provision of the oval opening 51 ensures that the lever 42 can rotate on the axle 44 despite axial movement of the actuating member 46, without the risk of the device being jammed.

The pressure piston 47 is sealingly slidable in the housing 1, thereby separating a pressure chamber 53 from the remaining unpressurised space 54. To have a defined pressure chamber 53 available in the inactivated position shown, a stop 55 is provided in the housing 1, against which the pressure piston 47 abuts when in its rest position. In this rest position, the pressure piston 47 is held by a spring 56, disposed in a circular groove 57 in the pressure piston 47 and bearing against a stop 58 in the housing.

The chamber 53 is connected to a user component via the line 4. Via the suction connector 59, the pump 1 2-with the motor 10 runningdelivers pressure fluid from the pressure chamber 53 to the pressure accumulator 3 through a check valve 60 opening against the pressure of the pressure accumulator. The suction connector 59 communicates with the pressure fluid reservoir 1 6 via a check valve 61. In this arrangement, the spring 62 of the check valve is designed such that a pressure of, for instance, 2 bar at the most is allowed to develop in the pressure chamber 53. If fluid is fed via the line 4 which is pressurised to a higher extent, the check valve 61 will open and transmit the surplus pressure fluid to the pressure fluid reservoir 16.

In the case of one of the user components AS connected to the line 4 being switched on, a pressure of approximately 1 to 2 bar will develop in the pressure chamber 53 caused by the return of the pressure fluid. Assuming that a pressure of about 80 bar prevailed in the pressure accumulator 3 at the time the user component was switched on, the head 30 will, on the one hand, have a specific travel to the end surface 41 of the second piston 31, but will, on the other hand, also have a specific clearance from the stops 39.

As a result of pressure in the pressure chamber 53, the pressure piston 47 will be displaced, the actuating rod 46 will move the lever 42, and the forward movement of the pressure piston 47 will be transformed into a backward movement of the second piston 31 due to the point of rotation 44 of the lever 42. As, however, the ball end 45 of the lever 42 has a slight axial clearance in the radial groove 43, the ball end 45 will be moved into abutment with the side 63 of the groove 43 only after a slight forward movement of the pressure piston 47 and will displace the second piston 31 to the right-hand side with the pressure piston 47 continuing to move. This results in an intervention in the switching range of the upper-hand switching device and in a switching on of an immediate pump feed by closing the microswitch 5.

When this happens, not only will the pump 11 deliver pressure fluid from the pressure fluid reservoir 1 6 to the accumulator, but the pump 1 2 will also supply the pressure fluid prevailing in the pressure chamber 53 to the pressure accumulator 3.

The pressure in the pressure accumulator will now rise to 90 bar and, at that moment, the end surface 40 of the head 30 will abut the end surface 41 of the second piston 31 again and will displace that piston to the lefthand side against the force of the lever 42, thus switching off the microswitch 5 again and interrupting the pump feed. If pressure fluid continues to be fed to the pressure chamber 53 via the line 4, the pressure piston 47 will continue to be displaced to the lefthand side; however, in doing so, the pressure piston will not be able to transmit its forward movement to the lever 42. In order to be, nevertheless, in a position to execute a forward movement, the spring 48 is provided which is compressed due to the force acting on the pressure piston 47.With this arrangement, the switching device does not only have the function of pressure control, but the pressure chamber 53 serves at the same time as a volume accumulator for the pump 1 2.

If the pressure in the pressure accumulator drops in this position on account of the higher pressure fluid demand by the connected user components, the first position 24 will move away again from the microswitch 5 to the right-hand side due to the force of the spring 28. However, in this working position, the second piston 31 will not remain in the position into which it was shifted by the first piston 24, since the force of the spring 48 acts on the second piston 31 via the actuating member and the lever 42 and keeps the second piston in abutment with the head 30.

Consequently, the microswitch will move to the right-hand side upon a slight movement of the first piston 24 and will switch on again at once; the pressure will be immediately reincreased to 90 bar.

Thus, the entire switching device 2 has the following effect: Fluctuations of pressure up to 20 bar, for example, are admitted in the pressure accumulator 3 under normal operating conditions, controlled by the first piston 24 and the second piston 31 fastened to the first piston 24 in the manner of a lost motion clutch. This is quite sufficient for feeding the connected user component HV. The motor is put into operation only rarely due to such a hysteresis which must be admitted to be comparatively great. If, however, the other user component AS is switched on, requiring a higher and considerably more constant pressure level, the arrangement comprising pressure piston 47, actuating member 46 and lever 42 will influence the remaining switching device in such a manner that the hysteresis width will be reduced to a few bar (1 to 2 bar).

Switching devices of this kind are particularly advantageous for use in vehicles with anti-skid control systems. A hydraulic brake force boosting unit, allowing comparatively great fluctuation of pressure, may be provided as a first user component HV connected to the pressure accumulator 3. If, however, an antiskid control operation is intended with the help of the pressure fluid in the pressure accumulator 3, the accumulator pressure is required to be relatively constant to ensure a perfect control operation. This object may be achieved in an easy way by the embodiment described. The increase of the switching-off threshold may be determined by the proportioning of the spring 48. It is, of course, also possible to realise the hydraulic modes of operation described herein by an electromechanic switching device or by an electronic switching device. However, these switching devices would be required to transform the hydraulic pressure signals into electric signals, thus increasing expense. The switching device described may be used without any difficulties and without entailing a particularly great expenditure of power and electrical equipment in any pressure system, in which various user components are connected to one pressure accumulator and in which these various user components expect different minimum feed pressures from the accumulator.

Claims

1. A pressure control device for a pressure accumulator, especially for automotive vehicles fitted with a brake slip control system, the pressure accumulator being fed by a disconnectible pump and at least two user components, requiring different minimum feed pressures for correct operation, being adapted to be connected to the pressure accumulator, characterised in that a switching device is provided which switches on the pump drive in the event of a user port falling below the lowest minimum feed pressure, representing the bottom switching threshold, which switching device switches off the pump drive upon attainment of a maximum pressure in the pressure accumulator, representing the top switching threshold and being at least equal to the highest minimum feed pressure of the other user component, and in that the bottom switching threshold for switching on the pump drive is increased to the level of the highest minimum feed pressure when the user component with the highest minimum feed pressure is operated.

2. A device as claimed in claim 1, characterised in that a pressure sensor scans the accumulator pressure and transmits an electric signal to an electronic control device which governs the pump drive in dependence on electronically established switching thresholds, with at least the bottom switching threshold being adapted to be modified as a function of the switch-on user components.

3. A device as claimed in claim 1, characterised in that the switching device comprises a first pressure sensor, acted upon the accumulator pressure, and a second pressure sensor, acted upon by the pressure of a return line of a user component, and by an electric switch, this switch being jointly controlled by the first and the second pressure sensor.

4. A device as claimed in claim 3, characterised in that the first pressure sensor comprises a first piston acting on the electric switch against the force of a spring and by means of a second piston, and in that the second pressure sensor comprises a pressure piston connected with the second piston via a lever arrangement.

5. A device as claimed in claim 4, characterised in that the first piston and the second piston are interconnected by a lost motion clutch and in that a friction member acts on the second piston.

6. A device as claimed in claim 5, characterised in that the friction member is located in gn opening of the housing of the switching device and is urged radially against the circumferential surface of the second piston by means of a spring.

7. A device as claimed in claim 4, characterised in that the lever arrangement comprises a pivoted lever, engaging with one end portion in a radial opening of the second piston and an actuating member, which is connected to the pressure piston and is fastened to the other end portion of the lever.

8. A device as claimed in claim 7, characterised in that the actuating member is connected to the pressure piston in such a manner that the pressure piston acts on the actuating member via a spring when moving in the direction of the switching-on of the switch and acts on the actuating member directly when moving in the opposite direction.

9. A device as claimed in claim 8, characterised in that the force of the spring is greater than the friction contact between the friction member and the second piston.

1 0. A device as claimed in claim 7, characterised in that the ball-headed end portion of the lever is located in the radial opening with axial clearance.

11. A device as claimed in claim 8, characterised in that the pressure piston is acted upon by another spring in the same direction as the first-mentioned spring.

1 2. A device as claimed in claim 7, characterised in that the actuating member includes a pivot engaging in an oval opening of the lever.

1 3. A device as claimed in any of the preceding claims, characterised in that the top switching threshold for switching off the pump drive is increased when the user component with the highest minimum feed pressure is operated.

14. A pressure control device for a pressure accumulator substantially as described with reference to the accompanying drawing.