GB2030642A

GB2030642A - Hydraulic Pressure Producing Systems

Info

Publication number: GB2030642A
Application number: GB7930898A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1978-09-07
Filing date: 1979-09-06
Publication date: 1980-04-10
Also published as: FR2435620A1; DE2838918A1; JPS6342121B2; JPS5536698A; GB2030642B

Abstract

A reciprocating piston 2 operated by a spring 3 and a cam 5 draws hydraulic fluid from a reservoir 24 and delivers pressurised fluid to a hydraulic accumulator 13. When the pressure at the accumulator reaches an upper limit a piston 18 unseats a valve 19 and consequently a valve 16 connects a pressure line 11 to the reservoir and the accumulator to a servo-motor 26, 27 through a pressure-regulator 28. The servo- motor thus separates the piston 2 from the cam 5 and so interrupts the pumping action. In other embodiments, Figs. 2 and 3 (not shown), the servo-motor operates a clutch through which the cam is driven. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Hydraulic Pressure-producing Systems The present invention relates to hydraulic pressure-producing systems.

A hydraulic pressure-producing system usuaily comprises a pump, an accumulator and a reservoir.

In a motor vehicle various devices such as a hydraulic brake booster, an anti-lock regulating system for a vehicle braking system, a powerassisted steering system or a level regulator require differing powers for operation. Thus, for example, a hydraulic brake booster requires a peak power of approximately 1,000 W for the short period at commencement of braking, although it only requires an average of 1 W. An anti-lock regulating system requires 80 to 300 W whilst it is operating. When the vehikle is stationary, a power-assisted steering system requires approximately 1000 W, whereas it requires only 30 to 50 W when travelling on a motorway. The same also applies to a level regulator.

In general, hydraulic pumps in motor vehicles (primarily for a steering aid and for level regulation) are driven continuously by the internal combustion engine. This operation requires a fluid which lubricates satisfactorily. In accordance with the present state of the art, a mineral oil fluid having adequate lubricating properties is used.

However, this fluid cannot readily be used in a brake system, owing, inter alia, to the fact that it has too low a boiling point, which can lead to failure of the brake circuit in the event of thermal over-loading. However, the lubricating property of the brake fluid of present day quality is only adequate for intermittently operating pumps.

Based on the power requirements given above, during the average operating time of a motor vehicle of 3000 hours, a conventionally operated pump would have to endure up to 20 hours operating time for the brake force booster and approximately 10 hours for the ABS (anti-lock regulating) function.

The conventional pumps are operated continuously. When the accumulator is full, they pump the fluid in a virtually pressure-free circuit by virtue of a corresponding position of a charging valve. If this charging valve is mounted at a great distance from the pump, rotational-speeddependent power losses occur which are considerable at high rotational speeds. However, if the charging valve is directly combined with the pump, the pressure line is continuously under high pressure, thus placing high demands on the pressure hose which, in general, must be flexible owing to the vibrational stress caused by the vibrating internal combustion engine.

According to the present invention a hydraulic pressure-producing system for making available pressure medium for hydraulic drives in a motor vehicle comprises a pump, an accumulator and a reservoir for hydraulic medium, and an actuating device responsive to pressure of hydraulic medium in the accumulator for selectively rendering the pump operative and inoperative whereby when in use the pump is actuated intermittently.

A hydraulic pressure-producing system embodying the present invention can have the advantage that the pump can be made from relatively inexpensive materials, since the pump functions relatively infrequently. Moreover, a fluid having relatively poor lubricating properties can be, used, such as conventional brake fluid. Finally, when in use the pump pressure line is under high pressure only during relatively short period of time during which the pump is functioning, so that the pressure hose can also be of relatively simple and inexpensive construction.

The invention will be further described by way of example with reference to the accompanying drawings in which: Fig. 1 is a diagram of a hydraulic pressure medium producing system according to one embodiment of the invention; Fig. 2 is a diagrammatic detail illustration of a pump and coupling, according to a second embodiment of the invention, and Fig. 3 shows a further variant of the pump and the coupling.

Referring first to Fig. 1 a hydraulic pressure medium producing system comprises a piston pump 1 having a piston 2 which is driven against the force of a spring 3 by a camshaft 4 of an internal combustion engine (not illustrated) of a motor vehicle. The spring 3 is disposed between a pump housing 7 and a foot 6 intended to abut against a cam 5 of the camshaft 4.

The pump piston 2 defines in part a pump working chamber 8 which is connected at one end to a suction line 9 and at the other end to a pressure line 11 by way of a pressure valve 10.

The pressure line 11 leads by way of a non-return valve 12 to an accumulator 13, and a branch line 14 leads from the accumulator 1 3 to a working chamber 1 5 of a control valve spool 16. The branch line 14 is controlled by a change-over valve 17 having a working piston 18 and a gate valve 19. The control valve spool 16 has two control edges 20 and 21 and is subjected to the force of a spring 22 which normally maintains the valve spool 1 6 in its left hand end position. The control edge 20 controls a line connection 23 leading to a reservoir 24, and the control edge 21 is located in a suction line connection 25 which is connected at one end to a working chamber 26 of a cut-off piston 27 arranged in the pump housing 7, and at the other end to a pressure regulator 28.

The pressure regulator 28 is intended for regulating the accumulator pressure to approximately 5 bar.

The cut-off piston 27 provided in the pump housing has a piston rod 29 which has an enlarged end portion 30 which can act upon the foot 6 of the pump piston 2.

The system so far described operates as follows: When the pump 1 is in its illustrated position, its pump piston 2 is at bottom dead centre. When the pump 1 is operating, the cut-off piston 27 is maintained inoperative under suction line pressure. When a predetermined pressure is obtained in the accumulator 1 3 by means of the pump, the piston 18 of the change-over valve 17, which piston is subjected to hysteresis, moves upwardly and opens the gate valve 19, with the result that the accumulator pressure enters the working chamber 1 5 of the control valve spool 1 6. The control valve spool 1 6 moves to the right against the force of the spring 22, and the control edge 20 connects the pressure line 11 to the reservoir 24, and the control edge 21 closes the suction line connection leading to the pressure regulator 28. A relatively low pressure of, for example, 5 bar is fed into the suction line connection 25 by the pressure regulator 28. This pressure causes the cut-off piston 27 and its end portion 30 to move to the left and to disengage the pump piston 2 from the cam 5 of the camshaft 4. The pump 1 is thereby rendered inoperative.

Fig. 2 shows a different pump 31 and a different coupling 32. In this embodiment, a pump piston 33 is actuated by a rotary drive 34. An actuating piston 35 is secured to the drive 34 and can rotate and move longitudinally in its working cylinder 36. One end of the actuating piston 35 is subjected to the force of a spring 37 which seeks to move a part of the coupling 32 to the left into its driving position. A working chamber 38 which corresponds to the working chamber 26 of Fig. 1, and which is connected to the suction line connection 25, is located at the other side of the actuating piston 35.

When a sufficiently high pressure prevails in the accumulator 13, a pressure of approximately 5 bar is introduced into the suction line connection 25. The actuating piston 35 moves to the right against the force of the spring 37, to release the coupling 32, and stop the pump 31.

Fig. 3 shows that it is also possible to dispense with rotation of the actuating piston 40 by separating the actuating piston 40 from the pump shaft 41 by means of a diaphragm 39.

It may also be mentioned that the change-over valve 17 and the control valve spool 1 6 can constitute parts of a hydraulic central control.

Furthermore, it is possible to drive the piston pump 1 by means of a rocker arm instead of the cam shaft 4. It is also conceivable to drive the piston pump by means of an auxiliary shaft, preferably by means of a distributor drive.

In the embodiment of Fig. 2, it is also possible to perform the rotary drive by means of a cam shaft. Furthermore, it is also possible to effect the rotary drive by means of a generator.

Alternatively, it is conceivable to effect the drive by means of an auxiliary shaft, preferably the shaft of an oil pump of a motor vehicle lubricating system.

Finally, it is also possible, within the scope of the invention, to combine the drive with a petrol pump or an injection pump.

Claims

1. A hydraulic pressure-producing system for making available pressure medium for hydraulic drives in a motor vehicle, comprising a pump, an accumulator and a reservoir for hydraulic medium, an actuating device responsive to pressure of hydraulic medium in the accumulator for selectively rendering the pump operative and inoperative whereby when in use the pump is actuated intermittently.

2. A hydraulic pressure-producing system as claimed in claim 1, in which the actuating device is a cut-off piston which when in use is maintained ineffective under suction line pressure when the pump is being actuated and is subjected to accumulator pressure for the purpose of rendering the pump inoperative.

3. A hydraulic pressure-producing system as claimed in claim 2, in which when in use the cutoff piston is subjected to a partial pressure of the - accumulator pressure for the purpose of rendering- the pump inoperative, and that the level of this partial pressure is controlled by a pressure regulator.

4. A hydraulic pressure-producing system as claimed in any of claims 1 to 3, including an accumulator-pressure-dependent change-over valve and a control valve spool of which the change-over valve is subjected to hysteresis and is located in a pressure line from the pump, and the control valve spool is located in a suction line of the pump.

5. A hydraulic pressure-producing system as claimed in claim 4, in which the change-over valve and the control valve spool are parts of a hydraulic central control.

6. A hydraulic pressure-producing system as claimed in any of claims 1 to 5, in which the pump has a piston drivable by an eccentric, and the actuating device has a coupling device for rendering the eccentric drive ineffective.

7. A hydraulic pressure-producing system as claimed in claim 6, in which the piston of the pump is drivable by a camshaft.

8. A hydraulic pressure-producing system as claimed in claim 6, in which the piston of the pump is drivable by a rocker arm.

9. A hydraulic pressure-producing system as claimed in claim 6, in which the piston pump is drivable by an auxiliary shaft.

10. A hydraulic pressure-producing system as claimed in any of claims 1 to 5, in which the pump has a rotary drive and the actuating device has a coupling device for rendering the rotary drive ineffective.

11. A hydraulic pressure-producing system as claimed in claim 10, in which the coupling device has a rotatable and longitudinaily movable actuating piston.

12. A hydraulic pressure-producing system as claimed in claim 10, in which the coupling device has an actuating piston which is only longitudinally movable.

13. A hydraulic pressure-producing system as claimed in any of claims 10 to 12, in which the rotary drive is performed by a camshaft.

14. A hydraulic pressure-producing system as claimed in any of claims 10 to 12, in which the rotary drive is performed by a generator.

1 5. A hydraulic pressure-producing system as claimed in any of claims 10 to 12, in which the rotary drive is performed by an auxiliary shaft.

1 6. A hydraulic pressure-producing system as claimed in claim 15, in which the auxiliary shaft is a shaft of an oil pump of the motor vehicle lubricating system.

1 7. A hydraulic pressure-producing system as claimed in any of claims 1 to 16, in combination with a petrol pump.

1 8. A hydraulic pressure-producing system as claimed in any of claims 1 to 16, in combination with a fuel injection pump.

1 9. A hydraulic pressure-producing system, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 1 of the accompanying drawings.

20. A hydraulic pressure-producing system, as claimed in claim 19, but including a pump constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 2 of the accompanying drawings.

21. A hydraulic pressure-producing system as claimed in claim 20, but including the modification constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 3 of the accompanying drawings.