DE2745532A1 - DEVICE FOR A SERVO STEERING SYSTEM - Google Patents

Description

CAM GEARS LIMITED Munich, 10.10.77

4-5 Wilbury Way, P-508/77

Hitchin, Hertfordshire, Pu / a England

Device for a power steering system

The invention; relates to a device for a power-amplified Steering system for vehicles.

A steering gear that can be operated exclusively by hand via the steering wheel is required in many cases for generation the steering movements require a considerable amount of effort on the part of the driver, which is particularly disadvantageous in the case of heavy-duty vehicles makes noticeable. It is already known to use hydraulic power amplification to facilitate steering to use. However, if a malfunction occurs in such a hydraulic system, the hydraulic power amplification drops either completely off or at least largely off, which means that there is a risk that the The driver of the vehicle loses control of his vehicle.

The object of the invention is to this deficiency by a new device for hydraulic power amplification for to remedy a vehicle steering system that provides sufficient power amplification even in the event of a malfunction or partial failure the steering gear guaranteed.

This object is achieved according to the invention in that two hydraulic circuits connected in parallel are provided

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and are connected to a control valve, each hydraulic circuit having a pressure medium tank, a pump, a supply line and a return line has that the control valve can be actuated in this way as a function of the relative pressure in the two supply lines is that a line connection for the pressure fluid from one or both hydraulic circuits to one Force control valve is closed.

Such a device is particularly advantageous if, according to the invention, both pumps are operated simultaneously. Each pump then delivers about half of the total pressure medium throughput. This has the advantage that Smaller pumps can be used, since each only has to convey half the amount of pressure medium.

Alternatively, however, the device can also be operated with only one main or primary pump, in which case the the other pump serves as a replacement or standby pump, which is only used in the event of a fault in the effective hydraulic system is switched on. A pressure-dependent switch is used for this, which automatically starts the secondary pump, as soon as a fault, in particular a pressure drop, occurs in the primary system.

In contrast to the simultaneous operation of the pumps, where each pump delivers around half of the amount of pressure medium, In the second case, both the primary pump and the secondary pump must deliver the entire amount of pressure medium. This has the advantage that in the event of malfunctions in a system, the force gain remains the same while it becomes lower in synchronous operation due to the lower pressure medium flow.

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According to a preferred embodiment, the valve housing of the control valve has on the pump side in pairs arranged openings for the inlet and the return of the pressure medium, as well as a depending on the Fluid pressure in the two pump feed lines between an open and a closed position sliding valve slide, each inlet opening and pump-side return opening in the open position is in communication with an associated outlet opening or return opening and is in the closed position Position one of the inlet openings and the corresponding one the return port on the pump side are closed.

According to a further feature of the invention, the valve slide takes its closed position when the pressure at the two inlet openings is approximately the same. Falls the pressure at one of the two inlet openings drops noticeably, for example as a result of a fault in a pump or a leak in the valve inlet, then a pressure difference arises between the two inlet openings of the control valve. As a result, the valve slide moves into a position that closes this state, so that the Inlet and return openings of this disturbed circuit are closed, while the other circuit continues remains effective.

The device according to the invention also has the advantage that two liquid containers connected to one another via a line available. Since this line is arranged relatively far above the bottom of the two containers it acts as a weir. Therefore, if a leak should occur in one of the hydraulic systems, pressure medium will flow only from the container concerned, while the other container remains functional and hydraulic fluid up to the height of the connecting line. Thanks the-

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With this connecting line, the two containers can also be filled from a single filling opening and the respective liquid level is almost always the same in both containers.

Further features of the invention emerge from the subclaims.

The invention is described below with reference to second exemplary embodiments shown in the drawing. Show it:

Figure 1 shows a first embodiment of a hydraulic system for a power steering gear according to the invention;

Figure 2 shows a second embodiment of a hydraulic system for a power steering gear according to the invention.

As can be seen from FIG. 1, it is known per se power steering gear arranged in a housing, which is connected to a steering column 4-, the other end of which carries a steering wheel 6.

The steering system has two hydraulic circuits connected in parallel through which hydraulic fluid flows. Each circuit has a pump 22 or 24 and one of each Containers 26 and 28 respectively assigned to the pump in each case. The two containers are connected to one another via a line 30. A control valve 32 is arranged between the two pumps and a power control valve 10 is more common Design type. The power control valve 10 is a control valve with underlap in the rest position, so that in the rest position of the Valve, the hydraulic fluid from the pumps can flow freely into the container until the force

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Control valve 10 a force amplification is effective on the steering gear. The control valve 32 has a Valve housing 34, the inlet openings 36 and 38, as well as backflow ports 40 and 42 and correspondingly provided outlet ports 44 and 46 and backflow ports 48 and 50 owns. All of the openings mentioned open from the outside of the control valve 32 in a cylindrical one provided within the housing 34 Bore 52. Inlet ports 36 and 38 are over Bores 54 and 56 with their respective assigned Front side 58, 60 of the cylindrical bore 52 connected. Inside the bore, a piston-like longitudinal slide designated 62 is provided, which consists of five, spaced apart disc-shaped segments 64, 66, 68, 70 and 72, the diameter of which is roughly the same as that of the hole. The segments are each connected to one another by a part 74 of smaller diameter connected so that six chambers 76, 78, 80, 82, 84 and 86 are formed in the bore 52. The control valve is therefore a directional valve acting as a flow regulator. The outlet ports 44 and 46 are via a common one Line 88 is connected to the power control valve 10, while the return ports 48 and 50 have a common one Return line 90 connected to the power control valve 10 are. The pumps 22 and 24 are connected to the respectively associated inlet openings 36 and 38 via feed lines 92 and connected and the inlet-side return openings 40 and 42 are connected to the associated containers 26 and 28 via return lines 96 and 98.

The illustrated steering system can be used with pump 22 as the main pump and with pump 24 as a normally switched off stand-by auxiliary pump are operated, the is only switched on if the pump 22 fails. In such a mode of operation, the pumps 22 and 24 are used as the primary

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and secondary pump "denotes while theirs, respectively associated hydraulic circuits are referred to as primary and secondary circuits.

During operation, pressure fluid is then conveyed through the line 92 to the inlet opening 36 via the primary pump 22. The pressure fluid flows from the opening 36 into the chamber 82 and through the line 88 to the power control valve 10. The secondary pump 24 is switched off, so that at the Inlet opening 38 there is a significantly lower pressure than at opening 36. Inlet openings 36 and 38 are open via the lines 5 ^ and 56 each with an end face Chamber 86 and 76 in connection. As a result of the different Pressure in the two chambers 86 and 76 moves the valve slide 62 from its position shown to the right, so that through the segments 68 and 66, the inlet opening 38 and the return port 50 of the secondary pump is closed will. This separates the hydraulic system operated by the secondary pump 24 from that of the primary pump.

The pumped hydraulic fluid therefore flows from the power control valve 10 through the return line 90 to the chamber 84 and through the input-side return line 96 into the Container 26 and from there to the primary pump 22 back.

If there is a fault in the primary pump or in the primary circuit occurs, there is a reduction in the flow of liquid and thus a pressure drop at the inlet opening 36, so that the pressure in the chamber 86 also drops. As a result of the falling pressure, a pressure-sensitive device (not shown) becomes Switch the secondary pump 24 switched on. The hydraulic fluid is thus conveyed to the inlet opening 38. As a result, the pressure at the inlet port and the chamber 76 increases, so that the valve slide is moved to the left into a position in which the segments 68 and 70 the inlet opening 36 and the return opening 48

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the primary pump closes. In this way, the primary pump and the primary circuit become separate from the secondary circuit separated. The pressure fluid now passes from the inlet opening 38, the chamber 80 and the supply line 88 to the Power control valve 10. The return line takes place through the return line 90, the chamber 78 and the return line 98 to container 28 and back to secondary pump 24.

When the fault in the primary pump 22 or in the primary circuit has been eliminated, the primary pump can be switched on again so that the secondary pump is switched off. About the pressure gradient between the front chambers 76 and of the control valve 32, the valve slide 62 returns to its Starting position back.

In the preferred embodiment, both pumps 22 and 24 operate concurrently. In this case it becomes hydraulic fluid through both lines 92 and 94 to the inlet ports 36 and 38 pumped. The pressure medium flows from there through the chambers 82 and 80 to the power control valve 10. The return of the pressure medium takes place through line 90 and the chambers 78 and 84 and through the return lines 96 and 98 into the containers 26 and 28 and from there to the pumps 22 and 24. The inlet openings 36 and 38 are above the lines 54 and 56 with the end chambers 86 and 76 in connection. Is the pressure in the two supply lines 92 and 94 approximately the same, the pressure in the chambers 86 and 76 is also the same, and the valve slide 62 is in its illustrated, centrally open position held, in which the hydraulic fluid from both pumps into the power control valve 1o flows.

If there is a fault in one of the two pumps or in the primary circuits occurs, the liquid throughput is

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ringer and leads to a corresponding pressure drop at the inlet opening 36 and thus in the end face Chamber 86. Since there are now different pressures in the front chambers 86 and 76, it moves the valve slide to the side of the lower pressure, so in the present example to the left, so that the segments 68 and 70 close the inlet port 36 as well as the the pump 22 associated return port 48, whereby the pump 22 is separated from the secondary circuit of the pump 24 will.

The inlet and return ports, those of the secondary pump 24 are assigned, of course, remain here open, so the power amplification via the pump ate remains effective. Appropriately, a suitable display device installed, which indicates the failure of the primary pump 22. If there are faults in the pump 24 or of the supply line 94, then the valve slide 62 moves to the right and closes the inlet opening 38 and the valve-side return opening 50 of the pump 24.

The hydraulic system shown in Figure 2 corresponds essentially to that of Figure 1 with the exception of something differently designed control valve 32.

Corresponding parts in the two systems have the same reference symbols for the sake of clarity. That too Control valve 32 designed as a directional control valve with underlapping in the rest position has a single outlet opening here 100 and two opening into the cylindrical bore 52 Return ports 102 and 104.

The valve slide 62 here consists of four segments 106, 108, HO and 112, which are connected to one another via parts that are smaller in cross section are connected so that chambers 116, 118, 120 and 122, 124 are formed between the segments and the bore.

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The inlet opening 36 is connected to the end chamber 116 via a feed line 126, and the inlet line 38 is connected to the front chamber 124 via a feed line 128.

When the valve slide 62 is in the illustrated, is in the middle switch position, the Eii lassleitung are 36 and 38 in communication with chamber 120.

In this hydraulic system, the pump can also be used as the main pump and the pump 24 as a replacement or stand-by pump which is only used in the event of a pump failure.

In this case, during operation via the primary pump, pressure fluid is fed through the line 92 into the chamber 120 and conveyed through line 88 to power control valve 10. The secondary pump 24 is switched off, so that in the chamber 124 there is a much lower pressure than in the chamber. As a result of the existing between chambers 124 and 116 The pressure gradient moves the valve slide 62 to the left in relation to FIG. 2, so that the segments 108 and 106, inlet port 38 and return port 104 for the secondary pump 24 close. As a result, the secondary pump 24 and the associated secondary pump circuit separated from the primary circuit and the primary pump 22.

The pressure fluid now flows out of the force control valve 10 through the line 90 and the chamber 122 as well the return line 96 into the container 26 back.

If the primary pump 22 or its associated primary circuit fails, the pressure in the chamber 116 drops. At the same time, the secondary pump is switched on in the manner already described, so that the pressure in the Kanuner

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increases sharply. The valve slide moves as a result of the changed pressure conditions between chambers 116 and 124 62 to the side of low pressure, i.e. to the right, into a position in which the segments 110 and 112 the inlet port 36 and the outlet port 103 of the primary pump 22 close. As a result, the primary pump 22 and the primary circuit of the secondary pump 24 and its Secondary circuit separated.

The pressure fluid now flows from the inlet opening 38 through the chamber 120 and the line 88 to the power control valve 10. The pressure fluid flows back through line 90 via chamber 118 and the return line 98 in the container 28.

In this operating mode, which is preferably to be used, both pumps work simultaneously to circulate the hydraulic fluid leads 92 and 94 through chamber 120 and conduit 88 to promote the power control valve 10. The pressure fluid is returned via line 90 through the Chambers 122 and 118 and return lines 96 and 98 to containers 26 and 28.

If the primary pump 22 or the primary circuit fails, the pressure in the end chamber 116 drops and the valve part 62 moves to the right and closes the inlet opening 36 and the return opening 102 of the pump 22, so that the pump 22 '"and the line 92 to the secondary circuit of the pump 24. Since the inlet and return openings of the pump 24 remain open, the pump 24 continues to deliver pressure fluid for the power amplification, but if the pump 24 or the line 94 fails, the valve slide moves 62 to the left and closes the inlet opening 38 and the return opening 104 of the pump 24. As in the arrangement according to FIG. 1, a display device can be installed which indicates a fault in the pumps.

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The two hydraulic systems described offer the advantage that two separate hydraulic fluid containers 26 and 28 are provided, ie are connected to one another via a line 30.

Since the connecting line 30 is relatively far above is arranged from the bottom of the two containers, it acts as a weir. Should therefore be in one of the hydraulic If a leak occurs in the systems, the pressure medium only flows out of the respective container, while the other container remains functional and contains hydraulic fluid up to the level of the connecting line 30. Thanks to this connecting line the two containers can also be filled from a single filling opening and the respective The liquid level is almost always the same in both tanks.

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Claims (18)

Patent claims 1.! Device for a power steering system for —'Vehicles, characterized in that two hydraulic circuits connected in parallel are provided which are in operative connection with a control valve (32), each hydraulic circuit having a pressure medium tank (6, 28), a pump (22, 24), a supply line (92, 94) and a return line (96 or 98), that the control valve (32) can be actuated in this way as a function of the relative pressure in the two feed lines (92, 94) is that a line connection for the pressure fluid from one or both hydraulic circuits to one Force control valve (10) is closed. 2. Device according to claim 1, characterized by such a design of the control valve (32), that at substantially the same pressures in the two feed lines (92, 94) pressure fluid in the power control valve (10) flows. 3. Device according to claims 1 and 2, characterized in that the control valve (32) is a Housing (34) with inlet and outlet openings (35, 38, 40, 42, 44, 46, 48, 50) which are connected to the two hydraulic 809815/0872 ORIGINAL INSPECTED circuits and the power control valve (10) are in communication and that a with respect to the valve housing (34-) in Depending on the liquid pressure in the two feed lines (92, 94) movable, the flow of the pressure medium through the inlet and outlet openings controlling valve slide (62) is provided. 4. Device according to claim 3 »characterized in that the valve housing (3 ⁷ O on the pump side arranged in pairs openings for the supply and return (92, 9 ^ or 96, 98) of the pressure medium and at least one corresponding to the force control valve (10) associated outlet opening (44 ·, 46 or 100), as well as two correspondingly arranged return openings (46, 48 or 102, 104) that the valve slide (62) in a bore (52) in the valve housing (34) between an open position , in which the pump-side inlet opening and return opening (36, 38, 40, 42) of one of the circuits is in communication with a corresponding outlet opening and return opening for the power control valve, is movable, and a closed position in which said inlet opening and the said associated one Return opening are closed, while the pump-side inlet opening and return opening of the other circuit with a correspondingly assigned outlet and return opening for the K raft control valve is connected, see Figure 1. 5 · Device according to claim 3 »marked thereby e t that the valve housing (34) on the pump side arranged in pairs openings for the inlet (92, 94) and return (96, 98) of the pressure medium and at least one corresponding outlet opening assigned to the force control valve (10) (44, 46 and 100), as well as two correspondingly arranged return openings (46, 48 and 102, 104) that the - 3 009815/0872 Valve slide (62) in a bore (52) in the valve housing (34) between an open position, in the pump-side inlet port and return port of each circuit communicates with the outlet port and return port, and one closed Position is movable in which the inlet opening and the associated return opening of one of the circuits are closed, see Figure 2. 6. Device according to claim 4 or 5, characterized in that the end-face valve chambers (76, 86 or 116, 124) from the end faces of the bore (52) and the end faces of the segments (64, 72, or 106, 112) of the valve slide (62) are limited. 7. Device according to claim 6, characterized in that g e k e η η - ζ e ic η e t that the valve housing (3 * 0 of the control valve (32) connecting bores (5 ^, 56) which connect each inlet opening (36, 38) to the respectively assigned end chamber (76, 86 or 112, 116). 8. Device according to claim 7 »characterized in that that the two inlet openings (36, 38) on either side of the through the center of the control valve (32) are perpendicular to the longitudinal center axis of the plane, each inlet opening over a the connecting holes (5 ^ »or 56) with an associated front chamber (86, 76) is connected on the same side. (Figure 1). 9. Device according to claim 7 »characterized in that the inlet openings (36, 38) based on the longitudinal central cross-section on opposite sides of the valve housing (3 ¹ O are provided, each inlet opening via one of the connecting bores (126, 128) with an associated on the opposite 809815/0872 Side of the intended end chamber is connected (Figure 2). 10. Device according to one of claims 4 to 9, characterized in that the valve slide (62) spaced apart segments (6A, 66, 68, 70, 72 or 106, 108, 110, 112), which in the bore (52) of the valve housing (34) slide in a liquid-tight manner and the intermediate pieces (7 ⁷ 01 connecting the segments which form chambers (78, 80, 82, 84) with the inner wall of the bore through which the connection to the respective openings can be established. 11. Device according to claim 10, characterized in that each inlet and return opening (36, 38, 40, 42) in the open position of the valve slide (62) is in communication with the respectively assigned intermediate chamber. 12. Device according to claim 11, characterized in that each outlet and return opening (44, 46 or 48, 50) in the open position of the valve slide (62) with the respectively assigned intermediate chamber communicates. 13. Device according to claim 10, characterized in that both inlet openings in the open Position of the valve part with a common intermediate chamber (120) are in communication. 14. Device according to claim 13, characterized in that a single outlet opening (100) is provided, which is in communication with the common intermediate chamber (120). 809815/0872 15. Device according to claim 10, characterized in that the inlet opening (36, 38) is one Hydraulic circuit and its associated outlet opening (40, 42) each with the associated intermediate chamber (78, 84) in the open position of the valve slide (62) are in communication, while the inlet and outlet openings of the other circuit are closed. 16. Device according to claim 10, characterized in that in the control valve (32) for both Inlet openings (36, 38) a common intermediate chamber (120) is provided, with only one of the inlet openings in the open position of the valve slide (62) is in communication with this chamber. 17 · Device according to claims 1 to 16, characterized in that the pressure medium container (26, 28) communicate with one another through a connecting line (30) attached near their upper edge, as well as have a single filler opening. 18. Method of operating a power steering system according to claim 1, characterized in that the pumps (22, 24) of both hydraulic systems run simultaneously are operated. - 6- 809815/0872