WO1990002071A1 - Servo-assisted steering system - Google Patents

Abstract

A servo-assisted steering system, in particular for motor vehicles, comprises a pump (6) and a servo motor (5) supplied with hydraulic fluid through a distributor valve (2). Steering deflection generates, at a control edge (16, 17, 31) of a pressure valve (2, 37, 48, 73), a pressure which can be boosted by means of a pressure-boosting element (2, 43) in function of predetermined parameters. The boosted pressure is applied to the hydraulic servo motor (5) via valve edges (11, 12) separated from the pressure control in a distributor valve (4, 25, 26, 49, 50 74).

Description

 Power steering

The invention relates to an auxiliary power steering system according to the preamble of claim 1.

In this steering, an electrically controlled three-way flow control valve regulates an amount of oil for steering depending on the driving speed, which affects the steering forces.

In this known steering system, however, it is disadvantageous that the steering forces depend on the quantity supplied to the power steering unit. When turning in, oil flows to the actuator, so that the amount of oil that flows over the active control edge of the control valve of the steering unit decreases with increasing steering speed and therefore more adjustment distance, that is, more steering force is required for the same steering pressure. This regulation makes the steering force dependent on the steering speed, which has a particularly disruptive effect in the case of a throttled quantity, since in this case the steering force increases greatly as the steering speed increases.

Another disadvantage is that the control range within which the oil quantity can be adjusted is limited. A certain amount of oil cannot be undercut, otherwise the possible steering speed will be too low. On the other hand, the maximum amount of oil must not become too large so that the pump is not overstressed and overheated. It follows that the range of variation of the steering forces at different speeds is relatively limited. The present invention has for its object to provide an auxiliary power steering system of the type mentioned, in which the above-mentioned disadvantages do not occur, in particular in which there is a wide range of steering variations, and in such a way that it is possible to influence the fact that when parking small steering forces occur with high servo pressure and that the steering forces are significantly greater when driving fast and low servo pressure.

According to the invention, this object is achieved by the features mentioned in the characterizing part of claim 1.

In contrast to the prior art, the amount of oil is not regulated, but rather the pressure which is generated by the pressure valve in connection with the pressure booster.

This means that you can now influence the steering force so that when parking a high servo gain occurs with small steering forces, while when driving fast there is a low servo pressure and the steering forces to be applied by the driver are correspondingly greater.

Another advantage of the invention is that no reaction or reaction chambers are necessary so that there is a reaction force on the driver, as e.g. in the power steering according to DE-OS 31 22 369 is proposed in a complex manner.

Two orifices can be provided for regulating the pressure amplification, which are acted upon by the pump pressure between the pressure booster and the distribution valve, where is adjustable with at least one aperture.

If both orifices are adjustable, the pump pressure can be set as a multiple of the pressure upstream of the pressure valve depending on the opening of the two orifices.

The distribution valve can be of any known type. In an advantageous embodiment, it can be a positively controlled valve spool, whereby the valve spool and the pressure valve can be arranged in a common housing and the control edges of the valve spool and the pressure valve can be placed at different points on the circumference if the valve spool is designed as a rotary slide.

Advantageous further developments and features according to the invention result from the further subclaims and from the exemplary embodiments described below with reference to the drawing.

It shows:

Fig. 1: a schematic representation of an embodiment with a positive-controlled distribution valve

Fig. 2: a schematic diagram of a similar embodiment of the invention with a different position of the pressure booster Fig. 3: a third embodiment of the invention with two valves as a distributor valve

4: a similar embodiment as that of FIG.

 3, the two valves being arranged after the pressure valve

Fig. 5: a further embodiment, wherein the distribution valve is a 4/3-way valve

Fig. 6: different steering characteristics.

The mode of operation is explained below with reference to the exemplary embodiment shown in FIG. 1.

As essential components, the power steering system has a supply unit 1, a pressure booster 2, a pressure valve 3 and a distribution valve or steering valve 4, from which a hydraulic servomotor 5 depending on the axial position of the piston 9 of the distribution valve 1 and 4 Pressure medium is supplied.

The hydraulic supply 1 consists of egg ner servo pump 6, which sucks pressure medium, generally oil, from a tank 7.

The pump 6 promotes a constant oil flow from the tank 7 to the distribution valve 4 and at the same time via the pressure booster 2 to the pressure valve 3. When a steering torque is applied, both the control piston 8 of the pressure valve 3 and the control piston 9 of the distribution valve 4 move by using a connection glieα 35, on which a steering handwheel 36 engages, are connected to one another.

The shift initially opens a control edge 13 in the distribution valve 4, so that the connection from the cylinder space 14 of the servomotor 5 to the tank 7 remains open. Simultaneously scnl i eats the control edge 10 and the control edge 11 is opened so that the cylinder space 15 of the servomotor 5 can be acted upon by servo pressure. With a further displacement of the pistons 8 and 9 to the right, the free cross section at the control edge 16 in the pressure valve 3 begins to decrease and pressure is built up in front of the pressure valve 3.

The curve a in FIG. 6 shows a typical pressure curve of the servo pressure upstream of the pressure valve 3 as a function of the piston travel; i.e. the actuating torque or the force to be exerted on the steering handwheel.

The pressure booster 2 consists of a pressure compensator 18 and two orifices 19 and 20, at least one of which is adjustable. The pressure compensator is acted upon on one side 21 with the pressure according to characteristic curve a in FIG. 1 and on the other side 22 with a part of the pump pressure. If the pump pressure becomes lower, the pressure on the side 21 of the pressure compensator 18 predominates and the valve slide moves in the closing direction. However, this increases the resistance to the constant current of the pump, so that the pump pressure rises again. If the pump pressure is too high, the pressure on the side 22 of the pressure compensator 18 predominates and the valve slide moves in the “opening” direction. This lowers the resistance to the oil flow and the pump pressure drops. With the aid of the variable or adjustable orifices 19 and 20, the proportion of the pump pressure which is present on the side 22 of the pressure compensator 18 can be changed from 0 bar to the pump pressure. This can be expressed by:

P ₂₂ = A. P _pump

With P ₂₂ = pressure on side 22, .P _pump pump pressure and A = 0 ... 1.

Since the pressure compensator keeps the pressure on both sides 21 and 22 the same, the following also applies with P ₂₁ = pressure on side 21:

P ₂₁ = P ₂₂ = A. P _pump or formed 1

P _pump = A .P ₂₁ A = 0 ... 1

This means that depending on A or, in other words, the opening of the two orifices 19 and 20, the pump pressure is an arbitrary multiple of the pressure before the pressure valve 3.

For example, if the orifice 20 is completely closed, P ₂₂ = P _pump , if the orifice 19 is completely closed, P ₂₂ = 0. In particular, A against 0 can achieve a gain that goes against ∞.

6 shows with curves b - e the pump pressure which can be achieved by various reinforcements. The gain ¹ A is at b = 2, at c = 4, at d = 8 and at e = 32. With the help of a suitable setting of the orifices 19 and 20, any desired steering characteristic can be set in this way. In particular, with large amplification, only small displacement paths and thus small steering forces, for example when parking, are required, while with small amplification, for example when driving fast, large actuation forces occur.

The adjustment of the two diaphragms 19 and 20 can take place via an electrical converter 37 seen in connection with an evaluation electronics 38 (shown in dashed lines). For example, the adjustment depending on the driving speed, the cross-section and the like.

The exemplary embodiment described in FIG. 2 functions in the same way as that described in FIG. 1 insofar as it concerns the control pistons 8 and 9. For design reasons this game may be an advantage. However, the pressure booster 2 is arranged here after the pressure valve 3. As in FIG. 1, the pressure booster 2 also consists of a pressure compensator and two adjustable orifices 19 and 20, and the pressure is constantly regulated on both sides 23 and 24 of the pressure compensator. Therefore, an equation can also be drawn up here: ^P 23 ^{= P} 24 or

AP _pump = P _pump - ΔP

With A = 0 ... 1, P _pump = pump pressure, Δ P pressure drop in pressure valve 3.

Formed results:

 In this exemplary embodiment, too, there is a pump pressure that depends on the amplification factor from here

and the pressure drop in the pressure valve 3 depends. And here, too, the factor A depends solely on the apertures 19 and 20, which can also be used to set any gain between 1 and..

In the embodiment shown in FIG. 3, the pump 6 in neutral position promotes oil in equal parts through valves 25 and 26 to the pressure valve 27 and through this to the tank 7. If the piston 28 of the pressure valve 27 is moved to the right, for example, it closes first the edge 29 in the pressure valve 27, while the edge 30 opens further. With increasing displacement of the piston 28, pressure is built up on the edge 31 in the pressure valve. As soon as there is some pressure, the valve 26 begins to switch. The piston 90 of the valve 26 is acted upon by pump pressure on one side 32, oil flowing in via an orifice 89 and an axial bore 37, but cannot continue to flow through a transverse bore 34 in the piston 90 because of the closed edge 29. On the other Ren side 33 of the piston 90 is part of the pump pressure, the size of which is determined by the orifices 19 and 20. Due to the different pressure at the piston ends, the piston 90 of the valve 26 moves downward. First, the edge 85 closes, via which the cylinder space 15 of the hydraulic servomotor 5 was connected to the tank 7.

A little later, the edge 86 opens, with which the cylinder space 15 is now connected to the pressure side of the pump 6. In the valve 25, the piston 39 is subjected to the pressure on the side 40 via a transverse bore 42 and an axial bore 38, which pressure is generated at the edge 31 in the pressure valve 27, the connection being established via a pressure line. On the side 41, the piston 39 is subjected to part of the pump pressure in accordance with the position of the orifices 19 and 20. If the pressure on the side 40 predominates, the piston 39 moves downward and narrows the free cross section of the edge 43. This increases the resistance of this edge and the pump pressure increases accordingly.

it A = 0...1 entsprechend den Blenden 19 und 20,If the pump pressure now becomes too high, so that the pressure on the side 41 of the piston 39 now predominates, the piston 39 moves upwards, the cross section of the edge 43 is increased and the pump pressure drops. Here again there is the already known pressure compensator, for which the same applies as in FIG. 1:

it A = 0 ... 1 according to panels 19 and 20,

P _pump = pump pressure, P ₄₀ = pressure drop in pressure valve 27.

The edge 44 remains open and the edge 45 closed over the entire control path of the piston 39, so that the cylinder space 14 is connected to the tank 7.

When the edge 31 in the pressure valve 27 is completely closed, a residual opening to the tank 7 remains in the form of an aperture 46. So that the piston 39 does not switch, the pressure on the side 40 of the piston 39 must not be greater than the part of the pump pressure which is present on the side 41. The ratio of the two apertures 46 to 47 must therefore be at least equal to or greater than the maximum ratio of the apertures 19 to 20.

In this exemplary embodiment, the distribution of the pressure oil is not force-controlled as in the exemplary embodiments according to FIGS. 1 and 2, but pressure-controlled. The two valves 25 and 26 correspond to the steering valve 4 of FIGS. 1 and 2, while at the same time they also take on the tasks of the pressure booster 2, always alternately depending on the direction of rotation.

The game shown in FIG. 4 is of a similar type to that described in FIG. 3, the arrangement of the parts being analogous to that described in FIG. 2, ie in this case a pressure valve 48 is upstream of the combined one Pressure intensifiers / distribution valves 49.50 arranged. In neutral position, the pump 6 delivers oil in equal parts through the pressure valve 48 and the valves 49 and 50 to the tank 7. If the piston 51 of the pressure valve 48 is moved to the right, for example, the edge 52 closes first, while the edge 53 opens further. With increasing displacement of the piston 51, pressure is built up at the edge 54. As soon as there is some pressure, the valve 50 starts to switch. The piston 55 of the valve 50 is connected to the tank 7 on one side 56 via the orifice 72. On the other side 57 of the piston 55 is part of the pump pressure, the size of which is determined by the orifices 19 and 20.

Due to the different pressure at the piston ends, the piston 55 of the valve 50 moves upwards. First, the edge 60 closes, via which the cylinder chamber 14 of the hydraulic servomotor 5 was connected to the pressure side of the pump 6. A little later, the edge 61 opens, with which the cylinder space 14 is now connected to the tank 7.

Mit P_Pumpe = Pumppendruck, A = 0...1 entsprechend der Stellung der Blenden 19 und 20 und Δ P = Druckabfall an der Kante 54 im Ventil 48. In the valve 49, the piston 64 is acted upon on one side 65 by the pump pressure reduced by the pressure drop at the edge 54 in the pressure valve 48. On the other side 66 of the piston 64, part of the pump pressure is present in accordance with the position of the orifices 19 and 20. At the edge 67 in the valve 49, the pressure on the side 65 is regulated so that it corresponds exactly to the pressure on the side 66. This results in an exactly the same function as in FIG. 2 for the pressure booster 2 and the following applies:

With P _pump = _pump pressure, A = 0 ... 1 corresponding to the position of orifices 19 and 20 and Δ P = pressure drop at edge 54 in valve 48.

The edge 68 remains open and the edge 69 closed over the entire control path of the piston 64, so that the cylinder space 15 is connected to the pressure side of the pump. When the edge 54 in the pressure valve 48 is completely closed, a remaining opening to the valve 49 in the form of the orifice 70 remains. So that the piston 64 of the valve 49 does not switch, the pressure on the side 65 must not be less than the part of the pump pressure that is present on the side 66. The ratio of the two apertures 70 to 71 must therefore be at least equal to or less than the minimum ratio of the apertures 19 and 20.

In the exemplary embodiment according to FIG. 5, the pressure drop at the edges 75 or 76 is amplified with the aid of the pressure booster 2 exactly as in FIG , which is designed as a 4/3-way valve. If the piston 79 of the pressure valve 73 is deflected to the right, for example, the edge 78 is first closed and the edge 77 opens further. With a larger displacement, pressure is regulated at the edge 75 and amplified by the pressure booster 2. The side 81 of the piston 80 in the distribution valve 74 is connected to the tank 7 via the edge 76, while the side 82 is subjected to the pressure at the edge 75 of the pressure valve 73. As soon as there is some pressure on the edge 75, the piston 80 switches to the right against the force of the centering springs 83 and 84. This will print the Pump 6 connected to the cylinder chamber 15, while the cylinder chamber 14 remains ve rbun with the tank. If the piston 79 of the pressure valve 73 is brought back into the neutral position, the two sides 81 and 82 of the distribution valve 74 are both connected to the tank 7 via the edges 75 and 76. The centering springs 83 and 84 now also return the piston 80 of the valve 74 to the neutral position.

B e z u g s z e i c h e n l i s t e

Supply unit 31 edge

 Pressure amplifier 32 page

 Pressure valve 33 side

 Distribution valve 34 cross bore

 Actuator 35 connecting link

Pump 36 steering wheel

 Tank 37 converter

 Control piston 38 evaluation electronics

Control piston 39 pistons

 Control edge 40 side

 Control edge 41 page

 Control edge 42 cross hole

 Control edge 43 edge

 Cylinder space 44 edge

 Cylinder chamber 45 edge

 Control edge 46 aperture

 Control edge 47 aperture

 Pressure compensator 48 pressure valve

 Orifice B 49 valve

 Orifice 50 valve

 Page 51 Pistons

 Page 52 Edge

 Page 53 edge

 Page 54 edge

 Valve 55 pistons

 Valve 56 side

 Pressure valve 57 page

 Piston 60 edge

 Edge 61 edge

Edge 64 pistons page

page

Edge

Edge

Edge

cover

cover

cover

Pressure valve

Distribution valve edge

Edge

Edge

Edge

piston

piston

page

page

Centering spring Centering spring edge

Edge

cover

piston

Claims

Patent claims 1. power steering, in particular for motor vehicles, with a pump and with a servomotor supplied with pressure medium from a distribution valve, d a d u r c h g e k e n n z e i c h n e t that when turning in on a control edge (16, 17, 31) of a pressure valve (3,27, 48, 73) pressure is generated, which can be amplified with the aid of a pressure intensifying element (2,43) depending on predetermined parameters, and that with the amplified Pressure is applied to the hydraulic servomotor (5) via valve edges (11, 12) separated from the pressure control in a distribution valve (4, 25, 26, 49, 50, 74). 2. power steering system according to claim 1, d a d u r c h g e k e n n z e i c h n e t that two orifices (19, 20) are provided for pressure amplification, which are acted upon by the pump pressure, at least one orifice (19, 20) being adjustable. 3. power steering system according to claim 2, d a d u r c h g e k e n n z e i c h n e t that both panels (19, 20) are adjustable. 4. power steering system according to one of claims 1-3, d a d u r c h g e k e n n z e i c h n e t that the pressure intensifying member (2) is provided with a control piston (18) which is designed as a pressure compensator, one pressure side (22) with the pressure influenced by the orifices (19, 20) and the other side (21) with the pressure between the Pressure boosting member (2) and the pressure valve (3) is acted upon. 5. power steering system according to one of claims 1-4, d a d u r c h g e k e n n z e i c h n e t that the pressure intensifying member (2) with the two orifices (19, 20) is located in front of the pressure valve (3,27,73). 6. power steering system according to one of claims 2-4, d a d u r c h g e k e n n z e i c h n e t that the pressure intensifying member (2) is located downstream of the pressure valve (3,48) in the flow direction, both orifices (19,20) being acted upon by the pump pressure upstream of the pressure valve (3). 7. power steering system according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the distributor valve has two valves (25, 26 and 49, 50) with valve pistons (39, 90 and 55, 64) provided with control edges (86, 61) for pressure control of the servomotor (5), whereby in the two valves ( 25,26 or 49,50) a pressure reinforcement with control edges (43) is integrated. 8. power steering system according to claim 7, d a d u r c h g e k e n n z e i c h n e t that the two valve pistons (39.90 and 55.64) are designed as pressure compensators, one pressure side (32 and 40 or 56 and 65) with the pressure of the pump (6) and the other end face (33 and 41 or 66 and 67) are each subjected to the pressure influenced by the two orifices (19, 20). 9. power steering system according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the distribution valve is a positively controlled valve spool (9) is. 10. power steering system according to claim 9, d a d u r c h g e k e n n z e i c h n e t that the valve slide (9) and the piston (8) of the pressure valve (3) are connected to one another via a common adjusting member (35). 11. power steering system according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the distribution valve is designed as a 4/3-way valve. 12. Power steering system according to one of claims 1-11, d a d u r c h g e k e n n z e i c h n e t that the two diaphragms (19, 20) via an evaluation unit (37, 38) as a function of the driving speed, the lateral acceleration or the like. are adjustable. 13. Power steering system according to one of claims 1-12, d a d u r c h g e k e n n z e i c h n e t that the distribution valve (4,25,26,49,50,74) and the pressure valve (3,27,48,73) are arranged in a common housing. 14. power steering system according to claim 13, d a d u r c h g e k e n n z e i c h n e t that the distribution valve is designed as a rotary valve and that the control edges of the rotary valve and the control edges (16,17,31) of the pressure valve (3,27,48,73) at different Places the scope.