WO2000010863A1

WO2000010863A1 - Control unit for a hydrostatic steering arrangement

Info

Publication number: WO2000010863A1
Application number: PCT/DK1999/000443
Authority: WO
Inventors: Nils E. Sevelsted; Tage Christiansen
Original assignee: Danfoss Fluid Power A/S
Priority date: 1998-08-21
Filing date: 1999-08-20
Publication date: 2000-03-02
Also published as: DE19837983A1; GB0100424D0; AU5154299A; GB2362622A

Abstract

A control unit (1) for a hydrostatic steering arrangement has two alternatively operable control systems having a common steering member, said control unit having in a housing drill hole (31) a sleeve-shaped inner rotary slide (33), which is connected with an inlet shaft, and a sleeve-shaped outer rotary slide (32), which is connected with a measuring motor (39), both rotary slides being mutually rotatable at a predetermined angle against the force of a spring (40). The first control unit has an interlocking device (41), which connects the two rotary slides (32, 33) unrotatably with each other when the first control system (1) is non-active. Thus, a dead band in the non-active control system disappears, which improves the operation comfort.

Description

Control unit for a hydrostatic steering arrangement

The invention concerns a control unit for a hydrostatic steering arrangement with two alternatively operable control systems having a common steering member, said control unit having in a housing bore a sleeve-shaped inner rotary slide, which is connected with an inlet shaft, and a sleeve-shaped outer rotary slide, which is connected with a measuring motor, both rotary slides being mutually rotatable at a predetermined angle against the force of a spring.

This state of the art is known from DE 196 22 731 Al . A common steering handwheel is connected with the inlet shaft of the first control unit. Via an intermediary shaft, the inlet shaft of the second control unit is rotatably connected with the orbiting gear wheel and thus with the outer rotary slide of the first control unit. Via motor lines, both control units are connected with a belonging steering motor.

During normal operation, a change-over valve short-circuits the motor lines of the second control system, so that only the first control system is active. If an error occurs in this system, the change-over valve changes over and short-circuits the motor lines of the first control system, so that only the second control system is active. This gives a high degree of working reliability.

The invention is based on the task of providing a control unit for a hydrostatic steering arrangement as described in the introduction, which offers a higher degree of steering comfort.

According to the invention, this task is solved in that the first control unit has a interlocking device, which connects the two rotary slides unrotatably with each other when the first control system is non-active.

By means of the interlocking device, the dead band between the outer and the inner rotary slide required for the normal operation of the first control unit is turned off. Also when, during an emergency, the active second control unit is operated via the first control unit, an increase of the dead band is not effected. The driver only feels the dead band known for one control unit.

Advantageously, the interlocking device can be automatically activated in dependence of the inlet pressure of the first control unit. The inlet pressure, already operating the change-over valve in the known case, here triggers an additional switching function. For this purpose only short channels are required.

Preferably, the interlocking device is arranged inside the inner rotary slide. This gives a space-saving embodiment.

This is particularly achieved in that the interlocking device has an interlocking pin, which is unmovingly held in the outer rotary slide and which penetrates the inner rotary slide with a play, and a piston extending unrotatably inside the inner rotary slide, which piston carries a fork engaging with the interlocking pin. This fork secures the interlocking pin against rotation.

It is recommended that in the direction of the interlocking position the piston is loaded by a spring, and in the opposite direction the piston is loaded by the inlet pressure. On failing or too low inlet pressure, that is, inactivity of the belonging control system, the piston automatically assumes the interlocking position under the influence of the spring. It is also advantageous that in the interlocking position the piston opens a channel system, which connects the pressure chambers of the measuring motor with each other. Short-circuiting all pressure chambers of the measuring motor substantially reduces the steering torque, as the rotor of the measuring motor of the inactive control unit must only be turned with a fraction of its normal load.

A very simple opportunity of realising this design involves that the measuring motor is an orbit motor, whose commutation takes place by means of commutation openings in the housing bore and in the outer rotary slide, and that the inner rotary slide has connecting bores leading to the commutation openings, which connecting bores are connectable through an annular groove on the piston in the interlocking position of the piston.

In the following the invention is described on the basis of preferred embodiments in connection with the drawings, showing:

Fig. 1 a hydrostatic steering arrangement of a known design, for which the control unit according to the invention is suitable

Fig. 2 a section through a control unit according to the invention

Fig. 3 an exploded view of the inner and outer rotary slides

Fig. 1 shows a first control system 1 and a second control system 2. The first control system 1 has a first control unit 3, whose pump connection P is connected with a controllable pump 5 via a pump line 4, and whose tank connec- tion T is connected with the tank 7 via a tank line 6. The two motor connections L and R are connected with a first steering motor 10 via motor lines 8 and 9, respectively. In a similar way, a second control unit 11 is provided, whose pump connection P is connected with a pump 13 supplying a constant volume via a pump line 12, and whose tank connection T is connected with the tank 7 via a tank line 6. The two motor connections L and R are connected with a second steering motor 16 via motor lines 14 and 15, respectively. The pistons 17 and 18 of the two steering motors 10 and 16 are connected with each other via a common piston rod 19, which also acts upon the wheels to be steered (not shown) . A steering handwheel 20 is connected with the inlet shaft 21 of the first control unit 3. This steering unit 3 has an outlet shaft 22, which is connected with the inlet shaft 23 of the second control unit 11.

A change-over valve 24 can assume an operating position A, in which the motor lines 14 and 15 of the second control system are connected with each other, and an emergency position B, in which the motor lines 8 and 9 of the first control system 1 are connected with each other. On switching it is provided that there are no intermediary posi- tions, in which the motor lines of both control systems are connected with each other. A slide serves as adjusting device 25. On one front side the inlet pressure PP acts, which is picked up from the pump line 4 and supplied via a pressure signal line 26. On the opposite side a spring 27 and the load pressure LS act, which are supplied from the LS-connection of the first control unit 3 via a pressure signal line 28 and additionally affects the supply of the first pump 5.

Via a line 29 the pump 5 can supply additional consumers, if required also by way of a priority valve. Besides, the tank 7a, from which the first pump 5 takes in pressure fluid, is placed in a higher level than the tank 7b, from which the second pump 13 takes in pressure fluid.

This gives the following mode of operation: When the steering arrangement is turned on, that is, both pumps 5 and 13 are activated, the force produced by the inlet or pump pressure PP exceeds the force of the spring 27 and the force produced by the load pressure LS, so that the change-over valve 24 switches into the operating position A. This means that in the first control system 1 the control unit 3 supplies a pressure fluid amount to the steering motor, which corresponds to the rotation angle. The second control unit 11 is supplied with pressure fluid from the pump 13, however exerts no force on the steering motor 16, as the two motor lines 14 and 15 are short-circuited. Thus, the operation of the second control unit requires no, or almost no, additional torque on the steering handwheel 20.

When the pump 5 fails or supplies no more fluid due to a line rupture, for example of the motor lines 8 and 9, the inlet pressure PP drops drastically, causing the changeover valve 24 to switch to the emergency position B. Now, the second control system 2 is fully active, whereas the motor side of the first control unit 3 is short-circuited. Consequently, the torque required to operate the steering handwheel 20 is only slightly higher than the torque required to operate the second control unit. Also when, due to a line rupture, the tank 7a of the first pump 5 is completely empty, the second pump 11 can work without problems, as its tank 7b and its take-in opening, respectively, are arranged in a lower level, thus providing sufficient pressure fluid for the second control system. The automatic switching from the operating position A to the emergency position B causes a change from the control system 1 to the control system 2; however, the torque required for the steering remains substantially the same. As the change-over valve 24 is displaced on each starting and stopping of the steering arrangement, and the control unit 11 is displaced on each operation of the steering handwheel 20, it is ensured that in case of an emergency the change-over valve 24 and the control unit 11 are sure to function.

Fig. 2 shows a section through the first control unit 3. In a housing 30 there is a drill-hole 31, in which an outer rotary slide 32 and an inner rotary slide 33 are arranged. The inner rotary slide 33 is connected with the inlet shaft 21 via a plug-in coupling 34. The outer rotary slide 32 is connected with an articulated shaft 36 via a connecting pin 35, which again engages with an externally toothed gear wheel 37. Together with an internally toothed gear wheel 38 the gear wheel 37 forms a measuring motor 39. Springs 40 provide that the rotary slides 32 and 33 can be distorted in relation to each other by a pread- justed angle, however remaining in a neutral middle position when the steering handwheel 20 is not operated. When the steering handwheel 20 is turned, pressure fluid flows, depending on the direction of the turning, via the motor line 14 or 15 into the steering motor 16, the pressure fluid flowing through the measuring motor 39, which makes the outer rotary slide 32 follow via the rotation direc- tion of the inner rotary slide 33.

To produce the interlocking device 41 according to the invention, an interlocking pin 42 is provided, whose both ends are fixedly held in the outer rotary slide 32, and which penetrates the inner rotary slide 33 with a play in the circumferential direction. A piston 43, which is un- rotatably connected with the inner rotary slide 33, carries a fork 44, which, in the position shown, engages with the interlocking pin 42. In the interlocking direction the piston is loaded by a spring 45, whereas the opposite pressure chamber 46 is connected, via a channel 47 penetrating the housing 30, the outer rotary slide 32, the inner rotary slide 33 and an insert 48, with the inlet chamber 49 of the housing 30 carrying inlet pressure P. The piston 43, the fork 44 and the spring 45 are arranged inside the inner rotary slide 33.

If the inlet pressure P is missing, the control system 2 assumes its inactive position through the change-over valve 24, in which position the fork 41 engages with the interlocking pin 42, as shown. Thus, the outer rotary slide and the inner rotary slide are unrotatably connected with each other. The dead band normally existing during operation disappears.

Additionally, the piston 43 has an annular groove 50, which connects a series of connecting drill holes 51 inside the inner rotary slide 33 with each other. These connecting drill holes cooperate with commutation openings 52 in the outer rotary slide 32, which again cooperate with commutation drill holes 53 in the housing 30, which lead to the pressure chamber 54 of the measuring motor 39 formed between the gear wheel 37 and the toothed ring 38. Thus, remaining pressure fluid in the measuring motor 39 can be circulated at a very low torque.

The two rotary slides 32 and 33 with the openings 52 and 51 are shown in detail in Fig. 3.

The second control unit 11 has a similar embodiment, however, needs no interlocking device 41 like the control unit 3 according to Fig. 2. The connection between the two control units can be effected in that the outlet shaft 22 of the first control unit 3 is an articulated shaft connected with the gear wheel 37, which shaft is connected with the inlet shaft 23 of the second control unit via a flexible coupling.

During normal operation the change-over valve 24 assumes its position A, and the first control system is active. The driver steers the vehicle in the normal way by means of the steering handwheel 20. The second control unit 11 is in the interlocking position shown, which means that in the second control unit 11 the dead band between the inner and the outer rotary slides is insignificant, and also the fact that the gear wheel 37 of the measuring motor follows requires no large torques.

If the pump 5 of the first control system 1 fails or another error occurs, the second control system 2 is activated, and in the first control unit 3 the piston 43 is displaced to the interlocking position, which means that the dead band is eliminated and the measuring motor 39 is short-circuited. Therefore, the operation of the second control unit means no differences to the driver in relation to the operation of the first control unit, so that a high steering comfort is obtained.

Claims

Patent claims

1. Control unit for a hydrostatic steering arrangement with two alternatively operable control systems having a common steering member, said control unit having in a housing bore a sleeve-shaped inner rotary slide, which is connected with an inlet shaft, and a sleeve- shaped outer rotary slide, which is connected with a measuring motor, both rotary slides being mutually rotatable at a predetermined angle against the force of a spring, characterised in that the first control unit (3) has a interlocking device (41), which connects the two rotary slides (32, 33) unrotatably with each other when the first control system (1) is non-active.

2. Control unit according to claim 1, characterised in that the interlocking device (41) can be automatically activated in dependence of the inlet pressure (P) of the first control unit (3) .

3. Control unit according to claim 1 or claim 2, characterised in that the interlocking device (41) is arranged inside the inner rotary slide (33) .

4. Control unit according to one of the claims 1 to 3, characterised in that the interlocking device (41) has an interlocking pin (42) , which is unmovingly held in the outer rotary slide (32) and which penetrates the inner rotary slide (33) with a play, and a piston (43) extending unrotatably inside the inner rotary slide

(33), which piston carries a fork (44) engaging with the interlocking pin (42) .

5. Control unit according to one of the claims 1 to 4, characterised in that in the direction of the interlocking position the piston (43) is loaded by a spring (45), and in the opposite direction the piston (43) is loaded by the inlet pressure (P) .

6. Control unit according to one of the claims 1 to 5, characterised in that in the interlocking position the piston opens a channel system, which connects the pressure chambers (54) of the measuring motor (39) with each other.

7. Control unit according to claim 6, characterised in that the measuring motor (39) is an orbit motor, whose commutation takes place by means of commutation openings (52) in the housing bore (31) and in the outer rotary slide (32), and that the inner rotary slide (33) has connecting bores (51) leading to the commutation openings, which connecting bores (51) are con- nectable through an annular groove (50) on the piston (43) in the interlocking position of the piston.