Hydraulic steering system

Abstract

A hydraulic steering system (1) is provided having a steering device (2) and a symmetrically acting steering motor (3), said steering device (2) comprising a supply port arrangement having a high pressure port (P) and a low pressure port (T), a working port arrangement having two working ports (L, R), a control valve (14), two working lines (18, 19) each connecting said control valve (14) with one of said working ports (L, R), and a measuring motor (23). Such a hydraulic steering system should show a comfortable steering behavior. To this end said measuring motor (23) is arranged in one of said working lines (18, 19).

Claims

1. A hydraulic steering system having a steering device and a steering motor, said steering device comprising a supply port arrangement having a high pressure port (P) and a low pressure port (T), a working port arrangement having two working ports (L, R), a control valve, two working lines each connecting said control valve with one of said working ports (L, R), and a measuring motor, wherein said measuring motor is arranged in one of said working lines, wherein said high pressure port (P) and said low pressure port (T) are connected by means of a port check valve opening from said low pressure port (T) to said high pressure port (P), wherein releasable blocking means are located between said low pressure port (T) and said tank.

2. The hydraulic steering system according to claim 1, wherein said control valve comprises a neutral position in which said two working lines are connected.

3. The hydraulic steering system according to claim 2, wherein in said neutral position said high pressure port (P) and said low pressure port (T) are connected to each other via throttling means.

4. The hydraulic steering system according to claim 3, wherein said throttling means comprise a first orifice between said high pressure port (P) and a connection of said two working lines.

5. The hydraulic steering system according to claim 4, wherein said throttling means comprise a second orifice between said low pressure port (P) and said connection of said two working ports (L, R).

6. The hydraulic steering system according to claim 5, wherein said measuring motor comprises two measuring motor ports, each measuring motor port being connected to said one of said working lines and each measuring motor port being connected to a tank via a respective check valve opening in a direction to said measuring motor port.

7. The hydraulic steering system according to claim 4, wherein said measuring motor comprises two measuring motor ports, each measuring motor port being connected to said one of said working lines and each measuring motor port being connected to a tank via a respective check valve opening in a direction to said measuring motor port.

8. The hydraulic steering system according to claim 3, wherein said measuring motor comprises two measuring motor ports, each measuring motor port being connected to said one of said working lines and each measuring motor port being connected to a tank via a respective check valve opening in a direction to said measuring motor port.

9. The hydraulic steering system according to claim 2, wherein said measuring motor comprises two measuring motor ports, each measuring motor port being connected to said one of said working lines and each measuring motor port being connected to a tank via a respective check valve opening in a direction to said measuring motor port.

10. The hydraulic steering system according to claim 1, wherein said measuring motor comprises two measuring motor ports, each measuring motor port being connected to said one of said working lines and each measuring motor port being connected to a tank via a respective check valve opening in a direction to said measuring motor port.

11. A hydraulic steering system having a steering device and a steering motor, said steering device comprising a supply port arrangement having a high pressure port (P) and a low pressure port (T), a working port arrangement having two working ports (L, R), a control valve, two working lines each connecting said control valve with one of said working ports (L, R), and a measuring motor, wherein said measuring motor is arranged in one of said working lines, wherein said measuring motor comprises two measuring motor ports, each measuring motor port being connected to said one of said working lines and each measuring motor port being connected to a tank via a respective check valve opening in a direction to said measuring motor port.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A preferred embodiment of the invention will now be described in more detail with reference to the drawing, wherein:

(2) FIG. 1 shows schematically a hydraulic steering system and

(3) FIG. 2 shows schematically an over center valve.

DETAILED DESCRIPTION

(4) A steering system 1 comprises a steering device 2 and a steering motor 3.

(5) The steering motor 3 is a symmetrically acting steering motor. In the present case the steering motor 3 is in form of a cylinder 4 in which a piston 5 is arranged. The piston 5 divides the interior of the cylinder in a first pressure chamber 6 and a second pressure chamber 7. The piston 5 is provided with a first piston rod 8 running through the first pressure chamber 6 and with a second piston rod 9 running through the second pressure chamber 7. The piston rods 8, 9 have the same diameter. Therefore, the piston 5 comprises a first pressure area 10 in the first pressure chamber 6 and a second pressure area 11 in the second pressure chamber 7, wherein the first pressure area 10 and the second pressure area 11 are of the same size.

(6) The steering device 2 comprises a supply port arrangement having a high pressure port P and a low pressure port T. As shown, the high pressure port P is connected to a pump 12 which is driven by a motor (not shown) of a vehicle to be steered by said steering system 1. The low pressure port T is connected to a tank 13.

(7) The steering device 2 furthermore comprises a working port arrangement having a first working port L and a second working port R. The first working port L is connected to the first pressure chamber 6 and the second working port R is connected to the second pressure chamber 7.

(8) The steering device 2 comprises a control valve 14. The control valve 14 is connected to a steering wheel 15 or any other steering member. More precisely, the control valve 14 comprises a spool 16 which is rotatably arranged within a sleeve 17. Upon actuation of the steering wheel 15 spool 16 is rotated relative to sleeve 17 to open and close fluid paths which will be explained below.

(9) The steering device 2 comprises a first working line 18 connecting the control valve 14 with the first working port L and a second working line 19 connecting the control valve 14 and the second working port R.

(10) The figure shows the neutral position of the control valve 14. In the neutral position the control valve 14 forms a connection path 20 connecting the two working lines 18, 19. The connection path 20 is connected to the high pressure port P via first throttling means 21 and to the low pressure port T via second throttling means 22. In the neutral position of the control valve 14 a flow of hydraulic fluid from the pump 12 to the tank 13 is possible. However, the flow is limited by the two throttling means 21, 22. Throttling means 21, 22 form a pressure divider. When throttling means 21, 22 have the same throttling resistance, a pressure in the connection path 20 corresponds to a half of the pressure difference between the high pressure port P and the low pressure port T.

(11) In a first steering position control valve 14 connects the high pressure port P and the first working line 18 as well as the second working line 19 and the low pressure port T.

(12) In a second steering position control valve 14 connects high pressure port P and the second working line 19 as well as the first working line 18 and the low pressure port T.

(13) The steering device 2 furthermore comprises a measuring motor 23 which is located in the first working line 18. It could, however, be located in the second working line 19 as well.

(14) The measuring motor 13 is driven by the hydraulic fluid passing through the first working line 18. As shown, the measuring motor is connected by means of a schematically shown connection 24 to the sleeve 17. The fluid passing the measuring motor 23 drives the measuring motor 23 and the sleeve 17 so that sleeve 17 follows the movement of spool 16 so that after a certain amount of hydraulic fluid has passed through control valve 14, control valve 14 assumes again the neutral position.

(15) Since the measuring motor 23 is located in one of the working lines, in the present case in the first working line 18, there is no delay in actuating the measuring motor 23 when changing the steering direction.

(16) The measuring motor 23 is connected to tank 13 by means of two check valves 25, 26, each check valve 25, 26 opening in a direction towards said measuring motor 23. This means that the measuring motor 23 can suck hydraulic fluid from tank 13 in each direction of operation, for example if hydraulic fluid is missing due to leakages or the like.

(17) A pump check valve 27 is located between the pump 12 and the high pressure port P and opens in a direction towards the high pressure port P.

(18) A port check valve 28 is located in a line connecting the high pressure port P and the low pressure port T and opens in a direction from the low pressure port T towards the high pressure port P.

(19) Blocking means in form of an over center valve 29 are arranged in a tank line 30 connecting the low pressure port T and tank 13.

(20) Over center valve 29 comprises a first actuating port 31 and a second actuating port 32. The first actuating port 31 is connected to the first working port L. The second actuating port 32 is connected to the low pressure port T. A spring 33 acts in a direction opposite to the direction of pressure at the two actuating ports 31, 32.

(21) Over center valve 29 comprises a valve element 34 in which an over center check valve 35 is arranged. The over center check valve 35 opens in a direction from the low pressure port T to tank 13.

(22) During normal operation pump 12 supplies hydraulic fluid under pressure from tank 13 to the high pressure port P. The pump check valve 27 is opened by this pump pressure and the port check valve 28 is closed. The steering direction is determined by the position of the control valve 14.

(23) In an emergency steering mode the pressure of pump 12 is too low. In this case the steering wheel 15 is rotated in a direction in which the high pressure port P is connected to the measuring motor 23. The measuring motor 23 pumps hydraulic fluid under pressure into the first pressure chamber 6. Hydraulic fluid escaping from the second pressure chamber 7 can build up a pressure at the low pressure port T since the over center valve 29 is closed by means of spring 33. There is not sufficient pressure at the first actuating port 31 and there is no sufficient pressure at the second actuating port 32. The pressure at the low pressure port T can open the port check valve 28. However, if the pressure at the low pressure port T becomes too high, the over center valve 29 is opened due to the pressure at the second actuating port 32.

(24) If in the emergency steering mode the steering wheel is rotated in the opposite direction the measuring motor 23 sucks hydraulic fluid out of the first pressure chamber 6 thereby lowering the pressure at the first working port L and lowering the pressure at the first actuating port 31 of the over center valve 29 thereby closing the over center valve 29 by means of the action of the spring 33.

(25) Hydraulic fluid pressurized by the measuring motor 23 is guided to the low pressure port T and builds up a pressure opening port check valve 28 so that the pressurized hydraulic fluid can reach the second working port R and can be supplied to the second pressure chamber 7.

(26) FIG. 2 shows schematically the functional elements of the over center valve 29.

(27) Over center valve 29 comprises the valve element 34 which is connected to a piston 36. The valve element 34 is directly loaded by a pressure at the second actuating port 32 and indirectly loaded by the pressure at the first actuating port 31 via said piston 36. The effective pressure area of piston 36 is, for example, by the factor 5 larger than the effective pressure area of valve element 34. Therefore a much lower pressure at the first actuating port 31 is sufficient to move valve element 34 and to open over center valve 29.

(28) The over center check valve 35 comprises a check valve element 37 which is loaded by spring 33 (or another spring, if appropriate). When, for example, valve element 34 of over center valve 29 is blocked by dirt or any other means, the check valve element 37 can be lifted from the valve element 34 when the force generated by the pressure at the second actuating port 32 exceeds the force of spring 33.

(29) While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.