HYDRAULIC STEERING SYSTEM FOR AN AGRICULTURAL WORK MACHINE

Description

[0001] The present invention relates to a hydraulic steering system for an agricultural working machine according to the preamble of claim 1. Furthermore, the invention relates to a method for operating a hydraulic steering system and to an agricultural working machine, in particular a tractor, with a hydraulic steering system.

[0002] A hydraulic steering system for a work machine designed as a wheel loader is known from DE 10 2008 015 729 A1. A hydraulic pump in a hydraulic circuit is provided to supply a hydraulic steering unit of the hydraulic steering system during normal operation. In addition, an emergency steering pump is rigidly coupled to a travel drive by a gearbox. This emergency steering pump supplies the hydraulic steering system with hydraulic oil depending on the travel speed both during normal operation and in emergency operation, i.e. in the event of a hydraulic pump failure, in order to maintain steering capability during emergency operation. The emergency steering pump coupled to the travel drive always draws hydraulic oil from a common tank, i.e. both during normal operation and emergency operation, and pumps it into the circuit of the hydraulic steering system or a storage element.A priority valve is installed downstream of the emergency steering pump to switch the supply of hydraulic oil pumped by the emergency steering pump between the hydraulic steering system and the accumulator. The constant pumping of hydraulic oil into the hydraulic steering system circuit by the emergency steering pump has the disadvantage that a constant loss of hydraulic oil occurs in the hydraulic steering system, depending on the vehicle speed.

[0003] Based on the above-mentioned prior art, the invention is based on the object of developing a hydraulic steering system of the type mentioned at the outset, which is characterized by improved efficiency.

[0004] This object is achieved by a hydraulic steering system having the features of independent claim 1. Advantageous embodiments and further developments can be found in the dependent claims. Furthermore, the object is achieved by a method for operating a hydraulic steering system having the features of independent claim 11 and an agricultural work machine according to claim 13.

[0005] According to claim 1, a hydraulic steering system for an agricultural work machine is proposed, comprising a steering unit connected to a hydraulic circuit, a main steering pump serving to supply the hydraulic circuit of the steering system during normal operation, and an emergency steering pump serving to supply the hydraulic circuit during both normal and emergency operation. According to the invention, during normal operation of the hydraulic steering system, a volume flow delivered by the emergency steering pump is taken as a partial volume flow from the volume flow delivered by the main steering pump. This has the effect that the pressure provided by the main steering pump is always present at the suction side or pump inlet of the emergency steering pump at the emergency steering pump, which runs both in normal and emergency operation, during normal operation, so that no volume flow-related losses caused by the emergency steering pump occur in the hydraulic circuit.

[0006] In particular, the emergency steering pump is designed as a constant displacement pump.

[0007] According to a preferred development, the emergency steering pump, which delivers depending on the driving speed, is assigned a valve arrangement through which the emergency steering pump is connected to the hydraulic circuit, wherein the partial volume flow taken from the hydraulic circuit on the pressure side of the main steering pump is returned to the hydraulic circuit by the valve arrangement in a direction-dependent manner during normal operation of the steering system.

[0008] In particular, the main steering pump is operated depending on the speed of a drive motor of the agricultural machine.

[0009] To extract the partial volume flow during normal operation of the steering system, the valve arrangement can have two pairs of check valves. A first check valve of each pair of check valves supplies the partial volume flow to the suction side of the emergency steering pump, which adjusts itself depending on the direction of travel, and a second check valve on the pressure side or the pump outlet of the emergency steering pump returns the partial volume flow to the hydraulic circuit of the steering system. For this purpose, the first check valves of the two pairs of check valves are connected to the pressure side of the hydraulic circuit via a common hydraulic line. During normal operation, the hydraulic oil is thus always extracted using the hydraulic pressure generated by the main steering pump.

[0010] Furthermore, it is advantageous if the first check valves of the respective check valve pair of the valve arrangement have different, in particular higher, opening pressures than the second check valves. By arranging the various first and second check valves of the respective check valve pair with different opening pressures, the priority and suction behavior of the emergency steering pump can be controlled.

[0011] According to a further development, a withdrawal point and a feed point can be provided in the hydraulic circuit, at which the partial volume flow is withdrawn or returned by the emergency steering pump during normal operation, between which a check valve is arranged. The withdrawal point, the check valve, and the feed point are arranged downstream of the main steering pump. The withdrawal point and feed point provided in the hydraulic circuit, between which the check valve is arranged, are always located on the pressure side of the main steering pump.

[0012] Furthermore, a pressure relief valve can be arranged downstream in a supply line connecting the check valve to the steering unit. The pressure relief valve can be used to drain hydraulic oil returned by the emergency steering pump at the feed point to the tank if an adjustable maximum pressure in the hydraulic circuit is exceeded. This can serve to protect the main steering pump and the emergency steering pump, as well as the other hydraulic components provided in the hydraulic circuit of the steering system for operating the steering unit.

[0013] In particular, two check valves can be assigned to the emergency steering pump, one of which is arranged in a line between a tank and the emergency steering pump, and the other in a branch line that branches off from the line between the tank and the first check valve and opens into a supply line connecting the emergency steering pump and the valve arrangement. The two check valves assigned to the emergency steering pump ensure that, when the direction of travel is reversed, the partial volume flow is only drawn off by the first check valve of the respective check valve pair of the valve arrangement, which is connected to the suction side of the emergency steering pump, which adjusts itself depending on the direction of travel.

[0014] It is intended that the two check valves assigned to the emergency steering pump block in the direction of the tank.

[0015] In emergency mode, the emergency steering pump can draw hydraulic oil from the tank via one of the two check valves assigned to the emergency steering pump, depending on the direction of travel. When driving forward, the pressure side or pump outlet of the emergency steering pump remain the same in normal and emergency steering mode. When changing from normal to emergency mode while driving forward, the pressure level on the suction side as the pump inlet changes to the suction pressure level. When changing from normal to emergency mode while reversing, the pressure side and the suction side of the emergency steering pump change.

[0016] This allows the emergency steering pump to feed the hydraulic oil into the supply line downstream of the hydraulic circuit's check valve via one of the two second check valves in the valve assembly, depending on the direction of travel. Depending on the direction of travel, the hydraulic oil supplied by the emergency steering pump can be fed through the second check valve of the respective check valve pair in the valve assembly at the feed point downstream of the check valve to maintain the operation of the steering unit in emergency mode.

[0017] Furthermore, the object posed at the outset is achieved by a method having the features of the independent claim 11.

[0018] According to the independent claim 11, a method for operating a steering system, in particular according to one of claims 1 to 10, for an agricultural work machine with a steering unit which is connected to a hydraulic circuit of the steering system and which is supplied with hydraulic oil during normal operation by a main steering pump of the hydraulic circuit and during normal and emergency operation by an emergency steering pump of the hydraulic circuit is proposed, wherein during normal operation of the hydraulic steering system, a volume flow delivered by the emergency steering pump is taken as a partial volume flow from the volume flow delivered by the main steering pump. Reference may be made to all embodiments of the steering system according to the invention.

[0019] Thus, a valve arrangement comprising two pairs of non-return valves can be assigned to the emergency steering pump which delivers depending on the driving speed and which connects the emergency steering pump to the hydraulic circuit, whereby the partial volume flow taken from the hydraulic circuit is returned during normal operation by the valve arrangement depending on the direction of travel, whereby the partial volume flow taken is fed to the respective suction side of the emergency steering pump which is adjusted depending on the direction of travel by a first non-return valve of the respective pair of non-return valves depending on the direction of travel and is returned to the hydraulic circuit by a second non-return valve on the pressure side of the emergency steering pump which is adjusted depending on the direction of travel.

[0020] According to a further teaching according to claim 13, which has an independent meaning, an agricultural working machine, in particular a tractor, with a hydraulic steering system is claimed, wherein the steering system of the working machine is designed according to one of claims 1 to 10 and is set up to carry out the method according to claim 11 or 12.

[0021] The present invention is explained in more detail below with reference to an embodiment shown in the drawings.

[0022] They show: Fig. 1 shows a schematic and exemplary side view of an agricultural machine with a hydraulic steering system; and Fig. 2 shows a simplified circuit diagram of the hydraulic steering system.

[0023] In Fig. 1is a schematic and exemplary side view of an agricultural working machine 1 with a hydraulic steering system 10. The agricultural working machine 1 is designed in particular as a tractor 2. The working machine 1 has four ground engagement means 3, 4, which are each arranged in pairs on a front axle 5 and a rear axle 6 of the working machine 1. For example, the ground engagement means 3 designed as wheels form a pair of wheels of the front axle 5, viewed in the forward direction of travel, and the ground engagement means 4 designed as wheels form a pair of wheels of the rear axle 6, viewed in the direction of travel. To actuate the ground engagement means 3, a double-acting first steering cylinder and to actuate the ground engagement means 4, a double-acting second steering cylinder can be provided on the respective axle 5, 6. The Fig. 1Steering cylinders (not shown) are controlled by the hydraulic steering system 10. The steering wheel 7, which can be operated by an operator of the agricultural work machine 1, is coupled in a manner known per se to a steering unit 12, a so-called orbitrol, which causes the deflection of the steering wheel 7 to control the flow rates of a hydraulic oil through a hydraulic circuit 11 of the steering system 10.

[0024] In Fig. 2A simplified circuit diagram of the hydraulic steering system 10 is shown. The steering system 10 comprises the hydraulic steering unit 12 arranged in the hydraulic circuit 11. During normal operation of the steering system 10, a main steering pump 13 serves to supply the hydraulic circuit 11 or the steering unit 12 of the steering system 10. Furthermore, an emergency steering pump 14, which serves to supply the steering unit 12 during normal operation and in emergency operation, is part of the hydraulic circuit 11. The emergency steering pump 14 has the task of ensuring the steerability of the agricultural work machine 1 in the event of a failure of the main steering pump 13.

[0025] The main steering pump 13 is operated depending on the speed of a drive motor of the agricultural work machine 1. In contrast, the emergency steering pump 14, which can preferably be designed as a constant-displacement pump, is operated depending on the driving speed.

[0026] The main steering pump 13 draws hydraulic oil from a common tank T through a filter F upstream of the main steering pump 13. The hydraulic oil flows through a delivery line 15 via a check valve 16 to another filter F in the delivery line 15. The check valve 16 blocks the flow towards the main steering pump 13. A priority valve 17 is connected upstream of the steering unit 12. The priority valve 17 directs the hydraulic oil flow to the steering unit 12 via a further check valve 18 when the hydraulic oil is needed there to perform steering maneuvers. If the main steering pump 13 delivers more volume flow than is required by the steering unit 12, the priority valve 17 directs the excess volume flow back to the tank T. The excess volume flow can also be supplied to other consumers of the agricultural machine 1.

[0027] In emergency operation, the emergency steering pump 14 can be fed by the hydraulic oil in the tank T. For this purpose, the emergency steering pump 14 can suck the hydraulic oil from the tank T through an upstream filter F.

[0028] During normal operation of the hydraulic steering system 10, a volume flow delivered by the emergency steering pump 14 during driving operation is taken from the volume flow delivered by the main steering pump 13 as a partial volume flow at a withdrawal point 20. For this purpose, a valve arrangement 19 is assigned to the emergency steering pump 14, which delivers depending on the driving speed, and through which the emergency steering pump 14 is connected to the hydraulic circuit 11. Depending on the direction of travel, the partial volume flow taken from the hydraulic circuit 11 during normal operation is fed back to the hydraulic circuit 11 via the valve arrangement 19 at an inlet point 21. The check valve 16, which prevents backflow to the valve arrangement 19, is arranged between the withdrawal point 20 and the inlet point 21. A withdrawal line 22 connects the withdrawal point 20 to the valve arrangement 19. A inlet line 23 connects the valve arrangement 19 to the inlet point 21.At the feed point 21, a pressure relief valve 24 is connected via a supply line 25.

[0029] The pressure relief valve 24 can be used to discharge hydraulic oil returned to the feed point 21 by the emergency steering pump 14 to the tank T when an adjustable maximum pressure in the hydraulic circuit 11 is exceeded. This serves to protect the main steering pump 13 and the emergency steering pump 14 as well as all other hydraulic components provided in the hydraulic circuit 11 of the steering system 10 for operating the steering unit 12.

[0030] The valve arrangement 19 has two pairs of check valves that are identical in design. One pair of check valves is formed by a first check valve 26A and a second check valve 27A, and another pair of check valves is formed by a first check valve 26B and a second check valve 27B. The partial volume flow taken off at the extraction point 20 is fed to the suction side of the emergency steering pump 14, which is adjusted depending on the direction of travel, by the first check valve 26A, 26B of the respective check valve pair of the valve arrangement 19, and is returned to the hydraulic circuit 11 of the steering system 10 through the corresponding second check valve 27A, 27B on the pressure side of the emergency steering pump 14. The first check valve 26A and the second check valve 27A of one pair of check valves orThe first check valve 26B and the second check valve 27B of the other check valve pair are connected to each other independently by supply lines 28 and 29, respectively. The two first check valves 26A, 26B of each check valve pair block in the direction of the extraction point 20, while the two second check valves 27A, 27B of each check valve pair open in the direction of the feed point 21. Preferably, the first check valves 26A, 26B of the respective check valve pair of the valve arrangement 19 have different, in particular higher, opening pressures than the second check valves 27A, 27B.

[0031] During normal operation, the partial volume flow from the extraction point 20 passes through the extraction line 22 to the first check valves 26A, 26B. When the working machine 1 travels forward, the partial volume flow passes via the check valve 26A through the supply line 28, which opens into a line 30 between the filter F and the emergency steering pump 14, to the suction side or pump inlet of the emergency steering pump 14, which is established during forward travel.

[0032] Two check valves 31, 32 are assigned to the emergency steering pump 14. One check valve 31 is located in the line 30 between the tank T and the emergency steering pump 14, and the other check valve 32 is located in a branch line 33, which branches off from the line 30 between the tank T and the check valve 31 and opens into the supply line 29 connecting the emergency steering pump 14 and the valve assembly 19. Both check valves 31, 32 assigned to the emergency steering pump 14 block flow toward the tank T.

[0033] The emergency steering pump 14 conveys the partial volume flow on the pressure side that occurs during forward travel, or rather the pump outlet of the emergency steering pump 14, through the supply line 29 to the check valve 27A of this check valve pair of the valve arrangement 19. Via the check valve 27A, the partial volume flow reaches the feed point 21 and thus back into the hydraulic circuit 10. During normal operation, the extraction and return of the partial volume flow by the emergency steering pump 14 always takes place on the pressure side of the main steering pump 13. When the work machine 1 starts up, the hydraulic oil is thus extracted by the emergency steering pump 14 at the extraction point 20 upstream of the check valve 16 and returned downstream of the check valve 16 to the feed point 21. This ensures that there is no loss of volume flow to the steering unit 12.

[0034] When the work machine 1 travels backwards, the partial volume flow from the check valve 26B passes through the supply line 29 to the suction side of the emergency steering pump 14, which is set during reversing. The emergency steering pump 14 pumps the hydraulic oil via the supply line 28 back to the check valve 27B of this check valve pair of the valve arrangement 19. Via the check valve 27B, the partial volume flow reaches the feed point 21 and thus back into the hydraulic circuit 10. Accordingly, when the work machine 1 starts moving backwards, the hydraulic oil is withdrawn from the emergency steering pump 14 upstream of the check valve 16 and returned downstream of the check valve 16, whereby there is no loss in the volume flow to the steering unit 12.

[0035] The two check valves 31 and 32 assigned to the emergency steering pump 14 prevent the partial volume flow from overflowing during normal operation, regardless of the direction of travel.

[0036] In emergency operation, i.e. if the main steering pump 13 fails, it does not deliver hydraulic oil to the steering unit 12, which also interrupts the supply to the emergency steering pump 14 via one of the two pairs of check valves in the valve arrangement 19. As a result, the emergency steering pump 14 automatically begins to suck hydraulic oil from the tank T via the check valve 31 when driving forward and delivers a speed-dependent volume flow to the steering unit 12. The delivery takes place via the same components of the hydraulic circuit 11 as by the main steering pump 13 in normal operation.

[0037] The hydraulic oil sucked in through the check valve 31 during forward travel in emergency mode is fed by the emergency steering pump 14 through the supply line 29 via the check valve 27A of the valve arrangement 19 into the hydraulic circuit 11 at the feed point 21. During reverse travel in emergency mode, hydraulic oil is automatically sucked from the tank T via the check valve 32 and fed into the hydraulic circuit 11 through the supply line 28 via the check valve 27B of the valve arrangement 19 at the feed point 21. List of reference symbols 1 work machine 33 Branch management 2 tractor 3 Ground intervention equipment F filter 4 Ground intervention equipment T tank 5 Front axle 6 Rear axle 7 steering wheel 10 Steering system 11 Hydraulic circuit 12 Steering unit 13 Main steering pump 14 Emergency steering pump 15 conveyor line 16 check valve 17 Priority valve 18 check valve 19 Valve arrangement 20 sampling point 21 Feed-in point 22 Withdrawal line 23 Feed line 24 pressure relief valve 25 supply line 26A First check valve 26B First check valve 27A Second check valve 27B Second check valve 28 supply line 29 supply line 30 Line 31 check valve 32 check valve

Claims

1. A hydraulic steering system (10) for an agricultural working machine (1, 2), with a steering assembly (12) which is connected to a hydraulic circuit (11) of the steering system (10), with a main steering pump (13) which serves to supply the hydraulic circuit (11) in normal operation as well as with an emergency steering pump (14) which serves to supply the hydraulic circuit (11) in normal operation and in emergency operation, characterized in that in the normal operation of the hydraulic steering system (10), a volumetric flow delivered by the emergency steering pump (14) is withdrawn from the volumetric flow delivered by the main steering pump (13) as a partial volumetric flow.

2. The hydraulic steering system (10) according to claim 1, characterized in that the emergency steering pump (14), delivering in a manner which is dependent on drive speed, is associated with a valve assembly (19) through which the emergency steering pump (14) is connected to the hydraulic circuit, wherein in normal operation, the partial volumetric flow withdrawn from the hydraulic circuit (11) on the delivery side of the main steering pump (13) is returned thereto through the valve assembly (19) in a manner which is dependent on travel direction.

3. The hydraulic steering system (10) according to claim 2, characterized in that the valve assembly (19) has two non-return valve pairs, wherein the partial volumetric flow is supplied, in a manner which is dependent on travel direction, to the respective intake side of the emergency steering pump (14), set in a manner which is dependent on travel direction, through a first non-return valve (26A, 26B) of the respective non-return valve pair of the valve assembly (19) and is returned to the hydraulic circuit (11) of the steering system (10) through a second non-return valve (27A, 27B) on the delivery side of the emergency steering pump (14).

4. The hydraulic steering system (10) according to claim 3, characterized in that the first non-return valves (26A, 26B) of the respective non-return valve pair of the valve assembly (19) have opening pressures which are different from the second non-return valves (27A, 27B), in particular higher.

5. The hydraulic steering system (10) according to one of the preceding claims, characterized in that a withdrawal point (20) and an injection point (21) are provided in the hydraulic circuit (11) at which, in normal operation, the partial volumetric flow is withdrawn or returned through the emergency steering pump (14), between which a non-return valve (16) is disposed, wherein the withdrawal point (20), the non-return valve (16) and the injection point (21) are disposed downstream of the main steering pump (13).

6. The hydraulic steering system (10) according to claim 5, characterized in that a pressure limiting valve (24) is disposed downstream in a supply line (15) connecting the non-return valve (16) to the steering assembly (12).

7. The hydraulic steering system (10) according to one of the preceding claims, characterized in that two non-return valves (31, 32) are associated with the emergency steering pump (14), wherein one non-return valve (31) is disposed in a line (30) between a tank (T) and the emergency steering pump (14) and the other non-return valve (32) is disposed in a branch line (33) which branches off the line (30) between the tank (T) and the first non-return valve (31) and discharges into a supply line (29) connecting the emergency steering pump (14) and the valve assembly (19).

8. The hydraulic steering system (10) according to claim 7, characterized in that the two non-return valves (31, 32) associated with the emergency steering pump (14) block in the direction of the tank (T).

9. The hydraulic steering system (10) according to claim 7 or claim 8, characterized in that in emergency operation, the emergency steering pump (14) draws hydraulic oil out of the tank (T) travel direction-dependently via one of the two non-return valves (31, 32) associated with the emergency steering pump (14).

10. The hydraulic steering system (10) according to claims 7 to 9, characterized in that the emergency steering pump (14) delivers the hydraulic oil into the supply line (15) behind the non-return valve (16) travel direction-dependently via one of the two second non-return valves (27A, 27B) of the valve assembly (19).

11. A method for operating a hydraulic steering system (10) for an agricultural working machine (1, 2), with a steering assembly (12) which is connected to a hydraulic circuit (11) of the steering system (10), and which in normal operation is supplied with hydraulic oil through a main steering pump (13) of the hydraulic circuit (11) and which in normal operation and in emergency operation is supplied through an emergency steering pump (14), characterized in that in normal operation of the hydraulic steering system (10), a volumetric flow delivered by the emergency steering pump (14) is withdrawn from the volumetric flow delivered by the main steering pump (13) as a partial volumetric flow.

12. The method according to claim 11, characterized in that a valve assembly (19) having two non-return valve pairs and which connects the emergency steering pump (14) to the hydraulic circuit (11) is associated with the emergency steering pump (14) which delivers in a manner which is dependent on drive speed, wherein in normal operation, the partial volumetric flow withdrawn from the hydraulic circuit (11) is returned through the valve assembly (19) in a manner which is dependent on travel direction, wherein the withdrawn partial volumetric flow is supplied, in a manner which is dependent on travel direction, to the respective intake side of the emergency steering pump (14), set in a manner which is dependent on travel direction, through a first non-return valve (26A, 26B) of the respective non-return valve pair and is returned to the hydraulic circuit (11) through a second non-return valve (27A, 27B) on the delivery side of the emergency steering pump (14).

13. An agricultural working machine (1), in particular a tractor (2), with a hydraulic steering system (10), characterized in that the steering system (10) is constructed in accordance with one of claims 1 to 10 and is configured to carry out the method in accordance with claim 11 or claim 12.