Hydraulic arrangement and commercial vehicle

Abstract

The invention relates to a hydraulic arrangement (42) for a commercial vehicle (10) comprising a variable displacement hydraulic pump (46) and a supply port (48) as an interface for supplying hydraulic consumers (58, 60, 62) of the commercial vehicle (10). An adjustment control (64), dependent on an output pressure (p_a) of the variable displacement pump (46), serves to adjust the variable displacement pump (46). The arrangement (42) also includes an auxiliary hydraulic pump (70) and an auxiliary supply port (52) as an interface for the auxiliary supply of at least some of the consumers (60, 62). Furthermore, the arrangement (42) includes a hydraulic valve unit (56) with multiple switching positions (56-0, 56-a). The valve unit (56) is arranged in the flow path between a pump outlet (54) of the variable displacement pump (46) and the supply port (48).In a first switching position (56-0) of the valve unit (56), the pump outlet (54) of the variable displacement pump (46) is hydraulically connected to the supply port (48) and hydraulically disconnected from the auxiliary pump outlet (72) of the auxiliary pump (70). In a second switching position (56-a) of the valve unit (56), the pump outlet (54) of the variable displacement pump (46) is hydraulically disconnected from the supply port (48) and hydraulically connected to the auxiliary pump outlet (72) of the auxiliary pump (70). The invention further relates to a commercial vehicle (10) with such a hydraulic arrangement (42).

Description

[0001] The invention relates to a hydraulic arrangement for a commercial vehicle with a hydraulic variable displacement pump for supplying hydraulic consumers of the commercial vehicle. The invention further relates to a commercial vehicle with such a hydraulic arrangement.

[0002] It is common practice to use variable displacement pumps in tractors to supply internal or external hydraulic components (e.g., implements). The variable displacement pump is driven, preferably via a gearbox, by the vehicle's or tractor's drive engine. When the drive engine is started, the variable displacement pump's control is often set to a maximum delivery position, i.e., to deliver the maximum hydraulic flow rate. This requires a correspondingly high drive power from the drive engine. A cold start of the vehicle can further increase the variable displacement pump's power consumption due to the increased viscosity of the hydraulic fluid.

[0003] The present invention is based on the objective of proposing a hydraulic arrangement and a commercial vehicle which reduces the power required for the variable displacement pump when starting the commercial vehicle.

[0004] This problem is solved by a hydraulic arrangement having the features of claim 1 and by a commercial vehicle having the features of claim 13.

[0005] Further advantageous embodiments of the hydraulic arrangement and the commercial vehicle according to the invention are evident from the dependent claims.

[0006] According to claim 1, a hydraulic arrangement for a commercial vehicle is proposed, comprising a variable displacement hydraulic pump and a supply connection as an interface for supplying hydraulic consumers. These consumers include internal vehicle consumers and, optionally, external consumers (e.g., in the case of an attachment). The variable displacement pump's delivery rate or flow rate is adjustable by a control unit, which depends on the pump's output pressure and, optionally, on one or more other physical quantities. Furthermore, the hydraulic arrangement includes an auxiliary hydraulic pump and an auxiliary supply connection as an interface for providing supplementary power to at least some of the hydraulic consumers (e.g., a steering system and / or braking system), particularly in an emergency where the variable displacement pump fails.A hydraulic valve unit is arranged in the hydraulic flow path between a variable displacement pump outlet and the supply connection. It has several, in particular two or three, switching positions. In a first switching position of the valve unit, the variable displacement pump outlet is hydraulically connected to the supply connection and hydraulically isolated from an auxiliary pump outlet. In a second switching position of the valve unit, the variable displacement pump outlet is hydraulically isolated from the supply connection and hydraulically connected to the auxiliary pump outlet.

[0007] The pump outlet, or variable displacement pump outlet, can be a hydraulic outlet directly on the variable displacement pump itself or be a hydraulic outlet of a pump unit containing the variable displacement pump. Similarly, the auxiliary pump outlet can also be a hydraulic outlet directly on the auxiliary pump itself or be a hydraulic outlet of an auxiliary pump unit containing the auxiliary pump.

[0008] With variable displacement pumps, the delivery rate or flow rate of the pumped hydraulic fluid (e.g., oil) can be adjusted not only by varying the drive speed, but also while maintaining a constant drive speed of the variable displacement pump. Various parameters are conceivable as control variables, such as the current hydraulic pressure, particularly at the variable displacement pump outlet and / or at a hydraulic feedback port where a hydraulic feedback pressure from hydraulic consumers is present. The respective control variable(s) can influence a suitable variable displacement control, which adjusts the variable displacement pump's delivery rate, particularly continuously.

[0009] The adjustment control can be switched between a conveying position with a maximum conveying rate and a conveying position with a minimum conveying rate. Preferably, a hydraulic adjustment cylinder is used for this purpose.

[0010] The hydraulic arrangement according to the invention achieves the technical objective of providing a predetermined target pressure as output pressure at the pump outlet of the variable displacement pump during the start-up phase of the commercial vehicle's drive motor. This output pressure, controlled by the variable displacement control, results in the lowest possible, and in particular a minimal, delivery rate from the variable displacement pump. This minimizes the power consumption of the variable displacement pump, thereby reducing the load on the drive motor and the starter motor of the commercial vehicle during the start-up phase.

[0011] This desired physical state of the variable displacement pump during the start-up phase of the commercial vehicle is supported by the auxiliary pump and the valve unit. The valve unit can be actuated to its second switching position, in which the variable displacement pump output is hydraulically connected to the auxiliary pump output and hydraulically disconnected from the supply connection. This second switching position enables the activated auxiliary pump to build up a predetermined target pressure at the variable displacement pump output. Thus, the variable displacement pump, and consequently the drive motor and the starter motor of the commercial vehicle, can be supported with low energy losses during the start-up phase.

[0012] The first switching position of the valve unit is preferably its rest or starting position. This first switching position can be activated particularly after the commercial vehicle has been started. The variable displacement pump can then properly supply the consumers with hydraulic fluid.

[0013] The predetermined target pressure at the pump outlet is preferably defined such that it corresponds to at least a pressure differential at the variable displacement control, which results in a minimum delivery rate of the variable displacement pump. This pressure differential (e.g., approximately 26 bar) can be referred to as a control pressure differential and is, in particular, a difference between the outlet pressure at the pump outlet and a feedback pressure from hydraulic consumers.

[0014] A pump drive shaft that drives the variable displacement pump is mechanically connected, in particular via a gearbox, to an output shaft of the drive motor.

[0015] During the starting process of the commercial vehicle, the auxiliary pump can be used to build up a predetermined target pressure at the pump outlet and consequently reduce or minimize the delivery rate of the variable displacement pump during the starting phase. This avoids the conventionally required drive power during the starting process, thus relieving the load on the variable displacement pump, the drive motor, and the starter motor of the commercial vehicle, especially during a cold start with high viscosity hydraulic fluid. The starting process of the commercial vehicle can be carried out with significantly less power, which also supports the technical process of a successful cold start.

[0016] Preferably, the valve unit is in its second switching position when the variable displacement pump and the auxiliary pump are stationary. This allows the desired or predetermined outlet pressure or setpoint pressure to be built up at the variable displacement pump outlet without the variable displacement pump itself having to do so. This condition at the variable displacement pump outlet can advantageously be established immediately before starting the vehicle's drive engine, so that the variable displacement pump has a significantly reduced or minimal power consumption during the engine start-up process. This reduces power losses from the drive engine and the starter motor during the vehicle start-up process.

[0017] Furthermore, preferably, the hydraulic arrangement has at least one of the following states or features when the output pressure at the variable displacement pump outlet has increased after reaching or exceeding a predetermined target pressure: The valve unit is in a different switching position than the second switching position. This other switching position is, in particular, its first switching position. The auxiliary pump drive is reduced or deactivated. This takes into account that, after reaching or exceeding the predetermined setpoint pressure, the variable displacement pump either no longer needs support from the auxiliary pump or only to a lesser extent, so that correspondingly, no or only a reduced amount of drive energy is required for the auxiliary pump. The variable displacement pump is driven. The hydraulic arrangement can be controlled such that, with increasing output pressure, the variable displacement pump is only driven after reaching or exceeding the predetermined setpoint pressure and consequently with reduced or minimal pump displacement. The variable displacement pump is driven, in particular, by the starting drive motor.

[0018] The valve unit preferably has at least one further switching position in addition to the first and second switching positions. This further switching position of the valve unit, which can be designated as a disconnect switching position, is designed such that, when activated, the output of the variable displacement pump is disconnected from the supply connection and from the output of the auxiliary pump.

[0019] This disconnect switch position is advantageously activated when the predetermined target pressure has been reached or exceeded at the outlet of the variable displacement pump in the second switch position. This ensures that, even in the event of hydraulic leaks in the hydraulic consumers, the pressure built up at the outlet of the variable displacement pump is maintained using simple technical means during the activated disconnect switch position. This allows, for example, the necessary pressure at the pump outlet to be maintained during the start-up phase of the drive motor without the need to activate the auxiliary pump.

[0020] Preferably, after the start-up phase of the drive motor, the valve unit is moved from the aforementioned disconnect switching position to its first switching position, in which the output of the variable displacement pump is hydraulically connected to the supply connection and thus supplies the consumers with hydraulic medium.

[0021] In a further advantageous embodiment, the hydraulic arrangement in the flow path between the outlet of the auxiliary pump and the auxiliary supply connection includes a hydraulic auxiliary valve unit with several switching positions, in particular two switching positions. In a first switching position, the outlet of the auxiliary pump is hydraulically connected to the auxiliary supply connection. In a second switching position, the outlet of the auxiliary pump is hydraulically disconnected from the auxiliary supply connection. The first switching position of the auxiliary valve unit is preferably its rest position or initial position.

[0022] The auxiliary valve unit's functionality allows the hydraulic connection between the auxiliary pump and the auxiliary supply port to be disconnected or interrupted when the auxiliary pump is running, by activating the second switching position of the auxiliary valve unit. With this second switching position, the auxiliary valve unit supports energy-efficient operation of the auxiliary pump, as no flow or volumetric flow from the auxiliary pump towards the auxiliary supply port occurs, even in the event of leaks in the hydraulic components.

[0023] Preferably, the auxiliary valve unit and the valve unit are at least temporarily in their respective second switching position when the auxiliary pump is driven. This combination of switching positions allows a target pressure to be efficiently built up at the outlet of the variable displacement pump before the commercial vehicle's drive engine is started.

[0024] In another combination of switching positions, the auxiliary valve unit and the valve unit are at least temporarily in their respective first switching position when the variable displacement pump is driven. This combination of switching positions ensures a reliable supply to the hydraulic consumers during and / or after the start-up phase of the drive motor. Should the variable displacement pump fail, emergency hydraulic operation for at least some hydraulic consumers, especially safety-relevant consumers (e.g., brake and / or steering system), can be easily ensured without special technical effort by simply driving or activating the auxiliary pump.

[0025] In a further preferred embodiment, the valve unit and / or the auxiliary valve unit can be controlled to change its switching position depending on sensor signals from a pressure sensor. This pressure sensor is hydraulically connected, in particular, to the output of the auxiliary pump or to the output of the variable displacement pump. This allows the detection of reaching or exceeding the aforementioned predetermined setpoint pressure at the output of the variable displacement pump to be technically simple and reliable. The pressure sensor is, for example, connected to a control unit that processes the pressure sensor signals and controls the valve unit and / or the auxiliary valve unit and / or other valves in the hydraulic arrangement. Control can be based on the pressure sensor signals and / or other signals or data (e.g., speed of the drive motor, bus signals from a control and / or data bus of the commercial vehicle).

[0026] The valve unit and / or the auxiliary valve unit is preferably designed as a directional control valve with multiple switching positions, in particular as a proportional valve.

[0027] In an advantageous embodiment, the valve unit has a hydraulic control input which is hydraulically connected to the output of the variable displacement pump. A switching position of the valve unit can be changed or activated via the control input. The valve unit is dimensioned for this control such that the switching position of the valve unit changes when the predetermined setpoint pressure at the variable displacement pump output is reached or exceeded. In particular, the previously described isolation switching position is then automatically established, in which the output of the variable displacement pump is hydraulically isolated from the supply connection and from the output of the auxiliary pump.

[0028] To activate their individual switching positions, the valve unit and / or auxiliary valve unit can be reliably controlled or actuated in various suitable ways. For example, direct electrical control, particularly via an electromagnet, is provided. Alternatively, indirect control via a hydraulic pilot valve is provided, which is electrically controlled and exerts a hydraulic control pressure on the valve unit or auxiliary valve unit.

[0029] The hydraulic pilot valve preferably has a control pressure port which is hydraulically connected to a hydraulic control pressure inlet of the valve unit or the auxiliary valve unit. This allows the valve unit or the auxiliary valve unit to be actuated by a hydraulic control pressure. The pilot valve is designed such that, in one switching position of the pilot valve, the control pressure port is hydraulically connected to a hydraulic tank, and in another switching position of the pilot valve, it is hydraulically connected to the outlet of the auxiliary pump. This allows the output pressure of the auxiliary pump to be used to change the switching position of the affected valve unit or auxiliary valve unit when the pilot valve is actuated (especially electrically).

[0030] The invention further relates to a commercial vehicle, preferably an agricultural or forestry towing vehicle (e.g. a tractor or tractor) or a construction machine, with a drive motor and with a hydraulic arrangement according to one of claims 1 to 12.

[0031] The commercial vehicle according to the invention exhibits the advantages of the hydraulic arrangement described above. The hydraulic arrangement enables the variable displacement pump to operate efficiently before, during, and after the starting process of the commercial vehicle's drive engine. In particular, conventional problems during the starting phase of the drive engine can be avoided during a cold start. Thus, the hydraulic arrangement allows the variable displacement pump, the drive engine, and the starter motor to operate with particularly low energy losses during a cold start with a high viscosity hydraulic fluid. The starting process of the commercial vehicle can be carried out with significantly less power consumption, which also supports the technical success of a cold start.

[0032] The commercial vehicle may have a drive motor for driving the variable displacement pump included in the hydraulic arrangement.

[0033] Preferably, the auxiliary supply connection is hydraulically connected to a braking system and / or a steering system of the commercial vehicle. This creates the technical prerequisites for a technically simple emergency operation of the braking and / or steering system, as the hydraulic arrangement according to the invention can be integrated into the commercial vehicle in a modular fashion, and the auxiliary pump can be hydraulically connected to the auxiliary supply connection. This hydraulic connection can be direct or indirect (e.g., by interposing the auxiliary valve unit).

[0034] The invention is explained in more detail below with reference to the accompanying drawings. Components that are identical or comparable in function are identified by the same reference numerals. The drawings show: Fig. 1 a schematic representation of a commercial vehicle according to the invention, Fig. 2 a hydraulic circuit diagram with the hydraulic arrangement according to the invention in a first embodiment, Fig. 3 a hydraulic circuit diagram with the hydraulic arrangement according to the invention in a further embodiment, Fig. 4a a further embodiment of a valve unit within the hydraulic arrangement according to the invention, Fig. 4b a further embodiment of a valve unit within the hydraulic arrangement according to the invention, Fig. 5a a first embodiment of a pilot valve for controlling the valve unit, and Fig. 5b a further embodiment of the pilot valve.

[0035] Fig. 1 Figure 1 shows a schematic representation of an agricultural utility vehicle 10 according to the invention, in particular in the form of a tractor, with a drive train 20. The utility vehicle 10 further comprises a cab 12, a front axle 14, and a rear axle 26. The utility vehicle 10 can have one or more ground engagement means in the form of wheels 28. The drive train 20 comprises a drive motor 22, which can be designed as an internal combustion engine, and a transmission structure 30, which can be composed of various individual transmission components.

[0036] The commercial vehicle 10 has a hydraulic arrangement 42 with a pump unit 40. As in Fig. 2 and Fig. 3 As can be seen, the drive motor 22 can drive the transmission structure 30, which, via a transmission component and a pump drive shaft 44, drives a variable displacement pump 46 of the pump unit 40. The hydraulic arrangement 42 can be integrated into the commercial vehicle 10 in a modular fashion. This modular integration of the hydraulic arrangement 42 into the commercial vehicle 10 can be supported by various hydraulic interfaces. These interfaces can include a supply connection 48, a feedback connection 50, and an auxiliary supply connection 52.

[0037] According to Fig. 2 A pump output 54 of the pump unit 40 can be connected to the supply port 48 via a hydraulic valve unit 56 to supply hydraulic consumers 58 of the commercial vehicle 10. The consumers 58 include, among others, a steering system 60 and a brake system 62. An adjustment control 64 for adjusting a hydraulic delivery rate of the variable displacement pump 46 depends on its output pressure p_a and on a load sensing pressure at the feedback port 50.

[0038] Furthermore, the arrangement 42 comprises an auxiliary pump unit 66 with an auxiliary pump 70 driven by an auxiliary pump motor 68 (e.g., an electric motor). The auxiliary pump output 72 can be hydraulically connected to the auxiliary supply connection 52 via an auxiliary valve unit 74. In the event of a failure of the pump unit 40, the auxiliary pump unit 66 can, for example, provide an emergency supply to hydraulically required components, in particular the steering system 60 and the brake system 62.

[0039] The valve unit 56 according to Fig. 2 It is designed like a 3 / 2-way valve. In its first switching position 56-0, corresponding to the rest position, the pump outlet 54 is hydraulically connected to the supply port 48 and hydraulically separated from the auxiliary pump outlet 72. In the second switching position 56-a, the pump outlet 54 is hydraulically separated from the supply port 48 and hydraulically connected to the auxiliary pump outlet 72.

[0040] The auxiliary valve unit 74 according to Fig. 2 It is designed as a 2 / 2-way valve. In its first switching position 74-0, corresponding to the rest position, the auxiliary pump output 72 is hydraulically connected to the auxiliary supply port 52. In the second switching position 74-a, the auxiliary pump output 72 is hydraulically disconnected from the auxiliary supply port 52.

[0041] On the input side, the variable displacement pump 46 and the auxiliary pump 70 are each connected to a hydraulic tank 76. The hydraulic fluid delivered to the consumers 58 flows back into the hydraulic tank 76.

[0042] A pressure sensor 78 with a pressure input 80 is connected to the auxiliary pump output 72. Alternatively, the pressure input 80 is connected to the pump output 54. A signal output 82 of the pressure sensor 78 is connected to an electrical control unit 84, which processes, among other things, the output signals or sensor signals S of the pressure sensor 78. In this way, the control unit 84 can detect the current pressure at the auxiliary pump output 72 and / or the current output pressure p_a at the pump output 54. Depending on this pressure detection, the control unit 84 can, among other things, control the valve unit 56 and the auxiliary valve unit 74 to change their respective switching positions.

[0043] To support the operation of the hydraulic arrangement 42, a hydraulic check valve 86 is interposed between the auxiliary pump output 72 and an output 90 of the auxiliary pump unit 66. Furthermore, the auxiliary pump 70 is combined with a hydraulic pressure valve 88.

[0044] Fig. 3 Figure 42 shows another embodiment of the hydraulic arrangement 42. In this embodiment, there is no auxiliary valve unit 74. The output 90 of the auxiliary pump unit 66 is then directly hydraulically connected to the auxiliary supply connection 52.

[0045] The aforementioned hydraulic interfaces - supply connection 48, feedback connection 50, auxiliary supply connection 52 - can preferably be arranged directly on the respective component (e.g. pump unit 40, auxiliary pump unit 66, valve unit 56, auxiliary valve unit 74) of the hydraulic arrangement 42 or be arranged at a distance from the respective component of the hydraulic arrangement 42 by means of a cable-like extension.

[0046] In another embodiment ( Fig. 4a The valve unit 56 has, in addition to the first and second switching positions 56-0 and 56-a, a third switching position in the form of a disconnect switching position 56-t. In the case of the disconnect switching position 56-t being activated, the pump output 54 of the variable displacement pump 54 is hydraulically disconnected from the supply connection 48 and simultaneously also hydraulically disconnected from the auxiliary pump output 72 or from the auxiliary pump unit 66.

[0047] The valve unit 56 with the two switching positions 56-0, 56-a and the valve unit 56 with the three switching positions 56-0, 56-a, 56-t can optionally be designed as a continuously variable directional control valve, as shown in Fig. 4a depicted.

[0048] In another embodiment ( Fig. 4b The valve unit 56 has a control input 92 which is hydraulically connected to the pump output 54 of the variable displacement pump 46. This allows a specific switching position of the valve unit 56, in particular the disconnect switching position 56-t, to be automatically activated by the hydraulic control pressure applied to the control input 92. In the embodiment according to Fig. 4a In contrast, the disconnect switch position 56-t is activated by electrical control via the control unit 84.

[0049] In general, the valve unit 56 and the auxiliary valve unit 74 can be directly electrically controlled via the control unit 84 to activate a different switching position.

[0050] In the embodiment according to Fig. 4b The valve unit 56 is dimensioned and its control can be combined by the control unit 84 with the hydraulic control input 92 such that an activated electromagnet 94, together with a pressure limiting spring 96, holds the valve unit 56 in the second switching position 56-a until the predetermined setpoint pressure p_setpoint is reached at the pump outlet 54. This setpoint pressure p_setpoint causes the valve unit 56 to be switched to the switching position 56-t via the control input 92.

[0051] Alternatively, the valve unit 56 and / or the auxiliary valve unit 74 can each be controlled via an electrically controlled hydraulic pilot valve 98. The pilot valve 98 is in Fig. 5a und Fig. 5b The pilot valve 98 is shown in two possible embodiments. In both embodiments, the pilot valve 98 is designed as a directional control valve with two switching positions 98-0, 98-a, wherein in the embodiment according to Fig. 5b The position is continuously adjustable. Switching position 98-0 is preferably the rest position of the pilot valve 98. The pilot valve 98 has a control pressure port 100, which is hydraulically connected to a hydraulic control pressure inlet 102 of the valve unit 56 or the auxiliary valve unit 74. In switching position 98-0, the control pressure port 100 is hydraulically connected to one or the hydraulic tank 76. In switching position 98-a, the control pressure port 100 is hydraulically connected to the auxiliary pump outlet 72 or the outlet 90 of the auxiliary pump unit 66.

[0052] Using the described hydraulic logic, the starting phase of the drive motor 22 can be supported with particularly low energy losses, which offers technical advantages, especially during a cold start.

[0053] Before the commercial vehicle 10 starts, the variable displacement control 64, in particular its adjusting cylinder, is usually set to a delivery position for maximum delivery rate due to the pressure conditions at the pump outlet 54 and at the feedback port 50. However, the aim is to keep the power consumption of the variable displacement pump 46 as low as possible during the start-up phase of the commercial vehicle 10 and consequently to set the variable displacement control 64, in particular its adjusting cylinder, to a delivery position for minimum delivery rate. This aim is achieved with the hydraulic arrangements 42 according to Fig. 2 and Fig. 3 reached.

[0054] In the hydraulic arrangement 42 according to Fig. 2 Starting from the rest positions or first switching positions 56-0, 74-0 of the valve unit 56 and the auxiliary valve unit 74, the control unit 84 detects an intended start of the drive motor 22 (e.g., via received bus signals from a vehicle bus, such as ISOBUS or CAN). The control unit then switches the valve unit 56 and the auxiliary valve unit 74 to their second switching positions 56-a, 74-a. In addition, the auxiliary pump motor 68 is activated by the control unit 84, so that the auxiliary pump 70 is driven and the output pressure p_a at the pump outlet 54 increases, while the variable displacement pump 46 remains stationary. As soon as the increasing output pressure p_a reaches or exceeds a predetermined target pressure p_target – depending on the system, e.g., approximately 26 bar – the variable displacement control 64 is in its minimum delivery position, so that the variable displacement pump 46 has no or only a minimal power consumption.This significantly reduces the power consumption of the variable displacement pump 46 during the start-up phase of the commercial vehicle 10, thereby relieving the drive motor 22 and its starter motor during the start-up phase.

[0055] Since the output pressure p_a is continuously detected by the pressure sensor 78, the control unit 84 can control the hydraulic arrangement 42 as desired after reaching or exceeding the predetermined setpoint pressure p_setpoint. In particular, after reaching or exceeding the predetermined setpoint pressure p_setpoint, the auxiliary pump motor 68 is reduced in its drive speed or switched off. The drive motor 22 is started, and after reaching a stable speed, the valve unit 56 and the auxiliary valve unit 74 are moved to their respective first switching positions 56-0, 74-0, and to their rest positions, respectively. The valve unit 56 then allows the variable displacement pump 46 to supply the hydraulic consumers.

[0056] The hydraulic arrangement 42 according to Fig. 3 works in contrast to the embodiment according to Fig. 2 without the auxiliary valve unit 74, so that the output 90 is directly hydraulically connected to the auxiliary supply port 52. In the event of an intended start of the drive motor 22, the hydraulic arrangement 42 is configured according to Fig. 3 In principle, it is controlled in the same way as in the variant according to Fig. 2 First, the valve unit 56 is switched from its rest position or first switching position 56-0 to its second switching position 56-a. Then, as shown in the Fig. 2 As described, the auxiliary pump 70 is driven. However, should leaks occur at the hydraulic consumers 58, the auxiliary pump 70 requires a greater drive power than in the variant according to Fig. 2 , in order to achieve the predetermined target pressure p_target at the pump outlet 54. Furthermore, continued operation of the auxiliary pump 70 may be useful or necessary during the start-up phase of the drive motor 22 in order to maintain the required hydraulic pressure p_target at the pump outlet 54 during the start-up phase.

[0057] Alternatively, when performing according to Fig. 3 The aforementioned continued operation of the auxiliary pump 70 during the start-up phase of the drive motor 22 can be avoided by equipping the valve unit 56 with the additional disconnect switching position 56-t ( Fig. 4a, Fig. 4bAfter reaching or exceeding the predetermined target pressure p_target, the valve unit 56 can then be moved from the second switching position 56-a to the disconnect switching position 56-t in order to maintain the achieved target pressure p_target. At a suitable time, in particular after the drive motor 22 has started, the valve unit 56 is moved from the disconnect switching position 56-t to its rest position or first switching position 56-0 by means of the control unit 84.

Claims

1. Hydraulic arrangement (42) for a commercial vehicle (10) with a hydraulic variable displacement pump (46) and a supply connection (48) as an interface for supplying hydraulic consumers (58, 60, 62) of the commercial vehicle (10), with an adjustment control (64) dependent on an output pressure (p_a) of the variable displacement pump (46) for adjusting the variable displacement pump (46), with a hydraulic auxiliary pump (70) and an auxiliary supply connection (52) as an interface for the auxiliary supply of at least some of the consumers (60, 62), and with a hydraulic valve unit (56) containing a plurality of switching positions (56-0, 56-a), which is hydraulically arranged in the flow path between a pump outlet (54) of the variable displacement pump (46) and the supply connection (48), wherein the valve unit (56) has a first switching position (56-0) in which the pump outlet (54) of the Variable displacement pump (46) hydraulically connected to the supply connection (48) and from an output (72,90) of the auxiliary pump (70) is hydraulically separated, and - has a second switching position (56-a) in which the pump outlet (54) of the variable displacement pump (46) is hydraulically separated from the supply connection (48) and hydraulically connected to the outlet (72, 90) of the auxiliary pump (70).

2. Hydraulic arrangement according to claim 1, characterized in that the valve unit (56) is in its second switching position (56-a) when the variable displacement pump (46) is at a standstill and the auxiliary pump (70) is driven.

3. Hydraulic arrangement according to claim 2, characterized in thatwhen the output pressure (p_a) at the pump outlet (54) of the variable displacement pump (46) has increased after a predetermined target pressure (p_soll) at the pump outlet (54) has been reached or exceeded, it has at least one of the following features: - the valve unit (56) is in a different switching position (56-t, 56-0) than the second switching position (56-a); - the drive (68) of the auxiliary pump (70) is reduced or deactivated; - the variable displacement pump (46) is driven.

4. Hydraulic arrangement according to one of the preceding claims, characterized in that the valve unit (56) has a separating switching position (56-t) in which the pump outlet (54) of the variable displacement pump (46) is hydraulically separated from the supply connection (48) and from the outlet (72, 90) of the auxiliary pump (70).

5. Hydraulic arrangement according to claim 4, characterized in thatthe valve unit (56) assumes the isolating switching position (56-t) after reaching or exceeding a predetermined target pressure (p_soll) at the pump outlet (54) of the variable displacement pump (46).

6. Hydraulic arrangement according to claim 5, characterized in that the valve unit (56) assumes the first switching position (56-0) after the isolating switching position (56-t).

7. Hydraulic arrangement according to one of the preceding claims, characterized in that it has a hydraulic auxiliary valve unit (74) with a plurality of switching positions (74-0, 74-a) in the flow path between the outlet (72, 90) of the auxiliary pump (70) and the auxiliary supply connection (52), wherein - in a first switching position (74-0) the outlet (72, 90) of the auxiliary pump (70) is hydraulically connected to the auxiliary supply connection (52), and - in a second switching position (74-a) the outlet (72, 90) of the auxiliary pump (70) is hydraulically separated from the auxiliary supply connection (52).

8. Hydraulic arrangement according to one of the preceding claims, characterized in that the valve unit (56) and / or the auxiliary valve unit (74) - when the auxiliary pump (70) is driven, is in its respective second switching position (56-a, 74-a), and / or - when the variable displacement pump (46) is driven, is in its respective first switching position (56-0, 74-0).

9. Hydraulic arrangement according to one of the preceding claims, characterized in that the valve unit (56) and / or the auxiliary valve unit (74) can be controlled to change its switching position (56-0, 56-t, 56-a; 74-0, 74-a) in dependence on sensor signals (S) of a pressure sensor (78) which is hydraulically connected to the output (72, 90) of the auxiliary pump (70) or to the pump output (54).

10. Hydraulic arrangement according to one of the preceding claims, characterized in thatthe valve unit (56) has a control input (92) which is hydraulically connected to the pump output (54) of the variable displacement pump (46).

11. Hydraulic arrangement according to one of the preceding claims, characterized in that the valve unit (56) and / or the auxiliary valve unit (74) - can be controlled directly electrically, or - can be controlled via an electrically controllable hydraulic pilot valve (98).

12. Hydraulic arrangement according to claim 11, characterized in thatthe hydraulic pilot control valve (98) has a control pressure connection (100) which is hydraulically connected to a hydraulic control pressure inlet (102) of the valve unit (56) or the auxiliary valve unit (74), wherein the control pressure connection (100) - in one switching position (98-0) of the pilot control valve (98) is hydraulically connected to a hydraulic tank (76), and - in another switching position (98-a) of the pilot control valve (98) is hydraulically connected to the outlet (90) of the auxiliary pump (70).

13. Commercial vehicle (10) with a drive motor (22) and with a hydraulic arrangement (42) according to one of claims 1 to 12.

14. Commercial vehicle according to claim 13, characterized in that the drive motor (22) is drive-connected to the variable displacement pump (46).

15. Commercial vehicle according to claim 13 or 14, characterized in that the auxiliary supply connection (52) is hydraulically connected to a braking system (62) and / or to a steering system (60) of the commercial vehicle (10).

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