Demand-controlled hydrostatic drive system

Abstract

A demand-controlled hydrostatic drive system (1) comprising at least one consumer (V) supplied with pressure medium by a pump (2), wherein the pump (2) is continuously variable in its delivery volume and operates in an open circuit, wherein the pump (2) has a delivery volume control device (11) for changing the delivery volume, the setting of which is adjustable by means of an actuating device (12), wherein the drive system (1) comprises a load-sensing control valve (20) which is associated with an actuating piston device (13) of the actuating device (12) connected to the delivery volume control device and which is controlled by the delivery pressure of the pump (2), the highest load pressure of the consumers (V) and a load-sensing control pressure differential (ΔP). LS ) is controlled, comprises a load pressure pressure cut-off valve (50) which is assigned to a load pressure signaling line (10) carrying the highest load pressure of the consumers (V) and is set to a limit opening pressure (P LS) is set, and includes a relief valve (60) that controls the connection of a delivery line (5) of the pump (2) with a container (4) and that is controlled by the delivery pressure of the pump (2), the highest load pressure of the consumers (V) and a relief pressure differential (ΔP). UDW ) is controlled, characterized in that the load-sensing control pressure difference (ΔP) LS ) of the load-sensing control valve (20), the limit opening pressure (P LS ) of the load pressure pressure cut-off valve (50) and the relief pressure difference (ΔP UDW ) of the relief valve (60) is variable and adjustable, wherein the load-sensing control pressure differential (ΔP) LS ) of the load-sensing control valve (20), the limit opening pressure (P LS ) of the load pressure pressure cut-off valve (50) and the relief pressure difference (ΔP UDW ) of the relief valve (60) during operation of the drive system (1) are changeable.

Description

[0001] The invention relates to a demand-flow-controlled hydrostatic drive system comprising at least one consumer supplied with pressure medium by a pump, wherein the pump is continuously adjustable in its delivery volume and is operated in an open circuit, wherein the pump has a delivery volume adjusting device for changing the delivery volume, the setting of which is adjustable by means of an adjusting device, wherein the drive system comprises a load-sensing control valve which is assigned to an actuating piston device of the adjusting device connected to the delivery volume adjusting device and which is controlled by the delivery pressure of the pump, the highest load pressure of the consumers and a load-sensing control pressure difference, a load pressure pressure cut-off valve which is assigned to a load pressure signaling line carrying the highest load pressure of the consumers and is set to a limit opening pressure, and a relief valve,which controls the connection of a pump discharge line to a tank and which is controlled by the pump discharge pressure, the highest load pressure of the consumers and a relief pressure difference.

[0002] In load-sensing drive systems, the continuously variable displacement pump is equipped with a load-sensing control valve to actuate the pump when the load-sensing control pressure differential is exceeded, thereby reducing the displacement. The load-sensing control pressure differential is exceeded when the pump's discharge pressure exceeds the sum of the load-sensing control pressure differential and the highest load pressure of the consumers. The load-sensing control valve thus achieves demand flow control in a load-sensing drive system, adapting the flow delivered by the pump to the flow requested by the controlled consumers. The dynamics are determined by the inertia of the pump's actuating device. By controlling the pump's demand flow using the load-sensing control valve, only minimal power loss occurs in the drive system.In conventional load-sensing drive systems, the load-sensing control pressure differential at the load-sensing control valve is fixed and set to a specific value. In conventional load-sensing drive systems, the load-sensing control pressure differential is set to a fixed value of approximately 20 bar.

[0003] The relief valve, also known as a circulation pressure compensator or unload valve, relieves the pressure in the pump's delivery line to the tank when the relief pressure differential is exceeded. The relief pressure differential is exceeded when the pump's delivery pressure exceeds the sum of the relief pressure differential and the highest load pressure of the consumers. The relief valve has a higher dynamic response (factor of 10 to 100) and therefore a faster response time than adjusting the pump's delivery volume using the load-sensing control valve. However, by connecting the pump's delivery line to the tank, the relief valve causes a loss of line. In known load-sensing controlled drive systems, the relief pressure differential at the relief valve is fixed and set to a specific value. In known load-sensing drive systems, it is known to set the relief pressure differential to a value of approx.Set to 60 bar.

[0004] The load pressure cut-off valve is used to limit the maximum load pressure, which is routed in the drive system's load pressure signal line and applied to the load-sensing control valve, and to achieve pressure cut-off by reducing the pump's displacement. The load pressure cut-off valve is activated if the maximum load pressure exceeds the limit opening pressure. In known pumps for load-sensing drive systems, the limit opening pressure at the load pressure cut-off valve is fixed and set to a specific value.

[0005] Due to the fixed limit opening pressure on the load pressure pressure cut-off valve, the fixed relief pressure difference on the relief valve and the fixed load-sensing control pressure difference on the load-sensing control valve, known load-sensing drive systems have a predetermined characteristic due to the coordination of the limit opening pressure, the relief pressure difference and the load-sensing control pressure difference, for example a certain actuating behavior of the pump and response behavior of the load pressure pressure cut-off valve and the relief valve.

[0006] From DE 10 2010 048 893 A1 a demand-flow controlled hydrostatic drive system with a demand-flow valve and a pressure cut-off valve is known, wherein a pressure cut-off is provided at a selected consumer to protect the consumer pressure.

[0007] DE 10 2008 054 880 A1 discloses a demand-flow-controlled hydrostatic drive system in which the flow valve comprises control means which can be controlled by an electronic control unit and by means of which the control pressure difference value at the flow valve can be changed.

[0008] The present invention is based on the object of providing a pump of the type mentioned at the outset with which the system characteristics of the drive system can be changed in a simple manner.

[0009] This object is achieved according to the invention in that the load-sensing control pressure difference of the load-sensing control valve, the limit opening pressure of the load pressure pressure cut-off valve, and the relief pressure difference of the relief valve are variable and adjustable, wherein the load-sensing control pressure difference of the load-sensing control valve, the limit opening pressure of the load pressure pressure cut-off valve, and the relief pressure difference of the relief valve are variable during operation of the drive system. The inventive idea thus consists in making the load-sensing control pressure difference of the load-sensing control valve, the limit opening pressure of the load pressure pressure cut-off valve, and the relief pressure difference of the relief valve variable and changeable during operation of the drive system, and thus making the load-sensing control pressure difference, the limit opening pressure, and the relief pressure difference variable and combining them through variable specifications.The adjustable load-sensing control pressure difference, the adjustable limit opening pressure and the adjustable relief pressure difference enable a situation-dependent specification and / or automatic adjustment of the system characteristics of the hydrostatic drive system.

[0010] According to a preferred embodiment of the invention, the load-sensing control pressure differential of the load-sensing control valve, the limit opening pressure of the load pressure cut-off valve, and the relief pressure differential of the relief valve can be changed and specified depending on the operating situation of the drive system. This enables a simple, situation-dependent specification and / or automatic adaptation of the system characteristics of the hydrostatic drive system.

[0011] If the drive system can be controlled purely hydraulically using corresponding control pressures, for example if it has control valves for the consumers that can be actuated purely hydraulically using control pressures, it is possible to change the load-sensing control pressure difference of the load-sensing control valve, the limit opening pressure of the load pressure pressure cut-off valve and the relief pressure difference of the relief valve in a purely hydraulic way by detecting the corresponding operating situation based on the control pressures and passing the control pressures to the load-sensing control valve to change the load-sensing control pressure difference, to the load pressure pressure cut-off valve to change the limit opening pressure and to the relief valve to change the relief pressure difference via logic valves or control pressure cascades.

[0012] According to an advantageous embodiment of the invention, an electronic control device is provided for changing the load-sensing control pressure differential of the load-sensing control valve, the limit opening pressure of the load pressure cut-off valve, and the relief pressure differential of the relief valve. Using an electronic control device, a situation-dependent specification and / or automatic adjustment of the system characteristics of the hydrostatic drive system can be easily achieved by changing and adjusting the load-sensing control pressure differential of the load-sensing control valve, the limit opening pressure of the load pressure cut-off valve, and the relief pressure differential of the relief valve.

[0013] A situation-dependent specification and / or automatic adaptation of the system characteristics of the hydrostatic drive system by changing and adjusting the load-sensing control pressure differential of the load-sensing control valve, the limit opening pressure of the load pressure cut-off valve, and the relief pressure differential of the relief valve can be easily achieved in conjunction with an electronic control device if the electronic control device is operatively connected on the input side to actuating devices at which consumer movements can be specified. Depending on the consumer movement or the load movement controlled by the actuating devices,For consumer movements, typical consumer requirements can be taken into account even before the consumer's load pressure is reported back to the load-sensing control valve, the relief valve, and the load pressure relief valve when specifying the load-sensing control pressure differential, the relief pressure differential, and the limit opening pressure. The load-sensing control pressure differential of the load-sensing control valve, the limit opening pressure of the load pressure cut-off valve, and the relief pressure differential of the relief valve can be adjusted and specified according to the consumer requirement. This results in improved responsiveness of the drive system according to the invention. In an excavator, for example, the expected high pressure is higher for the consumer request "lift boom" than for the consumer request "lower boom."

[0014] The electronic control device can easily detect operating situations based on the actuation of the actuating devices and change the load-sensing control pressure difference of the load-sensing control valve, the limit opening pressure of the load pressure cut-off valve and the relief pressure difference of the relief valve according to the detected operating situation of the drive system.

[0015] Furthermore, the electronic control device can easily detect situation-typical consumer movement requirements based on the actuation of the actuating devices and can set the load-sensing control pressure difference of the load-sensing control valve, the limit opening pressure of the load pressure cut-off valve and the relief pressure difference of the relief valve to the corresponding specifications for the situation-typical consumer movement requirements.

[0016] According to an expedient embodiment of the invention, the load-sensing control pressure differential of the load-sensing control valve and the relief pressure differential of the relief valve are adjusted by means of the electronic control device such that the relief pressure differential of the relief valve is greater than the load-sensing control pressure differential of the load-sensing control valve. This adjustment and specification of the load-sensing control pressure differential and the relief pressure differential ensures that the relief valve only intervenes and connects the delivery line to the tank when the pump actuating device controlled by the load-sensing control valve, and thus the dynamics of the pump adjustment, cannot follow the dynamics of the drive system.This enables aggressive coordination of the pump's control device and the load-sensing control valve, which provides a spontaneous and rapid response to changes in the pump's delivery volume, as disruptive pressure peaks in the pump's delivery pressure are reduced by the relief valve, which has a smooth response. In the drive system according to the invention with variable characteristics, the behavior of a conventional load-sensing drive system can also be replicated as a special case by setting the load-sensing control pressure differential to approximately 20 bar and the relief pressure differential to approximately 60 bar.

[0017] According to an advantageous embodiment of the invention, the electronic control device detects a highly dynamic consumer movement request based on the actuation of the actuating devices and, in the case of a highly dynamic consumer movement request, adjusts the load-sensing control pressure differential of the load-sensing control valve and the relief pressure differential of the relief valve such that the relief pressure differential of the relief valve is smaller than the load-sensing control pressure differential of the load-sensing control valve. By specifying the load-sensing control pressure differential and the relief pressure differential, the relief valve is given priority over the load-sensing control valve, thus avoiding excessively dynamic demands on the pump's control device for adjusting the pump's delivery volume.Such a consumer movement requirement with a high dynamic can be, for example, the shaking of a bucket in an excavator, whereby the actuating device of the control valve controlling the bucket is actuated quickly in opposite directions.

[0018] According to an advantageous embodiment of the invention, the electronic control device changes the limit opening pressure of the load pressure cut-off valve depending on the actuation of the actuating devices. The limit opening pressure of the load pressure cut-off valve can be changed and specified in such a way that the actuating signals of the actuating devices that control the control valves of the consumers are interpreted as the requested volume flow and thus the requested consumer speed, or alternatively, the actuating signals of the actuating devices that control the control valves of the consumers are interpreted as the requested pressure and thus the requested force or torque of the consumer. The load-sensing drive system according to the invention can thus be operated in a load-sensing manner with a characteristic typical for throttle control systems.Furthermore, by varying the limit opening pressure of the load pressure cut-off valve depending on the actuation of the actuating devices and thus depending on the controlled consumer function of the drive system, different characteristic curves can be set between the actuation signal of the actuating device and the limit opening pressure. This allows a higher limit opening pressure to be set on the load pressure cut-off valve for certain operating situations, for example, in an excavator when controlling a boom during lifting operation.

[0019] The drive system according to the invention with variable characteristics makes it possible to provide a warm-up function for the drive system, in which the load-sensing control pressure difference of the load-sensing control valve and the relief pressure difference of the relief valve are adjusted, for example by means of the electronic control device, such that the relief pressure difference of the relief valve is smaller than the load-sensing control pressure difference of the load-sensing control valve. This setting ensures that the pump's delivery volume is increased and the pressure medium delivered by the pump circulates to the reservoir via the open relief valve and is thus warmed up. This warm-up function of the drive system can be easily carried out by the electronic control device after the start-up of a working machine and when the pressure medium temperature of the drive system and / or the ambient temperature is correspondingly cold.

[0020] The drive system according to the invention with variable characteristics further enables the provision of a standby function of the drive system, in which the load-sensing control pressure differential of the load-sensing control valve and the relief pressure differential of the relief valve are adjusted, for example, by means of the electronic control device such that the pump provides a standby volume flow at a standby pressure in the delivery line. By means of the electronic control device, it is easily possible to provide a combination of standby pressure and standby volume flow for standby operation of the drive system with low power loss in operating states in which no consumers are controlled by appropriately specifying the load-sensing control pressure differential and the relief pressure differential.

[0021] The drive system according to the invention with variable characteristics further enables the provision of a boost function of the drive system, in which the limit opening pressure of the load pressure cut-off valve is increased, for example, by means of the electronic control device. The electronic control device makes it easy to temporarily increase the limit opening pressure of the load pressure cut-off valve and thus the maximum pressure of the drive system in certain operating situations and operating states, for example, to free a jammed or stuck consumer.

[0022] The drive system with variable characteristics according to the invention further enables the electronic control device to detect fine control operation of the consumer based on the actuation of the actuating devices and to reduce the load-sensing control pressure differential of the load-sensing control valve for the fine control operation of the consumer. This allows the characteristic curve of the control valve controlling a consumer to be easily influenced, since reducing the load-sensing control pressure differential increases the fine control range of the control valve with small control valve deflection, and increasing the load-sensing control pressure differential enables larger volume flows through the control valve. The fine control range of a consumer can be easily detected by the electronic control device based on the magnitude of the actuation and thus the magnitude of the deflection of the actuating device.

[0023] According to an advantageous embodiment of the invention, the load-sensing control valve is acted upon by the pump's delivery pressure in the direction of reducing the pump's delivery volume, and by the highest load pressure of the consumers and a spring device in the direction of increasing the pump's delivery volume. To change the load-sensing control pressure difference of the load-sensing control valve, a delivery pressure signal acting in the direction of reducing the pump's delivery volume at the load-sensing control valve or a load pressure signal acting in the direction of increasing the pump's delivery volume at the load-sensing control valve can be influenced. By influencing, for example, lowering, the high-pressure signals at the load-sensing control valve formed by the delivery pressure signal or the load pressure signal, the load-sensing control pressure difference can be easily influenced and changed.

[0024] According to an alternative embodiment of the invention, in order to change the load-sensing control pressure difference of the load-sensing control valve, the setting of a spring device that specifies the load-sensing control pressure difference can be influenced. By changing the preload of the spring device that specifies the load-sensing control pressure difference, the load-sensing control pressure difference can be easily influenced and changed.

[0025] According to an alternative and advantageous embodiment of the invention, an adjustable preset force acting in the direction of increasing the pump's delivery volume can be generated on the load-sensing control valve to change the load-sensing control pressure differential of the load-sensing control valve. By applying an adjustable preset force to the load-sensing control valve, the load-sensing control pressure differential can be easily influenced and changed. This allows an existing load-sensing control valve controlled by the load pressure signal and delivery pressure signal as well as a spring device to be easily configured to change and adjust the load-sensing control pressure differential.

[0026] According to one embodiment of the invention, the limit opening pressure of the load pressure cut-off valve can be adjusted by adjusting the setting of a spring that sets the limit opening pressure. By changing the preload of the spring that sets the limit opening pressure, the limit opening pressure can be easily influenced and changed.

[0027] According to an alternative embodiment of the invention, an adjustable preset force acting in the direction of an opening position can be generated on the load pressure cut-off valve to change the limit opening pressure of the load pressure cut-off valve. By applying an adjustable preset force to the load pressure cut-off valve, the limit opening pressure can be easily influenced and changed. This allows an existing load pressure cut-off valve controlled by a load pressure signal and a spring to be easily designed to have a variable and adjustable limit opening pressure.

[0028] According to one embodiment of the invention, to change the relief pressure differential of the relief valve, a delivery pressure signal acting toward a flow position at the relief signal or a load pressure signal acting toward a blocking position at the relief valve can be influenced. By influencing, for example, lowering, the high-pressure signals formed by the delivery pressure signal or the load pressure signal at the relief valve, the relief pressure differential can be easily influenced and changed.

[0029] According to an alternative embodiment of the invention, the setting of a spring device that determines the relief pressure difference of the relief valve can be influenced to change the relief pressure difference. By changing the preload of the spring device that determines the relief pressure difference, the relief pressure difference can be easily influenced and changed.

[0030] According to an alternative and advantageous embodiment of the invention, a preset force acting in the direction of the blocking position can be generated on the relief valve to change the relief pressure differential of the relief valve. By applying an adjustable preset force to the relief valve, the relief pressure differential can be easily influenced and changed. This allows an existing relief valve controlled by the load pressure signal and discharge pressure signal as well as a spring device to be easily designed to change and adjust the relief pressure differential.

[0031] According to an advantageous embodiment of the invention, a pilot valve connected to a pressure source is provided to generate the adjustable preset force. With an additional pilot valve, an adjustable preset force can be easily generated from the pressure of the pressure source at the load-sensing regulator for specifying the load-sensing control pressure differential, at the relief valve for specifying the relief pressure differential, or at the load pressure pressure cutoff valve for specifying the limit opening pressure.

[0032] According to an advantageous embodiment of the invention, the pilot valve is designed as a pressure reducing valve with a variable set pressure. If the pressure reducing valves are electrically variable in their set pressure, they can be easily controlled by the electronic control unit to generate a corresponding preset force for setting the load-sensing control pressure differential, the relief pressure differential, and the limit opening pressure.

[0033] Further advantages and details of the invention are explained in more detail with reference to the embodiment shown in the schematic figure.

[0034] The figure shows the hydraulic circuit diagram of a load-sensing controlled drive system 1 according to the invention with a pump 2 that supplies one or more consumers V with pressure medium. The pump 2 is driven by a drive motor M, for example, an internal combustion engine.

[0035] The pump 2 is designed as a pump with continuously variable delivery volume, which is operated in an open circuit and can be adjusted on one side in terms of delivery volume between a "Min" position with minimum delivery volume and a "Max" position with maximum delivery volume. The pump 2 is connected to a container 4 via a line 3 to suck in pressure medium and delivers it into a delivery line 5. To control the direction and speed of movement, a control valve 7 is provided for each consumer V of the hydrostatic drive system 1, which control valve is designed as a directional control valve that throttles in intermediate positions. The figure only shows one control valve 7 for one consumer V. It is understood that further control valves 7 can be provided for other consumers V in a similar way.

[0036] The control valve 7 shown in the figure is connected to the delivery line 5, the container 4 and the pressure medium lines 8a, 8b leading to the consumer 6. In a neutral position 7a shown, which can be designed as a closed middle position, the connections are blocked. When the control valve 7 is actuated, the control valve 7 is actuated in the direction of the switching positions 7b or 7c, in which the control valve 7 controls the connection of the pressure medium lines 8a, 8b leading to the consumer 6 with the delivery line 5 and the container 4 and, depending on a control signal, releases a specific opening cross-section from the delivery line 5 to the pressure medium line 8a or 8b. In the switching positions 7b or 7c, the load pressure of the controlled consumer 6 is detected and reported to a load pressure reporting branch line 9.The load pressure signaling branch line 9 is connected to a load pressure signaling line 10 of the drive system 1, in which the highest load pressure of the controlled consumers V is present when several consumers V are controlled.

[0037] Pump 2 is designed as a load-sensing, adjustable-displacement pump, whose displacement can be adjusted by means of a displacement adjustment device 11, for example, an inclination-adjustable swash plate of a pump designed as an axial piston machine with a swash plate design. The displacement adjustment device 11 is adjustable by means of an adjustment device 12. The adjustment device 12 actuates an actuating piston device 13, which is operatively connected to the displacement adjustment device 11 for actuation.

[0038] The actuating piston device 13 has an actuating piston pressure chamber 13a, which acts in the direction of reducing the delivery volume and actuates the delivery volume adjusting device 11, and an actuating piston pressure chamber 13b, which acts in the direction of increasing the delivery volume and actuates the delivery volume adjusting device 11. The actuating piston pressure chamber 13b is connected to the delivery line of the pump 2 via a branch line 14. A spring 15 can be arranged in the actuating piston pressure chamber 13b.

[0039] The control device 12 is connected on the input side to the load pressure signaling line 10 carrying the highest load pressure of the consumers.

[0040] The actuating device 12 comprises a load-sensing control valve 20, which is connected to the delivery line 5 of the pump 2 by means of a branch line 21, to the container 4 by means of a reservoir line 22, and to the actuating piston pressure chamber 13a by means of a control line 23. The load-sensing control valve 20 has a control position 20a acting in the direction of a reduction in the delivery volume of the pump 2. In the control position 20a, the branch line 21 is connected to the control line 23. The two actuating piston pressure chambers 13a, 13b are thus acted upon by the delivery pressure of the pump 2. The actuating piston pressure chamber 13a has a larger area than the actuating piston pressure chamber 13b, whereby the actuating piston device 13 acts on the pump 2 in the direction of a reduction in the delivery volume. The load-sensing control valve 20 has a control position 20b acting in the direction of increasing the delivery volume of the pump 2.The load-sensing control valve 20 is designed as a control valve that throttles in intermediate positions. In the control position 20b, the branch line 21 is connected to the reservoir line 22. The actuating piston pressure chamber 13a is thus relieved of pressure to the reservoir 4, so that the actuating piston device 13 is acted upon by the delivery pressure of the pump 2 present in the actuating piston pressure chamber 13b, increasing the delivery volume. A throttle device 25, which can be formed by an orifice or a nozzle, is arranged in the branch line 21. A throttle device 26, which can be formed by an orifice or a nozzle, is arranged in the branch line 22. The throttle devices 25, 26 enable the adjustment behavior and the adjustment time of the delivery volume adjustment device 11 to be influenced.

[0041] The load-sensing control valve 20 is acted upon by the discharge pressure of the pump 2 in the direction of a reduction in the discharge volume of the pump 2. For this purpose, a control line 27 connected to the discharge line 5 is connected to a control surface 28 of the load-sensing control valve 20 acting in the direction of the control position 20a. The load-sensing control valve 20 is acted upon by the highest load pressure of the consumers in the direction of an increase in the discharge volume of the pump 2. For this purpose, a control line 29 connected to the load pressure signaling line 10 is connected to a control surface 30 of the load-sensing control valve 20 acting in the direction of the control position 20b. The load-sensing control valve 20 is further subjected to a load-sensing control pressure difference Δp LSwhich, together with the highest load pressure, acts in the direction of the control position 20b. The load-sensing control valve 20 is acted upon by the discharge pressure present in the control line 27 into the control position 20a acting in the direction of reducing the delivery volume of the pump 2, when the discharge pressure of the pump 2 is the sum of the highest load pressure of the consumers V present in the control line 29 and the load-sensing control pressure difference Δp LS The load-sensing control valve 20 continues to be acted upon by springs 24a, 24b.

[0042] According to the invention, the load-sensing control pressure difference Δp LSof the load-sensing control valve 20 is variable and adjustable. For this purpose, an adjustable preset force can be generated on the load-sensing control valve 20, acting in the direction of increasing the delivery volume of the pump 2. To generate the adjustable preset force, a pilot valve 31 is provided in the illustrated embodiment, which is connected to a pressure source 35 on the inlet side and generates a control pressure and thus a preset force on the outlet side, which acts on the load-sensing control valve 20 in the control position 20b acting in the direction of increasing the delivery volume of the pump 2. The pressure source 35 is designed, for example, as a feed pump of the drive system 1. The pressure source 35 is also drivingly connected to the drive motor M for drive purposes.

[0043] In the illustrated embodiment, the pilot valve 31 is designed as a pressure reducing valve 32 with a variable set pressure. In the illustrated embodiment, the pilot valve 31 is electrically variable in individual pressure and, for this purpose, has an electrical actuating device 33, for example, a magnet designed as a proportional solenoid.

[0044] The electrical actuating device 33 is connected to an electronic control device 40 for control, which is operatively connected on the input side to actuating devices 41, for example one or more joysticks.

[0045] The manually operable actuating devices 41 serve to specify consumer movements of the consumers V of the drive system 1. The electronic control device 40 also serves to control the control valves 7 of the drive system 1 that control the consumers V. The control valve 7 has corresponding electrical actuating devices 42a, 42b for its actuation in the direction of the switching positions 7b and 7c, for example magnets, which are connected on the output side to the control device 40 and can be actuated by the control device 40 by means of a corresponding actuating signal.In the illustrated embodiment, the control valves 7 can be actuated electro-hydraulically, for which purpose the control devices 42a, 42b are formed by electrically controllable control pressure valves 43a, 43b, for example pressure reducing valves, which are connected to the pressure source 35 on the input side and generate a control pressure acting on the control valve 7 on the output side.

[0046] The control device 12 further comprises a load pressure pressure cut-off valve 50, which is assigned to the load pressure signaling line 10 carrying the highest load pressure of the consumers to a limit opening pressure p LS is set.

[0047] The load pressure pressure cut-off valve 50 is arranged in a connecting line 51 which leads from the load pressure signaling line 10 to the container 4.

[0048] The load pressure cut-off valve 50 is designed as a pressure relief valve that is biased into a blocking position by a spring 52 and into an open position by the load pressure present in the load pressure signaling line 10. For this purpose, a control line 53 connected to the load pressure signaling line 10 is connected to a control surface 54 of the load pressure cut-off valve 50 acting in the direction of the open position. The load pressure cut-off valve 50 is biased into the open position by the highest load pressure of the consumer present in the control line 53 when the highest load pressure of the consumer present in the control line 53 exceeds the limit opening pressure p LS exceeds.

[0049] According to the invention, the limit opening pressure p LSof the load pressure cut-off valve 50 is variable and adjustable. For this purpose, an adjustable preset force acting in the direction of the open position can be generated on the load pressure cut-off valve 50. To generate the adjustable preset force, a pilot valve 55 is provided in the illustrated embodiment. The pilot valve 55 is connected to the pressure source 35 on the inlet side and generates a control pressure and thus a preset force on the outlet side, which acts on the load pressure cut-off valve 50 in the direction of the open position.

[0050] In the illustrated embodiment, the pilot valve 55 is designed as a pressure reducing valve 56 with a variable set pressure. In the illustrated embodiment, the pilot valve 55 is electrically variable in its set pressure and, for this purpose, has an electrical actuating device 57, for example, a magnet designed as a proportional solenoid.

[0051] The electrical actuating device 57 is connected to the electronic control device 40 for control purposes.

[0052] The control device 12 further comprises a relief valve 60 which controls the connection of the delivery line 5 of the pump 2 to the container 4.

[0053] The relief valve 60 is arranged in a connecting line 61 connecting the delivery line 5 to the container 4. The relief valve 60 is designed as a control valve that throttles in intermediate positions and has a blocking position 60a and a flow position 60b.

[0054] The relief valve 60 is acted upon by the discharge pressure of the pump 2 in the direction of the flow position 60b. For this purpose, a control line 62 connected to the discharge line 5 is connected to a control surface 63 of the relief valve 60 acting in the direction of the flow position 60b. The relief valve 60 is acted upon by the highest load pressure of the consumers in the direction of the blocking position 60a. For this purpose, a control line 64 connected to the load pressure signaling line 10 is connected to a control surface 65 of the relief valve 60 acting in the direction of the blocking position 60a. The relief valve 60 is further subjected to a relief pressure difference Δp UDWwhich, together with the highest load pressure, acts in the direction of the blocking position 60a. The relief valve 60 is acted upon by the discharge pressure present in the control line 62 into the flow position 60b when the discharge pressure of the pump is the sum of the highest load pressure of the consumer V present in the control line 64 and the relief pressure difference Δp UDW The relief valve 60 continues to be acted upon by springs 66a, 66b.

[0055] According to the invention, the relief pressure difference Δp UDWof the relief valve 60 is variable and adjustable. For this purpose, an adjustable preset force acting in the direction of the blocking position 60a can be generated on the relief valve 60. To generate the adjustable preset force, a pilot valve 70 is provided in the illustrated embodiment. The pilot valve 70 is connected to the pressure source 35 on the inlet side and generates a control pressure and thus a preset force on the outlet side, which acts on the relief valve 60 in the direction of the blocking position 60a.

[0056] In the illustrated embodiment, the pilot valve 70 is designed as a pressure reducing valve 71 with a variable set pressure. In the illustrated embodiment, the pilot valve 70 is electrically variable in its set pressure and, for this purpose, has an electrical actuating device 72, for example, a magnet designed as a proportional solenoid.

[0057] The electrical actuating device 72 is connected to the electronic control device 40 for control purposes.

[0058] In the drive system according to the invention, variable specifications for the load-sensing control pressure difference AP can be set by means of the electronic control device 40 by controlling the pilot valves 31, 55, 70 LS of the load-sensing control valve 20, for the limit opening pressure P LS of the load pressure cut-off valve 50 and for the relief pressure difference ΔP UDW of the relief valve 60. Due to the variable specifications, the load-sensing control pressure difference ΔP LS of the load-sensing control valve 20, the limit opening pressure P LS of the load pressure cut-off valve 50 and the relief pressure difference ΔP UDW of the relief valve 60 can be changed and combined in different ways. The adjustability and adjustability of the load-sensing control pressure difference ΔP LSof the load-sensing control valve 20, the limit opening pressure P LS of the load pressure cut-off valve 50 and the relief pressure difference ΔP UDW of the relief valve 60 enables a situation-dependent specification and / or an automatic adaptation of the characteristics of the drive system 1 according to the invention.

Claims

[1] Demand-flow-controlled hydrostatic drive system (1), which comprises at least one consumer (V) which can be supplied with pressure medium by a pump (2), wherein the pump (2) is continuously adjustable in terms of its delivery volume and is operated in an open circuit, wherein the pump (2) has a delivery volume adjusting device (11) for changing the delivery volume, the setting of which can be adjusted by means of an adjusting device (12), wherein the drive system (1) comprises a load-sensing control valve (20) which is assigned to an actuating piston device (13) of the adjusting device (12) which is connected to the delivery volume adjusting device and which is dependent on the delivery pressure of the pump (2), the highest load pressure of the consumers (V) and a load-sensing control pressure difference (ΔP LS ), comprises a load pressure pressure cut-off valve (50) which is assigned to a load pressure signaling line (10) carrying the highest load pressure of the consumers (V) and is set to a limit opening pressure (PLS ) and comprises a relief valve (60) which controls the connection of a delivery line (5) of the pump (2) to a container (4) and which depends on the delivery pressure of the pump (2), the highest load pressure of the consumers (V) and a relief pressure difference (ΔP UDW ) is controlled, characterized by that the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20), the limit opening pressure (P LS ) of the load pressure cut-off valve (50) and the relief pressure difference (ΔP UDW ) of the relief valve (60) is variable and adjustable, wherein the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20), the limit opening pressure (P LS ) of the load pressure cut-off valve (50) and the relief pressure difference (ΔP UDW ) of the relief valve (60) can be changed during operation of the drive system (1). [2] Hydrostatic drive system according to claim 1, characterized by that the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20), the limit opening pressure (P LS ) of the load pressure cut-off valve (50) and the relief pressure difference (ΔP UDW ) of the relief valve (60) can be changed and specified depending on the operating situation of the drive system (1). [3] Hydrostatic drive system according to claim 1 or 2, characterized by that to change the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20), the limit opening pressure (P LS ) of the load pressure cut-off valve (50) and the relief pressure difference (ΔP UDW ) of the relief valve (60) an electronic control device (40) is provided. [4] Hydrostatic drive system according to claim 3, characterized bythat the electronic control device (40) is operatively connected on the input side to actuating devices (41) at which consumer movements of the consumers (V) can be predetermined. [5] Hydrostatic drive system according to claim 3 or 4, characterized by that the electronic control device (40) detects operating situations based on the actuation of the actuating devices (41) and the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20), the limit opening pressure (P LS ) of the load pressure cut-off valve (50) and the relief pressure difference (ΔP UDW ) of the relief valve (60) is changed according to the detected operating situation of the drive system (1). [6] Hydrostatic drive system according to one of claims 3 to 5, characterized bythat the electronic control device (40) detects the consumer's movement request typical for the situation based on the actuation of the actuating devices (41) and the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20), the limit opening pressure (P LS ) of the load pressure cut-off valve (50) and the relief pressure difference (ΔP UDW ) of the relief valve (60) to the appropriate specifications for the consumer movement requirement typical of the situation. [7] Hydrostatic drive system according to one of claims 3 to 6, characterized by that by means of the electronic control device (40) the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20) and the relief pressure difference (ΔP UDW ) of the relief valve (60) are adjusted such that the relief pressure difference (ΔP UDW) of the relief valve (60) is greater than the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20). [8] Hydrostatic drive system according to one of claims 3 to 7, characterized by that the electronic control device (40) detects a consumer movement request with a high dynamic level based on the actuation of the actuating devices (41) and, in the case of a consumer movement request with a high dynamic level, the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20) and the relief pressure difference (ΔP UDW ) of the relief valve (60) is adjusted such that the relief pressure difference (ΔP UDW ) of the relief valve (60) is smaller than the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20). [9] Hydrostatic drive system according to one of claims 3 to 8, characterized bythat the electronic control device (40) determines the limit opening pressure (P LS ) of the load pressure pressure cut-off valve (50) is changed. [10] Hydrostatic drive system according to one of claims 1 to 9, characterized by that a warm-up function of the drive system (1) is provided, in which the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20) and the relief pressure difference (ΔP UDW ) of the relief valve (60) are adjusted such that the relief pressure difference (ΔP UDW ) of the relief valve (60) is smaller than the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20). [11] Hydrostatic drive system according to one of claims 1 to 10, characterized by that a standby function of the drive system (1) is provided, in which the load-sensing control pressure difference (ΔP LS) of the load-sensing control valve (20) and the relief pressure difference (ΔP UDW ) of the relief valve (60) are set such that the pump (2) provides a standby volume flow at a standby pressure in the delivery line (5). [12] Hydrostatic drive system according to one of claims 1 to 11, characterized by that a boost function of the drive system (1) is provided, in which the limit opening pressure (P LS ) of the load pressure pressure cut-off valve (50) is raised. [13] Hydrostatic drive system according to one of claims 3 to 12, characterized by that the electronic control device (40) detects a fine control operation of the consumer (V) based on the actuation of the actuating devices (41) and for the fine control operation of the consumer (V) the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20). [14] Hydrostatic drive system according to one of claims 1 to 13, characterized by that the load-sensing control valve (20) is acted upon by the delivery pressure of the pump (2) in the direction of a reduction of the delivery volume of the pump (2) and by the highest load pressure of the consumers (V) as well as a spring device (24a; 24b) in the direction of an increase of the delivery volume of the pump (2), wherein in order to change the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20), a delivery pressure signal acting in the direction of reducing the delivery volume of the pump (2) or a load pressure signal acting in the direction of increasing the delivery volume of the pump (2) can be influenced at the load-sensing control valve (20). [15] Hydrostatic drive system according to one of claims 1 to 13, characterized by that to change the load-sensing control pressure difference (ΔP LS) of the load-sensing control valve (20) a load-sensing control pressure difference (ΔP LS ) predetermining spring device (24a; 24b) can be influenced in its setting. [16] Hydrostatic drive system according to one of claims 1 to 13, characterized by that to change the load-sensing control pressure difference (ΔP LS ) of the load-sensing control valve (20), an adjustable preset force acting in the direction of increasing the delivery volume of the pump (2) can be generated on the load-sensing control valve (20). [17] Hydrostatic drive system according to one of claims 1 to 16, characterized by that to change the limit opening pressure (P LS ) of the load pressure pressure cut-off valve (50) a spring (52) which specifies the limit opening pressure can be influenced in its setting. [18] Hydrostatic drive system according to one of claims 1 to 16, characterized by that to change the limit opening pressure (P LS) of the load pressure pressure cut-off valve (50) an adjustable preset force acting in the direction of an opening position can be generated on the load pressure pressure cut-off valve (50). [19] Hydrostatic drive system according to one of claims 1 to 18, characterized by that to change the relief pressure difference (ΔP UDW ) of the relief valve (60), a delivery pressure signal acting in the direction of a flow position (60b) on the relief signal (60) or a load pressure signal acting in the direction of a blocking position (60a) on the relief valve (60) can be influenced. [20] Hydrostatic drive system according to one of claims 1 to 18, characterized by that to change the relief pressure difference (ΔP UDW ) of the relief valve (60) a relief pressure difference (ΔP UDW ) predetermining spring device (66a; 66b) can be influenced in its setting. [21] Hydrostatic drive system according to one of claims 1 to 18, characterized by that to change the relief pressure difference (ΔP UDW ) of the relief valve (60) a preset force acting in the direction of the blocking position (60a) can be generated on the relief valve (60). [22] Hydrostatic drive system according to claim 16 or 18 or 21, characterized by that a pilot valve (31; 55; 70) connected to a pressure source (35) is provided to generate the adjustable preset force. [23] Hydrostatic drive system according to claim 22, characterized by that the pilot valve (31; 55; 70) is designed as a pressure reducing valve (32; 56; 71) with a variable set pressure.

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