Hydrostatic drive system with pressure medium reservoir

Abstract

A hydrostatic drive system includes a hydraulic pump driven by a drive motor that generates a primary flow to supply a working load of the drive system and provides a secondary flow to load a pressure medium reservoir. A preload valve is provided, which is connected on the input side to the delivery line of the hydraulic pump and on the output side to a primary output line conducting the primary flow and to a secondary output line leading to the pressure medium reservoir and conducting the secondary flow. The preloading valve connects the conveying pipeline of the hydraulic pump with the main output pipeline and cuts off the auxiliary output pipeline at the first control position and connects the conveying pipeline of the hydraulic pump with the auxiliary output pipeline and cuts off the main output pipeline at the second control position. A reservoir loading valve is arranged in the secondary output line. The reservoir loading valve is designed as a motorized switching valve having a first switching position, in which the secondary outlet line is open, and a second switching position, in which a section of the secondary outlet line connected to the pressure medium reservoir is unloaded to the container.

Description

Technical Field

[0001] This invention relates to a hydrostatic drive system, comprising a hydraulic pump driven by a drive motor, wherein the hydraulic pump generates a main flow to supply at least one working load of the drive system and provides a secondary flow to load a pressure medium reservoir, wherein a preload valve is provided, which is connected on the input side to the delivery line of the hydraulic pump, and on the output side to a main output line guiding the main flow and a secondary output line guiding the secondary flow to the pressure medium reservoir, wherein the preload valve connects the delivery line of the hydraulic pump to the main output line and disconnects the secondary output line in a first control position, and connects the delivery line of the hydraulic pump to the secondary output line and disconnects the main output line in a second control position, wherein a reservoir loading valve is arranged in the secondary output line. Background Technology

[0002] This type of drive system is used in mobile work machinery, such as industrial trucks. A pressure medium reservoir is used to provide supply pressure to the drive system, such as a supply pressure. It is known to load the pressure medium reservoir using a hydraulic pump (which generates a main flow to supply at least one working load of the drive system, such as a working hydraulic system), by using a preload valve connected on the input side to the hydraulic pump's delivery line and on the output side to a main output line that guides the main flow and a secondary output line that guides the secondary flow to the pressure medium reservoir.

[0003] By using a pressure medium reservoir, a separate hydraulic pump that generates supply pressure for the drive system can be eliminated.

[0004] In known drive systems, an electronically controlled proportional pressure reducing valve is used to control the loading operation of a pressure medium reservoir. This valve is located in a secondary output line and controlled by an electronic control unit. This electronic control unit is connected on its input side to a sensor that detects the loading pressure of the reservoir. Thus, the loading of the pressure medium reservoir is controlled accordingly by adjusting the proportional pressure reducing valve based on the loading pressure detected by the sensor. Here, during loading, the proportional pressure reducing valve's electronically controlled predetermined pressure setting limits the loading pressure of the reservoir and ensures its safety.

[0005] Proportional pressure reducing valves are typically damped via orifices or nozzles to reduce vibration during their control. However, orifices or nozzles designed for damping proportional pressure reducing valves can cause a time delay in their response behavior at lower temperatures of the pressure medium. This means that the activation of the reservoir loading operation takes longer than required, resulting in unnecessarily prolonged operation of the hydraulic pump and, if the drive motor is designed as an electric motor powered by the traction battery of the work equipment, unnecessarily prolonged draw power from the traction battery. Because the actual pressure of the proportional pressure reducing valve is lower than the current specification of its electrical control current, the flow delivered by the hydraulic pump during this period will not be delivered to the pressure medium reservoir but will leak into the container through the preload valve.

[0006] Another drawback of using a proportional pressure reducing valve as a reservoir loading valve is that a predetermined value of electrical control current is required to achieve a certain pressure value as the loading pressure of the pressure medium reservoir. When the pressure medium temperature is high, the predetermined value of the electrical control current may be insufficient to reach the required pressure level in the pressure medium reservoir. Therefore, the shut-off pressure detected by the pressure sensor that monitors the loading pressure of the pressure medium reservoir will no longer be detected, and the hydraulic pump will continue to operate.

[0007] Furthermore, the electronically controlled proportional pressure reducing valve has a high structural cost and manufacturing cost for its function as a storage loading valve. Summary of the Invention

[0008] The objective of this invention is to provide a drive system of the type described at the beginning that improves upon the aforementioned drawbacks.

[0009] According to the present invention, the task is solved by configuring the storage loading valve as an electrically operated switching valve having a first switching position and a second switching position, wherein in the first switching position the secondary output line is open, and in the second switching position the section of the secondary output line connected to the pressure medium storage container is unloaded toward the container.

[0010] Therefore, according to the present invention, an electrically operated switching valve is provided as a storage loading valve, and this switching valve is arranged in the secondary output pipeline. Compared with an electrically controlled proportional pressure reducing valve, this electrically operated switching valve has a less complex structure and lower manufacturing cost.

[0011] Furthermore, the electric switching valve has only two defined switching positions, namely the first switching position and the second switching position. Therefore, the switching valve is not easily affected by vibration, and there is no need to dampen the switching valve through a throttling device or an air port. Thus, under low temperature conditions, the switching behavior of the switching valve will not have switching delay and related disadvantages.

[0012] Furthermore, the first switching position of the switching valve can be achieved in a simple way: the switching pressure can be reliably reached under high temperature conditions of the pressure medium, and the storage tank loading operation can be terminated by stopping the operation of the hydraulic pump at this switching pressure.

[0013] According to an advantageous embodiment of the invention, the switching valve is designed as a three-port, two-position, switching valve, with the first port connected to the section of the secondary output line connected to the preload valve, the second port connected to the section of the secondary output line connected to the pressure medium reservoir, and the third port connected to the container line leading to the container. This three-port, two-position, switching valve allows for a simple reservoir loading valve with minimal structural cost and low manufacturing cost.

[0014] According to an advantageous embodiment of the invention, the switching valve is loaded to a second switching position by a spring device and actuated to a first switching position by an electrical actuation device, particularly a switching magnet. By controlling the electrical actuation device, the switching valve can be easily and safely actuated to the first switching position for loading and operation of the pressure medium reservoir.

[0015] According to an advantageous embodiment of the invention, the switching valve is controlled by an electronic control device, which is operatively connected on its input side to a pressure sensor device that detects the pressure in the pressure medium reservoir. Therefore, the electronic control device can operate the switching valve based on the pressure in the pressure medium reservoir measured by the pressure sensor device, thereby easily initiating and terminating the loading operation of the pressure medium reservoir.

[0016] According to an advantageous embodiment of the invention, the drive motor is designed as an electric motor, which is operatively connected to an electronic control device for control. With the electronic control device, when the drive motor is designed as an electric motor, the electric motor can be easily switched on and off, or its speed controlled, based on the loading pressure of the pressure medium reservoir detected by the pressure sensor device, so as to load the pressure medium reservoir with the pressure medium delivered by the hydraulic pump.

[0017] According to an advantageous embodiment of the invention, a pressure limiting valve is provided to protect the loading pressure of the pressure medium reservoir.

[0018] According to an advantageous embodiment of the invention, a pressure limiting valve is connected to a control line on the input side and to a container line on the output side. The control line extends from the section of the secondary output line connected to the pressure medium reservoir to a control pressure surface of a preload valve, which loads the preload valve toward a second control position. Thus, the pressure in the section of the secondary output line connected to the pressure medium reservoir can be easily protected by the pressure limiting valve, wherein when the pressure limiting valve is open, the control pressure surface of the preload valve that loads the preload valve toward the second control position is unloaded from the container, thereby loading the preload valve to the first control position.

[0019] According to an advantageous embodiment of the invention, a pressure limiting valve is connected on the input side to the section of the secondary output line connected to the pressure medium reservoir and on the output side to a control pressure line leading to a control pressure surface of a switching valve, which loads the switching valve toward a second switching position. Thus, the pressure in the section of the secondary output line connected to the pressure medium reservoir can be protected in a simple manner by means of a pressure limiting valve, wherein the switching valve is actuated to the second switching position when the pressure limiting valve is open.

[0020] According to an advantageous embodiment of the invention, the control pressure line is unloaded into the container via an orifice device. Thus, the control pressure line can be unloaded into the container in a simple manner via the orifice device.

[0021] The present invention also relates to an industrial truck having a hydrostatic drive system according to the invention, wherein a working hydraulic system and / or a steering hydraulic system are provided as the working load, and a pressure medium reservoir is used as a pressure source for the drive system, supplying pressure to a pilot valve of a control directional valve of the working hydraulic system and / or to the hydraulic braking device of the industrial truck. According to the invention, the reservoir pressurization valve in the secondary output line is designed as a switching valve; therefore, in the industrial truck, a hydraulic loading circuit for the pressure medium reservoir used as a pressure source for the drive system can be provided in a cost-effective manner with minimal structural overhead.

[0022] A particular advantage is that industrial trucks have battery-electric drive systems.

[0023] This invention has a number of advantages.

[0024] The storage loading valve, designed as an electrically switching valve, is simple in structure, cost-effective, and robust.

[0025] Storage loading valves designed as electrically switchable valves have only two defined switching positions and are not prone to vibration because of the limited number of switching positions. Therefore, storage loading valves designed as electrically switchable valves do not require damping measures in the form of orifices or nozzles.

[0026] Since there is no damping mechanism and no damping is required, the reservoir loading valve, designed as an electrically switching valve, also has no time delay in the case of cold pressure media, and therefore does not cause unnecessary power / energy loss due to flow to the container. Attached Figure Description

[0027] Further advantages and details of the invention will be described in detail with reference to the embodiments shown in the schematic diagrams. Hereinafter:

[0028] Figure 1 A circuit diagram of a first embodiment of a drive system according to the present invention is shown;

[0029] Figure 2 A circuit diagram showing a second embodiment of the drive system according to the present invention is shown; and

[0030] Figure 3 A circuit diagram of a third embodiment of the drive system according to the present invention is shown.

[0031] Figures 1 to 3 A circuit diagram of the hydrostatic drive system 1 according to the present invention is shown. Identical components are labeled with the same reference numerals. Detailed Implementation

[0032] The hydrostatic drive system 1 has a hydraulic pump 2 driven by a drive motor, which operates in an open circuit. In the illustrated embodiment, the drive motor M is configured as an electric motor. The hydraulic pump 2 draws pressure medium from a container 3 and inputs the pressure medium into a delivery line 4. The hydraulic pump 2 generates a main flow or main volumetric flow HV and a secondary flow or secondary volumetric flow NV, wherein the main flow is used to supply at least one working load A of the drive system 1, and the secondary flow is used to load (Laden) the pressure medium reservoir 5.

[0033] Drive system 1 has a working hydraulic system and / or steering hydraulic system of an industrial truck (preferably an industrial truck with a battery-electric drive system) as a working load A. Pressure medium reservoir 5 serves as a pressure source for drive system 1, supplying pressure to the pilot valve V of the control directional valve of the working hydraulic system and / or to the hydraulic braking device B of the industrial truck. The pilot valve V is preferably designed as an electrically controlled pilot valve, which generates control pressure for the control directional valve of the working hydraulic system through the loading pressure (Ladedruck) of pressure medium reservoir 5. The control directional valve is used to control the direction and speed of movement of the load in the working hydraulic system.

[0034] The preload valve 6 is connected on the input side to the delivery line 4 of the hydraulic pump 2 and on the output side to the main output line 7 that guides the main flow HV and to the auxiliary output line 8 that leads to the pressure medium reservoir 5, in which the auxiliary flow NV is guided.

[0035] The preload valve 6 has a first control position 6a and a second control position 6b. In the first control position, the delivery line 4 of the hydraulic pump 2 is connected to the main output line 7 and the auxiliary output line 8 is closed. In the second control position, the delivery line 4 of the hydraulic pump 2 is connected to the auxiliary output line 8 and the main output line 7 is closed. In the illustrated embodiment, the preload valve 6 is designed as a proportional valve that can be throttled in an intermediate position and has an intermediate position 6c, in which the delivery line 4 of the hydraulic pump 2 is connected to both the main output line 7 and the auxiliary output line 8.

[0036] A storage loading valve 20 is arranged in the secondary output pipeline 8.

[0037] The storage loading valve 20 is designed as an electrically operated switching valve 21, which has a first switching position 21a and a second switching position 21b. In the first switching position, the secondary output pipeline 8 is opened, and in the second switching position, the section 8a of the secondary output pipeline 8 connected to the pressure medium storage tank 5 unloads towards the container 3.

[0038] The switching valve 21 is designed as a three-port, two-position switching valve. It is connected at the first port to the section 8b of the secondary output line 8 that connects to the preload valve 6, at the second port to the section 8a of the secondary output line 8 that connects to the pressure medium reservoir 5, and at the third port to the container line 22 leading to the container 3.

[0039] At the first switching position 21a of the switching valve 21, the first interface is connected to the second interface and the third interface is closed, so the auxiliary output pipeline 8 is open and the connection with the container pipeline 22 is closed.

[0040] At the second switching position 21b of the switching valve 21, the first interface is closed, and the second interface is connected to the third interface. Therefore, the section 8a of the auxiliary output pipeline 8 connected to the pressure medium container 5 is unloaded to the container 3, and the section 8b of the auxiliary output pipeline 8 connected to the preload valve 6 is closed.

[0041] The switching valve 21 is loaded to the second switching position 21b by the spring device 23 and operated to the first switching position 21a by the electrical operating device 24 (e.g., switching magnet).

[0042] The switching valve 21 is controlled by an electronic control unit 25, which is connected on the input side to a pressure sensor device 26 that detects the loading pressure in the pressure medium reservoir 5. The electronic control unit 25 is also connected to an electrical operating device 24 for control and operation.

[0043] In addition, for control purposes, the electronic control unit 25 is also connected to the drive motor M, which is designed as an electric motor.

[0044] The preload valve 6 is loaded towards the first control position 6a by the pressure in section 8b of the secondary output line 8. For this purpose, a control line 9 is provided, which extends from section 8b of the secondary output line 8 to the control pressure surface of the preload valve 6, which acts towards the first control position 6a. A throttling device 10, such as a nozzle or orifice, is provided in the control line 9.

[0045] The preload valve 6 is loaded by the spring device 11 toward the second control position 6b.

[0046] The control line 12, which is connected to section 8a of the secondary output line 8, is connected to a control pressure surface that acts in the direction of the second control position 6b.

[0047] A shut-off valve 30, which opens toward the pressure medium reservoir 5, is arranged in section 8a of the secondary output line 8 leading to the pressure medium reservoir 5. In the illustrated embodiment, the shut-off valve 30 is designed as a spring-loaded check valve. The shut-off valve 30 prevents the pressure medium reservoir 5 from emptying into the delivery line 4.

[0048] To protect the maximum permissible loading pressure of the pressure medium reservoir 5, a pressure limiting valve 40 is provided.

[0049] exist Figure 1 In this embodiment, the pressure limiting valve 40 is connected to the control line 12 on the input side and to the container line 22 on the output side. The control line extends from the section 8a of the secondary output line 8 connected to the pressure medium reservoir 5 to the control pressure surface of the preload valve 6, which loads the preload valve 6 toward the second control position 6b. The spring chamber of the pressure limiting valve 40 is connected to the container line 22 via the unloading line 41.

[0050] exist Figure 2 and Figure 3 In this embodiment, the pressure limiting valve 40 is connected on the input side to section 8a of the auxiliary output line 8 connected to the pressure medium storage 5 and on the output side to the control pressure line 45, which leads to the control pressure surface of the switching valve 21, which loads the switching valve 21 toward the second switching position 21b.

[0051] The control pressure line 45 unloads into the container 3 through the orifice device 46. For this purpose, a branch line 47 is provided, which connects the control pressure line 45 to the container line 22 and has the orifice device 46 arranged in the branch line.

[0052] exist Figure 2 and Figure 3 In the middle, the spring chamber of the pressure limiting valve 40 is connected to the container pipe 22 through the unloading pipe 41.

[0053] exist Figure 2 In the middle, the pressure limiting valve 40 is connected on the input side downstream of the shut-off valve 30 to section 8a of the auxiliary output pipeline 8, which is connected to the pressure medium container 5.

[0054] exist Figure 3 In the middle, the pressure limiting valve 40 is connected on the input side upstream of the shut-off valve 30 to section 8a of the auxiliary output pipeline 8, which is connected to the pressure medium container 5.

[0055] Figures 1 to 3 The operating mode of drive system 1 is as follows.

[0056] With the help of the pressure sensor device 26, the electronic control device 25 can identify the loading status of the pressure medium reservoir 5 and start and stop the loading process of the pressure medium reservoir 5 by controlling the drive motor M and the switching valve 21.

[0057] If the loading pressure of the pressure medium reservoir 5 detected by the pressure sensor device 26 is lower than the predetermined lower pressure threshold in the control device 25, the control device 25 initiates the loading of the pressure medium reservoir 5 by controlling the drive motor M and manipulating the switching valve 21 to the switching position 21a by the control actuation device 24.

[0058] The hydraulic pump 2, driven by the drive motor M, delivers the pressure medium to the auxiliary output pipeline 8 when the preload valve 6 is in the control position 6b, and delivers the pressure medium to the pressure medium storage tank 5 through the switching valve 21 in the switching position 21a and the open shut-off valve 30, thereby loading the pressure medium storage tank 5.

[0059] The drive motor M and the switching valve 21 are controlled by the control device 25 for such a long period of time until the pressure sensor device 26 detects that the loading pressure of the pressure medium reservoir 5 has reached a predetermined upper pressure threshold. When the upper pressure threshold is reached, the electronic control device 25 terminates the loading of the pressure medium reservoir 5 by terminating the control of the motor M and the control of the actuation device 24 of the switching valve 21, thereby actuating the switching valve 21 to the switching position 21b by the spring device 23.

[0060] exist Figure 1In the illustrated embodiment, if the pressure limiting valve 40 responds in the pressurization mode of the pressure medium reservoir 5, then in Figure 1 When the pressure limiting valve 40 is opened, the section 8a of the control line 12 and the auxiliary output line 8 to the container line 22 is unloaded. This causes power loss because when the switching valve 21 is actuated to the switching position 21a, the flow delivered by the hydraulic pump 2 flows to the container 3 through the open pressure limiting valve 40.

[0061] exist Figure 2 and Figure 3 In this embodiment, if the pressure limiting valve 40 responds in the loading mode of the pressure medium reservoir 5, the switching valve 21 is loaded to the switching position 21b by the pressure in the control pressure line 45 when the pressure limiting valve 40 is open. This minimizes the impact on the switching valve. Figure 1 The power loss that occurs in the embodiments.

Claims

1. A hydrostatic drive system (1) comprising a hydraulic pump (2) driven by a drive motor (M), wherein the hydraulic pump (2) generates a main flow (HV) to supply at least one working load (A) of the drive system (1) and provides a secondary flow (NV) to load a pressure medium reservoir (5), wherein, A preload valve (6) is provided, which is connected on the input side to the delivery line (4) of the hydraulic pump (2) and on the output side to the main output line (7) that guides the main flow (HV) and the auxiliary output line (8) that leads to the pressure medium reservoir (5) and guides the auxiliary flow (NV). The preload valve (6) connects the delivery line (4) of the hydraulic pump (2) to the main output line (7) and shuts off the auxiliary output line (8) in a first control position (6a) and in a second control position (6b) connects the delivery line (4) of the hydraulic pump (2) to the main output line (7) and shuts off the auxiliary output line (8). 4) Connected to the secondary output line (8) and disconnected from the main output line (7), wherein a storage loading valve (20) is arranged in the secondary output line (8), characterized in that the storage loading valve (20) is constructed as an electrically operated switching valve (21) having a first switching position (21a) and a second switching position (21b), wherein in the first switching position the secondary output line (8) is open, and in the second switching position the section (8a) of the secondary output line (8) connected to the pressure medium storage tank (5) is unloaded to the container (3).

2. The hydrostatic drive system (1) according to claim 1, characterized in that, The switching valve (21) is configured as a three-port two-position switching valve, which is connected at the first port to the section (8b) of the secondary output pipeline (8) that connects to the preload valve (6), at the second port to the section (8a) of the secondary output pipeline (8) that connects to the pressure medium reservoir (5), and at the third port to the container pipeline (22) leading to the container (3).

3. The hydrostatic drive system (1) according to claim 1 or 2, characterized in that, The switching valve (21) is loaded to the second switching position (21b) by the spring device (23) and operated to the first switching position (21a) by the electrical operating device (24), in particular the switching magnet.

4. The hydrostatic drive system (1) according to any one of claims 1 to 3, characterized in that, The switching valve (21) is controlled by an electronic control device (25), which is connected on the input side to a pressure sensor device (26) that detects the pressure in the pressure medium reservoir (5).

5. The hydrostatic drive system (1) according to claim 4, characterized in that, The drive motor (M) is an electric motor and is operatively connected to the electronic control device (25) for control.

6. The hydrostatic drive system (1) according to any one of claims 1 to 5, characterized in that, A pressure limiting valve (40) is provided to ensure the loading pressure of the pressure medium reservoir (5).

7. The hydrostatic drive system (1) according to claim 6, characterized in that, The pressure limiting valve (40) is connected to the control line (12) on the input side and to the container line (22) on the output side. The control line extends from the section (8a) of the auxiliary output line (8) connected to the pressure medium reservoir (5) to the control pressure surface of the preload valve (6), which loads the preload valve (6) toward the second control position (6b).

8. The hydrostatic drive system (1) according to claim 6, characterized in that, The pressure limiting valve (40) is connected on the input side to the section (8a) of the auxiliary output line (8) connected to the pressure medium reservoir (5) and on the output side to the control pressure line (45), which leads to the control pressure surface of the switching valve (21), which loads the switching valve (21) toward the second switching position (21b).

9. The hydrostatic drive system (1) according to claim 8, characterized in that, The control pressure line (45) unloads into the container (3) by means of the orifice device (46).

10. An industrial truck comprising a hydrostatic drive system (1) according to any one of the preceding claims, wherein, The working hydraulic system and / or steering hydraulic system are set as the working load (A), and the pressure medium reservoir (5) is used as the pressure source for the drive system (1) to supply the pilot valve of the control directional valve of the working hydraulic system (A) and / or to supply the hydraulic braking device of the industrial truck.

11. The industrial truck according to claim 10, characterized in that, This industrial truck features a battery-electric drive system.

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