Valve assembly, hydraulic system, and work machine

Abstract

The invention relates to a valve assembly (18) for a hydraulic system (16) of a work machine (10). The valve assembly has a system pressure valve (30) which is designed to set a system pressure in the hydraulic system (16). The system pressure valve (30) has a displaceable valve piston (32) and a spring (34). In an open position of the system pressure valve (30), the system pressure in the hydraulic system (16) can be reduced. The valve piston (32) is preloaded in the direction of a closed position by the spring (34). The system pressure valve (30) is designed to be pressed in the direction of the open position by the system pressure applied to the valve piston (32). The valve assembly (18) has an adjusting device (50) which is designed to hydraulically set a preload of the spring (34). The invention also relates to a hydraulic system (16) and to a work machine (10).

Description

[0001] ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24

[0002] Valve arrangement, hydraulic system and working machine

[0003] The present invention relates to a valve arrangement for a hydraulic system of a machine. Furthermore, the invention relates to a hydraulic system and a machine.

[0004] State of the art

[0005] Working machines often have a hydraulic system. This system provides power for various tasks, such as powering work. It also supplies components like buckets or other attachments. The hydraulic system is typically designed for a maximum system pressure to ensure sufficient pressure is supplied to these components under all operating conditions. This maximum system pressure is usually set by a pressure relief valve. However, this can lead to significant hydraulic losses.

[0006] There are also hydraulic systems in which the system pressure can be variably adjusted. However, the valves required for this are expensive custom-made products to ensure a sufficient flow rate. Furthermore, with such a variably adjustable system pressure, an undesirable pressure loss can occur in the event of a malfunction.

[0007] DE 10 2021 213 981 A1 describes a hydraulic control system for an automatic transmission. DE 10 2013 210 907 A1 describes an arrangement and a method for controlling a volume flow.

[0008] Description of the invention

[0009] A first aspect concerns a valve arrangement for the hydraulic system of a machine. The valve arrangement can be designed to set a system pressure of the hydraulic system, or at least to set a maximum and, alternatively or additionally, a minimum system pressure. The system pressure can be a pressure (ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24) with which consumers can be supplied. However, a pressure change before or within the actual consumer can also be provided for the supply. The system pressure can be a central pressure level that is adjusted for different consumers. The hydraulic system can have a pump by means of which the pressure supply is provided. The pump can be driven, for example, by an electric motor or an internal combustion engine. The machine can be, for example, an agricultural machine or a construction machine.Examples of agricultural machinery include a combine harvester and a tractor. Examples of construction machinery include a wheel loader and an excavator. The hydraulic system can, for example, provide work power. The hydraulic system can supply consumers, such as attachments or tools of the machine. For example, a bucket can be raised and lowered by the hydraulic system. When these consumers are used, a static pressure drop can occur. A pressure drop can also occur due to a flow rate. Accordingly, the system pressure should be raised back to a set pressure when consumers are switched on, or maintained at the set pressure. For fuel efficiency, the set pressure can be adjustable, for example, depending on the vehicle's condition. For instance, the set pressure can be predetermined based on the driving speed and whether or not attachments are fitted.A pressure increase can also occur when the use of an attachment is terminated or interrupted. For example, the system pressure may rise after a bucket movement has ended. This pressure increase can be limited or prevented to avoid pressure spikes in the hydraulic system.

[0010] The valve assembly includes a system pressure relief valve designed to regulate the system pressure in the hydraulic system. For example, the system pressure relief valve can isolate or connect a section of the hydraulic system to the pressure side of the pump. For instance, the system pressure relief valve can connect the pressure side of the pump to a vent, allowing pressure to be released to an oil reservoir. ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24

[0011] The system pressure relief valve can have a movable valve piston and a spring. The system pressure relief valve can have a valve body. The valve piston can be axially movable within the valve body. The valve piston can have a spring seat. The spring can be mounted on the spring seat. For example, the spring can rest against an axial end of the valve piston, which forms the spring seat. The spring can be a compression spring. The spring can be a helical spring. The spring can be a metallic spring. The spring can be contained within the valve body. The valve body can, for example, have contact surfaces and be a metallic element. The designation "system pressure relief valve" is for identification purposes only. The system pressure relief valve can be designed like other valves. For example, the system pressure relief valve can be designed as a 2 / 2 valve.For example, a section of the hydraulic system where system pressure is supplied can be connected to the first port of the system pressure relief valve. A vent, which is pressurized to atmospheric pressure, can be connected to the second port of the system pressure relief valve. The system pressure relief valve can have only two positions. It can also have more positions and be designed as a proportional valve. The spring can be pre-tensioned, for example, in both positions or only one of the positions of the system pressure relief valve.

[0012] The system pressure relief valve is adjustable between an open position, in which the system pressure in the hydraulic system is reduced via the system pressure relief valve, and a closed position. In the closed position, the system pressure in the hydraulic system can essentially be maintained or increased. The valve piston can be moved accordingly between the open and closed positions. In the open position, the two ports of the system pressure relief valve are fluidically connected, allowing the system pressure to be reduced. In the closed position, the two ports of the system pressure relief valve are fluidly separated, allowing the system pressure to be maintained or increased. ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24

[0013] The valve piston is biased towards the closed position by the spring. The spring thus pushes the valve piston, for example, in the direction of the closed position. The system pressure relief valve is designed to be pushed towards the open position by the system pressure acting on the valve piston. For example, the valve piston has an actuating surface on one side facing away from the spring, which is connected to a section of the hydraulic system where the system pressure acts. The system pressure pushes the valve piston, for example, axially against the spring and thus towards the open position. For example, the spring acts on the valve piston at one end, and the system pressure at the opposite end. The system pressure can also drop due to a high flow rate at consumers, causing the system pressure relief valve to close due to the spring.The force exerted by the spring and the opposing force of the system pressure determine the position of the valve piston and thus the state of the system pressure relief valve. If the force exerted on the valve piston by the system pressure is less than the spring force, the system pressure relief valve closes. Consequently, the system pressure can either rise or remain constant, as the connection to a vent is interrupted. The spring can thus define a minimum system pressure. If the force exerted on the valve piston by the system pressure is less than the spring force, the system pressure relief valve opens. Consequently, a maximum system pressure can be defined. The system pressure relief valve can also be designed as a pressure-limiting valve.

[0014] The valve assembly also includes an adjusting device. This device is designed to hydraulically adjust the spring preload. For example, the adjusting device can hydraulically move a surface on which the spring rests to adjust the preload. This hydraulic adjustment eliminates the need for additional actuators, such as electric motors, or manual adjustment. Adjustment can be performed, for example, during operation. The adjusting device does not, for instance, directly apply a hydraulic force to the valve piston to push it towards the closed position and thus adjust the system pressure.This allows the valve piston to be adjusted quickly, as, for example, no hydraulic fluid or a sluggish hydraulic adjustment system (ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24) impedes the movement of the spring and, alternatively or additionally, the valve piston. Furthermore, the hydraulic adjustment device allows for the simple implementation of variable system pressure with only a few additional components.

[0015] The valve assembly or hydraulic system may include a control device that controls the adjusting device. The control device may be designed to adjust the spring preload depending on a detected vehicle condition. This vehicle condition may, for example, correspond to a required system pressure and, alternatively or additionally, to a required flow rate.

[0016] In one embodiment of the valve arrangement, the spring may be located in a vented chamber. For example, the vented chamber may be a space at least partially bounded by the valve body. The chamber may be an interior space of the valve body. Alternatively or additionally, the chamber may be bounded by the valve piston and a bearing element for the spring, which will be described later. A vented chamber may, for example, be free of any liquid. The vented chamber may, for example, not be filled with hydraulic fluid from the hydraulic system. The vented chamber may, for example, be filled with air or another gas. This allows the spring to compress and extend freely without being hindered by any liquid. Furthermore, no liquid, for example, impedes the adjustment of the preload.

[0017] In one embodiment of the valve arrangement, the system pressure valve may have a bearing element that is hydraulically displaceable by means of the adjusting device. The spring may be mounted on the bearing element, for example, with an axial end facing away from the valve piston. The spring preload can be hydraulically adjustable by moving the bearing element. The bearing element may have a recess for receiving an end portion of the spring. The bearing element may be mounted axially movable on the valve body. The bearing element may be arranged coaxially with the valve body. The bearing element may seal with the valve body. The bearing element may at least partially delimit a space that can be pressurized by the adjusting device, optionally together with the valve body and a sealing element.Hydraulic pressure in the printable space can be adjusted by the adjusting device to move the bearing element and thus modify the spring preload. The bearing element can be axially displaceable. The spring can be positioned between the valve piston and the bearing element. The spring can, for example, be clamped between the valve piston and the bearing element. The adjustment range of the bearing element can be limited, for example, by two stops.

[0018] In one embodiment of the valve arrangement, a basic spring preload can be mechanically adjusted. For example, washers can be arranged between the spring and the valve piston, and alternatively or additionally between the spring and the bearing element. This allows the basic spring preload to be modified during manufacturing. This makes the basic preload adaptable to a specific application or tolerances. The basic preload can be applied when the hydraulic adjustment device is deactivated. The basic preload can also be adjusted, for example, by a screw. The screw can, for instance, allow for adjustment of the axial length of the bearing element. The mechanical adjustment of the basic preload can be performed, for example, in addition to the hydraulic preload adjustment.The mechanical adjustment of the basic preload cannot be performed during operation. The overall spring preload can result from a fixed mechanically predetermined basic preload and a variably hydraulically adjusted preload.

[0019] In one embodiment of the valve arrangement, the adjusting device can be operated using the system pressure. For example, the adjusting device can apply the maximum system pressure to the bearing element to increase the preload. In this case, a separate pressure supply for the adjusting device is not necessary. The adjusting device can be designed to operate at a minimum pressure specified by the system pressure valve. ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24

[0020] The system pressure, combined with a minimum spring preload set by the adjusting device, allows the spring preload to be increased even further. For example, the bearing element is fully extended, and the system pressure has dropped to the minimum pressure determined by the minimally preloaded spring. Despite this, the adjusting device can still press the bearing element against the spring towards the valve piston to increase the spring preload. For this purpose, the respective surfaces of the bearing element are adequately dimensioned with respect to the spring's strength and thus matched to the spring.

[0021] In one embodiment of the valve arrangement, the adjusting device may include a preload valve. The preload valve is designed to set a hydraulic pressure by means of which the spring preload is adjusted. For example, the preload valve is used to adjust the pressure acting on the bearing element. The designation as a preload valve is for identification purposes only. The preload valve can be designed like other valves. For example, the preload valve can be a 2 / 2 valve. The preload valve can also be a proportional valve. The preload valve can also be a 3 / 2 valve, where, for example, one of the ports is not used. Such a valve may be available more cost-effectively for this application than a 2 / 2 valve. The preload valve can be adjustable between an open and a closed position.In the open position of the preload valve, the preload of the bearing element can be increased, for example, due to rising pressure acting on the bearing element. Accordingly, the target pressure for the system pressure can be increased. In the closed position of the preload valve, the preload of the bearing element can be decreased, for example, due to falling pressure acting on the bearing element. Accordingly, the target pressure for the system pressure can be reduced. In the closed position, the pressureable space on the bearing element is connected, for example, to a vent. In the open position, the pressureable space on the bearing element is pressurized, for example, by the system pressure and thus connected, for example, to a section of the hydraulic system carrying system pressure. ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24.

[0022] The pre-tensioning valve can be normally open. This means the pre-tensioning valve can be in its default open position. In the event of a cable break or other control failure, the pre-tensioning valve can then automatically return to its open position. For example, the pre-tensioning valve is pre-tensioned towards its open position by an additional spring. This ensures that maximum system pressure is always available in the event of a fault, allowing attachments to continue operating. This way, for example, safety-critical systems can continue to be adequately supplied. Alternatively, the pre-tensioning valve can be normally closed. This allows a minimum system pressure to be set in the event of a fault.

[0023] In one embodiment of the valve arrangement, the adjusting device may include a bypass through which the oil used to preload the spring flows off. For example, the bypass can connect the pressurized space on the bearing element to a vent. The bypass may include a throttle. Controlled leakage can occur through the bypass. The bypass can improve system behavior when adjusting the preload. This can make the system behavior more robust. For example, the pressure on the bearing element, and thus the spring preload, can be regulated with a simple valve with only two switching positions. The leakage can be, for example, 1 to 2 liters per minute, while the total flow rate in the hydraulic system is approximately 500 liters per minute.

[0024] A second aspect concerns a hydraulic system of a machine. The hydraulic system can have the valve arrangement described in the first aspect, optionally without the additional shaft. The respective advantages and further features are described in the first aspect, whereby embodiments of the first aspect also constitute embodiments of the second aspect and vice versa. The system pressure in the hydraulic system can be adjusted via the valve arrangement. The hydraulic system can include a pump. The pump allows the hydraulic system to be pressurized. The hydraulic system can include a vent. The hydraulic system can include an oil reservoir. The hydraulic system can include a consumer. The hydraulic system can include a temperature sensor. (ZF Friedrichshafen AG File 305418, Friedrichshafen, 2024-09-24)

[0025] Depending on the detected temperature, a filter can, for example, be bypassed. The hydraulic system may include additional valves, such as a temperature-controlled filter bypass valve, a pressure differential-controlled filter bypass valve, a radiator safety valve, and a lubrication pressure valve. Furthermore, a pressure-reducing valve or other element may be provided if the system pressure adjustable via the valve arrangement does not meet the requirements of the machine.

[0026] A third aspect concerns a machine with the hydraulic system according to the second aspect and, alternatively or additionally, with the valve arrangement according to the first aspect. The respective advantages and further features can be found in the descriptions of the first and second aspects, whereby embodiments of the first and second aspects also constitute embodiments of the third aspect, and vice versa. The machine may have a drive train. The pump may be driven by the drive train. The machine may have a consumer. The consumer may be supplied with hydraulic pressure via the hydraulic system.

[0027] Brief description of the characters

[0028] Fig. 1 schematically illustrates a working machine with a hydraulic system and a consumer.

[0029] Fig. 2 schematically illustrates a valve arrangement for the hydraulic system of the working machine.

[0030] Detailed description of embodiments

[0031] Fig. 1 schematically illustrates a working machine 10, which here is configured as a tractor. The working machine 10 has a drive train 12, which, with an internal combustion engine or an electric motor, drives a pump 14 of a hydraulic system 16 of the working machine 10. The hydraulic system 16 also has a valve arrangement 18, further details of which are shown in Fig. 2. ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24. The hydraulic system 16 is designed to supply a consumer 20 with a system pressure. In the example shown, the consumer 20 is designed as a hydraulic cylinder by means of which a bucket 22 or fork can be moved up and down. In another embodiment, the working machine 10 has other or additional consumers. The system pressure is adjustable by the valve arrangement 18.

[0032] Figure 2 illustrates the valve assembly 18, with some parts shown in a sectional view and others only schematically. The valve assembly 18 includes a system pressure valve 30. The system pressure valve 30 is designed to adjust the system pressure in the hydraulic system 16. The system pressure valve 30 has a movable valve piston 32, a spring 34, and a valve body 36. The valve piston 32 is mounted to be axially displaceable along its longitudinal extent in the valve body 36.

[0033] The system pressure relief valve 30 is adjustable between an open position, in which the system pressure in the hydraulic system 16 is reduced via the system pressure relief valve 30, and a closed position. The closed position is illustrated in Fig. 2, where the valve piston 32 is located to the right in the valve body 36 in the plane of Fig. 2. The system pressure relief valve 30 has a first port 38, which is connected to a section of the hydraulic system 16 where the system pressure is present. The system pressure relief valve 30 has a second port 40, which is connected to a vent of the hydraulic system 16. In the closed position, the two ports 38 and 40 are fluidically separated from each other, at least at the system pressure relief valve 30. In the open position, the valve piston 32 is displaced to the left in the plane of Fig. 2 relative to the valve body 36 and the position shown in Fig. 2.In the open position, the two ports 38 and 40 are fluidically connected, at least at the system pressure valve 30, thereby reducing the pressure in the section of the hydraulic system 16 relative to the system pressure. This allows a desired setpoint pressure for the system pressure to be adjusted.

[0034] The valve piston 32 is biased towards the closed position by the spring 34. For this purpose, the spring 34 is supported against the valve piston 32 in a recess of the valve piston 32 facing the piston (ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24) with one axial end section. At an axially opposite end section, the spring 34 is supported in a recess of a bearing element 42. The bearing element 42 is hydraulically axially movable, as will be explained further below. At one axial end facing away from the spring 34, the valve piston 32 is acted upon by the system pressure in a region 44. The system pressure valve 30 is designed to be pressed towards the open position by the system pressure acting on the valve piston 32 in region 44.The spring force acting on the valve piston 32 and the opposing hydraulic force at area 44 determine whether the system pressure valve 30 is open or closed. This allows the system pressure to be set.

[0035] The valve assembly 18 further comprises an adjusting device 50, which is designed to hydraulically adjust the preload of the spring 34. This adjustment is performed during operation of the machine 10, allowing a variable setpoint for the system pressure to be specified. For this purpose, the bearing element 42 is hydraulically displaceable along the same axis as the valve piston 32 and seals against the valve piston 32. A sealing element 52 is fixed to the valve body 36 on a side axially opposite the spring 34. The valve body 36, the bearing element 42, and the sealing element 52 thus form a chamber 54 that can be pressurized by the adjusting device 50. The pressure in the chamber 54 is adjustable, thereby allowing the bearing element 42 to be displaced. The spring 34, mounted on the bearing element 42, can thus be additionally compressed or extended to change the preload.This allows a force to be modified at which the system pressure valve 30 opens or closes, thus also allowing the setpoint for the system pressure to be adjusted.

[0036] The adjusting device 50 has a pre-charge valve 56 designed as a 2 / 2-way valve for adjusting the pressure in chamber 54. The pre-charge valve 56 is normally open. The pre-charge valve 56 is supplied with the system pressure. In the event of a failure, the current system pressure is applied to chamber 54, thereby increasing the pre-charge and also the system pressure up to a maximum system pressure. Chamber 54 is also connected to a bypass 58 (ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24).

[0037] Throttle 60 is connected to the vent, here via the second port 40 of the system pressure valve 30. Due to the controlled leakage of oil at this point, which pre-tensions the spring 34, the system behavior can be particularly robust and the position of the bearing element 42 can be easily adjusted. Overall, a variable system pressure can thus be provided using simple standard components.

[0038] The spring 34 is arranged in a vented chamber 62. In one embodiment, the vented chamber 62 is connected to the vent, and in another embodiment, it is a sealed, gas-filled chamber. In this embodiment, the vented chamber 62 is not filled with hydraulic fluid. The bearing element 42 seals the printable chamber 54 from the vented chamber 62 at the valve body 36. Furthermore, the valve piston 32 seals the vented chamber 62 against the two connections 38 and 40 of the system pressure valve 30. Because of the vented chamber 62, no fluid impedes the compression and extension of the spring 34. In addition, the bearing element 42 can be moved quickly, since gas in the vented chamber 62 can be compressed or expanded and can alternatively or additionally flow in or out quickly. This prevents pressure spikes.In contrast, in a space 62 filled with hydraulic fluid, the hydraulic fluid would first have to flow in or out, which could significantly slow down the movement of the bearing element 42.

[0039] The spring force 34 and the forces acting on the bearing element 42 to displace it and increase the preload are coordinated. With a minimum system pressure, which can be set by the system pressure valve 30, and a minimum preload of the spring 34 set by the adjusting device 50, the force that can act on the bearing element 42 through the space 54 pressurized with this minimum system pressure is still sufficiently large to increase the preload of the spring 34.

[0040] A basic preload of the spring 34 is mechanically adjustable at the factory. Thus, with the space 54 unprinted and the bearing element 42, as shown in Fig. 2, shifted fully to the left, the spring 34 is still preloaded and therefore clamped between the bearing element 42 and the valve piston 32 in the closed position. This basic preload of the spring 34 can be mechanically adjusted by changing the distance between a bearing surface of the spring 34 on the bearing element 42 and a bearing surface of the spring 34 on the valve piston 32. In the illustrated embodiment, two washers 64 are inserted between the spring 34 and its bearing surface on the valve piston 32 for this purpose. The basic preload can be predetermined by the number and thickness of these washers 64 during assembly of the system pressure valve 30.In another embodiment, the washers 64 are arranged alternatively or additionally between the spring 34 and its bearing surface on the bearing element 42. The basic tension is then modified during operation by the adjusting device 50.

[0041] ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24

[0042] Reference mark

[0043] 10 working machine

[0044] 12 Powertrain

[0045] 14 Pump

[0046] 16 Hydraulic system

[0047] 18 Valve arrangement

[0048] 20 consumers

[0049] 22 shovels

[0050] 30 System pressure valve

[0051] 32 valve pistons

[0052] 34 spring

[0053] 36 valve bodies

[0054] 38 First connection

[0055] 40 Second connection

[0056] 42 Bearing element

[0057] 44 area

[0058] 50 Adjustment device

[0059] 52 Locking element

[0060] 54 Printable Space

[0061] 56 Pre-tensioning valve

[0062] 58 Bypass

[0063] 60 Throttle

[0064] 62 Ventilated room

[0065] 64 washers

Claims

ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24 Patent claims 1. Valve arrangement (18) for a hydraulic system (16) of a working machine (10), wherein the valve arrangement comprises a system pressure valve (30) designed to adjust a system pressure in the hydraulic system (16), wherein the system pressure valve (30) comprises a movable valve piston (32) and a spring (34), wherein the system pressure valve (30) is adjustable between an open position, in which the system pressure in the hydraulic system (16) is reduced via the system pressure valve (30), and a closed position, wherein the valve piston (32) is biased by the spring (34) in the direction of the closed position, wherein the system pressure valve (30) is designed to be pressed in the direction of the open position by the system pressure acting on the valve piston (32), wherein the valve arrangement (18) further comprises an adjusting device (50) designed to hydraulically adjust a preload of the spring (34).

2. Valve arrangement (18) according to claim 1 , characterized in that the spring (34) is arranged in a vented space (62).

3. Valve arrangement (18) according to claim 1 or 2, characterized in that the system pressure valve (30) has a bearing element (42) which can be hydraulically displaced by means of the adjusting device (50), on which the spring (34) is mounted, wherein a preload of the spring (34) can be adjusted by moving the bearing element (42).

4. Valve arrangement (18) according to one of the preceding claims, characterized in that a basic preload of the spring (34) is mechanically set.

5. Valve arrangement (18) according to one of the preceding claims, characterized in that the adjusting device (50) is operated with the system pressure and is designed to be able to further increase the preload of the spring (34) when a minimum system pressure is specified by the system pressure valve (30) and a minimum preload of the spring (34) is set by the adjusting device (50). ZF Friedrichshafen AG File 305418 Friedrichshafen 2024-09-24 6. Valve arrangement (18) according to one of the preceding claims, characterized in that the adjusting device (50) has a preload valve (56) which is configured to set a hydraulic pressure by means of which the preload of the spring (34) is set, wherein the preload valve (56) is normally open.

7. Valve arrangement (18) according to one of the preceding claims, characterized in that the adjusting device (50) has a bypass (58) through which oil, with which the spring (34) is pre-tensioned, flows away.

8. Hydraulic system (16) of a working machine (10) with a valve arrangement (18) according to one of the preceding claims, wherein a system pressure is adjustable with the valve arrangement (18).

9. Working machine (10) with a hydraulic system (16) according to claim 6 and a consumer (20) which can be supplied hydraulically with the system pressure through the hydraulic system (16).

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