Hydraulic system for excavator

Abstract

A hydraulic system of an excavator in standby mode: when a safety handle is not activated, the displacement of a main pump is controlled to be a set protection displacement, so that a standby valve is at a maximum opening area; when the safety handle is changed from not activated to activated, the displacement of the main pump is controlled to decrease from the protection displacement to a standby displacement, so that the opening area of the standby valve is ramped to decrease from the maximum opening area to a set demand opening area.

Description

Technical Field

[0001] This application relates to a standby control scheme for an excavator hydraulic system. Background Technology

[0002] During normal excavator operation, the time spent in standby mode accounts for approximately 5-10% of the total operating time. In standby mode, the engine reduces its speed to enter a low-speed range, while the hydraulic system requires a fast response. Therefore, a standby valve is installed to maintain a certain pressure and flow rate in the main pump. In one existing excavator hydraulic system, the pilot pump provides pilot oil pressure directly to the standby valve without passing through a switch valve controlled by a safety handle. This allows the standby valve to be closed to a very small degree even when the safety handle is not raised, maintaining low pressure and low flow rate in the main pump. This standby control scheme requires a direct oil path from the pilot pump to the standby valve, necessitating the creation of openings and oil passages within the main valve body leading to both the main valve control path and the standby valve. Summary of the Invention

[0003] The purpose of this application is to provide a standby control scheme for excavator hydraulic systems that simplifies the hardware structure related to excavator standby control.

[0004] Therefore, this application provides an excavator hydraulic system in one aspect, comprising:

[0005] The main pump is configured to output hydraulic oil.

[0006] Pilot pump, configured to output pilot oil pressure;

[0007] A main valve assembly includes a high-pressure oil circuit, a pilot oil circuit, a main valve, and a standby valve. The high-pressure oil circuit is configured to receive hydraulic oil from the main pump, and the pilot oil circuit is configured to receive pilot oil pressure from the pilot pump. The control-end oil pressure of the main valve and the standby valve is taken from the pilot oil circuit. The standby valve has a maximum opening area when no control-end oil pressure is received and an opening area related to the magnitude of the control-end oil pressure when control-end oil pressure is received.

[0008] The switching valve, whose position is controlled by the safety handle of the excavator, disconnects the pilot pump from the pilot oil circuit when the safety handle is not activated, and connects the pilot pump to the pilot oil circuit when the safety handle is activated.

[0009] The control unit is configured to operate in the excavator's standby mode:

[0010] When the safety handle is not activated, the displacement of the main pump is controlled to a set protection displacement, so that the standby valve is at its maximum opening area, and the protection displacement is higher than the standby displacement of the main pump.

[0011] When the safety handle changes from inactive to active, the displacement of the main pump is reduced from the protection displacement to the standby displacement, so that the opening area of ​​the standby valve is reduced from the maximum opening area to the set required opening area.

[0012] In one embodiment, the standby valve is equipped with a pilot valve, which is disposed between the control end of the standby valve and the pilot oil circuit. The control unit controls the control end oil pressure output by the pilot valve to the standby valve by controlling the opening degree of the pilot valve.

[0013] In one implementation, when the excavator is in standby mode, and the safety handle changes from inactive to active, the control unit controls the main pump's displacement to decrease stepwise from the protection displacement to the standby displacement.

[0014] In one embodiment, the protection discharge capacity is set to a proportion of the maximum discharge capacity of the main pump; or, the protection discharge capacity is set to 6 to 12 times the standby discharge capacity.

[0015] In one embodiment, the protective displacement is set based on ensuring that the main pump has a safe output pressure when the standby valve is at its maximum opening area under the standby condition of the excavator.

[0016] In one embodiment, the required opening area is set to 0.1 to 0.05 times the maximum opening area of ​​the standby valve.

[0017] In one implementation, the required opening area is set based on the pressure build-up requirements in the hydraulic system when the excavator is about to transition from standby to working condition.

[0018] In one embodiment, the protective discharge capacity is 230-300 liters / minute, and the required opening area is 6-15 square millimeters.

[0019] In one embodiment, the rate at which the standby valve decreases from the maximum opening area to the required opening area is set based on suppressing pressure fluctuations in the hydraulic system.

[0020] In one embodiment, the control unit is configured to, when the safety handle changes from active to inactive, control the displacement of the main pump to increase stepwise from the current displacement to the protection displacement, and control the opening area of ​​the standby valve to increase stepwise from the required opening area to the maximum opening area.

[0021] According to this application, in the hydraulic system of an excavator, the control oil pressure of the standby valve is drawn from the common control oil circuit in the main valve body. There is no need to form a separate opening and oil circuit for the standby valve in the main valve body to control the oil pressure. The standby control scheme of the excavator is realized through software control, thus simplifying the structure of the main valve body, simplifying the manufacturing process of the main valve body, and reducing its manufacturing cost. Attached Figure Description

[0022] The foregoing and other aspects of this application will be more fully understood and appreciated through the following detailed description with reference to the accompanying drawings, in which:

[0023] Figure 1 This is a schematic diagram of an exemplary excavator hydraulic system to which the present application applies;

[0024] Figure 2 This is an exemplary flowchart of the standby control scheme for the excavator hydraulic system according to this application. Detailed Implementation

[0025] This application generally relates to a standby control scheme for an excavator hydraulic system. An exemplary excavator hydraulic system to which this control scheme is applied... Figure 1 The central part is displayed.

[0026] See Figure 1 The excavator's hydraulic system includes a first main pump P1, a second main pump P2, and a pilot pump P3, all driven by engine 1. The first main pump P1 and the second main pump P2 supply hydraulic oil to the excavator's hydraulic actuators (not shown) via the main valve assembly Vb.

[0027] Both the first main pump P1 and the second main pump P2 are variable displacement pumps, with adjustable displacement, for example, by adjusting the swashplate angle within the pump. The displacement of each of the first main pump P1 and the second main pump P2 can vary between the maximum and minimum displacement.

[0028] Pilot pump P3 is used to supply pilot oil pressure to each main valve in the main valve assembly Vb via switching valve Vs, thereby controlling the switching of the main valves. Pilot pump P3 can have a constant output pressure, for example, 30 to 45 bar.

[0029] It should be noted that the first main pump P1 and the second main pump P2 shown in the figure are just examples. Different models of excavators may require different numbers of main pumps.

[0030] The main valve assembly Vb includes a main valve body (not shown) and various valve cores assembled within the main valve body to form individual main valves and corresponding pilot valves. The main valve body can be a single piece or a combination of multiple valve bodies.

[0031] The main valve body contains parallel first high-pressure oil passage Lh1, first low-pressure oil passage Lt1, second high-pressure oil passage Lh2, second low-pressure oil passage Lt2, pilot oil passage Lp, and pilot return oil passage Lr. The first high-pressure oil passage Lh1 is connected to the output of the first main pump P1, and the second high-pressure oil passage Lh2 is connected to the output of the second main pump P2. The first low-pressure oil passage Lt1, the second low-pressure oil passage Lt2, and the pilot return oil passage Lr are connected to the oil tank.

[0032] The pilot oil circuit Lp is connected to the output of the pilot pump P3 via the switching valve Vs. The switching valve Vs controls the connection between the pilot pump P3 and the pilot oil circuit Lp. In the illustrated example, the switching valve Vs is a two-position three-way valve, and its position is controlled by the safety handle 2. In the first position (when the safety handle 2 is inactive), the switching valve Vs is closed, disconnecting the output of the pilot pump P3 from the pilot oil circuit Lp and connecting the pilot oil circuit Lp to the oil tank. In the second position (when the safety handle 2 is raised), the switching valve Vs is open, connecting the output of the pilot pump P3 to the pilot oil circuit Lp.

[0033] The main valve assembly Vb includes exemplary main valves Vm1 and Vm2. The inlet of main valve Vm1 is connected to a first high-pressure oil circuit Lh1, and its return port is connected to a first low-pressure oil circuit Lt1 and a second low-pressure oil circuit Lt2. The inlet of main valve Vm2 is connected to a second high-pressure oil circuit Lh2, and its return port is connected to both the first and second low-pressure oil circuits Lt1 and Lt2. The working ports of main valves Vm1 and Vm2 are connected to their respective hydraulic actuators.

[0034] The two control terminals of the main valve Vm1 are connected to pilot valves Vp11 and Vp12, respectively, and the two control terminals of the main valve Vm2 are connected to pilot valves Vp21 and Vp22, respectively. These pilot valves are all electromagnetically controlled pressure reducing valves, each connected to the pilot oil circuit Lp and the pilot return oil circuit Lr. They are used to receive pilot oil pressure from the pilot oil circuit Lp, reduce the pilot oil pressure, and provide it to the corresponding control terminals of the main valves to control the valve positions and opening degrees of the main valves Vm1 and Vm2.

[0035] It is understandable that the main valve assembly Vb also includes the main valve and corresponding pilot valve for other hydraulic actuators.

[0036] The main valve assembly Vb also includes standby valves Vc1 and Vc2. The valve positions of standby valves Vc1 and Vc2 are controlled by pilot valves Vp1 and Vp2, respectively. Pilot valves Vp1 and Vp2 are electromagnetically controlled pressure reducing valves, each connected to the pilot oil circuit Lp and the pilot return oil circuit Lr. They receive pilot oil pressure from the pilot oil circuit Lp, reduce the pilot oil pressure, and supply it to the corresponding control terminals of standby valves Vc1 and Vc2 to control their valve positions and opening degrees (opening areas). Standby valves Vc1 and Vc2 are normally open valves, meaning they are in their first normal position, held at their maximum opening degree (opening area, for example, approximately 100–150 square millimeters). Upon receiving pilot oil pressure from pilot valves Vp1 and Vp2, standby valves Vc1 and Vc2 are switched to an opening degree (opening area) corresponding to the magnitude of the pilot oil pressure, or even closed.

[0037] The advantage of this main valve assembly Vb is that the oil pressure of the pilot valves Vp1 and Vp2 of the standby valves Vc1 and Vc2 and the pilot valves of each main valve are all taken from the common pilot oil circuit Lp. There is no need to form separate openings and oil circuits in the main valve body for the pilot pump P3 to directly connect to the pilot valves Vp1 and Vp2 associated with the standby valves Vc1 and Vc2 without passing through the switching valve Vs. Therefore, the number of openings and oil circuits in the main valve body is reduced.

[0038] When the excavator is in standby mode and safety handle 2 is not activated, the switch valve Vs is in the closed position. Pilot oil pressure from pilot pump P3 is not supplied to pilot oil circuit Lp. Therefore, the control terminals of standby valves Vc1 and Vc2 do not receive control oil pressure, and standby valves Vc1 and Vc2 are in the open position, connecting the first high-pressure oil circuit Lh1 with the first low-pressure oil circuit Lt1, and the second high-pressure oil circuit Lh2 with the second low-pressure oil circuit Lt2. In the excavator's standby mode, existing technology typically sets the main pumps P1 and P2 to a set standby displacement (small displacement) condition. The hydraulic oil output from the main pumps P1 and P2 flows to the oil tank through standby valves Vc1 and Vc2 respectively, resulting in low pressure in the main pumps P1 and P2, which affects their lifespan.

[0039] To avoid this situation, this application proposes a standby control scheme for excavators. The basic concept is as follows: When the excavator is in standby mode and the safety handle is not activated, the main pump is controlled to operate at a large displacement (completely opposite to the setting method in existing technologies), and the standby valve is at its maximum opening area. When the safety handle is activated, the main pump's displacement is quickly reduced from the large displacement to the set standby displacement, and the standby valve gradually decreases from its maximum opening area to the required opening area. To fully protect the main pump, this required opening area can be 0.1 to 0.05 times the maximum opening area of ​​the standby valve.

[0040] Specifically, in the excavator's standby mode, when safety handle 2 is inactive, the switch valve Vs is in the first valve position. The output oil pressure of pilot pump P3 is not supplied to the pilot oil circuit Lp, and pilot valves Vp1 and Vp2 do not supply pilot oil pressure to the control terminals of standby valves Vc1 and Vc2, causing standby valves Vc1 and Vc2 to be in the first valve position and fully open. In this state, the main pumps P1 and P2 are set to a large displacement, for example, approximately 230–300 liters / minute. To fully protect the main pumps, this large displacement can be set as a percentage of the maximum displacement of main pumps P1 and P2, for example, 50%–80%; or, this large displacement can be set to 6–12 times the standby displacement.

[0041] At this time, standby valves Vc1 and Vc2 are at their maximum opening area, for example, about 100 to 150 square millimeters.

[0042] By controlling the main pumps P1 and P2 at a large displacement, sufficient output pressure can be ensured to protect them. The large displacement of main pumps P1 and P2 is significantly higher than their respective set standby displacement. This large displacement can be determined based on ensuring that main pumps P1 and P2 have a safe output pressure (e.g., not less than 30 bar) when the standby valves Vc1 and Vc2 are at their maximum opening area under excavator standby conditions. Therefore, this large displacement can be referred to as the protective displacement.

[0043] After safety handle 2 is activated, the switching valve Vs switches to the second valve position, supplying the output oil pressure of pilot pump P3 to pilot oil circuit Lp. Pilot valves Vp1 and Vp2, based on the controlled valve core position, supply pilot oil pressure to the control terminals of standby valves Vc1 and Vc2 at a set pressure (lower than the output pressure of pilot pump P3), causing the opening area of ​​standby valves Vc1 and Vc2 to decrease from the maximum opening area to the required opening area, for example, approximately 6 to 15 square millimeters. In this state, the displacement of the main pumps P1 and P2 is rapidly (stepwise) reduced from the maximum displacement back to the set standby displacement, for example, 25 to 35 liters / minute.

[0044] The required opening area of ​​standby valves Vc1 and Vc2 can be set based on the pressure build-up requirements (response speed) of main pumps P1 and P2 in the first high-pressure oil circuit Lh1 and the second high-pressure oil circuit Lh2 when the excavator is about to enter the working condition from the standby condition.

[0045] By sloping down the standby valves Vc1 and Vc2 from their maximum opening area to the required opening area, excessive pressure fluctuations in the first high-pressure oil circuit Lh1 and the second high-pressure oil circuit Lh2 can be avoided.

[0046] The rate and extent of reduction in the opening area of ​​standby valves Vc1 and Vc2 can be achieved by controlling the magnitude of the control current applied to pilot valves Vp1 and Vp2. The control current of pilot valves Vp1 and Vp2 determines the opening degree of pilot valves Vp1 and Vp2, which in turn determines the output control pressure value after the pilot oil pressure is reduced by pilot valves Vp1 and Vp2. The output control pressure value determines the opening area of ​​standby valves Vc1 and Vc2.

[0047] After safety handle 2 is activated, the reduction of the opening area of ​​standby valves Vc1 and Vc2 and the reduction of the displacement of main pumps P1 and P2 can be initiated almost simultaneously. However, the end time of the reduction of the opening area of ​​standby valves Vc1 and Vc2 is later than the end time of the reduction of the displacement of main pumps P1 and P2. The ramp-like reduction rate of the opening area of ​​standby valves Vc1 and Vc2 is preset and adjustable, mainly to suppress the output pressure fluctuations of main pumps P1 and P2 and the pressure fluctuations in the first high-pressure oil circuit Lh1 and the second high-pressure oil circuit Lh2, so that the pressure fluctuations are kept below the set pressure fluctuation threshold.

[0048] Furthermore, under any operating condition of the excavator (working or standby), if the safety handle 2 is switched from the active to the inactive state, the switching valve Vs closes. Although the supply from the pilot pump P3 to the pilot oil circuit Lp is cut off, a certain pressure remains in the pilot oil circuit Lp. This causes the pilot valves Vp1 and Vp2 to directly switch to zero opening, allowing the opening areas of the standby valves Vc1 and Vc2 to jump directly to their maximum opening area without the need for a ramp-up increase. Simultaneously, the displacement of the main pumps P1 and P2 is rapidly (stepwise) increased from the current displacement (current working displacement or standby displacement) to the maximum displacement.

[0049] The aforementioned excavator standby control scheme is essentially a protection scheme used to protect the main pumps P1 and P2 from operating under low pressure.

[0050] It should be noted that the hydraulic system of an excavator may contain different numbers of main pumps (one or more main pumps), corresponding standby valves and high-pressure oil circuits. The control scheme of this application is applicable to the hydraulic system of an excavator with various numbers of main pumps.

[0051] The above control scheme can be executed by the excavator's control unit (not shown). This control unit executes a standby control process during the excavator's standby period. Figure 2 The diagram shows that the number of main pumps and related standby valves is not limited in this control process.

[0052] See Figure 2 In step S1, the control unit determines that the safety handle signal Flag becomes 0 (representing inactivity).

[0053] Next, in step S2, the control unit controls the main pump displacement Vg to increase to the set maximum displacement in a stepwise manner, and controls the standby valve opening area Sc to increase to the maximum opening area in a stepwise manner.

[0054] Next, in step S3, the control unit continuously monitors the changes in the safety handle signal Flag. If the safety handle signal Flag becomes 1 (representing activation), then step S4 is executed.

[0055] In step S4, the control unit controls the main pump displacement Vg to decrease stepwise to the set standby displacement, and controls the standby valve opening area Sc to decrease rampwise to the required opening area.

[0056] Next, in step S5, the control unit waits for the work command from the excavator, controls the displacement of the main pump and the valve position of the corresponding main valve based on the work command; at the same time, it monitors the full handle signal Flag, and if the full handle signal Flag becomes 0, it returns to step S1.

[0057] According to the excavator hydraulic system of this application, the control oil pressure of the standby valve is drawn from the common control oil circuit in the main valve body, eliminating the need to create a separate opening and oil circuit for controlling the oil pressure in the main valve body for the standby valve. In the standby control scheme, the standby control scheme of the excavator is implemented through software control, thus simplifying the structure of the main valve body, simplifying the manufacturing process of the main valve body, and reducing its manufacturing cost.

[0058] While this application has been described herein with reference to specific embodiments, the scope of this application is not limited to the details shown. Various modifications may be made to these details without departing from the basic principles of this application.

Claims

1. A hydraulic system for an excavator, comprising: The main pumps (P1; P2) are configured to output hydraulic oil. Pilot pump (P3) is configured to output pilot oil pressure; A main valve assembly (Vb) includes a high-pressure oil passage, a pilot oil passage, a main valve, and a standby valve. The high-pressure oil passage is configured to receive hydraulic oil from the main pump, and the pilot oil passage is configured to receive pilot oil pressure from the pilot pump. The control oil pressure of the main valve and the standby valve is taken from the pilot oil passage. The standby valve has a maximum opening area when no control oil pressure is received and an opening area related to the magnitude of the control oil pressure when control oil pressure is received. The switch valve (Vs) is controlled by the safety handle (2) of the excavator. When the safety handle is not activated, the switch valve disconnects the pilot pump from the pilot oil circuit. When the safety handle is activated, the switch valve connects the pilot pump to the pilot oil circuit. The control unit is configured to operate in the excavator's standby mode: When the safety handle is not activated, the displacement of the main pump is controlled to a set protection displacement, so that the standby valve is at its maximum opening area, and the protection displacement is higher than the standby displacement of the main pump. When the safety handle changes from inactive to active, the displacement of the main pump is reduced from the protection displacement to the standby displacement, so that the opening area of ​​the standby valve is reduced from the maximum opening area to the set required opening area.

2. The excavator hydraulic system as described in claim 1, wherein, The standby valve is equipped with a pilot valve, which is located between the control end of the standby valve and the pilot oil circuit. The control unit controls the control end oil pressure output by the pilot valve to the standby valve by controlling the opening degree of the pilot valve.

3. The excavator hydraulic system as described in claim 1, wherein, When the excavator is in standby mode, and the safety handle changes from inactive to active, the control unit controls the main pump's displacement to decrease stepwise from the protection displacement to the standby displacement.

4. The excavator hydraulic system as described in claim 1, wherein, The protection discharge capacity is set as a percentage of the maximum discharge capacity of the main pump; or, the protection discharge capacity is set as 6 to 12 times the standby discharge capacity.

5. The excavator hydraulic system as described in claim 1, wherein, The protection displacement is set based on ensuring that the main pump has a safe output pressure when the standby valve is at its maximum opening area under the standby condition of the excavator.

6. The excavator hydraulic system as described in any one of claims 1-5, wherein, The required opening area is set to 0.1 to 0.05 times the maximum opening area of ​​the standby valve.

7. The excavator hydraulic system as described in any one of claims 1-5, wherein, The required opening area is set based on the pressure build-up requirements of the hydraulic system when the excavator is about to enter the working condition from the standby condition.

8. The excavator hydraulic system as described in any one of claims 1-5, wherein, The protective discharge capacity is 230~300 liters / minute, and the required opening area is 6~15 square millimeters.

9. The excavator hydraulic system as described in any one of claims 1-5, wherein, The sloping reduction rate of the standby valve from the maximum opening area to the required opening area is set based on suppressing pressure fluctuations in the hydraulic system.

10. The excavator hydraulic system as described in any one of claims 1-5, wherein, The control unit is configured to, when the safety handle changes from active to inactive, control the main pump's displacement to increase stepwise from the current displacement to the protected displacement, and control the standby valve's opening area to increase stepwise from the required opening area to the maximum opening area.

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