Decoupling type power system of electric drive wheel loader

Abstract

A decoupling type power system of an electric drive wheel loader comprises a power battery; the first motor, the second motor and the electric cylinder are respectively powered by the power battery; the first hydraulic pump is driven by the first motor, hydraulic oil is supplied to the steering oil cylinder through the first hydraulic pump, and the steering oil cylinder is configured to drive wheels of the electrically-driven wheel loader to steer; the second hydraulic pump is driven by the second motor, hydraulic oil is supplied to the large arm oil cylinder through the second hydraulic pump, and the large arm oil cylinder is configured to drive a large arm of the electric drive wheel loader to ascend and descend; the electric cylinder is configured to drive a bucket of the electric drive wheel loader to rotate relative to a large arm. The power system has high energy efficiency.

Description

Technical Field

[0001] The present application relates to a decoupled power system for an electric drive wheel loader, and each drive branch included therein is decoupled from each other. Background Art

[0002] A wheel loader is a soil-shoveling and transporting device widely used in factory operations, and is often used to transport and load materials to a desired location, such as loading onto a truck. A wheel loader mainly includes a traveling part (wheels) and an actuator part. The actuator part usually includes a steering cylinder, a boom cylinder, and a bucket cylinder. Traditional wheel loaders use a diesel engine as a common power source for the traveling part and the actuator part. With the increasing strictness of emission standards in regions, wheel loaders powered by electric motors have been developed, which are called electric drive wheel loaders. Refer to Figure 1 , the decoupled power system of an electric drive wheel loader generally includes an electric motor Em for driving the actuator part, and another electric motor (not shown) for driving the traveling part. The output shaft of the electric motor EM for the actuator part drives a first hydraulic pump P1 and a second hydraulic pump P2. The output end of the first hydraulic pump P1 is connected to the inlet port of a priority valve Vp. The two outlet ports of the priority valve Vp are respectively connected to the inlet ports of a steering control unit Vs and a main control valve Vm. The output end of the second hydraulic pump P2 is also connected to the inlet port of the priority valve Vp. The working oil port of the steering control unit Vs is connected to a steering cylinder C1 for supplying hydraulic oil to the steering cylinder C1 to control the steering of the traveling part. The outlet port of the main control valve Vm is connected to a boom cylinder C2 and a bucket cylinder C3 for supplying hydraulic oil to the boom cylinder C2 and the bucket cylinder C3 to control the operation of the bucket. The priority valve Vp is used to selectively supply the output hydraulic oil of the first hydraulic pump P1 to the steering cylinder C1, or to the boom cylinder C2 and the bucket cylinder C3. In such a power system, there are hydraulic losses at the first hydraulic pump P1, the second hydraulic pump P2, the priority valve Vp, and the main control valve Vm, and it is difficult to achieve energy recovery when the boom descends. Summary of the Utility Model

[0003] The purpose of the present application is to provide a decoupled power system for an electric drive wheel loader, which can improve the energy efficiency of the power system.

[0004] To this end, the present application provides a decoupled power system for an electric drive wheel loader, which includes:

[0005] A power battery;

[0006] A first electric motor, a second electric motor, and an electric cylinder respectively powered by the power battery;

[0007] A first hydraulic pump driven by the first motor, a steering cylinder supplied with hydraulic oil by the first hydraulic pump, the steering cylinder being configured to drive the wheels of the electric wheel loader to steer;

[0008] A second hydraulic pump driven by the second motor, a boom cylinder supplied with hydraulic oil by the second hydraulic pump, the boom cylinder being configured to drive the boom of the electric wheel loader to lift and lower;

[0009] The electric cylinder is configured to drive the bucket of the electric wheel loader to rotate relative to the boom.

[0010] In one embodiment, both the first hydraulic pump and the second hydraulic pump are variable pumps.

[0011] In one embodiment, the variable mechanism of the first hydraulic pump is regulated by the load of the steering cylinder.

[0012] In one embodiment, the first hydraulic pump supplies hydraulic oil to the steering cylinder via a steering control unit.

[0013] In one embodiment, the steering control unit has at least three valve positions and at least includes the following oil ports: an inlet port, a return port, a load sensing port, and at least two working ports; wherein, the inlet port is connected to the output end of the first hydraulic pump, the return port is connected to the fuel tank, the load sensing port is connected to the load sensing oil circuit, the working ports are connected to the oil chambers of the steering cylinder, and the load sensing oil circuit is connected to the variable mechanism of the first hydraulic pump to adjust the displacement of the first hydraulic pump.

[0014] In one embodiment, the second hydraulic pump is a double-acting pump with a hydraulic pump working condition and a hydraulic motor working condition, and the second hydraulic pump supplies hydraulic oil to the boom cylinder via a main control valve.

[0015] In one embodiment, the second motor is an electric - generator integrated machine with a motor working condition and a generator working condition, the motor working condition corresponding to the hydraulic pump working condition of the second hydraulic pump, and the generator working condition corresponding to the hydraulic motor working condition of the second hydraulic pump.

[0016] In one embodiment, the power system further includes a traveling motor configured to drive the drive wheels of the electric wheel loader to rotate.

[0017] In one embodiment, the traveling motor includes: a single motor that drives all the drive wheels of the electric wheel loader to rotate; or motors respectively equipped for each drive wheel of the electric wheel loader.

[0018] In one embodiment, the first motor, the second motor, the electric cylinder, and the traveling motor are connected to the power battery via a power distribution unit.

[0019] In the decoupled power system of the electric drive wheel loader of the present application, each drive branch is decoupled from each other, and the priority valve in the decoupled power system of the traditional electric drive wheel loader is cancelled, avoiding the hydraulic loss here.

[0020] In addition, the drive branch for driving the boom is decoupled from the drive branches of the steering system and the bucket respectively, so that power recovery during the lowering of the boom can be achieved in a further embodiment. The decoupled power system of the electric drive wheel loader of the present application can improve energy efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] By referring to the following detailed description with reference to the accompanying drawings, the present application can be further understood. In the drawings:

[0022] Figure 1 is a schematic structural diagram of a decoupled power system of an electric drive wheel loader according to a prior art implementation;

[0023] Figure 2 is a schematic structural diagram of a decoupled power system of an electric drive wheel loader according to an embodiment of the present application;

[0024] Figure 3 is a schematic diagram of an embodiment of a steering control unit in the power system. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present application generally relates to a wheel loader, which is a pure electric drive type, and is therefore called an electric drive wheel loader. The actions of the wheel loader are realized by wheels and actuators. The actuators include a steering mechanism, a boom, a bucket, etc. The actions of the wheels and each actuator are driven by a power system. Figure 2 A feasible embodiment of the power system is shown in

[0026] Referring to Figure 2 , the decoupled power system of the electric drive wheel loader of the present application includes a power battery B as the vehicle power source. The power battery B is usually rechargeable. The power distribution unit PDU is connected to the output terminal of the power battery B for distributing the electric energy of the power battery B to each electrical component.

[0027] A first motor Em1 is connected to an output terminal of the power distribution unit PDU so as to be powered by the power battery B through the power distribution unit PDU. The first motor Em1 is usually an AC motor. In this case, the first motor Em1 is connected to the output terminal of the power distribution unit PDU through a first DC-AC converter DCAC1. In some embodiments, the first motor Em1 can be a DC motor. In this case, the first motor Em1 is connected to the output terminal of the power distribution unit PDU through a first DC-DC converter (not shown).

[0028] The output shaft of the first motor Em1 is connected to the first hydraulic pump P1 to drive the first hydraulic pump P1 to operate. The first hydraulic pump P1 is a variable pump, such as a piston pump, with a maximum displacement of, for example, 80 cc / rev. The output end of the first hydraulic pump P1 is connected to the oil inlet P (or called P port) of the steering control unit Vs, the oil return port T (or called T port) of the steering control unit Vs is connected to the fuel tank, and the two working oil ports of the steering control unit Vs are connected to the steering cylinder C1. The steering cylinder C1 is used to control the steering mechanism to drive the wheels to turn. In Figure 2 the example shown, the steering cylinder C1 is a double-rod cylinder, used to drive the left and right steering wheels to turn respectively, and the two working oil ports of the steering control unit Vs are respectively connected to the two side oil cavities of the steering cylinder C1. Alternatively, the steering cylinder C1 may include two single-rod cylinders (see Figure 3 the example shown), driving the left and right steering wheels to turn respectively, and each working oil port of the steering control unit Vs is respectively connected to the rod chamber of one steering cylinder and the non-rod chamber of the other steering cylinder. The steering control unit Vs includes a load sensing oil circuit Ls, and feeds back the load pressure of the steering cylinder during the steering of the loader sensed in the load sensing oil circuit Ls to the variable mechanism of the first hydraulic pump P1, thereby adjusting the displacement of the first hydraulic pump P1.

[0029] The second motor Em2 is an electric motor-generator integrated machine, connected to the other output end of the power distribution unit PDU, so as to be powered by the power battery B through the power distribution unit PDU. The second motor Em2 is usually an alternating current motor. In this case, the second motor Em2 is connected to the output end of the power distribution unit PDU through the second DC-AC converter DCAC2. In some embodiments, the second motor Em2 may adopt a direct current motor. In this case, the second motor Em2 is connected to the output end of the power distribution unit PDU through a second DC-DC converter not shown.

[0030] The output shaft of the second motor Em2 is connected to the second hydraulic pump P2 to drive the second hydraulic pump P2 to operate. The second hydraulic pump P2 is a variable pump, such as a piston pump, with a maximum displacement of, for example, 145 cc / rev. The output end of the second hydraulic pump P2 is connected to the oil inlet of the main control valve Vm, and the oil outlet of the main control valve Vm is connected to the boom cylinder C2. The second hydraulic pump P2 is a double-acting pump, having a hydraulic pump working condition and a hydraulic motor working condition.

[0031] The main control valve Vm is a two-position four-way valve in the illustrated example, having an oil inlet, a first working oil port, a second working oil port, and an oil return port. The oil inlet is connected to the output port of the second hydraulic pump P2, the oil return port is connected to the fuel tank, the first working oil port is connected to the rodless cavity of the boom cylinder C2, and the second working oil port is connected to the rod cavity of the boom cylinder C2. In the neutral valve position of the main control valve Vm, the above four oil ports are all blocked. When the boom is lifted, the main control valve Vm is controlled to the working valve position, the second motor Em2 is controlled to the motor condition, the second hydraulic pump P2 is controlled to the hydraulic pump condition, the oil inlet of the main control valve Vm is communicated with the first working oil port, and the second working oil port is communicated with the oil return port. Thus, the second hydraulic pump P2 drives the boom cylinder C2 to act forward, and the piston rod of the boom cylinder C2 extends, causing the boom to lift. When the boom is lowered, the main control valve Vm remains in the working valve position, the second motor Em2 is controlled to the generator condition, and the second hydraulic pump P2 is controlled to the hydraulic motor condition (for example, the swash plate of the piston pump is at a negative swing angle). Thus, the bucket and the load drive the boom to lower, driving the piston rod of the boom cylinder C2 to retract, that is, the boom cylinder C2 acts in the reverse direction. The hydraulic oil in the rodless cavity of the boom cylinder C2 is pressed into the second hydraulic pump P2 in the hydraulic motor condition through the first working oil port and the oil inlet of the main control valve Vm, driving the second hydraulic pump P2 to rotate. The second hydraulic pump P2 drives the second motor Em2 in the motor condition to generate electricity. The electricity generated by the second motor Em2 is charged to the power battery B, thereby realizing the power recovery (regenerative function) when the boom is lowered.

[0032] According to the specific function of the boom cylinder C2, the main control valve Vm can adopt a form with other valve positions and oil ports, and needs to be configured to be able to achieve the regenerative function. For example, a regeneration valve position can be added to the main control valve Vm. When the boom is lowered, the main control valve Vm is switched to the regeneration valve position to achieve the regenerative function.

[0033] The bucket is driven by an electric cylinder Ce. The electric cylinder Ce can convert the input electric energy into the linear motion of the piston rod, thereby driving the bucket to rotate relative to the boom. The electric cylinder Ce can be an AC electric cylinder. In this case, the input end of the electric cylinder Ce is connected to the output end of the power distribution unit PDU through the third DC-AC converter DCAC3. In some embodiments, the electric cylinder Ce can be a DC electric cylinder. In this case, the input end of the electric cylinder Ce is connected to the output end of the power distribution unit PDU through a third DC-DC converter (not shown).

[0034] In addition, a traveling motor Em3 for driving the wheels to rotate is connected to the output end of the power distribution unit PDU. The traveling motor Em3 can be an AC motor. In this case, the input end of the traveling motor Em3 is connected to the output end of the power distribution unit PDU via a fourth DC-AC converter DCAC4. In some embodiments, the traveling motor Em3 can be a DC motor. In this case, the input end of the traveling motor Em3 is connected to the output end of the power distribution unit PDU via a fourth DC-DC converter (not shown).

[0035] The traveling motor Em3 can include a single motor, and its motor shaft is connected to the drive wheels among the wheels via a speed reduction mechanism and a differential. Alternatively, the traveling motor Em3 can include wheel motors in the form of in-wheel motors integrated in each driving vehicle. Each wheel motor can be connected to the output end of the power distribution unit PDU via a common fourth DC-AC converter DCAC4, or can be connected to the output end of the power distribution unit PDU via its own DC-AC converter.

[0036] The Figure 2 decoupled power system of the electric drive wheel loader of the present application shown Figure 1 is compared with the traditional power system of the electric drive wheel loader shown to show the differences between the two. In the Figure 1 power system shown, the output end of the first hydraulic pump P1 supplies oil to the steering cylinder C1 via a priority valve Vp, or supplies oil to the boom cylinder C2 and the bucket cylinder C3. The output end of the second hydraulic pump P2 supplies oil to the boom cylinder C2 and the bucket cylinder C3 via a main control valve Vm. Therefore, Figure 1 each drive branch of the power system shown is dynamically coupled. On the contrary, in the power system of the present application, the first hydraulic pump P1 only supplies oil to the steering cylinder C1, the second hydraulic pump P2 only supplies oil to the boom cylinder C2, and the bucket is driven by an electric cylinder Ce. Therefore, each drive branch of the power system of the present application is dynamically decoupled. By adopting the decoupled power system of the present application, the priority valve is eliminated, and the hydraulic loss caused by the setting of the priority valve can be reduced.

[0037] The steering control unit Vs in the power system of the present application can be implemented in any configuration capable of realizing the foregoing functions. For example, Figure 3 a feasible structure of the steering control unit Vs is shown in Figure 3As shown in the figure, the steering control unit Vs includes a steering control valve 2 associated with the mechanical steering gear 1 of the loader. The valve position of the steering control valve 2 follows the steering wheel of the loader. In the illustrated example, the steering control valve 2 is a three-position seven-way valve, including the following seven oil ports: an oil inlet port (P port), an oil return port (T port), a load sensing oil port (Ls port), two working oil ports, and two auxiliary oil ports. Among them, the oil inlet port is connected to the output end of the first hydraulic pump P1, the oil return port is connected to the fuel tank, the load sensing oil port is connected to the load sensing oil circuit Ls, the two auxiliary oil ports are connected to the two oil inlet ports of the mechanical steering gear 1, and the two working oil ports are connected to the steering cylinders. The first control end of the steering control valve 2 is driven by the steering wheel of the loader, and the second control end of the steering control valve 2 is connected to the oil outlet of the mechanical steering gear 1.

[0038] In this example, the steering cylinder includes two single-rod cylinders, namely the left steering cylinder C11 and the right steering cylinder C12. One working oil port is connected to the rod chamber of the left steering cylinder C11 and the rodless chamber of the right steering cylinder C12, and the other working oil port is connected to the rodless chamber of the left steering cylinder C11 and the rod chamber of the right steering cylinder C12.

[0039] In the neutral valve position of the steering control valve 2, all the oil ports are disconnected from each other. By turning the steering wheel of the loader, the steering control valve 2 is switched to the first or second working valve position (depending on the steering wheel rotation direction).

[0040] In the first working valve position of the steering control valve 2, the T port is communicated with the second working oil port, the P port is communicated with the first working oil port (preferably throttled), the first auxiliary oil port is communicated with the first working oil port, the P port is communicated with the second auxiliary oil port (preferably throttled), and the Ls port is communicated with the second auxiliary oil port (or communicated to between the P port and the second auxiliary oil port). The hydraulic oil from the first hydraulic pump P1 is supplied to the left steering cylinder C11 and the right steering cylinder C12 through the P port and the first working oil port, so that the piston rod of the left steering cylinder C11 extends and the piston rod of the right steering cylinder C12 retracts.

[0041] In the second working valve position of the steering control valve 2, the T port is communicated with the first working oil port, the P port is communicated with the Ls port, the P port is communicated with the first auxiliary oil port (preferably throttled), the P port is communicated with the second working oil port (preferably throttled), and the second auxiliary oil port is communicated with the second working oil port. The hydraulic oil from the first hydraulic pump P1 is supplied to the left steering cylinder C11 and the right steering cylinder C12 through the P port and the second working oil port, so that the piston rod of the left steering cylinder C11 retracts and the piston rod of the right steering cylinder C12 extends.

[0042] At any working valve position of the steering control valve 2, the oil pressure at the P port is applied to the mechanical steering gear 1 through two oil inlets of the mechanical steering gear 1 and is transmitted to the second control end of the steering control valve 2 through the oil outlet of the mechanical steering gear 1. After the steering wheel is released, the oil pressure at the second control end of the steering control valve 2 helps the steering control valve 2 to reset from the current working valve position to the neutral valve position.

[0043] As can be understood by those skilled in the art, the steering control valve 2 can be designed to have other numbers of valve positions and oil ports; the steering control unit Vs can also include hydraulic components such as a priority valve and a safety valve.

[0044] The main control valve Vm in the power system of the present application is only used to control the boom cylinder C2, so a simple two-position four-way valve can be used, which is simpler than the main control valve Vm that controls both the boom cylinder C2 and the bucket cylinder C3 in Figure 1 and the hydraulic loss at the main control valve Vm will also be reduced.

[0045] In addition, the first hydraulic pump P1 and the second hydraulic pump P2 are variable pumps, which can improve the hydraulic efficiency and function of the power system. In addition, the second hydraulic pump P2 is a dual-mode pump, which can be used as a generator to recover the potential energy during the lowering of the boom, improving the energy utilization rate of the power system.

[0046] Although the present application is described herein with reference to specific embodiments, the scope of the present application is not limited to the details shown. Various modifications can be made to these details without departing from the basic principles of the present application.

Claims

1. A decoupled power system for an electric drive wheel loader, characterized in that Comprising: Power battery (B); A first motor (Em1), a second motor (Em2), and an electric cylinder (Ce) respectively powered by the power battery (B); A first hydraulic pump (P1) driven by the first motor (Em1), and a steering cylinder (C1) supplied with hydraulic oil by the first hydraulic pump (P1), the steering cylinder (C1) being configured to drive the wheels of the electric drive wheel loader to steer; A second hydraulic pump (P2) driven by the second motor (Em2), and a boom cylinder (C2) supplied with hydraulic oil by the second hydraulic pump (P2), the boom cylinder (C2) being configured to drive the boom of the electric drive wheel loader to lift and lower; The electric cylinder (Ce) is configured to drive the bucket of the electric drive wheel loader to rotate relative to the boom.

2. The decoupled power system of the electric drive wheel loader according to claim 1, characterized in that, Both the first hydraulic pump (P1) and the second hydraulic pump (P2) are variable pumps.

3. The decoupled power system of the electric drive wheel loader according to claim 2, characterized in that, The variable mechanism of the first hydraulic pump (P1) is regulated by the load of the steering cylinder (C1).

4. The decoupled power system of the electric drive wheel loader according to claim 3, characterized in that, The first hydraulic pump (P1) supplies hydraulic oil to the steering cylinder (C1) via a steering control unit (Vs).

5. The decoupled power system of the electric drive wheel loader according to claim 4, characterized in that, The steering control unit (Vs) has at least three valve positions and at least includes the following oil ports: an inlet port, a return port, a load sensing port, and at least two working ports; wherein, the inlet port is connected to the output end of the first hydraulic pump (P1), the return port is connected to the fuel tank, the load sensing port is connected to a load sensing oil circuit (Ls), the working ports are connected to the oil chambers of the steering cylinder, and the load sensing oil circuit (Ls) is connected to the variable mechanism of the first hydraulic pump (P1) to adjust the displacement of the first hydraulic pump (P1).

6. The decoupled power system of the electric drive wheel loader according to claim 2, wherein, The second hydraulic pump (P2) is a double-acting pump with a hydraulic pump condition and a hydraulic motor condition, and the second hydraulic pump (P2) supplies hydraulic oil to the boom cylinder (C2) via a main control valve (Vm).

7. The decoupled power system of the electric drive wheel loader according to claim 6, characterized in that, The second motor (Em2) is an electric motor - generator integrated machine with a motor condition and a generator condition, the motor condition corresponding to the hydraulic pump condition of the second hydraulic pump (P2), and the generator condition corresponding to the hydraulic motor condition of the second hydraulic pump (P2).

8. The decoupled power system of the electric drive wheel loader according to any one of claims 1-7, characterized in that, The power system further includes a traveling motor (Em3) configured to drive the drive wheels of the electric drive wheel loader to rotate.

9. The decoupled power system of the electric drive wheel loader according to claim 8, characterized in that, The traveling motor (Em3) includes: A single motor that drives all the drive wheels of the electric drive wheel loader to rotate; or Motors respectively equipped for each drive wheel of the electric drive wheel loader.

10. The decoupled power system of the electric drive wheel loader according to claim 8, characterized in that, The first motor (Em1), the second motor (Em2), the electric cylinder (Ce), and the traveling motor (Em3) are connected to the power battery (B) via a power distribution unit (PDU).

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