A hydraulic system for an electric loader and a control method for the hydraulic motor.

Abstract

This invention discloses a hydraulic system for an electric loader and a hydraulic motor control method. A hydraulic accumulator and pressure sensor are installed on the oil lines connecting the hydraulic pump to the steering system and the working device. A multi-way directional valve without mid-position return oil is also installed to control the connection to the working device. The hydraulic motor is then controlled according to two operating conditions: the working device is not in operation and it is in operation. By setting the accumulator and controlling the hydraulic system pressure threshold, the motor is controlled at a certain speed or torque. This ensures that when the working device is not in operation, the hydraulic pump has the highest efficiency, and there is no overflow or pressure loss along the friction path caused by mid-position return oil. When the working device is in operation, it avoids overflow and inter-valve pressure loss caused by high pressure and low flow rate and by the working device's limit.

Description

Technical Field

[0001] This invention relates to the field of electric loaders, and more specifically to a hydraulic system for an electric loader and a method for precise control of the motor. Background Technology

[0002] Loaders are widely used in railway freight yards, port terminals, mining operations, and farm loading and unloading, as well as in construction. With the increasing tightening of global fossil energy supply and rising requirements for greenhouse gas emissions, the emission, energy-saving, and economic requirements of loaders have also gained attention, leading to the development of electric loaders.

[0003] Electric loaders, by decoupling the drive unit from the hydraulic system, can operate the hydraulic system only when required for flow or pressure, significantly reducing pressure losses along the pipeline, between valves, and during overflow in the loader's hydraulic system. Existing hydraulic control methods fall into two categories:

[0004] First, when the vehicle is stationary (not in drive and the operating lever is not in motion), the hydraulic motor is given a lower speed control to ensure that the vehicle's braking and steering systems are always ready to work; after the vehicle starts moving (when the gear is engaged or the operating lever signal is not zero), the hydraulic motor is given a higher speed control to ensure that the vehicle meets its flow and pressure requirements.

[0005] Secondly, when the vehicle is stationary, the hydraulic motor is given a lower speed control to ensure that the vehicle's braking and steering systems are always ready to work; when the vehicle starts to move, the hydraulic motor is given different speeds according to the opening degree of the operating handle to reduce the overflow of the hydraulic system.

[0006] The first approach significantly reduces hydraulic system pressure loss during high-speed travel and material shoveling, as well as overflow loss during the shoveling process, compared to traditional loaders. The second approach, building on the first, reduces hydraulic system pressure loss when the vehicle is moving and the working device is not in operation, and reduces hydraulic system overflow loss when the hydraulic system requires high pressure but low flow. Both approaches are significant; however, neither can completely eliminate pressure loss and overflow loss.

[0007] This application proposes a loader hydraulic system and control method that eliminates pressure loss along the hydraulic line when the hydraulic system is not in operation, thereby avoiding overflow loss. Summary of the Invention

[0008] To achieve the above-mentioned objectives, the present invention provides a hydraulic system for an electric loader and a hydraulic motor control method.

[0009] The technical solution adopted in this invention is:

[0010] A hydraulic system for an electric loader, characterized in that:

[0011] A hydraulic accumulator and a pressure sensor are installed on the oil line from the hydraulic pump to the steering system and the working device; the pressure sensor signal is fed back to the vehicle controller; a multi-way directional valve without neutral return oil is provided and connected to the working device.

[0012] Furthermore:

[0013] The hydraulic system includes a hydraulic motor, which drives the hydraulic pump.

[0014] A priority valve is provided at the oil circuit branch point from the hydraulic pump to the steering system and the working device. The priority valve preferentially connects to the steering system, and an overflow valve is provided at the outlet of the hydraulic pump to connect to the oil tank.

[0015] The multi-way directional valve without mid-position return oil is connected between the priority valve and the working device. The multi-way directional valve without mid-position return oil is controlled by the electronically controlled multi-way valve control handle through the pilot valve. The signal of the electronically controlled multi-way valve control handle is fed back to the vehicle controller.

[0016] Furthermore:

[0017] The maximum pressure of the accumulator is selected according to the overflow pressure of the loader's hydraulic pump outlet to ensure that the accumulator can still work normally when the system reaches the overflow pressure.

[0018] The charging pressure of the accumulator is selected according to the overflow pressure of the loader's steering system to ensure that the steering system can still work normally when the accumulator charging pressure is at its lowest level.

[0019] The capacity of the accumulator is selected based on the sum of the volumes of the two steering cylinders of the loader, so as to ensure that after the accumulator is filled with oil, the loader can turn from the steering limit position on one side to the steering limit position on the other side.

[0020] The maximum measurement value of the pressure sensor is selected according to the overflow pressure of the loader's hydraulic pump outlet, so as to ensure that the pressure sensor can still measure a signal when the system reaches the overflow pressure.

[0021] A hydraulic motor control method for an electric loader hydraulic system, characterized in that:

[0022] Calibration should be performed before the experiment:

[0023] Maximum flow rate Q when the loader's bucket cylinder retracts the bucket a—u ;

[0024] Maximum flow rate Q of the loader's bucket cylinder during bucket tipping a—d ;

[0025] Maximum flow rate Q during loading of the boom cylinderb—u ;

[0026] Maximum flow rate Q during the descent of the loading boom cylinder b—d ;

[0027] Loader hydraulic pump outlet overflow pressure P a ;

[0028] Loader steering system overflow pressure P b ;

[0029] The torque value T of the hydraulic motor when the loader system pressure reaches the stable overflow pressure. max ;

[0030] Settings: The system has two pressure regulation values, a and b. The value of a is in the range (0, P). a -P b The values ​​of b are between (0, a) and (a).

[0031] Then, the hydraulic motor is controlled according to two working conditions: when the working device is not in motion and when it is in motion.

[0032] 1) When the working device is not in operation

[0033] When the system pressure is less than P a When -a, the motor is operated at the rated speed of the hydraulic pump;

[0034] When the system pressure is greater than or equal to P a -a, and less than P a When -b is used, the motor is set to operate at the lowest speed of the hydraulic pump;

[0035] When the system pressure is greater than or equal to P a -b, or, the motor torque is greater than T. max At that time, set the motor speed to zero;

[0036] 2) When the working device is in motion

[0037] When the system pressure reaches P a Or the motor torque reaches T max And the motor speed ω corresponding to the opening signal of the bucket cylinder or boom cylinder operating handle M-c Greater than or equal to the motor feedback speed ω M-b At this time, the motor is controlled by torque, and the torque value is T. max ;

[0038] When the system pressure reaches P a Or the motor torque reaches T max And the motor speed ω corresponding to the opening signal of the bucket cylinder or boom cylinder operating handle M-c Less than the motor feedback speed ω M-bAt that time; or, the system pressure is less than P. a And the motor torque is also less than T. max At that time, the motor is controlled by its speed, and the speed value is:

[0039] ω M-c =max(ω M-min , (T a-u Q a-u +T a-d Q b-u +T b-u Q a-d +T b-d Q b-d ) / L)

[0040] in:

[0041] ω M-min This is the minimum speed of the hydraulic pump;

[0042] L represents the displacement of the hydraulic pump;

[0043] T a-u The opening value of the operating handle during the bucket-collecting process of the bucket cylinder is between [0, 1].

[0044] T a-d The opening value of the operating handle during the tipping process of the bucket cylinder is between [0, 1].

[0045] T b-u The opening value of the operating handle during the lifting process of the boom cylinder is between [0, 1].

[0046] T b-d The opening value of the operating handle during the lowering of the boom cylinder is between [0, 1].

[0047] For the Q a—u Q a—d Q b—u Q b—d The calculation method is as follows:

[0048] Q a-u =V a-u-max πd a-1 2 / 4

[0049] Q a-d =V a-d-max π(d a-1 2 -d a-2 2 ) / 4

[0050] Q b-u =V b-u-max πd b-1 2 / 4

[0051] Q b-d =V b-d-max π(d b-1 2 -d b-2 2 ) / 4

[0052] in:

[0053] V a-u-max The fastest speed at which the hydraulic cylinder piston moves when the loader's bucket cylinder retracts the bucket is measured by the working handle reaching its limit position.

[0054] V a-d-max The maximum speed at which the hydraulic cylinder piston moves when the loader's bucket tilting cylinder moves is measured by the working handle reaching its limit position.

[0055] V b-u-max The maximum speed at which the hydraulic cylinder piston moves when the loading boom cylinder is lifted is measured by the working handle reaching its limit position.

[0056] V b-d-max The maximum speed at which the hydraulic cylinder piston moves when the loading boom cylinder drops is measured by the working handle at its limit position.

[0057] d a-1 The inner diameter of the loader bucket cylinder;

[0058] d a-2 Outer diameter of the piston push rod of the loader bucket cylinder;

[0059] d b-1 The inner diameter of the loading boom cylinder;

[0060] d b-2 Outer diameter of the piston push rod of the loader boom cylinder.

[0061] This invention, when the working device is not in use, ensures the hydraulic pump operates at its highest efficiency by controlling the accumulator and the hydraulic system pressure logic threshold. This prevents pressure losses along the pipeline caused by overflow and mid-position return oil, thereby improving the overall vehicle efficiency and the effective utilization of electrical energy, and extending the working time of the electric loader. When the working device is in use, the motor control mode is switched according to the operating handle opening and system pressure (motor torque), avoiding overflow and inter-valve pressure losses caused by high pressure and low flow rate, as well as by the working device's limits. This not only reduces energy waste but also plays a crucial role in the thermal management of the electric loader's hydraulic system. Attached Figure Description

[0062] Figure 1 This is a diagram of the improved hydraulic system of the loader. Detailed Implementation

[0063] The technical solution of the present invention will now be clearly and completely described in conjunction with the embodiments and accompanying drawings.

[0064] I. Hydraulic System

[0065] like Figure 1 As shown, the hydraulic system of the electric loader of the present invention includes: a hydraulic motor 1 and a hydraulic pump 2. The hydraulic motor drives the hydraulic pump to work according to the instructions of the vehicle controller 3; an overflow valve 4 connected to the outlet of the hydraulic pump for high-pressure overflow of the system; a priority valve 5 connected to the intersection of the system oil circuit leading to the steering system 6 and the working device 7, prioritizing the conduction of the steering system hydraulic circuit; a multi-way directional valve 8 without return oil, connected between the priority valve and the working device 7, for adjusting different working states; an accumulator 9 and a pressure sensor 10 connected to the oil circuit between the hydraulic pump 2 and the priority valve 5, for storing energy in the high-pressure working oil and detecting the pressure in the working oil circuit, and the pressure sensor 10 signal is fed back to the vehicle controller 3; an electronically controlled multi-way valve control handle 11, used for switching working states and feeding back the operation signal to the vehicle controller 3. The operation command of the electronically controlled multi-way valve control handle is transmitted to the multi-way directional valve 8 without return oil through the pilot valve 12, for opening the corresponding valve position of the multi-way directional valve 8 without return oil.

[0066] The key improvements made by this invention to the hydraulic system are: installing an accumulator and a pressure sensor between the hydraulic pump and the priority valve; replacing the existing multi-way directional valve with a neutral return valve with a multi-way directional valve without a neutral return valve; and connecting the pressure sensor signal to the vehicle controller.

[0067] Existing multi-way directional valves with center-position return oil are mainly used to address the energy loss problem caused by overflow due to the power coupling between the travel and working devices in traditional loaders. Electric loaders have already decoupled the travel and working devices, making it unnecessary to use multi-way directional valves with center-position return oil. Furthermore, eliminating the center-position return oil reduces the pressure build-up time of the working device, improving system efficiency. Accumulators are used for energy recovery from high-pressure oil.

[0068] Component selection:

[0069] The maximum pressure of accumulator 9 is based on the overflow pressure P of the overflow valve at the outlet of the loader's hydraulic pump. a The accumulator is selected to ensure it can still operate normally when the system reaches overflow pressure; the accumulator's charging pressure is based on the loader's steering system overflow pressure P. b The 90% limit is selected to ensure that the steering system can still work normally when the accumulator is in its lowest state; the capacity of the accumulator is selected according to the sum of the volumes of the two steering cylinders of the loader, so that after the accumulator is full of oil, the energy stored in it can ensure that the loader can turn from the steering limit position on one side to the steering limit position on the other side.

[0070] The maximum measured value of pressure sensor 10 is based on the overflow pressure P of the overflow valve at the outlet of the loader's hydraulic pump. a This is selected to ensure that the pressure sensor can still detect a signal when the system reaches overflow pressure.

[0071] II. Control Methods

[0072] Calibration 1: Measure the fastest speed of hydraulic cylinder piston movement during the loader's bucket tilting, bucket retraction, and boom lifting / lowering operations, and calculate the corresponding maximum flow rate based on the cylinder diameter and the fastest speed, denoted as Q. a—u Q a—d and Q b—u Q b—d :

[0073] Q a-u =V a-u-max πd a-1 2 / 4

[0074] Q a-d =V a-d-max π(d a-1 2 -d a-2 2 ) / 4

[0075] Q b-u =V b-u-max πd b-1 2 / 4

[0076] Q b-d =V b-d-max π(d b-1 2 -d b-2 2 ) / 4

[0077] in:

[0078] Q a—u This refers to the maximum flow rate when the loader's bucket cylinder retracts the bucket.

[0079] Q a—d This refers to the maximum flow rate when the loader's bucket cylinder tipps the bucket.

[0080] Q b—u This is the maximum flow rate during the lifting of the loading boom cylinder;

[0081] Q b—d This is the maximum flow rate when the loading boom cylinder is lowered;

[0082] V a-u-maxThe fastest speed at which the hydraulic cylinder piston moves when the loader's bucket cylinder retracts the bucket is measured by the working handle reaching its limit position.

[0083] V a-d-max The maximum speed at which the hydraulic cylinder piston moves when the loader's bucket tilting cylinder moves is measured by the working handle reaching its limit position.

[0084] V b-u-max The maximum speed at which the hydraulic cylinder piston moves when the loading boom cylinder is lifted is measured by the working handle reaching its limit position.

[0085] V b-d-max The maximum speed at which the hydraulic cylinder piston moves when the loading boom cylinder drops is measured by the working handle at its limit position.

[0086] d a-1 The inner diameter of the loader bucket cylinder;

[0087] d a-2 Outer diameter of the piston push rod of the loader bucket cylinder;

[0088] d b-1 The inner diameter of the loading boom cylinder;

[0089] d b-2 Outer diameter of the piston push rod of the loader boom cylinder.

[0090] Calibration 2: The system pressure reaches the stable overflow pressure P a The torque value T fed back by the motor max .

[0091] When the loader is powered on, the hydraulic motor enters the start state. The control of the hydraulic motor is divided into two working conditions: the working device is in motion and the working device is not in motion.

[0092] 1. The working device is in a static state (the signal of the electric multi-way valve operating handle is 0).

[0093] When the working device is not in operation, the hydraulic system mainly ensures the pressure requirements of the steering system, at which time the pressure is determined by the overflow pressure P at the hydraulic pump outlet. a and steering system overflow pressure P b The system pressure is controlled by logical threshold values ​​at upper and lower limits. When the system pressure is greater than P... a Or the motor torque is greater than T max The motor stops working when the system pressure is less than P. b When the motor starts working, the specific control method is to control the motor speed based on the overflow pressure at the hydraulic pump outlet:

[0094]

[0095] ωM-c ω represents the motor's rotational speed. M-e ω is the rated speed of the hydraulic pump. M-min This is the minimum speed of the hydraulic pump.

[0096] The control method is as follows:

[0097] When the system pressure P is less than P a When -a (the value of a is between 0 and (P) a -P b Between 0.5 and 0.5, we prioritize 0.5 to make the motor speed equal to the rated speed of the hydraulic pump (pump's own parameters);

[0098] When the system pressure P is greater than or equal to P a -a, and less than P a When -b (the value of b ranges from 0 to a, with 0.1 preferred here), the motor speed is set to be equal to the minimum speed of the hydraulic pump (pump's own parameter);

[0099] When the system pressure P is greater than or equal to P a -b, or, the motor torque T is greater than the maximum value T. max At that time, set the motor speed to zero.

[0100] 2. Working status of the working device (the signal of the electric multi-way valve operating handle is not 0).

[0101] When the working device is operating, the hydraulic pump prioritizes power to the steering system. Power is then supplied to the working device only after the steering system's oil requirements are met. However, since the vehicle rarely steers simultaneously during operation, especially when the working device is operating at high speed or pressure, the flow rate and pressure required by the steering device are negligible when the working device is in operation. When the vehicle controller receives the opening signal of the bucket cylinder or boom cylinder operating handle from the electronically controlled multi-way valve operating handle, it first controls the speed of the hydraulic motor.

[0102] Its speed control is expressed as:

[0103] ω M-c =max(ω M-min , (T a-u Q a-u +T a-d Q b-u +T b-u Q a-d +T b-d Q b-d ) / L)

[0104] in:

[0105] ω M-c This refers to the motor's rotational speed;

[0106] ωM-min This is the minimum speed of the hydraulic pump;

[0107] L represents the displacement of the hydraulic pump;

[0108] T a-u The opening value of the operating handle during the bucket-collecting process of the bucket cylinder is between [0, 1].

[0109] T a-d The opening value of the operating handle during the tipping process of the bucket cylinder is between [0, 1].

[0110] T b-u The opening value of the operating handle during the lifting process of the boom cylinder is between [0, 1].

[0111] T b-d The opening value of the operating handle during the lowering of the boom cylinder is between [0, 1].

[0112] so,

[0113] When the system pressure reaches P a Or the motor torque reaches T max (Whichever is achieved first) and the motor speed ω corresponding to the opening signal of the bucket cylinder or boom cylinder operating handle transmitted from the electronically controlled multi-way valve operating handle. M-c Greater than or equal to the motor feedback speed ω M-b At that time, the motor needs to operate at the maximum pressure P of the hydraulic system. a Or the maximum torque T of the motor max Torque control is performed to achieve the target torque value, which is T. max .

[0114] Until the system pressure is greater than or equal to P a Or the motor torque is greater than or equal to T max Simultaneously, the motor speed ω corresponding to the opening signal of the bucket cylinder or boom cylinder operating handle transmitted from the electronically controlled multi-way valve operating handle... M-c Less than the motor feedback speed ω M-b At that time, or when the system pressure is less than P a And the motor torque is also less than T. max Then, the motor speed is controlled.

[0115] Therefore, motor control includes both torque and speed, as shown below:

[0116]

[0117] Where M(ω) M-c T M-c ) is the motor control function.

[0118] In motor torque control mode, T M-c=T max ;

[0119] In motor speed control mode, ω M-c =max(ω M-min , (T a-u Q a-u +T a-d Q b-u +T b-u Q a-d +T b-d Q b-d ) / L).

Claims

1. A method of controlling a hydraulic motor of an electrically powered loader hydraulic system, the method comprising: The hydraulic system is: Including hydraulic motor, the hydraulic motor drive connection hydraulic pump; The hydraulic pump to the steering system and the oil circuit bifurcation of the work device is provided with a priority valve, the priority valve priority access to the steering system, and the overflow valve is provided at the outlet of the hydraulic pump to the tank; The hydraulic pump to the steering system and the oil circuit of the work device is installed with hydraulic accumulator and pressure sensor, the pressure sensor signal feedback to the vehicle controller; A multi-way reversing valve without neutral return is provided, the multi-way reversing valve without neutral return is connected between the priority valve and the work device, the multi-way reversing valve without neutral return is controlled by the electric control multi-way valve control handle through the pilot valve control, the electric control multi-way valve control handle signal feedback to the vehicle controller; The maximum pressure of the accumulator is selected according to the overflow pressure of the loader hydraulic pump outlet, so as to ensure that the accumulator can still work normally when the system reaches the overflow pressure; The charging pressure of the accumulator is selected according to the overflow pressure of the loader steering system, so as to ensure that the steering system can still work normally when the charging pressure of the accumulator is in the lowest state; The capacity of the accumulator is selected according to the sum of the volumes of the two steering cylinders of the loader, so as to ensure that the loader can turn from one side steering limit position to the other side steering limit position after the accumulator is filled with oil; The maximum measurement value of the pressure sensor is selected according to the overflow pressure of the hydraulic pump outlet of the loader, so as to ensure that the pressure sensor can still measure the signal when the system reaches the overflow pressure; On this basis, calibration before test: Maximum flow rate of a loader roll-over cylinder when the bucket is being filled Q a—u ; Maximum flow of a loader roll-over cylinder when rolling over Q a—d ; Maximum flow rate of a loader boom cylinder during lift Q b—u ; Maximum flow rate of a loader boom cylinder on drop Q b—d ; Loader hydraulic pump outlet relief pressure P a ; Loader steering system relief pressure P b ; Torque value of hydraulic motor when system pressure of loader reaches steady relief pressure T max ; Setting the two pressure regulating quantities of the system a and b , a have values between (0, P a - P b ) and between (0, b a ) respectively.​​ Then control the hydraulic motor according to two working conditions of no action and action of the work device: 1) When the work device is not in action When the system pressure is less than P a - a the motor is operated at the rated speed of the hydraulic pump. When the system pressure is greater than or equal to P a -a , and less than P a - b , the motor is operated at the minimum rotational speed of the hydraulic pump. When the system pressure is greater than or equal to P a -b , or the motor torque is greater than T max , the motor speed is equal to zero. 2) When the work device is in action When the system pressure reaches P a or the motor torque reaches T max , and the motor speed corresponding to the swing cylinder or boom cylinder operation handle opening signal ω M-c is greater than or equal to the motor feedback speed ω M-b , the motor is controlled by torque, and the torque value is T max ; when the system pressure reaches P a or the motor torque reaches T max , and the motor speed corresponding to the swing cylinder or boom cylinder operation handle opening signal ω M-c is less than the motor feedback speed ω M-b ; or, the system pressure is less than P a and the motor torque is also less than T max , the motor is controlled at a speed, and the speed value is: ω M-c =max （ ω M-min ， （ T a-u Q a-u + T a-d Q b-u + T b-u Q a-d + T b-d Q b-d ） / L ） Among them: ω M-min Minimum rotational speed of the hydraulic pump; L is the displacement of the hydraulic pump; T a-u for the opening value of the operating handle during the bucket collection process, between [0, 1]; T a-d is the opening value of the operating handle for the slewing cylinder during the slewing process, between [0, 1]; T b-u for the boom cylinder lifting process, the opening value of the operating handle is between [0, 1]; T b-d For the boom cylinder down fall process, the opening value of the operating handle is between [0, 1].

2. The hydraulic motor control method according to claim 1, characterized in that: The Q a—u , Q a—d , Q b—u , Q b—d The calculation method is: Q a-u =V a-u-max πd a-1 2 / 4 Q a-d =V a-d-max π ( d a-1 2 - d a-2 2 ) / 4 Q b-u =V b-u-max πd b-1 2 / 4 Q b-d =V b-d-max π ( d b-1 2 - d b-2 2 ) / 4 Among them: V a-u-max The fastest speed of the hydraulic cylinder piston movement for loading the loader bucket cylinder with the bucket is measured by the working handle to the extreme position. V a-d-max The maximum speed of the hydraulic cylinder piston movement for loading the loader bucket cylinder is measured by the handle to the extreme position. V b-u-max To measure the maximum speed of the hydraulic cylinder piston movement when the loader boom cylinder is lifted, the working handle is measured to the extreme position. V b-d-max The fastest speed of the hydraulic cylinder piston movement for the loading boom cylinder drop is measured to the limit position of the operating handle. d a-1 Loader roll-over cylinder bore diameter; d a-2 Loader roll-over cylinder piston push rod outside diameter; d b-1 Loader boom cylinder bore diameter; d b-2 Loader boom cylinder piston push rod outside diameter.

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