Control system and control method for variable rotating speed of metering pump of electric excavator

Abstract

The invention provides a variable-speed control system and a variable-speed control method for a metering pump of an electric excavator. The variable-speed control system comprises a complete machine controller, a motor controller, a motor, the metering pump and a battery, the complete machine controller is used for sending a control instruction to the motor controller; the motor controller is used for receiving a control instruction sent by the vehicle control unit, obtaining electric energy from a battery and outputting current and voltage to the motor through modulation of an inverter of the motor controller so as to enable the motor to rotate; and the motor is combined with the metering pump to form a power source for supplying oil to a load-sensitive multi-way valve system of the excavator. According to the device, the motor is adopted to drive the metering pump to form a power source to supply oil to the load-sensitive multi-way valve, a load pressure feedback pipeline from the load-sensitive multi-way valve to the pump is omitted, and the advantages of the motor in speed regulation precision, speed regulation response time and speed regulation stability are fully exerted.

Description

Technical Field

[0001] The invention relates to a variable speed control system and a control method for a quantitative pump of an electric excavator, belonging to the technical field of excavator control. Background Art

[0002] Pure electric excavator systems are zero-carbon emission drive systems that align with national development goals and can effectively alleviate resource constraints and air pollution. The electrification of construction machinery is rapidly developing. However, current pure electric excavators simply replace the engine with an electric motor, fixing the speed at a fixed value and a single constant power point. These systems fail to develop a dedicated control strategy tailored to the hydraulic system's powertrain, failing to fully utilize the motor's advantages in speed regulation accuracy, response time, and stability. This results in low overall energy efficiency and a poor user experience. Furthermore, they fail to leverage the motor's ability to withstand short periods of overload when exposed to high power loads. Summary of the Invention

[0003] The purpose of the present invention is to provide a variable speed control system and control method for a quantitative pump of an electric excavator, which replaces the traditional motor plus plunger pump by a motor plus a quantitative pump, and gives full play to the advantages of the motor in speed regulation accuracy, speed regulation response time and speed regulation stability.

[0004] In order to achieve the above objectives / solve the above technical problems, the present invention is implemented by adopting the following technical solutions.

[0005] In one aspect, the present invention provides a variable speed control system for a quantitative pump of an electric excavator, comprising: a whole machine controller, a motor controller, a motor, a quantitative pump and a battery;

[0006] The whole machine controller is used to send control instructions to the motor controller;

[0007] The motor controller is used to receive control instructions sent by the vehicle controller, obtain electrical energy from the battery, modulate it through its own inverter, and output current and voltage to the motor to make the motor rotate;

[0008] The motor is combined with a quantitative pump to form a power source for supplying oil to the load-sensing multi-way valve system of the excavator;

[0009] The battery is used to provide electrical energy to the motor controller.

[0010] Furthermore, it also includes: a pressure sensor, which is used to collect the outlet pressure P of the quantitative pump p and maximum load pressure P Lmax And transmit it to the whole machine controller as a control instruction for adjusting the motor operating speed.

[0011] In a second aspect, the present invention provides a control method according to the above-mentioned electric excavator quantitative pump variable speed control system, comprising the following steps:

[0012] According to the maximum output power of the motor and the maximum discharge power of the battery Ps, calculate the set power P of the metering pump Pset ;

[0013] According to the set power P of the metering pump Pset Calculate the pressure turning point of the metering pump corresponding to the gear position based on the predetermined speed of the metering pump corresponding to the gear position and the displacement of the metering pump;

[0014] According to the set power of the quantitative pump combined with the maximum load pressure P Lmax and the displacement of the metering pump to calculate the target speed of the motor corresponding to the gear;

[0015] When the maximum load pressure P Lmax When the pressure is less than the turning point of the corresponding gear of the metering pump, according to the outlet pressure P of the metering pump p and maximum load pressure P Lmax The pressure difference between the two adjusts the motor speed in real time;

[0016] When the maximum load pressure P Lmax When the pressure is greater than the turning point of the pressure of the corresponding gear of the metering pump, the motor operating speed is the target speed of the corresponding gear.

[0017] Furthermore, the maximum output power of the motor is determined as follows:

[0018] When the motor controller current temperature T mc Lower than the upper limit temperature T of the motor controller for normal operation mcmax ; Current motor temperature T mo Lower than the upper limit temperature T of the motor for normal operation momax , and when the battery power SOC>battery SOC threshold, the maximum output power of the motor is the instantaneous power P of the motor controller MCS ;

[0019] Otherwise, the maximum output power of the motor is the rated operating power P of the motor controller. MCL .

[0020] Furthermore, the method for obtaining the set power of the metering pump is specifically as follows:

[0021] Maximum output power of the motor and maximum discharge power of the battery P s Take the smaller value between the two and set the power;

[0022] Among them: the maximum discharge power of the battery P s The specific method of obtaining is:

[0023] Calculate the maximum discharge power of the battery based on the battery capacity SOC.

[0024] Furthermore, the expression for calculating the pressure turning point of the metering pump corresponding to the gear position according to the set power of the metering pump combined with the predetermined speed of the metering pump gear position and the displacement of the metering pump is specifically:

[0025] ;

[0026] in: is the pressure turning point of the metering pump, is the set power of the metering pump, The preset speed for the metering pump corresponding to the gear position, is the displacement of the metering pump.

[0027] Furthermore, the set power of the quantitative pump is combined with the maximum load pressure P Lmax As well as the displacement of the metering pump, the expression for calculating the target speed of the motor corresponding to the gear is:

[0028] ;

[0029] in: is the motor target speed, is the maximum load pressure, is the set power of the metering pump, is the displacement of the metering pump.

[0030] Furthermore, according to the outlet pressure P of the metering pump p and maximum load pressure The pressure difference between the two adjusts the motor speed in real time, specifically:

[0031] When the pressure difference ΔP is less than the set pressure difference ΔP set The lower limit of , the whole machine controller increases the motor speed with a gradient Δn;

[0032] When the pressure difference ΔP is greater than the set pressure difference ΔP set The upper limit of the motor speed is reduced by the controller with a gradient of Δn.

[0033] The calculation method of the gradient Δn is specifically as follows:

[0034] ;

[0035] in: It is the speed gradient of the load-sensing multi-way valve system when it is unloaded. is the pilot pressure of the load-sensing multi-way valve system, x is the speed gradient correction coefficient, It is the pilot pressure when the corresponding valve port of the load-sensing multi-way valve system is opened. To achieve the pilot pressure required for the maximum pressure difference of the load sensing multi-way valve system, Set the maximum speed gradient for the load-sensing multi-way valve system;

[0036] Where: Set pressure difference ΔP set The calculation method is as follows:

[0037] ;

[0038] in: Set the pressure difference for the load sensing multi-way valve system when it is unloaded. is the pilot pressure of the load-sensing multi-way valve system, k is the pressure difference correction coefficient, P o It is the pilot pressure when the corresponding valve port of the load-sensing multi-way valve system opens in response to the corresponding action, P imax To achieve the pilot pressure required for the maximum pressure difference of the load sensing multi-way valve system, Sets the maximum differential pressure for load sensing valve systems.

[0039] The set pressure difference ΔP set The adjustment method of the gradient Δn is as follows:

[0040] When the speed and flow rate are low, the set pressure difference ΔP is reduced. set and gradient ;

[0041] When the motor starts and accelerates, increase the set pressure difference ΔP set and gradient ;

[0042] When working at high speed and large flow, increase the set pressure difference ΔP set and gradient .

[0043] Furthermore, under the no-load working condition of the load-sensing multi-way valve system, when the load pressure When the time of zero is greater than T1 and less than T2, the motor operates at the set minimum speed.

[0044] When the load pressure P Lmax When the time of zero is greater than or equal to T2, the motor operating speed is zero;

[0045] Where: T 1、 T2 is the preset motor idling time, T1<T2.

[0046] Compared with the existing technology, the present invention has the following beneficial effects: the present invention uses a motor with variable speed to drive a quantitative pump to form a power source to supply oil to the load-sensitive multi-way valve, replacing the traditional motor plus plunger pump, giving full play to the advantages of the motor in speed regulation accuracy, speed regulation response time, and speed regulation stability; it can effectively improve the comfort and stability of operation and enhance the driver's driving experience;

[0047] The present invention develops a special control strategy for the power system based on the hydraulic system. The system pressure difference and constant power point can be adaptively adjusted. It also takes advantage of the motor's ability to perform short-term overload operation when encountering high-power loads, which can improve the safety and economy of the entire vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a schematic diagram of the hydraulic system principle of the present invention;

[0049] Figure 2 To set the power flow chart;

[0050] Figure 3 This is a schematic diagram of the motor control of the present invention;

[0051] Figure 4 This is the idle speed control flow chart. DETAILED DESCRIPTION

[0052] It should be noted that:

[0053] The technical solution of the present invention is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0054] The term "and / or" simply describes a relationship between related objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, or B exists alone. Additionally, the character " / " generally indicates an "or" relationship between the related objects.

[0055] Example 1

[0056] like Figure 1 An embodiment shown in the figure provides a variable speed control system for a quantitative pump of an electric excavator, comprising: a whole machine controller 1, a motor controller 2, a motor 3, a quantitative pump 4 and a battery;

[0057] The whole machine controller 1 is electrically connected to the motor controller 2, the motor controller 2 is electrically connected to the motor 3, the output shaft of the motor 3 is connected to the metering pump 4, the first connection point of the metering pump 4 is connected to the oil tank to suck oil from the oil tank, the second connection point of the metering pump 4 is connected to the pressure reducing valve 5, the metering pump 4 outputs the hydraulic oil through the pressure reducing valve 5 and supplies the hydraulic oil to the pilot handle 6, after the pilot handle 6 receives the two hydraulic oils output by the pressure reducing valve 5, the two hydraulic oils are respectively input to the two throttle ports 7 through the hydraulic pipeline to control the size of the throttle ports 7, the two throttle ports 7 are connected to the pressure compensating valve 8 through the hydraulic pipeline, the pressure compensating valve 8 outputs the hydraulic oil to the corresponding actuator 9 to perform the corresponding action; the actuator 9 and the pressure compensating valve 8 A shuttle valve 10 is connected between them; the third connection point of the metering pump 4 is connected to a first pressure sensor, which collects the outlet pressure of the metering pump 4 and transmits it to the whole machine controller 1 through an electrical hard line; the fourth connection point of the metering pump 4 is connected to the relief valve 11, which realizes the overflow effect when the system exceeds the flow rate; the pilot handle 6 is connected to a second pressure sensor and a third pressure sensor, which collect the pilot pressure of the left handle and the right handle respectively, and transmits it to the whole machine controller 1 through an electrical hard line; the fourth pressure sensor is connected to the shuttle valve 10 and the relief valve through a hydraulic pipeline, collects the maximum load pressure, and transmits it to the whole machine controller 1 through an electrical hard line, and the whole machine controller 1 is used to send control instructions to the motor controller 2;

[0058] The motor controller 2 is used to receive control instructions sent by the vehicle controller, obtain electrical energy from the battery, modulate the current and voltage through its own inverter, and output the current and voltage to the motor 3 to rotate the motor 3;

[0059] The motor 3 and the metering pump 4 form a power source for supplying oil to the load-sensing multi-way valve system of the excavator;

[0060] The battery is used to provide electrical energy to the motor controller 2 .

[0061] Also includes: a pressure sensor, the pressure sensor is used to collect the outlet pressure P of the quantitative pump 4 p and maximum load pressure P Lmax The control instructions are then transmitted to the whole machine controller 1 and used to adjust the operating speed of the motor 3 .

[0062] Example 2

[0063] like Figures 2-4 As shown, this embodiment provides a control method according to the above electric excavator quantitative pump variable speed control system, including the following steps:

[0064] Step 1: Calculate the set power P of the metering pump based on the maximum output power of the motor and the maximum discharge power Ps of the battery. Pset , specifically including:

[0065] Step 1.1: The maximum output power of the motor is determined as follows:

[0066] When the motor controller current temperature T mc Lower than the upper limit temperature T of the motor controller for normal operation mcmax ; Current motor temperature T mo Lower than the upper limit temperature T of the motor for normal operation momax , and when the battery power SOC>battery SOC threshold, the maximum output power of the motor is the instantaneous power P of the motor controller MCS ;

[0067] Otherwise, the maximum output power of the motor is the rated operating power P of the motor controller. MCL .

[0068] Step 1.2: Maximum battery discharge power P s The method for obtaining , specifically:

[0069] Calculate the maximum discharge power of the battery based on the battery capacity SOC;

[0070] Step 1.3: The method for obtaining the set power of the metering pump is as follows:

[0071] Maximum output power of the motor and maximum discharge power of the battery P s The smaller value between the two is taken as the set power.

[0072] Step 2: According to the set power P of the metering pump Pset Combined with the predetermined speed of the metering pump corresponding to the gear and the displacement of the metering pump, the pressure turning point of the metering pump corresponding to the gear is calculated. The expression of the pressure turning point is:

[0073] ;

[0074] in: is the pressure turning point of the metering pump, is the set power of the metering pump, The preset speed for the metering pump corresponding to the gear position, is the displacement of the metering pump.

[0075] Step 3: According to the set power of the quantitative pump and the maximum load pressure P Lmax As well as the displacement of the fixed pump, calculate the target speed of the motor corresponding to the gear. The expression of the target speed is:

[0076] ;

[0077] in: is the motor target speed, is the maximum load pressure, is the set power of the metering pump, is the displacement of the metering pump.

[0078] Step 4: When the maximum load pressure P Lmax When the pressure is less than the turning point of the corresponding gear of the metering pump, according to the outlet pressure P of the metering pump p and maximum load pressure P Lmax The pressure difference ΔP between the two adjusts the motor speed in real time.

[0079] When the maximum load pressure P Lmax When the pressure is greater than the turning point of the corresponding gear of the metering pump, the motor operating speed is the target speed of the corresponding gear, specifically including:

[0080] When the pressure difference ΔP is less than the set pressure difference ΔP set The lower limit of , the whole machine controller increases the motor speed with a gradient Δn;

[0081] When the pressure difference ΔP is greater than the set pressure difference ΔP set The upper limit of the motor speed is reduced by the controller with a gradient of Δn.

[0082] Where: Calculate the set pressure difference Δ P set , the expression is:

[0083] ;

[0084] in: Set the pressure difference for the load sensing multi-way valve system when it is unloaded. is the pilot pressure of the load-sensing multi-way valve system, k is the pressure difference correction coefficient, P o It is the pilot pressure when the corresponding valve port of the load-sensing multi-way valve system opens in response to the corresponding action, P imax To achieve the pilot pressure required for the maximum pressure difference of the load sensing multi-way valve system, Sets the maximum differential pressure for load sensing valve systems.

[0085] The calculation method of gradient Δn is as follows:

[0086] ;

[0087] in: It is the speed gradient of the load-sensing multi-way valve system when it is unloaded. is the pilot pressure of the load-sensing multi-way valve system, x is the speed gradient correction coefficient, It is the pilot pressure when the corresponding valve port of the load-sensing multi-way valve system is opened. To achieve the pilot pressure required for the maximum pressure difference of the load sensing multi-way valve system, Set the maximum speed gradient for the load-sensing multi-way valve system;

[0088] Wherein: the set pressure difference ΔP set The adjustment method of the gradient Δn is as follows:

[0089] When the speed and flow rate are low, the set pressure difference ΔP is reduced. set and gradient ;

[0090] When the motor starts and accelerates, increase the set pressure difference ΔP set and gradient ;

[0091] When working at high speed and large flow, increase the set pressure difference ΔP set and gradient .

[0092] Step 5: Under the no-load working condition of the load-sensing multi-way valve system, when the load pressure When the time of zero is greater than T1 and less than T2, the motor operates at the set minimum speed. Lmax When the time of zero is greater than or equal to T2, the motor operating speed is zero, where: T 1、 T2 is the preset motor idle time, T1 <T2。

[0093] Example 3

[0094] This embodiment provides a method for controlling the variable speed of a fixed displacement pump of an electric excavator.

[0095] The whole machine controller collects the battery SOC, and then obtains the maximum discharge power Ps of the battery by looking up the table. Since the battery discharge capacity is different when the SOC is different, the larger the battery SOC, the stronger the battery discharge capacity and the greater the discharge power;

[0096] When the current temperature of the motor controller is lower than the upper limit temperature of the normal operation of the motor controller by 90°C, the current temperature of the motor is lower than the upper limit temperature of the normal operation of the motor by 100°C, and the battery SOC>30%, the maximum output power of the motor is the instantaneous power P of the motor controller. MCS Otherwise, the maximum output power of the motor is the rated operating power P of the motor controller. MCL .

[0097] Maximum output power of the motor and maximum discharge power of the battery P s The smaller value between the two is used to set the power P Pset .

[0098] Set power of metering pump Combined with the preset speed of the metering pump gear and metering pump displacement , calculate the pressure turning point of the metering pump corresponding to the gear The expression is:

[0099] ;

[0100] Set power of metering pump Combined with maximum load pressure P Lmax and metering pump displacement , calculate the expression of the target speed of the motor corresponding to the gear , specifically:

[0101] ;

[0102] When the whole machine is just started and has not yet moved, the motor runs at the preset speed of the corresponding gear. When the operator operates the handle and the maximum load pressure P Lmax Less than the pressure turning point of the corresponding gear of the metering pump At this time, according to the outlet pressure P of the metering pump p and maximum load pressure P Lmax The pressure difference between the two adjusts the motor speed in real time, and the pressure difference ΔP is less than the set pressure difference ΔP set The lower limit of the pressure difference ΔP is greater than the set pressure difference ΔP. set The upper limit of the motor speed is Δn, and the whole machine controller reduces the motor speed with a gradient Δn;

[0103] Set the pressure difference ΔP and speed gradient ΔP set The pressure will change according to the pilot signal of the handle. When the pilot pressure of the handle is less than the pilot pressure of the corresponding valve port of the load-sensitive multi-way valve system, the pressure difference ΔP is set at this time. set When the pilot pressure of the handle is greater than the pilot pressure of the corresponding valve port of the load-sensing multi-way valve system, the set pressure difference ΔP set and gradient Δn will increase with the pilot pressure of the handle, with the maximum upper limits being and At this time, the motor speed will be adjusted in real time. When the pressure difference ΔP is at ΔP set The lower limit and ΔP set The upper limit of the pressure difference ΔP set The sum gradient Δn no longer changes, and the motor speed no longer changes, and it runs at the current speed;

[0104] When the maximum load pressure P Lmax Greater than the pressure turning point of the corresponding gear of the metering pump , the motor rotates at the target speed corresponding to the gear run.

[0105] When the whole machine is in no-load condition, the load pressure When the time of zero is greater than T1 and less than T2, the motor operates at the set minimum speed. Lmax When the time of zero is greater than or equal to T2, the motor operating speed is zero.

[0106] The present invention adopts a motor with variable speed to drive a quantitative pump to form a power source to supply oil to the load-sensitive multi-way valve instead of the traditional motor plus plunger pump, giving full play to the advantages of the motor in speed regulation accuracy, speed regulation response time, and speed regulation stability; it can effectively improve the comfort and stability of control and enhance the driver's driving experience.

[0107] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which are all protected by the present invention.

Claims

1. A variable speed control system for a quantitative pump of an electric excavator, characterized in that: include: Machine controller, motor controller, motor, dosing pump and battery; The whole machine controller is used to send control instructions to the motor controller; The motor controller is used to receive control instructions sent by the vehicle controller, obtain electrical energy from the battery, modulate it through its own inverter, and output current and voltage to the motor to make the motor rotate; The motor is combined with a quantitative pump to form a power source for supplying oil to the load-sensing multi-way valve system of the excavator; The battery is used to provide electrical energy to the motor controller.

2. The electric excavator quantitative pump variable speed control system according to claim 1, characterized in that: Also includes: Pressure sensor, which is used to collect the outlet pressure P of the quantitative pump p and maximum load pressure P Lmax And transmit it to the whole machine controller as a control instruction for adjusting the motor operating speed.

3. A control method for a variable speed control system of a quantitative pump of an electric excavator according to any one of claims 1 to 2, characterized in that: The following steps are involved: According to the maximum output power of the motor and the maximum discharge power of the battery Ps, calculate the set power P of the metering pump Pset ; According to the set power P of the metering pump Pset Calculate the pressure turning point of the metering pump corresponding to the gear position based on the predetermined speed of the metering pump corresponding to the gear position and the displacement of the metering pump; According to the set power of the quantitative pump combined with the maximum load pressure P Lmax and the displacement of the metering pump to calculate the target speed of the motor corresponding to the gear; When the maximum load pressure P Lmax When the pressure is less than the turning point of the corresponding gear of the metering pump, according to the outlet pressure P of the metering pump p and maximum load pressure P Lmax The pressure difference between the two adjusts the motor speed in real time; When the maximum load pressure P Lmax When the pressure is greater than the pressure turning point of the corresponding gear of the metering pump, the target speed of the corresponding gear is used as the motor operating speed.

4. The electric excavator quantitative pump variable speed control method according to claim 3, characterized in that: The maximum output power of the motor is determined as follows: When the motor controller current temperature T mc Lower than the upper limit temperature T of the motor controller for normal operation mcmax , the current motor temperature T mo Lower than the upper limit temperature T of the motor for normal operation momax , and when the battery power SOC>battery SOC threshold, the maximum output power of the motor is the instantaneous power P of the motor controller MCS ; Otherwise, the maximum output power of the motor is the rated operating power P of the motor controller. MCL .

5. The electric excavator quantitative pump variable speed control method according to claim 3, characterized in that: The method for obtaining the set power of the quantitative pump is specifically as follows: Maximum output power of the motor and maximum discharge power of the battery P s The smaller value between the two is taken as the set power.

6. The electric excavator quantitative pump variable speed control method according to claim 3, characterized in that: The expression for calculating the pressure turning point of the metering pump corresponding to the gear position according to the set power of the metering pump, the predetermined speed of the metering pump gear position, and the displacement of the metering pump is specifically: ； in: is the pressure turning point of the metering pump, is the set power of the metering pump, The preset speed for the metering pump corresponding to the gear position, is the displacement of the metering pump.

7. The electric excavator quantitative pump variable speed control method according to claim 3, characterized in that: The set power of the quantitative pump is combined with the maximum load pressure P Lmax As well as the displacement of the metering pump, the expression for calculating the target speed of the motor corresponding to the gear is: ； in: is the motor target speed, is the maximum load pressure, is the set power of the metering pump, is the displacement of the metering pump.

8. The electric excavator quantitative pump variable speed control method according to claim 3, characterized in that: According to the outlet pressure P of the metering pump p and maximum load pressure The pressure difference between the two adjusts the motor speed in real time, specifically: When the pressure difference ΔP is less than the set pressure difference ΔP set The lower limit of , the whole machine controller increases the motor speed with a gradient Δn; When the pressure difference ΔP is greater than the set pressure difference ΔP set The upper limit of the motor speed is reduced by the controller with a gradient of Δn. The calculation method of the gradient Δn is specifically as follows: ； in: It is the speed gradient of the load-sensing multi-way valve system when it is unloaded. is the pilot pressure of the load-sensing multi-way valve system, x is the speed gradient correction coefficient, It is the pilot pressure when the corresponding valve port of the load-sensing multi-way valve system is opened. To achieve the pilot pressure required for the maximum pressure difference of the load sensing multi-way valve system, Set the maximum speed gradient for the load-sensing multi-way valve system; Where: Set pressure difference ΔP set The calculation method is as follows: ； in: Set the pressure difference for the load sensing multi-way valve system when it is unloaded. is the pilot pressure of the load-sensing multi-way valve system, k is the pressure difference correction coefficient, P o It is the pilot pressure when the corresponding valve port of the load-sensing multi-way valve system opens in response to the corresponding action, P imax To achieve the pilot pressure required for the maximum pressure difference of the load sensing multi-way valve system, Sets the maximum differential pressure for load sensing valve systems.

9. The electric excavator quantitative pump variable speed control method according to claim 3, characterized in that: Under the no-load working condition of the load-sensing multi-way valve system, when the load pressure When the time of zero is greater than T1 and less than T2, the motor operates at the set minimum speed. When the load pressure P Lmax When the time of zero is greater than or equal to T2, the motor operating speed is zero; Where: T 1、 T2 is the preset motor idle time, T1 <T2。

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