Control Method and Control Device for Energy Recovery System of Electric Forklift

Abstract

The present application discloses a control method and a control device for an energy recovery system of an electric forklift, and the technical field to which it belongs is forklift control technology. The control method for the energy recovery system of the electric forklift includes: calculating a total target braking torque value according to the pedal angle of the electric brake pedal; determining a maximum braking torque value; determining a motor braking torque limit value; determining a motor charging torque limit value; setting the minimum value among the above three values as a reference braking torque value; judging whether the reference braking torque value is greater than or equal to the total target braking torque value; if so, controlling the drive motor to brake according to the total target braking torque value; if not, controlling the drive motor to brake according to the reference braking torque value, and adjusting the valve opening of the electro-hydraulic proportional valve so that the brake brakes according to the remaining braking torque value. The present application can maximize the recovery of kinetic energy on the premise of ensuring the safety of the forklift.

Description

Technical Field

[0001] The present application relates to the technical field of forklift control, and particularly relates to a control method and a control device for an energy recovery system of an electric forklift. Background Art

[0002] With the rapid development of the logistics industry, electric special operation equipment such as forklifts plays an increasingly important role in material handling operations. However, forklifts need to start and stop frequently during operation, resulting in the waste of kinetic energy being converted into heat through friction during braking. In addition, the converted heat causes the hydraulic oil to overheat, and additional energy is consumed to dissipate the heat of the hydraulic oil.

[0003] In related technologies, there is a solution to use an energy recovery system (i.e., an electric braking system) of an electric forklift to recover kinetic energy. However, in order to ensure the safety of the vehicle braking, in the above solution, when the remaining battery power is too high or the power is reduced, the braking recovery function is directly stopped, resulting in a large loss of kinetic energy. In addition, related technologies rely entirely on electric motor braking to recover kinetic energy. When the braking demand is large, the design requirements of the braking deceleration cannot be met, and accidents are likely to occur.

[0004] Therefore, how to maximize the recovery of kinetic energy while ensuring the safety of the forklift is a technical problem that those skilled in the art need to solve currently. Summary of the Invention

[0005] The purpose of the present application is to provide a control method and a control device for an energy recovery system of an electric forklift, which can maximize the recovery of kinetic energy while ensuring the safety of the forklift.

[0006] To solve the above technical problems, the present application provides a control method for an energy recovery system of an electric forklift, which is applied to a control device of the energy recovery system of the electric forklift. The energy recovery system of the electric forklift further includes a power battery, a drive motor, a brake, an electric brake pedal, and an electro-hydraulic proportional valve. The electro-hydraulic proportional valve is used to control the braking force of the brake by adjusting the pressure of the hydraulic oil. The control method for the energy recovery system of the electric forklift includes:

[0007] Calculating a total target braking torque value according to the pedal angle of the electric brake pedal;

[0008] Determining a maximum braking torque value according to the rotational speed of the drive motor;

[0009] Determining an electric motor braking torque limit according to the power limit level of the drive motor;

[0010] Determining a motor charging torque limit according to the remaining power and the cell temperature of the power battery;

[0011] Set the minimum value among the maximum braking torque value, the motor braking torque limit value, and the motor charging torque limit value as the reference braking torque value;

[0012] Determine whether the reference braking torque value is greater than or equal to the total target braking torque value;

[0013] If so, control the drive motor to brake according to the total target braking torque value; wherein, when the drive motor brakes, the recovered kinetic energy is used to charge the power battery;

[0014] If not, control the drive motor to brake according to the reference braking torque value, and adjust the valve opening of the electro-hydraulic proportional valve so that the brake brakes according to the remaining braking torque value; wherein, the remaining braking torque value is the difference between the total target braking torque value and the reference braking torque value.

[0015] Optionally, before calculating the total target braking torque value according to the pedal angle of the electric brake pedal, it further includes:

[0016] Obtain the sensor signal collected by the pedal angle sensor;

[0017] Calculate the pedal angle of the electric brake pedal according to the sensor signal;

[0018] If the pedal angle of the electric brake pedal is greater than the preset angle, enter the step of calculating the total target braking torque value according to the pedal angle of the electric brake pedal;

[0019] Correspondingly, after calculating the total target braking torque value according to the pedal angle of the electric brake pedal, it further includes:

[0020] If the rotational speed of the drive motor is less than or equal to the preset rotational speed, adjust the valve opening of the electro-hydraulic proportional valve so that the brake brakes according to the total target braking torque value.

[0021] Optionally, determining the maximum braking torque value according to the rotational speed of the drive motor includes:

[0022] Obtain the motor external characteristic curve of the drive motor;

[0023] Query the maximum braking torque value corresponding to the rotational speed of the drive motor on the motor external characteristic curve.

[0024] Optionally, determining the motor braking torque limit value according to the power limit level of the drive motor includes:

[0025] Detect the operating state of the drive motor, and determine the power limit level of the drive motor according to the operating state;

[0026] Determine the torque coefficient of the motor under the power limit state according to the power limit level;

[0027] Query the maximum braking torque value corresponding to the speed of the drive motor on the external characteristic curve of the motor;

[0028] Set the product of the torque coefficient of the motor under the power limit state and the maximum braking torque value as the braking torque limit of the motor.

[0029] Optionally, determine the motor charging torque limit according to the remaining power and cell temperature of the power battery, including:

[0030] Read the remaining power, cell temperature and battery voltage of the power battery;

[0031] Query the battery allowable charging current corresponding to the remaining power and the cell temperature;

[0032] Calculate the motor charging torque limit according to the battery allowable charging current, the battery voltage and the speed of the drive motor.

[0033] Optionally, adjust the valve opening of the electro-hydraulic proportional valve so that the brake brakes according to the remaining braking torque value, including:

[0034] Calculate the target current value according to the remaining braking torque value and the current value proportional coefficient of the electro-hydraulic proportional valve;

[0035] Set the current value of the electro-hydraulic proportional valve as the target current value, so as to adjust the valve opening of the electro-hydraulic proportional valve and make the brake brake according to the remaining braking torque value.

[0036] Optionally, it further includes:

[0037] If an electric braking function off command is received, do not respond to the change in the pedal angle of the electric brake pedal.

[0038] This application also provides a control device for an electric forklift energy recovery system. The electric forklift energy recovery system further includes a power battery, a drive motor, a brake, an electric brake pedal and an electro-hydraulic proportional valve. The electro-hydraulic proportional valve is used to control the braking force of the brake by adjusting the pressure of the hydraulic oil. The control device of the electric forklift energy recovery system includes:

[0039] A total torque calculation module, configured to calculate a total target braking torque value according to the pedal angle of the electric brake pedal;

[0040] A first torque determination module, configured to determine the maximum braking torque value according to the speed of the drive motor;

[0041] A second torque determination module, configured to determine a motor braking torque limit value according to the power limit level of the drive motor;

[0042] A third torque determination module, configured to determine a motor charging torque limit value according to the remaining power and cell temperature of the power battery;

[0043] A reference torque determination module, configured to set the minimum value among the maximum braking torque value, the motor braking torque limit value, and the motor charging torque limit value as the reference braking torque value;

[0044] A decision module, configured to determine whether the reference braking torque value is greater than or equal to the total target braking torque value; if so, control the drive motor to brake according to the total target braking torque value; wherein, when the drive motor brakes, the recovered kinetic energy is used to charge the power battery; if not, control the drive motor to brake according to the reference braking torque value, and adjust the valve opening of the electro-hydraulic proportional valve so that the brake brakes according to the remaining braking torque value; wherein, the remaining braking torque value is the difference between the total target braking torque value and the reference braking torque value.

[0045] Optionally, the input end of the electro-hydraulic proportional valve is connected to an oil source, the output end of the electro-hydraulic proportional valve is connected to the input end of a shuttle valve, the output end of the shuttle valve is connected to the brake, and the brake is a wet brake.

[0046] Optionally, the electric forklift energy recovery system further includes a foot brake valve, the input end of the foot brake valve is connected to an oil source, the output end of the foot brake valve is connected to the input end of a shuttle valve, and the output end of the shuttle valve is connected to the brake.

[0047] The present application provides a control method for an energy recovery system of an electric forklift. The energy recovery system of the electric forklift includes a power battery, a drive motor, a brake, an electric brake pedal, and an electro-hydraulic proportional valve. In this solution, the total target braking torque value is calculated based on the pedal angle of the electric brake pedal, and the braking mode is determined by comparing the total target braking torque value with the reference braking torque value that the motor can achieve. The present application determines the maximum braking torque value according to the rotational speed of the drive motor, determines the motor braking torque limit value according to the power limit level of the drive motor, and determines the motor charging torque limit value according to the remaining power and cell temperature of the power battery, so as to use the minimum value among the above three torque values as the reference braking torque value; selecting the minimum value as the reference braking torque value can ensure the safety of the braking process and avoid overload. If the reference braking torque value is greater than or equal to the total target braking torque value, the drive motor is directly controlled to brake according to the total target braking torque value; if the reference braking torque value is less than the total target braking torque value, the drive motor and the electro-hydraulic proportional valve are controlled to brake. The present application can dynamically determine the reference braking torque value that the drive motor can output according to the rotational speed, power limit level of the drive motor, and the state of the power battery, ensuring maximum energy recovery within a safe range. During the braking process, the torque of the drive motor is not higher than the reference braking torque value, which can balance the safety of the braking process and the kinetic energy recovery effect. Therefore, the present application can maximize the recovery of kinetic energy on the premise of ensuring the safety of the forklift. The present application also provides a control device for an energy recovery system of an electric forklift, which has the above beneficial effects and will not be elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0049] Figure 1 It is a flowchart of a control method for an energy recovery system of an electric forklift provided by an embodiment of the present application;

[0050] Figure 2 It is a schematic diagram of the principle of an energy recovery system of an electric forklift provided by an embodiment of the present application;

[0051] Figure 3 It is a schematic diagram of an external characteristic curve of a motor provided by an embodiment of the present application;

[0052] Figure 4 It is an energy management control flowchart of a braking energy recovery system of a heavy-duty electric forklift provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0053] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the following will clearly and completely describe the technical solutions in the embodiments of this application with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts belong to the scope of protection of this application.

[0054] Please refer to the following Figure 1 , Figure 1 which is a flowchart of a control method for an energy recovery system of an electric forklift provided by an embodiment of this application.

[0055] The specific steps may include:

[0056] S101: Calculate the total target braking torque value according to the pedal angle of the electric brake pedal.

[0057] Among them, this embodiment can be applied to a control device of an energy recovery system of an electric forklift. The above-mentioned energy recovery system of the electric forklift further includes a power battery, a drive motor, a brake, an electric brake pedal, and an electro-hydraulic proportional valve. The electro-hydraulic proportional valve is used to control the braking force of the brake by adjusting the pressure of the hydraulic oil. The above control device can be a vehicle control unit (VCU). The above forklift can be an electric forklift powered by a power battery and driven by a drive motor, such as a heavy-duty electric forklift. The above brake can be a wet brake.

[0058] The above brake can be a brake in the motor-driven walking system. The brake can be installed at the wheel end of the drive axle. The brake and the electro-hydraulic proportional valve are connected by a pipeline. The electro-hydraulic proportional valve is a control valve that can adjust the pressure or flow rate of the hydraulic oil in proportion according to the input signal (current or voltage). The electro-hydraulic proportional valve can control the braking force of the brake by adjusting the pressure of the hydraulic oil, thereby achieving braking.

[0059] Please refer to Figure 2 , Figure 2It is a schematic diagram of the principle of an energy recovery system for an electric forklift provided by an embodiment of the present application. The energy recovery system for an electric forklift is also called an electro-hydraulic composite braking system for a heavy electric forklift. The system includes a control device (i.e., vehicle-mounted controller VCU, Vehicle Control Unit) 1, an accelerator pedal 2, an electro-brake pedal (including a brake pedal angle sensor) 3, an electro-hydraulic proportional valve (also called a proportional pressure reducing valve) 4, a foot brake valve 5, a shuttle valve 6, an oil source 7, a vehicle-mounted instrument 8, a power battery 9, a motor (i.e., a drive motor) and a controller 10, a parking hydraulic brake 11, a differential 12, and a wet brake 13. The power battery can perform charging and discharging operations with the drive motor. The figure shows the input and output lines of the VCU, the CAN (Controller Area Network, controller area network bus) control line. There can be hydraulic connections, mechanical connections, or high-voltage connections between each device. The motor-driven walking system includes a drive axle with a wet brake, a differential, a parking brake, and a drive motor and a controller. The accelerator pedal and the brake pedal angle sensor are connected to the signal input end of the control device. The output end of the control device is connected to the electro-hydraulic proportional valve. The oil source is connected to the input ends of the electro-hydraulic proportional valve and the foot brake valve. The output ends of both are connected to the input end of the shuttle valve. The output end of the shuttle valve is connected to the wet brake of the vehicle drive axle. The vehicle-mounted instrument and the drive motor control device perform information interaction with the electro-hydraulic proportional valve through the CAN bus. The power battery is connected to the motor controller through a high-voltage line.

[0060] When the driver steps on the electro-brake pedal, the brake pedal angle sensor transmits the angle signal to the control device. The control device can calculate the total target braking torque value according to the pedal angle (i.e., pedal opening) and the braking torque curve. The total target braking torque value reflects the driver's braking demand and is used for subsequent braking energy recovery and hydraulic braking distribution.

[0061] This step is based on the premise that the electro-brake function of the forklift is not turned off. If a command to turn off the electro-brake function is received, it will not respond to the change in the pedal angle of the electro-brake pedal. At this time, the driver can brake through the foot brake valve.

[0062] S102: Determine the maximum braking torque value according to the rotational speed of the drive motor.

[0063] Among them, before this step, there can be an operation of obtaining the rotational speed of the drive motor at the current moment. This embodiment can pre-store the corresponding relationship between the rotational speed and the maximum braking torque value, and determine the maximum braking torque value corresponding to the rotational speed at the current moment based on this corresponding relationship. The above-mentioned maximum braking torque value refers to the maximum reverse torque that the drive motor can generate in the braking mode.

[0064] As a feasible implementation manner, the present embodiment can determine the maximum braking torque value by using the external characteristic curve of the motor. The specific process is as follows: Obtain the external characteristic curve of the drive motor; query the maximum braking torque value corresponding to the speed of the drive motor on the external characteristic curve of the motor. Please refer to Figure 3 , Figure 3 FIG. Figure 3 is a schematic diagram of an external characteristic curve of a motor provided by an embodiment of the present application. The abscissa represents the ratio of the speed of the motor to the maximum speed, and the ordinate represents the maximum braking torque value.

[0065] S103: Determine the motor braking torque limit according to the power limit level of the drive motor.

[0066] Among them, in this step, the power limit level of the drive motor can be determined according to the state of the drive motor. Before this step, the corresponding relationship between the power limit level and the motor braking torque limit can be stored in advance, and then the motor braking torque limit corresponding to the power limit level of the drive motor at the current moment can be determined based on the above corresponding relationship. The motor braking torque limit refers to: the torque upper limit value set to prevent the motor from being overloaded, overheated or damaged during the braking process.

[0067] As a feasible implementation manner, the motor braking torque limit can be determined by the following method: Detect the operating state of the drive motor, determine the power limit level of the drive motor according to the operating state; determine the torque coefficient of the motor power limit state according to the power limit level; query the maximum braking torque value corresponding to the speed of the drive motor on the external characteristic curve of the motor; set the product of the torque coefficient of the motor power limit state and the maximum braking torque value as the motor braking torque limit. The torque coefficient can be a proportionality coefficient with a value range of 0 to 1, which is used to represent the proportion of the braking torque that the drive motor can output at the current power limit level. The above power limit level can also be set by the motor manufacturer.

[0068] S104: Determine the motor charging torque limit according to the remaining power and cell temperature of the power battery.

[0069] Among them, before this step, the remaining power (SOC, State of Charge) and cell temperature of the power battery can also be obtained. Before this step, the corresponding relationship between the remaining power, cell temperature and motor charging torque limit can be stored in advance, and the motor charging torque limit corresponding to the current remaining power and cell temperature can be determined based on this corresponding relationship.

[0070] The above motor charging torque limit refers to the braking torque value that the motor can safely output in the braking energy recovery mode, so as to prevent the motor and the battery from being overloaded, overheated or damaged during the charging process.

[0071] As a feasible implementation manner, the motor charging torque limit value can be calculated in the following way: read the remaining power, cell temperature and battery voltage of the power battery; query the battery allowable charging current corresponding to the remaining power and the cell temperature; calculate the motor charging torque limit value based on the battery allowable charging current, the battery voltage and the rotational speed of the drive motor.

[0072] Specifically, in this embodiment, the battery allowable charging current corresponding to the remaining power and the cell temperature can be queried from the power battery pulse recharge ammeter;

[0073] Table 1 Power battery pulse recharge ammeter

[0074]

[0075] Table 1 shows the corresponding relationship between the remaining power SOC, the cell temperature and the battery allowable charging current. The battery allowable charging current is the 30S pulse recharge current, and the unit is ampere.

[0076] S105: Set the minimum value among the maximum braking torque value, the motor braking torque limit value and the motor charging torque limit value as the reference braking torque value.

[0077] Based on obtaining the maximum braking torque value, the motor braking torque limit value and the motor charging torque limit value, this step can set the minimum value among the above three values as the reference braking torque value.

[0078] The reference braking torque value refers to the upper limit of the safe braking torque determined according to multiple limiting conditions (such as the maximum braking torque value of the motor, the motor braking torque limit value and the motor charging torque limit value) in the braking energy recovery system. The above method of determining the reference braking torque value can ensure the safety of the braking process, prevent the motor, battery or vehicle system from being overloaded, and maximize the energy recovery efficiency within the safe range.

[0079] S106: Judge whether the reference braking torque value is greater than or equal to the total target braking torque value; if so, enter S107; if not, enter S108.

[0080] Among them, this step compares the reference braking torque value with the total target braking torque value to determine the braking method, so as to ensure the safety and energy recovery efficiency of the braking process.

[0081] If the reference braking torque value is greater than or equal to the total target braking torque value, the drive motor can be used for braking completely to achieve maximum energy recovery; if the reference braking torque value is less than the total target braking torque value, it means that the braking ability of the drive motor is insufficient, and hydraulic braking needs to be called as a supplement. The above scheme can give priority to using the drive motor to brake and recover kinetic energy on the premise of ensuring safety, and use hydraulic braking as a supplement when it is insufficient.

[0082] S107: Control the drive motor to brake according to the total target braking torque value.

[0083] Among them, this step is based on the reference braking torque value being greater than or equal to the total target braking torque value. At this time, the drive motor can be controlled to brake according to the total target braking torque value. When the drive motor brakes, the recovered kinetic energy is used to charge the power battery.

[0084] S108: Control the drive motor to brake according to the reference braking torque value, and adjust the valve opening of the electro-hydraulic proportional valve so that the brake brakes according to the remaining braking torque value.

[0085] Among them, this step is based on the reference braking torque value being less than the total target braking torque value. At this time, the drive motor can be controlled to brake according to the reference braking torque value, and the valve opening of the electro-hydraulic proportional valve is adjusted so that the brake brakes according to the remaining braking torque value. The remaining braking torque value is the difference between the total target braking torque value and the reference braking torque value.

[0086] This embodiment can pre-store the corresponding relationship between the valve opening of the electro-hydraulic proportional valve and the braking torque of the brake. Based on this corresponding relationship, the valve opening of the electro-hydraulic proportional valve can be adjusted so that the brake brakes according to the remaining braking torque value. The sum of the braking torque of the drive motor and the braking torque of the brake is equal to the total target braking torque value. The electro-hydraulic proportional valve indirectly realizes the adjustment of the braking force by controlling the pressure or flow rate of the hydraulic system.

[0087] This embodiment provides a control method for an energy recovery system of an electric forklift. The energy recovery system of the electric forklift includes a power battery, a drive motor, a brake, an electric brake pedal, and an electro-hydraulic proportional valve. In this solution, the total target braking torque value is calculated based on the pedal angle of the electric brake pedal. By comparing the total target braking torque value with the reference braking torque value that the motor can achieve, the braking mode is determined. In this embodiment, the maximum braking torque value is determined according to the rotational speed of the drive motor, the electric motor braking torque limit value is determined according to the power limit level of the drive motor, and the motor charging torque limit value is determined according to the remaining power and cell temperature of the power battery, so as to take the minimum value of the above three torque values as the reference braking torque value; selecting the minimum value as the reference braking torque value can ensure the safety of the braking process and avoid overload. If the reference braking torque value is greater than or equal to the total target braking torque value, the drive motor is directly controlled to brake according to the total target braking torque value; if the reference braking torque value is less than the total target braking torque value, the drive motor and the electro-hydraulic proportional valve are controlled to brake. This embodiment can dynamically determine the reference braking torque value that the drive motor can output according to the rotational speed of the drive motor, the power limit level, and the state of the power battery, ensuring maximum energy recovery within a safe range. During the braking process, the torque of the drive motor is not higher than the reference braking torque value, which can balance the safety of the braking process and the kinetic energy recovery effect. Therefore, this embodiment can achieve maximum kinetic energy recovery while ensuring the safety of the forklift.

[0088] As for Figure 1 As a further introduction to the corresponding embodiment, before calculating the total target braking torque value according to the pedal angle of the electric brake pedal, the sensor signal collected by the pedal angle sensor can also be obtained; the pedal angle of the electric brake pedal is calculated according to the sensor signal; if the pedal angle of the electric brake pedal is greater than the preset angle, the step of calculating the total target braking torque value according to the pedal angle of the electric brake pedal is entered. The above preset angle can be 0 degrees or an angle to prevent accidental touch (such as 5 degrees).

[0089] After calculating the total target braking torque value according to the pedal angle of the electric brake pedal, if the rotational speed of the drive motor is less than or equal to the preset rotational speed, the valve opening of the electro-hydraulic proportional valve is adjusted so that the brake brakes according to the total target braking torque value; if the rotational speed of the drive motor is greater than the preset rotational speed, the operations of S102 - S108 are entered. The above control strategy can give priority to using hydraulic braking at low speeds to ensure the braking effect and vehicle safety, while avoiding the problem of poor braking effect of the electric motor.

[0090] As for Figure 1For further introduction of the corresponding embodiment, the valve opening of the electro-hydraulic proportional valve can be adjusted in the following manner: calculate the target current value according to the remaining braking torque value and the current value proportionality coefficient of the electro-hydraulic proportional valve; set the current value of the electro-hydraulic proportional valve to the target current value, so as to adjust the valve opening of the electro-hydraulic proportional valve and make the brake brake according to the remaining braking torque value.

[0091] Specifically, the electro-hydraulic proportional valve can adjust the position of the spool according to the target current value, changing the pressure and flow rate of the hydraulic oil. The adjusted hydraulic oil is delivered to the brake, pushing the brake piston to generate a braking force matching the remaining braking torque value. The above solution can supplement the braking force through hydraulic braking when the electric motor braking force is insufficient, ensuring that the vehicle can decelerate or stop safely, and at the same time achieving precise braking control.

[0092] In order to avoid unnecessary energy consumption, the kinetic energy recovery technology has emerged. For example, in related technologies, there is a heavy-duty electric forklift electro-hydraulic composite braking system and control method. This solution adopts the form of a double braking pedal. While retaining the original foot-operated hydraulic braking pedal, an additional recovery pedal and an electro-hydraulic proportional valve braking circuit are added. The maximum braking torque is determined according to the angle of the recovery pedal, and the principle of giving priority to electric motor braking is adopted to coordinate and control the electric motor braking torque and the hydraulic braking torque controlled by the proportional valve, maximizing the recovery of kinetic energy under the condition of ensuring the safe driving of the vehicle.

[0093] In related technologies, there are also braking force distribution control methods, braking systems and braking methods for electric loaders, whose principles are similar to those of the heavy-duty electric forklift electro-hydraulic composite braking system and control method. However, in the process of using the electric braking system, it is inevitable that the motor and battery will operate with limited power and derating. If the system does not handle the above situations accordingly, it is very easy to cause safety accidents. Therefore, kinetic energy recovery energy management, as an important module in the kinetic energy recovery control system, has been widely concerned at present.

[0094] Currently, for the battery and motor power limitation of the kinetic energy recovery system of electric industrial vehicles or electric vehicles, the kinetic energy recovery is usually directly cancelled. When a failure occurs in the hydraulic oil circuit or the drive motor, the electric braking recovery function is cancelled, and the foot valve is directly used for braking. Related technologies prohibit charging the battery when the remaining battery power is too high, and do not consider the influence of temperature on the battery charging power, so the solution is incomplete.

[0095] In the related art, there is also an energy management solution. In this solution, the vehicle controller determines the battery charging power table according to the voltage, current, remaining power and temperature information fed back by the battery system BMS (Battery Management System), and then determines the maximum charging torque of the battery according to the motor speed; according to the maximum allowable braking torque of the motor fed back by the motor controller MCU (Microcontroller Unit), the energy recovery torque value of the braking system is comprehensively obtained, and finally the actual motor recovery torque is obtained by associating with the pedal angle. Although this solution takes into account the battery recharge power and the motor power generation power limit, it does not consider how to ensure the braking effect of the braking system when the motor recovery torque is insufficient.

[0096] Although the above related art takes into account the situation of power reduction operation of the battery and the motor during kinetic energy recovery, there are the following problems:

[0097] 1. The influencing factors considered for power reduction braking are not comprehensive enough: The related technology only considers stopping the braking recovery function when the state of charge (SOC) of the battery is too high, but does not consider the influence of temperature on the SOC of the battery. The allowable recharge current of the battery is related to both too high and too low temperatures.

[0098] 2. The solution is relatively simple: The existing solution is to prohibit kinetic energy recovery once power reduction operation occurs. Although it can ensure the safety of vehicle braking, at this time the battery still allows a certain recharge current. Directly canceling the recovery function will cause kinetic energy to be wasted in vain; the related technology comprehensively considers the influence of the SOC of the battery and the cell temperature on the recharge power, and also considers the influence of motor power reduction on the braking torque. Therefore, this solution can also recover part of the kinetic energy when the battery and the motor are powered down, but if the total braking torque is greater than the final braking torque of the motor, no corresponding hydraulic (mechanical) braking compensation is performed, resulting in a relatively small total braking torque actually executed, which cannot meet the design requirements of the braking deceleration and is likely to cause accidents.

[0099] This embodiment adds an energy management function, comprehensively considers the influencing factors of battery recharge power reduction and motor power reduction braking, and obtains the final braking torque allowed to be executed by the motor through parameter calculation and program judgment. Within the range allowed by the battery recharge power and the motor braking power, electric braking is preferentially used. When the electric braking torque cannot meet the total target braking torque requirement, the electro-hydraulic proportional valve is used for braking torque compensation. Therefore, this embodiment can not only ensure that when the battery and the motor are powered down, the braking intensity is only related to the pedal angle, but also ensure that the recharge power does not exceed the allowable values of the battery and the motor, and at the same time maximize the kinetic energy recovery.

[0100] The following uses specific embodiments to illustrate the energy management control scheme of the braking energy recovery system of heavy-duty electric forklifts:

[0101] When the driver cancels the electric braking function, only the foot valve braking can be performed.

[0102] When the electric braking function is effective, if the driver steps on the electric braking pedal for kinetic energy recovery, the control device first collects the signal of the braking pedal angle sensor, calculates the total target braking torque according to the opening of the braking pedal, detects the remaining power value of the power battery, the cell temperature, and the current speed of the motor, and according to the maximum braking torque value that the motor can provide 、the braking torque limit of the motor under the power limit state of the motor 、the maximum motor charging torque limit allowed by the battery (i.e., the battery allowed torque limit) to determine the reference braking torque value (also known as the motor target torque limit value) ,the control device calculates the electro-hydraulic proportional valve current value according to to complete the hydraulic braking pressure compensation.

[0103] Please refer to Figure 4 , Figure 4 which is the energy management control flow chart of a heavy-duty electric forklift braking energy recovery system provided by an embodiment of the present application, and specifically includes the following steps:

[0104] Step 1: Collect the electric braking pedal angle signal and detect the remaining power value of the power, the cell temperature, and the current speed of the motor.

[0105] Step 2: Calculate the total target braking torque value according to the pedal angle 。

[0106] The above steps 1 and 2 can be executed by the signal acquisition and calculation module, and the unit of the total target braking torque is Newton meter (Nm).

[0107] Step 3: Determine whether the current motor speed is greater than the critical speed ; if so, go to step 4; if not, go to step 7.

[0108] Step 4: Determine the maximum braking torque value that the motor can provide according to the external characteristic curve of the motor and the current speed ; determine the braking torque limit of the motor according to the motor power limit level ; determine the motor charging torque limit according to the charging power table 。

[0109] Step 5: Calculate the reference braking torque value 。

[0110] The unit of the reference braking torque value is Newton meter (Nm), and Min means taking the minimum value.

[0111] Step 6: Determine if it is greater than ; if so, then , ; if not, then , . represents the actual output torque of the drive motor, with the unit of Newton-meter (Nm); represents the current value of the electro-hydraulic proportional valve (i.e., the target current value), with the unit of milliampere (mA); K represents the current value proportionality coefficient of the electro-hydraulic proportional valve.

[0112] Step 7: = 0, .

[0113] The energy management control strategy of the electro-hydraulic composite braking system provided in this embodiment is as follows:

[0114] Determine whether the current motor speed is greater than the preset speed for kinetic energy recovery (i.e., the minimum threshold speed ), if not satisfied, set the actual output torque of the drive motor to 0, and all braking forces are provided by the hydraulic braking force regulated by the electro-hydraulic proportional valve. At this time, the current value of the electro-hydraulic proportional valve is ; if satisfied, enter the energy management control process of the electro-hydraulic composite braking system, obtain the maximum braking torque that the motor can provide at the current speed according to the motor external characteristic curve and the current speed , determine the torque limit value under the motor power limit state according to the motor power limit level , where is the torque coefficient in the motor power limit state (this parameter is determined by the motor manufacturer), T is the torque value allowed at the current speed of the motor, determine the maximum motor charging torque limit allowed by the battery according to the battery charging ammeter , where is the battery allowable charging current obtained by looking up the table; is the battery voltage, which is obtained by the control device collecting battery information through CAN communication; n is the current speed of the motor, and take the minimum value of the three as the reference braking torque value ; if the total target braking torque , then the actual output torque of the drive motor (i.e., the motor target braking torque) , calculate to determine the control pressure corresponding to the current value of the electro-hydraulic proportional valve. If , then the actual output torque of the drive motor , and the control pressure of the electro-hydraulic proportional valve is 0.

[0115] This embodiment comprehensively considers the influencing factors of battery recharge power reduction and motor power reduction braking, and obtains the reference braking torque value that the motor is finally allowed to execute through parameter calculation and program judgment. ; This embodiment preferentially uses electric motor braking. If , then calculate to determine the control pressure corresponding to the electro-hydraulic proportional valve current value, and drive the torque actually output by the motor . If , then the control pressure of the electro-hydraulic proportional valve is 0. .

[0116] This embodiment adopts the form of a double braking pedal. While retaining the traditional foot-operated hydraulic braking pedal, an additional electric braking recovery pedal and an electro-hydraulic proportional valve braking circuit are added. The maximum braking torque is determined according to the electric braking recovery pedal, and the principle of giving priority to electric motor braking is adopted to coordinately control the braking torque of the electric motor and the hydraulic braking torque controlled by the proportional valve, so as to maximize the recovery of kinetic energy under the condition of ensuring the safe driving of the vehicle; the traditional foot-operated valve braking can be used to ensure the safety of the system in case of emergency or electric braking failure.

[0117] This embodiment comprehensively considers the influencing factors of battery recharge power reduction and motor power reduction braking, detects the remaining power of the power battery and the cell temperature, calculates the maximum allowable recharge current of the battery under the current temperature and SOC conditions, and combines the battery voltage and the motor speed to obtain the allowable recharge torque of the battery. According to the allowable braking torque fed back by the motor MCU and the external characteristic torque of the motor, the minimum value of the three is taken as the reference braking torque value; the overall braking torque is obtained by detecting the angle of the electric braking pedal, and the principle of giving priority to electric motor braking is adopted. When the reference braking torque value cannot meet the total target braking torque requirement, the electro-hydraulic proportional valve is used for braking torque compensation. This embodiment not only ensures the safety and reliability of the electro-hydraulic composite braking system, but also can maximize the recovery of kinetic energy without exceeding the recharge power when the battery and the motor have power reduction failures, achieving the effect of energy saving. This embodiment solves the problem that the braking deceleration does not meet the driver's requirements when the battery and the motor of the braking energy recovery system of a heavy-duty electric forklift operate at reduced power, and at the same time ensures the maximization of kinetic energy recovery under the power limit state.

[0118] A control device for an energy recovery system of an electric forklift provided by an embodiment of the present application. The energy recovery system of the electric forklift further includes a power battery, a drive motor, a brake, an electric braking pedal, and an electro-hydraulic proportional valve. The electro-hydraulic proportional valve is used to control the braking force of the brake by adjusting the pressure of the hydraulic oil. The control device for the energy recovery system of the electric forklift includes:

[0119] A total torque calculation module, configured to calculate a total target braking torque value according to the pedal angle of the electric braking pedal;

[0120] The first torque determination module is used to determine the maximum braking torque value according to the rotational speed of the drive motor;

[0121] The second torque determination module is used to determine the electric motor braking torque limit according to the power limit level of the drive motor;

[0122] The third torque determination module is used to determine the motor charging torque limit according to the remaining power and cell temperature of the power battery;

[0123] The reference torque determination module is used to set the minimum value among the maximum braking torque value, the electric motor braking torque limit, and the motor charging torque limit as the reference braking torque value;

[0124] The decision module is used to determine whether the reference braking torque value is greater than or equal to the total target braking torque value; if so, control the drive motor to brake according to the total target braking torque value; wherein, when the drive motor brakes, the recovered kinetic energy is used to charge the power battery; if not, control the drive motor to brake according to the reference braking torque value, and adjust the valve opening of the electro-hydraulic proportional valve so that the brake brakes according to the remaining braking torque value; wherein, the remaining braking torque value is the difference between the total target braking torque value and the reference braking torque value.

[0125] Further, the input end of the electro-hydraulic proportional valve is connected to the oil source, the output end of the electro-hydraulic proportional valve is connected to the input end of the shuttle valve, the output end of the shuttle valve is connected to the brake, and the brake is a wet brake.

[0126] Further, the electric forklift energy recovery system further includes a foot brake valve, the input end of the foot brake valve is connected to the oil source, the output end of the foot brake valve is connected to the input end of the shuttle valve, and the output end of the shuttle valve is connected to the brake.

[0127] Further, it further includes:

[0128] The angle analysis module is used to obtain the sensor signal collected by the pedal angle sensor before calculating the total target braking torque value according to the pedal angle of the electric brake pedal; is also used to calculate the pedal angle of the electric brake pedal according to the sensor signal; is also used to enter the step of calculating the total target braking torque value according to the pedal angle of the electric brake pedal if the pedal angle of the electric brake pedal is greater than the preset angle;

[0129] The decision module is further used to, after calculating the total target braking torque value according to the pedal angle of the electric brake pedal, if the rotational speed of the drive motor is less than or equal to the preset rotational speed, adjust the valve opening of the electro-hydraulic proportional valve so that the brake brakes according to the total target braking torque value.

[0130] Further, the process by which the first torque determination module determines the maximum braking torque value according to the rotational speed of the drive motor includes: obtaining the external characteristic curve of the drive motor; querying the maximum braking torque value corresponding to the rotational speed of the drive motor on the external characteristic curve of the motor.

[0131] Further, the process by which the second torque determination module determines the motor braking torque limit value according to the power limit level of the drive motor includes: detecting the operating state of the drive motor, determining the power limit level of the drive motor according to the operating state; determining the torque coefficient of the motor power limit state according to the power limit level; querying the maximum braking torque value corresponding to the rotational speed of the drive motor on the external characteristic curve of the motor; setting the product of the torque coefficient of the motor power limit state and the maximum braking torque value as the motor braking torque limit value.

[0132] Further, the process by which the third torque determination module determines the motor charging torque limit value according to the remaining power and cell temperature of the power battery includes: reading the remaining power, cell temperature and battery voltage of the power battery; querying the battery allowable charging current corresponding to the remaining power and the cell temperature; calculating the motor charging torque limit value according to the battery allowable charging current, the battery voltage and the rotational speed of the drive motor.

[0133] Further, the process by which the decision-making module adjusts the valve opening of the electro-hydraulic proportional valve so that the brake brakes according to the remaining braking torque value includes: calculating the target current value according to the remaining braking torque value and the current value proportional coefficient of the electro-hydraulic proportional valve; setting the current value of the electro-hydraulic proportional valve as the target current value, so as to adjust the valve opening of the electro-hydraulic proportional valve and make the brake brake according to the remaining braking torque value.

[0134] Further, the decision-making module is also used to not respond to the change in the pedal angle of the electro-brake pedal if an electro-brake function off command is received.

[0135] Since the embodiments of the device part correspond to the embodiments of the method part, for the embodiments of the device part, please refer to the description of the embodiments of the method part, which will not be elaborated here.

[0136] This application also provides a storage medium, on which a computer program is stored, and when the computer program is executed, the steps provided by the above embodiments can be implemented. The storage medium may include: various media such as USB flash drives, mobile hard disks, read-only memories (ROM), random access memories (RAM), magnetic disks or optical discs that can store program codes.

[0137] The present application also provides an electronic device, which may include a memory and a processor. A computer program is stored in the memory. When the processor calls the computer program in the memory, the steps provided in the above embodiments can be implemented. Of course, the electronic device may also include various network interfaces, power supplies and other components.

[0138] The various embodiments in the specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple. For the relevant parts, reference can be made to the description in the method part. It should be noted that for those of ordinary skill in the art in the technical field of the present application, without departing from the principle of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the protection scope of the present application.

[0139] It should also be noted that in this specification, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including the said element.

Claims

1. A control method for an energy recovery system of an electric forklift, characterized in that, A control device applied to the energy recovery system of an electric forklift. The energy recovery system of the electric forklift further includes a power battery, a drive motor, a brake, an electric brake pedal, and an electro-hydraulic proportional valve. The electro-hydraulic proportional valve is used to control the braking force of the brake by adjusting the pressure of the hydraulic oil. The control method of the energy recovery system of the electric forklift includes: Calculating a total target braking torque value according to the pedal angle of the electric brake pedal; Determining a maximum braking torque value according to the rotational speed of the drive motor; Determining a motor braking torque limit according to the power limit level of the drive motor; Determining a motor charging torque limit according to the remaining power and cell temperature of the power battery; Setting the minimum value among the maximum braking torque value, the motor braking torque limit, and the motor charging torque limit as the reference braking torque value; Judging whether the reference braking torque value is greater than or equal to the total target braking torque value; If so, controlling the drive motor to brake according to the total target braking torque value; wherein, when the drive motor brakes, the recovered kinetic energy is used to charge the power battery; If not, controlling the drive motor to brake according to the reference braking torque value, and adjusting the valve opening of the electro-hydraulic proportional valve so that the brake brakes according to the remaining braking torque value; wherein, the remaining braking torque value is the difference between the total target braking torque value and the reference braking torque value.

2. The control method of the energy recovery system of the electric forklift according to claim 1, characterized in that, Before calculating the total target braking torque value according to the pedal angle of the electric brake pedal, it further includes: Obtaining a sensor signal collected by a pedal angle sensor; Calculating the pedal angle of the electric brake pedal according to the sensor signal; If the pedal angle of the electric brake pedal is greater than a preset angle, entering the step of calculating the total target braking torque value according to the pedal angle of the electric brake pedal; Correspondingly, after calculating the total target braking torque value according to the pedal angle of the electric brake pedal, it further includes: If the rotational speed of the drive motor is less than or equal to a preset rotational speed, adjusting the valve opening of the electro-hydraulic proportional valve so that the brake brakes according to the total target braking torque value.

3. The control method of the energy recovery system of the electric forklift according to claim 1, characterized in that, Determining the maximum braking torque value according to the rotational speed of the drive motor, including: Obtaining the motor external characteristic curve of the drive motor; Querying the maximum braking torque value corresponding to the rotational speed of the drive motor on the motor external characteristic curve.

4. The control method of the energy recovery system of the electric forklift according to claim 1, wherein, Determining the motor braking torque limit according to the power limit level of the drive motor, including: Detecting the operating state of the drive motor and determining the power limit level of the drive motor according to the operating state; Determining a torque coefficient in the motor power-limited state according to the power limit level; Querying the maximum braking torque value corresponding to the rotational speed of the drive motor on the motor external characteristic curve; Setting the product of the torque coefficient in the motor power-limited state and the maximum braking torque value as the motor braking torque limit.

5. The control method of the energy recovery system of the electric forklift according to claim 1, characterized in that, Determining the motor charging torque limit according to the remaining power and cell temperature of the power battery, including: Reading the remaining power, cell temperature, and battery voltage of the power battery; Querying the battery allowable charging current corresponding to the remaining power and the cell temperature; The motor charging torque limit value is calculated based on the allowable charging current of the battery, the battery voltage, and the rotational speed of the drive motor.

6. The control method of the energy recovery system of the electric forklift according to claim 1, characterized in that, Adjusting the valve opening of the electro-hydraulic proportional valve to enable the brake to brake according to the remaining braking torque value includes: Calculating a target current value based on the remaining braking torque value and the current value proportionality coefficient of the electro-hydraulic proportional valve; Setting the current value of the electro-hydraulic proportional valve to the target current value so as to adjust the valve opening of the electro-hydraulic proportional valve and enable the brake to brake according to the remaining braking torque value.

7. The control method of the energy recovery system of the electric forklift according to claim 1, characterized in that, It further includes: If an electric braking function off command is received, no response is made to the change in the pedal angle of the electric brake pedal.

8. A control device for an energy recovery system of an electric forklift, characterized in that, The electric forklift energy recovery system further includes a power battery, a drive motor, a brake, an electric brake pedal, and an electro-hydraulic proportional valve. The electro-hydraulic proportional valve is used to control the braking force of the brake by adjusting the pressure of the hydraulic oil. The control device of the electric forklift energy recovery system includes: A total torque calculation module for calculating a total target braking torque value according to the pedal angle of the electric brake pedal; A first torque determination module for determining a maximum braking torque value according to the rotational speed of the drive motor; A second torque determination module for determining a motor braking torque limit value according to the power limit level of the drive motor; A third torque determination module for determining a motor charging torque limit value according to the remaining power and cell temperature of the power battery; A reference torque determination module for setting the minimum value among the maximum braking torque value, the motor braking torque limit value, and the motor charging torque limit value as the reference braking torque value; A decision module for determining whether the reference braking torque value is greater than or equal to the total target braking torque value; if so, controlling the drive motor to brake according to the total target braking torque value; wherein, when the drive motor brakes, the recovered kinetic energy is used to charge the power battery; if not, controlling the drive motor to brake according to the reference braking torque value and adjusting the valve opening of the electro-hydraulic proportional valve to enable the brake to brake according to the remaining braking torque value; wherein, the remaining braking torque value is the difference between the total target braking torque value and the reference braking torque value.

9. The control device of the energy recovery system of the electric forklift according to claim 8, characterized in that, The input end of the electro-hydraulic proportional valve is connected to an oil source, the output end of the electro-hydraulic proportional valve is connected to the input end of a shuttle valve, and the output end of the shuttle valve is connected to the brake, and the brake is a wet brake.

10. The control device of the electric forklift energy recovery system according to claim 8, characterized in that, The electric forklift energy recovery system further includes a foot brake valve. The input end of the foot brake valve is connected to an oil source, the output end of the foot brake valve is connected to the input end of the shuttle valve, and the output end of the shuttle valve is connected to the brake.

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