Speed control method of electric forklift

Abstract

The invention discloses a speed control method of an electric forklift, and relates to the technical field of electric vehicle control. The method specifically comprises the following steps that an accelerator pedal signal representing the acceleration intention of a driver is obtained; based on the change rate of the accelerator pedal signal, generating a pre-compensation torque for actively compensating the dynamic response delay of the vehicle through a feedforward control channel; generating a correction torque for correcting the steady-state speed error through a feedback control channel based on the deviation between the target speed and the actual speed of the vehicle; and synthesizing the pre-compensation torque and the correction torque to generate a final target torque instruction, and driving a motor to operate based on the final target torque instruction. The acceleration response time of the electric forklift is shortened, and the dynamic performance of the electric forklift under the complex working condition is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electric vehicle control, in particular to a speed control method of an electric forklift. BACKGROUND

[0002] As a kind of key material handling equipment, electric forklift is widely used in warehouse, logistics, production workshop and other indoor and outdoor working scenes due to its zero emission, low noise and low use cost. In modern logistics system, operation efficiency is one of the core indicators to measure the level of warehouse management, and the driving performance of electric forklift, especially the acceleration response speed, directly determines the efficiency of goods handling, stacking and loading. Therefore, how to optimize the speed control of electric forklift and improve its dynamic response characteristics has become an important technical issue in the field.

[0003] Currently, the speed closed-loop feedback control strategy based on the opening degree of the accelerator pedal is generally adopted for the electric forklift in service. The typical working principle is as follows: the operator sets a desired target speed by stepping on the accelerator pedal; the vehicle controller receives the target speed signal and simultaneously collects the actual driving speed of the forklift through the speed sensor installed on the wheel or drive motor. Then, the controller compares the target speed with the actual speed and calculates the deviation between them. Based on the deviation, the controller generates a regulating signal to control the motor driver and adjust the output torque of the drive motor, so as to drive the forklift to accelerate, decelerate or maintain uniform speed, and finally the actual speed tends to the target speed.

[0004] However, the technical personnel found in practice that the above-mentioned traditional closed-loop feedback control method has significant response delay. This control strategy is essentially a "post-compensation" mechanism, that is, only after detecting the deviation between the actual speed and the target speed, the controller starts to adjust. The whole process includes multiple links such as "signal collection-deviation calculation-command adjustment-motor response-system inertia overcoming", and each link needs to consume a certain time, and the accumulation of these times leads to the overall response delay of the system. When the operator steps on the accelerator pedal quickly and expects the vehicle to speed up immediately, he will feel obvious "delay", and the acceleration process of the vehicle is not "followed" enough, which affects the smoothness and accuracy of the operation. At the same time, the anti-load disturbance ability is poor. The working conditions of the forklift are complex and changeable, and the load weight (empty, half load, full load) and driving road conditions (flat ground, slope) will change frequently. These changes are huge external disturbances to the drive system. For example, when the forklift switches from empty load state to full load state, the inertia of the whole vehicle increases sharply, and the original PID control parameters are often difficult to adapt to the new system model, resulting in a significant lengthening of the acceleration time. Similarly, when entering the uphill section, the newly added slope resistance also requires the controller to spend more time to compensate, which further deteriorates the acceleration performance.

[0005] Therefore, how to shorten the acceleration response time of the electric forklift and improve its dynamic performance under complex working conditions has become a technical problem to be solved. SUMMARY

[0006] The main purpose of the present application is to provide a speed control method for an electric forklift, aiming to shorten the acceleration response time of the electric forklift and improve its dynamic performance under complex working conditions.

[0007] In order to achieve the above-mentioned purpose, the present application provides a speed control method for an electric forklift, comprising the following steps: obtaining an acceleration pedal signal representing the driver's acceleration intention; based on the rate of change of the acceleration pedal signal, generating a pre-compensation torque for actively compensating the vehicle dynamic response delay through a feedforward control channel; based on the deviation between the target speed of the vehicle and its actual speed, generating a correction torque for correcting the steady-state speed error through a feedback control channel; synthesizing the pre-compensation torque and the correction torque to generate a final target torque instruction, and driving the motor to operate based on the final target torque instruction.

[0008] In an embodiment of the present application, the step of generating a pre-compensation torque comprises: based on the rate of change of the acceleration pedal signal and a preset vehicle dynamic model, predicting the target torque required for the vehicle to accelerate, and calculating the pre-compensation torque according to the difference between the target torque and the current actual output torque of the motor.

[0009] In an embodiment of the present application, it further comprises a parameter self-adaptive adjustment step: in response to the change of the vehicle operating state, dynamically adjusting the control parameters in the vehicle dynamic model.

[0010] In an embodiment of the present application, the vehicle operating state comprises at least one of the real-time load state or the real-time speed state of the vehicle.

[0011] In an embodiment of the present application, the step of synthesizing specifically comprises: independent amplitude limiting processing is performed on the pre-compensation torque and the correction torque respectively, and then the sum torque of the two is synthesized and limited in amplitude.

[0012] In an embodiment of the present application, the step of synthesizing further comprises: after the sum torque is limited in amplitude, a preset dead zone is applied to the sum torque, and the sum torque after the dead zone processing is low-pass filtered to eliminate current spikes and mechanical jitter.

[0013] In an embodiment of the present application, the feedback control channel adopts a proportional-integral-derivative control algorithm to generate the correction torque.

[0014] In an embodiment of the present application, the target speed is determined according to the opening value of the accelerator pedal signal.

[0015] With the above technical solution, the speed response time of the electric forklift can be significantly shortened, especially when the load changes sharply and the road conditions are complex, the electric forklift can quickly respond to the operation instructions of the driver, significantly improving the operation efficiency of the electric forklift, while ensuring the stability of the vehicle operation, greatly improving the operation experience of the electric forklift driver, and improving the operation safety and reliability of the electric forklift. BRIEF DESCRIPTION OF DRAWINGS

[0016] The present application will be described in detail below with specific embodiments and drawings, in which: Figure 1 The flow structure diagram of the first embodiment of the present application is shown. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present application more clear, the present application will be described in detail below in combination with the drawings and embodiments. It should be understood that the following specific embodiments are only used to explain the present application and do not limit the present application.

[0018] As Figure 1 shown, in order to achieve the above-mentioned purpose, the present application proposes a speed control method for electric forklift, comprising the following steps: obtaining an accelerator pedal signal representing the driver's acceleration intention; based on the rate of change of the accelerator pedal signal, generating a pre-compensation torque for actively compensating for the delay of vehicle dynamic response through a feedforward control channel; based on the deviation between the target speed of the vehicle and its actual speed, generating a correction torque for correcting the steady-state speed error through a feedback control channel; combining the pre-compensation torque and the correction torque to generate a final target torque instruction, and driving the motor to operate based on the final target torque instruction.

[0019] Specifically, the present embodiment discloses a speed control method for electric forklift, comprising the following specific implementation steps: Firstly, the opening signal of the accelerator pedal is obtained in real time by the displacement or angle sensor installed on the accelerator pedal of the electric forklift, to reflect the current acceleration demand of the electric forklift by the driver, and after the accelerator pedal opening signal is converted from analog to digital, it is input to the main control unit of the electric forklift.

[0020] Subsequently, the main control unit of the electric forklift acquires the accelerator pedal opening value at the current time by real-time sampling of the accelerator pedal opening signal and records the value in the cache memory of the main control unit.

[0021] Then, the main control unit of the electric forklift compares the accelerator pedal opening value at the current time with the accelerator pedal opening value at the previous sampling time, and calculates the rate of change of the current accelerator pedal opening based on the ratio of the difference between the two opening values to the corresponding sampling time interval. The specific calculation formula is: rate of change of accelerator pedal opening = (accelerator pedal opening at current time - accelerator pedal opening at previous time) / (current time - previous time).

[0022] Next, the vehicle dynamic model built-in the main control unit of the electric forklift calculates the pre-compensation torque for actively compensating for the response delay of the power system of the electric forklift (including the drive motor, motor controller, and vehicle transmission system) in advance based on the rate of change of the accelerator pedal opening, and outputs the torque through the feedforward control channel of the electric forklift. At the same time, the main control unit of the electric forklift monitors the actual speed of the electric forklift in real time through the vehicle speed sensor, determines the target running speed of the electric forklift based on the accelerator pedal opening signal of the driver, and further calculates the speed error by differencing the target speed and the actual speed.

[0023] The main control unit uses the built-in PID feedback control algorithm to calculate and generate a correction torque signal for correcting the steady-state speed error according to the size of the speed error, and outputs the torque through the feedback control channel of the electric forklift; Subsequently, the main control unit performs synthesis processing on the pre-compensation torque signal output by the feedforward control channel and the correction torque signal output by the feedback control channel, i.e., first independently limits the amplitude of each torque signal to ensure that each torque signal does not exceed the short-term overload torque threshold allowed by the drive motor of the electric forklift.

[0024] Then, the main control unit of the electric forklift sums the two torque signals after amplitude limiting to obtain an initial synthesized torque signal.

[0025] Further, the main control unit of the electric forklift limits the amplitude of the initial synthesized torque signal again to ensure that the size of the synthesized torque signal does not exceed the maximum output torque threshold allowed by the drive motor, and sets a torque dead zone. When the size of the synthesized torque signal is within a certain range near zero, the main control unit directly sets the torque signal to zero to prevent vehicle jitter caused by the gap in the mechanical transmission system. Further, the main control unit smoothes the synthesized torque signal by using a first-order low-pass filter to eliminate current spikes caused by sudden changes in the torque signal; and the final target torque command is obtained after the above processing.

[0026] Finally, the main control unit of the electric forklift outputs the final target torque command to a space vector pulse width modulation module, which generates a three-phase pulse width modulation (PWM) drive signal according to the target torque command and inputs it to a power module of the electric forklift. The power module outputs a corresponding drive current to the drive motor of the electric forklift to drive the motor to operate, thereby achieving fast and accurate speed control of the electric forklift. During the above operation, the main control unit of the electric forklift continuously collects parameters such as the current operating load, battery capacity, and vehicle speed of the electric forklift and inputs them to a parameter self-adaptive adjustment module. According to the real-time state information of the vehicle, the control parameters such as gain and time constant of the vehicle dynamic model in the feedforward control channel are dynamically adjusted to optimize the speed response performance of the electric forklift under different working conditions.

[0027] The above technical solution can significantly shorten the speed response time of the electric forklift, especially when the load changes dramatically and the road conditions are complex, the electric forklift can quickly respond to the operation instructions of the driver, significantly improve the operating efficiency of the electric forklift, and at the same time, the stability of the vehicle operation is taken into account, greatly improving the operation experience of the electric forklift driver and improving the operating safety and reliability of the electric forklift.

[0028] In an embodiment of the present application, the step of generating a pre-compensation torque includes: Based on the rate of change of the accelerator pedal signal and a preset vehicle dynamic model, the target torque required for the vehicle to accelerate is predicted, and the pre-compensation torque is calculated according to the difference between the target torque and the current actual output torque of the motor.

[0029] Specifically, in this embodiment, the main control unit of the electric forklift collects and calculates the rate of change of the accelerator pedal signal in real time, and according to the vehicle dynamic model pre-stored in the main control unit, the target torque required for the vehicle to accelerate under the current working condition is obtained by inputting the rate of change of the accelerator pedal signal. The main control unit of the electric forklift measures and obtains the current actual output torque of the motor in real time through the torque sensor installed on the output shaft of the motor. Then, the main control unit of the electric forklift performs difference operation on the predicted target torque and the current actual output torque of the motor to obtain the pre-compensation torque for actively compensating for the delay of the dynamic response of the electric forklift, and the specific calculation formula is: pre-compensation torque = predicted target torque - current actual output torque of the motor.

[0030] The above technical scheme can actively compensate for the delay in the speed control process of the electric forklift in real time and accurately, effectively improving the speed response performance of the electric forklift and the driving experience.

[0031] In an embodiment of the present application, the method further comprises a parameter self-adaptive adjustment step: The control parameters in the vehicle dynamic model are dynamically adjusted in response to changes in the vehicle operating state.

[0032] Specifically, in the embodiment, the main control unit of the electric forklift collects the actual operating state parameters of the electric forklift in real time, including but not limited to the actual driving speed of the vehicle, the current load of the vehicle, the real-time power of the battery, and the road condition information.

[0033] The main control unit transmits the real-time collected operating state parameters to the built-in parameter self-adaptive adjustment module. The parameter self-adaptive adjustment module dynamically adjusts the control parameters of the vehicle dynamic model in real time according to the changes in the actual operating state parameters of the vehicle. The control parameters specifically include the gain coefficient and the time constant of the dynamic model.

[0034] The specific adjustment method is that the parameter self-adaptive adjustment module compares the actual operating state parameters of the vehicle with the pre-set model parameter corresponding relationship, and automatically calculates the optimal control parameters under the current working condition according to the pre-set adaptive control algorithm, and then updates the adjusted control parameters to the vehicle dynamic model in real time.

[0035] The above technical scheme can ensure that the vehicle dynamic model maintains the best prediction accuracy under different working conditions, further improves the accuracy and adaptability of the speed response of the electric forklift, and effectively improves the comprehensive operating performance of the vehicle.

[0036] In an embodiment of the present application, the vehicle operating state includes at least one of the real-time load state or the real-time speed state of the vehicle.

[0037] Specifically, the real-time load state of the vehicle is measured in real time by the weighing sensor installed on the forklift fork mechanism or the bearing structure, and the real-time speed state of the vehicle is measured in real time by the speed sensor installed on the driving wheel or the motor output shaft of the vehicle.

[0038] The main control unit of the electric forklift inputs the real-time load state or the real-time speed state to the parameter self-adaptive adjustment module. The parameter self-adaptive adjustment module dynamically calculates the control parameters in the vehicle dynamic model through the pre-set parameter adaptive control algorithm according to the difference between the load state or the speed state and the pre-set reference parameters. The control parameters include but are not limited to the gain coefficient and the time constant of the vehicle dynamic model.

[0039] Then, the main control unit updates the control parameters after dynamic adjustment to the vehicle dynamic model in real time, so that the vehicle dynamic model is optimally matched with the actual running state of the electric forklift.

[0040] The above technical solution can ensure that the vehicle dynamic model can accurately predict torque demand in the vehicle acceleration process under different load conditions or speed conditions, thereby improving the accuracy and rapid response capability of the electric forklift speed control and enhancing the adaptability of the electric forklift to different working conditions.

[0041] In an embodiment of the present application, the step of synthesizing specifically comprises: The pre-compensation torque and the modified torque are independently limited in amplitude, and then the sum torque of the two is limited in amplitude.

[0042] Specifically, in this embodiment, the main control unit of the electric forklift first independently limits the amplitude of the pre-compensation torque output by the feedforward control channel and the modified torque output by the feedback control channel.

[0043] The specific method of independent amplitude limiting is to compare each torque signal with the pre-set single-channel maximum torque threshold allowed by the electric forklift drive motor, and when the torque signal of any channel exceeds the single-channel maximum torque threshold, the torque signal of the channel is limited to the single-channel maximum torque threshold. Subsequently, the main control unit of the electric forklift sums the above two independently limited torque signals to generate an initial sum torque signal, and further limits the amplitude of the initial sum torque signal.

[0044] The specific method of secondary amplitude limiting is to compare the initial sum torque signal with the pre-set maximum output torque threshold allowed by the electric forklift drive motor, and when the initial sum torque signal exceeds the maximum output torque threshold, the main control unit limits the sum torque signal to within the maximum output torque threshold.

[0045] The above technical solution can effectively avoid the impact of excessive torque output by any one of the feedforward control channel and the feedback control channel or the superposition of the two on the motor, thereby ensuring the safety and stability of the electric forklift drive motor operation and significantly improving the overall operation stability of the electric forklift.

[0046] In an embodiment of the present application, the step of synthesizing further comprises: After limiting the amplitude of the sum torque, a pre-set dead zone is applied to the sum torque, and the sum torque after dead zone processing is low-pass filtered to eliminate current spikes and mechanical jitter.

[0047] Specifically, in the embodiment, the main control unit of the electric forklift first performs secondary amplitude limiting processing on the total torque after the pre-compensation torque and the correction torque are combined, and then applies a preset dead zone to the total torque after the amplitude limiting processing. Specifically, the preset dead zone is a predetermined torque threshold interval set near zero torque. When the total torque after the amplitude limiting is located in the preset dead zone, the main control unit directly sets the total torque to zero to eliminate the mechanical jitter caused by the gap in the transmission mechanism of the electric forklift.

[0048] Next, the main control unit of the electric forklift performs smoothing filtering processing on the total torque after the dead zone processing by using a built-in first-order low-pass filter. Specifically, the first-order low-pass filter has a preset cutoff frequency for effectively eliminating the motor drive current spikes caused by the rapid change of the total torque signal.

[0049] By using the above technical solution, the current spikes and mechanical transmission system jitter phenomena caused by the rapid change of the total torque during the acceleration control process of the electric forklift can be significantly inhibited, and the stability, comfort and reliability of the electric forklift operation are further improved.

[0050] In an embodiment of the present application, the feedback control channel generates the correction torque by using a proportional-integral-derivative control algorithm.

[0051] Specifically, the main control unit obtains the speed error between the target speed of the vehicle and the actual speed of the electric forklift measured by the speed sensor in real time; the main control unit inputs the above speed error into the built-in PID control algorithm module to process the speed error through the pre-set proportional (P) link, integral (I) link and derivative (D) link.

[0052] Specifically, the proportional link generates a proportional control quantity according to the size of the current speed error, the integral link integrates the accumulation of the speed error over time to generate an integral control quantity, and the derivative link differentiates the trend of the speed error to generate a derivative control quantity; then, the main control unit performs summation operation on the above proportional control quantity, integral control quantity and derivative control quantity to calculate the correction torque signal output by the feedback control channel.

[0053] By using the above technical solution, the speed error of the electric forklift can be effectively corrected quickly, and the system has high steady-state accuracy and dynamic response speed, thereby significantly improving the stability and reliability of the speed control system of the electric forklift.

[0054] In an embodiment of the present application, the target speed is determined according to the opening value of the accelerator pedal signal.

[0055] Specifically, the real-time position information of the accelerator pedal is acquired by a displacement or angle sensor installed on the accelerator pedal, and is transmitted to the main control unit after analog-digital conversion; the main control unit of the electric forklift is provided with a mapping relationship table or a function model between the pre-calibrated accelerator pedal opening value and the target speed, which is obtained based on actual running calibration experiment of the vehicle; the main control unit looks up or calculates the corresponding target speed of the electric forklift according to the current accelerator pedal opening value, so as to determine the target speed of the electric forklift at the current time.

[0056] The above technical scheme can ensure that the target speed of the electric forklift is consistent with the acceleration operation intention of the driver, and effectively improve the accuracy, responsiveness and driver operation comfort of the electric forklift acceleration control process.

[0057] The above description is only the preferred embodiments of the present application, and does not limit the patent scope of the present application. Any equivalent structural transformation, direct / indirect application in other related technical fields, or direct / indirect application in other related technical fields within the inventive concept of the present application and the contents of the specification and drawings are included in the patent protection scope of the present application.

Claims

1. A speed control method of an electric fork lift truck, characterized by, The method comprises the following steps: obtaining an accelerator pedal signal representing the driver's acceleration intention; generating a pre-compensation torque for actively compensating the vehicle dynamic response delay via a feedforward control channel based on the rate of change of the accelerator pedal signal; generating a correction torque for correcting the steady-state speed error via a feedback control channel based on the deviation between the target speed and the actual speed of the vehicle; synthesizing the pre-compensation torque and the correction torque to generate a final target torque instruction, and driving the motor to operate based on the final target torque instruction.

2. The speed control method of a motorized fork truck according to claim 1, wherein The step of generating the pre-compensation torque comprises: predicting the target torque required for the vehicle to accelerate based on the rate of change of the accelerator pedal signal and a preset vehicle dynamic model, and calculating the pre-compensation torque according to the difference between the target torque and the current actual output torque of the motor.

3. The speed control method of a motorized fork truck according to claim 2, wherein It also comprises a parameter self-adaptive adjustment step: dynamically adjusting the control parameters in the vehicle dynamic model in response to changes in the vehicle operating state.

4. The speed control method of a motorized fork truck according to claim 3, wherein The vehicle operating state comprises at least one of the real-time load state or the real-time speed state of the vehicle.

5. The speed control method of a motorized fork truck according to claim 1, wherein The step of synthesizing specifically comprises: independently limiting the pre-compensation torque and the correction torque, and then limiting the sum torque of the two.

6. The speed control method of a motorized fork truck according to claim 5, wherein The step of synthesizing also comprises: applying a preset dead zone to the sum torque after limiting, and low-pass filtering the sum torque after the dead zone processing to eliminate current spikes and mechanical jitter.

7. The speed control method of a motorized fork truck according to claim 1, wherein The feedback control channel adopts a proportional-integral-derivative control algorithm to generate the correction torque.

8. The speed control method of a motorized fork truck as set forth in claim 1, wherein, The target speed is determined according to the opening value of the accelerator pedal signal.

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