Control method of proportional electromagnetic valve for hydraulic retarder

Abstract

The invention discloses a control method of a proportional electromagnetic valve for a hydraulic retarder. The control method mainly solves the technical problems that an existing control method is long in pressure response time, large in overshoot, poor in following performance and the like. The control method comprises the steps that feedback pressure of a working cavity of the hydraulic retarder and input signals of a proportional electromagnetic valve are periodically collected; the current target pressure request state is judged, and the current target current of the proportional electromagnetic valve is calculated in a corresponding mode according to the judgment result; calculating to obtain the current duty ratio of the proportional electromagnetic valve; and finally, the flutter is superposed, and the final duty ratio is output, so that the control of the proportional electromagnetic valve for the hydraulic retarder is realized. According to the control method, accurate control over the proportional electromagnetic valve can be achieved, and the control method has the advantages of being short in response time, small in overshoot and good in following performance.

Description

Technical Field

[0001] The present invention relates to a vehicle-mounted electronic control method, and in particular to a control method for a proportional solenoid valve used in a hydraulic retarder. Background Art

[0002] A hydraulic retarder is an auxiliary braking device typically installed on the drive shaft of a heavy-duty vehicle. It primarily consists of a stator, rotor, working chamber, oil charging and discharging mechanism, and heat sink. The hydraulic retarder's operating principle is that the rotor rotates with the drive shaft. During operation, under the influence of an external control system, compressed air enters the upper portion of the oil tank, allowing the oil to enter the upper end of the stator through the oil inlet pipe and then into the enclosed working chamber formed by the rotor and stator. Driven by the rotor blades, the oil circulates and impacts the stator blades, causing the kinetic energy to change, generating a braking torque that hinders the rotation of the rotor impeller, thereby reducing the speed of the drive shaft and slowing the vehicle. During the deceleration process, the proportional solenoid valve on the hydraulic retarder allows precise control of the compressed air pressure in the working chamber, thereby achieving precise control of the hydraulic retarder's braking torque, making it adaptable to different operating conditions.

[0003] Traditional proportional solenoid valve control methods primarily employ current-based PID control methods. For example, Chinese invention patent publication number CN108980441 A discloses a PWM-based proportional solenoid valve drive method. This method obtains the impedance value R of the proportional solenoid valve, detects the drive voltage P applied to the proportional solenoid valve, and detects whether the target current has changed, thereby estimating the duty cycle. A controller then outputs a PWM signal to the proportional solenoid valve with the estimated duty cycle. Simultaneously, the actual current flowing through the proportional solenoid valve is detected and compared with the target current. Closed-loop control is then used to adjust the duty cycle until the difference between the actual current and the target current is less than or equal to the error value. This control method eliminates most of the control rise time, achieving rapid control and significantly shortening the target current adjustment time. However, due to the low rigidity of the gas, there is a significant lag in the control of the gas pressure in the working chamber. Existing PID control methods suffer from long pressure response times, large overshoot, and poor tracking, thus failing to meet the system's control requirements. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problems of the existing control method such as long pressure response time, large overshoot, poor followability, etc., and to provide a control method for a proportional solenoid valve for a hydraulic retarder.

[0005] To achieve the above objectives, the technical solutions provided by the present invention are:

[0006] A control method for a proportional solenoid valve for a hydraulic retarder is characterized in that it comprises the following steps:

[0007] Step 1: Periodically collect the feedback pressure of the hydraulic retarder working chamber and the input signal of the proportional solenoid valve; the input signal includes the feedback current and the system voltage;

[0008] Step 2: Based on the target pressure of the hydraulic retarder working chamber and the feedback pressure collected in step 1, determine the current target pressure request state. If the current target pressure is greater than the feedback pressure, the current target pressure request state is positive. Further determine whether the overshoot state has been entered. If the overshoot state has been entered, execute step 3. If the overshoot state has not been entered, execute step 4.

[0009] If the current target pressure is less than the feedback pressure, the current target pressure request state is return, and step 4 is executed;

[0010] If the current target pressure is equal to the feedback pressure, the current target pressure request state is to maintain the existing state, and the current target current of the proportional solenoid valve is the current feedback current. In this case, step 5 is executed;

[0011] Step 3: Calculate the overshoot current in the overshoot state and combine it with the feedforward current of the proportional solenoid valve to calculate the current target current of the proportional solenoid valve;

[0012] Step 4: Calculate the current offset value in the forward non-overshoot state or the return state, and combine it with the feedforward current of the proportional solenoid valve to calculate the current target current of the proportional solenoid valve;

[0013] Step 5: Based on the current target current of the proportional solenoid valve obtained in step 2, step 3, or step 4, combined with the feedback current and system voltage collected in step 1, calculate the current duty cycle of the proportional solenoid valve;

[0014] Step 6: Dither is superimposed on the current duty cycle obtained in step 5, and the final duty cycle is output, thereby realizing the control of the proportional solenoid valve for the hydraulic retarder.

[0015] Furthermore, in step 1, the feedback pressure and feedback current need to be subjected to mean filtering, and the filtering window is the vibration period divided by the sampling period.

[0016] Furthermore, the dither period is 50ms to 150ms; and the sampling period is 1ms to 10ms.

[0017] Furthermore, in step 2, the method for determining whether the overshoot state has been entered is:

[0018] If the difference between the current target pressure and the feedback pressure is greater than the set overshoot threshold, it indicates that the overshoot state has been entered, and the overshoot state will be exited when the difference between the target pressure and the feedback pressure is less than the set steady-state threshold; the overshoot threshold is greater than the steady-state threshold;

[0019] If the difference between the current target pressure and the feedback pressure is less than or equal to the set overshoot threshold, it means that the overshoot state has not been entered.

[0020] Furthermore, in step 3, the current target current of the proportional solenoid valve is calculated by the following formula:

[0021] TargetCurrent=CurrentBase+OverloadCurrent

[0022] Where TargetCurrent is the current target current of the proportional solenoid valve; CurrentBase represents the feedforward current of the proportional solenoid valve, and its value is directly obtained by querying the interpolation table based on the target pressure; OverloadCurrent represents the current overshoot current, and its value is directly obtained by querying the interpolation table based on the target pressure and the difference between the target pressure and the feedback pressure.

[0023] Furthermore, in step 4, the current target current TargetCurrent of the proportional solenoid valve is calculated by the following formula:

[0024] TargetCurrent=CurrentBase+CurrentOffset

[0025] Where CurrentBase represents the feedforward current of the proportional solenoid valve, and its value is directly obtained by querying the interpolation table based on the target pressure. CurrentOffset represents the current offset value in the non-overshoot state or the return state, and its calculation formula is as follows:

[0026]

[0027] Where Kp is the proportional coefficient; Ki is the integral coefficient; Err p is the difference between the target pressure and the feedback pressure, and Err p =targetPress-actualPress, targetPress is the target pressure, actualPress is the feedback pressure.

[0028] Furthermore, in step 5, the current duty cycle of the proportional solenoid valve TargetDuty (n) Calculated by the following formula:

[0029] TargetDuty (n) =DutyBase+DutyOffset (n)

[0030] Among them, DutyBase represents the feedforward duty cycle, which is directly obtained through the current target current and system voltage of the proportional solenoid valve; DutyOffset (n) Indicates the current duty cycle offset, and

[0031] DutyOffset (n) =Kp * Err i(n) +∑Ki*Err i(n) +Kd*(Err i(n) -Err i(n-1) )

[0032] Where Kp is the proportional coefficient; Ki is the integral coefficient; Kd is the differential coefficient; Err i(n) Is the difference between the current target current and the feedback current; Err i(n-1) It is the difference between the target current and the feedback current in the previous cycle; n represents the sequence number of the sampling cycle.

[0033] Furthermore, in step 6, the final duty cycle Duty (n) Calculated by the following formula:

[0034] Duty (n) =TargetDuty (n) +Amplitude×f(t)

[0035] Where Amplitude is the dither amplitude; f(t) is a periodic function with time as the independent variable, specifically a triangular wave or a sine wave with the dither period as the period, and several points are evenly sampled in each period of the waveform.

[0036] Furthermore, the number of sampling points Wherein, T1 represents the dither period, and T2 represents the sampling period.

[0037] Furthermore, the number of sampling points is an even number.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The present invention provides a control method for a proportional solenoid valve used in a hydraulic retarder. This method, based on periodically collected feedback pressure from the hydraulic retarder's working chamber and the proportional solenoid valve's input signal, accurately determines the current pressure request state and then precisely calculates the proportional solenoid valve's current duty cycle. This method then superimposes dither and outputs the final duty cycle, ultimately achieving precise control of the proportional solenoid valve. This method meets system control requirements and offers the advantages of short response time, minimal overshoot, and excellent tracking performance.

[0040] 2. The control method of a proportional solenoid valve for a hydraulic retarder provided by the present invention superimposes dither, which can reduce the influence of hysteresis and friction on the performance of the proportional solenoid valve, thereby improving the control accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of a flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to make the objects, advantages and features of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and specific examples. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0043] like Figure 1 As shown, this embodiment provides a control method for a proportional solenoid valve for a hydraulic retarder. Taking a controller of a hydraulic retarder as an example, the purpose of the controller is to control the pressure of the gas in the working chamber of the hydraulic retarder, with the target pressure varying within a range of 0 to 3.5 Bar. The specific control method includes the following steps:

[0044] Step 1: Periodically collect feedback pressure from the hydraulic retarder's working chamber and the input signal from the proportional solenoid valve. In this embodiment, the input signals include feedback current and system voltage. The feedback pressure and feedback current are subjected to mean filtering, and the filtering window is the dither period T1 divided by the sampling period T2. The dither period T1 and sampling period T2 are pre-set based on control requirements. In this embodiment, the dither period T1 is 50ms to 150ms, and the sampling period T2 is 1ms to 10ms.

[0045] It should be noted that this embodiment increases the dither period to prevent the "stickiness" effect, thereby realizing the dither function. Due to the influence of the dither function, the control period of the current feedback control should be the dither period, thereby avoiding the influence of the dither on the feedback current.

[0046] Step 2: Based on the target pressure of the hydraulic retarder working chamber and the feedback pressure collected in step 1, determine the current target pressure request status:

[0047] (1) When the target pressure changes, if the current target pressure is greater than the feedback pressure, the current target pressure request state is positive, and further judgment is made as to whether the pressure has entered the overshoot state. If the pressure has entered the overshoot state, step 3 is executed; if the pressure has not entered the overshoot state, step 4 is executed; specifically:

[0048] If the difference between the current target pressure and the feedback pressure is greater than the set overshoot threshold Limit1, it means that the overshoot state has been entered. At this time, step 3 is executed. After that, as the target pressure changes, the difference between the target pressure and the feedback pressure Err p When the pressure is less than the set steady-state threshold Limit2 or the overshoot time is reached, the overshoot state is exited. Generally, Limit1>Limit2. In this embodiment, Limit1 is set to 0.15 bar and Limit2 is set to 0.03 bar.

[0049] The above Err p =targetPress-actualPress, where targetPress is the target pressure and actualPress is the feedback pressure.

[0050] If the difference between the current target pressure and the feedback pressure is less than or equal to the set overshoot threshold, it indicates that the overshoot state has not been entered, and step 4 is entered.

[0051] (2) When the target pressure changes, if the current target pressure is less than the feedback pressure, the current target pressure request state is return, and step 4 is executed.

[0052] (3) If the current target pressure is equal to the feedback pressure, the current target pressure request state is to maintain the existing state, and the current target current of the proportional solenoid valve is the current feedback current. At this time, step 5 is executed.

[0053] Step 3: Calculate the overshoot current in the overshoot state and combine it with the feedforward current of the proportional solenoid valve to calculate the current target current of the proportional solenoid valve. Specifically:

[0054] TargetCurrent=CurrentBase+OverloadCurrent

[0055] Where TargetCurrent is the current target current of the proportional solenoid valve; CurrentBase represents the feedforward current of the proportional solenoid valve, i.e., CurrentBase = f(targetPress). The value of the feedforward current is directly obtained by querying the interpolation table according to the target pressure. The interpolation table is obtained from the characteristic curve of the proportional solenoid valve, which reflects the relationship between the target pressure and the feedforward current. OverloadCurrent represents the current overshoot current, i.e., OverloadCurrent = f(targetPress, Err p ), the value of the overshoot current is determined by the target pressure and the difference between the target pressure and the feedback pressure, and can be directly obtained by querying the interpolation table.

[0056] Step 4: Calculate the current offset value in the forward non-overshoot state or the return state, and combine it with the feedforward current of the proportional solenoid valve to calculate the current target current of the proportional solenoid valve, specifically:

[0057] TargetCurrent=CurrentBase+CurrentOffset

[0058] Where CurrentBase represents the feedforward current of the proportional solenoid valve, and its specific value is as described above. CurrentOffset represents the current offset value in the non-overshoot state or return state, and its calculation formula is as follows:

[0059] CurrentOffset=Kp * Err p +∑Ki*Err p

[0060] Where Kp is the proportional coefficient and Ki is the integral coefficient. The traditional PI algorithm retains the anti-saturation limiting of the integral term and the limiting of the current offset value. p is the difference between the target pressure and the feedback pressure. To improve the response speed, when the target pressure changes, the integral term ∑Ki*Err is p Cleared to zero.

[0061] In the above formula, Kp and Ki can be adjusted according to actual conditions. The specific adjustment methods are as follows: p When Err is less than or equal to C, the system is considered to have entered a stable state, where C is the tolerance of the target pressure. At this time, Kp and Ki should be smaller. p >C, the system is considered to be in a slow-step adjustment state. At this time, Kp and Ki need to be larger, and due to the compressibility of the gas, in order to reduce overshoot, the operating cycle of the current offset value needs to be relatively extended.

[0062] Step 5: Based on the current target current of the proportional solenoid valve obtained in step 2, step 3, or step 4, combined with the system voltage and feedback current collected in step 1, calculate the current duty cycle TargetDuty of the proportional solenoid valve (n) , specifically:

[0063] TargetDuty (n) =DutyBase+DutyOffset (n)

[0064] Among them, DutyBase represents the feedforward duty cycle, which is directly obtained through the current target current and system voltage of the proportional solenoid valve, that is, DutyBase = f(Targetcurrent,systemVoltage). This relationship represents the relationship between the target current of the proportional solenoid valve, the system voltage systemVoltage and the duty cycle. In this embodiment, this relationship is a two-dimensional table. (n) Indicates the current duty cycle offset, and

[0065] DutyOffset (n) =Kp * Err i(n) +∑Ki*Err i(n) +Kd*(Err i(n) -Err i(n-1) )

[0066] Where Kp is the proportional coefficient; Ki is the integral coefficient; Kd is the differential coefficient. All three are customized while retaining the traditional PID algorithm's anti-saturation limiting of the integral term and the limiting of the duty cycle offset; Err i(n) Is the difference between the current target current and the feedback current; Err i(n-1) Is the difference between the target current and the feedback current in the previous cycle; n represents the sampling cycle number. In order to improve the response speed, when the system voltage changes significantly, the current integral term ∑Ki*Err is i(n) Cleared to zero.

[0067] Step 6: Dither is superimposed on the current duty cycle obtained in step 5, and the final duty cycle is output, thereby realizing the control of the proportional solenoid valve for the hydraulic retarder.

[0068] The final duty cycle Duty (n) Calculated by the following formula:

[0069] Duty (n) =TargetDuty (n) +Amplitude×f(t)

[0070] Where Amplitude is the vibration amplitude; f(t) is a periodic function with time as the independent variable, specifically a triangular wave or a sine wave with the vibration period as the period, and several points are evenly sampled in each period of the waveform. The number of sampling points is Where T1 is the dither period, and T2 is the sampling period. In this implementation, f(t) is a triangular wave with eight sampling points, which are sequentially taken from an array of {0, 0.5, 1, 0.5, 0, -0.5, -1, -0.5}.

[0071] In summary, the present invention utilizes a dual-loop series control strategy of pressure loop and current loop, distinguishes between the forward stroke and the return stroke in the pressure closed-loop control loop, adopts a segmented control strategy for the forward stroke, and adopts a PI control method for the return stroke, which has the advantages of short response time, small overshoot, and good followability.

[0072] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A control method for a proportional solenoid valve for a hydraulic retarder, characterized in that: The following steps are involved: Step 1: Periodically collect the feedback pressure of the hydraulic retarder working chamber and the input signal of the proportional solenoid valve; the input signal includes the feedback current and the system voltage; Step 2: Based on the target pressure of the hydraulic retarder working chamber and the feedback pressure collected in step 1, determine the current target pressure request state. If the current target pressure is greater than the feedback pressure, the current target pressure request state is positive. Further determine whether the overshoot state has been entered. If the overshoot state has been entered, execute step 3. If the overshoot state has not been entered, execute step 4. If the current target pressure is less than the feedback pressure, the current target pressure request state is return, and step 4 is executed; If the current target pressure is equal to the feedback pressure, the current target pressure request state is to maintain the existing state, and the current target current of the proportional solenoid valve is the current feedback current. In this case, step 5 is executed; Step 3: Calculate the overshoot current in the overshoot state and combine it with the feedforward current of the proportional solenoid valve to calculate the current target current of the proportional solenoid valve; Step 4: Calculate the current offset value in the forward non-overshoot state or the return state, and combine it with the feedforward current of the proportional solenoid valve to calculate the current target current of the proportional solenoid valve; Step 5: Based on the current target current of the proportional solenoid valve obtained in step 2, step 3, or step 4, combined with the feedback current and system voltage collected in step 1, calculate the current duty cycle of the proportional solenoid valve; Step 6: Dither is superimposed on the current duty cycle obtained in step 5, and the final duty cycle is output, thereby realizing the control of the proportional solenoid valve for the hydraulic retarder.

2. The control method of the proportional solenoid valve for a hydraulic retarder according to claim 1, characterized in that: In step 1, the feedback pressure and feedback current need to be subjected to mean filtering, and the filtering window is the vibration period divided by the sampling period.

3. The control method of the proportional solenoid valve for a hydraulic retarder according to claim 2, characterized in that: The dither period is 50ms to 150ms; the sampling period is 1ms to 10ms.

4. The control method of the proportional solenoid valve for a hydraulic retarder according to claim 3, characterized in that: In step 2, the method for determining whether the overshoot state has been entered is: If the difference between the current target pressure and the feedback pressure is greater than the set overshoot threshold, it indicates that the overshoot state has been entered. When the difference between the target pressure and the feedback pressure is less than the set steady-state threshold, the overshoot state is exited; the overshoot threshold is greater than the steady-state threshold; If the difference between the current target pressure and the feedback pressure is less than or equal to the set overshoot threshold, it means that the overshoot state has not been entered.

5. The control method of the proportional solenoid valve for a hydraulic retarder according to claim 4, characterized in that: In step 3, the current target current of the proportional solenoid valve is calculated by the following formula: TargetCurrent=CurrentBase+OverloadCurrent Where TargetCurrent is the current target current of the proportional solenoid valve; CurrentBase represents the feedforward current of the proportional solenoid valve, and its value is directly obtained by querying the interpolation table based on the target pressure; OverloadCurrent represents the current overshoot current, and its value is directly obtained by querying the interpolation table based on the target pressure and the difference between the target pressure and the feedback pressure.

6. The control method of the proportional solenoid valve for a hydraulic retarder according to claim 4, characterized in that: In step 4, the current target current TargetCurrent of the proportional solenoid valve is calculated by the following formula: TargetCurrent=CurrentBase+CurrentOffset Where CurrentBase represents the feedforward current of the proportional solenoid valve, and its value is directly obtained by querying the interpolation table based on the target pressure. CurrentOffset represents the current offset value in the non-overshoot state or the return state, and its calculation formula is as follows: CurrentOffset=Kp * Err p +∑Ki*Err p Where Kp is the proportional coefficient; Ki is the integral coefficient; Err p is the difference between the target pressure and the feedback pressure, and Err p =targetPress-actualPress, targetPress is the target pressure, actualPress is the feedback pressure.

7. The control method for a proportional solenoid valve for a hydraulic retarder according to claim 5 or 6, characterized in that: In step 5, the current duty cycle of the proportional solenoid valve is TargetDuty (n) Calculated by the following formula: TargetDuty (n) =DutyBase+DutyOffset (n) Among them, DutyBase represents the feedforward duty cycle, which is directly obtained through the current target current and system voltage of the proportional solenoid valve; DutyOffset (n) Indicates the current duty cycle offset, and DutyOffset (n) =Kp * Err i(n) +∑Ki*Err i(n) +Kd*(Err i(n) -Err i(n-1) ) Where Kp is the proportional coefficient; Ki is the integral coefficient; Kd is the differential coefficient; Err i(n) Is the difference between the current target current and the feedback current; Err i(n-1) It is the difference between the target current and the feedback current in the previous cycle; n represents the sampling cycle number.

8. The control method of the proportional solenoid valve for a hydraulic retarder according to claim 7, characterized in that: In step 6, the final duty cycle Duty (n) Calculated by the following formula: Duty (n) =TargetDuty (n) +Amplitude×f(t) Where Amplitude is the dither amplitude; f(t) is a periodic function with time as the independent variable, specifically a triangular wave or a sine wave with the dither period as the period, and several points are evenly sampled in each period of the waveform.

9. The control method for the proportional solenoid valve for a hydraulic retarder according to claim 8, characterized in that: The number of sampling points Wherein, T1 represents the dither period, and T2 represents the sampling period.

10. The control method of the proportional solenoid valve for a hydraulic retarder according to claim 9, characterized in that: The number of sampling points is an even number.

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