A method for hill holding and hill exiting of an electric vehicle

Abstract

The application relates to a method for hill holding and hill exiting of an electric vehicle, which comprises the following steps: acquiring a calibration two-dimensional table of brake opening degree and brake torque, and latching the brake opening degree under a set condition; determining whether to enable a hill holding control flag under the set condition; when the hill holding control flag is detected, outputting a given rotating speed of rotating speed closed-loop control during hill holding; adopting the rotating speed closed-loop control to realize motor hill holding control; when the hill holding control flag is received, automatically exiting the hill holding control and switching to torque control. The technical scheme can quickly increase hill holding output torque, effectively shorten the hill holding distance, smoothly switch the hill holding control, have no force leakage feeling, and have no whole vehicle rear walking feeling during hill exiting. The hill holding control is entered in advance, hill parking is quickly realized without shaking, and the hill holding distance is effectively shortened.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electric vehicle control, and particularly relates to a method for hill holding and hill exiting of an electric vehicle. BACKGROUND

[0002] When the vehicle is parked on a slope, the driver will experience forward or backward sliding due to the action of the component force of the self gravity without operation, which is harmful to the safe driving of the vehicle. In order to prevent the vehicle from sliding on the slope, most electric vehicles have a hill holding function, which can keep the vehicle stationary on the slope for several seconds when the driver's foot is away from the accelerator pedal without stepping on the brake pedal or the accelerator pedal, so as to facilitate the driver to easily transfer the foot from the accelerator pedal to the brake pedal or from the brake pedal to the accelerator pedal, thereby preventing accidents caused by the vehicle sliding.

[0003] In order to prevent the vehicle from sliding on the slope, most pure electric vehicles use an electric motor to realize the hill holding function. Generally, whether the hill holding condition is reached is determined when the driver does not operate, that is, does not step on the brake pedal or the accelerator pedal, and the electric motor controller realizes the speed closed loop control based on the zero speed given. The response time of the speed closed loop control exists a delay, which leads to the hill holding not timely enough and often causes a certain sliding distance on the slope. Moreover, when the driver steps on the brake pedal to exit the hill holding, the hill holding is also exited, which causes a certain force leakage feeling and the vehicle rear sliding. SUMMARY

[0004] The purpose of the present application is to provide a method for hill holding and hill exiting of an electric vehicle, so as to solve the problem that the response time of the speed closed loop control exists a delay when the electric vehicle exits the hill holding, which leads to the vehicle sliding on the slope or causing a force leakage feeling when the hill holding is exited.

[0005] To achieve the above purpose, the present application is realized by the following technical scheme:

[0006] A method for hill holding and hill exiting of an electric vehicle, comprising the following steps:

[0007] S1, obtaining a calibration two-dimensional table of the brake opening degree and the brake torque, and latching the brake opening degree under the set condition;

[0008] S2, determining whether the hill holding control flag is enabled under the set condition;

[0009] S3, when the hill holding control flag of step S2 is detected, outputting the given speed of the speed closed loop control during the hill holding;

[0010] S4, realizing the motor hill holding control by using the speed closed loop control;

[0011] S5, when the reset hill holding control flag is received, automatically exiting the hill holding control and switching to the torque control.

[0012] Further, the brake opening degree confirmation method of step S1 is that, if the whole vehicle is detected to be coasting after the accelerator is released, the accelerator torque when the motor starts to coast is recorded, the brake opening degree corresponding to the accelerator torque is found according to the two-dimensional table of brake opening degree and brake torque, and the brake opening degree is latched; if the coasting is detected to be caused by releasing the brake, the brake opening degree when the coasting occurs is latched.

[0013] Further, the judging method of enabling the hill hold control flag of step S2 is that, when the whole vehicle is without accelerator and brake, the whole vehicle is in forward gear, if the whole vehicle is detected to have rear coasting speed, the hill hold control flag is determined to be enabled; when the whole vehicle is in reverse gear, the hill hold control flag is determined to be enabled when the front coasting speed is detected.

[0014] Further, the given speed method of the speed closed loop control of step S3 is that, when the hill hold control flag is detected to be enabled, the given target speed of the hill hold control is fixed to a non-zero speed; when the actual detected vehicle speed is in the opposite direction of the coasting direction, the target speed of the hill hold control is switched to zero.

[0015] Further, the closed loop control of step S4 adopts proportional integral algorithm, as follows:

[0016] Err(n) = Ref(n) - Fdb(n);

[0017] Up(n) = Kp*Err(n);

[0018] delta_Ui(n) = Ki*Err(n); Formula (1)

[0019] Ui(n) = Ui(n-1) + delta_Ui(n);

[0020] Out(n) = Up(n) + Ui(n);

[0021] In the above formula, Out(n) is the speed closed loop output, Err(n) is the error signal, Kp is the proportional gain, Ki is the integral gain, Ref(n) is the speed closed loop given quantity, Fdb(n) is the speed closed loop feedback quantity, Ui(n-1) and Ui(n) are the speed closed loop integral quantities calculated last time and this time respectively.

[0022] Further, when the coasting speed is detected, the target speed, i.e. Ref(n) in the above formula, is non-zero, the rear coasting speed or the front coasting speed, i.e. Fdb(n) in the above formula, is larger than the target speed Ref(n), that is, the input speed difference Err(n) of the speed PI loop is increased, so that the output Out(n) of the speed closed loop is increased.

[0023] Further, the reset condition of the reset of the hill hold control flag in step S5 is one of the following conditions: first, the accelerator is stepped, and the accelerator signal is greater than the hill hold torque, second, the neutral gear is engaged or the hill hold allowable time is up, third, the brake is stepped, and the depth of the stepped brake is greater than the latched brake depth in the brake depth latching module.

[0024] Further, the control system comprises a brake depth latching module, a hill roll judging module, a target speed judging module, a hill hold control module and a hill hold exit module.

[0025] The present application has the following advantages:

[0026] The present application can quickly increase the hill hold output torque, effectively shorten the hill hold distance, smoothly switch the hill hold control, have no power leakage feeling, and have no whole vehicle rear roll feeling when the hill hold is exited. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The present application has the following advantages: DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be described in detail below with reference to the accompanying drawings, and the following examples are only exemplary and can only be used to explain and illustrate the technical solutions of the present application, but cannot be interpreted as a limitation of the technical solutions of the present application.

[0029] As shown in Figure 1 The control system of the hill holding and hill hold exiting method of the electric vehicle of the present application comprises the following modules: a brake depth latching module, a hill roll judging module, a target speed judging module, a hill hold control module and a hill hold exit module.

[0030] The brake depth latching module: obtains a calibrated two-dimensional table of brake opening and brake torque, if the whole vehicle roll is detected after the driver releases the accelerator, records the accelerator torque size when the motor starts to roll, finds the brake opening and brake torque two-dimensional table according to the accelerator torque, obtains the corresponding brake opening under the accelerator torque, and latches the brake opening; if the hill roll is detected due to the driver's release of the brake, the brake opening just before the hill roll is latched.

[0031] The hill roll judging module: judges whether to enable the hill hold control flag, when the whole vehicle has no accelerator and no brake, the whole vehicle is in forward gear, if the whole vehicle has a rear roll speed is detected, it is determined to enable the hill hold control flag. Similarly, when the whole vehicle is in reverse gear, it is determined to enable the hill hold control flag when the front roll speed is detected.

[0032] Target Speed ​​Judgment Module: This module outputs the setpoint speed for closed-loop speed control during hill-climbing. When the hill-climbing control flag is detected as enabled, the output target speed for hill-climbing control is fixed at a non-zero speed, artificially increasing the difference between the current motor speed and the target speed, thereby enabling rapid provision of hill-climbing torque in subsequent hill-climbing speed control stages. When the actual detected vehicle speed is the speed in the opposite direction of the hill-climbing direction, such as the forward speed in forward gear or the reverse speed in reverse gear, the target speed for hill-climbing control is switched to 0.

[0033] Hill-start control module: This module uses closed-loop speed control to achieve motor hill-start control. It receives the target speed output from the target speed determination module and the given speed from the closed-loop speed control. Closed-loop control typically uses a proportional-integral (PI) algorithm, as follows:

[0034] Err(n) = Ref(n) – Fdb(n);

[0035] Up(n) = Kp * Err(n);

[0036] delta_Ui(n)=Ki*Err(n); Formula (1)

[0037] Ui(n)=Ui(n-1)+delta_Ui(n);

[0038] Out(n) = Up(n) + Ui(n);

[0039] In the above formula, Out(n) is the closed-loop output of speed, Err(n) is the error signal, Kp is the proportional gain, Ki is the integral gain, Ref(n) is the closed-loop setpoint of speed, Fdb(n) is the closed-loop feedback of speed, and Ui(n-1) and Ui(n) are the closed-loop integral quantities of speed calculated in the previous and current calculations, respectively.

[0040] When a slope-climbing speed is detected, the target speed, i.e., Ref(n) in the above formula, is non-zero. The difference between the backward slope speed or the forward slope speed, i.e., Fdb(n) in the above formula, and the target speed Ref(n) is artificially increased. In other words, the input speed difference Err(n) of the speed PI loop increases, thereby increasing the output Out(n) of the speed closed loop. This allows the motor to output more torque more quickly to stop the slope.

[0041] Hill-holding exit module: Resets the hill-holding control flag. There are three reset conditions: First, the driver presses the accelerator and the accelerator signal is greater than the hill-holding torque; second, the driver shifts to neutral or the allowed hill-holding time is reached; third, the driver presses the brake. When the driver presses the brake to a depth greater than the brake depth already locked in the brake depth latch module, the hill-holding control is automatically exited and torque control is switched to avoid the feeling of power loss after exiting the speed closed-loop control by pressing the brake, which could cause the vehicle to roll backward.

[0042] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary and that changes can be made in detail without departing from the principles and spirit of the application. The scope of the application is therefore defined by the appended claims and their equivalents.

Claims

1. A method of hill holding and hill exiting for an electric vehicle, characterized by, The method comprises the following steps: S1, obtaining a calibration two-dimensional table of brake opening degree and brake torque, and latching the brake opening degree under a set condition; S2, determining whether to enable the hill-hold control flag under the set condition, and the determination method is as follows: when the vehicle has no accelerator and no brake, the vehicle is in forward gear, if the vehicle is detected to have a rear rolling speed, it is determined to enable the hill-hold control flag; when the vehicle is in reverse gear, it is determined to enable the hill-hold control flag when the front rolling speed is detected; S3, when the hill-hold control flag in step S2 is detected, outputting a given speed of the speed closed-loop control in the hill-hold state, and the given speed of the speed closed-loop control is a fixed non-0 speed when the hill-hold control flag is detected to be enabled; when the actual detected vehicle speed is a speed in the opposite direction of the rolling direction, the target speed of the hill-hold control is switched to 0; S4, realizing the motor hill-hold control by using the speed closed-loop control, and the closed-loop control uses a proportional integral algorithm, as follows: Equation (1) In the above formula, Out(n) is the output of the speed closed-loop control, Err(n) is an error signal, Kp is a proportional gain, Ki is an integral gain, Ref(n) is a given quantity of the speed closed-loop control, Fdb(n) is a feedback quantity of the speed closed-loop control, Ui(n-1) and Ui(n) are respectively the speed closed-loop integral quantity calculated last time and this time; S5, when the hill-hold control flag is received, automatically exiting the hill-hold control and switching to torque control.

2. The method of claim 1, wherein, The brake opening degree confirmation method in step S1 is as follows: if the rolling is detected to occur after the accelerator is released, the accelerator torque size when the motor first has the rolling speed is recorded, the two-dimensional table of brake opening degree and brake torque is searched according to the accelerator torque, the brake opening degree corresponding to the accelerator torque is obtained, and the brake opening degree is latched; If the rolling is detected to be caused by the operation of releasing the brake, the brake opening degree when the rolling just occurs is latched.

3. The method of claim 1, wherein, When the rolling speed is detected, the target speed, that is, Ref(n) in the above formula, is non-0, the rear rolling speed or the front rolling speed, that is, Fdb(n) in the above formula, is larger than the target speed Ref(n), that is, the input speed difference Err(n) of the speed PI loop is increased, so that the output Out(n) of the speed closed-loop control is increased.

4. The method of hill holding and hill exiting for electric vehicles of claim 1, wherein, The reset conditions of the hill-hold control flag in step S5 are as follows: first, the accelerator is stepped on and the accelerator signal is greater than the hill-hold torque, second, the neutral gear is engaged or the hill-hold allowed time is up, and third, the brake is stepped on, and when the depth of stepping on the brake is greater than the latched brake depth in the brake depth latching module.

5. The method of hill holding and hill exiting for electric vehicles of claim 1, wherein, The method comprises a brake depth latching module, a rolling judgment module, a target speed judgment module, a hill-hold control module, and a hill-hold exit module.

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