KR20110114120A - Vehicle reference speed estimation method - Google Patents

Abstract

The present invention relates to a vehicle reference speed estimation method for estimating a reference speed of a vehicle by estimating the deceleration speed of the vehicle in an electronic control system of the vehicle.
To this end, the present invention estimates the deceleration speed of the vehicle by using sensor information such as engine torque information and brake pressure of the vehicle according to the driving and control conditions of the vehicle, and then estimates the reference speed of the vehicle based on this. Accurate and proper control performance can be implemented to improve the reliability of vehicle reference speed estimation.

Description

Vehicle reference speed estimation method {ESTIMATED METHOD OF REFERENCE SPEED IN A VEHICLE}

The present invention relates to a method for estimating a vehicle reference speed, and more particularly, to a method for estimating a reference speed of a vehicle by estimating a deceleration speed of the vehicle in an electronic control system of the vehicle.

As the engine performance of the vehicle is improved, the driving speed of the vehicle is also increased. Accordingly, various electronic control systems are installed in the vehicle in order to improve driving stability and ensure braking stability. The electronic control system of the vehicle includes an anti-lock brake system (hereinafter referred to as ABS) that prevents slippage of the wheel during braking and a traction control system that prevents slippage of the wheel during sudden start. (Traction Control System; hereinafter referred to as TCS), Electronic Stability Control (ESC) that combines ABS and TCS to stably maintain the vehicle's driving posture during acceleration or cornering.

The electronic control system of such a vehicle must be able to accurately calculate the slip generation amount of the wheel in order to realize proper control performance. The slip λ of each wheel is calculated by Equation 1 below.

[Equation 1]

λ = (Vveh-Vwhl) / Vveh

In Equation 1, Vveh is vehicle speed and Vwhl is wheel speed.

The wheel speed can be obtained by the detection value of the wheel speed sensor, and the vehicle speed can be obtained by the estimated vehicle reference speed (Vref) based on the wheel speed information. . Therefore, accurate estimation of the vehicle reference speed (Vref) is required to realize accurate and proper control performance.

Conventionally, an algorithm for estimating a vehicle reference speed through selecting a reference wheel speed that is closest to the actual vehicle speed (selecting a reference wheel) among four wheels and performing appropriate filtering / limbing processing has been popularized. In this case, it is common to select a reference wheel as a fast wheel among non-drive wheels and a fastest wheel during braking control during normal driving. Recently, however, various functions have been added to the electronic control system of the vehicle, and as the various functions are controlled in combination, it is necessary to estimate the vehicle reference speed more accurately.

The present invention is to propose a vehicle reference speed estimation method for estimating the deceleration speed of the vehicle using the engine information and sensor information of the vehicle according to the driving situation, and then estimating the reference speed of the vehicle based on this.

To this end, the method of estimating a vehicle reference speed according to an aspect of the present invention includes determining a driving state of a vehicle using a wheel speed sensor and a pressure sensor; Selecting a reference wheel according to a driving condition of the vehicle; Estimating the deceleration of the vehicle according to the driving situation and the control situation of the vehicle; Estimating a reference speed of the vehicle using the selected reference wheel and the estimated deceleration of the vehicle.

The driving situation of the vehicle is classified into a braking situation and a case which is not a braking situation; Non-braking situations include acceleration, parking brake, ESC brake control and normal driving.

The deceleration of the vehicle is estimated using the engine torque and the brake pressure in the electronic control system of the vehicle.

The estimating of the reference speed of the vehicle may be performed by calculating a reference speed of the vehicle using the deceleration estimated by inputting the selected reference wheel.

As described above, after estimating the deceleration speed of the vehicle by using sensor information such as engine torque information and brake pressure of the vehicle according to the driving and control conditions of the vehicle, and estimating the reference speed of the vehicle based on the estimated speed More accurate and proper control performance can be implemented to improve the reliability of vehicle reference speed estimation.

1 is a hydraulic circuit diagram of an electronic control system for a vehicle according to an embodiment of the present invention.
2 is a block diagram of an electronic control system for a vehicle according to an embodiment of the present invention.
3 is a flowchart illustrating a method of estimating a vehicle reference speed in an electronic control system for a vehicle according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a hydraulic circuit diagram of an electronic control system for a vehicle according to an embodiment of the present invention.

In FIG. 1, in the electronic control system of a vehicle according to an exemplary embodiment of the present disclosure, the driver's foot force is doubled by the booster through the brake pedal 11 and transmitted to the master cylinder 10 when the ABS is braked. The hydraulic pressure formed in the master cylinder 10 is the wheel cylinders 11a to 1 through the first and second traction control valves 29a and 29b and the first solenoid valves 21a to 21d, which are normally NO valves. 11d). In order to return the brake oil of each wheel cylinder 11a-11d, the 1st solenoid valves 21a-21d are closed-controlled and the 2nd solenoid valves 22a-22d which are NC valves which normally maintain a closed state are opened. Brake oil is temporarily stored in the low pressure accumulators 25a to 25b. The low pressure accumulators 25a to 25b function to supply the brake oil toward the hydraulic pumps 23a to 23b when a certain amount of oil is filled, and the high pressure accumulators installed downstream of the hydraulic pumps 23a to 23b ( 26a to 26b serve to damp the pulsation caused by the operation of the hydraulic pump 24 while temporarily storing the pressurized oil in the hydraulic pumps 23a to 23b. Depending on the vehicle, even if the high pressure accumulators 26a to 26b are removed, there is no problem in the hydraulic circuit of the brake device. This is because the purpose of installation of the high pressure accumulators 26a to 26b is to attenuate the pulsation caused by the operation of the hydraulic pumps 23a to 23b.

On the other hand, when the ABS is not controlled, the brake oil is discharged through the first solenoid valves 21a to 21d.

In the electronic control system of the vehicle, opening and closing of the first and second solenoid valves 21a to 21d and 22a to 22d are controlled by an electronic control unit 50 (ECU), which will be described later. Control the driving of the hydraulic pumps (23a to 23b) at the same time to re-press the fluid returned along the hydraulic line toward each of the wheel cylinders (11a to 11d). ) Braking can be achieved.

When the vehicle according to an embodiment of the present invention receives a force in the lateral direction, the first and second solenoid valves 21a to 21d and 22a to 22d are opened, and the braking pressure forming valves 28a to 28b are opened. After the brake oil is supplied from the cylinder 10 and the first and second traction control valves 29a to 29b are closed, the brake motor is formed by driving the hydraulic pumps 23a to 23b driving motor 24. The braking pressure thus formed is transmitted to the respective wheel cylinders 11a to 11d through the first solenoid valves 21a to 21d so that the wheels FL, RR, RL, and FR are operated before the brake pedal 11 is operated by the driver. The brake pedal 11 is already in a braking state, or at least a certain degree, so that it is in a state immediately before entering the braking state.

2 is a block diagram of an electronic control system for a vehicle according to an embodiment of the present invention.

In FIG. 2, an electronic control system for a vehicle according to an exemplary embodiment of the present invention includes a wheel speed sensor 40, a steering angle sensor 42, a yaw rate sensor 44, a lateral acceleration sensor 46, and a pressure sensor 48. ), The electronic control unit 50, the brake control unit 52, the engine control unit 54 and the parking brake control unit 56 are further included.

The wheel speed sensor 40 is installed on a plurality of wheels FL, RR, RL, and FR, respectively, and detects the speed of each wheel FL, RR, RL, and FR to control the electronic control unit. Pass in 50.

The steering angle sensor 42 is provided on the steering shaft of the handle and detects the steering angle and the steering angular velocity according to the steering wheel operation of the driver and transmits the steering angle to the electronic control unit 50.

The yaw rate sensor 44 detects a yaw rate (turning speed) of the vehicle and transmits the yaw rate to the electronic control unit 50.

The lateral acceleration sensor 46 detects the lateral acceleration Ax of the vehicle and transmits it to the electronic control unit 50, and the pressure sensor 48 applies the brake pressure of the master cylinder 10 which is changed according to the braking intention of the driver. Detects and delivers to the electronic control unit 50.

The electronic control unit 50 receives the signals transmitted from the wheel speed sensor 40, the steering angle sensor 42, the yaw rate sensor 44, the lateral acceleration sensor 46, and the pressure sensor 48 to receive the braking force and the wheel ( FL, RR, RL, and FR are determined to output a signal for controlling brake pressure and engine torque of each of the wheels FL, RR, RL, and FR to the brake control unit 52 and the engine control unit 54.

In addition, the electronic control unit 50 selects a reference wheel for estimating a vehicle reference speed according to a driving condition of the vehicle, estimates acceleration / deceleration using engine torque and brake pressure during actual driving of the vehicle, and then selects it. Estimated vehicle reference speed and estimated acceleration / deceleration. In this case, in the case of the four-wheel drive in which the longitudinal acceleration sensor is separately installed, the longitudinal acceleration of the vehicle may be detected from the longitudinal acceleration sensor like the lateral acceleration sensor.

The brake control unit 52 controls the brake hydraulic pressure supplied to the wheel cylinders 11a to 11d according to the braking signal output from the electronic control unit 50 to cooperatively control the ABS control block 53 to secure the vehicle's stability as much as possible. To generate a braking pressure.

The engine controller 54 controls the driving force of the engine by cooperatively controlling the engine torque according to the engine control signal output from the electronic control unit 50 to cooperatively control the TCS control block 55 to ensure the stability of the vehicle.

The parking brake controller 56 applies an additional braking force to the rear wheels RR and RL according to the parking brake control signal output from the electronic control unit 50 to optimize the braking force of the vehicle. Cooperative control with the control block 57 to distribute the braking force.

Hereinafter, the operation process and the effect of the vehicle reference speed estimation method configured as described above will be described.

3 is a flowchart illustrating a method of estimating a vehicle reference speed in an electronic control system for a vehicle according to an embodiment of the present invention.

In FIG. 3, the electronic control unit 50 determines the driving situation of the vehicle by using the given information (100).

The driving situation of the vehicle can be classified into two categories, a braking situation and a non-braking situation.

For example, when the driver operates the brake pedal 11, the pressure sensor 48 senses the pressure generated in the master cylinder 10 according to the operation of the brake pedal 11 and transmits the pressure to the electronic control unit 50. .

Therefore, the electronic control unit 50 receives the master pressure value transmitted from the pressure sensor 48 to determine the braking intention of the driver. The condition for determining the driver's braking will be determined that the vehicle is braking when the driver operates the brake pedal 11 above the reference value for the vehicle deceleration and the pressure sensor 48 of the master cylinder 10 is above the reference value. In addition, in the case of using the ABS control without using the vehicle attitude control device, the master pressure level may be estimated using the vehicle deceleration condition to determine whether the vehicle deceleration is greater than or equal to the reference deceleration, and thus the driver's braking intention may be determined.

As described above, when the vehicle is in a braking state according to the driver's braking intention, all of the four wheels FL, RR, RL, and FR are decelerated, and negative slip occurs.

Non-braking situations can be categorized into four categories: acceleration, parking brake, ESC brake control and normal driving.

Acceleration is when all four wheels (FL, RR, RL, FR) drive slip occurs in the four-wheeled vehicle, and parking brake is due to the operation of the parking brake Rear wheel (RR, RL) This is the case where abnormal negative slip occurs.

The driving situation of such a vehicle is summarized in [Table 1] below.

TABLE 1

Thereafter, the electronic control unit 50 selects a reference wheel for estimating the vehicle reference speed according to the driving situation of the vehicle determined in step 100 (110). That is, the reference wheel for estimating the vehicle reference speed is selected for each case according to the category classified in [Table 1].

For example, when the driving situation of the vehicle is a braking situation, the fastest wheel among the four wheels is selected as the reference wheel.

Also, when the driving condition of the vehicle is not a braking condition, the slowest wheel of the four wheels is selected as the reference wheel in the acceleration situation, and the slip size of the front wheel in the parking brake situation when the driving condition of the vehicle is not the braking condition. Select the small wheel as the reference wheel.

Also, when the driving condition of the vehicle is not a braking situation, the ESC brake control selects a wheel having a small slip size among the wheels other than the ESC control wheel as a reference wheel, and operates normally when the driving condition of the vehicle is not a braking condition. In the situation, the fast wheel among the non-drive wheels and the wheel with the smallest slip among the third fast wheels are selected as reference wheels.

Thus, the reference wheels selected according to the driving conditions of the vehicle are summarized in the following [Table 2].

TABLE 2

After selecting the reference wheel according to the driving condition of the vehicle, the electronic control unit 50 estimates the acceleration / deceleration of the vehicle using the engine torque and the brake pressure as follows (120).

In general, the longitudinal equation of motion acting on the vehicle is shown in [Equation 1] below.

[Equation 1]

In Equation 1, Fx is the longitudinal force of the vehicle, M is the vehicle mass, _av is the longitudinal acceleration of the vehicle, T _e is the engine torque, and T _fric is the friction torque. N _tf is the torque converter efficiency, I _e is the moment of inertia of the engine, I _t is the moment of inertia of the torque converter, I _d is the moment of inertia of the drive shaft, and I _w is the mass inertia of the wheel. Moment, R is the tire effective _companion , a _w is the angular acceleration of the wheel, T _t is the output torque, F _brk is the braking force, F _rollresist is the rolling resistance, F _aeroresist is the air resistance, g is the acceleration of gravity, M _eff is the effective mass, θ is the road inclination angle, and μ _rr is the road friction coefficient.

When neglecting the road surface gradient and the air resistance and rolling resistance acting on the vehicle, the acceleration of the vehicle during acceleration can be calculated using the engine torque and gear ratio during acceleration since F _brk = 0. However, the effective mass (M _eff ) is measured as shown in [Equation 2] after running.

[Equation 2]

Since the vehicle response to the engine torque input is slow, a low pass filter (LPF) is performed on the estimated a _v value.

However, since a time delay occurs in the transmission of the engine torque during gear shifting, and the accuracy of the estimated a _v value is deteriorated, the acceleration estimation in this section is suspended.

The longitudinal motion equation acting on the vehicle during braking is shown in Equation 3 below.

[Equation 3]

The equation of wheel motion acting on the vehicle during braking is shown in Equation 4 below.

[Equation 4]

In Equation 4, T _f is Front Axle torque, T _r is Rear Axle torque, I _f is Front wheel moment of inertia, I _r is Rear wheel moment of inertia, w _f is front wheel angular acceleration, w _r is the rear wheel angular acceleration, N _f is the front wheel vertical drag, N _r is the rear wheel vertical drag, μ _f is the front wheel road friction coefficient, _{r r} is the rear wheel road friction coefficient, and P _f is the front wheel wheel brake pressure, P _r is the rear wheel brake pressure.

If [Equation 3] and [Equation 4] are linked together, a relational expression such as the following [Equation 5] can be obtained.

[Equation 5]

Therefore, the deceleration estimation of the vehicle is performed using the braking force transmitted to each wheel during braking (where _f and a _r are braking torque coefficients for the braking forces P _f and P _r) . This is a characteristic value, so it can be defined by testing for each vehicle.)

Likewise, a low pass filter (LPF) is performed by setting an appropriate time constant for the deceleration value calculated during braking.

As such, when the reference wheel is selected according to the driving situation of the vehicle, and the deceleration is estimated using the engine torque and the brake pressure, the electronic control unit 50 uses the deceleration estimated as the input of the selected reference wheel. The reference speed of the vehicle is calculated as shown in Equation 6 below (130).

[Equation 6]

Input X: selected wheel speed

Output Y: Vehicle Reference speed

Diff (n) = X (n) -Y (n-1)

Delta_V (n) = [a × Diff (n) + b × Delta_V (n-1) + c × Av (n)] / d

In Equation 6, a, b, c, and d are time constants and are variable in some cases.

Therefore, Y (n) = Y (n-1) + Delta_V (n).

In this way, the reference speed of the vehicle is estimated through the calculation process of [Equation 6].

10: master cylinder 11: brake pedal
40: wheel speed sensor 42: steering angle sensor
44: yaw rate sensor 46: lateral acceleration sensor
48: pressure sensor 50: electronic control unit
52 brake control 54 engine control
56: parking brake control unit

Claims (4)

Determining a driving situation of the vehicle using a wheel speed sensor and a pressure sensor;
Selecting a reference wheel according to a driving condition of the vehicle;
Estimating the deceleration speed of the vehicle according to the driving situation and the control situation of the vehicle;
Estimating a reference speed of the vehicle using the selected reference wheel and the estimated deceleration of the vehicle. The method of claim 1,
The running situation of the vehicle,
Classified as braking situation and non-braking situation;
If the braking situation is not the vehicle reference speed estimation method including an acceleration situation, a parking brake situation, an ESC brake control situation, a normal driving situation. The method of claim 2,
And a deceleration rate of the vehicle is estimated using engine torque and brake pressure in the electronic control system of the vehicle. The method of claim 3,
Estimating the reference speed of the vehicle,
And calculating the reference speed of the vehicle by using the estimated deceleration as the input of the selected reference wheel.

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