JPH0599014A - Detection method for frictional factor on road surface - Google Patents

Abstract

PURPOSE:To accurately detect a friction coefficient on a road surface for a vehicle. CONSTITUTION:A friction coefficient mu on a driving road surface is calculated and detected by, for instance, the following equation: mu=(TWP-Ialpha)/mWgr, or mu=(mrTWP+IR)/mWg(mr<2>+I), where TWP is a maximum value of a shaft torque TW of a driving wheel in respect to a driving road surface immediately before slipping, mWg is a vehicle weight applied to the driving wheel, I is an inertial moment from a detection part of the shaft torque to the tire tread of the rear wheel, F is frictional force generated on the tire tread of the rear wheel, N is repulsive force in a perpendicular direction applied from the road surface to the rear wheel, (r) is a diameter of the rear wheel, and R is a running resistance of the vehicle. Thus, a road surface friction coefficient is accurately detected from torque generated on the tire tread of the driving wheel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a friction coefficient on a road surface of a vehicle.

[0002]

2. Description of the Related Art There is a type in which an accelerator pedal operation amount (depression amount) is detected and a throttle valve provided in an intake system of an engine is driven and controlled by an actuator in accordance with the operation amount. In some cases, traction control is performed to reduce the engine torque and then gradually increase the integral torque to suppress slip while maintaining the driving force at an optimum level.
(See Japanese Patent Laid-Open No. 1-218932, etc.).

[0003]

However, in such a conventional traction control device, since the torque is reduced only when the wheel slip occurs, a control delay may occur at the initial stage of the slip, and good traction control cannot be performed. was there. Also, in vehicles equipped with an automatic transmission, in order to prevent slipping of wheels when traveling on a road surface with a small friction coefficient such as a snow road, the shift map is changed to a snow mode in which the higher speed gear side is used than the mode for normal running. Although there is one that can be switched, the switching of this mode is currently performed manually at the discretion of the driver, so that the appropriate mode may not be used.

Therefore, the applicant of the present application detects the shaft torque of the drive wheels, determines that slip occurs when the shaft torque decreases when the engine is not decelerating, and the slip occurs immediately before the shaft torque decreases. Determined as the maximum axial torque that can be generated on the traveling road surface.When the maximum axial torque is generated, the maximum frictional force is generated between the drive wheel and the traveling road surface. We proposed a method that detects the friction coefficient of the road surface by calculation from the vehicle weight applied to the drive wheels and the diameter of the drive wheels (Japanese Patent Application No. 3-1091).

However, in order to accurately obtain the friction coefficient of the traveling road surface, it is necessary to detect the torque of the ground contact surface of the drive wheel, and the torque of the ground contact surface and the axial torque of the drive wheel generate each torque. The moment of inertia between the parts is different by the amount of the angular acceleration acting, and thus the detected value of the road surface friction coefficient has an error. The present invention has been made in view of the above conventional problems.
An object of the present invention is to provide a method for indirectly detecting a friction coefficient of a traveling road surface, which is required to be detected in order to more appropriately perform gear shift control and the like, during traveling, and more accurately detecting the friction coefficient.

[0006]

Therefore, a road surface friction coefficient detecting method according to the present invention detects the torque of an engine mounted on a vehicle and the torque of a drive shaft connected to driving wheels of the vehicle, respectively. When the shaft torque decreases when the engine torque is not decreasing, the shaft torque detected immediately before the decrease, the moment of inertia of the portion from the torque detecting portion of the drive shaft to the ground surface of the drive wheel, and the angular acceleration of the drive wheel. The friction coefficient of the traveling road surface is calculated based on the loss torque obtained as the product of the above and the specifications of the vehicle.

Further, the angular acceleration of the driving wheels, the running resistance of the vehicle obtained from the detected axial torque and the detected value of the vehicle speed,
A value estimated and calculated based on the specifications of the vehicle may be used.

[0008]

When the engine torque is not reduced, the axial torque of the drive wheels does not decrease before the drive wheels slip.
When the drive wheels slip, the shaft torque is greatly reduced. Therefore, when the reduction of the axial torque is detected under the above conditions, it is when the drive wheel slips, and immediately before that, the value of the torque (ground plane torque) generated on the ground surface of the drive wheel is generated between the drive wheel and the road surface. It is equal to the value obtained by multiplying the maximum frictional force by the wheel diameter of the drive wheel, and the maximum frictional force is obtained from the specifications (weight) of the vehicle and the friction coefficient of the road surface. The friction coefficient of the road surface can be obtained.

The ground contact torque of the drive wheel coincides with the shaft torque when the drive wheel rotates at a constant speed, but during acceleration / deceleration, the moment of inertia of the portion from the shaft torque detecting portion to the ground contact surface of the drive wheel becomes equal to the drive wheel. Is a value obtained by subtracting a torque component (a positive value at the time of acceleration) obtained by multiplying the angular acceleration from the shaft torque.
Therefore, the road surface friction coefficient can be detected by calculation based on the axial torque immediately before the reduction of the axial torque, the loss torque obtained as the product of the inertia moment and the angular acceleration of the drive wheels, and the vehicle specifications.

Further, the angular acceleration of the drive wheels can be obtained by differentiating the rotational speed of the drive wheels with a sensor, but the detected axial torque, the running resistance of the vehicle obtained from the detected value of the vehicle speed, and various vehicle characteristics. The calculation may be performed based on the original value, and the rotation speed sensor for the drive wheel is not necessary.

[0011]

EXAMPLES Examples of the present invention will be described below. In FIG. 1 showing the system configuration of one embodiment, a throttle valve 4 driven by an actuator 3 such as a step motor is provided in an intake passage 2 of an engine 1 mounted on a vehicle.

And, normally, the control unit 5
However, the target torque of the engine 1 is set according to the operation amount (depression amount) of an accelerator pedal (not shown) detected by the accelerator sensor 6, and the control unit 5 opens the actuator 3 to bring the engine torque close to the target torque. Degree control signal is output, and the opening degree of the throttle valve 4 is controlled via the actuator 3 by the signal.

Further, in order to detect the friction coefficient μ of the traveling road surface, a torque sensor 8 for detecting the axial torque of the drive wheel, that is, the rear wheel 7 in this embodiment, is an axle (drive shaft) connected to the rear wheel 7.
A vehicle speed sensor 10 for detecting a vehicle speed by detecting the rotation speed of the output shaft of the transmission 9 is provided in the automatic transmission 9 with a torque converter connected to the output shaft of the engine 1. Torque sensor 8, vehicle speed sensor 10
The signal from is input to the control unit 5,
The control unit 5 controls the rear wheel 7 based on each detection signal.
When the slip occurs, the friction coefficient μ of the road surface is detected, and traction control described later is performed according to the friction coefficient μ.

The detection of the friction coefficient μ by the control unit 5 and the engine torque control based on the detected value will be described below with reference to the flow chart shown in FIG. In step (denoted as S in the figure. The same applies hereinafter) 1, the first target torque T ₁ is set according to the operating conditions including the operation amount of the accelerator pedal. In step 2, the axial torque T _W of the rear wheel 7 detected by the torque sensor 8 is A / D converted.

In step 3, the engine torque T _e is calculated. This is obtained as a value proportional to the basic fuel injection amount T _P (= K · Q / N; K is a constant, Q is the intake air flow rate, and N is the engine speed) obtained in another routine. The function of step 3 corresponds to the engine torque detecting means. In step 4, it is determined whether the engine torque T _e is decreasing.

When the determination in step 4 is NO, that is, when the engine torque T _e is not decreasing (monotonically increasing), the process proceeds to step 5 and it is determined whether the shaft torque T _W has decreased. When the determination in step 5 is YES,
That is, while the engine torque T _e is monotonically increasing, the shaft torque T _W
If is decreased, the process proceeds to step 6 and it is determined whether or not this state is the first time.

If it is determined in step 6 that it is the first time, it is determined that the axial torque T _e has decreased as a result of slippage of the rear wheels 7, and the previous detected value T _W-1 of the axial torque is the current value. Since it is the maximum axial torque that can be generated with respect to the friction coefficient μ of the traveling road surface, the friction coefficient μ is calculated back in step 7 as follows. As shown in FIG. 3, vehicle body weight is m, vehicle body running acceleration is a, vehicle weight applied to rear wheels (driving wheels) is m _W , rear wheel angular acceleration is α, gravitational acceleration is g, and rear wheel axle torque detection is performed. Section, the moment of inertia from the rear wheel contact surface is I, the frictional force generated on the rear wheel contact surface is F, the vertical reaction force that the rear wheel receives from the contact surface is N, the rear wheel diameter is r, and the vehicle travels. Resistance is R, vehicle traveling direction (x-axis direction), vertical direction (y-axis direction), drive wheel rotation direction (z-axis rotation direction)
The equation of motion of is set as follows.

X-axis direction: ma = μmg−R (1) y-axis direction: m _W g = N (2) z-axis rotation direction: Iα = T _W −Fr (3) Just before the rear wheel slips (during grip), F _MAX = μ
N = μm _W g ··· (4) When gripping, a = rα ...
Since (5) holds, F _MAX = ma + R = mrα + R = μm _W g (6) From formulas (1), (4) and (5), (6) From formulas (3) and (4), F _MAX = The _{(T WP -Iα) / r =} μm W g ··· (7) ∴μ = (mrα + R) / m W g = (T WP -Iα) / m W gr ··· (8), (6 ), (7), (mrα + R) r = T _WP −Iα → (mr ² + I) α = T _WP −Rr → α = (T _WP −Rr) / (mr ² + I) (9) Then, substituting equation (9) into equation (8), μ = [(mr ² + I) T _WP −I (T _WP −Rr)] / m _W g (mr ² + I) ∴μ = (mr T _WP + IR ) / _{M W} g (mr ² + I) (10) Therefore, if the grip limit torque T _WP generated on the contact surface of the drive wheels and the running resistance at that time are known, the specifications of the vehicle that are known in advance can be obtained. It is clear that can be used to calculate the coefficient of friction μ.

Here, the rolling resistance has the greatest effect as the running resistance, which changes depending on the vehicle speed. However, the value for the vehicle speed is experimentally obtained in advance and stored in the RAM as a map, so that the vehicle speed can be improved. Sensor 10
A value corresponding to the vehicle speed detected by can be obtained by searching the map. In addition, the component of gravity acts in the direction along the road on a sloped road, and the component increases the running resistance on the upslope and decreases the running resistance on the downslope. If a sensor is provided and the component force acting on the slope is detected and the increase / decrease is corrected, the road surface friction coefficient on the slope can also be accurately obtained.

If a sensor for detecting the rotational speed of the driving wheel is provided, the angular acceleration α of the driving wheel can be directly detected. Therefore, the expression μ using α in (8) μ = (T _WP -Iα) μ can be obtained as is with / m _W gr, but by converting it using running resistance, loss torque obtained by multiplying the moment of inertia and angular acceleration, which is approximately the same, only by detecting the vehicle speed without an acceleration sensor. It is possible to detect the road surface friction coefficient μ based on the contact surface torque considering

Next, the routine proceeds to step 8, where an increasing rate Δμ for gradually increasing the target torque for traction control from the initial value is set as described later. This is the value of μ obtained in step 6 as shown in FIG. 4, or from the map preset for the vehicle running acceleration a and the axial torque T _W-1 as a value related to the μ. Set by searching.
It should be noted that Δμ is set to be larger as each of the above values is larger.

At step 9, the second target torque T ₂ for traction control is set by the following equation with respect to the friction coefficient μ obtained at step 7. T ₂ = K _s μm _W g / i However, K _s is a torque excess rate, and in order to output the engine torque so as to optimally maintain the slip rate of the rear wheel 7 with respect to the maximum axial torque that can be generated, It is set to an appropriate value smaller than 1. Further, i = final gear ratio × (gear ratio of automatic transmission) × (torque ratio of torque converter).

If the determination in step 4 is YES, the determination in step 5 is NO, or the determination in step 6 is NO, that is, except immediately after the rear wheel 7 slips, proceed to step 10. After μ is updated with the value obtained by adding the increase rate Δμ set in step 7 to μ, the process proceeds to step 9 and the second target torque T ₂ is set and updated by the above-described arithmetic expression.

The function of step 9 corresponds to traction control target torque setting means. Next, at step 11, the magnitude of the first target torque T ₁ for the accelerator operation amount obtained at step 1 and the second target torque T ₂ for traction control obtained at step 9 are compared and judged, and ₁ ≦ T when ₂ is set as the target torque T to be respectively output by selecting T ₂ proceeds to step 13 when the select T ₁ proceeds to step 12 T _1> T _2.

In step 14, a drive signal is output to the actuator 3 so that the throttle valve opening degree will correspond to the target torque T. In this way, the friction coefficient μ of the traveling road surface can be accurately detected in consideration of the loss torque acting due to the moment of inertia from the shaft torque detection unit to the ground contact surface of the drive wheel, and therefore, it is optimal for the road surface condition. Traction control performance is obtained. FIG. 5 shows changes in various state quantities during traction control according to this embodiment.

[0026]

As described above, according to the present invention, it is possible to detect the friction coefficient of the traveling road surface while detecting the change in the axial torque of the driving wheels, and the axial torque detecting unit detects the driving wheels. The road surface friction coefficient can be detected more accurately based on the torque of the contact surface obtained by taking into consideration the loss torque generated as the product of the moment of inertia up to the contact surface and the angular acceleration of the drive wheels.

If the angular acceleration of the drive wheels is converted using the axial torque and the running resistance, the road surface friction coefficient can be detected without providing a sensor for directly detecting the angular acceleration. If traction control or the like is performed using such a road surface friction coefficient, control performance can be improved.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart showing detection of a road surface friction coefficient and engine torque control according to the embodiment.

FIG. 3 is a diagram showing states of various forces generated on a driving wheel.

[Fig. 4] Various maps for setting the increasing rate of the friction coefficient in the above embodiment.

FIG. 5 is a graph showing changes in various state quantities according to the above embodiment.

[Explanation of symbols]

 1 Engine 5 Control Unit 7 Rear Wheel 8 Torque Sensor 10 Vehicle Speed Sensor

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Atsumi Hoshina 1671 Kasukawacho, Isesaki City, Gunma Prefecture 1 NIPPON ELECTRONIC DEVICE CO., LTD.

Claims (2)

[Claims] 1. A torque of an engine mounted on a vehicle and a torque of a drive shaft connected to drive wheels of the vehicle are respectively detected,
When the shaft torque decreases when the engine torque is not decreasing,
The shaft torque detected immediately before the decrease, the loss torque obtained as the product of the moment of inertia of the portion from the torque detection portion of the drive shaft to the ground contact surface of the drive wheel, and the angular acceleration of the drive wheel, and the specifications of the vehicle. A method for detecting a road surface friction coefficient, characterized by detecting the friction coefficient of a traveling road surface based on the following. 2. The angular acceleration of the drive wheels is estimated and calculated on the basis of the detected axial torque, the running resistance of the vehicle obtained from the detected value of the vehicle speed, and the specifications of the vehicle. Method for detecting road friction coefficient.