JPH0466844A - Detecting method of friction coefficient of road surface - Google Patents

Abstract

PURPOSE:To enable accurate measurement of a friction coefficient of a road surface in steering, by detecting a steering wheel angle, a vehicle speed and an operating pressure of a power steering device by using sensors respectively when a steering wheel is steered. CONSTITUTION:In order to output its operation control signals to a rear-wheel control valve 10 and a front-wheel steering valve 5, a controller 15 is connected electrically to various sensors. Among these sensors, there are a vehicle speed sensor 26 detecting a vehicle speed V, a wheel angle sensor 16 detecting a wheel angle thetaH of a steering wheel 4, a rear-wheel steering angle sensor 17 detecting a rear-wheel steering angle thetaR and pressure sensors 18 and 19 detecting an operating pressure (power steering pressure) DELTAP of a power steering device 2, and sensor signals from them are supplied to the controller 15. In a road surface mu computing element of the controller 15, a road surface mu is calculated from the power steering pressure DELTAP, the wheel angle thetaH and the vehicle speed V according to a prescribed formula.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention provides a road surface friction coefficient detection method for detecting the condition of a road surface, that is, whether or not the road surface is slippery and the degree thereof, while a vehicle is running. Regarding.

(Prior Art) For example, in driving a vehicle, detecting the road surface friction coefficient, so-called road surface μ, is an important element in ensuring the maneuverability of the vehicle. For example, depending on the vehicle's driving condition,
In the case of a 4-wheel steering type (4WS) that also steers the rear wheels, when controlling the steering angle of the rear wheels, the road surface μ
Unless this is also taken into consideration, it is not possible to ensure sufficient maneuverability.

(Problem to be Solved by the Invention) By the way, the value of road surface μ depends on the condition of the road surface, that is, when the road surface is dry, when the road surface is wet, or when there is snow on the road surface. Because of the large difference, when controlling the steering angle of the rear wheels, it is necessary to adjust the road surface μ when steering the vehicle.
It is desired to be able to detect However, conventionally, it has been difficult to accurately detect road surface μ while the vehicle is running, and in practical rear wheel steering angle control, the road surface is assumed to be a high μ road. The purpose is to improve the handling stability of the vehicle. For this reason, conventional rear wheel steering angle control cannot ensure sufficient steering stability when the vehicle travels on a low μ road.

Therefore, in order to improve steering stability on low-μ roads, there is a need for a method that can accurately detect road surface μ while the vehicle is running.

This invention was made based on the above-mentioned circumstances,
An object thereof is to provide a method for detecting a road surface friction coefficient that can accurately detect the road surface friction coefficient during steering in a vehicle equipped with a power steering device.

(Means for Solving the Problems) When a vehicle is steered, the detection method of the present invention detects the sideslip angle of the front wheels determined from the steering wheel angle and the vehicle speed, and the cornering force determined from this sideslip angle and the coefficient of road friction. In consideration of the fact that the cornering force and the operating pressure of the power steering device are almost proportional to each other, a calculation means for calculating the road surface friction coefficient from the steering wheel angle, vehicle speed, and operating pressure is prepared in advance, and This can be implemented by providing sensor means for detecting the steering wheel angle, vehicle speed, and operating pressure of the power steering device, respectively.

(Function) According to the above-mentioned detection method, when the steering wheel is turned, the sensor means detects the steering wheel angle, the vehicle speed, and the operating pressure of the power steering device, and then based on these detected values, , the road surface friction coefficient can be detected from the calculation means.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 schematically shows an automobile equipped with a four-wheel steering system, and in the figure IL and IR indicate the front left wheel and the front right wheel, respectively. The front left wheel 1L and the front right wheel IR are connected to the front wheel power steering device 2 via tie rods 3, respectively.

The front wheel power steering device 2 includes a rack and pinion mechanism operated by a steering handle 4, and a front wheel steering actuator that is coupled to the rack and pinion mechanism and is constituted by a hydraulic cylinder.

The front wheel steering actuator is connected to one hydraulic pump 7 of the pump unit 6 via a front wheel steering valve 5 with a phase advance function operated by a steering handle 4 . That is, the pump unit 6 is composed of two pumps connected in tandem and driven by an engine 8, and the other hydraulic pump 9 is connected to a rear wheel steering actuator 11 via a rear wheel steering valve 10. There is.

The rear wheel steering actuator 11 also consists of a hydraulic cylinder, and its piston rod is connected to the
It is connected to left and right rear wheels 13L and 13R.

In addition, in FIG. 1, 14 indicates a reservoir tank.

The front wheel steering actuator is actuated according to the steering direction by being supplied with hydraulic oil from the hydraulic pump 7 via the front wheel steering valve 5 as the steering handle 4 is steered. The operation of the actuator 11 is controlled by a controller 15. That is, when the steering wheel 4 is steered, the controller 15 supplies an operation control signal to the rear wheel steering valve 10 according to the driving state, and thereby, the hydraulic pump 9 is activated via the rear wheel steering valve 10. Hydraulic oil supplied to the rear wheel steering actuator 10 from
Control its operation.

Further, the controller 15 can also supply an operation control signal to the front wheel steering valve 5, and from this, the front wheel steering actuator 11, that is, the left and right front wheels IL, Steering is possible by advancing the IR.

As described above, the controller 15 controls the rear wheel control valve I.
The controller 15 is electrically connected to various sensors and meters in order to output operation control signals to the O and front wheel steering valves 5. That is, the sensors include a vehicle speed sensor 26 that detects the vehicle speed V, a steering wheel angle sensor 16 that detects the steering wheel angle θH of the steering wheel 4, a rear wheel steering angle sensor 17 that detects the rear wheel steering angle θR, and a front wheel steering actuator. That is, there are pressure sensors 18 and 19 that detect the operating pressure of the power steering device 2, so-called power steering pressure, and sensor signals from these sensors are supplied to the controller 15. In this embodiment, the power steering pressure is determined by detecting the pressures PL and PR in the left and right pressure chambers (not shown) of the front wheel steering actuator using a pair of pressure sensors 18 and 19, and The differential pressure between the pressure chambers is determined as the power steering pressure based on the sensor signal.

The controller 15 described above has a built-in detection circuit for detecting the road surface friction coefficient, that is, the road surface μ, based on the supplied sensor signal, and the configuration of the detection circuit is shown in the block diagram of FIG. has been done.

First, the power steering pressure ΔP found from the pressure sensors 18 and 29
1 The steering wheel angle θH and the vehicle speed V from the steering wheel angle sensor 16 are supplied to the road surface μ calculation section 20 in the controller 15. Among these data, the power steering pressure ΔP is calculated based on the pressure PL from the pressure sensors 18 and 19, After calculating the differential pressure between PR, that is, the power steering pressure ΔP, by the subtraction unit 22, -1,
The signal is supplied to the road surface μ calculation section 20 via the phase compensation filter 21.

Here, the phase compensation filter 21 is a filter that not only removes noise but also compensates for the phase advance of the power steering pressure ΔP with respect to the steering wheel angle θH during the transition period of steering of the steering wheel 4. In other words, as shown in FIG. 3, when the steering wheel 4 is turned in, the power steering pressure ΔP rises quickly and greatly with respect to the steering wheel angle θH, whereas when the steering wheel 4 is turned back, the power steering pressure ΔP rises significantly with respect to the steering wheel angle θH. On the other hand, the power steering pressure ΔP falls earlier, but by filtering the power steering pressure ΔP with the phase compensation filter 21, the phase shift between the steering wheel angle θH and the power steering pressure ΔP can be reduced. Can be removed. The characteristics of the power steering pressure ΔP with respect to the steering wheel angle θH described above are due to the characteristics of the front wheel steering valve 5 described above.

The road surface μ calculation unit 20 detects or calculates the road surface μ from the power steering pressure ΔP, the steering wheel angle θH, and the vehicle speed V. The principle of the calculation will be explained below with reference to FIG. do.

When the right front wheel IR is steered, the traveling direction R of the right front wheel IR
Let βf be the inclination angle of the right front wheel IR relative to the side slip angle, the cornering force CF can be expressed by the following equation.

CF-βf ・μ Here, cornering force C for sideslip angle βf
As shown in FIG. 5, F varies greatly depending on the road surface condition, and the higher the road surface μ, the larger the value becomes as the sideslip angle βf increases. In addition, in Figure 4, L
indicates a line along the longitudinal direction of the vehicle body, and δf indicates the front wheel steering angle.

Cornering force CF and power steering pressure ΔP are the fourth
As is clear from the figure, there is a nearly proportional relationship from a mechanical perspective, so if the above equation is rewritten using the power steering pressure ΔP, the following equation can be obtained.

ΔP=CI·β[·μ (1) where CI is a constant.

On the other hand, regarding sideslip angle βf, vehicle speed V, steering wheel angle θ
It can be expressed by the following formula from H and road surface μ.

βf=C3・V2・θH/(μ102・V2)...
(2) In both cases, C2 and C3 are constants.

From equations (1) and (2), the ratio between the power steering pressure ΔP and the steering wheel angle θH, that is, ΔP/θH, can be expressed by the following equation.

ΔP/eH=uc1-C3-V'/ (μ+C2・V2) (3) Therefore, the power steering pressure ΔP, the steering wheel angle θH, and the vehicle speed V supplied to the road surface μ calculating section 20 are expressed by the above equation (3). By substituting , the road surface μ can be calculated.

The road surface μ calculated by the road surface μ calculating section 20 is then outputted via the μ fluctuation limiting section 23 and the stabilizing filter 24. When the rate is within a predetermined range, the next stabilizing filter 2
4, and the stabilizing filter 24 outputs the road surface μ.
This is a filter to stabilize the value of road surface μ.

The road surface μ calculation routine executed by the detection circuit of FIG. 2 is shown in the flowcharts of FIGS. 6 and 7, and this flowchart will be briefly explained below.

First, in step S1 of FIG. 6, the pressure sensor 18.1
9. Pressure PL, PR, /λ Handle angle θH1 Vehicle speed V detected from the steering wheel angle sensor 16 and vehicle speed sensor (meter)
Then, in the next step S2, the differential pressure between the pressures PR and PL, that is, the power steering pressure ΔP (
-PR-PL) is calculated. And power steering pressure Δ
In the next step S3, the above-mentioned phase compensation filter processing is applied to P, and in the next step S4, it is determined whether the steering wheel 4 is turned or is held. It is determined whether or not there is one. This determination can be made from the magnitude of the steering wheel angle θH and its change trend.

If the determination in step S4 is negative (No), the process returns to step S1 and the above steps are repeated.
On the other hand, if the determination in step S4 is positive (Yes), it is determined in step S5 whether the absolute value of the steering wheel angle θH is a predetermined value θ1 (for example, 10° or more). Here, too, if the determination is negative, the process returns to step S1 and the subsequent steps are repeated.On the other hand, if the determination is positive, the power steering pressure ΔP and the steering wheel are The ratio to the angle θH, that is, ΔP/θH, is calculated and obtained.

After this, in step S7 of FIG. 7, it is determined whether the direction of the power steering pressure ΔP and the direction of the steering wheel angle θH are the same.
That is, it is determined whether the sign of ΔP/θH is positive or not. If the determination here is negative, it is determined that a phase inversion has occurred between the power steering pressure ΔP and the steering wheel angle θH due to the filter processing in step $3, and in this case,
Returning to step S1, the steps described above are repeated. On the other hand, if the determination in step S7 is positive, in the next step S8, μ is read out as a coefficient from the map. This map defines μ as a coefficient corresponding to the vehicle speed V, as shown in FIG. 8, and is stored in advance in a memory (not shown) in the controller 15.

Here, the coefficient μ corresponds to a coefficient within 0 in the following equation, which is a rewrite of the above equation (3).

μ= (1+C2・V” / (CI・C3・V2)]
-ΔP/θH (4) That is, the coefficient μ can be expressed by the following formula.

Kμ=10C2-V'/(CI-C3-V')...(
5) Therefore, the map shown in FIG. 8 is obtained from the above equation (5).

In the next step S9, μ is added to the coefficient read in step S8, and the value calculated in step S6, that is, ΔP/θ
By multiplying by H, the road surface μ is calculated. That is, this means that the road surface μ is calculated from the above equation (3) based on ΔP/θH and the vehicle speed V.

Thereafter, in step SIO, it is determined whether the calculated rate of change of road surface μ, that is, its differential value dμ/dt, is within a predetermined value Δμ (for example, 0.2μ/5ec).

If the determination here is negative, the process returns to step S1; on the other hand, if the determination is positive, the process proceeds to the next step S1.
After filter processing is performed to stabilize the value of the road surface μ at step SI2, the road surface μ is outputted at step SI2.

As described above, in this embodiment, when the steering wheel 4 is steered while the vehicle is running, the road surface μ can be detected, so the rear wheel steering angle is controlled based on the detected road surface μ. This makes it possible to optimally control the steering angle of the rear wheels according to the road surface conditions, thereby improving steering stability.

As mentioned above, in one embodiment, the detected power steering pressure Δ
Since P is subjected to phase compensation filter processing, the phase lead of the power steering pressure ΔP during the transition period of steering of the steering wheel 4 can be removed.

Further, in calculating the road surface μ, it is determined in step S5 that when the steering wheel angle θH is equal to or greater than a predetermined value, that is, when the front wheels are steered and the power steering pressure ΔP substantially rises, The road surface μ can be calculated accurately only when the power steering pressure ΔP and the steering wheel angle θH are in the same direction. That is, it is possible to accurately calculate the road surface μ by removing the influence of the characteristics of the front wheel steering valve 5, the inertia of the front wheels, and the like.

On the other hand, step S4. S5. If any of the results is negative in the determination at S7, the steps from step S8 onward will not be executed, and in this case, the previously calculated value of road surface μ will be maintained.

Furthermore, in this embodiment, even if the road surface μ is calculated by performing the steps after step S8, if the rate of change in the road surface μ is larger than the predetermined value Δμ, it is determined in step SIO that the road surface μ is The value of is not updated, and even if the determination in step S10 is positive, the road surface μ is output after filtering for stabilization, so the road surface μ that is output is There are no sudden changes, and the value remains stable.

This invention is not limited to the one embodiment described above, and various modifications are possible. For example, in one embodiment:
In detecting the power steering pressure, a pair of pressure sensors 18 and 19 measure the pressure in the left and right pressure chambers of the front wheel steering actuator.
Then, the pressure difference between the pressure chambers is determined as the power steering pressure ΔP.As shown in FIG. Then, the power steering pressure ΔP is calculated from the source pressure of the hydraulic pump 7.
It is also possible to calculate In this case, in the block diagram of FIG. 2, the power steering source pressure Ps is supplied to the phase compensation filter 21, and in the step of FIG. 6, the power steering source pressure Ps is read instead of the pressures PL and PR. It will be.

Moreover, in this case, in the flowchart of FIG. 7, step S7 is bypassed. Further, when using the source pressure Ps of the hydraulic pump 7 as the power steering pressure, it is preferable to increase the predetermined value θl in the determination in step S5 to ensure a large dead zone for the steering wheel angle θH.

Furthermore, in the above explanation, the detected road surface μ is used to control the steering angle of the rear wheels, but the detected road surface μ can also be applied to traction control. Of course.

(Effects of the Invention) As explained above, according to the method for detecting the coefficient of friction of the road surface of the present invention, the coefficient of friction of the road surface can be detected from the steering wheel angle, vehicle speed, and operating pressure of the power steering device when the steering wheel is turned. Can be detected accurately. Therefore, each time the steering wheel is turned while driving, it is possible to obtain the coefficient of friction of the road surface at that point in time, so even if the road surface conditions change, the steering wheel can still be turned. In some cases, the friction coefficient of the road surface can be detected in advance, and based on this friction coefficient, for example, the steering angle of the rear wheels can be controlled.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a schematic diagram showing a four-wheel steering system for an automobile, FIG. 2 is a block diagram showing a procedure for calculating road surface μ, and FIG. 3 is a steering wheel steering system. Figure 4 is a graph showing the relationship between the angle and power steering pressure. Figure 4 is a graph showing the relationship between the sideslip angle of the front wheels and its cornering force. Figure 5 is a graph showing the cornering force that varies depending on the road surface condition with respect to the sideslip angle. The graphs, Figures 6 and 7 are
FIG. 8, a flowchart showing a routine for calculating road surface μ, is a graph showing μ as a coefficient with respect to vehicle speed. 4... Steering handle, 7... Hydraulic pump,
15... Controller, 16... Knoll angle sensor, 18, 19. 25...pressure sensor, 26...
・Vehicle speed sensor. Applicant Mitsubishi Motors Corporation Agent Patent Attorney Kan Nagato 1 Figure 2 Figure 3 Layer gap Figure 5 O-sliding angle Figure

Claims (1)

[Claims] In a vehicle equipped with a power steering device, when the vehicle is steered, the sideslip angle of the front wheels determined from the steering wheel angle and vehicle speed, the cornering force determined from this sideslip angle and the coefficient of road friction, and this cornering force Considering that there is an almost proportional relationship between the coefficient of friction and the operating pressure of the power steering device, a calculation means is prepared to calculate the coefficient of road friction from the steering wheel angle, vehicle speed, and operating pressure, and when the steering wheel is turned. A method for detecting a coefficient of friction of a road surface, characterized in that a steering wheel angle, a vehicle speed, and an operating pressure of a power steering device are respectively detected by a sensor means, and a coefficient of friction of a road surface is detected by the calculation means based on these detected values.