JPH04185559A - Method of detecting road surface friction coefficient and device used therefor - Google Patents

Abstract

PURPOSE:To detect a coefficient of road surface friction even at the time of linear driving, regardless of steering or non-steering mode by using the reaction, from a wheel as a parameter for the detection of a coefficient of road surface friction, at a time when the wheel is turned and steered periodically at a frequency which does not affect the behavior of a vehicle. CONSTITUTION:The stroke of a power cylinder 20 for turning and steering rear wheels 11L, 11R, is controlled by a control valve 13 for HICAS provided in a HICAS control unit (controller) 21 as well as in a steering gear, according to the velocity and the front wheel steering reaction, detected by a velocity sensor 23, and the turning steering angle is thus adjusted in an optimal way. A reaction sensor 30 is provided on a link part of the output shaft of the power cylinder 20, and the signal related to the detected reaction is input to the controller 21. When the coefficient of road surface friction is detected at the time of driving of a vehicle, the wheel is turned and steered periodically at no less than the frequency, with which the value of the yaw rate/fixed steering angle becomes almost zero, and, for which the value of the power of tyre/fixed steering angle is not less than zero. The reaction from the wheel is detected, and the coefficient of road surface friction is detected based on the information related to the reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a road surface friction coefficient detection method and an apparatus used therefor, which can detect the road surface friction coefficient between wheels and the road surface even when driving straight ahead. be.

(Prior Art) A conventional example of a technology for detecting a road surface friction coefficient is disclosed in, for example, Japanese Patent Laid-Open No. 1-204865.

In this conventional example, the amount of steering of the steering mechanism (in this case,
Based on three parameters: steering angle and steering force), and vehicle speed, the road surface friction coefficient in the relevant driving situation is detected (
decision).

(Problems to be Solved by the Invention) In the conventional example described above, since the amount of steering of the steering mechanism is used as an essential parameter for detecting (determining) the road surface friction coefficient, steering by the driver is not required when driving straight ahead ( The road surface friction coefficient cannot be detected while the vehicle is running (or the amount of steering is extremely small), and even if the road surface friction coefficient is determined using only the remaining parameter, the vehicle speed, the desired detection accuracy cannot be ensured.

The present invention aims to solve the above-mentioned problems by using the reaction force from the wheels when the wheels are periodically steered at a frequency that does not affect vehicle behavior as a parameter for detecting the coefficient of road friction. shall be.

(Means for Solving the Problems) For this purpose, the method of the present invention detects the road surface friction coefficient while the vehicle is running by moving the wheels at a frequency higher than the frequency at which the yaw rate/fixed steering angle value is approximately zero, and when the tire A feature characterized in that the wheel is periodically steered at a frequency at which the value of force/fixed steering angle is equal to or greater than zero, the reaction force from the wheels is detected, and the road surface friction coefficient is detected based on the reaction force information. and
In addition, the device used to implement the method periodically steers the wheels at a frequency that is equal to or higher than the frequency at which the value of yaw rate/fixed steering angle is approximately zero, and at a frequency where the value of tire force/fixed steering angle is greater than or equal to zero. A steering mechanism, a reaction force detection means for detecting a reaction force received by the steering mechanism from the wheels, and a road surface friction coefficient detection means for detecting a road surface friction coefficient based on reaction force information from the reaction force detection means. It is characterized by the following:

(Function) According to the present invention, the wheels have a periodicity at a frequency higher than the frequency at which the value of yaw rate/fixed steering angle is approximately zero, and at a frequency at which the value of tire force/fixed steering angle is greater than or equal to zero. However, it is generally known that periodically steering the wheels at such a frequency does not affect vehicle behavior. Therefore, the reaction force from the wheels that is generated in response to this periodic steering is detected, and based on the reaction force information, the coefficient of road friction is detected even when driving straight, regardless of whether steering is being performed or not. can do.

(Example) Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram showing the configuration of a vehicle equipped with a device used for implementing the road surface friction coefficient detection method of the present invention.
, IOR indicates left and right front wheels, and IIL and lIR indicate left and right rear wheels.

This device is manufactured by Nissan Motor Co., Ltd. (formerly CAS III: High
hCapacityActively-'Contr
It is a system developed under the name of olled 5uspension), and the steering wheel 12, HICA
Control valve 13 for S, control valve 14 for power steering, steering gear 15, HIC
AS pump 16, power steering pump 17,
It comprises a reservoir tank 18, a rear suspension 19, a power cylinder 20, an old CAS control unit (hereinafter referred to as a controller) 21, a HICAS solenoid valve 22, a vehicle speed sensor 23, and the like. For the detailed configuration of the old CAS n, please refer to Nissan Motor Co., Ltd. (Taru's "Silvia" Service Bulletin, published in May 1988, page C-85, Shiba C-88).

In this HICAS II, a controller 21 and a HICAS control valve 13 provided in the steering gear control the rear wheels 11 according to the vehicle speed and the front wheel steering reaction force.
This system controls the stroke of the power cylinder 20 that steers the L and IIR, thereby optimizing the steering angle of the rear wheels.

By the way, in this example, in addition to the above-mentioned HICAS II system, a reaction force sensor 30 is provided at the link part of the output shaft of the power cylinder 20, and a signal related to the reaction force from the rear wheel detected by the reaction force sensor 30 is sent to the controller. 21. Although FIG. 1 shows an example in which the reaction force sensors 30 are installed near the wheels of the left and right output shafts 20a and 20b of the power unit cylinder 20, it is functionally effective even if they are installed only on either the left or right. It is enough. In such a case, the detection signal of the reaction force sensor 30 is used as reaction force information, and in the case of the configuration shown in FIG.
The average value of the detection signals FI+F2 is used as reaction force information.

The controller 21 executes the control program shown in FIG. 2 to detect the road surface friction coefficient. That is, first, in step 101 in FIG. 2, an excitation signal is input from the controller 43 to the old CAS solenoid valve 22.

This excitation signal is, for example, rear wheel 11L, IIR ±1 m.
It is assumed that the vehicle is steered at a steering angle equivalent to m and a frequency of 2 Hz.

The opening degree of the old CAS solenoid 22 is adjusted by the input of this excitation signal, and the hydraulic pressure supplied from the old CAS pump 16 to the old CAS control valve 13 is increased or decreased. Activate the power cylinder 20 as an actuator,
Power cylinder 20 is rear wheel ILL.

11R generates a fixed steering angle equivalent to ±1mm at a frequency of 2Hz. Here, a frequency characteristic as shown in Fig. 3 is established between the yaw motion of the vehicle and the steering angle (fixed steering angle), and the frequency (A
It is generally known that periodic steering of the wheels at a frequency higher than 2 Hz for a car and approximately IHz for a B car, generally less than 2 Hz does not affect vehicle behavior. It is being However, if the above frequency is too high, the cornering force of the wheels (tires) (
The tire force/steering angle value (in this case, CF/steering angle or SAT/steering angle) is important because the response of CF) and self-lining torque (SAT) is lost, which interferes with the running of the vehicle.
It is necessary that the frequency is greater than or equal to zero.

From the above, the appropriate frequency range suitable for detecting the road surface friction coefficient (hereinafter referred to as road surface μ) according to the present invention is 2 Hz to 3 Hz for car A, as shown in FIG. 4.

When the rear wheels 11L and IIR are steered periodically under the above conditions, CF and SAT occur in the rear wheels 11L and IIR, so in the next step 102, the rear wheels 11L and IIR are steered.
The reaction forces F, , F2 are detected by reaction force sensors 30 (eg, load cells), respectively. These reaction forces F,, F2
is a value according to the above-mentioned CF and SAT, and the rear wheel IL
Since the rudder angles of L and IIR are fixed rudder angles equivalent to ±1 mm, in the next step 103, the average value of the reaction forces F, F2 (that is, reaction force information) is calculated by the rudder angle (fixed rudder angle) θ. The cornering power (CF
/θ) or self-lining power (SAT/θ)
Calculate.

Since this CF/θ (or SAT/θ) exhibits the characteristics shown in FIG. 5 with respect to the road surface μ, in the next step 104
Road surface μ is detected (determined) based on F/θ (or SAT/θ). When detecting this road surface μ, since the characteristics shown in FIG. 4.5 differ depending on the vehicle speed V, the controller 21 actually detects the current A map suitable for the vehicle speed V is selected and used from among a plurality of maps shown in FIGS. 4 and 5, which are stored in advance for each vehicle speed V in a ROM (not shown).

By executing steps 101 to 104, it is possible to detect the road surface μ even when the vehicle is traveling without the driver steering the vehicle, such as when the vehicle is traveling straight. Therefore, using this road surface μ, in the next step 105, the alarm control or HIC control described in detail below is performed.
Performs AS control. In the case of alarm control, when the road surface μ remains below a predetermined value (for example, 0.3) for a predetermined period of time (for example, several seconds), an alarm device (not shown) is activated and the driver is informed that the road surface μ has changed (decreased). ) to alert the driver to certain driving conditions (for example, snowy roads). Also H
In the case of ICAS control, the controller 21 changes the steering angle characteristics as shown in FIG. 6 based on the road surface μ, and when the road surface μ is high, the response is increased and the negative phase term is increased to improve turning performance. It achieves nimble driving characteristics, and also ensures safety by lowering responsiveness and reducing the negative phase term when the road surface μ is low, and achieves appropriate control that responds to any road surface condition. Note that in this example, road surface μ detection and old CAS control (four-wheel steering control) are combined, but the invention is not limited to this. A mechanism capable of variable control (for example, a variable steering gear ratio mechanism) may be used. In addition, in step 105, instead of performing the above-mentioned warning control and old CAS control, the limit turning G is determined based on the road surface μ, and the steering force is changed just before reaching the limit under the road surface μ condition, so that the driver does not need to turn the steering wheel any further. It may also be possible to perform variable steering force control to improve safety by recognizing that steering the vehicle will reach its limit.

(Effects of the Invention) Thus, as described above, the road surface friction coefficient detection method of the present invention and the device used therefor detect the reaction force from the wheels when the wheels are periodically steered at a frequency that does not affect vehicle behavior. Since it is used as a parameter for detecting the road surface friction coefficient, the road surface friction coefficient can be detected based on the reaction force information even when driving straight ahead, regardless of the presence or absence of steering.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a vehicle equipped with a device used to implement the road surface friction coefficient detection method of the present invention, and FIG. 2 is a flowchart showing a control program for road surface friction coefficient detection by the controller 21 in the above embodiment. Figure 3 is a diagram showing the frequency characteristics between the vehicle yaw motion and the steering angle in the same example, Figure 4 is a diagram showing the frequency characteristics between the tire force and the steering angle in the same example, and Figure 5 is a diagram showing the frequency characteristics between the tire force and the steering angle in the same example. is a diagram showing the relationship between the tire force/steering angle and the road surface friction coefficient in the same example, and FIG. 6 is a diagram showing an example of the steering angle characteristic of the old CAS control in the same example. 10L, IOR...Front wheel 11L, IIR
... Rear wheel 13 ... Control valve for HICAS 14 ... Control valve for power steering 19 ... Rear suspension 20 ... Power cylinder 21 ... HICAS control unit (controller) 22 ...) IICAS So? Noid 23...
Vehicle speed sensor 30...Reverse force sensor Fig. 3 Fig. 4 Frequency (Hz)

Claims (1)

[Claims] 1. When detecting the road surface friction coefficient while the vehicle is running, the wheel is moved at a frequency equal to or higher than the frequency at which the value of the yaw rate/fixed steering angle is approximately zero, and the value of the tire force/fixed steering angle is greater than or equal to zero. 1. A method for detecting a road surface friction coefficient, comprising: periodically steering at a frequency such that the wheels are turned, detecting a reaction force from the wheels, and detecting a road surface friction coefficient based on the reaction force information. 2. While the vehicle is running, the road surface friction coefficient detection device detects the road surface friction coefficient when the wheels are rotated at a frequency higher than the frequency at which the value of yaw rate/fixed steering angle is approximately zero, and when the value of tire force/fixed steering angle is greater than zero. a steering mechanism that periodically steers the steering at a frequency that is equal to or less than 100 nm; a reaction force detection means that detects a reaction force that the steering mechanism receives from the wheels; and a road surface friction coefficient that is determined based on reaction force information from the reaction force detection means. 1. A road surface friction coefficient detection device, comprising a road surface friction coefficient detection means for detecting a road surface friction coefficient.