JP2009190467A - Road surface friction coefficient estimating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately obtain a highly precise road surface friction coefficient estimation value in a road surface friction coefficient estimation device for estimating a road surface friction coefficient from a relation between a vehicle body deceleration, front and rear wheel slide rate difference and a road surface friction coefficient. <P>SOLUTION: A road surface friction coefficient instantaneous value calculation part 2e sets a road surface friction coefficient instantaneous value μM by referring to a map showing the relation of Gx-ds-μ. When the road surface friction coefficient instantaneous value μM is equal to or more than μMH, and a vehicle body deceleration Gx is equal to or more than GXH, when the road surface friction coefficient instantaneous value μM is equal to or more than μMM, and the vehicle body deceleration Gx is equal to or more than GXM, or when the road surface friction coefficient instantaneous value μM is equal to or more than μML, and the vehicle body deceleration Gx is equal to or more than GXL, a road surface friction coefficient setting part 2g updates this time road surface friction coefficient μn with a road surface friction coefficient instantaneous value μM. When the body speed V is equal to or less than the vehicle speed threshold, when an absolute value ¾θH¾ of a steering angle is equal to or more than a steering threshold, when the acceleration opening θACC is equal to or more than the threshold, and when the vehicle body deceleration Gx is equal to or more than the threshold, the road surface friction coefficient setting part 2g outputs the value of the previous road surface friction coefficient. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a road surface friction coefficient estimating device that accurately estimates a road surface friction coefficient based on a relationship among a vehicle body deceleration, a front and rear wheel slip ratio difference, and a road surface friction coefficient.

  In recent years, various control techniques for traction control, braking force control, torque distribution control, and the like have been proposed and put into practical use in vehicles. Many of these techniques use a road surface friction coefficient for calculation or correction of necessary control parameters, and in order to appropriately execute the control, it is necessary to estimate an accurate road surface friction coefficient.

For example, in Japanese Patent Application Laid-Open No. 2003-237558, the average wheel speed of four wheels is obtained as a vehicle body speed, the vehicle body speed is differentiated and calculated as the longitudinal acceleration of the vehicle, and the hydraulic multi-plate of the power distribution control device during main brake braking When the clutch is engaged in the release direction, the difference between the wheel speed of the rear wheel and the wheel speed of the front wheel is divided by the wheel speed of the front wheel to calculate the slip speed difference variable (front / rear wheel slip ratio difference), and the longitudinal acceleration of the vehicle, A technique for estimating a road surface state based on a map set in advance based on a slip speed difference variable is disclosed.
JP 2003-237558 A

  However, in the technique disclosed in Patent Document 1 described above, it is generally known that the relationship between the vehicle body deceleration, the difference between the front and rear wheel slip ratios, and the road surface friction coefficient is, for example, as shown in FIG. There is a problem that in a region where the difference between the front and rear wheel slip ratios is small, errors increase and it is impossible to estimate an accurate road friction coefficient. That is, the difference between the front and rear wheel slip ratios is also caused by steering, so when turning a large amount, the difference between the front and rear wheel slip ratios due to the turning is increased, and the error is large, and the accuracy is high. There is a problem that the value cannot be estimated. And if the value of the road surface friction coefficient including many errors is used for various types of vehicle control, there is a risk that stable and appropriate control cannot be performed.

  The present invention has been made in view of the above circumstances, and in a road surface friction coefficient estimation device that estimates a road surface friction coefficient from the relationship between vehicle body deceleration, front / rear wheel slip ratio difference, and road surface friction coefficient, a highly accurate road surface friction coefficient estimation value is provided. An object of the present invention is to provide a road surface friction coefficient estimating device that appropriately outputs the vehicle and enables stable and appropriate vehicle control.

  The present invention relates to a road surface friction coefficient setting device for setting a road surface friction coefficient of a road surface on which a vehicle is traveling, steering angle detection means for detecting a steering angle of a steering, and vehicle body deceleration detection for detecting vehicle body deceleration. Means, wheel speed detecting means for detecting the wheel speed of each wheel, vehicle speed detecting means for detecting the vehicle speed of the vehicle, and the slip ratio of the front wheels and the slip ratio of the rear wheels based on the wheel speed and the vehicle speed. Front / rear wheel slip ratio difference detecting means for detecting the difference as a front / rear wheel slip ratio difference, storage means for previously storing the vehicle body deceleration, the front / rear wheel slip ratio difference and the road surface friction coefficient, and the vehicle body deceleration detection means The road surface friction coefficient setting means for estimating the road surface friction coefficient from the storage means based on the vehicle body deceleration detected in step 5 and the front and rear wheel slip ratio difference detection means detected by the front and rear wheel slip ratio difference detection means, and the steering angle is preset. Over the threshold It is characterized in that a prohibition means for prohibiting the estimation of the road surface friction coefficient when.

  According to the road surface friction coefficient estimating apparatus according to the present invention, the following effects can be obtained.

(1) By defining the execution condition for setting the road surface friction coefficient by the steering angle by the prohibiting means, the influence of errors caused by steering can be eliminated in a region where the difference between the front and rear wheel slip ratios is small. Estimation can be performed.

(2) Further, the road surface friction coefficient setting means has a front and rear wheel slip ratio difference reference value according to the vehicle body deceleration for determining when the road surface friction coefficient is high or low. Then, the threshold of the steering angle by the prohibiting means is set to be equal to or less than the steering angle at which the front and rear wheel slip ratio is generated by the steering operation (steering). As a result, when the road surface friction coefficient is high, the difference between the front and rear wheel slip ratios becomes lower. Therefore, the difference between the front and rear wheel slip ratios (the front and rear wheel slip ratios) for determining that the road surface friction coefficient is at least high when setting the road surface friction coefficient. It is required to detect (difference reference value). On the other hand, the difference between the front and rear wheel slip ratios is also generated by turning, and becomes particularly large when driving at low speeds. The effect of turning can be eliminated when determining a high value, and the road surface friction coefficient can be estimated with high accuracy.

  As described above, according to the present invention, in the road surface friction coefficient estimating device that estimates the road surface friction coefficient from the relationship between the vehicle body deceleration, the front and rear wheel slip ratio difference, and the road surface friction coefficient, an accurate road surface friction coefficient estimated value is appropriately output. In addition, it is possible to perform stable and appropriate vehicle control.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 6 show an embodiment of the present invention, FIG. 1 is a functional block diagram showing the configuration of a road surface friction coefficient estimating device, FIG. 2 is a flowchart of a road surface friction coefficient estimating program, and FIG. 3 continues from FIG. FIG. 4 is an explanatory diagram showing the turning of the vehicle in a two-wheeled vehicle model, FIG. 5 is an explanatory diagram showing the relationship between the front and rear wheel slip rate difference and the steering rudder angle, and FIG. 6 is the vehicle body deceleration and the front and rear wheel slip rate difference. It is explanatory drawing which shows the relationship of a road surface friction coefficient.

First, the concept of estimation will be described prior to the description of the system configuration and system processing of the road surface friction coefficient estimation apparatus according to the present embodiment. In this road surface estimation, the grip state between the wheel and the road surface is determined based on the slip rate difference Sfr. Here, the “slip rate difference Sfr” refers to a difference between the “slip rate Sf of the front wheel” and the “slip rate Sr of the rear wheel” as shown in the following equation (1).
Sfr = Sf−Sr (1)

The slip ratio S related to a certain wheel is expressed as a ratio between the difference between the wheel speed v and the vehicle body speed Vb and the vehicle body speed Vb, and is defined so that the value becomes positive. This slip ratio S is uniquely calculated by the basic formula shown in the formula (2).
S = (v−Vb) / Vb (or S = (Vb−v) / Vb) (2)

When the left and right front wheels and the left and right rear wheels are regarded as one wheel, the front wheel side is defined as vf, and the rear wheel speed is defined as vr, equation (1) is based on equation (2) as follows: (3) shown can be rewritten.
Sfr = (vf−vr) / Vb (3)

  In FIG. 1, reference numeral 1 denotes a road surface friction coefficient estimation device that is mounted on a vehicle and estimates a road surface friction coefficient. The road surface friction coefficient estimation device 1 includes a control unit 2 that includes four wheels as wheel speed detection means. A wheel speed sensor 3, a steering wheel angle sensor 4 as a steering angle detecting means, an accelerator opening sensor 5, a brake pedal switch 6 and other sensors and switches are connected to each other, and the four wheel speed ωfl (front left wheel speed), ωfr ( Right front wheel speed), ωrl (left rear wheel speed), ωrr (right rear wheel speed), steering wheel angle (steering angle) θH, accelerator opening θACC, and brake operation signal are input.

  In addition, the vehicle has a known traction control device 7 that reduces the driving force when the driving wheel slips or is about to slip, and controls the braking force during braking to prevent the wheel from being locked. A known anti-lock brake system (ABS) 8 and a skid prevention device 9 for preventing the behavior of a side slip of the vehicle are mounted, and these operation signals are also input to the control unit 2. The above-described skid prevention device 9 compares, for example, the actual yaw moment with the target yaw moment obtained based on the equation of motion of the vehicle, and when the current driving state of the vehicle is an understeer tendency, A predetermined braking force is applied to the turning inner rear wheel, and in the case of an oversteer tendency, a predetermined braking force is applied to the turning outer front wheel to prevent the vehicle from slipping.

  Then, the control unit 2 of the road surface friction coefficient estimation device 1 executes a road surface friction coefficient estimation program, which will be described later, based on each input signal described above, and sets and outputs the road surface friction coefficient (the road surface friction coefficient setting value μn is set). Output). That is, as shown in FIG. 1, the control unit 2 includes a speed calculation unit 2a, a deceleration calculation unit 2b, a front and rear wheel slip rate difference calculation execution condition determination unit 2c, a front and rear wheel slip rate difference calculation unit 2d, and a road surface friction coefficient instantaneous It is mainly composed of a value calculation unit 2e, a road surface determination execution condition determination unit 2f, and a road surface friction coefficient setting unit 2g.

The speed calculation unit 2a receives the wheel speeds ωfl, ωfr, ωrl, and ωrr of each wheel from the four-wheel wheel speed sensor 3, and the front wheel speed Vf by the following equation (4) and the rear wheel by the following equation (5). The wheel speed Vr is calculated, and the rear wheel speed Vr is set as the pseudo vehicle speed V.
Vf = (ωfl + ωfr) / 2 (4)
Vr = V = (ωrl + ωrr) / 2 (5)

  The vehicle body speed V is output to the deceleration calculation unit 2b, the front and rear wheel slip rate difference calculation execution condition determination unit 2c, and the front and rear wheel slip rate difference calculation unit 2d. The front wheel speed Vf and the rear wheel speed Vr are It is output to the wheel slip rate difference calculation unit 2d. Thus, the speed calculation part 2a is provided as a vehicle speed detection means.

  The deceleration calculation unit 2b receives the vehicle speed V from the speed calculation unit 2a, and performs a differentiation process on the vehicle speed V to calculate the vehicle deceleration Gx, thereby calculating the front / rear wheel slip rate difference calculation execution condition determination unit 2c, The road surface friction coefficient instantaneous value calculation unit 2e, the road surface determination execution condition determination unit 2f, and the road surface friction coefficient setting unit 2g are output. Thus, the deceleration calculation part 2b is provided as a vehicle body deceleration detection means.

  The front / rear wheel slip ratio difference calculation execution condition determination unit 2c includes a steering angle θH from the steering wheel angle sensor 4, an accelerator opening θACC from the accelerator opening sensor 5, a vehicle speed V from the speed calculation unit 2a, and a deceleration calculation unit. The vehicle body deceleration is input from 2b.

If any one of the following four conditions is satisfied, the front / rear wheel slip ratio difference calculation unit 2d calculates the front / rear wheel slip ratio difference ds, and the road surface friction coefficient setting unit 2g performs vehicle body deceleration Gx−front / rear wheels. It is determined that it is not suitable for estimation of a new road surface friction coefficient μn using the relationship of slip rate difference ds−road surface friction coefficient μ. This determination result signal is output to the front and rear wheel slip ratio difference calculation unit 2d and the road surface friction coefficient setting unit 2g.
・ Condition 1… V ≦ Vc (for example, 20 km / h)
・ Condition 2 ... | θH | ≧ θH1 (for example, 60 deg)
・ Condition 3… θACC ≧ θACC1 (for example, 0%)
Condition 4 ... Gx ≧ Gxc1 (for example, 4 m / s ² )
Here, each of the above-described conditions will be described. First, condition 1 will be described.

In the present embodiment, in the road surface friction coefficient instantaneous value calculation unit 2e, when the front and rear wheel slip ratio difference ds is, for example, 0.006 (0.6%) or less as the reference value of the front and rear wheel slip ratio difference ds, The road surface friction coefficient is determined to be a high μ value of 0.75 or more. Therefore, the wheel speed information needs to have an accuracy sufficient to detect the front / rear wheel slip ratio difference ds of 0.006 (0.6%). If the resolution of the wheel speed detected by the four-wheel wheel speed sensor 3 is, for example, 0.05, the minimum vehicle speed (vehicle speed threshold) Vc that can determine the road surface is obtained from the following equation.
Vc = 0.05 / 0.006 = 8.3 (km / h) (6)

  In addition, the vehicle speed at which the calculation of the front / rear wheel slip ratio difference ds and the estimation of the road surface friction coefficient μn are performed in consideration of a decrease in the vehicle speed during estimation of the road surface friction coefficient (e.g., estimated to take 800 ms) and other errors. The threshold is set as Vc = 20 km / h.

  As is clear from the above equation (6), when the resolution of the wheel speed detected by the four-wheel wheel speed sensor 3 is further roughened, or the reference value of the front-rear wheel slip ratio difference ds is set to a smaller value. In this case, the vehicle speed threshold value Vc needs to be set to a larger value.

Next, Condition 2 will be described with reference to FIG.
The speed difference between the front and rear wheels occurs even when steering is performed. Since the front-rear wheel speed ratio due to steering is greatest during low-speed driving, the steering angle range in which the logic can operate is obtained by Ackermann geometry. In FIG. 4, since the front wheel speed Vf = Rf · ω and the rear wheel speed Vr = Rr · ω, the front-rear wheel slip ratio difference ds is obtained by the following equation.
ds = (Vf−Vr) / Vr = (Rf · ω−Rr · ω) / Rr · ω
= (Rf-Rr) / Rr = Rf / Rr-1
= (1 / cos (δf)) − 1 (7)
Here, δf is a front wheel steering angle, and δf = θH / n (n is a steering gear ratio: for example, 16.5). The characteristics obtained by the equation (7) are shown in FIG.

  In the above equation (7), when the steering angle θH2 at which the front / rear wheel slip rate difference ds is equal to or less than the above-described 0.006 (0.6%) is calculated, θH2 = 105 (deg). That is, it can be seen that when the steering is about 105 (deg), the threshold of 0.006 (0.6%) is exceeded. Considering disturbances and the like, the actual steering threshold must be set to a smaller angle. In this embodiment, the absolute value of steering angle | θH | is larger than θH1 = 60 (deg) (front and rear wheels). When the slip ratio difference ds is equivalent to 0.001 (0.1%)), it is set so that the calculation of the front and rear wheel slip ratio difference ds and the estimation of the road surface friction coefficient μn are not performed.

Next, Condition 3 will be described.
If a driving force is applied during main brake braking, the front-rear wheel slip rate difference ds may be disturbed and may not be determined. In this embodiment, the accelerator opening θACC is greater than θACC1 (for example, 0%). When it is larger, the setting is made so that the calculation of the front / rear wheel slip ratio difference ds and the estimation of the road surface friction coefficient μn are not performed.

Next, condition 4 will be described.
When the vehicle body deceleration Gx increases, the relationship between the vehicle body deceleration Gx and the front-rear wheel slip ratio difference ds becomes nonlinear. Further, if the logic is operated only in a region where the vehicle body deceleration Gx is small, there is a concern that the determination accuracy may be lowered. Therefore, in the present embodiment, when the vehicle body deceleration Gx is Gxc1 (for example, 4 m / s ² ) or more, it is set not to calculate the front / rear wheel slip ratio difference ds and to estimate the road surface friction coefficient μn.

  Thus, the front and rear wheel slip ratio difference calculation execution condition determination unit 2c is provided as a prohibiting unit.

The front and rear wheel slip ratio difference calculation unit 2d receives the vehicle body speed V, the front wheel speed Vf, and the rear wheel speed Vr from the speed calculation unit 2a, and the front and rear wheel slip ratio difference calculation execution condition determination unit 2c receives the front and rear wheel slip ratio difference. A determination result signal indicating whether or not to calculate ds is input. Then, in the determination result that the front / rear wheel slip ratio difference calculation execution condition determination unit 2c calculates the front / rear wheel slip ratio difference ds, the front / rear wheel slip is calculated by the following expression (8) based on the expression (3). The rate difference ds is calculated and output to the road surface friction coefficient instantaneous value calculation unit 2e. That is, the front and rear wheel slip ratio difference calculation unit 2d is provided as a front and rear wheel slip ratio difference detecting means.
ds = | Vf−Vr | / V (8)

  The road surface friction coefficient instantaneous value calculation unit 2e receives the vehicle body deceleration Gx from the deceleration calculation unit 2b and the front and rear wheel slip rate difference ds from the front and rear wheel slip rate difference calculation unit 2d. Then, a preliminarily stored map showing the relationship between the vehicle body deceleration Gx, the front-rear wheel slip ratio difference ds, and the road surface friction coefficient μ is temporarily referred to, and the road surface friction coefficient (in this embodiment, the road surface friction coefficient instantaneous (Referred to as a value) μM is set, and this road surface friction coefficient instantaneous value μM is output to the road surface friction coefficient setting unit 2g. Thus, the road surface friction coefficient instantaneous value calculation unit 2e is provided as a storage unit, and is provided as a road surface friction coefficient setting unit together with the road surface friction coefficient setting unit 2g.

  Note that a map indicating the relationship between the vehicle body deceleration Gx, the front-rear wheel slip ratio difference ds, and the road surface friction coefficient μ stored in advance is, for example, as shown in FIG. This is a map with the front-rear wheel slip ratio difference ds as the axis, and the road friction coefficient is 0.75 to the above-mentioned value of 0.006 (0.6%) on the high μ value side where the vehicle body deceleration Gx becomes small. A straight line (reference value) is obtained and set in advance by experiments or the like. In addition, a straight line having a predetermined slope with a road surface friction coefficient of 0.4 has been determined as a reference through experiments and the like. Based on these reference lines, the value of the road surface friction coefficient in the middle area is interpolated. Is estimated.

The road surface determination execution condition determination unit 2f receives a brake ON-OFF signal from the brake pedal switch 6, and receives a vehicle body deceleration Gx from the deceleration calculation unit 2b. Then, it is determined whether or not the state where the brake is ON and the vehicle body deceleration Gx is Gxc2 (for example, 0.5 m / s ² ) or more continues for a certain time (for example, 800 ms), and continues for a certain time. If this is the case, it is determined that the estimated value of the current road friction coefficient is a highly accurate value estimated under stable conditions, and a signal permitting the adoption of the estimated value is set as the road friction coefficient. To part 2g.

  The road surface friction coefficient setting unit 2g receives the respective operation signals from the traction control device 7, the ABS 8, and the skid prevention device 9, receives the vehicle body deceleration Gx from the deceleration calculation unit 2b, and executes the difference calculation of the front and rear wheel slip ratio. The determination result signal is input from the condition determination unit 2c, the instantaneous road surface friction coefficient value μM is input from the road surface friction coefficient instantaneous value calculation unit 2e, and the determination result of the adoption of the present estimated value is input from the road surface determination execution condition determination unit 2f. A signal is input. When any one of the traction control device 7, ABS 8, and skid prevention device 9 is operating, the current road surface friction coefficient μn is set as a low μ value (for example, 0.3). Output.

  In addition, when the determination result from the front / rear wheel slip ratio difference calculation execution condition determination unit 2c does not execute the setting or the determination result from the road surface determination execution condition determination unit 2f does not execute the setting, The road surface friction coefficient μn−1 is set as the current road surface friction coefficient μn and output.

Furthermore, none of the traction control device 7, ABS 8, or skid prevention device 9 is operating, and the determination results from the front and rear wheel slip rate difference calculation execution condition determination unit 2c and the road surface determination execution condition determination unit 2f are permitted to execute. In some cases, the road surface friction coefficient instantaneous value μM is μMH (for example, 1.0) or more and the vehicle body deceleration Gx is GXH (for example, 2.0 m / s ² ) or more. When the value μM is μMM (for example, 0.75) or more and the vehicle body deceleration Gx is GXM (for example, 1.3 m / s ² ) or more, or the road surface friction coefficient instantaneous value μM is μML (for example, 0 .3) When the vehicle body deceleration Gx is GXL (for example, 0.5 m / s ² ) or more, the current road surface friction coefficient μn is updated with the road surface friction coefficient instantaneous value μM. μMH>μMM> μML, GXH>GXM> GXL (see FIG. 6). That is, as the braking force (= vehicle deceleration) increases, the wheel speed difference between the front and rear wheels increases and the accuracy of road surface determination improves. However, if this is taken into consideration and a large braking force is used as a condition for starting the determination, the frequency of road surface determination decreases. In the present embodiment, in order to achieve both responsiveness and accuracy, a deceleration threshold value at the start of determination corresponding to each road surface friction coefficient instantaneous value μM is set.

Next, a road surface friction coefficient estimation program executed by the control unit 2 of the above-described road surface friction coefficient estimation device 1 will be described with reference to the flowcharts of FIGS.
First, in step (hereinafter abbreviated as “S”) 101, necessary parameters, that is, four-wheel wheel speeds ωfl, ωfr, ωrl, ωrr, steering angle θH, accelerator opening degree θACC, brake ON-OFF signal, traction The operation signals of the control device 7, ABS 8, and skid prevention device 9 are read.

  Next, proceeding to S102, the previous road surface friction coefficient μn-1 is read. For example, 0.7 is read as the medium μ value as the initial value of the previous road surface friction coefficient μn−1.

  Next, the process proceeds to S103, where the speed calculation unit 2a calculates the front wheel speed Vf, the rear wheel speed Vr, and the pseudo vehicle speed V according to the above-described formulas (4) and (5).

  Next, proceeding to S104, the deceleration calculation unit 2b calculates the vehicle body deceleration Gx by differentiating the vehicle body speed V.

  Next, the process proceeds to S105, where the road surface friction coefficient setting unit 2g determines whether any of the traction control device 7, ABS 8, or skid prevention device 9 is operating. If it is operating, the process proceeds to S106. Thus, the current road surface friction coefficient μn is set as a low μ value (for example, 0.3) (μn ← 0.3), and the process proceeds to S126.

  If none of them is operating, the process proceeds to S107. The processing of S107 to S110 is processing executed by the front / rear wheel slip rate difference calculation execution condition determination unit 2c. In S107, the vehicle speed V is compared with a vehicle speed threshold Vc (for example, 20 km / h), If V> Vc, the process proceeds to S108.

  In S108, the absolute value | θH | of the steering angle is compared with a steering threshold θH1 (for example, 60 deg). If | θH | <θH1, the process proceeds to S109.

  In S109, the accelerator opening θACC is compared with the accelerator opening threshold θACC1 (eg, 0%). If θACC <θACC1, the process proceeds to S110.

In S110, the vehicle body deceleration Gx is compared with the vehicle body deceleration threshold Gxc1 (for example, 4 m / s ² ). If Gx <Gxc1, the process proceeds to S111.

  On the other hand, if V ≦ Vc in S107, or | θH | ≧ θH1 in S108, or θACC ≧ θACC1 in S109, or Gx ≧ Gxc1 in S110, the front-rear wheel slip ratio difference ds is calculated, and the road surface friction coefficient μn. The process proceeds to S114 without setting the current road friction coefficient μn to the previous road surface friction coefficient μn−1 (μn ← μn−1), and the process proceeds to S126.

  When the process proceeds from S110 to S111, the front / rear wheel slip ratio difference calculation unit 2d calculates the front / rear wheel slip ratio difference ds by the above-described equation (8).

  Next, in S112, the road surface friction coefficient instantaneous value calculation unit 2e refers to a map indicating the relationship between the vehicle body deceleration Gx, the front and rear wheel slip rate difference ds, and the road surface friction coefficient μ, which are stored in advance. Set the instantaneous value μM.

Next, the process proceeds to S113, where the road surface determination execution condition determination unit 2f is in a state where the brake is ON and the vehicle deceleration Gx is equal to or greater than Gxc2 (for example, 0.5 m / s ² ) for a certain time (for example, 400 ms). ) If it is determined whether or not it has continued for a certain period of time, it is determined that the current estimated value of the road friction coefficient is a highly accurate value estimated under stable conditions, and S115 If the above condition is not satisfied, the process proceeds to S114, where the current road surface friction coefficient μn is set to the previous road surface friction coefficient μn-1 (μn ← μn-1), and the process proceeds to S126. .

When the above condition is satisfied in S113 and the process proceeds to S115, the road surface friction coefficient setting unit 2g compares the road surface friction coefficient instantaneous value μM with the road surface friction coefficient instantaneous value threshold μMH (for example, 1.0). . As a result of this comparison, if the road surface friction coefficient instantaneous value μM is μMH or more (μM ≧ μMH), the process proceeds to S116, and the vehicle body deceleration Gx and the vehicle body deceleration threshold GXH (for example, 2.0 m / s ² ) are set. In comparison, if the vehicle body deceleration Gx is equal to or greater than GXH (Gx ≧ GXH), the process proceeds to S117, the current road surface friction coefficient μn is updated with the instantaneous road surface friction coefficient μM (μn ← μM), and the process proceeds to S126. If the vehicle deceleration Gx is smaller than GXH (Gx <GXH), the process proceeds to S118, where the current road surface friction coefficient μn is set to the previous road surface friction coefficient μn-1 (μn ← μn-1). Proceed to S126.

If the road surface friction coefficient instantaneous value μM is lower than μMH (μM <μMH) as a result of the determination in S115 described above, the process proceeds to S119, and the road surface friction coefficient instantaneous value μM and the road surface friction coefficient instantaneous value threshold μMM (for example, , 0.75). As a result of this comparison, if the road surface friction coefficient instantaneous value μM is μMM or more (μM ≧ μMM), the process proceeds to S120, and the vehicle body deceleration Gx and the vehicle body deceleration threshold GXM (for example, 1.3 m / s ² ) are set. In comparison, if the vehicle body deceleration Gx is equal to or greater than GXM (Gx ≧ GXM), the process proceeds to S121, the current road surface friction coefficient μn is updated with the instantaneous road surface friction coefficient μM (μn ← μM), and the process proceeds to S126. If the vehicle deceleration Gx is smaller than GXM (Gx <GXM), the process proceeds to S122, where the current road surface friction coefficient μn is set to the previous road surface friction coefficient μn-1 (μn ← μn-1). Proceed to S126.

If the road surface friction coefficient instantaneous value μM is lower than μMM (μM <μMM) as a result of the determination in S119 described above, the process proceeds to S123, and the road surface friction coefficient instantaneous value μM and the road surface friction coefficient instantaneous value threshold μML (for example, , 0.3). As a result of this comparison, if the road surface friction coefficient instantaneous value μM is greater than or equal to μML (μM ≧ μML), the process proceeds to S124, and the vehicle body deceleration Gx and the vehicle body deceleration threshold GXL (for example, 0.5 m / s ² ) are set. In comparison, if the vehicle body deceleration Gx is equal to or greater than GXL (Gx ≧ GXL), the process proceeds to S125, the current road surface friction coefficient μn is updated with the instantaneous road surface friction coefficient μM (μn ← μM), and the process proceeds to S126. If the vehicle deceleration Gx is smaller than GXL (Gx <GXL), the process proceeds to S114, and the current road surface friction coefficient μn is set to the previous road surface friction coefficient μn-1 (μn ← μn-1). Proceed to S126.

  The current road friction coefficient μn is set in any one of the above-described S106, S114, S117, S118, S121, S122, and S125. When the process proceeds to S126, the current road friction coefficient μn is output.

  In S127, the current road friction coefficient μn is replaced with the previous road friction coefficient μn−1 (μn−1 ← μn), and the program exits.

  The road surface friction coefficient estimated value μn set as described above is output to an external display device (not shown), for example, and used to call the driver's attention by displaying on the instrument panel or the like. Alternatively, it is output to the engine control unit, the transmission control unit, the driving force distribution control unit between the front and rear shafts or between the left and right wheels, the brake control unit (none of which are shown), and contributes to the setting of the control amount in each control unit Is done.

  For example, when used for front-rear driving force distribution control of a four-wheel drive vehicle in which the front shaft: rear shaft torque distribution can be varied by a transfer clutch between 100: 0 and 50:50, fuel efficiency improvement and front-rear driving force distribution control In order to achieve both, it is necessary to reduce the unnecessary rear wheel transmission torque on the high μ road and reduce the internal circulation torque, and on the low μ road, it is necessary to generate a predetermined rear wheel transmission torque with an emphasis on stability. Therefore, the fastening force of the transfer clutch torque is controlled according to the estimated road surface friction coefficient estimated value μn, and the rear wheel torque distribution ratio is continuously changed.

  As described above, according to the present embodiment, in the road surface friction coefficient estimation device that estimates the road surface friction coefficient μ from the relationship between the vehicle body deceleration Gx, the front and rear wheel slip ratio difference ds, and the road surface friction coefficient μ, the vehicle body speed V is the vehicle speed threshold value. When Vc or less, the absolute value | θH | of the steering angle is equal to or greater than the steering threshold θH1, or when the accelerator opening θACC is equal to or greater than the accelerator opening threshold θACC1, the vehicle deceleration Gx is equal to or greater than the vehicle deceleration threshold Gxc1. In this case, the previous road surface friction coefficient is not estimated, and the previous road surface friction coefficient value is output. And in particular, by defining the execution condition of the road surface friction coefficient by the steering angle, it is possible to eliminate the influence of errors caused by steering in a region where the difference between the front and rear wheel slip ratios is small, and to estimate the road surface friction coefficient with high accuracy. It can be carried out. And it becomes possible to perform appropriate vehicle control stably by performing control of various vehicle behavior control apparatuses etc. with a highly reliable road surface friction coefficient.

In the present embodiment, the road surface is when the brake is ON and the vehicle deceleration Gx is Gxc2 (for example, 0.5 m / s ² ) or more for a certain period of time (for example, 800 ms). Since the friction coefficient is estimated, it is possible to prevent the estimation of the road surface friction coefficient during instantaneous braking with little deceleration, and to estimate the road surface friction coefficient with stable and high accuracy. Is possible.

Functional block diagram showing the configuration of the road surface friction coefficient estimation device Flowchart of road friction coefficient estimation program Flowchart continuing from FIG. Explanatory drawing showing turning of vehicle with two-wheeled vehicle model Explanatory diagram showing the relationship between the difference between the front and rear wheel slip ratios and the steering angle Explanatory drawing showing the relationship between vehicle body deceleration, front and rear wheel slip ratio difference, and road surface friction coefficient Explanatory drawing showing the relationship between vehicle body deceleration, front and rear wheel slip ratio difference and road surface friction coefficient according to the prior art

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Road surface friction coefficient estimation apparatus 2 Control part 2a Speed calculation part (vehicle speed detection means)
2b Deceleration calculation unit (vehicle deceleration detection means)
2c Front-rear wheel slip ratio difference calculation execution condition determining unit (prohibiting means)
2d Front and rear wheel slip ratio difference calculation unit (front and rear wheel slip ratio difference detection means)
2e Road surface friction coefficient instantaneous value calculation unit (storage means, road surface friction coefficient setting means)
2f Road surface determination execution condition determination unit 2g Road surface friction coefficient setting unit (road surface friction coefficient setting means)
3 4-wheel wheel speed sensor (wheel speed detection means)
4 Handle angle sensor (steering angle detection means)
5 Accelerator opening sensor 6 Brake pedal switch 7 Traction control device 8 ABS
9 Side slip prevention device

Claims (2)

In the road surface friction coefficient setting device for setting the road surface friction coefficient of the road surface on which the vehicle is traveling,
Steering angle detection means for detecting the steering angle of the steering;
Vehicle body deceleration detecting means for detecting the vehicle body deceleration of the vehicle;
Wheel speed detection means for detecting the wheel speed of each wheel;
Vehicle speed detecting means for detecting the vehicle speed of the vehicle;
Based on the wheel speed and the vehicle speed, front and rear wheel slip ratio difference detecting means for detecting a difference between a front wheel slip ratio and a rear wheel slip ratio as a front and rear wheel slip ratio difference;
Storage means for storing in advance the relationship between vehicle body deceleration, front and rear wheel slip rate difference, and road surface friction coefficient;
Road surface friction coefficient setting means for estimating a road surface friction coefficient from the storage means based on the vehicle body deceleration detected by the vehicle body deceleration detection means and the front and rear wheel slip ratio difference detected by the front and rear wheel slip ratio difference detection means;
Prohibiting means for prohibiting estimation of the road surface friction coefficient when the steering angle is equal to or greater than a preset threshold;
A road surface friction coefficient estimating device comprising: The road surface friction coefficient setting means has at least a front and rear wheel slip ratio difference reference value corresponding to the vehicle body deceleration, and the detected front and rear wheel slip ratio difference with respect to the detected vehicle body deceleration is greater than the front and rear slip ratio difference reference value. When it is small, it is judged that the road surface friction coefficient is high,
2. The road surface friction coefficient estimating apparatus according to claim 1, wherein the preset threshold value used in the prohibiting means is set to be equal to or less than a steering angle at which the front and rear wheel slip ratio difference reference value is generated by the steering operation. .

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