JP2009184624A - Road surface friction coefficient setting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make improvement of estimated frequency and estimated accuracy compatible in a road surface friction coefficient setting device for estimating a road surface friction coefficient from the relationship among vehicle body deceleration, a front and rear wheel sliding ratio difference and the road surface friction coefficient. <P>SOLUTION: A road surface friction coefficient instantaneous value arithmetic part 2e refers to a map showing the relationship of Gx-ds-μ and sets a road surface friction coefficient instantaneous value μM. A road surface friction coefficient setting part 2g updates a road surface friction coefficient μn of this time by the road surface friction coefficient instantaneous value μM when the road surface friction coefficient instantaneous value μM is μMH or more and the vehicle body deceleration Gx is GXH or more, when the road surface friction coefficient instantaneous value μM is μMM or more and the vehicle body deceleration Gx is GXM or more, or when the road surface friction coefficient instantaneous value μM is μML or more and the vehicle body deceleration Gx is GXL or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a road surface friction coefficient setting device that accurately estimates a road surface friction coefficient based on a relationship among a vehicle body deceleration, a front / 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 The clutch engagement is controlled 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, the slip speed difference variable is calculated, and the vehicle longitudinal acceleration and slip speed difference variables are used as the basis. Further, a technique for estimating a road surface state based on a map set in advance is disclosed.
JP 2003-237558 A

  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. The larger the is, the larger the wheel speed difference between the front and rear wheels is, and the accuracy of road surface determination is improved. However, if a large braking force is used as a condition for starting the road surface friction coefficient determination in consideration of this, there is a problem that the frequency of road surface determination decreases.

  The present invention has been made in view of the above circumstances, and in the road surface friction coefficient setting device for setting 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, the frequency of setting the road surface friction coefficient is improved. An object of the present invention is to provide a stable and easy-to-use road friction coefficient setting device that achieves both improved accuracy.

  The present invention includes a vehicle body deceleration detecting means for detecting vehicle body deceleration, a front and rear wheel slip ratio difference detecting means for detecting a difference in slip ratio between the front and rear wheels, the vehicle body deceleration, the front and rear wheel slip ratio difference, and a road surface friction coefficient. The road surface friction coefficient setting means for setting the road surface friction coefficient from the storage means based on the vehicle body deceleration and the slip ratio difference between the front and rear wheels, and the set road surface friction. Road surface friction coefficient updating means for updating the current road surface friction coefficient with a coefficient, and the road surface friction coefficient updating means permits updating in accordance with the vehicle body deceleration.

  According to the road surface friction coefficient setting device of the present invention, the following effects can be obtained.

(1) Since the vehicle body deceleration, the front / rear wheel slip ratio difference, and the road surface friction coefficient have a predetermined relationship, if this relationship is stored in advance, the vehicle body deceleration and the front / rear obtained from a sensor, calculation, etc. The road friction coefficient can be set from the difference in the wheel slip rate. Here, the update to the current road surface friction coefficient by the road surface friction coefficient set by the storage means is permitted according to the vehicle body deceleration, so that both the improvement of the estimation frequency of the road surface friction coefficient and the estimation accuracy are achieved. be able to. That is, when the vehicle body deceleration is low, the difference between the front and rear wheel slip ratios is small, so the accuracy of the road surface friction coefficient is not good. On the other hand, when the vehicle body deceleration is larger, the difference between the front and rear wheel slip ratios becomes more prominent and the accuracy of the road surface friction coefficient is improved. However, if the vehicle body deceleration is excessively increased, the frequency of setting the road surface friction coefficient decreases. On the other hand, the present invention focuses on the fact that a low road friction coefficient can be set with high accuracy even when the vehicle deceleration is low, and by allowing the road friction coefficient to be updated according to the vehicle deceleration, the frequency of setting the road friction coefficient is Both improvement in accuracy and improvement in accuracy can be achieved. Note that the present invention is not limited to permitting the update to the current road surface friction coefficient according to the road surface friction coefficient set by the storage means according to the vehicle body deceleration, but the road surface friction coefficient by the storage means according to the vehicle body deceleration. A similar effect can be achieved by limiting the setting range. In this case, for example, when the vehicle body deceleration is low, a low road friction coefficient setting range by the storage means may be permitted, and a high road friction coefficient setting range may be prohibited.

(2) By permitting an update to a higher road surface friction coefficient as the vehicle body deceleration increases, the road surface friction coefficient can always be accurately set at an optimal timing.

(3) A vehicle body deceleration threshold value corresponding to the road surface friction coefficient stored in the storage means is provided, and when the vehicle body deceleration value is lower than the vehicle body deceleration threshold value, the road surface friction coefficient corresponding to the vehicle body deceleration threshold value is higher. By prohibiting the update of the road surface friction coefficient, it is possible to prohibit the setting of the road surface friction coefficient on the higher side where the difference between the front and rear slip ratios is small and the accuracy of the road surface friction coefficient deteriorates.

(4) The road surface friction coefficient is updated when braking is applied and when the vehicle deceleration is equal to or higher than a preset threshold value for more than the set time, so that almost no deceleration occurs. It is possible to prevent estimation of the road surface friction coefficient during instantaneous braking, and it is possible to estimate a stable and accurate road surface friction coefficient.

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 setting device, FIG. 2 is a flowchart of a road surface friction coefficient estimation 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 setting device 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 setting device that is mounted on a vehicle and estimates a road surface friction coefficient. The road surface friction coefficient setting device 1 includes a control unit 2, a four-wheel wheel speed sensor 3, a steering wheel. Sensors and switches such as an angle sensor 4, an accelerator opening sensor 5, a brake pedal switch 6 and the like are connected, and four-wheel wheel speed ωfl (left front 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.

  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 setting 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, and the front wheel speed Vf and the rear wheel speed Vr are It is output to the wheel slip rate difference calculation unit 2d.

  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 corresponds to 0.001 (0.1%)), the calculation is performed so that the calculation of the front and rear wheel slip ratio difference ds and the setting 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 this embodiment, when the vehicle body deceleration Gx is Gxc1 (for example, 4 m / s ² ) or more, setting is made so as not to calculate the front-rear wheel slip ratio difference ds and to set the road surface friction coefficient μn.

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 a road surface friction coefficient setting unit.

  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, 1.7 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) If 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 instantaneous road surface friction coefficient μM (= the road surface friction coefficient). Update means: 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 the road surface determination improves. In this embodiment, in order to achieve both responsiveness and accuracy, a deceleration threshold value for determination start is set for each instantaneous road friction coefficient μM. Thus, the road surface friction coefficient setting unit 2g is provided with road surface friction coefficient update means.

Next, a road surface friction coefficient estimation program executed by the control unit 2 of the above-described road surface friction coefficient setting 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 body deceleration Gx is equal to or greater than Gxc2 (for example, 0.5 m / s ² ) for a certain time (for example, 800 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, 1.7 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 set 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, none of the traction control device 7, the ABS 8, and the skid prevention device 9 is operating, and the front / rear wheel slip ratio difference execution execution condition determination section 2c and the road surface determination execution condition determination section. When the determination result from 2f is permission to execute, 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, 1.7 m / s ² ) or more. Or when the road surface friction coefficient instantaneous 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 When the instantaneous value μM is μML (for example, 0.3) or more and the vehicle body deceleration Gx is GXL (for example, 0.5 m / s ² ) or more, the current road surface friction coefficient μn is used as the instantaneous value of the road surface friction coefficient. Update with μM. 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, a deceleration threshold value at the start of determination corresponding to each instantaneous value of the road surface friction coefficient μM is set, that is, as the vehicle body deceleration increases, an update to a higher road surface friction coefficient is permitted. Since it did in this way, the improvement of the estimation frequency of a road surface friction coefficient and the improvement of an estimation precision is aimed at, and there exists an outstanding effect that it is stable and is convenient. In the present embodiment, three types of regions of μMH or more, μMM or more, and μML or more are set as regions of the road surface friction coefficient instantaneous value μM, and threshold values GXH, GXM, and GXL of the vehicle body deceleration Gx are set respectively. However, the road surface friction coefficient instantaneous value μM region may be set to two types, and a threshold value of the vehicle body deceleration Gx may be provided for each. Alternatively, the road surface friction coefficient instantaneous value μM region may be set to four or more types. A threshold value of the vehicle body deceleration Gx may be provided for each.

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.

Next, a second embodiment will be described.
In the first embodiment, after obtaining the instantaneous value of the road surface friction coefficient by referring to the map, the detected vehicle body deceleration is compared with the deceleration threshold value, and the road surface friction coefficient is updated according to the result. That is, after the road surface friction coefficient is always set with reference to the map, the road surface friction coefficient is updated to the value set on the map if the condition regarding the vehicle body deceleration threshold is satisfied. On the other hand, in the second embodiment, it is first determined whether or not the vehicle body deceleration satisfies the condition regarding the vehicle body deceleration threshold, and if so, the predetermined range of the road surface friction coefficient corresponding to the vehicle body deceleration is set. Is permitted, and setting of other predetermined ranges is prohibited. More specifically, three vehicle body deceleration threshold values (GXH, GXM, GXL) are set in advance corresponding to the regions (μMH, μMM, μML) where the road surface friction coefficient is estimated. The detected vehicle deceleration Gx is compared with each deceleration threshold. When the detected vehicle deceleration Gx is greater than or equal to GXL and less than or equal to GXL, the map is referred to. When the referenced road surface friction coefficient is greater than or equal to μML and less than or equal to μMM, the referenced road surface friction coefficient is set as the current road surface friction coefficient. (= Update) and prohibit (= restrict) the setting when μMM or more. Next, when the detected vehicle deceleration Gx is not less than GXM and not more than GXH, it is determined whether or not the referenced road surface friction coefficient is not less than μMM. When it is less than μMM, the referred road friction coefficient is set as the current road friction coefficient, and when it is more than μMM, setting is prohibited. When the detected vehicle deceleration Gx is equal to or greater than GXH, the road surface friction coefficient referred to by referring to the map is set as the current road surface friction coefficient. The object of the present invention can also be achieved by the above method.

Functional block diagram showing the configuration of the road surface friction coefficient setting 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 setting apparatus 2 Control part 2a Speed calculation part 2b Deceleration calculation part (vehicle body deceleration detection means)
2c Front and rear wheel slip ratio difference calculation execution condition determination unit 2d Front and rear wheel slip ratio difference calculation unit (front and rear wheel slip ratio difference detecting 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 update means)
3 Wheel speed sensor 4 Wheel angle sensor 5 Accelerator opening sensor 6 Brake pedal switch 7 Traction control device 8 ABS
9 Side slip prevention device

Claims (10)

Vehicle body deceleration detection means for detecting vehicle body deceleration,
Front and rear wheel slip ratio difference detection means for detecting front and rear wheel slip ratio difference;
Storage means for storing in advance the relationship between the vehicle body deceleration, the front-rear wheel slip ratio difference, and the road surface friction coefficient;
Road surface friction coefficient setting means for setting a road surface friction coefficient from the storage means based on the vehicle body deceleration and the slip ratio difference between the front and rear wheels;
Road surface friction coefficient updating means for updating the current road surface friction coefficient with the set road surface friction coefficient,
The road surface friction coefficient setting device, wherein the road surface friction coefficient update means permits updating according to the vehicle body deceleration.   The road surface friction coefficient setting device according to claim 1, wherein the road surface friction coefficient update means permits an update to a higher road surface friction coefficient as the vehicle body deceleration increases.   The road surface friction coefficient updating means has a vehicle body deceleration threshold value corresponding to the road surface friction coefficient stored in the storage means, and when the vehicle body deceleration value is lower than the vehicle body deceleration threshold value, the vehicle body deceleration threshold value is set. The road surface friction coefficient setting device according to claim 1 or 2, wherein updating of the road surface friction coefficient to a higher side than the corresponding road surface friction coefficient is prohibited.   The road surface friction coefficient updating means has a first vehicle body deceleration threshold value and a second vehicle body deceleration threshold value that is larger than the first vehicle body deceleration threshold value, and the vehicle body deceleration is the first vehicle body deceleration threshold value. 4. An update to a lower side than a predetermined road surface friction coefficient is permitted when the vehicle body deceleration threshold is not less than the second vehicle body deceleration threshold and not more than the second vehicle body deceleration threshold. Road surface friction coefficient setting device.   Updating the road surface friction coefficient by the road surface friction coefficient updating means is performed when the brake is applied and the state where the vehicle body deceleration is equal to or higher than a preset threshold value continues for a set time or longer. The road surface friction coefficient setting device according to any one of claims 1 to 4. Vehicle body deceleration detection means for detecting vehicle body deceleration,
Front and rear wheel slip ratio difference detection means for detecting front and rear wheel slip ratio difference;
Storage means for storing in advance the relationship between the vehicle body deceleration, the front-rear wheel slip ratio difference, and the road surface friction coefficient;
Road surface friction coefficient setting means for setting a road surface friction coefficient from the storage means based on the vehicle body deceleration and the slip ratio difference between the front and rear wheels;
With
The road friction coefficient setting device, wherein the road surface friction coefficient setting means limits a setting range of the road surface friction coefficient by the storage means according to the vehicle body deceleration.   The road surface friction coefficient setting device according to claim 6, wherein the road surface friction coefficient setting means permits a setting range to a higher road surface friction coefficient as the vehicle body deceleration increases.   The road surface friction coefficient setting means has a vehicle body deceleration threshold value corresponding to the road surface friction coefficient stored in the storage means, and when the vehicle body deceleration value is lower than the vehicle body deceleration threshold value, the vehicle body deceleration threshold value is set. 8. The road surface friction coefficient setting device according to claim 6, wherein setting of the road surface friction coefficient to a side higher than the corresponding road surface friction coefficient is prohibited.   The road surface friction coefficient setting means has a first vehicle body deceleration threshold value and a second vehicle body deceleration threshold value that is larger than the first vehicle body deceleration threshold value, and the vehicle body deceleration is the first vehicle body deceleration threshold value. 9. The setting according to claim 6, wherein a setting to a lower side than a predetermined road surface friction coefficient is permitted when the vehicle body deceleration threshold is not less than the second vehicle body deceleration threshold. Road surface friction coefficient setting device.   The setting of the road surface friction coefficient by the road surface friction coefficient setting means is performed when the brake is applied and the vehicle deceleration is equal to or higher than a preset threshold value for a set time or longer. The road surface friction coefficient setting device according to any one of claims 6 to 9.

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