JPH11148395A - Road surface mu detection device for vehicle and vehicle traveling controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To positively detect a road surface with low frictional coefficient μ, and change over characteristics of throttle opening control based on the detected results of an accelerator opening according to road surface conditions. SOLUTION: If slipping rate exceeds a prescribed value even once while a traction control system is operating, large slipping frequency is counted for each accelerator opening (S4). When the large slipping frequency is a discrimination value stored in advance for each accelerator opening or more (S5), it is discriminated as a low μroad. When the low μ road is discriminated, the characteristics of a targeted throttle opening against accelerator opening is changed to low μ road characteristics (delayed opening characteristics) where the targeted throttle opening corresponding to the same accelerator opening is a targeted throttle opening in basic characteristics or less (S9).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle road surface .mu. Detecting device and a vehicle traveling control device, and more particularly, to detecting a state where a road surface friction coefficient .mu. Is low, and a throttle when a road surface friction coefficient .mu. The present invention relates to a technique for changing an opening control characteristic.

[0002]

2. Description of the Related Art Heretofore, there has been known a vehicle engine having a configuration in which a throttle actuator is controlled based on an accelerator opening to open and close a throttle valve. Also,
On a road surface having a small friction coefficient μ (hereinafter referred to as a low μ road), if the torque transmitted to the drive wheels is too large,
A vehicle has been proposed in which the opening characteristic in the throttle control is changed to a characteristic for a low μ road when the road is on a low μ road because slipping of the drive wheels is likely to occur (Japanese Patent Laid-Open No. Hei 5-5-2). No. 071374).

[0003]

As a method of detecting a low μ road, there is a method of detecting a slip state of a wheel from a detected value of a wheel speed and estimating a friction coefficient μ of a road surface from the slip state. However, in such a method, the determination error is large, and in a city area at the time of snowfall in which μ change frequently occurs, a low μ and a high μ determination are switched each time. Further, there is a problem in that the determination of the low μ road and the high μ road is frequently switched, so that the throttle opening degree characteristic is frequently changed, giving the driver an uncomfortable feeling.

On the other hand, in the method of estimating the road surface μ depending on the accelerator operation by the driver, there are many erroneous determinations because the variation between the drivers is large, and further, in the method of estimating the road surface μ based on the engine water temperature, oil temperature and the like. However, since only the temperature condition can be indirectly determined, there is a problem that reliability is lacking. The present invention has been made in view of the above-described conventional problems, and provides a device capable of detecting a road surface μ more accurately with less error.In addition, in a control for switching a throttle opening degree characteristic according to a road surface μ, an unnecessary throttle is used. It is an object of the present invention to provide a vehicle travel control device capable of stably controlling the throttle opening with appropriate characteristics according to the road surface μ while avoiding switching of the opening characteristics.

[0005]

Therefore, a vehicle road surface μ detecting apparatus according to the first aspect of the present invention is configured as shown in FIG. In FIG. 1, a slip ratio detecting means detects a slip ratio between a wheel and a road surface, and an accelerator opening detecting means detects an accelerator opening.

Further, the large slip occurrence number counting means counts the number of occurrences of the large slip in which the slip ratio detected by the slip ratio detection means exceeds a predetermined value for each accelerator opening. On the other hand, the threshold value storage means stores in advance the threshold value of the number of occurrences of the large slip for each accelerator opening.

The low μ road determining means determines that the number of large slip occurrences for each accelerator opening counted by the large slip occurrence counting means is greater than the threshold value for each accelerator opening stored in the threshold storage means. When it is large, it is determined that the vehicle is traveling on a road surface with a small friction coefficient μ. According to this configuration, when a large slip in which the maximum value of the slip ratio exceeds a predetermined value occurs, the number of occurrences of the large slip is counted for each accelerator opening, and the threshold stored for each accelerator opening and the threshold value are stored. The count value is compared with the count value, and when the count value becomes larger than the threshold value, it is estimated that the friction coefficient μ of the road surface is reduced due to snowfall, freezing, or the like. Here, by counting the number of times of occurrence of a large slip for each accelerator opening and comparing it with a threshold value for each accelerator opening, the occurrence of a large slip is due to a small friction coefficient μ of the road surface, or It is distinguished whether it is caused by excessive driving torque.

The slip ratio between the wheel and the road surface can be obtained as a difference between a reference vehicle speed (driven wheel speed) and a wheel speed of a driving wheel by providing a sensor for detecting the wheel speed of the vehicle. In a vehicle provided with a so-called traction control system (hereinafter, also referred to as TCS), a slip occurrence state can be determined as an operation state of the TCS.
When the slip ratio exceeds the predetermined value even once even during the operation of, the count value can be counted up and counted.

According to a second aspect of the present invention, when the slip that does not exceed the predetermined value, the slip rate of which is detected by the slip rate detecting means, continuously occurs for a predetermined number of times or more, the large slip occurrence number counting means is used. A configuration is provided in which reset means for resetting the count value by the number of small slips is provided. According to such a configuration, even if a slip occurs, the slip ratio at that time is relatively small, and
When such small slips continue for a predetermined number of times or more, the count value of the number of large slips is reset.

Thus, when the count value of the number of occurrences of the large slip exceeds the threshold value, the determination result of the low μ road is also canceled with the reset of the count value. In other words, if a state in which a large slip ratio does not appear even if a slip occurs continues, it is presumed that the vehicle has exited the low μ road. It is determined that the change has been made.

According to the present invention, when it is determined that no slip has occurred for a predetermined time or more based on the slip ratio detected by the slip ratio detecting means, the count value of the large slip occurrence count means is determined. The reset means by the non-slip time for resetting is provided. According to such a configuration, when a state in which no slip occurs, specifically, a state in which the detected slip rate does not exceed the value for slip determination continues for a predetermined time or more, the number of occurrences of the large slip is reduced. Reset.

Thus, when the count value of the number of occurrences of the large slip exceeds the threshold value, the determination result of the low μ road is also canceled with the reset of the count value. That is, when the occurrence of the slip is not longer than the predetermined time, it is estimated that the vehicle has left the low μ road. Therefore, by resetting the number of times of occurrence of the large slip, it is determined that the road has been switched to the high μ road. Things.

On the other hand, the invention according to claim 4 is configured as shown in FIG. In FIG. 2, a slip rate detecting means detects a slip rate between a wheel and a road surface, and a starting temperature detecting means detects an engine temperature at the time of starting the engine. The slip occurrence count means detects slip occurrence based on the detected slip rate, and counts the number of slip occurrences from a predetermined time before to the present time.

When the engine temperature at the time of starting the engine is equal to or lower than a predetermined temperature and the number of occurrences of the slip is equal to or higher than a predetermined number, the low μ road determination means runs on a road having a small friction coefficient μ. Judge that there is. According to such a configuration, the engine temperature at the start is estimated to correspond to the normal outside air temperature, if the engine is stopped for a corresponding time, and the engine temperature at the start is, for example, 0 ° C. or less. When the temperature is low as described above, the possibility of freezing of the road surface and snow is high, but the environmental condition at the start is not always continued due to the rise in temperature during driving and changes in the driving area. It may be a very high μ road. Therefore, it is determined whether or not the number of occurrences of slips in the latest predetermined time is equal to or more than a predetermined number, and when the engine temperature at the time of starting is low, and slip has recently occurred at a frequency equal to or more than a predetermined number. In this method, it is assumed that the state in which the vehicle easily slips at the time of starting is continuing, and the low μ road is determined.

The engine temperature at the time of starting can be detected as a temperature of a cooling water or a temperature of a lubricating oil of the engine.
If the engine is provided with a water temperature sensor or an oil temperature sensor, the engine can be used for determining the road surface μ. The invention according to claim 5 is configured as shown in FIG. In FIG. 3, the actuator is for opening and closing the throttle valve of the engine, and the accelerator opening detecting means detects the accelerator opening.

The target opening setting means sets a target throttle opening based on the accelerator opening detected by the accelerator opening detecting means. The control means controls the actuator based on the target throttle opening set by the target opening setting means. On the other hand, the vehicle road surface μ detection device is the one according to any one of the above-described claims 1 to 4, and the opening degree characteristic changing means is configured to determine the low μ road determination that constitutes the vehicle road surface μ detection device. When the means determines that the vehicle is traveling on a road surface having a small friction coefficient μ, the characteristic of the target throttle opening with respect to the accelerator opening in the target opening setting means is set to the target throttle opening corresponding to the same accelerator opening. However, the characteristic is changed to a low μ road characteristic that is equal to or less than the target throttle opening in the basic characteristic.

According to this configuration, when the road is a low μ road, the characteristic of the target throttle opening with respect to the accelerator opening is changed from the basic characteristic to the characteristic for the low μ road, and the throttle opening with respect to the accelerator opening is suppressed low. It prevents excessive drive torque from being applied. In the invention according to claim 6, the low μ
Basic characteristic return means for gradually returning the characteristic of the target throttle opening degree changed to the road characteristic to the basic characteristic in accordance with the elapsed time since the determination of the low μ road by the low μ road determination means is released. The configuration was provided.

According to this configuration, the characteristic of the throttle opening with respect to the accelerator opening gradually returns to the basic characteristic after switching from the low μ road to the high μ road.

[0019]

According to the first aspect of the present invention, the low μ road can be determined from the slip ratio and the number of times of occurrence of the slip in consideration of the state of the driving torque. There is an effect that it can be determined as a general tendency. According to the second aspect of the present invention, based on the fact that the slip having a relatively low slip rate is continuously generated,
There is an effect that switching from a low μ road to a high μ road can be properly and stably determined.

According to the third aspect of the present invention, when the slip has not occurred for a predetermined time or more, the switch from the low μ road to the high μ road is determined, so that the low μ road can be determined more than necessary. There is an effect that continuation can be avoided.
According to the fourth aspect of the invention, there is an effect that the low-μ road can be determined in response to a change in the environmental condition while easily detecting the temperature environment.

According to the fifth aspect of the invention, when the vehicle is traveling on a low μ road, the throttle valve opening relative to the accelerator opening is suppressed lower than when traveling on a high μ road, and slip occurs due to excessive driving torque. There is an effect that it can be prevented beforehand. According to the invention described in claim 6, there is an effect that the throttle opening characteristic corresponding to the low μ road can be shifted to the basic characteristic (high μ road opening characteristic) without giving the driver an uncomfortable feeling.

[0022]

Embodiments of the present invention will be described below. FIG. 4 is a system configuration diagram of the vehicle according to the embodiment. The engine 1 shown in the figure is a V-type six cylinder,
An injector is provided for each cylinder. The injector may be configured to inject fuel directly into the combustion chamber of each cylinder, instead of injecting fuel into the intake port.

The exhaust from each cylinder is supplied to the left and right banks 1a,
After merging individually for each 1b and passing through the catalyst 2a for the left bank and the catalyst 2b for the right bank, the exhaust gases of the left and right banks merge and pass through the muffler 3 to be discharged into the atmosphere. The injector provided for each cylinder opens according to an injector drive signal from an ECM (Engine Control Module) 4 containing a microcomputer, and supplies fuel to each cylinder.

Detection signals from various sensors are input to the ECM 4, and a valve opening drive time of the injector, that is, a fuel injection amount is determined based on the detection signals. Examples of the various sensors include an air flow meter 5 for detecting an intake air amount QA of the engine 1, a crank angle sensor 6 for detecting a crank angle of the engine 1, and a water temperature sensor 13 for detecting a cooling water temperature TW representing an engine temperature. Is provided.

The throttle valve 7 for adjusting the intake air amount QA of the engine 1 is not opened and closed mechanically in conjunction with an accelerator pedal (not shown), but is opened and closed by a motor 8 as an actuator. The ECM 4 sets a target throttle opening based on an accelerator pedal opening (hereinafter referred to as an accelerator opening) detected by an accelerator opening sensor 9 (accelerator opening detecting means) (a target opening). Setting means), and controls the motor 8 so as to achieve the target throttle opening (control means).

In this embodiment, a traction control system (hereinafter, referred to as TCS)
The TCS control unit (TC
SC / U) 10 receives detection signals from wheel speed sensors 11a, 11b, 11c, and 11d provided for each of the four wheels, and outputs the engine speed (rpm), accelerator opening, engine Information such as load is input by communication via the LAN.

And the TCS control unit
10 calculates the slip ratio of the driving wheel (between the wheel and the road surface) based on the various signals, and requests the ECM 4 to reduce the torque according to the slip ratio when the slip ratio exceeds an allowable value. Output a signal. The ECM 4 that has received the torque-down request signal performs a fuel cut (temporary stop of fuel supply) in response to the torque-down request, thereby reducing the engine output torque. To reduce the occurrence of slip.

In FIG. 4, reference numeral 12 denotes an automatic
Transmission control unit (A / T
C / U), and the A / T control unit 12 may also output a fuel cut request signal to the ECM 4 during gear shifting. FIG. 5 shows the ECM4 and TCS
FIG. 2 is a block diagram showing a control function by a control unit 10.

First, the control function of the TCS control unit 10 will be described. The wheel speed detector 101 detects the rotation speed of each wheel based on the signals from the wheel speed sensors 11a to 11d. The wheel speed comparison calculation unit 102 compares the rotation speed of the front wheel (driven wheel) with the rotation speed of the rear wheel (drive wheel), and the slip ratio calculation unit 103 (slip ratio detection means) calculates the slip ratio based on the result. I do.

The required torque-down amount calculating section 104 calculates the required torque-down amount based on the calculated slip ratio. Then, the torque-down control signal output unit 105
Then, a torque down request signal indicating the torque down request amount is output to the ECM 4. Next, the fuel injection control by the ECM 4 will be described.

First, an engine speed detector 111 detects an engine speed NE (rpm) based on a signal from the crank angle sensor 6, and an intake air amount detector 112 based on a signal from the air flow meter 5. To detect the intake air amount QA. The basic fuel injection pulse width calculation unit 113 calculates the basic pulse width Tp of the drive signal output to the injector based on the detected engine speed NE and the intake air amount QA.

The fuel injection pulse width calculation unit 114 corrects the basic pulse width Tp according to the engine coolant temperature TW and the like to calculate the final injection pulse width Ti. Then, the drive circuit 115 outputs a drive signal having the injection pulse width Ti to the injector 119 of each cylinder at an injection timing synchronized with the engine rotation. Meanwhile, the TCS
Control unit 10 torque-down control signal output section
The torque-down request signal from 105 is input to the torque-down request cylinder cut number calculation unit 116 of the ECM 4 to calculate the fuel cut request cylinder number according to the torque-down request amount.

The calculated fuel cut request cylinder number is:
This is output to the fuel cut cylinder number judging section 117, and the fuel cut cylinder number judging section 117 actually calculates the fuel cut cylinder number based on the operating region determined from the basic pulse width Tp representing the engine load and the engine speed NE. The number of cylinders for which fuel cut is performed is determined. When the number of cylinders for which fuel cut is actually performed is determined by the fuel cut cylinder number determining unit 117, a combination (pattern) of cylinders for which fuel cut is performed in accordance with the number of fuel cut cylinders in a fuel cut cylinder pattern designating unit 118.
Is specified.

Then, the fuel cut possibility final determination section 120 determines whether or not to finally execute the fuel cut based on the result of a failure diagnosis or the like performed separately. The fuel cut cylinder designated by the fuel cut cylinder pattern designation section 118 is output to the fuel injection pulse width calculation section 114, and the fuel injection amount (fuel injection pulse width) of the cylinder designated as the fuel cut cylinder is output. Is set to 0.

In the fuel cut cylinder pattern designating section 118, it is preferable to switch the combination of the cylinders for performing the fuel cut at predetermined time intervals so that the cylinders for performing the fuel cut are substantially uniform in the left and right banks. By the way, in the present embodiment, the target throttle opening is set based on the detected value of the accelerator opening as described above. As a characteristic for converting the accelerator opening into the target throttle opening, the friction coefficient μ is Two basic characteristics are set in advance: basic characteristics (high μ road characteristics) corresponding to a high dry road surface and low μ road characteristics corresponding to a wet road surface (including frozen and snowy road surfaces) having a low friction coefficient μ. The characteristics to be referred to are switched based on the determination result of the road surface μ.

The characteristics for the low μ road are as shown in FIG.
The target throttle opening corresponding to the same accelerator opening is a characteristic that is equal to or less than the target throttle opening in the basic characteristics. When the road is a low μ road, the target throttle opening is determined according to the low μ road characteristic (hereinafter also referred to as a slow opening characteristic). By setting the target throttle opening, the driving torque with respect to the accelerator opening is suppressed, and the occurrence of slip can be prevented.

The switching control between the low μ road characteristic and the basic characteristic (high μ road characteristic) performed by the ECM 4 will be described with reference to the flowchart of FIG. In the flowchart of FIG. 7, in S1, T
It is determined whether CS is in operation. The operation of the TCS indicates that the TCS control unit 10 detects a slip with a slip ratio exceeding an allowable value and outputs a torque-down request.

When the TCS is in operation,
Proceeding to S9 (opening characteristic changing means), the low-μ road characteristic (slow opening characteristic) is selected, and the slow opening characteristic selection flag is set to 1. If the low μ road characteristic (slow opening characteristic) is selected during the TCS operation as described above, the throttle opening is suppressed in addition to the fuel cut control based on the torque reduction request, and the slip state is reduced. It can be promptly resolved.

On the other hand, the elapsed time from the end of the TCS operation is measured in S2.
When it is determined that the TCS is not operating at S3, the process proceeds to S3, where it is determined whether or not within a predetermined time (for example, 30 seconds) from the end of the operation of the TCS. Select the μ road characteristic (slow opening characteristic).

As described above, if the characteristics for the low μ road (slow opening characteristics) are continued within a predetermined time after the end of the TCS operation, the characteristics are frequently switched in a situation where starting and stopping are repeated in an urban area. Can be avoided. In S4, when the slip ratio exceeds a predetermined value even once during the operation of the TCS, the number of occurrences of large slips for each accelerator opening is counted up (means for counting the number of occurrences of large slips). However, the count-up during one TCS operation is limited to one time, and the number of occurrences of the large slip corresponding to the accelerator opening at the time when the slip occurs is counted up. Further, the predetermined value is a slip ratio higher than a threshold value for determining a torque-down request, and is a value capable of distinguishing between a dry road surface and a wet road surface.

The number of occurrences of the large slip is reset (reset to 0) under the following three conditions. (1) When the state where the slip ratio does not exceed the predetermined value during the TCS operation continues for a predetermined number of times (for example, two times) or more (reset means by the number of small slip occurrences) (2) For a predetermined time (for example, 10 minutes), the TCS When the non-operation state continues (reset means by non-slip time) (3) When the key switch is turned off In the above-mentioned reset condition (1), the slip ratio exceeds the predetermined value which is a judgment value of a large slip. The condition is that there is no such condition. However, this is a condition that does not exceed the predetermined value at least, and a value lower than the predetermined value that is a determination value of a large slip may be used as the reset condition.

In S5, as shown in FIG.
4 is compared with the judgment value (threshold value) for each accelerator opening stored in the memory (threshold storage means) 4 and the number of occurrences of large slips counted up for each accelerator opening. When the number of occurrences has been counted, it is determined that the vehicle is traveling on the low μ road (low μ road determining means), and the process proceeds to S9.

If the number of occurrences of the large slip is determined for each accelerator opening as described above, the friction coefficient μ of the road surface can be estimated in consideration of the difference in the slip ratio due to the difference in the driving torque. Further, since the reset condition (1) is to confirm that the state where the slip rate is relatively low continues even if a slip occurs, the reset condition changes in the direction in which the friction coefficient μ of the road surface increases. Can be reliably determined.

However, the reset condition of the above (1) requires the occurrence of slip, so that the reset cannot be performed if the operation that does not cause the slip is performed. It can be avoided that the reset is performed according to the reset condition and the characteristic for low μ road (slow opening characteristic) is unnecessarily continued. Further, by resetting when the key switch is turned off, it is possible to prevent the road surface μ from being erroneously determined due to the count result of the previous operation.

On the other hand, if it is determined in S5 that the number of occurrences of the large slip is not equal to or greater than the determination value, the process proceeds to S7, in which the coolant temperature TW (S6: Start-up temperature detection means)
It is determined whether the temperature is equal to or lower than a predetermined temperature (for example, 0 ° C.).
When the engine water temperature at the time of starting is equal to or lower than the predetermined temperature, the process proceeds to S8, and it is determined whether or not the number of times of operation of the TCS from before a predetermined time (for example, 10 minutes) to the present is equal to or more than a predetermined number (for example, once). (Slip occurrence count means).

When the engine water temperature at the time of starting is equal to or lower than a predetermined temperature, the possibility of freezing of the road surface or snow is estimated. Temperature conditions are not always possible. Therefore, when the water temperature at the time of starting is low, it is determined whether or not a slip actually supporting the possibility of freezing of the road surface or snow cover has occurred, based on the number of times of operation of the TCS within a predetermined time in recent years. It is.

Then, the TCS within the latest predetermined time
If the number of operations is equal to or greater than the predetermined number, the process proceeds to S9, where the low μ road characteristic (slow opening characteristic) is selected (low μ road determination means). Further, when the engine water temperature at the time of starting is equal to or lower than the predetermined temperature, but the number of times of operation of the TCS within the latest predetermined time is less than the predetermined number of times (for example, 0), the temperature condition at the time of starting may be freezing or snow accumulation. However, at least at present, it is determined that the road is not a low μ road, and the process proceeds to S10 to set the late opening flag to 0.

On the other hand, when it is determined in S7 that the starting water temperature has exceeded the predetermined temperature, that is, during the TCS operation and within the predetermined time after the operation is completed, the number of occurrences of the large slip is less than the determination value, and , Even when the starting water temperature is high,
Proceeding to S10, the late opening flag is set to 0. Next S11
Then, it is determined whether the previous value of the late opening flag is 1 or not to determine whether the condition is the first time (at the time of releasing the slow opening selection) from the condition for selecting the low μ road characteristic (slow opening characteristic). Determine whether or not.

When the previous slow opening flag is 1 and has been reset to 0 this time, the process proceeds to S12, and a timer for measuring the elapsed time after the slow opening selection is released is started. In the next step S13 (basic characteristic return means), the target throttle opening is set in accordance with the following equation so as to gradually return from the low μ road characteristic (slow opening characteristic) to the basic characteristic.

Target throttle opening = slow opening characteristic opening +
(Basic characteristic opening-slow opening characteristic opening) × (K / 100) Here, the slow opening characteristic opening and the basic characteristic opening are obtained from the accelerator opening according to the slow opening characteristic and the basic characteristic shown in FIG. Target throttle opening. Further, as shown in FIG. 9, K represents the basic opening degree characteristic return rate (%) which is set to be larger as the elapsed time after the delayed opening selection is released is longer. The opening gradually approaches the basic characteristic opening, and K becomes final (for example, the elapsed time
When it is set to 100% at 50 seconds), it returns to the target throttle opening according to the basic characteristics (see FIG. 10).

As described above, if the slow opening characteristic (low μ road characteristic) is gradually returned to the basic characteristic,
It is possible to avoid giving the driver an uncomfortable feeling.

[Brief description of the drawings]

FIG. 1 is a basic configuration block diagram of a vehicle road surface μ detection device according to claim 1.

FIG. 2 is a block diagram showing a basic configuration of a vehicle road surface μ detecting apparatus according to claim 4.

FIG. 3 is a block diagram of a basic configuration of a vehicle traveling control device according to claim 5;

FIG. 4 is a system configuration diagram of the vehicle according to the embodiment;

FIG. 5 is a control block diagram according to the embodiment;

FIG. 6 is a graph showing characteristics of a target throttle opening degree in the embodiment.

FIG. 7 is a flowchart showing detection of a road surface μ and switching of an opening degree characteristic in the embodiment.

FIG. 8 is a diagram showing a threshold (judgment value) of the number of times of large slip occurrence in the embodiment.

FIG. 9 is a diagram showing a return rate K to a basic characteristic in the embodiment.

FIG. 10 is a diagram showing a state of returning to basic characteristics in the embodiment.

[Explanation of symbols]

 Reference Signs List 1 engine 4 ECM 5 air flow meter 6 crank angle sensor 7 throttle valve 8 motor 9 accelerator opening sensor 10 TCS control unit 11a to 11d wheel speed sensor 13 water temperature sensor

Claims (6)

[Claims] 1. A slip ratio detecting means for detecting a slip ratio between a wheel and a road surface, an accelerator opening detecting device for detecting an accelerator opening, and a slip ratio detected by the slip ratio detecting means being a predetermined value. Large slip occurrence count means for counting the number of occurrences of large slips exceeding the accelerator opening degree, threshold storage means for storing a threshold value of the large slip occurrence number in advance for each accelerator opening degree, and the large slip occurrence number When the number of occurrences of large slips for each accelerator opening counted by the counting means is larger than the threshold value for each accelerator opening stored in the threshold storage means, it is determined that the vehicle is traveling on a road surface having a small friction coefficient μ. And a low-μ road determining means. 2. A small resetting means for resetting a count value in said large slip occurrence number counting means when a predetermined number of consecutive slips whose slip rate detected by said slip rate detecting means does not exceed said predetermined value occurs. 2. The vehicle road surface μ detecting apparatus according to claim 1, further comprising a reset unit that sets the number of slips. 3. A non-slip time for resetting a count value in said large slip occurrence count means when it is determined that no slip has occurred for a predetermined time or more based on a slip rate detected by said slip rate detection means. The vehicle road surface μ detecting device according to claim 1 or 2, further comprising resetting means. 4. A slip rate detecting means for detecting a slip rate between a wheel and a road surface; a starting temperature detecting means for detecting an engine temperature at the time of starting the engine; and a generation of a slip based on the detected slip rate. And a slip occurrence count means for counting the number of slip occurrences from a predetermined time before to the present time; and wherein the engine temperature at the time of starting is equal to or lower than a predetermined temperature, and wherein the number of slip occurrences is equal to or higher than a predetermined number. A low μ road determining means for determining that the vehicle is traveling on a road surface having a small friction coefficient μ. 5. An actuator for opening and closing a throttle valve of an engine, an accelerator opening detecting means for detecting an accelerator opening, and a target throttle opening based on the accelerator opening detected by the accelerator opening detecting means. A vehicle travel control device comprising: target opening setting means to be set; and control means for controlling the actuator based on the target throttle opening set by the target opening setting means. While the vehicle road surface μ detecting device according to any one of the above, when the low μ road determining unit determines that the vehicle is traveling on a road surface having a small friction coefficient μ, the target opening degree setting unit The characteristic of the target throttle opening with respect to the accelerator opening is such that the target throttle opening corresponding to the same accelerator opening is equal to or less than the target throttle opening in the basic characteristics. Vehicle running control apparatus characterized in that a degree of opening characteristic changing means for changing the μ road characteristics. 6. The characteristic of the target throttle opening degree changed to the characteristic for the low μ road is gradually changed to a basic characteristic in accordance with the elapsed time after the determination of the low μ road is canceled by the low μ road determining means. 6. The vehicle travel control device according to claim 5, further comprising a basic characteristic returning means for returning the vehicle to the vehicle.