JPH05142240A - Body-speed estimating apparatus for four-wheel driving vehicle - Google Patents

Abstract

PURPOSE:To estimate the speed of a vehicle body adequately. CONSTITUTION:An acceleration VBF corresponding to a wheel speed is compared with an actual acceleration GX, and whether a wheel starts slipping or not is judged with a slip-starting judging means 216f. When the wheel starts slipping, the values corresponding to the actual acceleration GX are integrated with time based on a body speed VB0 corresponding to the wheel speed obtained at this time and the actual acceleration GX. The obtained speed value is added to the body speed VB0 corresponding to the wheel speed and the body speed is computed. This body speed is made to be the estimated body speed VB with a body-speed estimating means 216g corresponding to the actual acceleration. When the slip of the wheel is the slip caused by the acceleration of the vehicle, the lower limit is clipped so that the value GX of the actual acceleration used in the body-speed estimating means 216g corresponding to the actual acceleration becomes 0 or the positive specified value or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive vehicle body speed estimating apparatus for estimating a vehicle body speed in a four-wheel drive type automobile (four-wheel drive vehicle) in which all wheels can slip, and more particularly to a traction control. The present invention relates to a vehicle body speed estimation device for a four-wheel drive vehicle, which is suitable for use in a four-wheel drive vehicle having a device such as a mechanism that requires a vehicle body speed to control the vehicle.

[0002]

2. Description of the Related Art In a four-wheel drive vehicle, since all wheels can slip on the road surface, the vehicle speed (abbreviated as vehicle speed) cannot be reliably obtained from the wheel speed (abbreviated as wheel speed). It is necessary to estimate a value close to the speed. Such vehicle body speed estimating means includes the following.

That is, a wheel speed sensor (also abbreviated as a wheel speed sensor) is usually attached to each of the four wheels, and the wheel speed V3 (here, the second smallest wheel speed V3 among the detected values of these wheel speed sensors). The wheel speed is a value obtained by converting the number of rotations of the wheel into a vehicle speed level, and the wheel speed is numbered in order from the largest wheel speed) as the estimated vehicle body speed VB. Of the estimated vehicle body speed VB, the estimated vehicle body speed corresponding to this wheel speed is VBF.

In a four-wheel drive vehicle, it can be inferred that all the wheels are slipping on the road surface even if they are slight, but the actual vehicle speed is calculated based on which of the four wheels. It is considered to be higher than the vehicle speed (actual vehicle speed). Therefore, it can be estimated that the vehicle speed obtained as the smallest value V4 of the four wheel speed values is the closest to the actual vehicle speed.

On the other hand, in the detection by the wheel speed sensor, an accurate value may not be obtained due to disturbance or the like. Therefore, in consideration of the detection reliability, the second smallest wheel speed V3 is adopted as the estimated vehicle body speed VB instead of the smallest value V4.

By the way, on a low μ road (a road surface having a low friction coefficient μ), the slip amount of any wheel becomes large,
The second wheel speed V3 from the smallest is also the smallest wheel speed V
4 is also a value that is significantly different from the actual vehicle speed. Therefore, when the wheel slips (when slipping beyond the limit), it is necessary to obtain the estimated vehicle body speed VB by means different from the above.

Therefore, first of all, the estimated vehicle body speed VBF
Acceleration of the vehicle body obtained from (VBF ′ = dVBF / d
t) and a longitudinal acceleration sensor (a longitudinal G sensor) provided on the vehicle
It is determined whether or not the wheel slips beyond the limit by comparing it with the actual acceleration value (GX) detected in.

That is, when the following expression (1) is satisfied,
It is assumed that the wheels have slipped more than the limit. VBF ′> GX + α (1) where α: constant (a constant that can be set according to the slip allowable range)

When the wheels slip more than the limit, the estimated vehicle body speed VB ₀ estimated when it is determined that the wheels slip more than the limit and the longitudinal acceleration sensor input at each control cycle. The estimated vehicle body speed VB is calculated by the following equation (2) based on the actual acceleration GX. That is, the value obtained by accumulating the constant β and adding the constant γ to the actual acceleration GX input from the longitudinal acceleration sensor for each control cycle is equal to the elapsed time (that is, if time T has elapsed, t
(= O to t = T) and the estimated vehicle body speed VB ₀ is calculated by adding this value to the estimated vehicle body speed VB ₀ . Note that, of the estimated vehicle body speed VB, the estimated vehicle body speed calculated based on the actual acceleration is VB ₂ . VB ₂ = VB ₀ + ∫ (β · GX + γ) dt ··· (2)

Further, the estimated vehicle body speed VB ₂ calculated by the equation (2) corresponds to the wheel speed V3.
When it becomes equal to F (= V3) (when VB ₂ = V3 is established), the vehicle speed estimation in consideration of the slip of the wheel by the formula (2) is stopped, and the above-mentioned VBF (= V
3) is set as the estimated vehicle speed VB.

Based on the estimated vehicle body speed VB calculated by such means, a control signal is output from the controller to each control unit for controlling the traction control or the like.

Incidentally, assuming that the actual acceleration GX is substantially constant after the start of the slip, the actual acceleration GX at the start of the slip is assumed.
It is also conceivable to obtain the estimated vehicle speed VB ₂ by the following equation (2) ′ using ₀ (= constant). VB ₂ = VB ₀ + ∫ (β · GX ₀ + γ) dt ··· (2) ′

[0013]

By the way, normally, the constants β and γ in the equation (2) or (2) ′ are β = 1 and γ =
Although it is set to 0, in such a case, the following problems may occur.

That is, FIG. 8 shows changes in the vehicle body speed when the vehicle body speed is properly estimated during acceleration, with the horizontal axis representing the time axis, and the alternate long and short dash line represents the actual vehicle body speed VBR. The broken line shows the estimated vehicle body speed VB ₂ , and the solid line shows the estimated vehicle body speed VBF.

As shown in FIG. 8, when the wheel slip amount is small, the wheel speed V3 becomes substantially equal to the actual vehicle body speed VBR, but when the wheel slip amount becomes large, the wheel speed V3 becomes the actual vehicle body speed VBR. It will be somewhat different. At this time, as described above, the slip of the wheel can be determined by comparing the acceleration based on the wheel speed V3 with the actual acceleration, and if it is determined that there is more slip than necessary, the estimated speed VB ₀ at the time of the slip determination is used to incline ( β ・ GX
The estimated vehicle body speed VB ₂ is set like the straight line + γ).

When the estimated vehicle body speed VBF (that is, the wheel speed V3) passes the peak and approaches the actual vehicle body speed, VBF = VB ₂ is established, the calculation of the estimated vehicle body speed VB ₂ is stopped, and the estimated vehicle body speed VB ₂ is estimated. The estimated vehicle body speed VBF (= wheel speed V3) is adopted as the vehicle body speed VB.

By the way, the estimated vehicle speed VB at the time of slip
_{When 2} is set lower, the estimated vehicle body speed VB ₂ may be set as shown in FIG. 9 with respect to the actual vehicle body speed. In FIG. 9, the horizontal axis represents the time axis, the alternate long and short dash line represents the actual vehicle body speed VBR, the broken line represents the estimated vehicle body speed VB ₂ , and the solid line represents the estimated vehicle body speed VBF.

As shown in FIG. 9, when the slip amount of the wheel is small, it is similar to that of FIG. 8, but when the slip amount of the wheel becomes large, the wheel based on the comparison between the acceleration based on the wheel speed V3 and the actual acceleration as described above. Can determine the slip of
When it is determined that there is more slip than required, the estimated vehicle body speed VB ₂ is set from the estimated speed VB ₀ at the time of slip determination as a straight line with a slope (β · GX + γ).

At this time, if the detected value of the actual acceleration GX is small, that is, the accuracy of the G sensor is poor, or the accurate acceleration cannot be detected due to vehicle body vibration due to road surface disturbance or the like, the GX is detected. As the value decreases, the slope of the estimated vehicle body speed VB ₂ becomes smaller, as shown by the broken line, and the estimated vehicle body speed VB gradually decreases and falls below the actual vehicle body speed VBR.

Therefore, the estimated vehicle speed VBF (that is,
Also getting closer to the actual vehicle speed and the wheel speed V3) is past the peak, because the wheel speed V3 will not be lower than the actual vehicle speed, not the VBF = VB _2, the estimated vehicle speed VB is estimated at the time of the wheel slip The estimated vehicle body speed VB ₂ which keeps the state and further deviates from the actual vehicle body speed VBR is adopted as the estimated vehicle body speed VB, and the proper vehicle body speed cannot be estimated.

Therefore, a means for setting the value of the constant β or the constant γ in the equation (2) or (2) 'to be larger than the above value can be considered. That is, the constant β is set to an appropriate value of β> 1, or the constant γ is set to an appropriate value of γ> 0.

As a result, the inclination of the estimated vehicle speed VB ₂ becomes large, so that even if the detected value of the actual acceleration GX is small,
The estimated vehicle body speed VB ₂ can be maintained at or above the actual vehicle body speed VBR, VBF = VB ₂ can be set, and the estimation at the time of slip can be returned to the estimation at the time of non-slip.

However, when the value of the constant β or the constant γ is set to a large value as described above, the estimated vehicle body speeds VBF and VB ₂ must be released unless the driver loosens the accelerator during the slip.
May be set as shown in FIG. 10 with respect to the actual vehicle speed. In FIG. 10, the horizontal axis is the time axis, the alternate long and short dash line shows the actual vehicle body speed VBR, the broken line shows the estimated vehicle body speed VB ₂ , and the solid line shows the estimated vehicle body speed VBF.

As shown in FIG. 10, if the driver does not loosen the accelerator even after the wheel slips, the wheel continues to slip, so the estimated vehicle speed VBF does not approach the actual vehicle speed VBR.

On the other hand, with respect to the estimated vehicle body speed VB ₂ , the value of the constant β or the constant γ is set to be large, and therefore the slope (β · GX + γ) of the estimated vehicle body speed VB ₂ is greater than the slope of the actual vehicle body speed VBR. And the estimated vehicle speed VB ₂
Will greatly exceed the actual vehicle speed VBR.

Therefore, the estimated vehicle body speed VBF may not approach the actual vehicle body speed VBR, that is, VBF = VB ₂ may occur even though the wheels are slipping, and after that, even during the slipping. Regardless, the estimated vehicle body speed VBF in the non-slip state is adopted, and the proper vehicle body speed cannot be estimated.

Further, if the acceleration sensor has poor accuracy or is not properly attached, there are the following problems.

That is, FIG. 11 is a graph showing the characteristics of the acceleration sensor. Acceleration 0 is set below the linear characteristic portion of the sensor, and the acceleration sensor output a corresponding to this acceleration 0 is set as the lower limit to correspond to the acceleration. You can get the output.

By the way, when the output of the acceleration sensor is lower than the output a when the acceleration sensor has a poor accuracy or a bad mounting, the controller 15 adopts the negative acceleration corresponding to this output for the calculation, and it is erroneous. There is a possibility that the estimated vehicle speed may be calculated and output, and it may not be possible to stably and accurately control the driving state of the vehicle.

The present invention was devised in view of the above problems, and an object of the present invention is to provide a vehicle body speed estimating device for a four-wheel drive vehicle, which can appropriately estimate the vehicle body speed.

[0031]

Therefore, a vehicle body speed estimating device for a four-wheel drive vehicle according to the present invention is a vehicle body speed estimating device for estimating a vehicle body speed in a four-wheel drive vehicle.
Wheel speed detecting means for detecting a wheel speed, wheel speed corresponding body speed estimating means for estimating a vehicle speed based on the wheel speed, and wheel speed corresponding body speed estimated by the wheel speed corresponding body speed estimating means Wheel speed corresponding acceleration calculating means for calculating the acceleration, actual acceleration detecting means for detecting the actual acceleration of the vehicle body, and comparing the wheel speed corresponding acceleration with the actual acceleration to determine whether the wheel has started slipping. When the slip start determining means determines that the wheel has started slipping, a value related to the actual acceleration is calculated based on the vehicle speed corresponding to the wheel speed and the actual acceleration obtained at this time. A vehicle corresponding to an actual acceleration in which the speed value obtained by integration is added to the vehicle speed corresponding to the wheel speed to calculate the vehicle speed, and the vehicle speed thus obtained is used as the estimated vehicle speed. When the slip of the wheels is a slip accompanying the acceleration of the vehicle, the lower limit clip is performed so that the value of the actual acceleration used by the actual acceleration-corresponding vehicle speed estimating means becomes 0 or a positive predetermined value or more. It is characterized by being set as follows.

A vehicle speed estimating apparatus for a four-wheel drive vehicle according to a second aspect of the present invention is a vehicle speed estimating apparatus for estimating a vehicle speed in a four-wheel drive vehicle, wherein a wheel speed detecting means for detecting a wheel speed and the wheel are provided. Wheel speed corresponding vehicle speed estimating means for estimating a vehicle speed based on speed, wheel speed corresponding acceleration calculating means for calculating acceleration based on the wheel speed corresponding vehicle speed estimated by the wheel speed corresponding vehicle speed estimating means, An actual acceleration detecting means for detecting the actual acceleration of the vehicle body, a slip start judging means for judging whether the wheel starts slipping by comparing the wheel speed corresponding acceleration with the actual acceleration, and the slip start judging means. When it is determined that the wheel has started slipping, the value related to the actual acceleration is calculated based on the vehicle speed corresponding to the wheel speed and the actual acceleration obtained at this time. A speed value obtained by integration is added to the vehicle speed corresponding to the wheel speed to calculate the vehicle speed, and the vehicle speed is used as an estimated vehicle speed. In the case of a slip associated with, the upper limit clipping is set so that the value of the actual acceleration used by the vehicle acceleration estimating means corresponding to the actual acceleration becomes 0 or a predetermined negative value or more.

[0033]

In the vehicle speed estimating device for a four-wheel drive vehicle according to the present invention, the wheel speed is detected by the wheel speed detecting means, and the vehicle speed corresponding to the wheel speed is calculated based on the wheel speed. Is estimated.

Further, the wheel speed corresponding acceleration calculating means calculates the acceleration based on the wheel speed corresponding vehicle speed estimated by the wheel speed corresponding vehicle speed estimating means, and the slip start judging means calculates the actual wheel speed corresponding acceleration with the wheel speed corresponding acceleration. The acceleration is compared to determine if the wheel has begun to slip.

When the actual acceleration-corresponding vehicle body speed estimating means determines that the wheel has started slipping by the slip start judging means, the wheel speed-corresponding vehicle body speed and the actual acceleration obtained at this time A vehicle speed is calculated by adding a speed value obtained by time-integrating a value related to the actual acceleration to the vehicle speed corresponding to the wheel speed, and the vehicle speed thus obtained is set as an estimated vehicle speed.

At this time, if the slip of the wheels is the slip associated with the acceleration of the vehicle, the lower limit is clipped so that the value of the actual acceleration used by the actual acceleration-corresponding vehicle body speed estimating means is 0 or a positive predetermined value or more. , The above calculation is performed.

Further, in the vehicle body speed estimating apparatus for a four-wheel drive vehicle according to the second aspect of the present invention, similar to the apparatus of the first aspect,
The vehicle speed is estimated based on the wheel speed by the vehicle speed corresponding vehicle speed estimating means, the acceleration is calculated based on the vehicle speed corresponding vehicle speed by the wheel speed corresponding acceleration calculating means, and the wheel starts slipping by the slip start determining means. It is determined whether or not. Then, when the actual acceleration-corresponding vehicle body speed estimation means determines that the wheel has started slipping by the slip start determination means, the actual acceleration is related to the wheel speed-corresponding vehicle body speed and the actual acceleration obtained at this time. A speed value obtained by time-integrating the values is added to the wheel speed-corresponding vehicle body speed to calculate the vehicle body speed, and this vehicle body speed is set as the estimated vehicle body speed.

At this time, when the slip of the wheels is the slip accompanying the deceleration of the vehicle, the upper limit of the actual acceleration value used by the actual acceleration-corresponding vehicle body speed estimating means is set to 0 or a predetermined negative value or more. Then, the above calculation is performed.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle speed estimating device for a four-wheel drive vehicle as an embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of the main part of the device, FIG. 2 is a schematic diagram showing the configuration of a drive system of an automobile equipped with the device,
3 is a flow chart showing the operation of the main part, FIG. 4 is a graph showing an example of vehicle speed estimation, and FIGS. 5 and 6 are graphs showing the characteristics of the correction coefficient of the integrand (value relating to the actual acceleration). 7 is a graph showing an example of vehicle speed estimation.

The vehicle body speed estimating apparatus for a four-wheel drive vehicle of this embodiment is used in a vehicle drive system control (traction control) apparatus, and as shown in FIG. 1, has a function of controlling a drive state. Central processing unit (CPU)
It is provided inside.

First, referring to FIG. 1, the overall structure of a vehicle drive system including the vehicle speed estimation device for a four-wheel drive vehicle will be described.

In FIG. 2, reference numeral 2 is an engine, and the output of the engine 2 is transmitted to the output shaft 8 via the torque converter 4 and the automatic transmission 6. The output of the output shaft 8 is transmitted via an intermediate gear 10 to a planetary gear type differential device 12 as an operating device that distributes engine torque between the front wheels and the rear wheels to a required state.

The output of the planetary gear type differential device 12 is, on the one hand, the reduction gear mechanism 19 and the differential gear device 1 for the front wheels.
Front and left front wheels 16, 1 from axles 17L, 17R via 4
8 to the left and right rear axles via the bevel gear mechanism 15, the propeller shaft 20, the bevel gear mechanism 21, and the differential gear device (rear differential) 22 for the rear wheels as the left and right wheel differential mechanism. It is transmitted to the wheels 24, 26.

In the planetary gear type differential device 14, the output torque of the engine between the front wheels and the rear wheels is restricted by restricting (or limiting) the differential between the front wheel side output section and the rear wheel side output section. A hydraulic multi-plate clutch 28 is attached as a differential limiting means or a differential adjusting means capable of changing the distribution.

That is, the hydraulic multi-plate clutch 28 includes the sun gear 121 (or ring gear 123) and the carrier 125.
The frictional force is changed by the control pressure applied to its own hydraulic chamber, and the differential between the sun gear 121 (or ring gear 123) and the carrier 125 is constrained.

As a result, the planetary gear type differential device 12 is
By appropriately controlling the hydraulic multi-plate clutch 28 from the completely free state to the locked state, the distribution of torque transmitted to the front wheel side and the rear wheel side can be controlled. When the hydraulic multi-plate clutch 28 is completely locked, for example, the front wheel: rear wheel ratio is 5 depending on the front-rear distribution of the vehicle weight.
Since the predetermined ratio is 0:50 or 60:40, assuming that the front wheel: rear wheel ratio is about 30:70 in the completely free state, the front wheel: rear wheel ratio is 30:70 to 50: 5.
It can be controlled in the range of 0, 30:70 to 60:40.

Further, here, the rear differential 22 is also provided with a differential limiting mechanism 23 so that the torque distribution between the left and right wheels can be adjusted through the differential limiting.

Further, reference numeral 30 is a steering wheel angle sensor for detecting a rotation angle from the neutral position of the steering wheel 32, that is, steering wheel angle θ, and 34a and 34b are lateral accelerations Gyf acting on the front and rear portions of the vehicle body, respectively. G
It is a lateral acceleration sensor that detects yr. In this example, the two detection data Gyf and Gyr are averaged to be lateral acceleration data. However, the lateral acceleration sensor 34 is provided near the center of gravity of the vehicle body.
It is also possible to provide only one and use this detected value as lateral acceleration data. Reference numeral 36 is a longitudinal acceleration sensor that detects the longitudinal acceleration Gx acting on the vehicle body, 38 is a throttle position sensor that detects the throttle opening θt of the engine 2, 39
Is the engine key switch of engine 2, 40, 42, 4
4, 46 are left front wheel 16, right front wheel 18, left rear wheel 2 respectively
6, a wheel speed sensor for detecting the rotational speed of the right rear wheel 28, and the outputs of these switches and each sensor are input to the controller 48.

Reference numeral 50 is an antilock brake device, and this antilock brake device 50 operates in conjunction with the brake switch 50A. That is, when the brake switch 50A is turned on when the brake pedal 51 is stepped on, an antilock brake operation signal is output in conjunction with this, and the antilock brake device 50 is operated. Further, when the operation signal of the antilock brake is output, at the same time, a signal indicating the state is output from the controller 4
8 is input. Reference numeral 52 is a warning light that is turned on based on a control signal from the controller 48.

The controller 48 includes a CPU, a ROM, a RAM, an interface, etc., which are not shown, but are necessary for the control described later.

Reference numeral 54 is a hydraulic pressure source, and 56 is a pressure control valve system (hereinafter referred to as pressure control valve system) which is interposed between the hydraulic pressure source 54 and the hydraulic chamber of the hydraulic multi-plate clutch 28 and controlled by a control signal from a controller 48. Control valve).

Further, this vehicle is provided with an automatic transmission, and the reference numeral 160 is a shift lever 1 of the automatic transmission.
It is a shift lever position sensor (shift range detecting means) that detects the selected shift range of 60A, and this detection information is also sent to the controller 48.

Further, the engine speed N detected by the engine speed sensor (engine speed sensor) 170.
e and the transmission rotation speed Nt detected by the transmission rotation speed sensor (transmission rotation speed sensor) 180 are also sent to the controller 48.

In this example, a traction control system 151 is also provided. That is, the engine 2 includes the main throttle valve 152 whose opening is controlled according to the depression amount of the accelerator pedal 162, and constitutes an accelerator pedal system engine output adjusting device together with the accelerator pedal 162 and the coupling measure. ..

An auxiliary throttle valve 153 as an engine output control means that is controlled independently of the accelerator pedal system engine output adjusting device is provided in the intake passage of the engine 2 in series with the main throttle valve 152. .. The sub-throttle valve 153 is driven by a motor, and this motor is drive-controlled based on the detection results of the rear wheel speed sensors 44, 46, the front wheel speed sensors 40, 42, the engine speed sensor 170, the engine load sensor 172, and the like.

By the way, in each control described above, one of the control elements is
The vehicle body speed is required as one of them, and the vehicle body speed estimated by the vehicle body speed estimating device is used.

The vehicle body speed estimating device will now be described. As shown in FIG. 1, this device includes the wheel speed sensors (wheel speed detecting means) 40 to 46 and the vehicle speed corresponding vehicle speed estimating means 216a. A wheel speed corresponding acceleration calculating means 216e, a longitudinal acceleration sensor (actual acceleration detecting means) 36, a slip start judging means 216f, an actual acceleration corresponding vehicle speed estimating means 216g, a slip end judging means 216h, and an estimated vehicle speed. And an estimated vehicle body speed setting means 216i for setting

Reference numeral 216 indicates a vehicle body speed estimation unit in the controller 48, and reference numerals 216b and 216d indicate filters for preventing data variation by averaging the previous data and the current data.

Vehicle speed estimation means 216a corresponding to wheel speed
Is the second lowest wheel speed V3 among the detected values of the wheel speed sensors 40 to 46 (here, the wheel speed is a value obtained by converting the rotation speed of the wheel into a vehicle speed level, and the wheel speed is higher). (Numbered in order from 1) is adopted as the estimated vehicle speed VB. The estimated vehicle speed V
Of B, the estimated vehicle speed corresponding to this wheel speed is VB
Let it be F.

As described in the description of the conventional example, this is
In a four-wheel drive vehicle, it can be inferred that all of the wheels are slipping on the road surface, even if they are slight, but even if the vehicle speed is calculated based on any of the four wheels, the actual vehicle speed (actual vehicle speed ). Therefore, it can be estimated that the vehicle speed obtained as the smallest value V4 of the four wheel speed values is the closest to the actual vehicle speed. However, in the detection by the wheel speed sensor, an accurate value may not be obtained due to disturbance or the like. Therefore, in consideration of the detection reliability, the second smallest wheel speed V3 is adopted as the estimated vehicle body speed VB instead of the smallest value V4.

The wheel speed-corresponding acceleration calculating means 216e is
Acceleration V is obtained by differentiating the wheel speed corresponding vehicle speed VBF estimated by the wheel speed corresponding vehicle speed estimation means 216a with respect to time.
BF '(= dVBF / dt) is calculated.

The slip start judging means 216f compares the wheel speed corresponding acceleration VBF 'with the actual acceleration GX detected by the longitudinal acceleration sensor 36 to judge whether the wheel starts slipping.

This is a low μ road (a road surface having a low friction coefficient μ).
Etc., the slip amount of any wheel becomes large, and the second wheel speed V3 from the smallest wheel speed is the smallest wheel speed V4.
However, the value is significantly different from the actual vehicle speed. For this reason,
When the wheel slips (when slipping beyond the limit),
It is necessary to obtain the estimated vehicle body speed VB by means different from the above.

Therefore, first, the above-mentioned estimated vehicle speed VBF
Acceleration of the vehicle body obtained from (VBF ′ = dVBF / d
t) and a longitudinal acceleration sensor (a longitudinal G sensor) provided on the vehicle
It is determined whether or not the wheels are slipping beyond the limit by comparing with the value (GX) of the actual acceleration detected in.

That is, when the following expression (1) is satisfied,
It is assumed that the wheels have slipped more than the limit. VBF ′> GX + α (1) where α: constant (a constant that can be set according to the slip allowable range)

Vehicle speed estimating means 216g corresponding to actual acceleration
When the slip start determining means 216f determines that the wheel has started slipping, the actual vehicle speed VB ₀ corresponding to the wheel speed obtained at the start of the slip and the actual acceleration GX input from the longitudinal acceleration sensor 36 in each control cycle. Based on and, the vehicle speed (vehicle speed corresponding to the actual acceleration) VB ₂ is calculated.

That is, a value obtained by accumulating a constant β and adding a constant γ to the actual acceleration GX input from the longitudinal acceleration sensor in each control cycle (= β · GX + γ; this is referred to as “value relating to actual acceleration”). , The estimated vehicle body speed VB is calculated by integrating only the elapsed time (that is, from time t = o to time t = T when time T has elapsed) and adding this value to the estimated vehicle speed VB ₀ . VB ₂ = VB ₀ + ∫ (β · GX + γ) dt ··· (2)

At this time, in the acceleration state, the value of the actual acceleration GX used as the data is the predetermined value GX ₅ (≧ 0).
Clipped above. That is, when the value of the actual acceleration GX used as data is smaller than the predetermined value GX ₅ ,
It is set to use GX ₅ as the actual acceleration data GX. This is a process performed in order to prevent the deceleration G signal from being input even during acceleration due to insufficient accuracy of the G sensor or improper mounting.

The value of GX ₅ is the minimum acceleration value that can be considered when the wheels are accelerating and slipping on the actual road surface (excluding a steep uphill road of an extremely low μ road).
It is about the size. Further, GX ₅ may be set to 0 to simply prevent the input of the deceleration G signal.

On the other hand, at this time, in the decelerated state, the value of the actual acceleration GX used as the data is clipped to the predetermined value GX ₅ (≦ 0) or less. That is, when the value of the actual acceleration GX used as data is larger than the predetermined value GX ₆ (≦ 0), GX ₆ is set to be used as the actual acceleration data GX. Contrary to the above, this is a process performed to prevent the acceleration G signal from being input even during deceleration due to insufficient accuracy of the G sensor or improper mounting.

The value of GX ₆ is the lowest acceleration value that can be considered when the wheels are decelerating and slipping on an actual road surface (except for a steep downhill road of an extremely low μ road).
It is about the size. Further, GX ₆ may be set to 0 to simply prevent the input of the acceleration G signal.

Incidentally, assuming that the actual acceleration GX is substantially constant after the start of the slip, the actual acceleration GX at the start of the slip
It is also conceivable to obtain the estimated vehicle speed VB ₂ by the following equation (2) ′ using ₀ (= constant). VB ₂ = VB ₀ + ∫ (β · GX ₀ + γ) dt ··· (2) ′

In this device, the constant β or γ in the equation (2) or (2) ′ is changed after an appropriate time has elapsed after the start of slip, and the value [(β
GX + γ) or (β · GX ₀ + γ)] is set to change over time.

That is, as shown in FIG. 5, for example, the value of β after the start of slip (initial value) is set to be slightly larger than 1 and the value of β is changed after an appropriate time (for example, time t ₁ ). Change slightly smaller than 1.

As a result, the estimated vehicle body speed VB ₂ changes so that the inclination becomes smaller midway (after the time t _{1 has} elapsed) as shown by the curve VB in FIG. 4, and the estimated vehicle body speed VB changes to the actual vehicle body speed VBR. However, even if the driver does not loosen the accelerator during the slip, the value of VBF is close to the actual vehicle speed VBR.
It becomes VB ₂ , and it is possible to appropriately judge the end of wheel slip.

Further, as shown in FIG. 6, for example, the value of γ after the start of slip (initial value) is set to be slightly larger, and after a suitable time (for example, time t ₁ ) has elapsed, the value of γ is set to a value larger than this. Change it slightly smaller.

Also in this case, the estimated vehicle speed VB ₂ is shown in FIG.
As shown by the curve VB, the slope changes so as to decrease in the middle (after the time t ₁ elapses), and the estimated vehicle body speed VB becomes larger than the actual vehicle body speed VBR but becomes a value close to the actual vehicle body speed VBR. , Even if the driver does not loosen the accelerator during the slip, VBF should be applied near the actual vehicle speed VBR.
= VB ₂ .

Although both β and γ may be set to change as described above, it is also possible to set only one of β and γ as described above and set the other to an appropriate constant value. Be done. Further, it may be possible to set the change of β or γ in this case to be performed a plurality of times.

After the slip start is determined, the estimated vehicle body speed VB ₂ calculated by the equation (2) or (2) 'becomes equal to the estimated vehicle body speed VBF (= V3) corresponding to the wheel speed V3 after the slip start determination means 216h. If so (when VB ₂ = V3 is established), it is determined that the slip has ended.

The estimated vehicle body speed setting means 216i sets the estimated vehicle body speed VBF corresponding to the wheel speed V3 to the estimated vehicle body speed VB at the time of a specific slip (until it is judged that the slip has started and after it has been judged that the slip has ended). Then, at the time of slip (between the start of slip determination and the end of slip determination), the estimated vehicle body speed VB ₂ calculated by the equation (2) or (2) ′ is set to the estimated vehicle body speed VB. It is supposed to do.

However, the estimated vehicle body speed setting means 216i
Is a fixed condition (for example, a state in which the wheel speed is somewhat higher than a target speed (target speed) during traction control), the estimated vehicle body speed VB ₂ is adopted within a fixed time (for example, time t Limited to ₃ ).

That is, for example, when the state where the wheel speed V3 is higher than the target speed VA to some extent (for example, V ₀ or more) (V3 ≧ VA + V ₀ ) continues for more than t ₀ time after the start of the slip during the traction control, the slip end judging means. 216
Estimated vehicle speed V
Stop the adoption of B _2, it is adapted to adopt the estimated vehicle speed VBF corresponding to the wheel speed V3 of the estimated vehicle body speed VB.

The estimated vehicle body speed setting means 2
Instead of setting the estimated vehicle body speed VB by 16i, the slip end determination means 216h is set to V3 during traction control.
If the state of ≧ VA + V ₀ continues for t ₀ hours or more after the start of slip, the estimated vehicle body speed VB ₂ becomes equal to the estimated vehicle body speed VBF (=
Even if it is not equal to V3), it may be configured to determine that the slip has ended.

The actual acceleration-corresponding vehicle body speed estimating means 21
The calculation by 6g may be performed only from the time when it is determined that the slip has started to the time when it is determined that the slip has ended.

Then, based on the estimated vehicle body speed VB calculated by such means, a control signal is output from the controller to each control section for controlling the traction control or the like.

Since the vehicle body speed estimating apparatus for a four-wheel drive vehicle as one embodiment of the present invention is constructed as described above, the vehicle body speed that serves as a vehicle control reference is estimated, for example, by the flowchart shown in FIG. Will be carried out.

That is, in step S1, the wheel speed sensors 40 to 4 attached to the front, rear, left and right four wheels, respectively.
6 wheel speeds VFR (abbreviated as FR), VFL
(Abbreviated as FL), VRR (abbreviated as RR), VRL
(Also abbreviated as RL) is detected and read by the vehicle body speed estimation unit 216 of the controller 48, and the G sensor 2
Thus, the acceleration / deceleration GX of the vehicle body is detected and read by the vehicle body speed estimation unit 216.

Then, in step S2, a filtering process is performed and the previous data and the current data are averaged.

Next, in step S3, step S
Each wheel speed VFR, VFL, VRR
Of the VRL, the second wheel speed V3 from the bottom is selected as the estimated vehicle speed VBF [VBF = Select
(VFR, VFL, VRR, VRL)].

Then, it is determined in steps S4, S5, S13 and S14 whether the vehicle is in a predetermined acceleration state.

That is, in step S4, the differential value VBF 'of the reference speed VBF is greater than or equal to a preset value VBF1', and the acceleration / deceleration GX of the vehicle body is
It is determined whether or not the value is equal to or greater than the preset value GX ₁ .

In step S5, the reference speed V
A value obtained by adding a preset value GX ₃ to the acceleration / deceleration GX of the vehicle body, which is a differential value of BF, VBF ′ (GX + GX ₃ ).
It is determined whether or not the above.

When the determinations at steps S4 and S5 are both YES, that is, the acceleration VBF 'calculated by the reference speed is equal to or higher than a predetermined value, and the acceleration / deceleration GX of the vehicle body is equal to or higher than a predetermined value. When the acceleration VBF 'calculated from the reference speed exceeds the acceleration / deceleration GX of the vehicle body by a predetermined amount or more, the process proceeds to step S6, and a flag FLAG indicating that the wheels are in the acceleration slip state.
(1) is set to "1".

On the other hand, if the determination in step S4 is no, the process proceeds to step S13, in which the differential value VBF 'of the reference speed VBF is smaller than the preset value VBF2', and It is determined whether the acceleration / deceleration GX of the vehicle body is smaller than a preset value GX2.

In step S14, VBF ', which is the differential value of the reference speed VBF, is the acceleration / deceleration GX of the vehicle body.
From, it is determined whether it is smaller than the value obtained by subtracting the preset value GX4.

When the determinations at steps S13 and S14 are both YES, that is, the acceleration VBF 'calculated from the reference speed is smaller than a predetermined value,
When the acceleration / deceleration GX of the vehicle body is smaller than the predetermined value and the acceleration VBF ′ calculated by the reference speed is lower than the acceleration / deceleration GX of the vehicle body by more than a predetermined amount, step S1
5, the flag FLAG (2) indicating that the wheel is in the acceleration slip is set to "1".

FLAG (1)
If (2) and (2) are set, that is, if it is determined whether the wheel is in the acceleration slip state or the deceleration slip state, the estimated vehicle body speed VB is calculated for each acceleration / deceleration slip.

First, in step S7, the flag FL is set.
If it is determined that AG (1) is 1, the vehicle is in the acceleration slip state, and therefore the vehicle speed estimation at the time of the acceleration slip is performed in steps after step S8. If it is determined in step S7 that the flag FLAG (1) is not 1, the process proceeds to step S16. And step S
If it is determined in 16 that the flag FLAG (2) is 1, the vehicle is in the deceleration slip state, so that the vehicle speed estimation during the deceleration slip is performed in steps after step S17. Further, in step S16, the flag FLA
If it is determined that G (2) is not 1, the vehicle is not in the slipping state, and therefore, vehicle speed estimation during non-slip is performed in steps after step S20.

To estimate the vehicle speed during non-slip, first, in step S20, the estimated vehicle body speed VBF corresponding to the wheel speed is set to the estimated vehicle body speed VB, and in step S21, the estimation operation performed during acceleration / deceleration slip is continued. The values of the timers t ₁ and t _{2 which} are counted as time are cleared to “0”.

To estimate the vehicle body speed during acceleration slip, first in step S8, the characteristics of the constants (correction coefficients) β and γ in the value (β · GX + γ) related to the actual acceleration for obtaining the estimated vehicle body speed VB ₂ are calculated. To set. Here, β and γ during acceleration are indicated by β ₁ and γ ₁ , respectively.

These β ₁ and γ ₁ are set in accordance with the elapsed time t after the start of the acceleration slip determination. For β ₁ , for example, as shown in FIG. 5, a value after slip start (initial value) is set to be slightly larger than 1 and is changed to be slightly smaller than 1 after an appropriate time has elapsed. For γ ₁ ,
For example, as shown in FIG. 6, the value after the start of slip (initial value) is set to be slightly larger, and is changed to be slightly smaller than this after an appropriate time has elapsed.

Then, in step S9, the estimated vehicle speed VB during acceleration is calculated by the following equation (4). Note that in the formula (4), the value of β ₁ × GX + γ ₁ is added as the estimated vehicle speed VB (n) for each control cycle, which is the same integral calculation as that of the formula (2). Is. VB (n) = VB (n-1) + (β ₁ × GX + γ ₁ ) (4) where (β ₁ × GX + γ ₁ ) is a value equal to or greater than a preset predetermined value GX _5. Shall be taken.

Then, in step S10, it is determined whether or not the estimated vehicle speed VB (= VB ₂ ) has reached the vehicle speed VBF, and if not, the next time the vehicle speed is estimated, ( The estimated vehicle body speed VB ₂ in step S9 for adding β ₁ × GX + γ ₁ ) is used as the estimated vehicle body speed VB.

In such estimation operation, in step S11, the state in which the traction control is being performed and the wheel speed is equal to or higher than the target wheel speed + V ₀ (V ₀ is a positive predetermined value) continues for a predetermined time t ₀ or more. It continues until judged.

Then, in step S11, YES
If it is determined that the predetermined acceleration state has ended, the flag FLAG (1) is reset to "0" in step S12.

Accordingly, in the next vehicle body speed estimation, the process proceeds to step S20 through steps S4, S5, S7 and S16, and in step S20, the estimated vehicle body speed VBF which is the second wheel speed V3 from the bottom is determined. Estimated vehicle speed V
B. This adoption continues until the determination in step S4 or S5 becomes YES.

By the way, in the present embodiment, β ₁ and γ ₁ are
As described above, the value set to a large value is changed to a small value after a predetermined time. On the contrary, at the beginning, β ₁ =
1, γ ₁ = 0, and the estimated vehicle body speed V
B ₂ surely approaches the estimated vehicle speed VBF.

Therefore, even if the vehicle body speed VB is estimated using such a method, the estimation can be performed with high accuracy.

Further, in the present embodiment, even if only _one of β ₁ and γ ₁ is changed and the other is held constant, accurate estimation is performed in substantially the same manner as described above.

On the other hand, in estimating the vehicle body speed during deceleration slip, first in step S17, constants (correction coefficients) β and γ in the value (β · GX + γ) relating to the actual acceleration for obtaining the estimated vehicle body speed VB _2. Set the characteristics of. here,
Β and γ during deceleration are shown as β ₂ and γ ₂ , respectively.

These β ₂ and γ ₂ are set according to the elapsed time t after the start of the determination of deceleration slip. It is set almost the same as β ₁ and γ ₁ .

Then, in step S18, the estimated vehicle speed VB during acceleration is calculated by the following equation (4) '.
In equation (4) ′, the value of β ₂ × GX−γ ₂ is added as the estimated vehicle body speed VB (n) for each control cycle, which is the same as the calculation of equation (2). It is an integral calculation. VB (n) = VB (n-1) + (β ₂ × GX-γ ₂ ) (4) 'However, (β ₂ × GX-γ ₂ ) is a predetermined value GX6 set in advance. The following values shall be taken.

Then, in step S19, it is determined whether the estimated vehicle body speed VB (= VB ₂ ) has reached the vehicle body speed VBF, and if not, the next time the vehicle body speed is estimated, The estimated vehicle body speed VB _{2 obtained} in step S18 for adding β ₂ × GX−γ ₂ ) is used as the estimated vehicle body speed VB. Such an estimation operation is continued until the estimated vehicle body speed VB reaches the reference speed VBF in step S19.

If the estimated vehicle speed VB (= VB ₂ ) has reached the vehicle speed VBF, it is determined in step S22 that the deceleration slip state has ended, and the flag FLAG (2) is set.
Is reset to "0".

Thus, in the next vehicle body speed estimation, in step S20, the second wheel speed V3 from the bottom is calculated.
The estimated vehicle body speed VBF is defined as the estimated vehicle body speed VB,
This adoption continues until the determination in step S4 or S5 becomes YES.

If NO is determined in step S19, the flag FLAG (2) is reset to "0" in step S22, assuming that the deceleration slip state has ended, and the vehicle speed is estimated the next time. Is
In step S20, the estimated vehicle body speed VBF, which is the second wheel speed V3 from the bottom, is set as the estimated vehicle body speed VB.

As a result, the estimated vehicle body speed VB ₂ changes so that the inclination becomes smaller midway (after the lapse of time t ₁ ) as shown in FIG. 4, and the estimated vehicle body speed VB is greater than the actual vehicle body speed VBR. Although the value is close to the actual vehicle speed VBR, even if the driver does not loosen the accelerator during the slip, VBF = VB ₂ at a position close to the actual vehicle speed VBR.
Therefore, it is possible to properly determine the end of the wheel slip.

Further, even if the estimated vehicle body speed VB ₂ does not easily become equal to the estimated vehicle body speed VBF due to the changes in β and γ described above, that is, even if the slip end judging means 216h does not judge the slip end. , A state in which the wheel speed V3 is higher than the target speed VA to some extent (V ₀ or more) during traction control (V3 ≧ VA + V ₀ ).
If the time t has continued for t ₀ or more after the start of slip, the adoption of the estimated vehicle body speed VB ₂ is stopped, and the estimated vehicle body speed VBF corresponding to the wheel speed V3 is adopted as the estimated vehicle body speed VB. As a result, as shown in FIG. 7, for example, the problem that the slip end determination is not made despite the fact that the slip has actually ended is resolved, and the vehicle body speed VB can be accurately estimated.

Further, in the acceleration state, the value of the actual acceleration GX used as the data is clipped to the predetermined value GX ₅ (≧ 0) or more, and in the deceleration state, the value of the actual acceleration GX used as the data is the predetermined value GX ₆ Clipped below (≤ 0), so negative acceleration (deceleration) during acceleration slip
GX is input, or positive acceleration GX during deceleration slip
Is prevented, and the vehicle speed VB can be estimated with high accuracy.

By the way, in the present embodiment, β, γ (β ₁ ,
As described above, γ ₁ or β ₂ , γ ₂ ) is changed to a small value after a predetermined time from a value that is set to a large value, but conversely, at the beginning, β = 1 and γ = 0 are set. Even if the estimated vehicle speed VB ₂ is configured to increase with the lapse of the estimation start time, the estimated vehicle speed VB ₂ reliably approaches the estimated vehicle speed VBF in a region close to the actual vehicle speed VBR.

Therefore, even if the vehicle body speed VB is estimated using such a method, the vehicle speed can be estimated with high accuracy.

Further, in the present embodiment, even if only _one of β ₁ and γ ₁ is changed and the other is held constant, accurate vehicle speed estimation is performed in the same manner as described above.

During the traction control, V3 ≧ VA +
If the state of V ₀ continues for t ₀ hours or more after the start of slip,
It is possible to accurately estimate the vehicle speed only by changing β or γ as described above while omitting the time limitation of stopping the use of the estimated vehicle body speed VB ₂ .

Further, both β and γ are set to appropriate constant values, the end of slip is defined as a constant time from the start of slip, and the vehicle body speed VB ₂ at the time of slip is adopted for a limited time so that the vehicle body at the time of non-slip is not restricted. The vehicle speed can be estimated with a certain degree of accuracy simply by switching to adopting the speed VBF.

[0125]

As described above in detail, according to the vehicle body speed estimating apparatus for a four-wheel drive vehicle of the first aspect of the present invention, in the vehicle body speed estimating apparatus for estimating the vehicle body speed in the four-wheel drive vehicle, the wheel speed is estimated. Wheel speed detecting means for detecting the vehicle speed, a vehicle speed corresponding vehicle speed estimating means for estimating the vehicle speed based on the wheel speed, and an acceleration based on the wheel speed corresponding vehicle speed estimated by the wheel speed corresponding vehicle speed estimating means. The wheel speed corresponding acceleration calculating means, the actual acceleration detecting means for detecting the actual acceleration of the vehicle body, and the wheel speed corresponding acceleration and the actual acceleration are compared to determine whether or not the wheel starts slipping. When it is determined by the slip start determination means that the wheels have started slipping, the slip start determination means determines the vehicle speed based on the wheel speed corresponding to the wheel speed and the actual acceleration. A speed value obtained by time-integrating a value related to the actual acceleration is added to the vehicle speed corresponding to the wheel speed to calculate a vehicle speed, and an actual acceleration corresponding vehicle speed estimating means that uses the vehicle speed as an estimated vehicle speed; When the slip of the wheels is the slip accompanying the acceleration of the vehicle, the lower limit clipping is set so that the value of the actual acceleration used by the vehicle speed estimating means corresponding to the actual acceleration becomes 0 or a positive predetermined value or more. With this configuration, it is possible to accurately estimate the vehicle body speed when the wheels slip during acceleration, and to use appropriate vehicle body speed data for various controls such as vehicle running control, engine control, and steering control. It becomes possible to contribute to improvement of reliability of various controls.

According to the vehicle body speed estimating apparatus for a four-wheel drive vehicle of the present invention, the wheel speed detecting means for detecting the wheel speed in the vehicle body speed estimating apparatus for estimating the vehicle body speed in the four-wheel drive vehicle. And a wheel speed corresponding vehicle speed estimating means for estimating a vehicle speed based on the wheel speed, and a wheel speed corresponding acceleration for calculating acceleration based on the wheel speed corresponding vehicle speed estimated by the wheel speed corresponding vehicle speed estimating means. Calculating means, actual acceleration detecting means for detecting the actual acceleration of the vehicle body, slip start judging means for judging whether the wheel has started slipping by comparing the wheel speed corresponding acceleration and the actual acceleration, When it is determined by the slip start determination means that the wheel has started slipping, the actual acceleration is calculated based on the vehicle speed corresponding to the wheel speed and the actual acceleration obtained at this time. A speed value obtained by time-integrating this value is added to the wheel speed-corresponding vehicle body speed to calculate the vehicle body speed, and the vehicle body speed is used as an estimated vehicle speed. Is a slip associated with the deceleration of the vehicle, the upper limit clipping is set so that the value of the actual acceleration used by the actual acceleration-corresponding vehicle body speed estimating means becomes 0 or a predetermined negative value or more. It becomes possible to accurately estimate the vehicle body speed when the wheels slip during deceleration, so that proper vehicle body speed data can be used for various controls such as vehicle traveling control, engine control, steering control, etc. Therefore, it can contribute to the improvement of the reliability of various controls.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main configuration of a vehicle body speed estimation device for a four-wheel drive vehicle as one embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration of a drive system of a vehicle including a vehicle body speed estimation device for a four-wheel drive vehicle as one embodiment of the present invention.

FIG. 3 is a flowchart showing an operation of a main part of a vehicle body speed estimating device for a four-wheel drive vehicle as one embodiment of the present invention.

FIG. 4 is a graph showing a vehicle speed estimation example of a vehicle body speed estimation device for a four-wheel drive vehicle as one embodiment of the present invention.

FIG. 5 is a graph showing a characteristic of a correction coefficient in the vehicle body speed estimation device for a four-wheel drive vehicle as one embodiment of the present invention.

FIG. 6 is a graph showing a characteristic of a correction coefficient in a vehicle body speed estimation device for a four-wheel drive vehicle as one embodiment of the present invention.

FIG. 7 is a graph showing a vehicle speed estimation example of a vehicle body speed estimation device for a four-wheel drive vehicle as one embodiment of the present invention.

FIG. 8 is a graph showing a vehicle speed estimation example of a conventional vehicle body speed estimation device for a four-wheel drive vehicle.

FIG. 9 is a graph showing a vehicle speed estimation example of a conventional vehicle body speed estimation device for a four-wheel drive vehicle.

FIG. 10 is a graph showing a vehicle speed estimation example of a conventional vehicle body speed estimation device for a four-wheel drive vehicle.

FIG. 11 is a graph showing characteristics of acceleration detecting means of a conventional vehicle body speed estimating device for a four-wheel drive vehicle.

[Explanation of symbols]

 36 longitudinal acceleration sensor (actual acceleration detecting means) 40 to 46 wheel speed sensor (wheel speed detecting means) 216a wheel speed corresponding vehicle speed estimating means 216b, 216d filter 216e wheel speed corresponding acceleration calculating means 216f slip start judging means 216g actual acceleration corresponding Body speed estimating means 216h Slip end judging means 216i Estimated body speed setting means 216 Body speed estimating section

Claims (2)

[Claims] 1. A vehicle speed estimating apparatus for estimating a vehicle speed in a four-wheel drive vehicle, a wheel speed detecting means for detecting a wheel speed, and a vehicle speed corresponding vehicle speed estimating means for estimating a vehicle speed based on the wheel speed. A wheel speed corresponding acceleration calculating means for calculating an acceleration based on the wheel speed corresponding vehicle speed estimated by the wheel speed corresponding vehicle speed estimating means; an actual acceleration detecting means for detecting an actual acceleration of the vehicle; Slip start determination means for determining whether the wheel has started slipping by comparing the wheel speed-corresponding acceleration with the actual acceleration, and the slip start determination means obtained at this time when it is determined that the wheel has started slipping. A speed value obtained by time-integrating a value related to the actual acceleration based on the vehicle speed corresponding to the wheel speed and the actual acceleration is set to the vehicle speed corresponding to the wheel speed. An actual acceleration corresponding vehicle speed estimating means for adding the calculated vehicle speed to obtain the estimated vehicle speed, and an actual acceleration corresponding vehicle speed estimating means in the case where the slip of the wheels is a slip accompanying the acceleration of the vehicle. The vehicle body speed estimation device for a four-wheel drive vehicle is set so that the lower limit clipping is performed so that the value of the actual acceleration used in (3) becomes 0 or a positive predetermined value or more. 2. A vehicle speed estimating device for estimating a vehicle speed in a four-wheel drive vehicle, a wheel speed detecting means for detecting a wheel speed, and a vehicle speed corresponding vehicle speed estimating means for estimating a vehicle speed based on the wheel speed. A wheel speed corresponding acceleration calculating means for calculating an acceleration based on the wheel speed corresponding vehicle speed estimated by the wheel speed corresponding vehicle speed estimating means; an actual acceleration detecting means for detecting an actual acceleration of the vehicle; Slip start determination means for determining whether the wheel has started slipping by comparing the wheel speed-corresponding acceleration with the actual acceleration, and the slip start determination means obtained at this time when it is determined that the wheel has started slipping. A speed value obtained by time-integrating a value related to the actual acceleration based on the wheel speed corresponding vehicle speed and the actual acceleration is set to the wheel speed corresponding vehicle speed. An actual acceleration corresponding vehicle speed estimating means for adding the calculated vehicle speed to the estimated vehicle speed, and an actual acceleration corresponding vehicle speed estimating means when the wheel slip is a slip accompanying deceleration of the vehicle. The vehicle body speed estimation device for a four-wheel drive vehicle is set so that the upper limit clipping is performed so that the value of the actual acceleration used in (3) becomes 0 or a negative predetermined value or more.