JP4701941B2 - Vehicle body speed estimation device - Google Patents

Description

  The present invention relates to a vehicle body speed estimation device, and more particularly to a vehicle body speed estimation device in which braking / driving force is applied to each wheel and at least braking force is controlled independently of each other.

Various body speed estimation devices for vehicles such as automobiles have been proposed, and as one of the body speed estimation devices for four-wheel drive vehicles, for example, as described in Patent Document 1 below, 2. Description of the Related Art Conventionally, there has been known a vehicle body speed estimation device configured to estimate a vehicle body speed based on the minimum wheel speed of four wheels and to estimate a vehicle body speed based on the maximum wheel speed of the four wheels when the vehicle is decelerated. ing.
JP-A-10-141104

  In the conventional vehicle body speed estimation device as described above, there is no wheel to which braking force is applied when the vehicle is accelerated, and the wheel speed of any wheel is higher than the vehicle body speed, and conversely when the vehicle is decelerated. It is assumed that there is no wheel to which driving force is applied, and the wheel speed of any wheel is equal to or less than the vehicle body speed.

  However, for example, in a four-wheel drive vehicle, if the braking / driving force of each wheel is controlled independently of each other for the purpose of improving the running performance of the vehicle or controlling the running motion of the vehicle, the vehicle is in an acceleration state. Even if there is a wheel to which braking force is applied, the wheel speed of the wheel may be lower than the vehicle body speed, and conversely, there is a wheel to which driving force is applied even when the vehicle is in a deceleration state. However, the wheel speed of the wheel may be higher than the vehicle body speed.

  However, in the above-described conventional vehicle body speed estimation device, there is no wheel to which braking force is applied when the vehicle is accelerated, and the wheel speed of any wheel is higher than the vehicle body speed, and conversely when the vehicle is decelerated. There is no wheel to which driving force is applied, and it is assumed that the wheel speed of any wheel is equal to or less than the vehicle speed. Therefore, a wheel to which braking force is applied even when the vehicle is in an accelerated state When the wheel speed of the wheel is lower than the vehicle body speed, or there is a wheel to which driving force is applied even when the vehicle is in a deceleration state, and the wheel speed of the wheel is higher than the vehicle body speed. The vehicle speed cannot be estimated accurately.

  The present invention is configured to estimate the vehicle body speed based on the minimum wheel speed of the four wheels when the vehicle is accelerated, and to estimate the vehicle body speed based on the maximum wheel speed of the four wheels when the vehicle is decelerated. The main problem of the present invention is that the relationship between the slip ratio of the wheel and the friction coefficient of the road surface is a linear relationship. Therefore, by focusing on the fact that the relationship of the friction coefficient of the road surface to the slip ratio of the wheel is constant regardless of the braking / driving state of the wheel, the vehicle speed can be accurately estimated regardless of the braking / driving state of the wheel. is there.

  According to the present invention, the main problem described above is the vehicle body speed estimating device for a vehicle in which the braking / driving force is applied to each wheel and at least the braking force is controlled independently of each other according to the present invention. Means for detecting the wheel speed of each wheel, means for estimating the friction coefficient of the road surface for each wheel, and determining whether the braking / driving force of each wheel is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface And at least two wheels whose braking / driving force is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, the braking / driving force is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface. It is achieved by a vehicle body speed estimation device comprising vehicle body speed calculation means for calculating a vehicle body speed based on the wheel speeds of two wheels and a friction coefficient of a road surface.

  Further, according to the present invention, in order to effectively achieve the above main problem, in the configuration of claim 1, the braking / driving force of three wheels or more is less than the braking / driving force corresponding to the maximum friction coefficient of the road surface. Yes, when all the wheels are in the driving state or when all the wheels are in the braking state, the two wheels are configured to be the two wheels having the largest difference in wheel speed (configuration of claim 2) .

  Further, according to the present invention, in order to effectively achieve the above main problem, in the configuration of claim 1, the braking / driving force of three wheels or more is less than the braking / driving force corresponding to the maximum friction coefficient of the road surface. When there are two or more wheels in driving state and one wheel in braking state, one of the two wheels is a wheel having a lower wheel speed among wheels in driving state, and the two wheels The other of the wheels is configured to be a wheel in a braking state (structure of claim 3).

  Further, according to the present invention, in order to effectively achieve the above main problem, in the configuration of claim 1, the braking / driving force of three wheels or more is less than the braking / driving force corresponding to the maximum friction coefficient of the road surface. Yes, when the driving wheel is one wheel and the braking wheel is two or more wheels, one of the two wheels is a driving wheel and the other wheel is a braking wheel. It is comprised so that it may be a wheel with a higher wheel speed (structure of Claim 4).

  According to the present invention, in order to effectively achieve the above-mentioned main problems, in the configuration of claim 1, the braking / driving force of the four wheels is less than the braking / driving force corresponding to the maximum friction coefficient of the road surface. Yes, when two of the four wheels are in a driving state and the other two wheels are in a braking state, one of the two wheels is a wheel having a lower wheel speed of the two wheels in a driving state, and the two wheels The other of the wheels is configured to be a wheel having a higher wheel speed among the two wheels in a braking state (configuration of claim 5).

  According to the present invention, the means for estimating the friction coefficient of the road surface detects the ground contact load of each wheel in the configuration of the above-mentioned claims 1 to 5 in order to effectively achieve the above main problems. And a means for detecting the braking / driving force of each wheel, and configured to estimate a friction coefficient of the road surface based on a ratio of the braking / driving force to the ground load (configuration of claim 6).

  According to the present invention, in order to effectively achieve the main problems described above, in the configuration according to any one of claims 1 to 6, the determination means includes a change amount of wheel braking / driving force and a change amount of wheel speed. And determining whether the braking / driving force is less than or equal to the braking / driving force corresponding to the maximum friction coefficient of the road surface (configuration of claim 7).

  According to the present invention, in order to effectively achieve the main problems described above, in the configuration of claims 1 to 7, the braking / driving force exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface. When the braking / driving force exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface, the vehicle body speed calculation means calculates the wheel speed of the wheel at the reference time and the reference time from the reference time. The wheel speed of the wheel is calculated as the sum of the elapsed time and the change amount of the vehicle body speed calculated based on the longitudinal acceleration of the vehicle.

  When the braking / driving force is less than or equal to the braking / driving force corresponding to the maximum friction coefficient of the road surface, the relationship of the friction coefficient of the road surface to the slip ratio is substantially constant regardless of the slip ratio, and the slip ratio, the vehicle speed and the wheel There is also a certain relationship between speed. Therefore, as will be described in detail later, when the braking / driving force is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, the vehicle body speed can be estimated based on the wheel speeds of the two wheels and the friction coefficient of the road surface. .

  According to the configuration of claim 1, it is determined whether the braking / driving force of each wheel is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, and the braking / driving force corresponds to the maximum friction coefficient of the road surface. When there are at least two wheels that are less than the braking / driving force, the vehicle body speed is calculated based on the wheel speeds of the two wheels that are less than the braking / driving force corresponding to the maximum friction coefficient of the road surface and the friction coefficient of the road surface. Therefore, the vehicle body speed can be accurately estimated regardless of the braking / driving state of the wheels.

  Further, when the vehicle body speed is estimated based on the wheel speeds of the two wheels and the friction coefficient of the road surface according to the configuration of claim 1, the braking / driving force of three wheels or more is applied to the maximum friction coefficient of the road surface, as will be described in detail later. When all the wheels are in the driving state or all the wheels are in the braking state, the greater the difference between the wheel speed of the two wheels and the friction coefficient of the road surface, the more accurately the vehicle speed It is preferable that the difference between the wheel speeds of the two wheels is large.

  According to the configuration of claim 2, the braking / driving force of three or more wheels is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, and all the wheels are in a driving state or all the wheels are in a braking state. Sometimes, the two wheels are the two wheels with the largest difference in wheel speed, so that the vehicle speed can be accurately estimated even when all wheels are in driving state or all wheels are in braking state. Can do.

  Further, when the vehicle body speed is estimated based on the wheel speeds of the two wheels and the friction coefficient of the road surface according to the configuration of claim 1, the braking / driving force of three wheels or more is applied to the maximum friction coefficient of the road surface, as will be described in detail later. When there is a driving wheel and a braking wheel, the vehicle speed is estimated more accurately as the difference between the wheel speed of the two wheels and the friction coefficient of the road surface is smaller. Therefore, it is preferable that the difference between the wheel speeds of the two wheels is small.

  According to the configuration of claim 3, the braking / driving force of three or more wheels is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, the number of driven wheels is two or more, and the number of braked wheels is one. Sometimes, one of the two wheels is in the driving state, the wheel having the lower wheel speed, and the other of the two wheels is in the braking state, so that one wheel is in the driving state. The vehicle speed can be accurately estimated even when the other wheel is in a braking state, and the wheel having the higher wheel speed among the wheels in the driving state is set to one of the two wheels. The vehicle body speed can be accurately estimated based on the wheel speed and the friction coefficient of the road surface, which are smaller in comparison.

  According to the configuration of claim 4, the braking / driving force of three or more wheels is less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, the driving wheel is one wheel, and the braking wheel is two or more wheels. In some cases, one of the two wheels is a wheel in a driving state, and the other of the two wheels is a wheel having a higher wheel speed among wheels in a braking state, so that one wheel is in a driving state. The vehicle speed can be accurately estimated even when the other wheel is in the braking state, and the wheel with the lower wheel speed among the wheels in the braking state is set as the other of the two wheels. Accordingly, the vehicle body speed can be accurately estimated based on the wheel speed and the friction coefficient of the road surface, which have a smaller difference than the above.

  According to the configuration of claim 5, the braking / driving force of the four wheels is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, two of the four wheels are in a driving state, and the other two wheels are in a braking state. One of the two wheels is a wheel with a lower wheel speed of the two wheels in a driving state, and the other of the two wheels is a wheel with a higher wheel speed of two wheels in a braking state. So, if one of the two wheels is the driving wheel, the wheel with the higher wheel speed, or the other of the two wheels is the braking wheel, the wheel with the lower wheel speed. Compared to the case, the vehicle speed can be calculated based on the wheel speed and the friction coefficient of the road surface with a small difference, so that the vehicle speed can be estimated more accurately than in the case of other wheel combinations. it can.

  According to the configuration of the sixth aspect, the ground load of each wheel and the braking / driving force of each wheel are detected, and the friction coefficient of the road surface is estimated for each wheel based on the ratio of the braking / driving force to the ground load. Therefore, the friction coefficient of the road surface of each wheel can be accurately estimated.

  In general, when the braking / driving force of the wheel is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, the relationship between them is independent of the magnitude of the change amount of the wheel braking / driving force and the change amount of the wheel speed. When the braking / driving force of the wheel exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface, the relationship between the change amount of the wheel braking / driving force and the change amount of the wheel speed is substantially constant. Is not substantially constant.

  According to the configuration of the seventh aspect, whether the braking / driving force is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface based on the relationship between the change amount of the braking / driving force of the wheel and the change amount of the wheel speed. Therefore, it can be reliably and accurately determined whether or not the braking / driving force of the wheel is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface.

  According to the configuration of claim 8, when the braking / driving force exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface, the braking / driving force exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface. Using the time point as the reference time point, the wheel speed of the wheel is calculated as the sum of the wheel speed of the wheel at the reference time point and the amount of change in the vehicle speed calculated based on the elapsed time from the reference time point and the longitudinal acceleration of the vehicle. Therefore, the relationship between the amount of change in wheel braking / driving force and the amount of change in wheel speed is substantially constant even for wheels whose braking / driving force exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface. The assumed wheel speed can be calculated.

[Body speed estimation principle]
According to the present invention, as described above, the vehicle body speed is calculated based on the wheel speed of the two wheels whose braking / driving force is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface and the friction coefficient of the road surface. The principle of estimating the vehicle speed according to the invention will be described.

(1) When one wheel is in the driving state and the other wheel is in the braking state As is well known, the wheel speed of the wheel in the driving state is Va, the wheel speed of the wheel in the braking state is Vb, If the speed is Vv, the slip ratio Sa of the wheel in the driving state and the slip ratio Sb of the wheel in the braking state are expressed by the following equations 1 and 2, respectively.
Sa = (Va−Vv) / Va (1)
Sb = (Vb−Vv) / Vv (2)

Further, when the braking / driving force of the wheel is equal to or less than the braking / driving force corresponding to the maximum friction coefficient μamax (acceleration side) and μdmax (deceleration side) of the road surface, as shown in FIG. Since the relationship with the friction coefficient of the road surface may be considered to be linear, and the ratio of the friction coefficient of the road surface to the slip ratio of the wheels may be considered to be the same in both the driving state and the braking state, Assuming that the friction coefficient μa of the road surface for the wheel in the driving state and the friction coefficient μd of the road surface for the wheel in the braking state, the following is between the friction coefficient μa and μb of the road surface and the slip ratios Sa and Sb of the wheel: There is a relationship of the following formula 3.
μa / Sa = μb / Sb (3)

By substituting the above formulas 1 and 2 into the above formula 3, the vehicle body speed Vv when the vehicle moves forward and backward can be calculated by the following formulas 4 and 5, respectively.

Since the friction coefficient of the road surface is the ratio of the braking / driving force Fx of the wheel to the ground load of the wheel, if the ground load of the wheel in the driving state is Na and the ground load of the wheel in the braking state is Nb, the driving is performed. The road surface friction coefficient μa for the wheel in the state and the road surface friction coefficient μb for the wheel in the braking state can be calculated by the following equations 6 and 7, respectively.
μa = Fx / Na (6)
μb = Fx / Nb (7)

(2) When both wheels are in the driving state or braking state As is well known, assuming that the wheel speeds of the two wheels are V1 and V2, the slip ratios S1 and S2 of the two wheels in the driving state are respectively given by The slip ratios S1 and S2 of the two wheels in the braking state represented by 8 and 9 are represented by the following equations 10 and 11, respectively.

S1 = (V1-Vv) / V1 (8)
S2 = (V2-Vv) / V2 (9)
S1 = (V1-Vv) / Vv (10)
S2 = (V2-Vv) / Vv (11)

If the braking / driving force of the wheel is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, the relationship between the slip ratio of the wheel and the friction coefficient of the road surface may be considered to be linear. Assuming that the friction coefficient μ1 and μ2 of the road surface with respect to the wheels, the road surface is either in the case where the two wheels are in the driving state (FIG. 5A) or in the braking state (FIG. 5B). There is a relationship of the following formula 12 between the friction coefficients μ1 and μ2 of the wheel and the slip ratios S1 and S2 of the wheel.
μ1 / S1 = μ2 / S2 (12)

Substituting the above formulas 8 and 9 or the above formulas 10 and 11 into the above formula 12, rearranging the vehicle body speed Vv of the vehicle according to the following formula 13 regardless of whether the two wheels are in a driving state or a braking state. It can be calculated.
Vv = V1V2 (μ1−μ2) / (μ1V1−μ2V2) (13)

If the contact loads of the two wheels are N1 and N2, the road surface friction coefficients μ1 and μ2 for the two wheels can be calculated by the following equations 14 and 15, respectively.
μ1 = Fx / N1 (14)
μ2 = Fx / N2 (15)

(3) When the braking / driving force of the wheel exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface When the braking / driving force of the wheel exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface, Since the relationship between the braking / driving force of the wheel and the friction coefficient of the road surface is not linear, the vehicle body speed Vv cannot be calculated using the wheel speed of the wheel as it is. Therefore, when the braking / driving force of the wheel exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface, the wheel is assumed when the relationship between the braking / driving force of the wheel and the friction coefficient of the road surface is linear. The vehicle wheel speed Vv of the vehicle is calculated using the wheel speed.

  Assuming that the relationship between the braking / driving force of the wheel and the friction coefficient of the road surface is linear, the wheel speed of the wheel is the time when the braking / driving force of the wheel exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface. Can be considered as the sum of the wheel speed of the wheel at the reference time and the change in the vehicle speed from the reference time. The change in the vehicle speed from the reference time is the elapsed time and before and after the vehicle. Calculation is possible based on acceleration.

Therefore, if the wheel speed of the wheel at the reference time is Vwo, the elapsed time from the reference time is T, and the longitudinal acceleration of the vehicle is Gx, the braking / driving force of the wheel corresponds to the maximum friction coefficient of the road surface. If the force is exceeded, the wheel speed Vw of the wheel is calculated according to the following equation 16, and the vehicle body speed Vv of the vehicle is calculated using the wheel speed.

[Preferred embodiment of problem solving means]
According to one preferable aspect of the present invention, in the configuration of the first to eighth aspects, the vehicle is a four-wheel drive vehicle in which braking / driving force is applied to the four wheels and at least braking force is controlled independently of each other. It is comprised so that it may exist (the preferable aspect 1).

  According to another preferred embodiment of the present invention, in the configuration of the preferred embodiment 1 described above, the vehicle imparts driving force to the four wheels independently of each other and imparts braking force to the four wheels independently of each other. It is comprised so that it may be a four wheel drive vehicle (preferable aspect 2).

  According to another preferred embodiment of the present invention, in the configuration of the preferred embodiment 1, the vehicle is capable of independently applying braking force to the four wheels and controlling the driving force distribution of at least the left and right wheels. The vehicle is configured to be a four-wheel drive vehicle in which driving force is applied to the left and right wheels (preferred aspect 3).

  According to another preferred aspect of the present invention, in the configuration of the above-described claims 1 to 8 or the preferred aspects 1 to 3, the vehicle body speed calculation means is configured such that the braking / driving force and the slip ratio are substantially linear. When there are at least two wheels in the area, the vehicle speed is calculated based on the wheel speed of the two wheels and the friction coefficient of the road surface in which the braking / driving force and the slip ratio are in a substantially linear region. (Preferred aspect 4)

  According to another preferred aspect of the present invention, in the configuration of the above-described claims 1 to 8 or the preferred aspects 1 to 4, the vehicle body speed calculation means is configured such that the difference between the wheel speeds of the two wheels is greater than or equal to a reference value. In some cases, the vehicle body speed is calculated based on the wheel speeds of the two wheels and the friction coefficient of the road surface (preferred aspect 5).

  According to another preferred embodiment of the present invention, in the configuration of the above-mentioned claims 1 or 3 to 8 or the preferred embodiments 1 to 5, the vehicle body speed calculating means has one of the two wheels in a driving state and When the other of the two wheels is in a braking state, the vehicle body speed is calculated according to the above formula 4 or formula 5 (preferred aspect 6).

  According to another preferred aspect of the present invention, in the configuration of the above-mentioned claim 1 or 2 or 6 to 8 or the preferred aspects 1 to 5, the vehicle body speed calculation means is configured such that both of the two wheels are in a driving state or When in a braking state, the vehicle body speed is calculated according to the above equation 13 (preferred aspect 7).

  According to another preferred embodiment of the present invention, in the configuration of the above-mentioned claim 1 or 2 or 6 to 8 or the preferred embodiment 1 to 5 or 7, the vehicle body speed calculation means drives both wheels. When the vehicle is in a state or a braking state, the vehicle body speed is calculated according to a conventional method (preferred aspect 8).

  According to another preferred embodiment of the present invention, in the configuration of the above-described claims 1 to 8 or the preferred embodiments 1 to 8, the vehicle body speed calculation means is configured to use a difference in wheel speed as a reference for any of the four wheels. When it is less than the value, the vehicle speed is calculated according to the conventional method (preferred aspect 9).

  According to another preferred aspect of the present invention, in the configuration of claim 8, the vehicle body speed calculation means calculates the change amount of the vehicle body speed as an integrated value of the longitudinal acceleration of the vehicle from the reference time to the present. (Preferred embodiment 10).

  The present invention will now be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram showing a first embodiment of a vehicle body speed estimating device according to the present invention applied to an in-wheel motor type four-wheel drive vehicle.

  In FIG. 1, 10FL and 10FR respectively indicate left and right front wheels that are steering wheels, and 10RL and 10RR respectively indicate left and right rear wheels that are non-steering wheels. Electric motors 12FL and 12FR, which are in-wheel motors, are incorporated in the left and right front wheels 10FL and 10FR, respectively, and the left and right front wheels 10FL and 10FR are driven by the electric motors 12FL and 12FR. Similarly, electric motors 12RL and 12RR, which are in-wheel motors, are incorporated in the left and right rear wheels 10RL and 10RR, respectively, and the left and right front wheels 10RL and 10RR are driven by the electric motors 12RL and 12RR.

  During normal driving of the vehicle, electric power charged in a battery (not shown in FIG. 1) is supplied to each of the motors 12FL to 12RR through the drive circuit. Driving force is applied independently of each other. When the vehicle is decelerated, regenerative braking is performed by the electric motors 12FL to 12RR as necessary, and the electric power generated by the regenerative braking may be charged to the battery via the drive circuit.

  The driving force of the electric motors 12FL to 12RR is controlled by the driving force control electronic control device 16 based on the accelerator opening φ as the accelerator pedal depression amount not shown in FIG. .

  The friction braking force of the left and right front wheels 10FL, 10FR and the left and right rear wheels 10RL, 10RR is controlled by controlling the braking pressure of the corresponding wheel cylinders 22FL, 22FR, 22RL, 22RR by the hydraulic circuit 20 of the friction braking device 18. The Although not shown in the drawing, the hydraulic circuit 20 includes a reservoir, an oil pump, various valve devices, etc., and the braking pressure of each wheel cylinder is normally determined by the amount of depression of the brake pedal 24 and depression of the brake pedal 24 by the driver. The brake pedal is controlled by the driver by controlling the oil pump and various valve devices by the electronic control device 28 for controlling the braking force as necessary. Control is performed regardless of the amount of depression of 24.

  Although not shown in detail in FIG. 1, each of the driving force control electronic control device 16 and the braking force control electronic control device 28 includes a microcomputer and a driving circuit. The microcomputer includes, for example, a CPU, a ROM, And a RAM and an input / output port device, which are connected to each other via a bidirectional common bus.

  In addition to the signal indicating the accelerator opening φ from the accelerator opening sensor 14, the driving force control electronic control device 16 receives wheel speeds Vwi (i = fl, fr, rl, rr), a signal indicating the ground load Ni (i = fl, fr, rl, rr) of each wheel from the load sensors 32FL to 32RR, and a signal indicating the longitudinal acceleration Gx of the vehicle from the longitudinal acceleration sensor 34. . Also, the braking force control electronic control unit 28 has a signal indicating the master cylinder pressure Pm from the pressure sensor 36, and a corresponding wheel braking pressure (wheel cylinder pressure) Pbi (i = fl, fr, rl,) from the pressure sensors 38FL to 38RR. rr) is input. The driving force control electronic control device 16 and the braking force control electronic control device 28 exchange signals with each other as necessary.

  The electronic control unit 16 for controlling the driving force normally operates in accordance with a driving force control routine not shown in the drawing based on the accelerator opening φ that is the acceleration / deceleration operation amount of the driver, and the target driving force Fdti (i = fl, fr, rl, rr) are calculated, and the motors 12FL to 12RR are controlled so that the driving force Fdi of each wheel becomes the corresponding target driving force Fdti. The driving force control electronic control device 16 determines whether or not the traction control start condition is satisfied for each wheel according to a traction control routine not shown in the figure, and starts the traction control for any wheel. When the condition is satisfied, traction control known in the art for suppressing the drive slip of the wheel is performed until the traction control end condition is satisfied.

  On the other hand, the braking force control electronic control unit 38 normally controls the target braking pressure Pbti of each wheel based on the master cylinder pressure Pm that is the amount of braking operation by the driver according to a braking force control routine not shown in the figure. Then, control is performed so that the braking pressure Pbi of each wheel becomes the corresponding target braking pressure Pbti. The braking force control electronic control unit 38 determines whether or not the anti-skid control start condition is satisfied for each wheel in accordance with an anti-skid control routine not shown in the figure, and the anti-skid for any wheel is determined. When the control start condition is satisfied, anti-skid control known in the art for suppressing braking slip of the wheel is performed until the end condition for anti-skid control is satisfied.

  In addition, the driving force control electronic control unit 16 performs braking / driving force Fdbi (i = fl, fr, rl, rr) of each wheel based on the driving force Fdi and braking force Fbi of each wheel according to the flowchart shown in FIG. ) And the friction coefficient μi (i = fl, fr, rl, rr) of the road surface for each wheel based on the braking / driving force Fxi and the ground load Ni, and the road surface of two wheels with different wheel speeds Vwi. A vehicle body speed Vv is calculated based on the friction coefficient μi and the wheel speed Vwi, and the traction control and anti-skid control are executed using the vehicle body speed Vv.

  Next, the vehicle body speed estimation control in the illustrated embodiment 1 will be described with reference to the flowchart shown in FIG. The control according to the flowchart shown in FIG. 2 is started when the driving force control electronic control device 16 is activated, and is repeatedly executed every predetermined time until an ignition switch (not shown) is turned off. Is done.

  First, in step 10, a signal indicating the ground load Ni of each wheel detected by the load sensors 32FL to 32RR is read, and in step 20, it is supplied to the motors 12FL to 12RR according to the driving force control routine. The driving force Fdi of each wheel is calculated based on the driving current to be calculated, and the braking force Fbi of each wheel is calculated based on the braking pressure Pbi of each wheel input from the electronic control device 38 for braking force control. The braking / driving force Fxi of each wheel is calculated as the difference between the braking force Fbi and the braking force Fbi.

  In step 30, the road surface friction coefficient μi is calculated for each wheel as the ratio Fxi / Ni of the braking / driving force Fxi to the ground load Ni based on the braking / driving force Fxi and the ground load Ni of each wheel.

  In step 40, it is determined whether or not the relationship between the slip ratio Si of the wheel and the friction coefficient μi of the road surface is in a substantially linear region of the so-called μ-S diagram, that is, the braking / driving force of the wheel. It is determined whether or not Fxi is equal to or less than the maximum friction coefficient μmax of the road surface, and whether or not there are two or more wheels in which the relationship between Si and μi is in a substantially linear region, When a positive determination is made, the process proceeds to step 60, and when a negative determination is made, the process proceeds to step 50.

  Whether the relationship between the wheel slip ratio Si and the road friction coefficient μi is in a substantially linear region is determined, for example, by the ratio of the change amount of the wheel speed Vwi to the change amount of the braking / driving force Fxi of the wheel. It may be performed by determining whether or not it is within a predetermined range.

In step 50, the wheel speed Vwi is calculated based on the longitudinal acceleration Gx of the vehicle for a wheel in which the relationship between the wheel slip ratio Si and the road friction coefficient μi is not in a substantially linear region. For example, assuming that the relationship between the slip ratio Si of the wheel and the friction coefficient μi of the road surface has shifted from a substantially linear region to a non-linear region, the wheel speed of the wheel at the reference time is expressed as Vwoi. Assuming that the elapsed time from the reference time is T, the wheel speed Vwi is calculated according to the following equation 17 corresponding to the above equation 16.

  In step 60, it is determined whether or not there are one or more wheel combinations whose wheel speeds Vwi are different from each other by ΔVo (positive constant), that is, a set of wheel combinations whose slip ratios Si are different from each other by a reference value or more. If a positive determination is made, the process proceeds to step 80. If a negative determination is made, the vehicle body is determined in step 70 in any manner known in the art. The speed Vv is calculated, and then the process returns to step 10.

  In step 80, the wheels in the driving state (wheels where the braking / driving force Fxi is the driving force) and the wheels in the braking state (the braking / driving force Fxi is different from each other) are wheel combinations whose wheel speeds Vwi are different from each other by ΔVo (positive constant). It is determined whether or not there is a wheel (braking force). If a negative determination is made, the process proceeds to step 110. If an affirmative determination is made, the process proceeds to step 90.

  In step 90, the two wheel speeds Vwi used for calculating the vehicle body speed Vv and the two wheels for determining the friction coefficient μi of the road surface are specified, and the driving state of the two specified wheels is determined. The wheel speed Vwi is set to Va, and the wheel speed Vwi of the braked wheel is set to Vb.

  In general, when there are two or more combinations of wheels whose wheel speeds Vwi are different from each other by ΔVo, and there are a driving wheel and a braking wheel, the vehicle body speed Vv is the wheel speed of the driving wheel and the braking wheel. Since it is a value between the wheel speeds, the two wheels used for the calculation of the vehicle body speed Vv are preferably a driving wheel and a braking wheel with a small difference in wheel speed. For example, as shown in FIG. 8, if the wheel speed of the wheel B is higher than the wheel speed of the wheel C when there are the braked wheel A and the driven wheels B and C, the wheels A and C The estimated error ΔVvac of the vehicle body speed Vv estimated based on the wheel speed of the vehicle is smaller than the estimated error ΔVvab of the vehicle body speed Vv estimated based on the wheel speeds of the wheels A and B.

  On the other hand, when there are two or more combinations of wheels whose wheel speeds Vwi are different from each other by ΔVo and each of these wheels is in a driving state or when any of those wheels is in a driving state, the vehicle body speed Vv The two wheels used for calculation are preferably two wheels having a large difference in wheel speed. For example, as shown in FIG. 9, when there are driven wheels A, B, and C, the wheel speed of the wheel A is higher than the wheel speed of the wheel B, and the wheel speed of the wheel B is the wheel of the wheel C. If it is higher than the speed, the estimation error ΔVvac of the vehicle body speed Vv estimated based on the wheel speeds of the wheels A and C is larger than the estimation error ΔVvab of the vehicle body speed Vv estimated based on the wheel speeds of the wheels A and B. small.

  Therefore, in step 90, when the wheel speed Vwi is a set of combinations of wheels different from each other by ΔVo, the two wheels used for the calculation of the vehicle body speed Vv are determined as those wheels. In addition, when there are two or more combinations of wheels whose wheel speeds Vwi are different by ΔVo or more, two or more wheels are in the driving state, and one wheel is in the braking state, the two used for calculation of the vehicle body speed Vv are used. The wheel is determined as a wheel having a lower wheel speed and a braked wheel among the driven wheels.

  Further, when there are two or more combinations of wheels whose wheel speeds Vwi are different from each other by ΔVo, one wheel is in the driving state, and two or more wheels in the braking state, the two used for calculating the vehicle body speed Vv are used. The wheel is determined as the wheel having the higher wheel speed among the driving wheel and the braking wheel. Furthermore, when there are two or more combinations of wheels whose wheel speeds Vwi are different by ΔVo or more, two wheels are used in the driving state, and two wheels are in the braking state, two wheels used for calculation of the vehicle body speed Vv are used. Are determined as the wheel with the lower wheel speed of the two wheels in the driving state and the wheel with the higher wheel speed of the two wheels in the braking state.

  In step 100, for example, the traveling direction of the vehicle is determined based on a shift position detected by a shift position sensor not shown in FIG. 1, and the two wheels identified in step 90 are determined. The road surface friction coefficients are μa and μb, respectively, and the vehicle body speed Vv is calculated according to the above formula 4 when the vehicle moves forward based on the wheel speeds Va and Vb and the road surface friction coefficients μa and μb. The vehicle body speed Vv is calculated.

In step 110, the two wheel speeds Vwi used for calculating the vehicle body speed Vv and the two wheels for determining the road friction coefficient μi are the wheels with the highest wheel speed Vwi and the wheels with the lowest wheel speed Vwi. The wheel speed Vwi of the wheel with the higher wheel speed of the two specified wheels is set to V1, and the wheel speed Vwi of the wheel with the lower wheel speed is set to V1.
Set to 2.

  In step 120, the road surface friction coefficients for the two wheels specified in step 110 are μ1 and μ2, respectively, and the wheel speeds V1 and V2 and the road surface friction coefficients μ1 and μ2 are used in accordance with equation 13 above. The vehicle body speed Vv is calculated.

  Thus, according to the illustrated embodiment 1, the braking / driving force Fxi of each wheel is calculated in step 20, the road friction coefficient μi is calculated for each wheel in step 30, and Si and When it is determined that there are no more than two wheels in which the relationship of μi is in a substantially linear region, in step 50, the relationship between the slip ratio Si of the wheel and the friction coefficient μi of the road surface is in a substantially linear region. The wheel speed Vwi is calculated based on the longitudinal acceleration Gx of the vehicle with no wheels.

  In step 60, it is determined that there are one or more combinations of wheels whose wheel speeds Vwi are different from each other by ΔVo or more. In step 80, a combination of wheels whose wheel speeds Vwi are different from each other by ΔVo or more is in a driving state and a braking state. If it is determined that there are two wheels, the two wheels for determining the two wheel speeds Vwi and the road friction coefficient μi used for the calculation of the vehicle body speed Vv are identified in step 90. The vehicle body speed Vv is calculated on the basis of the wheel speed Va of the driven wheel and the road friction coefficient μa, the wheel speed Vb of the braked wheel and the road friction coefficient μb.

  Therefore, according to the first embodiment shown in the drawing, even in a situation where the four wheels are mixed with the driving wheel and the braking wheel, in other words, the wheel to which the braking force is applied even when the vehicle is in the driving state. When the wheel speed of the wheel is lower than the vehicle body speed, or there is a wheel to which driving force is applied even when the vehicle is in a braking state, and the wheel speed of the wheel is higher than the vehicle body speed. In addition, the vehicle body speed Vv can be calculated reliably and accurately.

  For example, FIG. 6 shows a situation where the left front and rear wheels are in a braking state, the right front and rear wheels are in a driving state, and the vehicle is in an accelerating state. The wheel speed Vwfl of the left front wheel is larger than the wheel speed Vwrl of the left rear wheel, the wheel speed Vwfr of the right front wheel is larger than the wheel speed Vwrr of the right rear wheel, and the vehicle is in an accelerated state as shown in FIG. The vehicle body speed Vv is assumed to be higher than the wheel speed Vwfl of the left front wheel and lower than the wheel speed Vwrr of the right rear wheel.

  In the above-described conventional vehicle body speed estimation device, the vehicle body speed Vv is estimated to be the same value as the wheel speed Vwrl of the left rear wheel in the above situation, and the vehicle body speed Vv is accurately estimated. I can't.

  On the other hand, according to the first embodiment shown in the drawing, as described above, the wheel speed Vwfl of the second lowest left front wheel, the wheel speed Vwrr of the second highest right rear wheel, and the friction coefficient of the road surface of these wheels are as described above. Since the vehicle body speed Vv is calculated, the vehicle body speed Vv can be accurately estimated.

  Further, according to the first embodiment shown in the figure, even if it is determined in step 60 that there is at least one combination of wheels whose wheel speeds Vwi are different from each other by ΔVo, the wheel speeds Vwi are different from each other by ΔVo in step 80. If it is determined that there is no driving wheel and no braking wheel in the wheel combination, in step 110, two wheel speeds Vwi and a road surface friction coefficient μi used for calculating the vehicle body speed Vv are determined. The two wheels are identified as the wheel having the highest wheel speed Vwi and the wheel having the lowest wheel speed Vwi. In step 120, the wheel speeds V1 and V2 of these two wheels and the friction coefficients μ1 and μ2 of the road surface are set. Based on this, the vehicle body speed Vv is calculated.

  Therefore, according to the first embodiment shown in the figure, the vehicle body speed Vv can be calculated reliably and accurately regardless of the conventional vehicle body speed estimation method even when all four wheels are in the driving state or the braking state. it can.

  FIG. 3 is a flowchart showing a vehicle body speed calculation control routine in Embodiment 2 of the vehicle body speed estimation apparatus according to the present invention. In FIG. 3, the same step number as the step number shown in FIG. 2 is assigned to the same step as the step shown in FIG.

  In the second embodiment, steps 10 to 30 and steps 50 to 120 are executed in the same manner as in the first embodiment. When step 30 is completed, the slip ratio Si of the wheel and the road surface are determined in step 45. It is determined whether or not there is a wheel whose friction coefficient μi is in the non-linear region of the so-called μ-S diagram. If a negative determination is made, the process proceeds to step 60. If an affirmative determination is made, the process proceeds to step 60. Proceed to 50.

  Thus, according to the second embodiment shown in the figure, as in the first embodiment, the vehicle body speed Vv can be reliably and accurately adjusted even in a situation where four wheels are mixed with a driven wheel and a braked wheel. Even in a situation where all four wheels are in a driving state or a braking state, the vehicle body speed Vv can be calculated reliably and accurately regardless of the conventional vehicle body speed estimation method.

  In particular, according to the illustrated embodiment 2, if it is determined in step 45 that there is a wheel in which the relationship between the slip ratio Si of the wheel and the friction coefficient μi of the road surface is in the non-linear region of the so-called μ-S diagram. At 50, the wheel speed Vwi is calculated based on the longitudinal acceleration Gx of the vehicle for the wheel, so that at least one pair of wheel speeds is not less than the reference value regardless of the wheel speed of the four wheels. The vehicle body speed Vv can always be calculated based on the wheel speeds of the two wheels suitable for calculating the vehicle body speed of the four wheels and the friction coefficient of the road surface.

  According to the first and second embodiments shown in the figure, in step 90, there are three or more wheel combinations in which the wheel speed Vwi differs from each other by ΔVo or more, there are a driving wheel and a braking wheel, and there is a driving state or braking. When the number of wheels in the state is one, the two wheels used for the calculation of the vehicle body speed Vv are determined to be two wheels having a small difference in wheel speed, and there are four wheels whose wheel speeds Vwi are different from each other by ΔVo, When there are two wheels in the driving state and two wheels in the braking state, the two wheels used for the calculation of the vehicle body speed Vv are the wheel having the lower wheel speed of the two driving wheels and the braking. Of the two wheels in the state, the wheel with the higher wheel speed is determined.

  Therefore, when there are three or more wheel combinations in which the wheel speed Vwi is different by ΔVo or more, there is a driving wheel and a braking wheel, and the driving or braking wheel is a single wheel, the vehicle body speed Vv is calculated. When the two wheels used in the vehicle are determined to be two wheels having a large difference in wheel speed, there are four wheels whose wheel speeds Vwi are different from each other by ΔVo or more, the driven wheels are two wheels, and the braking state is In the case where the wheels are two wheels, the two wheels used for the calculation of the vehicle body speed Vv are the wheel with the higher wheel speed of the two wheels in the driving state and the wheel speed of the two wheels with the braking state. The vehicle speed Vv can be calculated more accurately than when the lower wheel is determined.

  Further, according to the first and second embodiments shown in the drawings, in any of the situation where the four wheels are in a state of being mixed with the driven wheels and the braked wheels, and all of the four wheels are in the driven state or the braking state, When the wheel speed difference between the two wheels is also less than the reference value, steps 80 to 120 are not executed, and the vehicle body speed Vv is calculated at step 70 in any manner known in the art. The wheel speed of the two wheels and the friction of the road surface are small compared to the case where the steps 80 to 120 are executed even in the situation where the difference between the wheel speeds of both wheels is less than the reference value. It is possible to reliably prevent deterioration of the estimation accuracy of the vehicle body speed due to the calculation of the vehicle body speed based on the coefficient.

  Further, according to the first and second embodiments shown in the drawings, when a negative determination is made at step 40 or when an affirmative determination is made at step 45, the slip ratio Si of the wheel is determined at step 50. And the wheel speed Vwi is calculated on the basis of the longitudinal acceleration Gx of the vehicle for wheels whose relationship between the road surface friction coefficient μi and the road surface friction coefficient μi are not in a substantially linear region, compared with the case where the wheel speed Vwi is not calculated. Thus, the possibility of estimating the vehicle body speed Vv in steps 90 and 100 or steps 110 and 120 can be increased.

  Although the present invention has been described in detail with reference to specific embodiments, the present invention is not limited to the above-described embodiments, and various other embodiments are possible within the scope of the present invention. It will be apparent to those skilled in the art.

  For example, in the first and second embodiments described above, the motors 12FL to 12RR are in-wheel motors, but the motor generator may be provided on the vehicle body side, and the driving source of each wheel is an engine other than the motor. Even if it is a drive source, a drive source is a drive source common to at least two wheels, and the drive force of a drive source may be transmitted to each wheel so that drive force distribution control is possible.

  In the first and second embodiments described above, when all four wheels are in a driving state or a braking state, as long as the difference between at least one set of wheel speeds is equal to or greater than a reference value, the steps 110 and 120 are performed. The vehicle body speed Vv is calculated based on the wheel speed of the two wheels and the friction coefficient of the road surface, but at least one set of wheel speeds is greater than or equal to a reference value, but all four wheels are driven. Alternatively, when the vehicle is in a braking state, the vehicle body speed Vv may be corrected so as to be calculated in an arbitrary manner known in the art.

  In the first and second embodiments described above, it is related to whether the four wheels are in a state where a wheel in a driving state and a wheel in a braking state are mixed, or whether all four wheels are in a driving state or a braking state. The reference value for determining whether or not the difference between at least one pair of wheel speeds is greater than or equal to the reference value is the same, but this reference value is a situation where four wheels are mixed with a driving wheel and a braking wheel. Or different values depending on whether all four wheels are in a driving state or a braking state.

  In the first and second embodiments, the ground load Ni of each wheel used for calculating the friction coefficient μi of the road surface for each wheel is detected by the load sensors 32FL to 32RR. As for the ground load Ni of each wheel, for example, the amount of change ΔNi of the ground load of each wheel is calculated based on the longitudinal acceleration and lateral acceleration of the vehicle, and the static ground load Noi and the ground load of each wheel in the stationary state of the vehicle are calculated. You may obtain | require as a sum with variation | change_quantity (DELTA) Ni.

  In the first and second embodiments described above, the driving force Fdi of each wheel is calculated based on the driving current supplied to the motors 12FL to 12RR, and each wheel input from the braking force control electronic control unit 38 is calculated. The braking force Fbi of each wheel is calculated based on the braking pressure Pbi, and the braking / driving force Fxi of each wheel is calculated as the difference between the driving force Fdi and the braking force Fbi. In the case of a common drive source between the two wheels, the drive force Fdi of each wheel may be calculated based on the drive force (torque) of the drive source and the distribution ratio of the drive force between the wheels.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows Example 1 of the vehicle body speed estimation apparatus by this invention applied to the wheel-in-motor type four-wheel drive vehicle. 3 is a flowchart showing a vehicle body speed estimation control routine in the first embodiment. 7 is a flowchart showing a vehicle body speed estimation control routine in Embodiment 2 of the vehicle body speed estimation apparatus according to the present invention. It is a graph which shows the relationship between the slip ratio of a wheel, and the friction coefficient of a road surface about the case where a wheel exists in a drive state and a braking state. It is a graph which shows the relationship between the road surface friction coefficients (micro | micron | mu) 1 and (micro | micron | mu) 2, and the slip ratios S1 and S2 of a wheel about the case where two wheels are in a drive state (A) and the case where it is in a braking state (B). It is explanatory drawing which shows the condition where the left front-rear wheel is in a braking state, the right front-rear wheel is in a driving state, and the vehicle is in a driving state. It is a graph which shows the relationship between the wheel speed Vwi of each wheel and the vehicle body speed Vv in the condition shown by FIG. It is a graph which shows the estimation error of the vehicle body speed Vv about the case where there is one wheel in a braking state and two wheels in a driving state. It is a graph which shows the estimation error of the vehicle body speed Vv about the case where there are three wheels in the drive state.

Explanation of symbols

12FL to 12RR motor generator 14 accelerator opening sensor 16 electronic control device for driving force control 18 friction braking device 24 brake pedal 28 electronic control device for braking force control 30FL to 30RR wheel speed sensor 32FL to 32RR load sensor 34 longitudinal acceleration sensor 36 , 38FL ~ 38RR Pressure sensor

Claims (8)

  A vehicle body speed estimation device in which braking / driving force is applied to each wheel and at least braking force is controlled independently of each other, and means for detecting the wheel speed of each wheel, and estimating a friction coefficient of a road surface for each wheel Means for determining whether the braking / driving force of each wheel is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, and the braking / driving force corresponding to the maximum friction coefficient of the road surface When there are at least two wheels below, the vehicle speed is calculated based on the wheel speed of the two wheels whose braking / driving force is less than the braking / driving force corresponding to the maximum friction coefficient of the road surface and the friction coefficient of the road surface And a vehicle body speed estimating device.   When the braking / driving force of three or more wheels is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, when all the wheels are in the driving state or when all the wheels are in the braking state, the two wheels The vehicle body speed estimation device according to claim 1, wherein the two wheels have the largest difference.   When the braking / driving force of three or more wheels is less than or equal to the braking / driving force corresponding to the maximum friction coefficient of the road surface, when the driving wheel is two or more wheels and the braking wheel is one wheel, one of the two wheels is driven. The vehicle body speed estimation device according to claim 1, wherein a wheel speed of a wheel in a state is lower, and the other of the two wheels is a wheel in a braking state.   When the braking / driving force of three or more wheels is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, one of the two wheels is driven when the driving wheel is one wheel and the braking wheel is two or more wheels. 2. The vehicle body speed estimating device according to claim 1, wherein the other of the two wheels is a wheel having a higher wheel speed among the wheels in a braking state.   When the braking / driving force of the four wheels is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface, when two of the four wheels are in a driving state and the other two wheels are in a braking state, one of the two wheels is 2. The wheel according to claim 1, wherein one of the two wheels in a driving state is a wheel having a lower wheel speed, and the other of the two wheels is a wheel having a higher wheel speed among two wheels in a braking state. Vehicle body speed estimation device.   The means for estimating the friction coefficient of the road surface includes a means for detecting a ground contact load of each wheel and a means for detecting a braking / driving force of each wheel, and the friction of the road surface based on a ratio of the braking / driving force to the ground load. 6. The vehicle body speed estimation device according to claim 1, wherein a coefficient is estimated.   The determination means determines whether the braking / driving force is equal to or less than the braking / driving force corresponding to the maximum friction coefficient of the road surface based on the relationship between the change amount of the braking / driving force of the wheel and the change amount of the wheel speed. The vehicle body speed estimation device according to claim 1, wherein the vehicle body speed estimation device is a vehicle body speed estimation device. When the braking / driving force exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface, the vehicle speed calculation means is defined with the time when the braking / driving force exceeds the braking / driving force corresponding to the maximum friction coefficient of the road surface as a reference time point. Calculates the wheel speed of the wheel as the sum of the wheel speed of the wheel at the reference time and the amount of change in vehicle speed calculated based on the elapsed time from the reference time and the longitudinal acceleration of the vehicle. The vehicle body speed estimation device according to claim 1, wherein the vehicle body speed estimation device is a vehicle body speed estimation device.

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