JP5263068B2 - Vehicle slip determination device - Google Patents

Description

  The present invention relates to a device that performs vehicle body speed estimation and wheel slip determination (determination of whether or not a wheel is in a slip state).

  When the wheel tire force exceeds the limit (maximum friction circle) determined by the friction coefficient of the road surface and the ground contact load during braking / driving of a vehicle such as an automobile, the wheel is The vehicle loses gripping force on the road surface, falls into a slip state, and the acceleration / deceleration performance, turning performance, and behavioral stability of the vehicle decrease. Therefore, a vehicle is often equipped with a device for determining whether or not one of the wheels is slipping (slip determination), and the wheel is slipping (or may be). ), Control for adjusting braking / driving slip such as traction control (TRC) and ABS control is executed.

  The slip state of the wheel is detected by determining that the wheel speed is excessively higher than the vehicle body speed. Therefore, in order to perform the slip determination, it is necessary to detect or acquire the vehicle body speed value in real time. In this regard, in ordinary vehicles, a ground speed sensor that can directly detect the vehicle body speed is not often provided. Therefore, in the case of a two-wheel drive vehicle having driven wheels, The wheel speed is referred to. However, in the case of a vehicle in which all wheels are operated as drive wheels, such as a four-wheel drive vehicle, the slip ratio or slip amount may be excessive at any wheel during all-wheel drive. The wheel speed of this wheel cannot be referred to as the vehicle speed as it is. Therefore, when acquiring the vehicle body speed value during acceleration / deceleration of such a vehicle (in a state where braking / driving torque is applied to all the wheels of the vehicle), for example, the lowest value of the wheel speeds of all the wheels ( Appropriate among the vehicle speed value estimated from the longitudinal acceleration of the vehicle (at the time of acceleration) or the maximum value (when the vehicle is decelerated) (for example, given by [preceding vehicle speed] + [longitudinal acceleration] × [time]). Is selected as an estimated value of the vehicle body speed (see, for example, Patent Document 1).

JP-A-8-43417 JP 2000-52964 A

  In the vehicle wheel slip determination as described above, there are some problems to be improved as described below.

(I) When calculating the vehicle body speed value (or its candidate value) from the longitudinal acceleration of the vehicle, as the longitudinal acceleration value, the time differential value of the wheel speed value detected by the wheel speed sensor or the detected value of the longitudinal G sensor Can be considered. In this regard, the wheel speed differential value obtained from the output value of the wheel speed sensor is likely to include an error component in a high frequency band due to a road step or a seam, and the detected values of the front and rear G sensors are road surface gradient, temperature drift, etc. It is easy to include the error component of the low frequency band by. Therefore, in the calculation of the vehicle body speed value (or its candidate value), the component obtained by removing the high frequency component from the wheel speed differential value using the low-pass filter and the front-rear G sensor detection value using the high-pass filter. For example, a longitudinal acceleration value given by superimposing a component obtained by removing a low frequency component from the signal is used (see Patent Document 2). However, when the grip force between the wheel and the road surface is lost and the wheel slips, the wheel speed differential value obtained by removing the high frequency error component from the two values giving the longitudinal acceleration value is no longer accurate. The vehicle's longitudinal acceleration component is no longer represented. That is, while the wheel is in the slip state, the component obtained by removing the high frequency component from the wheel speed differential value using the low-pass filter includes an error, and is thus estimated from the longitudinal acceleration of the vehicle. The vehicle body speed value (or its candidate value) may deviate from the actual vehicle body speed value. In fact, when the wheel is in a slip state, the wheel speed differential value increases because the wheel rotational speed is likely to change, and as a result, the estimated vehicle body speed approaches the wheel speed excessively, and the slip state is determined. It has been found that the time period or opportunity to be lost is lost (see embodiment section).

(Ii) In the slip determination as described above, the vehicle body speed estimated value is the wheel speed value that is the most delayed among the wheel speeds of the four wheels, that is, when the vehicle is accelerated, The wheel speed that is determined by using the lowest value among them, the highest value among the wheel speeds of all wheels at the time of deceleration of the vehicle, and compared with the estimated vehicle speed is the wheel speed value that is most changing, That is, the highest value of the wheel speeds of all the wheels is used when the vehicle is accelerated, and the lowest value of the wheel speeds of all the wheels is used when the vehicle is decelerated. Therefore, it is necessary to determine whether the vehicle is accelerating or decelerating and switching the wheel speed used for slip determination as appropriate. Become. Of course, the determination can be made for a while by depressing the brake pedal or the accelerator pedal, but there is a state that cannot be determined by the presence or absence of the depression of the pedal, such as a deceleration state by an engine brake.

(Iii) The above vehicle slip determination is based on the estimated change in the vehicle speed derived from the most delayed wheel speed value of all the wheel speeds and the most advanced change in the wheel speeds of all the wheels. When the difference between the vehicle wheel speed value and the wheel speed value is determined, it is determined that the difference between the vehicle body speed estimated value and the wheel speed value is the result of the determination of the outer wheel and the inner wheel during turning of the vehicle. May vary depending on the wheel speed difference. That is, during the turning of the vehicle, the difference between the vehicle body speed estimated value and the wheel speed value changes by the amount of the wheel speed difference between the turning outer wheel and the turning inner wheel, and the slip determination may be inaccurate.

  Thus, an object of the present invention is to provide a device capable of solving the problem in vehicle slip determination as described above and performing slip determination with higher accuracy.

  ADVANTAGE OF THE INVENTION According to this invention, the slip determination apparatus of the vehicle improved so that a vehicle body speed value can be estimated more accurately and a determination result can be obtained more accurately is provided.

  In one aspect, a vehicle slip determination device according to the present invention includes a first wheel speed value obtained by a first wheel speed sensor, and a vehicle body speed estimated value determined based on a vehicle body longitudinal acceleration value. And a slip determination unit for determining the slip state of the wheel based on the above. When it is determined by the slip determination unit that none of the wheels is in the slip state, the vehicle body longitudinal acceleration value is determined from the differential value of the second wheel speed value obtained by the second wheel speed sensor. The value obtained by adding the value obtained by removing the frequency component higher than the predetermined frequency and the value obtained by removing the frequency component lower than the predetermined frequency from the acceleration value obtained by the longitudinal acceleration sensor is used. It is done. However, when any of the wheels is determined to be in the slip state by the slip determination unit, the value obtained by removing the frequency component lower than the predetermined frequency from the acceleration value obtained by the longitudinal acceleration sensor is the vehicle body. It is used as a longitudinal acceleration value. In such a configuration, the first wheel speed value and the second wheel speed value used for calculating the vehicle body speed estimated value are wheel speed values of wheels different from each other. The first wheel speed value is the wheel speed value of the most rapidly changing wheel speed value of each wheel, and the second wheel speed value is the most delayed of the wheel speed value of each wheel. It should be understood that the wheel speed value is not limited to this. In the above configuration, since the wheel speed increases during acceleration, the "wheel speed value with the most change" is the highest value among the wheel speeds of the four wheels. The “wheel speed value with a delayed change” is the minimum value of the wheel speeds of the four wheels. On the other hand, since the wheel speed is reduced during deceleration, the "wheel speed value with the most change" is the minimum value of the wheel speeds of the four wheels. The “value” is the maximum value among the wheel speeds of the four wheels. The “predetermined frequency” is lower than the frequency of (most of) the error component superimposed on the high frequency band of the wheel speed sensor output value and is superimposed on the low frequency band of the output value of the longitudinal acceleration sensor ( The frequency may be set as appropriate by the device designer.

  As already described, the wheel speed differential value obtained from the wheel speed sensor output value can contain many error components in the high frequency band, and the detection value of the longitudinal acceleration sensor can contain many error components in the low frequency band. When the tire surface is securely gripping the road surface, that is, when the wheel is in the grip state, the vehicle speed sensor obtains a highly accurate vehicle longitudinal acceleration value for estimating the vehicle speed value used for slip determination. It is obtained by adding the value obtained by removing the high frequency error component from the differential value of the wheel speed value and the value obtained by removing the low frequency error component from the acceleration value obtained by the longitudinal acceleration sensor. It is conceivable to use a value (Patent Document 2). However, when the tire surface is slipping with respect to the road surface, that is, when the wheel is in a slip state, the wheel can be rotated regardless of the progress of the vehicle body. Even after the error component is removed, the vehicle body longitudinal acceleration value can deviate.

  Therefore, in the present invention, as described above, when it is determined that the wheel is in the slip state, the vehicle body longitudinal acceleration value is obtained by removing the low frequency error component from the acceleration value obtained by the longitudinal acceleration sensor. Using the value, the configuration of the apparatus is modified so that the output of the wheel speed sensor of the wheel in the slip state is not reflected in the vehicle body longitudinal acceleration value. In this case, since the component of the wheel speed differential value is not added to the vehicle body longitudinal acceleration value and the low frequency component of the acceleration value of the longitudinal acceleration sensor is removed, the low frequency component of the vehicle body longitudinal acceleration value is relatively attenuated. However, when the wheel is in a slip state, the change in the vehicle body speed is small, so that the amount of deviation between the true vehicle body longitudinal acceleration value and the vehicle body longitudinal acceleration value in which the low frequency component is attenuated is small. In addition, since the period during which the wheel is in a slip state is generally relatively short, the effect of the low frequency component of the vehicle body longitudinal acceleration value on the estimated vehicle speed is (the wheel speed of the slipped wheel). It has been experimentally confirmed that the accuracy of the estimated vehicle speed is improved by the configuration of the present invention (as compared to the case where an error in the differential value is used). Irradiation).

  In the embodiment, the vehicle body speed estimated value is obtained by adding a value obtained by multiplying the vehicle body longitudinal acceleration value by a predetermined time to the previous value of the vehicle body speed estimated value and a time integral value of the vehicle body longitudinal acceleration value. It may be determined based on the second wheel speed value. In more detail, when the second wheel speed value is within a range determined by a predetermined range from the time integral value of the vehicle body longitudinal acceleration value, the second wheel speed value is selected as the vehicle body speed estimated value. When the second wheel speed value is outside the value range, the boundary value in the value range closest to the second wheel speed value may be selected as the estimated vehicle speed value.

  In another aspect, the slip determination device of the present invention includes, in another aspect, a first wheel speed value that changes most among wheel speed values of each wheel of the vehicle and a wheel speed value of each wheel of the vehicle. The slip state of the wheel is determined on the basis of the estimated vehicle body speed value determined based on the second wheel speed value with the most delay, and the wheel speed difference between the turning outer wheel and the turning inner wheel of the vehicle. Alternatively, the wheel slip of the vehicle based on the wheel speed value of the wheel speed value of each wheel of the vehicle that is delayed in change from at least one wheel speed value and the wheel speed difference of the inner turning outer wheel of the vehicle. The state may be determined.

  As already mentioned, in the apparatus that is the subject of the present invention, basically, the tire such as the slip amount obtained from the difference between the first wheel speed value that is most advanced and the estimated vehicle speed When the slip state of the wheel is determined by detecting that an arbitrary index amount indicating the degree of slip of the vehicle is excessive, the index amount such as the slip amount is determined by the wheel speed difference of the outer and inner wheels during the turning of the vehicle. If it changes, it will become impossible to determine the slip state of a wheel correctly. Therefore, in order to solve such a problem, in the present invention, in addition to the wheel speed value and the vehicle body speed estimation value, the wheel speed difference of the inner ring outside the turning is also taken into account, and the slip state of the wheel is more accurately determined. An attempt is made to determine. More specifically, for example, in the apparatus of the present invention, the absolute value of the difference between the first wheel speed value and the vehicle body speed estimated value is turned from the wheel speed value of the outer turning wheel calculated from the lateral acceleration of the vehicle. When the value obtained by subtracting the wheel speed value of the inner ring (the wheel speed difference of the inner ring outside the turning) is larger than the value added to the allowable slip amount determined based on the estimated vehicle body speed, it is determined that the wheel is in the slip state. It may be. In this configuration, the wheel speed difference between the inner and outer wheels of the turning is not based on the wheel speed values of the outer and inner wheels that may be in a slip state, but the wheel speed of the inner and outer wheels that are calculated from the lateral acceleration. Therefore, the difference between the wheel speeds of the turning inner and outer wheels does not reflect the degree of tire slip, and therefore, the influence of the wheel speed difference of the turning inner and outer wheels can be excluded from the slip determination regardless of the tire condition. It becomes possible.

  The configuration for eliminating the influence of the wheel speed difference of the inner turning outer wheel from the slip determination is incorporated in the slip determination device together with the configuration for changing the vehicle body longitudinal acceleration determination method according to the slip state of the wheel described above. Good.

  Further, in the slip determination device as described above, it is necessary to switch the wheel speed value to be used for the slip determination depending on whether the vehicle is accelerating or decelerating as understood from the above. In the past, such switching was performed by depressing the brake pedal or accelerator pedal. However, in an actual vehicle, the vehicle is accelerated or decelerated regardless of pedal operation, such as when the engine brake is used. There is. Even in such a case, in order to accurately switch the wheel speed value according to the acceleration / deceleration state of the vehicle, the device of the present invention outputs the error value in the low frequency band from the output value of the longitudinal acceleration sensor, particularly the output value. The wheel speed value to be used for the slip determination may be switched depending on the removed value.

  In the present invention, it is difficult to directly detect the vehicle body speed, and therefore it is difficult to accurately know the slip state of the wheels, particularly in a four-wheel drive vehicle, in various modes. It can be said that it is possible to reduce erroneous determinations regarding the slip state of the wheels. As understood from the above description, according to the configuration of the apparatus of the present invention, the error component of the wheel speed sensor output value when the wheel is in the slip state and the wheel speed of the turning outer and inner wheels in the turning wheel. By eliminating the influence of differences and the like, it is possible to more reliably determine when it is truly slipping, and reduce the period and opportunity to erroneously determine that it is slipping despite not being slipping. It is expected that

  Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the present invention.

FIG. 1 shows a schematic diagram of an automobile in which a preferred embodiment of a slip determination device according to the present invention is realized. FIG. 2 shows the configuration of the slip determination device in the form of a control block diagram. FIG. 3 shows the configuration of each part in the slip determination device of FIG. 2 in the form of a control block diagram. (A) is an acceleration / deceleration determining unit, (B) is a vehicle body speed estimating unit, (C) a turning outer / inner wheel speed difference calculating unit, and (D) is a configuration of a slip determining unit. (Ca) is a figure explaining the principle of calculation of the estimated value of the wheel speed difference inside a turning outside. The upper part of FIG. 4 shows a wheel speed value when the wheel is in a slip state (solid line—all wheel speeds of four wheels are shown in an overlapping manner), a vehicle speed estimated value by the apparatus of the present invention (solid thin line). ), An example of a time change of a vehicle speed estimated value (one-dot chain line) according to the prior art and a vehicle speed value (dotted line) detected by GPS is shown. The lower part of FIG. The period during which the slip determination (solid line) by the apparatus and the slip determination (one-dot chain line) by the prior art are made is shown.

  The present invention will now be described in detail with reference to a few preferred embodiments with reference to the accompanying drawings. In the figure, the same reference numerals indicate the same parts.

Overview Figure 1 of the device is a four-wheel drive vehicle which the preferred embodiment of the slip determination device of the present invention is mounted is schematically shown. In the figure, the vehicle 10 having the left and right front wheels 12FL and 12FR and the left and right rear wheels 12RL and 12RR is changed to the front and rear wheels according to the depression of an accelerator pedal (not shown) by the driver in a normal manner. A driving device 16 that generates a driving force is mounted. In the example shown in the drawing, the drive unit 16 is driven by a hybrid drive unit 18 in which an engine and an electric motor are connected by a differential gear unit, an electric motor alone, or a driving torque or rotation from a gasoline or diesel engine alone. The driving force is transmitted to the center differential (or transfer) 22 via the transmission (transmission) 20, and further to the front wheels 12FL, 12FR and the rear wheels 12RL, 12RR via the front wheel side differential 24 and the rear wheel side differential 26. Each is transmitted. Although not shown for simplicity, the vehicle 10 is provided with a braking system device that generates a braking force on each wheel and a steering device that controls the steering angle of the front wheels, as in a normal vehicle.

  The operation of the vehicle drive device and the braking device is controlled by the electronic control device 50, and the configuration and operation of the slip determination device of the present invention are realized by a part of the electronic control device 50. The electronic control unit 50 may include a microcomputer having a CPU, a ROM, a RAM, and an input / output port device, which are connected to each other by a bidirectional common bus, and a driving circuit. The electronic control unit 50 includes wheel speed sensors 40i (i are FL, FR, RL, RR, that is, a left front wheel, a right front wheel, a left rear wheel, a right rear wheel, unless otherwise specified). A signal Vwi indicating the wheel speed from the drive unit 18, output state information (rotation speed, torque, etc.), accelerator pedal depression amount, longitudinal acceleration detected by the longitudinal G sensor 60a, lateral A signal such as lateral acceleration detected by the G sensor 60b is input. In addition to the above, it should be understood that various detection signals for obtaining various parameters necessary for various controls to be executed in the vehicle of the present embodiment may be input.

  The slip determination device realized in the electronic control device 50 basically estimates the vehicle body speed based on the wheel speed value and the vehicle body longitudinal acceleration value that are most delayed in the change, and the estimated vehicle body speed value. It is a device that determines whether or not the wheel is in a slip state from the difference between the (vehicle body speed estimated value) and the most rapidly changed wheel speed value. However, the device of the present invention is particularly suitable when (a) the acceleration / deceleration state of the vehicle is determined based on the detection value of the longitudinal G sensor, and (b) The high frequency component of the detected value of the front and rear G sensor is determined from the low frequency component of the differential value of the wheel speed value with the most delayed change and the high frequency component of the detected value of the front and rear G sensor. And (c) taking into account the wheel speed difference between the turning inner and outer wheels in the difference between the estimated vehicle speed and the wheel speed in determining whether or not the wheel is slipping. Thus, the vehicle body speed value is estimated with higher accuracy than before, and the slip state is determined with higher accuracy. Hereinafter, the internal configuration and operation of the slip determination device will be described in detail.

Internal configuration of the apparatus The internal configuration of the slip determination apparatus of the present invention is configured as shown in the form of a block diagram in FIG. It should be understood that the illustrated configuration and the operation thereof are actually realized by a processing operation of a CPU or the like in the electronic control unit during operation of the vehicle. First, referring to FIG. 2, the slip determination device generally includes the following processing areas.
(I) Region for determining the acceleration / deceleration state of the vehicle based on the detection value of the front / rear G sensor 60a (acceleration / deceleration determination unit 50c)
(Ii) While referring to the acceleration / deceleration state of the vehicle, among the wheel speed values detected by the wheel speed sensor 40i of each wheel, the most rapidly changing wheel speed value (first wheel speed value) is determined. A region that is selected as a wheel speed value and the wheel speed value (second wheel speed value) that is most delayed is selected as a reference wheel speed value (minimum value selection unit 50a, maximum value selection unit 50b, switching unit 50d).
(Iii) Area for determining the high frequency component of the vehicle longitudinal acceleration value from the detection values of the longitudinal G sensor 60a and the lateral G sensor 60b (adder 50j, square root calculator 50k, switching unit 50l, high pass filter 50m)
(Iv) Region in which the vehicle body speed estimated value is determined based on the vehicle body longitudinal acceleration value and the reference wheel speed value (differentiator 50e, low-pass filter 50f, adder 50g, switching unit 50h, vehicle body speed estimating unit 50i)
(V) A region for calculating an estimated value of the wheel speed difference between the outer ring and the inner ring during turning of the vehicle based on the detection value of the lateral G sensor 60b (outer and inner ring wheel speed difference calculating unit 50n)
(Vi) A region for determining whether or not the wheel is in a slip state based on the determination wheel speed value, the vehicle body speed estimation value, and the estimated value of the inner wheel speed difference of the turning outer wheel (slip determination unit 50n)

The configuration of each of the above regions is as follows.
(I) Acceleration / deceleration state determination region In a conventional four-wheel drive vehicle speed estimation or slip determination device, whether a vehicle is in an acceleration state or a deceleration state is determined by whether or not the brake pedal is depressed. It was done. However, in that case, this cannot be determined when the vehicle is decelerated by engine braking or the like. Therefore, in the device of the present invention, the acceleration / deceleration state of the vehicle is determined by the output value of the front / rear G sensor 60a, so that when the vehicle is decelerating even when the brake pedal is not depressed, It is determined that the vehicle is decelerating. Specifically, in the region for determining the acceleration / deceleration state of the vehicle, as shown in FIG. 3A, the longitudinal acceleration value detected by the longitudinal G sensor 60a in the acceleration / deceleration determining unit 50c. Is passed through the high-pass filter 52a to remove low-frequency components such as drift, offset error, and uphill slope deviation, and then input to the comparators 52b and 52c (see (Note) below). In the comparator 52b, the longitudinal acceleration value from which the low frequency component has been removed is compared with the acceleration determination threshold value,
(Longitudinal acceleration value)> (Acceleration judgment threshold)
When this state continues for a predetermined time, a signal indicating the acceleration state is output and input to the RS flip-flop 52d. On the other hand, in the comparator 52c, the longitudinal acceleration value from which the low frequency component has been removed is compared with the deceleration determination threshold value,
(Longitudinal acceleration value) <(Deceleration threshold)
When this state continues for a predetermined time, a signal indicating a deceleration state is output and input to the RS flip-flop 52d. In the RS flip-flop 52d, when a signal indicating the acceleration state is received from the comparator 52b, the acceleration / deceleration determination output is set to the acceleration state and is held until a signal indicating the deceleration state is received from the comparator 52c. When a signal indicating the deceleration state arrives, the acceleration / deceleration determination output is set to the deceleration state, and is held until a signal indicating the acceleration state arrives from the comparator 52b. Therefore, the acceleration / deceleration determination output is always configured to indicate one of the acceleration state and the deceleration state. Typically, for example, the acceleration determination threshold value is set to -0.5 m / s ² and the deceleration determination threshold value is set to -1.0 m / s ² , whereby constant speed (including when the vehicle is stopped) is set. It is set to be in an acceleration state when traveling. With this configuration, neither the accelerator pedal nor the brake pedal is depressed, and it is determined that the vehicle is in a decelerating state when the vehicle is decelerated by engine braking.
[(Note) Normally, the acceleration / deceleration does not become constant, so it is practically possible to determine the acceleration / deceleration state using the detection value from which the low frequency component has been removed. ]

(ii) Wheel speed selection region In the wheel speed selection region, the minimum value selection unit 50a selects and outputs the smallest one of the wheel speed values of the four wheels, and the maximum value selection unit 50b selects the four wheels. The largest wheel speed value is selected and output. Then, the minimum value and the maximum value of the wheel speed are allocated to the reference wheel speed value and the determination wheel speed value in the switching unit 50d according to the state indicated by the acceleration / deceleration determination output. Since the reference wheel speed value is the wheel speed value with the most delayed change, the minimum value is assigned in the acceleration state, and the maximum value is assigned in the deceleration state. On the other hand, the determination wheel speed value is the wheel speed value that changes most. Therefore, the maximum value is assigned in the acceleration state, and the minimum value is assigned in the deceleration state.

(iii) Vehicle Longitudinal Acceleration Value High Frequency Component Determination Region As already mentioned, the low frequency band of the detection value output by the longitudinal G sensor is likely to contain error components due to road surface gradient, temperature drift, and the like. Therefore, in the vehicle body longitudinal acceleration value used for estimating the vehicle body speed, which will be described later, a value obtained by removing the low frequency band component from the detection value output by the longitudinal G sensor is used. In particular, during cornering while decelerating, the cornering ring drag contributes to deceleration, so that the lateral acceleration is also considered as a deceleration component. (It is known from actual vehicle data that it is difficult to be affected by the cornering ring drag during acceleration turning. Therefore, the detected value of the lateral G sensor does not need to be considered during acceleration.) Thus, the apparatus according to the present embodiment uses the detected values of the front and rear G sensors at the time of acceleration as the vehicle body longitudinal acceleration values of G sensor detection used for estimating the vehicle speed, and at the time of deceleration, between the front and rear G sensors and the lateral G sensor. Both detection values are configured to be used. Specifically, as illustrated in FIG. 2, when the state indicated by the acceleration / deceleration determination output is the acceleration state, the detection value from the front / rear G sensor 60a is selected by the switching unit 50l. On the other hand, when the state indicated by the acceleration / deceleration determination output is a deceleration state, the square root of the square sum of the detected values of the front and rear G sensor 60a and the detected value of the lateral G sensor 60b calculated through the adder 50j and the calculator 50k is switched. The part 50l is selected. The value thus selected passes through the high-pass filter 50m to remove the low-frequency component, and is sent to the vehicle body speed estimation region described later. The cutoff frequency of the high-pass filter 50m is set to a predetermined frequency by the designer so that most of the error components (including DC components) in the low frequency band of the front and rear G sensor 60a and / or the lateral G sensor 60b are removed. May be.

(iv) Body speed estimation area As described in the section of “Background Art”, in the all-wheel drive state of a four-wheel drive vehicle, a slip amount occurs in any wheel. The wheel speed cannot be referred to as the vehicle speed as it is. Therefore, in the apparatus of the present invention, in order to determine the vehicle body speed value, the reference wheel speed value selected in the wheel speed selection area, that is, the wheel speed value of the wheel with the most delayed change, The wheel speed value with the smallest slip amount among the wheels, that is, the wheel speed value considered to be the closest to the vehicle body speed among the wheel speeds of the four wheels (of the wheel speeds of all wheels, the lowest value during acceleration) From the vehicle body longitudinal acceleration, the vehicle speed is estimated as follows: [Previous vehicle speed estimated value] + [Car body longitudinal acceleration value] x [Time]
Is compared with the current vehicle speed value predicted by the above, and a value assumed to be appropriate is selected as an estimated value of the vehicle speed. Regarding the vehicle longitudinal acceleration value used here, as already described, the wheel speed differential value obtained from the output value of the wheel speed sensor is likely to include an error component in a high frequency band due to a road step or a seam. The detection value of the G sensor tends to include an error component in a low frequency band due to road surface gradient, temperature drift, or the like. Therefore, basically, as the longitudinal acceleration value of the vehicle body, a component obtained by removing a high frequency component higher than a predetermined frequency from the wheel speed differential value using a low pass filter, and a longitudinal G sensor using a high pass filter A value obtained by superimposing a component obtained by removing a low frequency component lower than a predetermined frequency from the detection value (at the time of deceleration, the square root of the square sum of the front and rear G sensor detection value and the lateral G sensor detection value) Used. However, when one of the wheels slips, the wheel speed value is likely to deviate from the true vehicle speed, and the differential value may deviate from the true vehicle longitudinal acceleration value. Increases nature. Therefore, in the apparatus of the present invention, after it is determined that one of the wheels is in a slip state, the wheel speed differential value is not used at all, and a predetermined frequency is determined from the front / rear / lateral G sensor detection values using a high-pass filter. A component itself obtained by removing a lower frequency component lower than that is used as the vehicle body longitudinal acceleration value.

  Specifically, first, as shown in FIG. 2, the reference wheel speed value selected in the wheel speed selection area is differentiated by the differentiator 50e, and passes through the low-pass filter 50f to remove the high frequency component. (The removal band of the low-pass filter 50f is set to be substantially the same as the transmission band of the high-pass filter 50m. Therefore, the entire band is covered by combining the transmission band of the low-pass filter and the transmission band of the high-pass filter 50m. That is, the transfer functions of the low-pass filter 50e and the high-pass filter 50m are set to have a relationship opposite to each other. Thus, the differential value of the reference wheel speed value from which the high-frequency component has been removed is the high-frequency component of the front-rear / lateral G sensor detection value acquired from the vehicle longitudinal acceleration value high-frequency component determination region in the adder 50g. Superposed and input to one of the two input ends of the switching unit 50h. The high frequency component of the front / rear / lateral G sensor detection value is input as it is to the other input end of the switching unit 50h, and the switching unit 50h causes the wheel to slip in accordance with the determination output of the slip determination unit 50o described later. If the vehicle body longitudinal acceleration value is determined, a value obtained by superimposing the reference wheel speed differential value from which the high frequency component has been removed and the high frequency component of the longitudinal / lateral G sensor detection value is selected. When it is determined that the wheel is slipping, the high frequency component of the longitudinal / lateral G sensor detection value is selected as the vehicle body longitudinal acceleration value. The vehicle body longitudinal acceleration value thus selected is input to the vehicle body speed estimation unit 50i.

The interior of the vehicle body speed estimation unit 50i has a configuration shown in detail in FIG. 3B. First, using a vehicle body longitudinal acceleration value (vehicle body Gx), a multiplier 54a, an adder 54c, By the multiplier 54e and the adder 54g, the vehicle body speed upper limit value Vx_limit_u becomes Vx_limit_u = (p · Gx + qu) · Δt + Vxest_pre (1a)
The vehicle body speed lower limit value Vx_limit_l becomes Vx_limit_l = (p · Gx + ql) · Δt + Vxest_pre (1b) by the multiplier 54b, adder 54d, multiplier 54f, and adder 54h.
Determined by. Here, p is a gain with respect to the longitudinal acceleration value of the vehicle body, and is set based on an error of the G sensor. For example, if the error of the G sensor is about ± 10%, p may be set to 1 / 0.9. qu (> 0) and ql (<0) are constants that may be set experimentally, and Δt is a minute time (control cycle time). Vxest_pre is an estimated vehicle body speed value Δt time before the present time given by the unit delay unit 54i. In short, the vehicle body speed upper limit value and the vehicle body speed lower limit value given by the above (1a) and (1b) are the current values when the vehicle body longitudinal acceleration value and the vehicle body speed estimation value so far are given. This corresponds to the upper and lower limits of the assumed vehicle speed.

Thus, when the vehicle body speed upper limit value and the vehicle body speed lower limit value are determined, the upper / lower limiter 54j determines the vehicle body speed upper limit value, the vehicle body speed lower limit value, and the reference wheel speed value Vw_std according to the following equation: An estimated vehicle speed Vxest is determined.
Vxest = mid {Vx_limit_u, Vw_std, Vx_limit_l} (2)
Here, mid is an operator that selects the middle numerical value among the numerical values in parentheses. Therefore, when the reference wheel speed value is between the vehicle body speed upper limit value and the vehicle body speed lower limit value, the reference wheel speed value is set to the vehicle body speed estimated value, and the reference wheel speed value is higher than the vehicle body speed upper limit value. Sometimes, the vehicle body speed upper limit value is set to the vehicle body speed estimated value, and when the reference wheel speed value is lower than the vehicle body speed lower limit value, the vehicle body speed lower limit value is set to the vehicle body speed estimated value.

(V) Turning outer / inner wheel speed difference calculation region During turning of the vehicle, the turning outer wheel rotates faster than the turning inner wheel by the action of the differential 24 or 26. On the other hand, as will be described later, in this device, whether or not the wheel is slipping is determined by the determination wheel speed value, that is, the wheel speed value that has been most changed and the estimated vehicle speed, that is, It is determined by the magnitude of the difference from the reference wheel speed value whose change is delayed or a value determined based on the reference wheel speed value. Accordingly, when the pair of wheels corresponding to the judgment wheel speed value and the reference wheel speed value is in the relationship between the turning outer wheel and the turning inner wheel, the wheel speed difference between the turning outer wheel and the wheel speed difference is the difference between the judgment wheel speed value and the vehicle body speed estimation value. It can get in and cause an incorrect slip determination. Therefore, in the apparatus of the present embodiment, in the slip determination described later, in order to compensate for the wheel speed difference of the outer turning inner ring (without using the wheel speed value), an estimated value of the wheel speed difference of the outer turning inner ring (without using the wheel speed value) The wheel speed difference between the inner and outer wheels assumed from the turning state of the vehicle is calculated.

Specifically, referring to FIG. 3 (ca), when no wheel is in a slip state in a turning vehicle, the turning radius r is determined by the lateral acceleration Gy and the wheel speed value V1 of the turning inner wheel. From
r = V1 ² / Gy (3a)
Given by. Similarly, when the wheel speed value V2 of the turning outer wheel is used,
r + T = V2 ² / Gy (3b)
The relationship is obtained. When r is deleted from the above equations (3a) and (3b),
V2−V1 = Gy · T / (V2 + V1) (3c)
The relationship is obtained. Here, since it can be assumed that V2-V1 << 2V1, if V2-V1 is ignored in the denominator,
V2−V1 = Gy · T / 2V1 (3d)
The relationship is obtained. Here, since the vehicle body speed value Vx is used instead of V1, the wheel speed difference between the turning outer wheel and the turning inner wheel is as follows.
V2-V1 = Gy · T / 2Vx (3e)
Given by. In the actual apparatus, in the outer / inner wheel speed difference calculation unit 50n, as shown in FIG. 3C, the vehicle speed estimated value Vxest and the lateral G sensor detection value (from the high-pass filter 56a include an error). The wheel speed difference between the turning outer wheel and the turning inner wheel given by the right side of the above equation (3e) using the multiplier 56b, the multiplier 56c, and the divider 56d Is calculated and given to the slip determination unit 50a.

(Vi) Slip determination area In the slip determination area, the determination wheel speed value and the vehicle body speed are determined by using the determination wheel speed value, the vehicle body speed estimation value, and the turning outer wheel speed difference estimation value determined in each of the above areas. It is determined whether or not the magnitude of the difference from the estimated value exceeds an allowable amount, and it is determined whether or not the wheel is in a slip state. In this device, when it is determined that the determination wheel speed value is in the slip state, it is determined that “the wheel is in the slip state”.

Specifically, in the slip determination unit 50o, as shown in FIG. 3D, first, the absolute value of the difference between the determined wheel speed value and the vehicle body speed estimated value is the absolute value of the adder 58a. It is calculated by the value calculator 58b and input to the comparator 58e. On the other hand, the estimated vehicle speed is also input to the allowable slip amount map, and the allowable slip amount is determined. The allowable slip amount is an allowable slip amount at the current vehicle speed, and when the actual slip amount exceeds the allowable slip amount, it is determined that the wheel is in a slip state. The allowable slip amount is typically a constant value when the vehicle body speed value is between 0 and a predetermined vehicle speed value. When the vehicle body speed value exceeds the predetermined vehicle speed value, the allowable slip amount is substantially reduced to the vehicle body speed value. It may be a proportionally increasing amount and may be determined experimentally or theoretically by the designer. Thus, when the allowable slip amount is determined, an adder 58d adds an estimated value of the wheel outer wheel speed difference to the allowable slip amount to compensate for the wheel speed difference of the inner wheel that is turning [the following ( Note) Reference] is input to the comparator 58e. Then, in the comparator 58e, when the absolute value of the difference between the determined wheel speed value and the estimated vehicle speed exceeds the (compensated) allowable slip amount, it is determined that the wheel is in a slip state. . When such a determination is made, the information is given to the switching unit 50h of the vehicle body speed estimation region, and the vehicle body longitudinal acceleration value is switched.
[(Note) During acceleration of the vehicle, the wheel speed value V2 of the turning outer wheel is selected as the determination wheel speed value, and the wheel speed value V1 (<V2) of the turning inner wheel is selected as the reference wheel speed value. The absolute value V2-V1 of the difference between the determination wheel speed value and the vehicle body speed estimated value includes a turning outer / inner wheel speed difference. Therefore, by increasing the allowable slip amount by the difference between the inner and outer wheel speeds of the turning outer side, it is possible to avoid the slip determination being erroneously output. During deceleration of the vehicle, the wheel speed value V1 (<V2) of the inner turning wheel is selected as the determination wheel speed value, and the wheel speed value V2 of the outer turning wheel is selected as the reference wheel speed value. Since the absolute value of the difference (V1-V2) between the determination wheel speed value and the vehicle body speed estimation value is V2-V1, the allowable slip amount is increased by the difference between the turning outer wheel speed and the inner wheel speed difference as in acceleration. This avoids the slip determination being erroneously output. ]

Operation of the apparatus The apparatus of the present embodiment described above operates as follows.
(A) Acceleration / Deceleration Determination As already described, the acceleration / deceleration determination unit 50c determines that the vehicle is in an accelerated state when the vehicle is stopped, and the switching unit 50d and the switching unit 50l are set to the acceleration side. While the vehicle is starting and accelerating, the determination of the acceleration state is maintained as it is. After that, when the vehicle is decelerated and the state where the front and rear G sensor detection value falls below the deceleration determination threshold continues for a predetermined time, an acceleration / deceleration determination unit The determination of 50c is switched to the deceleration state, and the switching unit 50d and the switching unit 50l are set to the deceleration side. Next, when the deceleration (absolute value of acceleration) decreases and the state where the longitudinal G sensor detection value exceeds the acceleration determination threshold value continues for a predetermined time, the determination of the acceleration / deceleration determination unit 50c switches to the acceleration state, and the switching unit 50d The switching unit 50l is set on the acceleration side. Therefore, the output of the acceleration / deceleration determining unit 50c always indicates either the acceleration state or the deceleration state.

(B) Non-slip state When the vehicle is accelerated, the maximum wheel speed value is selected as the determination wheel speed value, the minimum wheel speed value is selected as the reference wheel speed value, and the vehicle body longitudinal acceleration value includes the wheel speed. The sum of the low frequency component of the differential value of the sensor detection value and the high frequency component of the front and rear G sensor detection value is selected. Further, when the vehicle is decelerated, the minimum wheel speed value is selected as the determination wheel speed value, the maximum wheel speed value is selected as the reference wheel speed value, and the vehicle body longitudinal acceleration value includes the wheel speed sensor detection value. The sum of the low frequency component of the differential value and the high frequency component of the square root of the square sum of the front and rear G sensor detection values and the lateral G sensor detection values is selected. When none of the wheels are in the slip state, the differential value of the wheel speed sensor detection value and the front / rear / lateral G sensor are theoretically equal except for the sensor-specific error component, and the vehicle longitudinal acceleration value is the true vehicle body The vehicle body speed is estimated normally.

(C) At the time of transition to the slip state If any wheel enters the slip state at the time of acceleration of the vehicle, the wheel speed value increases and is selected as the determination wheel speed value, and the slip determination unit 50o determines the determination wheel speed. When the difference between the value and the vehicle body speed value (determined based on the reference wheel speed) exceeds the allowable slip amount, it is determined that the wheel is in the slip state. On the other hand, when one of the wheels slips during deceleration of the vehicle, the wheel speed value decreases and is selected as the determination wheel speed value. In the slip determination unit 50o, the determination wheel speed value and the vehicle body speed value are When the magnitude of the difference exceeds the allowable slip amount, it is determined that the wheel is in a slip state.

  Regarding the detection at the time of transition to the slip state, if all the four wheels are in the slip state, the reference wheel speed value, which is the wheel speed value that is most delayed in the change, is also the determination wheel that is most advanced in the change. Therefore, it is conceivable that the difference between the determination wheel speed value and the reference wheel speed value cannot be detected, and the slip state cannot be detected. However, in this case, the high-frequency component of the differential value of the reference wheel speed value increased due to the rapid change of the reference wheel speed value is removed by the low-pass filter, while the rapid change of the reference wheel speed value (the wheel is in a slip state). Therefore, it is not reflected in the front / rear / lateral G sensor detection values. Therefore, the vehicle body longitudinal acceleration value does not follow a sudden change in the reference wheel speed value, and the vehicle body upper and lower vehicle speed upper limit values and lower limit values determined from the vehicle body longitudinal acceleration value also do not follow the sudden change in the reference wheel speed value. Therefore, the difference between the vehicle body speed upper limit value / lower limit value and the determination wheel speed value increases, and it is determined that the vehicle has shifted to the slip state.

(D) Slip state When it is determined that the wheel is in the slip state, the information is transmitted to various control devices that suppress the slip of the wheel, such as a TRC device or an ABS control device of the vehicle. Further, in response to the slip determination output, the vehicle speed estimation region switching unit 50h is switched, and the output of the high-pass filter 50m in the vehicle longitudinal acceleration value high frequency component determination region is directly input to the vehicle body speed estimation unit 50i. The vehicle body speed estimation is executed without using the wheel speed differential value component. During this time, the low frequency component of the vehicle longitudinal acceleration value input to the vehicle speed estimation unit 50i is substantially 0, and the vehicle longitudinal acceleration value here does not completely match the true longitudinal acceleration of the vehicle body. However, when the wheel is in the slip state, the change in the vehicle speed becomes small, and the period in which the wheel is in the slip state does not last for a long time. The error in the estimated vehicle speed due to being present can be substantially ignored. This was confirmed experimentally (see “Experimental Example”).

(E) When shifting to a non-slip state In a vehicle with wheels in a slip state, the vehicle body speed increases (acceleration) or decreases (deceleration), or the wheel speed decreases (acceleration) by various control devices. ) Or increase (during deceleration), and the difference between the vehicle speed and the wheel speed is reduced, the difference between the judgment wheel speed value and the estimated vehicle speed is less than the allowable slip amount, and the wheel is not in the slip state. It is determined. When such determination is made, the vehicle speed estimation region switching unit 50h is switched, and the vehicle speed estimation unit 50i reduces the output of the high-pass filter 50m in the vehicle body longitudinal acceleration value high frequency component determination region and the low wheel speed differential value. The vehicle speed estimation using the value superimposed with the frequency component is resumed.

Experimental Example In order to show the effectiveness of the above-described device of the present invention, the vehicle speed value estimated using the device of the present invention and the GPS (Global Positioning System) in a vehicle in which the wheels actually slipped ) Was compared with the vehicle speed measured by the vehicle speed measuring device. The upper part of FIG. 4 shows the wheel speed value (solid bold line) at that time, the estimated vehicle body speed value by the device of the present invention (solid thin line), and the prior art device (the low vehicle speed differential value for estimating the vehicle speed even in the slip state). The time change of the vehicle body speed estimated value (one-dot chain line) by the thing using a frequency component) and the vehicle body speed value (broken line) by the GPS vehicle body speed measuring device is shown. As is apparent with reference to the figure, while the wheel speed value rises and decreases in a mountain shape in the figure, the estimated vehicle speed value by the device of the present invention is the estimated vehicle speed value by the GPS vehicle speed measuring device. Generally agreed. On the other hand, it has been observed that the estimated vehicle speed by the device of the prior art is displaced to a side significantly higher than the vehicle speed value by the GPS vehicle speed measuring device and approaches the wheel speed. In addition, when the slip determination is performed by the device of the present invention and the device of the prior art in the situation shown in the figure, as shown in the lower part of FIG. (Solid line) corresponds to a period in which the wheel speed and the vehicle body speed measured by the GPS vehicle body speed measuring device are significantly different from each other, and is longer than the period (dotted line) in which the state of the art is determined to be in the slip state. It was long. As described above, the estimated vehicle speed by the device of the present invention substantially matches the vehicle speed value by the GPS vehicle speed measuring device, and the slip determination matches the period in which the wheel speed and the vehicle speed deviate. From these facts, it was confirmed that according to the apparatus of the present invention, the vehicle body speed value was estimated more accurately than before, and the slip determination could be performed more accurately.

  Although the above description has been made in relation to the embodiment of the present invention, many modifications and changes can be easily made by those skilled in the art, and the present invention is limited to the embodiment exemplified above. It will be apparent that the invention is not limited and applies to various devices without departing from the inventive concept.

  For example, the device of the present invention may be applied to a two-wheel drive vehicle when the vehicle body speed value cannot be determined from the wheel speed value of the driven wheel. Further, in the configuration in which the wheel speed difference between the turning outer wheel and the turning inner wheel of the vehicle is taken into account in the determination of the slip state of the wheel, the estimated vehicle speed is determined based on the second wheel speed value that is most delayed in change. Determined by any other method, for example, a method using other wheel speed values or average values of wheel speed values, vehicle speed information obtained from GPS, or speed information obtained from an in-vehicle camera. It may be a vehicle body speed value. In that case, in the determination of the wheel speed value selected as the determination wheel speed value and the comparison between the determination wheel speed value and the vehicle body speed value, the wheel speed difference between the turning outer wheel and the turning inner wheel of the vehicle is taken into consideration. It may be. Further, the wheel speed difference between the turning outer wheel and the turning inner wheel of the vehicle does not depend on the configuration exemplified in the above-described embodiment, and changes more than at least one wheel speed value among the wheel speed values of each wheel of the vehicle. Delayed wheel speed value (when accelerating, the wheel speed value is relatively lower than at least one wheel speed value, and when decelerating, the wheel speed value is relatively higher than at least one wheel speed value. In the configuration for determining the slip state of the wheel using the

DESCRIPTION OF SYMBOLS 10 ... Vehicle body 12FL, FR, RL, RR ... Wheel 14 ... Accelerator pedal 16 ... Drive device 18 ... Drive unit 20 ... Transmission 22 ... Center differential 24 ... Front wheel differential 26 ... Rear wheel differential 40FL, FR, RL, RR ... Wheel speed Sensor 50 ... Electronic control device 60a, 60b ... Front and rear G sensor, lateral G sensor

Claims (6)

  A slip determination device for a vehicle, wherein the wheel speed of the vehicle is determined based on a first wheel speed value obtained by a first wheel speed sensor and a vehicle body speed estimated value determined based on a vehicle body longitudinal acceleration value. A slip determination unit that determines a slip state, and the vehicle body longitudinal acceleration value is obtained by a second wheel speed sensor when the slip determination unit determines that the vehicle wheel is not in a slip state. In addition, a value obtained by removing a frequency component higher than a predetermined frequency from the differential value of the second wheel speed value and a component having a frequency lower than the predetermined frequency are removed from the acceleration value obtained by the longitudinal acceleration sensor. A value obtained by adding the obtained value is used, and when the slip determination unit determines that the vehicle wheel is in a slip state, the value obtained by the longitudinal acceleration sensor is obtained. And wherein the values from the velocity value obtained by removing the component of a frequency lower than the predetermined frequency is used.   2. The apparatus according to claim 1, wherein the first wheel speed value is a wheel speed value that is most changed among wheel speed values of each wheel of the vehicle, and the second wheel speed value is the value of the vehicle. A device characterized in that it is a wheel speed value of which the change is most delayed among wheel speed values of each wheel.   3. The apparatus according to claim 1, wherein a time integral value of the vehicle body longitudinal acceleration value is obtained by adding a value obtained by multiplying the vehicle body longitudinal acceleration value by a predetermined time to the previous value of the vehicle body speed estimated value. The vehicle speed estimation value is determined based on a time integral value of the vehicle body longitudinal acceleration value and the second wheel speed value.   4. The device according to claim 1, wherein the second wheel speed value is within a value range determined in a predetermined range from a time integral value of the vehicle body longitudinal acceleration value. When a wheel speed value is selected as the vehicle body speed estimation value and the second wheel speed value is outside the range, the boundary value in the range closest to the second wheel speed value is the vehicle body speed estimation value. A device characterized by being selected as:   The apparatus according to claim 2, wherein the slip determination unit determines a slip state of the wheel of the vehicle based on the first wheel speed value, the vehicle body speed estimated value, and a wheel speed difference of the turning inner wheel of the vehicle. An apparatus characterized by determining. 6. The apparatus according to claim 5 , wherein an absolute value of a difference between the first wheel speed value and the vehicle body speed estimated value is determined based on a wheel speed value of a turning outer wheel calculated from a lateral acceleration of the vehicle. An apparatus for determining that a wheel of the vehicle is in a slip state when a value obtained by subtracting a speed value is larger than a value obtained by adding to an allowable slip amount determined based on the estimated vehicle body speed value.

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