JP2008261303A - Vehicle traction control device - Google Patents

Abstract

In traction control of an all-wheel drive vehicle such as a four-wheel drive vehicle, a road surface condition on which the vehicle travels is determined when it is determined to reduce the drive output of the vehicle in response to detection of an all-wheel slip sign. Identify and consider the need for drive output reduction and avoid performing unnecessary drive output reduction.
A traction control device for an all-wheel drive vehicle according to the present invention includes an all-wheel slip sign detecting means for detecting a sign that all of the drive wheels are in a slip state, and a vehicle running for identifying a road surface condition. Including a driving force loss estimating means for estimating the loss of driving force in the vehicle and a driving force control means for controlling the driving force in the driving wheels of the vehicle, and when signs that all the wheels are in a slip state are detected, The driving force is reduced when the driving force loss up to that time is equal to or less than a predetermined value.
[Selection] Figure 3

Description

  The present invention relates to a driving force control device for a vehicle such as an automobile, and more particularly, to a driving force control device that performs traction control (TRC) for avoiding excessive slip of driving wheels of a vehicle.

When driving a vehicle such as an automobile, the slip ratio or slip amount of the drive wheel (hereinafter referred to as “drive slip”) exceeds the limit determined by the friction coefficient of the road surface and the contact load (maximum friction circle). ")" Is too large, the drive wheel loses the grip on the road surface and falls into a slip state (see note below). Therefore, traction control (TRC) for adjusting the drive slip may be executed as travel control for avoiding the drive wheel from falling into such a slip state. In TRC, when the wheel speed of the driving wheel becomes excessively higher than the vehicle speed (body speed), it is determined that the driving wheel has slipped and is transmitted from the driving device such as an engine or an electric motor to the driving wheel. The driving torque is reduced or the braking device is operated to reduce the rotation of the driving wheel. Then, by reducing the rotation of the driving wheel, driving slip is suppressed, and the grip force of the tire is maintained (so as not to exceed the maximum friction circle). According to the operation of the TRC, as is well known, the vehicle does not slip even on a road surface having a low coefficient of friction (relatively slippery) such as a frozen road surface or a snowy road. The start / acceleration performance of the vehicle is improved, and the running behavior of the vehicle can be stabilized. Further, the TRC suppresses the unnecessary rotation of the wheel, and the drive energy is efficiently used for driving the vehicle, so that the energy efficiency is also improved.
[Note] The “slip state” means a state where the wheel “slides” on the road surface, and is different from “slip” which means a deviation between the vehicle speed and the wheel speed in the case of “driving slip”.

  In the TRC, as described above, the slip state of the drive wheel is detected by determining that the wheel speed of the drive wheel is excessively higher than the vehicle speed. Therefore, in order to execute TRC, it is necessary to detect or acquire the vehicle speed value in real time. In this regard, ordinary vehicles are not often provided with a ground speed sensor that can directly detect the vehicle speed, so in the case of a two-wheel drive vehicle having driven wheels (where no drive slip occurs). Refers to the wheel speed of the driven wheel as the vehicle speed. However, in the case of a vehicle in which all wheels such as a four-wheel drive vehicle operate as drive wheels (all-wheel drive vehicle), the drive slip may be excessive in any wheel during all-wheel drive. Any wheel speed cannot be referred to as the vehicle speed as it is. Therefore, in such an all-wheel drive vehicle, when the vehicle speed value is acquired at the time of acceleration of the vehicle (in a state where drive torque is applied to all the wheels of the vehicle), for example, the rotational speed is the lowest or two. Can be generated in the vehicle based on the wheel speed of the second lowest wheel as an approximate value of the vehicle speed, or based on the value of the G sensor (longitudinal acceleration sensor) or the friction coefficient of the road surface estimated using that value For example, the current vehicle speed value is appropriately estimated with reference to the acceleration (see, for example, Patent Document 1). Especially in the latter case, the upper limit of acceleration, that is, the upper limit of the vehicle speed that can be generated at the present time, from the limit of acceleration that can be generated in the vehicle under the current road surface condition and the vehicle speed up to immediately before, Vehicle speed] + [acceleration upper limit value] × [time] (the previous vehicle speed is cumulatively determined from the wheel speed when no driving slip occurs), and the actual vehicle speed is Under the assumption that it should be lower than the upper limit value of the vehicle speed, an appropriate wheel speed is selected as the vehicle speed (approximate value) among all the wheels.

In the TRC of an all-wheel drive vehicle as described above, when all the drive wheels are in a slip state (all-wheel slip state), it becomes more difficult to accurately estimate the current vehicle speed value. However, as already described, according to the method of estimating the upper limit value of the vehicle speed from the acceleration upper limit value calculated based on the longitudinal acceleration or the road surface friction coefficient by the G sensor, all the driving wheels have fallen into the slip state or all the wheels It is possible to detect that there is a possibility that the wheels have slipped at the same time (a sign that all wheels are in a slip state, a sign that all wheels slip). In other words, if the wheel speed of a certain drive wheel is higher than the upper limit value of the vehicle speed as described above, then the drive wheel will reach the actual vehicle speed even if the actual vehicle speed value itself is not accurately known. It can be estimated that the engine is rotating at an excessively high speed (idling). If any wheel speed of the driving wheels of the vehicle is excessive as compared with the upper limit value of the vehicle speed, it can be estimated that all the wheels of the vehicle are in a slip state or that there is a possibility. If it is estimated that the all-wheel slip state is present, in other words, if an all-wheel slip sign is detected, the output of the drive device is reduced, thereby suppressing an increase in the drive slip and It is possible to recover or maintain the grip force.
JP2002-127881

  According to the control method capable of detecting all-wheel slip signs even if the vehicle speed value cannot be accurately detected or estimated as described above, it is relatively slippery, such as a frozen road surface or a snowy road, and the road surface friction coefficient is low. It is possible to provide stable and safe traveling of the vehicle even on a road surface that easily falls into an all-wheel slip state. However, according to the research of the inventor of the present invention, even when the all-wheel slip sign is detected by the above-described method, depending on the road surface condition, the output of the driving device or the driving force applied to the driving wheel can be reduced. It has been found that the need for reduction may be low.

  For example, in the case of a smooth or even road surface with a low coefficient of friction, such as a uniform frozen road surface or a wet road surface, if all the wheels fall into the slip state from the grip state simultaneously while the vehicle is running, the vehicle acceleration Therefore, when the all-wheel slip sign is detected and the possibility of the all-wheel slip state is estimated, it is preferable to reduce the output of the driving device. However, road surfaces with a non-uniform surface with a low coefficient of friction, such as snowy roads, roads where snow and ice are mixed, and roads where snow or ice is crushed when the vehicle travels (roads with a crisp feeling). In this case, even if an all-wheel slip sign is detected temporarily or transiently in the vehicle, the vehicle may be able to accelerate and travel relatively stably. In such a situation, when the driving force is reduced in response to detection of the all-wheel slip sign, the driver may feel that the car does not run, i.e., the vehicle acceleration is insufficient. is there. In such a case, it can be said that the necessity for reducing the driving force is low.

  In order to prevent the low-necessity output reduction processing as described above or to eliminate the lack of acceleration of the vehicle, not only the frictional state of the road surface but also further differences in the road surface condition are identified. It will be necessary to reflect this in the control mode for reducing the driving force or driving torque applied to the driving wheel or the output of the driving device. However, in the conventional TRC, a control method that takes into account the difference in road surface conditions as described above has not been proposed.

  According to the present invention, the possibility of an all-wheel slip state, that is, an all-wheel slip sign is detected in the TRC of an all-wheel drive vehicle in which all wheels such as a four-wheel drive vehicle operate as drive wheels. When the driving force is reduced in response to this, the road surface condition where the vehicle travels is identified by a new method, and the necessity of reducing the driving force is taken into account, thereby executing more detailed driving control. A TRC device for a vehicle configured to be provided is provided.

  The traction control device for a vehicle in which all the wheels are drive wheels according to the present invention as described above includes an all-wheel slip sign detecting means for detecting a sign that all the drive wheels are in a slip state when all the wheels are driven, and a vehicle running The driving force loss estimating means for estimating the driving force loss and the driving force control means for controlling the driving force in the driving wheels of the vehicle, the driving force control means is basically composed of a conventional device and Similarly, when the all-wheel slip state estimating means detects that all the drive wheels are in a slip state, the drive force on the drive wheels of the vehicle is reduced. It is executed when the wheel slip sign is detected and when the driving force loss estimated by the driving force loss estimating means is not more than a predetermined value. Here, “a sign that all the driving wheels are in a slip state” means a state in which there is a possibility that it is not possible to accurately determine whether or not all the wheels are in a slip state. Further, the “loss of driving force” is, if necessary, the amount of driving force or driving output applied to the vehicle that is not reflected in the acceleration of the vehicle.

  In determining whether or not to reduce the driving force in the above-described configuration of the present invention, in addition to detecting a sign that all the wheels are in the slip state, the driving force loss estimation means until then is estimated. The loss of driving force is referred to in order to identify the state of the road surface on which the vehicle travels. When the road surface is relatively uniform, the driving force output from the vehicle driving device is efficiently reflected in the driving of the vehicle while each of the driving wheels holds the gripping force. The loss of driving force is small. On the other hand, when the road surface is relatively uneven, for example, on a snowy road or a road where snow and ice are mixed (a road where the driver feels crispy while the vehicle is running) Even if each of them holds the gripping force, the transmission efficiency of the force from the driving force output from the driving device of the vehicle to the road surface is low, and the loss of the driving force increases (transiently, the driving wheels are individually Can slip.) Therefore, by referring to the magnitude of the driving force loss, it is possible to identify whether the running road surface is a uniform road or a non-uniform road. And when the road surface is relatively non-uniform, that is, when the loss of driving force is large, as already mentioned, even if the sign that all wheels slip is detected, Since the vehicle can travel relatively stably, in that case, the necessity for reducing the driving force is low.

  Therefore, in the operation of the apparatus of the present invention described above, even if an all-wheel slip sign is detected, the loss of driving force up to that point (not the loss at the moment when the all-wheel slip sign is detected) is referred to. If the loss of the driving force is large and exceeds a predetermined value, it is determined that the road surface is a non-uniform road. In this case, the driving force is not reduced and the state is maintained as it is ( Because the road surface is uneven, even if the all-wheel slip state becomes transient, there is a high possibility that the all-wheel slip state will be immediately released.) Thus, if the vehicle can travel relatively stably even when all-wheel slip signs are detected, such as a snowy road or a road where snow and ice are mixed, the driving force is not reduced. It becomes possible to reduce the lack of acceleration such as “the car does not run”. On the other hand, when the all-wheel slip sign is detected, if the loss of the driving force is small and not more than a predetermined value, it is determined or estimated that the road surface is a uniform road. In this case, the driving force is reduced. As a result, the driving slip, that is, the wheel speed of the driving wheel is controlled in the driving wheel so that the grip force is maintained in the driving wheel.

  In the above-described configuration of the device of the present invention, the driving force loss is an amount that is not reflected in the acceleration of the vehicle as described above. Therefore, when estimating the loss of the driving force, the driving force loss estimation means preferably calculates the loss of the driving force during the traveling of the vehicle based on the driving force generated by the vehicle driving device and the longitudinal acceleration of the vehicle. You may come to calculate. The driving force generated by the vehicle drive device may be estimated or detected by an arbitrary method for those skilled in the art. In particular, in the case of a hybrid vehicle or an electric vehicle, the output torque is calculated with considerable accuracy, and these values are advantageously used. The output value of the G sensor may be used for the longitudinal acceleration of the vehicle. Further, the loss of driving force during traveling of the vehicle includes a component that is lost due to a factor other than the degree of uniformity or nonuniformity of the road surface, that is, a loss due to so-called traveling resistance. Therefore, more preferably, the loss of the driving force is a value obtained by multiplying the longitudinal force of the vehicle by the weight of the vehicle from the driving force generated by the vehicle driving device (acceleration force generated in the vehicle body) and the running resistance of the vehicle. It may be an amount obtained by subtracting the loss due to. In the control of the device of the present invention, the loss of the driving force is referred to to identify whether the road surface on which the vehicle is traveling is uniform or non-uniform, and therefore an all-wheel slip sign is detected. The previous value is referenced, not the instantaneous value of time. Since the condition of the road surface should be judged at least in the range in which the road surface extends, the value of the driving force loss is not an instantaneous value but a value in a certain time width, for example, The primary delay amount of driving force loss, average value, integrated value, smoothed value, etc. are employed.

  In addition, regarding the detection of the all-wheel slip sign having the above-described configuration, typically, the all-wheel slip sign detection means estimates the upper limit value of the vehicle speed that can occur in the vehicle based on the longitudinal acceleration value of the vehicle. An upper limit value estimation means is included, and when all the wheel speeds of the drive wheels are larger than the upper limit value of the vehicle speed by a predetermined value or more, it may be determined that there is an indication that all of the drive wheels are in a slip state. . That is, the current vehicle speed may not be accurately measured or estimated during all-wheel drive. Further, the upper limit value of the vehicle speed in this case is preferably the upper limit value of the acceleration that can be generated in the vehicle determined based on the current longitudinal acceleration value of the vehicle and the vehicle speed of the vehicle before the measurement of the longitudinal acceleration. It may be determined based on. Therefore, if the wheel speed value when no driving force is applied to at least one of the wheels of the vehicle is obtained, the upper limit value of the vehicle speed at the time of all-wheel drive is calculated, and therefore all-wheel slip It is possible to detect signs or estimate the slip condition of all wheels.

  In the above-described embodiment of the present invention, the driving force reduction processing on the driving wheels of the vehicle by the driving force control means is an indication that all of the driving wheels are in the slip state by the all-wheel slip sign detecting means. May be executed after a state in which the loss of the driving force estimated by the driving force loss estimating means until that time is not more than a predetermined value continues for a predetermined period. Whether the road surface is uniform or non-uniform can be identified by the loss of driving force as described above, but even if the loss of driving force is small, an all-wheel slip sign may be detected transiently. In such a case, if the driving force is reduced every time an all-wheel slip sign is detected, the driver may still feel uncomfortable with the lack of acceleration or subsequent fluctuations in the driving force. There is sex. On the other hand, if the all-wheel slip sign continues for a predetermined time, there is a high possibility that the all-wheel slip state is actually set. Therefore, the reduction of the driving force may be performed after the all-wheel slip sign has continued for a predetermined time to prevent unnecessary reduction of the driving output.

  In the driving force reduction process in the above-described configuration of the device of the present invention, the driving force control means typically reduces the output of the vehicle driving device, thereby reducing the driving force of the vehicle. Reduce driving force. A brake device may be used to suppress excessive drive slip, but in that case, it is necessary to consider the loss caused by the brake device in the estimation of the “loss of drive force”. The use efficiency of the output energy of the drive device also deteriorates. Therefore, as described above, it is preferable to reduce the driving force in the driving wheels of the vehicle by reducing the output of the driving device (however, when the output response of the driving device is slow, a braking device is used in combination). May be.)

  Further, when the above driving force reduction is performed, preferably, the sum of the driving forces of the driving wheels of the vehicle is a value obtained by multiplying the maximum friction coefficient of the road surface on which the vehicle travels by the vertical load of the vehicle. The driving force on the driving wheels of the vehicle is reduced. As understood from the driving mechanism of the vehicle, when starting or accelerating the vehicle, the limit value of the total driving force that contributes to the acceleration of the vehicle is that the tire force of each wheel reaches the maximum friction circle. It is the sum of the tire force at the time. Therefore, an all-wheel slip sign is detected (in this case, it is assumed that the driver is requesting an acceleration higher than the acceleration that can be generated on the current road surface), and the driving force is reduced. If the tire force of each wheel is reduced to a state where it reaches the maximum friction circle, the tire of each wheel can be brought into a state in which the grip force is maintained at the maximum. The size of the maximum friction circle is given by the maximum friction coefficient of the road surface multiplied by the ground contact load of each wheel. Therefore, the sum of the driving forces of the driving wheels of the vehicle multiplies the maximum friction coefficient of the road surface by the vertical load of the vehicle. By setting this value, the acceleration performance of the vehicle is maintained at a maximum level.

  The present invention provides a TRC for avoiding an all-wheel slip condition in an all-wheel drive vehicle such as a four-wheel drive vehicle in which drive slip occurs in all wheels and it is difficult to accurately determine the vehicle speed. When performing, in addition to monitoring the driving slip or wheel speed of the tires of each wheel, by monitoring the driving force loss of the vehicle, grasp the situation of the road surface on which the vehicle is traveling in more detail, It can be said that the driving force reduction process by the TRC is performed more accurately. As can be understood from the above description, according to the control configuration of the present invention, the frequency of unnecessarily reducing the driving force is reduced, and the acceleration performance of the vehicle in a road surface state that can travel relatively stably is impaired. It is prevented. As a result of such control, the opportunity for the driver to feel that “the vehicle does not run” is reduced, and therefore the operation burden on the driver is reduced.

  In one aspect of the above-described configuration of the present invention, driving at the moment when an all-wheel slip sign appears as a loss of driving force referred to (estimated) to determine road conditions. It should be understood that reference is made to the value of the driving force loss prior to when the all-wheel slip sign is detected, not the instantaneous value of the power loss. In the conventional TRC, basically, the driving force is controlled based on the relationship between the current wheel speed value and the vehicle speed value (in order to estimate the vehicle speed, The value may be referred to, but it is for calculating the current vehicle speed value, and it is not essential that the value is before the estimation time.) On the other hand, in the case of the present invention, since the factor that spreads in the length direction such as the degree of road surface uniformity or smoothness is to be reflected in the control, the primary delay amount of the driving force loss, etc. In addition, the loss of driving force before the estimation time is referred to. For this reason, TRCs that perform control with reference to values prior to the current time will be rarely seen in the past.

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

  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.

Configuration of Device FIG. 1A schematically shows a four-wheel drive vehicle on which a preferred embodiment of the TRC device of the present invention is mounted. 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 generates driving force on the front and rear wheels in accordance with the depression of the accelerator pedal 14 by the driver in a normal manner. A driving device 16 is mounted. In the illustrated example of the drive device 16, the drive torque or rotational drive force from the hybrid drive unit 18 in which the engine and the electric motor are connected by a differential gear device is applied to the transmission (transmission) 20. Then, it is transmitted to the center differential (or transfer) 22 and further transmitted 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, respectively. Instead of the drive unit 18, an electric motor alone, or a gasoline or diesel engine alone may be used. 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 TRC 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 θa, longitudinal acceleration α detected by the G sensor 30, etc. Signal is input. In addition to the above, various detection signals for obtaining various parameters necessary for various controls to be executed in the vehicle of the present embodiment, for example, the yaw rate detected by the yaw rate sensor, and detected by the G sensor. It should be understood that the lateral acceleration and the vertical load of each wheel from a load sensor provided on each wheel may be input.

  More specifically, the TRC device 50a realized in the electronic control device 50 includes a drive control device 50b of the drive unit 18 and a braking device, as schematically shown in FIG. It communicates with a braking control device 50c that controls the operation of (not shown) to control the output of the drive unit 18 or the operation of the braking device. The drive control device 50b controls the operation of each part of the drive unit 18 in any known manner on the basis of the accelerator pedal depression amount θa to reflect the drive request from the driver. Adjust the output. On the other hand, as shown in the figure, the braking control device 50c calculates the rotational speed of the wheel from the pulse-type electrical signal that is sequentially generated every time the wheel rotates by a predetermined amount by the wheel speed sensor 40i of each wheel. By multiplying the wheel radius, the wheel speed value r · ω is calculated. Further, in the braking control device 50c, a road surface friction coefficient estimating unit 50d for estimating the maximum friction coefficient of the road surface of each wheel is provided, and the estimated maximum friction coefficient μi of the road surface of each wheel is determined by braking control or It can be used in the TRC of the present invention described later in detail.

  The TRC device 50a of the present invention is generally described in the output value (power), output torque value or generated driving force value of the drive unit 18 from the drive control device 50b, and in each wheel from the brake control device 50c. Using the wheel speed value r · ωi, the maximum friction coefficient μi (estimated value) of the road surface, the vehicle longitudinal acceleration signal from the G sensor, etc., the vehicle speed is estimated (vehicle speed estimation unit 52), all wheels (four Wheel) Slip indication (indication that all wheels are in the slip state at the same time) is detected (four-wheel slip indication detection unit 54), and driving force loss is estimated (driving force loss estimation unit 56), resulting in excessive driving slip. When a predetermined condition is satisfied, such as a case where an all-wheel slip sign is detected, a control command is given to the drive control device 50b to reduce the drive force of the drive unit 18 (drive force control unit 58). , Execute TRC to suppress drive slip. In particular, as will be described in detail below, in the driving force control unit 58, when an all-wheel slip sign is detected, it is estimated that the loss of driving force during traveling of the vehicle is small and the road surface is smooth. Only when this is done, it is configured to command the reduction of the driving force, thereby reducing the frequency with which the driving force is reduced unnecessarily. The drive control device 50b, the brake control device 50c, and the TRC device 50a may be separate or integrated. It should be understood by those skilled in the art that the configuration and processing operation of the control device described above are realized by the microcomputer operating according to an embedded program. Hereinafter, the operation of the TRC in the apparatus of the present invention will be described.

Normal TRC operation in a four-wheel drive vehicle As is well known in this field, the slip ratio of each wheel when a vehicle is driven {(wheel speed) − (vehicle speed)} / (vehicle speed) ... (1)
However, if the friction coefficient between the tire and the road surface increases beyond a value that saturates, that is, a value that gives the maximum friction coefficient of the road surface, the tire loses gripping force and enters a slip state. Therefore, in TRC,
(Wheel speed)-(vehicle speed) ... (1a)
And when this value exceeds a predetermined control threshold, the output of the drive device is reduced so that the wheel speed is reduced. (See FIG. 2A. Note that the operation of such a TRC is known, and a more detailed description can be found in any document in this field.)

  Therefore, in order to execute the TRC as described above, it is necessary to know the vehicle speed value. However, as described in the “Background Art” section, when all-wheel drive of a four-wheel drive vehicle is performed, In this case, a drive slip occurs, and any wheel can be in a slip state. Therefore, there is no wheel speed that can be used as it is. Therefore, in the case of all-wheel drive of a four-wheel drive vehicle, the vehicle speed value is determined by using the vehicle longitudinal acceleration value detected by the G sensor or the estimated value of the maximum friction coefficient of the road surface. The upper limit value of the vehicle speed that can be generated is calculated using the upper limit value of the acceleration that can be generated in the vehicle inside. Thereafter, the upper limit value of the vehicle speed is compared with the wheel speed of each wheel, and an appropriate wheel speed is selected as the vehicle speed (vehicle speed estimation unit 52).

Specifically, first, using the longitudinal acceleration value α of the vehicle detected by the G sensor, the upper limit value αup of the acceleration is αup = α + Δα (2)
And given. Δα is determined by an arbitrary method such as a predetermined value experimentally or theoretically determined to be given an upper limit value αup of acceleration that can be generated in the vehicle or a current running condition of the vehicle. Value. Thereafter, the upper limit value Vxup of the vehicle speed is obtained by using the vehicle speed value (previous value) Vxf before the acceleration value α is acquired,
Vxup = Vxf + αup · Δt (3)
(See FIG. 2B). Here, Δt is the time from the time when Vxf is given to the present time (it should be understood that Vxf is given from the previous vehicle speed value. In the first calculation of the estimation of the vehicle speed, For example, the wheel speed value when no driving torque is applied to the driving wheel is referred to as the previous value.) Then, the lowest value or the second lowest value in the group consisting of the wheel speeds r · ωi and Vxup of each wheel is set as the current vehicle speed Vx. In an actual apparatus, the lower limit value αdown of the acceleration that can be generated in the vehicle is αdown = α−Δα (2a) as a lower guard of the estimation calculation.
The lower limit value Vxdown of the vehicle speed is
Vxdown = Vxf + αdown · Δt (3a)
The vehicle speed value Vx is given by
Vx = MID {Vxup, r · ωi, Vxdown} (3b)
Determined by MID is an operator that selects an intermediate value between the values in {}.

  According to the above vehicle speed estimation calculation, if any of the driving wheels holds the gripping force, any of the wheel speeds of the wheels holding the gripping force is selected as the vehicle speed. Then, using the vehicle speed value, the value of (wheel speed) − (vehicle speed) in the formula (1a) is referred to for each wheel, and the value of (wheel speed) − (vehicle speed) is controlled for any wheel. When the threshold value is exceeded, the output of the driving device is reduced according to the normal operation mode of the TRC (driving force control unit 58).

Operation of TRC when all-wheel (four-wheel) slip signs are detected When the wheel speed of each wheel is higher than the upper limit value Vxup of the vehicle speed in the above calculation of the vehicle speed (see FIG. 2C), Since all the wheel speeds exceed the upper limit value of the expected vehicle speed, it is highly possible that all the wheels are in the slip state. Therefore, when the minimum value of the wheel speed is greater than Vxup among the four wheels, it may be determined that the all-wheel slip state is present. However, in this regard, whether or not the wheel is actually slipping is determined by whether or not the value of (wheel speed r · ωi) − (vehicle speed Vx) exceeds the control threshold value. In a situation where the wheel speed of the wheel is larger than the upper limit value Vxup of the vehicle speed and the upper limit value of the vehicle speed is selected as the vehicle speed, the reliability of the selected vehicle speed is extremely low, so (wheel speed r · ωi) − (vehicle speed Vx ) Cannot be accurately determined whether or not each wheel is in a slip state. Therefore, when the wheel speeds of all the wheels are larger than the upper limit value Vxup of the vehicle speed, there is a possibility that all the wheels are in a slip state, that is, there is an indication that all the wheels are in a slip state.

  When all the wheels are in a slip state, basically, a reduction in the output of the drive unit 18 is commanded in order to immediately reduce the drive slip of all the wheels and restore and maintain the grip force of the tire. . However, as already mentioned in the section of “Disclosure of the Invention”, when an indication that all the wheels are slipping is detected, it is not a smooth and uniform road surface such as a frozen road surface, but a snow road. On roads with a non-uniform surface with a low coefficient of friction, such as roads where snow and ice are mixed, or roads where snow or ice is crushed when the vehicle is running (roads with a crisp feeling) It has been found that the vehicle can accelerate relatively stably, and in that case, if the driving force is reduced, the driver feels that the acceleration is insufficient. Further, the all-wheel slip sign determined from the fact that “the wheel speed r · ωi is larger than the vehicle speed upper limit value Vxup” only indicates that there is a high possibility that all the wheels are in the slip state. It is not a reliable indication that the wheel is slipping. Therefore, the control processing of the apparatus according to the present invention can identify the road surface condition as described above, or can take into account the uncertainty of all-wheel slip signs, and the vehicle can be accelerated and driven relatively stably. In some cases, the driving force is not reduced.

(I) Identification of road surface condition In the apparatus of the present invention, as described above, a smooth and uniform road surface such as a frozen road surface, a snow road, Attempts are made to discriminate from uneven road surfaces such as road surfaces in which snow and ice are mixed, or road surfaces on which snow or ice is crushed when the vehicle travels (road surfaces with a crisp feeling). Such road surface characteristics are identified by referring to the loss of driving force in the traveling vehicle, that is, the magnitude of the amount of driving force applied to the vehicle that is not reflected in the acceleration of the vehicle.

  As schematically shown in FIG. 3 (A), when the vehicle is running on a smooth and uniform road surface, if the wheels are kept in a grip state, the vehicle drive device gives the drive wheels. The driving force or driving torque is efficiently used for the action with the road surface and reflected in the acceleration of the vehicle. Therefore, the loss of driving force is relatively small. On the other hand, as shown in FIG. 3B, when the road surface on which the vehicle travels has a rough and uneven surface on which a driver feels crispy such as a snowy road, The transmission efficiency of the driving force or driving torque applied to the driving wheels to the road surface is relatively low (driving torque is also spent on snow deformation and ice crushing), and the increase in vehicle acceleration increases the smoothness and uniformity of the road surface. Since it is smaller than the case, the loss of driving force becomes relatively large.

The loss of the driving force is an amount that is not reflected in the vehicle acceleration α out of the driving force applied to the vehicle.
(Loss of driving force ΔF) = Fr−M · α−Rr (4)
Given by. Here, Fr is a value obtained by converting the output torque Tr of the driving device into a unit of driving force, and M is the weight of the vehicle. Rr is a driving force loss caused by factors other than a difference in road surface characteristics, a so-called running resistance component. The running resistance component Rr may be determined by any method known in this field, for example, using a map prepared in advance with various running conditions of the vehicle as parameters.

By the way, the above formula (4) gives a loss of driving force at a certain point or moment, that is, at a certain point on the road surface, but the road surface condition to be identified depends on the traveling direction of the vehicle. Judgment should be made with reference to the state in the section (length) that extends to. Therefore, when determining whether or not to execute the driving force reduction process when an all-wheel slip sign is detected or later, in order to identify the road surface condition (or characteristic), the driving force loss until then is determined. Need to refer to the situation or history of Accordingly, when determining whether or not to execute the driving force reduction process in the control process of the present invention, the road surface condition is, for example, the primary delay amount ΔFrt of the driving force loss given by the equation (4). ,
ΔFrt = ∫e ^{a (t−τ)} · bΔF (τ) · dτ (5)
It is determined with reference to the size of. Here, a and b are constants set as appropriate, and the integration interval is 0 to t (current time). The time constant of the first-order lag may be set experimentally or theoretically (for example, may be about 1 second to several seconds). In addition, instead of the first-order lag amount ΔFrt, the average of a predetermined interval before the current time point A value, an integrated value, a smoothed average value, or the like may be employed. In the present embodiment, the loss of the driving force is referred to for identifying the road surface condition, but instead, the loss of the driving output (power) or the driving torque may be referred to. It should be understood that (in that case, the unit of Formula (4) is appropriately converted).

  The driving force loss and the first-order delay amount may be always calculated by the driving force loss estimation unit 56 while the vehicle is traveling. Whether the road surface is a rough uneven road or a smooth uniform road is determined by whether or not the primary delay amount of the driving force loss is larger than a predetermined value set experimentally or theoretically. May be.

(ii) Control processing when all-wheel slip sign is detected FIG. 4 shows the above-described driving force loss (primary delay) when the all-wheel slip sign is detected in the apparatus (driving force control unit 58) of the present invention. Is a flowchart showing a process that is repeatedly executed at a predetermined cycle period during driving of the vehicle, with reference to (quantity) as one of the determination criteria. It is. Referring to the figure, in the control process, first, it is determined whether or not there is an all-wheel slip sign (step 10). In this determination, when all the wheel speeds are larger than the upper limit value Vxup of the vehicle speed obtained by the above equation (3) by a predetermined value A or more, that is, for all the wheels,
r · ωi−Vxup> A (6)
Is established, it may be determined that there is an all-wheel slip sign (information is passed from the all-wheel slip sign detection unit 54 to the driving force control unit 58). The predetermined value A may be 0 or a positive constant. When the all-wheel slip sign is detected, the first-order lag amount of the driving force loss calculated by the driving force loss estimation unit 56 is referred to, and it is determined whether or not the value is smaller than a predetermined value. (Step 20).

  Here, if the primary delay amount of the driving force loss is equal to or greater than a predetermined value, the running road surface has a low road surface friction coefficient such as a snowy road, a road surface in which snow and ice are mixed, and a road surface with a crisp feeling. Is determined to be a road surface having a non-uniform surface, the driving force reduction processing by TRC is not executed, and the current processing cycle ends. On the other hand, if the primary delay amount of the driving force loss is smaller than a predetermined value, the road surface is considered to be smooth or uniform, so it is determined whether or not a predetermined time has elapsed since the occurrence of the all-wheel slip sign. (Step 30).

  In step 30, it is determined whether or not the predetermined time has elapsed since the occurrence of the all-wheel slip sign in order to determine whether or not the possibility of being in the all-wheel slip state is considerably high. . As already mentioned, the all-wheel slip sign does not reliably indicate the occurrence of an all-wheel slip condition. In fact, all-wheel slip signs can be detected instantaneously or transiently even when the road surface is smooth or uniform. Therefore, in the illustrated embodiment, after the all-wheel slip sign is first detected, the system waits for a predetermined time (in a state where the driving force loss is equal to or less than the predetermined value), that is, is in an all-wheel slip state. After waiting until the possibility becomes considerably high (the longer the all-wheel slip sign duration is, the more likely that the all-wheel slip state will be), the driving force reduction process is executed. Configured to be Accordingly, the present processing cycle is terminated (return) without executing the driving force reduction process (step 40) until a predetermined time has elapsed after the occurrence of the all-wheel slip sign. On the other hand, if the all-wheel slip sign is detected and the driving force loss falls below a predetermined value while a processing cycle is repeatedly executed, it is determined that the all-wheel slip state has occurred. Then, a driving force reduction process is executed (step 40).

  In the driving force reduction process, preferably, the sum of the driving forces transmitted from the driving device to the driving wheels is set to a value obtained by multiplying the current maximum friction coefficient of the road surface by the vertical load of the vehicle. In the case of normal TRC, on the assumption that the vehicle speed is accurately detected or estimated, as described above, the rotation of the drive wheel is reduced so that the difference between the wheel speed of the drive wheel and the vehicle speed does not become excessive. However, in a situation in which an all-wheel slip sign is detected, the selected vehicle speed is the upper limit value Vxup of the vehicle speed given by the above equation (3), and therefore the reliability is low. On the other hand, when the all-wheel slip sign is continuously detected for a predetermined time and the probability that the all-wheel slip state is considerably high, the driving force requested by the driver or the vehicle is It can be considered that the driving force that can be generated in the vehicle, that is, the maximum limit value (maximum friction circle) of the grip force of the vehicle tire is exceeded. Therefore, in the apparatus of the present invention, the driving force generated in the vehicle is reduced to the maximum limit value of the grip force of the vehicle tire, that is, the value obtained by multiplying the maximum friction coefficient of the road surface by the vertical load of the vehicle. Thus, it is possible to maximize the acceleration performance in a state where the grip force of the tire is maximized under the current driving conditions of the vehicle.

Specifically, the total driving force in the driving wheel set during the driving force reduction process is
(Total driving force) = (maximum friction coefficient of road surface) × M · g (7)
(G is gravitational acceleration). The maximum friction coefficient of the road surface here may be an average value or a minimum value of the maximum friction coefficient μi of the road surface obtained for each wheel. However, in an all-wheel slip state, it can be assumed that the vehicle is traveling at the maximum acceleration, so the value of (maximum friction coefficient of the road surface) × g in equation (7) is It may be a longitudinal acceleration value detected by the G sensor. Thus, when the drive force reduction process is executed, a drive force reduction command is issued from the drive force control unit 58 of the TRC device to the drive control device 18a.

  When the driving force reduction process is executed as described above, the tire grip force is recovered or maintained in the driving wheel. In this regard, it should be understood that if the tire grip force is maintained, the driving force is efficiently transmitted to the road surface, so that the loss of the driving force does not increase. Therefore, if the above-described apparatus of the present invention is functioning effectively, the driving force loss is maintained at a low value when the running road is smooth and the road is smooth (the road surface is rough or uneven). In this case, since the driving force is not reduced, the driving force loss remains large.)

  The driving force reduction process described above may be executed only when the friction state of the ground road surface of the left and right wheels of the vehicle is substantially the same. In the case of road surfaces in which the left and right wheels have different frictional states, i.e., straddle road surfaces, a driving force or wheel speed reduction process of any other mode is usually executed. Therefore, in the control process of FIG. 4, a determination process (step 15) for determining whether or not the road surface is a straddle road surface may be incorporated, and if it is a straddle road surface, the processing cycle is terminated. Whether or not the road surface is a crossing road surface is determined, for example, by referring to the road surface friction coefficient estimated for each wheel when the difference in the road surface friction coefficient between the left and right wheels is equal to or greater than a predetermined value.

  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 principle of the present invention is applicable when each wheel is provided with a drive motor (in-wheel motor) and the driving force is controlled by each wheel, and such a case also belongs to the scope of the present invention. . Further, the driving force reduction process according to the present invention, that is, the method of setting the sum of tire forces to a value obtained by multiplying the maximum friction coefficient of the road surface by the vehicle load, is applied to all-wheel drive vehicles. In this case, the present invention can also be applied to the case where ABS control is executed (in this case, it is not necessary to determine the loss of driving force).

FIG. 1A shows a schematic diagram of an automobile in which a preferred embodiment of a TRC device according to the present invention is realized. FIG. 1B shows the configuration of the TRC device, drive control device, and braking control device of the present invention in the form of a control block diagram. FIG. 2A is a diagram showing the relationship between the wheel speed and the vehicle speed according to normal TRC. When the deviation from the vehicle speed becomes excessive and exceeds the control start threshold, the wheel speed is reduced to the control end threshold. In FIG. 2B, the vehicle speed of the all-wheel (four-wheel) drive vehicle at the current time point is selected from the group of the vehicle speed upper limit value Vxup and the wheel speed rωi determined from the vehicle speed previous value Vxf and the acceleration upper limit value. It is the figure which represented typically the process to perform. FIG. 2C is a view similar to FIG. 2B, but shows a state in which an all-wheel slip sign is detected. FIG. 3 is a diagram for explaining that the loss of driving force varies depending on the road surface on which the vehicle travels. (A) is a case of a smooth and uniform road surface such as a frozen road surface, and (B) is a case of a road surface in which snow and ice are mixed. FIG. 4 shows, in the form of a flowchart, a control process for determining whether to execute a driving force reduction process when an all-wheel slip sign is detected in the TRC of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Car 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 30 ... G sensor 40FL, FR, RL, RR ... Wheel speed sensor 50 ... Electronic control unit

Claims (8)

  A traction control device for a vehicle in which all wheels are drive wheels, all-wheel slip sign detection means for detecting signs that all of the drive wheels are in a slip state during all-wheel drive, and driving force during travel of the vehicle A driving force loss estimating means for estimating the loss of the vehicle and a driving force control means for controlling the driving force at the driving wheels of the vehicle, and all the driving wheels are in a slip state by the all-wheel slip indication means. When a sign is detected, when the loss of the driving force estimated by the driving force loss estimating unit up to that time is equal to or less than a predetermined value, the driving force control unit calculates the driving force on the driving wheels of the vehicle. A device characterized by reducing.   The apparatus according to claim 1, wherein the all-wheel slip sign detection means includes vehicle speed upper limit value estimation means for estimating an upper limit value of a vehicle speed that can occur in the vehicle based on a longitudinal acceleration value of the vehicle. An apparatus for determining that there is an indication that all of the drive wheels are in a slip state when all the wheel speeds of the drive wheels are greater than a predetermined value by a predetermined value or more than the upper limit value of the vehicle speed.   3. The apparatus according to claim 2, wherein the upper limit value of the vehicle speed is determined based on a current longitudinal acceleration value of the vehicle and an acceleration upper limit value that can be generated in the vehicle and before the measurement of the longitudinal acceleration. The apparatus is determined based on a vehicle speed of the vehicle.   2. The apparatus according to claim 1, wherein the driving force loss estimating means calculates a driving force loss during the traveling of the vehicle based on the driving force generated by the vehicle driving device and the longitudinal acceleration of the vehicle. A device characterized by that.   5. The apparatus according to claim 4, wherein the loss of driving force during travel of the vehicle is obtained by multiplying the longitudinal acceleration of the vehicle by the weight of the vehicle from the driving force generated by the driving device of the vehicle. A device characterized by being an amount obtained by subtracting a loss due to running resistance.   2. The apparatus according to claim 1, wherein the all-wheel slip sign detecting means detects signs that all of the driving wheels are in a slip state, and the driving power loss estimated by the driving power loss estimating means until then is detected. The driving force control means reduces the driving force on the driving wheels of the vehicle after a state where the value is equal to or less than a predetermined value continues for a predetermined period.   2. The apparatus according to claim 1, wherein the driving force control means reduces a driving force at driving wheels of the vehicle by reducing an output of the driving device of the vehicle.   8. The apparatus according to claim 7, wherein the sum of the driving forces of the driving wheels of the vehicle is a value obtained by multiplying a maximum friction coefficient of a road surface on which the vehicle travels by a vertical load of the vehicle. A device characterized by reducing driving force.

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