JP5018051B2 - Vehicle driving force control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for controlling the vehicle driving force, which apparatus can avoid the remarkable deterioration of the behavior to be generated when the tire gripping force of a driving wheel of the vehicle has exceeded its critical value in an accelerating period of the vehicle in the neighborhood of the critical performance, and can be safely used for practical use. <P>SOLUTION: The apparatus for controlling the driving force executes the driving force distribution, in which the tire gripping force of at least one driving wheel exceeds the critical value earlier than those of other diving wheels, when the driving forces of a plurality of driving wheels are independently controlled in the vehicle capable of independently controlling the driving forces of a plurality of the driving wheels. The driving forces of a plurality of the driving wheels can be controlled so as to be lower than the critical limit corresponding to the tire gripping force of other driving wheels when the tire gripping force of at least one driving wheel arrives at its critical value. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a driving force control device for a vehicle such as an automobile. More specifically, the present invention relates to the distribution of driving force to each wheel of a vehicle so as to improve the limit (acceleration) performance of the vehicle when driving the vehicle. The present invention relates to a driving force control device to be controlled.

  In the field of vehicle motion control, in order to improve the limit performance during turning acceleration by making the best use of the tire grip force of the wheels, that is, for the purpose of further increasing the maximum acceleration that can be stably output. It has been proposed to control the driving force distribution between the front, rear, left and right wheels in a vehicle (see, for example, Patent Document 1 and Non-Patent Document 1). In a turning vehicle, when the driving force of the wheels is simply increased to the maximum that can be generated uniformly, the tire grip force of some driving wheels (vector sum of driving force (front / rear force) and lateral force) However, since the vehicle is slipping beyond the limit, the maneuverability is deteriorated, and even if the driving force can be increased at other wheels, the driving force cannot be further increased as a whole vehicle. Even if the driving force is forcibly increased, a yaw moment that changes the turning direction is induced in the vehicle, and the acceleration direction of the vehicle does not necessarily coincide with the direction desired by the driver. Therefore, in the driving force distribution control aiming at improving the limit performance at the time of turning acceleration as described above, the tire grip force is maximized while canceling the yaw moment that changes the turning direction of the vehicle (suppressing the yaw rate change). By adjusting the distribution of the driving force or driving torque between the left and right wheels or between the front and rear and left and right wheels so that it is increased (to the limit that no tire slips), this enables acceleration in the desired turning direction It has been proposed to increase as much as possible. If the driving force distribution that raises the limit performance of such a vehicle is achieved, the vehicle can run at a higher speed, and the vehicle can maximize the driving energy without slipping the wheel even during turning at a high acceleration. Therefore, the energy efficiency when driving the vehicle is also improved.

  However, conventionally, the driving force distribution control as described above is not very advantageous in terms of energy efficiency even if it is executed in a normal vehicle configuration, and is therefore not practically used. In vehicles such as automobiles, the braking force or braking torque can be freely distributed by independently adjusting the braking device of each wheel. Basically, a single engine or motor or other drive device is evenly distributed to the left and right drive wheels (in a four-wheel drive vehicle, as is well known, torque distribution to the front and rear wheels is performed by a center differential or the like. ing.). In such a configuration, when a difference in driving force or driving torque is to be applied between the left and right wheels, the driving torque of each driving wheel is transmitted from the driving device to the wheel as in traction control (TRC). The driving torque is adjusted by applying a braking torque by a braking device at each wheel. In other words, in order to obtain the left-right difference of the driving force according to the distribution control, the driving energy once given from the driving device to the wheels is consumed by the braking and is wasted, so even if the driving force distribution control is executed, the energy efficiency Is not very advantageous.

However, in recent years, with the advancement of so-called variable driving force distribution differentials, it has become possible to achieve low-cost distribution of drive torque from a single drive device to the left and right drive wheels (not just front and rear). Therefore, driving force distribution control is becoming one of practical controls in ordinary vehicles. An example of the driving force distribution control using the function of such a driving force variable distribution differential is proposed in Non-Patent Document 1, for example.
JP 2005-67229 A “Development of a four-wheel drive force free control system” Satoshi Mori, Koji Shibata Preliminary Journal of Automotive Technology Development No.76-05, p.19-24

  In the driving force distribution control as described above, the optimum driving force or driving torque to the front, rear, left and right wheels that gives the maximum acceleration that can be generated in the desired turning direction is considered in consideration of load movement between the wheels of the turning vehicle. Allocation is determined. At that time, if the structure of the drive system of the vehicle (from the drive device to the drive wheels) is configured so that the drive force to each wheel can be freely distributed, in the description of the embodiment of the present invention described later. As will be explained, it has been found that an optimal driving force distribution can be determined that achieves a state where the tire grip force of all the driving wheels is increased to the maximum while maintaining the yaw rate (or lateral acceleration) constant. . Therefore, according to such control, the maximum acceleration that can be achieved in the desired turning direction can be obtained with the tire grip force of each driving wheel increased to the limit. In this state, as already mentioned, theoretically, Since all the driving wheels do not slip and all the energy given to the driving wheels contributes to the acceleration of the vehicle, the energy efficiency is also improved.

  However, according to the driving force distribution control as described above, while the actual vehicle is accelerating and turning at the limit performance, the total driving force of the vehicle further increases, or the change of the road surface condition or other disturbance causes the driving wheel to move. If the tire grip force exceeds the limit, there is a possibility that all the drive wheels will slip all at once from the state where the tire grip force is increased to the maximum (the tire force of all the drive wheels is maximum simultaneously) (Or beyond) the friction circle). If this happens, the behavior of the vehicle will deteriorate rapidly, and it will become extremely unstable, and it will be difficult to return the behavior of the vehicle to a stable state if there are almost no drive wheels that maintain the grip state. It becomes.

  Thus, in order to safely implement the driving force distribution control for improving the acceleration limit performance as described above, the vehicle behavior may be significantly deteriorated when the tire grip force exceeds the limit. Although this should be taken into consideration, this is not considered much in the conventional driving force distribution control.

  According to the present invention, the vehicle behavior that may occur when the tire grip force of the driving wheel exceeds the limit during acceleration of the vehicle at or near its limit performance (hereinafter referred to as “limit region”) is significant. Provided is a vehicle driving force control apparatus that is improved so as to avoid deterioration and to safely implement driving force distribution control. The configuration of the present invention is particularly useful in the driving force control apparatus that executes the driving force distribution control for improving the limit performance at the time of turning acceleration of the vehicle as described above. It should be understood that it may be applied in control.

  The driving force control device of the present invention as described above is a driving force control device used in a vehicle that can independently adjust the driving forces of a plurality of driving wheels of a vehicle, and each of the driving forces of a plurality of driving wheels is independent. In the control, the tire grip force of at least one drive wheel is over the limit before the tire grip force of the other drive wheels is executed. According to such a configuration, even if the tire grip force of the wheel exceeds the limit due to an increase in the total driving force or other disturbance, the driving force is set so that only at least one driving wheel exceeds the limit first. It is expected that the tire grip force of the drive wheels will not exceed the limit all at once, and the movement of the vehicle will be safer than before. If the vehicle is a four-wheel drive vehicle and the vehicle is accelerating turning, the driving wheel whose tire slip force exceeds the limit before other wheels has the most margin during turning (the limit of tire grip force). May be the front wheel outside the turn. In the front-wheel drive vehicle or the rear-wheel drive vehicle, when the drive wheels are a pair of left and right wheels, the drive force is controlled so that one drive wheel exceeds the limit before the other. The drive wheel may be on the outside of the turn.

  The above-described configuration of the present invention is such that, for example, when the tire grip force of the at least one driving wheel reaches its limit, the tire grip force of the other driving wheel becomes lower than the corresponding limit, or the tire grip force This may be achieved by controlling the driving force of the plurality of drive wheels such that the magnitude of is allowed to increase to a value below the corresponding limit. By controlling the driving force so that the tire grip force becomes the limit only for some of the driving wheels, but not all of the driving wheels, the increase in the total driving force or disturbance of the entire vehicle or all the driving wheels Even when the tire grip force is increased (or when the tire grip force is relatively large with respect to the corresponding limit value), the driving wheel whose tire grip force has reached the limit exceeds the limit. However, the other drive wheels are more likely to be kept in the grip state. Therefore, it is avoided that the driving wheels slip all at once and the vehicle behavior is extremely deteriorated as before.

  In an embodiment, the apparatus of the present invention comprises means for determining a target turning state quantity representing a desired turning direction of the vehicle, means for determining a road surface friction coefficient on a plurality of drive wheels, Means for determining the distribution of the driving force from the current total driving force to a plurality of driving wheels, and the means for determining the distribution of the driving force maintains the target turning state quantity using the total driving force and the road surface friction coefficient It may be configured to determine the distribution of the driving force to be performed. At this time, the distribution of the driving force is such that when the tire grip force of the at least one driving wheel reaches the limit, the tire grip force of the other driving wheels becomes lower than the corresponding limit. ("Distribution of driving force" is a distribution of driving force to each driving wheel.) In such a driving force distribution state, when the total driving force of the vehicle further increases or due to the influence of other disturbances, Even if the tire grip force of all drive wheels increases relative to the corresponding limit, the limit is first exceeded only for the drive wheel whose tire grip force has already reached the limit. In the wheel, tire grip is maintained, thus avoiding extreme deterioration or instability of vehicle behavior. The “target turning state amount” representing the desired turning direction of the vehicle is an arbitrary amount of target value indicating the turning direction of the vehicle, that is, the target yaw rate determined by the steering angle and the steering angle by the driver's steering. Or it may be a target lateral acceleration.

  In the above control mode, the driving force distributed to each wheel is determined according to how close the tire grip force of each wheel is to its respective limit. In other words, where the limit value of the tire grip force becomes the reference value in the control, the absolute value of the limit value of the tire grip force is a function of the friction coefficient of the road surface and the wheel load. Since it changes according to the road surface condition, it is difficult to handle as a reference value in control. Therefore, in the device of the present invention, the ratio of the tire grip force to the limit value of the tire grip force is used as an index for expressing how close the tire grip force of each wheel is to the respective limit. A certain “tire load factor” is adopted (the tire load factor increases as the tire grip force approaches its limit value, and becomes 1 when the tire grip force reaches the limit value), and the distribution of the driving force of each wheel May be determined based on the tire load factor. In that case, in the control device, the distribution of the driving force calculated by the means for determining the distribution of the driving force limits the tire load factor of each of the plurality of driving wheels so as not to exceed the respective predetermined value. A predetermined value of the tire load factor of at least one drive wheel is set to be greater than a predetermined value of the tire load factor of the other drive wheels, thereby increasing the total driving force of the vehicle or When a situation occurs in which the tire load factor of the drive wheels increases at the same time due to the influence of other disturbances, the tire grip force of at least one of the drive wheels can first exceed the limit.

  In the above-described embodiment, when the vehicle is a four-wheel drive vehicle and the front, rear, left, and right wheels of the vehicle are drive wheels, the distribution of the drive force is based on the total drive force of the vehicle being driven between the front and rear wheels. It can be determined based on the force distribution ratio, the driving force distribution ratio between the left and right front wheels, and the driving force distribution ratio between the left and right rear wheels. Therefore, when controlling the driving force, the above three distribution ratios are determined from the road surface friction coefficient, the total driving force, and the target turning state quantity, thereby determining the distribution of the driving force. If the vehicle is a two-wheel drive vehicle, the distribution of the driving force is determined based on a driving force distribution ratio that distributes the total driving force of the vehicle between the left and right driving wheels. In this case, the friction coefficient of the road surface The driving force distribution ratio between the left and right driving wheels is determined from the total driving force and the target turning state quantity, and the driving force is controlled so that the driving force distribution ratio is achieved.

  By the way, the device of the present invention may execute the driving force distribution control according to the present invention only when the tire grip force of the driving wheel approaches its limit. Therefore, in the apparatus of the present invention, when the tire grip force or the tire load factor of any one or more drive wheels exceeds a predetermined threshold value, that is, approaches the limit, The distribution of the driving force for maintaining the target turning state quantity may be determined using the force and the road surface friction coefficient. The predetermined threshold may be set experimentally or theoretically. As a result, the calculation of the driving force distribution using the total driving force, the road surface friction coefficient, and the target turning state quantity only needs to be performed when the tire load factor or the tire grip force is equal to or greater than a predetermined threshold. The amount is greatly reduced.

  Note that, according to the series of configurations of the above-described embodiment, during the execution of the driving force distribution control, the tire grip force or the tire load factor of at least one driving wheel is allowed to increase to the limit, and the other When the distribution of the driving force is set so that the tire grip force or the tire load factor of the driving wheel is limited to less than the limit, the “at least one driving wheel is allowed to increase the tire grip force or the tire load factor to the limit. "May be determined according to the turning direction of the vehicle. The “at least one driving wheel” may be a front outer wheel when the vehicle is a four-wheel drive vehicle, or a front outer wheel or a rear wheel when the vehicle is a two-wheel drive vehicle.

  In general, the present invention limits the tire grip force of all the drive wheels all at once even if a situation that exceeds the tire grip force of the drive wheels occurs during acceleration of the vehicle (particularly during turning acceleration). Beyond this, it can be said that the driving force control device controls the driving force distribution so that all the driving wheels are prevented from slipping. According to the configuration of the present invention, even when the vehicle is driven at the limit performance of the vehicle, the tire grip force is not increased to the limit except for the specific drive wheel. The maximum acceleration that can be generated is reduced compared to the case where the limit is increased (the control that maximizes the limit performance of the vehicle is increased to the limit of the tire grip force of all the driving wheels of the vehicle). Strictly speaking, in the case of the present invention, maximization in the limit performance is not performed.) However, instead of slightly reducing the maximum acceleration that can be generated, the possibility of all the drive wheels falling into a slip state at the same time is reduced, thereby improving the safety of the control and driving force distribution control in the past. In comparison, it becomes more practical.

  It should be understood that the control of the present invention has a different control objective from the conventional driving force control. The driving force control or the driving force distribution control that has been proposed in the past mainly includes the case where the tire grip force of each wheel does not exceed the limit, including the case of distributing the driving force for the purpose of improving the limit acceleration performance. In other words, the magnitude or distribution of the driving force of each wheel is controlled so that the slip state of the wheel itself does not occur. In other words, the previous control does not cause any wheel to slip. (However, in this case, a state in which the tire grip force of all the driving wheels of the vehicle increases to a limit value is allowed. If, for example, the total driving force increases, the driving force of all wheels increases, all or most of the driving wheels slip all at once, and therefore the behavior of the vehicle becomes extremely unstable. Become a.). On the other hand, in the case of the present invention, rather than suppressing the occurrence of the slip state of the wheel itself, even if the slip of the wheel occurs, the driving force of the driving wheel is prevented from falling into the slip state at that time. The distribution is controlled to control safety, and the aim of the control of the present invention is to ensure safety after the wheel falls into a slip state.

  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.

Diagram 1 of the device is a four-wheeled vehicle in which the preferred embodiment of the driving force control device of the present invention is mounted is schematically shown. In the figure, in a vehicle 10 having left and right front wheels 12FL and 12FR and left and right rear wheels 12RL and 12RR, a driving force is generated in all the wheels in accordance with the depression of the accelerator pedal 14 by the driver in a normal manner. And a steering device 30 for steering the left and right front wheels. In the illustrated example of the drive device 16, the driving torque or rotational driving force from the engine 18 is transmitted to the center differential (or transfer) 22 via the transmission (transmission) 20, and further, the front wheel side driving force is variable. It is transmitted to the front wheels 12FL, 12FR and the rear wheels 12RL, 12RR via the differential 24 and the rear wheel side driving force variable differential 26, respectively (electric type in which an electric motor is used instead of the engine 18 or between the engine and the electric motor) It may be a hybrid drive device having both. Further, the steering device 30 transmits the rotation of the steering wheel 32 rotated by the driver to the tie rods 36L, R via the steering gear mechanism 34, and steers the front wheels 12FL, FR. Although not shown for simplicity, the vehicle 10 is provided with a braking system device that generates a braking force on each wheel in the same manner as a normal vehicle.

  In the above configuration, the driving force distribution ratio k between the front and rear wheels in the center differential, and the driving force distribution ratios kf and kr between the left and right wheels of the front wheel side and rear wheel side variable driving force differentials are normally set. Basically, the driving force from the driving device 16 is set to be distributed evenly to all the wheels (base setting. However, the driving force of the front and rear wheels distributed by the center differential is not uniform for any purpose. There can be.) However, when the tire grip force of each wheel increases and approaches its limit, when executing the driving force distribution control by the driving force control device of the present invention, the distribution ratio is to realize the driving force distribution as described later. Is changed. The variable width of the driving force distribution ratio of each differential is limited by the specific structure and type of the differential mounted on the actual vehicle. However, in this specification, the driving of the present invention is limited. It is assumed that the entire range of distribution ratios that can be required for the force control device is feasible.

  The configuration and operation of the driving force control device of the present invention are realized by 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). And a signal representing the wheel speed Vwi from the sensor, a rotational speed Er of the engine from a sensor provided in each part of the vehicle, an accelerator pedal depression amount θa, and a steering angle sensor provided in the steering shaft 32a. A signal such as a steering angle δ from 32b 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 longitudinal acceleration or lateral acceleration, and the vertical load of each wheel from a load sensor provided on each wheel may be input. Then, to the differential controller corresponding to the differential driving force distribution ratios k, kf, kr determined in the manner described later (for example, a hydraulic control machine (not shown) that operates the clutch). Sent.

Operation of Driving Force Distribution Control The driving force distribution control in the driving force control apparatus of the present embodiment is generally described as driving force distribution control that maximizes the limit performance, that is, wheels (the vehicle in FIG. When the tire grip force of the four-wheel drive vehicle is all about drive wheels) approaches the limit value, the drive device 16 can increase the acceleration in the desired traveling direction of the vehicle as much as possible without slipping the wheels. The distribution of the driving force (or driving torque) transmitted from each wheel to each wheel is controlled. In this control, the desired traveling direction of the vehicle is determined by the steering angle δ by the driver's steering, and the turning direction of the vehicle is also changed according to the fluctuation of the steering angle δ. Therefore, the yaw rate (target yaw rate) determined by the steering angle δ is used as an index (target turning state amount) representing the desired turning direction of the vehicle. The total driving force output from the driving device 16 is determined based on the accelerator pedal depression amount θa by the driver or the engine rotational speed Er, and the tire grip force (the driving force on the wheel (front / rear force) and the lateral force) is determined. Is determined as a function of the road friction coefficient and the ground contact load at each wheel. The load of each wheel is a function of the load movement amount by the longitudinal acceleration (function of total driving force) and lateral acceleration (function of yaw rate) of the vehicle. Therefore, after all, in the above driving force distribution control, when the current total driving force is assigned to each wheel, the target yaw rate is set (when the steering angle δ is constant) using the total driving force, the road surface friction coefficient, and the target yaw rate as reference parameters. The distribution amount or the distribution ratio of the driving force to each wheel that does not change and gives the maximum acceleration (no tire slips) is determined. [In this specification, the road surface friction coefficient is a friction coefficient that gives the maximum (limit) friction force by (road surface friction coefficient) x (contact load) in the wheel, and depends on the slip ratio of the wheel. It is the maximum value of the changing (apparent) friction coefficient. ]

  In the driving force distribution control, the driving force distribution has been determined and executed so that the tire grip force is allowed to increase to the corresponding limit value in all the driving wheels. However, in the present invention, in one drive wheel, the tire grip force is allowed to increase to its corresponding limit value, but in the other drive wheels, the tire grip force is The driving force is distributed so as not to exceed a value lower than the corresponding limit value, for example, 90% of the limit value.

FIG. 2 shows a control process of the driving force control apparatus of the present invention in the form of a flowchart (the illustrated control process may always be executed during operation of the vehicle). Referring to the figure, in the processing, first, from the parameters referred in the control, that is, the accelerator pedal depression amount θa or the engine speed Er, etc., all the wheels at the current engine output are obtained. The road surface friction coefficient μ estimated by an arbitrary method based on the total driving force Dt that can be applied, the wheel speed Vwi and the vehicle speed Vs (for example, the average value or the minimum value of all wheel speeds). And the target yaw rate γt determined by the steering angle δ, the vehicle speed Vs, and the like are respectively acquired or calculated (step 10). The target yaw rate γt is a well-known relational expression between the steering angle δ and the yaw rate when it is assumed that the vehicle achieves neutral steering.
γt = (Vs / l) δ (1)
May be determined. Here, l is the distance between the axles of the front and rear wheels (wheel base). The left turn direction is positive.

Next, in order to determine whether or not to change the driving force distribution ratio from the base setting, the current tire load factors eti of all the wheels are calculated (step 20). As already mentioned, the tire load factor is a ratio between the current tire grip force and its limit value, and is defined by the following equation (see FIG. 2B).
eti = (Di ² + Fi ² ) ^1/2 / μ · Wi · g (2)
Here, Di is the longitudinal force (driving force) of each wheel, Fi is the lateral force of each wheel, Wi is the vertical load of each wheel, and g is the gravitational acceleration. Di, Fi, and Wi may be calculated in the following manner, respectively.

If the longitudinal force Di of each wheel is accelerating, the total driving force Dt is expressed as follows using the current differential driving force distribution ratio k (center), kf (front wheel side), kr (rear wheel side). Calculated by the formula. (Where k is the distribution ratio of the driving force to the rear wheels, kf is the distribution ratio of the driving force allocated to both front wheels to the right front wheel, and kr is the driving allocated to both rear wheels. (It is defined as the distribution ratio of driving force to the right rear wheel of force)
D _FL = Dt · (1-k) · (1-kf) (3)
D _FR = Dt · (1−k) · kf
D _RL = Dt · k · (1-kr)
D _FR = Dt · k · kr
It should be understood that k, kf, and kr are base settings when the driving force distribution control for improving the limit performance according to the present invention is not executed as described above.

The vertical load Wi of each wheel is calculated by the following equation in consideration of the influence of the load movement amount Δx in the longitudinal direction due to acceleration of the vehicle and the lateral load movement amounts Δyf and Δyr due to the centrifugal force in the respective front and rear wheels. Given by.
W _FL = (1/2) M · l r / l− (1/2) Δx−Δyf (4)
W _FR = (1/2) M · l r / l− (1/2) Δx + Δyf
W _RL = (1/2) M · l f / l + (1/2) Δx−Δyr
W _FR = (1/2) M · lf / l + (1/2) Δx + Δyr
Here, M is the vehicle weight, and lf and lr are distances from the front and rear wheel shafts to the center of gravity of the vehicle, respectively. The amount of forward load movement Δx due to vehicle acceleration and the amount of lateral load displacement Δyf, Δyr due to centrifugal force are:
Δx = H · Dt / (l · g) (5)
Δyf = H · M · Rf · Yg / (Tr · g)
Δyr = H · M · Rr · Yg / (Tr · g)
Given in. Here, H is the height of the center of gravity, Rf and Rg are the roll stiffness distribution in the front and rear wheels, and Tr is the tread length. Yg is the lateral acceleration,
Yg = Vs · γt (6)
(If the vehicle is in a normal state, the current yaw rate of the vehicle may be considered to match the target yaw rate.)

なお、上記の式の大括弧内において、第一項が遠心力に釣り合うための力の成分であり、第二項が、前後力Ｄｉにより発生するヨーモーメントに釣り合うための前後輪間の横力の移動分である。第一項の括弧内に於いては、車両停止時の前輪又は後輪へ割り当てられる車重から加速による荷重移動量の分が補正されている。 Further, the lateral force of each wheel is corrected from the force for balancing the centrifugal force in each of the front and rear wheels to the amount of movement of the lateral force between the front and rear wheels to balance the yaw moment generated by the front and rear force Di. Further, since it is considered that the distance between the left and right wheels is distributed in proportion to the vertical load, it is given by the following equation.

In the brackets of the above formula, the first term is a component of force for balancing the centrifugal force, and the second term is the lateral force between the front and rear wheels for balancing the yaw moment generated by the longitudinal force Di. The amount of movement. In the parentheses in the first term, the amount of load movement due to acceleration is corrected from the vehicle weight assigned to the front or rear wheels when the vehicle is stopped.

  The calculation of Wi and Fi described above may be executed more strictly in consideration of the front wheel steering angle δ and the slip angle of each wheel, and it is understood that the expression in that case can be arbitrarily configured by those skilled in the art. It should be.

  Thus, when the current tire load factor eti of each wheel is calculated by the above formulas (2) to (7), it is determined whether the tire load factor eti of each wheel exceeds a predetermined threshold Th. (Step 30). The predetermined threshold may be 0.8, for example. Further, since the magnitude of the limit value of the tire grip force varies depending on whether the vehicle is outside or inside the turn or the front and rear of the vehicle (the degree of tire margin is different), the threshold value Th may be different for each wheel. Good. Here, if the tire load factor eti of each wheel does not exceed the predetermined threshold Th, the driving force distribution ratios k, kf, kr of the differentials remain at the base setting (or returned to the base setting) ( Step 35). However, if the tire load factor exceeds the threshold value for at least one wheel, the vehicle acceleration has reached the limit range (base setting makes it difficult to distribute the driving force with a margin in the tire load factor). Determination is made and the driving force distribution ratios k, kf, kr of each differential are changed to execute the driving force distribution control for maximizing the limit performance (step 40).

  In step 40, the values of the driving force distribution ratios k, kf, kr are prepared in advance using the lateral acceleration Yg (calculated from the target yaw rate γt), the road surface friction coefficient μ, and the total driving force Dt as parameters. The map may be selected from a combination map of distribution ratios k, kf, and kr. The combination of the driving force distribution ratios k, kf, kr selected from the map, if allowed to increase to the limit of the tire grip force in all wheels (as before), then the target yaw rate γt, road surface A combination in which the tire load factor of all wheels is 1.0 or less in the friction coefficient μ and the total driving force Dt, that is, the tire grip force of each wheel does not exceed the corresponding limit value; Become. However, as already mentioned, in the driving force distribution control of the present invention, the tire load factor does not reach the limit value 1 except for the turning outer front wheel, for example, tires other than the turning outer front wheel. The distribution of driving force is controlled so that the load factor does not increase beyond 0.9. In other words, in the control device of the present invention, the combination of the driving force distribution ratios k, kf, kr selected from the map is a combination that prevents the tire load factor from exceeding a predetermined value in all the wheels. The predetermined value is an arbitrarily set value of 1.0 for the front outer wheel and less than 1.0 for the other wheels. The map preparation will be described later.

  Thus, when the driving force distribution ratio k, kf, kr value is determined in step 35 or step 40, a control command is transmitted to the controller of each differential (step 50), and the control is repeated.

Adjustment of the driving force distribution ratio map The combination of the driving force distribution ratios k, kf, kr to be determined in step 40 of FIG. 2 is the predetermined upper limit value for all wheels (for example, the front outer wheel of the turn). The tire load factor eti must be 1.0 or less for other than 1.0. As easily understood from the equations (2) to (7), the tire load factor eti is the total driving force Dt, the road surface friction coefficient μ, the lateral acceleration Yg (calculated by the equation (6) from the target yaw rate γ) and the driving force. Since it is a function of the distribution ratios k, kf, and kr, the tire load factor eti is set to each predetermined upper limit for all wheels, with an arbitrary road friction coefficient μ, lateral acceleration Yg, and total driving force Dt as given parameters. By searching for the driving force distribution ratios k, kf, and kr that are less than or equal to the values, the driving force distribution ratios k, kf, and kr when the road surface friction coefficient μ, the lateral acceleration Yg, and the total driving force Dt are given are determined. be able to.

According to a calculation experiment by the inventor of the present invention, an arbitrary road friction coefficient μ, lateral acceleration Yg, and total driving force Dt are given parameters, and the driving force distribution ratios k, kf, and kr are variable over the entire range. By changing the values of the driving force distribution ratios k, kf, kr in the driving force Di of the above equation (3) and calculating the tire load factor eti of each wheel of the above equation (2), all wheels The condition that the tire load factor eti is equal to or lower than a predetermined upper limit value, for example,
About the front outer wheel FO for turning et _FO ≦ 1.0
Other than that,
eti ≦ 0.9 (8)
(I is the turning inner front wheel, turning outer rear wheel, turning inner rear wheel)
It was found that the ranges of the driving force distribution ratios k, kf, and kr that satisfy the above are determined as a three-dimensional region (see FIG. 3A). In addition, the range of the driving force distribution ratios k, kf, and kr that gives the tire load factor eti that satisfies the above condition (8) is reduced as the total driving force Dt increases for a given road surface friction coefficient μ and lateral acceleration Yg. (The tire load factor eti increases overall) (see FIG. 3B), and the tire load factors of all the wheels reach their respective upper limit values,
About the front outer wheel FO for turning et _FO = 1.0
Other than that,
eti = 0.9 (8a)
Then, it was found that the driving force distribution ratios k, kf, and kr converge to one combination (FIG. 3C). Therefore, the map used in step 40 of FIG. 2 is the driving force distribution ratio k, over the entire range of the road surface friction coefficient μ, the lateral acceleration Yg and the total driving force Dt that is assumed in the traveling of the vehicle. The tire load factor etti is calculated for the entire variable range of kf and kr, and the ranges of the driving force distribution ratios k, kf, and kr where the tire load factor eti of all the wheels is equal to or less than a predetermined upper limit value are obtained. It can be prepared by selecting an appropriate value (for example, the center value of the range) from the range of the obtained driving force distribution ratios k, kf, and kr.

  FIG. 4 shows, in the form of a flowchart, processing for determining the values of the driving force distribution ratios k, kf, and kr when a certain road surface friction coefficient μ and lateral acceleration Yg are given in the above map preparation. Is. As will be understood by those skilled in the art, if the total driving force is not very high, the tire load factor of all the wheels is not more than the above upper limit value even if the driving force distribution ratios k, kf, and kr are set as the base settings. Obviously, in this case, it is not necessary to change the driving force distribution ratios k, kf, and kr (see the processing of steps 20, 30, and 35 in FIG. 2). Therefore, in the illustrated process, first, the driving force distribution ratios k, kf, and kr are set in the base setting, and the tire load factor of all the wheels is calculated while increasing the total driving force from an arbitrarily low value. . (Accordingly, it is possible to confirm the range of conditions of the total driving force Dt, the road surface friction coefficient μ, and the lateral acceleration Yg that can be handled by the base setting driving force distribution ratio. Then, when the total driving force Dt increases to some extent, and when the tire load factor of all wheels approaches the upper limit to some extent, the driving force distribution ratios k, kf, kr are changed for the first time from that point. The tire load factor is calculated, and the range of the driving force distribution ratios k, kf, kr satisfying the above condition (8) and the center value thereof (on the map) are considered considering which of the left and right sides is outside or inside the turn. The value to be adopted is determined.

  Referring to FIG. 4, first, an arbitrary low value Dt0 is set as the total driving force Dt (step 100), and using the base setting driving force distribution ratios k, kf, kr, equations (2)-(7 ), The tire load factor eti of all the wheels is calculated (step 110). Then, it is determined whether or not the calculated tire load factor eti for all wheels exceeds a predetermined threshold Th, for example, 0.8 (step 120). As described above, if the total driving force Dt is small, the tire load factor eti does not exceed a predetermined threshold value (meaning that the base setting driving force distribution ratio can be sufficiently handled). The total driving force is increased by a predetermined amount ΔDt (step 130), and steps 110 and 120 are repeated. Such processing is repeated until any tire load factor eti exceeds a predetermined threshold Th while gradually increasing the total driving force.

  When any of the tire load factors eti exceeds a predetermined threshold Th (step 120), this time, the tire load factors eti of all the wheels are calculated over the entire variable range of the driving force distribution ratios k, kf, and kr (step 120). Step 140). Here, the driving force distribution ratio is the variable load range (kmin, kmax), and the driving force distribution ratios k, kf, kr are set at appropriate nick widths Δk, and the tire load factors eti of all the wheels for all combinations. [A three-dimensional lattice with a lattice width Δk is assumed in the three-dimensional space of k, kf, and kr, and the tire load factor eti is calculated for all of the lattice points. ] Corresponding to whether the left or right is on the outside or inside of the turn (when the left turn (Yg> 0), the right front wheel is set to the outside of the turn), the above conditions (8) are given, and k, kf, kr A range is identified (step 150). In this regard, when considering a three-dimensional space of the driving force distribution ratios k, kf, kr, as already described, a set of (k, kf, kr) satisfying the above condition (8) is a three-dimensional region. Is known to be identified as Therefore, the set of combinations of k, kf, and kr that satisfy the above condition (8) is specified by detecting the coordinates of the boundary surface of the region in the three-dimensional space of the driving force distribution ratios k, kf, and kr. can do. It should be understood that identification of the boundaries of the k, kf, and kr regions that satisfy the above condition (8) can be done by any method for those skilled in the art. For example, as shown in FIG. 5, the tire load factor eti is calculated while k and kf are fixed and kr is changed by a minute amount Δk, and the lower limit krlow and the upper limit krhigh satisfying the condition (8) are determined. (Refer to steps 210 to 270) is repeated while changing kf by a minute amount Δk (see steps 280 to 290), and further, the operation is repeated while changing k by a minute amount Δk (steps 300 to 310). Reference), the coordinates of the boundary surface of the region satisfying the condition (8) can be specified.

  Next, in step 150, after identifying the k, kf, and kr regions that satisfy the above condition (8), there is a significant combination of k, kf, and kr that falls within the k, kf, and kr regions [ When there are three-dimensional space grid points] (step 160), the combination of the center points of the region is selected as the driving force distribution ratio k, kf, kr of the total driving force Dt at that time (step 170). The center point is, for example, the center of gravity of the region of k, kf, kr that satisfies the above condition (8) (the sum of the coordinate values k, kf, kr of the boundary surface divided by the number of coordinates of the boundary surface, etc. ). The reason why the center point is selected is that it is assumed that the tire load factor has almost the same margin for any wheel (the center point has a distance (margin) to the boundary surface in any direction). .

  Thus, when the selected values of the driving force distribution ratios k, kf, kr in the total driving force Dt (and the road surface friction coefficient μ and the lateral acceleration Yg) at that time are determined, the total driving force Dt is determined by a predetermined increment ΔDt. Increase (step 180), steps 140-170 are repeated, and the selection values of the driving force distribution ratios k, kf, kr in the total driving force Dt are sequentially determined. When this process is repeated and the total driving force Dt is increased, as already described, the driving force distribution ratios k, kf, and kr that give the tire load factor satisfying the condition (8) converge to one point, that is, The tire load factor eti reaches the upper limit in the control of the present invention (depending on the size of the knurled width Δk, a combination (grid point) of k, kf, and kr that satisfies the upper limit of the tire load factor is calculated. It can be several.) Therefore, when the total driving force Dt is further increased (step 180), the region does not exist in the determination at the next step 160, and thus the processing is completed. Thereafter, the road surface friction coefficient μ and the lateral acceleration Yg are changed, and the same calculation as in FIG. 4 is repeated, and the entire range assumed for the road surface friction coefficient μ and the lateral acceleration Yg corresponds to the total driving force Dt. A map of the driving force distribution ratios k, kf, kr is prepared by determining the selection values of the driving force distribution ratios k, kf, kr.

  In the actual traveling vehicle, when the driving force distribution ratio of each differential is set by the map of the driving force distribution ratios k, kf, and kr described above, in each wheel (right and left corresponding to the turning direction) The driving force is adjusted so as to satisfy the condition (8) (one of the above is set to the outside of the turn). Further, since the lateral acceleration Yg is used as a parameter in the calculation of the map, by selecting the map value (k, kf, kr) in the lateral acceleration Yg corresponding to the target yaw rate during control. Even in the distribution of the driving force after the control, the lateral acceleration and the yaw rate are maintained at their target values, so that the vehicle is accelerated in a desired direction.

  When the tire load factor of all the wheels increases due to the increase in the total driving force Dt or the lateral acceleration Yg or the decrease in the road friction coefficient, each wheel driving force is distributed according to the map of the driving force distribution ratio k, kf, kr. Therefore, the above condition (8a) is always reached. In this state, the tire load factor is 1.0 or less except for the front outer wheel, so the limit has not been reached. Therefore, even if the effect of increasing the tire load factor is added to the vehicle and the front outer wheel of the turn exceeds the limit, the other wheels are expected to maintain the grip state without exceeding the limit. As a result, it is possible to avoid a significant deterioration in the vehicle behavior (when the front wheel outside the turn begins to slip, it is expected that the VSC and other control devices that stabilize the behavior will be activated. By maintaining the grip state except for the front wheels, behavioral repair will be performed better than if all wheels slip.)

  In the above map preparation, the process of changing the driving force distribution ratios k, kf, kr from the base setting is executed after the tire load ratio exceeds the threshold Th (step 120). However, the driving force distribution ratios k, kf, and kr are determined by the procedure of calculating the region of the driving force distribution ratios k, kf, and kr from the initial value Dt0 of the total driving force and determining the center value thereof. (However, the amount of calculation and the amount of map data increase.) In that case, steps 20, 30, and 35 in FIG. 2 may be omitted, and step 40 may always be executed. In the above map preparation, the tire load factor threshold Th may be set to the condition (8a), that is, the upper limit value. When the map prepared in this way is used, the driving force distribution control for changing the driving force distribution ratio cannot satisfy the condition (8) with the base setting driving force distribution ratio while the vehicle is running. Sometimes it will be executed for the first time. In this case, the driving force distribution ratio of the base setting is used up to the usable limit, and the driving force distribution ratio is changed from the base setting as soon as the tire load factor of any wheel exceeds the upper limit value. Change is likely to be abrupt. Further, since the prepared map is composed of a set of driving force distribution ratios (k, kf, kr) using the total driving force Dt, the friction coefficient μ, and the lateral acceleration Yg as variables, the map preparation process shown in FIG. In the example, calculation processing is illustrated in which the friction coefficient μ and the lateral acceleration Yg are fixed and the total driving force Dt is gradually increased. However, the total driving force Dt and one of the friction coefficient μ and the lateral acceleration Yg are fixed. Thus, it should be understood that a similar map can be prepared by gradually changing the other one of the friction coefficient μ and the lateral acceleration Yg.

In the case of a two-wheel drive vehicle, the driving force distribution control in the case of a four-wheel drive vehicle can be similarly performed in the case of a two-wheel drive vehicle. The control during traveling of the vehicle may be the same as the process shown in FIG. However, for front-wheel drive vehicles, only the left and right front wheels are drive wheels, so the tire load factor is calculated only for the left and right front wheels. In that case, the equations (3) to (7) may be set as k = 0. In the rear wheel drive vehicle, only the left and right rear wheels are drive wheels, so the tire load factor is calculated only for the left and right rear wheels. In that case, equations (3)-(7) may be set as k = 1. Map preparation may be performed as in FIG. In step 140, it is only necessary to change only kf for the front wheel drive vehicle and only kr for the rear wheel drive vehicle. Conditions (8) and (8a)
About turning outer wheel et _OUT ≦ 1.0
About turning inner ring et _IN ≦ 0.9 (9)
To be corrected.

  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 determination of the driving force distribution ratios k, kf, and kr in step 40 of FIG. 2 is determined from a map prepared in advance, but during the vehicle control, the target yaw rate γt and the road surface at that time It may be calculated sequentially using the friction coefficient μ and the total driving force Dt. (In the case of a two-wheel drive vehicle, since the driving force distribution ratio to be changed is one, it does not take much time to calculate during control.) The principle of the present invention is the driving force by braking of each wheel. It can be applied to the case of distribution, or when each wheel is provided with a driving 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.

FIG. 1A shows a schematic diagram of an automobile in which a preferred embodiment of a driving force control apparatus according to the present invention is realized. FIG. 2A is a flowchart showing the operation of the control device according to the preferred embodiment of the present invention. FIG. 2B is a diagram illustrating the tire load factor. FIG. 3 shows a change in the combination range of driving force distribution ratios in which the tire driving factors of all the driving wheels are less than or equal to the upper limit values as the total driving force Dt increases at a certain road surface friction coefficient μ and lateral acceleration Yg. It is a figure explaining what to do. In the figure, in the three-dimensional space of (k, kf, kr), the boundary surface of the region that satisfies the condition (8) is shown. The change range of (k, kf, kr) is 0 to 1.0 for k and 0.5 to 1.0 for kf and kr. Further, the road surface friction coefficient μ = 1.0 and the lateral acceleration Yg = 4.9 m / s ² (while turning left). FIG. 3A shows an area (usable range) that satisfies the condition (8) when the total driving force Dt = 2400 Nm, and a base setting point exists in the area (an area between two boundaries). To do. FIG. 3B shows a region (boundary surface thereof) that satisfies the condition (8) when Dt = 3800 Nm. The region contracts and the base setting point is outside the region (if k, kf, If kr remains at the base setting, one of the wheels will slip beyond the limit, and by setting k, kf, kr within the range, the limit performance of the vehicle will increase. FIG. 3C shows (k, kf, kr) that satisfies the condition (8a). In the illustrated calculation example, when Dt = 4260 Nm, k = 0.53, kf = 0.82, It converged to one point of kr = 0.62. FIG. 4 is a flowchart showing a procedure for preparing a map of combinations of driving force distribution ratios used in step 40 of FIG. In the figure, the usable range of k, kf, and kr is a three-dimensional region of k, kf, and kr that satisfies the condition (8). FIG. 5 is a flowchart illustrating a procedure for determining a combination region of a driving force distribution ratio in which a tire load factor of all driving wheels is equal to or less than an upper limit value in a certain road surface friction coefficient μ, a lateral acceleration Yg, and a total driving force Dt. It is expressed in the form of Null means no value. The variable range [kmin, kmax] of Δk and the distribution ratio may be different for each differential. S225 is for omitting the execution of calculation after changing kr since the lower limit and the upper limit of kr are determined when S220 becomes YES after S220 becomes YES. Similar processing may be performed for kf and k.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Vehicle body 12FL, FR, RL, RR ... Wheel 14 ... Accelerator pedal 16 ... Drive device 18 ... Engine 20 ... Transmission 22 ... Center differential 24 ... Front wheel drive force variable differential 26 ... Rear wheel drive force variable differential 30 ... Steering device 32 ... Steering wheel 32 ... Steering angle sensor 40FL, FR, RL, RR ... Wheel speed sensor 50 ... Electronic control unit

Claims (10)

A vehicle driving force control device capable of independently adjusting the driving forces of a plurality of driving wheels of a vehicle, wherein the driving forces of the plurality of driving wheels are controlled independently by at least one driving wheel. The distribution of the driving force is performed so that the tire load factor, which is the ratio of the tire grip force to the limit value of the tire grip force, which is permitted in this case, is higher than the tire load factor permitted in the other driving wheels. apparatus.   2. The apparatus of claim 1, wherein when the tire grip force of the at least one drive wheel reaches its limit, the tire grip force of the other drive wheel is lower than a corresponding limit. A device characterized by controlling a driving force.   2. The apparatus of claim 1, wherein when the tire grip force of the at least one drive wheel reaches its limit, the magnitude of the tire grip force of the other drive wheel increases to a value lower than the corresponding limit. A device for controlling a driving force of the plurality of driving wheels so as to allow the driving force.   4. The apparatus according to claim 1, wherein the front, rear, left and right wheels of the vehicle are the plurality of drive wheels, and the at least one drive wheel is a front wheel outside the turn when the vehicle turns. apparatus.   4. The apparatus according to claim 1, wherein the plurality of driving wheels are a pair of left and right driving wheels, the at least one driving wheel is one of the pair of left and right driving wheels, and the other driving wheel is the device. A device that is the other of a pair of left and right drive wheels. 4. The apparatus according to claim 1, wherein means for determining a target turning state amount representing a desired turning direction of the vehicle , means for determining a road surface friction coefficient on the plurality of drive wheels, and the vehicle. Means for determining the distribution of the driving force from the current total driving force to the plurality of driving wheels, and means for independently controlling the driving force of the plurality of driving wheels according to the distribution of the driving force, Means for determining the distribution of the driving force determines the distribution of the driving force for maintaining the target turning state quantity using the total driving force and the road surface friction coefficient, and the distribution of the driving force is a tire grip of the at least one driving wheel. When the force reaches the limit, the distribution is such that the tire grip force of the other drive wheels is lower than the corresponding limit.   7. The apparatus of claim 6, further comprising means for determining a tire load factor that is a ratio of a tire grip force to a limit value of the tire grip force of the plurality of drive wheels, wherein the tire load factor exceeds a predetermined threshold value. The means for determining the distribution of the driving force at the time calculates the distribution of the driving force for maintaining the target turning state quantity using the total driving force and the road surface friction coefficient.   7. The apparatus according to claim 6, wherein the front, rear, left and right wheels of the vehicle are driving wheels, and the distribution of the driving force is determined by the total driving force of the vehicle, the driving force distribution ratio between the front and rear wheels, and the driving between the left and right front wheels. The apparatus is determined based on a force distribution ratio and a driving force distribution ratio between the left and right rear wheels.   7. The apparatus according to claim 6, wherein the plurality of driving wheels are a pair of left and right driving wheels, and the distribution of the driving force is determined based on a driving force distribution ratio between the left and right driving wheels. Device to do.   7. The apparatus according to claim 6, wherein the target turning state quantity is selected from the group consisting of a steering angle by a driver's steering, a target yaw rate determined from the steering angle, and a target lateral acceleration.

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