JP5082694B2 - Vehicle driving force distribution control device - Google Patents

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 distribution 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 of the vehicle is induced, and the traveling direction of the vehicle does not necessarily match the direction desired by the driver. Therefore, in the driving force distribution control for the purpose of 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 (the limit that no tire slips). It has been proposed to adjust the distribution of the driving force or driving torque between the left and right wheels or between the front and rear left and right wheels so as to increase the acceleration in the desired turning direction as much as possible. Yes. 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, in a normal vehicle configuration, the driving force or driving torque is evenly distributed from the driving device such as a single engine or motor to the left and right driving wheels. When the control is to be executed, the driving torque of each driving wheel is applied to the driving torque transmitted from the driving device to the wheel by the braking device at each wheel, as in traction control (TRC). It will be adjusted by doing. Accordingly, since the driving energy once given to the wheels from the driving device is consumed by the braking and is wasted, even if the driving force distribution control is executed, the energy efficiency is not very advantageous. However, in recent years, the so-called variable driving force distribution differential (differential device) has made it possible to distribute the drive torque from a single drive device to the left and right drive wheels at low cost (not only front and back). Driving force distribution control is becoming one of the practical controls in ordinary vehicles. Examples of driving force distribution control using the function of such a driving force variable distribution differential are proposed in Non-Patent Document 1 and Patent Documents 2-4, for example.
JP 2005-67229 A JP2005-82009 JP2005-112007 JP 2006-69519 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 vehicle drive system (from the drive unit to the drive wheels) is configured so that the drive force to each wheel can be freely distributed or independently adjusted, the lateral acceleration (or yaw rate) is quasi-steady. It has been found that an optimal driving force distribution can be determined that achieves a state in which the tire grip force of all the driving wheels is increased to the maximum while keeping the driving force 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, a differential or a driving force distribution device that is actually mounted on a vehicle has various restrictions on the distribution of the driving force. For example, in the case of an electronically controlled coupling method (speed constraint method) or a torque sensitive type differential that is often employed in the center differential of a four-wheel drive vehicle, the rotational speed of the rotating shaft to which the driving force is distributed or the front and rear Since the driving force distribution mode is determined by the difference in the rotational speed of the wheels, the driving force is distributed by the center differential when determining the driving force distribution amount (driving force disassembly / disassembly) of each wheel. It is necessary to consider the rotational speed of each of the rotating shafts.

  Thus, an object of the present invention is to provide a four-wheel drive vehicle that employs a speed constraint type or torque sensitive type differential in which the distribution of the driving force is determined according to the rotational speed of the rotary shaft to the center differential as described above. Another object of the present invention is to provide a driving force distribution control device capable of determining the optimal distribution of driving force or driving torque to the front, rear, left and right wheels for improving the limit performance during turning acceleration of the vehicle as described above.

  According to the present invention, the above-mentioned problem is achieved by a vehicle driving wheel comprising a speed-constrained or torque-sensitive center differential and a driving force distribution differential that distributes the driving force of at least one of the front and rear wheels. A driving force distribution control device for a four-wheel drive vehicle that distributes the driving force at a variable distribution ratio to a total driving force generated in the vehicle, a front wheel rudder angle, a front wheel slip angle, and a rear wheel slip angle. The total driving force is determined by each wheel driving force determined based on the product of the slip ratio of each wheel of the vehicle and the driving stiffness of each corresponding wheel when the driving force distribution differential is determined based on each driving force. This is achieved by a device that controls the operation of the driving force distribution differential to be distributed to the wheels. In the configuration of the present invention, the driving force distributed to each wheel may be adjusted so that the tire grip force of the driving wheel of the vehicle does not exceed the limit.

  In the structure of the vehicle drive system (from the drive unit to the drive wheels), if it is configured to be able to freely distribute the drive force to all the drive wheels, to improve the limit performance during turning acceleration When determining the optimal distribution of the driving force or driving torque to the front, rear, left and right wheels, it was only necessary to consider the driving force distributed to each wheel and the lateral force generated depending on the turning state of the vehicle at that time. When a speed constraint type or torque sensitive type differential is used for the center differential, as described above, these differentials are restricted in the relationship between the rotational speeds of the front and rear wheels. The rotation speed between the front and rear wheels or the wheel speed is determined under a predetermined constraint condition. At that time, the driving force actually generated in each wheel is given by the product of the slip rate of each wheel and the driving stiffness of each wheel, and the slip rate is a function of the vehicle speed and the wheel speed. The vehicle speed depends on the rudder angle of the front wheels, the front wheel slip angle, and the rear wheel slip angle. Therefore, eventually, the distribution of the driving force of each wheel is determined based on the total driving force generated in the vehicle, the rudder angle of the front wheel, the front wheel slip angle, and the rear wheel slip angle, as described above. This is determined based on the product of the slip ratio of each wheel of the vehicle and the driving stiffness of each corresponding wheel when the driving force distribution differential is actuated.

  In the vehicle to which the above-described device of the present invention is applied, when the center differential is a speed constraint type driving force distribution device, the distribution operation of the center differential driving force is controlled by the constraint rate with respect to the rotational speed of the front and rear rotating shafts. Will be. Therefore, in this case, in the apparatus of the present invention, the driving force of each wheel of the vehicle is the total driving force, the restraint rate of the rotational speed of the front and rear rotating shafts of the speed restraint type driving force distributor, and the driving force distribution. It may be given by the driving force distribution ratio of the left and right wheels of the differential.

  Further, in the vehicle to which the above-described device of the present invention is applied, when the center differential is a torque-sensitive driving force distribution device, the distribution operation of the center differential driving force is determined by the front and rear wheel speeds, and is active. Therefore, the distribution ratio of the driving force of the center differential is not controlled from the apparatus of the present invention. Therefore, in that case, in the apparatus of the present invention, the driving force of each wheel of the vehicle is given by the total driving force and the driving force distribution ratio of the left and right wheels of the driving force distribution differential. Good.

  In the embodiment, the driving force of each wheel is typically determined by using the vehicle speed, the turning state amount, the total driving force, and the road surface friction coefficient of each wheel as input parameters. That is, the distribution of driving force for actually controlling the movement of the vehicle may be determined by giving these values. Here, “distribution of driving force” is a distribution of driving force to each driving wheel. Further, the “turning state amount” may be an arbitrary amount indicating the turning direction of the vehicle, that is, a steering angle, a yaw rate, a lateral acceleration, or the like by the driver's steering. Here, the turning state quantity used as the input parameter may be an actual measurement value or a target value determined by the driver's steering.

  In the above control mode, preferably, 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. It may be like this. In that case, the absolute value of the tire grip force limit value is a function of the friction coefficient of the road surface and the wheel load, where the limit value of the tire grip force becomes the reference value in the control. Moreover, since it changes according to the road surface condition, it is difficult to handle it 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 described above, the distribution of the driving force may be a distribution that limits the tire load factor of each of the plurality of driving wheels so as not to exceed the respective predetermined value.

  According to the present invention, in general, the driving force capable of securing the grip force of the four wheels even when the speed constraint type or torque sensitive type driving force distribution device is mounted as the center differential in the four-wheel drive vehicle. Allocation control is expected to be executed. The speed constraint type or torque sensitive type differential or driving force distribution device has the trouble that the constraint condition must be considered in the rotational speed of the rotating shaft of the front and rear wheels, but the driving force distribution ratio can be freely changed. This is superior to the variable driving force distribution differential in terms of adoption record, mounting space, weight, and cost, and this makes driving force distribution control more practical than before.

  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. 1 (A) a four-wheeled vehicle in which the preferred embodiment of the driving force distribution control apparatus 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 on the front wheels in accordance with the depression of the accelerator pedal 14 by the driver in a normal manner. A driving device 16 and a steering device 30 for steering the left and right front wheels are mounted. In the example shown in the figure, 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 in the driving device 16, and further, the front wheel side differential 24 and It is transmitted to the front wheels 12FL, 12FR and the rear wheels 12RL, 12RR through the rear wheel side differential 26 (electric type in which an electric motor is used instead of the engine 18 or a hybrid type having both an engine and an electric motor). It may be a drive device). 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, either one or both of the front wheel side differential and the rear wheel side differential uses a differential that can distribute the driving force of the left and right wheels in accordance with the driving force distribution ratios kf and kr (the driving force distribution is For variable differentials, it is assumed that the entire range of distribution ratios that can be required by the driving force distribution control device of the present invention can be realized). The center differential is mounted with an electronically controlled coupling type or torque sensitive type differential.

  An electronically controlled coupling type differential (differential device) is a so-called “speed-constrained differential”, in which the rotational torque from the engine or drive device is applied to the propulsion shafts on the front and rear wheels. In the process of distributing to the rotating torque, the distribution amount of the driving force transmitted to each of the two propulsion shafts is adjusted by adjusting the strength to restrain the rotation of the two propulsion shafts to electronic control. It is a differential. When the differential of this system is mounted as a center differential, specifically, the control command given to the differential is a restraint rate cr that determines the degree of restraint of mutual rotation of the propeller shaft to the front and rear wheels. Become. That is, when the value of the restraint rate cr is 0, the rotational speed of the propulsion shafts of the front and rear wheels is independent, and the rotational torque is distributed at a predetermined distribution ratio. On the other hand, when the value of the restraint ratio cr is increased (cr> 0), the rotational speeds of the propulsion shafts of the front and rear wheels are gradually constrained to each other. Is completely constrained, that is, the propulsion shafts of the front and rear wheels are directly connected, and the rotational speeds of the propulsion shafts of the front and rear wheels coincide with each other. When the rotational speeds of the propulsion shafts of the front and rear wheels are constrained by a restraint ratio cr, that is, when cr> 0, the driving force of each wheel is the slip ratio of each wheel (depending on the wheel speed of each wheel). And the driving stiffness.

On the other hand, in the case of a torque-sensitive differential (torque-sensitive LSD), in the process in which the rotational torque from the engine or driving device is distributed to the rotational torque of the propulsion shafts on the front and rear wheels, In addition, the driving force is distributed such that the driving force distributed to the shaft with the slower rotational speed among the propulsion shafts on the rear wheel side relatively increases. For example, the driving force distribution of the front and rear wheels when the rotation speeds of the propulsion shafts on the front wheel side and the rear wheel side are equal is the front wheel: rear wheel = 4: 6
When the front wheel side rotational speed> the rear wheel side rotational speed is established, the driving force distribution of the front and rear wheels is
Front wheel: Rear wheel = 3: 7
When front wheel side rotational speed <rear wheel side rotational speed is established,
Front wheel: Rear wheel = 5: 5
It becomes. (The above distribution ratio values are only examples, and are not limited to these.)

  In a vehicle in which a differential in which the distribution of the driving force changes depending on the rotational speed of the rotary shaft to which the driving force is distributed as described above, in each case, as described in more detail later, each wheel The distribution of driving force is determined in consideration of the wheel speed. When the center differential is a speed-constrained differential while the vehicle is running, the restraint ratio (front / rear wheel distribution) and the driving force distribution ratio (left / right wheel distribution) that give the disassembly / disassembly determined in consideration of the wheel speed. ) Is given to the corresponding differential as a control amount, and the distribution of the driving force to each wheel is executed. When the center differential is a torque sensitive differential, the driving force distribution ratio (left / right wheel distribution) is given as a control amount to the left / right distribution differential, and the distribution in the center differential is passively determined.

  The configuration and operation of the driving force distribution 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, detected by the G sensor 42. It should be understood that longitudinal acceleration or lateral acceleration, and vertical load of each wheel from a load sensor provided on each wheel may be input. Then, the driving force distribution ratios kf and kr of each diff determined in a manner described later are transmitted to the corresponding def controller.

Operation of Driving Force Distribution Control Generally speaking, the control in the driving force distribution control apparatus of the present embodiment is so-called driving force distribution control that maximizes the limit performance, that is, in a vehicle in a certain turning state. In this state, the distribution of the driving force (or driving torque) transmitted from the driving device 16 to each wheel is controlled so that the acceleration can be increased as much as possible while the tire grip force is maintained without slipping all the driving wheels. is there. FIG. 1B shows an example of the control configuration of the control device of the present invention that executes such driving force distribution control in the form of a block diagram.

  Referring to the figure, in the driving force distribution control device, the vehicle speed Vs (50a) of the current vehicle determined by an arbitrary method based on the information of the wheel speed sensor and the turning state are referred to. The total driving force Dt (50c) required for the vehicle determined based on the lateral acceleration Yg of the center of gravity position of the vehicle from the lateral G sensor 42 of the vehicle and the accelerator pedal depression amount θa or the engine speed Er by the driver. ) And the road surface friction coefficient μi (50b), which may be estimated by an arbitrary method using the information on the wheel speed sensor, the front-rear G sensor, or other information, are input to the arithmetic processing unit (50d). [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. The arithmetic processing unit 50d uses the input data as a parameter and determines the right / left distribution ratio of the driving force of the front wheels and / or the rear wheels that gives an optimal driving force distribution, which is determined in advance by a calculation method described in detail later. The combination of kf, kr and the center differential constraint ratio cr (only in the case of the speed constraint type) is determined, and the left / right distribution ratio kf, kr and / or the constraint ratio cr is transmitted to the corresponding differential controller. Each controller generates a control command for realizing the received control amount, and adjusts the operating state of the differential. Thus, when the total driving force increases and the driving force distribution is not executed, the driving force distribution is shifted from the uniform distribution while maintaining the turning state even if any driving wheel loses the gripping force. Thus, the total driving force can be increased in a state where all the driving wheels maintain the gripping force, and the limit performance of the vehicle is improved.

Here, the distribution ratio or restraint rate given to each differential that gives the optimum driving force distribution is, if necessary, that the tire grip force does not exceed its corresponding limit value in all the driving wheels. This is a value that distributes driving force to the vehicle and thereby improves the limit performance of the vehicle. In this regard, since the limit of the tire grip force of each wheel changes depending on the contact load of each wheel, it is complicated to calculate using the magnitude of the force limit value itself as an index value. Therefore, in the present invention, “tire load factor” is used as an index representing how close the tire grip force of each wheel is to its limit value. The tire load factor eti (i = FL (front left wheel), FR (right front wheel), RL (left rear wheel), RR (right rear wheel)) is the ratio of the current tire grip force and its limit value. Yes, the following equation eti = (Di ² + Fi ² ) ^1/2 / μi · Wi · g (1)
(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. FIG. 2 (A)). reference.)
Is a value defined by The distribution ratio or restraint rate given as a control command to each differential is the tire load factor eti of each wheel,
eti ≦ 1.0 (2)
It is set to satisfy. Di, Fi, and Wi may be calculated in the manner described in detail later.

Outline of processing for determining front / rear wheel right / left distribution ratio and / or center differential rotation restraint ratio As described above, in the driving force distribution control of the present invention, the vehicle speed Vs, lateral acceleration Yg, The right / left distribution ratio of the front and rear wheels and / or the rotational constraint ratio of the center differential that gives the driving force distribution in which the tire load factor eti of all the wheels satisfies the condition (2) with respect to the friction coefficient μi and the (required) total driving force Dt. Is determined. However, the front / rear wheel left / right distribution gives the driving force distribution in which the tire load factor eti of all the wheels satisfies the condition (2) from the running conditions such as the vehicle speed Vs, the lateral acceleration Yg, the road surface friction coefficient μ, and the (required) total driving force Dt. It is difficult to analytically and directly calculate the combination of ratio and / or center differential rotation constraint. Therefore, in the process of determining the combination of the actual distribution ratio and restraint rate, the vehicle speed Vs, the lateral acceleration Yg, the road surface friction coefficient μ, and the (required) total driving force Dt are combined in the traveling of a certain arbitrary vehicle. The tire load factor eti of all wheels is calculated while variously changing the combination of the distribution ratio and the restraint rate within the settable range, and the distribution ratio satisfying the condition (2) One of the combinations of constraint rates is determined. In an actual vehicle, when a combination of a distribution ratio and a restraint rate is determined by such a method, it takes a calculation time. Therefore, it is preferably determined by calculation under a driving condition assumed in advance. A map giving a combination of the distribution ratio and the restraint ratio is prepared. While the vehicle is running, the vehicle speed Vs, lateral acceleration Yg, road friction coefficient μ, and (required) total driving force Dt are used as input parameters. An appropriate combination may be selected (if the calculation speed of the electronic control device is in time, the combination of the distribution ratio and the constraint ratio corresponding to the immediate driving condition may be immediately determined by calculation. )

  In the following, the tire load factor calculation process in the driving condition combining the vehicle speed Vs, the lateral acceleration Yg, the road surface friction coefficient μ, and the (required) total driving force Dt, and the tire load factor calculation process are used. The process of determining the combination of distribution ratio and constraint rate will be described.

Calculation of tire load factor When the driving force of the four wheels can be freely adjusted in a vehicle as illustrated in FIG. 1 (A), as understood from the equation (1), the tire load factor eti is: Under traveling conditions of a certain vehicle speed Vs, lateral acceleration Yg, road surface friction coefficient μ, and (required) total driving force Dt, front / rear wheel driving force distribution ratio k, front wheel driving force left / right distribution ratio kf, rear wheel driving force The left and right distribution ratio kr is used to calculate the driving force Di, the ground load Wi, and the lateral force Fi of each wheel. However, when the center differential is a speed constraint type or torque sensitive type differential, the driving force distribution ratio of the center differential is determined by the wheel speed difference between the front and rear wheels (rotational speed difference between the front and rear propulsion shafts). Therefore, the value of each wheel driving force Di required for calculating the tire load factor eti cannot be determined unless the wheel speed is determined. Therefore, in the present invention, in short, in calculating the tire load factor eti, the driving force distribution ratio k of the center differential is assumed to be a temporary value (typically, when the differential does not execute the variable distribution operation of the driving force). (The value of the distribution ratio), the driving force Di, the ground load Wi, and the lateral force Fi of each wheel are calculated. After that, after determining the wheel speed, each wheel is determined based on the determined wheel speed. The driving force Di is recalculated. In the following, first, calculation processing of the driving force Di, the contact load Wi, and the lateral force Fi of each wheel for calculating the tire load factor at a given differential distribution ratio kf, kr, k will be described. Then, the process which resets the driving force Di of each wheel based on wheel speed is demonstrated. In the following calculation, the left turning direction is positive.

(I) Calculation processing of Di, Wi, Fi at distribution ratios kf, kr, k First, the front-rear force Di of each wheel is set to the distribution ratio of the driving force of the front wheel side, the rear wheel side, and the center differential kf, kr, When k is assumed, the total driving force Dt is used and expressed by the following equation. (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 _RR = Dt · k · kr

In addition, the vertical load Wi of each wheel takes into account the influence of the load movement amount Δx in the front-rear direction due to acceleration of the vehicle and the load loads Δyf, Δyr in the lateral direction due to the centrifugal force in the front and rear wheels, respectively. It is expressed by an equation (see FIG. 2B).
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 _RR = (1/2) M · l f / l + (1/2) Δx + Δyr
Here, M is the vehicle weight, lf and lr are distances from the front and rear wheel shafts to the center of gravity of the vehicle, and l is the distance between the front and rear wheel axles (wheel base). In the above, the load movement amount Δx in the direction from the front wheel axis to the rear wheel axis due to acceleration of the vehicle is:
Δx = H · ((D _FL + D _FR ) cos δ + D _RL + D _RR / (l · g) (5a)
Given by. Further, the load movement amount Δyf from the left side to the right side of the front wheel in the lateral direction takes into account the load movement due to centrifugal force and the load movement of the lateral component of the vehicle of the driving force of the front wheel,
Δyf = H · ((M · Rf · Yg (cosδ + βf · sinδ) + (D _FL + D _FR ) sinδ) / (Tr · g) (5b)
The amount of load movement from the left side to the right side of the rear wheel in the lateral direction is given by
Δyr = H · M · Rr · Yg / (Tr · g) (5c)
Given by. Here, H is the height of the center of gravity, Rf and Rg are the roll stiffness distributions at the front and rear wheels, and Tr is the tread length. Yg is the lateral acceleration, δ is the front wheel steering angle, and βf and βr are the slip angles of the front wheels and the rear wheels (see FIG. 2B). Since the slip angles βf and βr are very small,
cosβf = cosβr = 1; sinβf = βf, r; sinβr = βr
(Hereinafter, when using the above approximation, “˜” is used in the expression).

上記の式の大括弧内において、第一項及び第二項が遠心力に釣り合うための力の成分である。例えば、前輪についてより詳細に述べれば（図２（Ｃ））、前輪軸上に作用する遠心力は、前記の加速時の前後方向の荷重移動を考慮した前輪軸の質量の割り当て分と、横加速度から、
（Ｍ・ｌｒ／ｌ−Δｘ）・Ｙｇ …（６ａ）
により与えられ、これと、駆動力の旋回半径方向成分（Ｄ_ＦＬ＋Ｄ_ＦＲ）・sinβf〜（Ｄ_ＦＬ＋Ｄ_ＦＲ）・βfと横力の旋回半径方向成分（Ｆ_ＦＬ＋Ｆ_ＦＲ）・cosβf〜（Ｆ_ＦＬ＋Ｆ_ＦＲ）との釣り合いの式
（M・lr／l−Δx）・Yg＝（Ｄ_ＦＬ＋Ｄ_ＦＲ）・βf＋（Ｆ_ＦＬ＋Ｆ_ＦＲ）
から、前輪横力和として、
Ｆｆ＝（Ｆ_ＦＬ＋Ｆ_ＦＲ）＝（M・lr／l−Δx）・Yg−（Ｄ_ＦＬ＋Ｄ_ＦＲ）・βf …（６ｂ）
を得る。同様に、後輪についても、その横力和として、
Ｆｒ＝（Ｆ_ＲＬ＋Ｆ_ＲＲ）＝（M・lf／l＋Δx）・Yg−（Ｄ_ＲＬ＋Ｄ_ＲＲ）・βｒ …（６ｃ）
が得られる。


Regarding the lateral force Fi of each wheel, first, the sum Ff of the lateral forces of the left and right front wheels and the sum Fr of the lateral forces of the left and right rear wheels are balanced with the centrifugal force in each of the front and rear wheels. From the condition that the generated yaw moment is balanced with the yaw moment generated by the lateral force difference ΔF between the front and rear wheels generated at the front and rear wheels, the sum Ff of the lateral forces of the left and right front wheels and the sum Fr of the lateral forces of the left and right rear wheels are determined. The Then, assuming that the lateral force sums Ff and Fr of the front and rear wheels are distributed to the left and right wheels in proportion to the vertical load, the lateral force Fi of each wheel is expressed by the following equation.

In the brackets of the above formula, the first term and the second term are force components for balancing the centrifugal force. For example, if the front wheel is described in more detail (FIG. 2C), the centrifugal force acting on the front wheel shaft is calculated as follows: From acceleration,
(M · l r / l−Δx) · Yg (6a)
And the turning radial component of the driving force (D _FL + D _FR ) · sin βf to (D _FL + D _FR ) · βf and the turning radial component of the lateral force (F _FL + F _FR ) · cos βf to (F Formula of balance with ( _FL + F _FR ) (M · l r / l -Δx) · Yg = (D _FL + D _FR ) · βf + (F _FL + F _FR )
From the front wheel lateral force sum,
_{Ff = (F FL + F FR} ) = (M · l r / l-Δx) · Yg- (D FL + D FR) · βf ... (6b)
Get. Similarly, for the rear wheel,
Fr = (F _RL + F _RR ) = (M · l f / l + Δx) · Yg− (D _RL + D _RR ) · βr (6c)
Is obtained.

The third terms ΔFf and ΔFr in square brackets in the equation (6) are the lateral forces from the front wheels to the rear wheels obtained from the formula of the balance of the yaw moment caused by the longitudinal force Di and the lateral force difference between the front and rear wheels. It represents the amount of movement. Referring to FIG. 3, the yaw moment by each wheel driving force is
(D _RR −D _RL + (D _FR −D _FL ) cos δ) (Tr / 2) + (D _FR + D _FL ) sin δ · lf (6d)
It is expressed. Considering that this yaw moment and the yaw moment ΔF · l due to the lateral force movement amount ΔF perpendicular to the axle from the front wheel to the rear wheel are balanced, the lateral force movement amount ΔF is
ΔF = {(D _RR −D _RL + (D _FR −D _FL ) cos δ) (Tr / 2) + (D _FR + D _FL ) sin δ · lf} / l (6e)
It can be expressed as. Accordingly, the movement amounts ΔFf and ΔFr of the lateral forces of the front and rear wheels obtained from the condition of balance of the yaw moment are respectively
ΔFf = ΔF · cosδ (6f)
ΔFr = ΔF
It can be. The reason why ΔFf is multiplied by cos δ is that the lateral force of the front wheels is inclined by the steering angle δ from the direction perpendicular to the axle. Thus, in the lateral force expression of the expressions (6b) and (6c), the expression in the brackets of the expression (6) is obtained by subtracting or adding the movement amount of the expression (6f). It becomes.

By the way, among the expressions of the driving force Di, the ground load Wi, and the lateral force Fi of each wheel, which are the variables of the tire load factor equation (1), the latter two include the slip angle βf of each wheel. , Βr and front wheel rudder angle δ are included. βf and βr are represented by using the cornering powers kpf and kpr of the front wheels and the rear wheels, respectively.
βf = (F _FL + F _FR ) / 2 kpf (7a)
βr = (F _RL + F _RR ) / 2 kpr (7b)
Given by. The front wheel steering angle δ is
δ = βf−βc + (lf · γ) / Vs (7c)
(Where βc is the slip angle of the center of gravity of the vehicle, and γ is the yaw rate.)
The slip angle βc of the center of gravity is βr− (lr · γ) / Vs, and the yaw rate γ is γ = Yg / Vs.
δ = βf−βr + 1 · Yg / Vs ² (7d)
It is expressed. Accordingly, the values of the ground load Wi and the lateral force Fi can be obtained by solving the simultaneous equations of the equations (6), (7a), (7b), and (7d) with respect to the slip angles βf, βr and the steering angle δ. . The specific calculation may be performed by numerical calculation (convergence calculation) of an arbitrary method. When actually solving the simultaneous equations numerically, after obtaining values for the slip angles βf and βr and the steering angle δ, Then, the ground load Wi and the lateral force Fi are obtained by substituting the results into the equations (4) and (6).

  Thus, according to the above expression, the tire load factor when a certain drive distribution ratio kf, kr, k is given can be calculated. It should be understood that the calculation process according to the above formula may be used for calculating each wheel tire load factor in a vehicle in which the drive distribution ratios kf, kr, k are freely given. .

(ii) Correction when the center differential driving force distribution depends on the wheel speed difference between the front and rear wheels As already mentioned, the rotation at which the center differential driving force distribution ratio k is transmitted from the front and rear propulsion shafts of the differential to the front wheels or rear wheels. When it is determined depending on the speed, in order to calculate the driving force of each wheel or the driving force distribution ratio of the center differential, it is necessary to determine the rotational speed of the front and rear propulsion shafts or the wheel speed of each wheel. In that case, in order to determine the driving force value or the driving force distribution ratio specifically for each wheel, the differential is not operated (when the front and rear wheels are not restrained from rotation), or at a predetermined distribution ratio. Reference is made to the rotational speeds Vwf and Vwr of the front wheels and the rear wheels (values converted into units of wheel speeds) when the driving force distribution is executed on the wheels. Therefore, first, a method for calculating the rotational speeds Vwf and Vwr of the front wheels and the rear wheels when the front and rear wheel driving force distribution is executed at a predetermined distribution ratio will be described.

When the front and rear wheel driving force distribution is executed at a predetermined distribution ratio, the rotational speeds Vwf and Vwr of the front wheels and the rear wheels are average values of the wheel speeds Vwi (= rotational speed × radius) of the left and right wheels, respectively. If you think about it,
_{Vwf = (Vw FL + Vw FR} ) / 2 ... (8a)
_{Vwr = (Vw RL + Vw RR} ) / 2 ... (8b)
It is represented by In each wheel, the slip ratio Si is determined by the wheel speed Vwi and the moving speed (moving speed in the rotating direction) Vf, Vr along the rotating surface of each wheel (for the sake of simplicity, the center point of the front and rear axles). Substituting with the moving speed.)
(Front wheel) Si = (Vwi−Vf) / Vf; (Rear wheel) Si = (Vwi−Vr) / Vr (9)
So Vwi is
(front wheel)
Vwi = (Si + 1) Vf (9a)
(Rear wheel)
Vwi = (Si + 1) Vr (9b)
It can be expressed as.

In the above formulas (9a) and (9b), the moving speeds Vf and Vr in the rotational direction of each wheel are obtained by using the moving speed vectors Vsf and Vsr of each wheel,
Vf = Vsfcos βf to Vsf
Vr = Vsrcos βr to Vsr
(Refer to FIG. 4). The moving speed vectors Vsf and Vsr of the respective wheels are respectively determined by using the turning radii Rf and Rr and the yaw rate γ (= Yg / Vs) at the center of each axle.
Vsf = Rf · γ; Vsr = Rf · γ
Therefore, after all, the moving speeds Vf and Vr in the rotation direction of each wheel are
Vf = Rf · γcosβf to Rf · γ (10a)
Vr = Rr · γ cos βr to Rr · γ (10b)
It is expressed. The turning radii Rf and Rr are respectively shown in FIG.
Rf = (R ² + lf ² −2lf · R · sin βc) ^1/2
˜ (R ² + lf ² −2lf · R · βc) ^1/2 (10c)
Rf = (R ² + lr ² + 2lr · R · sinβc) ^1/2
˜ (R ² + lr ² + 2lr · R · βc) ^1/2 (10d)
(The above equation is obtained by the Pythagorean theorem using a perpendicular drawn from the turning center O to the center axis of the vehicle). Note that R is the turning radius of the center of gravity, and is given by R = Vs ² / Yg, and βc is the slip angle of the center of gravity.

In the above formulas (9a) and (9b), the slip ratio is calculated using the driving force Di and the driving stiffness Ki of each wheel.
Si = Di / Ki (11)
Given by. The driving stiffness Ki is proportional to the contact load Wi of each wheel,
Ki = κWi (11a)
And the amount given. κ is a proportional coefficient, and is given experimentally or theoretically in advance. Thus, according to the equations (9a) to (11a), the rotational speeds Vwf and Vwr of the front wheels and the rear wheels of the equations (8a) and (8b) are expressed by the driving force Di of each wheel and other traveling conditions. . When the rotational speeds Vwf and Vwr of the front and rear wheels can be calculated, the driving force distribution ratio by the center differential or the driving force value of each wheel is determined from these values. Note that the calculation method of the driving force distribution ratio by the center differential or the value of the driving force of each wheel differs depending on the type of the differential as described below.

(In the case of speed constraint type differential)
When the center differential is a speed constraint type differential, as already mentioned, the driving force transmitted to the front and rear wheel propulsion shafts is adjusted by adjusting the degree of restraint of the propulsion shaft rotation on the front and rear wheels. The degree of restraint of the rotation of the propulsion shaft to the front and rear wheels is set by the restraint rate cr, and this cr is determined when the rotation of the propulsion shaft to the front and rear wheels is unconstrained (when not operating). The rotational speeds Vwf and Vwr are related to the rotational speeds Vcwf and Vcwr of the front wheels and the rear wheels when the rotation of the propulsion shaft to the front and rear wheels is restricted (during operation) by the following formula.
cr = 1-dW '/ dW (12)
here,
dW ′ = | Vcwr−Vcwf |
dW = | Vwr−Vwf |
Is the absolute value of the rotational speed difference given as Therefore, the restraint ratio cr is given, and the sum (or average value) of the rotational speeds of the front and rear wheels when the differential is in operation and when it is not in operation is equal.
Vcwr + Vcwf = Vwr + Vwf (13)
Then, the rotational speed of the front and rear wheels when the differential is operating is
Vcwf = Vwf− (cr / 2) (Vwf−Vwr) (14a)
Vcwr = Vwr + (cr / 2) (Vwf−Vwr) (14b)
Given by. In particular, when cr = 1 (direct connection state),
Vcwf = Vcwr = (Vwr + Vwf) / 2 (14c)
It becomes.

As described above, when the rotational speeds Vcwf and Vcwr of the propulsion shafts of the front and rear wheels are determined, the wheel speeds and slip ratios of the front and rear left and right wheels are calculated using these values and the left / right distribution ratio kf or kr of the driving force. And the driving force is determined. Specifically, first, the left and right driving forces Di are respectively applied to the front and rear wheels.
D _FL · kf = D _FR · (1−kf) (15a)
D _RL · kr = D _RR · (1−kr) (15b)
Therefore, according to the relational expressions (9), (11), and (11a), each wheel vertical load Wi (formula (4)) and moving speeds Vf and Vr (formulas (10a, b)) and Kf · W _FL (Vw _FL −Vf) = (1−kf) · W _FR (Vw _FR −Vf) (16a)
kr · W _RL (Vw _RL −Vr) = (1−kr) · W _RR (Vw _RR −Vr) (16b)
Is established. This condition and the average value of the wheel speeds of the left and right wheels coincide with the rotational speed of the propulsion shaft, that is,
_{Vw FL + Vw FR = 2Vcwf ...} (16c)
Vw _RL + Vw _RR = 2Vcwr (16d)
From these conditions, the wheel speed Vwi of each wheel is calculated. Thereafter, the calculated wheel speed Vwi is substituted into the equation (9) to calculate each wheel slip ratio Sci at the time of the operation of the speed constraint type differential, and further, the relationship of the equation (11), that is,
Dci = Ki · Sci (17)
Thus, each wheel driving force Dci at the time of operation of the speed constraint differential is represented by the product of each wheel slip ratio Sci and driving stiffness Ki. The subscript c indicates the amount when the rotational constraint of the differential is in operation.

Thus, the tire load factor eti is calculated using the driving force Dci (Equation (17)), vertical load Wi (Equation (4)), and lateral force Fi (Equation (6)) of each wheel until the above. Become. In this regard, the moving speeds Vf and Vr in the rotational direction of the front wheels and the rear wheels used for calculating the respective wheel driving forces Dci when the vertical load Wi, the lateral force Fi, and the speed-constrained differential diff are operated are expressed by Equation (3) It is a value calculated by giving the driving force distribution ratio k of the center differential. Accordingly, when the calculation is executed more strictly, the value of k is changed so that the value of the driving force Dci of each wheel in Expression (17) matches the value of each wheel driving force Di of Expression (3). While numerical operations are performed,
Dci = Di (18)
The tire load factor may be determined using the driving force Di, the vertical load Wi, and the lateral force Fi. In the process of repeating the calculation of the driving force Dci, the vertical load Wi, and the lateral force Fi so that the condition (18) is satisfied, the values of the slip angles βf, βr, etc. are recalculated, but the equation (13) , (14a-c), the front and rear wheel rotational speeds Vwf and Vwr when the diff is not operated are obtained by using the value of the driving force distribution ratio k when the diff is not operated without recalculation. It should be noted that what is used is always used.

(For torque sensitive differential)
When the center differential is torque sensitive, as already mentioned, the driving force distribution ratio is
Depending on the magnitude relationship between the rotational speeds Vwf and Vwr of the propulsion shafts on the front and rear wheels, for example,
(a) When Vwf = Vwr Front wheel: Rear wheel = 4: 6
(b) When Vwf> Vwr Front wheel: Rear wheel = 3: 7
(c) When Vwf <Vwr Front wheel: Rear wheel = 5: 5
It is determined as follows. Therefore, when specifically calculating, first, assuming that (a) is satisfied, each wheel driving force Di, vertical load Wi, and lateral force Fi are calculated under given driving conditions, The rotational speeds Vwf and Vwr of the propulsion shafts on the front wheel side and the rear wheel side of the formula (8a, b) are calculated, the magnitude relationship is determined, and the driving force distribution ratio of the center differential is determined from the above (a) to (c). Selected. Then, each wheel driving force Di, vertical load Wi, and lateral force Fi are calculated again using the driving force distribution ratio of the selected center differential, and the tire load factor eti is calculated. [Rarely, depending on the driving conditions, the calculation may be executed again, and the rotational speeds Vwf and Vwr of the propulsion shafts on the front wheel side and the rear wheel side in the equations (8a, b) may be reversed. As a driving force distribution ratio, (a) is selected and the tire load factor eti is calculated. ]

Determination of the driving force distribution ratio and the restraint rate Thus, according to the calculation described above, the driving force can be determined for a given driving condition (vehicle speed Vs, road surface friction coefficient μ, lateral acceleration Yg, total driving force Dt). Given the combination of distribution ratios kf, kr and restraint ratio cr (in the case of speed-constrained center differential) or the combination of drive force distribution ratios kf, kr (in the case of torque-sensitive center differential), the tire load factor of each wheel is calculated. The As described above, in the actual vehicle drive distribution control, the tire load factor needs to satisfy the condition (2) for all the wheels. Therefore, in the present invention, a combination of driving force distribution ratios (hereinafter simply referred to as “combination of driving force distribution ratios”) with driving conditions as input parameters, the driving force distribution ratios kf and kr and the constraint ratio cr The combination of the driving force distribution ratios that gives the tire load factor satisfying the condition (2) is determined while variously changing the combinations.

According to the calculation experiment by the inventor of the present invention, the value of the driving force distribution ratio (kf, kr, cr) or the driving over the entire variable range of the combination of the driving force distribution ratios in a given traveling condition. When the force distribution ratio (kf, kr) is changed and the tire load factor eti of each wheel in the above equation (1) is calculated, the tire load factor eti of all the wheels satisfies the condition (2). It has been found that the range of the combination is determined as a three-dimensional (in the case of a speed-constrained center differential) or a two-dimensional (in the case of a torque-sensitive center differential) (see FIG. 5). In addition, the range of the driving force distribution ratio that gives the tire load factor eti that satisfies the above condition (2) decreases as the total driving force Dt increases for a given road friction coefficient μ, lateral acceleration Yg, and vehicle speed Vs ( The tire load factor eti increases as a whole.), All wheels have eti = 1.0 (2a)
It has been found that it converges to a combination of one driving force distribution ratio kf, kr, cr. Thus, the driving force distribution ratio that gives the condition (2) is the driving force distribution ratio in the entire range of the vehicle speed Vs, the road surface friction coefficient μ, the lateral acceleration Yg, and the total driving force Dt that is assumed in the travel of the vehicle. The tire load factor eti is calculated for the entire variable range of kf, kr, cr, and the ranges of the driving force distribution ratios kf, kr, cr for which the tire load factor eti of all the wheels is 1.0 or less are obtained. It can be determined by selecting an appropriate value (for example, the center value of the range) from the range of the driving force distribution ratio obtained as a result.

  FIGS. 6 and 7 show that when the center differential is a speed-constrained differential, the total driving force Dt is gradually increased at a certain road friction coefficient μ, lateral acceleration Yg, and vehicle speed Vs while the driving force distribution ratio is changed. Processing for determining a combination (kf, kr, cr) value sequentially and preparing a map of the combination (kf, kr, cr) of the driving force distribution ratio using the total driving force Dt as a variable is in the form of a flowchart. It is a representation. As will be understood by those skilled in the art, if the total driving force is not so high, the driving force distribution ratio or the restraint rate is set as a base (the state where each differential is not operated: normally, for left and right distributed differentials, kf = kr = 0.5, center differential, even if cr = 0), it is clear that the tire load factor of all wheels is below the above upper limit value, in which case the driving force distribution ratios kf, kr, restraint There is no need to change the rate cr. Therefore, in the illustrated process, first, the combination of the driving force distribution ratios is set based on the base setting, and the tire load factors of all the wheels are 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, the lateral acceleration Yg, and the vehicle speed Vs 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 kf and kr or the restraint rate cr are set for the first time from that point. The tire load factor is calculated by changing the driving force distribution ratio combination range that satisfies the above condition (2) and the selection value (for example, the center value) is determined.

  Referring to FIG. 6, first, an arbitrary low value Dt0 is set as total driving force Dt (step 100), base setting driving force distribution ratios kf, kr (= 0.5, etc.), constraint rate cr. (= 0, etc.) is used to calculate the tire load factor eti of all the wheels as described above (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 1.0 (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 one of the tire load factors eti exceeds a predetermined threshold Th (step 120), the tire load factors eti of all the wheels are calculated over the entire variable range of the driving force distribution ratios kf and kr or the restraint rate cr. (Step 140). Here, the driving force distribution ratio is calculated in the variable ranges (kmin, kmax), kf, kr, cr, respectively, with appropriate nick width Δk, and the tire load factors eti of all wheels for all combinations [ In a three-dimensional space of kf, kr, cr, a three-dimensional lattice having a lattice width Δk is assumed, and tire load factors eti are calculated for all of the lattice points. ], The range of kf, kr, cr giving the above condition (2) is specified (step 150). In this regard, when considering a three-dimensional space of kf, kr, cr, as already described, a set of (kf, kr, cr) that satisfies the above condition (2) is specified as a three-dimensional region. I know that. Therefore, a set of combinations of kf, kr, cr satisfying the above condition (2) can be specified by detecting the coordinates of the boundary surface of the region in the three-dimensional space of kf, kr, cr. . It should be understood that identification of the boundaries of the kf, kr, and cr regions that satisfy the above condition (2) can be done by any method for those skilled in the art. For example, as shown in FIG. 7, the tire load factor eti is calculated while cr and kf are fixed and kr is changed by a minute amount Δk, and the lower limit krlow and the upper limit krhigh of kr satisfying the condition (2) 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 cr by a minute amount Δk (steps 300 to 310). Reference), the coordinates of the boundary surface of the region satisfying the condition (2) can be specified.

  Next, after specifying the kf, kr, and cr regions that satisfy the above condition (2) in step 150, there is a significant combination of kf, kr, and cr that enters the kf, kr, and cr regions [ When there are grid points in the three-dimensional space] (step 160), the combination of the center points of the area is determined as the driving force distribution ratios kf, kr, cr of the total driving force Dt at that time, and stored as map values (Step 170). The center point may be, for example, the center of gravity of the region satisfying the above condition (2) (e.g., the sum of the coordinate values kf, kr, cr of the boundary surface divided by the number of coordinates of the boundary surface). 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 kf, kr, cr in the total driving force Dt (and vehicle speed vs, road friction coefficient μ and lateral acceleration Yg) at that time are determined, the total driving force Dt is increased by a predetermined increment ΔDt. (Step 180) and Steps 140-170 are repeated, and the selected values of kf, kr, cr 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, kf, kr, cr giving tire load factors satisfying the condition (2) converge at one point, that is, tire load factors eti. Reaches the upper limit in the control of the present invention (depending on the size of the knurled width Δk, several combinations (grid points) of kf, kr, cr satisfying the upper limit of the tire load factor are calculated. There is a possibility.) 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.

In the actual traveling vehicle, when the driving force distribution ratio or the restraint rate of each differential is set by the map of the driving force distribution ratios kf, kr, cr, the condition (2) is set for each wheel. The driving force is adjusted so as to be satisfied, and the limit acceleration is improved in a state where all wheels maintain the gripping force. Further, since the lateral acceleration Yg is used as a parameter in the calculation of the map, the value of the map (kf, kr, cr) in the instantaneous lateral acceleration Yg is selected at the time of control, and then the control is performed. Even in the distribution of the driving force, the lateral acceleration is maintained. The lateral acceleration is expressed by equation (7d)
δ = βf−βr + l · Yg / Vs ²
Therefore, when the driver changes the steering angle by changing the steering angle, the vehicle is reflected in the lateral acceleration. , It will be accelerated in the desired direction.

  In the above map preparation, the process of changing the driving force distribution ratios kf, kr, cr from the base setting is executed after the tire load factor exceeds the threshold Th (step 120). However, the driving force distribution ratios kf, kr, and cr are determined by calculating the region of the driving force distribution ratios kf, kr, cr and determining the center value from the initial value Dt0 of the total driving force. May be. Further, the map to be prepared is composed of a set of driving force distribution ratios (kf, kr, cr) using the total driving force Dt, the vehicle speed Vs, the friction coefficient μ, and the lateral acceleration Yg as variables. In the preparation process, the vehicle speed Vs, the friction coefficient μ, and the lateral acceleration Yg are fixed, and the calculation process in which the total driving force Dt is gradually increased is illustrated. However, the total driving force Dt, the vehicle speed Vs, the friction coefficient μ, It should be understood that a similar map can be prepared by fixing any two of the lateral accelerations Yg and gradually changing the remaining one.

  When the center differential is of a torque sensitive type, the process of sequentially changing cr (steps 300 and 310) is not executed in the process of FIG. Further, in the above example, it is explained that the present invention can be applied to a case where a differential having a variable driving force distribution ratio to the left and right wheels is adopted for both the front and rear wheels. When the driving force distribution ratio is fixed, a value of the fixed distribution ratio is given to the corresponding driving force distribution ratio kf or kr, and processing for changing the driving force distribution ratio (steps 260 and 270, or Steps 280 and 290) are not executed.

  In an actual vehicle, instead of preparing a map in advance, when the combination of the driving force distribution ratios is determined under immediate driving conditions, the processing of FIG. 7 (step 140 in FIG. 150), the processes of steps 160 and 170 in FIG. 6 are executed. If there is no usable range of cr, kf, kr in step 160, the total driving force Dt should not be increased.

  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, in the above example, the driving force distribution control is executed so that the tire load factor satisfies the condition (2), that is, it is allowed to increase to the limit for all the wheels. The tire force is allowed to increase to the limit only for one wheel, for example, only the front wheel outside the turn, and for other wheels, the increase in tire force is limited to a predetermined amount below the limit value. May be. In that case, it is avoided that all the wheels reach the limit at the same time, so that it is avoided that the driving force of all the wheels exceeds the limit at the same time.

FIG. 1A is a schematic diagram of an automobile in which a preferred embodiment of a driving force distribution control device according to the present invention is realized. FIG. 1B shows the configuration of the driving force distribution control device of the present invention in the form of control blocks. FIG. 2A is a diagram illustrating the tire load factor. FIG. 2B shows a vector of force components to be referred to when calculating the load movement amount of each wheel due to the driving force and centrifugal force in the vehicle during turning acceleration. FIG. 2C shows the relationship between centrifugal force, lateral force, and driving force vector referred to when calculating the lateral force of each wheel of the vehicle during turning acceleration. In (B) and (C), the vehicle is handled as a two-wheel model. FIG. 3 shows a vector of force components related to a balance of yaw moments acting on the vehicle referred to when calculating the lateral force of each wheel of the vehicle during turning acceleration. ΔF corresponds to a lateral force movement amount that moves from the front wheel to the rear wheel that opposes the yaw moment due to the left-right difference in driving force. FIG. 4 is a diagram for explaining a method of calculating moving speeds Vf, Vr and turning radii Rf, Rr in the rotational direction of the front wheels and rear wheels, which are referred to in order to calculate the slip ratio of each wheel of the vehicle during turning acceleration. is there. In order to clearly show the configuration, the slip angle is shown to be larger than the actual one, but cos βf (r) ˜1 at the moving speeds Vsf · cos βf and Vrs · cos βr in the rotation direction of each wheel. An approximation is used. In the figure, the vehicle is treated as a two-wheel model. FIG. 5 shows a range of combinations of driving force distribution ratios in which the tire load factor of all the driving wheels is an upper limit value of 1.0 or less at a certain vehicle speed Vs, road friction coefficient μ, lateral acceleration Yg, and total driving force Dt. Is shown in a three-dimensional space of (kf, kr, cr). In the illustrated example, the vehicle speed Vs = 60 km / h, the road surface friction coefficient μ = 1.0, the lateral acceleration Yg = 3.92 m / s ² (while turning left), and the total driving force Dt = 5000 N. When the total driving force is increased, the region of (kf, kr, cr) where the tire load factor of all the driving wheels becomes the upper limit value 1.0 or less converges to one point (not shown). FIG. 6 is a flowchart showing a procedure for preparing a map of combinations of driving force distribution ratios in the form of a flowchart. In the figure, the usable range of kf, kr, cr is a three-dimensional region of kf, kr, cr that satisfies the condition (2). FIG. 7 shows a combination region of driving force distribution ratios in which the tire load factor of all the driving wheels is an upper limit value of 1.0 or less at a certain vehicle speed Vs, road friction coefficient μ, lateral acceleration Yg, and total driving force Dt. The procedure for determining is shown in the form of a flowchart. Null means no value. The variable range [kmin, kmax] or [crmin, crmax] of Δk or Δcr and the distribution ratio or constraint 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 side differential 26 ... Rear wheel side differential 30 ... Steering device 32 ... Steering wheel 32 ... Steering angle sensor 40FL, FR, RL, RR ... Wheel speed sensor 50 ... Electronic control unit

Claims (4)

Driving force of driving wheels of a four-wheel drive vehicle provided with a center differential of speed constraint type or torque sensitive type and a driving force distribution differential that distributes the driving force of at least one of the left and right driving wheels of the front wheel or rear wheel at a variable distribution ratio A vehicle driving force distribution control device that performs the distribution control of the vehicle, wherein the tire driving force of the driving wheels of the vehicle does not exceed its limit, and the total driving force generated in the vehicle and the steering angle of the front wheels, Based on the product of the slip ratio of each wheel of the vehicle and the corresponding driving stiffness of each wheel when the driving force distribution differential is calculated based on the front wheel slip angle and the rear wheel slip angle The operation of the driving force distribution differential is controlled so that the total driving force is distributed to the wheels by each wheel driving force determined in this manner.   2. The apparatus according to claim 1, wherein the center differential is a speed-constrained driving force distribution device, and the driving force of each wheel of the vehicle is the total driving force and the front and rear of the speed-constrained driving force distribution device. An apparatus characterized by being given by a restriction ratio of a rotational speed of a rotating shaft and a driving force distribution ratio of left and right wheels of the driving force distribution differential.   2. The apparatus according to claim 1, wherein the center differential is a torque-sensitive driving force distribution device, and the driving force of each wheel of the vehicle includes the total driving force and the driving forces of the left and right wheels of the driving force distribution differential. A device characterized by being given by the distribution ratio.   2. The apparatus according to claim 1, wherein the driving force of each wheel is determined by using the vehicle speed of the vehicle, the amount of turning state, the total driving force, and the road surface friction coefficient of each wheel as input parameters. .

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