JP5261303B2 - Driving force control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving force control device having improved turning performance of a vehicle. <P>SOLUTION: A driving force control device 100 includes a friction coefficient estimation means 101 for estimating a road surface friction coefficient, a grounding load calculation means 102 for calculating a grounding load of a front wheel, a lateral force calculation means 103 for calculating a lateral force of a front wheel, an allowable driving force calculation means 104 for calculating allowable driving force for a front wheel based on the outputs of the friction coefficient estimation means, grounding load calculation means and lateral force calculation means, and a driving force control means 106 for controlling the driving force so as to make the driving force for the front wheel not more than an allowable driving force. The control device further includes an allowable driving force correction means 105 for increasing/correcting an allowable driving force in response to the increase in a steering angle of a front wheel. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a driving force control apparatus that controls a driving force of a vehicle such as an automobile so as not to deviate from a frictional circle limit of a tire, and particularly relates to an improved vehicle turning performance.

The driving force control (traction control) device limits the output of the engine so that the driving force does not deviate from the friction circle limit of the tire and excessive slip occurs.
As a conventional technique related to vehicle control in consideration of such a tire friction circle, for example, Patent Document 1 discloses a target longitudinal force and a lateral force so as not to exceed a friction circle set based on estimation of a road surface friction coefficient (μ). And a motion control device that corrects the target yaw moment and controls the braking / driving force.
Patent Document 2 describes that in an acceleration slip control device for a vehicle, when the acceleration target and the turning target of the vehicle exceed a friction circle, the acceleration target is set so as to maintain the turning target.
Further, in Patent Document 3, in a driving force control device that performs driving torque reduction control so that the driving slip amount of the driving wheel achieves the target slip amount, the driving force is compensated so as to compensate for the decrease in driving force due to cornering resistance. It describes that the target slip ratio in force control is corrected.

Japanese Patent Laid-Open No. 2000-190832 JP-A-8-261030 JP-A-5-149156

In the techniques described in Patent Documents 1 and 2, by limiting the driving force so as not to exceed the friction circle limit, slipping of the driving wheel is prevented and the stability of the vehicle behavior is ensured. Therefore, the driving force tends to be excessively suppressed.
In addition, in order to properly maintain the cornering state of the vehicle, a minimum driving force that overcomes the cornering resistance is required, and in the steered wheels, the cornering force can be reduced by effectively utilizing the centripetal force inside the turning by the driving force. It is possible to increase the cornering performance. However, in the above prior art, control is performed based on the lateral force of the vehicle body when the tire slip angle is zero, and consideration is given to improving cornering performance by increasing the allowable driving force in consideration of the steering angle. It has not been.

On the other hand, in the technique described in Patent Document 3, the steering angle of the front wheels is taken into consideration, but the characteristics of the driving force with respect to the slip ratio largely fluctuate near the limit of the tire grip, and thus become unstable. It is difficult to perform appropriate slip ratio correction without considering the road surface μ and the friction circle. Further, if the slip ratio is further increased and corrected when the driving force is large, there is a concern that the tire lateral force is reduced and the cornering performance is deteriorated.
In view of the above-described problems, an object of the present invention is to provide a driving force control device that improves the turning performance of a vehicle.

The present invention solves the above-described problems by the following means.
The invention of claim 1 includes a friction coefficient estimating means for estimating a friction coefficient of a road surface, a ground load calculating means for calculating a ground load of a front wheel, a lateral force calculating means for calculating a lateral force of the front wheel, and the friction coefficient. An allowable driving force calculating means for calculating an allowable driving force of the front wheel based on outputs of the estimating means, the ground load calculating means, and the lateral force calculating means, and a driving force of the front wheel not more than the allowable driving force. A driving force control device comprising a driving force control means for controlling a driving force, comprising: an allowable driving force correction means for increasing and correcting the allowable driving force in response to an increase in the steering angle of the front wheels. It is a force control device.

According to a second aspect of the present invention, the driving force control means increases the total driving force of the vehicle based on a value obtained by multiplying the increase correction amount of the allowable driving force by the reciprocal of the vehicle front wheel axle weight distribution ratio. The driving force control apparatus according to claim 1.
According to a third aspect of the present invention, the driving force control means increases the total driving force of the vehicle based on a value obtained by multiplying the increase correction amount of the allowable driving force by the inverse of the front wheel driving force distribution ratio of the vehicle. The driving force control apparatus according to claim 1.
According to a fourth aspect of the present invention, when the corrected allowable driving force is less than or equal to a predetermined value, the driving force control means reduces the rate of change of the driving force with respect to the displacement of the accelerator pedal to which the driver inputs an acceleration request. The driving force control apparatus according to any one of claims 1 to 3, wherein the driving force control apparatus is configured as described above.

According to the present invention, the following effects can be obtained.
(1) By correcting the increase in the allowable driving force according to the increase in the rudder angle of the front wheels, even if the acting direction of the tire lateral force is tilted backward with respect to the turning center side by providing the rudder angle It is possible to improve the cornering performance of the vehicle by increasing the cornering force by effectively utilizing the friction circle of the tire to the vicinity of the limit on the turning center side by bringing the acting direction of the resultant force of the force and the lateral force of the tire closer to the turning center side. it can.
In addition, by using the driving force control based on the estimation of the road surface friction coefficient, it is not necessary to use a region where the driving force characteristics with respect to the slip ratio are unstable as in the existing slip control, so that stable control is performed. Can do.
(2) By increasing the total driving force of the vehicle based on the value obtained by multiplying the increase correction amount of the allowable driving force of the front wheels by the reciprocal of the front wheel axle load distribution ratio of the vehicle, according to the front and rear axle load distribution. In the AWD vehicle to which the driving force is distributed, the front wheel grip can be effectively utilized.
(3) By increasing the total driving force of the vehicle based on a value obtained by multiplying the increase correction amount of the allowable driving force of the front wheels by the reciprocal of the front wheel driving force distribution ratio of the vehicle, the driving force is increased at a predetermined distribution ratio. The front wheel grip can be effectively utilized in the distributed AWD vehicle.
(4) A tire that requires a delicate accelerator operation by reducing the rate of change of the driving force with respect to the displacement of the accelerator pedal to which the driver inputs an acceleration request when the allowable driving force after correction is equal to or less than a predetermined value. When driving near the grip limit, the accelerator response is insensitive and the driver's ease of handling can be improved.

It is a figure which shows the structure of the power train of the vehicle by which Example 1 of the driving force control apparatus to which this invention is applied is provided. It is a figure which shows the structure of Example 1 of the driving force control apparatus to which this invention is applied. It is a schematic diagram which shows the friction circle | round | yen of a right-and-left front-and-rear wheel, front-back force, and lateral force. 6 is a graph illustrating an example of a correlation between an accelerator opening and a throttle opening in the driving force control apparatus according to the first embodiment. 3 is a flowchart illustrating an operation during traction control control in the driving force control apparatus according to the first embodiment. It is a schematic diagram which shows the generation | occurrence | production state of the tire force at the time of turning in the comparative example and Example 1 of this invention.

  An object of the present invention is to provide a driving force control device that improves the turning performance of a vehicle, and corrects an increase in the allowable driving force calculated so as to be within the friction circle limit of the front wheels in accordance with the sin component of the steering angle of the front wheels. The problem was solved by increasing the cornering force.

Embodiment 1 of a driving force control apparatus to which the present invention is applied will be described below.
The driving force control apparatus according to the first embodiment is provided in, for example, a four-wheel AWD (total wheel drive) automobile such as a passenger car, and performs traction control control for suppressing engine output so as to prevent tire slip due to excessive driving force. Is what you do.
As shown in FIG. 1, the power train of the vehicle includes an engine 10, a torque converter 20, a transmission mechanism 30, an AWD transfer 40, a front differential 50, a rear differential 60, and the like.

The engine 10 is a power source for driving the vehicle, and is an internal combustion engine such as a gasoline engine. The engine 10 adjusts the output by changing the intake air amount by opening and closing a throttle valve (not shown) provided in the intake pipe.
The torque converter 20 is a fluid coupling that transmits the output of the engine 10 to the speed change mechanism 30 and includes a lockup clutch that directly connects the input side and the output side.
The transmission mechanism unit 30 is, for example, a stepless transmission (CVT) having a variator including a pair of variable pulleys, a chain, a belt, or the like, a step AT having a plurality of planetary gear sets, and the like. The output of the engine 10 is increased / decreased.

The AWD transfer 40 distributes and transmits the driving force input from the speed change mechanism 30 to the front differential 50 and the rear differential 60.
The AWD transfer 40 includes a center differential 41, a transfer clutch 42, and the like.
The center differential 41 includes, for example, a complex planetary gear set, and distributes torque to the front differential 50 and the rear differential 60 so that the torque distribution ratio is, for example, about 4: 6. The center differential 41 also functions as a differential mechanism that absorbs differential rotation of the front differential 50 and the rear differential 60 caused by, for example, a difference between front and rear wheel trajectories during turning.
The transfer clutch 42 is differential limiting means for restricting the differential between the front and rear wheel side output portions of the center differential 41. The transfer clutch 42 includes, for example, a wet multi-plate clutch driven by hydraulic pressure or electromagnetic force, and the fastening force (clutch pressing force) is controlled by a transfer control device (not shown).

  The front differential 50 transmits the front wheel side driving force transmitted from the AWD transfer 40 to the right front wheel 51 and the left front wheel 52 while finally decelerating. Further, the front differential 50 functions as a differential mechanism that absorbs differential rotation between the right front wheel 51 and the left front wheel 52.

  The rear differential 60 transmits the rear wheel driving force transmitted from the AWD transfer 40 to the right rear wheel 61 and the left rear wheel 62 while finally decelerating. The rear differential 60 functions as a differential mechanism that absorbs differential rotation between the right rear wheel 61 and the left rear wheel 62.

  As shown in FIG. 2, the vehicle includes a transmission control unit 71, a vehicle speed sensor 72, a rudder angle sensor 73, a rack thrust calculation means 74, a front and rear G sensor 75, a lateral G sensor 76, a yaw rate sensor 77, and the like. Can communicate with a driving force control apparatus 100 described later via an in-vehicle LAN such as a CAN communication system.

The transmission control unit 71 controls the transmission mechanism 30 and the lock-up clutch of the torque converter 20.
The vehicle speed sensor 72 is provided in a hub bearing housing that supports each wheel, and transmits a vehicle speed pulse signal corresponding to the rotation of the hub to which the wheel is fixed.
The steering angle sensor 73 is provided in a steering mechanism that converts the rotation of a steering wheel (handle) (not shown) into a reciprocating motion in the vehicle width direction and transmits it to the hub bearing housing of the left and right front wheels via tie rods. The rudder angle sensor 73 includes an encoder that detects an angular position of a steering shaft that is a rotation shaft coupled to the steering wheel.
The rack thrust calculation means 74 calculates the rack thrust that the rack of the steering gear box pushes and pulls the tie rod. The calculation of the rack thrust is obtained, for example, by correcting the assist force of the electric power steering device in consideration of the friction of the steering system. The rack thrust is balanced with the self-aligning torque of the left and right front wheels 51 and 52 during turning or the like.
The front / rear G sensor 75 detects acceleration in the front / rear direction acting on the vehicle body.
The lateral G sensor 76 detects the acceleration in the vehicle width direction acting on the vehicle body.
The yaw rate sensor 77 detects a rotational angular velocity around the vertical axis of the vehicle body.

  The driving force control device 100 includes a road surface μ estimated value calculation unit 101, a ground load calculation unit 102, a lateral force calculation unit 103, an allowable driving force calculation unit 104, an allowable driving force correction value calculation unit 105, an engine output control device 106, an accelerator. A sensor 107, a throttle actuator 108, and the like are provided.

The road surface μ estimated value calculation unit 101 estimates a road surface friction coefficient by detecting tire slip, and calculates a road surface μ estimated value. When the tire grip limit approaches when turning, the road surface μ estimated value calculation unit 101 changes the pneumatic trail even if the tire's grip limit is not reached, and the linearity between the side force and the self-aligning torque is lost. Is used to calculate the estimated value of the road surface μ.
Specifically, the road surface μ estimated value calculation unit 101 determines that the actual rack thrust calculated by the rack thrust calculation means 74 is less than a predetermined value below the reference rack thrust calculated sequentially from the vehicle speed, steering angle, etc. of the vehicle. The road surface μ estimated value is calculated from the vehicle body lateral acceleration and yaw rate.
Such a road surface friction coefficient estimation method is presented in detail by the applicant of the present application in, for example, Japanese Patent Application Laid-Open No. 2008-168877.

F_zfo：前外輪の接地荷重
F_zfi：前内輪の接地荷重
F_zro：後外輪の接地荷重
F_zri：後内輪の接地荷重
F_zf0：一定速直進時の前輪接地荷重
F_zr0：一定速直進時の後輪接地荷重
dF_zx：加減速による前後軸間の荷重移動
dF_zyf：旋回による左右前輪間の荷重移動
dF_zyr：旋回による左右後輪間の荷重移動
The ground load calculation unit 102 calculates the ground load of each wheel using the following formulas 1 to 4.

F _zfo : _Contact load of front outer ring
F _zfi : Grounding load of front inner ring
F _zro : Grounding load of the rear outer ring
F _zri : Ground contact load of the rear inner ring
F _zf0 : Front wheel ground contact load when _traveling straight at a constant speed
F _zr0 ： Rear wheel ground load when _driving straight at a constant speed
dF _zx : Load movement between front and rear axes by acceleration / deceleration
dF _zyf : Load transfer between left and right front wheels by turning
dF _zyr : Load transfer between left and right rear wheels by turning

The load movement dF _zx between the front and rear axes due to acceleration / deceleration is obtained by the following equation 5.

The load movement dF _zyf between the left and right front wheels by turning is obtained by the following equation (6).

The load movement dF _zyr between the left and right rear wheels by turning is obtained by the following equation (7).

F_yfo：前外輪の横力
F_yfi：前内輪の横力
F_yro：後外輪の横力
F_yri：後内輪の横力
The lateral force calculation unit 103 calculates the lateral force generated by the tire of each wheel (see FIG. 3) using the following equations 8 to 11.

F _yfo ： Side force of front outer ring
F _yfi : Lateral force of front inner ring
F _yro : Lateral force of rear outer ring
F _yri : Lateral force of rear inner ring

F_{xf_c}：前輪の許容駆動力
F_{xr_c}：後輪の許容駆動力
F_{xfi_c}：前内輪の許容駆動力
F_{xri_c}：後内輪の許容駆動力
The allowable driving force calculation unit 104 calculates the allowable driving force of the front and rear wheels using the following expressions 12 and 13.

F _{xf_c} : Allowable driving force of front wheels
F _{xr_c} : Allowable driving force of rear wheel
F _{xfi_c} : Allowable driving force of front inner ring
F _{xri_c} : Allowable driving force of rear inner ring

F_{xf_s}：前輪の許容駆動力補正量
θ_H：ハンドル角
ｎ：ステアリングギヤ比
The allowable driving force correction value calculation unit 105 calculates the allowable driving force correction amount for the front wheels using the following equation (14).

F _{xf_s} : Allowable driving force correction amount for front wheels θ _H : Steering wheel angle n: Steering gear ratio

The engine output control device 106 calculates the allowable driving force F _{x_C} for the vehicle as a whole using the following Expression 15.

The engine output control device 106 is connected to an accelerator sensor 107 that detects the position (accelerator opening) of an accelerator pedal, which is an input unit through which a driver inputs an acceleration request. The engine output control device 106 drives the throttle actuator 108 of the electric throttle valve provided in the engine 10 so that the total driving force of the vehicle has the above-described allowable driving force _{Fx_C} as an upper limit according to the accelerator opening. To control the output of the engine 10.

Further, when the allowable driving force F _{x_C} is less than a predetermined value and the tire grip has insufficient margin, the engine output control device 106 reduces the rate of change of the throttle opening relative to the accelerator opening, and is insensitive to the throttle response. I have to.
As shown in FIG. 5, the engine output control device 106 sequentially monitors the allowable driving force F _{x_C} , and if this is less than a predetermined value C, the engine _opening control device 106 determines the throttle opening degree according to the value of the allowable driving force F _{x_C} . Reduce the rate of change. Specifically, when the allowable driving force F _{x_C} is zero, the change rate of the throttle opening is set to the value of the allowable driving force F _{x_C} so that the change rate of the throttle opening with respect to the accelerator opening is also zero. Change linearly accordingly.
When the driver returns the accelerator pedal, the throttle opening is lowered while following the history of the accelerator opening-throttle opening (the locus in FIG. 5) when the accelerator pedal is depressed.

Next, the operation of the driving force control apparatus according to the first embodiment will be described step by step for each step in FIG.
<Step S01: Input various sensor values>
The driving force control apparatus 100 acquires various sensor values necessary for the various calculations described above from the CAN communication system.
Thereafter, the process proceeds to step S02.
<Step S02: Calculate road surface μ estimated value>
The road surface μ estimated value calculation unit 101 calculates a road surface μ estimated value.
Thereafter, the process proceeds to step S03.
<Step S03: Calculate contact load of each wheel>
The ground load calculation unit 102 calculates the ground load of each wheel.
Thereafter, the process proceeds to step S04.
<Step S04: Set allowable driving force>
The allowable driving force calculation unit 104 sets the allowable driving force of the front wheels using the outputs of the road surface μ estimated value calculation unit 101, the ground load calculation unit 102, and the lateral force calculation unit 103.
Thereafter, the process proceeds to step S05.
<Step S05: Correct allowable driving force according to front wheel rudder angle>
The allowable driving force correction value calculation unit 105 calculates an allowable driving force correction amount for the front wheels. The engine output control device 106 calculates the allowable driving force of the vehicle by the above-described equation 15 using the allowable driving force correction amount of the front wheels.
Thereafter, the process proceeds to step S06.
<Step S06: Throttle control based on allowable driving force>
The engine output control device 106 drives the throttle actuator 108 in response to the acceleration request input from the accelerator sensor 107 to control the output of the engine 10, and the driving force of the vehicle at this time is the allowable driving force calculation unit 104. The allowable driving force of the vehicle that is set based on the allowable driving force of the front wheel calculated by the above and the allowable driving force correction amount of the front wheel calculated by the allowable driving force correction value calculation unit 105 is limited.
Thereafter, the series of processing is terminated (returned).

Next, the effect of Example 1 mentioned above is demonstrated in contrast with the comparative example of this invention demonstrated below. The driving force control device of the comparative example does not perform an increase correction according to the steering angle of the front wheel allowable driving force in the first embodiment.
FIG. 6 is a schematic diagram illustrating a state of generation of lateral force during turning in the comparative example and the first embodiment.
As shown in FIG. 6A, in the comparative example in which the steering angle is not considered in the friction circle control, the driving force is hardly allowed when the lateral force of the tire is approaching the friction circle limit. In this case, the lateral force of the tire acts in the rearward pulling direction due to the influence of the rudder angle, and the driving force is not allowed. Thus, the tire friction circle limit cannot be effectively used up to near the limit in the turning center direction.

  On the other hand, according to Example 1 shown in FIG. 6 (b), even when the tire has used up the lateral force almost to the friction circle limit, the allowable driving force correction amount according to the steering angle of the front wheels is obtained. By permitting the driving force based on this, it is possible to bring the acting direction of the front / rear force of the tire force and the resultant force of the lateral force closer to the turning center direction, and the tire friction circle limit is used up in the turning center direction, as shown in FIG. The cornering force can be increased by the indicated ΔCF to improve the cornering performance of the vehicle.

Further, since the allowable driving force of the vehicle is set based on a value obtained by multiplying the corrected allowable driving force of the front wheels by the reciprocal of the front / rear axle load distribution ratio, the AWD vehicle in which the driving force is distributed in the front-rear direction. Even so, the front wheel friction circle limit can be used up effectively.
Furthermore, when there is no margin in the grip and the allowable driving force of the vehicle is less than the predetermined value C, the rate of change of the throttle opening with respect to the accelerator opening is reduced and the accelerator response is made insensitive, requiring a delicate operation. Even in the vicinity of the grip limit, the ease of handling of the driver in driving can be improved.

Ｄ：前輪の駆動力配分比（０〜１）

以上説明した実施例２においても、上述した実施例１の効果と実質的に同様の効果を得ることができる。 Next, a second embodiment of the driving force control apparatus to which the present invention is applied will be described. In the following description, the same reference numerals are assigned to portions that are substantially the same as those of the first embodiment described above, the description thereof is omitted, and differences are mainly described.
The engine output control device 106 in the driving force control device of the second embodiment calculates the allowable driving force F _{x_C} for the entire vehicle using the following equation 16 instead of the equation 15 described above.

D: Driving force distribution ratio of front wheels (0 to 1)

In the second embodiment described above, it is possible to obtain substantially the same effect as that of the first embodiment described above.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the technical scope of the present invention.
(1) The configuration of the driving force control device is not limited to that of the above-described embodiment, and can be changed as appropriate. For example, the method of calculating the road surface friction coefficient, the contact load, the lateral force, etc. is not limited to the method of the embodiment, and can be changed as appropriate. Also, the hardware configuration is not limited to the configuration of the embodiment.
(2) The driving force control device of the embodiment is provided in, for example, an AWD vehicle, but the present invention is not limited to this, and may be applied to an FWD vehicle or an AWD vehicle other than the configuration of the embodiment. it can.
(3) In the driving force control apparatus of the embodiment, the driving force is generated from, for example, a gasoline engine. However, the present invention is not limited to this, and a vehicle, an electric vehicle, or an engine having another type of internal combustion engine such as a diesel engine. -It is applicable also to an electric hybrid vehicle etc.

DESCRIPTION OF SYMBOLS 10 Engine 20 Torque converter 30 Transmission mechanism part 40 AWD transfer 41 Center differential 42 Transfer clutch 50 Front differential 51 Right front wheel 52 Left front wheel 60 Rear differential 61 Right rear wheel 62 Left rear wheel 71 Transmission control unit 72 Vehicle speed sensor 73 Steering angle sensor 74 Rack thrust calculation means 75 Front-rear G sensor 76 Lateral G sensor 77 Yaw rate sensor 100 Driving force control device 101 Road surface μ estimated value calculation unit 102 Ground load calculation unit 103 Lateral force calculation unit 104 Allowable driving force calculation unit 105 Allowable driving force correction value calculation 106 engine output control device 107 accelerator sensor 108 throttle actuator

Claims (4)

Friction coefficient estimating means for estimating the friction coefficient of the road surface;
A contact load calculating means for calculating the contact load of the front wheel;
Lateral force calculating means for calculating the lateral force of the front wheel;
An allowable driving force calculating means for calculating an allowable driving force of the front wheel based on an output of the friction coefficient estimating means, the ground load calculating means, and the lateral force calculating means;
A driving force control device comprising: driving force control means for controlling the driving force such that the driving force of the front wheels is equal to or less than the allowable driving force;
A driving force control device comprising: an allowable driving force correction unit that increases and corrects the allowable driving force in response to an increase in the steering angle of the front wheels. The driving force control means increases the total driving force of the vehicle based on a value obtained by multiplying an increase correction amount of the allowable driving force by a reciprocal of a front wheel axle weight distribution ratio of the vehicle. The driving force control apparatus described in 1. The driving force control means increases the total driving force of the vehicle based on a value obtained by multiplying the increase correction amount of the allowable driving force by the inverse of the front wheel driving force distribution ratio of the vehicle. The driving force control apparatus described in 1. The driving force control means reduces the rate of change of driving force with respect to displacement of an accelerator pedal to which a driver inputs an acceleration request when the corrected allowable driving force is a predetermined value or less. The driving force control apparatus according to any one of claims 1 to 3.

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