JP2006062505A - Suspension device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a suspension device for a vehicle capable of realizing stable vehicle behavior by controlling a tow angle properly during turn. <P>SOLUTION: While the vehicle turns, a slip angle α of a wheel is calculated based on amount of upper and lower stroke detected by a stroke sensor 12 and lateral force of a tire generated by the slip angle α is estimated. A tow angle Δδ is added to each wheel so that lateral force of the tire becomes lateral force of the tire when the slip angle α does not occur to suppress fluctuation of lateral force of the tire. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vehicle suspension apparatus that individually steers each wheel to improve running stability.

In a conventional vehicle suspension device, during straight running, a wheel slip angle generated by a suspension stroke is calculated based on the wheel stroke speed, and a toe angle in a direction to suppress the slip angle is determined by an actuator. It has been known that the straightness of a vehicle is improved by adding the wheels individually (see, for example, Patent Document 1).
JP 2003-137123 A

  However, the above conventional vehicle suspension device adds a toe angle in a direction that suppresses the slip angle. For example, when a slip angle is generated by scuffing when the vehicle is in a turning state, If only the toe angle corresponding to the slip angle is added, the total lateral force generated by the turning inner and outer wheels changes depending on the effect of wheel load changes on the left and right wheels. End up.

Therefore, the lateral force generated by the front two wheels or the rear two wheels during turning changes, causing a change in the balance of the force in the vehicle lateral direction and the balance of the moment in the vehicle yaw direction, making the vehicle behavior unstable. There is a problem.
Therefore, the present invention has been made paying attention to the unsolved problems of the above-described conventional example, and when the vehicle is turning, the toe angle control can be appropriately performed to realize a stable vehicle behavior. An object of the present invention is to provide a vehicle suspension device.

  In order to achieve the above object, the vehicle suspension apparatus according to the present invention detects that the vehicle is turning by the turning detection means, detects the vertical stroke amount of each wheel by the stroke amount detection means, and detects the slip angle. The calculation means calculates the slip angle of the wheel based on the vertical stroke amount detected by the stroke amount detection means, and when the turning detection means detects that the vehicle is turning, the toe angle control means, The toe angle of each wheel is controlled so that the fluctuation of the lateral force sum of the turning inner and outer wheels due to the slip angle calculated by the slip angle calculating means is suppressed.

  According to the present invention, when a slip angle caused by scuffing occurs while the vehicle is turning, the toe angle is controlled so as to eliminate the tire lateral force fluctuation of each wheel. It is possible to suppress a change in the balance of moments in the vehicle yaw direction and realize a stable vehicle behavior, and the driver can perform a desired vehicle operation without a sense of incongruity.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a vehicle suspension apparatus according to a first embodiment of the present invention. In FIG. 1, 1 is a vehicle to which the present invention is applied, 2FL and 2FR are front wheels as driven wheels, and 2RL and 2RR are drive wheels. As the rear wheel.
Front and rear suspension members are attached to the vehicle 1, front wheels 2FL and 2FR are attached to a front wheel suspension member 10, and rear wheels 2RL and 2RR are attached to a rear wheel suspension member 11 via suspension arms.

Each of the wheels 2FL to 2RR can independently add a front left wheel actuator 6FL, a front right wheel actuator 6FR, and a rear left wheel to which a rotation angle (toe angle) about an axis orthogonal to the ground contact plane of the wheel center can be added. An actuator 6RL and a rear right wheel actuator 6RR are provided.
The operation of the actuators 6FL to 6RR of each wheel is controlled by the hydraulic control device 16, and a command value for the actuator movement amount of each wheel calculated by the control unit 17 described later is output to the hydraulic control device 16. It is configured as follows.

  Therefore, for example, when the rear right wheel actuator 6RR is extended, the rear right wheel is steered to the left by the actuator movement amount command value, and to the right when the rear right wheel actuator is contracted. Further, when the rear left wheel actuator 6RL is extended, the rear left wheel is steered to the right, and when contracted, it is steered to the left. Thus, the wheels 2FL to 2RR can be individually steered, and the toe angle of each wheel can be individually controlled.

These actuators 6FL to RR constitute toe angle control means.
The vehicle 1 also includes a front left wheel stroke sensor 12FL, a front right wheel stroke sensor 12FR, and a rear left wheel as stroke amount detection means for detecting the vertical stroke amount ST _i (i = FL to RR) of each wheel relative to the vehicle body. Stroke sensor 12RL and rear right wheel stroke sensor 12RR, and these detection signals are input to a control unit 17 to be described later.

  Further, the vehicle 1 includes a yaw rate sensor 18 that detects a yaw rate γ, a lateral acceleration sensor 19 that detects a vehicle lateral acceleration Ay, a wheel speed sensor 20 that serves as a vehicle speed detection unit that detects a vehicle speed V, and a steering angle δ. A steering angle sensor 21 to detect and a steering torque sensor 22 to detect the steering torque T are provided, and these detection signals are input to the control unit 17.

  Then, the control unit 17 makes a toe angle so as to eliminate the fluctuation of the tire lateral force caused by the wheel contact point lateral movement (scuff) caused by the suspension stroke during the turning of the vehicle based on the vehicle state quantity and the driver operation quantity. The actuator movement amount command value to be added to each wheel is calculated, and the actuator movement amount command value is output to the hydraulic control device 16.

  Here, the vehicle state quantities are the vertical stroke amount ST of the stroke sensors 12FL to 12RR, the yaw rate γ of the yaw rate sensor 18, the lateral acceleration Ay of the lateral acceleration sensor 19, and the vehicle speed V of the wheel speed sensor 20. The driver operation amount is the steering angle δ of the steering angle sensor 21, and the steering torque T of the steering torque sensor 22 can be used instead of the steering angle δ.

In this configuration, an electric motor type actuator may be used as an actuator for controlling the toe angle of each wheel. In this case, the hydraulic control device 16 serves as an electric actuator driver. Further comprising a sensor such as an accelerometer, instead of the stroke sensor 12FL~12RR provided in each wheel may be estimated stroke ST _i of the suspension.

Next, the toe angle addition control process performed by the control unit 17 will be described with reference to the flowchart shown in FIG. This toe angle addition control process is executed by a timer interrupt process every predetermined time (for example, every 10 msec).
In this toe angle addition control process, first, in step S1 of FIG. 2, various data from each sensor are read. Specifically, the vertical stroke amount ST, yaw rate γ, lateral acceleration Ay, vehicle speed V, steering angle δ, steering torque T, and actual actuator position detected by the sensors are read.

  Next, the process proceeds to step S2 to determine whether or not the host vehicle is turning. This determination is made based on the magnitude of the steering angle δ, for example, and when the steering angle δ exceeds a predetermined value, it is determined that the host vehicle is turning. When it is determined that the host vehicle is turning, the process proceeds to step S3. When it is determined that the host vehicle is not turning, the timer interruption process is terminated and the process returns to a predetermined main program.

  In step S3, the tire lateral force generated in each wheel is calculated. Specifically, the control unit 17 has a vehicle model. First, the slip angle β of each wheel and the wheel of each wheel are determined from the vehicle state quantities such as the stroke amount ST, the yaw rate γ, and the lateral acceleration Ay read in step S1. The load W is calculated. Then, based on the calculated slip angle β and wheel load W of each wheel, the tire lateral force generated in each wheel is calculated with reference to a tire characteristic map provided in advance in the control unit 17. The tire lateral force calculated here is a lateral force generated on each wheel when a tire side slip angle due to scuffing does not occur during vehicle turning.

The tire lateral force of each wheel may be directly measured by a load sensor built in the wheel or hub.
Next, in step S4, as will be described later, a slip angle calculation process for calculating a tire side slip angle by the scuffing of each wheel, that is, a slip angle α is performed, and the process proceeds to step S5. In step S5, as will be described later, target toe angle calculation processing for calculating the target toe angle Δδ is performed. The target toe angle in the present embodiment is a toe angle added to each wheel so that the sum of generated lateral forces of the inner and outer wheels during turning is always constant.

Next, in step S6, a target actuator position for adding the target toe angle Δδ of each wheel calculated in step S5 to a predetermined wheel is calculated. Then, the process proceeds to step S7 to drive the actuator 6. After the command value of the actuator movement amount is output to the hydraulic control device 16, the timer interrupt process is terminated, and the process returns to a predetermined main program.
In the process of FIG. 2, the process of step S2 corresponds to the turning detection means.

FIG. 3 shows the processing of steps S6 and S7 in a control loop.
First, the difference between the actual actuator position read in step S1 and the target actuator position calculated in step S6 is multiplied by a feedback gain to be converted into a hydraulic pressure output. As the feedback gain, a value derived by PID control theory, optimal control theory, or the like can be used.
The actuator 6 is operated by outputting the hydraulic pressure output to the actuator 6. That is, a value obtained by multiplying the difference between the target actuator position and the actual actuator position by the feedback gain is the command value for the actuator movement amount in the present embodiment.

Next, details of the slip angle calculation process in step S4 will be described.
FIG. 4 is a view showing a coordinate system and a stroke sensor of the suspension device, and is a view of the rear left wheel as viewed from the front of the vehicle. The wheel 2RL is slidably held by a wheel side member 26 called a knuckle arm, and the wheel 2RL can swing by contraction of an impact absorbing member 27 called a spring and a shock absorber.
Here, the lateral direction of the vehicle is defined as the Y axis, the vertical direction of the vehicle is defined as the Z axis, and the longitudinal direction of the vehicle is defined as the X axis.

The suspension strokes, and the stroke amount ST _RL which is the displacement of the shock absorbing member of the rear left wheel generates the vertical displacement Z _RL of the wheel center of the rear left wheel and the scuff amount Y _RL which is the lateral displacement of the ground center of the rear left wheel.
The relationship between the scuff amount Y _{RL and} the stroke amount ST _RL is determined by the pivot position of the suspension arm. In the present invention, it is assumed that characteristic values as shown in FIG.

As shown in FIG. 5, the generated scuff amount Y _RL is set to increase as the impact absorbing member 27 is largely displaced up and down, that is, as the absolute value of the stroke amount ST _RL increases.
In FIG. 5, the vehicle having a higher virtual rotation center position of the suspension and a higher roll center position, which is the rotation center of the vehicle in the roll direction, has a larger scuff amount than a low vehicle, and thus has the effect of the present invention. It is also effective in a vehicle equipped with a suspension that controls the roll center by changing the suspension pivot position.
If the scuff amount Y _RL can be detected using a displacement meter or the like, it is not necessary to previously have a characteristic value indicating the relationship of the scuff amount Y _RL to the stroke amount ST _RL .
Then, the tire side slip angle, that is, the slip angle α _RL is calculated from the scuff amount Y _RL derived in this way.

FIG. 6 is a diagram showing the slip angle by scuffing, and shows the rear left wheel 2RL. The scuff slip angle α _RL is calculated by the following equation.
α _RL = tan ⁻¹ (Vy _RL / Vx _RL ) (1)
Here, Vx _RL is a vehicle front-rear direction speed at the rear left wheel, and Vy _RL is a time differential (scuff speed) of the rear left wheel scuff, which is expressed by the following equation (2).
Vy _RL = dY _RL / dt (2)
The vehicle longitudinal speed Vx _RL is a value calculated from the vehicle speed V detected by the wheel speed sensor 20 and the yaw rate γ detected by the yaw rate sensor 18.

As shown in FIG. 6 (a), the slip angle α _RL of the rear left wheel is obtained from the angle formed by the vector of the scuff speed Vy _RL and the vehicle longitudinal speed Vx _RL , thereby causing the tire to slip sideways and to the right Lateral force Fy _RL acts. At this time, the wheel 2RL moves to 2'RL.
FIG. 6B shows a case where a toe angle Δδ _RL corresponding to the slip angle α _RL generated by scuffing is added. By thus adding the toe angle .DELTA..delta _RL, tire without causing skidding, tire lateral force is not generated. Therefore, the wheel 2RL is steered like 2'RL.

On the other hand, the slip angle α _RR due to the scuffing of the rear right wheel is calculated by the following equation.
α _RR = tan ⁻¹ (Vy _RR / Vx _RR ) (3)
Here, Vx _RR is the speed in the vehicle front-rear direction at the rear right wheel, and Vy _RR is the time differential (scuff speed) of the rear right wheel scuff, which is expressed by the following equation (4).
Vy _RR = dY _RR / dt (4)
The vehicle longitudinal speed Vx _RR is a value calculated from the vehicle speed V detected by the wheel speed sensor 20 and the yaw rate γ detected by the yaw rate sensor 18.

Next, the rear wheel generated lateral force when the vehicle 1 makes a right turn will be described with reference to FIGS.
FIG. 7 is a view of the vehicle 1 as viewed from above. When the vehicle 1 turns right, the rear right wheel 2RR normally strokes to the rebound side (extension side), and the rear left wheel 2RL strokes to the bound side (contraction side). A scuff change occurs due to the stroke, the rear right wheel 2RR moves to 2'RR, and the rear left wheel 2RL moves to 2'RL. Accordingly, the slip angle of the rear right wheel 2RR changes by α _RR by scuffing, and the slip angle of the rear left wheel changes by α _RL by scuffing.

The sum of the rear wheel slip angle β _R determined by the vehicle slip angle β and the yaw rate γ, the rear right wheel slip angle α _RR, and the rear left wheel slip angle α _RL is the actual tire slip angle.
The slip angle of the rear right wheel 2RR is an angle formed by the tire and the vector 24 that is the sum of the rear right wheel slip angle α _RR and the rear wheel slip angle β _R. The slip angle of the rear left wheel 2RL is the rear left wheel slip angle. The angle formed by the tire 25 and the vector 25 which is the sum of α _RL and the rear wheel slip angle β _R. Although the slip angle of the turning outer wheel (rear left wheel) increases, the slip angle of the inner turning wheel (rear right wheel) decreases.

FIG. 8 is a diagram showing the relationship between the rear wheel generated lateral force and the slip angle, where the horizontal axis represents the slip angle and the vertical axis represents the lateral force. The lateral force with respect to the slip angle is usually represented by a reference characteristic indicated by a solid line, and changes as the wheel load of the wheel increases or decreases.
When the vehicle 1 is turning right, the wheel load of the rear left wheel 2RL increases and the wheel load of the rear right wheel 2RR decreases as the vehicle turns. Therefore, the lateral force characteristic of the rear left wheel 2RL is indicated by a broken line L, and the lateral force characteristic of the rear right wheel 2RR is indicated by a one-dot chain line R.

The lateral force of the rear left and right wheels at the rear wheel slip angle β _R is a value indicated by point A and point B. The lateral force indicated by points A and B is a lateral force generated on the rear left and right wheels when a slip angle due to scuffing does not occur during turning.
When the suspension strokes due to road surface irregularities during turning and the like, a scuff is generated, the scuff generates a slip angle, and the rear left wheel 2RL has a slip angle α _RL and the rear right wheel 2RR has a slip angle α _RR . Further, the wheel loads of the rear left wheel 2RL and the rear right wheel 2RR change (increase).

As a result, the lateral force characteristic of the rear left wheel 2RL becomes as indicated by a broken line L ′, and the lateral force characteristic of the rear right wheel 2RR becomes as indicated by an alternate long and short dash line R ′. Then, the lateral force generated by the rear left wheel 2RL increases from the point A to the point A ′, and the lateral force generated by the rear right wheel 2RR decreases from the point B to the point B ′.
Although the inner ring lateral force decreases and the outer ring lateral force increases, the amount of increase from point A to point A ′, that is, the amount of increase in lateral force due to outer ring scuffing ΔA is the amount of decrease from point B to point B ′, ie The amount of lateral force decrease ΔB due to the inner ring scuff is different. For this reason, the sum of the lateral force at point A and the lateral force at point B and the sum of the lateral force at point A ′ and the lateral force at point B ′ are different in magnitude. That is, the lateral force sum between the inner ring and the outer ring changes with the scuff change.

If a toe angle corresponding to the slip angle generated by the scuff is added to each wheel as in the conventional device, the lateral force generated by the rear left wheel 2RL decreases from the point A ′ to the point A ″, and the rear right wheel The lateral force generated by 2RR increases from point B ′ to point B ″.
However, due to the increase in wheel load due to scuffing, the sum of the lateral force at point A ″ and the lateral force at point B ″, and the sum of the lateral force at point A ′ and the lateral force at point B ′ Are different in size. That is, the lateral force sum of the rear left and right wheels fluctuates only by adding a toe angle corresponding to the slip angle by scuffing.

When tire lateral force fluctuations occur due to scuffing changes, changes in the balance of force in the lateral direction of the vehicle and the balance of moments in the vehicle yaw direction may affect the behavior of the vehicle. There is a problem that vehicle operation is hindered and vehicle behavior becomes unstable.
Therefore, in the present invention, a stable vehicle behavior is realized by adding a toe angle to each wheel so as to eliminate the tire lateral force fluctuation accompanying the scuff change.

Next, details of the target toe angle calculation process in step S5 in FIG. 2 will be described.
The target toe angle in the present embodiment is a toe angle for canceling the lateral force fluctuation due to the scuff and making the tire slip angle so that the lateral force generated by the tire is always constant even with respect to the wheel load fluctuation. is there.
FIG. 9 shows a state similar to that of FIG. During turning, the rear right wheel 2RR, which is an inner wheel, is in a point B, and the rear left wheel 2RL, which is an outer wheel, is in a point A state. At this time, when the wheel load of the left and right wheels changes due to road surface irregularities and the scuffing occurs due to the suspension stroke, the state of the inner ring is changed from point B to point B ′ and the outer ring is changed from point A to point A ′. Change. Therefore, as described above, the lateral force generated by each of the inner and outer wheels changes, and the lateral force sum generated by the inner and outer wheels also fluctuates, thereby destabilizing the vehicle behavior.

Therefore, in the present embodiment, toe angle control is performed so that the inner ring lateral force Fy _in becomes the inner ring lateral force when no scuffing occurs due to road surface irregularities or the like. That is, the inner ring lateral force when the road surface irregularity or the like indicated by the point B is not generated becomes the target lateral force Fy _in ^* , which is the lateral force calculated in step S3.
Here, the inner ring lateral force Fy _in is estimated by first estimating the inner ring load Wr _in from the vehicle state quantities such as the stroke amount ST, the yaw rate γ, and the lateral acceleration Ay, and calculating the inner ring load Wr _in and the step S4. This is done by referring to the tire characteristic map stored in the control unit 17 based on the slip angle α _RR of the rear inner wheel (rear right wheel 2RR).

Of course, you may make it measure directly with the load sensor incorporated in a wheel or a hub.
Then, the target toe angle Δδ _RR of the inner ring is calculated so that the inner ring lateral force Fy _in calculated in this way becomes equal to the target lateral force Fy _in ^* calculated in step S3. Similarly, the outer wheel target toe angle Δδ _RL is calculated so that the outer ring lateral force Fy _out is equal to the target lateral force Fy _out ^* .

When the target toe angle Δδ _RR is added to the inner ring, the inner ring is in a state of a point B ″, and when the toe angle Δδ _RL is added to the outer ring, the outer ring is in a state of a point A ″. Here, the lateral force at the point B ″ and the lateral force at the point B are equal, and the lateral force at the point A ″ and the lateral force at the point A are equal. Therefore, the sum of the lateral forces between the inner ring and the outer ring is irregular road surface. It does not fluctuate when scuffing occurs due to, etc., and always has a constant size.

FIG. 10 shows a time series of the scuff amount, the slip angle due to the scuff, and the command toe angle when the toe angle addition control in the present embodiment is performed. FIG. 10 (a) shows the rear left wheel 2RL, FIG. ) Shows the rear right wheel 2RR.
In FIG. 10, the upper part is the time series response of the scuff change. When a scuff change as illustrated in the rear left wheel 2RL and the rear right wheel 2RR occurs, the scuff change amount is time-differentiated (formula (2)), and the value divided by the wheel speed is substituted into the formula (1). By doing so, the slip angle by the scuff shown in the middle is calculated. As shown in the upper row, since the difference in scuffing is provided between the rear left wheel and the rear right wheel, the slip angle due to the scuff shown in the middle row also results in different left and right wheels.

  Finally, the command toe angle becomes an arrow shown in the lower part. Here, the curve indicated by the solid line is a lateral force constant toe angle at which the tire lateral force is constant regardless of the scuff change, and the curve indicated by the broken line is a slip angle due to the scuff shown in the middle stage. In this way, the tire lateral force that changes from moment to moment is estimated, and the difference between the lateral force constant toe angle and the slip angle due to scuffing is taken as the command toe angle. In other words, if the lateral force constant toe angle exceeds the slip angle by scuffing, the toe angle is added by δ− in the direction to decrease the toe angle, and in the opposite case, the toe angle is added by δ + in the direction to increase the toe angle. Is done.

Next, the operation of this embodiment will be described.
Now, it is assumed that the driver does not perform a steering operation and the host vehicle is traveling straight ahead. In this case, in the toe angle addition control process shown in FIG. 2, it is determined in step S2 that the host vehicle is not in a turning state, the toe angle addition control process is terminated, and the vehicle goes straight without adding a toe angle to each wheel. Continue running.

From this state, it is assumed that the driver steers to the right and the vehicle turns right. At this time, assuming that there is no road surface irregularity and the suspension does not stroke, only the slip angle βr is generated in the rear left and right wheels, and a lateral force corresponding to the slip angle βr and the wheel load Wr is generated. That is, in FIG. 9, the rear right wheel 2RR, which is the turning inner wheel, is in the state of point B, and the inner wheel lateral force Fy _in is generated, and the rear left wheel 2RL, which is the outer turning wheel, is in the state of point A, and the outer wheel lateral force Fy. _{An out} occurs.

Since the suspension is not stroked and no slip angle due to scuffing occurs, the slip angles α _RL and α _RR are estimated to be zero (0) in step S4, and the lateral force sum of the turning inner and outer wheels varies. It is determined that the vehicle behavior does not become unstable. Accordingly, in step S5, the target toe angle Δδ is calculated to be zero (0), and the turning travel is continued without adding a toe angle to each wheel.

Thereafter, assuming that the suspension strokes due to road surface irregularities or the like, slip angles α _RL and α _RR due to scuffing are estimated in step S4. Then, it is estimated that the lateral force sum of the inner and outer rings fluctuates due to the generation of the slip angles α _RL and α _RR and the change of the wheel load. That is, in FIG. 9, when the rear right wheel 2RR changes its state from the point B to the point B ′ and the rear left wheel 2RL changes its state from the point A to the point A ′, It is estimated that the lateral force sum of the inner and outer rings changes depending on when scuffing occurs.

Therefore, in step S5, the inner ring lateral force Fy _in when the scuff is generated is added to the inner ring so as to be equal to the target lateral force Fy _in ^* that is the inner ring lateral force when the scuff is not generated. The target toe angle Δδ _{RR to} be calculated is calculated so that the outer ring lateral force Fy _out when the scuff is generated is equal to the target lateral force Fy _out ^* which is the outer ring lateral force when the scuff is not generated. toe angle .DELTA..delta _RL to be added with respect to the outer ring is calculated.

Then, an actuator movement amount command value for adding the target toe angle Δδ _RR to the rear right wheel 2RR is output to the hydraulic control device 16, whereby the rear right wheel actuator 6RR is contracted. The rear right wheel 2RR is steered to the right. Further, the actuator movement amount command value for adding the target toe angle Δδ _RL to the rear left wheel 2RL is output to the hydraulic control device 16, so that the rear left wheel actuator 6RL is expanded and the rear left wheel 2RL. Is steered to the left.

Accordingly, in FIG. 9, the rear right wheel 2RR is in the state of the point B ″, and the rear left wheel 2RL is in the state of the point A ″. Therefore, the sum of the lateral forces of the turning inner and outer wheels does not fluctuate between when the road surface is irregular and the scuff is generated and when it is not constant.
Thus, in the first embodiment, when the host vehicle is in a turning state, the suspension strokes due to road surface irregularities, etc., and scuffing occurs, resulting in the lateral force of the turning inner and outer wheels when a slip angle occurs. Since the toe angle is added to each wheel so that the sum does not fluctuate, the vehicle behavior can be prevented from becoming unstable due to the fluctuation of the lateral force sum, and the desired vehicle can be provided without giving the driver a sense of incongruity. The operation can be performed.

  When the vehicle is in a turning state, the lateral force when the scuff is not generated is set as the target lateral force, and the lateral force when the scuff is generated is matched with the target lateral force. Since the toe angle is added to the wheels, the lateral force sum of the inner and outer wheels can always be kept constant even if scuffing occurs due to road surface irregularities during turning, and fluctuations in the lateral force sum are reliably suppressed. can do.

Next, a second embodiment of the present invention will be described.
In the second embodiment, a toe angle is added to each wheel so that the lateral force sum of the front left and right wheels and the lateral force sum of the rear left and right wheels follow a predetermined reference model.
That is, in the toe angle addition control process executed by the control unit 17, the lateral force sum of the front two wheels and the rear two wheels according to the steering angle δ and the vehicle speed V in step S5 of FIG. 2 in the first embodiment. Except for calculating the target toe angle Δδ so that the lateral force sum of the two matches the predetermined normative model, the same processing as the processing of FIG. 2 is executed, and thus detailed description thereof is omitted.

Here, as the reference model, a front-rear and rear-rear vehicle model called a two-wheel model as shown in FIG. 11 is applied. In the figure, 101F is the front wheel, 101R is the rear wheel, and G is the center of gravity. Further, it is assumed that the front-rear direction distance between the front wheel 101F and the rear wheel 101R is l, the distance from the center of gravity G to the front wheel 101F is lf, and the distance from the center of gravity G to the rear wheel 101R is lr.
Further, assuming that the front wheel actual steering angle is δ, the vehicle side slip angle is β, the yaw rate is γ, and the vehicle speed is V, the tire lateral forces Fyf and Fyr generated by the front wheels 101F and the rear wheels 101R are expressed by the following equations.
Fyf = Kf (δ−β−lf · γ / V) (5)
Fyr = Kr (−β + lr · γ / V) (6)
Here, Kf and Kr are equivalent cornering powers of the front and rear wheels.

If the equivalent cornering powers of the front and rear wheels in the reference model of the vehicle equipped with the suspension device of the present invention are Kf ^* and Kr ^* , the tire lateral force, that is, the target lateral force of the front and rear wheels generated by the front and rear wheels of the reference model. Fyf ^* and Fyr ^* are expressed by the following equations.
Fyf ^* = Kf ^* (δ−β−lf · γ / V) (7)
Fyr ^* = Kr ^* (− β + lr · γ / V) (8)
Here, the front lateral actual steering angle δ, the vehicle side slip angle β, the yaw rate γ, and the vehicle speed V use measured values by sensors, and the target lateral forces Fyf ^* and Fyr ^* change from moment to moment.

Further, the vehicle behavior can be changed by changing the equivalent cornering powers Kf ^* and Kr ^* of the front wheels and the rear wheels, which are reference models. For example, when traveling at a high speed on a straight line, the equivalent cornering power Kr ^* of the rear wheels is increased to increase the stability against disturbances such as crosswinds, or the equivalent cornering power Kf ^* of the front wheels at the start of turning is increased. The turning ability can be increased. Thus, by changing the equivalent cornering powers Kf ^* and Kr ^* of the front and rear wheels in accordance with the vehicle state, it can be felt as if the vehicle performance has been improved.

In this embodiment, toe angle addition control is performed on the front wheels so that the lateral force average of both front left and right wheels becomes Fyf ^* / 2, and the rear wheel so that the lateral force average of both rear left and right wheels becomes Fyr ^* / 2. Toe angle addition control is performed on
FIG. 12 shows the relationship between the tire slip angle and the tire lateral force of the rear right wheel 2RR serving as the inner turning wheel and the rear left wheel 2RL serving as the outer turning wheel when the vehicle turns right. In the case of the conventional suspension, when the suspension strokes due to road surface irregularities when turning, scuffing occurs, and when the wheel load of each wheel changes, the inner ring changes from point B to point B ', and the outer ring changes from point A to point A'. Changes, and the lateral force generated by each of the inner and outer rings changes. As a result, the sum of the lateral forces generated by the inner and outer rings also varies. Therefore, there is a problem that the vehicle behavior becomes unstable.

Therefore, in the present embodiment, the toe angle is controlled so that the lateral force average of the rear left and right wheels becomes Fyr ^* / 2 obtained from the equation (8). That is, by adding the toe angle Δδ _RR to the inner ring, the inner ring is in the state of point B ″, and by adding the toe angle Δδ _RL to the outer ring, the outer ring is in the state of point A ″.
As a result, even if the suspension strokes due to road surface irregularities when turning, scuffing occurs, and the wheel load of each wheel changes, the sum of the lateral forces generated by the left and right wheels is always Fyr ^* , so that the tires Lateral force fluctuations are eliminated, and the effect of scuffing on vehicle plane motion is eliminated.

As described above, in the second embodiment, the sum of the lateral forces of the front two wheels and the sum of the lateral forces of the rear two wheels follows the two-wheel model as a predetermined reference model according to the steering angle and the vehicle speed. Since a toe angle is added to each wheel, the lateral force sum of the inner and outer wheels can always be kept constant even when scuffing occurs due to road surface irregularities during turning, so that fluctuations in the lateral force sum can be assured. Can be suppressed.
In addition, since the toe angle control is performed by applying the two-wheel model as the predetermined reference model, it is possible to make the vehicle have the vehicle behavior desired by the driver without depending on the dimensions, inertia, and tire characteristics of the vehicle. .

Next, a third embodiment of the present invention will be described.
In the third embodiment, the ratio of the lateral force to the wheel load during turning is equal for the inner and outer wheels.
That is, in the toe angle addition control process executed by the control unit 17, in step S5 of FIG. 2 in the first embodiment, the ratio of the lateral force to the wheel load at the turning inner and outer wheels is determined according to the wheel load of each wheel. Except for calculating the target toe angle Δδ so as to be equal, a process similar to the process of FIG. 2 is executed, and thus detailed description thereof is omitted.

FIG. 13 is a diagram showing a tire generated lateral force with respect to a tire friction circle of a rear left wheel (turning outer wheel) and a rear right wheel (turning inner wheel) in the conventional suspension and the suspension of the present invention. FIG. 13A shows the case of a conventional suspension. Considering that the friction coefficient μ of the road surface is the same for both wheels, when the vehicle is turning right, the rear left wheel, which is the turning outer wheel, has a larger wheel load than the rear right wheel, so the tire friction circle becomes larger, the ratio of the lateral force Fyr _out the turning outer against the wheel load Wr _out of the outer turning wheel is generated does not coincide with the ratio of the lateral force Fyr _in the turning inner wheel is generated for a wheel load Wr _in the turning inner. That is, Fyr _out / Wr _out ≠ Fyr _in / Wr _in .

For this reason, the performance of the inner and outer tires cannot be sufficiently exhibited in a state where the lateral acceleration is high. In addition, since the tire forcibly generates a lateral force greater than the product of the wheel load W and the road surface coefficient μ, there is a problem that the tire tread surface is also worn.
Therefore, in the present invention, as shown in FIG. 13B, when it is considered that the friction coefficient μ of the road surface is the same for both wheels, the ratio of the lateral force Fyr _out generated by the turning outer wheel to the wheel load Wr _out of the turning outer wheel , the turning inner wheel so as to match the rate of the lateral force Fyr _in generated for wheel load Wr _in the turning inner. That is, a target toe angle that satisfies the relationship of the following equation is added.
Fyr _out / Wr _out = Fyr _in / Wr _in (9)
Here, the rear wheel generated lateral force sum Fyr is: Fyr = Fyr _out + Fyr _in (10)
This rear wheel generated lateral force sum Fyr is the lateral force of the reference model in the second embodiment described above. In the present embodiment, the case where the lateral force sum of the left and right wheels follows the two-wheel model described above is described, but the present invention is not limited to this.

Then, Fyr _out and Fyr _in calculated by the equations (9) and (10) are set as the target lateral forces Fyr ^* _out and Fyr ^* _in of the rear outer wheel, and the generated lateral force of each wheel matches the target lateral force. In this way, the target toe angle Δδ is calculated and toe angle addition control is performed.
FIG. 14 is a diagram illustrating the relationship between the tire slip angle and the tire lateral force of the rear right wheel serving as the inner turning wheel and the rear left wheel serving as the outer turning wheel in the present embodiment. In the case of a conventional suspension, when the suspension strokes due to road surface irregularities when turning, scuffing occurs, and when the wheel load changes, the lateral force generated by each of the inner and outer rings changes, and the sum of the lateral forces generated by the inner and outer rings also increases. Fluctuates and makes vehicle behavior unstable.

However, in this embodiment, the target lateral forces of the inner and outer wheels are Fyr ^* _out and Fyr ^* _in calculated by the equations (9) and (10), and the ratio of the tire-generated lateral force to the wheel load is the left and right wheels. It will be equal to each other, and the tire lateral force performance of both wheels will be fully demonstrated.
Further, since the rear wheel generated lateral force sum Fyr is set so as to follow the reference model, the lateral force sum generated by both the left and right wheels is not changed, and the vehicle behavior is not affected.

  As described above, in the fourth embodiment, the toe angle is added to each wheel so that the ratio of the lateral force to the wheel load during turning is equal between the inner and outer wheels. Force can be generated, the characteristics of the tire can be fully utilized, and a phenomenon in which the inner ring lateral force is saturated first or a phenomenon in which the outer ring lateral force is saturated first can be eliminated.

  In each of the above embodiments, the case of the double wishbone type suspension as shown in FIG. 4 has been described as having a scuff change characteristic as shown in FIG. 5, but the present invention is not limited to this. This type can be applied to either a strut type or a multi-link type, and any suspension type capable of adding a toe angle can be applied. Furthermore, the scuff change characteristic is not the characteristic shown in FIG. 6, but any characteristic is possible as long as it is within the operating range of the actuator for toe angle control.

1 is a schematic configuration diagram of a vehicle in an embodiment of the present invention. It is a flowchart which shows the toe angle addition control process performed with the control unit of FIG. It is a figure which shows the control loop of actuator position control. It is a figure which shows the coordinate system and stroke sensor of a suspension apparatus of a rear left wheel. It is a figure which shows the relationship between a suspension stroke and a scuff amount. It is a figure explaining the slip angle produced by scuffing. It is a figure explaining the rear wheel generated lateral force at the time of right turn. It is a figure which shows the relationship between the rear wheel generation | occurrence | production lateral force and slip angle when not performing toe angle control. It is a figure which shows the relationship between the rear wheel generation | occurrence | production lateral force and slip angle in 1st Embodiment. It is a figure which shows the time series of toe angle control in this invention. It is a figure explaining a two-wheel model. It is a figure which shows the relationship between the rear wheel generation | occurrence | production lateral force and slip angle in 2nd Embodiment. It is a figure which shows the tire generation lateral force with respect to a tire friction circle. It is a figure which shows the relationship between the rear wheel generation | occurrence | production lateral force and slip angle in 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vehicle 2FL-RR Wheel 6FL-RR Actuator 10 Front wheel suspension member 11 Rear wheel suspension member 12FL-RR Stroke sensor 16 Hydraulic control device 17 Control unit 18 Yaw rate sensor 19 Lateral acceleration sensor 20 Wheel speed sensor 21 Steering angle sensor 22 Steering torque sensor

Claims (3)

In the vehicle suspension device that individually controls the toe angle of each wheel,
A turn detection means for detecting that the vehicle is turning, a stroke amount detection means for detecting the vertical stroke amount of each wheel, and a wheel slip angle based on the vertical stroke amount detected by the stroke amount detection means. When the calculated slip angle calculating means and the turning detection means detect that the vehicle is turning, fluctuations in the lateral force sum of the turning inner and outer wheels due to the slip angle calculated by the slip angle calculating means are suppressed. Thus, a vehicle suspension apparatus comprising a toe angle control means for controlling a toe angle of each wheel.   A steering angle detecting means for detecting a steering angle; and a vehicle speed detecting means for detecting a vehicle speed, wherein the toe angle control means is detected by the steering angle detected by the steering angle detecting means and the vehicle speed detecting means. Based on the vehicle speed, the lateral force of the front wheels and the rear wheels is calculated from a predetermined reference model, and the toe angle of each wheel is controlled so that the lateral force sum follows each other using the lateral force as a target value. The vehicle suspension apparatus according to claim 1.   A wheel load detecting means for detecting a wheel load of each wheel, wherein the toe angle control means is a ratio of the generated lateral force to the wheel load according to the wheel load of each wheel detected by the wheel load detecting means; The vehicle suspension apparatus according to claim 1, wherein the toe angle of each wheel is controlled so that the wheel is equal or substantially equal between the turning inner and outer wheels.

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