JP3065808B2 - Vehicle steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forcible steering control of a rear wheel or a front wheel according to a steering state of a vehicle.
The present invention relates to an improvement in a vehicle steering system that enhances drivability and stability of a vehicle.

[0002]

2. Description of the Related Art Conventionally, a steering apparatus for a vehicle of this type determines a steering ratio of a rear wheel according to a vehicle speed with respect to a steering angle of a front wheel corresponding to a steering operation amount. It is known that the steering control of the rear wheels is known, but with this one, it is possible to obtain the steering performance that matches the driver's intention at any vehicle speed, but on the other hand, in the initial stage when the driver operates the steering. In this state, the front wheels and the rear wheels often have the same phase, and there is a regret that the turning performance of the vehicle in the initial state is low.

For this reason, conventionally, for example, Japanese Unexamined Patent Publication No.
In the device disclosed in Japanese Patent Publication No. 268, a control target yaw rate of a vehicle is calculated based on a steering amount of a driver, and a yaw rate of the vehicle is actually measured. The feedback control amount is calculated, and the steering angle of the rear wheel is feedback-controlled with the feedback control amount, thereby quickly generating a yaw rate even in the initial state of the steering operation, thereby improving the turning performance of the vehicle in this initial state. Is increasing.

[0004]

However, in the above-mentioned conventional feedback control, the feedback control amount is calculated only in accordance with the deviation between the actual measured value of the yaw rate and the control target value, and the rear wheels are steered. For this reason, there is also a limit in accurately controlling the actual yaw rate to the control target value.

Therefore, for example, it is conceivable to employ state feedback control instead of the above feedback control. In this state feedback control, in addition to the yaw rate, a plurality of state variables of the vehicle, for example, the sideslip angle of the wheel, the cornering force of the front wheel and the rear wheel, and the like are estimated to grasp the motion state of the vehicle. Since the control target is controlled using the plurality of state variables of the vehicle, if the steering angle of the front wheel or the rear wheel is feedback-controlled so that the yaw rate generated in the vehicle becomes the control target value, the vehicle is always controlled. Therefore, it is possible to control the vehicle optimally for drivability and stability, for example, by generating a target yaw rate and improving the turning performance of the vehicle at the time of steering operation.

In this case, the state feedback control uses a linear equation as a state equation, and a plurality of state quantities of the vehicle are estimated on the basis of the linear equation. When the dynamic characteristics of the vehicle change due to nonlinear motion that deviates from the linear equation,
The estimated plurality of state quantities deviate from the optimal value, and as a result, the vehicle does not generate the control target yaw rate, and there is a regret that the vehicle becomes unstable. Therefore, for example, separately from the state feedback control, a second control law that is essentially stable in the nonlinear region is prepared in advance, and the second control law is used in the nonlinear region, so that the dynamic characteristics of the vehicle can be improved. It is conceivable to ensure good vehicle stability even when shifting from the linear region to the non-linear region.

However, in the case where the steering control of the front wheels or the rear wheels is switched between the state feedback control and the second control law as described above, the second control law ensures the stability of the vehicle. It is common to adjust the characteristic to increase the understeer tendency for the purpose of performing the operation. For this reason, after the state is switched from the state feedback control to the second control law and the vehicle recovers the stability, the second state is quickly adjusted. It is desired to switch from the control law to the state feedback control again.

[0008] The present invention has been made in view of the above point, and an object of the present invention is to use the state feedback control and the second control law for the steering control of the front wheels or the rear wheels as described above, and to perform both the controls. When the switching is selected between the linear region and the non-linear region, after switching from the state feedback control to the second control law, an excessive increase in the understeer tendency of the vehicle is prevented, and the switching to the state feedback control is performed early. It is in.

[0009]

In order to achieve the above object, according to the present invention, the stability of the vehicle is changed after the steering control of the front wheels or the rear wheels is switched from the state feedback control to the second control law. The state feedback control is shifted to the state feedback control at an early stage at the time of recovery, and the point at which the stability starts to recover is set to the point at which the actual yaw rate of the vehicle exceeds the maximum value and goes to a small value.

That is, as a concrete solution of the present invention, as shown in FIG. 1, a steering means 20 for steering the front wheel or the rear wheel separately from the steering is provided, and the side slip angle of the wheel is controlled. Area discriminating means 34 for discriminating whether the cornering force of the wheel is in a linear area or a non-linear area that varies proportionally, and at least a front wheel or a rear wheel based on the actual yaw rate of the vehicle and the estimated side slip angle of the wheel. A state feedback control means for calculating a target control amount for steering and performing state feedback control of an actual yaw rate of the vehicle to a control target yaw rate; and a second state control means for stably controlling the front wheels or the rear wheels in the nonlinear region.
When the cornering force of the wheel is in the linear region, the steering unit 20 is controlled by the state feedback control unit 30 so that the cornering force of the wheel is in the non-linear region. At this time, a control switching means 32 for switching the steering control of the front wheels or the rear wheels so that the steering means 20 is controlled by the second control means 31 is provided. Further, the yaw rate detecting means 36 for detecting the actual yaw rate of the vehicle, and the control of the front or rear wheel is controlled by the control switching means 32 so as to perform the second control.
When the actual yaw rate detected by the yaw rate detection means 36 exceeds the maximum value during the control by the control means 31, the state feedback control means 30
And return means 33 for forcibly returning to the control of the steering means 20 by the control means.

[0011]

According to the above-mentioned structure, according to the first aspect of the present invention,
In the linear region, the state feedback control means 30 is selected by the control switching means 32, and the steering angle of the front wheel or the rear wheel is state feedback controlled by the operation means 20, so that the yaw rate acting on the vehicle is always accurately adjusted to the control target value. In accordance with this, good driving characteristics of the vehicle can be obtained as intended by the control.

On the other hand, in the nonlinear region, the second control means 31 is selected by the control switching means 32 instead of the state feedback control means 30. As a result, the steering angle of the front wheel or the rear wheel is stably controlled based on the second control law, so that the motion of the vehicle is stabilized.

Further, after the steering control of the front wheels or the rear wheels is switched from the control by the state feedback control means 30 to the control by the second control means 31, when the actual yaw rate of the vehicle exceeds the maximum value, When the actual yaw rate converges and the vehicle stability starts to recover for the first time, the return means 33 controls the steering of the front wheels or the rear wheels by the second control means 3.
1, the control is forcibly switched back to the control by the state feedback control means 30, so that the increase in the tendency of the vehicle to understeer after the stability of the vehicle is restored is suppressed or eliminated.

[0014]

As described above, according to the vehicle steering system of the first aspect of the present invention, the state feedback control is selectively used in the linear region, and the second control is essentially stable in the nonlinear region. After the second control law is selected and used, the vehicle is switched back to the state feedback control when the actual yaw rate of the vehicle exceeds the maximum value. To improve the running performance of the vehicle, improve the stability of the vehicle in the non-linear region, and recover the stability of the control by the second control law. The increase in the tendency of the vehicle to understeer can be suppressed to a small extent, and the drivability of the vehicle can be improved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 is a schematic plan view of a vehicle steering system according to the present invention, wherein 1 is a steering wheel, 2 is left and right front wheels, 3
Is a left and right rear wheel, 10 is a front wheel steering device that steers the left and right front wheels 2 and 2 by operating the steering 1, and 20 is a left and right rear wheel 3 according to steering of the front wheels 2 and 2 by the front wheel steering device 10. 3 is a rear wheel steering device as steering means for steering the third wheel.

The front wheel steering device 10 has a relay rod 11 arranged in the width direction of the vehicle body, and both ends of the rod 11 are tie rods 12, 12 and a knuckle arm 1, respectively.
It is connected to the left and right front wheels 2, 2 via 3, 13.
The relay rod 11 is provided with a rack and pinion mechanism 14 for moving the relay rod 11 right and left in conjunction with the operation of the steering wheel 1. In this configuration, the front wheels 2, 2 are steered.

On the other hand, the rear wheel steering device 20 has a relay rod 21 disposed in the vehicle width direction in the same manner as described above, and both ends of the rod 21 are respectively connected via tie rods 22, 22 and knuckle arms 23, 23. And are connected to the left and right rear wheels 3,3. The relay rod 21 is provided with a centering spring 22 for urging the rod 21 to a neutral position, and a rack-and-pinion mechanism 23. The mechanism 23 includes a clutch 24, a speed reduction mechanism 25. ,
When the clutch 24 is engaged, the relay rod 21 is moved in the vehicle width direction via the rack-and-pinion mechanism 23 by rotating the motor 26 when the clutch 24 is engaged, so that the rear wheels 3 are moved to the motor 26. The steering is steered by an angle corresponding to the rotation amount.

The motor 26 is connected to the control unit 2
9 is driven and controlled. The control unit 29
As shown in FIG. 3, the steering angle of the rear wheel 3 is internally controlled by the motor 26 based on at least the actual yaw rate at which the state of the vehicle can be estimated and the side slip angle of the wheel (hereinafter referred to as LQG control). LQG control means 30 as state feedback control means, vehicle speed sensitive MAP control means 31 as second control means, and LQG control by LQG control means 30 and MAP control by vehicle speed sensitive MAP control means 31 are selectively performed. It basically has control switching means 32 for switching. The vehicle speed-sensitive MAP control means 31 relatively understeers the target steering angle of the rear wheel 3 to be controlled based on the map stored in advance so that the control is stable, in accordance with the vehicle speed and the front wheel steering angle. The steering angle of the rear wheels 3 is controlled by the motor 26 to the target steering angle by the motor 26, so that the target steering angle is determined uniquely so that the characteristic tends to be strong. Therefore, as shown in FIG. In the cornering force characteristics of the wheel, the control is stable even in a nonlinear region where the change in the cornering force is not proportional to the side slip angle β.

As shown in FIG. 3, the control unit 29 includes a lateral acceleration sensor 35 for detecting a lateral acceleration acting on the vehicle, and a yaw rate sensor as a yaw rate detecting means for detecting an actual yaw rate acting on the vehicle. 36, a rear wheel steering angle sensor 3 for detecting a steering angle of the rear wheel 3
7, a front wheel steering angle sensor 38 for detecting a steering angle of the front wheel 2
And a vehicle speed sensor 39 for detecting the vehicle speed are input.

Next, the drive control of the motor 26 by the control unit 29 will be described with reference to the control flow of FIG. In FIG. 5, when the control timing for each set cycle is reached in step S1, the above-mentioned sensors 3 are set in step S2.
Vehicle speed Vs, front wheel steering angle Fs based on detection signals of 6 to 39
tg, rear wheel steering angle Rstg, yaw rate d レ イ / dt occurring in the vehicle, and lateral motion Yg acting on the vehicle are measured for the motion state amount of each vehicle.

In step S3, a control target yaw rate yrt of the vehicle is calculated based on the following equation.

[0023] Here, A is the stability factor, and L is the wheelbase of the vehicle. Thereafter, the front wheel steering speed df is calculated from the following equation based on the previous value and the current value of the front wheel steering angle Fstg detected by the front wheel steering angle sensor 38 in step S4.

Df = {Fstg (n) −Fstg (n−1)} * k (k is a proportionality constant) Then, in step S5, the steering angle control amount RMAP of the rear wheels 3 in the vehicle speed sensitive MAP control is calculated in advance. Calculate. That is, after calculating the proportional constant r on the map corresponding to the vehicle speed Vsp shown in the same step, the MAP control amount RMAP is obtained by multiplying the calculated proportional constant r by the front wheel steering angle Fstg.

Further, in steps S6 and S7, LQ
The steering angle control amount RFB of the rear wheel 3 in the G control is calculated.
That is, first, in step S6, the observer (state observer)
To calculate and estimate the vehicle state quantity and observation quantity. Here, the state quantity of the vehicle includes the side slip angle β of the vehicle, the change speed dRstg / dt of the steering angle of the rear wheel, the cornering force Cff of the front wheel, and the cornering force Cf of the rear wheel.
Estimate four kinds of r. As the amount of vehicle observation, six types are calculated and estimated by adding the steering angle Rstg of the rear wheels and the yaw rate dψ / dt acting on the vehicle to the four types of estimated state quantities. However, the steering angle Rstg of the rear wheel and the yaw rate dψ
/ Dt uses an actually measured value. Here, the estimation of the state quantity and the observed quantity of the vehicle is performed by calculation based on the following state equation and output equation, with the estimated state quantity of the vehicle as xob and the estimated observed quantity of the vehicle as yob.

Dxob / dt = Aob * xob + Bob
* Y + Job * RFB (n-1) yob = Cob * xob + Dob * y where Aob, Bob, Cob, Dob and Job are observer gains, RFB is an LQG control amount, and y
Are the measured yaw rate dψ / dt and the LQG control amount RFB value.

Thereafter, at step S7, the LQG control amount R
FB is calculated. In this calculation, first, the measured yaw rate dψ
/ Dt and the control target yaw rate yrt (dψ / d
The integral amount Sig of (t-yrt) is expressed by the equation Sig (n) = Sig (n-1) + (d （/ dt-yr
After the calculation based on t), the LQG control amount RFB is calculated by the following equation using the integrated value Sig and the estimated observation amount yob as follows: RFB = -F * yob-FI * Sig. Here, F and FI are control gains.

After calculating the LQG control amount RFB as described above, it is determined in step S8 whether or not the flag F = 3 (that is, the MAP control is being performed as described later). Therefore, in steps S9 and S10, it is determined whether or not the cornering force of the wheel is in a transition region set near the boundary between the linear region and the non-linear region shown in FIG. Is determined.
Specifically, this determination is made in step S9 by comparing the set front wheel steering speed dl1 for generating the side slip angle βo on the side of the linear region defining the transition region in FIG. 6 with the actual front wheel steering speed df. In step S10, the actual front wheel steering speed df is compared with a value dl1 + Δdf obtained by adding the speed width Δdf corresponding to the width of the transition region to the set front wheel steering speed dl1. As a result, if it is in the linear region of df <dl1, in step S11, the rear wheel steering angle control amount R is set to the LQG control amount RFB calculated in step S7 (R = RFB), and in step S12. Flag F = 1
(LQG control is being performed), and the drive of the motor 26 is controlled by the control amount R in step S16 to control the steering of the left and right rear wheels 3, 3.

On the other hand, if it is in the nonlinear region of dl1 + .DELTA.df <df, the steering angle control amount R
Is set to the MAP control amount RMAP calculated in step S5 (R = RMAP), and in step S14, a flag F = 3 (during MAP control) is set, and step S1 is performed.
In step 6, the motor 26 is driven and controlled by the control amount R (= RMAP), and the left and right rear wheels 3 and 3 are steered.

On the other hand, dl1 <df <dl1 + Δd
If it is in the transition region of f, the control amount RTR of the third control law in this transition region is calculated in step S15. This control amount RTR is calculated as a control amount obtained by weighting and distributing the LQG control amount RFB and the MAP control amount RMAP by a simple proportion based on the position where the actual front wheel steering angle df takes in the transition region based on the following equation.

[0031] RTR = c * RMAP + (1-c) * RFB where dl2 = dl1 + .DELTA.df.

When the control amount RTR based on the third control law is determined as described above, the control amount RTR is determined in step S16.
The drive of the motor 26 is controlled by the TR, and the left and right rear wheels 3,
3 for steering control.

On the other hand, in step S8, the flag F = 3
In the case of (under MAP control), first, in step S17, it is determined whether or not the vehicle is turning, in order to return to LQG control early. This determination is based on the actual yaw rate absolute value | d
ψ / dt | and the absolute value of the front wheel steering angle | fstg | are compared with set values dψl / dt, fstgl corresponding to turning, respectively, and | dψ / dt | ≧ dψl / dt and | fstg |
If the vehicle is turning at fstgl, it is determined in step S18 whether the actual yaw rate of the vehicle has exceeded the maximum value based on the determination flow of FIG. In this determination, the change rate Δdψ / dt of the actual yaw rate of the vehicle is determined in step Sa in the determination flow of FIG.
dt (n) | and the actual value | dｄ / dt (n-1) |
The sign of ψ / dt is determined in step Sb, and Δdψ / dt
If <0, that is, if the actual yaw rate exceeds the maximum value, the flag RF is set to 1 in step Sc, and Δdψ
When the actual yaw rate of / dt> 0 is increasing, the flag RF is set to 0 in step Sd.

When it is determined whether the actual yaw rate of the vehicle has exceeded the maximum value as described above, the value of the flag RF is determined in step S19 in FIG. In this case, the process immediately proceeds to step S11, where the steering angle control amount R for the rear wheel is set to the LQG control amount RFB (R = RFB), and the steering control for the rear wheel 3 is changed from the MAP control to L.
Switch back to QG control. On the other hand, if the yaw rate is increasing at RF = 0, the steering angle control amount R for the rear wheels is set to the MAP control amount RMAP as usual in step S13 (R =
RMAP), the steering control by the MAP control of the rear wheel 3 is continued.

Therefore, in the control flow of FIG.
Steps S6 and S7 constitute the state feedback control means 30, and step S5 defines the second
Control means 31 using MAP control as a control law
Is composed. In addition, in steps S9 and S10, as shown in FIG. 6, the area discriminating means 34 for discriminating whether the cornering force of the wheel is in a linear area or a nonlinear area in which the cornering force changes proportionally to the side slip angle β of the wheel.
The motor 26 is controlled by the LQG control amount RFB of the LQG control means 30 when the cornering force of the wheel is in the linear area in response to the output of the area determination means 34 in steps S11 and S13. When the vehicle is in the non-linear region, the control switching means 32 is configured to switch the steering control of the rear wheels 3 so as to control the motor 26 by the vehicle speed sensitive MAP control of the second control means 31. Further, step S of the control flow of FIG.
8, according to the determination flow of S17 to S19 and FIG.
During the AP control, the actual yaw rate change rate Δd / dt becomes a negative value and the actual yaw rate d //
When dt exceeds the maximum value, the steering angle control amount R of the rear wheel 3 is immediately set as the LQG control amount RFB, and the steering control of the rear wheel 3 is forcibly switched from the MAP control to the LQG control. Means 33 are constituted.

Therefore, in the above embodiment, the steering speed df of the front wheels is slower than the set value dl1 (df <dl).
1) In the case, the cornering force of the wheel is in the linear region, and the steering angle of the rear wheels 3, 3 is LQG controlled by the LQG control means 30. In this case, since the dynamic characteristic of the vehicle satisfies the above-mentioned equation of state, the state quantity x by the observer is obtained.
ob and the observable amount yob are accurately estimated, so that the yaw rate of the vehicle is accurately controlled to the control target value yrt,
The intended vehicle motion characteristics are obtained, and the driving performance and stability of the vehicle are improved.

On the other hand, the front wheel steering speed df exceeds the set value dl2 (= dl1 + Δdf) and is fast (dl2 <d).
In case f), the sideslip angle of the wheel is in the non-linear region. In this case, in the LQG control, the dynamic characteristics of the vehicle do not satisfy the above-mentioned equation of state, and an error easily occurs in the state quantity xob or the like by the observer. Therefore, the control becomes unstable and the motion of the vehicle becomes unstable. There are cases. However, in this non-linear region, the control switching means 32 selects the vehicle speed sensitive MAP control by the second control means 31 which is inherently stable in this non-linear region, and the steering angles of the rear wheels 3, 3 are changed to the vehicle speed Vs and the vehicle speed Vs. Since the control is performed with the MAP control amount RMAP corresponding to the front wheel steering angle Fstg, the running stability of the vehicle is sufficiently secured.

Further, when the steering angle control of the rear wheels 3 is switched from the LQG control to the vehicle speed sensitive MAP control, the change rate Δdψ / dt of the actual yaw rate of the vehicle becomes a negative value, and the actual yaw rate becomes the maximum value. At this point, the vehicle has started to recover stability. If the MAP control continues in this situation, the vehicle tends to understeer due to the understeer tendency of the MAP control.
At this time, the steering control of the rear wheel 3 is quickly changed from the MAP control to the L control.
Since the mode is switched back to the QG control, the increase in the tendency of the vehicle to understeer after the start of the stability recovery is suppressed to a small extent, and the driving performance of the vehicle is improved.

FIG. 7 shows another embodiment. In the above-mentioned embodiment, instead of the rear wheels 3 and 3 being subjected to steering control using the rear wheel steering device 20, the front wheels 2 and 2 are electrically controlled separately from the steering. This is applied to a steering control.

That is, in the steering system shown in FIG.
The rear wheel steering device 20 shown in FIG. 1 is not provided, and the rack and
A pinion mechanism 40 and a motor 41 for driving the mechanism 40
And the drive of the motor 41 is controlled by the control unit 29. Other configurations are the same as those of the above-described embodiment. However, in the present embodiment, when the rear wheels are steered and the rear wheels are steered in the opposite phase to the front wheels, the front wheels are steered. Steering control to increase the angle,
In the above embodiment, when the steering control of the rear wheels is performed in the same phase, in the present embodiment, the steering control may be performed to reduce the steering angle of the front wheels.

In the above description, in the LQG control, there are six types of estimated observable amounts of the vehicle, namely, the side slip angle β of the vehicle, the change speed dRstg / dt of the steering angle of the rear wheel, and the cornering force of the front wheel and the rear wheel. Cff, Cfr, the steering angle Rstg of the rear wheels, and the yaw rate dψ /
Although the state of the vehicle was accurately observed using dt, it is sufficient to observe the state of the vehicle at least by observing the actual yaw rate of the vehicle and the estimated sideslip angle of the wheel.

In the above description, the second control means 3
Although the vehicle speed sensitive MAP control was used as the control law in 1,
The second control law is only required to be able to stably control the rear wheels 3 and 3 in a nonlinear region where the cornering force does not change proportionally. For example, feed forward control other than MAP control, fuzzy control , Feedback control or the like may be used.

[Brief description of the drawings]

FIG. 1 is a block diagram of the first embodiment of the present invention.

FIG. 2 is a diagram illustrating an overall configuration of a steering device that also steers a rear wheel of a vehicle.

FIG. 3 is a diagram showing a block configuration of steering control of a rear wheel.

FIG. 4 is a diagram showing a control flow of rear wheel steering control.

FIG. 5 is a diagram showing a flow of determining whether or not the actual yaw rate acting on the vehicle has exceeded a maximum value.

FIG. 6 is a diagram showing a cornering force characteristic with respect to a side slip angle of a wheel.

FIG. 7 is a diagram showing an overall configuration of a steering device that steers a front wheel.

[Explanation of symbols]

Reference Signs List 1 steering 3 rear wheel (wheel) 20 rear wheel steering device 26 motor 29 control unit 30 LQG control means (state feedback control means) 31 vehicle speed sensitive control means (second control means) 32 control switching means 33 return means 34 area discrimination Means 35 Lateral acceleration sensor 36 Yaw rate sensor (yaw rate detecting means) 37 Rear wheel steering angle sensor 38 Front wheel steering angle sensor 39 Vehicle speed sensor

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI B62D 117: 00 137: 00 (56) References JP-A-4-138967 (JP, A) JP-A-62-247971 (JP, A) JP-A-4-143168 (JP, A) JP-A-62-247979 (JP, A) JP-A-62-294472 (JP, A) JP-A-3-57771 (JP, A) JP-A-63-291776 (JP JP, A) JP-A-1-262268 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6/00 B62D 7/14

Claims (1)

(57) [Claims] A steering device for steering a front wheel or a rear wheel separately from a steering wheel, and whether the cornering force of the wheel is in a linear region or a nonlinear region in which a cornering force of the wheel changes proportionally to a side slip angle of the wheel. Calculating a target control amount for front-wheel or rear-wheel steering based on at least the actual yaw rate of the vehicle and the estimated sideslip angle of the wheels, and performing state feedback control of the actual yaw rate of the vehicle to the control target yaw rate. Feedback control means, second control means capable of stably controlling the front wheel or the rear wheel in the non-linear region, and the state feedback control when the cornering force of the wheel is in the linear region, receiving the output of the region discriminating means. Means for controlling the steering means so that the cornering force of the wheels is in a non-linear region. Control switching means for switching the steering control of the front wheels or rear wheels so that the steering means is controlled by the second control means, a yaw rate detection means for detecting an actual yaw rate of the vehicle, and a front wheel by switching the control switching means. Alternatively, if the actual yaw rate detected by the yaw rate detection means exceeds a maximum value while the steering control of the rear wheels is being performed by the second control means, the control of the steering means by the state feedback control means is forcibly performed. A steering device for a vehicle, comprising: a return unit for returning the vehicle to a proper position.