Apparatus for controlling steer angle of rear wheels of vehicle

• US 4,720,790 A
• Filed: 05/15/1985
• Issued: 01/19/1988
• Est. Priority Date: 05/21/1984
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisa Tyota CUO Kenkyusho
• Original Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation)
• Inventors: Fukui, Katsuhiko, Miki, Kazuo, Hayashi, Yasutaka, Sumi, Kazumasa, Ishiguro, Michio
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): Black, Thomas G.
• Application Number:
  US06/734,332
• Time in Patent Office: 979 Days
• Field of Search: 364/559, 364/424, 364/426, 180/140, 180/142, 180/143, 180/79.1, 280/91
• US Class Current: 701/41
• CPC Class Codes: B62D 7/159 characterised by computing methods or stabilisation processes or systems, e.g. responding to yaw rate, lateral wind, load, road condition

Abstract

A rear wheel steer angle controlling apparatus for vehicles having steerable front and rear wheels, adapted for controlling the steer angle of rear wheels in response to the operation of the steering wheel for steering the front wheels. When the steering wheel is operated quickly, a rear wheel steer angle is formed in the counter direction to the direction of the front wheel steer angle, so that the response to the steering input for turning the vehicle is improved. Conversely, when the steering wheel is operated slowly, a rear wheel steer angle is formed in the same direction as the front wheel steer angle, thus enhancing the stability of the vehicle running straight. When the vehicle is running at a high speed, the rear wheel steer angle is formed always in the same direction as the front wheel steer angle regardless of the speed of operation of the steering wheel, so that the steering stability during high speed running is improved. When a yawing moment is generated due to a disturbance such as lateral wind, the rear wheel steer angle is automatically controlled in such a manner as to negate the yawing moment, thus compensating for the lateral displacement of the vehicle without requiring correcting steering operation by the driver.

Claims

1. A rear wheel steer angle controlling apparatus for automatically controlling a steer angle of rear wheels of a vehicle by controlling an actuator mechanism for generating the steer angle of the rear wheels in response to an operation of a steering wheel for generating a steer angle of front wheels of said vehicle, said apparatus comprising:

a steering wheel displacement detecting means for detecting a steering wheel displacement and for generating a steering wheel displacement signal representing the steering wheel displacement;

a judging means for judging a rotation speed of said steering wheel from said steering wheel displacement signal; and

a controlling means for controlling said actuator mechanism in accordance with a result of judgement by said judging means such that;

(a) said steer angle of the rear wheels is generated in the direction counter to a direction of steer angle of the front wheels when said steering wheel is operated at a high rotation speed; and

(b) said steer angle of the rear wheels is generated in the same direction as the steer angle of the front wheels when said steering wheel is operated at a low rotation speed.

2. A rear wheel steer angle controlling apparatus according to claim 1, wherein said controlling means controls said actuator mechanism in accordance with a result of judgement by said judging means and said steering wheel displacement signal such that:

(a) a steer angle of the rear wheels corresponding to the level of said steering wheel displacement signal is formed in the direction counter to a direction of the steer angle of the front wheels when said steering wheel is operated at a high rotation speed; and

(b) a steer angle of the rear wheels corresponding to the level of said steering wheel displacement signal is generated in the same direction as the steer angle of the front wheels when said steering wheel is operated at a low rotation speed.

3. A rear wheel steer angle controlling apparatus according to claim 1, wherein said judging means comprises means for judging the angular frequency of said steering wheel displacement signals as said rotation speed of said steering wheel.

4. A rear wheel steer angle controlling apparatus according to claim 1, wherein said judging means judges the rotation speed of said steering wheel by using a transfer function G(S) expressed by the following formula and controls said actuator mechanism in accordance with the result of judgement:

##EQU20## where, Kd and Ke are constants which meet the condition of 0<

Kd<

Ke, S is a complex frequency and T is a primary delay time constant.

5. A rear wheel steer angle controlling apparatus according to claim 1, wherein said judging means includes:

a first sample hold circuit for sampling said steering wheel displacement signal at a predetermined period and holding the sampled signal thus producing a stepped voltage signal;

a differential amplifier for subtracting said stepped voltage signal from said steering wheel displacement signal thus outputting a saw-tooth voltage signal;

a second sample hold circuit for sampling said saw-tooth voltage signal at a predetermined period and holding the sampled signal thus outputting a voltage signal;

an absolute value circuit for outputting the absolute value of said voltage signal outputted from said second sample hold circuit; and

;

a comparator circuit for comparing said absolute value outputted from said absolute value circuit with a predetermined voltage corresponding to a high steering wheel operation speed and another predetermined voltage corresponding to a low steering wheel operation speed.

6. A rear wheel steer angle controlling apparatus according to claim 1, wherein said steering wheel displacement detecting means is constituted by a potentiometer having a linear resistor to which a voltage is applied and a slider for sliding linearly on said resistor in accordance with the operation of said steering wheel, while said judging means and said controlling means include:

an operation amplifier having a resistor connected between an output terminal and an inversion terminal thereof;

a coefficient device having an input terminal connected to the output terminal of said operation amplifier and an output terminal connected to said actuator mechanism;

a first resistor connected at one end thereof to said inversion terminal of said operation amplifier and at the other end thereof to the output terminal of said potentiometer;

a second resistor connected at one end thereof to the non-inversion terminal of said operation amplifier and at the other end thereof to the output terminal of said potentiometer; and

a capacitor connected at one end thereof to the non-inversion terminal of said operation amplifier and grounded at the other end thereof.

7. A rear wheel steer angle controlling apparatus for automatically controlling the steer angle of rear wheels of a vehicle by controlling an actuator mechanism for generating the steer angle of rear wheels in response to an operation of a steering wheel for generating a steer angle of front wheels of said vehicle, said apparatus comprising:

a steering wheel displacement detecting means for detecting a steering wheel displacement and for generating a steering wheel displacement signal representing the steering wheel displacement;

a judging means for judging a rotation speed of said steering wheel from said steering wheel displacement signal;

a physical amount detecting means for detecting a physical amount related to a velocity of said vehicle and outputting a physical amount signal; and

a controlling means for controlling said actuator mechanism in accordance with a result of judgement by said judging means and said physical amount signal such that;

(a) when said steering wheel is operated at a high rotation speed, a steer angle of the rear wheels is formed in the direction counter to a direction of steer angle of the front wheels such as to provide a small radius of turning circle of said vehicle when said physical amount is small and, when said physical amount is large, said steer angle of the rear wheels is determined such as to provide a greater radius of turning circle than that obtained when said physical amount is small; and

(b) when said steering wheel is operated at a low rotation speed, a steer angle of the rear wheels is formed in the same direction as the steer angle of the front wheels.

8. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means and said physical amount signal such that:

(a) when said steering wheel is operated at a high rotation speed and said physical amount is below a predetermined value, a steer angle of the rear wheels is generated in the direction counter to the direction of the steer angle of the front wheels;

(b) when said steering wheel is operated at a low rotation speed and said physical value is below said predetermined value, a steer angle of the rear wheels is formed in the same direction as the steer angle of the front wheels; and

(c) when said physical amount exceeds said predetermined value, a steer angle of the rear wheels is generated in the same direction as the steer angle of the front wheels regardless of the rotation speed of said steering wheel.

9. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means and said physical amount signal such that:

(a) when said steering wheel is operated at a high rotation speed and said physical amount is below a predetermined value, a steer angle of the rear wheels is generated in the direction counter to a direction of steer angle of the front wheels;

(b) when said steering wheel is operated at a low rotation speed and said physical value is below said predetermined value, a steer angle of the rear wheels is formed in the same direction as the steer angle of the front wheels; and

(c) when said physical amount exceeds said predetermined value, no steer angle of the rear wheels is generated regardless of the rotation speed of said steering wheel.

10. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means and said physical amount signal such that:

(a) when said steering wheel is operated at a high rotation speed a steer angle of the rear wheels which becomes smaller as said physical value is increased is generated in the direction counter to a direction of steer angle of the front wheels; and

(b) when said steering wheel is operated at a low rotation speed a steer angle of the rear wheels which becomes smaller as said physical amount is increased is formed in the same direction as the steer angle of the front wheels.

11. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means and said physical amount signal such that:

(a) when said steering wheel is operated at a high rotation speed and said physical amount is below a predetermined value, a steer angle of the rear wheels which becomes smaller as said physical amount is increased is generated in the direction counter to a direction of steer angle of front wheels;

(b) when said steering wheel is operated at a high rotation speed and said physical value exceeds said predetermined value, a steer angle of the rear wheels which becomes greater as said physical amount is increased is formed in the same direction as the steer angle of the front wheels; and

(c) when said steering wheel is operated at a low rotation speed, a steer angle of the rear wheels which becomes greater as said physical amount is increased is formed in the same direction as the steer angle of the front wheels.

12. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means and said physical amount signal to generate to steer angle δ

r of the rear wheels which meets the following conditions;

space="preserve" listing-type="equation">On condition of V≦

Vc δ

r=f(δ

h)

space="preserve" listing-type="equation">On condition of V>

Vc δ

r=K.sub.1 δ

h

where,

V;

vehicle running velocity

Vc;

predetermined value of vehicle running velocity

δ

h;

steering wheel angle

f(δ

h);

steer angle proportional to the steering wheel angle and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the steer angle of the front wheels when the steering wheel is operated at a low rotation speed

K₁ ;

small positive constant.

13. A rear wheel steer angle controlling apparatus according to claim 7, wherein said physical amount related to vehicle running velocity is one selected from the group consisting of the vehicle running velocity, yaw rate, lateral acceleration of vehicle, product of yaw rate and vehicle running velocity and product of the vehicle running velocity and the lateral acceleration.

14. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following conditions;

space="preserve" listing-type="equation">On condition of |f(d)|>

f(d)c δ

r=f(δ

h)

space="preserve" listing-type="equation">On condition of |f(d)|>

f(d)c δ

r=K.sub.1 δ

h

where

f(d);

physical amount related to lateral displacement of the vehicle, representing one of a yaw rate, lateral accelration, product of the yaw rate and vehicle running velocity and product of the lateral acceleration and the vehicle running velocity

f(d)_c ;

predetermined value of physical amount related to the lateral displacement corresponding to predetermined value Vc of the vehicle running velocity

δ

h;

steering wheel angle

F(δ

h);

steer angle proportional to the steering wheel angle and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the steer angle of the front wheels when the steering wheel is operated at a low rotation speed

K₁ ;

small positive constant.

15. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following conditions;

space="preserve" listing-type="equation">δ

r=f(δ

h)/(K.sub.2 V+K.sub.3)

where

V;

vehicle running velocity

δ

h;

steering wheel angle

f(δ

h);

steer angle proportional to the steering wheel angle and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the steer angle of the front wheels when the steering wheel is operated at a low rotation speed

K₂ ;

positive constant for attaining coincidence of dimension

K₃ ;

constant for preventing the denominator from becoming zero.

16. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following conditions;

space="preserve" listing-type="equation">δ

r=f(δ

h)·

K.sub.4 ·

(Vmax-V)

where,

V;

vehicle running velocity

δ

h;

steering wheel angle

f(δ

h);

steer angle proportional to the steering wheel angle and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the steer angle of the front wheels when the steering wheel is operated at a low rotation speed

Vmas;

maximum vehicle running velocity

K₄ ;

small positive constant.

17. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following condition;

space="preserve" listing-type="equation">δ

r=f(δ

h)/(K.sub.2 |f(d)|+K.sub.3)

where

δ

h;

steering wheel angle

f(δ

h);

steer angle proportional to the steering wheel angle and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the steer angle of the front wheels when the steering wheel is operated at a low rotation speed

f(d);

physical amount related to lateral displacement of the vehicle, representing one of a yaw rate, lateral acceleration, product of the yaw rate and vehicle running velocity and product of the lateral acceleration and thevehicle running velocity

K₂ ;

positive constant for attaining coincidence of demension

K₃ ;

constant for preventing the denominator from becoming zero.

18. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following condition;

space="preserve" listing-type="equation">δ

r=f(δ

h)·

K.sub.4 ·

(|f(d)max|-|f(d)|)

where

δ

h;

steering wheel angle

f(δ

h);

steer angle proportional to the steering wheel angle and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the steer angle of the front wheels when the steering wheel is operated at a low rotation speed

f(d);

physical amount related to lateral displacement of the vehicle, representing one of a yaw rate, lateral acceleration, product of the yaw rate and vehicle running velocity and product of the lateral acceleration and the vehicle running velocity

f(d) max;

maximum value of physical amount related to the lateral displacement of vehicle corresponding to maximum vehicle running velocity

K₄ ;

small positive constant.

19. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following condition;

space="preserve" listing-type="equation">δ

r=f(δ

h)+K.sub.5 ·

V·

δ

h

where,

V;

vehicle running velocity

δ

h;

steering wheel angle

f(δ

h);

steer angle proportional to the steering wheel angle and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the steer angle of the front wheels when the steering wheel is operated at a low rotation speed K₅ ;

small positive constant.

20. A rear wheel steer angle controlling apparatus according to claim 7, wherein said controlling means controls said actuator mechanism in accordance with the resuslt of judgement by said judging means and said physical amount signal to generate a steer angle r of the rear wheels which meets the following condition:

space="preserve" listing-type="equation">δ

r=f(δ

h)+K.sub.5 ·

|f(d)|·

δ

h

where

δ

h;

steering wheel angle

f(δ

h);

steer angle proportional to the steering wheel angle and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the steer angle of the front wheels when the steering wheel is operated at a low rotation speed

f(d);

physical amount related to lateral displacement of the vehicle, representing one of a yaw rate, lateral acceleration, product of the yaw rate and vehicle running velocity and product of the lateral acceleration and the vehiclee runing velocity

K₅ ;

small positive constant.

21. A rear wheel steer angle controlling apparatus for automatically controlling a steer angle of rear wheels of a vehicle by controlling an actuator mechanism for generating the steer angle of the rear wheels in response to an operation of a steering wheel for generating a steer angle of front wheels of said vehicle, said apparatus comprising:

a steering wheel displacement detecting means for detecting a steering wheel displacement and for generating a steering wheel displacement signal representing the steering wheel displacement;

a judging means for judging a rotation speed of said steering wheel from said steering wheel displacement signal;

a physical amount detecting means for detecting a physical amount related to a lateral displacement of said vehicle and outputting a physical amount signal; and

a controlling means for controlling said actuator mechanism in accordance with a result of judgement by said judging means and said physical amount signal, such that a steer angle of rear wheels is genrated as the sum of;

(a) a first angle proportional to said steering wheel displacement and set in the direction counter to a direction of steer angle of the front wheels when said steering wheel is operated at a high rotation speed and in the same direction as the steer angle of the front wheels when said steering wheel is operated at a low rotation speed; and

(b) a second angle proportional to said physical amount and set in the same direction as generation of said physical amount.

22. A rear wheel steer angle controlling apparatus according to claim 21, wherein said physical amount related to the lateral displacement of the vehicle is one selected from the group consisting of yaw rate, later acceleration of vehicle, product of the yaw rate and vehicle running velocity and product of the vehicle running velocity and the lateral acceleration.

23. A rear wheel steer angle controlling apparatus according to claim 22, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means, said steering wheel displacement signal and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following condition;

space="preserve" listing-type="equation">δ

r=f(δ

h)+K.sub.6 ·

r

where,

r;

yaw rate

F(δ

h);

steer angle proportional to the steering wheel displacement and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the direction of steer angle of the front wheels when the steering wheel is operated at a low rotation speed.

K₆ ;

small constant.

24. A rear wheel steer angle controlling apparatus according to claim 22, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means, said steering wheel displacement signal and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following condition;

space="preserve" listing-type="equation">δ

r=f(δ

h)+K.sub.7 ·

V·

r

where,

V;

vehicle running velocity

r;

yaw rate

f(δ

h);

steer angle proportional to the steering wheel displacement and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the direction of steer angle of the front wheels when the steering wheel is operated at a low rotation speed

K₇ ;

small constant.

25. A rear wheel steer angle controlling apparatus according to claim 22, wherein said controlling means controls said actuator mechanism in accordance with the result of jdugement by said judging means, said steering wheel displacement signal and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following conditions;

space="preserve" listing-type="equation">On condition of V≦

Vc δ

r=f(δ

h)+K.sub.6 ·

r

space="preserve" listing-type="equation">On condition of V>

VC δ

r=K.sub.1 ·

δ

h

where,

V;

vehicle running velocity

Vc;

predetermined value of vehicle running velocity

r;

yaw rate

Sh;

steering wheel angle

f(δ

h);

steer angle proportional to the steering wheel displacement and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the direction of steer angle of the front wheels when the steering wheel is operated at a low rotation speed

K₁, K₆ ;

small constants.

26. A rear wheel steer angle controlling apparatus according to claim 22, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means, said steering wheel displacement signal and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following condition;

space="preserve" listing-type="equation">δ

r=f(δ

h)/(K.sub.1 ·

V+K.sub.3)+K.sub.8 ·

r

where,

V;

vehicle running velocity

r;

yaw rate

f(δ

h);

steer angle proportional to the steering wheel displacement and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the direction of steer angle of the front wheels when the steering wheel is operated at alow rotation speed

K₁, K₈ ;

small constants

K₃ ;

constant used for preventing denominator from becoming zero.

27. A rear wheel steer angle controlling apparatus according to claim 22, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means, said steering wheel displacement signal and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following condition;

space="preserve" listing-type="equation">δ

r=f(δ

h)/(K.sub.1 ·

V+K.sub.3)+K.sub.9 ·

V·

V

where,

V;

vehicle running velocity

r;

yaw rate

f(δ

h);

steer angle proportional to the steering wheel displacement and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the direction of steer angle of the front wheels when the steering wheel is operated at a low rotation speed

K₁, K₉ ;

small constants

K₃ ;

constant used for preventing denominator from becoming zero.

28. A rear wheel steer angle controlling apparatus according to claim 22, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means, said steering wheel displacement signal and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the folloing condition;

space="preserve" listing-type="equation">δ

r=f(δ

h)·

K.sub.4 ·

(Vmax-V)+K.sub.10 ·

r

where

V;

vehicle running velocity

Vmax;

maximum vehicle running velocity

r;

yaw rate

f(δ

h);

steer angle proportional to the steering wheel displacement and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated a high rotation speed and in the same direction as the direction of steer angle of the front wheels when the steering wheel is operated at a low rotation speed

K₄, K₁₀ ;

small constant.

29. A rear wheel steer angle controlling apparatus according to claim 22, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means, said steering wheel displacement signal and said physical amount signal to generate a steer angle r of the rear wheels which meets the following condition:

space="preserve" listing-type="equation">δ

r=f(δ

h)·

K.sub.4 ·

(Vmax-V)+K.sub.11 ·

V·

r

where,

V;

vehicle running velocity

Vmax;

maximum vehicle running velocity

r;

yaw rate

f(δ

h);

steer angle proportional to the steering wheel displacement and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the direction of steer angle of the front wheels when the steering wheel is operated at a low rotation speed K₄, K₁₁ ;

small constants.

30. A rear wheel steer angle controlling apparatus according to claim 22, wherein said controlling means controls said actuator mechanism in accordance with the result of judgement by said judging means, said steering wheel displacement signal and said physical amount signal to generate a steer angle δ

r of the rear wheels which meets the following conditions;

space="preserve" listing-type="equation">On condition of δ

r≦

δ

rc δ

r=f(δ

h)+K.sub.7 ·

V·

r

space="preserve" listing-type="equation">On condition of δ

r>

δ

rc δ

r=δ

rc

where,

V;

vehicle running velocity

r;

yaw rate

f(δ

h);

steer angle proportional to the steering wheel displacement and set in the direction counter to a direction of steer angle of the front wheels when the steering wheel is operated at a high rotation speed and in the same direction as the direction of steer angle of the front wheels when the steering wheel is operated at a low rotation speed

rc;

predetermined steer angle of the rear wheels

K₇ ;

a small constant.

31. A rear wheel steer angel controlling apparatus for automatically controlling a steer angle of rear wheels of a vehicle by controlling an actuator mechanism for generating the steer angle of the rear wheels in response to an operation of a steering wheel for generating a steer angle of front wheels of said vehicle, said apparatus comprising:

a steering wheel displacement detecting means for detecting a steering wheel displacement and for generating a steering wheel displacement signal representing the steering wheel displacement;

a judging means for judging a rotation speed of said steering wheel from said steering wheel displacement signal;

a physical amount detecting means for detecting a physical amount related to a lateral displacement of said vehicle and outputting a physical amount signal;

a steer angle detecting means for detecting the steer angle of the rear wheels and outputting a steer angle signal; and

a controlling means for controlling said actuator mechanism in accordance with the result of judgement by said judging means, said physical amount signal and said steer angle signal, such that a steer angle of the rear wheels is generated as the sum of;

(a) a first angle proportional to said steering wheel dislacement and set in the direction counter to a direction of steer angle of the front wheels when said steering wheel is operated at a high rotation speed and in the same direction as the steer angle of the front wheels when said steering wheel is operated at a low rotation speed; and

(b) a second angle proportional to said physical amount and set in the same direction as generation of said physical amount.

32. A rear wheel steer angle controlling apparatus according to claim 31, wherein said controlling means controls said actuator mechanism such that no steer angle of the rear wheels is formed when the level of said steering wheel displacement signal is below a predetermined level.

33. A rear wheel steer angle controlling apparatus according to claim 31, wherein said sum δ

r of said first and second angles is given by the following formula;

##EQU21## where, Kd, Ke;

constants which meet the condition of 0<

Kd<

Ke

S;

complex frequency

T;

time constant of primary delay

N;

steering gear ratio

δ

f;

steer angle of front wheels

Kn;

proportional constant

V;

vehicle running speed

r;

yaw rate.

34. A rear wheel steer angle controlling apparatus according to claim 31, wherein said physical amount detecting means includes a velocity detector for detecting the vehicle running velocity and outputting a vehicle running velocity signal, a yaw rate detector for detecting the yaw rate and outputting a yaw rate signal, and a multiplier circuit for multiplying said vehicle running velocity signal and said yaw rate signal with each other, said judging means includes a phase shifting circuit for outputting a signal which has a phase delay with respect to said steering wheel displacement signal, said phase delay being increased within the range of °

to 180°

as the angular frequency of said steering wheel displacement signal is increased, and said controlling means includes an adder circuit for adding the output from said multiplier circuit and the output of said phase shifting circuit to each other.

35. A rear wheel steer angle controlling apparatus according to claim 34, wherein said controlling means further includes a dead zone circuit which does not produce output when the output of said phase shifting circuit falls within a predetermined range around 0 (zero) and produces an output corresponding to the output of said phase shifting circuit when said output of said shifting circuit falls out of said predetermined range.