||||||||||||||||| USOO50979 7A

United States Patent 19) 11 Patent Number: 5,097,917

Serizawa et al. (45) Date of Patent: Mar. 24, 1992
(54) STEERING SYSTEM OF VEHICLE 4,871,040 10/1989 Zuraski et al. ..................... 80/79.
75) Inventors: Mitsuya Serizawa; Makoto Sato; FOREIGN PATENT DOCUMENTS
Yoshimitu Akuta, all of Tochigi, 3536563 4/1986 Fed. Rep. of Germany ..... 80/79.
Japan 82669 7/1981 Japan .................................. 80/79.
73) Assignee: Honda Gilken Kogyo Kabushiki 43473 3/1985 Japan.
Kaisha, Tokyo, Japan 742232 6/1980 U.S.S.R. ............................. 80/79.
76694. 9/1980 U.S.S.R. ... 80/79.
(2) Appl. No.: 289,213 933525 6/982 U.S.S.R. ... 180/79.1
34454 1/1985 U.S.S.R. ............................. 180/79.
22 Filed: Dec. 23, 1988
30 Foreign Application Priority Data Primary Examiner-Mitchell J. Hill
Attorney, Agent, or Firm-Irving M. Weiner; Joseph P.
Dec. 26, 1987 (JP) Japan ................................ 62-33083 Carrier; Pamela S. Burt
Dec. 26, 1987 (JP) Japan ................................ 62-33084
(57) ABSTRACT
51) int. C. ........................... B62D 5/04; B60C 1/00 A steering system for a vehicle includes a steering
52 U.S. C. .................................... 180/79.1; 340/.465 mechanism mechanically separated form a steering han
58 Field of Search ...................... 180/79.1, 140, 141,
180/142, 143; 340/.465 dle and having a motor for steering road wheels, a steer
(56) References Cited
ing detector for detecting a steering operation of the
handle, a steered angle sensor for detecting steered
U.S. PATENT DOCUMENTS angles of the road wheels, and a control circuit mecha
3,338,328 8/1967 Cataldo .............................. 180/79.1 nism for driving the motor to thereby steer the road
3,882,953 5/1975 Maisch .......... 80/79. X wheels in response to detected signals from the steering
3,944.04 3/1976 Maisch et al. ...................... 180/79.1 detector and steered angle sensor. The steered angle
4,624,334 liv986 Kelledes et al. ................... 180/79.1 sensor comprises a measuring member which makes
4,771,843 9/1988 Shimizu .............................. 180/79. rotational movements in proportion to the steered an
4,832,149 5/1989 Degonde ....... ... 180/40 X gles of the road wheels and occupies a constant space
4,834,205 5/1989 Mizuno et al. ... ... 80/79. X
4,836,319 6/1989 Haseda et al. .... 80/79.1 X relative to the vehicle.
4,853,672 8/1989 Yasuda et al. .................... 80/79.1
4,869,335 9/1989 Takahashi ......................... 180/79.1 8 Claims, 8 Drawing Sheets

4R.
U.S. Patent Mar. 24, 1992 Sheet 1 of 8 5,097,917

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U.S. Patent Mar. 24, 1992 Sheet 2 of 8 5,097,917

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U.S. Patent Mar. 24, 1992 Sheet 4 of 8 5,097,917

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U.S. Patent Mar. 24, 1992 Sheet 5 of 8 5,097,917

F G. 6
P P2O
P Reset N-(d+b)/2
Counters P2
P3 6-S -N P
Steer P22
S- S-N
road wheels

t<>
Steer
In One rood wheels
direction P5
P P Steer
I
P Yes
Pes
NCGs
Yes
5
Ps Input 6h
P24 Yes

a -s - F2s
P7 Input eh
Steer
rOdd wheels YeS P7 Ps
in the other P26
direction

Ps Exceptional
P27 <65d.
Yes
Control
Nornd
P2s Control
Yes Po IG.SW.
b - is turned off P29 Ps
P Stop
P2 Pso
<ses No PW. off
Yes P3
N-(a + b )/2
U.S. Patent Mar. 24, 1992 Sheet 6 of 8 5,097,917

Steer
rodd Wheels road wheels
in one in the other
direction direction
U.S. Patent Mar. 24, 1992 Sheet 7 of 8 5,097,917

Steering 6h
angle
SeSOf

Vehicle
speed
SeSO

Yow rote
SerSOr

Steeringeh
angle
SeSOf

f7
Vehicle
speed V
SeSO

Occeleration
SeSO
U.S. Patent Mar. 24, 1992 Sheet 8 of 8 5,097,917

Steering
angle
SerSOr

SerSOf

Steeringeh
angle
SeSO

Steering
speed 6h
SeSO

Vehicle
speed
SerSOf
 5,097,917
2
nals from said steering detector and said steered angle
STEERING SYSTEM OF VEHICLE sensor to thereby steer said road wheels, wherein: said
steered angle sensor comprises a measuring member
BACKGROUND OF THE INVENTION which makes rotational movements in proportion to
l. Field of the Invention said steered angles of said road wheels and has a station
The present invention relates to a steering system of a ary occupying space.
vehicle, particularly, it relates to a steering system of a Other objects, features and advantages of the present
vehicle in which a steering handle and steering mecha invention will become more apparent from the follow
nisms of wheels are separated mechanically. ing description of the preferred embodiment of the
2. Description of the Relevant Art O present invention when considered in connection with
In Japanese Utility Model Patent Application Laid the accompanying drawings.
Open No. 43473/1985 (laid open to public inspection on BRIEF DESCRIPTION OF THE DRAWINGS
Mar. 27, 1985) a steering system of a vehicle in which a
steering handle and steering mechanisms of road wheels FIG. 1 is a schematic plan view of a vehicle including
are mechanically separated is disclosed. In this steering a steering system according to the preferred embodi
system, a steering sensor for detecting steering opera ment of the present invention,
tion is provided on the steering handle. In a front wheel FIG. 2 is a perspective view of a front wheel steering
steering mechanism and a rear wheel steering mecha mechanism and a rear wheel steering mechanism in the
nism, motors for driving steering wheels and steered steering system,
angle sensors for detecting steered angles of the steered 20 FIG. 3 is a sectional view of essential portions of the
wheels are disposed respectively. The front and rear front wheel steering mechanism,
steering mechanism notors are energized in response to FIG. 4 is a sectional view of essential portions of the
output signals from the steering sensors, front and rear rear wheel steering mechanism,
wheel steered angle sensors, a speed sensor etc., FIG. 5 is an enlarged sectional view of an encoder
whereby the front and rear wheels are steered. 25 constituting a portion of a steered angle sensor of the
In the aforesaid Japanese Utility Model Patent Appli
cation Laid Open No. 43473/1985, since the steering front wheel steering mechanism,
FIG. 6 is a schematic flow chart of wheel neutral
handie and the steering mechanisms of the wheels are
separated mechanically, the whole steering system can position restoring processing effected by a control cir
cuit of the steering system when an ignition switch is
be freely arranged. 30
in the steering system aforementioned, however, turned on,
FIG. 7 is a schematic flow chart of wheel neutral
sensors for detecting steered angles of the front and rear position restoring processing effected by the control
wheels are constituted by potentiometers. Thus, at least, circuit when an ignition switch is turned off,
for example, a space for partial displacement of an out
put rod interposed between the motor and wheels is 35 a steered FIGS. 8 and 9 are timing charts of the output signal of
occupied by the potentiometer. As a result, the front angle sensor including the encoder, and
and rear steering mechanisms tend to become large. FIGS. 10 through 13 are functional block diagrams of
Moreover, since output of the potentiometer is an ana four kinds of normal control modes in the steering sys
log signal, its accuracy is apt to become problematic. In te.
this respect, the problem of accuracy of the detect sig- 40 DESCRIPTION OF THE PREFERRED
nal can be solved if a digital linear displacement meter is EMBODIMENTS
used in place of the potentiometer. However, while the
digital linear displacement meter is relatively costly, the In FIGS. 1 and 2, reference numeral 11 indicates a
trend of the large-sized steering mechanism still re steering handle, 12 denotes a front wheel steering mech
mains. 45 anism for steering right and left front wheels 14FR,
In view of the problems in the conventional steering 14FL, 13 is a rear wheel steering mechanism for steer
system of the vehicle as aforementioned, the present ing right and left rear wheels 14RR, 14RL. The steering
invention has been devised to solve them effectively. handle 11, front wheel steering mechanism 12 and rear
SUBJECT MATTER OF THE INVENTION
wheel steering mechanism 13 are independent and sepa
rated mechanically from one another. The steering
It is an object of the present invention to provide a handle 11, steering mechanisms 12, 13, a control unit 21
steering system of a vehicle which is, in the steering to be described later, and so on, constitute a steering
system of the vehicle in which a steering handle and system 100 of a vehicle according to the preferred em
steering mechanism are separated mechanically, capa bodiment of the present invention.
ble of detecting wheel steered angles accurately with 55 The steering handle 11 is secured to the upper end of
less expensive mechanisms while restraining the steer the steering shaft 15, which is supported rotatably by a
ing mechanisms from becoming large. car body via a bracket 16. In the midway of the steering
In order to attain the aforesaid object, according to shaft 15, an encoder 17 and a tachogenerator 18 are
the present invention, there is provided a steering sys installed, and at the lower end thereof, a reaction force
tem for a vehicle having a steering handle, a steering 60 generator 19 having a spring element 22 and dampening
mechanism mechanically separated from said steering element 23 is provided. The encoder 17 is a steering
handle and having a motor for steering road wheels of angle sensor which is coupled to the steering shaft 15
the vehicle, a steering detector for detecting steering via a gearing mechanism 20 for detecting a steering
operation of the handle and producing a steering opera angle 6h, and the tachogenerator 18 is a steering speed
tion signal, a steered angle sensor for detecting steered 65 sensor which is coupled to the steering shaft 15 via the
angles of the road wheels and producing a steered angle gearing mechanism 20 for detecting a steering speed 6h.
signal, and control circuit means for driving the motor The encoder 17 and tachogenerator 18 are connected to
of the steering mechanism in response to detected sig a microcomputer unit (MCU)21 as a control circuit.
 5,097,917
3 4.
The encoder 17 outputs the detect signal representing As particularly shown in FIG. 5, the encoder 38
the steering angle 6h to the MCU21, and the tachogen includes a cylindrical magnet holding member 45 fixed
erator 18 outputs the detect signal representing the to the periphery of the ball nut 43 of the ball-nut mecha
steering speed 6h to the MCU21. In the figure, refer nism 32 by a lock nut 44, a generally cylindrical perma
ence numeral 99 indicates an ignition key. nent magnet 46 fixed to the periphery of the holding
The spring element 22 of the reaction force generator member 45 and rotating integrally with the ball nut 43,
19 is constituted by a torsion spring and the like and and a sensor body 48 mounted on the box 35 by a
urges the steering handle 11 to a neutral position. The bracket 47 and connected to the MCU21. The magnet
dampening element 23 is constituted by a damper and 46 includes a main magnetic-pole portion 46a wherein a
the like using a viscous fluid and generates a resistance O large number (e.g. 60 poles) of magnetic poles are ar
force corresponding to the steering speed 8h of the ranged in the rotating direction with constant intervals,
steering handle 11. The reaction force generator 19 and a submagnetic-pole portion 46b wherein a small
urges the handle 11 normally to the neutral position, number (e.g. two poies) of magnetic poles are arranged
and gives a suitable reaction force to steering operation in the rotating direction. The magnetic pole portions
of the driver for the steering handle 11. If the driver 15 46a, 46b are constituted by connecting axially via a
releases his hand from the handle 11, it is restored to the spacer 46c. The sensor body 48 has magnetic-sensitive
neutral position gently by the reaction force generator elements 48a, 48b such as an MR element whose resis
19. tance value varies by the magnetic variation or a hall
As particularly shown in FIG. 3, in the front wheel device which generates electric voltage by variation of
steering mechanism 12, a rod 36F is supported movably 20 the magnetic force, and detective of monentum of the
in the lateral direction of the vehicle and fixed radially magnet 46. The sensor body 48 is connected to the
by a hollow box 35F mounted on the car body laterally, MCU21 and outputs a signal indicating the rotation of
and a motor 24F is installed in the box 35F coaxially the magnet 46 to the MCU21. The magnetic-sensitive
with the rod 36. In the box 35F, an encoder 38F for elements 48a, 48b of the sensor body 48 are arranged
detecting the front wheel steered angle 6f is disposed. 25 with a predetermined interval in the rotating direction
Opposite ends of the rod 36F are coupled respectively at a phase difference of 90' opposing to the main mag
to knuckles 37FR, 37FL of the right and left front netic-pole portion 46a of the magnet 46. One magnetic
wheels 14FR, 14FL via tie-rods. The motor 24F is con sensitive element 48c is disposed opposing to the sub
stituted by a field magnet 26F secured to the inner wall magnetic-pole portion 46b of the magnet 46. As shown
of the box 35F and a rotor 27F interposed rotatably 30 in FIGS. 8 and 9, two magnetic sensitive elements 48a,
between the field magnet 26F and rod 36F. The rotor 48b detect the magnetic variation due to the rotation of
27F comprises a cylindrical output shaft 28F fitted ro the main magnetic-pole portion 46a of the magnet 46,
tatably to the rod 36F and a laminated iron core 29F and output rectangular pulse detecting signals A, B
secured coaxially and integrally to the periphery of the having the phase difference of 90 respectively. The
output shaft 28F. In the iron core 29F, skew grooves are 35 pulse signals A, B are inputted to a counter (not shown).
formed and an armature winding 30F is wound in multi Since the pulse signals are generated at every rotation
plex winding. The output shaft 28F, as shown in FIG. 3, of the ball nut 43 by a small angle, a high resolution can
is supported by the box 35F rotatably at its right end via be obtained. One magnetic-sensitive element 48c detects
a ball bearing 31F, and coupled to the rod 36F at its left the magnetic variation by the sub-magnetic-pole por
end via a ball-nut mechanism 32Fso that power is trans tion 46b of the magnet 46 and outputs a correcting pulse
ferable. The armature winding 30F is connected to the signal to the MCU21. The pulse signals A, B are input
MCU21 via a commutator 33F secured to the output ted further to D-input and CLK terminals of a D flip
shaft 28F on the right hand part in the figure, and a flop (not shown) of the MCU21. Thus, the output signal
brush 39F supported in a holder 34F and contacted C of the D flip-flop has either a low potential level '0' or
resiliently to the commutator 33F. The ball-nut mecha 45 a high potential level '1' responsive to the phase differ
nism 32F is supported by the box 35F via ball bearings ence between the signals A, B. That is, when the signal
41F, 42F, and includes a generally cylindrical ball nut B is ahead of the signal A by the phase difference of 90'
43F engaged to the output shaft 28F of the motor 24F at by steering the wheels in one direction, as shown in
the left end in the figure by a spline and the like, and a FIG. 8, the output signal C of the D flip-flop is main
number of balls interposed movably between ball SO tained in the low level potential '0'. Conversely, when
grooves formed in the inner circumferential surface of the wheels are steered in the other direction and the
the ball nut 43F and ball grooves formed in the periph signal B is behind the signal A by the phase difference of
eral surface of the rod 36F. The ball nut 43F rotates 90', as shown in FIG. 9, the output signal C of the D
together with the output shaft 28F of the motor 24F, flip-flop is maintained in the high potential level '1'.
and is stationary axially to the output rod 36F. From Thus, the phase difference between the signals A, B,
another viewpoint, the occupying space of the ball nut namely, the output level of the signal C represents the
43F is stationary. On the peripheral surface of the rod steered direction of the wheels. As will be understood,
36F, ball grooves are formed throughout the range the encoder 38 occupies a constant space relative to the
corresponding to the sliding distance in the lateral di vehicle; although the magnet 46 and the holding mem
rection of the vehicle. Rotational quantity of the ball ber 45 rotate with the ball nut 43 in proportion to the
nut 43F is proportional to the axial movement of the steered angles of the road wheels.
output shaft 36F or the wheel steered angles. As shown in FIG. 4, the rear wheel steering mecha
FIG. 5 shows essential portions of a steered angle nism 13, the same as the front wheel steering mechanism
sensor of the front wheel steering mechanism 12. Since 12, comprises a box 35R supported by the car body and
the construction shown in FIG. 5 is in common with 65 a rod 3.6R supported movably in the lateral direction of
those of the rear wheel steering mechanism 13 in de the vehicle and fixed radially by the box 35R, and oppo
scription, a suffix letter F of the parts numeral in FIG. site ends of the rod 3.6R are connected to knuckles
3 will be omitted. 37RR, 37RL of right and left rear wheels 14RR, 14RL.
 5,097,917
5 6
in the box 35R, a motor 24R connected to the MCU21 angle 8 when the electric current I applied to the motor
is provided coaxially with the rod 36R, and an output 24 exceeds a predetermined value 0, or a cumulative
shaft 28R of the motor 24R is coupled to the rod 36R value of the counter, as one maximum steering angle a
via a ball-screw mechanism 32R, whereby the rear (P4, P5, P6). The electric current increases suddenly
wheels 14RL, 14RR are steered by the motor 24R. at an original marginal steering position of the steering
Steered angles of the rear wheels 14RL, 14RR are de system or when the wheel contacts to the curb and the
tected by an encoder 38R. Since the rear wheel steering like. By Step P3-P6, the marginal steering position of
mechanisn 13 has basically the same construction as the the wheels 14 in one direction can be obtained.
front wheel steering mechanism 12 except the smaller Thereafter, similarly, the CPU energizes the motor 24
output and stroke of the rod 36R, its description will be O to steer the wheels 14 in the other direction (P7), and
omitted by affixing R to the like reference numeral of stores a steered angle 8 when the electric current I
the parts corresponding to the front wheel steering applied to the motor 24 exceeds a predetermined value
mechanism 12. In FIGS. 3 and 4, the front and rear IO as the other maximum steering angle b (P8. P9. P10).
wheel steering mechanisms 12, 13 are drawn in a gener By Steps P7-P10, the marginal steering position of the
ally equal contraction scale for comparison. 5 wheels 14 in the other direction can be obtained.
in the following, corresponding component parts of Then, the CPU calculates a steering range S by sub
the front wheel steering mechanism 12 and the rear tracting the maximum steering angle b in the other
wheel steering mechanism 13 are represented by numer direction from the maximum steering angle a in one
als without affixing letters, and the front wheels 14FL, direction aforementioned, and determines whether the
14FR and the rear wheels 14RL, 14RR are represented 20 steering range S is larger than a predetermined value S0
by reference numeral 14. (P11, P12). If the steering range Sthus obtained is larger
The MCU21 includes a CPU (not shown) and further than the predetermined value S0, the CPU calculates
driving circuits etc. which energize the motor 24 of the mean value N of the aforesaid maximum steering
respective steering mechanisms 12, 13 in response to the angles a, b, or a true neutral position (P13), and corrects
output signal of the CPU. To the MCU21, the aforesaid 25 the cumulative value of the counter or the detect
encoder 17 for the steering handle, tachogenerator 18 steered angle 6 by using the mean value N (P14). By
and encoders 38 of respective steering mechanisms 12, processing in Step P14, the cumulative value of the
13 are connected. A lateral acceleration sensor 49, yaw counter shows the correct steered angle 8. The CPU
rate sensor 50 and speed sensors, 40FL, 40FR, 40RL, then energizes the motor 24 to steer the wheels 14 to the
40RR disposed on respective front, rear, right and left 30 true neutral position in response to the value of the
wheels 14FL, 14FR, 14RL, 14RR are further connected corrected steered angle 8 (P15, P16). Then, the CPU
to the MCU21. The MCU21 includes the D flip-flop detects the steering angle 6h of the steering handle 11
and counter as aforementioned and processes the output and confirms whether the steering handle 11 is restored
signal of respective encoders 38. Respective speed sen to the neutral position (6h=0) by the spring element 22
sors 40 (represented by numeral without affixing letter) 35 (P17, P18), and if it is in the neutral position, goes to the
detect the vehicle speed V and output the signal repre normal control (P19).
senting the vehicle speed V to the MCU21. Similarly, In the normal control in Step P19, the steered angle 8,
the lateral acceleration sensor 49 outputs the signal steering force etc. are decided in response to detect
representing the lateral acceleration y to the MCU21, signals from respective sensors and the wheels 14 are
and the yaw-rate sensor 50 outputs the signal represent steered. w
ing the yaw-rated to the MCU21. The MCU21 pro Contents of the normal control in Step P19 will be
cesses the input signals in the CPU to decide target described later.
control values such as target steering angles, steering While, when the wheel 14 contacts obstacles such as
forces etc. respectively for the front and rear wheels, the curb and the like, and it is determined that the steer
and outputs the control signal representing the target 45 ing range S is below the predetermined value S0 (P12),
control values to the driving circuit. The driving circuit the CPU obtains the mean value N of maximum steering
energizes the motor 24F of the front wheel steering angles a, b (P20) to correct the cumulative value of the
mechanism 12 and the motor 24R of the rear wheel counter or the detect steered angle 6 by the mean value
steering mechanism 13 in response to the control signal N (P21), and energizes the motor 24 to steer the wheels
inputted from the CPU. 14 to the neutral position of the steering range S at that
Next, functional operation of the steering system 100 time (P22, P23). Furthermore, the CPU confirms that
will be explained with reference to FIGS. 6 and 7. Since the steering handle 11 is at the neutral position (P24,
operations of the steering system 100 for the front P25) based on the signal Oh from the encoder17 and the
wheels 14FL, 14FR and the rear wheels 14RL, 14RR signal Oh from the tachogenerator 18. Thereafter, the
are basically the same, in the following description, they 55 CPU gives a warning or alarm by a buzzer, lamp or the
are represented generically by the steering wheels 14. like (P26) and goes to the exceptional control with
In the front and rear steering system 100, by the CPU restriction (P27). In the exceptional control (P27), the
of the MCU21, a start adjustment is effected in Steps CPU restrictively sets the vehicle speed or the possible
P1-P30 of FIG. 6 when the ignition switch is turned on, running distance, and after the vehicle has moved a
and when it is turned off, an end adjustment is per predetermined distance, processes to urge reinitializa
formed in Steps Q1-Q9 of FIG. 7. tion etc. If the ignition switch is turned off (P28) after
In FIG. 6, when the ignition switch is turned on (P1), such control (P27), the CPU stops the alarm or warning
a counter for counting pulses of the output signals A (P29) and turns off the power source (P30).
and B of the encoder 38 is reset (P2). In Step P2, irre In the end adjustment, as shown in FIG. 7, if the
spective of the position of the handle 11 at that time, the 65 ignition switch is turned off (Q1) after the normal con
handle position is supposed to be in a neutral position. trol is effected once in Step P19 of FIG. 6, the steered
Thereafter, the CPU energizes the motor 24 to steer the angle 8 of the wheels 14 is read from the cumulative
wheels 14 to the left or right (P3), and stores a steered counter value or the steering angle 8h of the steering
 5,097,917
7 8
wheel 11 (Q2). If the steered angle 8 is not zero or the As already described, the CPU of the MCU21 calcu
wheels 14 are not in the neutral position (Q3), the CPU lates input signals from respective sensors 17, 18, 40, 49,
energizes the motor 24 to steer the wheels 14 to the 50 to decide target control values of respective target
neutral position (Q4, Q5, Q6, Q7, Q8), and thereafter steered angles and target steering forces of the front
turns off the power source (Q9). wheels 14FL, 14FR and the rear wheels 14RL, 14RR,
In the steering system 100 aforementioned, the and outputs control signals representing the target con
steered angle 5 of the wheels 14 is detected by an incre trol values to the driving circuits of the motors. The
ment-type encoder 38 disposed in the stationary occu driving circuits energize the motor 24F of the front
pying space and including the magnet 46. The encoder wheel steering mechanism 12 and the motor 24R of the
38 does not need to occupy the space for displacement O rear wheel steering mechanism 13 in response to the
of the output rod 36, thus dimensions of the steering detected signals from acceleration sensor 49 and yaw
mechanisms 12, 13 in the lateral direction are hardly rate sensor 50 which correspond respectively to state
increased. Since the cumulative counter value based quantity detecting means. The MCU21 corresponds to
upon the output signal of the encoder 38 is the digital target state quantity setting means and rear wheel
signal, the steered angle 8 can be obtained as a very 5 steered angle deciding means.
accurate digital signal and prevents the steering mecha In FIGS. 10, 11, 12 and 13, various functions per
nisms 12, 13 from becoming large. Besides, the encoder formed by the MCU21 are shown in block diagrams as
38 has a simple construction, so that it can be provided independent construction elements for the convenience
at a low cost. Consequently, the total cost of the steer of explanation.
ing system 100 can be reduced. 20 FIG. 10 shows the first embodiment of the normal
The neutral position (6f, 6f=0) of the wheels 14 is control P19. In the first embodiment, the yaw-rate sen
detected newly whenever the ignition switch is turned sor 50 is used as state quantity detecting means.
on as shown in FIG. 6. Thus, the steered angles; 8f, 8r In this embodiment, as to the front wheels 14FL,
of the wheels 14 are not necessary to be stored by, for 14FR, based upon the handle steered angle 8h detected
example, a non-volatile memory while the ignition 25 by the steering angle sensor 17, the target front wheel
switch is turned off. steered angle 8fo (6fo or K1.6h: K1 = constant) is decided
On the other hand, since the handle 11 is urged to the by a front wheel target steered angle deciding device
neutral position by the reaction force generator 19, it is 21a of the MCU21. A true steered angle 8 of the front
restored to the neutral position automatically once the wheels 14FL, 14FR is detected by the front wheel
driver leaves the vehicle. As described hereinabove, the
30 steered angle sensor 38F. The MCU21 energizes the
wheels are restored to the neutral position at ON/OFF motor 24F responsive to the deviation between the
target steered angle 6fo and the true steered angle 8f,
of the ignition switch. That is, at ON/OFF of the igni and drives the front wheels 14FL, 14FR by the motor
tion switch, the handle steering position and the wheel 24F to steer to the target steered angle 6fo. As to the
steered position are readjusted. Thus, the steering angle 35 rear wheel 14RL, 14RR, based upon the handle steering
indicated by the steering handle will correspond to the angle 8h and vehicle speed V, the target yaw-rate do is
actual steering angle of the road wheels when starting a decided as a function f2 of the handle steering angle 6h
steering operation of the vehicle. In this respect, it is and vehicle speed V by a target yaw-rate deciding de
preferable, while Steps P2-P18 and P2-P26 of FIG. 6 vice 21b. An actual yaw-rate d is detected by the yaw
are processed, if "angle adjusting operation of the steer rate sensor 50, and the rear wheel target steered angle
ing handle and wheels' is notified to the driver by a bro is decided by a rear wheel steered angle deciding
suitable display such as a lamp, voice generator and the device 21c responsive to the deviation between the
like. As will be understood from the foregoing discus target yaw-rate do and the true yaw-rate d. A true
sion, the position restoring processing of FIGS. 6-7 steered angle 8r of the rear wheels 14RL, 14RR is de
effected by the CPU of the MCU 21 and the reaction 45 tected by a rear wheel steered angle sensor 38R. The
force generator 19 collectively constitute an angle ad MCU21 energizes the motor 24R responsive to the
justing means for driving the steering handle and the deviation between the rear wheel target steered angle
road wheels to thereby render a steering angle of the 5ro and the true steered angle 6r to steer the rear wheels
steering handle and a steered angle of the road wheels 14RL, 14RR to the target steered angle 5ro.
into correspondence with each other at the occurrence Now, in the front and rear wheel steering system
of at least one of an ON operation and an OFF opera according to Japanese Utility Model Patent Application
tion of an ignition switch of the vehicle. Laid Open aforementioned, the rear wheel steered
In the aforesaid relevant art, if the steering handle is angle 8r is decided fixedly responsive to steering condi
operated for any reason while the ignition switch is off, tions such as the handle steering angle 6h, vehicle speed
the handle remaines at the steered position, while the 55 V etc. Thus, there is the possibility that turning behav
wheels are not steered. Thus, there is the possibility that ior of the vehicle changes by the operating conditions
the steering angle indicated by the steering handle will such as acceleration and deceleration, steering speed
not correspond to the actual steering angle of the road and so on. Conversely, even if the steering conditions of
wheels when starting the steering operation next. the vehicle are constant, if loading conditions, road
In the above description, the wheels 14 are restored conditions etc. are changed, there is a possibility that
in the neutral position at both ON and OFF of the igni the turning behavior is influenced responsive to the
tion switch. However, restoring operation of the wheels changes. As a result, in order to obtain the turning be
14 to the neutral position is sufficient to be effected, at havior desired by the driver, the driver must correct the
least, either at ON or OFF of the ignition switch. The handle steering angle 8h additionally.
encoder 38 is not necessarily disposed at the location 65 In the embodiment shown in FIG. 10, however,
mentioned above. while the target steered angle 6fo of the front wheels
Next, normal control effected in Step P19 of FIG. 6 14FL, 14FR is decided fixedly by the handle steering
will be explained with reference to FIGS. 10 to 13. angle 8h and realized, target steered angle 6ro of the
 5,097,917
9 10
rear wheels 14RL, 14RR is decided and realized to deciding device 21c' as a function f3 of the deviation A
obtain the target yaw-rate do to be set based on the between the target lateral acceleration 0 and true lateral
handle steering angle 8h and vehicle speed V. Thus, acceleration ; true steered angle 6f of the front wheels
ideal yaw-rate characteristics or steering characteristics 14FL, 14FR; and vehicle speed V. Also, in the fourth
can be obtained without being influenced by various 5 embodiment, running conditions of the vehicle, drivers
factors such as the vehicle suspension geometry, a driv will, and so on, can be reflected on the vehicle behavior
ing method of the front and rear wheels, weight distri for a comfortable steering feeling.
bution to the front and rear wheels and so on, and by The normal control method in FIGS. 10 to 13 is also
changes of the loading condition of the vehicle. In the applicable in the front and rear wheel steering system
control method of FIG. 10, a high versatility applicable 10 having a mechanical coupling between the steering
in the vehicle having different suspension specification, handle and the steering mechanisms.
suspension type etc. can be obtained without changing As described heretofore, according to the control
the basic control method. methods in FIGS. 10 to 13, the target state quantity is
According to the control method of FIG. 10, the rear decided in response to the steering conditions, and at
wheel steered angle 8r is controlled responsive to the 15 the same time, the target steered angle Öro of the rear
deviation between the yaw-rated and the target yaw wheels is decided based on the deviation between the
rate do of the vehicle. Thus, even when the vehicle is target state quantity and the actual state quantity. Thus,
subjected to disturbances such as side wind or the like, even when the loading state etc. are changed, an ideal
irrespective of operation of the steering handle 11, the state quantity satisfactory to the steering conditions can
rear wheels 14RL, 14RR are steered automatically and 20 be obtained. The aforesaid control methods are readily
influence of the disturbance is reduced. applicable in the front and rear wheel steering system
In the control method of FIG. 10, various target having different various vehicle factors of the suspen
values are calculated and decided by the functions. sion geometry etc., thus a high versatility can be ob
However, the various target values can be set by a table tained. Furthermore, state variations caused by the
look-up method using a memory map. 25 disturbance can be responded to without operating the
FIGS. 11, 12 and 13 show respectively second to steering handle.
fourth embodiments of the normal control. In the foll Although there have been described what are at pres
lowing, description will be omitted by showing like ent considered to be the preferred embodiments of the
parts of the embodiment of FIG. 10 by like numerals. present invention, it will be understood that the inven
In the control method of the second embodiment of 30 tion may be embodied in other specific forms without
FIG. 11, the lateral acceleration is employed as the departing from spirit or essential characteristics thereof.
vehicle state quantity, and the target lateral acceleration The present embodiments are therefore to be consid
o is set by a target lateral acceleration deciding device ered in all aspects as illustrative, and not restrictive. The
21b' in response to the handle steering angle 6h and scope of the invention is indicated by the appended
vehicle speed V. An actual lateral acceleration is de- 35 claims rather than by the foregoing description.
tected by a lateral acceleration sensor 49. The target What is claimed is:
steering angle 8ro of the rear wheels 14RL, 14RR is 1. A steering system for vehicle having a steering
decided based on the deviation between the target lat handle, a steering mechanism mechanically separated
eral acceleration 0 and actual lateral acceleration . from said steering handle and having a motor for steer
In the third embodiment of FIG. 12, the target 40 ing road wheels of the vehicle, a steering sensor for
steered angle 8fo of the front wheels 14FL, 14FR is detecting steering operation of the handle and produc
decided as a function f of the handle steering angle 8h, ing a steering operation signal, a steered angle sensor for
steering speed 8h and vehicle speed V by a front wheel detecting steered angles of the road wheels and produc
target steered angle deciding device 21a'. The target ing a steered angle signal, and control circuit means for
yaw-rate dbo is decided as a function f2 of the handle 45 driving the motor of the steering mechanism in response
steering angle 6h, steering speed 6h and vehicle speed V to detected signals fron said steering sensor and said
by a target yaw-rate deciding device 21b'. The target steered angle sensor to thereby steer said road wheels,
steered angle 8ro of the rear wheels 14RL, 14RR is wherein:
decided by a rear wheel target steered angle deciding said steered angle sensor comprises a measuring mem
device 21c' based on the deviation Ad between the 50 ber which makes rotational movements in propor
target yaw-rate do and the true yaw-rate do; the true tion to said steered angles of said road wheels and
steered angle 8f of the front wheels 14FL, 14FR; and occupies a constant space relative to said vehicle.
the vehicle speed V. 2. A steering system for a vehicle according to claim
In the third embodiment of FIG. 12, the target 1, wherein:
steered angle 6ro of the rear wheels 14RL, 14RR is 55 said measuring member of said steered angle sensor
decided by considering the steering speed 6h and the comprises a permanent magnet member which
true steered angle 8f of the front wheels 14FL, 14FR. rotates in proportion to said steered angles of said
Thus, running conditions of the vehicle such as the road wheels and has a plurality of magnetic poles
friction coefficient of the road surface and the driver's arranged in a rotational direction of said permanent
will can be reflected for a comfortable steering feeling. 60 magnet member, and
In the fourth enbodiment of FIG. 13, as the vehicle said steered angle sensor further comprises a station
state quantity, the lateral acceleration is employed. As ary magnet-sensitive element for detecting a rota
same as the third embodiment of FIG. 12, the target tional quantity of said permanent magnet member
lateral acceleration ois decided by a target lateral accel to output to said control circuit means.
eration deciding device 21b as a function f, of the handle 65 3. A steering system for vehicle according to claim 2,
steering angle 6h, steering speed 6h and vehicle speed wherein:
V. The target steered angle 8roof the rear wheels 14RL, said control circuit means comprises means for cor
4RR is decided by a rear wheel target steering angle recting a wheel neutral position by driving said
 5,097,917
11 12
motor of said steering mechanism such that said sensor for detecting steered angles of said road wheels
road wheels are steered completely through a and producing a steered angle signal, and control circuit
range of then possible steering angles of said road means for driving said motor of said steering mecha
wheels, to thereby establish a correct neutral posi nism in response to detected signals from said steering
tion of said road wheels to be detected by said 5 sensor and said steered angle sensor to thereby steer said
steered angle sensor, in response to at least one of road wheels, wherein:
an ON operation of an OFF operation of an igni said steering system comprises an angle adjusting
tion switch of the vehicle. means for driving at least one of said steering han
4. A steering system for a vehicle according to claim dle and said road wheels to thereby render a steer
1, wherein: O
ing angle of said steering handle and a steered angle
said steering system further comprises means for nor of said road wheels into correspondence with each
mally urging said steering handle to its neutral other, at an occurrence of at least one of an ON
position, and operation and an OFF operation of an ignition
said control circuit means comprises means for restor switch of said vehicle.
ing a wheel neutral position by driving said motor 15
7. A steering system for a vehicle according to claim
to thereby restore said road wheels to neutral posi 6, wherein:
tions thereof, in response to at least one of an ON said control circuit means comprises means for restor
operation and an OFF of an ignition switch of the ing a wheel neutral position by driving said motor
vehicle.
5. A steering system for a vehicle according to claim 20 to thereby restore said road wheels to neutral posi
1, wherein: tions thereof, in response to at least one of said ON
said steering mechanism comprises a front wheel operation and said OFF operation of said ignition
steering mechanism and a rear wheel steering switch of said vehicle, and
mechanism. said angle adjusting means comprises said restoring
6. A steering system for a vehicle having a steering 25 means and means for normally urging said steering
handle, a steering mechanism mechanically separated handle to its neutral position.
from said steering handle and having a motor for steer 8. A steering system according to claim 6, wherein
ing road wheels of said vehicle, a steering sensor for said steering mechanism is adapted to steer at least front
detecting steering operation of said steering handle and road wheels of the vehicle.
producing a steering operation signal, a steered angle 30 s

35

45

50

55
 UNITED STATES PATENT AND TRADEMARK OFFICE
CERTIFICATE OF CORRECTION
PATENT NO. : 5,097,917 Page 1 of 2
DATED March 24, 1992
INVENTOR(S) : Serizawa et al.
it is certified that entor appears in the above-identified patent and that said Letters Patent is hereby
corrected as shown below:
In The Abstract, line 2, change "form" to --from--.
Column 2, line 51, after "21" insert a----.
Column 3, line 2, change "éh" to --9h-;
Column 3, line 4, change "eh" to -9h--.
Column 6, line 53, change "Oh" to -9h-;
Column 6, line 54, change "Oh" to --9h--.
Column 9, line 31, change "acceleration" to -acceleration y-;
Column 9, line 33, change "is" to --y-;
Column 9, line 35, change "is" to -y is-;
Column 9, line 39, change "and" to -y and-;
Column 9, line 39, change "acceleration." to -acceleration y.--;
Column 9, line 62, change "is" to -y is-;
Column 9, line 64, change "is" to y is-;
Column 10, line 1, change "A" to -ay-;
Column 10, line 2, change "" to --y-;
Column 10, line 3, change ";" to --y;--.
 UNITED STATES PATENT AND TRADEMARK OFFICE
CERTIFICATE OF CORRECTION
PATENT NO. : 5,097,917 Page 2 of 2
DATED : March 24, 1992
INVENTOR(S) : Serizawa, et al.
it is certified that error appears in the above-indentified patent and that said Letters Patent is hereby
corrected as shown below:
Column 11, 1ine l8, change 'OFF' to --OFF operation--.

Signed and Sealed this

Twenty-eighth Day of September, 1993

(a tea
BRUCE LEHMAN

Attesting Officer Commissioner of Patents and Trademarks