Automotive suspension system with roll-stabilizer having road condition-dependent torsion modulus, and control of torsional modules

An automotive suspension system has a roll stablizer with an adjustable torsion modulus. The torsion modulus of the stabilizer is adjusted depending upon road surface conditions and other parameters. A controller is associated with the stabilizer to adjust its torsion modulus. When the vehicle is moving on a relatively smooth road surface, the torsion modulus of the stabilizer is adjusted toward to a relatively high value. On the other hand, when the vehicle travels along a rough road, the torsion modulus is adjusted toward a lower value.

The present invention relates generally to an automotive suspension system 
including a roll-stabilizer having a torsion modulus which adjust to 
changing road conditions. The invention further relates to control of the 
variable-torsion-modulus-type roll-stabilizer for adjusting the rigidity 
of the suspension system depending upon road conditions. 
In general, a roll-stabilizer comprises a torsion bar which resists 
torsional forces due to the movement of the vehicle. Relatively high 
roll-stability enhances drivability for changing lanes and so forth as the 
vehicle cruises along a smoothly surfaced road. On the other hand, high 
roll-stability degrades traction or road-holding ability when the vehicle 
is travelling along rough roads where the road surface is uneven. Such 
relatively low traction or road-holding ability may adversely affect 
steering and drivability on rough roads. Furthermore, on rough roads, due 
to relatively high roll-stability or high rigidity of the stabilizer, the 
traction of the left- and right-hand wheels tend to differ significantly, 
causing differential transmission of driving torque which further degrades 
drivability and/or performance. The differential traction of the wheels 
may also adversely affect braking or deceleration characteristics, 
subjecting the vehicle to serious danger. 
SUMMARY OF THE INVENTION 
The principle object of the present invention is to allow adjustment of the 
torsion modulus for a roll-stabilizer in a vehicle suspension system. 
Another and more specific object of the invention is to provide a 
combination of a roll-stabilizer with a variable torsional modulus and a 
control system for controlling the torsion modulus of the stabilizer 
according to vehicle driving conditions. 
A further object of the present invention is to provide a torsion modulus 
control system which responds to road conditions to which the vehicle is 
subjected to adjust the torsion modulus appropriately. 
In order to accomplish the above-mentioned and other objects and 
advantages, there is provided, according to the present invention, a 
roll-stabilizer in a vehicle suspension system, which incorporates means 
for adjusting its torsion modulus. The torsion modulus adjusting means 
detects one or more torsion modulus control parameters. Preferably, these 
torsion modulus control parameters include features of road-surface 
conditions which affect drivability and riding comfort. In the preferred 
procedure, the torsion modulus is adjusted to a relatively low range when 
the vehicle is travelling along a rough road. This ensures riding comfort 
and good road traction. On the other hand, the torsion modulus is adjusted 
to a relatively high range when the vehicle is travelling along a smooth 
road so as to provide good drivability and higher cornering force. 
According to the preferred embodiment of the present invention, an 
automotive vehicle suspension system comprises first means for rotatably 
supporting a pair of vehicle wheels while pivotably supporting a vehicle 
body, a roll stabilizer extending perpendicular to the vehicle axis and 
producing a damping force against rolling moment applied to the first 
means ("rolling moment" referring to forces which would result in rotation 
of the vehicle about its longitudinal axis), the stabilizer including a 
second means for adjusting the torsion modulus of the stabiizer so as to 
control the damping force or spring to be produced, an actuator responsive 
to a control signal for operating the second means, a detector adapted to 
detect a preselected vehicle driving condition-indicative parameter and 
produce a detector signal indicative thereof, and a controller responsive 
to the detector signal for deriving a desired value of the torsion modulus 
and feeding a control signal indicative of the derived value of the 
torsion modulus to the actuator.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, particularly to FIG. 1, the vehicle 
illustrated has a swing-arm-type rear wheel suspension system which 
comprises suspension arms 10 for supporting the vehicle body 12 in 
conjunction with the road wheels 14. Although this has not been 
illustrated, the suspension system may further comprise strut assemblies 
including shock absorbers and suspension coil springs. The free ends of an 
essentially U-shaped roll stabilizer 16 are connected to the suspension 
arms 10. In addition, the roll stabiizer 16 is pivotably suspended from 
the vehicle body by means of brackets 18. 
The stabilizer 16 generally comprises a pair of essentially L-shaped 
torsion bars 16a and 16b adapted to resist torsion forces generated when 
the vehicle turns. Throughout this disclosure, this resistance against 
torsional forces provided by the stabilizer will be referred to as 
"torsion modulus". 
As shown in FIGS. 1 to 3, the torsion bars 16a and 16b are connected to 
each other through a torsion modulus adjusting mechanism 100 which is 
adapted to adjust the damping characteristic of the suspension system 
through the modification of the torsion modulus of the stabilizer in a 
manner set forth below and may be hereafter referred to as "adjuster 100". 
In the shown embodiment, the adjuster 100 switches the torsion modulus of 
the stabilizer between a relatively LOW torsion modulus and a relatively 
HIGH torsion modulus, in two-way fashion. The adjuster is connected to a 
controller 200 which is, in turn, connected to one or more sensors 
adaptped to sense a preselected control parameter or parameters. In the 
shown embodiment, a road sensor 202 is used to sense the smoothness of the 
road surface. The road sensor 202 is adapted to emit or transmit 
ultrasonic waves toward the road surface and to detect or receive 
ultrasonic waves reflected by the road surface. As shown in FIG. 1, the 
road sensor 202 is mounted at the front end of the vehicle, in the shown 
embodiment. However, the point at which the road sensor is mounted is not 
limitted to the shown position. Furthermore, a plurality of road sensors 
may alternatively be used. 
FIG. 3 shows the detailed structure of the adjuster 100. The adjuster 100 
comprises a hollow cylinder 102 having one end 104 rigidly secured to the 
end 16c of the torsion bar 16a. A closure 106 is fitted to the other end 
108 of the cylinder 102. The closure 106 defines a central opening 110 
through which the end 16d of the torsion bar 16b extends into the internal 
space of the cylinder 102. A sealing ring 112 is fitted on the periphery 
of the opening 110 to allow thrusting motion of the torsion bar 16b 
relative to the cylinder while establishing a fluid-tight seal with the 
outer periphery of the torsion bar 16b. A thrusting piston 114 is provided 
at the end 16d of the torsion bar 16a within the closed internal space of 
the cylinder 102. The piston 114 divides the internal space of the 
cylinder into two chambers 116 and 118 each of which is filled with a 
magnetic fluid. The magnetic fluid may be a colloidal fluid composed of 
powdered ferromagnetic material such as magnetite, mangano-ferrite, nickel 
ferrite or the like, the 100 to 200 Anstrom particles of which are coated 
with a linear unsaturated fatty acid base surface-active agent such as 
oleic acid, linolenic acid or the like, dispersed in a solvent such as an 
aliphatic hydrocarbon, an aromatic hydrocarbon, or water or the like with 
an anionic detergent. Such colloidal fluids have better dispersiveness 
than other kinds of suspensions and are not subject to sedimentation or 
flocculation, i.e. separation of the solid and liquid phases, thus 
ensuring an even composition with relatively strong magnetism. Therefore, 
the magnetic fluid set forth above has the characteristics of both a 
ferromagnetic material and a fluid. 
When the magnetic fluid is placed in a magnetic field, the particles of the 
ferromagnetic material are energized to align with the magnetic field, 
resulting in differential concentrations of the ferromagnetic material in 
the fluid. The severity of the concentration differentials is related to 
the magnitude of the magnetic field appllied. Internal friction in the 
magnetic fluid is related to the concentration of the ferromagnetic 
material at the point of maximum concentration in the fluid. This internal 
friction of the magnetic fluid affects the torsion modulus of the 
stabilizer 16. 
In order to apply a magnetic field to the magnetic fluid enclosed in the 
cylinder 102, magnetic coils 118 are wound around the outer periphery of 
the cylinder. The coils 118 are connected to a driver circuit 120 which 
is, in turn, connected to the controller 200 to receive a control signal 
as shown in FIG. 4. The driver circuit 118 responds to the control signal 
from the controller 200 by energizing or deenergizing the coils 118. In 
practice, when the controller 200 judges from the selected control 
parameters that the torsion modulus of the stabilizer should be HIGH, the 
driver circuit 120 is operated to feed a driver signal to the coil to 
excite the coils, and, on the other hand, when the controller 200 judges 
that the torsion modulus should be LOW, the driver circuit 118 is held 
inoperative to prevent supply of the driver signal thus holding the coil 
in a deenergized state. 
FIG. 4 schematically shows the fundamental structure of the torsion modulus 
control system for the stabilizer 16. The control system includes the 
controller 200, the road sensor 202 and the driver circuit 120. As set 
forth above, the road sensor 202 produces a pulse-form sensor signal Rp 
when reflected ultrasonic waves are detected. A discriminator 204 built 
into the cotroller 200 discriminates road surface conditions on the basis 
of the intervals between the sensor signal pulses. In practice, the 
discriminator 204 samples the pulse intervals between a predetermined 
number of sensor signal pulses and derives the range of variation of the 
pulse intervals. When the variation range derived from the sampled pulse 
intervals is within a predetermined range, then the discriminator judges 
that the vehicle is running on a smooth road. On the other hand, if the 
variation range is outside of the predetermined range, the discriminator 
judges that the vehicle is on a rough road. 
The discriminator 204 sends a road condition indicative signal to a control 
signal generator 206 in the controller 200. The control signal generator 
206 is responsive to the road condition indicative signal to derive the 
control signal to be sent to the driver circuit. 
As set forth above, when vehicle is judged to be on a smooth road, the 
control signal goes HIGH to activate the driver circuit. On the other 
hand, when the road condition indicative signal indicates that the vehicle 
is on a rough road, the control signal goes LOW to make the driver circuit 
inoperative. 
The control signal generator 206 is also connected to the road sensor 202 
to control the operating timing of the latter. In order to control the 
operation timing of the road sensor 202, the control signal generator 206 
sends timing pulses to the road sensor at fixed intervals. As shown in 
FIG. 5, a timing pulse T.sub.p is received by a monostable multivibrator 
208 in the road sensor 202. The monostable multivibrator 208 is triggered 
by the timing pulse T.sub.p to send a trigger signal to a gate circuit 210 
which is interposed between an ultrasonic wave generator 212 and an 
ultrasonic wave transmitter 214. The gate circuit 210 becomes conductive 
in response to the trigger signal from the monostable multivibrator 208 
and so passes the ultrasonic waves to the transmitter 214. Then, the 
ultrasonic waves are transmitted towards the road surface through the 
transmitter 214. Reflected components of the ultrasonic waves are received 
by a ultrasonic receiver 216. The receiver sends the received ultrasonic 
wave to a shaping circuit 218 through an amplifier 220. The shaping 
circuit 218 outputs the sensor signal Rp whenever reflected ultrasonic 
waves are detected by the receiver 216. 
It should be appreciated that such a road sensor for detecting road surface 
conditions has been disclosed in Japanese Patent First Publication Nos. 
56-153267 and 56-153268, both published on Nov. 27, 1981. The disclosure 
of the above-identified Japanese Patent First Publications would be hereby 
incorporated by reference for the sake of disclosure. In addition, 
although a road sensor detecting road conditions by means of ultrasonic 
wave has been specifically disclosed in the preferred embodiment of the 
invention, the sensor is not necessarily an ultrasonic-based sensor but 
can use light, laser beams and so forth. For example, U.S. Pat. No. 
4,105,216, issued on Aug. 8, 1978, to Donald E. Graham et al, Japanese 
Patent First Publication No. 57-182544, published on Nov. 10, 1982, and 
British Patent First Publication No. 2,090,495, published on July 7, 1982 
respectively disclose sensors for detecting road surface conditions or 
displacement of sprung and unsprung masses in the vehicle suspension 
system photo-electrically. The contents of these publications are hereby 
incorporated by reference for the sake of disclosure. Furthermore, 
Japanese Patent First Publication No. 59-42468, published on Mar. 9, 1984, 
discloses a procedure for discriminating unevenness of the road surface on 
the basis of a road sensor utilizing ultrasonic waves. The disclosed 
procedure in this Japanese Patent First Publication is also hereby 
incorporated by reference for the sake of disclosure. 
The torsion modulus control system in accordance with the first embodiment 
of the invention will be described in detail with reference to FIGS. 6 to 
10. As shown in FIG. 6, the controller 200 of this first embodiment 
comprises a microprocessor including an input/output interface 230, memory 
232 including RAM, ROM and registers, and a CPU 234. The controller 200 is 
connected to the road sensor 202 through the input/output interface 230. 
Also, the controller 200 is connected via the interface 230 to a steering 
sensor 236 which detects the angular steering position with respect to its 
neutral position and produces a steering position indicative signal. The 
controller 200 is also connected to the driver circuit 120 to energize or 
deenergize the coil 118 by means of the control signal. 
The road sensor 202 comprises the circuitry set forth with reference to 
FIG. 5 and sends the pulse-form road sensor signal to the controller 200 
via the interface 230. On the other hand, the steering sensor 236 may 
comprise a kind of potentiometer, the output voltage of which depends on 
the angular steering position as shown in FIG. 7. Since the steering 
sensor 236 of the shown embodiment thus produces an angular steering 
position-indicative analog signal which will be hereafter referred to as 
"steering sensor signal", an analog-to-digital (A/D) converter 238 is 
inserted between the steering sensor 236 and the interface 230. 
A potentiometer-type steering sensor would be mounted near or on a steering 
column (not shown) is such a way that its total resistance will vary 
according to the angular position of the steering wheel with respect to 
its neutral position. Though the steering sensor illustrated in the shown 
embodiment was chosen because it could be easily applied to the torsion 
modulus control system of the first embodiment, the steering sensor may 
take numerous other forms. For example, U.S. Pat. No. 4,342,279, to 
Yasutoshi SEKO et al and assigned to the assignee of this invention, 
discloses a device for detecting steering angle and steering direction of 
a steering wheel in an automotive vehicle, including a pair of fixed 
contacts and a movable contact. The movable contact is arranged in 
connection with the fixed contacts in such a way that, when the steering 
wheel rotates in one direction, the movable contact engages only the first 
fixed contact, and when the steering wheel rotates in the opposite 
direction, the movable contact engages only the second fixed contact. Upon 
the basis of signal produced whenever the movable contact contacts one of 
the fixed contacts, the steering angle and steering direction are 
detected. The device further comprises a counter which counts occurrences 
of contact with one of the fixed contacts to monitor the angular position 
of the steering wheel. In the co-pending U.S. patent applications Ser. 
Nos. 580,175 and 580,174, both filed on Feb. 15, 1984 and commonly 
assigned to the assignee of this invention, a steering sensor which 
detects steering angle variation photoelectrically is illustrated. 
Such steering sensors may be applied to the control system of the present 
invention. Therefore, the contents of U.S. Pat. No. 4,342,279 and U.S. 
patent applications Ser. Nos. 580,175 and 580,174 are hereby incorporated 
by reference. 
The ROM of the controller 200 includes a memory block 240 storing the main 
program illustrated in FIG. 8 (to be explained in detail later) and a 
memory block 242 storing an interrupt program for processing the road 
sensor signals for monitoring road surface conditions, as illustrated in 
FIGS. 9 and 10 and will be explained later with respect thereto. 
RAM of the controller 200 includes a counter t 244 connected to a clock 
signal generator 246 to count the clock signal pulses in order to measure 
the interval between successive road sensor pulses, and a counter T 248 
also connected to the clock generator 246 to count clock pulses. Though 
the counters t and T 244 and 248 are illustrated separately for the sake 
of disclosure, they can in practice constitute a single common counter 
performing the required functions on a time-sharing basis. RAM further has 
counters C.sub.ln and C.sub.Ln 250 and 251 and a counter CNT 252. 
CPU 234 has flag registers FRO and FH. The flag register FRO is set when 
the road surface is smooth and is reset when a rough road is detected. The 
flag register FH is set when the coils 118 are energized to stiffen the 
stabilizer and is reset when the coils 118 are deenergized. The CPU also 
has a block of registers 254 including 10 cells R.sub.l1, . . . R.sub.l10 
each of which is adapted to store distance data indicative of the 
vehicle-body-to-road-surface distance derived on the basis of measured 
time interals between successive road sensor signal pulses Rp, and a 
register 256 including 5 cells R.sub.L1 . . . R.sub.L5 each of which is 
adapted to store an average distance value L.sub.n between the body and 
the road surface. 
Operation of the above control system will be described hereafter with 
reference to FIGS. 8 to 10. FIG. 8 is a flowchart of the main program to 
be executed periodically. The main program can be interrupted arbitrarily 
by the interrupt program of FIGS. 9 and 10. The interrupt program of FIGS. 
9 and 10 is adapted to monitor surface conditions of the road and set or 
reset the flag registr FRO depending upon the road surface conditions. 
Referring to FIG. 8, immediately after starting execution of the main 
program, the flag register FH is checked at a step 1002 to judge if the 
torsion modulus of the stabilizer 16 is currently HIGH or LOW. If the flag 
register FH is in the set state, the register FRO is checked at a step 
1004. When the register FRO is in the set state, program ends. On the 
other hand, when the register FRO is in its reset state, then, the control 
signal is changed to the LOW level to change the torsion modulus of the 
stabilizer to its lower level at a step 1006. After this, the register FH 
is reset at a step 1008. Then, the program ends. 
If the register FH is reset when checked at the step 1002, then the 
register FRO is checked as in the step 1004, at a step 1010. If the 
register FRO is reset when checked at the step 1010, the program ends. If 
the register FRO is set when checked at the step 1010, then steering 
sensor signal St is read from a temporary register 260 in the interface 
and written into a register R.sub.St 262 at a step 1011. The register 
R.sub.St is adapted to store the current steering sensor signal value 
St.sub.new and the steering sensor signal value St.sub.old from the 
immediately preceding cycle, and to replace the older steering angular 
position data, i.e. steering angle sensor value St.sub.old with the fresh 
steering sensor signal value as St.sub.new upon receipt of a fresh 
steering sensor signal. At a step 1012, the steering sensor signal values 
St.sub.new and ST.sub.old are read from the register R.sub.St. These 
values are compared at a step 1014 to derive the difference .DELTA.St 
therebetween. The derived difference is checked with a predetermind 
reference value .DELTA.St.sub.ref which defines a steering angle variation 
range representing the absence of significant steering adjustment at a 
step 1016. 
When the absolute value .vertline..DELTA.St.vertline. is equal to or less 
than the reference value .DELTA.St.sub.ref, when checked at the step 1016, 
then, a timer flag register FTM 264 is checked at a step 1018. If the 
timer flag register FTM is in its reset state, then the timer T 248 is 
started at a step 1020 and FTM is set at a step 1021. After this step 
1020, the timer value T is read out and compared with a time-over 
reference value T.sub.up at a step 1022. If the timer value T is less than 
the time-over reference T.sub.up, then the program ends. In this case, 
since the flag register FH was in the reset state when checked at the step 
1002 and the status of the flag register FH is unchanged, the coils 118 
will still be in the deenergized position so that the torsion modulus of 
the stabiilzer will remain LOW. On the other hand, when the timer value T 
reaches the time-over reference T.sub.up, the control signal is changed to 
its HIGH level at a step 1023 and the flag register FH is set at a step 
1024. As a result, the coils 118 are energized to change the torsion 
modulus of the stabilizer to HIGH. After this, the timer T and the timer 
flag register are reset at a step 1026. 
If the timer flag FTM is in its set state when checked at the step 1018, 
the step 1020 of starting the timer T is skipped and the program goes 
directly to the step 1022. On the other hand, if the absolute value of the 
difference St between the new and old steering sensor signal values 
St.sub.new and St.sub.old exceeds the reference value St.sub.ref when 
checked at the step 1016, then the program jumps to the step 1026 to reset 
the timer T and the timer flag register FTM. 
The steps 1011 to 1026 judge the vehicle driving state. Conceptually, when 
the vehicle is on a curved road it will occasionally roll due to 
compliance of the suspension. If this occurs just after travelling over a 
rough road, the stabilizer may remain excessively stiff causing the 
vehicle to be held in transversely inclined state. The steps 1011 to 1026 
prevent this satisfactorily. 
FIGS. 9 and 10 show the interrupt program. Initialization takes place at 
the initial step 2002. In the initialization step, the timers t and T 244 
and 248, the registers R.sub.ln and R.sub.lLn 254 and 256, and counters 
C.sub.ln and C.sub.lLn 250 and 251 are all reset. After this, the 
sub-routine illustrated in FIG. 10 is performd at a step 2004. 
In the sub-routine of FIG. 10, a timer t 244 is started at a step 2004-1. A 
timing pulse Tp is fed to the monostable multivibrator 208 at a given 
timing, e.g. every 0.02 sec., to periodically trigger the latter, at a 
step 2004-2. Whenever the monostable multivibrator 208 is triggered, the 
road sensor transmits ultrasonic waves toward the road surface through the 
ultrasonic transmitter 214. Immediately after or at approximately the 
moment of receipt of the timing pulse Tp by the monostable multivibrator, 
the timer value tn is read and stored in a temporary register 266, at a 
step 2004-3. Then, the road sensor signal Rp is checked at a step 2004-4. 
The step 2004-4 is repeatedly performed until a road sensor signal pulse 
Rp is received. After a road sensor signal pulse Rp is detected, the timer 
signal value t.sub.n+1 is read and stored in the temporary register 260, 
at a step 2004-5. Thereafter, the difference Td between the timer signal 
values t.sub.n and t.sub.n+1 is calculated at a step 2004-6. The obtained 
difference Td is indicative of the time period between transmission and 
reception of one burst of ultrasonic waves. Since the ultrasonic waves 
travel at approximately the speed of sound V, the distance ln between the 
road sensor and the road surface can be calculated from: 
EQU l.sub.n =V.times.Td/2 
Calculations according to this equation are performed at a step 2004-7. The 
derived distance value l.sub.n is written into the corresponding block 
Rl.sub.n of the register 254 at a step 2004-8. Thereafter, the counter 
Cl.sub.n is incremented by 1 at a step 2004-9. The counter value Cl.sub.n 
is compared with 10 at a step 2004-10. If the counter value Cl.sub.n is 
less than 10, control returns to the step 2004-2. On the other hand, when 
the counter value Cl.sub.n reaches 10, the sub-routine ends and control 
returns to the next step of the interrupt program of FIG. 9. 
As will be appreciated herefrom, distance l.sub.1 . . . l.sub.10 are 
sampled and stored in the register 254 during execution of the 
sub-routine. 
Returning to the interrupt program of FIG. 9, at a step 2006, average 
L.sub.n of the ten stored distance values in the register 254 is 
calculated from: 
##EQU1## 
The obtained result L.sub.n is written into the corresponding block 
R.sub.L1 . . . R.sub.L5 of the register 256, at a step 2008. Then, the 
counter C.sub.Ln is incremented by 1 at a step 2010. The counter value 
C.sub.Ln is compared with 5 at a step 2012. If counter value C.sub.LN is 
less than 5, control returns to the step 2004 to repeat the steps 2004 to 
2010 five times in order to obtain five average values L.sub.1 . . . 
L.sub.5. When the counter value C.sub.Ln reaches 5, then a reference value 
L.sub.n is calculated by averaging the average values L.sub.1 . . . 
L.sub.5 according to: 
##EQU2## 
at a step 2014. At that time, the timer T is started to measure running 
time, at a step 2016. 
At a step 2017, the reference value L.sub.n and the distance data l.sub.n 
are read out. The reference value L.sub.n is compared with the distance 
data stored in the register 254 at a step 2018. If an absolute value 
.vertline.L.sub.n -l.sub.n .vertline. is equal to or greater than a 
reference differential value V.sub.0, then the counter value CNT of 
counter 252 is incremented by 1 at a step 2020. Thereafter, the timer T is 
checked with a time-up threshold, at a step 2022. On the other hand, when 
the absolute value .vertline.L.sub.n -l.sub.n .vertline. is less than the 
differential threshold V.sub.0, then, the step 2020 is skipped and control 
goes directly to the step 2022. If time is not yet up, the CPU accesses 
the next block Rl.sub.n+1 of the register 254 holding the next distance 
value l.sub.n+1 and replaces the distance value l.sub.n compared with the 
reference value L.sub.n with the next distance value l.sub.n+1, at a step 
2024. Thereafter control returns to the step 2017. The steps 2017 to 2024 
form a loop to be repeated until a predetermined period of time, e.g. 1 
sec. expires and expiration of the predetermined period of time is 
recognized at the step 2022. During execution of the interrupt program, 
time intervals between the road sensor pulses Rp are sampled approximately 
every 0.02 sec. Average distance between the vehicle body and the road 
surface is thus calculated every 0.2 sec. on the average. Therefore, 
overall run time of the interrupt program may be slightly more than 1 sec. 
After the predetermined period of time expires, the counter value CNT is 
compared with a road condition threshold M at a step 2026. If the counter 
value CNT is less than the road condition threshold M, the register FRO is 
set at a step 2028. On the other hand, when the counter value CNT is equal 
to or greater than M, the register FRO is reset at a step 2030. 
It should be appreciated that, although the shown embodiment has been 
directed to the swing-arm type suspension system with the roll stabilizer, 
the present invention is not limited in application to such swing-arm 
suspensions but is applicable to any type of suspension systems to which a 
roll stabilizer is applicable. 
FIGS. 11 to 18 show the second embodiment of the torsion modulus control 
for the roll stabilizer according to the present invention. 
FIGS. 11 and 12 show the structure of a roll stabilizer 30 to be utilized 
in the second embodiment. The roll stabilizer 30 comprises a transverse 
bar section 32 and a pair of parallel bar sections 34 and 36. The 
transverse bar section 32 extends essentially perpendicular to the vehicle 
axis and has a circular cross-section. The transverse bar section 32 is 
connected to hollow cylndrical bearing sections 38 and 40 at both ends. 
The parallel bar sections 34 and 36 have end segments 42 and 44 of 
circular cross-section adapted to rotatably engage the bearings 38 and 40 
of the transverse bar section 32. The parallel bar sections 34 and 36 also 
have rectangular cross-section major sections 46 and 48, each of which has 
one end 50 and 52 connected to a suspension arm 51 through a connecting 
rod 53 which allows free rotation of the associated bar 34 or 36. 
The cylindrical cross-section end segments 42 and 44 of the parallel bar 
sections 34 and 36 extend beyond the ends of the bearing portions 38 and 
40. Link plates 54 and 56 are rigidly fitted onto the protruding ends of 
the parallel bar sections 34 and 36. The link plates 54 and 56 are 
rotatable about the bearing sections 38 and 40 together with the parallel 
bar sections 34 and 36. The link plates are connected to each other 
through a linkage 58. In addition, the link plate 54 is associated with an 
actuator 60 through an actuation rod 62 engaging to an elongated opening 
64 of the link plate 54. The actuator 60 may comprise an 
electromagnetically operative solenoid. The actuator is adapted to be 
energized by a control signal fed from a controller 300 to rotate the link 
plate 54 along with the parallel bar section 34 through 90.degree. from 
the shown neutral position. When the actuator 60 is energized, the link 
plate 56 is also rotated according to rotation of the link plate 54 to 
pivot the parallel bar 36 through 90.degree. within the bearing section 
40. 
As shown in FIG. 13, at the neutral position, the parallel bar sections 34 
and 36 lie with their wider sides 34w (36w) horizontal. At this position, 
since resistance of the parallel bar sections 34 and 36 against vertical 
bending moment which is applied when the vehicle wheel bounds or rebounds 
is relatively small, the torsion force to be applied to the transverse bar 
section 32 of the stabilizer 30 is large. When the actuator 60 is 
energized, the parallel bar sections 34 and 36 are rotated to lie with 
their shorter sides 34s (36s) horizontal, as shown in phantom line in FIG. 
13. At this position, the bending stress of the parallel bar sections 34 
and 36 is increased, i.e., the torsion force to be applied to the 
transverse bar section 32 of the stabilizer becomes smaller. 
When an essentially smooth road surface is detected by a road sensor 400 
which can be the same as the sensor 202 of the foregoing first embodiment 
or some other sensor, one variation of which will be illustrated later, 
the actuator 60 may be energized to enforce a HIGH torsion modulus for the 
stabiilzer 30. On the other hand, when a rough road surface is detected by 
the road sensor 400, the actuator 60 is deenergized to return the torsion 
modulus of the stabilizer 30 to the lower level. 
FIG. 14 illustrates another road sensor used in the second embodiment, 
which may be generally referred to as "road sensor 400". The road sensor 
400 generally comprises a linear potentiometer associated with a shock 
absorber 402 which is cooperative with a suspension coil spring 404 for 
damping relative displacement between the vehicle body and the wheel axle 
extending from a wheel hub 406 of the suspension arm 51. The linear 
potentiometer of the road sensor 400 is adapted to measure movement of the 
piston of the shock absorber 402. 
FIGS. 15(A) and 15(B) respectively show variation of the outputs of the 
road sensor 400 on a smooth road and on a rough road while the vehicle is 
moving at 40 km/h. On the other hand, FIGS. 16(A) and 16(B) show variation 
of the outputs of the road sensor 400 as the vehicle travels over a smooth 
road and over a rough road at a speed of 60 km/h. As will be appreciated 
herefrom, when the vehicle is travelling over an essentially smooth road, 
the piston stroke of the shock absorber 402 is relatively short and its 
frequency is relatively high. Although the amplitude of vibration may vary 
with vehicle speed, the variation range of the road sensor outputs is 
fairly constant and relatively narrow while the vehicle is running on a 
smooth road. On the other hand, as will be seen from FIGS. 15(B) and 
16(B), variation of the road sensor outputs on a rough road is relatively 
great. Therefore, by detecting the variation range of the road sensor 
outputs, it can be recognized whether the vehicle is travelling on a 
smooth road or a rough road. 
Experimentation has shown that when vehicle travels along a smooth road, 
the road sensor output has a frequency of approximately 12 to 13 Hz due to 
vibration of the unsprung wheel axle in response to relatively small 
unevennesses in the road surface, and, when the vehicle moves along a 
rough road, the road sensor output contains a combination of the 
high-frequency component at 12 to 13 Hz due to small unevennesses in the 
road surface and a low-frequency component at 1 to 2 Hz due to relatively 
large unevennesses in the rough road. Therefore, when the road sensor 
outputs are averaged, the average value for the smooth road will become 
approximately zero when the high-frequency vibration component is 
eliminted. On the other hand, when the vehicle travels along a rough road, 
the average value will remain relatively great even after the 
high-frequency component is eliminated. 
In the shown embodiment, the road sensor outputs are sampled periodically, 
e.g. every 0.02 sec. An average value Ln is obtained from ten sampled road 
sensor outputs. In order to eliminate the high-frequency component, a 
given number of average values are again averaged. The given number M is 
selected so as to obtain a cut-off frequency fc equal to or less than 0.5 
Hz, which may be determined from: 
EQU m=0.443/(T.times.10.times.fc)=4.43 
where m is the number of the average values to be averaged, T is the 
inter-pulse interval, in this case about 0.02 sec., and fc is the cut-off 
frequency. 
As will be appreciated herefrom, when 5 average values are again averaged, 
the cut-off frequency becomes equal to or less than 0.5 Hz and thus the 
high-frequency component can be successfully eliminated. The average value 
Ln obtained by further averaging of the average values Ln will be 
hereafter referred to as "reference value". This reference value may vary 
as illustrated in dotted line in FIGS. 15(A), 15(B), 16(A) and 16(B). 
Thus, the surface quality of the road, at least to the extent of 
distinguishing rough roads from smooth roads, can be discerned by 
comparison of the road sensor output values with the reference value. A 
smooth road surface is recognized when the difference V between the 
reference value Ln and the road sensor output value DS.sub.n is within a 
given range as defined by a threshold V.sub.0. The threshold V.sub.0 may 
adjusted depending upon the vehicle speed Vs. When the difference between 
the road sensor outputs DS.sub.n and the reference value Ln is greater 
than the threshold V.sub.0, it may be judged that the vehicle is moving on 
a rough road. 
According to the aforementioned procedure, the controller 300, as shown in 
FIG. 17 adjusts the torsion modulus of the stabilizer depending upon road 
conditions. 
Similarly to the aforementioned first embodiment, the controller comprises 
a microprocessor including an input/output interface 302, a memory 304 
including RAM and ROM, CPU 306 which includes a plurality of registers 
described later in conjunction with a control program. The interface 302 
of the controller 300 is connected to the road sensor 400 and a vehicle 
speed sensor 308 which is per se well known. In addition, the interface 
302 is connected to a driver circuit 310 of the actuator 60 to supply the 
control signal Cs. Since the road sensor output DS is in the form of an 
analog signal, an analog-to-digital (A/D) converter 312 is required to 
generate a binary signal corresponding to the road sensor output. 
CPU 306 has a register 314 including a plurality of memory cells R.sub.DS1, 
R.sub.DS2 . . . corresponding one-to-one with road sensor output values 
DS.sub.1, DS.sub.2 . . . , a register 316 including 5 cells blocks 
R.sub.L1 . . . R.sub.L5 which hold respectively corresponding average 
values L.sub.n. CPU 306 also includes a register 317 sorting a road 
condition indicative flag FRO which is set when a smooth road surface is 
detected and reset when the when the actuator 60 is in its deenergized 
position. 
ROM has a memory block 318 storing threshold values V.sub.0 in the form of 
a look-up table which may be accessed in terms of the vehicle speed sensor 
signal value Vs. ROM also has memory blocks 320 storing a control program 
executed periodically to control the torsion modulus of the stabilizer 30. 
If necessary, the control program may be separated into a main program 
which may be similar to that illustrated in FIG. 8 and an interrupt 
program for setting and resetting the road condition indicative flag FRO 
similar to the interrupt program of FIGS. 9 and 10. 
In the control program of FIG. 18 and 19, the system is initialized at an 
initial step 3002. Initialization includes resetting of counters C.sub.ln 
322 which count sampled road sensor signals, counter C.sub.Ln 324 which 
counts the number of average values derived, counter CNT 326 which counts 
occurrences of the difference V between the road sensor signal value 
l.sub.n and the reference value Ln being equal to or greater than the 
threshold V.sub.0, as well as previously-mentioned registers FRO, FH, 317 
and 319. 
Then, at a step 3004, a sub-routine illustrated in FIG. 19, is executed to 
sample 10 road sensor signal values l.sub.1 . . . l.sub.10. 
In the sub-routine, the road sensor value DS.sub.n is read and transferred 
to the corresponding memory block R.sub.DSn at a step 3004-1. Then, a 
counter Cl.sub.n is incremented by 1 at a step 3004-2. The counter value 
Cl.sub.n is compared with "10" at a step 3004-3. If the counter value 
Cl.sub.n is less than 10, control returns to the step 3004-1. This loop of 
the steps 3004-1, 3004-2 and 3004-3 is repeated approximately every 0.02 
sec. and continues until the counter value Cl.sub.n reaches 10. 
When the counter value Cl.sub.n reaches 10, then counter C is reset at a 
step 3004-4. Then, control returns to the main program and the average 
value Ln is derived from: 
##EQU3## 
at a step 3006. The derived average value Ln is written into a temporary 
register 328 in the memory 304 at a step 3008. 
Thereafter, the counter C.sub.Ln is incremented by 1 at a step 3010. The 
counter value C.sub.Ln is compared with "5" at a step 3012. If the counter 
value C.sub.Ln is less than 5, control returns to the step 3004. On the 
other hand, when the counter value C.sub.Ln reaches 5, the reference value 
L.sub.n is calculated at a step 3014 from: 
##EQU4## 
Then, the vehicle speed sensor signal value V.sub.s is read out at a step 
3016. On the basis of the read vehicle speed sensor signal value V.sub.s, 
the look-up table in the memory block 318 in ROM is accessed to retrieve a 
threshold value V.sub.0, at a step 3018. The obtained threshold value 
V.sub.0 is stored in the temporary register 328. The timer T is then 
started at a step 3020. 
At a step 3022, the reference value L.sub.n and the road sensor signal 
value DS.sub.n are read out. The road sensor signal values DS.sub.n are 
read in sequence starting with the first and are replaced with the next 
one each time the road surface discriminating steps 3024 to 3030 are 
performed. The absolute difference .vertline.L.sub.n -DS.sub.n .vertline. 
between the reference value L.sub.n and the corresponding road sensor 
signal value DS.sub.n is derived and compared with the threshold value 
V.sub.0 stored in the temporary register 328, at a step 3024. If the 
absolute value is equal to or greater than the threshold value, then the 
counter CNT is incremented by 1, at a step 3026. Thereafter, the timer 
value T is checked at a step 3028 so as to check whether or not a 
predetermined time has expired. On the other hand, if the absolute value 
is less than the threshold value, then the step 3026 is skipped and 
control goes directly to the step 3028. 
Until the timer value T reaches a given value representative of the 
predetermined period of time, the steps 3022 to 3028 are repeated. 
Therefore, if time has not expired when checked at the step 3028, control 
returns to the step 3022. During this operation, the memory block which is 
to be accessed to retrieve the next road sensor signal value DS.sub.n is 
updated with the block R.sub.DSn+1, at a step 3030. Therefore, in the next 
cycle of operation, the road sensor value R.sub.DSn+1 would be read out. 
The aforementioned loop of the steps 3022 to 3030 is repeated for the 
predetermined period of time, e.g. 1 sec. 
When time is up when checked at the step 3028, then the counter value CNT 
is compared with a predetermined value M at a step 3032. The predetermined 
value M is a threshold between smooth and rough road surfaces. Therefore, 
when the counter value CNT is equal to or greater than the predetermined 
value M, then the road surface on which the vehicle is travelling is 
judged to be rough and otherwise, the vehicle is judged to be on a smooth 
road surface. When a rough road surface is detected by comparison of the 
counter value CNT with the predetermined value M, then actuator 60 is 
deenergized, which engenders the LOW torsion modulus of the stabilizer 30, 
at a step 3034. At the same time, the flag FH in the flag register 316 is 
reset. On the other hand, is a smooth road surface is detected at the step 
3032, the actuator 60 is energized to enforce the HIGH torsion modulus of 
the stabilizer at a step 3036. After one of the steps 3034 and 3036, the 
program ends. 
FIG. 20 shows a modification of the road sensor utilized in the 
aforementioned second embodiment of the torsion modulus control system for 
the roll stabilizer according to the present invention. In this 
modification, the road sensor 80 generally comprises a piezoelectric 
element 82. The piezoelectric element 82 is sandwiched between an upper 
spring seat 84 seating the upper end of the suspension coil 86 and a 
fitting bracket 88 through which the strut assembly 90 of the suspension 
is fixed to the vehicle body. The piezoelectric element 82 is fitted 
around a piston rod 92 of a shock absorber 94. 
The piezoelectric element 82 produces an analog signal having a value which 
varies depending upon the amplitude of vibrations transmitted through the 
shock absorber and the piston rod thereof. The analog signal produced by 
the piezoelectric element should correspond to the analog signal produced 
by the stroke potentiometer of the second embodiment. 
It should be noted that, in the shown second embodiment, the torsion 
modulus of the stabilizer is determined depending only on the road surface 
conditions as detected by the road sensor, however, it is possible to 
employed the same procedure as explained with respect to the first 
embodiment with reference to FIG. 7. In addition, although specific 
embodiments which binarily adjust the torsion modulus of the stabilizer 
between discreet LOW and HIGH values have been disclosed for better 
understanding of the invention, it is also possible for the torsion 
modulus to vary continuously depending upon selected suspension control 
parameters. Furthermore, the specific parameters employed in the shown 
embodiments should be understood to be mere examples and can be replaced 
with any suitable parameters.