Vehicle height control system

A vehicle height control system wherein vehicle height control is inhibited when the vehicle is turning and in a rolling state, the state when the control is inhibited being based upon the vehicle's speed from a speed sensor, the steering angular velocity of a steering wheel from a steering angle sensor and the outputs from sensors detecting the height of the vehicle body on both sides of the vehicle with respect to the wheels, which by the pattern of their outputs, represent that the vehicle is inclined from side-to-side and in the rolling state.

BACKGROUND OF THE INVENTION 
This invention relates to a vehicle height control system, and in 
particular to a highly reliable vehicle height control system in which a 
vehicle height control is inhibited for an apparent variation, i.e. a 
temporary change of the vehicle's height arising at the time when a 
vehicle is turning. 
A vehicle height control system has been proposed in Japanese patent 
application laid-open No. 56-60711 in which the vehicle's height is 
adjusted to a target level by means of sensors capable of detecting the 
change of the vehicle's height. It is known that a vehicle's height is 
advantageously controlled as the load weight of a vehicle is changed. 
However, the vehicle's height also changes with the change of the surface 
of a road or during the turning of the vehicle during the running 
operation thereof, in spite of the fact that the load weight of the 
vehicle is not actually changed. To control the vehicle's height each time 
such an apparent change occurs does not improve performance as well as 
being uncomfortable to a vehicle's driver or passengers. 
Therefore, it is required in a vehicle height control system that the 
vehicle's height be controlled as soon as the load weight is actually 
changed when the vehicle is stopped but that the vehicle's height not be 
controlled for apparent changes of the vehicle's height during the running 
of the vehicle. 
To this end, one may consider that no vehicle height control should be 
carried out during the running mode thereof. However, the following 
problems will then arise: 
(1) If the vehicle's height is controlled according to the change of the 
load weight when the vehicle is stopped and the vehicle is started before 
the vehicle height control has not yet been completed, the vehicle's 
height is changed owing to the acceleration thereof, resulting in the 
completion of the vehicle height control although the vehicle's height has 
not yet attained the target level according to the actual load weight. In 
this case, since the vehicle height control is not re-activated until the 
vehicle is again stopped, the vehicle height control is not yet completed; 
(2) If an air leakage in the air suspension occurs during the vehicle's 
running for a long time interval, the vehicle's height is gradually 
reduced due to that air leakage and can not be corrected by the vehicle 
height control. Furthermore, multi-level or multi-stage control can not be 
carried out for different vehicle driving speeds, in which, for example, a 
lower vehicle's height is set for a high speed running. 
As indicated above, if the vehicle height control is completely inhibited 
during the running mode of a vehicle, an effective vehicle height control 
is not achieved. Thus, there has been already proposed a system for 
solving the above problems in which the vehicle control is initiated 
immediately in response to the change of the vehicle's height in the 
stopped state while during the running the initiation of the vehicle 
height control is delayed by means of a timer or the time interval for 
determining the initiation of the vehicle height control is extended. 
However, although this system can inhibit the initiation of the vehicle 
height control for the variation of road surfaces during the running mode, 
it can not inhibit said initiation in a case such as the turning of a 
vehicle where the vehicle's height is being changed for a relatively long 
interval. This is because if one intends to inhibit the vehicle height 
control from operating for changes in the vehicle's height during the time 
of long internal turning, the control system of the prior art must delay 
the initiation of the vehicle height control during the running mode by a 
long time interval or to extend the time interval for the determination of 
the vehicle height control whereby it will be difficult to initiate the 
actual vehicle height control when required. To the contrary, if one 
intends to surely carry out the normal or real vehicle height control 
during the running mode, it is advantageous in the prior art to shorten 
the delay time of the initiation of the vehicle height control or to 
shorten such a long time interval for the determination of the initiation 
of the vehicle height control. However in the prior art system, such a 
vehicle height control will be disadvantageously initiated even for the 
apparent change of the vehicle's height during the vehicle's turning for a 
long time interval. 
According to such conventional systems, particularly during the running of 
a vehicle, it is difficult to distinguish between an actual change in the 
vehicle's height and a temporary change in the vehicle's height due to the 
turning of the vehicle and the like, so that if the vehicle height control 
is desired to be carried out quickly during the running mode of operation 
of the vehicle, it is difficult to inhibit the vehicle height control 
during the turning. 
On the other hand, SAE paper 770396 on pages 11-22 discloses "Electronic 
Sensing for Vehicle Height Control" by R. W. Hegel et al, in which optical 
vehicle's height sensors and an air pressure source for the vehicle height 
control are employed for weight and space savings and simplified 
installation; SAE paper 840258 on pages 1-12 discloses "Chassis Electronic 
Control Systems" by M. Mizuguchi et al, in which optical vehicle's height 
sensors and an air pressure source are also employed while fail-safe 
mechanisms are incorporated in the event of system failure and a central 
diagnostic terminal is provided for system checking. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to provide a highly 
reliable vehicle height control system wherein the vehicle height control 
is not initiated when it is determined that the vehicle is turning even 
though the condition of the initiation of the vehicle height control is 
met. 
To achieve this object, the present invention provides a vehicle height 
control system including: vehicle's body height sensors (3a,3b) for 
detecting one of a plurality of classified height ranges to which the 
height of the vehicle's body (1) with respect to the vehicle's wheel or 
the vehicle's wheel axle belongs, a steering angle sensor (9) for 
detecting the steering angle of a steering wheel of the body (8), a 
vehicle speed sensor (13) for detecting the speed of the vehicle's wheels 
(7), a control unit (2) for determining the initiation or the stop of the 
vehicle height control, and a suspension (6a,6b) which incorporates the 
vehicle's height adjusting mechanism (6,11,12,14-18). This control unit 
comprises first means for determining the turning state of the vehicle on 
the basis of outputs from the vehicle speed sensor, the steering angle 
sensor and the vehicle's body height sensors, and second means for 
inhibiting the vehicle height control while the vehicle is in the turning 
state. 
Preferably, the first means comprises means for calculating the speed of 
the vehicle, means for calculating a threshold value for the steering 
angular velocity according to the vehicle speed, and means for 
determining, as the turning state, the amount of side-to-side inclination 
of the vehicle representing that the vehicle is in a rolling state based 
upon the outputs of the vehicle's body height sensors when the steering 
angular velocity exceeds the threshold value. This means for determining 
the rolling state of the vehicle comprises means for determining that the 
vehicle body is inclined from side-to-side from the outputs of the 
vehicle's body height sensors which represent by the pattern of their 
outputs that the vehicle is turning. 
Alternatively, the first means comprises means for calculating the speed of 
the vehicle, means for calculating a threshold value for the steering 
angular velocity according to the vehicle speed, and means for 
determining, as the turning state, that the vehicle body is in a rolling 
state when the steering angular velocity does not exceed the threshold 
value. In this alternative embodiment, when the vehicle body has been in a 
rolling state, and the outputs of the vehicle's body height sensors do not 
indicate the normal state, the steering wheel is not returned to its 
normal position, and the speed of the vehicle is not zero, the vehicle 
height control is inhibited. 
Furthermore, the control unit may comprise means for releasing the 
inhibiting of the vehicle height control when the outputs of the vehicle's 
body height sensors return to a normal position, when the steering wheel 
is reversely rotated, or when the speed of the vehicle becomes zero.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
There will now be described a vehicle height control system according to 
the present invention along the preferred embodiment thereof. 
In FIG. 1 showing one preferred embodiment of a vehicle height control 
system according to the present invention, are shown a vehicle's body 1, a 
control unit 2, vehicle's body height sensors 3a and 3b, an arm 4 of the 
vehicle's height sensor 3a or 3b, a rod 5, suspensions 6a and 6b, 
vehicle's wheels 7, a steering wheel 8, a steering angle sensor 9, a 
steering shaft 10, a compressor 11, a reserve tank 12, a vehicle speed 
sensor 13, an inflation valve 14, an exhaust valve 15, air valves 16 and 
17, and an air pipe 18. 
The control unit 2 reads out the information output from the vehicle's body 
height sensors 3a and 3b, the vehicle speed sensor 13, and the steering 
angle sensor 9 to determine the initiation and the stop of a vehicle 
height control. In the case where a vehicle lifting control is desired, 
the compressor 11 is driven according to the air flow requirements, the 
inflation valve 14 is opened, the exhaust valve 15 is closed, and the air 
valves 16 and 17 are opened/closed according to the required adjustments, 
whereby the height of the vehicle's body 1 is lifted by means of the 
suspension 6a and 6b associated with a vehicle height control mechanism. 
In the case where a vehicle lowering control is desired, the inflation 
valve 14 is closed, the exhaust valve 15 is opened, and the air valves 16 
and 17 are opened/closed according to the required adjustments, whereby 
the height of the vehicle's body 1 is lowered by means of the suspensions 
6a and 6b. 
The arrangement of the vehicle's body height sensor 3a will now be 
described with reference to FIG. 2. It is to be noted that the vehicle's 
body height sensor 3b is similarly applied. The vehicle's body height 
sensor 3a is mounted on the vehicle's body 1. The arm 4 interconnects a 
disc 36 having slits formed therethrough in the sensor 3a with the rod 5 
fixed to a vehicle's wheel axle 30. Photo-interrupters 33, 34, and 35 
output on/off electrical signals on the basis of an optical on/off 
(passage/interruption) pattern provided by the slits in the disc 36 in 
accordance with the rotary angle of the disc 36. In this vehicle's body 
height sensor 3 thus arranged, the change of the height between the 
vehicle's body 1 and the vehicle's wheels 7 or the vehicle's wheel axle 30 
will operate the rod 5 and the arm 4 to rotate the slit 36, whereby coded 
signals corresponding to various heights are output as detected signals 
from the photo-interrupters 33, 34, and 35. In this embodiment, a 3-bit 
code signal is output from terminals A, B, and C whereby the change of the 
vehicle's body height in the range of 2.sup.3 =8 can be detected. 
In FIG. 3 showing one example of the suspension 6 forming a vehicle height 
control mechanism, an air path 50 is connected to an air chamber 51 around 
which a coil spring 52 is provided. A shock absorber 53 is connected to an 
interconnecting portion 54 with the vehicle's wheel axle 30. 
Air fed through the air path 50 to the air chamber 51 increases the 
pressure of the air chamber 51 whereby the vehicle's height, i.e. the 
height between the vehicle's body 1 and the interconnecting portion 54, 
which is connected to the vehicle's wheel axle 30 may be lifted. On the 
other hand, air may be exhausted through the air path 50 from the air 
chamber 51, thereby lowering the vehicle's height. The compressor 11, the 
valves 14 and 15, the air valves 16 and 17, and the reserve tank 12 which 
form the vehicle's height adjusting means are required for such air feed 
and air exhaustion. This vehicle's height adjusting means may also include 
an air cleaner and/or an air drier (not shown). 
FIGS. 4 and 5 show the mounting positions of the vehicle sensors 3a and 3b. 
Particularly, FIG. 4 shows one embodiment in which a single front 
vehicle's height sensor 3a is mounted on the side of a front wheel 7 and a 
single vehicle's height sensor 3b is mounted on the side of a rear wheel 
7, the positions of those sensors being arranged in a diagonal line with 
respect to the front and the rear wheels as can be seen in FIG. 4 while 
FIG. 5 shows another embodiment in which two vehicle's height sensors 3a 
are mounted on the respective sides of the front wheels 7 and two 
vehicle's height sensor 3b are mounted on the respective sides of the rear 
wheels 7. 
FIGS. 6A-6C show an arrangement of the steering angle sensor 9 in which 
FIG. 6A shows a perspective view thereof, FIG. 6B shows a front view 
thereof, and FIG. 6C shows a side view, for illustrating the relationship 
of light switches 91, 92 and a circular slit plate 97 having a plurality 
of slits or apertures 94 circumferentially formed therethrough. The light 
switches 91 and 92 respectively comprise a set of a photo-transistor 95 
and an LED 96, each set forming a light switch called a photo-interrupter. 
With the slit plate 97 being rotated owing to the steering operation of 
the steering wheel 8, the plate 97 traverses the light switches, whereby 
the light switch 91 or 92 is switched on while the apertures 94 of the 
plate 97 are passing under the light switch 91 or 92, and is otherwise 
switched off while a mask portion 93 of the slit plate 97 other than the 
apertures 94 is passing under the light switch 91 or 92 to cause 
photo-interruption of the respective light sources. The plate 97 is 
mounted on the shaft 10 of the steering wheel 8 so as to rotate according 
to the rotation of the steering wheel 8. If the relationship between a 
lateral width T of the mask portion 93 or the apertures 94 in the slit 
plate 97 and the distance D of the transistors 95 is set so that (3/2)T=D 
holds, the output pulse signals of the two light switches 91 and 92 will 
be mutually different in electrical angle by 90.degree.. 
Next, one embodiment for detecting a steering angle will be described. FIG. 
7 shows waveforms SW1 and SW2 detected by the steering angle sensor 9 
shown in FIG. 1. The waveforms SW1 and SW2 are respectively output from 
the light switches 91 and 92 of the sensor 9 at a rate of one pulse each 
time the steering wheel 8 is rotated by 30.degree., and have output pulse 
edges of a-c-a-c and b-d-b-d, respectively for the case where the steering 
wheel is rotated in the clockwise (C.W.) direction. It is to be noted that 
the period of these pulses corresponds to the rotating speed of the 
steering wheel 8. The time chart shown in FIG. 7 illustrates the case 
where the steering wheel is initially rotated in the clockwise direction 
at a uniform rate after which it is rotated in a counterclockwise (C.C.W.) 
direction at a uniform rate just after a pulse edge "a" of SW1 has risen. 
By monitoring the order in which the pulse edges are generated, i.e., 
a-b-c-d for C.W. rotation and a-d-c-b for C.C.W. rotation, a change in the 
direction of rotation can be detected. Furthermore, by measuring the 
intervals of the pulse edges from one pulse edge "a" to the next pulse 
edge "a", from one pulse edge "b" to the next pulse edge "b" and so on 
during the periods P1, P2, P3, P4,--and so on as shown in FIG. 7, the 
variation of the steering angular velocity can be continuously measured, 
and by integrating the angle of 30.degree./4 per inter-pulse edges of a-b, 
b-c, and so on during the forward rotation, the total steering angle can 
be detected. 
When the rotating direction of the steering wheel 8 is reversed from the 
C.W. direction to the C.C.W. direction, the respective change in the order 
of pulse edge generation from a-b-c-d to a-d-c-b is detected, whereby the 
determination of the steering angular velocity from the edge intervals and 
the calculation of the total steering angle are once interrupted. 
Then, by detecting that the order in which the pulse edges are generated is 
a-d-c-b-a, it can be determined that the steering wheel's rotation is 
C.C.W., and by calculating the steering angular velocity or the total 
steering angle momently from the periods of P11, P12, P13, P14 and so on 
as shown in FIG. 7, it is possible to detect the steering angular velocity 
and the steering angle per se in the C.C.W. rotation as in the C.W. 
rotation. 
It is clear that such a detection method and a calculation can be readily 
realized by employing a micro-computer, by counting the periods of the 
pulse edge intervals each time the pulse edges of SW1 and SW2 are input to 
the micro-computer, and by counting the passing frequency of the pulse 
edges and storing the same in a memory. 
Also, since the steering angular velocity and the total steering angle can 
be updated every 30.degree./4, i.e., during the period P1, then the period 
P2, then the period P3, and so on in this embodiment, a highly accurate 
detection of the steering angle having a good responsiveness can be 
achieved. It is to be noted that while this embodiment has been described 
with the steering angle sensor 9 outputting one pulse each time the 
steering wheel is rotated by 30.degree., such a steering wheel sensor may 
be of a type which issues one pulse per any number of degrees (rotary 
angles). 
In FIG. 8 showing a block diagram of the arrangement of the control unit 2 
shown in FIG. 1, an input circuit 40 receives as an input therein the 
output of the front vehicle's height sensor 3a, an input circuit 41 
receives as an input therein the output of the rear vehicle's height 
sensor 3b, an input circuit 42 receives as an input therein the outputs of 
the steering angle sensor 9 and the vehicle speed sensor 13, an output 
circuit 45 provides as an output therefrom control signals to the 
compressor 11 and the valves 14-17, and a CPU interconnects the input 
circuits 40-42 with the output circuit 45 as well as a memory 43. 
The operation of the vehicle height control system thus arranged according 
to this invention will now be described with reference to the flow chart 
shown in FIG. 9. 
First of all, the current speed of the vehicle is calculated in order to 
actively take advantage of the vehicle height control function to adjust 
the vehicle's height to multi-levels according to the vehicle speed, or to 
change the time interval for determining the initiation of the vehicle 
height control according to the stopped state or the running state of the 
vehicle (step 72). It is well known to any one of ordinary skill in the 
art to determine the vehicle speed from the average value of the periods 
of the output pulses of the speed sensor 13. 
Then, a threshold value for the steering angular velocity is calculated 
(interpolated among various stored threshold values) according to the 
vehicle speed determined as above, in order to detect a certain rolling 
state at all times by changing the above threshold value according to the 
vehicle speed because the higher the vehicle speed becomes, the larger the 
lateral acceleration which the vehicle's body 1 may be subject to becomes 
with respect to the steering angular velocity (step 73). Therefore, a 
higher threshold value is selected for a low vehicle speed while a lower 
threshold value is selected for a high vehicle speed. 
The steering angular velocity is then calculated by using the output of the 
steering angle sensor 9, and is then compared with the above noted 
threshold value for the steering angular velocity according to the current 
vehicle speed (step 74). If the steering angular velocity exceeds the 
threshold value, it is then determined whether or not the vehicle is 
rolled by monitoring the respective output signals of the height sensors 
(step 80). On the other hand, if it is determined in step 75 with 
reference to the state of the memory 43 which will be described later that 
the vehicle has been rolled even though it is determined in step 74 that 
the threshold value is not exceeded, it is determined in steps 76-78 
whether or not the vehicle is being continuously rolled. 
The determination of the presence/absence of the rolling is carried out by 
the use of the output information of the vehicle's height sensors 3a and 
3b mounted on the side of the front and the rear wheels as indicated in 
step 80. As already mentioned, the vehicle's height sensors 3a and 3b are 
mounted one each at respective positions in a diagonal line to the front 
and the rear wheels 7 as shown in FIG. 4, or they are mounted two each, 
i.e. four in total at the respective positions of the front and the rear 
wheels 7 as shown in FIG. 5. This description will now be made with 
reference to the case where the vehicle's height sensors are disposed as 
shown in FIG. 4. 
Although the vehicle's height sensors may detect the distance, divided into 
some levels or stages, between the vehicle's body 1 and the vehicle's 
wheel axle 30, it is now assumed for convenience's sake that the vehicle's 
height sensors output a logic "high" (H) signal when the level of the 
vehicle's body 1 is higher than a normal level while they output a logic 
"low" (L) signal when the level of the vehicle's body 1 is lower than the 
normal level. In a usual change of the load weight due to passengers 
getting on or off the vehicle, it is assumed that both of the vehicle's 
height sensors output H or L signal, or either of them output H or L 
signal. 
The logic output of the vehicle's height sensors 3a, and 3b in the above 
noted normal condition serves to initiate the vehicle height control to 
restore the vehicle's height to the normal level. However, since the 
vehicle's body 1 is rolled during the turning, the vehicle's height 
sensors output H or L signal as indicated above in spite of no change of 
the load weight. Namely, in FIG. 4, turning to the right, the vehicle's 
body 1 is inclined to the left due to the centrifugal force whereby the 
front and the rear sensors 3a and 3b respectively output H and L signals. 
Conversely, turning to the left, the vehicle's body 1 is inclined to the 
right whereby the sensors 3a and 3b respectively output L and H signals. 
Therefore, by the comparison of the outputs of the front and the rear 
vehicle's height sensors 3a and 3b, it can be determined which side (right 
or left) of the vehicle's body 1 is rolled (step 81). 
Thus, if it is determined at step 74 that the steering angular velocity 
exceeds the threshold value and if it is determined at step 81 from the 
information of the vehicle's height sensors 3a and 3b that the vehicle's 
body 1 is rolled, this state is stored for example, by storing a roll flag 
in the memory 43 in step 82. 
On the other hand, if it is determined in step 74 that the steering angular 
velocity is lower than the threshold value, it is then determined in step 
75 with reference to the state of the memory 43 whether or not the 
vehicle's body 1 is now being rolled as mentioned above. If it is being 
rolled, it is then determined in steps 76-78 whether or not the rolling 
has been completed. Namely, the completion of the rolling is determined in 
step 79 to reset the memory 43, by meeting at least one of the 
requirements that the outputs of the vehicle's height sensors have 
indicated the state free from rolling (step 76), the steering wheel 8 has 
returned to the normal position (step 77), and the vehicle speed has 
become 0 Km/h (step 78). If none of the above requirements are met, it is 
determined that the vehicle's body 1 is still being rolled, and the memory 
43 which has already stored the state of rolling in step 82 stores this 
state indicating the rolling, in step 83. It is to be noted that step 76 
corresponds to the combination of steps 80 and 81. It is also to be noted 
that the significance of the memory 43 resides in determining whether or 
not the rolling has ceased. 
Then in step 84, the determination of the initiation of the vehicle height 
control is carried out from the information of the vehicle's height 
sensors 3a and 3b, and if the vehicle height control is found to be 
necessary in step 85, it is then determined in step 86 from the output of 
the speed sensor 13 whether the vehicle is running or stopped. If the 
vehicle is running, it is then determined in step 87 whether or not the 
vehicle's body 1 is now being rolled, as done in step 80. If the vehicle 
is not running (stopped) or is running but not being rolled, then the 
vehicle height control is initiated while if the vehicle is running and 
being rolled, then in step 88 the vehicle height control is inhibited 
until the completion of the rolling of the vehicle. 
Thus, it is possible to prohibit the vehicle height control with respect to 
such an apparent change or variation of the vehicle's height. Also, if 
there is a change of the vehicle's height when the rolling is completed or 
when the rolling is absent, the vehicle height control can be immediately 
done. 
The detection of the steering direction and the steering angular velocity 
may be readily made by means of a sensor which generates two pulse trains 
having a phase difference therebetween of approximately 90.degree., one 
pulse being generated per a predetermined rotation of the steering wheel, 
in which the steering direction is detected on the basis of the order of 
the pulse edges and the steering angular velocity or the steering angle in 
the rotation of the same direction is updated per the edges of the two 
pulse trains. 
As stated above, according to the present invention, from the steering 
angular velocity of a steering wheel from a steering angle sensor and the 
output information of vehicle's height sensors, that the vehicle is being 
rolled is detected in which case an unnecessary vehicle height control 
irrespective of any change of the actual load weight is avoided by 
prohibiting the vehicle height control from operating even though the 
outputs of the vehicle's height sensors indicate some deviation of the 
vehicle's height from a target level, resulting in a highly reliable 
vehicle height control system. 
It is to be noted that while the present invention has been described with 
reference to the above embodiments illustrated in the accompanying 
drawings, it should not be limited to them and may be applied with various 
modifications thereof without departing from the spirit of the invention.