Method and apparatus for sensing air pressure in pneumatic suspension units for vehicles

A method and apparatus for sensing air pressure in pneumatic suspension units for a vehicle, such as a motorcycle, comprising: air pressure sensors capable of sensing air pressures in pneumatic suspension units to generate an output signal when the air pressures are below a predetermined level; a vehicle speed sensor capable of sensing vehicle speed to generate an output signal when the vehicle speed exceeds a predetermined level; a signal processor adapted to receive output signals from the pressure sensors and the vehicle speed sensor and generate an output when the air pressures in the pneumatic suspension units are below a predetermined level while the vehicle speed continues to be in excess of a predetermined level for more than a predetermined period of time. An indicating device produces an indicating signal when it receives an output signal from the signal processor.

FIELD OF THE INVENTION 
The present invention relates to a method and a device for sensing air 
pressure in pneumatic suspension units for vehicles. The method and device 
are applicable to motorcycles whose front and rear wheels are suspended by 
front and rear pneumatic suspension units operated independently of each 
other and when the air pressure in the air suspension units is lowered 
below a definite level, the device can produce an indicating signal for 
the rider. 
DESCRIPTION OF THE PRIOR ART 
When a motorcycle is stopped on the road, the rider keeps it standing with 
his feet touching the ground. In such a case, the weight on the motorcycle 
is naturally less than that in the case where the motorcycle is traveling 
on the road with the rider's feet on the foot-rests. 
A suitable air pressure in a pneumatic suspension unit should be determined 
taking the total weight on the motorcycle into consideration. Therefore, 
it is, in many cases, not proper to detect the air pressure in a pneumatic 
suspension unit when the motorcycle is stopped with the rider's feet 
touching the ground, and to assess whether the detected value is suitable 
or not. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a method and device for 
sensing air pressure in pneumatic suspension units for vehicles, which 
permits sensing air pressure in a pneumatic suspension unit which 
continues to be below a predetermined level for more than a predetermined 
period of time while the vehicle is running at a speed higher than a 
predetermined speed, and immediately informing the rider or driver of the 
vehicle of such air pressure in the pneumatic suspension unit. 
Another object of the present invention is to provide a method and device 
for sensing air pressure in a pneumatic suspension unit for vehicles, 
which permits sensing air pressures in front and rear pneumatic suspension 
units only when the vehicle is running with the total weight thereon 
applied to the vehicle, determining whether the air pressures are less 
than a definite level, and actuating an indicating device when the air 
pressures are less than said definite level. 
To these ends, the present invention contemplates a device for sensing air 
pressure in pneumatic suspension units for vehicles, comprising: air 
pressure sensors capable of sensing air pressure in pneumatic suspension 
units to generate an output signal when the air pressures are below a 
predetermined level; a vehicle speed sensor capable of sensing vehicle 
speed to generate an output signal when the speed exceeds a predetermined 
level; a signal processor adapted to receive output signals from the air 
pressure sensors and the vehicle speed sensor to generate an output when 
the air pressures in the pneumatic suspension units are below a 
predetermined level while the vehicle speed continues to exceed a 
predetermined level for more than a predetermined period of time; and an 
indicating device adapted to receive an output signal from the signal 
processor to give an indication of air pressure below said predetermined 
level. 
The above and other objects, features and advantages of the invention will 
become apparent from the following description of the preferred 
embodiments taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Several embodiments of the present invention will be described with 
reference to the accompanying drawings. 
Referring to FIGS. 1-5, a motorcycle M has front and rear wheels Wf, Wr 
which are suspended from a frame F of the motorcycle M via front and rear 
pneumatic suspension units Sf,Sr, respectively. The front pneumatic 
suspension unit Sf is provided with a first air pressure sensor S.sub.1 
capable of sensing the air pressure therein, and the rear pneumatic 
suspension unit Sr is provided with a second air pressure sensor S.sub.2 
capable of sensing the air pressure therein. A speedometer Ms of the 
motorcycle M is incorporated with a vehicle speed sensor Ss (See FIG. 3). 
The rear pneumatic suspension unit Sr comprises two buffer air cylinders 
Sr.sub.1, Sr.sub.2 which are connected to the second air pressure sensor 
S.sub.2 via communication conduits C.sub.1, C.sub.2, respectively, as 
shown in FIG. 2. The second air pressure sensor S.sub.2 is connected via a 
line C.sub.3 to a signal processor 13 which will be described later. 
Each of the first and second air pressure sensors S.sub.1, S.sub.2 
comprises a pressure switch, and is adapted to generate an output signal 
of a high level when the air pressure sensed is higher than a 
predetermined level. The relation between output levels of these air 
pressure sensors S.sub.1,S.sub.2 and variations in air pressures is shown 
in the following table. 
TABLE 1 
______________________________________ 
Output level of air pressure 
Air pressure sensors 
______________________________________ 
Not less than 
predetermined level 
High 
Lower than 
predetermined level 
Low 
______________________________________ 
The vehicle speed sensor Ss, which is shown in FIGS. 3,4, includes a 
speedometer Ms, an oscillatory plate 2 oscillated in accordance with the 
movement of a shaft 1 of a pointer of the speedometer Ms, a photoelectric 
means 3 mounted close to a peripheral portion of the oscillatory plate 2, 
and an inverter circuit 4 for inverting the output from the photoelectric 
means 3. The oscillatory plate 2 has a recess 5 in a peripheral portion 
thereof which has an angular extent corresponding to a certain angle of 
oscillation in turn corresponding to a certain range of vehicle speeds 
less than a predetermined value (for example, 16 km/h). The photoelectric 
means 3 is provided with a light emitter 6 and a light receiver 7. The 
photoelectric means 3 is adapted such that, when the vehicle speed is less 
than a predetermined level, the light from the light emitter 6 passes 
through the recess 5 to reach the light receiver 7, and when the vehicle 
speed is greater than a predetermined level, the light from the emitter 6 
is intercepted by a non-recessed section of a peripheral portion of the 
oscillatory plate 2 due to the oscillation thereof in accordance with an 
increase in the vehicle speed so that the light does not reach the light 
receiver 7. When the light from the light emitter 6 does not reach the 
light receiver 7, the output from the photoelectric means 3 is at a low 
level so that a signal of high level is produced at the output of inverter 
circuit 4 which indicates that the vehicle speed is not less than a 
predetermined level. 
The relation between the level of the output from the inverter circuit 4, 
i.e. the level of the output from the vehicle speed sensor Ss and 
variations in the vehicle speed is shown in the following table. 
TABLE 2 
______________________________________ 
Output level of vehicle 
Vehicle speed speed sensor 
______________________________________ 
Lower than 
predetermined level 
Low 
Not less than 
predetermined level 
High 
______________________________________ 
Referring to FIG. 5, output signals from the first and second pressure 
sensors S.sub.1, S.sub.2 are fed to the inputs of a first AND circuit 8, 
and the output signal from the first AND circuit 8 is inverted in an 
inverter 9, and fed to a second AND circuit 10 together with the output 
signal from the vehicle speed sensor Ss. The output signal from the second 
AND circuit 10 is fed to the input of a timer circuit 11. An output signal 
produced by the timer circuit 11 causes an alarm or indicating device 12 
to be actuated. The indicating device 12 comprises a lamp or a buzzer, 
which is mounted in the dashboard on the motorcycle M. 
The first and second AND circuits 8, 10, inverter 9, and timer circuit 11 
constitute the signal processor 13 of the present invention. Reference 
numeral 14 denotes a main switch, and 15 a battery to complete the 
circuit. 
The operation of the above embodiment will be described hereinafter. 
First, the main switch 14 is closed. 
When the vehicle speed is below a predetermined level, the output from the 
vehicle speed sensor Ss is at a low level. Accordingly, the output from 
the second AND circuit 10 is at a low level so that the indicating device 
12 is not actuated irrespective of the output levels of the first and 
second pressure sensors S.sub.1, S.sub.2. 
When both of the air pressures in the front and rear pneumatic suspension 
units Sf, Sr are not less than a predetermined level, both of the outputs 
from the first and second air pressure sensors S.sub.1, S.sub.2 are at a 
high level. Accordingly, the output from the first AND circuit 8, into 
which the outputs from the first and second air pressure sensors S.sub.1, 
S.sub.2 are fed, is at a high level. Since the output from the first AND 
circuit 8 is inverted by the inverter 9 to a low level, the output from 
the second AND circuit 10 is a low level. Therefore, the indicating device 
12 is not actuated irrespective of the output level of the vehicle speed 
sensor Ss. 
When the vehicle speed exceeds a predetermined level and the air pressure 
in one or both of the front and rear pneumatic suspension units Sf, Sr is 
below a predetermined level, the output of the vehicle speed sensor Ss is 
at a high level, and the output from one or both of the first and second 
air pressure sensors S.sub.1, S.sub.2 is at a low level. Therefore, an 
output signal of a low level is generated in the first AND circuit 8, and 
an output at a high level is produced by the inverter 9. The output of 
high level from the inverter 9 and the output of high level from the 
vehicle speed sensor Ss are simultaneously fed to the second AND circuit 
10 so that an output of high level is generated therein. The output of 
high level from the second AND circuit 10 causes the timer circuit 11 to 
be energized. After a certain period of time (for example, 6 seconds) has 
elapsed, an output of high level generated in the timer circuit 11 will 
actuate the indicating device 12. 
For example, when the motorcycle is running on a bumpy road, the air 
pressures in the first and second pneumatic suspension units Sf, Sr, which 
are generally kept not less than a predetermined level, are momentarily 
lowered below a predetermined level due to the buffer effect of these 
suspension units Sf, Sr thereby to cause the second AND circuit 10 to 
generate an output of high level which is fed into the timer circuit 11. 
However, this input time is too short to exceed the delayed time set by 
the timer circuit 11 so that the output from the timer circuit 11 remains 
at a low level. Accordingly, the indicating device 12 is not actuated. 
FIG. 6 shows another embodiment of the present invention, in which the same 
reference numerals and symbols are used for the parts corresponding to 
those of the first embodiment. 
When the main switch 14 is closed, the light emitted from the light emitter 
6 reaches the light receiver 7 (in the case where the vehicle speed is 
lower than a predetermined level) so that transistors Q.sub.1, Q.sub.2 are 
saturated. As a result, a transistor Q.sub.3 is cut off. An electric 
current flows to the base of a transistor Q.sub.4 through a resistor 
R.sub.1 to saturate the transistor Q.sub.4 and allow the output of the 
vehicle speed sensor to be grounded. Consequently, an output signal of low 
level is generated in the vehicle speed sensor Ss. 
In the meantime, a capacitor C.sub.1 in the signal processor 13 begins to 
be charged due to a resistor R.sub.3 connected therein. However, the 
voltage of the capacitor C.sub.1 does not reach a predetermined level 
until a predetermined period of time has elapsed, so that the base 
potential of a transistor Q.sub.5 is not sufficiently low. Accordingly, 
transistors Q.sub.5, Q.sub.6 are kept cut off, to allow a transistor 
Q.sub.7 to be saturated. Thus, an electric current flows to the indicating 
device 12. 
When a predetermined period of time has elapsed after the capacitor C.sub.1 
begins to be charged, the base potential of the transistor Q.sub.5 is 
suffieiently lowered so that the transistor Q.sub.5 is saturated. Then, an 
electric current flows to a capacitor C.sub.2 through a resistor R.sub.8, 
transistor Q.sub.5 and resistor R.sub.4 to start charging the capacitor 
C.sub.2. The electric current further flows to the base of the transistor 
Q.sub.6 through the resistor R.sub.5 so that the base potential thereof is 
increased to saturate the transistor Q.sub.6. As a result, the base 
potential of the transistor Q.sub.7 is lowered to cut off the transistor 
Q.sub.7, and an electric current does not flow to the indicating device 
12. Thus, the indicating device stops giving an indication. 
By virtue of the above-described structure, an electric current is 
automatically supplied to the indicating device 12 for only a 
predetermined period of time after the main switch 14 has been closed. 
Therefore, faults in the indicating device 12 and the circuit for 
actuating the indicating device 12 can be detected each time the main 
switch 14 is operated. 
When the vehicle speed exceeds a predetermined level, the light from the 
light emitter 6 is intercepted or does not reach the light receiver 7 so 
that the transistors Q.sub.1, Q.sub.2 are cut off. As a result, an 
electric current flows to the base of the transistor Q.sub.3 through a 
resistor R.sub.0 to increase the base potential of the transistor Q.sub.3. 
Thus, the transistor Q.sub.3 is saturated. Consequently, the base 
potential of the transistor Q.sub.4 is lowered so that the transistor 
Q.sub.4 is cut off to allow an output of high level to be generated in the 
vehicle speed sensor Ss. 
When the air pressures in the front and rear pneumatic suspension units Sf, 
Sr are above a predetermined level and the switches for the first and 
second air pressure sensors S.sub.1, S.sub.2 are closed, the base 
potential of the transistor Q.sub.5 is kept at a low level so that the 
transistor Q.sub.7 is cut off. Consequently, an electric current does not 
flow to the indicating device 12. 
When the air pressure in one or both of the front and rear pneumatic 
suspension units Sf, Sr is less than a predetermined level with the switch 
for one or both of the first and second air pressure sensors S.sub.1, 
S.sub.2 opened, in the circumstance that the vehicle speed exceeds a 
predetermined level with the output signal from the vehicle speed sensor 
Ss at a high level, the capacitor C.sub.1 starts discharging through the 
resistors R.sub.2, R.sub.3. After a predetermined period of time has 
elapsed, the base potential of the transistor Q.sub.5 is increased so that 
the transistor Q.sub.5 is cut off. As a result, the capacitor C.sub.2 
starts discharging through the resistors R.sub.5, R.sub.6. When the base 
potential of the transistor Q.sub.6 is lowered, the transistor Q.sub.6 is 
cut off so that an electric current flows to the base of the transistor 
Q.sub.7 through a resistor R.sub.7. When the base potential of the 
transistor Q.sub.7 is thus increased, the transistor Q.sub.7 is saturated. 
As a consequence, an electric current flows to the indicating device 12 to 
energize the same to provide an indication. 
In the above embodiments, the outputs from the first and second air 
pressure sensors S.sub.1, S.sub.2 are fed to the signal processor 13. 
However, one of the air pressure sensors S.sub.1, S.sub.2 may be omitted. 
Namely, the output from only one of the air pressure sensors S.sub.1, 
S.sub.2 may be fed to the signal processor 13. 
As has been described in detail above, the present invention permits 
actuating the indicating device to give an indication when the air 
pressures in the pneumatic suspension units are lower than a predetermined 
level with the vehicle speed continuing to exceed a predetermined level 
for more than a predetermined period of time. Namely, the present 
invention contemplates sensing the air pressures in the pneumatic 
suspension units and if they continue to be below a level in a 
predetermined range while the vehicle is running at a speed in excess of a 
predetermined level, this condition is conveyed to the rider or driver. 
Therefore, the rider or driver is immediately informed of the necessity of 
repairing the pneumatic suspension units. In fact, the device according to 
the present invention is very useful to maintain the shock absorbing 
functions of the pneumatic suspension units in a normal condition. 
Moreover, the indicating device is not actuated in response to a momentary 
decrease in air pressure in the pneumatic suspension units which occurs 
while the vehicle is traveling, for example, on a bumpy road. In other 
words, the indicating device can be prevented from being erroneously 
actuated. 
Since the signal processor provided in the device according to the present 
invention has a fault-checking circuit which permits automatically 
supplying electric current to the indicating device for a predetermined 
period of time when starting the signal processor, faults in the 
indicating device and the circuit for actuating the indicating device can 
be checked each time the main switch is operated. 
Since the indicating device is adapted to be actuated when the vehicle 
speed is in excess of a predetermined value with the air pressure in one 
or both of the front and rear pneumatic suspension units continuing to be 
below a predetermined level for more than a predetermined period of time, 
suitable air pressures in the front and rear pneumatic suspension units 
can be accurately checked while the vehicle is running on a road with the 
total weight thereon acting on the vehicle. Moreover, the device according 
to the present invention prevents the indicating device from being 
erroneously actuated even when variations in air pressures in the 
pneumatic suspension units occur due to shock absorbing actions thereof 
while the vehicle is running on the road. 
The present invention is not, of course, limited to the above-described 
embodiments and it may be modified in various ways withing the scope of 
the appended claims.