Intake pipe pressure indicating system for an internal combustion engine of a vehicle

An intake pipe pressure indicating system for an internal combustion engine of a vehicle having an intake pipe including a supercharger and a throttle valve. The system comprises sensors which detect the internal pressure of the intake pipe at an upstream position and at a downstream position, respectively, with respect to the throttle valve and provides corresponding output signals. A comparator provides a logic signal based on the result of a comparison between the output signal from either of the sensors and a reference value. A selection circuit is provided which is adapted to select and to transmit and output either of the output signals on the basis of the logic signal, and a single indicator is provided which is adapted to provide an indication corresponding to the output signal of the selection circuit. The respective intake pipe pressures at the upstream position and at the downstream position with respect to the throttle valve can be selectively indicated by a single indicator in a continuous manner so that the indicator is used effectively.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to an intake pipe pressure 
indicating system for an internal combustion engine of a vehicle. More 
particularly, the invention relates to an intake pipe pressure indicating 
system for an internal combustion engine of a vehicle provided with a 
supercharger. 
2. Description of Relevant Art 
It has been known to provide an indicating system for vehicles having an 
internal combustion engine provided with a supercharger, such as a 
motorcycle provided with a turbo-supercharger, in order to indicate an 
operating state of the supercharger. Generally, the operating state of the 
supercharger is represented by a pressure within an intake pipe 
(hereinafter referred to as "intake pipe pressure") between the 
supercharger and a throttle valve disposed downstream thereof. Where the 
indicating system has a voltmeter or the like employed as an indicator for 
indicating the intake pipe pressure, the indicating pointer thereof will 
not move during the idling state of the engine in which no supercharge is 
effected and the indicator is fed with pressure signals which are too 
faint, thus causing a problem inasmuch as when the supercharge starts, the 
indicator abruptly indicates supercharged pressures. 
The present invention effectively overcomes such problem attendant the 
conventional intake pipe pressure indicating systems for an internal 
combustion engine of a vehicle. 
SUMMARY OF THE INVENTION 
The present invention provides an intake pipe pressure indicating system 
for an internal combustion engine of a vehicle including an intake pipe 
having a supercharger and a throttle valve disposed downstream of the 
supercharger. The indicating system comprises a first sensor for detecting 
an internal pressure of the intake pipe downstream of the supercharger and 
upstream of the throttle valve and providing a first signal according 
thereto, a second sensor for detecting an internal pressure of the intake 
pipe downstream of the throttle valve and providing a second signal 
according thereto, a comparator for providing a logic signal based on a 
comparison between at least either of the first and second signals and a 
predetermined reference value, a selection circuit for selecting either 
the first or second signal on the basis of the logic signal and providing 
an indication signal according thereto, and a single indicator adapted to 
receive the indication signal to thereby provide an indication according 
to the indication signal. 
It is an object of the present invention to provide an intake pipe pressure 
indicating system for an internal combustion engine of a vehicle provided 
with a supercharger, wherein intake pipe pressures upstream and downstream 
of a throttle valve disposed downstream of the supercharger can be 
continuously indicated with a signal indicator, so that the intake pipe 
pressure is indicated by means of the single indicator while ranging from 
the idling to the supercharged state of the engine. 
Another object of the present invention is to provide an intake pipe 
pressure indicating system for an internal combustion engine of a vehicle 
including a supercharger which, in addition to attaining the foregoing 
object, also provides an automatic and continuous indication of the intake 
pipe pressure downstream of the throttle valve while the engine is idling 
and upstream thereof while the engine is heavily loaded, by means of a 
single indicator. In this manner, visual recognition of the indication is 
facilitated when driving, while the vehicle space consumed by the system 
as well as the cost of the system is effectively reduced. 
A further object of the present invention is to provide an intake pipe 
pressure indicating system for an internal combustion engine of a vehicle, 
which has an indicator adapted to provide a visually comprehensible 
indication of the level of the intake pipe pressure when driving, while 
permitting a ready and instantaneous visual confirmation of the intake 
pipe pressure in combination with other parameters, such as the speed of 
travel of the vehicle, so as to thus represent the travel state of the 
vehicle and reduce mental fatigue on the part of the driver. 
The above and further objects, features and advantages of the present 
invention will become apparent from the following detailed description of 
preferred embodiments of the invention when read in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
With reference to FIG. 1, symbol S generally designates an intake system of 
an internal combustion engine of a vehicle. The intake system S, as known, 
comprises an air cleaner 1, a compressor 2, an intake pipe 3 and a 
throttle valve 4. The air taken in through a suction inlet (not shown) is 
supplied to a cylinder (not shown) of the internal combustion engine 
through the intake pipe 3 including the throttle valve 4 after being 
compressed by the compressor 2. A sensor 5 which detects the pressure of 
air compressed by the compressor 2 (supercharging pressure) is disposed 
upstream of the throttle valve 4, while a sensor 6 detecting actual supply 
pressures to the engine, i.e., the boost pressure, provided by reducing 
the supercharging pressure with the throttle valve 4, is disposed 
downstream of the throttle valve 4. 
The sensors 5 and 6 detect internal pressures within the intake pipe 3 in 
respective portions thereof in which the sensors 5 and 6 are disposed. The 
detected internal pressures are converted into electric signals a and b, 
respectively, and the electric signals a and b are applied to a fuel 
injector (not shown) of the engine to control the operation of the fuel 
injector, and are selectively applied through an electric circuit E to a 
single pressure indicator 7 comprising a voltmeter or the like which 
indicates the corresponding detected pressure. 
FIG. 3 shows output characteristics of the sensors 5 and 6, in which 
changes in the respective output voltage signals a and b with those in the 
intake pipe pressure are shown for the sensors 5 and 6. As shown, the 
output signal a of the sensor 5 changes substantially linearly with the 
absolute pressure at a comparatively small gradient, while the output 
signal b of the sensor 6, which signal b is simultaneously used as an 
input to control the engine, changes substantially linearly at a 
comparatively large gradient. It will be understood, however, that the 
sensors 5, 6 are not limited to such particular characteristics, and may 
be designed as desired. 
Referring now to FIG. 2, the electric circuit E for selectively 
transmitting either the output signal a of the sensor 5 or the output 
signal b of the sensor 6, comprises a comparator A adapted to compare the 
actual output signal b of the sensor 6 with an internal reference voltage 
signal bo of the same magnitude as an output voltage of the sensor 6 
corresponding substantially to atmospheric pressure. Electric circuit E 
further comprises a selection circuit B which selectively decides which 
signal, i.e., either the output signal a or b, is to be transmitted to be 
output as a signal S to the indicator 7 on the basis of a logic signal l 
provided by the comparator A. Also provided is an amplifier circuit C 
adapted to convert the output signal S of the selection circuit into a 
final signal f and apply the final signal f to the indicator 7. 
The comparator A includes an operation amplifier 8 and resistances 9 and 10 
forming a potentiometer for setting the reference voltage bo. The 
reference voltage bo and the output signal b of the sensor 6 are applied 
to the negative terminal (-) and the positive terminal (+), respectively, 
of the operation amplifier 8 to provide the logic signal l. The selection 
circuit B comprises a circuit 14 for transmitting the output signal b, 
including resistances 11 and 12 connected in series and grounded through a 
resistance 13, and a circuit 17 for transmitting the output signal a, 
including resistances 15 and 16 connected in series and also grounded 
through the resistance 13. The circuits 14 and 17 have grounding circuits 
18 and 19, respectively, connected between the resistances 11 and 12 and 
between the resistances 15 and 16, respectively, for shunting energy. Each 
of the grounding circuits 18 and 19 has the switching function thereof 
actuated on the basis of the logic signal l. The terminal voltage of the 
resistance 13 is then output as the output signal S. 
In the above-described arrangement, the output signals a and b as 
transmitted through the selection circuit B are adequately divided by the 
resistances 13, 16 and 12, 13, respectively, so as to cancel the 
difference in the output characteristics of the sensors 5 and 6. 
The grounding circuit 18 includes an emitter-grounded npn transistor 20 
which is adapted to receive the logic signal l at the base thereof and to 
function as a switching element, and a diode 21 connected to the collector 
of the transistor 20 and to a line connecting the resistances 11 and 12. 
The grounding circuit 19 includes an emitter-grounded npn transistor 22 as 
a switching element, the base of which is connected to the collector of 
the transistor 20 while the collector of transistor 22 is connected to a 
line connecting the resistances 15 and 16. 
The amplifier circuit C comprises an amplifier 23 which amplifies the 
signal S applied to the positive terminal (+) thereof and provides a final 
signal f. 
A terminal 15 is connected to an external power source (not shown). A 
steady DC voltage is applied to the terminal 15. 
When the output signal b is lower than the set reference voltage bo, the 
output signal l of the differential amplifier 8 is at a low level so that 
the transistor 20 is switched off and the transistor 22 is switched on. 
Consequently, the electrical energy of the output signal a of the sensor 5 
is shunted and grounded through the transistor 22, whereas the output 
signal b of the sensor 6 is amplified by the amplifier 23 and indicated by 
the indicator 7. When the level of the output signal b of the sensor 6 is 
higher than the reference voltage bo, the output signal l of the 
differential amplifier 8 is at a high level so that the transistor 20 is 
switched on and the transistor 22 is switched off. Consequently, the 
electrical energy of the output signal b of the sensor 6 is shunted and 
grounded through the transistor 20, whereas the output signal a of the 
sensor 5 is amplified by the amplifier 23 and indicated by the indicator 
7. 
It will be apparent from the foregoing description that the operating state 
of the engine, i.e., idling operation as opposed to high-load operation, 
is discriminated through comparison between the reference voltage bo, 
which is set by the resistances 9 and 10, and the output signal b of the 
sensor 6. When the engine is in an idling condition, the actual boost 
pressure is indicated by the indicator 7 on the basis of the output signal 
b of the sensor 6, whereas when the engine is in a high-load condition, 
the supercharging pressure is indicated by the indicator 7 on the basis of 
the output signal a of the sensor 5. Accordingly, the single indicator 7 
can be used effectively for indicating the intake pipe pressure in the 
overall operating range of the engine, i.e., from idling operation through 
high-load operation, because the indicator 7, which otherwise has been 
adapted to indicate the supercharging pressure, can now also indicate the 
boost pressure when the engine is in an idling condition. Further, 
although the electrical energy shunting circuits 18, 19 are controlled on 
the basis of the results of the comparison between the output signal b of 
the sensor 6 and the reference voltage bo in this embodiment, the 
electrical energy shunting circuits may alternatively be adapted to be 
controlled on the basis of the result of a comparison between the output 
signal a of the sensor 5 and another predetermined reference voltage. 
Still further, the indicator 7 is not limited to only a voltmeter, but may 
alternatively comprise another known indicator, such as an ammeter or a 
digital indicator, for example. 
Referring now to FIGS. 4 through 6 which illustrate a second embodiment of 
the invention, a motorcycle is shown as generally comprising a frame 101 
provided with front and rear wheels 102, an engine 103 disposed at an 
intermediate portion of the frame, a fuel tank 104 disposed over the 
engine 103, and a driver's seat 105 disposed behind the fuel tank 104. The 
engine 103 is provided with a turbo-supercharger 110 comprising an exhaust 
turbine 107 disposed in the exhaust pipe 106 and a compressor 109 disposed 
in the intake pipe 108. Provided in the intake pipe 108 is a prechamber 
111 after the compressor 109 and a throttle valve 112 after the prechamber 
111. 
An instrument panel 114 as shown in FIG. 6 is attached to the rear side of 
the head pipe connected to the front part of the frame 101. A bar graph 
type indicator 115 extending laterally of the instrument panel 114 is 
disposed at substantially the central part of the instrument panel 114. A 
pressure sensor 116 is disposed on one side of the intake pipe 108 at a 
downstream position with respect to the compressor 109 for detecting the 
intake pipe pressure. An output signal of the pressure sensor 116 is 
transmitted to the indicator 115 through an electronic controller 117 and 
indicated by the indicator 115 in a stepped pattern which extends in steps 
from the central part of the indicator 115 toward the opposite ends of the 
indicator 115 in a band expansion manner corresponding to the increase of 
the intake pipe pressure. A low-pass filter 118 is connected to the output 
side of the pressure sensor 116. The indicator 115 may be of a liquid 
crystal type, light emission diode type or discharge tube type. The width 
of the bright strip-shaped indicating pattern increases gradually with the 
increase of the intake pipe pressure from a width d.sub.1 as a negative 
intake pressure zone, through a width d.sub.2 as a moderate intake 
pressure zone to a width d.sub.3 as a high intake pressure zone. A width 
d.sub.4 indicates the "red" or warning zone. 
The instrument panel 114 is designed to have substantially a trapezoidal 
shape and is tilted substantially forwardly. The indicator 115 is disposed 
at the upper part of the central portion of the instrument panel 114. A 
tachometer 119 and a speedometer 120 are disposed adjacent to the 
indicator 115 on the respective sides thereof. Also provided is a fuel 
gauge 121, a temperature gauge 122 and a clock 123, respectively. 
In the above-described second embodiment, only a single pressure sensor 116 
is shown for ease of explanation. However, it will be understood that 
another pressure sensor may be provided at an upstream position with 
respect to the throttle valve 112 as is the case in the first embodiment. 
The system may then be arranged so as to selectively indicate the 
respective output signals of the two pressure sensors in a continuous 
manner by the indicator 115 corresponding to the operating condition of 
the engine, i.e., idling operation or high-load operation, after 
processing the output signals of such pressure sensors through the 
electronic controller 117. 
Although there have been described what are at present considered to be the 
preferred embodiments of the invention, it will be understood that the 
invention may be embodied in other specific forms without departing from 
the spirit or essential characteristics thereof. The present embodiments 
are therefore to be considered in all respects as illustrative, and not 
restrictive. The scope of the invention is indicated by the appended 
claims rather than by the foregoing description.