Idling rotational speed control system for a diesel engine

A diesel engine control system comprises an engine speed circuit for controlling the engine so that the rotational speed of the engine when idling is at least the required minimum rotational speed suited to the determined engine speed, engine temperature, and battery condition. Thereby, the engine control system makes it possible to control the rotational speed of the engine automatically when idling without manual operation.

DETAILED DESCRIPTION OF THE PRESENT INVENTION 
The present invention relates to a rotational speed control system for a 
diesel engine, and more particularly to a diesel engine control system 
capable of automatically controlling the rotational speed of the engine at 
the time of idling. 
In the prior art, in a vehicle in which a diesel engine is mounted, for 
instance, to warm up the engine when it is idling, the driver manually 
operates a control lever connected to a fast idle mechanism to increase 
the fuel supplied to the engine by a fuel injection pump, thereby stepping 
up the rotational speed of the engine. 
However, the manual operation of the control lever is trouble-some. 
Further, it is very difficult to precisely step up the rotational speed of 
the engine to the predetermined rotational speed required when idling on 
the basis of the driver's own judgement. 
While the engine is idling, it happens frequently that it is necessary to 
operate an accessory, such as an air conditioner which consumes a lot of 
power. Further, it may happen that idling of the engine is required when 
the battery voltage is below a predetermined level. In either case, it is 
necessary to increase the rotational speed of the engine. However, the 
conventional rotational control system makes it necessary to operate the 
lever manually or continue to press the accelerator pedal. 
SUMMARY OF THE INVENTION 
With the above in mind, an object of the invention is to provide a 
rotational speed control system for a diesel engine which makes it 
possible to automatically control the engine so that the determined 
rotational speed becomes the predetermined idling speed setting value, for 
instance, in the case of warming the engine by idling. 
Another object of the invention is to provide a rotational speed control 
system for a diesel engine which, when the engine is idling and the engine 
temperature or the battery condition is abnormal, makes it possible to 
control the engine so that the rotational speed of the engine becomes the 
predetermined speed. 
A further object of the invention is to provide a rotational speed control 
system for a diesel engine which eliminates manual operation relying on 
the driver's judgement, thereby making it possible to precisely step up 
the rotational speed of the engine to the predetermined idling speed. 
A still further object of the invention is to provide a rotational speed 
control system for a diesel engine which makes it possible to shorten the 
time required for warming-up, and prevent excessive discharge of the 
battery, or overheating of the engine.

In these drawings, the same reference numerals indicate the same or similar 
elements of the rotational speed control system for a diesel engine 
according to the present invention. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the present invention will now be described in 
detail, for the purposes of explanation. 
Referring to FIG. 1, reference numeral 1 denotes an engine rotational speed 
sensor which senses the rotational speed of an engine (not shown) to 
produce a signal S.sub.1 corresponding to the rotational speed of the 
engine. The engine rotational speed sensor 1 includes a pulse generator 11 
comprising as best shown in FIG. 2, a light source 11a, a photocell 11b, 
and an injection pump pulley 11c which is disposed between the light 
source 11a and the photocell 11b and rotates in synchronism with the 
engine. Slits 11d are formed in the injection pump pulley 11c. The pulse 
signal generator further comprises a wave shaping circuit 12 which 
suitably shapes the pulse signal outputted from the photo receiving 
element 11b to produce the desired rectangular waveform, and an 
integration circuit 13 which converts the output of the wave shaping 
circuit 12 into a voltage corresponding to the frequency of the signal. 
In practice, the rotational speed of the injection pump pulley 11c may be 
set to, for example, one half of that of the engine. 
Reference numeral 2 denotes a temperature sensor which senses the 
temperatures of the oil or water in the engine. The temperature sensor 2 
comprises a water temperature sensor 21, such as a thermistor, which 
detects the temperature of cooling water of the engine, a cold condition 
detecting circuit 22 producing an output signal S.sub.2 when the water 
temperature is below 20.degree. C., and an overheating condition detecting 
circuit 23 producing an output signal S.sub.3 when the water temperature 
is above 110.degree. C., and an OR gate 24 connected to the outputs of the 
cold condition detecting circuit 22 and the overheating condition 
detecting circuit 23. In place of or in addition to the water temperature 
sensor 21, an oil temperature sensor may be used to sense the temperature 
of the engine oil. 
Reference numeral 4 denotes a battery condition sensor which senses the 
voltage of a battery 3 and the load condition of the battery 3. The 
battery condition sensor circuit 4 comprises a battery voltage sensing 
circuit 41 producing an output signal when the output voltage of the 
battery 3 is below 10 V, and an air conditioner operation detector 42 
producing an output signal S.sub.5 when the air conditioner is switched 
on, and an OR gate connected to the outputs of the battery voltage sensing 
circuit 41 and the air conditioner detector 42. 
Reference numeral 5 denotes a reference speed setting circuit producing an 
output signal S.sub.6 for setting the rotational speed of the engine when 
idling in normal conditions. Reference numeral 6 denotes an engine speed 
setting circuit which determines on the basis of input signals, a required 
engine speed if this engine speed is above a predetermined minimum. These 
input signals are: the output signal S.sub.1 of the engine speed sensor 1, 
the output signals S.sub.2 and S.sub.3 of the temperature sensor 2, the 
output signals S.sub.4 and S.sub.5 of the battery condition sensor 3, and 
the output signal S.sub.6 of the reference rotational speed setting 
circuit 5. 
The engine rotational speed setting circuit 6 comprises a decision circuit 
61 producing an output signal So of which the value is determined on the 
basis of the input signals S.sub.1 to S.sub.6, a rectangular wave 
generator 63 producing a rectangular wave signal of which the frequency is 
40 Hz, and a duty factor control circuit 62 responsive to the output 
signal So to change the duty factor of the rectangular wave signal 
inputted from the rectangular wave generator 63. More particularly, the 
decision circuit 61 has three actions. The first is to set the value of 
the output signal S.sub.0 so that the rotational speed of the engine is at 
least 1,200 r.p.m. when the input signal S.sub.2 or S.sub.3 is inputted 
thereto. The second is to set the value of the output signal S.sub.0 so 
that the rotational speed of the engine is at least 900 r.p.m. when the 
input signal S.sub.4 or S.sub.5 is inputted thereto. The third is to set 
the value of the output signal S.sub.0 so that the rotational speed of the 
engine is 650 r.p.m. 
Referring to FIG. 2, reference numeral 7 denotes a driving means controlled 
by the pulse signal P.sub.0 outputted from the engine speed setting 
circuit 6, which actuates a control lever 10 of a fuel injection pump not 
shown. 
More particularly, the driving means 7 comprises a control valve consisting 
of a regulating pressure control valve 71 to which a vacuum pressure is 
supplied, and a duty factor control solenoid valve 72 which controls an 
output vacuum by varying the ratio between the constant vacuum pressure 
regulated by the regulating control valve 71 and air in accordance with 
the duty factor of the pulse signal P.sub.0. 
The driving means 7 further comprises an actuator 73 which becomes 
operative in accordance with a stroke corresponding to the output vacuum 
from the control valve 7 to actuate the control lever 10. 
In the regulating pressure control valve 71, reference numeral 71a denotes 
a diaphragm, 71b a valve provided in the diaphragm 71a so as to face the 
opening of a pipe 8a to communicate with a vacuum pump 8, 71c a spring for 
biasing the diaphragm 71a downwardly, and 71d an opening exposed to air. 
In the duty factor control solenoid valve 72, reference numeral 72a denotes 
a diaphragm, 72b a solenoid, 72c a spring for biasing the diaphragm 72a 
upward so as to open the valve 72e, 72d a plunger fixed on the valve 72e 
mounted in the diaphragm 72a, and 72f an opening exposed to air. 
The actuator 73 comprises a diaphragm 73a, a spring 73b for biasing the 
diaphragm 73a upwardly and a driving rod 73c one end of which is fixed to 
the diaphragm 73a while the other end is fixed to the control lever 10. 
The vacuum pump 8 is driven together with a generator 9 by the engine. 
FIG. 3 shows a graph illustrating a relationship between a duty factor 
(pulse width/period) of the pulse signal P.sub.0 and a vacuum pressure 
supplied to the actuator 73. 
The operation of the preferred embodiment of the present invention will now 
be described. 
Reference is first made to the case where the engine temperature and 
battery conditions are normal. 
When the engine is started, and is idling, the pulley 11c shown in FIG. 2 
rotates in synchronism with the engine. Then, light emitted from the light 
source 11a is intermittently interrupted by the rotating slit 11d. The 
photocell 11b receives the beam to produce a pulse train having a 
frequency proportional to the speed of the engine. The pulse train signal 
is converted into a rectangular pulse by a wave shaping circuit 12 shown 
in FIG. 1, and then the rectangular pulse is inputted to an integration 
circuit 13. The integration circuit 13 changes the frequency of the 
rectangular pulse signal into a corresponding voltage to supply the 
decision circuit 61 with an output signal S.sub.1 corresponding to the 
speed of the engine. 
The decision circuit 61 compares this signal S.sub.1 with a signal S.sub.6 
outputted from the reference speed setting circuit 5 to feed an output 
signal S.sub.0 to the duty factor control circuit 62 so that the 
rotational speed of the engine is maintained at about 650 r.p.m. In this 
duty factor control circuit 62, control is effected by the signal S.sub.0 
so that the duty factor of a rectangular pulse having a frequency of 40 Hz 
is inputted from the oscillator 63 is zero. Thus, a zero duty factor pulse 
signal P.sub.0 is supplied to the solenoid 72b of the duty factor control 
solenoid valve 72 shown in FIG. 2. 
The solenoid 72b is not rendered operative by a signal of which the duty 
factor is zero. Accordingly, the diaphragm 72a of the solenoid valve 72 is 
held at the upper position by the force of the spring 72c. The valve 72e 
is positioned away from the opening 71e of the constant pressure control 
valve 71. Accordingly, although the regulated vacuum pressure (about 300 
mmHg) is supplied from the vacuum pump 8 to the solenoid valve 72 and 
regulated by the regulating pressure control valve 71 comprising the 
spring 71c and the valve 71b provided in the diaphragm 71a, the chamber of 
the solenoid valve 72 is substantially open to the atmosphere through the 
opening 72f. As is clear from FIG. 3, the vacuum pressure is not supplied 
to the actuator 73. As a result, the diaphragm 73a of the actuator 73 is 
held at the upper position by the force of the spring 73b. Accordingly, 
the driving rod 73c does not render the control lever 10 operative. The 
fuel injection pump continues to supply a predetermined amount of fuel 
into the engine, with the result that the engine idles at 650 r.p.m. 
Meanwhile, if when idling the temperature measured by the temperature 
sensor 21 is below 20.degree. C., the cold condition detecting circuit 22 
produces an output signal S.sub.2. On the other hand, if the temperature 
measured by the sensor 21 is above 110.degree. C., the overheating 
detecting circuit 23 produces an output signal S.sub.3. Both outputs 
S.sub.2 and S.sub.3 are supplied to the decision circuit 61 through an OR 
gate 24. 
The decision circuit 61 changes the output signal S.sub.0 in response to 
the signals S.sub.2 or S.sub.3 so that the rotational speed of the engine 
is, for instance, at least 1,200 r.p.m. The duty control circuit 62 
controls the duty factor of the 40 Hz rectangular pulse signal in 
accordance with the signal S.sub.0 to feed a pulse signal P.sub.0 to the 
duty control solenoid valve 72. 
The solenoid 72b of the duty control solenoid valve 72 is energized by this 
pulse signal P.sub.0, thereby pressing down the plunger 72d against the 
force of the spring 72c. 
Accordingly, the valve 72e provided at the end of the plunger 72d moves 
toward the opening 71e of the regulating control valve 71 so as to cover 
it. As a result, the vacuum pressure is substantially all supplied to the 
actuator 73. As a result, the diaphragm 73a of the actuator 73 is pulled 
down against the compression force of the spring 73b. Thereby, the driving 
rod 73c fixed to the diaphragm 73a is drawn downward to move the control 
lever clockwise by a predetermined amount. As a result, the opening angle 
of the control lever 10 is varied. Accordingly, the amount of fuel 
supplied to the engine from the fuel injection pump increases, so that the 
engine rotates at at least 1,200 r.p.m. 
Thus, even when the engine is cold, the engine speed is maintained at 1,200 
r.p.m., and stalling is prevented, thereby making it possible to effect 
warm-up. On the other hand, if the engine should be idling while in an 
overheated condition, the speed of the engine is increased by the change 
in the engine speed setting signal, thereby increasing the cooling effect 
of a cooling fan which rotates in synchronism with the engine, to increase 
heat radiation from the engine. 
Thus, once the engine is warmed up (20.degree. C.-110.degree. C.), the cold 
condition detecting circuit 22 or the overheating condition detecting 
circuit 23 stops outputting the signal S.sub.2 or S.sub.3. Accordingly, 
the decision circuit 61 changes the output signal S.sub.0 so that the 
rotational speed of the engine is lowered to reach a value equal to about 
650 r.p.m. 
The duty factor of the output signal P.sub.0 of the duty factor control 
circuit 62 becomes zero, whereby the control lever returns to an initial 
position. Thus, the engine speed is maintained at the predetermined value 
for idling. 
The operation of the engine will now be discussed in the case when the 
condition of the battery fitted to the vehicle is abnormal. 
If the output voltage of the battery 3 becomes lower than 10 V or if an air 
conditioner whose power dissipation is large is switched on, the low 
voltage detecting circuit 41 or the air conditioner operation detecting 
circuit 42 feeds a signal S.sub.4 or S.sub.5 to the decision circuit 61 
through an OR gate 43. The decision circuit 61 changes the output signal 
S.sub.0 so that the engine rotates at a speed of at least, for example, 
900 r.p.m. in response to the signal S.sub.4 or S.sub.5. The duty factor 
control circuit 62 controls the duty factor of the 40 Hz rectangular wave 
pulse signal inputted from the oscillator 63 in accordance with the signal 
S.sub.0 so that the duty factor comes to a predetermined value, and 
outputs a corresponding pulse signal P.sub.0 to the solenoid valve 72. 
Thereby, in a similar way to the preceding case, the solenoid valve 72 
feeds a vacuum pressure dependent on the duty factor of the pulse signal 
P.sub.0 to the actuator 73. As a result, the driving rod 73c of the 
actuator 73 is drawn downward by an amount corresponding to the vacuum 
pressure. Thereby, the control lever 10 is rotated clockwise to increase 
the amount of fuel being injected into the engine from the fuel injection 
pump so that the engine rotates at a speed of at least 900 r.p.m. 
As is clear from the foregoing description, when the output voltage of the 
battery 3 goes below 10 V, or when an air-conditioner whose power 
dissipation is large is switched on, the engine rotates at at least 900 
r.p.m. Because of this, the power generated by the generator 9 increases, 
thereby to compensate the battery voltage. 
When the air-conditioner is stopped or the battery is sufficiently charged 
up, the low voltage detecting circuit 41 or the air-conditioner operation 
detecting circuit 42 stops outputting signal S.sub.4 or S.sub.5. As a 
result, the engine returns to normal idling at about 650 r.p.m. 
It is to be noted here that an electric motor may be used as the driving 
means 7 of the above embodiment. Also, of course, the various 
predetermined rotational speeds of the engine are not limited to those in 
the above description but may be set according to the requirements of 
various vehicles. 
As seen from the preferred embodiment of the present invention, the 
rotational speed control device for a diesel engine is constituted so as 
to automatically control the rotational speed in accordance with the 
temperature condition of the engine and the condition of the battery. 
Accordingly, the control device according to the present invention makes 
it possible to eliminate manual operation depending on the driver's 
judgement, whereby the diesel engine is controlled at predetermined idling 
speeds. As a result, this device is advantageous in making warming-up 
easy, preventing excessive discharge of the battery, and preventing 
overheating of the engine or stalling. 
While the present invention has been particularly shown and described with 
reference to preferred embodiments thereof, it will be understood by those 
skilled in the art that the foregoing and other changes in form and 
details may be made therein without departing from the spirit and scope of 
the invention.