Fuel injection system electromagnetic-valve controlled type

In a fuel injection system for an engine, a first controller calculates circuit rotational angle of a crankshaft on the basis of reference pulses and scale pulses from a detector for detecting rotation of the crankshaft. The first controller outputs a drive pulse representative of a closing command moving an electromagnetic valve to a closed position, at a timing with reference to the current rotational angle, to control a period, within which the valve is in the closed position, during forward stroke of a plunger. A second controller intermittently outputs drive pulses representative of the closing command, at an initial stage of engine start-up, independently of the crankshaft rotational angle. A time duration of each drive pulse from the second controller is shorter than a time duration required for the plunger forward stroke, and a period within which each drive pulse is not outputted from the second controller is also shorter than the time duration required for the plunger forward stroke.

BACKGROUND OF THE INVENTION 
The present invention relates to a system for controlling fuel injection by 
means of an electromagnetic valve. 
A fuel injection system of electromagnetic-valve controlled type for use in 
diesel engines is disclosed, for example, in Japanese Patent Appln. 
Laid-Open Nos. 56-151228, 56-154134, 61-268844, 61-286541 and 61-286716, 
U.S. Pat. No. 4,395,987 corresponding to the above Japanese Patent Appln. 
Laid-Open Nos. 56-151228 and 56-154134, and U.S. Ser. No. 865,125 filed on 
May 8, 1986 corresponding to the above Japanese Patent Appln. Laid-Open 
No. 61-268844. The fuel injection system of this kind comprises a fuel 
injection pump as a basic component. The fuel injection pump includes a 
pump housing, a plunger associated with the pump housing for reciprocative 
movement in interlocked relation to a crankshaft of the engine, and a fuel 
pressurizing chamber associated with the pump housing and having a volume 
variable in response to reciprocative movement of the plunger. The fuel 
pressurizing chamber communicates with a fuel supply source through a 
supply passage, and communicates with fuel injection nozzles of the engine 
through forcible delivery passage means. The supply passage is closed 
during a major portion of a forward stroke of the plunger, and is opened 
during a backward stroke of the plunger. In addition, a release passage is 
provided, which is connected to the fuel pressurizing chamber and which is 
adapted to be opened and closed by an electromagnetic valve. During the 
forward stroke of the plunger which reduces the volume of the pressurizing 
chamber, the fuel is released from the fuel pressurizing chamber through 
the release passage for a period within which the electromagnetic valve is 
in an open position. On the other hand, the fuel is forcibly delivered to 
the fuel injection nozzles of the engine through the forcible-delivery 
passage means only for a period within which the electromagnetic valve is 
in a closed position. 
The above-described electromagnetic valve is usually controlled in the 
following manner. That is, rotation detecting means outputs reference 
pulses each indicative of passage of the engine crankshaft through a 
reference rotational position, and scale pulses indicative of angular 
movement of the crankshaft every a predetermined angular extent. In 
response to receipt of the reference pulses and the scale pulses from the 
rotation detecting means, control means calculates current rotational 
angle of the crankshaft and current number of revolutions per unit time or 
rotational speed thereof. The control means also receives data from a 
sensor for detecting an amount of depression of an accelerator pedal and a 
sensor for detecting temperature of engine cooling water. On the basis of 
these data and the engine rotational speed calculated as described above, 
the control means calculates a target injection timing and a target fuel 
injection amount. On the basis of the results of this calculation, the 
control means outputs a drive pulse for a closing command to a drive 
circuit for the electromagnetic valve. The drive pulse has a time duration 
corresponding to the target fuel injection amount. The drive pulse is 
outputted when the current rotational angle of the engine crankshaft 
reaches a target injection timing. 
By the way, in the system disclosed in the above patents, a starter motor 
is operated at start-up of the engine to rotate the crankshaft. The 
plunger is reciprocated in interlocked relation to the crankshaft. In this 
connection, the control means cannot calculate the rotational angle of the 
crankshaft, until the control means receives the first reference pulse 
from the rotation detecting means, indicative of passage of the crankshaft 
through the reference rotational position. By this reason, the control 
means does not output the drive pulse for the closing command to the drive 
circuit for the electromagnetic valve. Thus, during the forcible-delivery 
stroke of the plunger, the fuel within the fuel pressurizing chamber is 
released through the release passage means, so that the fuel is not 
injected. Accordingly, at the initial stage of the start-up, torque due to 
combustion of fuel is not entirely generated, but torque is generated only 
by the starter motor. Thus, such a problem might arise that the start-up 
is not stabilized. 
In a fuel injection system disclosed in Japanese Patent Application 
Laid-Open No. 61-258951, the electromagnetic valve is maintained closed 
until the reference pulses each indicative of passage of the crankshaft 
through the reference rotational position is outputted, and fuel is 
injected over the entire period of the forward stroke of the plunger. 
Since, in this system, fuel injection is carried out from the beginning at 
the engine start-up, the start-up is stabilized. However, the system has 
such a problem that, because the fuel is supplied excessively, black smoke 
is produced from the engine. 
Japanese Patent Application Laid-Open No. 61-8440 discloses a system in 
which when a microcomputer is temporarily brought to a malfunction state 
at the start-up, a drive pulse of a given duty ratio is outputted to an 
actuator, and a control rack of the fuel injection pump is controlled by 
the actuator so as to be brought to a predetermined position, thereby 
controlling the fuel injection amount to a predetermined value. However, 
the system is not of electromagnetic-valve controlled type, and is not 
believed relevant to the present invention. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a fuel injection system for an 
engine, in which fuel is supplied from the initial stage of the engine 
start-up, and excessive supply of fuel is prevented to avoid generation of 
black smoke from the engine. 
According to the invention, there is provided a fuel injection system for 
an engine, comprising: 
(a) a fuel injection pump having a pump housing, a plunger associated with 
the pump housing and reciprocatively movable in relation to rotation of a 
crankshaft of the engine, and a fuel pressurizing chamber associated with 
the pump housing and variable in volume in response to reciprocative 
movement of the plunger; 
(b) supply passage means supplying fuel to the fuel pressurizing chamber, 
the supply passage means being closed substantially during a forward 
stroke of the plunger and being opened substantially during a backward 
stroke of the plunger; 
(c) forcible-delivery passage means connecting the fuel pressurizing 
chamber to at least one fuel injection nozzle of the engine; 
(d) release passage means communicating with the fuel pressurizing chamber; 
(e) an electromagnetic valve provided in the release passage means and 
movable between a closed position where the release passage means is 
closed and an open position where the release passage means is opened, the 
fuel being released from the fuel pressurizing chamber through the release 
passage means for substantially a period within which the electromagnetic 
valve is in the open position and within which the plunger is in the 
forward stroke, the fuel being permitted to be pressurized within the fuel 
pressurizing chamber for substantially a period within which the 
electromagnetic valve is in the closed position and within which the 
plunger is in the forward stroke, the pressurized fuel being forcibly 
delivered to the fuel injection nozzle of the engine through the 
forcible-delivery passage means; 
(f) rotation detecting means for substantially detecting passage of the 
crankshaft of the engine through a reference rotational position to output 
a reference pulse each time the crankshaft passes through the reference 
rotational position, and for substantially detecting angular movement of 
the crankshaft every a predetermined angular extent to output scale 
pulses; 
(g) first control means receiving each reference pulse and the scale pulses 
from the rotation detecting means to calculate current rotational angle of 
the crankshaft, the first control means outputting a drive pulse 
representative of a command moving the electromagnetic valve to the closed 
position, at a timing with reference to the current rotational angle, to 
control a period, within which the electromagnetic valve is in the closed 
position, during the forward stroke of the plunger, thereby controlling 
fuel injection; and 
(h) second control means intermittently outputting drive pulses 
representative of the command moving the electromagnetic valve to the 
closed position, at an initial stage of start-up of the engine, 
independently of the rotational angle of the crankshaft at least based on 
the reference pulses, wherein a time duration of each of the drive pulses 
outputted from the second control means is shorter than a time duration 
required for the forward stroke of the plunger, and a period within which 
each of the drive pulses is not outputted from the second control means is 
also shorter than the time duration required for the forward stroke of the 
plunger.

DETAILED DESCRIPTION 
An embodiment of the invention will be described below with reference to 
FIGS. 1 through 4. FIG. 1 shows a distributor type fuel injection pump 1 
for use in a diesel engine for a vehicle. The fuel injection pump 1 
comprises a pump housing 2 having defined therein a low pressure chamber 
3. The low pressure chamber 3 is filled with low pressure fuel from a fuel 
pump (not shown) which is arranged within the pump housing 2 and which is 
driven by a drive shaft 6 subsequently to be described. 
A plunger barrel 4 is fixedly inserted into a side wall of the pump housing 
2. A plunger 5 has one end portion which is inserted into the plunger 
barrel 4 for reciprocative movement and rotation relative thereto. The 
other end of the plunger 5 is connected, through a coupler 7, to one end 
of the drive shaft 6 coaxial to the plunger 5 in such a manner that 
rotation can be transmitted from the drive shaft 6 to the plunger 5 and 
that the plunger 5 is permitted to axially move relatively to the one end 
of the drive shaft 6. The drive shaft 6 extends through the wall of the 
pump housing 2 and has the other end projecting out of the pump housing 2. 
A crankshaft C of an engine E is connected to the projecting other end of 
the drive shaft 6 through reduction gear wheels (not shown). Thus, 
rotation of the crankshaft C is transmitted to the drive shaft 6. 
Within the pump housing 2, a ring-like roller holder (not shown) is 
arranged around the coupler 7, and a plurality of rollers 8 (only one 
shown) are supported by the roller holder. On the other hand, a face cam 9 
is fixedly mounted to the other end of the plunger 5. The face cam 9 is 
biased by a spring (not shown) into contact with the rollers 8. Thus, the 
plunger 5 is rotated by rotational force transmitted thereto from the 
drive shaft 6 and is reciprocated axially under the camming action of the 
rollers 8 and the face cam 9. 
The plunger barrel 4 has defined at its bottom a fuel pressurizing chamber 
10 which is variable in volume in response to reciprocative movement of 
the plunger 5. 
The plunger barrel 4 and the wall of the pump housing 2 are formed therein 
with a plurality of forcible-delivery passages 11 (only one shown) 
corresponding in number to cylinders of the engine E, and with a single 
supply passage 12. 
The forcible-delivery passages 11 have their respective one ends which open 
to an inner surface of the plunger barrel 4. The other ends of the 
respective forcible-delivery passages 11 are connected respectively to 
delivery valves (not shown) which are mounted to the pump housing 2 and 
which correspond in number to the engine cylinders. The delivery valves 
are connected respectively to fuel injection nozzles N of the engine E 
through respective pipes each of which forms an extension of a 
corresponding one of the forcible-delivery passages 11. 
The supply passage 12 has one end thereof which opens to the inner surface 
of the plunger barrel 4, and the other end which opens to the low pressure 
chamber 3. 
A plurality of groove-like suction passages 5a corresponding in number to 
the engine cylinders are formed in the peripheral surface of the plunger 5 
adjacent the one end thereof in circumferentially equidistantly spaced 
relation to each other. A single L-shaped discharge passage 5b is formed 
in the one end portion of the plunger 5. The discharge passage 5b is 
comprised of an axial section extending along an axis of the plunger 5 and 
a radial section extending at right angles to the axis of the plunger 5. 
The discharge passage 5b has one end which opens to one end face of the 
plunger 5, and the other end which opens to the peripheral surface of the 
plunger 5. 
During a backward stroke of the plunger 5 at which the one end face of the 
plunger 5 moves away from the bottom of the plunger barrel 4, any one of 
the plurality of suction passages 5a is brought into communication with 
the supply passage 12, so that the fuel within the low pressure chamber 3 
is supplied to the fuel pressurizing chamber 10 through the supply passage 
12 and the suction passage 5a. During a major portion of a forward stroke 
of the plunger 5 at which the one end face of the plunger 5 moves toward 
the bottom of the plunger barrel 4, the supply passage 12 is closed by the 
peripheral surface of the plunger 5. 
A cut-off electromagnetic valve 15 is mounted to the pump housing 2 to open 
the supply passage 12 during running of the engine E. 
During the forward stroke of the plunger 5, the discharge passage 5b is 
brought into communication with any one of the plurality of 
forcible-delivery passages 11. 
The fuel injection pump 1 is further formed therein with a release passage 
13 which is comprised of a passage section 13a formed in the plunger 
barrel 4 and two passage sections 13b and 13c formed in the wall of the 
pump housing 2. The passage sections 13a and 13b communicate with each 
other. The passage section 13a has one end which opens to the fuel 
pressurizing chamber 10. The passage section 13b has one end which opens 
to a recess 2a formed in the wall of the pump housing 2. The passage 13c 
has one end which opens to the recess 2a, and the other end which opens to 
the low pressure chamber 3. 
An electromagnetic valve 20 of normally open type is mounted to the wall of 
the pump housing 2. The electromagnetic valve 20 has a body 21 which has 
one end portion fixedly inserted into the recess 2a of the pump housing 2. 
The one end portion of the body 21 has an axial end face formed therein 
with an annular groove 21c. A plurality of passages 21a are formed in the 
one end portion of the body 21. The passages 21a are inclined with respect 
to an axis of the body 21, and are equidistantly spaced from each other 
about the axis of the body 21. The inclined passages 21a have their 
respective one ends in communication with the annular groove 21c. The 
other ends of the respective inclined passages 21a communicate with a 
passage 21b which is formed in the one end portion of the body 21 and 
which extends along the axis thereof. The annular groove 21c, the passages 
21a and the passage 21b form a part of the release passage 13. That is, 
the passages 21a communicate with the passage section 13b through the 
annular groove 21c, and the passage 21b communicates with the passage 
section 13c. A poppet valve member 22 is slidably supported in the body 
21, and has a forward end which can open and close an opening end of the 
passage 21b and, accordingly, the release passage 13. 
The poppet valve member 22 is biased by a coil spring 23 in such a 
direction as to open the release passage 13. An armature 24 is fixedly 
mounted to a base end of the poppet valve member 22, and a stator 25 is 
fixedly mounted to the other end of the body 21. A solenoid 26 is embedded 
in an end face of the stator 25 which is confronted with the armature 24. 
When the solenoid 26 is energized, the armature 24 is attracted toward the 
stator 26, whereby the poppet valve member 22 closes the release passage 
13 against the coil spring 23. 
The release passage 13 is closed only for a period selected by control of 
the electromagnetic valve 20. For substantially the period within which 
the release passage 13 is closed and within which the plunger 5 is in the 
forward stroke, the fuel within the fuel pressurizing chamber 10 is 
pressurized. When pressure of the pressurized fuel is brought to a value 
higher than the opening pressure of the delivery valves, and is further 
brought to a value higher than the opening pressure of the fuel injection 
nozzles N of the engine E, the pressurized fuel is injected from a 
selected one of the fuel injection nozzles N through the discharge passage 
5b and a corresponding one of the forcible-delivery passages 11 and 
through a corresponding one of the delivery valves and a corresponding one 
of the pipes. 
The fuel injection system comprises rotation detecting means 30 illustrated 
in FIG. 2. Specifically, a rotor 31 is fixedly mounted to the portion of 
the drive shaft 6 which projects out of the pump housing 2. A reference 
track 31a and a scale track 31b are formed along a peripheral surface of 
the rotor 31. A specific location on the reference track 31a is magnetized 
to have N and S poles. N and S poles are alternately arranged along the 
scale track 31b every an angular extent of 10 degrees, for example. A 
reference point detecting sensor 32a and a scale detecting sensor 32b each 
formed by a Hall effect element are arranged around the peripheral surface 
of the rotor 31 and are slightly spaced radially outwardly from the 
respective tracks 31a and 31b. The reference point detecting sensor 32a 
outputs a reference pulse Re each time the specific location on the 
reference track 31a passes by the reference point detecting sensor 32a, to 
thereby detect that the crankshaft C passes through the reference 
rotational position. On the other hand, the scale detecting sensor 32b 
outputs a scale pulse Sc each time the drive shaft 6 angularly moves by 
the predetermined angular extent, for example, by 10 degrees, to thereby 
detect angular movement of the crankshaft C every an angular extent of 20 
degrees. 
The fuel injection system comprises first control means 40, as shown in 
FIG. 3, for controlling movement of the electromagnetic valve 20 between 
the open and closed positions. 
The first control means 40 includes a rotational angle detecting circuit 41 
and a rotational speed detecting circuit 42. The rotational angle 
detecting circuit 41 receives each reference pulse Re from the reference 
point detecting sensor 32a and the scale pulses Sc from the scale 
detecting sensor 32b following the reference pulse Re, to calculate 
current rotational angle .theta.i of the crankshaft C. The rotational 
angle .theta.i is represented by graduations each corresponding to one 
scale pulse, that is, to the angular extent of 20 degrees. The rotational 
speed detecting circuit 42 receives the scale pulses Sc from the scale 
detecting sensor 32b to calculate the number of revolutions per unit time, 
that is, rotational speed Ne of the crankshaft C. Waveform shaping 
circuits and the like are interposed between the sensors 32a and 32b and 
the detecting circuits 41 and 42, but are omitted from FIG. 3. 
The first control means 40 further includes a target injection amount 
arithmetic circuit 43 and a target injection timing arithmetic circuit 44. 
Each of the arithmetic circuits 43 and 44 receives the signal Ne 
indicative of the engine rotational speed from the rotational speed 
detecting circuit 42. Each of the arithmetic circuits 43 and 44 also 
receives detecting signals indicative of an accelerator depression amount 
Ac, a boost pressure Bo, a fuel temperature Ft, a battery voltage Vc, 
engine cooling water temperature Wt and the like, from various sensors 35 
which are shown in a lump in FIG. 3 for simplification of illustration. On 
the basis of these data, the arithmetic circuits 43 and 44 calculate a 
target injection amount Q and a target injection timing .theta.t, 
respectively. The output signals from the sensors 35 are digitalized by 
A/D (analog/digital) converters (not shown). The target injection timing 
.theta.t is represented by the rotational angle of the crankshaft C at the 
initiation of fuel injection. 
A starter signal St from a starter switch 36 is further inputted into each 
of the target injection amount arithmetic circuit 43 and the target 
injection timing arithmetic circuit 44. The circuits 43 and 44 carry out 
such calculation as to increase the fuel injection amount at the start-up 
as compared with that within a period of usual engine running, and to 
expedite the fuel injection timing. Additionally, as is well known, when 
the starter switch 36 is turned on, the starter motor is driven to 
forcibly rotate the crankshaft C of the engine E. The ON signal of the 
starter switch 36 forms the starter signal St. 
On the basis of the target injection amount Q from the target injection 
amount arithmetic circuit 43 and the engine rotational speed Ne from the 
rotational speed arithmetic circuit 42, a pulse time duration arithmetic 
circuit 45 calculates a pulse time duration .DELTA.t.sub.1 corresponding 
to a time duration for which the release passage 13 is closed. 
On the basis of the detected rotational angle .theta.i having its minimum 
unit corresponding to one scale pulse Sc, from the rotational angle 
detecting circuit 41, and the engine rotational speed Ne, a pulse 
generation timing arithmetic circuit 46 calculates an accurate current 
rotational angle of the crankshaft C. When this actual rotational angle is 
brought into coincident with the rotational angle .theta.t representative 
of the target injection timing, the pulse generation timing arithmetic 
circuit 46 outputs a trigger signal Tg. 
When a first drive pulse generation circuit 47 receives the trigger signal 
Tg from the pulse generation timing arithmetic circuit 46, the first drive 
pulse generation circuit 47 outputs a drive pulse P.sub.1 to a drive 
circuit 48 for actuating the electromagnetic valve 20. The drive pulse 
P.sub.1 has a time duration which is determined by the pulse time duration 
from the pulse time duration arithmetic circuit 45. At the initiating 
point of the drive pulse P.sub.1, the solenoid 26 of the electromagnetic 
valve 20 is excited to close the release passage 13, thereby initiating 
fuel injection. At the terminating point of the drive pulse P.sub.1, the 
solenoid 26 is demagnetized to open the release passage 13, thereby 
terminating the fuel injection. As a result, optimum fuel injection 
control is carried out in compliance with the condition of the engine E 
and other running conditions. The drive pulse P.sub.1 is outputted only 
once during the forward stroke of the plunger 5 and, accordingly, fuel 
injection is effected only once. 
The above-described arrangement and function of the first control means 40 
are substantially the same as those of a conventional one. 
By the way, until the crankshaft C reaches the reference rotational 
position at the start-up, the reference point detecting sensor 32a does 
not output the reference pulse Re. Accordingly, the rotational angle 
detecting circuit 41 cannot calculate the rotational angle .theta.i of the 
crankshaft C, so that the trigger signal Tg is not outputted from the 
pulse generation timing arithmetic circuit 46. Therefore, the drive pulse 
P.sub.1 is not also outputted from the first drive pulse generating 
circuit 47. 
The fuel injection system of the invention is further provided with second 
control means 50. The second control means 50 comprises a pulse time 
duration setting circuit 51, and a second drive pulse generating circuit 
52 which receives information from the circuit 51 to output drive pulses 
P.sub.2. The outputs from the respective first and second drive pulse 
generating circuits 47 and 52 are sent to the drive circuit 48 through an 
OR circuit 53. 
The pulse time duration setting circuit 51 calculates a time duration 
.DELTA.t.sub.2 of each of the drive pulses P.sub.2 on the basis of the 
battery voltage Vc and the engine cooling water temperature Wt. It is 
necessary to increase the torque generated due to combustion of fuel when 
the battery voltage Vc is low so that the rotational torque of the starter 
motor is low and when the engine cooling water Wt is low so that the 
viscosity of lubricating oil is high. Accordingly, the lower the battery 
voltage Vc and the cooling water temperature Wt, the more the pulse time 
duration .DELTA.t.sub.2 is lengthened, while the higher the battery 
voltage Vc and the cooling water temperature Wt, the more the pulse time 
duration .DELTA.t.sub.2 is shortened. However, in view of the relation 
that the drive pulses P.sub.2 are outputted in synchronism with the scale 
pulses Sc subsequently to be described, the pulse time duration 
.DELTA.t.sub.2 is determined correspondingly also to the engine rotational 
speed Ne. That is, the pulse time duration .DELTA.t.sub.2 is determined 
such that the higher the rotational speed Ne, i.e., the shorter the pulse 
separation between each pair of adjacent scale pulses Sc, the shorter the 
pulse time duration .DELTA.t.sub.2. By this reason, .DELTA.t.sub.2 is 
possible to bring the drive pulses P.sub.2 to a duty ratio corresponding 
to the battery voltage Vc and the engine cooling water temperature Wt. The 
pulse time duration .DELTA.t.sub.2 is shorter than each drive pulse 
P.sub.1, and is usually shorter than the pulse separation between each 
pair of adjacent scale pulses Sc. 
The second drive pulse generating circuit 52 receives the starter signal St 
from the starter switch 36. In response to receipt of the starter signal 
St, the circuit 52 initiates to output the drive pulses P.sub.2 each 
having the time duration .DELTA.t.sub.2 obtained by the above-described 
calculation, independently of the rotational angle of the crankshaft C. 
Since the drive pulse P.sub.2 is outputted each time the scale pulse Sc is 
inputted, that is, each time the crankshaft C angularly moves by 20 
degrees, the drive pulses P.sub.2 are outputted a plurality of times 
during one forward stroke of the plunger 5. As a result, as shown in FIG. 
4, the electromagnetic valve 20 is repeatedly opened and closed bit by bit 
during one forward stroke of the plunger 5, so that the fuel is 
intermittently injected. 
Since the duty ratio of the drive pulses P.sub.2 corresponds to the battery 
voltage and the cooling water temperature as described above, injection of 
an optimum amount of fuel can be realized, making it possible to ensure 
start-up of the engine, and to eliminate such a deficiency that black 
smoke is produced due to excessive fuel injection amount. 
When the signals from the sensors 35 indicate that the battery voltage Vc 
is lower than, for example, 8 volts and that the engine cooling water is 
lower than 0 degree C., the pulse time duration setting circuit 51 outputs 
a fully closing command signal. When the second drive pulse generating 
circuit 52 receives the fully closing command signal, the circuit 52 
continuously sends a drive signal of a high (H) level to the drive circuit 
48. As a result, the fuel is injected for the entire period of the forward 
stroke of the plunger 5. It is preferable to bring the fuel injection 
amount to the maximum value when the battery voltage and the engine 
cooling water temperature are extremely low. 
At the above-mentioned start-up, the crankshaft C of the engine E reaches 
the reference rotational angle for a period within which the crankshaft C 
of the engine E makes two revolutions, that is, for a period within which 
the drive shaft 6 makes one revolution. At this time, the first one of the 
reference pulses Re is sent from the reference point detecting sensor 32a 
to the drive pulse generating circuit 52, so that outputting of the drive 
pulses P.sub.2 is halted. Then, the above-described usual start-up control 
due to the first control means 40 is initiated. 
FIG. 5 shows a modification of the aforesaid second control means. The 
second control means 50A according to the modification has a duty ratio 
setting circuit 51A in substitution for the pulse time duration setting 
circuit 51 illustrated in FIG. 3. The duty ratio setting circuit 51A 
calculates the duty ratio of the drive pulses P.sub.2, on the basis of the 
information on the engine cooling water temperature Wt and the battery 
voltage Vc. A second drive pulse generating circuit 52A is the same as the 
second drive pulse generating circuit 52 shown in FIG. 3 in that the 
circuit 52A initiates to output the drive pulses P.sub.2 in response to 
receipt of the starter signal St and that the circuit 52A halts to output 
the drive pulses P.sub.2 in response to receipt of the first one of the 
reference pulses Re. However, the second drive pulse generating circuit 
52A is different from the circuit 52 of FIG. 3 in that the circuit 52A 
outputs the drive pulses P.sub.2 on the basis of the aforesaid information 
on the duty ratio, at the timing of clock pulses CL in place of the scale 
pulses Sc. 
FIG. 6 shows second control means 50B according to another modification. 
The second control means 50B has a second pulse generating circuit 52B 
which is the same as the second drive pulse generating circuit 52 shown in 
FIG. 3 in that the circuit 52B begins to output the drive pulses P.sub.2 
in response to receipt of the starter signal St, halts to output the drive 
pulses P.sub.2 in response to receipt of the first one of the reference 
pulses Re, and outputs the drive pulses P.sub.2 in synchronism with the 
scale pulses Sc. However, the circuit 52B is different from the circuit 52 
of FIG. 3 in the following point. That is, the second pulse generating 
circuit 52B switches its output alternately to a high level and a low 
level in synchronism with the scale pulses, to thereby output the drive 
pulses P.sub.2 having a duty ratio of 50%. The arrangement may be such 
that the output is brought to the high level in response to one scale 
pulse Sc, the output is brought to the low level in response to the next 
but one scale pulse, and the output is brought to the high level at 
further next scale pulse, whereby the drive pulses P.sub.2 having the duty 
ratio of about 67% are outputted. 
FIG. 7 shows another embodiment of the invention, in which principal 
portions of the respective first and second control means are formed by a 
single microcomputer 60. The microcomputer 60 has inputted thereinto the 
reference pulses Re from the reference point detecting sensor 32a and the 
scale pulses Sc from the scale detecting sensor 32b. Further, the starter 
signal St from the starter switch 36 and the detecting signals from the 
aforesaid sensors 35 are also inputted into the microcomputer 60. 
The drive pulses P.sub.1 and P.sub.2 from the respective first and second 
pulse generating circuits 61 and 62 are sent to the drive circuit 48 
through respective first and second AND circuits 63 and 64 and through an 
OR circuit 65. A control signal from a control port of the microcomputer 
60 is sent to the first AND circuit 63, and is also sent to the second AND 
circuit 64 through an inverter 66. 
The microcomputer 60 executes interrupt routines shown respectively in 
FIGS. 8 and 9. That is, each time the scale pulse Sc is inputted, a flag 
indicative of presence and absence of inputting of the first one of the 
reference pulses Re is judged at a step 100 as shown in FIG. 8. When the 
flag is "0", the output from the control port is brought to "0" at a step 
101, and an initial control is executed at a step 102. That is, the 
microcomputer 60 calculates a duty ratio corresponding to the battery 
voltage and the cooling water temperature, and sends the calculation 
results to the second drive pulse generating circuit 62. The second drive 
pulse generating circuit 62 outputs the drive pulses P.sub.2 having the 
duty ratio obtained by the aforesaid calculation, in synchronism with the 
clock pulses, independently of the scale pulses Sc. At this time, the 
output from the control port, which is inverted by the inverter 65 into 
"1", is inputted into the second AND circuit 64, so that the second AND 
circuit 64 is opened. Thus, the drive pulses P.sub.2 are sent to the drive 
circuit 48, so that the electromagnetic valve 20 is controlled so as to be 
opened and closed bit by bit at a cycle shorter than the time period 
required for the forward stroke of the plunger 5. This control continues 
until the first one of the reference pulses Re is inputted. When the 
battery voltage and the cooling water temperature are lower than their 
respective predetermined values, the duty ratio may be brought to 100%. 
As the first one of the reference pulses Re is inputted, as shown in FIG. 
9, the flag is brought to "1" at a step 200. Accordingly, as the scale 
pulses are inputted after that, it is judged at the step 100 in the 
interrupt routine of FIG. 8 that the flag is "1". The control port is 
brought to "1" at a step 103, and the usual start-up control is executed 
at a step 104. That is, in a manner like that of the previously described 
embodiment, the pulse duration and the pulse generation timing are 
calculated. On the basis of the calculation results, the first drive pulse 
generating circuit 61 outputs the drive pulse P.sub.1. Since, at this 
time, the output "1" from the control port is inputted into the first AND 
circuit 63 so that the first AND circuit 63 is opened, the drive pulse 
P.sub.1 is sent to the drive circuit 48 to control the electromagnetic 
valve 20. 
In the above embodiment, the microcomputer 60 may have all of the functions 
of the respective circuits 61 through 66. 
The invention should not be limited to the above-mentioned specific forms. 
Various modifications and variations may be made to the invention. For 
example, in the usual control, either one of the initiating and 
terminating timings of the fuel injection may be controlled by the 
electromagnetic valve, and the other may be controlled by other mechanical 
control means. That is, the electromagnetic valve is moved to the closed 
position just before the initiating point of the forward stroke of the 
plunger. At the initial stage of the forward stroke, one of the suction 
passages in the plunger communicates with the supply passage in the wall 
of the pump housing, so that the fuel within the fuel pressurizing chamber 
is not pressurized. In this case, communication between the suction 
passage and the supply passage is intercepted to initiate the fuel 
injection, while the electromagnetic valve is moved to the open position 
to terminate the fuel injection. 
The rotation detecting means may take various forms. For example, the 
rotation detecting means may comprise a rotor having a single track, and a 
single sensor. In this case, N and S pole areas are regularly arranged 
alternately along a major portion of the entire circumferential length of 
the track, and this arranging manner is altered only at a single location 
to form a reference point. The output from the sensor forms a distinct 
waveform when the reference point passes by the sensor, so that reference 
pulses can be obtained. The rotation detecting means may be comprised of a 
gear wheel and a electromagnetic pickup sensor. 
The rotation detecting means may be associated with the crankshaft of the 
engine. Further, the rotation detecting means may be divided into a 
reference pulse output section and a scale pulse output section, in which 
one of the output sections is associated with the drive shaft and the 
other output section is associated with the crankshaft. 
The time duration setting circuit 51 of the second control means 50 in the 
embodiment illustrated in FIGS. 1 through 4 may calculate a pulse time 
duration in such a manner that the pulse time duration is brought to a 
duty ratio corresponding to the engine rotational speed, the fuel 
temperature and the like, in addition to the battery voltage and the 
cooling water temperature, or may calculate the pulse time duration on the 
basis of only the rotational speed information in such a manner that the 
pulse time duration is brought to a constant duty ratio. In addition, the 
pulse time duration may be calculated on the basis of information on the 
pulse separation between each pair of adjacent scale pulses, in place of 
the rotational speed information. 
The duty ratio setting circuit 51A of the second control means 50A in the 
embodiment illustrated in FIG. 5 may calculate the duty ratio 
correspondingly to the engine rotational speed, the fuel temperature and 
the like in addition to the battery voltage and the cooling water 
temperature, or may output information of a constant duty ratio. 
The release passage may not be connected directly to the fuel pressurizing 
chamber, but may be connected midway of the forcible-delivery passages. In 
this case, the release passage communicates indirectly with the fuel 
pressurizing chamber through the forcible-delivery passages. 
There may be a case where the drive pulse is outputted only once during the 
forward stroke of the plunger. Also in this case, the time duration of the 
drive pulse is shorter than the time duration required for the forward 
stroke of the plunger, and the period during which the drive pulse is not 
outputted is also shorter than the time duration required for the forward 
stroke of the plunger. In particular, there is a possibility that 
sufficient advantages of the invention can be achieved, if the drive pulse 
is once outputted at the timing of the scale pulses or at the timing of 
pulses divided by the scale pulses. The reason for this is that the 
generation timing of the scale pulses or the generation timing of the 
pulses divided by the scale pulses has a fixed relationship to the forward 
stroke of the plunger. 
The drive pulse indicative of the command to move the electromagnetic valve 
to the closed position may be brought to a low level, depending upon the 
type of the drive circuit for the electromagnetic valve. In addition, an 
electromagnetic valve of normally closed type may be employed. 
Further, it is to be understood that the invention is applicable to an 
in-line fuel injection system in which plungers corresponding in number to 
the engine cylinders are accommodated in the pump housing, to a unit 
injector in which an injection nozzle is incorporated, together with a 
plunger, in a housing, and to any other types of fuel injection systems 
which employ electromagnetic valves.