Fuel pressure control method and system for direct fuel injection engine

Based on the output signal of the fuel sensor, it is judged whether or not the fuel (liquid fuel) is detected in the high pressure fuel system. When the fuel is detected, the count value for counting the detecting time is compared with the predetermined value. If the count value is equal to or larger than the predetermined value, the electromagnetic type high pressure fuel regulator is rendered closed and the starter motor prohibition flag is cleared to admit energizing the starter motor. As a result of this, the engine is permitted to be started and thus the high pressure fuel pump starts to produce the high pressure in the high pressure fuel system, whereby a sticking or a scuffing in the fuel pump due to poor lubrication can be prevented and an overshoot of the fuel pressure or a void injection in the fuel injector can be avoided.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and a system for controlling a 
fuel pressure and more particularly to a method and a system for 
controlling a starter motor at an engine start of a direct fuel injection 
engine. 
Commonly, in a conventional high pressure type direct fuel injection 
engine, when an engine is stopped, the fuel pressure is relieved by 
opening a high pressure fuel regulator in a high pressure fuel system, so 
as to diminish the load of the components of the fuel system for securing 
durability and reliability thereof. 
However, when the fuel pressure is relieved at an engine stop, a vapor 
tends to be generated in the fuel system due to a sudden decrease in 
pressure of the fuel heated by a radiation from the engine, so that a 
defective engine starting may be caused because of a void injection at the 
fuel injector. 
To solve the problem, for example, Japanese utility model application laid 
open No. 1990-127769 discloses a technique to eliminate a vapor lock by 
operating only the fuel pump (feed pump) without operating the starter 
motor for a specified time when an ignition key switch is turned on and 
after the specified time elapses, namely, the vapor lock is eliminated 
from the fuel system, the starter motor is permitted to be operated to 
start the engine. However, when this technique is applied to the high 
pressure type direct fuel injection engine, since in this type of engine 
the fuel is supplied from the fuel tank to the high pressure fuel system 
by the feed pump in the low pressure fuel system and then the the fuel is 
pressurized up to a specified pressure by the high pressure fuel pump in 
the high pressure fuel system, there is a high possibility that the fuel 
is not supplied enough throughout the high pressure fuel system because of 
the residual vapor therein in operating only the feed pump for a specified 
time. Especially, at a hot restarting of engine, some portion of the fuel 
itself supplied to the high pressure fuel system is vaporized therein by 
the heated distribution pipes or the high pressure fuel pump in a high 
temperature, and as a result of this there occurs not only a hard starting 
due to the vapor lock but also a scuffing or a sticking in the sliding 
part of the high pressure fuel pump. 
SUMMARY OF THE INVENTION 
The present invention has been made taking the above situation into the 
consideration. It is a primary object of the present invention to provide 
a method for preventing a poor lubrication in the high pressure fuel pump 
which is caused by the vapor in the fuel system. 
Additionally, it is a further object of the present invention to provide a 
method for improving an engine startability, especially at a restarting 
under the hot condition of engine. 
To achieve the abovementioned objects, the fuel pressure control method for 
the high pressure type direct fuel injection engine according to the 
present invention comprises the steps of: prohibiting energization of a 
starter motor for rendering a high pressure fuel pump in the high pressure 
fuel system inoperative until a predetermined time elapses and at the same 
time operating a feed pump in the low pressure fuel system; and then 
permitting energization of the starter motor for rendering the high 
pressure fuel pump operative after the predetermined time elapses. 
Next, a brief explanation about the method according to the present 
invention will be made. 
First, when an engine is started, the starter motor is prohibited from 
being energized so as to prevent an engine cranking, namely, to prevent an 
operation of the high pressure fuel pump and at the same time the feed 
pump in the low pressure fuel system is operated to feed the fuel to the 
high pressure fuel system. On the other hand, it is checked whether the 
fuel in the high pressure fuel system is a liquid fuel or a fuel vapor 
(including a mixture of liquid fuel and bubbled fuel). When it is judged 
from detection of the liquid fuel for a predetermined time that the vapor 
is eliminated from the fuel in the high pressure fuel system, the starter 
motor is permitted to be operated for cranking so that the high pressure 
fuel pump operates to supply fuel to the fuel injector.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to FIG. 6, a reference numeral 1 denotes a direct fuel injection 
engine (in this first embodiment, a direct fuel injection two stroke 
engine). A cylinder head 2, a cylinder block 3 and a piston 4 form a 
combustion chamber 5 wherein a spark plug 7 and a fuel injector 8 are 
disposed. The spark plug 7 is connected to the secondary side of an 
ignition coil 6a. The primary side of the ignition coil 6a is connected 
with an igniter 6b. Further, a scavenging port 3a and an exhaust port 3b 
are provided in the cylinder block 3 and in a coolant passage 3c of the 
cylinder block 3 a coolant temperature sensor 9 is disposed. 
Further, an air delivery pipe 10 is connected to the above scavenging port 
3a. Upstream of the air delivery pipe 10 there is provided an air cleaner 
11 and downstream thereof there is provided a scavenging pump 12 which is 
driven by a crank shaft 1a. The scavenging pump 12 supplies the fresh air 
to the engine and at the same time scavenges the combustion chamber 5 
forcibly. In a by-pass passage 13 by-passing the above scavenging pump 12 
a by-pass control valve 15 operatively linked with an accelerator pedal 14 
is provided. Also an accelerator pedal opening sensor 16 is coupled with 
the accelerator pedal 14. In the abovementioned exhaust port 3b, an 
exhaust rotary valve 17 mechanically interlocked with the crankshaft 1a is 
disposed. An exhaust pipe 18 is coupled with the exhaust port 3b through 
the rotary valve 17. In the exhaust pipe 18, a catalytic converter 19 and 
a muffler 20 are mounted in this order from upstream to downstream. 
Further, a crank rotor 21 is coaxially coupled with the crank shaft 1a 
mounted on the cylinder block 3 and on the outer periphery of the crank 
rotor 21 a crank sensor 22 comprising an electromagnetic pick up and the 
like is provided. 
Further, a reference numeral 23 indicates a fuel system comprises a low 
pressure fuel system 23a which sends the fuel from a fuel tank 24, a high 
pressure fuel system 23b which feeds the fuel to the fuel injector 8 by 
applying a pressure and a fuel return system 23c which returns the fuel to 
the fuel tank 24 as a result of the pressure regulation. 
The low pressure fuel system 23a is a system for sending the fuel in the 
fuel tank 24 to a diaphragm type low pressure fuel regulator 27 via a fuel 
filter 26 by the pressure of a feed pump 25 and for feeding the fuel to a 
high pressure fuel pump 28 after the fuel pressure is regulated by the 
above low pressure fuel regulator 27. 
Further, the high pressure fuel system 23b is a system for sending the fuel 
fed from the low pressure fuel system 23a to an fuel injector 8 of each 
cylinder by means of the pressure applied by the above high pressure fuel 
pump 28 through a fuel feed passage along which a fuel sensor 29 for 
detecting the fuel (liquid fuel) therein, a high pressure fuel filter 30, 
an accumulator 31 for absorbing a pressure pulsation, and a fuel pressure 
sensor 32 for detecting the fuel pressure in the high pressure fuel system 
are disposed, after the fuel pressure is regulated by an electromagnetic 
(solenoid) type high pressure fuel regulator 33. 
The high pressure fuel pump 28 is composed of, for example, a plunger pump 
directly driven by an engine. In the high pressure fuel pump 28 there is 
provided a check valve at the suction port and at the discharge port 
respectively, so the fuel can pass through inside the fuel pump 28 freely 
even when an engine is stationary. 
Further, the above fuel sensor 29 is, for example, a capacitance type of 
sensor which detects whether the fuel feed passage is full of a liquid 
fuel (hereinafter referred to as just "fuel", unless defined otherwise) or 
not by the difference of a dielectric constant between liquid and gas. In 
this embodiment the fuel sensor 29 is disposed immediately downstream of 
the discharge port of the high pressure fuel pump 28 but may be disposed 
at any portion of the high pressure fuel system 23b (generally speaking, 
preferably downstream of the high pressure fuel system 23b) provided that 
the fuel filled up in the high pressure fuel pump 28 can be detected. 
Further, the low pressure fuel system 23c acts to send back the returning 
fuel from the diaphragm type low pressure fuel pump 27 and from the 
electromagnetic type high pressure fuel regulator 33 to the fuel tank 24. 
Since the high pressure fuel regulator 33 in this embodiment is a full 
time open type (open unless energized), the valve opening degree becomes 
small to raise the fuel pressure in the high pressure fuel system 23b as 
an ON duty DUTY becomes large. The valve is closed at the ON duty 
DUTY=100%. 
On the other hand, a numeral 40 of FIG. 7 is an electronic control unit 
(ECU) which comprises a CPU 41, a ROM 42, RAM 43, a backup RAM 44, an I/O 
interface 45 connecting these altogether through a bus line 46. Further, 
the ECU 40 incorporates therein a constant voltage circuit 47 which is 
connected to a battery 49 via a relay contact of an ECU relay 48 and at 
the same time connected to the battery 49 directly. Also a relay coil of 
the ECU relay 48 is connected to the battery 49 via an ignition key switch 
50. That is to say, the constant voltage circuit 47 stabilizes the voltage 
of the battery 49 and supplies the stabilized voltage to miscellaneous 
components in the ECU 40 when the ignition key switch 50 is turned on and 
a contact of the ECU relay 48 is made. When the ignition key switch 50 is 
turned off to break a contact of the ECU relay 48, the constant voltage 
circuit 47 supplies a backup voltage to the backup RAM 44. 
Further, the battery 49 is connected with a starter switch 51 and the 
starter switch 51 is connected to a starter motor 53 via a relay contact 
of a starter motor relay 52. Furthermore, the battery 49 is connected to 
the feed pump 25 via a relay contact of a feed pump relay 54. Also the 
battery 49 is connected to an input port of the I/O interface 45 and the 
battery voltage is monitored therein. The I/O interface 45 is connected to 
the starter switch 51, the fuel sensor 29, the crank angle sensor 22, the 
accelerator pedal opening angle sensor 16, the coolant temperature sensor 
9 and the fuel pressure sensor 32. 
On the other hand, an output port of the I/O interface 45 is connected to 
the igniter 6b for driving the ignition coil 6a, further to the relay coil 
of the starter motor relay 52 for delivering the power supply to the 
starter motor 53, the relay coil of the feed pump relay 54 for delivering 
the power supply to the feed pump 25, the fuel injector 8 and the 
electromagnetic type high pressure fuel regulator 33. 
Next, an operation of the ECU 40 will be explained according to flowcharts 
shown in FIGS. 1 to 5. 
First, when the ignition key switch 50 is turned on and the ECU 40 is 
energized, miscellaneous flags, a count value and an I/O port value are 
initiated. The flowcharts in FIGS. 1 and 2 indicate a fuel pressure 
control routine where it is judged whether a normal control transition 
flag F.sub.3, a fuel detection flag F.sub.2 and an initiation completion 
flag F.sub.1 are set or not at S101, S102 and S103 respectively. When the 
routine is the first execution, since these flags F.sub.3, F.sub.2 and 
F.sub.1 have been already cleared (F.sub.3 =0, F.sub.2 =0 and F.sub.1 =0), 
the process goes to S104 where a starter motor prohibition flag F.sub.ST 
is set (F.sub.ST =1). In case of F.sub.ST =1, the starter motor 53 is 
prohibited to be energized even when the starter switch 51 is turned on. 
Next, the process goes to S105 where an ON duty DUTY for the high pressure 
fuel regulator 33 is set to be 0 (%) (DUTY=0) and at the next step S106 
this value (0%) is set as an I/O port output value for the high pressure 
fuel regulator 33 for rendering the high pressure fuel regulator 33 fully 
open. Further, the process goes to S107 where an I/O port output value 
G.sub.1 for the relay coil of the feed pump relay 54 is set to 1 (G.sub.1 
=1) to energize the feed pump relay 54 for operating the feed pump 25. As 
a result of this, the feed pump starts to operate and the fuel starts to 
flow throughout the fuel system. At the next step S108 the initiation 
completion flag F.sub.1 is set (F.sub.1 =1) and then the process is 
returned to the main routine. 
In summary, the first execution of the fuel pressure control routine 
abovementioned comprises the steps of: prohibiting to energize the starter 
motor 53 for making the engine inoperative; rendering the high pressure 
fuel regulator 33 fully open for making the free flow of fuel in the fuel 
system; and starting to operate the feed pump 25 for circulating the fuel 
in the fuel system in order to purge the residual fuel vapor in the high 
pressure fuel system 23b. 
At the second execution of the fuel pressure control routine, since the 
initiation completion flag F.sub.1 has been set, the process is diverted 
from S103 to S109 where it is checked whether the fuel (liquid fuel) is 
detected or not in the high pressure fuel system 23b based on the output 
signal from the fuel sensor 29. In case where no fuel is detected, the 
process passes to S116 where a fuel detecting time count value C for 
counting the continuation time of the fuel detecting state is cleared 
(C=0) and then the routine returns to the main routine. In case where the 
fuel is detected at the second execution or at a specified time execution 
of the routine, the process goes from S109 to S110 at which the fuel 
detecting count value C is compared with a predetermined value C.sub.S to 
judge whether the fuel detecting state has continued for a predetermined 
time. The predetermined value C.sub.S corresponds to a predetermined time 
during which the fuel vapor is deemed to have been purged out almost 
completely, the high pressure fuel system 23b being filled up with fuel. 
This value C.sub.S is obtained beforehand from experiments or other means 
and is stored in the ROM 42. Even if the fuel is detected, C is less than 
C.sub.S (C&lt;C.sub.S) at the beginning and therefore the process goes from 
S110 to S 111 where the count value C is counted up (C=C+1) and the 
routine returns to the main routine. After a while, when C becomes equal 
to or larger than C.sub.S (C.gtoreq.C.sub.S), the process goes from S110 
to S112. At S112 the ON duty DUTY for the high pressure fuel regulator 33 
is set to be FFH (100%) and at the next step S113 the I/O port output 
value for the high pressure regulator 33 is set. As a result of this, the 
high pressure fuel regulator 33 is closed to raise the fuel pressure both 
in the low pressure fuel system 23a and the high pressure fuel system 23b. 
Further, the process goes to S114 where the fuel detecting flag F.sub.2 is 
set (F.sub.2 =1) and at the next step S115 the starter motor prohibition 
flag F.sub.ST is cleared (F.sub.ST =0) to permit energization of the 
starter motor 53. At S116 the count value C is cleared (C=0) and the 
routine returns to the main routine. 
When the engine is started by clearing the starter motor prohibition flag 
F.sub.ST, the high pressure fuel pump 28 driven by the engine operates to 
raise the fuel pressure P.sub.F in the high pressure fuel system 23b. In 
this case, since the fuel detecting flag F.sub.2 has been set, at the next 
execution of the routine the process passes from S102 to S117 where the 
fuel pressure P.sub.F in the high pressure fuel system 23b is compared 
with a predetermined normal pressure P.sub.H (for example, 1.times.Pa) to 
judge whether or not the fuel pressure P.sub.F in the high pressure fuel 
system 23b reaches the normal pressure P.sub.F. 
If P.sub.F .gtoreq.P.sub.H at S117, the process goes out of the routine. If 
the fuel pressure P.sub.F reaches the normal pressure P.sub.H (P.sub.F 
&gt;P.sub.H), the process goes from S117 to S118 where the normal control 
transition flag F.sub.3 is set (F.sub.3 =1) and the routine returns to the 
main routine. Since the normal control transition routine F.sub.3 is set, 
at the next execution of the routine the process is diverted from S101 to 
S119. At the steps after S119 the process transfers to a fuel pressure 
normal control to feedbackcontrol the fuel pressure. 
In this fuel pressure normal control, at S119 a target fuel pressure 
P.sub.FS is determined from a target fuel pressure look-up table 
parameterizing the engine speed N. The target fuel pressure look-up table 
is obtained from experimental data and the like in consideration of the 
performance required of the engine, the characteristics of the fuel pump 
and so on. As shown in a diagram of S119, the look-up table stored in 
predetermined addresses of the ROM 42 is so determined as the target fuel 
pressure P.sub.FS becomes high with the increase of the engine speed and 
becomes low with the decrease of the engine speed. 
Next, the process goes from S119 to S120 where a basic control amount, 
i.e., a basic duty D.sub.B for the high pressure fuel regulator 33 is 
determined from a predetermined basic control table or a formula 
parameterizing the target fuel pressure P.sub.FS. Further, at the next 
step S121, a deviation .DELTA.P between the target fuel pressure P.sub.FS 
and the fuel pressure P.sub.F is calculated (.DELTA.P=P.sub.FS -P.sub.F) 
and the process goes to S122. At S122, a proportional part feedback value 
P is obtained by multiplying a proportional constant K.sub.P in a 
proportional-plus-integral control by the above deviation .DELTA.P 
(P=K.sub.P .times..DELTA.P). Further, at S123, an integral constant 
K.sub.I in the proprtional-plus-integral control multiplied by the above 
deviation .DELTA.P is added to the last time integral feedback value 
I.sub.OLD read from the RAM 43, whereby a new integral feedback value I is 
obtained (I=I.sub.OLD +K.sub.I .times..DELTA.P). 
Next, the process goes to S124 where the last time feedback value I.sub.OLD 
stored in the RAM 43 is updated by the above integral feedback value I. At 
the next S125, an ON duty DUTY which is a feedback control amount for the 
high pressure fuel regulator 33, is determined by adding the above 
proportional feedback value P and the above integral feedback value I to 
the above basic duty D.sub.B (DUTY=D.sub.B +P+I) and the process goes out 
of the routine after the ON duty DUTY is set at S126. As a result of this, 
the feedback control is performed such that the target fuel pressure 
P.sub.FS is followed up by the fuel pressure P.sub.F. 
When the fuel vapor remains on in the high pressure fuel system 23b the 
liquid fuel is not detected continuously, and therefore start is 
prohibited by rendering the starter motor 53 inoperative. When the fuel 
vapor is purged out of the high pressure fuel system 23b and only the 
liquid fuel is detected therein, the engine is started by releasing the 
restriction to the starter motor 53. There is prevented not only a 
sticking or a scuffing in the high pressure fuel pump 28 due to a poor 
lubrication, but also an overshoot of the fuel pressure due to gas (vapor) 
compression or a void injection at the injector 8, whereby a good engine 
startability is obtained. 
A flowchart indicated in FIG. 3 is a starter motor control routine which is 
carried out at a specified interval only when the starter motor switch 51 
is in an "ON" position. First, at S201 the starter motor prohibition flag 
F.sub.ST is looked up to judge whether the starter motor 53 is permitted 
to be energized or not. In case of F.sub.ST =1, i.e., where the starter 
motor 53 is prohibited to be energized, the process is diverted to S202 at 
which an I/O port output value G.sub.4 for the starter motor relay 52 is 
set to be 0 (G.sub.4 =0) to switch the starter motor relay 52 off and then 
the routine is returned to the main routine. On the other hand, in case of 
F.sub.ST =0, i.e., where the starter motor 53 is permitted to be 
energized, the process is advanced to S203 at which the I/O port output 
value G.sub.4 is set to be 1 (G.sub.4 =1) to switch the starter motor 
relay 52 on and then the routine is returned to the main routine. As a 
result of this routine, the starter motor 53 is energized and an engine 
cranking is started. 
On the other hand, a flowchart indicated in FIG. 4 is a starter switch ON 
to OFF interruption routine. The routine is started to be carried out when 
the starter switch 51 is turned off. At S301, an I/O port output value 
G.sub.4 to the starter motor relay 52 is set to be 0 (G.sub.4 =0), so that 
the starter motor relay 52 is turned off and the routine is returned to 
the main routine. 
Further, a flowchart indicated in FIG. 5 is a fuel injection control 
routine which is carried out at a specified interval after the system is 
initiated. First, at S401 it is judged whether or not an engine speed N is 
"0", that is to say, an engine is rotated. If N=0, namely, the engine is 
stationary, the process goes to S402 where a fuel injection pulse width Ti 
is set to be 0 to stop the fuel injection and the routine is returned to 
the main routine. On the other hand, if N.noteq.0, the process is advanced 
from S401 to S403 where an optimum fuel injection pulse width T.sub.i is 
calculated based on an induction air amount Q, a target air-fuel ratio 
determined according to the engine speed N and others, an air-fuel ratio 
feedback correction coefficient and so on. At the next step S404 the above 
calculated fuel injection pulse width T.sub.i is set and therefrom the 
step goes out of the routine. As a result of this, a drive signal 
corresponding to the fuel injection pulse width T.sub.i is outputted with 
a specified timing to the fuel injector 8 of the corresponding cylinder 
and the fuel is injected therein accordingly. 
It will be understood that the preferred embodiment according to the 
present invention is not intended to be limited to just the preferred 
embodiment described thereabove. In an example, the high pressure fuel 
pump 28 may be an electrically driven fuel pump, instead of an engine 
direct drive type, and further the fuel sensor 29 may be a sensor for 
detecting a change of conductance by an existence or a nonexistence of the 
fuel, instead of a capacitance type. Furthermore, the electromagnetic type 
high pressure fuel regulator 33 may be a fuel regulator which regulates 
the fuel pressure by opening or closing a valve thereof with a certain 
level of electrical current (direct current), instead of a duty signal. 
The first embodiment aforementioned is an example applied to the two stroke 
engine, however this embodiment can be applied also to the four stroke 
engine without modifying the components of the fuel system. 
Next, the second embodiment according to the present invention will be 
explained. The second embodiment is applied mainly to a direct fuel 
injection four stroke engine capable of choosing a wide pulse width for 
fuel injection, compared to a direct fuel injection two stroke engine. The 
fuel pressure control system according to this second embodiment is 
characterized in that the components of the system are more simplified and 
therefore it is less costly than the system according to the first 
embodiment. 
Further, a brief explanation about the second embodiment will be made. 
Referring now to FIG. 9, the difference in components according to the 
second embodiment from the first embodiment in FIG. 6 is that: 
the electromagnetic type high pressure fuel regulator 33 is replaced with a 
mechanical type high pressure fuel regulator 35; a solenoid-operated stop 
valve 34 is equipped in a by-pass passage by-passing between the high 
pressure fuel system 23b and the fuel return system 23c; the fuel pressure 
sensor 31 is deleted; and the engine 1 is replaced with a direct fuel 
injection four stroke engine 1b that is commonly known. 
The mechanical type high pressure fuel regulator 35 is an ever-closed type 
of valve in which a spring biases a valve body to a valve seat to close 
it. The valve is opened by the pressure applied on the valve body against 
the spring force only when the fuel pressure exceeds a predetermined 
value, whereby it acts as regulating the fuel pressure of the fuel in the 
high pressure fuel system 23b to the predetermined value. The 
solenoid-operated stop valve 34 is a shut-off valve which opens when its 
solenoid is not energized and closes when energized and plays a role of 
permitting escape of a fuel vapor therethrough to the fuel tank 24 at an 
engine start. 
Next, an operation of the fuel pressure control system according to the 
second embodiment will be explained briefly by referring to FIGS. 7 and 8. 
When the power source is applied to the ECU 40, when the system is 
initiated, namely the initiation completion flag F.sub.1 =0, at the first 
execution of the routine the process goes to S122 where the starter motor 
prohibition flag F.sub.ST is set to be 1 so as to render the starter motor 
53 inoperative. At the next step S123 a stop valve opening flag F.sub.LS 
is set to be 1 so as to open the electromagnetic stop valve 34. At S124 
the I/O port output value G.sub.1 is set to be 1 to operate the feed pump 
25. Further, at S125 the initiation completion flag F.sub.1 is set to be 1 
and then the routine is returned to the main routine. 
At executions of the routine after the first execution, the process is 
diverted to S126 where it is judged whether or not the fuel is detected. 
If the fuel is detected, the process goes to S127 where it is judged 
whether or not the count value C exceeds the predetermined count value 
C.sub.S. If C.gtoreq.C.sub.S, at S128 the stop valve opening flag F.sub.LS 
is set to be 0 so as to shut-off the electromagnetic stop valve 34. 
Further at S129 the starter motor prohibition flag F.sub.ST is set to be 0 
so as to render the starter motor 53 operative. Further at S130 a 
pass-over flag F.sub.TR is set to be 1 and the routine is returned to the 
main routine after the count value C is cleared at S131. Once the 
pass-over flag F.sub.TR is set, the process is returned directly to the 
main routine through the first step S120 of this routine. 
Other routines described in the first embodiment, the starter motor control 
routine as shown in FIG. 3, the starter switch ON/FF interruption routine 
as shown in FIG. 4 and the fuel injection control routine as shown in FIG. 
5, these are carried out in the same manner as in the first embodiment. 
As a result of executing this fuel pressure control routine according to 
the second embodiment, at an engine start the fuel vapor in the fuel 
system is purged out through the stop valve 34 and when the fuel vapor is 
finished purging the stop valve 34 is closed to allow the pressure rise in 
the high pressure fuel system. Further at the same time the starter motor 
53 is energized to start of the engine. 
In summary, the present invention provides a fuel system characterized in 
that: 
when an engine is started, only a feed pump is operated to feed the fuel to 
the high pressure fuel system with a starter motor inoperative and after 
the high pressure fuel system is filled up with the fuel the starter motor 
is rendered operative, so that a sticking and a scuffing due to the 
residual fuel vapor in the high pressure fuel pump can be prevented and 
further an overshoot of the fuel pressure and a void fuel injection can 
also be avoided, whereby an excellent effect on the starting performance 
of engine is attained. 
While the presently preferred embodiment of the present invention has been 
shown and described, it is to be understood that this disclosure is for 
the purpose of illustration and that various changes and modifications may 
be made without departing from the scope of the invention as set forth in 
the appended claims.