Fuel injection device in diesel engine

In controlling a fuel injection quantity by spilling a part of fuel fed from a high pressure chamber of a fuel injection pump using a high pressure electromagnetic valve which is on-off controlled by a driving circuit in accordance with engine operating conditions, switch means is provided between the high pressure electromagnetic valve and a power source, an output signal from the driving circuit is monitored, and the switch means is opened when the output signal from the driving circuit continues more than a predetermined period.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a fuel injection device in a deisel engine, and 
more particularly to improvements in a fuel injection device in a diesel 
engine, suitable for use in a motor vehicle diesel engine provided with an 
electromagnetic spill type fuel injection pump, wherein a fuel injection 
quantity is controlled by a high pressure electromagnetic valve which is 
on-off controlled in accordance with engine operating conditions. 
2. Description of the Prior Art 
Because of developments in digital control techniques in recent years, a 
so-called electronically controlled diesel engine, wherein a fuel 
injection pump in a diesel engine is electronically controlled, has been 
commercialized. 
There are various methods of electronically controlling the fuel injection 
pump, one of which is a method using an electromagnetic spill type fuel 
injection pump, wherein spill of fuel in the fuel injection pump is 
controlled by an electromagnetic valve. In this electromagnetic spill type 
fuel injection pump, upon the fuel injection quantity reaching a target 
valve, a spill port is released by a high pressure electromagnetic valve 
to control the fuel feed under the pressure, thus controlling the fuel 
injection quantity. 
When a diesel engine, wherein the fuel injection quantity is controlled by 
a high pressure electromagnetic valve, uses a normally closed type 
electromagnetic valve as a high pressure electromagnetic valve, the 
disconnection of a solenoid in the electromagnetic valve or the blocking 
of a path in the electromagnetic valve by extraneous matters results in a 
full quantity injection condition of the fuel injection pump, thus 
disabling its control and causing an overrun of engine speed. Furthermore, 
when a normally open electromagnetic valve is used, trouble in a control 
circuit, a short-circuit between a wire harness of the electromagnetic 
valve and a battery or the continuous passing of current through the 
solenoid, causes the full quantity injection conditions, resulting in the 
inability control the fuel injection quantity and the occurence of an 
overrun of engine speed as well. 
To obviate the above-described disadvantages, Japanese Patent Laid-Open No. 
47630/1981 discloses that, when an abnormal increase in engine speed is 
detected, a fuel cut solenoid is closed, thereby stopping the fuel supply. 
Furthermore, in Japanese Utility Model Application No. 13777/1984, the 
applicant discloses that, when a difference between a target engine speed 
and an actual engine speed exceeds a predetermined value, the fuel cut 
solenoid is closed in order to stop the fuel supply. 
In all of these conventional cases, however, a fuel cut solenoid separate 
from the electromagnetic spill valve is provided, such that when an 
abnormality in the engine speed is detected, the fuel supply is cut by the 
fuel cut solenoid. Then electromagetic valve itself is not protected and a 
power source voltage is applied to the electromagnetic spill valve due to 
a trouble in the electromagnetic valve driving circuit, a wire harness or 
the like. When current continues to flow through the electromagnetic spill 
valve, the valve falters. Furthermore, when an abnormality is detected 
from the engine speed, it is detected indirectly, resulting in too slow on 
engine response. 
Alternatively, U.S. Pat. No. 4,491,112 discloses a failsafe system for an 
engine control servomotor, wherein a servomotor command signal is compared 
with a feedback signal from the servomotor, and, when a difference 
therebetween is higher than a preset value for more than a preset time 
period, the servomotor is shut down. However, this invention does not 
attempt to protect the high pressure electromagnetic valve, as does the 
present invention. 
SUMMARY OF THE INVENTION 
The present invention has been developed to obviate the above-described 
disadvantages of the prior art and has as its object the provision of a 
fuel injection device in a diesel engine, capable of preventing secondary 
troubles such as coil short-circuit, valve blocking, burning and the like, 
which are caused by overheating due to continuous energizing of the high 
pressure electromagnetic valve. 
To this end, the present invention contemplates a fuel injection device in 
a diesel engine, wherein a fuel injection quantity is controlled by 
spilling a part of fuel fed from a high pressure chamber of a fuel 
injection pump using a high pressure electromagnetic valve which is on-off 
controlled by a driving circuit in accordance with engine operating 
conditions, said device basically comprising, as shown in FIG. 1: 
switch means provided between said high pressure electromagnetic valve and 
a power source; and 
trouble detecting means for monitoring an output signal from said driving 
circuit, and opening said switch means when said output signal from said 
driving circuit continues more than a predetermined period. 
A specific embodiment of the present invention is of such an arrangement 
that said switch means is a relay of normally open type to allow for the 
adequate counteraction of troubles. 
Another specific embodiment of the present invention is of such an 
arrangement that disconnection detecting means for detecting a 
disconnection of a wire between the high pressure electromagnetic valve 
and the driving circuit is further provided, so that troubles of a wider 
variety are counter measured. 
A further specific embodiment of the present invention is of such an 
arrangement that the trouble detecting means stops the energizing of a 
fuel cut valve connected in parallel to the high pressure electromagnetic 
valve upon the detection of a trouble. The driving of the fuel cut valve, 
which had been independent, is then driven through the same switch means, 
thus simplifying the necessary circuitry, reducing costs and improving the 
reliability of the system. 
A still further specific embodiment of the present invention is of such an 
arrangement that a means for closing the switch means withal the output 
signal of the driving circuit when a voltage of the power source is low 
and the engine is in a starting condition is further provided, thus 
preventing start failure due to a malfunction of the switch means during 
starting. 
According to the present invention, in controlling a fuel injection 
quantity by spilling a part of fuel fed from a high pressure chamber of a 
fuel injection pump using a high pressure electromagnetic valve on-off 
controlled by a driving circuit in accordance with engine operating 
conditions, switch means is provided between the high pressure 
electromagnetic valve and a power source, an output signal of the driving 
circuit is monitored and the switch means is opened when the output signal 
from the driving circuit continues more than a predetermined period. As a 
consequence, continuous energizing of the high pressure electromagnetic 
valve due to trouble in the electromagnetic valve driving circuit, a 
short-circuit of the wire harness between the electromagnetic valve and an 
electronic control unit and the like can be avoided, and secondary 
troubles such as a short-circuit of the solenoid, a sticking of the 
electromagnetic valve itself, a blocked valve due to the flowout of resin, 
a burned valve and the like, all of which are caused by overheating due to 
the continuous energizing of the high pressure electromagnetic valve, can 
be avoided, thereby improving the reliability of the system.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Detailed description will hereunder be given of an embodiment of a fuel 
injection device suitable for use in an electronically controlled diesel 
engine for a motor vehicle, said device according to the present invention 
being described with reference to the drawings. 
As shown in FIG. 2, in this embodiment, an intake-air temperature sensor 12 
for detecting intake-air temperature is provided at the downstream side of 
an air cleaner, not shown. Provided at the downstream side of this 
intake-air temperature sensor 12 is a turbo charger 14 including a turbine 
14A rotatable by heat energy of the exhaust gas and a compressor 14B 
rotatable in operational association with this turbine 14A. The upstream 
side of the turbine 14A of the turbocharger 14 and the downstream side of 
the compressor 14B communicate with each other through a waste gate valve 
15 which prevents an intake-air pressure from being raised excessively 
high. 
Provided in a venturi 16 disposed at the downstream side of the compressor 
14B is a main intake-air throttle valve 18 rotatable non-linearly in 
operational association with an accelerator pedal 17, for restricting an 
intake-air flow rate during times of engine idling and the like. The 
opening angle Accp of the accelerator pedal 17 (hereinafter referred to as 
a "accelerator opening") is detected by an accelerator position sensor 20. 
Provided in parallel to the main intake-air throttle valve 18 is an 
auxiliary intake-air throttle valve 22, the opening of which is controlled 
by a diaphragm device 24. Supplied to the diaphragm device 24 is vacuum 
generated by a vacuum pump 26 through a vacuum switching valve 28 or 30 
(hereinafter referred to as a "VSV"). 
Provided at the downstream side of the intake-air throttle valves 18 and 22 
is an intake pressure sensor 32 for detecting intake-air pressure. 
A cylinder head 10A of a diesel engine 10 is provided with an injection 
nozzle 34, a glow plug 36 and an ignition timing sensor 38, the forward 
ends of which are located in an engine combustion chamber 10B. 
Furthermore, provided on a cylinder block 10C of the diesel engine 10 is a 
water temperature sensor 40 for detecting the temperature of engine 
cooling water. 
Glow current is supplied to the glow plug 36 through a glow relay 37. 
Fuel is fed under pressure to the injection nozzle 34 from an 
electromagnetic spill type injection pump 42. The injection pump 42 
includes: a driving shaft 42A rotatable in operational association with 
the rotation of a crankshaft of the diesel engine 10; a feed pump 42B 
(FIG. 2 shows a state wherein the pump is developed through 90.degree.) 
solidly secured to the driving shaft 42A, for giving pressure to the fuel; 
a fuel pressure regulating valve 42C for regulating fuel feed pressure; a 
reference position sensor 44, for example an electromagnetic pickup, for 
detecting a reference position such as top dead center (TDC) from a 
displacement in rotation of a gear 42D solidly secured to the driving 
shaft 42A; an engine speed sensor 46, for example an electromagnetic 
pickup, for detecting an engine speed from a displacement in rotation of a 
gear 42E solidly secured to the driving shaft 42A; a roller ring 42H for 
reciprocating a face cam 42F and a plunger 42G and varying the timing 
thereof; a timer piston 42J (FIG. 2 shows a state wherein the timer piston 
is developed through 90.degree.) for varying a rotary position of the 
roller ring 42H; a timing control valve 48 (hereinafter referred to as a 
"TCV") for controlling the position of the timer piston 42J to control the 
injection timing; an electromagnetic spill valve 50 for varying fuel 
relief timing from the plunger 42G through a spill port 42K to control the 
fuel injection quantity; a fuel cut solenoid 52 for cutting the fuel 
during the presence of an abnormal condition; and a delivery valve 42L for 
preventing back flow and after-dripping of the fuel. 
Outputs from the intake-air temperature sensor 12, the accelerator position 
sensor 20, the intake pressure sensor 32, the ignition timing sensor 38, 
the water temperature sensor 40, the reference position sensor 44, the 
engine speed sensor 46, a glow current sensor 54 for detecting the glow 
current flowing through the glow plug 36, an air conditioner switch, a 
neutral safety switch and a vehicle speed signal are inputted to and 
processed in an electronic control unit 56 (hereinafter referred to as an 
"ECU"). The VSV 28, 30, the glow relay 37, the TCV 48, the electromagnetic 
spill valve 50 and the fuel cut solenoid 52 are controlled by outputs from 
the ECU 56. 
As shown in detail in FIG. 3, the ECU 56 includes: a central processing 
unit 56A (hereinafter referred to as a "CPU"") for performing various 
calculation processing; a multiplexer 56H (hereinafter referred to as a 
"MPX") for succesively taking in an output from the water temperature 
sensor 40, which is inputted through a buffer 56B, an output from the 
intake air temperature sensor 12, which is inputtted through a buffer 56C, 
an output from the intake pressure sensor 32, which is inputted through a 
buffer 56D, an output from the accelerator position sensor 20, which is 
inputted through a buffer 56E, a phase correction voltage signal, which is 
inputted through a buffer 56F and a tau correction voltage signal, which 
is inputted through a buffer 56G, an analog-digital converter 56J 
(hereinafter referred to as an "A/D converter") for converting analog 
signals outputted from the MPX 56H into digital signals and inputting the 
same into the CPU 56A; a wave form shaping circuit 56K for wave form 
shaping an output from the engine speed sensor 46 and inputting the same 
into the CPU 56A; a wave form shaping circuit 56L for wave form shaping an 
output from the reference position sensor 44 and inputting the same into 
the CPU 56A; a wave form shaping circuit 56M for wave form shaping an 
output from the ignition timing sensor 38 and inputting the same into the 
CPU 56A; a buffer 56N for inputting a starter signal into the CPU 56A; a 
buffer 56P for inputting an air conditioner signal into the CPU 56A; a 
buffer 56Q for inputtting a torque converter signal into the CPU 56A; a 
driving circuit 56R for driving the fuel cut solenoid 52 in accordance 
with the results of calculations made by the CPU 56A; a driving circuit 
56S for driving the TCV 48 in accordance with the results of calculations 
made by the CPU 56A; a driving circuit 56T for driving the electromagnetic 
spill valve 50 in accordance with the results of calculations made by the 
CPU 56A; a current detecting circuit 56U for detecting a current flowing 
through the electromagnetic spill valve 50 and feeding-back the same to 
the driving circuit 56T; a low voltage detecting circuit 56V for detecting 
a low voltage and inputting the same into the driving circuit 56T; a 
driving circuit 56W for outputting a self diagnosis signal (hereinafter 
referred to as a "diag signal") in accordance with the results of 
calculations made by the CPU 56A; and a driving circuit 56X for driving a 
warning lamp in accordance with the results of calculations made by the 
CPU 56A. 
The aforesaid phase correction voltage signal is a signal for correcting a 
phase difference between a normal position and an actual mounted position 
when the reference position sensor 44 is mounted to the injection pump 42. 
The aforesaid tau correction voltage signal is a signal for correcting a 
deviation in responsiveness due to a difference between individual parts 
of the injection pump 42. 
As shown in detail in FIG. 4, a failsafe circuit according to the present 
invention includes: a failsafe relay 60 of a normally open type connected 
in series to the upstream side of the electromagnetic spill valve 50, 
which is disposed on the output side of the driving circuit 56T; and a 
trouble detecting circuit 62 for monitoring an output of the driving 
circuit 56T and detecting the presence of the continuous energizing and 
disconnection of a wire harness between the electromagnetic spill valve 50 
and the driving circuit 56T, actuating the failsafe relay 60 and causing 
the energizing of the electromagnetic spill valve 50 and the fuel cut 
solenoid 52, which are connected in parallel, to stop. 
As shown in FIG. 4, the trouble detecting cirucuit 62 is mainly comprised 
of: transistors 62A and 62B; a capacitor 62C and a resistor 62D, which are 
set at sufficiently high time constants; a resistor 62E of relatively low 
resistance for discharge; a diode 62F; a comparator 62G; and a transistor 
62H for driving the failsafe relay 60 in accordance with an output from 
the comparator 62G and an output from the driving circuit 56R of the fuel 
cut solenoid 52. 
As a consequence, when the pressure of a terminal A driving the 
electromagnetic spill valve 50 is low, that is, the electromagnetic spill 
valve 50 is energized, the transistor 62A is turned off and the transistor 
62B is turned on, causing the capacitor 62C to be charged through the 
resistor 62D of relatively high resistance. The time constants of the 
capacitor 62C and the resistor 62D are set at sufficiently high values, 
whereby, when the duty ratio of the electromagnetic spill valve 50 becomes 
the timing driver of the circuit, pressure is not raised to a threshold 
level at which the value of an output G from the comparator 62G is brought 
to its low level. On the other hand, when the pressure at the terminal A 
reaches a level high enough to deenergize the electromagnetic spill valve 
50, the transistor 62A is turned on and the transistor 62B is turned off, 
causing the electric charge of the capacitor 62C to be rapidly discharged 
through the diode 62F and the resistor 62E of relatively low resistance. 
As a consequence, as shown in FIG. 5, an output from the comparator 62G 
continues to be on the high level under normal conditions to turn on the 
transistor 62H, whereby the failsafe relay 60 is energized. On the other 
hand, when trouble occurs, for example, in the electromagnetic spill valve 
driving circuit 56T, whereby the electromagnetic spill valve 50 is 
continously energized, or the wire harness between the electromagnetic 
spill valve 50 and the ECU 56 is short-circuited to ground, causing the 
electromagnetic spill valve 50 to be continuously energized as well, an 
electric potential at the point A continues to be low, whereby the 
transistor 62B continues to be on, causing the capacitor 62C to be charged 
and the electric potential at a point F to become high. The electric 
potential at a point G then becomes low, so that the failsafe relay 60 is 
turned off. When the resistor 62J is added, a disconnection of the wire 
harness between the electromagnetic spill valve 50 and the ECU 56 can be 
detected. Specifically, the electric charge is discharged through the 
resistor 62J at the time of the disconnection, causing the potential at 
the output of the comparator 62G to become low. 
When the CPU 56A is reset due to a pressure drop during starting, the 
electromagnetic spill valve 50 becomes continuously energized to improve 
the startability, whereby an output from a NAND gate 62K forcedly turns on 
the transistor 62A and turns off the transistor 62B, so that the trouble 
detecting cirucuit 62 according to the present invention is not actuated. 
Examples of the working wave forms of the respective sections in this 
embodiment are shown in FIG. 6. 
In this embodiment, the resistor 62J is added to the trouble detecting 
cirucuit 62 to detect a disconnection of the wire harness between the 
electromagnetic spill valve 50 and the driving circuit 56T thereof, so 
that the range of detectable troubles is wide. Additionally, the resistor 
56J can be dispensed with. 
Furthermore, in this embodiment, the fuel cut solenoid 52 is connected in 
parallel to the electromagnetic spill valve 50, so that the circuitry can 
be simplified, the costs can be reduced and the reliability of the system 
can be improved. 
Further, in this embodiment, the failsafe relay 60 is of the normally open 
type, so that the measures to counter the troubles are perfect.