Fuel injection system

A fuel injection system is proposed which can be triggered such that when control signals characterizing engine overrunning are present, fuel injection is interrupted. To this end a pressure relief valve is provided, which opens in the presence of control signals characterizing engine overrunning and lowers the fuel pressure upstream of the fuel metering locations and accordingly upstream of the injection valves as well to below the opening pressure of the injection valves, so that no further fuel is injected via the injection valves during engine overrunning.

BACKGROUND OF THE INVENTION 
The invention relates to a fuel injection system of the type described. A 
fuel injection system is already known in which a bypass around the 
throttle valve is closed during overrunning. This does not, however, 
assure that during engine overrunning fuel injection will be reliably 
interrupted, so as to reduce both fuel consumption and the emission of 
toxic exhaust components. 
OBJECT AND SUMMARY OF THE INVENTION 
The fuel injection system according to the invention has the advantage over 
the prior art in that during engine overrunning it is assured that fuel 
injection will be reliably interrupted, so that during overrunning fuel is 
not consumed unnecessarily and toxic exhaust components are not emitted. 
As a result, advantageous further embodiments of and improvements to the 
fuel injection system disclosed are possible. 
The invention will be better understood and further objects and advantages 
thereof will become more apparent from the ensuing detailed description of 
two preferred embodiments taken in conjunction with the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to FIG. 1, there will be seen a fuel injection system including 
an intake manifold 1 having a conical section 2 which contains an air flow 
rate member 3 beyond which there is located an induction tube region 4 
containing an arbitrarily settable throttle valve 5. Intake air flows 
through the induction tube in the direction of the arrow to a manifold 6 
from which it is directed via individual induction tube regions 7 to one 
or more cylinders 8 of an internal combustion engine. 
In the present case, the air flow rate member 3 is a baffle plate disposed 
transversely with respect to the direction of air flow and capable of 
displacement within the conical region 2 of the induction tube as an 
approximately linear function of the air flow rate through the tube. The 
air pressure between the air flow rate member 3 and the throttle valve 5 
will be constant provided that the restoring force acting on the air flow 
rate member 3 is constant and that the air pressure ahead of the member 3 
is also constant. The air flow rate member 3 controls the opening of a 
metering and distribution valve assembly 10. The motion of the air flow 
rate member 3 is transmitted by an operating lever 11 which is pivoted on 
the same shaft 13 as a correction lever 12 and which actuates the control 
slide 14 which is the movable member of the metering and distribution 
valve assembly 10. A mixture control screw 15 permits an adjustment of the 
desired fuel-air mixture. The end face 16 of the control slide 14 remote 
from the lever 11 experiences the pressure of a control fluid which is 
exerted onto the air flow rate member 3 and acts as a return force in 
opposition to the force of the flowing air. 
Fuel is supplied by an electric fuel pump 19 which aspirates the fuel from 
a fuel tank 20 and delivers it through a storage container 21, a filter 22 
and a fuel line 23 to the fuel metering and distribution assembly 10. 
The fuel supply line 23 splits into several branches which lead to chambers 
26 of the fuel valve assembly 10, whereby one side of a diaphragm 27 in 
each chamber is affected by fuel pressure. The chambers 26 also 
communicate with an annular groove 28 of the control slide 14. Depending 
on the axial position of the control slide 14, the annular groove overlaps 
control slits 29 to varying degrees permitting fuel to flow into chambers 
30 which are divided from the chamber 26 by the diaphragm 27. From the 
chambers 30, fuel flows through the injection channels 33 to the 
individual injection valves 34 which are located in the vicinity of the 
engine cylinders 8 in the induction tube region 7. The diaphragm 27 is the 
movable valve member of a flat seat valve which is held open by a spring 
35 when the fuel injection system is not operating. The diaphragm boxes 
defined, in each case, by a chamber 26 and a chamber 30, insure that the 
pressure drop at the metering valve 28, 29 is substantially constant 
independently of the relative overlap between the annular groove 28 and 
the control slits 29, i.e., independently of the fuel quantity metered at 
the metering valve 28, 29 and flowing to the injection valves 34. This 
insures that the metered out fuel is exactly proportional to the control 
path of the slide 14. 
During a pivoting displacement of the operating lever 11, the air flow rate 
member 3 is moved into the conical region 2 so that the varying annular 
cross section between the flow rate member and the conical wall remains 
proportional to the displacement of the air flow rate member 3. The force 
which generates the restoring force on the control slide 14 is a 
pressurized fluid, which, in this case, is fuel. To provide this fluid, a 
control pressure line 36 branches off from the main fuel supply line 23 
via a decoupling throttle 37. The control pressure line 36 communicates 
via a damping throttle 38 with a pressure chamber 39 into which one end 
face 16 of the control slide 14 extends. 
The control pressure line 36 contains a control pressure valve 42 which 
permits control fluid to return to the fuel tank 20 via a return line 43 
without pressure. The control pressure valve 42 permits changing the 
pressure which produces the restoring force during the warm-up of the 
engine in dependence on time and temperature. The control pressure valve 
42 is a flat seat valve having a fixed control valve seat 44 and a 
diaphragm 45 which is loaded in the closure direction by a spring 46. The 
spring 46 acts via a spring support 47 and a transmission pin 48 upon the 
diaphragm 45. When the engine temperature is below the normal operating 
temperature a first bimetallic spring 49 acts in opposition to the force 
of the spring 46. The bimetallic spring 49 carries an electric heater 50, 
the operation of which after starting causes a diminution of the force of 
the bimetallic spring 49 on the spring 46, and by this means the control 
pressure in the control pressure line 36 increases. 
A line 53 branches off from the fuel supply line 23 and a pressure 
regulator valve 54 is disposed in this line 43, by means of which a 
constant fuel pressure is maintained upstream of the fuel metering valve 
28, 29. The pressure regulator valve 54 shown by way of example in the 
drawing has a regulator piston 55, which can be displaced by the fuel 
pressure in the line 53 counter to the force of a regulator spring 56, so 
that fuel can flow over a regulator edge 57 out of the line 53 into the 
return line 43 and back to the fuel tank 20. At the same time, by means of 
the opening regulator piston 55, a barrier valve 58, which is disposed 
directly downstream of the pressure control valve 42 in the return line 
43, can be opened. To this end, the regulator piston 55, in the act of 
opening and when the engine is running, engages an actuation pin 59, which 
displaces the movable valve element 60 in the opening direction, counter 
to the force of a barrier spring 61. If the engine is shut off, then there 
is no further fuel supply on the part of the electric fuel pump 19, and 
the pressure regulator valve 54 closes. At the same time, the barrier 
spring 61 engaging the actuation pin 59 displaces the movable valve 
element 60 of the barrier valve 58 into the closed position, so that 
leakage of fuel from the control pressure line 36 via the pressure control 
valve 42 is precluded and the fuel injection system remains filled with 
fuel and ready for the next startup of the engine. In a bypass line 64 
around the pressure regulator valve 54, which branches off from the fuel 
supply line 23, there are an electromagnetic valve 65 and downstream 
therefrom a pressure relief valve 66, by way of which, when it is open, 
fuel can flow into the return line 43 and from there to the fuel tank 20. 
The electromagnetic valve 65 is connected to an electronic control 
appliance in a manner not shown and is triggered thereby in such a way 
that when control signals are present which characterize the overrunning 
condition on the part of the engine, this valve 65 opens. Engine 
overrunning is characterized, for instance, by the location of the 
throttle valve in a position for idling while the engine rpm are at a 
level above the idling level. The spring force of the pressure relief 
valve 66 is established such that the pressure relief valve 66 opens at a 
lower fuel pressure than the opening pressure of the injection valves. Now 
if the electromagnetic valve 65 opens during engine overrunning, then a 
lower fuel pressure is established by the pressure relief valve 66 
upstream of the fuel metering valve 28, 29, so that the injection valves 
34 and the pressure regulator valve 54 close; as a result, undesirable 
fuel injection is avoided and the formation of toxic exhaust gases is 
prevented. 
In the exemplary embodiment of FIG. 2, the elements having the same 
function as in the exemplary embodiment of FIG. 1 are given identical 
reference numerals. In a bypass line 69 branching off from the fuel supply 
line 23, an electromagnetic valve 70 which is open during normal engine 
operation and downstream thereof a first chamber 71 of a pressure relief 
valve 72 are disposed. The first chamber 71 of the pressure relief valve 
is connected either, as indicated by broken lines, directly with the 
return line 43 via a line 73 having a limiting throttle location 74, or 
via a line 75 having a limiting throttle location 76 with the return line 
43 upstream of the barrier valve 58. When the engine is not running, the 
barrier valve 58 thus also prevents leakage of fuel out of the line 75. In 
the first chamber 71 of the pressure relief valve 72, there is a spring 77 
which rests against a diaphragm 78, acting as the movable valve member, 
which separates the first chamber 71 from a second chamber 79. In the 
second chamber 79 there is a fixed valve seat 80, by way of which, when 
the pressure relief valve 72 is in the open position, fuel can flow into 
the return line 43. The second chamber 79 communicates via a line 81 with 
the fuel supply line 23. The spring force of the spring 77 of the pressure 
relief valve 72 is selected to be such that the pressure relief valve 
opens at lower pressures than the opening pressure of the injection valve. 
During normal engine operation, the electromagnetic valve 70 is open, and 
a fuel quantity limited by the limiting throttle location 76 flows via the 
first chamber 71 of the pressure relief valve 72 back to the return line 
43. Thus the same fuel pressure prevails in the first chamber 71 as in the 
second chamber 79 of the pressure relief valve 72, and the pressure relief 
valve 72 remains closed as a result of the supplementary force of the 
spring 77. When control signals characterizing engine overrunning are 
present, the electromagnetic valve 70 closes, and the fuel pressure in the 
first chamber 71 drops to the fuel pressure in the tank, which amounts to 
approximately 1 bar. As a result, the pressure relief valve 72 opens and 
thus the pressure directly upstream of the injection valves 34 also drops 
below the opening pressure of the injection valves 34, so that no further 
fuel is injected through the injection valves 34 in this operational state 
of the engine. 
The foregoing relates to preferred exemplary embodiments of the invention, 
it being understood that other embodiments and variants thereof are 
possible within the spirit and scope of the invention, the latter being 
defined by the appended claims.