Fuel injection system for an internal combustion engine

A high-pressure, continuous-delivery piston pump, controlled as a function of engine speed and load, supplies fuel to an accumulator supplying injectors. On the intake side of the pump, there is provided a throttle for metering the amount of fuel supplied by the pump. Via operating signals, the throttle is regulated by an electronic control device in such a manner as to supply the pump and pressurize only the amount of fuel strictly required for operating the injectors and the engine, thus eliminating any energy losses caused by fuel feedback to the tank, and drastically reducing fuel consumption.

BACKGROUND OF THE INVENTION 
The present invention relates to a fuel injection system as claimed in 
claim 1. p On known injection systems of this type, as per patent 
applications DE-OS 32 27 742 and EP-OS 0 149 598, the pressure accumulator 
is permanently connected to a duct on each injector via an annular 
compartment and throttle valve. Each injector presents an injection 
electrovalve for connecting the said duct to a fuel feedback pipe, thus 
releasing a pin on the injector closing the injection opening, and 
enabling fuel supply from a pressure compartment directly upstream from 
the injection opening. Fuel is supplied to the accumulator at a given 
pressure by means of a high-pressure hydraulic pump powered by the drive 
shaft via a gear, and the size of which depends on minimum required 
pressure at low engine speed, maximum fuel injection, and minimum pressure 
regulating speed. The disadvantage of such a system from the manufacturing 
standpoint is that pump design must conform with the requirements of 
different power engines, if optimum engine performance in terms of 
consumption and output is to be assured. This therefore amounts to 
manufacturing and storing a different pump for each type of engine, which 
inevitably results in increased manufacturing costs. 
A further drawback of known systems of the aforementioned type is that, 
being constant and designed to cater to maximum requirements, fuel supply 
by the high-pressure pump is invariably in excess of actual consumption, 
so that a large percentage of the fuel supplied by the pump must be fed 
back to the tank via a pressure regulator, the energy loss of which 
increases overall consumption or at least affects output of the engine. 
Yet a further drawback of known systems is that overheating of the fuel at 
the bottom of the tank often entails assembling an intercooler, which, in 
addition to further increasing manufacturing cost, may also increase fuel 
consumption. 
SUMMARY OF THE INVENTION 
The aim of the present invention is to provide a fuel injection system as 
claimed in claim 1, designed to overcome the aforementioned drawbacks 
associated with known systems, i.e. storing a large number of different 
pump sizes for the high-pressure system of different types of engines; and 
excess fuel supply and consumption under normal operating conditions. 
The above drawbacks are overcome by the system as claimed in claim 1. 
Under all operating conditions, and with no change in pump speed, the 
system according to the present invention provides for supplying and 
pressurizing only the exact amount of fuel required for combustion and 
operation of the injectors, thus reducing operating power, as compared 
with known systems featuring constant-delivery pumps, under partial-load 
conditions requiring reduced fuel pressurization. Eliminating fuel 
feedback to the tank provides for approximately 4% fuel saving at maximum 
power, and even more under normal partial-load conditions, as compared 
with known systems. By virtue of the pressure in the accumulator 
depending, not on the size of the pump, but on the throttle valve setting 
regulating the opening on the intake pipe and, therefore, the amount of 
fuel supplied to the pump, a limited number of pumps are sufficient for 
catering to a wide range of different engines. The injection system 
according to the present invention also responds rapidly to control. For 
example, when the throttle valve is opened fully, the pressure in the 
accumulator increases rapidly, which is of enormous advantage, 
particularly when accelerating. The system according to the present 
invention also provides for simplifying design and so reducing 
manufacturing cost. For example, the pressure regulator required on the 
fuel feedback pipe of known systems may be dispensed with entirely, or at 
least simplified, for example, in the form of a straightforward safety 
valve. 
Variable-delivery hydraulic pumps are currently employed for numerous 
applications, but are usually swash-plate types unsuitable for 
low-viscosity fluids, not to mention the high pressures involved in the 
present application. Claims 2 to 8 relate to further embodiments of the 
system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION 
Number 1 in FIG. 1 indicates a multiple cylinder Diesel engine, on which 
the injectors 2 (three in the example shown) are supplied from a tank 3. 
By means of a high-pressure piston pump 4, fuel is fed along pipe 5 to an 
accumulator 6 and along delivery pipe 7 to injectors 2. Via electric wires 
8, each injector 2 is controlled by an electronic control device 9 
supplied by battery 11, and which generates an injection signal, the form 
and length of which depend on the signals of a position and speed 
transducer 10 and other data. A fuel feedback pipe 12 runs from injectors 
2 back to tank 3. Between pressure pipe 5 and fuel feedback pipe 12, 
provision is made for a straightforward safety valve 13 which only opens 
at a pressure not encountered under normal operating conditions. 
Under normal operating conditions, therefore, no fuel is fed back from 
injectors 2 to tank 3 via pipe 12 and valve 13--a fuel saving solution 
made possible by virtue of the design features described in more detail 
later on. The fuel in tank 3 is sucked up by pre-delivery pump 16 through 
intake pipe 15 and filter 14, and pressurized as determined by 
low-pressure valve 17. At this point, the intake stroke of the pump 4 
piston forces it through throttle 18 and check valve 19, after which, the 
delivery stroke of the piston forces it through a further check valve 20 
on pipe 5 into pressure accumulator 6. High-pressure pump 4 is powered by 
drive shaft 21 via gear 22, which regulates the required speed ratio 
between drive shaft 21 and shaft 23 of pump 4. Depending on the type of 
engine involved, a pressure value is selected on electronic control device 
9 as a function of current speed, the position of accelerator 24 and other 
parameters, and compared with the actual pressure value as measured by a 
pressure sensor 25 on delivery pipe 7 to injectors 2. Any difference 
between the set and real values is adjusted by accordingly regulating 
throttle 18 via cable 26 connecting control device 9 to throttle 18 
upstream from the pump. 
By virtue of the above system, in particular, regulation of throttle 18 on 
the delivery pipe to pump 4, the present invention provides for ensuring 
that high-pressure pump 4 supplies and pressurizes only the exact amount 
of fuel required for operating the engine. Unlike known systems, injectors 
2 are supplied exclusively with fuel at optimum injection pressure, with 
no need for pressurizing excess fuel, which must only be fed back into 
tank 3. A further advantage of eliminating fuel feedback by regulating 
fuel supply via a fast-response throttle upstream from pump 4 is that, in 
the event of a sharp change in the position of the accelerator pedal, as 
when overtaking, throttle 18 is opened fully for enabling immediate supply 
of the required amount of fuel by the pump. As this briefly exceeds 
consumption, the pressure in accumulator 6 also increases rapidly. 
FIG. 2 shows a further embodiment wherein the high-pressure pump and the 
components up- and downstream from the same are assembled into a compact 
unit 27. In addition to the high-pressure piston pump, unit 27 also 
comprises the pre-delivery pump 16, as in FIG. 1, throttle 18 upstream 
from pump 4, the two check valves 19 and 20, and low-pressure valve 17. 
Drive shaft 23 on bearings 28 inside housing 29 of unit 27 corresponds with 
pump shaft 23 in the FIG. 1 embodiment, and provides for powering 
pre-delivery pump 16 supplying fuel from the tank into duct 30 at the 
pressure determined by low-pressure valve 17. From duct 30, a further duct 
31 feeds the fuel through throttle 18 (shown in the partially open 
position) and into intake duct 32 of high-pressure pump 4. The said pump 4 
comprises a piston 34 sliding inside a cylinder 44, and which is pressed 
by a spring 35 against an eccentric disc 36 located on shaft 23 and which 
moves the piston up and down. At each downstroke of piston 34 (FIG. 2), 
the fuel in intake duct 32 is sucked through check valve 19 and, when the 
piston moves back up, is forced through check valve 20 and along pressure 
pipe 5 to accumulator 6. 
In the FIG. 2 embodment, each turn of shaft 23 is accompanied by one stroke 
of piston 34 on pump 4, and the number of strokes per turn of drive shaft 
21, depending on the number of cylinders on the engine, is determined by 
gear 22. In the FIGS. 3 and 3a embodiment, on the other hand, gear 22 and 
eccentric disc 36 (FIG. 2) are replaced by a pump shaft in the form of 
camshaft 37 having a number of cams 38 (four in the example shown) 
according to the number of cylinders on the engine. 
A roller 39 traveling over cams 38 controls operation of a single piston 
34. In this case, too, camshaft 37 rests on bearings 28 inside housing 29. 
Unlike the FIG. 2 embodiment, the FIGS. 3 and 3a embodiment presents an 
external pre-delivery pump 16 and low-pressure valve 17, and pre-delivery 
pump 16 is powered, for example, electrically. In the FIGS. 3 and 3a 
embodiment also, throttle 18 and the two check valves 19 and 20 are 
located at the inlet or outlet of pump 4 inside housing 29. 
FIG. 4 shows a relatively straightforward embodiment wherein throttle 18 is 
regulated mechanically in the high-pressure pump intake pipe. In this 
case, the position of lever 40, adjustable in direction X, indicates the 
theoretical pressure value. As shown in FIG. 4, the said lever 40 provides 
for adjusting the aperture of throttle 18 mechanically, until the said 
theoretical pressure is attained in the accumulator. 
The said lever is positioned by the electronic control device on the 
engine, but may also be controlled directly by the accelerator pedal. Such 
a variation would eliminate the characteristic pressure curve, in which 
case injectors 2 could be controlled as a function of pressure and speed 
by an electronic control device 9 decidedly less complex than in the 
foregoing examples.