Fuel injection system for an internal combustion engine.

0001The present invention relates to a fuel injection system as claimed in Claim 1.

0002On 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 re­ quirements 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.

0003A 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.

0004Yet 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.

0005The 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.

0006The above drawbacks are overcome by the system as claimed in Claim 1.

0007Under 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.

0008Variable-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.

0009The present invention will be described in detail with reference to the accompanying drawings, in which : <ul id="ul0001" list-style="none"><li>Fig.1 shows a diagram of a fuel injection system for a high-speed multiple cylinder Diesel engine;</li><li>Fig.2 shows a section of one embodiment of a fuel pump featuring, upstream on the intake side, a throttle valve and pre-delivery pump;</li><li>Fig.s 3 and 3a show an axial and cross section respective­ly of a second embodiment of the said pump;</li><li>Fig. 4 shows a partially schematic view of a further embo­diment featuring mechanical throttle adjustment, e.g. via the accelerator rods of a motor vehicle.</li></ul>

0010Number 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 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.

0011Under 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.

0012By 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.

0013Fig. 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.

0014Drive 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.

0015In 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 Fig. 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.

0016A 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 Fig.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 Fig.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.

0017Fig.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.

0018The 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.