FEED SYSTEM FOR SUPERCHARGED DIESEL ENGINES

Abstract: A feed system for supercharged diesel engines allows high power outputs to be obtained for short periods of time without it being necessary to modify the engine radically, by the addition to a normal supercharging system of a three-­ way two-position valve (28) a predetermined threshold in the fuel delivery regulator (15), and a device (29) controlled by the engine accelerator (30) for actuating the valve (28).

Description: Feed System for Supercharged Diesel Engines The present invention relates to a feed system for supercharged diesel engines, which allows high power outputs to be achieved for predetermined short periods Of time. The motor vehicle industry currently has as one of its most important objectives the reduction of fuel consumption, both by reducing the weight of vehicles and by optimising the performance of power units, not the least through increasing the transmission ratios. The latter measure , which is one of those giving the greatest return from the point of view of fuel saving, involves, however, considerable loss of acceleration and pick-up and considerably penalises the overall performance of the vehicle. Vehicles having diesel engines which, even if provided with supercharging, have power outputs which are often inferior to those of the same models equipped with petrol engines are especially disadvantaged. The object of the present invention is to provide a feed system for supercharged diesel engines, which allows high power outputs to be obtained for predetermined short periods of time in order to maintain or to increase the acceleration and pick-up of a motor vehicle having high transmission ratios favourable from the aspect of fuel consumption. Accordingly, the present invention provides a feed systen for supercharged diesel engines, comprising a turbosupercharger driven by the engine exhaust, an automatic overpressure valve, a pressure sensor connected to the engine induction manifold and arranged to operate the overpressure valve at a predetermined pressure, and a fuel delivery regulator connected to the engine injection pump and controlled by the pressure in the induction manifold according to a predetermined law, characterised in that a normally open, three-way two-position valve is connected between the pressure sensor and the induction manifold, the fuel delivery regulator is arranged to increase the delivery of fuel from the injection pump substantially and automatically when the pressure in the induction manifold exceeds a predetermined threshold, and a device is associated with the engine accelerator control for actuating the three-way two-position valve in dependence on a predetermined position of the control. One embodiment of the invention will now be described by way of example, with reference to the appended drawings, in which: Figure 1 is a schematic view of a diesel engine provided with a feed system according to the present invention; Figure 2 is a sectional view of a component of the system illustrated in Figure 1; Figure 3 is a sectional view of another component of the system of Figure 1; Figure 4 is a view on an enlarged scale of a part of the component illustrated in Figure 2. With reference to the drawings, there is shown a diesel engine 1, which may equally well be of the direct or indirect injection type, provided with an exhaust manifold 2 which inlets into the turbine 3 of a turbosupercharger 4 having an exhaust 5 and connected to a compressor 6 which receives air from an air filter 8 through a duct 7. The compressor 6 directs compressed air to an induction manifold 9. An automatic overpressure valve 11, commonly called a "waste-gate", is mounted in series in a duct 10 connecting the exhaust manifold 2 to the exhaust 5, and is controlled by a pressure sensor 12 connected to the induction manifold 9 through a duct 13. The injection pump 14 has a device 15 for regulating the fuel delivery in dependence on the pressure existing in the induction manifold. This pressure is taken through a duct 16 connected to the duct 13. Figure 2 illustrates the part of the device 15 which senses the supercharging pressure existing in the manifold. It is formed by superimposed chambers 17, 18 separated by a resilient diaphragm 19. The upper of the two chambers is connected to the induction manifold through the duct 16 mentioned previously, while the lower chamber is open to the atmosphere. Connected in known manner to the diaphragm 19 is a small piston 20 which projects downwardly to slide in a seat 21, and has a profile (illustrated in Figure 4) having an annular groove 22 in its middle portion connected to a frusto-conical part 23. A feeler 25 is held against the profile of the piston by known meansnot illustrated. A spring 26 coaxial with the piston keeps the diaphragm 19 pressed upwardly with a force of a predetermined value, while a second spring 27, shorter than the previous one and also having a predetermined load, is positioned coaxially with the first and also bears, like the-previous one,on the lower wall of the chamber 18. In the duct 13 is located,in series, a three-way two-position valve 28 (illustrated in Figure 3) , for example , a solenoid valve, which, in its normally open position, allows the passage of pressure from the intake duct to the pressure sensor 12 while, in its closed position,it cuts off the act 13 and connects the pressure sensor 12 to the atmosphere. The valve 28 is controlled by a device 29 which is operated when the accelerator 30 reaches a predetermined open position which will generally be very close to the maximum. The control 29 simultaneously actuates the pump 31 of an injector 32 which emits atomised water into the intake duct 7 downstream of the air filter 8, the water being taken from an auxiliary tank 33. Operation of the device. wçhen the accelerator 30 does not surpass the predetermined open position ,the operation of the device corresponds exactly to that of a normal supercharging unit and will not be described since it is generally known, at least to a person skilled in the art. When the accelerator control 30 reaches the predetermined open position, however, the device behaves in the manner described below. The control 29 operates the valve 28 which moves from the normally open position illustrated in Figure 3 to the closed position in which the pressure sensor 12, which controls the waste-gate valve,is put into communication with the atmosphere,and the duct 13 extending from the inductionmanifold 9 is closed. Under these conditions the supercharging pressure in the intake duct almost instantly reaches values which are very high and/or at least greater than those existing in the normal operating range of the engine, in that all the exhaust gases are directed to the turbine 3 as a result of the fact that the waste-gate valve is inoperative. The high supercharging pressure value is sensed by the device 15 through the duct 16. As a result, the diaphragm 19 receives a strong downward thrust, compressing both the spring 26, which also occurs in the normal operating range of the engine, and the spring 27 which, having a higher calibrated value,is not normally compressed. The piston 20 will thus be thrust downward more than normal and the feeler 25, which controls the increase in the fuel flow of the injection pump, will be located in correspondence with the groove 22,causing the pump 14 to reach the maximum fuel flow level which the engine is able to withstand for short periods of time. Thus, there will be a sudden high surge in the power supplied by the engine. In order not to reduce the engine life, this high power may onlybeused for short periods and this can he easily achieved by, for example , incorporating a timer switch in the control 29,which cuts off the action of the control after a predetermined period of time even if the accelerator 30 remains in the predetermined open position. The device illustrated in Figure¯1 also has a water injector 32 and associated accessory devices, which is put into operation by the control 29 simultaneously with the valve 28. This allows the injection of a certain predetermined quantity of very finely atomised water into the intake duct upstream of the compressor 6 which, by mixing with the inducted air lowers the temperature both of the compressor and, a very important matter, of the compressed air directed to the combustion chamber to an appreciable extent. Thus, one of the greatest disadvantages of supercharged engines can be overcome without the need for providing a heat exchanger in the air supply system, which would be considerably more expensive or at least certainly more bulky and difficult to position.Clearly,however, the use of a water injection system like that described is an optional feature depending on the more or less harsh use for which the engine is intended. It will be understood that what has been described above may be varied widely without thereby departing from the scope of the invention.

Claims: Claims: 1. Feed system for supercharged diesel engines1 comprising: a turbosupercharger (4) driven by the engine exhaust; an automatic overpressure valve (13); a pressure sensor (12) connected to the engine induction manifold (9) and arranged to operate the overpressure valve (11) at a predetermined pressure, and a fuel delivery regulator (15) connected to the engine injection pump (14) and controlled by the pressure in the induction manifold (9) according to a predetermined law, characterised in that: a normally open, three-way two-position valve (28) is connected between the pressure sensor (12) and the induction manifold (9) the fuel delivery regulator (15) is arranged to increase the delivery of fuel by the injection pump (14) substantially and automatically when the pressure in the induction manifold (9) exceeds a predetermined threshold, and a device (29) is associated with the engine accelerator control (30) for actuating the three-way two-position valve (28) in dependence on a predetermined position of opening of the control (30). 2. Feed system according to Claim 1, characterised in that the three-way two-position valve (28) puts the pressure sensor (12) into communication with the induction manifold (9)its normally open position, and puts the pressure sensor (12) into communication with the atmosphere in its closed position. 3. Feed system according to Claim 1, characterised in that it further includes an injector (32) for injecting atomised water into the intake duct (7) of a compressor connected to the turbosupercharger (4) and the induction manifold (9), the injector (32) withdrawing the water fro a container (33). 4. Feed system according to Claim 3, characterised in that the injector (32) is operated by the device (29) simultaneously with the actuatdon of the threeway two position-valve (28).

Inventors: FILTRI, GIORGIO
Applicants: FIAT AUTO S.P.A.
Application year: 1983
Main classification: F02D23
IPC codes: F02B3, F02D23, F02M59