A FUEL-INJECTION PUMP WITH VARIABLE CYLINDER CAPACITY FOR DIESEL ENGINE INJECTION SYSTEMS

Abstract: A fuel-injection pump for diesel-engine injection systems, comprising at least one cylinder-piston unit (4, 5) with an associated intake valve (13) for the introduction of fuel delivered by an electrical supply pump (15, 17), and a delivery duct (12). Electronic means (18, 19, 20) are provided for modulating the electrical supply pump to vary the pressure of the fuel taken in by the cylinder-piston unit and consequently the bottom dead centre position of the piston and hence the length of its pumping stroke.

Description: A fuel-injection system for diesel engines with a variable pump cylinder capacity . The present invention relates generally to a fuel-injection system for diesel engines. More particularly the invention concerns a system comprising a fuel-injection pump having at least one cylinder in which a pumping piston driven by an eccentric is slidable between a bottom dead centre position and a top dead centre position and defines within the cylinder a pumping chamber which is connected to a fuel-intake duct and a fuel-delivery duct through an intake valve and a delivery valve respectively; an electric supply pump associated with the intake duct and supplying fuel from a tank to the injection pump. It is known from the FR-A-2585077 a fuel-injection system of the above type, wherein the variable flow rate of the pump is obtained by means of either a throttle or a distributor, which is provided with a control member associated with a reducer of the intake fuel pressure. The object of the present invention is to provide a fuel-injection system comprising an injection pump of the type described above which is arranged, by simple and practical means, to supply fuel at variable flow rate by means of the variation of its cylinder capacity. This object is achieved by the above defined fuel-injection system which is characterised by an equalising spring, the spring being interposed between the piston and the eccentric thus enabling the position of the bottom dead centre of the piston to be varied; and by an electronic control unit, the unit controlling the motor of the electric supply pump to vary the pressure of the fuel taken in by the pumping chamber of the injection pump and consequently the bottom dead centre position of the piston and the length of its pumping stroke. By virtue of this concept, the cylinder capacity is varied so as to vary the flow rate by means of the modification of the initial position of the piston, so varying its useful stroke, by means of the modulation of the pressure of the electrical supply pump. This modulation is conveniently controlled by means of a microprocessor connected to a pressure sensor in the delivery duct of the pump. The invention is applicable both to radial injection pumps and to in-line injection pumps. The invention will now be described in detail with reference to the appended drawing, provided purely by way of non-limiting example, in which a diagram of an injection pump system according to the invention with variable cylinder capacity is shown schematically. With reference to the drawing, part of a fuel-injection pump for a diesel-engine injection system is generally indicated 1. In the embodiment illustrated, the pump 1 is of radial type and, in known manner, includes a plurality (normally three) of pumping units arranged radially around a rotor with an eccentric 2. Each of the units, only one of which is shown at 3 in the drawing, comprises a cylinder 4 in which a piston 5 driven so as to reciprocate in a straight-line by means of the eccentric 2 is slidable. The interior of the cylinder 4 is divided by the piston 5 into an upper pumping chamber 6 and a lower chamber 7 whose base is defined by a cup-shaped member 8 urged against the surface of the camshaft 2 by a thrust spring 9. An equalising spring 10 is interposed between the base of the cup-shaped member 8 and the piston 5 and tends to keep the piston 5 in equilibrium with the pressure of the fuel supplied to the pumping chamber 6, when it is at its bottom dead centre position. As will be seen below, this pressure is variable so as to allow the initial position of the piston 5 and hence its useful pumping stroke to vary. The pumping chamber 6 is connected on the one hand to a fuel-intake duct 11 and on the other to a fuel-delivery duct 12 through an intake valve 13 and a delivery valve 14 respectively. The fuel is delivered to the intake duct 11 by means of a supply pump 15 connected to a fuel tank 16 and driven by means of an electric motor 17. This electric motor 17 is energised through an electronic control unit including a PWM modulator circuit 18 in turn controlled by means of a microprocessor 19 in dependence on the fuel pressure in the delivery duct 12. For this purpose, the microprocessor 19 is supplied by means of a pressure transducer 20 inserted in the delivery duct 12. A pressure-control device 21, constituted by a pressure regulator, or by a calibrated maximum-pressure valve is also associated with the delivery duct 12 in conventional manner. In operation, it is necessary for the pressure in the pumping chamber 6 always to be higher than that in the lower chamber 7. For this purpose, it suffices to keep the latter at amospheric pressure. The microprocessor 19 regulates the operation of the electric supply pump 15-17 in dependence on the fuel-delivery conditions through pressure signals from the transducer 20 and thus modulates the pressure of the fuel taken in by the pumping chamber 6. This enables the bottom dead centre position of the piston 5, that is its useful stroke, to be modified, thus varying the cylinder capacity of the pump 1 so as to achieve a variable fuel flow rate. Although the embodiment illustrated relates to a radial pump, the invention is also applicable to in-line pumps.

Claims: 1. A fuel-injection system for diesel engines, the system comprising a fuel-injection pump (1) having at least one cylinder (4) in which a pumping piston (5) driven by an eccentric (2) is slidable between a bottom dead centre position and a top dead centre position and defines within the cylinder (4) a pumping chamber (6) which is connected to a fuel-intake duct (11) and a fuel-delivery duct (12) through an intake valve (13) and a delivery valve (14) respectively; an electric supply pump (15) associated with the intake duct (11) and supplying fuel from a tank (16) to the injection pump (1); characterised by an equalising spring (10), the spring (10) being interposed between the piston (5) and the eccentric (2) thus enabling the position of the bottom dead centre of the piston (5) to be varied and by an electronic control unit (18, 19, 20), the unit (18, 19, 20) controlling the motor (17) of the electric supply pump (15) to vary the pressure of the fuel taken in by the pumping chamber (6) of the injection pump (1) and consequently the bottom dead centre position of the piston (5) and the length of its pumping stroke. 2. A fuel-injection system according to Claim 1, characterised in that the electronic control unit (18, 19, 20) includes a microprocessor (19) connected to an electrical pressure sensor (20) inserted in the delivery duct (12) of the injection pump (1).

Inventors: AUSIELLO, FRANCESCO PAOLO
Applicants: WEBER S.R.L.
Application year: 1988
Main classification: F02M59
IPC codes: F04B9, F02M59, F02B3