WO1988005498A1

WO1988005498A1 - A pump component in fuel injection pumps

Info

Publication number: WO1988005498A1
Application number: PCT/SE1988/000013
Authority: WO
Inventors: Bengt Gadefelt
Original assignee: Saab-Scania Aktiebolag
Priority date: 1987-01-20
Filing date: 1988-01-19
Publication date: 1988-07-28
Also published as: SE8700189D0; SE455627B

Abstract

Pump component in a fuel injection pump in which fuel injection is controlled by at least one piston (3) which is movable in a cylinder (2) and which defines above the piston a chamber or space (12) in which fuel injection pressure is generated. The purpose of the pump component is to enable the fuel injection pressure to build-up relatively slowly in the chamber (12), preferably at relatively low engine speeds, so as to reduce the so-called ignition delay. The invention is mainly characterized in that the cylinder wall incorporates at least one through-passing bore (14) through which fuel is pressed during upward movement of the piston (3) in the cylinder (2).

Description

A pump component in fuel injection pumps

The present invention relates to a pump component for use in a fuel injection pump for an internal combustion engine and comprising a cylinder in which there is housed a piston which defines a variable pump chamber in the cylinder and performs axial pump movements therein, and in which pump component the wall of the cylinder incorporates an inlet aperture which is exposed by the piston during a part of the piston movement such that fuel can flow into said pump space, and in which one end of the cylinder incorporates an outlet through which fuel under pressure can be pumped from said space, and in which the cylinder wall has provided therein a throughpassing bore which opens out into the chamber at a location between the inlet aperture and the outlet.

In the case of direct fuel-injection diesel engines, the combustion process which takes place in the combustion chamber of respective cylinders does not commence until a given period of time has lapsed from the time at which fuel was first injected into the engine cylinders. A relatively large quantity of fuel is able to enter the cylinders during this time interval, which is commonly referred to as ignition delay. When this relatively large quantity of fuel is ignited, a pronounced rise in pressure occurs in the com¬ bustion chamber during the initial stage of the combustion process. This pronounced increase in pressure, which is particularly manifest at low engine speeds, gives rise to high combustion noise levels and increases the proportion of harmful substances carried by the exhaust gases.

It is known that this ignition delay can be reduced by injecting a small amount of fuel into the cylinders before the main fuel injection takes place. However, in order to achieve lower combustion-noise levels and optimum exhaust compositions when applying this solution, it is necessary to control accurately the time interval between the fuel pre- -injection and main injection. Those arrangements known to the art for controlling the time lapse between the fuel pre-injection and main injection are relatively complicated and/or require the provision of separate fuel injection devices, in order to obtain sufficient pump capacity.

The object of the present invention is to provide a rela- tively inexpensive and simple arrangement which will reduce the aforesaid ignition delay without exhibiting the afore¬ mentioned drawbacks of known arrangements, preferably at relatively low engine speeds.

To this end. the inventive pump arrangement is characterized in that the through-passing bore in the cylinder wall forms a connection between the pump space and a fuel collecting chan¬ nel connected to a fuel tank, such as to enable a limited quantity of fuel to flow out from the pump space and thereby delay the build-up of fuel pressure in said space.

A small quantity of fuel is pressed out through the bore during upward movement of the piston in the cylinder, prefer¬ ably at relatively low engine speeds. Consequently, the fuel injection pressure will build up relatively slowly in the space above the piston, which is contributory in delaying the injection of fuel into the engine cylinders and in reducing the ignition delay. The ignition delay is not reduced to any appreciable extent at high engine speeds, since there is not time for fuel to be forced out through the bore at such high piston speeds.

The quantity of fuel forced out through the bore can be varied by varying the configuration of the bore. Thus, with the aid of one advantageous embodiment, it is possible to achieve lower combustion-noise levels and an optimum exhaust composition in a relatively simple and inexpensive fashion. Other features characteristic of the present invention will be apparent from the following claims and from the following description of an exemplifying embodiment of the invention made with reference to the accompanying drawings, in which

Figure 1 is a partially sectioned view in perspective of an inventive fuel-injection pump component and illustrates the pump component during an initial stage of an injection process; and

Figure 2 is a corresponding detailed view of the pump component during a final stage of the injection process.

Figure 1 illustrates a pump component 1 which, together with a plurality of similar pump components, forms part of a conventional fuel injection pump 8 for an internal combustion engine, more specifically a direct-in ection diesel engine.

The pump component 1 comprises a pump cylinder 2 and a pump piston 3 which is journalled for axial movement in the cylinder and which is urged into abutment with a cam shaft 4. by a downwardly acting force exerted by a thrust spring, not shown. The piston 3 is thus guided axially by the cam shaft 4. the rotational movement of which is produced through the engine transmission and is contingent on engine speed.

The piston 3 can also be rotated about its longitudinal axis in a known manner, with the aid of an axially displaceable control rod 5. the movement of which is governed by an engine-speed dependent regulator 6 and an engine-load sensor 7. The regulator 6 and the sensor 7 are illustrated solely schematically in Figure 1.

The piston 3 co-acts with two fuel inlet apertures or ports 10. 11 in the cylinder 2. Fuel is taken from a fuel tank (not shown) through two fuel channels 22, 23 formed in the fuel injection pump 8 and delivered to a chamber 12 above the piston 3. The chamber 12 communicates, via a radially extending bore 14 in the wall of the cylinder 2. with a fuel collecting channel 13 formed in the pump 8. The bore 14 is essentially circular in cross-section. The fuel connecting channel 13 is connected with the fuel tank of the vehicle.

As shown in Figures 1 and 2, the piston 3 is provided with an arcuate regulating edge 19, which forms an upper defining wall of an annular space 20 adjacent the cylindrical surface of the piston 3. The annular space 20 is connected with the chamber 12 above the piston 3 by an axial groove 21 in the outer surface of the piston 3.

Also shown in Figure 1 is a pressure valve 24. which is placed on the upper end of the pump component 1. The pressure valve 24 comprises a valve housing 25, in which a valve plunger 26 is urged against a valve seating 27 through the agency of a thrust spring 28. The valve 24 has connected thereto a pressure pipe 31 which joins the pump 8 to a fuel injector by means of which fuel is injected into the engine combustion chamber (not shown) .

The inlet apertures 10. 11 are exposed during an initial stage of a fuel injection sequence, as illustrated in Figure 1. This allows fuel to flow in the direction of the arrows in Figure 1, to fill the chamber 12 above the piston 3. and the space 20 adjacent the outer cylindrical surface of the piston 3. When, during its upward travel, the piston 3 reaches a position in which an upper edge 33 of the piston has passed both inlet apertures 10. 11. the fuel enclosed in the chamber 12 is compressed as a result of the continued upward movement of the piston. However, in accordance with the invention, a small part of the fuel enclosed by the chamber 12 will be forced out through the bore 14 in the cylinder wall during this compression of the fuel. Consequently, there is obtained a relatively slow build-up of the fuel pressure in the cham¬ ber 12 during this compression stroke of the piston. When the pressure in the chamber 12 reaches a pre-determined value, the valve plunger 26 is lifted against the action of the thrust spring 28 and fuel under high pressure is fed through the pressure pipe 31 for injection into the combustion chamber of the engine.

As the piston continues to move upwards, the regulating edge 19 will pass the inlet aperture 10, so as to connect the chamber 12 with said inlet aperture via the axially extending groove 21 in the piston 3. This connection is indicated with an arrow in Figure 2. When this connection is established, the pressure of the enclosed fuel will fall and the valve plunger 26 will be urged by the spring 28 into sealing abutment with the valve seating 27. therewith interrupting the injection of fuel into the engine combustion chamber.

It will be understood that the amount of fuel delivered by the pump 8 is determined by the distance a_ between the upper edge of the piston 3 and the regulating edge 19. Since the regulating edge 19 can be brought to different positions in relation to the inlet apertures 10, 11 in the cylinder 2 by twisting the cylinder 3. it is a simple matter to vary the quantities in which the fuel is delivered.

When the piston 3 has passed its top-dead-centre position and moves downwards in the cylinder 2 under the pressure of the thrust spring (not shown), a partial vacuum is created in the chamber 12 above the piston 3. Consequently, when the fuel inlet apertures 10, 11 are uncovered from the upper edge 33 of the piston 3, fuel will be drawn by suction in through the inlet apertures 10, 11 and refill the chamber 12 above the piston 3 and the space 20 adjacent the outer cylindrical surface of the piston. The fuel injection sequence is then repeated in the aforedescribed manner.

As the piston 3 moves upwards in the cylinder 2, a small amount of fuel is forced out through the bore 14 in accord- ance with the invention. Consequently, the build-up of fuel injection pressure in the chamber 12 above the piston 3 is relatively slow, which means that a longer period of time is taken to reach the pre-determined valve opening pressure. This in turn means that the injection of fuel is delayed, which results in a reduction in the ignition delay.

The quantities in which fuel is pressed 'from the cylinder can be varied, by modifying the bore 14 in different ways with regard to both its position in the cylinder 2 and its cross- -sectional shape. Thus, with a suitable embodiment it is possible to achieve lower combustion-noise levels and im¬ proved exhaust compositions in a relatively simple and in¬ expensive fashion.

The aforedescribed embodiment is not limitive of the inven¬ tion, but can be modified in.various ways within the scope of the following claims.

Claims

Cla ims

1. A pump component for use in a fuel injection pump (8) for an internal combustion engine, comprising a cylinder (2) in which there is housed a piston (3) which defines a variable pump chamber (12) in the cylinder (2 ) and performs axial pump movements therein, and in which pump component the wall of the cylinder incorporates at least one inlet aperture (10. 11) which is exposed by the piston (3) during part of the piston movement so that fuel can flow into the pump chamber (12). and in which one end of the cylinder (2) incorporates an outlet (31) through which pressurized fuel can be pumped from the pump chamber (12). and in which the cylinder wall has provided therein a through-passing bore (14) which opens out into the chamber (12) at a location between the inlet apertures (10. 11) and the outlet (31), characterized in that the bore (14) forms a connection between the chamber (12) and a fuel collecting channel (13) joined to a fuel tank, such as to allow a limited quantity of fuel to flow from the chamber (12) in order to delay the build-up of fuel pressure in the pump chamber (12).

2. A pump component according to claim 1, characterized in that the bore (14) extends substantially radially through the wall of the cylinder (2).

3. A pump component according to claim 1, characterized in that the bore (14) is substantially circular in cross-section.