GB2299138A - Fuel system - Google Patents

Abstract

A fuel injection system includes a rotary distributor member which is housed within a surrounding body (10). The body is formed by an inner sleeve (36) which is a close fit within an outer sleeve (37). Aligned recesses (38, 39) are formed in the presented surfaces of the two sleeves and these define an accumulator chamber in which is stored fuel at high pressure. The distributor acts to deliver fuel to outlets connected to the fuel injection nozzles of an engine, the fuel flowing from the accumulator chamber under the control of a valve.

Description

FUEL SYSTEM This invention relates to a fuel injection system for supplying fuel to an internal combustion engine and of the kind comprising an accumulator chamber, means for charging the accumulator chamber with fuel under pressure, valve means to control the flow of fuel under pressure from the accumulator chamber and rotary distributor member housed within a surrounding body for directing fuel to a plurality of outlet ports in turn during successive operations of said valve means.

An example of such a system is seen in Figure 2 of EP-A-0643221. As shown therein the rotary distributor member is housed within a body which is defined by an inner annular sleeve which is a close fit within an outer sleeve. At least the inner sleeve is formed from a high grade steel to resist wear as the distributor member rotates in use. The outer sleeve is formed form a lower grade of steel and the two sleeves are provided with various drillings some at least of which contain fuel at high pressure. The accumulator chamber is defined in a separate part which is secured to the housing of the apparatus and a complex connection arrangement is provided to connect the accumulator chamber to passages formed in the sleeves. The connecting arrangement includes a spigot which is mounted within a bore in the outer sleeve.

Apart from the need to provide a separate part to accommodate the accumulator chamber the connection arrangement has to be carefully constructed to ensure a fuel tight seal or seals.

The object of the present invention is to provide a system of the kind specified in an improved form.

According to the invention in a system of the kind specified said surrounding body is formed by inner and outer sleeves, the outer sleeve being a tight fit about the inner sleeve, the accumulator chamber being defined by aligned recesses formed in the inner peripheral surface of the outer sleeve and the outer peripheral surface of the inner sleeve respectively.

According to a further feature of the invention the chamber defined by the recess has a smaller axial dimension than its radial dimension.

An example of a fuel system in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of the system, and Figure 2 shows a practical detail of part of the system shown in Figure 1.

Referring to Figure 1 of the drawings the fuel system comprises a housing 10 in which is mounted a rotary cylindrical distributor member 11. The distributor member is arranged to be rotated in timed relationship with the associated engine by means of a drive shaft 12 which is shown to be separated from the distributor member but which in practice is coupled thereto. The distributor member includes a delivery channel which is in the form of an outwardly extending delivery passage 1 3 positioned to register in turn with a plurality of outlet ports 14 only one of which is shown. The outlet ports are connected to outlets 15 formed in the housing and there are as many outlet ports and outlets as there are engine cylinders.The outlets in use are connected to the injection nozzles of the associated engine and the usual delivery valves may be located in the outlets respectively.

The delivery passage 1 3 communicates with a circumferential groove 16 formed on the periphery of the distributor member and this is in constant communication with a passage 17 formed at least in part in the housing.

The passage 1 7 can communicate by way of an electromagnetically operable valve 18 with either a further passage 19 which is connected to an accumulator chamber 20 or with a drain passage 21.

The valve 18 is a two position valve and in one position as shown in the drawing, the passage 17 is connected to the drain 21. In the other position the connection to the drain is blocked off and the passage 1 7 communicates with the passage 19. The valve is controlled by an electromagnetic actuator which is supplied with current by an electronic control system 22. The control system acts to control the speed of the engine in accordance with various engine operating parameters and also in accordance with a demand signal which is provided by a transducer responsive to the position of the operator controlled throttle pedal of the vehicle associated with the engine. The control system may also receive signals indicative of the engine temperature and air temperature etc.In addition, it receives a signal or signals from a transducer system 23 which is responsive to the passage past a sensor, of teeth formed on the drive shaft 12. From this signal a signal can be derived indicative of the engine speed and also the engine position.

Assuming for the moment that the accumulator is charged with fuel at high pressure, when the delivery passage 13 is in register with an outlet port 14, the valve 18 can be operated to permit flow of fuel from the accumulator 20 to the outlet port and the fuel injection nozzle in communication therewith, so that fuel is supplied to the associated engine. The amount of fuel and the timing of delivery are controlled by varying the length of time the valve member of the valve 18 is in the alternative position to that shown and the instant at which the valve operates. When the valve member assumes the position shown the pressure in the passage 1 7 and the groove and delivery passage within the distributor member is reduced to drain pressure which may be the pressure within the pump housing.

In the example the accumulator is charged with fuel by means of a cam actuated high pressure fuel pump 8 which conveniently is in the form of a pair of reciprocable pumping plungers 24 located within a diametrically disposed bore 25 formed in a part of the distributor member which extends from the housing. At their outer ends the plungers are engaged by shoes respectively each of which carries a roller which can engage with the internal peripheral surface of an annular cam ring 26. The bore 25 is in constant communication with a circumferential groove 27 formed on the periphery of the distributor member and this communicates with the passage 19 and therefore the accumulator chamber 20 by means of a non-return valve 28 which may be constituted by one or more valves.The bore 25 is also in communication with a diametrically disposed inlet passage 29 formed in the distributor member and which when the plungers are allowed to move outwardly, communicates with a filling port or ports 30 formed in the housing 10.

The filling ports 30 communicate with the outlet of a low pressure vane type pump 31 the rotary part of which conveniently is secured to the rotary distributor member 11. The pump 31 has a fuel inlet 32 which by way of the usual filter 33, is connected to a source of supply. Associated with the pump 31 is a pressure control valve 34 which affords variable communication between the outlet and the inlet of the pump in order to control the fuel delivery pressure of the low pressure pump.

Conveniently the valve 34 is electrically controlled with the control being effected by the control system 22. The control system 22 also receives a signal from a sensor 35 which is responsive to the pressure of fuel within the accumulator.

The cam ring 26 is provided with a plurality of pairs of cam lobes the leading flanks of which considered in terms of the direction of rotation of the distributor member, impart inward movement to the plungers.

During such movement the inlet passage 29 is out of register with the filling ports 30 so that the fuel displaced by the plungers is supplied to the accumulator by way of the valve 28. As the rollers ride over the crests of the cam lobes, the plungers can move outwardly and it is whilst the plungers are under the control of the trailing flanks of the cam lobes that the passage 29 is in communication with a filling port 30. When such communication is established fuel can flow to the bore 25 from the low pressure pump and the amount of fuel which flows can be varied by adjusting the outlet pressure of the low pressure pump using the control valve 34. Adjusting the outlet pressure of the low pressure pump 31 does vary the quantity of fuel which flows into the bore 25 due to the restrictive nature of the passages which connect the outlet of the low pressure pump with the bore 25. The control system controls the setting of the valve 34 in response to the signal provided by the pressure transducer 35. It is therefore possible to regulate the pressure in the accumulator using the control valve 34 and valve only has to deal with and be designed for use with fuel at a low pressure. As an alternative to the control valve 34 an adjustable throttle 30A may be located in the passage connecting the outlet of the low pressure pump and the filling ports.

The ability to regulate the pressure within the accumulator is an important advantage of the present system over the usual cam actuated pump systems such as the normal distributor type pump in which the plungers form the high pressure pump, and the unit/injector type of pump. With these pumps ensuring that fuel is delivered at a sufficiently high pressure through the injection nozzle at low engine speeds means that at high engine speeds the pressure may be higher than is required.

With the system as described the pressure in the accumulator can be controlled so that the injection pressure is suitable for all engine operating speeds and loads. Furthermore, the construction of the pump embodies well known and well tried technology.

The valve 18 is shown as a two position spool valve with a single valve member. It can be replaced by two valves which are actuated separately with one valve acting when open to connect the accumulator to the passage 1 7 and the other acting when open to connect the passage 1 7 to the drain. In this way one valve can be used to start delivery of fuel and the other to terminate delivery of fuel. Other forms of valve can be used and in addition, instead of direct actuation by the actuator the valves may be actuated using a hydraulic or pneumatic arrangement.

Turning to Figure 2, this shows the construction of the housing 10 and it will be seen to comprise an inner sleeve 36 which is formed from high grade steel and an outer sleeve 37 formed from lower grade steel. The various passages which open onto the periphery of the distributor member are drilled in the two sleeves prior to assembly of the sleeves to form the housing.

Moreover, in accordance with the invention prior to the assembly of the sleeves there is machined in the outer peripheral surface of the inner sleeve a circumferential recess 38 and in the inner peripheral surface of the outer sleeve a further circumferential recess 39. The two recesses are positioned so that when the sleeves are assembled, they are in alignment with each other so as to form an annular accumulator chamber.

The location and the shape of the chamber have to be chosen with care in order to minimise distortion of the bore 40. The working clearance between the distributor member 11 and the bore has to be kept as small as possible in order to minimise leakage of fuel. However, the clearance has to be chosen so as to accommodate the thermal expansion of the distribution member which takes place before that of the housing when there is an increase in the fuel supply to the engine. In the worst situation the diametral clearance can fall to as low as 1 .5;jm.

Such distortion of the bore 40 due to the fuel pressure must therefore be less than this figure otherwise there is a risk of seizure. As shown in Figure 2 the accumulator chamber 40 is positioned mid way between the ends of the sleeves and has a cross-section the axial dimension of which is smaller than the radial dimension. The corners of the recesses which form the chamber are also radiused.

Variation of the mean radius of the chamber has an influence on the distortion which takes place. If the mean radius is increased the distortion of the sleeve which takes place tends to reduce the bore diameter at the ends of the sleeve and if the mean radius is reduced the distortion which takes place tends to reduce the bore diameter intermediate its ends.

If the axial length of the chamber is increased there tends to be a reduction in the diameter of the bore intermediate its ends whereas if the length is decreased the diameter of the bore tends to reduce towards its ends. The radius of curvature of the corners of the chamber also influences the distortion pattern of the bore.

However, by careful choices of the various dimensions it is possible to provide an accumulator chamber of sufficient volume with an acceptable distortion of the bore.

Claims (3)

1. A fuel injection system for supplying fuel to an internal combustion engine and comprising an accumulator chamber, means for charging the accumulator chamber with fuel under pressure, valve means to control the flow of fuel under pressure from the accumulator and a rotary distributor member housed within a surrounding body for directing fuel to a plurality of outlet ports in turn during successive operations of said valve means, said surrounding body being formed by inner and outer annular sleeves, the outer sleeve being a tight fit about the inner sleeve, the accumulator chamber being defined by aligned recesses formed in the inner peripheral surface of the outer sleeve and the outer peripheral surface of the inner sleeve respectively.

2. A system according to Claim 1, in which the chamber defined by the recess has a smaller axial dimension than its radial dimension.

3. A fuel injection system substantially as hereinbefore described with reference to the accompanying drawings.