Fuel injection assembly for internal combustion engine

A fuel injection assembly for an internal combustion engine comprises a pair of solenoid valves mounted on a common manifold defining a fuel supply passage which is filled with pressurized fuel at all times during operation of the engine. The solenoid valves discharge into a common chamber having a spray nozzle located at the downstream end thereof. No valve is located between the solenoid valves and the discharge end of the spray nozzle. In use, when the solenoid valves are open, the pressure drop across the solenoid valves is small with substantially the entire pressure drop associated with the assembly occurring across the nozzle. Accordingly a relatively low hold current is required by the solenoid valves.

This invention relates to a fuel injection assembly for an internal 
combustion engine, and in the preferred embodiment provides a fuel 
injection assembly particularly suitable for a high performance petrol 
engine. 
Known fuel injections assemblies for petrol engines have comprised a 
solenoid valve having a spray nozzle at the outlet thereof to provide a 
spray of fuel in response to opening of solenoid valve. With such known 
injectors the rate at which fuel can be injected is dependent on the 
pressure drop across the solenoid valve. The maximum pressure differential 
at which a solenoid valve will reliably operated is, in practice, 
determined by the operating current available. As a practical matter, the 
rate at which fuel can be injected with a conventional arrangement is 
severely limited with the result that a relatively long injection period 
is necessary in order to supply sufficient fuel per cylinder charge. In 
practice, a typical indirect (port) injector will be more or less 
continuously injecting under full throttle driving conditions. 
Whilst such injection assemblies have proved reasonably satisfactory for 
most engines, they do suffer from significant disadvantage. Firstly they 
have proved inadequate for very high performance engines such as those 
used, for example, in racing cars where it is necessary under full 
throttle conditions to provide a very large fuel flow rate. Secondly, even 
for conventional car engines the very long periods of injection required 
under full throttle conditions do not admit to precise control of the 
combustion conditions with the result that the engine will produce 
excessive pollutants. 
If the size of a conventional fuel injection assembly is increased to 
provide the desired fuel flow rate, the moment of inertia of the moving 
parts of the solenoid valve becomes large, and accordingly the maximum 
number of operations per second of the fuel injection assembly becomes 
undesirably limited. Also, if the size of the injection nozzle is made 
large enough to accommodate the desired maximum flow rate it becomes very 
difficult to provide accurate control of fuel flow at the very low flow 
rates required under engine idle conditions. If the physical size of the 
injection nozzle is kept small in order to avoid the problem of excessive 
moment of inertia referred to above, and the fuel pressure is increased in 
order to increase flow rate, the valve requires a very high level of hold 
current in order to maintain the valve open during injection periods. This 
leads to difficulties in the electronic control systems necessary to 
control opening of the solenoid valves. 
We have now found that the problems outlined above can be avoided if a 
plurality of solenoid valves are connected to a common chamber having at 
least one spray nozzle at the downstream end of thereof. By placing the 
spray nozzle at the downstream end of a common chamber to which the 
solenoid valves are connected the solenoid valves can operate under 
conditions where a relatively low pressure differential exists across the 
solenoid valve. Because the pressure differential across the solenoid 
valves is low, the fuel supply pressure can be increased without requiring 
an excessively high operating current for the solenoid valves. The high 
fuel pressure means that when the solenoid valves are open a large flow 
rate is produced, thereby permitting sufficient fuel for each induction 
stroke to be sprayed into the inlet manifold during a relatively short 
period of time. The short period required for injection can be precisely 
controlled as to duration and timing relative to crankshaft angle, and the 
precisely defined timing can readily be varied under electronic program 
control to suit particular engine operating conditions. 
Accordingly, one aspect of the present invention provides a fuel injection 
assembly for an internal combustion engine comprising: at least two 
solenoid valves, the outlets of which are connected to a common chamber; 
and at least one spray nozzle forming the downstream end of said common 
chamber to provide a spray of fuel in response to opening of at least one 
of the solenoid valves. 
It has been found that by appropriately designing the common chamber, no 
valving arrangement need be provided downstream of the solenoid valves 
themselves, i.e. no form of valve need be provided at the downstream end 
of the common chamber.

The invention will be better understood from the following description of a 
preferred embodiment thereof, given by way of example only, reference 
being had to the accompanying drawing wherein the single Figure is a view, 
partly in section, of a preferred embodiment of the invention. 
Referring to the drawing, the fuel injection assembly 1 comprises a pair of 
solenoid valves 2,3 secured to a manifold 4 in which is formed a fuel 
supply passage 5. In use, fuel under pressure is present at all times 
within the passage 5, and is supplied to the solenoid valves 3,4 via inlet 
openings 6,7. Advantageously, the solenoid valves 2,3 are of the type 
commonly used in conventional electronic petrol injection systems. 
The outlet end of each solenoid valve 2,3 is connected to a chamber 8 which 
is common to both solenoid valves. The downstream end of the chamber 8 is 
formed by a nozzle assembly 9 comprising a nozzle body 10, spray tip 11, 
and a feed tube 12. The feed tube 12 is in screw-threaded engagement with 
the body to clamp the tip 11 against an inturned flange 13 at the low 
extremity of the body. 
The entire nozzle assembly 9 is secured to the manifold 4 by a circlip 14 
and an O-ring 15 is provided to form a fluid seal between the nozzle 
assembly 9 and the manifold 4. 
The interior of the feed tube 13 forms part of the chamber 8, and the spray 
tip 11 forms the extreme downstream end of the chamber 8. It has been 
found that with the arrangement illustrated, air is readily bled from the 
chamber 8 and there is no tendency, in use, for fuel to leak from the 
injection assembly when the solenoid valves are closed. Accordingly, 
opening of one or both solenoid valves provides substantially 
instantaneous spray of fuel from the spray tip. 
Under idle only conditions, only one of the solenoid valves 2 need be 
energized in order to provide the relatively small amount of fuel 
required. As engine speed and load increases, the solenoid valves 2,3 are 
controlled by an electronic control system to meter the required amount of 
fuel at each opening. Under full throttle conditions, both solenoid valves 
open to provide the desired amount of fuel. As soon as the valves open 
fuel pressure builds within the chamber 8 producing a relatively small 
pressure differential across the valves. Thus, the fuel supply pressure in 
the passage 5 can be maintained at a level sufficient to produce a high 
rate of flow through the opening of the spray tip 11 when the valves are 
open. Accordingly, the required volume of fuel can be injected during a 
relatively short and precisely timed injection period. Further, because of 
the low pressure differential across the solenoid valves a relatively low 
current is required to hold the solenoid valves open. Accordingly, the 
solenoid valves can satisfactorily be operated by applying an initial high 
spike current to open the solenoid valves, and thereafter a relatively low 
hold current to maintain the solenoid valves open during the remainder of 
the injection period.