Field of the invention

The present invention relates to a fuel inj ected internal combustion engine with an inj ector for direct inj ection of fuel into the combustion chamber of the engine .

Background of the invention

Direct injection of fuel into the combustion chamber of an engine overcomes problems in conventional port injection systems caused by wetting of the intake manifold and the intake port. These problems, which are well documented, arise because the pool of fuel in the intake port disturbs the fuel metering when the engine is not operating under steady state conditions by introducing an element of hysteresis. In-cylinder fuel injections also allows the engine to run with a stratified charge, in other words the mixture strength can vary in different regions of the combustion chamber. This allows lean burn operation for fuel economy and can permit the load to be controlled in a spark ignited engine in the same manner as in a diesel engine, in other words by regulating the quantity of fuel injected in each cycle rather than by throttling of the air intake.

In a direct injection system in which the injector is exposed permanently into the combustion chamber, the injector must be designed to withstand the temperatures and pressures that arise during engine operation and this adds to the system cos .

To avoid this problem, it has been suggested to use a poppet valve to isolate the injector from the combustion chamber. In this case, the injector injects the fuel into a small chamber closed off from the main combustion chamber by the

poppet valve. The poppet valve subsequently opens to let the fuel in the injection chamber enter the main combustion chamber.

The injection chamber in this case stores fuel and risks reintroducing problems associated with wall wetting. Furthermore fuel preparation and atomisation is no longer controlled by the injector but is instead determined by the poppet valve when it opens and spurts the fuel out into the combustion chamber.

Summary of the invention

According to the present invention, there is provided an engine having a combustion chamber with one or more intake ports and an injector for directing a spray or jet of fuel directly into the combustion chamber, the injector being arranged in an injector chamber distinct from the engine intake port or ports and separated from the combustion chamber by a poppet valve that closes to isolate the injector from the combustion chamber during part of the engine operating cycle, the injector being opened only at times that the poppet valve is open and the spray or jet from the injector being arranged to pass through the orifice of the open poppet valve without wetting the walls of the injector chamber.

During the intake period of an engine, the pressure in the combustion chamber is low and it is possible to open the injector directly into the combustion chamber without damaging the injector. The injector may be exposed to the temperatures and pressures in the combustion chamber throughout the intake period as well as the latter part of the exhaust period and the early part of the compression period. This allows ample time to inject the quantity of fuel required, even under high load conditions.

The poppet valve of the injector chamber is opened generally in phase with the opening of the engine intake port but it can be allowed to remain open for a longer period than the intake period, and may be operated by a cam, a solenoid or a hydraulic actuator. The injector fuel pressure and the injection timing may be varied within this extended opening period of the poppet valve to achieve optimum charge stratification.

In the invention, the injector sprays directly into the combustion chamber and its spray pattern and atomisation quality are not compromised. In this respect, the injector may resemble a conventional injector as used to inject fuel into the intake port of an engine. Because of this, there is no need for a pressurised air charge to be provided inside the injector chamber to force the fuel out of the injector chamber as in other prior art proposals.

Furthermore, significant latitude is present in positioning the fuel spray from the injector within the combustion chamber to allow for better charge stratification. For example, the spray may be directed across the spark plug to form an ignitable mixture near the spark or it may be directed towards the intake port to achieve good mixing with the intake air.

A jet from the injector may alternatively be directed onto to a deflector formed in the combustion chamber or by the rear face of the open poppet valve. The deflector may in this case be ultrasonically vibrated to assist further in the atomisation of the injected fuel.

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which :

Figure 1 is a schematic representation of an engine combustion chamber fitted with an in-cylinder injector of the present invention,

Figure 2 is a section through an in-cylinder injector in accordance with a first embodiment of the invention, and

Figures 3 and 4 show similar section through two further alternative embodiments of injector.

Detailed description of the preferred embodiments

In Figure 1, there is shown schematically a combustion chamber of an internal combustion engine. The variable volume chamber 10 is defined between a piston 12 and a cylinder 14. Intake air is drawn into the combustion chamber 10 from an intake port 16 having a cam operated poppet valve 18 and the combustion gases escape through an exhaust port 20 also controlled by a cam operated poppet valve 22. A spark plug 24 is fitted in the cylinder head and an in-cylinder injector assembly 26, described in more detail below, supplies fuel directly into the combustion chamber 10 without passing through the intake port 16.

Turning now to Figure 2, the surface 50 is a wall of the combustion chamber. The injector assembly 26 is formed of a block 52 that is mounted in an opening in the cylinder head and that defines at its lower end an injector chamber 54 of small volume. The injector chamber 54 is separated from the

engine combustion chamber by a poppet valve 56 operated by an actuator 58, represented a a solenoid but which may alternatively be a cam or a hydraulic mechanism.

A conventional injector 60 as would normally be used for port injection is mounted in the block 52 and is formed with an elongate nozzle 62. The nozzle 62 terminates very close to the opening of the poppet valve 56 and is designed and positioned to direct its spray through the orifice of the open poppet valve without the spray wetting the walls of the injector chamber 54 formed in the block 52.

The injector 60 is only opened when the poppet valve 56 is also open so that fuel is discharged directly into the combustion chamber 10. The spray quality is determined by the injector nozzle 62 and can be directed at will to optimise fuel distribution so as to achieve charge stratification.

The poppet valve 56 is opened at times when the pressure in the combustion is low and is closed to isolate the injector 60 from the combustion chamber at least during the end of the compression period and the power period. This means that the poppet valve can be open throughout the intake period as well the later part of the exhaust period and the initial part of the compression period. This allows ample time to inject the required amount of fuel under, all engine operating conditions.

The injector fuel pressure and the injection timing may be varied within this extended opening period of the poppet valve to achieve optimum charge stratification. By injecting as late as possible into the compression period, the fuel may concentrated near the spark plug with a minimum time delay from ignition.

The injector assemblies 26' of Figures 3 and 4 differ from

that previously described in only minor respects. To avoid repeating the description, like components have been designated with like reference numerals, with the addition of primes to the numerals. In Figure 3, instead of the spray from the injector being aimed through the opening of the poppet valve 56' into the combustion chamber, the injector 60' produces a fine jet that is aimed to impinge on the rear surface of the poppet valve 56' and to bounce off this surface into the combustion chamber. A piezoelectric transducer is connected to an electrical HF audio signal to vibrate the poppet valve 56' ultrasonically so as to assist in fuel atomisation.

In Figure 4, the injector 60" is designed to produce a jet that is aimed at a deflector 72 positioned within the combustion chamber. Wall wetting of the deflector 72 is unimportant in that the deflector will itself be hot and in any event the fuel will already have been delivered to the combustion chamber.

The invention is equally applicable to two-stroke and four-stroke engines.