GB2453581A

GB2453581A - Equalising air fuel ratios between cylinders without detecting camshaft position in an internal combustion engine with shared inlet ports

Info

Publication number: GB2453581A
Application number: GB0719958A
Authority: GB
Inventors: David Hampshire
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-10-10
Filing date: 2007-10-10
Publication date: 2009-04-15
Also published as: GB0719958D0

Abstract

Air fuel ratios must be equal between all cylinders of an internal combustion engine. In an engine which has a single inlet port supplying two cylinders, air fuel ratios can be balanced between said cylinders without the need for camshaft phase sensing. From camshaft timing figures, the cylinder that would typically receive a lean mixture can be determined. This cylinder is then supplied with fuel from the injector when its inlet valve is open. The other cylinder in the shared-port pairing is supplied with fuel from the injector after one crankshaft revolution. Even if the inlet valve for this cylinder is not open, the fuel remains suspended within the inlet port ready for when the intake stroke begins. The intake strokes of the two cylinders A,B may be separated by 360{, fig.2, or by only 180{, fig.3, in which case although the injection event 6 does not coincide with the intake stroke of cylinder A, the fuel remains suspended within the inlet port until required, obviating the need for a camshaft phase sensor.

Description

I

EQUALLSING AIR FUEL RATIOS BETWEEN CYLINDERS WITHOUT DETECTING

CAMSHAYr POSON ZN AN INTERNAL COMBUSTION ENGINE WITH SHARED

INLET PORTS

The invention relates to a method for equalising air fuel ratios between two cylinders in an internal combustion engine, each of which share a single inlet port More particularly, the method describes how this can be achieved by an electronic management system without sequentially controlled fuel injection.

Many internal combustion engines share the same common inlet port between two or more cylinders.

This configuration saves physical space, allowing the power unit to fit into a smaller area. Fwthermore, it reduces the cost of producing engines as fewer raw materials are required. Such engines, and their corresponding electronic maigemn systems, must be designed so that air fuel ratios are kept equal in every cylinder that the common inlet supplies A mismatch in air fuel ratios will insult in loss of engine efficiency in terms of power output, fuel consumption and exhaust emissions. Long term running in this condition could also lead to permanent engine damage.

Due to the digital nature of electronic fuel injector operation, delivery of fuel to each cylinder of an internal combustion engine is ascertained by the time period for which the supplying fuel injector is held open. Within US Patent No. 5,477,830, && Ct al. describe bow these pulses can be synchronised so that fuel is injected into the shared intake port only during the specific intake strokes of individual cylinders. Timing the fuel injection pulses in such a mann ensures that all of the fuel from a single injection event is drawn into only one cylinder, which is the intended recipient of the intake charge.

Thus, each cylinder which is supplied by a single common inlet port receives the same metered quantity of fuel, provided that the injector duration remains constant Applying this sequential injection technique to each fuel injector ensures that the air fuel ratios are balanced throughout all cylinders of the engine.

Unfortunately, additional sensory hardware is required to detect the specific intake stroke of an individual cylinder. A four-stroke internal combustion engine will open the inlet valve of a single cylinder only once every 720° of crankshaft rotation. Thus, a camraft phase sensor is needed, which is capable of differentiating between the induction / compression stroke and the power I exhaust stroke of the Otto cycle. This will operate alongside a crankshaft position sensor which is capable of accurately referencing the top-dead-centre position of a single piston, which equates to 3600 of crankshaft rotation.

Naturally, the addition of a camshaft phase sensor will increase the monetary cost of the engine management system and increase complexity. A further complication is that many internal combustion engines that feature one or more shared inlet poris were designed before electronic fuel injection systems were developed. Therefore, retro-fitling a camshaft phase sensor is difficult to achieve.

The present invention enables accurate air fuel ratio control between two cylinders which are dependant on a single inlet port without the need for a camshaft phase sensor. This is achieved by injecting fuel into an inlet port once per 3600 of crankshaft rotation. This means there will be two injection events for a single Otto cycle (720° of crankshaft rotation). The first injection event is timed in a fully sequential manner. That is, fuel is injected only during the intake stroke of the cylinder which is the intended recipient Critically, the second injection event is not timed to coincide with an intake stroke. Rather, the injection event takes place after the previous injection event and once the crankshaft has rotated through 360°. As such, only half of the injection events are timed to coincide with the intake stroke of a cylinder.

Using the present invention, fully sequential injection can be achieved (despite the lack of a camshaft phase sensor) provided that the camsh2ft liming is as follows. If cylinder A and cylinder B are both supplied by the same common inlet port, the intake stroke for cylinder B must occur after 3600 of crankshaft rotation since the intake stroke for cylinder A. Commonly however, this is not the case; in many internal combustion engines, the intik strokes of a pairing of cylinders are separated by only 1800 of crankshaft relation. In audi an instance, if fuel were to be injected full-lime at a constant rate, one cylinder, X would receive seventy-five peivent of the mourning fuel, whereas cylinder Y, the other cylinder of the shared-port pairing would receive only twenty-five pen.ut of the incoming fuel. In a case such as this, the filly sequential injection event must occur on the intake stroke of cylinder Y. The subsequent mjcction event will occur not on the intake stroke of cylinder X but 180° of crankshaft rotation before the intake stroke. This fuel is suspended within the inlet port until cylinder X begins the intake stroke. Thus cylinder X and cylinder Y are the recipients of an equal measure of fuel and air fuel ratios are mintxined between both of the cylinders despite sharing a single inlet port, and in this case, operating with non-lävourable camshaft liming.

The invention will now be descri1ed with reference to the following drawings: Figure 1 shows the layout of a single inlet port and corresponding fuel supply which supplies two different cylinders of an internal combustion engine.

* Figure 2 shows the sequence el fuel injector events when the invention is able to provide fully sequential fuel injection, thus maintaining balance of air fuel ratios between two cylinders.

* Figure 3 shows the sequence of fuel injector events when the invention is unable to provide fully sequential fuel izUection yet balance of air fuel ratios between two cylinders can be maintained In Figure 1, the layout of a single inlet port is explained A single port aitmy is supplied with fuel by either single or multiple fuel injectors. Internally, the port is branched to feed two separate cylinders of the internal combustion engine. Note that the number of inlet valves that supply each cylinder is inconsequential. The invention aims to equallse the amount of fuel entering cylinder A and cylinder B from the fuel source, despite the fuel source operating in a digital manner and often in very short tUne -S.

Figure 2 shows the sequence of injection events when camshaft fimig is such that Intake strokes on the two cylinders are separated by 360°. In this example, maximum lift of the inlet valve for cylinder A (3) occurs 360° of crankshaft rotation before / after the maximum inlet valve lift for cylinder B (4). In this case, if fuel were injected non-stop and at a constant rate, cylinders A and B would both receive the name quantity of fuel; one crankshaft revolutions worth. Thus there is no dependani' cylinder for which the injection timing is cruciaL This means the fully sequential injection event (either I or 2 in this case) can QOInCidC with (3) or (4) and the air fuel ratios will remain balanced between cylinders A and B. Figure 3 explainc a more complex example, where cylinders A and B would not normally receive an equal quantity of fuel if fuel were injected non-stop and at a constant rate. This is because maximum inlet lift for cylinder B (8) occurs only 180° of crankshaft nation after maximum inlet valve lift for cylinder A (7). Cylinder B would typically receive less fuel than cylinder A, thus causing a lean mixture in cylinder B. For this reason, thc fully sequential injection event (5) is timed to coincide with maximum valve lift of the weak cylinder (8). The subsequent injection event occurs after 360° of crankshaft rotation. Although this injection event (6) does not coincide with the intake stroke of cylinder A (7), the fuel remains suspended within the inlet port until it is required Thus, there is no requirement for a camshaft phase sensor yet both cylinders A and B receive the name metered quantity of fuel, and air fuel ratio is balanced between the two cylinders.

Claims

1. A method for injecting a metered quantity of fuel from a fuel source into a desired cylinder of an intenmi combustion engine without requirement for cnmhtt phase sensing, despite said cylinder sharing a common inlet port with a different cylinder; achieved by injecting a quantity of fuel once per crankshaft revolution, such that injection coincides with the irmkç stroke of only one of said cylinders and subsequent injection occurs again after exactly one crankshaft revolution.

2. A method according to Claim 1, in wiuich the fuel injection event that coincides with an intake stroke supplies fuel to one of two cylinders sharing a single inlet port, which of the two is most prone to receiving less fuel should the fuel supply be operating constantly and at a cons'n1 rate with the engine in a running condition.

3. A method according to Claim I, in which fuel is sourced fum a single fuel injector.

4. A method arding to Claim i, in which fuel is sourced from multiple fuel injectors.

5. A method according to Claim 4, in which fuel is sourced from less than the total number of fuel injectors feeding a single inlet port when running conditions of an internal combustion engine dictate that this is favourable.

6. A method according to Claim 1, in which the fuel injection event which coincides with an intake stroke begins either before or after said intake stroke and the subsequent injection event occurs one crankshaft revolution after the Fevious Injection event.

7. A method according to Claim 6, in which the fuel injection event timing is moveable in relation to 1op-dead.cnire of an internal combustion engine, dependant on running conditions of the engine In question.

8. A method according to Claim 1, in which the metered quantity of fuel injected once per crankshaft revolution, is adjustable depending on running conditions of the engine in question.