GB2321085A

GB2321085A - Secondary air intake valve for a port-throttled i.c. engine

Info

Publication number: GB2321085A
Application number: GB9700505A
Authority: GB
Inventors: Paul Turner
Original assignee: Sagem SA
Current assignee: Sagem SA
Priority date: 1997-01-10
Filing date: 1997-01-10
Publication date: 1998-07-15
Anticipated expiration: 2017-01-10
Also published as: GB2321085B; GB9700505D0

Abstract

A secondary air intake (19) of a port throttle-controlled internal combustion engine supplies intake air during idling and is provided with a secondary valve (200) which prevents transmission of air pressure fluctuations to similar secondary air intakes of other cylinders (only one of which is shown) by virtue of a large cross-section inlet port (P1). The cross-sectional area of this inlet port is preferably at least ten times that of each outlet port (P2). Smoother idling and reduced emissions result. The outlet ports P2 are partially blocked by an axially movable piston 10 driven by a stepper motor 11 eg in response to a speed feedback signal from the engine management system.

Description

AIR INTAKE ARRANGEMENT FOR INTERNAL COMBUSTION ENGINE The present invention relates to an air intake arrangement for a multi-cylinder intemal combustion engine.

The invention is applicable particularly but not exclusively to a high performance fourstroke Otto cycle intemal combustion engine fitted with port throttles and controlled by an electronic engine management system.

The term "port throttle" means that the air supply for every cylinder is separate, with the flow being controlled by individual throttle valves for each. The advantages of port throttles include excellent transient response characteristics and low restriction to air flow.

This type of throttle is therefore commonly used for motorcycle and high performance automobile applications.

It is well known that, even without port throttles, particularly at engine idle speeds, the relatively large throttle valves are difficult to adjust precisely for the required air flow. A known solution to this problem is to use a secondary air by-pass system for idle speed operation. A secondary air by-pass system delivers air to the engine downstream of the throttle valve, effectively forming a separately controlled air supply system at idle speeds when the throttle valve is closed.

However, with port throttle controlled engines it is difficult to control the secondary airflow to each cylinder in a balanced fashion. For this reason it has been proposed to connect the air by-pass to a common control point, with a view to controlling the entire secondary air flow to the engine with a single control valve.

However, interconnecting the inlet ports in this way normally creates undesirable "cross talk", where negative pressure fluctuations and their associated gas flows are transmitted from one inlet port to the other. This "charge robbing", where one cylinder filling effectively "robs" the gas from its neighbours, tends to cause an unstable idle quality and unsatisfactory exhaust emissions levels. Interference may also be experienced under other speed-load conditions.

An object of the present invention is to overcome or alleviate the above problem.

Accordingly the invention provides an air intake arrangement for an internal combustion engine wherein each cylinder is provided with a respective throttle means arranged to control the primary airflow to its inlet and each throttle means is bypassed by a secondary air inlet arranged to provide a secondary airflow, the secondary air inlets communicating with respective outlets of a secondary valve means, said secondary valve means having an inlet which provides a lower resistance to air flow than an outlet and thereby impedes the transmission of pressure fluctuations between said secondary air inlets.

Preferably the inlet of the secondary valve means communicates directly with a plenum substantially at atmospheric pressure. This feature enhances the absorption of pressure fluctuations.

Preferably said secondary valve means comprises a movable valve element arranged to partially block the outlet ports of the secondary valve means to control secondary airflow but without directly obstructing the inlet port of the secondary valve means. This feature further enhances absorption of pressure fluctuations.

Preferably said secondary valve means comprises a cylindrical body having an axial air inlet and radial air outlets and said movable valve element is in the form of a piston arranged to partially block the ports of the radial air outlets.

The movable valve element (e.g. a piston) is suitably actuated by an electromechanical actuator (e.g. a stepper motor) under the control of a signal from an engine management system, particularly during idling, to control secondary airflow.

The potential problem of transmission of pressure fluctuations between the secondary air inlets is particularly acute when there is an overlap between the opening of the inlet and the closing of exhaust valves. Accordingly the present invention is particularly advantageous in such a situation.

The invention also extends to an internal combustion engine utilising an air intake system as defined above.

Further preferred features of the invention are defined in the dependent Claims.

A preferred embodiment of the invention is described below by way of example only with reference to Figure 1 of the accompanying drawing, wherein: Figure 1 is a somewhat diagrammatic representation, partly in section, of an intemal combustion engine in accordance with the invention.

Figure 2 is a plan view of an air intake arrangement in accordance with the invention; Figure 3 is a front elevation taken on Figure 2, and Figure 4 is a somewhat schematic cross-section taken on IV-VI of Figure 2.

Refening to Figure 1, one cylinder head 100 of a high-performance four-stroke petrol engine (having e.g. a power greater than 25 kW per litre capacity) is shown, and is controlled by various control signals from an electronic engine management system (not shown) of known type, such as the SAGEM MC2000 system for example.

A common secondary air control valve 200 regulates secondary air intake to the secondary air intakes 19,19' of the various cylinders. Typically there will be two or more cylinders, but for the sake of simplicity only two secondary air intakes are shown and only one cylinder head 100 is shown. However, all the cylinder heads are essentially identical.

Each cylinder has a primary air inlet 1 and a butterfly throttle valve 2 controlled by a conventional throttle grip for regulating air flow into the combustion chamber 9. Each air inlet 1 is drawn from a common air box and air filter (not shown). An electrically actuated fuel injector 4 injects petrol into the intake port 12. A spark plug 7 ignites the fuellair mixture and is energised by an ignition coil 6. Air intake is via one or more inlet valves 21 and exhaust is via one or more exhaust valves 22. Valve timing is controlled by one or more camshafts (not shown). There is overlap between the opening of the inlet valve(s) 21 and exhaust valve(s) 22, the degree of overlap optionally being controlled by control signals from an engine management system.

In accordance with the invention, each secondary air inlet 19 is provided with a common secondary valve 200 which ensures that no or only minimal reverse secondary air flow occurs during idling when throttles 2 are nearly closed. This is achieved by providing an inlet 20 on valve 200 which provides a lower resistance to air flow than its outlets 23, whose ports P2 are partially blocked by an axially movable piston 10 and which have a much smaller cross-section (e.g. 1/10 or less) than that of axial inlet port P1. For example the outlets 23 may have a bore of 6 mm diameter and the inlet 20 may have a bore of 19.5 mm diameter.

Hence there is obtained a fine balance between cylinder air flows A particularly during idling, which minimises unwanted emissions and gives a much better idle quality. The idle speed is controlled by a single signal to a stepper motor 11 which is coupled to piston 10. Piston 10 can be moved axially as shown by arrow 8 and the control signal can be. a speed feedback signal from the engine management system for example. Rapid fluctuations (i.e. those fluctuations which are shorter than the time constant of the stepper motor-piston assembly are controlled by modulating ignition timing and slower fluctuations are controlled by the stepper motor 11.

Components 4, 6 and 11 are preferably all controlled by signals from the engine management system. As noted above, stepper motor II is controlled primarily by a negative feedback signal in response to e.g. detected speed. The other control signals are well known ner se and therefore need not be described further.

In a variant the radial ports P2, which are regularly distributed about the circumference of the body of valve 200, are of rectangular rather than circular cross-section as illustrated at P2', in order to obtain a more linear relationship between the position of piston 10 and the airflow. However, satisfactory results have been obtained without this feature.

Figures 2, 3 and 4 show a further embodiment which is particularly suitable for 2 cylinder motorcycle engines. Two air inlets 1' of respective cylinders are integrated with a secondary air inlet (having an inlet port P1) in a casting 26. The top face of this casting is flat and is secured to an airbox (not shown).

A piston 10 is driven vertically by a stepper motor 11, and, as best shown in Figure 4, controls secondary airflow by partially blocking the port P2 of each bore 19" leading from secondary inlet port 19 past butterfly valve 2 in primary air inlet 1. Butterfly valve 2 is shown fully closed in Figure 4. It is controlled by a linkage (not shown) from a throttle actuator 25.

As in the embodiment of Figure 1, reverse secondary airflow is impeded to a much greater extent by port P2 (and its associated bore 19") than by port P1 and from there is little interaction between respective secondary airflows or to the different cylinders.

Claims

1. An air intake arrangement for an intemal combustion engine wherein each cylinder is provided with a respective throttle means arranged to control the primary airflow to its inlet and each throttle means is bypassed by a secondary air inlet arranged to provide a secondary airflow, the secondary air inlets communicating with respective outlets of a secondary valve means, said secondary valve means having an inlet which provides a lower resistance to air flow than an outlet and thereby impedes the transmission of pressure fluctuations between said secondary air inlets.

2. An air intake arrangement as claimed in Claim 1, wherein the inlet of the secondary valve means communicates directly with a plenum substantially at atmospheric pressure.

3. An air intake arrangement according to Claim 1 or Claim 2, wherein said secondary valve means comprises a movable valve element arranged to partially block the outlet ports of the secondary valve means to control secondary airflow but without directly obstructing the inlet port of the secondary valve means.

4. An air intake arrangement according to claim 3, wherein said secondary valve means comprises a cylindrical body having an axial air inlet and radial air outlets and said movable valve element is in the form of a piston arranged to partially block the ports of the radial air outlets.

5. An air intake arrangement according to Claim 3 or claim 4, wherein said movable valve element is controlled by electro-mechanical actuator means.

6. An air intake arrangement according to any preceding Claim, wherein the secondary valve means has an air inlet port whose cross-sectional area is at least twice the cross-sectional area of each of its air outlet ports.

7. An air intake arrangement according to any preceding claim wherein the secondary air inlets and primary air inlets of the cylinders are formed integrally in a common casting.

8. An internal combustion engine comprising an air intake arrangement according to any preceding Claim.

9. An intemal combustion engine as claimed in Claim 8, which is arranged to provide an overlap between the inlet and exhaust valve timing.

10. An internal combustion engine according to Claim 8 or Claim 9, wherein each throttle means is arranged to be kept partly open during idling.

11. An intemal combustion engine according to either of Claims 8 and 9 as dependent on Claim 5, wherein said secondary valve means is arranged to control the airflow into said secondary air inlets in response to a control signal.

12. An internal combustion engine substantially as described hereinabove with reference to Figure 1 or Figures 2, 3 and 4 of the accompanying drawings.