GB2389391A

GB2389391A - Movable charge motion flow deflector in the inlet port of an i.c. engine

Info

Publication number: GB2389391A
Application number: GB0305111A
Authority: GB
Inventors: Thomas Tsoi Hei Ma
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-06-06
Filing date: 2003-03-06
Publication date: 2003-12-10
Also published as: GB0305111D0

Abstract

The flow deflector 30 is mounted inside the bowl of an intake port above the head of an associated poppet valve 12. The deflector 30 is a thin shell, shaped to cover a substantial area of the inside wall of the port at the bend 18 where the port axis turns sharply to join with the poppet valve axis. The deflector 30 is moveable between a first position, fig.1, in which it blends smoothly with the wall of the port, and a second position, fig.2, in which it is spaced from the wall. The deflector 30 may have a pair of integral leaf springs 32 by which it is supported from the roof of the port. A control system causes a linkage member 34 to push or pull the deflector 30 between its first and second positions against the spring force of the leaf springs 32 to produce forward tumble or reverse tumble, respectively.

Description

238939 1

- 1 CHARGE MOTION FLOW DEFLECTOR

Field of the invention

5 The present invention relates to a flow deflector mounted inside an intake port of an internal combustion engine for varying the charge motion within the combustion chamber of the engine.

lo Background of the invention

It is known in an internal combustion engine having intake and exhaust poppet valves operating according to a four-stroke engine cycle to introduce tumble motion within the combustion chamber for promoting mixture turbulence and/or charge stratification during the intake and compression phases of the four-stroke cycle. It is also known in an internal combustion engine having intake and exhaust poppet valves operating according to a two-stroke so engine cycle to introduce tumble motion within the combustion chamber for promoting loop scavenging of the cylinder charge during the gas exchange phase of the two-

stroke cycle. Tumble is herein defined as the rotation of the cylinder charge in a plane parallel with the 5 longitudinal axis of the engine cylinder.

There are two directions of tumble motion, namely forward tumble and reverse tumble, according to the flow sequence past the walls of the combustion chamber. Forward 30 tumble is herein defined wherein the flow from the intake port entering the combustion chamber is directed predominantly across the roof of the combustion chamber before being deflected by the cylinder wall towards the piston. Reverse tumble is herein defined wherein the flow 35 from the intake port entering the combustion chamber is directed predominantly along the cylinder wall before being

- 2 deflected by the piston towards the roof of the combustion chamber. In the case of a poppet valved four stroke engine, 5 either direction of tumble motion is effective for promoting mixture turbulence and/or charge stratification, but other considerations, such as avoiding wetting of the fuel on the cylinder wall, favour the choice of forward tumble in order to reduce exhaust emissions.

In the case of a poppet-valved two-stroke engine, on the other hand, forward tumble is to be avoided because of the risk of short-circuiting of the intake air directly into the exhaust port without scavenging the cylinder contents 5 when the intake and exhaust valves are simultaneously open during the gas exchange phase. It is therefore important to introduce reverse tumble to ensure effective loop scavenging in two- stroke engine applications.

So Whilst it is possible to design an engine intake port to produce a predetermined tumble motion within the combustion chamber, it is desirable under certain conditions to vary either or both the intensity and the direction of tumble according to engine operating conditions. In :5 particular, in an engine with poppet-valves switchable to operate in either four stroke or two stroke cycle mode, it is desirable to select the tumble motion appropriately for each cycle mode, namely, forward tumble in four stroke mode and reverse tumble in two stroke mode.

Summary of the invention

With the aim of achieving the above-mentioned variation in tumble motion, there is provided according to the present 35 invention a flow deflector mounted inside the bowl of an intake port above the head of an associated poppet valve in an internal combustion engine, characterized in that the

- 3 deflector is shaped to cover a substantial area of the inside wall of the port at the bend in the port, the bend being where the port axis turns relatively sharply to join with the poppet valve axis, and further characterized in 5 that the deflector is moveable between a first and a second position such that the deflector blends smoothly with the port wall at the bend in the first position and separates away from the said wall when it is moved off the wall towards the centre of the bowl of the port in the second lo position.

In the invention, it is the flow deflector, not the wall of the intake port, that is responsible for deflecting the air flow at the bend towards the poppet valve. Thus 5 when the deflector is moved to the second position separated away from the wall at the bend and moved towards the centre of the bowl of the port, it effectively blocks a proportion of the port flow area at the bend thus restricting the air flow and causing it to turn earlier to exit the poppet valve JO opening through a smaller region of the opening. This alters both the velocity and the direction of the air jet entering the combustion chamber, thus altering the intensity and possibly the direction of tumble motion within the combustion chamber.

Preferably at least one leaf spring is provided attached at one end to the flow deflector for mounting the deflector in front of the port wall at the bend, and attached at the one other end to the roof of the port thus 30 supporting the flow deflector inside the port. The leaf spring and the deflector may of course be constructed in one piece of the same material.

In a preferred embodiment of the invention, the leaf 35 spring is springbiased to hold the deflector in the first position and a linkage member is provided aligned substantially along the intake port axis for pulling the

- 4 deflector to the second position against the spring-bias of the leaf spring.

In an alternative embodiment of the invention, the leaf 5 spring is spring-biased to hold the deflector in the second position and a linkage member is provided aligned substantially along the intake port axis for pushing the deflector to the first position against the spring-bias of the leaf spring.

In another alternative embodiment of the invention, the leaf spring is neutrally biased to hold the deflector between the first and the second positions and a linkage member is provided aligned substantially along the intake :5 port axis for pushing or pulling the deflector to its first or second position respectively against the spring force of the leaf spring.

A control system may be provided for setting the 20 position of the flow deflector in order to vary the intensity and/or direction of tumble charge motion within the combustion chamber according to engine operating conditions. In one example, in a direct fuel injection spark ignition engine, stratification of the injected fuel 25 surrounding the spark plug may be improved at low loads by changing from forward tumble to reverse tumble. In another example, in an engine with poppet-valves switchable to operate in either four stroke or two stroke cycle mode, the engine may be operated in four stroke mode with forward 30 tumble and in two stroke mode with reverse tumble.

Brief description of the drawing

The invention will now be described further by way of Is example with reference to the accompanying drawings in which Figures 1 is an isometric view of a preferred embodiment of a moveable flow deflector mounted

- - inside an intake port in the first position, and Figure 2 is an isometric view of the moveable flow deflector shown in Figure 1, moved to the second position. r :] Detailed description of the preferred embodiment

Figure 2 shows an isometric view of an intake port opened and closed by a poppet valve 12. The intake port has lo a primary flow passage 10 having a rectangular flow cross-

section extending from the entrance of the port to a bend 18 where the port 10 axis turns relatively sharply to join with the poppet valve 12 axis while the flow cross-section changes smoothly into a round flow cross-section 20 forming 15 a bowl inside the intake port above the head of the poppet valve 12. In so far described, the intake port and poppet valve are conventional.

Figure 1 shows the same isometric view of the intake So port with a moveable flow deflector 30 mounted inside it in the first position covering a substantial area of the port wall at the bend 18 and blending smoothly with the bend 18 (the bend 18 herein annotated the same as the deflector 30).

The deflector 30 is a thin shell formed in close fit with the port wall at the bend Is thus allowing unobstructed air flow in the same way as the bare intake port. A pair of leaf spring 32 integral with the flow deflector 30 are provided for mounting the flow deflector 30 in the first position shown. The leaf springs 32 are secured at one end 30 to the roof of the port by a weld joint (shaded region) thus supporting the flow deflector 30 inside the port.

In Figure 2, the flow deflector 30 is pulled to the second position by a linkage member 34 aligned substantially 35 along the intake port axis. The linkage member 34 overcomes the spring force of the leaf springs 32 and urges them to curl away from the wall while carrying the flow deflector

- 6 30. In this position, the intake air flow is caused to turn earlier by the flow deflector 30 before reaching the wall at the bend 18 thus altering the tumble charge motion within the combustion chamber of the engine.

A control system (not shown) sets the position of the flow deflector 30 and thereby varies the intensity and/or direction of tumble charge motion within the combustion chamber. Depending on the orientation of the intake port lo relative to the combustion chamber, the deflector 30 may be moved to the first or second position to produce forward tumble, and to the opposite position to produce reverse tumble according to engine operating conditions.

1b

Claims

- 7 CLAIMS

1. A flow deflector mounted inside the bowl of an intake port above the head of an associated poppet valve in 5 an internal combustion engine, characterized in that the deflector is shaped to cover a substantial area of the inside wall of the port at the bend in the port, the bend being where the port axis turns relatively sharply to join with the poppet valve axis, and further characterized in lo that the deflector is moveable between a first and a second position such that the deflector blends smoothly with the port wall at the bend in the first position and separates away from the said wall when it is moved off the wall towards the centre of the bowl of the port in the second position. 2. A flow deflector as claimed in claim 1, wherein at least one feat spring is provided attached at one end to the flow deflector for mounting the deflector in front of the 20 port wall at the bend, and attached at the one other end to the roof of the port thus supporting the flow deflector inside the port.

3. A flow deflector as claimed in claim 1 and 2, 25 wherein the leaf spring and the deflector are constructed in one piece of the same material.

4. A flow deflector as claimed in claim 1 and claim 2 or 3, wherein the leaf spring is spring-biased to hold the So deflector in the first position.

5. A flow deflector as claimed in claim 4, wherein a linkage member is provided aligned substantially along the intake port axis for pulling the deflector to the second as position against the spring-bias of the leaf spring.

- 8 6. A flow deflector as claimed in claim 1 and claim 2 or 3, wherein the leaf spring is spring-biased to hold the deflector in the second position.

5 7. A flow deflector as claimed in claim 6, wherein a linkage member is provided aligned substantially along the intake port axis for pushing the deflector to the first position against the spring-bias of the leaf spring.

c 8. A flow deflector as claimed in claim 1 and claim 2 or 3, wherein the leaf spring is neutrally biased to hold the deflector between the first and the second positions.

9. A flow deflector as claimed in claim 8, wherein a 5 linkage member is provided aligned substantially along the intake port axis for pushing or pulling the deflector to the first or second position respectively against the spring force of the leaf spring.

JO 10. A flow deflector as claimed in any preceding claim, wherein the deflector is moved to vary the intensity and/or direction of tumble charge motion within the combustion chamber according to engine operating conditions.

25 1l. A flow deflector as claimed in any preceding claim, wherein depending on the orientation of the intake port relative to the combustion chamber, the deflector is moved to the first or second position to produce forward tumble, and to the opposite position to produce reverse 30 tumble according to engine operating conditions.