GB2196386A

GB2196386A - Adjustable i.c. engine intake valve guide and baffle

Info

Publication number: GB2196386A
Application number: GB08706281A
Authority: GB
Inventors: Derek Frost
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1986-10-21
Filing date: 1987-03-17
Publication date: 1988-04-27
Also published as: GB8706281D0; GB8625170D0

Abstract

The intake valve guide 18 is mounted slidably and/or rotatably relative to the intake port 10 to enable the cross section of the intake port 10 to the restricted in the immediate vicinity of the intake valve 12. The guide 18 may adjust the position of a resilient vane (54, Figs. 3 and 4). The guide may regulate the speed, swirl or turbulence in accordance with throttle position. <IMAGE>

Description

SPECIFICATION Internal combustion engine The present invention is concerned with an internal combustion engine having separate valves for intake and exhaust, wherein an intake valve is constructed as a poppet valve seating against a stationary valve seat in the cylinder head and slidably retained in the cylinder head by means of a valve guide.

The design of the intake port of an engine is of importance in that it affects the speed of the air and the turbulence in the air entering the combustion chamber. At high engine speeds, the air intake is high and the size of the port should be as large as possible to permit a maximum charge to enter the cylinder. Lean burn at high engine speeds presents no problems and no special steps need to be taken to induce turbulence in the charge. In any event, at high engine speed, fuel economy is not as a high priority as engine performance.

At partial low and low engine speeds, on the other hand, the air intake speed through a large intake port is small and a charge with very little turbulence and swirl results which reduces the combustion efficiency. Lean burn with such a design cannot be achieved and modifying the intake port to facilitate lean burn will throttle the engine at high speeds. It can thus be seen that the requirements at different engine speeds conflict with one another and the design of the intake ports has hitherto been a compromise between lean burn efficiency at part load and idle and high speed performance.

With part load and at idling, a further disadvantage is that the main throttling of the air intake occurs at the entrance to the induction manifold and as a result the efficiency of the engine is reduced by air pumping losses at a time when the output power is reduce.

With a view to mitigating the foregoing disadvantages, in the present invention the valve guide is movably mounted in the cylinder head relative to the valve seat whereby to vary the port geometry so as to regulate the speed, swirl or turbulence of the charge for any given flow rate of air.

The valve guide may be movable in a direction parallel to the axis of the valve stem. In this case, the valve guide obstructs the intake port when lowered towards the valve seat but does not interfere with the air flow when retracted.

If desired, the lower end of the valve guide may be shaped to promote swirl and turbulence in the inducted air.

Alternatively, the valve guide may form part of a sleeve rotatable about the axis of the valve stem. In this case, the sleeve may comprise an aperture aligned with the intake port at high engine speeds and partly obstructing the intake port at lower engine speeds.

In order to promote swirl, a resilient tongue or vane may be mounted in the intake port to act as a deflector directing the air flow towards the aperture in the rotatable sleeve.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a section through an intake port constructed in accordance with a first embodiment of the invention, Figure 2 is a section similar to that of Figure 1 showing a second embodiment of the invention, Figure 3 is a section similar to that of Figure 1 showing a third embodiment of the invention, and Figure 4 is a schematic plan view of the embodiment shown in Figure 3.

In Figure 1, there is shown an intake port 10 fitted with a poppet valve 12 which is seated against a stationary valve seat 14 and has.a valve stem 16 guided in a valve guide 18. The valve stem 16 extends beyond the valve guide 18 and passes through a seat 20 for a valve spring. The spring is omitted from the drawing together with the valve operating mechanism as these parts are not germane to the invention.

The valve guide 18 is slidably mounted in a bore 24 in the cylinder head 22. The guide 18 is sealed relative to the bore 24 by means of an O-ring seal 26. The guide 18 is furthermore formed with a rack 30 engaged by a pinion 32, rotation of which by a control mechanism lowers and raises the valve guide 18 between the position shown in solid lines, in which the air flow is not obstructed, and the position shown in dotted lines, in which the cross section of the throat of the intake port 10 is severely reduced.

When the through flow cross section is reduced, throttling of the engine occurs at the intake port and this has two advantageous effects. The first is to increase the speed of the intake charge. This is required under part idle and load operating conditions in order to increase the energy in the intake charge and thereby improve combustion efficiency and assist lean burn. The second advantage is that pumping losses are reduced because of the proximity of the throttle to the combustion chamber.

In the embodiment shown in Figure 2, the valve guide is arranged to follow a helical path and rotates as it is lowered towards the valve seat 14. The lower end of the valve guide 18' as viewed carries an eccentric disc 40. Both end positions of the valve guide in the case of the embodiment of Figure 2 are shown in solid lines. When in its raised position, the valve guide 18' is rotated to remove the eccentric disc 40 from the air stream. When lowered, on the other hand, the eccentric disc 40 diverts the air stream to follow the long path around the valve stem thereby promoting swirl.

In Figure 3, the valve guide 50 is not mov able axially but is rotatable about the axis of the valve stem 16. The part of the guide 50 facing the intake port 10 has an aperture 52 which when aligned with the intake port 10 present no obstruction to the air stream. This is the position shown in solid lines in Figure 4 which shows a section through the intake port when viewed from above, with the intake valve removed.

A resilient tongue or vane 54 is mounted on a collar 56 which is a tight fit in the intake port 10, The tip of the vane 54 engages in the aperture 52, as best seen in Figure 4 and the vane is deflected as the valve guide 50 is turned from an aligned position to a misal igned position in which the through flow cross section is reduced. The vane 54 acts to direct the air stream towards the opening allowed by the aperture 52 thus gradually decreasing the cross section of the intake port instead of presenting the air flow with a sudden discontinuity. This design again increases the air velocity and directs the air stream in a tangential direction tending to promote swirl.

The control of the position of the valve guide to determine the geometry of the intake port must be matched to the speed of the engine and can be linked to the throttle control. The engine speed is still determined by the throttle in the case of a spark ignited engine and the design of the port is intended primarily to increase air speed and not to control the volume of the air intake. A vacuum is still therefore developed in the intake manifold which can be used to measure engine load and for other functions such as ignition advance/retard.

Claims

1. An internal combustion engine having separate valves for intake and exhaust, wherein an intake valve is constructed as a poppet valve seating against a stationary valve seat in the cylinder head and slidably retained in the cylinder head by means of a valve guide, wherein the valve guide is movably mounted in the cylinder head relative to the valve seat whereby to vary the port geometry so as to regulate the speed, swirl or turbulence of the charge for any given flow rate of air.

2. An engine as claimed in Claim 1, wherein the valve guide is movable in a direction parallel to the axis of the valve stem.

3. An engine as claimed in Claim 2, wherein the lower end of the valve guide is shaped to promote swirl and turbulence in the inducted air.

4. An engine as claimed in Claim 2 or 3, wherein the sleeve is movable along a helical path and rotates simultaneously with its movement towards and away from the valve seat.

5. An engine as claimed in Claim 1, wherein the valve guide forms part of a sleeve rotatable about the axis of the valve stem, the sleeve comprising an aperture aligned with the intake port at high engine speeds and partly obstructing the intake port at lower engine speeds.

6. An engine as claimed in Claim 5, wherein in order to promote swirl, a resilient vane is mounted in the intake port to act as a deflector directing the air flow towards the aperture in the rotatable sleeve.

7. An engine having an intake port constructed substantially as herein described with reference to and as illustrated in Figure 1, Figure 2 or Figures 3 and 4.