GB2229768A

GB2229768A - I.c. engine air intake system

Info

Publication number: GB2229768A
Application number: GB9004675A
Authority: GB
Inventors: Keith Gordon Hall
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-04-01
Filing date: 1990-03-02
Publication date: 1990-10-03
Also published as: GB8907403D0; GB9004675D0

Abstract

Each cylinder has an individual air intake pipe 1-4 and the pipes are connected in cluster formation to a primary air intake duct 8 whose volume is greater than three times that of the individual cylinder volume and provides a flow velocity of less than 20 m/s at maximum engine speed. The construction provides unidirectional flow and minimises inertial fluctuation of the air column and directional changes at the junction. The inertial supercharging may further be enhanced by ensuring that the volume of each air intake pipe is at least 1.25 times that of the individual cylinder volume. The air intake pipes may be arranged in the cluster in engine firing order or, if the engine has an even number of cylinders, with pairs of pipes in anti- phase. The throttle valve 6 is located adjacent the cluster of air intake pipes in the air intake duct and is of the butterfly type so adapted to seal the bore of the air intake duct when fully closed. The periphery of the throttle plate engages ridges or steps (12, 13, Fig. 3) around the bore of the air intake duct when fully closed. The throttle plate closes an opening in a wall (20, 21, Fig. 4) dividing the bore of the air intake duct when in the full throttle position to effect separate streams of air through the throttle body on either side of the throttle spindle. <IMAGE>

Description

AIR INTAKE SYSTEMS This invention relates to air intake systems for internal combustion engines and methods for achieving inertial supercharging therein.

It has long been considered that an individual intake pipe for each cylinder of an internal combustion engine, open directly to the atmosphere, achieves optimum breathing.

This is typified by the classic racing engine design.

One object of the present invention is to provide an improvement on the classic design.

Another object is to broaden the spread of engine torque.

A further object is to minimise leakage past the closed throttle blade in order to use a larger throttle yet retain a low idling speed for improved fuel economy and reduced emission of pollutants.

According to the present invention there is provided an internal combustion engine having two or more cylinders, characterised in that each cylinder has an individual air intake pipe and the air intake pipes from the at least two cylinders are combined in cluster formation into a primary air intake duct whose volume is greater than three times that of the individual cylinder volume.

Single length open ended intake pipes have been thought to achieve optimum inertial supercharging within their working range. However, this assumption overlooks the high inertial fluctuation of the air stream from pipes working in isolation. It has been found that the cluster formation, according to the invention, of typically three of four pipes connected in firing order sequence, provides inertial continuity and uni-directional flow, the rotational component of flow in the cluster volume running at half engine speed in a four stroke engine.

The principle that is optimised in the present invention is the 'Inertial Column' of air in the intake system. This behaves like a linear flywheel, indicating that large volume pipes are needed to improve low speed torque. The conventional practice of applying Helmholtz wave theory to induction tuning indicates the opposite, that small cross sectional areas are required to improve low speed torque.

In normal practice the energy of the inertial air column in the intake system is rapidly destroyed by flow reversals in the plenum chamber. The present invention minimises these flow reversals in the intake system by eliminating pipe runners and gathering the individual pipes into a cluster formation directly adjoining the air intake duct. The kinetic energy of the inertial air column in the air intake duct may then be better utilised in filling the cylinder.

Each cylinder helps sustain the inertial air column for the benefit of its neighbour and in turn benefits itself.

Another aim is to increase the capacity of the inertial air column within practical packaging constraints set by the engine housing. Conventional ducting between throttle and air filter is proportioned for maximum velocities in excess of 20 metres per second and volumes typically up to three times individual cylinder volume. According to the invention the ducts are larger than three times the individual cylinder volume and the air flow through the ducts is less than 20 metres per second.

In order that the invention may be clearly understood it will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of an air intake system according to the invention adapted for four cylinders, Figures 2a and 2b show schematically and in cross-section the arrangement of air intake pipes connected in cylinder firing order, Figure 3 is a cross section of the throttle venturi with the throttle valve fully closed, Figure 4 is a cross section of the throttle venturi shown in Figure 3 with the throttle valve fully open, and Figure 5 is a graph showing the relationship between engine speed and engine torque for a conventional engine and for an engine according to the invention.

Primary inlet pipes 1, 2, 3 and 4, see Figure 1, are gathered together in cluster formation so that their outer ends join at a collector piece 5. The collector piece 5 is joined to a throttle valve 6 positioned in a throttle body venturi 7. An air intake duct 8 connects the throttle body venturi 7 to an air filter 9. The length and cross-sectional area of the duct 8 determines predominantly the capacity of the inertial column of air.

According to the present invention the capacity of the duct 8 is at least three times greater than that of the individual cylinder volume.

The inlet pipes 1, 2, 3 and 4 are preferably attached to the cluster in engine firing order, see Figure 2, so that the inertial column of air in the duct 8 rotates at a constant rate. In Figure 2a the schematic layout of the intake pipes 1, 2, 3 and 4 is shown while in the cross sectional view Figure 2b the arrangement of the cluster in the collector piece 5 is shown.

When the engine has an even number of cylinders the air intake pipes 1, 2, 3 and 4 may be attached to the cluster 5 with pairs of pipes in anti-phase.

The throttle body 11, see Figure 3, carries small opposing steps 12 and 13 on the bore periphery. The steps 12 and 13 are located on either side of a throttle spindle 14.

The surface at rim of a throttle plate 15 carried by the spindle 14 makes face contact with the steps 12 and 13 when the throttle is in its closed position. The steps 12 and 13 may be fabricated from a resilient material.

When the throttle is fully open, see Figure 4, the air flow is separated into two streams 16 and 17 either side of a single throttle plate 18 set in a throttle body 19.

Separation is maintained by dividing walls 20 and 21 set centrally within the bore. When the throttle is partially open flow between the two streams 16 and 17 is possible through apertures 22 and 23 in the walls 20 and 21 so that the plate 18 remains fully balanced regarding the differential pressure between the two sides.

Clusters of more than three pipes suffer from interference effects between the cylinders, see Figure 5, which shows the torque/speed relationship for a conventional engine by the dashed curve 31 and an engine according to the invention by the line 32. The interference effect shows itself as a crater 33 in the torque/speed curve 31 below a certain critical interference speed. The intake system according to this invention increases the inertial energy to a level sufficient to supress this interference crater, as shown by a flat portion 34 on the line 32, and provides a substantially constant speed/torque relationship over a range of engine speeds from 2500 to 5000 revolutions per minute.

The invention provides a method of operating an internal combustion engine having two or more cylinders in which each cylinder has an individual air intake pipe and the air intake pipes from the at least two cylinders are combined in cluster formation into a primary air intake duct wherein the air flow at maximum engine speed is less than 20 metres per second. To achieve this rate of air flow it is necessary for the volume of the air intake duct to be greater than three times that of the individual cylinder volume. It will be seen that an engine according to the invention will provide constant torque of over a speed range of at least two to one.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

1. An internal combustion engine having two or more cylinders, characterised in that each cylinder has an individual air intake pipe and the air intake pipes from the at least two cylinders are combined in cluster formation into a primary air intake duct whose volume is greater than three times that of the individual cylinder volume.

2. An internal combustion engine according to claim 1 characterised in that the volume of each air intake pipe is at least 1.25 times that of the individual cylinder volume.

3. An internal combustion engine according to claims 1 or 2, characterised in that the air intake pipes are attached to the cluster in engine firing order.

4. An internal combustion engine according to claims 1 or 2, characterised in that the engine has an even number of cylinders and the air intake pipes are attached to the cluster with pairs of pipes in anti-phase.

5. An internal combustion engine according to any of the preceding claims, characterised in that a throttle valve is located between the cluster of air intake pipes and the air intake duct.

6. An internal combustion engine according to claim 5, characterised in that the throttle valve is of the butterfly type and is adapted to seal the bore of the air intake duct when fully closed.

7. An internal combustion engine according to claim 6, characterised in that the periphery of the throttle plate engages ridges or steps around the bore of the air intake duct when fully closed.

8. An internal combustion engine according to claims 6 or 7, characterised in that the throttle plate closes an opening in a wall dividing the bore of the air intake duct when in the full throttle position to effect separate streams of air through the throttle body on either side of the throttle spindle.

9. Internal combustion engines according to claim 1 and as herein described.

10. Internal combustion engines as particularly described with reference to and as shown in the accompanying drawings.

11. A method of operating an internal combustion engine according to any of the claims 1 to 10, characterised in that the air flow in the air intake duct at maximum engine speed is less than 20 metres per second.