GB2134980A - Internal combustion piston engine - Google Patents

Abstract

An engine has four cylinders 10, 11, 12, 13 whose axes are equi-angularly spaced on a pitch circle 14 and whose inlet and exhaust valves 16, 17 lie on respective pitch circles 14a, 14b, concentric with the pitch circle 14. An induction passage 20 is coaxial with the axis A of the pitch circles 14, 14A, 14b and four branch passages connect the passage 20 with respective ones of the inlet valves 16. The exhaust valves 17 are connected with a gallery 19 of progressively increasing section. The cylinders 10 to 13 are arranged to be fired in rotational sequence. Control of valve timing is disclosed. <IMAGE>

Description

SPECIFICATION Internal combustion piston engine This invention refatesto internal combustion piston engines.

The mostcommontypeoffourcylinder, internal combustion piston engine is ofthe in-line type having an inlet manifold extending substantially overthe engine length. Such an in-line arrangement gives rise to difficulties in providing a satisfactory induction system, to provide uniform distribution ofthe required air/fuel mixture overthewhole range of speeds and loads at which the engine is required to operate.

These difficulties arise from inter cylinder robbing, uneven suction impulses, poor mixture preparation and indifferent inter-cylinder distribution especially when operating from cold, during engine warm-up and when on full-load. The constantly changing deposition on, and boiling off,fromthewallsofthe inlet manifold of fuel with every change in manifold pressure leads to weak and rich mixture phases.

To achieve a good fuel consumption from an internal combustion piston engine the speed should be kept as low and the engine load as high as possible.

This may be done by providing a fuel/air ratio on the weak side of stoichiometric and increasing the engine load to restore the drop-off in power. This approach is not feasible without satisfactory inter-cylinder mixture distribution, and in known in-linefourcylinder engines the mixture distribution is at its worst under high load and low r.p.m.

Another disadvantage of known engines of this type is that the rectilinear motion imparted to the pistons is a very impure sine wave, since halfthe piston excursion from t.d.c. is achieved at approximately 75" crankshaft angle instead of 90 , due largely to the practical necessity of limiting the length ofthe connecting rods. This creates the need for extremely high inletvalve opening accelerations in orderto match the valve opening area to the piston velocity and atthis is not achieved the cylinder does not fill properlywiththe requiredfuellairmixture, and engine torque deteriorates.

It is an object of the engine which is the subject of the present invention to overcometheforegoing disadvantages.

According to the invention there is provided an internal combustion engine having four cylinders whose axes are substantially equi-angularly spaced on a pitch circle, inlet and exhaust valves in a head of each said cylinder, an induction passage concentric with the axis of said pitch circle, for branch passages connecting said induction passage with respective inlet valves, and means for introducing fuel into said induction passageata location therein which is substantially equally spaced from each of said inlet valves.

An embodiment ofthe engine ofthe invention already generally described herein, will now be briefly described with reference to the accompanying drawings, in which: Figure lisa schematictopview of an engine according to the invention, showing a central induction passage and branch passages leading from said induction passage to respective inlet valves of the four pistons of the engine; Figure 2 is a schematic part-sectional-view, to a larger scale on the line 2-2 of Figure 1, Figure 3 is a section on line 3-3 in Figure 2, and Figure 4 is a schematicviewthrough a pair of adjacent pistons ofthe engine, on line 4-4 in Figure 1.

Figure 1 shows the four piston-containing cylinders 10,11, 12,13 ofthe engine, arranged within a casing 15 with their respective axes on a pitch circle 14 having its axis indicated at A. Atthetop of each cylinder is an inlet valve 16 and an exhaustvalve 17 of conventional form, the inlet valves and the exhaust valve being arranged on innerandouterpitchcirclesl4a, 14b respectively concentric with the pitch circle 14. Figure 1 shows,foroneoftheexhaustvalves 17, an exhaust passage 18, corresponding exhaust passages (not shown) communicating with the others of the exhaust valves 17. Atoroidal exhaust gallery 19 of progressively increasing cross section, extends from the passage 18 and communicateswith the remaining valves 17.

Concentric with the centre of the pitch circle 14 is an induction passage 20. At its lower end it communicates with four, short, symmetrically arranged branch passages 21-24 respectively leading to the inlet valves 16 of the four cylinders.

Figure 2 shows a fuel injection nozzle 25 disposed centrally at the lower end ofthe passage 20, the nozzle 25 having a fuel inlet 26, and being arranged to supply fuel into the induction passage upstream ofthe branch passages 21-24.

The inlet and exhaustvalves 16,17 are operated by cams 28,29 carried by a cylindrical element 27 which is rotatable aboutthe axis A-A of the pitch circle on which the cylinders 10-13 are located. The element 27 is driven by the engine crankshaft at half the engine speed byashaft30,through a pinion 31.

The lift and timing oftheinletvalves 16 can be varied byadjusting the amount bywhich the cam 28 projects, and this is effected by mounting the cam 28 on a pin 32 which extends radially inwardly ofthe element27 and engages a support33 carried bythe element 27. An annular cam ring 34 with a sloped face 35 (Figure 3) is vertically movable and rotatable about the axis A-A by a lever36. The lever 36 is manually movabletoselecta desired speed of the engine. There may also be provided a device, of a known type, in which the lever 36 is additionally responsive to operation of an engine speed governor, so that the cam ring 34 is positioned in accordance with both desired and sensed engine speed.

The cam face 35 engages a complementaryface 37 on a further annular element 38 which is secured to the engine casing 15. The cam ring 34 coacts with a projection 39 on the cam 29 through needle roller bearings 40, only one of which is shown in Figure 3.

The projection 39 is spaced from the pin 30 so that pivotal movement ofthe cam 28 not only alters lift of the valves 16, but alterstheirtiming. An increase in valve lift is accompanied by an advance in valve opening and a delay in valve closure, and vice versa.

The operating face ofthe cam 28 engages the stem of each valve 16through a roller41 mounted on a plunger 42 slidable in the engine casing 15.

A similar arrangement for adjustment ofthe lift and timing ofthe exhaustvalves 17 may be incorporated if required.

Figure 4 shows a pair of adjacent pistons 50,51 in the cylinders 12,13 respectively. A rocker shaft 52 is located below the cylinders and extends along the axis shown at C-C in Figure 1.A A rocker element 53 is mounted on the shaft 52 below the cylinders 12,13, a similar element being located below the cylinders 10, 11. Opposed arms 54,55 ofthe element 53 are coupled by links 56,57 to the gudgeon pins ofthe respective pistons 50,51. The arms 54,55 subtend and arc S off 185 atthe axis ofthe shaft 52. Athird arm 58 of the element 53 is coupled bya connecting rod 59to a crank pin 60On a crankshaftwhich hastwosuch pins 1 80" apart.The radius ofthe pivotal connection ofthe arm 58 to the rod 59 is approximately 0.9 times the radiuss ofthe connections ofthe arms 54,55 to the links 56, 57 and liesat70 tothe arm 55. The arrangement is such that when piston 50 is moving upward, the piston in the diametrally opposite cylin der lOis also moving upward in unison, and the pistons in the cylinders 11, 13 are simultaneously moving downward in unison.

Itwill be noted thatthe links 56,57 are of unequal lengths, and these lengths are selected so that, in combination with the aforesaid dimensions of the rocker element 53, the factthatthe links 56,57 move be relatively small equal amounts on either side ofthe lines of action ofthe pistons and the position and throw of the crankshaft, the piston movement is substantially true simple harmonic motion. The effect is that the pistons are at mid point of their induction stroke after 90" rotation of the crankshaft, as opposed to 75" of crankshaft rotation in conventional engines.

In the present invention the increased time taken to reach mid-stroke, and hence maximum piston velocity, has the effectthat inlet valve opening need be less rapid than on conventional engines, reducing wear on the valve gear. Additionally, better cylinderfilling is obtained. The small angle through which the links 56, 57 pivot results in reduced side loads on the pistons, which reduces wear and enables the pistons them selvesto be lighter, and in particular shorter. The provision of diametrally opposite pistons moving upwardly or downwardly in unison ensures good rotational balance, and also permits the cylinders to be fired in rotational sequence, this latter feature improving the conditions forflow of the air/fuel mixture to the inlet valves 16.

Since the crankshaft has only two crankpins it is substantiallyshorterthan conventional crankshafts forfourcylinder engines. The crankshaft is thus simplerto manufacture and to harden without distortion. A crankshaft of this reduced length may be mounted in roller bearings, reducing the torque necessaryto startthe engine when cold, and reducing the load on an associated starter motor and battery, allowingthesecomponentsto be reduced in size and cost.

In the engine ofthe present invention, powercontrol iseffectedbyvariationofthe liftandtiming ofthe inlet valves 16. This provides that: (1) In engine operating conditions up to those requiring maximum inletvalve lift and opening time a high velocity of the airifuel mixture past the valve opening is obtained than occurs in an engine with fixed valve lift, this velocity being sonic or near sonic over a considerable part ofthe engine's cruising operation and the resulting turbulence provides an effective means of breaking up fuel droplets for mixture preparation, even from cold.

(2) The aforesaid increase in velocity provides improved swirl ofthe mixture in the cylinders, increasing combustion efficiency and permits effective burning of leanerfuellair ratios.

(3) The inside ofthe induction passage is, except for pulsation effects, maintained at a substantially constant, approximately atmospheric pressure irrespective of engine load, thereby elminating the weak and rich mixture phases which otherwise occur in a conventional engine as a result of fuel being deposited on, or boiling off,thewallsofthe induction passage with every change in the pressure therein.

(4) Overlap between inletvalve opening and ex haustvalveclosing is eliminated overthegreaterpart the engine operating range which prevents the airifuel mixture entering the exhaust system and, in combination with atmospheric pressure in the inlet manifold, tends to prevent exhaust gas from entering the induction system and diluting the air/fuel mixture.

(5) The variation of valve lift and timing with selected engine power and, if required, with sensed engine speed, avoids the valve timing compromise existing in conventional engines and provides a combination of high power at high speed with high torque at low speed.

Itwill be apparentthatthis method of engine load control can only hope to be successful on an engine which has good inter-cylinder mixture distribution when the gas velocity through the induction system is slow and when the internal pressure is near atmospheric and with a fuel introduction system which does not rely upon throttle edge jets or on the positions of a throttle plate for metering control.

Claims (10)

1. An internal combustion engine having four cylinders whose axes are substantially equi-angularly spaced on a pitch circle, inlet and exhaustvalves in a head of each said cylinder, an induction passage concentric with the axis of said pitch circle, four branch passages connecting said induction passage with respective inletvalves, and means for introducing fuel into said induction passage at a location therein which is substantially equally spaced from each of said inlet valves.

2. An engine as claimed in claim 1 in which said inlet valves are substantially equiangularly spaced about said pitch circle axis.

3. An engine as claimed in claim 1 or claim 2 in which diametrally opposite pairs of pistons in said cylinders are mechanically coupled for movement in unison, so that as one pair is moving upwardlythe other of said pairs is moving downwardly.

4. An engine as claimed in claim 3 in which each pair of adjacent pistons has a rocker element associated therewith, two connecting links coupling the pistons of an adjacent pairto respective arms af the associated rocket element, a crankshaft having two crankpins 1800 apart, and two connecting rods cou pling athird arm on said rockerelementsto respective ones of said crankpins.

5. An engine as claimed in claim 4 in which the dimensions of said links, said rocker elements, said connecting rods and said crankshaft are such that rotation of the crankshaft at a steady speed is accompanied by substantiallytrue simple harmonic linear motion of said pistons.

6. An engine as claimed in any preceding claim which includes means, responsive to operation of an engine speed selector device, forvars,/ing the lift of the inlet valves.

7. An engine as claimed in claim 6 in which said lift varying means includes means for varying the t iming dsaid inlet valves.

8. An engine as claimed in claim 6 or claim 7 in whish power output is regulated solely by operation of said liftvarying means.

9. An engine as claimed in any of claims 6to 8 in which said lift varying means is also responsive to a sensed value of engine speed.

10. An internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.