GB2082846A - Adaptor for I.C.E. ignition systems - Google Patents

Abstract

An ignition device for an internal combustion engine is modified by fitting to a cam (12) on a shaft (10) an adaptor comprising inner and outer elements (13, 14). The inner element (13) is lifted onto the cam and is then contracted by application of the outer element (14) to provide a tight fit on the cam. For this purpose, ribs (21) on the interior of the outer element (14) engage in recesses (22) of the inner element (13) and press inwards. The inner element is formed of plastics and has double-leaf walls (19, 20). The outer element (14) is of metal and has an outer layer of magnetised ferrite particles in a plastics matrix. A pick-up of the system is not illustrated. <IMAGE>

Description

SPECIFICATION Method of and adaptor for modifying an ignition-triggering device of an internal combustion engine and an engine so modified DESCRIPTION OF INVENTION This invention relates to the modification of an ignition triggering device of a spark ignition internal combustion engine, which device comprises a rotatable cam. A second aspect of the invention relates to an adaptor for use in the method and the invention also relates to an engine which has been modified by the method.

A spark ignition internal combustion engine having a Kettering ignition system includes an ignition triggering device comprising a shaft formed with or carrying a cam and which is rotated by the engine during operation.

The ignition triggering device further comprises a pair of switch contacts, one fixed contact and one movable contact. The movable contact is urged towards the fixed contact by a spring and is provided with a cam follower so engaged with the cam that as a lobe of the cam passes the cam follower the contacts are opened.

The contacts of a Kettering ignition system suffer from a number of disadvantages which are well known. In order to avoid these disadvantages, it has previously been proposed to remove the switch contacts and to provide a control circuit, a transducer and a rotor, the rotor being mounted on the cam for rotation therewith, the transducer being mounted in a fixed position near to the rotor and being responsive to rotation of the rotor to provide an electrical output signal to the control circuit which, in turn, controls the discharge of energy to spark plugs of the engine.In a typical modification of a Kettering ignition system, the transducer is an electromagnetic transducer and is adapted to respond to the movement of magnetic material comprised by the rotor The cam of a Kettering ignition system has a non-circular profile, as viewed along its axis of rotation, and, for modification of the system, it is usual to provide a rotor having a recess complementary to the cam and which is a sliding fit on the cam so that the rotor can simply be pushed onto the cam along the axis of rotation.

We have found that the dimensions'of cams fitted as original equipment in the ignition triggering devices of samples of a particular model of motor vehicle vary from one sample to another. This applies to various models of motor vehicle. The variation in dimensions of the cams are sufficiently great to give rise to difficulties if identical rotors are provided for modification of the ignition triggering devices of motor vehicles of a particular model. In some cases, the cams are so large that either the rotors cannot be pushed onto the cams or the rotors are split or otherwise damaged when pushed onto the cams and in other cases the rotors are a sufficiently loose fit on the cams for significant, erratic variations in the rotary position of the rotor relative to that of the cam to occur.It will be understood that any rotation of the rotor relative to the cam affects the timing of energisation of a spark plug in the operating cycle of the engine. If an engine has been used with a Kettering ignition system for a considerable period of time, then the cam may be worn sufficiently to prevent the rotor fitting tightly on the cam when known means are used for modifying the ignition system.

According to a first aspect of the present invention, an ignition triggering device for a spark ignition internal combustion engine is modified by fitting an inner element onto the cam of the device to engage a peripheral surface of the cam, whilst the inner element is on the cam an outer element is applied to the inner element in embracing relation therewith and the application of the outer element to the inner element brings about contraction of the inner element and thereby increases the pressure exerted on the cam by the inner element.

Since the inner element is contracted after it has been fitted onto the cam, the initial dimensions of the inner element can be such that it can be fitted without difficulty or damage onto an over-sized cam and, after the outer element has been fitted onto the inner element, the inner element can be a sufficiently tight fit to ensure that no rotation of the inner element relative to the cam will occur in use.

According to a second aspect of the invention there is provided an adaptor for modifying a rotatable cam, the adaptor comprising an inner element which, in use, is fitted onto the cam to engage a peripheral surface thereof with an axis of the inner element coinciding with an axis of rotation of the cam and an outer element adapted to be applied to the inner element whilst the inner element is on the cam to cause contraction of the inner element and thereby increase the pressure under which the inner element engages the cam.

There is also provided according to the invention an internal combustion engine having an ignition triggering device which includes a shaft rotated by the engine during operation. a cam formed on or rotated by the shaft, an inner element engaged with a peripheral surface of the cam to rotate therewith and an outer element which embraces the inner element and holds the inner element in pressure contact with said peripheral surface, the inner element having an axis which coincides with the axis of rotation of the shaft and cam.

It will be understood that, in an internal combustion engine in accordance with the invention, the cam of the ignition triggering device does not have the function of a cam but does have the form of a cam. Generally, the cam of an ignition triggering device of an internal combustion engine in accordance with the invention will have had the function of a cam in a Kettering ignition system, prior to modification of the ignition system in accordance with the present invention.

The ignition triggering device will include a transducer responsive to rotation of the inner and outer elements to provide an output signal to a control means for controlling the energisation of spark plugs of the engine. Either the inner element or the outer element may be adapted to bring about a response of the transducer, in the latter case the inner and outer elements preferably having respective formations which co-operate to restrain relative rotation of the elements in use.

An example of the modification of an ignition triggering device in accordance with the first aspect of the invention, using an example of an adaptor embodying the second aspect of the invention to provide an engine in accordance with the third aspect will now be described, with reference to the accompanying drawings, wherein is shown a perspective view of the shaft and cam of the ignition triggering device, together with inner and outer elements of an adaptor separated from one another and from the cam.

The drawing shows a shaft 10 of an ignition triggering device which is supported by means (not shown) for rotation about an axis 11. On the shaft there is formed or fixed a cam 12 which rotates with the shaft. The shaft, axis and cam are components of a known ignition triggering device of a Kettering ignition system of an internal combustion engine. The engine includes means for rotating the shaft 10 at a speed which is related directly to the speed of rotation of a crank shaft of the engine. Usually, the shaft 10 is driven at one half the speed of the engine crank shaft.

The ignition triggering device usually further comprises means for distributing electrical energy to the spark plugs of the engine and is referred to as a distributor. A distributor includes a rotor arm (not shown) which is fitted on an upper end portion of the shaft 10 for rotation therewith.

In order to modify the known ignition triggering device, there are removed from that device the fixed and movable electrical contacts (not shown) and the rotor arm normally carried on the end of the shaft 10. There is then fitted onto the cam 12 an adaptor comprising an inner element 1 3 and ar outer element 14. The rotor arm can then be refitted on the end portion of the shaft 10 and a transducer, responsive to rotation of the adaptor, is mounted in a fixed position with respect to the axis 11, possibly by means of mounting screws previously used for securing the fixed switch contact. The provision of a transducer and the mounting of a one-piece adaptor on the cam is well known.

The inner element 13 of the adaptor has the form of a sleeve and extends completely around the periphery of the cam 12. At one end, the element includes a radially inwardly projecting abutment in the form of a flange 15 which engages an end face of the cam to limit travel of the adaptor along the cam. At the opposite end, the inner element includes a radially outwardly projecting abutment in the form of a flange 1 6 which limits travel of the outer element 14 onto the inner element.

The inner element 1 3 extends completely around the cam 1 2 and, when pushed onto the cam, engages the peripheral surtace ot the cam at at least some positions. The inner element is adapted for contraction by the provision of axially extending slots 17 7 which are spaced apart around the axis and extend through the flange 1 6 and along the side wall of the inner element to the flange 1 5. The slots do not penetrate the flange 1 5. Furthermore, the inner element is formed of a plastics material which can flex resiliently sufficiently for each of the slots 1 7 to close up at the flange 1 6. By virtue of its resilience and of the presence of the slots 1 7, parts of the inner element other than the flange 1 5 can expand to fit over an over-sized cam. Typically, in an inner element intended to be fitted onto a cam having four lobes, there are four slots 1 7.

The inner element 13 is shaped to fit onto the cam 12 with each of the slots 1 7 adjacent to a corresponding lobe 1 8 of the cam. At positions between the slots 17, the inner element has a double wall comprising an inner leaf 19 and an outer leaf 20. The inner leaf is thinner than the outer leaf. Near to the slots 1 7, the wall of the inner element consists of a single leaf having a thickness exceeding that of the outer leaf 20. The inner leaf 1 9 lies sufficiently near to the axis 11 to prevent the inner element being fitted onto the cam with each lobe 18 lying mid-way between adjacent slots 1 7. Being relatively thin and formed of resilient material, the inner leaf 1 9 can flex as necessary to accommodate the immediately adjacent part of the cam.

The outer element 14 is of annular form and has an internal diameter which slightly exceeds the external diameter of the side wall of the inner element 13 but is less than the peripheral diameter of the flange 1 6. Means are provided for restraining relative rotation of the inner and outer elements when assembled together. These means include a plurality of projections 21 formed at the radially inwardly presented surface of the outer element. These projections are in the form of axially extending ribs, each having side surfaces lying substantially in respective radial planes. The radial dimension of each rib 21 decreases towards the axial extremities of the rib and has a constant value over a mid-portion of the rib. The outer element 14 is symmetrical about a plane perpendicular to the axis 11.

For receiving the ribs 21, there are formed in the inner element 14 a corresponding number of axially extending recesses 22 having side surfaces lying substantially in radial planes. The ribs are a sufficiently close fit in these recesses to restrain the inner and outer elements against relative rotation about the axis 11. Each of the recesses 22 has a radially outwardly facing surface 23 which is inclined at an acute angle, typically in the region of 50, to the axis 11. The depth of each recess has a maximum value adjacent to the flange 15 and a minimum value adjacent to the flange 1 6. The ribs 21 can enter the recesses 22 adjacent to the flange 1 5 without engaging the surfaces 23.As each rib is moved along the corresponding recess towards the flange 1 6, it engages the surface 23 and exerts radially inwardly directed pressure on the surface 23 of the inner element. In the particular example shown, each recess 22 lies centrally between a pair of adjacent slots 17. The inner element 1 3 is fitted onto the cam 12 without the outer element 14. The outer element is then applied to the outer element so that the ribs 21 engage in the recesses 22. As the ribs move over the surfaces 23, the inner element is contracted onto the cam so that the pressure under which the inner element engages the lobes 18 of the cam is increased. There may remain between the inner' leaves 19 and the cam clearance spaces.

The cam 12 illustrated has four lobes and is intended for use in the ignition system of a four cylinder engine. In cases where different numbers of cylinders are comprised by the engine, the number of lobes on the cam would be varied accordingly. Preferably, the outer element of an adaptor intended for use with such a different cam is arranged to establish pressure contact with the inner element of the adaptor at at least three positions spaced apart around the circumference of the inner element and the inner element is preferably formed with at least three axially extending slots. If required, the inner element may be arranged to engage in pressure contact with the cam at positions between the lobes rather than at the lobes. The outer element is preferably arranged to engage in pressure contact with the inner element at positions different from those at which the inner element engages under pressure contact with the cam.

The outer element 14 is conveniently composed of a metal ring, to the outer surface of which there is attached a layer of magnetic material, for example ferrite particles embedded in a plastics matrix. A required pattern of magnetic poles can then be induced on the outer element so that the required response of an eiectro-magnetic transducer to rotation of the adaptor will be brought about.

Claims (21)

1. An adaptor for modifying a rotary cam, the adaptor comprising an inner element which, in use, is fitted onto the cam to engage a peripheral surface thereof with an axis of the inner element coinciding with an axis of rotation of the cam, and an outer element adapted to be applied to the inner element whilst the inner element is on the cam to cause contraction of the inner element and thereby increase the pressure exerted on the cam by the inner element.

2. An internal combustion engine having an ignition-triggering device which includes a shaft rotated by the engine during operation, a cam formed on or rotated by the shaft, an inner element engaged with a peripheral surface of the cam to rotate therewith and an outer element which embraces the inner element and holds the inner element in pressure contact with said peripheral surface, the inner element having an axis which coincides with the axis of rotation of the shaft and cam.

3. An adaptor according to Claim 1 or an engine according to Claim 2 wherein the inner and outer elements have respective formations which co-operate to restrain relative rotation of the elements.

4. An adaptor according to Claim 1 or 3 or an engine according to Claim 2 or 3 wherein the inner element is arranged to extend completely around the cam and is adapted for contraction onto the cam by the application of pressure at selected positions on the element.

5. An adaptor or engine according to Claim 4 wherein the outer element is in pressure contact with the inner element at at least three positions spaced apart circumferentially.

6. An adaptor or engine according to Claim 4 or 5 wherein the inner element has a plurality of axially extending slots.

7. An adaptor according to any one of Claims 1 and 3 to 6 or an engine according to any one of Claims 2 to 6 wherein one or each of the inner and outer elements has surfaces which are inclined at an acute angle to the axis of the inner element and with which the other element co-operates during application of the outer element to the inner element.

8. An adaptor according to any one of Claims 1 and 3 to 6 or an engine according to any one of Claims 2 to 6 wherein the inner element has surfaces which are inclined at an acute angle to the axis of the inner element.

9. An adaptor or an engine according to Claim 8 wherein the outer element is symmetrical about a plane perpendicular to the axis of the inner element.

1 0. An adaptor or an engine according to Claim 9 wherein the outer element has at a radially inwardly presented surface of the outer element a plurality of projections for engaging said surfaces of the inner element.

1 An adaptor or engine according to Claim 10 wherein the radial dimension of each of said projections decreases towards the axial extremities of the projection.

12. An adaptor according to any one of Claims 1 and 3 to 11 or an engine according to any one of Claims 2 to 11 wherein the inner element has a radially inwardly projecting abutment at one end and a radially outwardly projecting abutment at the opposite end.

13. An adaptor or an engine according to Claim 12 wherein each abutment is in the form of a flange.

14. An adaptor or engine according to Claim 12 or Claim 13, in either case as appendant to any one of Claims 7 to 11, wherein said surfaces converge towards the axis in a direction from the radially outwardly projecting abutment to the radially inwardly projecting abutment.

15. An engine according to any one of Claims 2 to 14 wherein the cam has a plurality of lobes, the inner element is in pressure contact with the lobes and the outer element is in pressure contact with the inner element at positions spaced circumferentially from the lobes.

16. An engine according to Claim 15 wherein the inner element has double wall portions at positions spaced circumferentially from the lobes, the outer element being in pressure contact with an outer leaf of each double wall portion and the inner leaf of each double wall portion being thinner than the outer leaf.

17. An engine according to Claim 16 wherein there is between the inner and outer leaves of each double wall portion a cavity.

18. A method of modifying an ignition triggering device for a spark ignition internal combustion engine, which device comprises a rotatable cam, wherein an inner element is fitted onto the cam to engage a peripheral surface thereof, whilst the inner element is on the cam an outer element is applied to the inner element in embracing relation therewith and application of the outer element to the inner element brings about contraction of the inner element and thereby increases the pressure exerted on the cam by the inner element.

19. An adaptor comprising inner and outer elements substantially as herein described with reference to and as illustrated in the accompanying drawing.

20. A method substantially as herein described with reference to the accompanying drawing of modifying an ignition triggering device for a spark ignition internal combustion engine.

21. Any novel feature or novel combination of features disclosed herein or in the accompanying drawing.