GB2200720A

GB2200720A - Ignition distributor

Info

Publication number: GB2200720A
Application number: GB08729264A
Authority: GB
Inventors: Natale Parolini
Original assignee: Industrie Magneti Marelli SRL; Magneti Marelli SpA
Current assignee: Industrie Magneti Marelli SRL; Marelli Europe SpA
Priority date: 1986-12-17
Filing date: 1987-12-15
Publication date: 1988-08-10
Anticipated expiration: 2007-12-15
Also published as: IT208630Z2; GB8729264D0; BR6702871U; FR2608686A3; DE8716603U1; FR2608686B3; GB2200720B; ES2005481A6; IT8654208V0

Abstract

The ignition distributor comprises a hollow body, having a cup-shaped portion containing means for generating ignition pulses and an advance regulating device, and a tubular support portion in which an operating shaft of different material from that constituting the body is rotatably mounted. The operating shaft (16) has first and second annular shoulders (40a, 34a) arranged to cooperate respectively with first and second reaction surfaces (28, 30a) of the tubular portion (12b) of the hollow body (12); to form a strong axial connection between the operating shaft (16) and the body (12) of the distributor (10), the respective shoulders (40a, 34a) of the operating shaft (16) and reaction surfaces (28, 30a) of the body (12) are separated from each other by a distance (L) such that the difference in thermal expansion of the materials constituting the body (12) and the shaft (16) is negligible. <IMAGE>

Description

IGNITION DISTRIBUTOR The present invention relates to an ignition distributor for internal combustion engines, comprising a hollow body, having a cup-shaped portion containing means for generating ignition pulses and a device for regulating the advance, and a tubular support portion in which an operating shaft of material different from tat constituting the body is rotatably mounted.

In current ignition distributors, a small axial clearance is required between the shaft and the body in order to improve the reliability and precision of operation. of the distributor. In known distributors, the strong axial connection between the shaft and the body is usually achieved either by means of cooperation between a bush keyed onto the shaft and the free ena of the tubular portion of the body, or by means of cooperation between a plate associated with the advance regulating device and the base wall of the cup-shaped portion of the body, with the interposition of insulating washers and spacer washers calibrated according to the calibration of the axial shaft-body clearance.

For a small clearance, preset during assembly of the distributor at ambient temperature and normally less than 0.1 mm., the running temperature of the distributor can be such that the space is wholly absorbed by the differential thermal expansion between the steel shaft and the aluminium alloy body, giving rise to a notable increase in the quantity of friction especially between the plate of the advance regulating device and the body. Moreover, even in the absence of differential thermal expansion, this friction is high because of the axial thrust of the shaft on the body, originating from the helical gears which rotate the shaft. It has been observed that this high friction can cause softening or fusion of the insulating washers of plastics material interposed between the shaft and the body.

The object of the present invention is to provide an ignition distributor which does not have the above disadvantages and which is simple and economical to produce.

According to the invention, this object is achieved by virtue of the fact that the operating shaft of the distributor has first and second annular shoulders arranged to cooperate respectively with first and second reaction surfaces of the tubular portion of the hollow body to form a strong axial connection between the operating shaft and the body of the distributor, the respective shoulders of the operating shaft and reaction surfaces of the body being separated from each other by a distance such that the difference in thermal expansion of the materials constituting the body and the shaft is negligible.

By virtue of these characteristics, it is possible to preset very low values of axial shaft-body clearance without danger of "binding" of the shaft and the body due to differential thermal expansion. the above-mentioned axial thrust of the shaft and the body is also absorbed by one of the reaction surfaces of the body without the above problems of friction.

Preferably, the first reaction surface of the body consists of an end face of the tubular portion of the body facing away from the cup-shaped portion and the second reaction surface Qf the body consists of a lateral wall of an internal groove in the tubular portion of the body.

Furthermore, the second annular shoulder of the shaft is defined by an annular element located within the groove of the tubular portion of the body and keyed to the shaft by means of a connecting pin.

In this way, the strong axial connection between the shaft and the body is effected particularly rapidly to the benefit of the final production cost of the distributor.

Further advantages and characteristics of the distributor according to the invention will become clear from the detailed description which follows, purely by way of non-limiting example, with reference to the appended drawings, in which: Figure 1 is a partially sectioned lateral view of the distributor, and Figure 2 is a section taken on the line II-II of Figure 1.

With reference to the drawings, an ignition distributor is generally indicated 10 and comprises a hollow body 12 having a cup-shaped portion 12a and a tubular portion 12b within which an operating shaft 16 is rotatably mounted with the interposition of a self-lubricating bush 14. The shaft 16 drives the advance regulator and the ignition pulse generating means (not illustrated) housed within the portion 12a of the body 12. A plate 18 of the advance regulator device, keyed to the shaft 16 at 20, is partially visible in Figure 1.

Like conventional distributors, the distributor 10 also has a cap 22 fixed resiliently to the body 12 at 23 and a pneumatic advance corrector 24 fixed laterally to the cup-shaped portion 12a of the body 12.

The tubular portion 12b of the body 12 is provided with a flange 26 for fixing the distributor to the engine block (not illustrated).

At one end E, the tubular portion 12b has a frontal surface 28 and an internal groove 30 with lateral walls 30a and 30b respectively and a base wall 30c; in correspondence with the internal groove 30, the end E of the tubular portion 12b of the body 12 has a larger external diameter than the rest of the tubular portion.

There is a hole 32 through the tubular portion 12b in correspondence with the base wall 30c of the groove 30, of dimensions such as to allow a bush 34 to be passed through and keyed onto the shaft 16 by means of a connecting pin 36. The bush 34 defines a frontal surface 34a facing the lateral wall 30a of the groove 30.

A helical gear 40 intended to be connected to a rotating member of the engine is keyed to an end 16a of the control shaft 16 by a connecting pin 38. A frontal surface 40 is defined on the gear 40 and faces the surface 28 of the end E of the body 12 with the interposition of one or more calibrated spacer washers R.

During assembly, after the bush 34 has been introduced into the groove 30 through the hole 32, the shaft 16 is mounted coaxially with the tubular portion 12b of the body 12 so as to slide within the central hole of the bush 34. The bush 34 is then fixed to the shaft 16 by means of the pin 36 and the gear 40 is made fast to the shaft 16 in a similar manner, by means of the connecting pin 38. The axial clearance between the shaft 16 and the body 12, indicated G in Figure 1, can be adjusted by means of calibrated washers R.

During operation the helical gear 40 exerts an axial thrust on the shaft 16 in a direction away from the cup-shaped portion 12a (towards the right of Figure 1), this axial force being absorbed by contact between the frontal surface 34a of the bush 34 and the lateral wall 30a of the groove 30. Friction between these surfaces is low, since the part of the distributor 10 downstream of the flange 26 for connection to the engine block is in a bath of oil. The distance between the plate 18 of the automatic advance regulator and the body 12, indicated D in Figure 1, is such that, even at a high running temperature, the thermal expansion of the aluminium-alloy tubular portion 12b of t:7e bodv 52 relative to the lesser expansion of the steel shaft 16 never causes contact between the plate 18 and the body 12. The length, indicated L, of the portion of the body 12 and te relative portion of the shaft 16 which could bye involved in phenomena of differential thermal expansion is such that the expansion is wholly negligible relative to the required clearance G, even if the latter is less than one tenth of a millimetre.

Claims

1. An ignition distributor for internal combustion engines, comprising a hollow body, having a cup-shaped portion containing means for generating ignition pulses and an advance regulating device, and a tubular support portion in which an operating shaft of different material from that constituting the body is rotatably mounted, characterised in that the operating shaft has first and second annular shoulders arranged to cooperate respectively with first and second reaction surfaces of the tubular portion of the hollow body to form a strong axial connection between the operating shaft and the body of the distributor the respective shoulders of the operating shaft and reaction surfaces of the body being separated from each other by a distance (L) such that the difference in thermal expansion of the materials constituting the body and the shaft is negligible.

2. An ignition distributor according to Claim 1, characterised in that the first reaction surface of the body consists of an end face 8 of the tubular portion of this body facing away from the cup-shaped portion and in that the second reaction surface of the body consists of a lateral wall of an internal groove in the tubular portion of the body.

3. An ignition distributor according to Claim 2, in which a gear is keyed to the operating shaft to transmit drive from a rotating member of the engine, characterised in that the first annular shoulder of the shaft is defined by a frontal surface of the gear facing the body of the distributor.

4. An ignition distributor according to Claim 2, characterised in that the second annular shoulder of the shaft is defined by an annular element located within the groove of the tubular portion of the body and keyed to the shaft by means of a connecting pin

5. An ignition distributor according to Claim 4, characterised in that there is a hole located in correspondence with a base wall of the groove so as to allow the annular element to be inserted during assembly and keyed to the operating shaft,

6. An ignition distributor for an internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.