GB2261717A

GB2261717A - Piston cooling

Info

Publication number: GB2261717A
Application number: GB9124886A
Authority: GB
Inventors: Ian Coroon Middleton
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1991-11-22
Filing date: 1991-11-22
Publication date: 1993-05-26
Also published as: GB9124886D0

Abstract

An internal combustion engine comprises a piston 10 reciprocable in a cylinder bore 12 and connected by a connecting rod 18 to a crankshaft. A resiliently deformable gaiter 24 extends between the little end of the connecting rod 18 and the under-crown surface 16 of the piston 10 to define an oil cavity 36. Oil is introduced into the cavity 36 as the piston reciprocates in the bore 12 in order to cool the piston crown. Oil is introduced into the cavity either by a jet 32 passing through a hole 32 in the gaiter 24 or by being pumped oil along a passage in the connecting rod. <IMAGE>

Description

Title ENGINE COOLING Field of the invention The present invention relates to engine cooling and more specifically to the cooling of the pistons of an internal combustion engine.

Background of the invention In highly rated internal combustion engines it is necessary to provide under-crown cooling of the pistons to maintain the proper functioning of the piston rings and to eliminate cracking of the piston crowns and the pin boss areas, in which the gudgeon pins are journalled.

For this purpose, it is desirable to be able to hold the oil in the under-crown region to increase the heat transfer to the oil rather than just splash the oil on to the under-crown. This has been achieved in the prior art (see for example GB-A-2 050 564) by forming the undercrown of the pistons with oil retaining galleries or by attaching a so-called cocktail shaker device to the underside of the piston crown. Such constructions define cavities having restricted access passages at which a jet of oil is aimed from a nozzle stationarily mounted beneath the piston at the bottom of its stroke, the action of such devices being to retain the oil in the cavities for extended periods of time in order to improve the heat exchange.

As the piston descends in its bore, the cavity fills up rapidly but as it ascends the oil is thrown own by its own inertia and the cavity is not refilled effectively as the piston is rapidly moving away from the oil jet.

Incorporating oil galleries in the under-crown of the piston adds to the bulk of the piston and cannot be achieved in engines with small pistons. Furthermore securing a separately formed plate to the under-side of the piston crown is difficult to achieve as the pin bosses present an obstruction.

Object of the invention The present invention seeks to provide improved cooling of the piston crowns in highly rated internal combustion engines which can be achieved even with engines having small pistons.

Suinmarv of the invention According to the present invention, there is provided an internal combustion engine comprising a piston reciprocable in a cylinder bore and connected by a connecting rod to a crankshaft, a resiliently deformable gaiter extending between the little end of the connecting rod and the under-crown surface of the piston to define a cavity, and means for introducing oil into the cavity as the piston reciprocates in the bore in order to cool the piston crown.

The gaiter may readily be assembled by first mounting it over the end of the connecting rod and because it is resilient, it can be deformed to enable it to pass between the gudgeon pin bosses. After passing the bosses, the gaiter will by its own resilience sealing engage the under-side of the piston.

Oil may be introduced into the cavity either by means of a stationary nozzle arranged at the lower end of the bore or by pumping it along a duct provided for this purpose in the connecting rod and opening into the oil cavity.

The former case is preferred because of the ease of manufacture notwithstanding the fact that the cavity is not totally enclosed and that, during upstrokes of the piston, some oil can spill out of the hole through which the oil jet from the nozzle enters the cavity. The alternative of introducing oil through a passage in the connecting rod has the advantage that the oil cavity is closed at all times and oil can only escape when the pressure in the cavity causes the gaiter to separate from the under-side of the piston. However, this construction has the disadvantage of reducing the oil pressure at the big end bearing and weakening the connecting rod.

Brief descriotion of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic section through a piston and top part of a connecting rod of a first embodiment of the invention at the top or bottom of the piston stroke, Figure 2 is a similar view showing the piston in mid stroke, and Figures 3 and 4 are views similar to Figures 1 and 2 but showing an alternative embodiment of the invention.

Description of the preferred embodiments In Figures 1 and 2, a piston 10 which is generally conventional is formed on its under-side above the bosses for the gudgeon pin 14. with a hemispherical surface 16.

The connecting rod 18 is formed at its upper end with a short extension 20 having a surrounding groove 22. A resilient gaiter 24, made of an elastomeric material capable of withstanding high temperatures, has a central aperture which can be fitted over the extension 20 of the connecting rod 18 so that the gaiter engages in the groove 22 and is retained there by its own resilience.

The gaiter 24 is constructed as a diaphragm with corrugations 26 which allow the centre to flex relative to the perimeter. Thus, as shown in Figures 1 and 2, the perimeter of the gaiter 24 remains in sealing contact with the under-crown surface 16 of the piston 10 by virtue of its own resilience despite the pivoting of the connecting rod 18 relative to the piston 10.

The gaiter 24 is also formed with a small hole 30 which is aligned with an oil jet or column 32 emitted by a nozzle 34 arranged at the lower end of the cylinder bore 12. The oil jet 32 fills the cavity 36 defined between the gaiter 24 and the surface 16 during the downstroke of the piston as in the case of prior art cocktail shakers and oil galleries. During the upstroke of the piston, oil does tend to spill out of the hole 30 but because the hole is only small and because of the opposing pressure from the jet 32 the cavity 36 is not emptied even at high engine speeds and oil remains trapped in the cavity 36 to effect improved cooling of the piston crown.

The embodiment of Figures 3 and 4 differs from the first embodiment in that no hole is formed in the gaiter 24' and in place of the oil jet 32, oil is introduced into the cavity 36' through a passage 40 passing along the length of the connecting rod 18' and through slots in the little end bearing. The oil fills the cavity 36' at all times and escapes when the pressure in the cavity 36' causes the perimeter of the gaiter 24' to lift off the surface 16 of the piston 10. The sealing action of the gaiter 24' against the surface 10 creates a back-pressure which assists in maintaining adequate oil pressure at the big end bearing but nevertheless the embodiment of Figures 1 and 2 is preferred as it avoids the need for an passage in the connecting rod, which tends to weaken it.

In both described embodiments, the gaiter 24 or 24' may be provided with reinforced regions around its outer perimeter and around the hole which fits over the connecting rod 18. Such reinforcement may be achieved either by the use of an increased thickness of elastomeric material or by the use of metal springs. The gaiter may in effect be designed along the same lines as a bearing seal. Of course, the material from which the gaiter is made must be selected to be able to withstand the relatively high piston temperatures.

The advantages of using a flexible gaiter to define an oil cavity on the under-side of the piston are that clearances through which oil can leave the cavity on the upstroke of the piston can be minimised and that an oil retaining cavity can be provided in this manner even in small pistons. The number of component parts involved in defining the cavity is also reduced as compared with the prior art proposals which, together with the considerably simplified assembly procedure, enables significant cost reductions to be achieved.

Claims

1. An internal combustion engine comprising a piston reciprocable in a cylinder bore and connected by a connecting rod to a crankshaft, a resiliently deformable gaiter extending between the little end of the connecting rod and the under-crown surface of the piston to define a cavity, and means for introducing oil into the cavity as the piston reciprocates in the bore in order to cool the piston crown.

2. An internal combustion engine as claimed in claim 1, wherein the gaiter is formed with a hole, and a nozzle is mounted on the engine block beneath the piston to aim a jet of oil at the hole to fill the cavity between the gaiter and the piston.

3. An internal combustion engine as claimed in claim 1, wherein oil is introduced into the cavity between the gaiter and the piston by being pumped along a passage in the connecting rod.

4. An internal combustion engine as claimed in any preceding claim, wherein the gaiter is fitted to a groove in an extension of the connecting rod.

5. An internal combustion engine constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

Amendments to the claims have been filed as follows 1. An internal combustion engine comprising a piston reciprocable in a cylinder bore and connected by a connecting rod to a crankshaft, a resiliently deformable gaiter mounted on the little end of the connecting rod and extending to the under-crown surface of the piston to define a cavity, and means for introducing oil into the cavity as the piston reciprocates in the bore in order to cool the piston crown.

2. An internal combustion engine as claimed in claim 1, wherein the gaiter is formed of an elastomeric material.

3. An internal combustion engine as claimed in claim 1 or claims 2, wherein the gaiter is formed with a hole, and a nozzle is mounted on the engine block beneath the piston to aim a jet of oil at the hole to fill the cavity between the gaiter and the piston.

4. An internal combustion engine as claimed in claim 1 or claim 2, wherein oil is introduced into the cavity between the gaiter and the piston by being pumped along a passage in the connecting rod.

5. An internal combustion engine as claimed in any preceding claim, wherein the gaiter is fitted to a groove in an extension of the connecting rod.

6. An internal combustion engine constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.