GB2246833A

GB2246833A - Pistons for engines or motors

Info

Publication number: GB2246833A
Application number: GB9113050A
Authority: GB
Inventors: David Alec Parker
Original assignee: T&N Technology Ltd
Current assignee: Federal Mogul Technology Ltd
Priority date: 1990-06-23
Filing date: 1991-06-17
Publication date: 1992-02-12
Anticipated expiration: 2011-06-17
Also published as: GB9113050D0; GB2246833B

Abstract

A piston comprises a crown (12) and a skirt (20). At least a portion of the skirt (20) is formed of a ceramic material injection moulded directly on to the remainder of the skirt (20) or the crown (12). The ceramic material may provide at least one pad (24; 54; 76) which extends from a thrust surface of the skirt (20) to transmit lateral forces against a wall of an associated cylinder. <IMAGE>

Description

PISTONS FOR ENGINES OR MOTORS The present invention relates to pistons for engines or motors, for example, internal combustion engines, or hydraulic or pneumatic reciprocating motors. In particular, the invention relates to pistons comprising a crown and a skirt.

The present invention is concerned with the construction of the piston skirt; or to part of a skirt having at least one insert therein, the insert being of a different material from that of the remainder of the piston skirt.

It is known to reduce the weight of a piston by replacing a metal skirt with a skirt of a plastics material secured within the piston.

It is known to provide plastic inserts for several different purposes. Thus, for example, in UK patent specification No. 2162614 it is disclosed to provide on each of both thrust faces of a piston skirt a plurality of plastic inserts to transmit lateral thrusts of the piston against a cylinder wall. Further, in order to reduce wear of the plastic inserts it is disclosed that each plastic insert is bevelled appropriately to cause provided lubrication to be forced over the plastic inserts by a hydrodynamic action during the reciprocation of the piston.

Further, it is disclosed in UK patent specification No. 2162614 that the plastic inserts are secured within recesses formed in the outer surfaces of the skirts, for example, by the inserts each being held in the co-operating recess, possibly each recess being formed with undercut portions, and the insert being formed with tongues each of a shape to be held within the associated undercut portion.

It is an object of the present invention to provide a piston having a skirt of a novel and advantageous construction.

The invention provides a piston for an engine or a motor comprising a crown and a skirt, wherein at least a portion of the skirt is formed of a ceramic material injection mouLded directly on to the remainder of the skirt or the crown.

An advantageous ceramic material for a piston part has low friction surfaces, and provides a rigid part. Further, a ceramic piston part advantageously will not wear if an abrasive fuel is burnt in the engine.

The ceramic material may be moulded by employing conventional injection moulding techniques, the ceramic material including a suitable binder for the injection moulding process. Injection moulding is advantageous in that it enables the piston part to be fabricated with low tolerances and, therefore, less subsequent machining of the piston part is required. In addition, the piston parts so obtained, advantageously have few knit lines, or seams; and have only a small amount of flash inadvertently formed therewith.

A ceramic piston part also may be advantageous by reducing the weight of the piston by replacing an equivalent known piston part of greater weight than the provided ceramic piston part.

The skirt may be wholly of a suitable ceramic material secured within the piston in any convenient way.

The entire skirt of a piston in accordance with the invention may be formed of a ceramic material injection moulded on to the crown. The crown may be provided with a protrusion over which the skirt is injection moulded so that the protrusion is embedded in the ceramic material and acts to secure the skirt to the crown. Alternatively, the skirt may be injection moulded so that ceramic material of the skirt enters a groove in the crown so that the skirt is secured to the crown.

Preferably, the ceramic material provides at least one pad which extends from a thrust surface of the skirt to transmit lateral forces against a wall of an associated cylinder. This reduces friction and wear. The pad may have bevelled edges to cause lubricant to be forced over the pad during reciprocation of the piston.

The ceramic material may, alternatively, be injection moulded into a recess in the skirt and provides at least one pad which extends from a thrust surface of the skirt to transmit lateral forces against a wall of an associated cylinder. The pads may be bevelled as described above.

The present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a half section of one embodiment of a piston for an internal combustion engine, and in accordance with the present invention, the piston having a metal crown and a skirt wholly of a ceramic material; Figure 2 is a side elevation of another embodiment of a piston in accordance with the present invention, the piston having an integral metal crown and a metal portion of the skirt, and inserts of a ceramic material provided within the skirt; Figure 3 is a section taken on the line III III of part of the piston skirt of Figure 2, showing an insert; Figure 4 corresponds to Figure 1, but shows the ceramic piston skirt having plastic or ceramic inserts therein;; Figure 5 shows a portion of the skirt of another embodiment of a piston, the skirt having an insert therein, Figure 5a being a section of the skirt portion, and Figure 5b being a plan view looking in the direction of the arrow A of Figure 5a before the insert is provided; Figure 6 is a side elevational view of a fourth embodiment of a piston according to the invention; and Figure 7 is a half-sectional view taken on the line VII-VII in Figure 6.

The piston 10 shown in Figure 1 has a metal crown 12 of a conventional construction. The metal of the crown is an alloy of aluminium. Included in the crown 12 is a ring belt 14, and a boss 15 for the gudgeon pin (not shown). The gudgeon pin hole is indicated at 18; and the piston axis is indicated by the dotted line 17. Depending from the crown 12, and secured thereto, is a skirt 20.

In accordance with one aspect of the present invention, the skirt 20 is wholly of a suitable ceramic material.

In a method of fabricating such a Diston having a composite construction, the ceramic skirt 20 is formed on the crown 12 by employing a conventional injection moulding process. The ceramic material in powder form is dispersed in a suitable binder, and is injection moulded into a mould in which the crown 12 has been positioned. The ceramic material is, thus, directly moulded on to the crown.

In order to facilitate the securing of the skirt 20 to the crown 12, the crown is formed with an annular bulbous protrusion 21. The skirt 20 is injection moulded over the protrusion 21 so that the protrusion 21 is embedded in the ceramic material and acts to secure the skirt 20 to the crown 12.

The binder is removed by use of solvent or by heat treatment or both, and the ceramic material is then sintered in a furnace. In this manner, the metal crown 12 can be secured to the ceramic skirt 20 in a satisfactory manner.

The ceramic material of the skirt 20 provides pads 24 which extend from a thrust surface of the skirt 20 to transmit lateral forces against a wall of an associated cylinder (not shown). The pads 24 have bevelled edges 32 to cause lubricant to be forced over the pad during reciprocation of the piston in similar manner to that described in GB patent specification No. 2104188. The appearance of the pads 24 of the piston 10 is similar to the pads 24 shown in Figure 2. The skirt 20 surrounds the boss 15 and is spaced therefrom.

Figures 2 and 3 show a piston 40 which is a second embodiment of the invention. The piston 40 has a crown 12 and a skirt 20 of integral metal construction. The skirt 20 is provided with recesses 27 in its thrust surfaces in which pads 24 of ceramic material are moulded. The pads 24 are bevelled at their edges 32 for the same reason that the pads of the piston 10 are bevelLed. The ceramic material of the pads 24 is directly moulded into the recesses 27 which are slightly undercut to assist in retaining the pads in the recesses.

Figures 4 and 5 show a third embodiment of the invention in the form of a piston 50. The piston 50 is generally similar to the piston 10 in that a ceramic skirt 20 is directly moulded on to a metal crown 12. However, instead of the protrusion 21, the crown 12 of the piston 50 is provided with an annular groove 19 which is undercut and which is entered by the ceramic material to secure the skirt 20 to the crown.

The skirt 20 of the piston 50 is provided with apertures 52 in which inserts 54 are mounted to provide pads 24 similar to those of the pistons 10 and 40. The inserts 54 are directly moulded into the apertures 52 so that they overlap the edges of their aperture 52 on both the inner and outer surfaces of the skirt 20. The apertures 52 are provided with a shoulder 56 at the inward end thereof which is embedded in the material of the insert 54. The inserts 54 are made of ceramic material different from that forming the remainder of the skirt 20 or of a suitable plastics material.

Figures 5a and 5b show a modification of the piston 50 in which the apertures 52 are replaced by a recess 58 in the outer surface of the skirt 20 and six holes 60 through the skirt 20 opening into the recess 58. The material of the inserts 54 is moulded so that it passes through the holes 60.

Figures 6 and 7 show a fourth piston 70 which is illustrative of the invention. The piston 70 is generally similar to the piston 40 in that it has a metal crown 12 with an integral metal skirt portion 20. The skirt 20 has large apertures 72 in its thrust faces into which inserts 74 of ceramic material are injection moulded. The inserts 74 include three pads 76 similar to the pads 24 of the piston 10. The recess 72 has an inner sholder 78.

Thus, the whole of a piston skirt; or the remainder of a skirt having at least one insert provided therein, or at least one insert within a skirt of any suitable material other than a ceramic material; may be of any suitable ceramic material, for example, being of silicon nitride, or silicon carbide, which can be injection moulded by employing a suitable binder.

Claims

1. A piston for an engine or a motor comprising a crown and a skirt, wherein at least a portion of the skirt is formed of a ceramic material injection moulded directly on to the remainder of the skirt or the crown.

2. A piston according to Claim 1 wherein the entire skirt is formed of a ceramic material injection moulded on to the crown.

3. A piston according to Claim 2, wherein the skirt is injection moulded over a protrusion from the crown so that the protrusion is embedded in the ceramic material and acts to secure the skirt to the crown.

4. A piston according to Claim 2, wherein the skirt is injection moulded so that ceramic material of the skirt enters a groove in the crown so that the skirt is secured to the crown.

5. A piston according to any one of Claims 2 to 4, wherein the ceramic material provides at least one pad which extends from a thrust surface of the skirt to transmit lateral forces against a wall of an associated cylinder.

6. A piston according to Claim 5, wherein the pad has bevelled edges to cause lubricant to be forced over the pad during reciprocation of the piston.

7. A piston according to Claim 1, wherein the ceramic material is injection moulded into a recess in the skirt and provides at least one pad which extends from a thrust surface of the skirt to transmit lateral forces against a wall of an associated cylinder.

8. A piston according to Claim 7 wherein the pad has bevelled edges to cause lubricant to be forced over the pad during reciprocation of the piston.

9. A piston according to Claim 1, wherein the skirt is provided with apertures into which the ceramic material is injection moulded.

10. A piston according to Claim 9, wherein the ceramic material is injection moulded around a shouLder formed at the edge of the aperture to secure the ceramic material in the aperture.

11. A piston according to either one of Claims 9 and 10, wherein the ceramic material provides at least one pad which extends from a thrust surface of the skirt to transmit lateral forces against a wall of an associated cylinder.

12. A piston according to Claim 11, wherein the ceramic material provides a plurality of pads on the thrust surface.

13. A piston according to either one of Claims 11 and 12, wherein the or each pad has bevelled edges to cause lubricant to be forced over the pad during reciprocation of the piston.

14. A piston substantially as hereinbefore described with reference to and as shown in i) Figure 1 of the accompanying drawings; ii) Figures 2 and 3 of the accompanying drawings; iii) Figures 4 and 5 of the accompanying drawings; iv) Figures 6 and 7 of the accompanying drawings.