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A New Form of Piston Construction

22nd March 1932, Page 57
22nd March 1932
Page 57
Page 57, 22nd March 1932 — A New Form of Piston Construction
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WVWITH but few exceptions, practically every form of piston hitherto used in automobile practice has included a gudgeon pin as the coupling medium between the body of the piston and the connecting rod. Whilst this obviously permits motion on an axis parallel to the crankshaft, it does not allow for any discrepancy in alignment.

To overcome these troubles has been the object in the design of the Hurd piston, the sole concession for which is held by Mr. H. A. Triggs, of 155, Stafford Road, Croydon, who is desirous of disposing of the manufacturing rights.

There are many variations in the design, as described in patent specifications, but the two principal features consist of the employment of a balland-socket joint between the connecting rod and piston in place of the conventional gudgeon pin, and the use of a separate, demountable head.

Broadly speaking, there are two types of ball-and-socket joint ; in one case it consists of the ball end of the connecting-rod seating upon a split socket and implied by an inverted, cup-shaped member, with due provision for lubrication, The piston used in connection with this design consists of a skirt or guide portion, having a diametral channel cast in it. At the base of the channel is an aperture, sufficiently large to allow the ball end of the connecting rod to pass through. When this has been inserted the two socket pieces are slid into position and secured by means of the mouth of the inverted cup, which rests in channels cut in the sockets. Next, the crown portion of the piston is slid into position, its projections travelling along horizontal grooves machined in the sides of the channel in the guide portion of the piston skirt.

This design allows of contact between' the projection below the piston crown and the inverted cup, thereby transferring the downward thrust directly to the connecting rod instead of passing it through the walls of the piston. 'This allows much lighter construction and the employment of a bi-metal piston.

An optional design consists of a piston having a skirt which is connected to the crown by an interrupted-thread mechanism' of the type used in gnu breeches. In this case a gudgeon pin, fixed in the little-end of the connecting rod, is used, but it takes a hearing in forked members which, in their turn, are free, within limits, to oscillate in bearings secured between the crown and skirt of the piston, so that a certain amount of universal movement is allowed,

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