GB2206067A

GB2206067A - Crankpin grinders

Info

Publication number: GB2206067A
Application number: GB08714928A
Authority: GB
Inventors: Michael Laycock
Original assignee: Litton UK Ltd
Current assignee: Intermec Europe Ltd
Priority date: 1987-06-25
Filing date: 1987-06-25
Publication date: 1988-12-29
Anticipated expiration: 2007-06-25
Also published as: GB2206067B; GB8714928D0

Abstract

Method and apparatus for grinding a crankpin (20) of a crankshaft of a family of crankshafts, wherein the crankshaft (20) is rotated about an axis through the centre of a notional crankpin (16) of intermediate throw and a grinding wheel (10) is utilised to grind the crankpin (20) whose throw is greater or lesser than that of the notional crankpin (16). The grinding wheel (10) is controlled such than the distance between the axis of the notional crankpin (16) aid the axis of the grinding wheel (10) varies to compensate for such difference in the throws. <IMAGE>

Description

DESCRIPTION CRANKPIN GRINDERS.

The present invention relates to apparatus and method for grinding crankpins, and in particular, but not exclusively, to an apparatus and method for grinding the crankpins of a family of crankshafts.

An important aspect of all moving machinery is that the surfaces of some components are required to interact with the surfaces of other components, and although various lubricating methods are employed, it is a requisite that these surfaces are machined to a finish providing the least frictional contact possible. These components may also have to be macttined to precise dimensions to provide a component of accurate shape and uniform weight. The journals and cams of a camshaft are typical of such components. If the component requiring grinding requires a uniform circular cross-section and can be readily rotated about the axis of the circular crosssection, then the grinding technique is relatively simple, and centreless or plunge centreless grinding can be employed depending on the form of the workpiece on which the component requiring grinding is located.

The grinding operation becomes more complicated if the relevant component parts are of a non-circular or eccentric form, e.g. the cams of a camshaft and any eccentrics located on a camshaft. Cams and eccentrics are currently ground by employing computer-controlled machinery. In such a technique, the workpiece, e.g.

camshaft, is rotated about its centre, and the grinding wheel, having previously been brought into play with the relevant component, e.g. cam, moves in a direction transverse to the camshaft axis, towards and away from the camshaft. This transverse movement of the grinding wheel is dependent on the angle of rotation of the cam, so that the position of the grinding surface of the wheel follows the outer dimensions of the cam as the cam rotates. The shape of the cam dictates that the relative speed of travel of the grinding wheel over the surface of the cam increases as the curvature of the cam surface in contact with the grinding wheel increases. Computer control is also employed to maintain a constant relative speed of travel between the cam surface and grinding wheel.This constant relative speed of travel is achieved by increasing the speed of rotation of the cam as the grinding wheel passes over a section of decreasing curvature of the cam surface. This computer-controlled technique is also employed for the purpose of grinding eccentrics, and produces components with high quality finished surfaces.

However, this method can only be employed when the transverse distance over which the grinding wheel is required to move is in the order of a few centimetres. At greater distances of travel the control of the grinding operation becomes a problem due to the increased transverse distance travelled by the grinding wheel and its associated mounting and drive mechanism. Since the average speed of rotation of the workpiece must not decrease below about 90 rpm the grinding wheel has to travel this increased distance in a similar time as previously, which creates a problem with respect to the accurate control necessary to provide a high quality finish.

The form of a crankshaft presents the problem outlined hereinbefore, when grinding a crankpin. On rotating the crankshaft about its axis the throw of each crankpin is too great to allow the computercontrolled grinding technique outlined above, to be utilised.

At present, a method used for grinding crankpins involves clamping the crankshaft journals in fixtures, re-aligning the crankshaft and rotating the fixtures around an axis through the crankpin requiring grinding, whereby the crankpin rotates on its own stationary axis and the fixtures and clamped journals orbit the crankpin axis. The crankpin can then be ground using a conventional grinding wheel. However, the re-alignment of the crankshaft is a complex and time consuming operation, requiring complicated equipment, and since engine manufacturers commonly produce a family of crankshafts varying only in the throw of the crankpins, the use of the above-described re-alignment technique would require regular re-alignment or the unnecessary use of extra pre-set grinding machinery.

It would therefore be advantageous if relatively simple, readily available machinery, requiring less complex equipment and priming procedures, could be employed to grind the crankpins of a family of crankshafts of similar dimension but differing throw.

In accordance with a first aspect of the present invention, a method for grinding a crankpin of a crankshaft of a family of crankshafts comprises rotating the crankshaft about an axis through the centre of a notional crankpin of intermediate throw and utilizing a grinding wheel to grind the said crankpin whose throw is greater or lesser than that of the notional crankpin, the grinding wheel being controlled such that the distance between the axis of the notional crankpin and the axis of the grinding wheel varies to compensate for such difference in the throws.

In accordance with a second aspect of the present invention, apparatus for grinding crankpins on a crankshaft of a family of crankshafts comprises a mechanism for rotating the crankshaft about an axis through the centre of a notional crankpin of intermediate throw, a computer-controlled grinding wheel, movable relative to the axis of the notional crankpin in a direction transverse to such axis, whereby on rotation of the crankshaft, whose crankpin to be ground has a greater or lesser throw than said intermediate throw, such crankpin to be ground appears eccentrically to the grinding wheel.

In one embodiment of the present invention, the fixtures clamping the crankshaft to the rotation mechanism are releasably secured so as to allow the machine to be set up for use with a different family of crankshafts.

In another embodiment of the present invention, a plurality of grinding wheels can be provided whereby identically angularly disposed crankpins with equal throws can be simultaneously ground.

Preferably, the computer-control unit is readily re-programmable, to facilitate the grinding of crankpins of differing characteristics, e.g.

circumference.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fi. is a cross-sectional view in the direction of the axis of rotation of a crankshaft, belonging to a family of crankshafts, secured in the work station of the present invention with a crankpin in contact with a grinding wheel; Fig.2(a) is a cross-sectional view in the direction of the axis of rotation of a crankshaft within the same family of crankshafts as the crankshaft of Fig.l but with a greater crankpin throw; and Fig.2(b) is a similar cross-sectional view of the crankshaft of Fig.2(a) having rotated through 1800.

In Fig.l the ends of a crankshaft, belonging to a family of crankshafts, are clamped in identically opposite fixtures on two rotating members, of which only one (18) is illustrated, the crankshaft, including crank web 12 and main bearing journal 14 is then rotated in an orbit about an axis through the centre of crank pin 16 and through the centre of the rotating member 18 on the intersection of A-A' and B-B'. The grinding wheel of a computer-controlled grinding station is positioned in grinding contact with the crankpin 16 and grinds the crankpin 16 as it is rotated about its axis by the rotating mechanism.

The position of a crankpin 20 relative to the crankpin 16 is illustrated and is part of another crankshaft belonging to the family of crankshafts wherein the only varying dimension between the members of the crankshaft family is the throw of the crankpins.

In Fig.2(a) the crankshaft, including the crankpin 20, a crank web 22 and a main bearing journal 24 is secured in the same position in the grinding station as the crankshaft of Fig.l. The whole crankshaft of Fig.2 is rotated about the same axis passing through the centre of rotation of the rotating member 18 on the intersection of A-A' and B-B' as the crankshaft in Fig.l. Thus the crankpin 16 in Fig .1 can be considered to be a notional crankpin of intermediate throw on the crankshaft of Fig.2(a). However, due to the greater throw of the actual crankpin 20 the axis of rotation-of the crankshaft is not through the centre of crankpin 20, the intersection of B-B' and C-C', and therefore on rotation of the crankshaft the crankpin 20 rotates eccentrically about the axis through the centre of the rotating member 18, the intersection of A-A' and B-B'.

In Fig.2(b) the crankshaft of Fig.2(a) has rotated through 1800 and due to the eccentric rotation of crankpin 20 the point of contact between the grinding wheel 10 and the crankpin 20 has moved a lateral distance 26. On rotating a further 1800 said point of contact moves the same lateral distance but back, to the previous position of Fig.2(a). A method of computer-control is employed to facilitate the lateral movement of the grinding wheel 10 so that at all times during the grinding process the grinding surface of the grinding wheel 10 moves in sympathy to the surface of the crankpin 20 and maintains the required grinding contact with respect to factors such as the contact pressure and the speed of the grinding wheel 10 relative to the point of contact on the surface of the crankpin 20.

Similarly a crankpin on a crankshaft within the family but with a shorter throw than that of the notional crankpin, i.e., the crankpin 16 of Fig.l, could be ground. In both cases the lateral movement 26 required of the grinding wheel 10 is twice the difference between the throw of the crankpin 16 rotating about its own axis, the intersection of lines A-A' and B-B', and the throw of the crankpin rotating eccentrically. Since this distance 26 is relatively short, accurate computer-control of the grinding wheel can readily be achieved.

In the embodiment of the present invention illustrated hereinbefore, any one of the family of crankshafts can be readily secured in the fixtures of the rotating member, the position of the fixture on the rotating member being independant of the throw of the crankpin requiring grinding and so the need to re-align the fixtures for each of the crankshafts of the family is eliminated.

Claims

1. A method for grinding a crankpin of a crankshaft of a family of crankshafts, comprising rotating the crankshaft about an axis through the centre of a notional crankpin of intermediate throw and utilizing a grinding wheel to grind the said crankpin whose throw is greater or lesser than that of the notional crankpin, the grinding wheel being controlled such that the distance between the axis of the notional crankpin and the axis of the grinding wheel varies to compensate for such difference in the throws.

2. Apparatus for grinding crankpins on a crankshaft of a family of crankshafts comprising a mechanism for rotating the crankshaft about an axis through the centre of a notional crankpin of intermediate throw, a computer-controlled grinding wheel which is movable relative to the axis of the notional crankpin in a direction transverse to such axis whereby, on a rotation of the crankshaft, whose crankpin to be ground has a greater or lesser throw than said intermediate throw, such crankpin to be ground appears eccentrically to the grinding wheel.

3. Apparatus as claimed in claim 2, wherein fixtures for clamping the crankshaft to the rotation mechanism are releasably secured so as to allow the machine to be set up for use with a different family of crankshafts.

4. Apparatus as claimed in claim 2 or 3, wherein a plurality of grinding wheels is provided whereby identically angularly disposed crankpins with equal throws can be ground simultaneously.

5. Apparatus as claimed in claim 2, 3 or 4, including a computer-control unit for the grinding wheel which is adapted to be readily re-programmable, to facilitate the grinding of crankpins of differing dimensions, e.g. circumference.

6. A method for grinding a crankpin of a crankshaft of a family of crankshafts, substantially as hereinbefore described with reference to the accompanying drawings.

7. Apparatus for grinding crankpins on a crankshaft of a family of crankshafts, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.