GB1567597A

GB1567597A - Composite crankshaft and method for its assembly

Info

Publication number: GB1567597A
Application number: GB4841677A
Authority: GB
Original assignee: TOVARNA MOTORNIH VOZIL TOMOS KOPER N SOL O
Current assignee: TOVARNA MOTORNIH VOZIL TOMOS KOPER N SOL O
Priority date: 1977-11-21
Filing date: 1977-11-21
Publication date: 1980-05-21

Description

(54) A COMPOSITE CRANKSHAFT AND METHOD FOR ITS ASSEMBLY (71) We, TOVARNA MOTORNIH VOZIL ToMos KOPER, n.sol.o. a company established and existing under the laws of Yugoslavia, of Smarska c. 4, 66000 Koper, Yugoslavia, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a composite crankshaft and method for its assembly, and concerns a composite crankshaft for a two or more cylinder internal combustion engine having a housing for the crankshaft in which are separate individual precompression chambers for each cylinder.

Composite crankshafts for multiplecylinder two-stroke engines are known. As a rule, such composite crankshafts employ a first crankshaft portion of a single cylinder of the engine, which is connected to a second crankshaft portion of a second cylinder of the engine. The first crank of the second crankshaft portion is press fitted on the main journal of the first crankshaft portion. A journal for the connecting rod is press fitted in an eccentric borehole in the first crank. A second crank is arranged on the journal, which second crank has a main journal for the second crankshaft portion. In such a composite crankshaft there is at least one crank weakened by a central borehole for housing the press fitted main journal and by an eccentric borehole for housing the press fitted journal for the connecting rod. The double press fitting operation and the weakened wall between the central and eccentric boreholes gives rise in this crank to stresses causing- deformation of the crank itself and also causing deformation of the composite crankshaft. Additional deformation can also arise during heavy loads on the crankshaft during the operation of the engine.

Composite crankshafts are known also having cranks with central and eccentric boreholes in which double stresses in the weakened part between two bore holes are suppressed by means of a crank part extending into the main journal and provided with a central borehole, in which crank part is press fitted a thinner part of the main journal of the next crank. The protection against distortion of the press fitted part is achieved by means of a ribbed extension of the press fitted part of the main journal, which extension extends into a grooved part of the borehole in the crankshaft. With such a composite crankshaft there arise in the weakened part of the crank between the boreholes for the main journal and the boreholes for the connecting rod only stresses which are caused by press fitting the journal for the connecting rod. The reduction of influences which can cause deformation is, however, achieved by an expensive construction which does not always suppress the stress between the boreholes.

In a further known composite crankshaft, the problem of double boreholes in the crank is solved in such manner that the journal for the connecting rod or the main journal is made in one piece with the crank so that in each crank there is only one borehole in which the main journal or the journal for the connecting rod is press fitted. The manufacture of the crank provided with the journal for the connecting rod is, however, more expensive and more difficult than the manufacture of the crank provided with two boreholes. The assembly of such a composite crankshaft also becomes much more expensive by this construction.

There is thus a need for a composite crankshaft for a two or more cylinder internal combustion engine which reduces the stresses causing deformation of the crankshaft and which is cheaper.

According to the present invention there is provided a composite crankshaft for a two or more cylinder internal combustion engine having a housing for the crankshaft in which are separate individual precompression chambers, one for each cylinder wherein the composite crankshaft includes at least two crankshaft portions each associated with one cylinder of the engine, a first of which portions has a projecting main journal having a reduced diameter part and a second of which portions has a projecting main journal having a longitudinal bore therein in which the reduced diameter part is a press fit which is reinforced by a sealing ring which is heated and mounted for shrink fitting on the main journal of the second crankshaft portion when the reduced diameter part is press fitted in the longitudinal bore, the shrink fitted sealing ring being provided with labyrinth sealing means on its outer circumference for simultaneously separating the precompression chamber in the housing for the second crankshaft portion.

In this way the assembly of the crankshaft is simplified and two adjacent precompression chambers are sealed thereby reducing the assembly and sealing costs.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example to the accompanying single figure drawing, which shows in part longitudinal section, a composite crankshaft according to one embodiment of the invention. Crankshaft portions 1 and 2 each associated with a cylinder of a two or more cylinder internal combustion engine are mounted in a bearing bore 3 in a housing 13 of the engine. The portions 1 and 2 are fitted together by press fitting a reduced diameter part 4 of a main journal 5 projecting from the crankshaft portion 1 into a longitudinal bore 6 of a main journal 7 projecting from the crankshaft portion 2 so as to form a composite crankshaft for a two or more cylinder engine; in the case illustrated, for a two cylinder engine.

The longitudinal bore 6 in the axis of the main journal 7 communicates via a vent bore 8 with a precompression chamber 9 in the housing. The press fit between the reduced diameter part 4 of the main journal 5 and the longitudinal bore 6 is reinforced by means of a sealing ring 10 which is heated and shrink fitted on a part of the main journal 7 provided with the bore 6. On its outer circumference the shrink fitted sealing ring 10 has labyrinth sealing means in the form of two or more annular grooves 11 in which are inserted elastic sealing rings 12 radially cut through at one point and with their outer surfaces pressed against the bearing bore 13 of the crankshaft housing 3. The shrink fitted sealing ring 10 and elastic sealing rings 12 provide a separation and seal of the precompression chamber 9 of one cylinder from the compression chamber 14 of the other cylinder. The composite crankshaft according to the invention is assembled from a plurality of single cylinder crankshaft portions in such a way that the main journal 5 of the first crankshaft portion 1 is provided with the reduced diameter part 4 extending from the journal 5, while the main journal 7 of the second crankshaft portion 2 is provided with the longitudinal bore 6 made in the axis of the main journal 7, which part 4 is press fitted in the bore 6. When the crankshaft portions 1 and 2 are fitted together the bearing is mounted on the main journal 7 and the sealing ring 10 is shrink fitted on the main journal 7, with the elastic sealing rings 12 inserted in the annular grooves 11.

To this end the sealing ring 10 is heated to approximately 400"C prior to shrink fitting on the main journal 7. Immediately after sealing ring 10 has been shrink fitted, the reduced diameter part 4 of the main journal 5, previously provided with a bearing, is press fitted into the longitudinal bore 6. During press fitting of the part 4 in the bore 6, air escapes from the bore 6 through the vent bore 8.

During the insertion of the crankshaft portions into the bearing bore 3 of the housing 13, the elastic sealing rings 12 adapt themselves to the bore 3.

The radial cuts of the rings 12 are staggered relative to one another before the composite crankshaft is fitted into the housing 13 so as to assure labyrinth sealing between the precompression chambers 9 and 14 of the individual cylinders inspite of gaps between the rings 12 and the grooves 11 and inspite of the radial cuts in the elastic rings 12.

Although the invention has been described in terms of a two cylinder engine it is of course to be understood as being applicable to crankshafts for engines having more than two cylinders, for example three cylinders.

WHAT WE CLAIM IS: - 1. A composite crankshaft for a two or more cylinder internal combustion engine having a housing for the crankshaft in which are separate individual precompression chamber, one for each cylinder, wherein the composite crankshaft includes at least two crankshaft portions each associated with one cylinder of the engine, a first of which portions has a projecting main journal having a reduced diameter part and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the stresses causing deformation of the crankshaft and which is cheaper. According to the present invention there is provided a composite crankshaft for a two or more cylinder internal combustion engine having a housing for the crankshaft in which are separate individual precompression chambers, one for each cylinder wherein the composite crankshaft includes at least two crankshaft portions each associated with one cylinder of the engine, a first of which portions has a projecting main journal having a reduced diameter part and a second of which portions has a projecting main journal having a longitudinal bore therein in which the reduced diameter part is a press fit which is reinforced by a sealing ring which is heated and mounted for shrink fitting on the main journal of the second crankshaft portion when the reduced diameter part is press fitted in the longitudinal bore, the shrink fitted sealing ring being provided with labyrinth sealing means on its outer circumference for simultaneously separating the precompression chamber in the housing for the second crankshaft portion. In this way the assembly of the crankshaft is simplified and two adjacent precompression chambers are sealed thereby reducing the assembly and sealing costs. For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example to the accompanying single figure drawing, which shows in part longitudinal section, a composite crankshaft according to one embodiment of the invention. Crankshaft portions 1 and 2 each associated with a cylinder of a two or more cylinder internal combustion engine are mounted in a bearing bore 3 in a housing 13 of the engine. The portions 1 and 2 are fitted together by press fitting a reduced diameter part 4 of a main journal 5 projecting from the crankshaft portion 1 into a longitudinal bore 6 of a main journal 7 projecting from the crankshaft portion 2 so as to form a composite crankshaft for a two or more cylinder engine; in the case illustrated, for a two cylinder engine. The longitudinal bore 6 in the axis of the main journal 7 communicates via a vent bore 8 with a precompression chamber 9 in the housing. The press fit between the reduced diameter part 4 of the main journal 5 and the longitudinal bore 6 is reinforced by means of a sealing ring 10 which is heated and shrink fitted on a part of the main journal 7 provided with the bore 6. On its outer circumference the shrink fitted sealing ring 10 has labyrinth sealing means in the form of two or more annular grooves 11 in which are inserted elastic sealing rings 12 radially cut through at one point and with their outer surfaces pressed against the bearing bore 13 of the crankshaft housing 3. The shrink fitted sealing ring 10 and elastic sealing rings 12 provide a separation and seal of the precompression chamber 9 of one cylinder from the compression chamber 14 of the other cylinder. The composite crankshaft according to the invention is assembled from a plurality of single cylinder crankshaft portions in such a way that the main journal 5 of the first crankshaft portion 1 is provided with the reduced diameter part 4 extending from the journal 5, while the main journal 7 of the second crankshaft portion 2 is provided with the longitudinal bore 6 made in the axis of the main journal 7, which part 4 is press fitted in the bore 6. When the crankshaft portions 1 and 2 are fitted together the bearing is mounted on the main journal 7 and the sealing ring 10 is shrink fitted on the main journal 7, with the elastic sealing rings 12 inserted in the annular grooves 11. To this end the sealing ring 10 is heated to approximately 400"C prior to shrink fitting on the main journal 7. Immediately after sealing ring 10 has been shrink fitted, the reduced diameter part 4 of the main journal 5, previously provided with a bearing, is press fitted into the longitudinal bore 6. During press fitting of the part 4 in the bore 6, air escapes from the bore 6 through the vent bore 8. During the insertion of the crankshaft portions into the bearing bore 3 of the housing 13, the elastic sealing rings 12 adapt themselves to the bore 3. The radial cuts of the rings 12 are staggered relative to one another before the composite crankshaft is fitted into the housing 13 so as to assure labyrinth sealing between the precompression chambers 9 and 14 of the individual cylinders inspite of gaps between the rings 12 and the grooves 11 and inspite of the radial cuts in the elastic rings 12. Although the invention has been described in terms of a two cylinder engine it is of course to be understood as being applicable to crankshafts for engines having more than two cylinders, for example three cylinders. WHAT WE CLAIM IS: -

1. A composite crankshaft for a two or more cylinder internal combustion engine having a housing for the crankshaft in which are separate individual precompression chamber, one for each cylinder, wherein the composite crankshaft includes at least two crankshaft portions each associated with one cylinder of the engine, a first of which portions has a projecting main journal having a reduced diameter part and

a second of which portions has a projecting main journal having a longitudinal bore therein in which the reduced diameter part is a press fit which is reinforced by a sealing ring which is heated and mounted for shrink fitting on the main journal of the second crankshaft portion when the reduced diameter part is press fitted in the longitudinal bore, the shrink fitted sealing ring being provided with labyrinth sealing means on its outer circumference for simultaneously separating the precompression chamber in the housing for the first crankshaft portion from the precompression chamber in the housing for the second crankshaft portion.

2. A composite crankshaft according to claim 1, wherein the longitudinal bore is provided axially in the main journal of the second crankshaft portion and wherein a vent bore is provided in the main journal of the second crankshaft portion for communication at one end with the precompression chamber of the second crankshaft portion, which vent bore is in communication at its other end with the longitudinal bore.

3. A composite crankshaft according to claim 1 or claim 2, wherein the shrink fitted sealing ring has two or more annular grooves in its outer circumference in which are inserted elastic sealing rings which are radially cut through at one point and which are dimensioned such that their outer surfaces press against a bearing bore in the housing for the composite crankshaft, when the latter is present in the housing, to provide the labyrinth sealing means.

4. A method of assembling a composite crankshaft according to claim 3, including the steps of heating the sealing ring to approximately 400"C, mounting the heated sealing ring on the main journal of the second crankshaft portion, having inserted the elastic sealing rings in the annular grooves in the sealing ring, press fitting the reduced diameter part of the first crankshaft portion into the longitudinal bore of the second crankshaft portion, with air being allowed to escape from the longitudinal bore via the vent bore, and allowing the heated sealing ring to cool and shrink.

5. A composite crankshaft substantially as hereinbefore described with reference to the accompanying single figure drawing.

6. A method of assembling a composite crankshaft according to claim 4, substantially as hereinbefore described with reference to the accompanying single figure drawing.