WO1981003636A1

WO1981003636A1 - A method and an apparatus for joining crank shafts

Info

Publication number: WO1981003636A1
Application number: PCT/SE1981/000176
Authority: WO
Inventors: C Holmberg
Original assignee: Saab Scania Ab; C Holmberg
Priority date: 1980-06-13
Filing date: 1981-06-12
Publication date: 1981-12-24
Also published as: SE424151B; EP0053141A1; IT1144499B; SE8004409L; IT8148670A0; AU7224581A

Abstract

Method and apparatus for joining within accurate geometrical tolerances two crank shaft halves (D, M) via a crank pin (6) into a complete crank shaft (1). Each crank shaft half has a shaft (2, 3) which over a flange (12) continues into a crank disk (4, 5) in at least one of which there is at an accurate distance from the shaft made a through bore (7 and 8, respectively) for the crank pin. The crank pin may be separate or integral with one crank shaft half. The crank shaft halves are joined in that the crank pin is pressed into said bore(s) by the application of a press force (P) to the outer sides of the crank disks. During the pressing-in of the crank pin (6) into the bores (7, 8) of the crank disks the shafts (2, 3) of the crank shaft halves are carefully aligned in dependence of the accurate tolerances and are retained relative each other within said tolerances, while the crank pin in turn is allowed to be lined up by the bores of the crank disks, taking advantage of the possibilities of inclination of the crank pin relative to the crank disks and within the deformation zone of said press fit joint.

Description

A method and an apparatus for joining crank shafts

Technical field

The present invention relates to a method and an apparatus for joining, within accurate geometrical tolerances two crank shaft halves via a crank pin into a complete crank shaft, said crank pin being separate or part of one crank shaft half, each of which crank shaft halves comprises a shaft which by an intermediate flange continues into a crank disk, at least one of which having, at an accurate distance from the crank shaft, a through bore for receiving the crank pin. The crank shaft is completed in a pressing operation by a press fit joint between the crank pin and the respective crank disk bore.

Background art

In prior art methods and apparatus of the above mentioned kind it has appeared that the tolerances which in the manufacturing unavoidably must exist for the crank shaft halves, particularly for the centre distance of the crank pin bore to the shaft centre of the crank shaft half as well as the angle deviation of the crank pin bore from parallellism to the shaft of the crank shaft half, during the pressing-in procedure of the crank pin result in that the shafts of the complete crank shaft do not become parallel and do not either meet the tolerances of shaft - concentricity. Therefore, after the joining procedure a straightening operation has to be performed which is undesirable since i causes deformations which give rise to lasting stresses in the components of the press fit joint, said stresses then being superposed on to the normal stresses which appear during the rotation αf the crank shaft-in an internal combustion engine. Such, undesirable stress superpositions can cause breakage of the crank shaft, resulting in a shorter life duration than it should have normally.

Disclosure of the invention

The object of the present invention is to remedy said drawbacks by providing a method and an apparatus of the kind mentioned by way of introduction for joining crank shaft halves, said Imethod and apparatus producing a complete crank shaft the shafts of which, in the joining procedure, become parallel and concentic within stipulated tolerances. In this way the expensive and from a technical point of view undesirable straightening operation is dispensed with and the crank shaft retains its full strength.

This object is achieved by a method wherein the crank disks are placed in opposing relation, the crank pin being aligned with the bore(s) of the crank disk(s), and the shafts of the crank shaft halves are accurately aligned and retained within accurate tolerances during the pressing-in of the crank pin into said bore(s), while permitting the crank pin to be lined up by said bore(s) and thereby permitting inclination of the crank pin from perpendicularity to the crank disk(s) within the possibilities of the deformation zone of the press fit joint.

The apparatus for performing the method of the invention for joining said two shaft halves includes a press tool having two sections which are movable to and from each other in a pressing direction, means for positioning the crank disks in opposition and the crank pin aligned with the bore(s) of the crank disks there between, a shaft fixing stop in each of said sections for aligning said shafts in the pressing direction and a movable jaw cooperating in with the respective stop in a transversal plane to the shaft for retaining the shaft within the stipulated tolerances, said stops and jaws having in at least one of the press tool sections small axial extension lengths for permitting tilting of the shaft retained, pull means for seizing the shaft ends and holding the crank disks against supporting means, at least that press tool section which permits tilting having universally pivotable crank disk supporting means, as well as measuring means for acting on said tiltably retained shaft for measuring in two perpendicular planes, one of which includes the axes of the shafts and the crank pin, the angular deviations of the shaft in relation to predetermined master angular values, and tilting means acting on the shaft in said planes for tilting the shaft. Brief decription of the drawings

A preferred embodiment of the apparatus of the invention and its operation for joining two crank shaft halves via a separate crank pin will be described below in detail with reference to the enclosed drawings.

Fig. 1 illustrates in a perspective view the components of the press fit joint of the crank shaft, said components being shown after a first short portion of the pressing-in procedure, as well as the geometry of the crank shaft and the forces which during the joining procedure act upon the crank shaft halves.

Fig. 2 in a view of the complete joined crank shaft shows the accurate geometrical tolerances which by way of example are to be met by the crank shaft.

Fig. 3 shows at a larger scale a section through the press fit joint of the joined crank shaft and illustrates as a principle the inclination of the crank pin within the deformation zone.

Figs. 4 and 5 in partly sectional side elevational views, illustrate a joining apparatus according to the invention far the crank shaft halves and the crank pin of the crank shaft, said press fit joint being shown in different stages of the joining procedure.

Fig.6 is a sectional view taken along a line VI-VI in fig. 5 and shows as a principle sensors for measuring the actual angular positions of the shafts of the crank shaft halves in the joining apparatus.

Fig. 7, in a side elevational view of said joining apparatus, shows sensors for the determination, and adjustable stop means for limiting the length of the pressing-together movement of the press fit joint.

Fig. 8 is a sectional view taken along a line VIII-VIII in fig. 7 and shows in more detail the sensors and the stop.s shown in fig. 7. Fig. 9 is a side elevational view taken along a line IX-IX in fig. 8 and further illustrates the relation of a sensor to the flange of a crank shaft half.

Fig. 10 shows a side elevational view of said joining apparatus when the joining procedure is at an end.

Fig. 11 illustrates a master shaft manufactured within extremely accurate tolerances and by means of which master shaft the joining apparatus of the invention is calibrated.

Fig. 12 shows a complete crank shaft with a mounted connecting rod. This figure in greater detail explains those dimensions which are measured by the sensors shown in fig.s 7, 8 and 9.

Mode for carrying out the invention and industrial applicability

In a preferred embodiment of the invention described in detail below it is presupposed that the crank pin is initially separate from both crank shaft halves to be joined. Thus, the crank pin is press fitted to both said crank shaft halves.

In some cases it is preferred to have the crank pin initially integral with one crank shaft half. As mentioned at the end of description the invention also covers such cases.

First a typical crank shaft is described, said crank shaft parts being press fit joined.

In the drawings Fig. 2 shows a completely joined crank shaft 1 with accurate geometrical tolerances which by way of example are stipulated for the same. The complete crank shaft is joined from two crank shaft halves D and M which both include a shaft 2 and 3, respectively, and a crank disk 4 and 5, respectively, integrally manufactured therewith The complete crank shaft is obtained by means of a press fit formed between a crank pin 6 and crank pin bores 7 and 8 made in the respective crank, disks. In joining the press fit also a bearing 9, shown as a needle bearing, and a connecting rod 10 are mounted on the crank pin between the crank shaft halves, such that a unit 11 of motion transformance is provided, including the complete crank shaft with the connecting rod. Shafts 2 and 3 of the complete, joined crank shaft have four bearing portions A, B, C, and F which shall, be mutually concentric within a permissible interval of 0,025 mm, as is shown in Fig. 2. At the continuation of the shaft into the respective crank disk there is formed each a flange 12. For the joined crank shaft a dimension L encompassing these flanges shall be within a tolerance of ± 0,1 mm. Shafts 2 and 3 of the crank shafts terminate in threaded portions 13 and 14, respectively.

Fig. 3 shows a principal view of crank pin 6 press fitted into the two crank disks 4 and 5 of the joined crank shaft. As a result of manufacturing tolerances the two crank disk pin bores 7, 8 are mutually displaced in lateral respect, and the lower bore 8 in the figure also inclines relative to a normal N to crank disks 4 and 5. In the manufacturing, the tolerance of the location of the bore is based on the dimension E between the centre of bores 7, 8 and the centre axis of shafts 2 and 3, respectively, and is ± 0,01 mm.

A hatched, in reallity annular region 15 in both crank disks designates a deformation zone of the press fit joint, i.e. that portion closest to the bore wall of the crank disk which is geometrically determined by the pin and bore tolerances of the actual press fit joint and which is radially compressed when the crank pin is pressed into the crank disks. As shown in Fig. 3 the crank pin 6 (axis N¹) held within the deformation zone in the crank disk is inclined in relation to the normal N of said disks 4 and 5. This is most clearly seen by the fact the distal faces of the pin are not parallel to outer sides 16 and 17 of the crank disks. Due to the accurate manufacturing tolerances for the location of the pin bores in the crank disks, this inclination of the pin, which for sake of clarity is exaggerated in the figure, in reallity is of such a small magnitude that it does not detrimentally influence the operation of the bearing of the connecting rod. However, the possible inclination of the crank pin within the deformation zone is fully sufficient in order to facilitate, at the pressing of the pin into the two crank shaft halves D and M, a mutual alignment thereof with their shafts 2 and 3 in positions within the accurate tolerances which are shown in Fig. 2 and to be ratained thereafter in this carefully adjusted position during the pressing-in operation.

Fig. 1 in more details and principally illustrates the method of the invention for said alignment and retainment of the crank shaft halves during the joining operation. In the figure the crank shaft halves are provided with the crank pin therebetween and concentrically lined up with the crank pin bores. Bearing 9 and connecting rod 10 are passed on to the crank pin. According to the invention shafts 2, 3 of the two crank shaft halves, during the continued pressing of the crank pin into the crank disks, are retained in positions with their centre axis coinciding with an intersectional line between two mutually perpendicular planes X and Y. This is obtained in that shafts 2, 3 close by the flanges 12 are concentrically lined up with their bearing portions A and B placed in shaft fixing stops 18 and 19, respectively, being accurately adjusted relative each other in transversal planes to the shafts, said stops having a short extension length along the respective shaft for permitting tilting of the respective shaft. The shafts are retained in the stops by means of a force P_H acting on the respective shaft against the stop. Moreover, shafts 2, 3 are tilted in the shaft fixing stops 18, 18 over angles α and β in the planes X and Y, respectively, into tolerance true angular positions, through the application of forces P_x and P_y, respectively, acting in said planes at the shaft ends, and then are fixed in these positions.

The crank shaft halves D, M thus aligned and retained are then brought together carefully parallelly controlled relative each other in axial direction, maintaining the correct space alignments, and by means of a press force P applied on the crank disks at the crank pin, in order to complete the press fit joint between the crank pin and the crank disks. The bringing together of the crank disks progresses until the dimension L including the stipulated tolerances is obtained over the flanges 12.

A preferred embodiment of the joining apparatus is discribed below with reference to Fig.s 4 - 10. In the depicted apparatus the two imagined planes X and Y (see Fig. 11) are orientated with the Y-plane in the plane of the drawings and the X-plane in the normal thereto. As shown in Fig.s 4 and 5 the apparatus is built on a two-sectioned pillar stand press tool 20 which can be placed in a press and which comprises two press tool sections, an upper section 21 and a lower section 22. The two tool sections are movable to and from each other by means of the press and are during movement carefully and parallelly controlled relative each other by two guide columns 23, 24.

The aligning and fixing means of the joining apparatus for controlling the crank shaft halves and the crank pin are next to be described. In order to line up and fix the two crank shaft halves D, M and the crank pin 6 with bearing 9 and connecting rod 10 passed thereori the upper and lower sections have the following structure. The two press tool sections have two main members, one base plate 25 and 26, respectively, and an aligning member 27 and 28, respectively, for each crank shaft half. Two adjacent bores in the Y-plane, one guide pin bore 29 and one shaft bore 30, are made in the direction of motion of the press through the base plate and the aligning member of the two press tool sections. The guide pin bores 29 are accurately concentric and have in the aligning member such a diameter to guide as carefully and displaceably therein a guide pin 31 accurately fitting into the crank pin bores of the crank disks. The shaft bores 30 extend all through the tool sections in opposed positions and have such a diameter that there is ample clearance to shafts 2, 3 of the crank shaft halves which are insertable into said bores. A spherical recess 32 is made in the aligning members concentric with the guide pin bores 29, said recess having its centre of curvature on an imagined extension of the axis of the guide pin bores outside the aligning members. In this recess there is a complementary spherical segment plate 33 which has a centre hole 34 allowing ample clearance for the guide pin 31 to be displaced through the plate. The spherical face 35 of the plate resting in recess 32 is accurately fitted to the recess, the other face 36 of the plate is plane and constitutes a stop face for the outer sides 16, 17 of the crank disks. The face of the plate facing shafts 2, 3 has a groove to allow clearance between the plates and the flanges 12 of the shafts 2, 3 of the cranks shaft halves.

The shaft fixing stops 18, 19 are formed in the aligning members at a level with spherical segment plates 33 and are shaped as blocks grasping the shafts 2, 3 at portions A and B, respectively. As already mentioned the shaft fixing stops have a small axial extension length and have their respective stop face against the shaft accurately adjusted in relation to each other in transversal planes, such that the shafts of the crank shaft halves at the stops have their axes located in the intersectional line of the X- and Y-planes. Directly opposite each shaft fixing stop there is provided a jack operated jaw 37 movable to and from the shaft and having a dog portion 38 facing the shaft, said dog portion having the same small axial extension as the shaft fixing stops. The jack is excluded from the drawings and only its direction of action is illustrated by means of a force arrow P_H. At the end of each shaft 2, 3 there is a pull means 39A for holding crank disks 4, 5 of the crank shaft halves in contact to the plane face 36 of spherical segment plate 33. To this end said pull means has a pull bushing 39 threadable on to the threaded ends 13, 14 of shafts 2, 3, and a jack (not shown) connected to the pull bushing. In a similar way as mentioned above this jack is represented in the figure by force arrows P_D and P_M, respectively.

Guide pin 31 has such a length that it, maintaining guidance in the guide pin bore 29, can be pushed into crank disk 4, 5 in order to be guided into the same into its correct position for the pressing-in of the crank pin into crank pin bore 7, 8. The insertion of the guide pin into the crank disk is achieved by means of a pressure spring 40 which is placed between the guide pin and the respective base plate 25, 26. The guide pin has a push rod 41 passing through the pressure spring and extending into the base plate through a bore 42 where there is a stop screw 43 limiting the motion of the guide pin in the direction from the crank disk. The movement of the guide pin in the base plate is limited by the stop screw such that the guide pin, when its push rod 41 is. pushed in to about the stop screw, stands some tenths millimeters beyond the plane face 36 of the spherical segment plate 33.

Before the start of the pressing-in procedure and during a first stage thereof the crank pin is held by a principally shown crank pin fixing means 44 in a predetermined position between crank disks 4, 5 of crank shaft halves D, M in which position the pin is practically concentric to the guide pins 31 and consequently to the crank pin bores 7, 8 of the crank disks. Crank pin fixing means is pivotable between this fixing position and a parking position to the side of the crank shaft parts placed in the press tool. Connecting rod 10 passed on the pin via its bearing 9 rests with its piston pin bearing end 45 on the bottom of a guide groove 46 which extending parallel to the Y-plane is formed in the lower aligning member 28. Means of the joining apparatus for measuring and position aligning of the shafts of the crank shaft halves relative to each other are next to be described. Due to the fact that each of the crank shaft halves is supported by a tiltable spherical segment plate 33, and their shafts 2, 3 in their transversal planes are fixed by shaft fixing stops 18, 19 having a small axial extension length, each crank shaft half can be tilted over limited angular arcs X , β , e.g. from an incorrect angle position α₁,β ₁, to a correct one.

Fig.s 5 and 6 in principal illustrate those means 47A and 55A in the two sections 21, 22 of the press tool, by means of which the angular positions α₁,β₁ of shafts 2, 3 of the crank shaft halves D, M are measured and from these angular positions are positioned in relation to each other by tilting the shafts over angles αand β into angular positions complying with the tolerances in the X- and Y-planes. As best shown in Fig. 6 measuring means 47A for the angular positions of the shafts comprises for each shaft two gauge arms 47, 48 which, orientated perpendicular to the X- and Y-plane, respectively, are pivotable in a transversal plane to the shafts in that they are journalled in base plate 25 and 26, respectively.

Said gauge arms have one respective end 49, 50 spring biased against the shaft end of shaft 2, 3 the other end 51, 52 of the gauge arms contacting a sensor 53 provided to measure the angular position of the shaft in relation to a master shaft 54 of correct dimension and shape, said master shaft having been placed previously in the joining apparatus in a calibrating procedure. The master shaft is shown in

Fig. 11 and is subsequently described. Tilting means 55A is only shown in Fig.5 as two movement transferring arms 55, 56 grasping the pull bushing 39, said arms 55, 56 being orientated in the X- and Y- planes and being connected to not shown jacks, the actions of which are shown in said planes by means of force arrows P_x and P_y. Both sensor 53 and jacks P_x and P_y are connected to a not shown process computer, which is provided to control the entire operation as subsequently described.

Means of the joining apparatus for determining a correct pressing-in length of the crank pin is next to be described. In Fig.s 7 - 10 means 58A, 63A in the press tool sections 21, 22 of the joining apparatus is principally illustrated, said means facilitating determination of the length of the pressing-in movement of crank pin 6 for obtaining the dimension L shown in Fig.s 2 and 10 for the joined crank shaft over its flanges 12. Said means comprises measuring means 58A which measures deviations in the actual flange width dimensions k_D, k_M, for each individual crank shaft, of which Fig. 12 illustrates an example 57, in relation to the flanges of the master shaft 54 having a correct shape and dimensions. Said measuring means 58A has a gauge arm 58 which is orientated in an X-plane and which is pivotable in this plane journalled at its center in the aligning member 27, 28. The gauge arm has one end 59 spring biased against the distal surface 60 of flanges 12, and has its other end 61 contacting a sensor 62 which is provided to measure the axial position of the distal surface 60 of the flange in relation to a reference position for the same surface calibrated by means o f the master shaft. The sensor is connected to calculating means in the above mentioned process computer.

The process computer controls a means 63A which in dependence of the widths of the measured flanges 12 limits the press movement by means of a mechanical stop means. Said means 63A includes two fixed stops

63 orientated in the pressing direction and mounted in the upper aligning member 27 and spaced in the X-direction. Said stops are provided above a stop 64 which is adjustable in the pressing direction. To this end stop 64 has two plane wedges 65, one opposite each fixed stop. Said wedges are inclined in the Y-plane relative to a plane transversal to the pressing direction. In order to facilitate adjustment in the pressing direction the adjustable stop 64 has a U-configuration in a plane perpendicular to said direction and includes two parallell legs 66, 67 which extend in the Y-direction and are provided with guides journalled in the lower aligning member. Stop

64 is displaceable in the Y-direction by means of a not shown jack, the action of which is shown by a double-headed arrow P_L on the drawing; Plane wedges 65 which are provided at the leg ends, are withdrawn from or advanced to the fixed stops 63 at said displacement in the Y-direction of the adjustable stop. For actuating the different, above described means of aligning, fixing, measuring, positioning and limiting of the pressing-in length of the joining apparatus, as well as an industrial manipulator or robot which may be provided to "charge" the crank shaft halves, the crank pin, the needle bearing and the connecting rod into the joining apparatus, and to remove from the same the completed crank shaft, said means are controlled from a not shown control console by means of any suitable and not shown automatics. Said automatics then also includes the above mentioned process computer which in a manner known per se handles measured dimensions and on the basis thereof delivers command signals to the jacks for the positioning and fixing of the crank shaft halves and controls the above mention different means in a correct sequence for the entire joining operation.

The mastershaft for the calibration of the joining apparatus is next to be described. The master shaft 54 shown in Fig. 11 have for those portions and those dimensions which correspond to the portions and dimensions designated in Fig. 2, the same references as in Fig. 2, only with the addition of an index m. The master shaft is manufactured in one piece, the two shafts 2_m, 3_m being made with particular accuracy as to shape and dimensions and being accurately concentric with each other well within the tolerance shown in a symbol 69. That master shaft portion which corresponds to the crank disks and the space therebetween is shaped as a solid centre portion 68. As to shape and dimensions said centre portion is accurately correct only as regards its face 16_m , 17_m facing the shafts 2_m, 3_m and the flanges

12_m as well as a bore 7_m/8_m through said portion and located at a distance E_m to the centre axis of the shafts. The master shaft serves as a reference which is correct as to shape and dimensions for calibrating the joining apparatus. The above described measuring means 47A, 58A of the joining apparatus are set to zero by means of the master shaft which is lined up an fixed in the joining apparatus. Deviations, if any, as to shape and dimensions from the reference fixed by the master shaft can then be measured at the actual crank shaft halves which are placed in the joining apparatus to be joined in press fit as subsequently described. An individual crank shaft is now to described. An example of a completely joined individual crank shaft is shown in Fig.12. The flanges 12 of the crank shaft halves D, M have different widths, which for sake of clarity is exaggerated in the figure. The respective actual flange widths are designated by the dimension k_D and k_M.

The operation of the joining apparatus in assembling a crank shaft according to the method of the invention is explained below with reference to the different stages of the joining operation. First the lining up an fixing of the crank shaft halves and the crank pin in the press tool is described. The two crank shaft halves D, M and crank pin 6 to be joined, connecting rod 10 and its bearing 9 are placed in press tool 20 by means of an industrial robot such that the initial position shown in Fig.4 for the joining operation is obtained. The crank shaft half D is inserted into the upper press tool section 21, the shaft 2 being inserted into the shaft bore 30 and the crank disk 4 with its crank pin bore 7 being passed on the guide pin 31. By means of pull means 39A, pull bushing 39 of which is screwed on to the threaded portion 13 of the crank shaft half, the crank disk is pulled by means of force P_D into contact to the plane face 36 of the spherical segment plate 32. In a similar way the other crank shaft half M is placed into the lower press tool section 22 and there is pulled into contact.

Connecting rod 10 with mounted bearing 9 is passed on crank pin 6 and is placed on the lower aligning member 28 with piston journal end 45 in guide groove 46 and the crank pin at the crank pin bores 7, 8. The two crank shaft halves are fixed with their shafts 2, 3 against the shaft fixing stops 18, 19 by means of the jaws 37 which with their respective dog portion 38 press against the respective shaft with a relatively small tightening force P_H. Then the crank pin is fixed in a correct position concentrically to and between the two crank pin bores 7, 8 by being seized and retained by crank pin fixing means 44.

The measuring and the aligning of the shafts of the crank shaft halves in relation to each other and the press tool is now to be described. First the press in a slow motion brings the press tool sections together until approximately 3 mms remain before the crank pin enters the crank pin bores. During this slow motion of th'e press tool the following measures are taken: By means of measuring means 47A shown in Fig.s 6 and 7 the actual angular positions of shafts 2, 3 of the crank shaft halves are measured in relation to the angular reference position calibrated by means of the master shaft. An angular deviation, if any, of shafts 2, 3 in the X-plane relative of the reference position is measured by gauge arm 47 and sensor 53 as an error angle α₁. An angular deviation of the shafts in the Y-plane from the reference position is measured by gauge arm 48 and the sensor 53 as an error angle β ₁. The two error angle values α₁, and β₁ are supplied by the sensors 53 to the process computer which in response to these values delivers command signals to the jacks P_x, P_y of tilting means 55A. By means of the motion transferring arms 55, 56 said jacks tilt in directions opposite to said measured deviations the shafts into a correct angular reference position both in the X-plane and the Y-plane.

The determination of a correct pressing-in length for the crank pin is now to be described. In the course of the above mentioned measuring also the deviations of the actual flange widths k_D and k_M of flanges 12 are measured relative to the flange widths k of the master shaft and by means of measuring means 58A, shown in Fig.s 7 - 9. The gauge arm 56 and the sensor 62 which have been put to zero by means of the master shaft, supply the two deviation valuesΔZ_D andΔZ_M, respectively, from the master flange width k for the respective crank shaft half D, M and deliver the deviation values on to the process computer. The computer first adds said deviation values to the two master flange widths k for obtaining the combined width of the actual flange widths k_D and k_M, and then subtracts this width from the master dimension L_m for obtaining a calculated dimension L₁ which later is to be obtained over the outer faces 16, 17 of the crank disks after a terminated pressing-in of crank pin 6 into the crank disks, in order for the complete crank shaft to obtain over its flanges 12 the dimension L which is correct as to tolerances. In dependence of this calculated dimension L₁ the process computer delivers a command signal to the jack P_L of movable stop 64 which jack moves the stop in the Y-direction up to that position at which the distance in the pressing direction between the fixed stop 63 and the movable stop 64, 65 limits the pressing-in motion to said mentioned actual dimension L for the complete crank shaft.

The continued joining operation is now described. After said measurements and the alignment of the shafts 2, 3, the crank pin is pressed by means of force P, about 3 mms into each crank disk, this position being shown in Fig. 5. Now a further measurement is made by means of measuring means 47A in order to check if the pressing-in of the crank pin has changed the angular positions of the shafts from the aligned angular reference position. The computer records the amount of change of the angular positions of the shafts.

The angular deviation now recorded is caused by the effect of the crank pin tilted in the crank pin bores on the crank disks upon the pressing-in of said pin therein. In αrder to compensate for this continued effect in the pressing-in of the crank pin up to a complete press fit joint is reached, the computer is provided to deliver to tilting means 55A pulsed command signals for tilting shafts 2, 3 in directions opposite to the angular deviation directions and over certain excess angles α_e, β_e beyond shaft parallellism. The mangitudes of these excess angles are calculated by the computer and are dependent of the remaining pressing-in length. Of course said excess angles can be set to zero if desired. Since said excess angles are gradually reduced in the continued pressing-in of the crank pin, the completely joined crank shaft will have its shafts at angular positions within stipulated tolerances.

After this the process computer commands a tightening of jaws 37 of the shaft fixing stops 18, 19 for obtaining a position fixing of the crank shaft halves, as well as a disengagement of the grip of the crank pin fixing means 44 about the crank pin and a withdrawal of said fixing means to its parking position. Then the final pressing-in of the crank pin into the crank disks of the position fixed crank shaft halves takes place by means of force P with a fast motion of the press. The compression pressure used in this connection is monitored by the computer which is also provided to sense immediately that increase of the compression pressure which occurs when the mechanical stops 63,65 of press motion limiting means 63A are engaged at a complete, joined press fit. The computer is also provided to reduce at this moment the compressing pressure to zero such that the press motion is immediately interrupted and the stipulated correct dimension L is obtained for the complete crank shaft. At the end of the press stroke guide pins 31 have reached bottom and their push rods 41 engage stop screws 43, as shown in Fig. 10. Crank pin 6 has a shorter length than the smallest actual dimension L₁ which can exist and the guide pins have, when they reach their bottom position, adjusted the position of the crank pin in axial direction such that this is well within the outer sides of the crank disks. In the remaining end stages of the joining operation jaws 37 are removed from shafts 2, 3 and the actual angular positions of the shafts obtained in the joining procedure as well as the actual dimension L over flaπges 12, are measured by measuring means 47A and 56A in relation to the references of the master shaft. It is convenient to have the computer record the result of said measuring. Then the completely joined motion transforming unit 11, now also checked as to dimensions is picked out from the joining apparatus by the industrial robot.

The method of joining and the joining apparatus according to the invention as described above have proved to considerably reduce the rejection of complete crank shafts.

In the method and apparatus described the crank shaft is joined from two similar crank shaft halves and a separate crank pin, requiring said particular means 44 for positioning and fixing the crank pin.

However, the invention is also applicable in cases where the crank pin is initially integral with one of said crank shaft halves, in which case fixing and positioning means 44 can be dispensed with.

The above described apparatus can still be used in this modified method for joining the crank shaft halves, one of which includes the crank pin, presupposing only that the crank disk of the crank shaft half including the crank pin has a guide bore made in its outer side concentrically to the crank pin for receiving the guide pin 31. For the rest the apparatus operates in the same way as described above. In performing the modified method said apparatus may have an additional measuring means for measuring in the X- and Y-planes the angular position of the free end of the crank pin in order to secure the correct initial aligning with the crank bore in the opposing crank disk. Measuring values obtained from said additional measuring means are supplied to the process computer and are considered in the tilting of the crank shaft halves.

It is recognized that in some cases one crank shaft half can be rigidly fixed in one press tool section with its shaft parallel to the pressing direction, only the other crank shaft half being tiltably supported in the other press tool section. In these cases said one press tool section supporting the rigidly fixed crank shaft half will require positioning means securing a correct position of the crank disk in a plane transversal to the pressing direction, and fixing means for rigidly retaining the crank shaft half in the pressing direction. No measuring means or tilting means will be requried in this one press tool section. Said other press tool section permitting tilting of the crank shaft half is provided with the above mentioned means for measuring and aligning of the crank shaft half.

The method and apparatus according to the invention include all modifications within the frame of all three cases as discussed only limited by the scope of the claims.

Claims

1. A method for joining within accurate geometrical tolerances two crank shaft halves (D, M) via a crank pin (6) into a complete crank shaft, said crank pin being separate or part of one crank shaft half, each of said crank shaft halves (D, M) including a shaft (2, 3) which by intermediary of a flange (12) continues into a crank disk (4, 5), at least one of said crank disks having at an accurate distance from the shaft (2, 3) a through bore (7, 8) for receiving the crank pin (6), wherein the crank shaft halves (D, M) and the crank pin (6) are joined into a complete crank shaft by pressing the crank pin into said bore(s) for obtaining a press fit joint therebetween, c h a r a c t e r i z e d in that the crank shaft halves (D, M) are placed with their crank disks (4, 5) in opposed relation and the crank pin (6) aligned with said bore(s) (7, 8) therebetween and that during the pressin - in of the crank pin (6) into the bore(s) (7, 8) of the crank disk(s) (4, 5) the shafts of the crank shaft halves (D, M) are accurately aligned and retained relative each other within the accurate tolerances, while the crank pin (6) is permitted to be lined up by said bore(s), thereby permitting, within the possi bilities of the deformation zone (15) of the press fit joint, inclination of the crank pin (6) from perpendicularity to the crank disk(s) (4, 5).

2. The method as claimed in claim 1, c h a r a c t e r i z e d by retaining each shaft (2, 3) of the crank shaft halves (D, M) against an individual stop (18, 19) for aligning the shafts concentrically, at least one of said stops (18, 19) permitting tilting of the respective shaft, measuring after a first portion of the pressing - in operation the angular positions ( α₁ , β ₁ ) of the tiltable shaft(s) (2, 3) of the crank shaft halves in rela tion to predetermined master angles for determining deviations, if any, relative to said master angles and in two perpendicular planes (X, Y), one of which includes the axes of said shafts and the crank pin, tilting in said two planes the tiltable shaft(s) (2, 3) until compliance with the accurate tolerances, and sub sequently pressing the crank pin (6) into the crank disk bore(s) for forming the complete press fit joint.

3. The method as claimed in claim 2, c h a r a c t e r i z e d in that after the measuring of the angular positions (α₁,β₁) of said shaft(s), said tilting of the shaft(s) in said two perpendicular planes (X, Y) takes place opposite to the deviation directions of said angles. (α ₁, β₁) measured in said planes and to parallel lism or to excess angles (α_e,β_e) beyond shaft parallellism, said excess angles automatically being reduced to within tolerances in the final pressing-in operation in that the crank pin (6), when passing through the deformation zone (15) of the crank pin bore(s), tilts back said shaft(s).

4. The method as claimed in any one of claims 1 to 3, c h a r a c t e rized in that each crank shaft half (D, M) is placed in each a sec tion (21 , 22) of a press tool, the two sections of which, for obtai ning said press fit joint, are brought together in a controlled parallel relation, that said stop(s) (18, 19) permitting tilting engages the shaft (2, 3) close by said flange (12) along a short length of the shaft to permit said tilting thereof, and said two stops (18, 19) having an accurate relative location in the press tool sections for aligning the shafts in the pressing direction, that each crank shaft half (D, M) is supported for receiving the press force (P) axially against the side (16, 17) of the crank disk facing away from the crank pin (6) and at least the crank disk of the tiltable crank shaft half being supported for universal tilting rela tive to the respective press tool section (21, 22), that at least the crank disk (45) of the tiltable crank shaft half is positioned in that its crank pin bore (7, 8) for receiving the crank pin is lined up by a guide pin (31) inserting into the crank pin bore (7, 8) and to be pushed out therefrom by the crank pin against a spring back pressure when the crank pin is pressed into the crank disk(s).

5. The method as claimed in any one of the preceding claims, c h a r a c terized in that for each crank shaft half (D, M) the actual differential dimensions (Δ Z_D and Δ Z_M respectively) between the outer side of the crank disk and a master position for said outer side is measured, that the actual differential dimensions and the two master flange widths ( k ) are added for obtaining the actual flange widths ( k_D, k_M), and the sum of the actual flange widths are subtracted from a flange encompassing master dimension (L_m ), thereby obtaining a calculated dimension (L₁) over the outer sides of the crank disks, and that pressing of the crank pin into the crank disks is performe up to said last mentioned dimension (L₁).

6. An apparatus far press fit joining within accurate geometrical toleran ces two crank shaft halves (D, M) via a crank pin (6) into a complete crank shaft, said crank pin being separate or part of one crank shaft half, each of said crank shaft halves including a shaft (2, 3) which by intermediary of a flange (12) continues into a crank disk (4, 5) in at least one of which there is at an accurate distance from the shaft (2, 3) made a through bore (7, 8) for receiving the crank pin, said apparatus including a press tool (20) having two spaced sections (21, 22) to be moved towards each other in a pressing direc tion and in the opposite direction, c h a r a c t e r i z e d by including means for positioning the crank disks (4, 5) in opposed relation and the crank pin (6) aligned with said bore(s). therebetween, in each of said sections (21, 22) a shaft fixing stop (18, 19) being accurately provided relative to each other for aligning the shafts of the crank shaft halves concentrically in the pressing direction, and a movable jaw (37) cooperating with the respective stop in a transversal plane to the shaft for retaining the shaft within the tolerances, said stops and jaws having in at least one of said sections (21 , 22) small axial extension lengths for permitting tilting of the shaft retained, and that the press tool section (21, 22) including a stop and jaw that permit tilting of the shaft, has universally pivotable crank disk supporting means (33) for supporting said crank disk, and measuring means (47A) acting on the shaft for measuring in two perpendicular planes (X, Y), one of which includes the axes of the shafts (2, 3) and the crank pin (6), the angular deviations of the shaft in relation to predetermined master angular values, and tilting means (55A) acting on the shafts in said planes (X, Y) for tilting the shafts relative to the shaft fixing stop (18, 19).

7. The apparatus as claimed in claim 6, c h a r a c t e r i z e d in that said supporting means is a spherical segment plate (33) having a plane face for contacting the outer side of the crank disk and an opposing spherical bearing surface (35) having its center of cur vature located at the axes of said bore(s) (7, 8), and that said segment plate (33) is at a level with said shaft fixing stop (18, 19).

8. The apparatus as claimed in claim 7, c h a r a c t e r i z e d in that at least the press tool section (21, 22) including a stop and a jaw that permit tilting of the shaft has pull means (39A) to seize the shaft end (13, 19) of the crank shaft half and hold the crank disk (4, 5) against said supporting means (33).

9. The apparatus as claimed in any one of claims 6 to 8, c h a r a c t e r i z e d in that each press tool section (21, 22) includes measuring means (55A) for measuring in axial direction the actual differential dimensions (ΔZ_D, ΔZ_M,) of the widths (k_D, k_M,) of the flanges in relation to predetermined master flange dimensions (k), that calculating means are connected to the press tool for adding said differential dimensions and the two master flange dimensions (k) for obtaining the actual flange widths (k_D, k_M,) as well as subtract the sum of the actual flange widths from a flange encompassing master dimension (L_m) for obtaining a calculated dimension (L₁), over the outer sides (16, 17) of the crank disks, that the press tool includes stop means (63A) having a fixing stop member (63) in one press tool section (21) and a movable stop member (64, 65) in the other press tool section for varying the final distance between said sections and limiting the pressing-in of the crank pin (6) into the crank disk bore(s) (7, 8), said movable stop member (65) being adjustable in the pressing direction relative to the fixed stop member (63) and in dependence of the magnitude of the dimension (L₁) over the outer sides of said crank disks calculated in said calculating means.

10. The apparatus as claimed in any one of claims 6 to 9, c h a r a c t e r i z e d in that said positioning means include concentrically to the axes of said bore(s) a longitudinally displaceable guide pin (38) biased from an end position against the crank disk and displaceable through a bore (34) in said support means (33) and fitting into the crank disk bore (7, 8) for lining up the bore of the crank disk into a position for receiving the crank pin (6).