Method for joining a component to a shaft

Abstract

Method for joining a component (2) having a recess (8), in particular a cam (4), on a shaft (3), in particular on a camshaft tube, by pressing the component (2) with its recess (8) onto the shaft (3), characterized in that - a minimum coverage (Ü) required in the operating state min ) between the component (2) and the shaft (3), - a manufacturing tolerance (ΔN K ) of the recess (8) of the component (2) and a manufacturing tolerance (ΔR W ) of the shaft (3) is determined, - an overlap value (Ü) from the sum of the tolerances (ΔR W ,ΔN K ) and the minimum coverage (Ü min ) is formed, - the component (2) is heated to such an extent, depending on the contact area value (Ü), that the grooves (9) created during the subsequent pressing of the component (2) onto the shaft (3) do not exceed a predefined depth and the minimum contact area (Ü min ) is ensured when the component (2) has cooled down.

Description

The present invention relates to a method for joining a component on a shaft according to the preamble of claim 1.DE 199 38 791 B4 discloses a generic method for joining a component, here a cam, to a shaft, here a camshaft. The component is pushed onto the shaft by means of a longitudinal press fit. Viewed in the feed direction of the component, the latter has on its front face a groove surrounding a recess, which groove is of wedge-shaped design and has a slope running in a straight line or in an arc shape in the direction of the inner wall of the recess. In order to be able to facilitate the pressing of the component onto the shaft, a lubricant is introduced into the groove, which lubricant is continuously drawn from the groove into the recess of the component during the pushing-on process.The present invention is concerned with the problem of specifying an improved embodiment for a joining method of the generic type, which on the one hand allows the use of an unprocessed shaft with greater tolerances and at the same time allows a higher torque transmission between the shaft and a component joined thereto than is possible with components joined usually via a longitudinal press fit.This problem is solved according to the invention by the independent claims. Advantageous embodiments are the subject of the dependent claims.The present invention is based on the general idea of pushing a component onto a shaft, for example a cam on a camshaft tube, by means of longitudinal pressing and simultaneously heating the component, whereby not only a higher torque transmission is possible when the component is cooled, but at the same time also the grooves which are produced when the component is pressed onto the shaft can be limited with respect to their depth on account of the expansion of the component during heating and the risk of a component being seized is also reduced. Above all, however, the use of an unprocessed shaft is also possible, as a result of which the production costs can be reduced. The method according to the invention is thus used for joining a component having a recess, for example the said cam, to a shaft, for example to the said camshaft tube, by pressing the component with its recess onto the shaft. In this case, a minimum overlap between the component and the shaft is first defined, which should be ensured reliably in any case when the component-shaft connection for torque transmission is completely joined. Likewise, a tolerance of the recess of the component and a tolerance of the shaft are determined, wherein a coverage value is formed from these values, which is calculated from the sum of the tolerances of the component and the shaft and the minimum coverage. The term "tolerances" is to be understood here primarily as manufacturing tolerances. Subsequently, in the method according to the invention, the component is heated so strongly as a function of the overlap value that the grooves formed during the subsequent pressing of the component onto the shaft do not exceed a predefined depth and at the same time the minimum overlap in the cooled component can be ensured. In this case, the proviso applies that grooves which are produced are removed to a great extent by a subsequent grinding operation, with the result that, for example, the surface can be used as a bearing surface, in particular that possible rappings of the grooves are removed. By heating the component before the pressing on, the overlap to be overcome during the pressing-on process is reduced, since the component expands during the heating and thereby increases an inner diameter of its recess. The increase in the inner diameter in turn leads to grooves of less depth, as a result of which the post-processing of the shaft, for example by grinding, can be simplified. In particular, the grooves can also be completely removed by grinding. It is clear that the component can be pressed onto the shaft only under the action of force even in the heated state, so that this joining process clearly differs from the pure thermal joining. Rather, the method according to the invention is a novel combination of longitudinal pressing and thermal joining, as a result of which the connection between the component and the shaft is strengthened and torque transmission is thus increased and at the same time the mechanical loads on the shaft during pressing on of the components can be reduced. It is furthermore of particular advantage in the method according to the invention that now an unprocessed tube can be used for the shaft, which was not possible hitherto during the production of a conventional longitudinal press fit because of the comparatively large tolerances present in this case. In general, unprocessed shafts have a significantly higher tolerance range than ground shafts, for example, which is why in order to achieve a minimum overlap (excess of the shaft with respect to the recess of the component in the cold state), a large maximum total overlap must be selected, which makes it possible to reliably compensate for the tolerances occurring in the unprocessed shaft. Under certain circumstances, this leads to the overlap becoming so large that the component can no longer be joined or the minimum overlap just has to be selected to be significantly smaller, which in turn leads to the transmittable torque decreasing. However, if the minimum overlap is to be reliably ensured and the tolerances of the shaft or of the component are simultaneously taken into account, an overlap value must be selected which is formed from the sum of the tolerances of the shaft and of the component and the minimum overlap. The overlap value calculated in this way may still allow joining of the component by means of a longitudinal press fit, but the grooves formed during the pressing of the component onto the shaft become so deep that they can be removed again only with difficulty or not at all by later grinding of the shaft. There is also the increased risk of seizure, in particular if a plurality of components are joined onto the shaft one behind the other. Here, the method according to the invention starts by virtue of the longitudinal press fit being based on the overlap value calculated from the sum of the tolerances of the component and of the shaft and the minimum overlap, and at the same time heating the component to such an extent that the grooves produced during the pressing of the component onto the shaft do not exceed a predefined depth and are therefore tolerable, for example, or else can be removed without problems in a subsequent grinding process and at the same time the desired minimum overlap can be ensured when the component is cooled. The joining clearance when pressing the component onto the shaft is however always less than zero, so that the heated or heated component can also be pushed onto the shaft only with force. Thus, no thermal joining takes place in the classic sense, but rather grooves will also be formed on the shaft during the pressing-on of the component, which grooves however lie within a tolerable limit.Thus, several advantages can be achieved with the method according to the invention. On the one hand, an unprocessed shaft with comparatively large manufacturing tolerances can be used, which significantly reduces the costs. By taking into account the tolerances and the previously selected minimum overlap, on the other hand, the at least torque to be transmitted between the shaft and the component is ensured. By heating the component during pressing onto the shaft, the grooves formed in this case can furthermore be limited with respect to their depth, so that these are either to a tolerable extent or can easily be removed by means of subsequent grinding.In a further advantageous embodiment of the invention, the recess of the component, in particular of a cam, and / or the outer diameter of the shaft are measured before the joining. Thus, during the joining of the component, the joining temperature can be adjusted according to the pairing of the outer diameter of the shaft with the recess of the component. As a result, the process can be set more reliably to maintain the minimum overlap and to ensure the maximum permissible pressing. This naturally takes place all the more accurately when both joining partners have been measured. If only one of the joining partners was measured in advance, an increase in safety can still be achieved.In a further advantageous variant, only the outer diameter of the shaft is measured and then a component with a suitably manufactured recess is provided for joining. An improvement in the joining process can thus likewise be achieved and tolerance tears of the shaft which may not be further processed can also be reliably absorbed.The component is expediently heated to a temperature which is at least 30° higher than that of the shaft. Even these 30° make it possible to press the component onto the shaft more easily and at the same time both to use an unprocessed shaft and to ensure the minimum overlap required for the required torque transmission. At this point, it should also be mentioned that, in addition or as an alternative to heating the component, cooling of the shaft is of course also possible, which likewise makes it possible to ensure the required minimum overlap and thus the required torque transmission and at the same time to limit the depths of the grooves formed when the component is pressed onto the shaft. Usually, however, the components are heated, since this is possible much more easily, for example, by means of special induction heating than, for example, cooling the shaft. It must be noted in the method according to the invention that the stresses arising in the component after cooling down on the shaft must only become so great that they can be tolerated in the long term during operation.In a further advantageous embodiment of the solution according to the invention, the finished joined shaft and / or the components are / are ground. By means of a grinding process which follows the pressing of the components onto the shaft, in which grinding process the components, for example cams, and / or the shaft, the quality of the camshaft, for example, can be significantly increased and adapted to the requirement within the internal combustion engine.In a further advantageous embodiment of the method according to the invention, a lubricant is used for longitudinally pressing the at least one component onto the shaft. The use of such a lubricant substantially facilitates the pressing-on process and also reduces the risk of tilting of the component during the pressing-on.The invention is further based on the general idea of equipping a camshaft of an internal combustion engine with at least one component which is applied to a shaft of the camshaft according to the method described in the preceding paragraphs. The component can be, for example, a cam, a signal wheel, a transmitter wheel, a gearwheel, a belt wheel or else a bearing ring. In order to facilitate the pressing-on of the component, it can have a chamfer in the region of its recess, for example its bore, which surrounds the bore or the recess annularly and is configured in a wedge-shaped manner. Such a chamfer makes it easier for the component to slide over it via any unevennesses on the shaft.Further important features and advantages of the invention are evident from the dependent claims, from the drawings and from the associated description of the figures with reference to the drawings.It is understood that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the present invention.Preferred exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally the same components.They show, in each case schematically, FIG. 1 shows a camshaft according to the method according to the invention with components joined thereto, FIG. 2 shows a sectional illustration through the camshaft according to FIG. 1, FIG. 3 shows different sectional views through a shaft of the camshaft and a cam in the cold and heated state.According to FIG. 1, a camshaft 1 according to the invention of an internal combustion engine, not otherwise shown, has at least one component 2 which is joined to a shaft 3 of the camshaft 1 by a method according to the invention. The component 2 can be, for example, a cam 4, a signal wheel 5, a transmitter wheel, a gearwheel 6 or a belt wheel or a bearing ring 7. According to the invention, the components 2 are fixed on the shaft 3 of the camshaft 1 by means of a combined joining method, wherein the method represents a combination of thermal joining and pressing on.In the method according to the invention for joining the component 2 having a recess 8, for example a cam bore, to the shaft 3, a minimum overlap Ü min is first defined between the component 2 and the shaft 3. The minimum overlap Ü min is the dimension by which an outer diameter R w of the shaft 3 is greater than an inner diameter N K of the component 2 in the cold state (cf. FIG. 3 ). In order to be able to use an unprocessed shaft 3, the tolerances of the component ΔN K and of the shaft ΔR W are first determined. Subsequently, an overlap value Ü is formed from the sum of the tolerances ΔR W and ΔN K and the minimum overlap Ü min. The component 2 itself is now heated or heated so strongly as a function of the determined overlap value Ü that the grooves 9 formed during the subsequent pressing of the component 2 onto the shaft 3 do not exceed a predefined depth in the radial direction and at the same time the minimum overlap Ü min is ensured when the component 2 is cooled. By means of the additional heating or heating of the component 2, on the one hand, the depth of the grooves 9 can be reduced when the component 2 is pressed onto the shaft 3, but on the other hand, a comparatively high minimum overlap min and thus also a comparatively high torque transmission can be ensured.If, for example, the minimum overlap Ü min between component 2 and shaft 3 is to be 0.040 mm, it must be ensured that this is also not cancelled by the tolerances ΔR W of the shaft 3 or the tolerances ΔN K of the component 2. If, for example, the production tolerance of the shaft 3 is ΔR W= 0,1 mm and the tolerance ΔN K of the cold component 2 is 0.015 mm, then an overlap value Ü of Ü= Ü min+ ΔR W+ ΔN K= 0,040 mm+ 0.1+ 0.015=0.155 mm is determined from this. If the minimum overlap Ü is increased min for example to increase the transmittable torques, this would also mean an increase in the overlap value Ü, which would on the one hand significantly increase the force for pressing the component 2 onto the shaft 3 and on the other hand would cause significantly greater damage in the form of deep grooves 9 on the shaft 3. In order now also to make it possible in this case to join the component 2 on the shaft 3, the component 2 is heated according to the invention to such an extent that, on the one hand, the minimum overlap min is ensured when the component 2 is cooled, but, on the other hand, the grooves 9 do not exceed a predefined and tolerable depth. Grooves 9 that can be tolerated in this way can be eliminated, for example, during a subsequent grinding process.The component 2 is, of course, only heated in order to increase the diameter N of the recess 8, for example of the cam bore. However, even when the component 2 is heated, the joining clearance is always <0, so that the component 2, for example the cam 4, must also be pressed onto the shaft 3 of the camshaft 1 in the heated state.In order to be able to reliably ensure a desired torque transmission between the shaft 3 and the component 2, the minimum overlap min is between 0.01 and 0.7 mm. The upper limit is thereby determined decisively by the partial strength of the component 2 as well as its geometry and material. For the shaft 3, in principle an unprocessed tube or an at least singly or multiply drawn tube can be used. When selecting a cheaper tube, which may therefore also have poorer tolerances, the component 2 must then be heated to a correspondingly high degree in order to achieve the desired transmittable torque. Thus, for each application, the appropriate pairing between the depth of the grooves 9, the minimum overlap U min and the temperature of the heated component 2 can be selected.The shaft 3 is usually manufactured with a manufacturing tolerance of + / - 0.06 mm, in particular even with a manufacturing tolerance of only + / - 0.01 mm. For longitudinally pressing the at least one component 2 onto the shaft 3, a lubricant can additionally be used, which facilitates the sliding movement of the component 2 on the shaft 3. This lubricant is usually resistant to high temperatures in order not to be damaged by a strongly heated component 2. Of course, the alternative or additional cooling of the shaft 3 is also conceivable, whereby purely theoretically the same effect can be achieved. It is also conceivable to use a ground shaft, but some of the advantage is lost since the overlap must not be chosen to be too large in order to avoid major damage to the surface of the shaft 3, i.e. corrugations 9. The advantage of this embodiment lies in the omission of the re-grinding of the shaft 3. In general, a chamfer 10 can additionally be provided on the component 2 which encloses the recess 8 and additionally facilitates the pushing-on process onto the shaft 3.If one looks at FIG. 3, it can be seen that the shaft 3 has an outer diameter R W whereas the recess 8 of the component 2 has a diameter N K in the cold state and a diameter N W in the warm state. The difference between N W and N K describes the expansion effect which can be achieved by heating the component 2.With the method according to the invention, a combination of pressing on and thermal joining can thus be achieved, wherein, on the one hand, the grooves 9 formed on the shaft 3 of the component 2 are less deep, but, on the other hand, a predeterminable torque can be transmitted reliably on account of the predetermined minimum overlap Ü min. The combination of thermal joining with longitudinal pressing also makes it possible to use an unprocessed tube for the shaft 3, which makes it possible to produce a camshaft 1 in a significantly more cost-effective manner, for example.

Claims

Method for joining a component (2) having a recess (8), in particular a cam (4), on a shaft (3), in particular on a camshaft tube, by pressing the component (2) with its recess (8) onto the shaft (3), characterized in that - a minimum overlap (Ü min) desired in the operating state is defined between the component (2) and the shaft (3), - a production tolerance (ΔN K) of the recess (8) of the component (2) and a production tolerance (ΔR W) of the shaft (3) are determined, a covering value (Ü) is formed from the sum of the tolerances (ΔR W, ΔN K) and the minimum covering (Ü min) - the component (2) is heated so strongly as a function of the covering value (Ü) that the grooves (9) formed during the subsequent pressing of the component (2) onto the shaft (3) do not exceed a predefined depth and the minimum covering (Ü min) is ensured when the component (2) is cooled.Method according to Claim 1, characterized in that - the recess (8) of the component (2) and / or the diameter of the shaft (3) is measured before joining, - the component (2) is heated on the basis of the dimensions of the recess (8) and / or the diameter of the shaft (3), wherein grooves (9) which are produced during the subsequent pressing of the component (2) onto the shaft (3) do not exceed a predefined depth and the minimum overlap (Ü min) is ensured when the component (2) is cooled.Method according to Claim 1, characterized in that - the diameter of the shaft (3) is measured before joining, - the component (2) is produced to fit on the basis of the dimensions of the diameter of the shaft (3), wherein grooves (9) which are produced during the subsequent pressing of the component (2) onto the shaft (3) do not exceed a predefined depth and the minimum overlap (Ü min) is ensured when the component (2) is cooled.Method according to one of the preceding claims, characterized in that the component (2) is heated to a temperature which is at least 30° higher than that of the shaft (3).Method according to either of Claims 1 and 4, characterized in that the finished joined shaft (3) and / or the components (2) are / are ground.Method according to one of Claims 1 to 5, characterized in that the value chosen for the minimum overlap is 0.01 mm < Ü min< 0,7 mm.Method according to one of the preceding claims, characterized in that a lubricant is used for longitudinally pressing the at least one component (2) onto the shaft (3).Method according to one of the preceding claims, characterized in that a shaft (3) having a production tolerance (ΔR W) of ±0.06 mm, in particular of ±0.01 mm, is used.Camshaft (1) of an internal combustion engine having at least one component (2) which is joined to a shaft (3) of the camshaft (1) according to the method according to one of the preceding claims.Camshaft according to Claim 9, characterized in that the component (2) is a cam (4), a signal wheel (5), a transmitter wheel, a gearwheel (6), a belt wheel or a bearing ring (7).Camshaft according to Claim 9 or 10, characterized in that the component (2) has a chamfer (10) in the region of its recess (8) in order to facilitate the pressing on the shaft (3).Camshaft according to one of Claims 9 to 11, characterized in that - the minimum overlap is 0.01 mm < Ü min< 0,7 mm, and / or - the production tolerance (ΔR W) of the shaft (3) is ±0.06 mm, in particular ±0.01 mm, and / or - the shaft (3) is unprocessed or is a tube which is drawn at least once.

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