Method for producing camshaft
By accurately drawing and accurately measuring the outer diameter of the camshaft and processing the inner diameter of the cam, the problem of difficult control of the overlap amount and thermal bonding clearance when manufacturing the camshaft in the prior art is solved, inexpensive and high-precision camshaft manufacturing is achieved, and the energy required for thermal bonding and maximum overlapping amount are reduced.
Patent Information
- Application Number
- CN202311360422.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-10-19
- Publication Date
- 2025-04-22
AI Technical Summary
In the prior art, when manufacturing camshafts of internal combustion engines, it is difficult to achieve a sufficiently small overlap amount and an appropriate thermal bonding gap without increasing complexity and cost, resulting in changes in the cam structure or excessive maximum overlap amount and undesirable high stresses.
The cam shaft is manufactured by precisely pulling, and after the shaft is pulled, it is subject to a pulling detection of its actual outer diameter, and then the inner diameter of the cam is processed so that the maximum overlap during joint is between 15% and 90% of the shaft outer diameter tolerance, thereby reducing the energy required for thermal bonding and limiting the maximum overlap.
Inexpensive and higher precision camshaft manufacturing is achieved, reducing the energy required for thermal bonding and effectively avoiding critical stress on the bonded cam.
Smart Images
Figure CN119858003A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for producing a camshaft for an internal combustion engine, the camshaft having a shaft and at least one cam thermally connected to the shaft, and also to a camshaft produced using the method. Background Art
[0002] Camshafts are an integral component of many internal combustion engines. Camshafts have a shaft that engages at least one cam. The shaft and cam are usually joined by thermal joining methods, with the shaft and cam being connected via a cam-side joining surface that is usually arranged in a cam hole and a shaft-side joining surface.
[0003] In order to create a secure connection between shaft and cam, a minimum overlap is required to be able to transfer sufficient torque from the shaft to the cam or other component. At the same time, it must be ensured that the thermal joining process is still suitable even with maximum overlap.
[0004] At present, the tubes of the shafts for the camshafts are drawn to the target diameter by means of a drawing process. However, the resulting diameter tolerances of the shafts are such that, for the selection of a minimum overlap, at the other extreme of the tolerance level a maximum overlap is obtained, wherein, in order to achieve the required joint clearance, the cams to be joined must be heated very strongly due to the tolerances of the inner diameter, which in unfavorable cases leads to undesirable structural changes in the cams. Alternatively, it is also possible to cool the shaft in order to achieve the required joint clearance, wherein this is not only expensive and complex, but also leads to an excessively large maximum overlap and undesirably high stresses in the joined cams.
[0005] The shaft can also be ground to bring its outer diameter to acceptable tolerances, but this is also complex and expensive. Summary of the invention
[0006] The object of the present invention is therefore to specify a method by means of which a camshaft can be produced without the above-mentioned problems.
[0007] This problem is solved according to the invention by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.
[0008] The basic idea of the present invention is to construct the shaft of the camshaft as a component that is precisely drawn but not subjected to additional post-processing (eg grinding). Since the previously required turning or grinding process is omitted, the camshaft manufactured according to the present invention can be manufactured more cheaply overall.
[0009] After the shaft has been drawn, the actual outer diameter of the shaft is measured at least in a spot check manner, and then the inner diameter of the cam is machined so that the nominal machined size of the cam inner diameter is almost equal to the measured actual outer diameter of the shaft. The nominal machined size of the cam inner diameter does not have to be exactly the same as the measured actual outer diameter of the shaft. A diameter grade can be selected as the nominal size, for example 5μm increments. The tolerance of the outer diameter of the shaft resulting from the manufacturing process (drawing process) of the shaft is greater than the maximum overlap of the cam thermally joined to the shaft. Therefore, the (drawing) tolerance of the outer diameter of the shaft has no effect on the overlap. The maximum overlap is essentially determined by the tolerance of the inner diameter of the cam. For the overlap, only the fluctuations of the outer diameter within the drawing batch and the tolerance of the machined inner diameter of the cam need to be taken into account. This makes it possible to provide a camshaft with smaller tolerances overall, and less energy is required for the thermal joining of the cam. In addition, the maximum overlap can be limited, thereby reliably avoiding the generation of critical stresses, especially on the joined cam.
[0010] Throughout the application, the term "cam" also generally refers to other components that can be engaged on the shaft, for example, by shrink fit. Therefore, a "camshaft" can also be understood as a shaft assembly having a shaft and a component engaged on the shaft by shrink fit.
[0011] In an advantageous refinement, the inner diameter of the cam is machined so that the maximum overlap of the cam thermally bonded to the shaft is between 15% and 90% of the (drawing) tolerance of the shaft outer diameter. The great advantage here is that a smaller overlap can be achieved while eliminating machining of the shaft.
[0012] In an advantageous development, the inner diameter of the cam is machined so that the maximum overlap of the cam thermally engaged on the shaft is between 35% and 85% of the drawing tolerance of the shaft outer diameter. This has the advantage of a narrower overlap range and thus a higher torque accuracy, while at the same time causing a smaller load distribution on the cam due to the press fit.
[0013] In an advantageous refinement, the inner diameter of the cam is machined so that the maximum overlap of the cam heat-joined to the shaft is between 35% and 65% of the drawing tolerance of the shaft outer diameter. This can reduce the upper limit and provide more leeway in terms of the joining temperature during heat-joining.
[0014] The invention is also based on the general idea of manufacturing a camshaft according to the method described in the preceding paragraphs. This makes it possible to provide a camshaft that can be manufactured not only inexpensively but also with the highest precision. In addition, the camshaft can also be provided with smaller tolerances overall, wherein less energy is required for the thermal joining of the cams, since the joining temperature can be limited. The maximum overlap can also be limited, thereby reliably avoiding the generation of critical stresses, in particular, on the joined cams.
[0015] In an advantageous development, the cam-side contact surface of the cam of the camshaft is provided with a predefined roughness. The invention makes use of the knowledge that the friction between the cam-side contact surface and the shaft-side contact surface, which is responsible for connecting the shaft to the cam and thus for holding the shaft and the cam together, can be increased by roughening the cam-side contact surface. By increasing the friction between the two contact surfaces, the connection between the shaft and the cam is thereby strengthened and the torque that can be transmitted by the camshaft is thereby increased.
[0016] In a further embodiment of the solution according to the invention, the cam-side joining surface has a roughness that is established by a sandblasting method. In this case, preferably broken glass or glass granules are used as blasting materials in the sandblasting method for roughening the cam-side joining surface. Other advantageous blasting materials are in the form of cast grains and corundum. Also conceivable are blasting materials consisting of mixtures of the above-mentioned blasting materials and other blasting materials in the form of granules as well as any other mixtures.
[0017] In another preferred embodiment of the present invention, the cam side joint surface is roughened by optical methods. For example, the cam side joint surface is roughened by laser. It is also conceivable to roughen the cam side joint surface by chemicals, especially by etching.
[0018] It should be pointed out that a targeted, predefined roughening of the cam-side joint surface by a combination of the method forms described here and by a combination of the method forms described with other method variants is also achievable and therefore falls within the scope of the invention. It should also be noted that the improvements mentioned here for the connection between a cam and a shaft and the associated methods can be easily applied to the connection between a shaft and other joined components.
[0019] Further important features and advantages of the invention emerge from the dependent claims, the drawings and the associated description of the figures with reference to the drawings.
[0020] It should be understood that the features described above and to be explained below can be used not only in the respectively described combination, but also in other combinations or in a separate manner without departing from the scope of the present invention. The separately marked components described above and to be explained below of a superordinate unit such as a device, an apparatus or a component can form separate components of the unit or can also be integrated regions or sections of the unit, even if this aspect is shown in other ways in the figures. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components.
[0022] In which respectively schematically:
[0023] Figure 1 The method according to the present invention is shown;
[0024] Figure 2 A cross-sectional view of a camshaft according to the invention is shown for explaining the minimum overlap;
[0025] Figure 3 Shown as Figure 2 , to illustrate the maximum overlap. DETAILED DESCRIPTION
[0026] according to Figure 1 In the camshaft 1 for manufacturing an internal combustion engine according to the present invention (see also Figure 2 and Figure 3 ), wherein a camshaft 1 comprises a shaft 2 and at least one cam 3 thermally joined to the shaft, the cam being connected to a joining surface 5 on the shaft side via a joining surface 4 on the cam side or being in a connected state, first in method step A, the shaft 2 is drawn. However, the shaft is not reprocessed, in particular not ground. In the subsequent method step B, the actual outer diameter 7 of the shaft 2 is measured at least in a random manner. The actual outer diameter 7 has a tolerance caused by the drawing. Subsequently, in the subsequent method step C, the inner diameter of the cam 3 is processed so that the tolerance of the outer diameter of the shaft 2 caused by the drawing of the shaft 2 is greater than the maximum overlap 6 of the cam 3 thermally joined to the shaft 2. The maximum overlap 6 is obtained by the difference between the measured actual outer diameter 7 of the shaft 2 and the lower tolerance limit UTG of the cam hole of the cam 3.
[0027] Figure 2 and Figure 3 Here, a camshaft 1 according to the invention is shown, which has a shaft 2 and a cam 3 to be engaged with the shaft. An upper tolerance limit OTG and a lower tolerance limit UTG are plotted on the outer diameter of the shaft 2 and the inner diameter of the cam 3. The upper and lower tolerance limits correspond to the tolerances in manufacturing, i.e. the tolerances of the outer diameter 7 of the shaft 2 during drawing and the tolerances of the inner diameter of the engagement surface 4 on the cam side during machining. The nominal value NOM lies between the value OTG and the value UTG, i.e. the value that is sought in manufacturing, for example when drawing the shaft 2. The actually measured value of the actual outer diameter 7 of the shaft 2 deviates from this.
[0028] Figure 2 Also plotted in FIG. 8 is a minimum overlap 8 which results from the difference between the actually measured value of the actual outer diameter 7 of the shaft 2 and the upper tolerance limit OTG of the inner diameter of the cam bore.
[0029] Figure 3 In addition, a joint play 10 is indicated, which results from the difference between the diameter change 9 of the inner diameter of the cam 3 during assembly due to heating and the lower tolerance limit UTG of the inner diameter of the cam hole.
[0030] In general, the cam 3 has an eccentric shape, while the shaft 2 has a cylindrical (outer) shape and is designed according to the invention as a shaft, in particular a tube, which has been drawn only without further processing. In order to ensure a reliable thermal connection of the cam 3 to the shaft 2, the tolerance permitted in the shaft 2 with respect to the outer diameter is limited to ≤0.10 mm, preferably ≤0.08 mm, more particularly preferably ≤0.07 mm. After measuring the actual outer diameter 7 of the shaft 2, the inner diameter of the cam 3 is processed depending on the measured value, so that the tolerance of the outer diameter of the shaft 2 is greater than the maximum overlap 6 of the cam 3 thermally connected to the shaft 2.
[0031] Preferably, the inner diameter of the cam 3 is machined such that the maximum overlap 6 of the cam 3 thermally engaged on the shaft 2 is between 15% and 90%, in particular between 35% and 85%, of the (drawing) tolerance of the outer diameter of the shaft 2. The tolerances arising from the drawing process of the shaft 2 are between 15% and 90%, in particular between 35% and 85%. Figure 3 Axis 2 is labeled with “OTG” and “UTG”.
[0032] More particularly preferably, the inner diameter of the cam 3 can also be machined such that the maximum overlap 6 of the cam 3 thermally joined to the shaft 2 is between 35% and 65% of the (drawing) tolerance of the outer diameter of the shaft 2. In the case of a ground shaft, the maximum overlap of the cam thermally joined to the ground shaft is between 15% and 90%, so that the same cam press fit is achieved with the method according to the invention without grinding as with grinding. 35% to 65% This results in a narrow dispersion press fit with good manufacturability or an inexpensive and stable joining process.
[0033] During thermal joining, the shaft 2 and the cam 3 are joined together via the shaft-side joining surface 5 of the shaft 2 and the cam-side joining surface 4 of the cam 3. Here, the cam-side joining surface 4 can have a predetermined roughness, which is established by targeted roughening of these joining surfaces 4, thereby increasing the friction between the shaft-side joining surface 5 and the corresponding cam-side joining surface 4, which leads to an enhanced connection between the shaft 2 and the corresponding cam 3. Therefore, the maximum torque that can be transmitted by the camshaft 1, that is, in particular, torque or impulse, is increased.
[0034] However, it is considered to be particularly advantageous in the camshaft 1 according to the invention that a simple but precisely drawn shaft 2, in particular a tube, can be used without further processing, in particular grinding or turning, of the shaft 2. These previously required work steps can thus be omitted, whereby the camshaft 1 can be manufactured inexpensively overall. Precise drawing of the shaft 2 is understood to mean drawing the shaft 2 to a predetermined maximum tolerance of ≤0.10 mm, preferably ≤0.08 mm, more particularly preferably ≤0.07 mm of its actual outer diameter 7.
[0035] In general, the shaft 2 can be designed as a solid shaft or as a hollow shaft. The camshaft 1 can also be designed as a commercial vehicle camshaft.
[0036] The predefined roughness of the cam-side joint surface 4 can be established, for example, by a sandblasting method, wherein the sandblasting material can include cast grains, corundum, cullet or a mixture thereof. This allows, on the one hand, a high-quality roughening process and, on the other hand, an inexpensive roughening process. During thermal joining, the roughening process can also cause the tip of the roughening to penetrate into the shaft-side joint surface 5, thereby improving the torque transmission.
Claims
1. A method for producing a camshaft (1) for an internal combustion engine, the camshaft comprising a shaft (2) and at least one cam (3) to be thermally joined to the shaft, the cam being connected via a cam-side joining surface (4) to a shaft-side joining surface (5), wherein: - the shaft (2) is drawn without further machining, - measuring the actual outer diameter (7) of the shaft (2) at least in a random manner, - The inner diameter of the cam (3) is machined so that the tolerance of the outer diameter of the shaft (2) is greater than the maximum overlap (6) of the cam (3) thermally bonded to the shaft (2).
2. The method according to claim 1, It is characterized in that The inner diameter of the cam (3) is machined so that the maximum overlap (6) of the cam (3) thermally engaged on the shaft (2) is between 15% and 90% of the tolerance of the outer diameter of the shaft (2).
3. The method according to any one of claims 1 or 2, It is characterized in that The inner diameter of the cam (3) is machined so that the maximum overlap of the cam (3) thermally engaged on the shaft (2) is between 35% and 85% of the tolerance of the outer diameter of the shaft (2).
4. The method according to any one of claims 1 to 3, It is characterized in that The inner diameter of the cam (3) is machined so that the maximum overlap (6) of the cam (3) thermally engaged on the shaft (2) is between 35% and 65% of the tolerance of the outer diameter of the shaft (2).
5. Camshaft (1) produced according to the method of any of the preceding claims.
6. The camshaft according to claim 5, It is characterized in that The camshaft (1) is designed as a commercial vehicle camshaft.
7. The camshaft according to claim 5 or 6, It is characterized in that The engagement surface (4) on the cam side has a predefined roughness.
8. The camshaft according to claim 7, It is characterized in that The predefined roughness of the cam-side engagement surface (4) is established or roughened by a sandblasting method.
9. The camshaft according to claim 8, It is characterized in that The blasting material used for blasting the cam side engagement surface (4) comprises cast grains, corundum, cullet or a mixture thereof.