CROSS REFERENCE TO RELATED APPLICATIONS
The present application claims priority to German Patent Application No. 10 2015 116 116.8, entitled “Assembled Camshaft,” filed Sep. 23, 2015, the entire contents of which are hereby incorporated by reference for all purposes.
TECHNICAL FIELD
The invention refers to an assembled camshaft with injection cams, in particular for driving single-cylinder piston pumps (plug-in injection pumps) for diesel engines with direct fuel injection.
BACKGROUND
Various fuel injection systems employing differing types of injection pumps are known for diesel engines with direct fuel injection. Fuel injection systems exist that employ single-cylinder, distributor or in-line fuel injection pumps. One construction design of the single-cylinder fuel injection pump is the single-cylinder piston pump (also known as plug-in injection pumps). A group of plug-in injection pumps functionally corresponds to a row of in-line fuel injection pumps, although in this case each cylinder of the engine is controlled by a separate plug-in injection pump. Using plug-in injection pumps, it is possible to achieve fuel pressures of up to approximately 2000 bar, as well as a twin-phase injection.
High-pressure unit injectors can also be employed in Common Rail (CR) Direct Fuel Injection Systems and generally comprise (axial) piston pumps with a piston that is inserted into a cylinder and sealed. The piston can be periodically moved by an eccentric (i.e. one cam of the camshaft), the eccentric being coupled to the internal combustion engine, which is supplied with fuel by the injection system. In order to achieve a particularly compact integration it is common that such axial piston pumps are realized as plug-in injection pumps, which can be inserted into an opening of an engine component (hence the name “plug-in injection pump”) and fixedly attached to the engine component by screwing. A fuel injection system for a diesel engine in which high-pressure plug-in injection pumps, arranged in the crankcase of the engine and driven by means of a camshaft, supply diesel fuel to a supply storage (common rail) is known, e.g. from the publication DE 195 08 445 A1 (Kloeckner Humboldt Deutz AG).
In order to avoid the necessity of mounting a separate CR high-pressure injection pump onto a diesel engine, the above mentioned high-pressure plug-in injection pumps may be employed instead. These are usually driven by means of a camshaft, which itself is coupled to a crankshaft via a toothed belt. In order to have the needed amounts of injected fuel at one's disposal while employing as few plug-in injection pumps as possible (ideally a single plug-in pump), it is advisable to employ multiple cams (an injection cam that allows for more than two upstrokes per rotation). A multiple cam, however, in comparison with a single or dual cam, has a much larger diameter. In addition, when forging multiple cams one must take into consideration the fact that, in the case of a large injection cam, a cold upset forging of the material can only be carried out directly at the end of the cam shaft.
SUMMARY
The following is the description of a cam shaft arrangement. In accordance with one example of the present invention the camshaft arrangement includes a camshaft housing, a camshaft arranged in the camshaft housing, wherein the camshaft has at least one first cam, as well as a second cam which is larger than the at least one first cam and which is rigidly connected with the camshaft. The camshaft arrangement further includes a drive wheel which is rigidly mechanically connected with the second cam or with the camshaft, as well as a slide bearing that is arranged axially between the drive wheel and the second cam. A bearing bush of the slide bearing is arranged in the camshaft housing or in a bearing cover mounted on the camshaft housing. The second cam or the drive wheel or a nut screwed on the camshaft has a running surface for the slide bearing.
In addition, methods for manufacturing a camshaft arrangement are described.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in greater detail by means of the examples illustrated in the Figs. The illustrations are not necessarily true to scale and the invention is not to be understood as being limited to the illustrated aspects. Instead, emphasis is placed on illustrating the underlying principles of the invention.
FIG. 1 shows a section of a perspective illustration of a diesel engine with a common rail fuel injection system.
FIG. 2 shows a lateral view of the illustration of FIG. 1.
FIG. 3 shows a sectional view of the camshaft housing in accordance with a first embodiment of the invention.
FIG. 4 shows a sectional view of the camshaft housing in accordance with a second embodiment of the invention.
FIG. 5 shows a sectional view of the camshaft housing in accordance with a third embodiment of the invention.
FIG. 6 shows a sectional view of the camshaft housing in accordance with a fourth embodiment of the invention.
FIG. 7 shows a sectional view of the camshaft housing in accordance with a fifth embodiment of the invention.
In the Figs., like reference symbols designate identical, corresponding or similar components.
DETAILED DESCRIPTION OF THE EMBODIMENTS
In FIGS. 1 and 2, parts of a diesel engine, including attachments, is illustrated in relative detail. The actual illustration should only be regarded as an example and may have a completely different appearance in a practical implementation of the invention. In addition, in the following only those components of the engine will be described which are needed to understand the embodiments. In particular the camshaft housing will be described in greater detail.
FIG. 1 is a perspective illustration of the upper part of a diesel engine. The cylinder block (engine block) with the cylinder head 2 can be seen in the lower part of the illustration. The camshaft housing 1, in which the camshaft (cf. FIGS. 3-7) is arranged, is located in the upper part of the illustration. The toothed belt wheel 7 for driving the camshaft, as well as the toothed belt 8 that is placed around the toothed belt wheel 7, can be found on the left side of the illustration. On the right side of the illustration one can see the air collector 6 (also referred to as airbox).
On the top side of the camshaft housing 1 is a housing cover 9 on which the CR distributor pipe 5 (rail) is arranged. The connection conduit between the CR distributor pipe 5 and the plug-in injection pump 4 is designated with the reference symbol 5a. The connection conduit between the CR distributor pipe 5 and a CR injector 3 is designated with the reference symbol 5b.
FIG. 2 is a lateral view of FIG. 1 from the left side. The air collector has been omitted from FIG. 2 for the sake of clarity. Here one can see the plug-in injection pump 4, the camshaft housing 1 with an end section of the camshaft 10, the corresponding housing cover 9 and the toothed belt wheel 7, the CR distributor pipe 5 and the connection conduit 5a (pressure line) from the plug-in injection pump 4 to the distributor pipe 5. As was mentioned at the start, multiple cams are employed on the camshaft 10 in order to have at one's disposal the necessary amount of injected fuel with as few plug-in injection pumps as possible (ideally with one plug-in injection pump). A multiple cam, however, has, in comparison to a single or dual cam, a much larger diameter. The multiple cam, therefore, cannot be cast or forged in one piece together with the camshaft. After the manufacture of multiple cams by forging these can only be upset forged (or cold pressed) onto the end of the camshaft, which places undesirable constraints on the design of the camshaft (as well as on that of the entire fuel injection system).
FIG. 3 is a cross-sectional illustration of a part of the camshaft housing 1 in accordance with one embodiment of the invention. The section plane runs through the longitudinal axis of the camshaft 10 and is at a right angle to the housing cover 9. In the illustrated example, both a large multiple cam 13 and the toothed belt wheel 7 are fixedly mounted on a conical seat of the camshaft. The toothed belt wheel 7 and the conical seat 20 of the camshaft 10 form a tapered interference fit, wherein the toothed belt wheel is pressed onto the conical seat 20 by means of a nut 23 (e.g. a simple hexagonal nut).
The multiple cam 13 and the camshaft 10 form, by means of a feather key 12, a shaft-hub connection, whereby the multiple cam 13 can also be arranged on a conical seat 14 of the camshaft 10. In the following example, the multiple cam is pressed onto the conical seat by means of a special nut 15 that is screwed on the camshaft 10 (tapered interference fit). The feather key serves the purpose of precisely positioning the multiple cam 13. The special nut 15 is essentially a sleeve (hollow cylinder) with an internal thread on one segment of the sleeve's inner surface (the camshaft 10 has a corresponding external thread). The remaining segment of the sleeve's inner surface forms, together with the camshaft 10, a fit 17 (e.g. a transition fit, with no tolerance). When assembled, one abutting end of the sleeve presses the multiple cam 13 against the conical seat 14. The bearing forces from the camshaft 10 are conducted into the camshaft housing 1 via the tolerance-free fit 17.
At the same time, the external surface (shell surface) of the special nut 15 serves as the running surface for a slide bearing 18. The bearing bush can be a part of the camshaft housing 1 or can be mounted in a wall of the camshaft housing. The slide bearing 18 thereby also serves for the camshaft 10 as a feedthrough through the housing wall of the camshaft housing. As is generally the case in slide bearings, a shaft seal 19 is arranged between the running surface (the external surface of the special nut 15) and the bearing bush (the camshaft housing 1). In addition to the slide bearing 18, the camshaft is supported at further positions in slide bearings. The camshaft bearing brackets that belong to the slide bearings and that are fixed by means of screws 11, are designated with the reference symbol 21. Conventional (small) cams 13′ are arranged on the camshaft 10 between the bearing positions. The cams 13′ are manufactured in one piece together with the camshaft 10.
The assembly of the camshaft assembly in accordance with the example of FIG. 3 will now be described. First, the large multiple cam 13 is inserted into the open (without cover 9) camshaft housing 1. After this the feather key is inserted into the corresponding groove in the conical seat 14 and the camshaft 10 is thread through the hub of the multiple cam 13. The conical seat 20 is of smaller diameter than the conical seat 14, thereby allowing for the camshaft to be easily threaded through to the conical seat 14. After this the camshaft 10 is mounted in the camshaft housing 1 using the bearing brackets 21 and the screws 11. After this the slide bearing 18 is pressed into the camshaft housing, and (in FIG. 3 from the left) the special nut 15 is screwed onto the shaft, whereby the multiple cam 13 is pressed onto the conical seat 14. Following this the shaft seal 19 can be attached, the housing cover 9 can be put into place and the toothed belt wheel 7 can be pressed onto the conical seat 20 by means of the nut 23.
The embodiment of FIG. 4 is very similar to the previous example of FIG. 3. Only the slide bearing 18, and consequently the feedthrough of the camshaft 10 through the camshaft housing as well, are realized differently. The right side of the illustration in FIG. 4, in particular the bearing supports 21 with the screws 11 and the small cams 13′ positioned between them, are virtually identical to those in the previous example and will therefore not be described further. The conical seat 14, on which the multiple cam 13 is mounted by means of the feather key 12 is also identical to that of FIG. 3. The nut 15, however, by means of which the multiple cam 13 is pressed onto the conical seat 14, is realized in a simpler form, as the nut 15 is not a component of a slide bearing in the present example. The nut 15 may be a common hexagonal nut.
The toothed belt wheel 7, just as in the example of FIG. 3, is mounted on the conical seat 20 of the camshaft 10, whereby toothed belt wheel 8 and camshaft form a tapered interference fit in which the toothed belt wheel 7 is pressed against the conical seat 20 by means of the nut 23. However, the toothed belt wheel 7 here is wider (in the direction of the rotational axis of the camshaft 10) than in the previous example and has a ledge in the radial direction whose shell surface (in the peripheral direction) forms a running surface of the slide bearing 18. The bearing bush of the slide bearing 18 may be a part of the camshaft housing 1 or may be mounted in a wall of the camshaft housing. Thereby, for the camshaft 10, the slide bearing 18 also serves as a feedthrough through the housing wall of the camshaft housing. As in the previous example, a shaft seal 19 is arranged between the running surface (on the ledge of the toothed belt wheel 7) and the bearing bush (camshaft housing 1). In all other respects the example of 4 is identical to the previous example of FIG. 3.
The assembly of the camshaft assembly in accordance with the example of FIG. 4 will now be described. First the large multiple cam 13 is inserted into the open (without cover 9) camshaft housing 1. After this the feather key is inserted into the one corresponding slot in the conical seat 14 and the camshaft 10 is threaded through the hub of the multiple cam 13. The conical seat 20 is smaller in diameter than the conical seat 14, thereby allowing for the camshaft to be easily threaded through to the conical seat 14. After this the camshaft 10 is fixedly mounted in the camshaft housing 1 using the bearing supports 21 and the screws 11. After this the nut 15 is screwed onto the shaft (in FIG. 4 from the left), whereby the multiple cam 13 is pressed onto the conical seat 14. Following this the shaft seal can be inserted in the slide bearing bush in the camshaft housing 1, the toothed belt wheel 7 can be pressed onto the conical seat 20 by means of the nut 15, and the cover 9 can be placed on the camshaft housing 1.
FIG. 5 shows a further embodiment of an assembled camshaft, the multiple cam 13 and the toothed belt wheel 7 of which form an integral component. In other words, the toothed belt wheel 7 has a segment in the axial direction that forms the multiple cam 13. At the same time, the multiple cam 13 (of the toothed belt wheel 7) has a centered borehole (a cylindrical hole, coaxial to the rotational axis of the camshaft 10) which serves as a bearing bush for the slide bearing 18. The camshaft housing 1 has a sleeve 16 that has the form of a hollow cylinder and which can be an integrated component of the camshaft housing 1 or rigidly connected to the camshaft housing. The camshaft 10 is fed through the sleeve 16. The outer shell surface of the sleeve 16 forms, together with the centered borehole in the multiple cam 13, the slide bearing 18. When assembling the camshaft, the toothed belt wheel 7 with the multiple cam 13 are slid over the sleeve 16, whereby the camshaft 10 is also fed through the hub of the toothed belt wheel 7. The hub of the toothed belt wheel 7 and the camshaft 10 form, as in the previous examples, a tapered interference fit, whereby the toothed belt wheel 7 is pressed against the conical seat 20 of the camshaft 10 by means of a nut 23 (e.g. a hexagonal nut).
In accordance with the present example, the multiple cam 13 is mounted directly on the camshaft housing 1 (slide bearing 18 between multiple cam 13 and sleeve 16), allowing for the bearing forces from the multiple cam 13 to be directly conducted into the camshaft housing 1. The multiple cam is driven directly by means of the toothed belt wheel 7 (not indirectly via the camshaft 10), as the toothed belt wheel 7 and the multiple cam 13 comprise an integral component. A shaft seal 19 is arranged between the camshaft housing 1 and a ledge of the toothed belt wheel 7, similar to the previous example of FIG. 4. This means that the shaft seal is arranged between the multiple cam 13 and the toothed belt wheel 8. The remaining components, i.e. the bearing supports 21 with the screws 11, the small cams 13′ and the housing cover, are essentially identical to those in the previous examples and the respective descriptions of these components will, therefore, not be repeated.
The assembly of the assembled camshaft in accordance with the example of FIG. 5 will now be described. First the camshaft 10 is threaded through the feedthrough in the camshaft housing 1 (i.e. through the sleeve 16). After this the camshaft 10 is fixedly mounted in the camshaft housing 1 using the bearing brackets 21 and the screws 11. The toothed belt wheel 7 including the multiple cam 13 are placed onto the camshaft 10 from the outside, so that the multiple cam 13 is at least partially slid over the sleeve 16 on the camshaft housing 1 and the hub of the toothed belt wheel 7 is at least partially slid over the conical seat 20 of the camshaft 10. The toothed belt wheel 7 is then pressed against the conical seat 20 of the camshaft 10 by means of the nut 23. The assembly is completed by placing the housing cover 9 onto the camshaft housing 1. The multiple cam 13 is thus mounted on the outside of the camshaft housing 1 (on the sleeve 16) and sealed using the shaft seal 19.
FIG. 6 shows a further embodiment of an assembled camshaft in which, as opposed to the pervious examples of FIGS. 3 and 4, the multiple cam 13 does not form a tapered interference fit together with the camshaft 10, but rather a friction fit, wherein the multiple cam 13 is pressed against an abutting end 33 of the camshaft 10 by means of a screw 27, causing a friction-type connection to be formed between the multiple cam 13 and the camshaft 10. The screw 27 is fed through the multiple cam 13 via a centered borehole and is coaxial to the rotational axis of the camshaft 10. The multiple cam 13 is centered with respect to the camshaft 10 by means of a centering collar 26 that is arranged on the end of the camshaft 10. The multiple cam 13 has, on its side that lies opposite to the camshaft 10, a shaft segment 10′ that lies coaxially to the rotational axis of the camshaft 10. The shaft segment 10′ is hollow due to the centered borehole through which the screw 27 is fed. The shaft segment 10′ provided on the multiple cam 13 can in practice be regarded as an “extension”, i.e. as an integral part of the camshaft 10. A conical seat 20 is provided on the end of the shaft segment 10′ that lies opposite the multiple cam 13 onto which the toothed belt wheel 7 is pressed (forming a tapered interference fit, as in the previous examples). The toothed belt wheel 7 is pressed onto the conical seat 20 by means of the screw 27. This means that a single central screw fixedly mounts the multiple cam 13 onto the camshaft 10 (friction fit), as well as the toothed belt wheel 7 onto the shaft segment 10′ of the multiple cam 13.
The shaft segment 10′ of the multiple cam 13 also forms a running surface for the slide bearing 18, similar to the special nut 15 that is screwed onto the camshaft shown in FIG. 3. For assembly purposes, the bearing bush belonging to the slide bearing 18 (sleeve 16) is not directly arranged in the camshaft housing 1, but rather in a separate lateral housing cover 9′ (bearing cover), which is placed onto the camshaft housing 1 (and, e.g. fixed by means of screws 32) before the toothed belt wheel 7 is pressed onto the shaft segment 10′ yet after the multiple cam 13 with the shaft segment 10′ has been slid onto the centering collar 26 of the camshaft 10. The shaft seal 19 is also radially arranged between the sleeve 16 of the lateral housing cover 9′ and the shaft segment 10′ (as well as axially between slide bearing 18 and toothed belt wheel 7). The remaining components, i.e. the bearing supports 21 with the screws 11, the small cams 13′ and the housing cover 9, are essentially the same as those in the previous examples and their respective descriptions will, therefore, not be repeated.
The assembly of the camshaft assembly in accordance with the example of FIG. 6 will now be briefly described. First the camshaft 10 is inserted into the camshaft housing 1. After this the camshaft 10 is mounted in the camshaft housing 1 by means of the bearing brackets 21 and the screws 11. After this the multiple cam 13 is slid onto the centering collar 26 of the camshaft 10 and the bearing cover 9′, together with its integrated sleeve 16, is slid sideways over the shaft segment 10′ of the multiple cam 13, thereby forming the slide bearing 18 between the shaft segment 10′ and the sleeve 16. The bearing cover 9′ can be fixedly attached to the camshaft housing 1 by means of the screws 32. Following this the shaft seal 19 is slid from outside into the sleeve 16 (bearing bush). After this the toothed belt wheel 7 can be pressed onto the conical seat 20 of the shaft segment 10′. Both the tapered interference fit between toothed belt wheel 7 and the conical seat 20 of the shaft segment 10′ and the friction fit between the abutting end 33 of the camshaft 10 and the multiple cam 13 can be fixed by means of the central screw 17. The assembly is completed by placing the housing cover 9 onto the camshaft housing 1.
FIG. 7 shows a further embodiment of an assembled camshaft, similar to the one of FIG. 6. In accordance with the example of FIG. 7, however, the shaft segment 10′ is not an integrated component of the multiple cam 13, but rather of the toothed belt wheel. In this case, the multiple cam 13 can be upset forged (or shrunk) onto the end of the camshaft 10. In this embodiment the multiple cam 13 is an integral component of the camshaft 10, which, as was mentioned above, can only be easily realized when the (relatively large) multiple cam 13 is arranged on the end of the camshaft 10.
In the present example, the shaft segment 10′ has, on its end opposite the toothed belt wheel 7, a conical seat (truncated cone) that can be inserted into a corresponding interior taper 14′ in the camshaft in order to form a tapered interference fit. As in the previous example (FIG. 6), the shaft segment 10′ has a centered borehole coaxial to the rotational axis of the camshaft 10 through which a screw 27 can be fed. The screw can be screwed into a central internal thread in the camshaft (analogously to FIG. 6), whereby the toothed belt wheel 7, together with the shaft segment 10′, is pressed against the interior taper 14′ in the camshaft, thereby causing a friction-type connection to be formed.
As in the example of FIG. 6, the shaft segment 10′ forms the running surface of the slide bearing 18. For assembly purposes, the bearing bush belonging to the slide bearing 18 (sleeve 16) is not directly arranged in the camshaft housing 1, but rather, as in the example of FIG. 6, in a separate lateral housing cover 9′ (bearing cover), which is placed onto the camshaft housing 1 (and, e.g. fixed by means of screws 32) before the toothed belt wheel 7, together with shaft segment 10′, is pressed into the interior taper 14′ of the camshaft 10. The shaft seal 19 is also radially arranged between the sleeve 16 of the lateral housing cover 9′ and the shaft segment 10′ (as well as axially between slide bearing 18 and toothed belt wheel 7). The remaining components, i.e. the bearing supports 21 with the screws 11, the small cams 13′ and the housing cover 9, are essentially the same as those in the previous examples and their respective descriptions will, therefore, not be repeated.
The assembly of the assembled camshaft in accordance with the example of FIG. 7 will now be briefly described. First the camshaft 10 is placed into the camshaft housing 1. After this the camshaft 10 is fixedly mounted in the camshaft housing 1 by means of the bearing supports 21 and the screws 11. Following this the toothed belt wheel 7, together with its shaft segment 10′, is inserted into the sleeve 16 of the bearing cover 9′, albeit previous to this the shaft seal 19 is inserted into the sleeve. The truncated cone at the end of the shaft segment 10′ is inserted into the corresponding interior taper of the camshaft 10, by means of which the shaft segment 10′ is centered in respect to the rotational axis of the camshaft. The tapered interference fit between the interior taper 14 of the camshaft 10 and the truncated cone on the end of the shaft segment 10′ is then fixed by means of the central screw 17. Afterwards the bearing cover can be fixedly mounted on the camshaft housing 1 using screws 32. The assembly is completed by placing the housing cover 9 onto the camshaft housing 1.
Various individual aspects and individual technical features of each of these embodiments may be—provided nothing is explicitly stated to the contrary—combined with each other to form further embodiments. For example, in the embodiment illustrated in FIG. 7, a friction fit may be provided, instead of a tapered interference fit, between multiple cam 13 (with interior taper 14) and shaft segment 10′ and, analogously to FIG. 6, between camshaft 10 (with centering collar 26) and multiple cam 13. Furthermore, machine elements that are depicted in the examples illustrated here as comprising one piece may also be assembled from numerous separately manufactured parts. In the example of FIG. 6 the multiple cam 13 and the shaft segment 10′ form an integral component and have been manufactured in one piece. Alternatively, however, this integral component may also be assembled from two parts, for example by shrinking (or by means of other joining technologies) the multiple cam 13 onto the shaft segment 10′. The same may be said of the shaft segment 10′ and the toothed belt wheel 7 of FIG. 7. Depending on the application, in the example of FIG. 7 the bearing cover 9′ with the sleeve 16 could be an integral component of the camshaft housing 1, which would make it possible to do without the screwed connections (screws 32). In general, the tapered interference fits shown in the various embodiments may be replaced by other types of positive-locking or friction-locking (press joining) connections.
Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (units, assemblies, devices, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond—unless otherwise indicated—to any component or structure, which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure, which performs the function in the herein illustrated exemplary implementations of the invention.
In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.
Patent Application
20170081983
