U.S. patent application number 10/593014 was filed with the patent office on 2007-08-02 for method and device for grinding assembled camshafts with a high concentricity accuracy.
Invention is credited to Georg Himmelsbach.
Application Number | 20070178808 10/593014 |
Document ID | / |
Family ID | 34801961 |
Filed Date | 2007-08-02 |
United States Patent
Application |
20070178808 |
Kind Code |
A1 |
Himmelsbach; Georg |
August 2, 2007 |
Method and device for grinding assembled camshafts with a high
concentricity accuracy
Abstract
The invention relates to a method for grinding the bearing
points and assembled cams of camshafts and for levelling them with
the aid of a grinding machine and to a device for carrying out said
method, in particular making it possible to carry out a levelling
process by means of a levelling device on the same grinding machine
after grinding. In particular, when the bearing points are
finish-ground with the use of backrests as supports, said supports
are first removed from the engagement with the respective bearing
points of the camshaft and the concentricity of the bearing points
is measured, preferably in a middle area. After determining the
concentricity in the middle area, the levelling process is carried
out on the grinding machine on the basis of the measured
concentricity. The inventive device is also provided with a
levelling device integrated into the grinding machine.
Inventors: |
Himmelsbach; Georg;
(Haslach, DE) |
Correspondence
Address: |
JORDAN AND HAMBURG LLP
122 EAST 42ND STREET
SUITE 4000
NEW YORK
NY
10168
US
|
Family ID: |
34801961 |
Appl. No.: |
10/593014 |
Filed: |
January 27, 2005 |
PCT Filed: |
January 27, 2005 |
PCT NO: |
PCT/EP05/00806 |
371 Date: |
December 26, 2006 |
Current U.S.
Class: |
451/11 ;
451/62 |
Current CPC
Class: |
B24B 19/12 20130101;
B24B 49/04 20130101 |
Class at
Publication: |
451/011 ;
451/062 |
International
Class: |
B24B 51/00 20060101
B24B051/00; B24B 1/00 20060101 B24B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2004 |
DE |
10 2004 013 192.9 |
Claims
1-31. (canceled)
32. Method for grinding bearings and cams of an assembled camshaft
and straightening the assembled camshaft, comprising grinding the
bearings and the cams of the assembled camshaft on a grinding
machine and straightening the assembled camshaft on said grinding
machine.
33. Method according to claim 32, wherein the grinding comprises
finish grinding the bearings and rough grinding and finish grinding
the cams and the straightening is subsequent to the finish grinding
of the bearings and/or the rough grinding of the cams and/or the
finish grinding of the cams.
34. Method according to claim 33, wherein said finish grinding of
the bearings and said rough grinding and said finish grinding of
the cams and said straightening are carried out in a single
chucking.
35. Method according to claim 32 or 33, wherein the rough grinding
of the bearings is carried out at a first station of the grinding
machine and the rough grinding and finish grinding of the cams are
carried out at a second station of the grinding machine.
36. Method for grinding bearings and cams of an assembled camshaft
and straightening the assembled camshaft, comprising finish
grinding the bearings of the assembled camshaft on a first grinding
machine and then straightening the assembled camshaft on the first
grinding machine and rough grinding and finish grinding the cams of
the assembled camshaft on a second grinding machine.
37. Method for grinding bearings and cams of an assembled camshaft
and straightening the assembled camshaft, comprising finish
grinding the bearings of the assembled camshaft on a first grinding
machine, rough grinding and finish grinding the cams of the
assembled camshaft on a second grinding machine and, after the
rough grinding and the finish grinding of the cams, straightening
the assembled camshaft on the second grinding machine.
38. Method according to claim 37, wherein the rough grinding of the
cams is carried out at a first station of the second grinding
machine and the finish grinding of the cams is carried out at a
second station of the second grinding machine.
39. Method according to claim 36 or 37, further comprising
supporting the camshaft during the grinding of the bearings by
bringing supports into engagement with the camshaft in the vicinity
of the bearings and disengaging the supports from the camshaft for
the straightening.
40. Method according to claim 39, wherein the engaging of the
camshaft with the supports is carried out after the rough grinding
of the cams and before the finish grinding of the cams.
41. Method according to claim 39, wherein the supporting of the
camshaft during the grinding of the bearings and the disengaging of
the supports from the camshaft for the straightening comprise
engaging at least a center area of the camshafts with the supports
during the rough grinding of the cams, then, prior to the
straightening, disengaging the supports from at least a center area
of the camshaft for the straightening, thereafter again bringing
the supports into engagement with the camshaft in the vicinity of
the bearings and carrying out the finish grinding of the cams.
42. Method according to claim 32, 36 or 37, further comprising,
prior to the straightening, measuring a concentricity value or
concentricity deviation value for at least one bearing in a center
area of the camshaft.
43. Method according to claim 42, wherein the straightening is
carried out based on the measured concentricity value or
concentricity deviation value.
44. Method according to claim 32, 36 or 37, further comprising
rotating the camshaft at 50 to 200 revolution per minute during the
straightening.
45. Method according to claim 44, further comprising applying
compressive force to the camshaft in an area of a center bearing
thereof during the straightening.
46. Method according to claim 43, wherein the straightening is
carried out while the camshaft is stationary and the bearing having
the greatest deviation from concentricity is determined and a
compressive force is applied to said least concentric bearing in a
radial direction at a circumferential position at which the
greatest deviation from concentricity occurs.
47. Method according to claim 32, 36 and 37, wherein the camshaft
comprises a steel tube and includes a bend to be eliminated by the
straightening and the straightening comprises subjecting the
camshaft to pressure at least by area beyond the yield point of the
steel of said steel tube thereby to gradually essentially
completely remove the bend.
48. Method according to claim 35, wherein the straightening is
carried out at the first station.
49. Method according to claim 38, wherein the straightening is
carried out at the first station.
50. Method according to claim 35, wherein the straightening is
carried out at the second station.
51. Method according to claim 38, wherein the straightening is
carried out at the second station.
52. Method according to claim 48, wherein the straightening is
carried out also at the second station.
53. Method according to claim 49, wherein the straightening is
carried out also at the second station.
54. Apparatus for grinding bearings and/or cams of an assembled
camshaft and straightening the assembled camshaft, comprising a
grinding machine and, integrated into the grinding machine, a
device for straightening the assembled crankshaft after the
grinding.
55. Apparatus according to claim 54, further comprising, integrated
into the grinding machine, a concentricity measuring device for
measuring concentricity or concentricity deviation of said
camshaft.
56. Apparatus according to claim 55, wherein the grinding machine
further comprises a machine bed, a grinding headstock mounted to
the machine bed and having at least two grinding wheels each
mounted for pivoting into a grinding positive, and a workpiece
headstock and a workpiece tailstock each having a center between
which centers the camshaft is grippable, said concentricity
measuring device being attached to said grinding headstock or to
said machine bed and said straightening device being attached to
said grinding headstock.
57. Apparatus according to claim 54, wherein said grinding machine
further comprises a first station and a second station.
58. Apparatus according to claim 57, wherein said first station
comprises a station for finish grinding said bearings.
59. Apparatus according to claim 57, wherein said first station
comprises a station for finish grinding said bearings and rough
grinding said cams.
60. Apparatus according to claim 58 or 59, wherein said
straightening device is arranged in said first station.
61. Apparatus according to claim 57 or 58, wherein said second
station comprises a station for rough grinding and/or finish
grinding said cams.
62. Apparatus according to claim 61, wherein said straightening
device is arranged in said second station.
63. Apparatus according to claim 54, wherein the straightening
device comprises a roll straightening head comprising at least one
roller which engages the camshaft and the apparatus further
comprises a drive for rotating the camshaft while the roll
straightening head is in engagement with the camshaft.
64. Apparatus according to claim 63, further comprising a grinding
headstock and wherein the roll straightening head is attached to
the grinding headstock and comprises two rollers for engaging the
camshaft.
65. Apparatus according to claim 54, wherein the straightening
device comprises a pressure element for engaging the camshaft with
straightening force while the camshaft is not rotated.
66. Apparatus in accordance with claim 65, wherein the pressure
element is of prismatic shape having a recess for receiving one of
the bearings of the camshaft and engaging said one bearing with
straightening force at at least two circumferentially spaced
locations.
67. Apparatus in accordance with claim 65, wherein the pressure
element has a substantially flat surface for engaging the camshaft
with straightening force at one location.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to a method and an apparatus for
grinding assembled camshafts with high concentricity accuracy in a
grinding machine.
[0002] Assembled camshafts are assembled into a complete camshaft
by joining individual parts in the work processes that precede
grinding. The actual base body for the camshaft comprises a steel
tube that as a rule is cold-drawn and that can additionally have
depressions in areas between the individual cams. The cams are
produced separately and for instance are shrunk onto the
appropriate locations on the steel tube in a shrinking process,
whereupon turning and milling processes can take place prior to the
grinding. As a rule, the cams shrunken thereon are hardened in
advance. Such assembled camshafts have the advantage that they
enable a significant reduction in size compared to conventional
cast camshafts. In order to optimize this reduction in mass, an
attempt is made to keep the wall thickness of the steel tube as
thin as possible. The thinner the wall thickness in the steel tube
of the camshaft, the more such an assembled camshaft is then
relatively unstable as a separate component. It is true that this
instability is then somewhat eliminated when the camshaft is
installed in the engine in that the camshaft is received and held
in the sleeve bearings in the engine.
[0003] Another advantage of assembled camshafts is comprised in
that different materials can be used for cams and bearings in order
to be better able to take into account the different loads on the
component.
[0004] Moreover, the assembled camshafts have the advantage that
their production is also to an extent significantly more cost
effective. For these reasons, assembled camshafts are being used
more and more frequently in engines, it being recognized that,
despite the relative stabilization when installed due to the sleeve
bearings in the engine block, the demands for accuracy are growing,
in particular demands for concentricity accuracy for the
camshafts.
[0005] Due to the fact as described that the assembled camshafts
are relatively soft with respect to their longitudinal axis in
terms of bending, special demands are placed on the grinding
process for them and on their chucking during grinding. Two process
variants, differing in principle, are known when grinding the
bearings for the assembled camshafts. First, a so-called centerless
grinding process is used to grind the bearings, and second, the
bearings are ground such that the camshaft is gripped between
centers and the bearings are ground one after the other, parallel
or partially parallel. Since in this last known grinding method
steadies are used when the bearings are ground, relatively good
concentricity is attained with respect to the bearings arranged at
the shaft ends (outer bearings) relative to the inner bearings,
i.e., the bearings arranged in the center area of the camshaft.
Today concentricity requirements of for example 4/100 mm and less
are demanded that have to be maintained with certainty.
[0006] Processing, i.e. grinding, of such assembled camshafts
occurs in one or a plurality of chuckings. If it is possible to
chuck the camshaft at the same locations, it is not important for
the final quality of the produced camshafts whether the work is
performed with two or more chuckings or even with one chucking.
Another problem with assembled camshafts is that during grinding of
the bearings and the cam shape the workpieces become out of true
because of the energy added, because of the grinding process
itself, and because of the grinding of the hardened surfaces of the
cams. This process is known per se. In those workpieces that have
been joined cold and that have been hardened on their surfaces such
as for instance the cam surfaces, these influences release at least
some of the tensions contained in the material during grinding.
These tensions then lead to the shaft becoming out of true. This
means that the camshaft is no longer straight after grinding, that
is, a so-called out-of-true or eccentricity occurs that in
particular is increased at the inner bearings, even if only by a
few hundredths of a millimeter. This increase in the eccentricity
is ultimately responsible for the camshaft no longer staying within
the required tolerances with certainty.
[0007] It is therefore the object of the invention to create a
method and an apparatus for grinding assembled camshafts with
concentricity properties that are improved relative to the
accuracies that have been attainable in the past.
SUMMARY OF THE INVENTION
[0008] Using the inventive method and the inventive apparatus, what
is advantageously achieved is that the distortion on the finished
camshaft is significantly reduced or even eliminated altogether. In
the inventive method, in accordance with a first aspect the
grinding of bearings and cams of assembled camshafts as well as the
straightening of these camshafts is performed on a grinding
machine, and specifically the straightening is also performed on
this grinding machine after a grinding process. Preferably the
grinding process is either finish-grinding of the bearings and/or
rough-grinding of the cams and/or finish-grinding of the cams. In
accordance with one further development of the invention, the
method steps of finish-grinding the bearings, rough-grinding and
finish-grinding the cams, and straightening are performed in a
single chucking.
[0009] In accordance with another aspect of the invention, the
bearings of an assembled camshaft are first finish-ground on a
first grinding machine and then the cams of the camshaft are
rough-ground on a second grinding machine and are also
finish-ground on this grinding machine, the camshaft being
straightened on this second grinding machine after the
rough-grinding and/or after the finish-grinding.
[0010] In accordance with another aspect of the invention, the
bearings of an assembled camshaft are finish-ground on a first
grinding machine and straightened on the same grinding machine,
whereupon the rough-grinding and the finish-grinding of the cams of
the camshaft occurs on a second grinding machine. Naturally it is
possible that another straightening process can take place on the
second grinding machine. This straightening process can occur prior
to the rough-grinding and/or after the finish-grinding of the cams.
However, in accordance with the invention, preferably only a single
straightening process is performed.
[0011] For grinding bearings and cams of assembled camshafts on a
grinding machine, during the grinding of the bearings the camshaft
is preferably supported at bearings in particular on steadies, the
bearings first being finish-ground and then the supports, i.e., the
steadies, used during the grinding process being released.
Following this in a preferably second method step the bearings are
measured for concentricity accuracy, especially in the center area
of the camshaft. The measured concentricity value or the deviation
from ideal concentricity is preferably stored and is used in a
subsequent method step to straighten the camshaft on the same
grinding machine on this basis. Not only is the concentricity
improved with this straightening, but also the deviation from ideal
concentricity can even be nearly eliminated. This additional step
of straightening can occur after the finish-grinding of the
bearings and/or preferably after the rough-grinding of the cams
and/or after the finish-grinding of the cams. The bearings can be
used for introducing the forces necessary for the straightening
process. These straightening forces can also be introduced next to
the bearings, in any case into the steel tube.
[0012] In a component like a camshaft with sections that are
divided in the axial direction, as is known the maximum deviation
from concentricity generally occurs in the center area. Therefore
the bearing(s) is/are measured for concentricity in the center area
of the camshaft. Then the straightening forces for attaining the
most ideal possible concentricity are introduced in the area of
these bearings. In the following, concentricity shall be understood
in particular to be the concentricity of the inner bearings to the
outer bearings and of the bearing to the base circle of the
adjacent cam or pair of cams.
[0013] In accordance with the invention, it is important that a
straightening process is inserted between different grinding
operations. However, it is also possible to perform such a
straightening process after the conclusion of the last grinding
process. In any case, it is necessary to re-compensate the
concentricity properties that have degraded during grinding of the
bearings and/or cams as a result of the tensions released in order
to attain greater accuracy, i.e. greater precision in the
concentricity properties of the camshaft in the area of the center
bearings with respect to the end bearings of the camshaft. In
addition, the bearings are finish-ground. In a further step the cam
shape can be rough-ground, a straightening process following this
that is itself followed by a finish-grinding process for the cams.
A straightening process can again follow this. However, preferably
a single straightening process is used.
[0014] If the straightening process occurs after the rough-grinding
of the cams on the camshaft, preferably the supports in particular
in the form of steadies are again placed against the bearings,
whereupon the finish-grinding of the cams takes place.
[0015] Preferably the straightening is performed with the camshaft
rotating, the camshaft rotating in particular at a speed of 50-200
min.sup.-1. The actual straightening at this given speed is
preferably attained by applying a pressure force to the center
bearing of the camshaft. In this roll straightening process, it is
not entirely necessary to measure the camshaft with regard to
concentricity accuracy because the camshaft is loaded beyond the
yield point of its material during straightening.
[0016] In order to be able to bring about the straightening process
effectively, preferably the straightening occurs on the camshaft
preferably at least by area beyond the yield point of the material
of its steel tube. "By area" shall be construed in the following in
particular to mean that during the roll straightening corresponding
approximately to a flexing process at least areas of the steel tube
are rendered largely low-tension in the structure as a result of
remaining deformations. I.e., the material of the camshaft is
subjected to pressure, whereupon there is a gradual removal of the
bend in the camshaft to essentially 0 mm. The pressure force
exerted is thus reduced gradually so that the bend is also
reduced.
[0017] However, in accordance with another preferred exemplary
embodiment, it is also possible for the straightening to occur with
a stationary camshaft. In this case the deviation from ideal
concentricity is also initially determined at a bearing,
specifically the bearing that has the greatest deviation from ideal
concentricity is measured. As a rule this will be a bearing in the
center area of the camshaft. When measuring, the greatest
out-of-true or eccentricity is determined, i.e. the radial position
at which the deviation from concentricity is the greatest. Then the
pressure force is introduced at this radial site, intentional
bending of the camshaft being produced with this pressure force.
The introduction of the pressure force and the reduction in the
amount of this pressure force is matched to the actually measured
value of the concentricity deviation at the bearing in
question.
[0018] If all of the method steps are to be realized in a single
chucking in accordance with the first aspect of the invention, an
apparatus for performing the method in such a case has a grinding
machine with an appropriate number of grinding spindles and one
straightening device. This has the advantage that re-chucking
operations are not necessary and the care is not required that
would otherwise necessitate additional complexity and additional
costs to ensure nearly identical gripping conditions if there was
re-gripping. Surprisingly, it has now been demonstrated that the
desired results in terms of high accuracy in concentricity
properties of assembled camshafts can be achieved even when the
camshaft is again re-chucked on one grinding machine with a
plurality of work stations after the bearings have been
finish-ground or after the cams have been rough-ground and the
straightening process is then performed in the second chucking, but
on the same grinding machine. If at least nearly identical gripping
conditions can be attained during re-chucking, re-chucking can
occur even between any desired method steps.
[0019] Moreover, a concentricity measuring device is preferably
integrated into the grinding machine of the inventive apparatus. A
concentricity value or concentricity deviation value is determined
with this concentricity measuring device. The concentricity
measuring device is preferably connected via a control device to
the straightening device so that the straightening device is
optimally controllable based on the measured concentricity
deviation value for the straightening process, specifically such
that the concentricity deviation is at least largely eliminated
after straightening.
[0020] In accordance with the first aspect of the invention, the
method occurs on a single grinding machine. However, this grinding
machine can have two stations. The bearings are finish-ground at
the first station of this grinding machine. On the other hand, the
cams of the camshaft are rough-ground and finish-ground at the
second station. However, it is also possible for the rough-grinding
of the cams to be performed at the first station of the grinding
machine, whereupon the cams are finished-ground at the second
station of this grinding machine. The method step of straightening
the camshaft can then occur after the rough-grinding of the cams at
the first station. However, it is also possible to perform the
straightening method step subsequent to the finish-grinding of the
cams at the second station. Regardless of whether the camshaft is
straightened in the same chucking or the straightening is performed
at the first station or at the second station of the grinding
machine, the straightening process lasts approximately 5 to 15
seconds. This means that the straightening process itself is
significantly faster then a second grinding pass. In addition, unit
costs are substantially reduced because of the straightening.
Considering the fact that camshafts are always required in
relatively high numbers, unit costs play a significant role in
terms of the efficiency of the method. Surprisingly, it has now
been demonstrated that very good results can be attained in the
relatively brief period of 5 to 15 seconds in terms of improving
concentricity properties compared to concentricity properties that
can be attained with conventional technologies.
[0021] In accordance with the second and the third aspect of the
invention, the finish-grinding occurs on a first grinding machine
and the rough-grinding and finish-grinding of the cams occur on a
second grinding machine. In each case, the method is at least
partially realized on at least one grinding machine such that one
grinding process and one straightening process are performed on
this grinding machine. This can be straightening of the camshaft
after the bearings have been finish-ground on the first grinding
machine. However, this can also be straightening after the cams
have been rough-ground and/or finish-ground on the second grinding
machine. However, it is also possible for straightening to occur
both on the first grinding machine after the bearings have been
finish-ground and after the rough-grinding and/or finish-grinding
on the second grinding machine.
[0022] In accordance with another aspect of the invention, for
grinding bearings and cams of an assembled camshaft and for
straightening such an assembled camshaft, and specifically in
particular for performing the method according to the corresponding
method claims, in accordance with the invention the apparatus has a
grinding machine that is provided with a straightening device for
straightening the camshaft after a corresponding grinding process
and preferably is also provided with a concentricity measuring
device for measuring the concentricity or the concentricity
deviation of the camshaft. The concentricity measuring device, if
one is present, and the straightening device are inventively
integrated into the grinding machine. The apparatus in accordance
with the invention is a grinding machine, the actual grinding task
of which has been expanded to include a straightening process, the
concentricity measuring device preferably additionally being
integrated into this grinding machine. It is used for controlling
the straightening device, i.e. for performing the straightening
based on the measured concentricity value or the measured
concentricity deviation. It is thus possible to produce with such
an apparatus assembled camshafts whose base carrier is a hollow
shaft onto which the cams are pressed in particular in a joining
method with greater precision with respect to their concentricity
properties than is the case with the known grinding machines that
are not provided for the straightening step. It is only with the
inventive apparatus that straightening can be performed after a
grinding process within the same modified grinding machine.
Concentricity properties or deviations in concentricity properties
shall be understood to be how severely the bearing(s) deviate(s) in
the center area of the camshaft with regard to their concentricity
relative to the longitudinal axis of the camshaft from the
concentricity of the bearings at the end of the camshaft. These end
bearings are of course subjected far less to the concentricity
deviations than the bearings arranged in the center or in the
center area of the camshaft because the end bearings are each
gripped, specifically on the centers of the grinding machine.
[0023] The central part of the inventive apparatus, specifically
the grinding machine, has in a manner known per se a grinding
headstock that is borne on a machine bed and that can have two
grinding wheels that can each be pivoted into a grinding position
and that can have a workpiece headstock and tailstock received on a
grinding table. The assembled camshaft can be gripped between the
centers of the workpiece headstock and tailstock. The concentricity
measuring device is preferably on the grinding headstock or on the
grinding table and is attached in the straightening direction to
the grinding headstock.
[0024] Attaching the concentricity measuring device to the grinding
headstock or to the grinding table assures high measurement
accuracy because the measurement value is always coupled to the
grinding result obtained by the respective grinding wheel. This
also applies for the straightening device, which, by its
arrangement on the grinding headstock, assures that, in conjunction
with the highly precise measurement value for the concentricity
deviations, a straightening force can be applied correspondingly to
the camshaft and thus high precision can be attained in the
straightening process with the inventive apparatus.
[0025] In accordance with a preferred further development of the
invention, the grinding machine of the inventive apparatus has a
first station for grinding the bearings and/or rough-grinding the
cams of the camshaft and in which a straightening device can also
be provided for straightening the camshaft. Moreover, the second
station for finish-grinding the cams of the camshaft is also
provided with a straightening device. The grinding machine of the
inventive apparatus thus can have, but does not have to have, a
first station in which a straightening device can be provided. A
straightening device is preferably also provided in the second
station so that the straightening or where necessary the final
straightening of the camshaft can be performed after the cams have
been finish-ground. Naturally, in principle it is also possible to
divide the grinding process into two parts so that after the cams
have been rough-ground the straightening device is used and so that
also after the cams have been finish-ground the straightening
device provided on the second station can be used. The first
station and also the second station preferably have a straightening
device for this purpose. The grinding machine of the inventive
apparatus thus has complete flexibility. However, it is also
possible for the first station to be embodied such that the
bearings can be ground on it and the cams of the camshaft can be
rough-ground on it, the straightening device then being used either
after the bearings have been ground or after the subsequent
rough-grinding of the cams on the camshaft. Then only the
finish-grinding of the cams of the camshaft occurs in the second
station of the grinding machine of the inventive apparatus,
whereupon another straightening process, a so-called final
straightening process, can preferably follow. However, regardless
of how the grinding processes and straightening are divided between
the first and the second stations, there is preferably an attempt
to attain the required concentricity accuracy in the assembled
camshaft with a single straightening process. It is also possible
that the straightening device for the first station is not used
after the rough-grinding and only the straightening device for the
second station performs a single straightening process after the
finish-grinding of the cams.
[0026] The straightening device is preferably a roll straightening
head that is embodied such that straightening can be performed when
the camshaft is rotating. The rotation speed during the roll
straightening process performed by means of the roll straightening
head is preferably in the range of 50 to 200 revolutions per
minute. The roll straightening head preferably has rolls borne in
its forward area. "Forward area of the roll straightening head"
shall be understood to mean the area that is oriented directly
toward the area of the corresponding bearing on the camshaft to be
straightened. The roll straightening head is preferably attached to
the grinding headstock and preferably can be moved in the
X-direction toward the bearings of the camshaft. The movement of
the roll straightening head toward the bearings depends on the
concentricity deviations measured by the measuring device at the
bearing in question and thus determines the force to be exerted on
the camshaft at this bearing in order to be able to completely
perform this straightening process such that after straightening
has been performed the camshaft has the most ideal possible
concentricity, i.e., ideal concentricity properties.
[0027] It is understood that appropriate calculation and control
devices are provided for the control technology connection between
the measuring device and the straightening head, including the
appropriate actuators for converting the measured value to the
corresponding force introduced for desired bending. The measuring
is preferably not necessary when there is roll straightening. The
straightening head is embodied such that it gradually reduces,
i.e., decreases, the straightening force after the latter has been
introduced. The force that is exerted with the roll straightening
head on the appropriate bearing of the camshaft can be set high
enough that the elastic deformation range is exceeded so that a
straightening effect actually occurs using plastic deformation.
Using a gradual, thus gentle, adjustment to, i.e., reduction in,
the straightening force applied, the straightening process can be
gradually terminated during straightening while the camshaft
continues to rotate. This means it is possible to impart the
desired straightening effect to the center area of the camshaft,
which is subject to the most severe deformation.
[0028] In accordance with another preferred exemplary embodiment,
the straightening device is embodied as a pressure element
straightening head that performs the straightening while the
camshaft is stationary. During straightening performed with a
stationary camshaft, the measuring device cooperates in terms of
control technology with the straightening head via appropriate
electronic devices. First the measuring device determines the value
at which the corresponding bearing, seen in the radial direction at
the respective bearing, has the greatest out-of-true or
eccentricity and thus the greatest concentricity error. And it is
at this precise location or in this area of the greatest
out-of-time or eccentricity on the bearing of the camshaft that the
force is introduced by means of the pressure element straightening
head. This force is adjusted as a function of the measured
out-of-time or eccentricity such that the deformation goes into the
plastic range so that a lasting straightening effect is present.
The straightening head can be embodied such that this straightening
effect is attained in a single straightening process. However, it
is also possible to perform the straightening process in a
plurality of steps, whereby different forces can then be introduced
at different radial positions for eliminating the out-of-time or
eccentricity existing in the area of the bearing in question.
[0029] The pressure element straightening head is preferably
embodied as a borne prism having a recess by means of which a
certain area of the circumference of a corresponding bearing of the
camshaft can be enclosed, whereby a desired straightening force is
introduced across the circumferential area via at least two
circumferentially spaced locations of one bearing of the camshaft.
However, it is also possible to configure the prism such that
during the straightening process the two lateral flanks and the
base of the prism are positioned at the location on the
circumference of the bearing such that the straightening force is
then introduced via three locations. Matching the shape of the
prism to the diameter of the bearing to be ground in this manner
has the advantage that it enables effective straightening, in
particular when there is major out-of-time or eccentricity.
[0030] In addition, it is preferably possible that the pressure
element straightening head is a pressure element that has an
essentially flat surface for applying the straightening force. The
corresponding straightening force can be introduced via a location
on a bearing of the camshaft with the pressure element. Other
shapes are of course also conceivable instead of the flat surface
or the prism, such as for instance a curved shape, the radius of
which is greater than the radius of the corresponding bearing.
[0031] Additional advantages of and potential applications for the
invention shall now be explained in greater detail using the
description with respect to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 depicts an assembled camshaft that is chucked between
centers and the bearings of which are ground like this;
[0033] FIG. 2 depicts a camshaft that is chucked between two
centers and the cams of which are being ground;
[0034] FIG. 3 depicts an apparatus in accordance with the invention
with two stations, each for grinding and straightening the
camshaft;
[0035] FIGS. 4a through d depict the essential method steps in the
inventive method;
[0036] FIG. 5 depicts a roll straightening head of the inventive
apparatus at a bearing of the camshaft;
[0037] FIG. 6 depicts a pressure element straightening head with
swing-mounted prism during straightening at a bearing on the
camshaft;
[0038] FIG. 7 depicts a pressure element straightening head with
planar surface during straightening of a bearing; and
[0039] FIG. 8 depicts the principle of another exemplary embodiment
for the method or apparatus in accordance with the invention.
[0040] FIG. 1 is a principle depiction of the chucking of an
assembled camshaft 1, with corresponding bearings 2 and shrunk-on
cams 3, that is held between centers 14. The centers are arranged
on the workpiece headstock 12 and on the tailstock 13. The centers
14 are embodied such that they grip the ends of the tube-shaped
carrier of the camshaft in the center and at these ends attain a
corresponding clamping effect so that a torque can be transmitted
to the camshaft and so that the tension is not high enough however
that the camshaft will be deformed simply because of the clamping.
Two grinding wheels 23, 24 are depicted that are arranged on a
common grinding headstock 7 and that are moved into the grinding
position for grinding respective bearings 2 on the camshaft 1. A
steady 11 is arranged opposite the grinding wheel 23 for providing
support during the grinding process. The support of the steady 11
ensures that the grinding forces applied during grinding to the
bearing L2 of the camshaft 1 do not lead to deformation of the
camshaft. Another steady 11 is positioned at a location that is not
currently being ground. Moreover, the grinding wheel 24 is in
contact at a bearing L5. A corresponding straightening device is
not drawn in.
[0041] FIG. 1 illustrates the first method step, in accordance with
which the bearings 2 on the camshaft 1 are finish-ground first. All
of the bearings 2 must be finish-ground before a straightening
process or first straightening process can be performed.
[0042] FIG. 2 depicts a condition during the process in which the
cams are ground by grinding wheels 9, 10. The grinding wheel 9
rough-grinds the cams and the grinding wheel 10 finish-grinds the
cams. Steadies 11 support the bearings. The grinding wheels 9, 10
are embodied such that pairs of cams that enclose a bearing between
them are ground simultaneously. Analogous to FIG. 1, the camshaft 1
is also received between centers 14 of the workpiece headstock 12
and the tailstock 13. A chuck 28 is attached to the workpiece
headstock for radially carrying the camshaft 2.
[0043] FIG. 3 depicts an apparatus in accordance with the invention
in which the grinding machine comprises a first station 15 and a
second station 16. In the first station 15, a camshaft 1 is gripped
on centers between a workpiece headstock 12 and a tailstock 13.
Gripping is performed via centers 14 on the workpiece headstock 12
and on the tailstock 13. Steadies 11 are moved to bearings of the
camshaft 1 for supporting the latter. The steadies 11 can be moved
to the respective bearing for support using a displacement in the
X-direction. A grinding headstock 7 is arranged on a machine bed 8
opposing the steadies 11. The grinding headstock 7 can be pivoted
and there are two spindles, of which a first spindle bears a first
grinding wheel 9 and a second spindle bears a second grinding wheel
10. Pivoting the grinding headstock 7 pivots the respective
grinding wheels 9, 10 into the grinding position for grinding the
bearings. The bearings are finish-ground in the first station
15.
[0044] Arranged on the grinding headstock 7 is a concentricity
measuring device 5 that can be moved into a measuring position in
the center area of the camshaft by pivoting the grinding headstock
7. After the concentricity measuring device 5 has been pivoted into
its measuring position, it determines at a bearing to be measured
the bearing's concentricity properties or the deviation from ideal
concentricity. For purposes of ease of understanding, the
straightening device is only drawn in schematically at the first
station 15. The concentricity measuring device 5 controls the
straightening device based on the measured values for the
concentricity of the measured bearing in the center area of the
camshaft such that with it a force is introduced to the camshaft
after the steadies 11 have been moved out of their supporting
position for the bearings such that the camshaft is straightened
and thereafter has improved concentricity properties. The forces
introduced are high enough that the camshaft is brought closer to
or even into its ideal concentricity properties by means of a
lasting plastic deformation. The straightening preferably occurs
after the finish-grinding process for the bearings in the first
station 15 has concluded, specifically in the same chucking, and
lasts approx. 5 to 15 seconds. This is especially advantageous in
particular for large numbers of units in mass production as is the
case for camshafts.
[0045] In principle, however, it is possible to omit a
straightening process after the bearing grinding in the first
station 15 if the straightening is performed after the
rough-grinding or finish-grinding in the second station 16. The
advantage of straightening at the end of the finish-grinding
process for the cams is comprised in that it is then also possible
to use the straightening to eliminate the deformations that occur
because during grinding of the hardened surfaces of the cams
tensions are released that can contribute to deformations on the
entire camshaft. The basic structure of the second station 16 is
the same as that of the first station 15, the first station 15 and
the second station 16 being combined into a single grinding machine
4. This is a conventional modular structure, so that the advantage
of the inventive apparatus is particularly noteworthy because as a
rule the straightening occurs in the same chucking as the
respective grinding process. The second station 16 also has a
grinding headstock 7 that is borne on a machine bed 8. The grinding
headstock 7 has two spindles for each grinding wheel 9, 10.
Provided on the grinding headstock 7 in the area of the grinding
spindle for the grinding wheel 10 is a concentricity measuring
device 5 that is arranged such that when the grinding wheel 10 is
pivoted into its grinding position for finish-grinding the cams the
concentricity measuring device 5 can be moved to a bearing in the
center area of the camshaft. Measuring the bearing in the center
area of the camshaft is especially sensible and necessary because
that is where the distortion of the camshaft is the most severe.
For reasons of simplicity the straightening device is also only
drawn in schematically here in the second station 16, as well.
Naturally this concentricity measuring device 5 is also connected
via a control device (not shown) to the straightening device in
order to be able to determine the straightening force corresponding
to the shaft distortion and in order to be able, after applying
this straightening force, to remove the straightening device from
straightening contact with the camshaft while gradually reducing
the force applied.
[0046] The camshaft 1 itself is held between centers 14 in a chuck
28 of the workpiece headstock 12 on the one side and in a
corresponding center 14 of the tailstock 13 on the other side. The
camshaft 1 itself is supported at its bearings by one of the number
of steadies 11 corresponding to one of the number of bearings. In
addition, a dressing device 25 is arranged in the second station 16
for dressing the grinding wheels 9, 10.
[0047] FIGS. 4(a) to 4(d) are depictions of the camshaft 1 held
between centers 14 for different method steps that are performed in
the inventive apparatus. The camshaft 1 held between centers 14 is
supported at its bearings 2 by means of steadies 11 located between
cams 3 (FIG. 4a). The bearings 2 have already been finish-ground so
that the steadies 11 have been moved supportively against the
finish-ground bearings on the camshaft 1. The cams 3 are
rough-ground in this supported condition. What the support with the
steadies 11 attains is that, despite applying the grinding forces
to the cams 3, during grinding of the cam shape the deformation of
the camshaft 1 due to the grinding processes is limited.
[0048] After the cams 3 have been rough-ground, in accordance with
FIG. 4b) the steadies 11 are removed from contact with the camshaft
1. The camshaft 1 chucked between centers 14 is rotating and during
its rotation is measured by means of the concentricity measuring
device 5 for its concentricity or for deviations from
concentricity. This measurement is made at the center-most bearing
of the camshaft because it is here that the expected concentricity
deviation is greatest.
[0049] After the concentricity measuring device 5 has determined
the value for the concentricity deviation at the center-most
bearing, a signal corresponding to the measured value is fed to a
control device for the straightening device 6. With the steadies 11
no longer in contact, the straightening device 6 is moved to the
center bearing of the camshaft 1 based on this signal that reflects
the concentricity deviation. The force introduced to the camshaft 1
by means of the straightening device 6 is selected such that it is
greater than the yield point of the material of the camshaft in
order to attain a lasting deformation, including the desired
straightening effect. The deformations that occur as a result of
introducing grinding forces and as a result of the inner tensions
released during grinding are compensated by the straightening. The
concentricity measuring device 5 is preferably not used when roll
straightening is used.
[0050] When the straightening process in accordance with FIG. 4c)
has been performed after the cams have been finish-ground, which is
performed for instance in the second station 16 of the grinding
machine 4 (see FIG. 3), then FIG. 4a) depicts the condition in
which the finish-grinding of the cams, with simultaneous support of
the appropriate bearings by steadies 11, occurs or has already
concluded. In this case, after the straightening process in
accordance with FIG. 4c) has concluded, the camshaft is finished
with the greatest precision in terms of its concentricity
properties and can be removed from the grinding machine 4 or from
the second station 16 of the grinding machine 4.
[0051] If the processes depicted in accordance with FIGS. 4a)
through 4c) apply to a case in which the cams have first been
rough-ground, whereupon the straightening occurs, it is naturally
necessary to perform another method step with the inventive
apparatus. This is depicted in FIG. 4d), in which the steadies are
again moved against the corresponding bearings so that the
finish-grinding process for the cams 3 can then take place. The
actual grinding processes and the grinding wheels are not shown in
FIG. 4 for the sake of clarity, since the principle of the
structure of the grinding machine can be seen in FIG. 3. Naturally
a straightening process in accordance with FIG. 4c) can follow the
finish-grinding of the cams 3 in accordance with FIG. 4d).
[0052] FIG. 5 depicts an exemplary embodiment for a straightening
device for a case in which for straightening the camshaft is
received between the centers 14 of the workpiece headstock 12 and
the tailstock 13 and is rotationally driven during straightening.
For this, the straightening device is embodied as a roll
straightening head 17 that has two borne rollers at its forward
end. This roll straightening head 17 with its borne rollers 18 fits
the contour of a camshaft 1 in the area of its bearings. The
straightening device can be moved in the X-direction toward the
camshaft so that when the camshaft 1 rotates and the roller
straightening head 17 simultaneously applies pressure with is
rollers 18, the camshaft can be deformed such that it is subjected
to pressure beyond the yield point of its material. The
straightening forces are thus introduced into the camshaft 1 via
the rollers 18, which also rotate with the rotation of the
camshaft, at the locations where the rollers 18 contact the
respective bearing. After the maximum straightening force has been
introduced into the appropriate area of the bearing of the camshaft
1, the bend in the workpiece is then reduced by gradually
withdrawing this roll straightening head 17 to a bend value of 0 mm
for the workpiece. Rotationally symmetrical shafts can be
straightened relatively quickly and certainly using this roll
straightening process. In particular, this method can also be
employed on the grinding machine 4 of the inventive apparatus
because it is very rapid. Such a roll straightening method lasts
approx. 5 to 15 seconds. This is significantly shorter than a
second grinding process that would otherwise have to be performed
and with which the concentricity properties that are attained using
the inventive apparatus or the inventive method still could not be
attained.
[0053] FIG. 6 depicts another exemplary embodiment of a
straightening device. In this case it is a straightening device
that is suitable for a pressure straightening method. Such a
pressure straightening method takes place when the shaft is
stationary. In this case, first the concentricity or the deviation
from concentricity is measured at the center bearing of the
camshaft or at a bearing in the center area of the camshaft. Using
this measurement, the "highest point" in the bearing circumference
is measured in order to be able to determine the radial position at
which this maximum concentricity error occurs. With this pressure
straightening process, the camshaft 1 is now bent against its
maximum deflection such that this maximum deflection is eliminated
as completely as possible. This straightening process can also
occur in the chucking of the workpiece between the centers, whereby
after determining the maximum deflection, i.e. the maximum
concentricity error, the camshaft is rotated radially such that a
pressure element straightening head 19 is placed in the X-direction
in this area of the circumference of the corresponding bearing of
the camshaft 1 against the camshaft such that an appropriate
straightening force can be exerted against the latter. The pressure
element straightening head 19 has at its forward side a borne prism
20 that has a recess 21 so that a circumferential area of the
bearing of the camshaft 1 can be enclosed or received. The
straightening force is thus introduced into the recess 21 of the
borne prism 20 via two, where necessary even three, contact
areas.
[0054] In accordance with another exemplary embodiment for a
pressure element straightening head 19 is depicted in FIG. 7. The
pressure element straightening head 19 is provided with a pressure
element that has a flat or spherical (not shown) surface via which
the force is introduced into the area of the appropriate bearing.
Analogous with the exemplary embodiment in accordance with FIG. 6,
the straightening force is also introduced at the location in the
appropriate bearing of the camshaft 1 at which the greatest
deflection, i.e. the greatest concentricity error, occurs. In this
straightening method in accordance with FIGS. 6 and 7, the camshaft
is thus "bent" by a certain value against the highest
circumferential point in order to be able to compensate the
existing concentricity error. The workpiece is stationary during
straightening. The camshaft here is merely rotated via the C-axis
into the radial position required for straightening, but then is
held still in order to perform the straightening process.
[0055] These straightening methods are also suitable for
straightening a camshaft such that the shaft is supported by
steadies at the two outer bearings, instead of being held between
centers. In such a case, the center steady 11 can be removed from
contact so that the appropriate straightening device 6 or 19, 22
can be placed in contact with the center-most bearing of the
camshaft for straightening the latter. This is depicted in
principle in FIG. 8. Such a straightening process is primarily
frequently advantageous when the camshafts are to be ground in a
"centerless" manner prior to cam shape grinding.
[0056] In both straightening methods, the straightening device is
arranged on the grinding headstock and is preferably moved via the
X-axis. The movement values are determined during both
straightening methods using the camshaft geometry, the material,
and also the gripping of the machine and also by the hardness of
the cam surfaces. The movement values can be calculated in the
machine CNC control, specifically with respect to the previously
measured concentricity error. After straightening, concentricity
errors of up to less than 0.01 mm can be attained on the center
bearing. CBN grinding wheels are preferably used for grinding.
Legend
[0057] 1 Camshaft [0058] 2 Bearing [0059] 3 Cam [0060] 4 Grinding
machine [0061] 5 Concentricity measuring device [0062] 6
Straightening device [0063] 7 Grinding headstock [0064] 8 Machine
bed [0065] 9, 10 Grinding wheels [0066] 11 Steadies [0067] 12
Workpiece headstock [0068] 13 Tailstock [0069] 14 Centers for
gripping [0070] 15 First station of grinding machine [0071] 16
Second station of grinding machine [0072] 17 Roll straightening
head [0073] 18 Swing-mounted rollers [0074] 19 Pressure element
straightening head [0075] 20 Recess [0076] 22 Pressure element
[0077] 23, 24 Grinding wheels [0078] 25 Dressing devices [0079] 28
Chuck
* * * * *