WO2008076060A1

WO2008076060A1 - Method and medium for generating contact pattern images, and vehicle

Info

Publication number: WO2008076060A1
Application number: PCT/SE2007/050953
Authority: WO
Inventors: Johan TRÄFF
Original assignee: Scania Cv Ab (Publ)
Priority date: 2006-12-18
Filing date: 2007-12-07
Publication date: 2008-06-26
Also published as: SE530694C2; SE0602711L

Abstract

The invention relates to a method for generating contact pattern images of bevel gears, which gear comprises a crownwheel with teeth and a pinion with teeth, which method comprises the steps of applying a contact pattern image medium to the flank of at least one tooth, bringing the crownwheel and the pinion into mutual tooth engagement and rotating the crownwheel and the pinion in such a way that during said tooth engagement the medium applied to the flank is acted upon so that a contact pattern image is created, said medium comprising a flat means, e.g. tape, with a contact pattern image side and an adhesive side which faces towards the flank. The invention also relates to a medium intended for generating contact pattern images of bevel gears. The invention relates also to a vehicle comprising a bevel gear manufactured on the basis of contact pattern images generated with a contact pattern image medium.

Description

METHOD AND MEDIUM FOR GENERATING CONTACT PATTERN IMAGES,

AND VEHICLE

TECHNICAL FIELD

The invention relates to a method for generating contact pattern images of bevel gears according to the preamble of claim 1. The invention also relates to a medium for generating contact pattern images of bevel gears according to the preamble of claim 10, and a vehicle according to claim 18.

BACKGROUND

Bevel gears are used for power transmission to forward and rear axles of vehicles, e.g. trucks. Such gears take in principle the form of two components, a driving pinion and a crownwheel. The manufacture of these gears involves machining of the teeth on the crownwheel and the pinion in two stages. The first stage is soft machining in which the teeth are cut. After soft machining, the teeth are case-hardened. After the hardening, the teeth are machined by so-called lapping. Lapping involves a pinion being clamped against a crownwheel, the teeth being thereafter brought into engagement while at the same time lapping fluid is supplied. The fact that the crownwheel and the pinion are ground against one another results in the approval of the gear as a pair. It is therefore not possible to measure the pinion and the crownwheel each individually after the lapping, so they cannot be parted after the lapping but form a pair which has to be followed to final assembly. An alternative to lapping is so-called tooth grinding, a method which entails the crownwheel and the pinion each being ground individually to given tolerances.

The manufacture of such gears involves carrying out so-called contact pattern image tests at various phases of production. The contact pattern image test method comprises mainly the following steps. The first is to apply to a number of flanks of the crownwheel a stable dye, a contact pattern image dye. The second step, when the crownwheel and the pinion have been brought into mutual engagement, is to rotate them for a specified number of turns so that the dye on the flanks is rubbed off at the tooth contact. The third step is to evaluate the contact pattern image by making an imprint of it on tape. The image indicates where the load on the teeth is during operation. The test makes it possible to check that the mutual engagement of the teeth causes uniform load on the teeth as revealed by an image showing where the dye applied is rubbed off during engagement. The operator assesses whether the image has the correct positioning, shape and size according to specific guidelines for the particular case.

The soft machining may include a rolling test which is prepared for by the crownwheel being clamped in a test machine against a master pinion. After checking that the tooth clearance conforms to specified tolerances, tooth flanks on a number of teeth are coated with a stable dye, followed by the crownwheel and the pinion being brought into mutual engagement and by assessment of the resulting image.

Lapping also involves contact pattern image tests. The lapping of each new batch of gears requires resetting of a lapping machine. The relevant input data are obtained by running a crownwheel and a pinion against one another in a test machine. The resulting image is compared with an ideal image. On the basis of the operator's experience, the parameters of the lapping machine can then be set to shift the image to the desired position. When the operator has set the machine for the first gear, the same settings are thereafter used for the whole batch. For each batch made, image imprints are made on tape and are thereafter compared with the imprint made in the image test during the soft machining.

The lapping of gears is followed by washing off the lapping medium, which would otherwise cause premature gear wear, and by a final image check on every gear. If the image of a gear is not approved, the operator may try shifting the pinion sideways with a view to achieving a better result. If the correction is sufficient, the new position of the pinion is noted and the information passed on to final assembly. If the correction is not sufficient, i.e. if the image is not correct, the gear has to be machined again in the lapping machine.

Fitting the pinion involves applying the adjustment dimensions arrived at during the lapping. To achieve the correct dimensions, adjusting washers known as shims are placed between the gear housing and the pinion.

When the gear housing has been fully assembled, the contact pattern image is checked again. If it is approved, the gear housing is packaged for delivery to rear axle assembly. If the image is not approved, the operator may try adding or removing shims.

The lapping technique and the associated contact pattern image testing is a manual method with results which depend greatly on operator skill and experience. When the lapping machine is rigged, the operator assesses, on the basis of where the image is situated, how to set the machine so that the image after lapping will be in the right position. Rigging may take an inexperienced operator considerably more time than an experienced one, and when the process is underway the cycle time may vary depending on how much material has to be removed and exactly where on the teeth. As the time spent on lapping machines varies both with operator and with input material, it is difficult to calculate the capacity of these machines. Current practice is that the production manager assesses how many gears the operators should be able to produce per shift and indicates this as the capacity. There can be therefore no clear measure of the effectiveness with which resources are actually used.

Since lapping does not remove material to known geometries, contact pattern images are used as a means of verification. The operator decides, entirely on visual assessment, whether a gear has completed its lapping and is acceptable. This means that three different operators have to assess images and take decisions, one in the rig test at the cutting stage, one in the test on completion of lapping and one in the final test. It may therefore happen that an image found acceptable by one operator is rejected by another. Contact pattern image tests are also done during tooth grinding, since the best way of ensuring tooth quality is to test the engagement between crownwheel and pinion. As tooth grinding provides assurance that the crownwheel and the pinion will be identical each time, there is no need for each individual gear to be tested and spot checks will be sufficient. Nor is it necessary in tooth grinding for wheels and pinions of corresponding orders to be rolled against one another, since master wheels and pinions can be used.

Thus the disadvantages of contact pattern image testing as currently performed include the lack of any certain measure of image quality, since the basis of assessment may differ from person to person. It may be very difficult to make a correct assessment of an image, so making a proper assessment requires a great deal of experience. Assessment by an inexperienced person also takes more time, thereby reducing manufacturing capacity. Assessment by various different persons at different stages of production entails unsatisfactory results in terms of gear quality and the possibility of longer production times due to incorrect assessments, with consequently greater costs. If incorrect assessments are made in earlier image tests, the final image test during final assembly may in the worst case have to be repeated. If such an error is not detected by the image test during final assembly, a defective gear may be approved, which may lead to vehicle breakdown in operation.

OBJECT OF THE INVENTION

An object of the present invention is to provide a method for generating contact pattern images of bevel gears which provides an increased amount of, and more objective, information about tooth contact in gears.

Another object of the present invention is to provide a medium intended for generation of contact pattern images of bevel gears which provides an increased amount of, and more objective, information about tooth contact in gears. SUMMARY OF THE INVENTION

These and other objects indicated in the description set out below are achieved with a method, a medium and a vehicle as above which further exhibit the features indicated in the characterising parts of the attached independent claims 1, 10 and 18. Preferred embodiments of devices according to the invention are defined in the attached dependent claims 2-9 and 11-17.

An increased amount and more objective information about tooth contact in gears is provided by a method for generating contact pattern images of bevel gears which comprise a crownwheel with teeth and a pinion with teeth, which method comprises the steps of applying a contact pattern image medium to the flank of at least one tooth, bringing the crownwheel and the pinion into mutual tooth engagement and rotating the crownwheel and the pinion in such a way that during said tooth engagement the medium applied to the flank is acting upon in such a way as to create a contact pattern image, said medium comprising a flat means, e.g. tape, with an image side and an adhesive side which faces towards the flank. The possibility of obtaining a correct assessment of the image is improved. The image becomes easier to analyse, since the image means may have a predetermined shape/thickness, causing the results to be the same, unlike an applied dye, the thickness of which may vary on each occasion.

Moreover, the actual image means analysed and archived is not a tape imprint, thereby improving the quality of assessment. With better quality of images, less experience is needed for assessing them, thereby reducing the risk of incorrect assessment. The quality of manufacture of bevel gears is thus improved.

The means is preferably stuck removably to the flank. With removable image means, analysis can be carried out unhurriedly and no assessment need be done immediately on the crownwheel flank at the time of testing.

The image means preferably has on its non-adhesive side a preprinted pattern, e.g. a system of coordinates for evaluation of images. The advantage of this is to provide a measured value, thereby substantially eliminating the need for experience, since corrective settings can be effected on the basis of the measured value obtained.

The image means is preferably configured to substantially cover a flank of a crownwheel tooth. This affords the advantage of having different versions of the means for different types of gears and gear combinations, i.e. the means for respective versions being dimensioned to substantially cover the flank of the intended type of gear, thereby making it possible for a region, e.g. an elliptical or similar desired image region, to be predefined on the image side, adapted to the specific gear so that if the image produced by image test falls within that region the gear is approved. Image test assessment is thus further simplified.

The means preferably comprises at least two layers. With a plurality of layers, they may take the form of different layers. The uppermost layer may be capable of being rubbed off and the lower layer may be of a different colour so that a clear image can be obtained. A plurality of layers makes it possible to assess the load by seeing not only the surface affected but also how deep the stripping-off is, i.e. how many layers are stripped off, thereby further improving the quality.

The method preferably comprises the step of applying to the pinion, before the crownwheel and the pinion are brought into engagement, a contact pattern image dye transferable to the image means. The result will be a coloured image, i.e. it is the image which will be coloured and not the region round the image as in the state of the art. The result is a clearer image. For example, configuring the surface of the uppermost layer in such a way that it is suitable for receiving a dye results in a coloured image, thereby improving the quality of assessment. It is also possible for the surface of the first layer to be capable of being rubbed off and the surface of the second layer to be adapted to receiving a dye, thereby likewise providing a high-quality image.

The method preferably comprises the step of taking the image means away for archiving. The image means makes it possible to archive the actual image and not a tape imprint of it. The result is archiving of the exact image with measured values set against a system of coordinates or the like. The result is a basis of experience showing exactly what the contact pattern image of a batch of gears looks like, and should the particular batch, for example, fail, there will be archived measured values to show why.

The means preferably comprises a tab which, when the means is stuck to the flank, protrudes so as to make the means easy to remove.

An increased amount of, and more objective, information about tooth contacts in gears is provided by a medium intended for generating contact pattern images of bevel gears which comprise a crownwheel with teeth and a pinion with teeth, which medium is adapted to being applied to the flank of at least one tooth and to being acted upon so that a image is created when the crownwheel and the pinion are brought into mutual tooth engagement and are rotated, said medium comprising a flat means, e.g. tape, with an image side and an adhesive side which is intended to face towards the flank. The possibility of obtaining a correct assessment of the image is improved. The image becomes easier to analyse, since the image means may have a predetermined shape/thickness, causing the results to be the same, unlike an applied dye, the thickness of which may vary on each occasion. Moreover, the actual image means analysed and archived is not a tape imprint, thereby improving the quality of assessment. With better quality of images, less experience is needed for assessing them, thereby reducing the risk of incorrect assessment. Using the contact pattern image means thus improves quality of manufacture of bevel gears.

Further advantages and embodiments are indicated by the detailed description.

DESCRIPTION OF THE DRAWINGS

The present invention will be better understood by reading the following detailed description together with the attached drawings, in which the same reference notations denote the same parts throughout the various views, in which: Fig. 1 depicts schematically a plan view of a bevel gear.

Fig. 2 depicts schematically a portion of a crownwheel with a contact pattern image on a tooth flank according to the state of the art.

Fig. 3 depicts schematically a contact pattern image tape according to a preferred embodiment of the present invention.

Fig. 4 depicts schematically a portion of a crownwheel with contact pattern image tape according to Fig. 3 applied to a tooth flank.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the application, bevel gear means bevel gears, hypoid gears and similar gears for which contact pattern image tests are possible. Contact pattern image means an image which indicates visually where the load on gear teeth is during operation. Various characteristics such as durability, effectiveness and noisiness of gears affect the region where there is load on teeth, which is where the contact pattern image needs to be.

Fig. 1 depicts schematically a plan view of a bevel gear 1 comprising a gear housing 2 and a truncated conical crownwheel 3 which is accommodated in said gear housing, is rotatable about a halfshaft 4 and is adapted to being supported by differential bearings 5a, 5b. The bevel gear further comprises a truncated conical pinion 6 which is rotatable about a shaft 7, said shaft 7 being substantially perpendicular to the halfshaft 4 in such a way that the crownwheel and the pinion are brought into mutual engagement, said pinion being supported by a pinion bearing 8. As illustrated by the arrows A and B, it is possible, with a view to achieving optimum contact pattern images during gear manufacture, to adjust the crownwheel 3 and the pinion 6 relative to one another by using an adjustment means to move the crownwheel in its axial direction 4 according to the arrow A and/or the pinion in its axial direction 7 according to the arrow B.

Fig. 2 depicts schematically a portion of a crownwheel 3 showing two teeth 3a of the crownwheel. Each tooth 3a of the crownwheel has a tooth flank 3b. According to the state of the art, a contact pattern image medium in the form of a dye 3c intended for the purpose is adapted to being applied, e.g. in the same way as paint, to a number, e.g. three, of the flanks 3b of respective teeth 3a of said crownwheel 3, and to being rubbed off in such a way that a contact pattern image 3d is created when the crownwheel and the pinion are brought into mutual tooth engagement and are rotated. The contact pattern image 3d then takes the form of a portion rubbed off the dyed flank 3b as illustrated in Fig. 2.

Fig. 3 depicts schematically a contact pattern image means 10, e.g. contact pattern image tape according to a preferred embodiment of the present invention. The image means 10 takes the form of a flat means with a known, preferably uniform, thickness, e.g. tape, with a contact pattern image first side 11 and an adhesive second side 12.

The means has on the image side 11 a preprinted pattern 13 for image evaluation.

According to an embodiment, this pattern takes the form of a system of coordinates 13, an example of which is depicted in Fig. 3.

According to an embodiment, the means comprises at least two layers. The uppermost layer according to an embodiment is capable of being rubbed off. The layers according to an embodiment are preferably of different colours so that an image is made obvious by rubbing away of the uppermost layer. According to an embodiment, the surface of the uppermost layer is configured in such a way that it is suitable for receiving a dye. According to an embodiment, the image means 10 takes the form of one layer. According to an embodiment, the first layer is capable of being rubbed off and the surface of the second layer is adapted to receiving a dye. According to an embodiment, the means has more than two layers, which makes it possible to assess the load by seeing not only the surface affected but also how deep the stripping-off is, i.e. how many layers are stripped off. According to an embodiment, the image means 10 is configured with characteristics substantially like carbon paper, so that when, in cases where the means comprises a plurality of layers, the uppermost layer is rubbed it becomes coloured so that there is a clear image. These embodiments may of course be combined. The image means may be of any desired material and/or composition suitable for the purpose, e.g. some kind of polymer. In cases where there are various layers, they may be of the same or different materials and/or compositions.

Fig. 4 depicts schematically a portion of a crownwheel 3 with contact pattern image means, e.g. contact pattern image tape according to Fig. 3, applied to a tooth flank 3b of the crownwheel. The adhesive second side 12 is intended to face towards and be stuck releasably to the flank 3b. The surface of the adhesive side 12 is provided with an adhesive with suitable characteristics for the purpose, e.g. such that the means remains firmly on the flank 3b during the actual image test without risk of loosening and is thereafter easy to remove from the flank 3b for analysis and archiving.

The image means is configured to substantially cover a flank 3b of a tooth 3a of a crownwheel 3. Having different versions of the means for different gear types and combinations, e.g. so that the image means 10 in the respective version is dimensioned to substantially cover the flank 3b of the intended type of gear, makes it possible, as illustrated in Fig. 4, for a region 14, e.g. an elliptical or similar region, to be predefined on the image side 11 and adapted to the specific gear so that if in an image test the image falls within this region the gear is approved. If it falls outside this region 14, it will be easy to correct in accordance with the measured value obtained on the basis of where the image is situated in the system of coordinates 13 on the image side 11.

According to an embodiment, the means comprises a tab 15 which, when the image means 10 is stuck to the flank 3b, protrudes from the latter so that the image means 10 can easily be removed. The tab 15 is preferably numbered so that it is easy, when necessary, to see the number, 1 in the example in Figs. 3 and 4, on the respective crownwheel during measurement. This requires a corresponding marking on the crownwheel. The uppermost layer according to an embodiment is adapted to being rubbed off during tooth engagement with the pinion. According to an embodiment, the uppermost layer of the means is so arranged that during tooth engagement with the pinion it receives from the pinion a transferable contact pattern image dye applied to the pinion. These embodiments may, as previously mentioned, be combined so that the uppermost layer is rubbed away and the dye is transferred to the underlying layer.

The image side 11 of the means according to an embodiment is provided with a ring 16 which, as illustrated for example in Fig. 4, is situated at an upper corner of the means. The image side of the means according to an embodiment is further provided with a marking 17 for indexing on the teeth. The ring 16 is intended for the measuring tip of the gauge used for tooth clearance measurement, i.e. measurement of the play when the pinion is held still and the crownwheel can be moved just a little. With the assistance of the indexing marking, the image means can be applied at the same intended location on the tooth flank, thereby assuring quality of tooth flank clearance measurement. This dimension varies with the radius.

As previously mentioned, contact pattern image testing is carried out several times, first during production, which divides into two, and during the final assembly, when the crownwheel and the pinion are mounted into the gear housing.

Contact pattern image testing according to the present invention is generally carried out by a method applicable to the manufacture of bevel gears which comprises the steps of: sticking the contact pattern image means to the flank of a number, e.g. three, of the teeth of said crownwheel; - bringing the crownwheel and the pinion into mutual tooth engagement; rotating the crownwheel and the pinion a specified number of revolutions so that during said tooth engagement a contact pattern image is created by teeth of the pinion on the surface of the image means provided with a system of coordinates and applied to the flank; - removing the contact pattern image means for analysis; archiving the contact pattern image means. According to an embodiment, bringing the crownwheel and the pinion into engagement is preceded by the step of applying to the pinion a contact pattern image dye transferable to the means, which dye is transferred to the contact pattern image means during the step of rotating the crownwheel and the pinion.

In the embodiments described above, the image means is adapted to being stuck to a tooth flank of the crownwheel. Alternatively the image means may be stuck to a tooth flank of the pinion.

Claims

1. A method for generating contact pattern images of bevel gears, which gear comprises a crownwheel (3) with teeth (3a) and a pinion (6) with teeth, which method comprises the steps of applying a contact pattern image medium to the flank (3b) of at least one tooth, bringing the crownwheel (3) and the pinion (6) into mutual tooth engagement and rotating the crownwheel (3) and the pinion (6) in such a way that during said tooth engagement the medium applied to the flank (3b) is acted upon so that a contact pattern image is created, characterised in that said medium comprises a flat means (10), e.g. tape, with a contact pattern image side (11) and an adhesive side (12) which faces towards the flank.

2. A method according to claim 1, whereby the means (10) is stuck to the tooth flank (3b) of the crownwheel (3).

3. A method according to claim 1 or 2, whereby the means (10) is removably stuck to the flank (3b).

4. A method according to any one of claims 1-3, whereby the means (10) has on the contact pattern image side (11) a preprinted pattern (13), e.g. a system of coordinates

(13), for evaluation of contact pattern images.

5. A method according to any one of claims 1-4, whereby the means is configured to substantially cover the tooth flank (3b) of the crownwheel (3).

6. A method according to any one of claims 1-5, whereby the means (10) comprises at least two layers.

7. A method according to any one of claims 1-6, characterised by the step, before the crownwheel (3) and the pinion (6) are brought into engagement, of applying to the pinion (6) a contact pattern image dye which is transferable to the means (10).

8. A method according to any one of claims 1-7, further comprising the step of removing the means (10) for archiving.

9. A method according to any one of claims 1-8, whereby the means (10) comprises a tab (15) which, when the means (10) is stuck to the flank (3b), protrudes from the latter so that the means (10) is easy to remove.

10. A medium intended for generating contact pattern images of bevel gears, which gear (1) comprises a crownwheel (3) with teeth (3a) and a pinion (6) with teeth, which medium is adapted to being applied to the flank (3b) of at least one tooth, said medium being adapted to being acted upon so that a contact pattern image is created when the crownwheel (3) and the pinion (6) are brought into mutual tooth engagement and are rotated, characterised in that said medium comprises a flat means (10), e.g. tape, with a contact pattern image side (11) and an adhesive side (12) intended to face towards the flank (3b).

11. A medium according to claim 10, whereby the means (10) is configured to be stuck to the tooth flank (3b) of the crownwheel (3).

12. A medium according to claim 10 or 11, whereby the means (10) is configured to be removably stuck to the flank (3b).

13. A medium according to any one of claims 10-12, whereby the means (10) has on the contact pattern image side (11) a preprinted pattern (13), e.g. a system of coordinates (13), for evaluation of contact pattern images.

14. A medium according to any one of claims 10-13, whereby the means (10) is configured to substantially cover the tooth flank (3b) of the crownwheel (3).

15. A medium according to any one of claims 10-14, whereby the means (10) comprises at least two layers.

16. A medium according to any one of claims 10-15, whereby the means (10) is adapted to receiving from the pinion (6) a transferable contact pattern image dye applied to the pinion (6).

17. A medium according to any one of claims 10-16, whereby the means comprises a tab (15) which, when the means is stuck to the flank (3b), protrudes from the latter so that the means (10) is easy to remove.

18. A vehicle comprising a bevel gear (1) manufactured on the basis of contact pattern images generated by a medium according to any one of claims 10-17.