jabatan kejuruteraan mekanikal jj513

8/11/2019 Jabatan Kejuruteraan Mekanikal Jj513

1/12

JABATAN KEJURUTERAAN MEKANIKAL

POLITEKNIK KUCHING SARAWAK KM 22, JALAN MATANG, BEG BERKUNCI 3094

93050 KUCHING, SARAWAK

ENGINEERING DESIGN

JJ513

Student Name Mohd Sabaruddin Bin Mohd SallehZulaihi Kho Bin Haslim

Matrix No. 05DTP12F104905DTP12F1019

Program DTP4A - S1Subject (Code) JJ513


2/12

2

LIST OF CONTENTS

Title Page

PRODUCT 3 ANALYSIS 4SUGGESTION 10CONCLUSION 11REFRENCES 12


3/12

3

PRODUCT

BALL BEARINGSHELICAL GEARS

DRIVE SHAFT

Helical gear is a cylindrical shaped gear withhelicoid teeth.Helical gears operate with less noise andvibration than spurgears. At any time, the load on helical gears isdistributed overseveral teeth, resulting in reduced wear. Due totheir angularcut, teeth meshing results in thrust loads alongthe gear shaft.

This action requires thrust bearings to absorbthe thrust loadand maintain gear alignment. They are widelyused in industry.A negative is the axial thrust force the helixform causes.

Ball bearings are the mostcommon and most used type ofbearing found in a number ofobjects. Also known as anti-frictionbearings, ball bearings are smallmetallic or ceramic spheresused to reduce friction betweenaxles and shafts in numerousapplications. These bearings are

able to handle both thrust andradial loads, and are used forapplications where the load isrelatively small. Load in a ballbearing is transmitted from theouter surface to the ball, and fromthe ball to the inner surface.Since the ball is spherical inshape, it contacts the inner andouter race at a very small point,which helps it spin evenly andsmoothly. But the contact areaholding that load is very small, soif the bearing isoverloaded then the balls candeform, ruining the bearing. Ballbearings are often used inindividual cages to reduce frictionin axle assemblies or in a seriesto absorb the weightplaced on a moving part.

Thrust bearings are aparticular type of rotarybearing thatallow rotation betweenparts used but they aredesigned tosupport axial loads likevertical shafts for whichspherical,conical or cylindricalrollers are used. Theyare used ingearsets like in cartransmissions betweengears andbetween the housingand the rotating shafts.Thrust bearings are of

different varieties. Ballthrust bearingsare composed of ballbearings supported in aring. They areused in low thrustapplications where theradial load is very small.Thurst roller bearingsaremade of small taperedrollers arranged so thattheir axes converge at apoint on the axis of

THRUST BEARINGS

Support the gears and

bearings.


4/12

4

ANALYSIS

Tooth root optimisation of Powder Metal gears reducing stress from bendingand transient loads

A paper presented by Anders Flodin and Michael Andersson (Hgans AB) examinedthe concept of redesign of the tooth root geometry of PM gears to reduce bendingstresses.

In conventional gear cutting using a hob, there are significant restrictions on the range oftooth root radii that can be generated with the root being a function of the trochoidmovements of the hub flutes, gear rotation and the geometry of the tip of the hub.

PM manufacture, on the other hand, offers much greater freedom in designing toothroots to reduce bending stresses.

Fig. 1 Root geometries compared [1]

In this study, the following root geometries, as depicted in Fig. 1, were compared:

Original 1.99mm (as given by a hob tip radius = 0.8 mm)

Full radius

Optimised curve shape.

Asymmetric gear tooth


5/12

5

Finite element modelling has compared these root geometries in terms of peak stressesin the root (see Fig. 2 and Table 1).

Fig. 2 Tooth root stresses, static analysis, a) original, b) max radius, c) optimizedand d) asymmetric.Note, same stress scale for all geometries [1]

Table 1 Peak stress in tooth root [1]

It has been demonstrated that it is possible to reduce root stress in a gear toothby replacing the cut trochoid root shape with a curve shape defined by a spline that is


6/12

6

designed, iteratively, to reduce root stress. It is also possible to manufacture a gear withthis root shape in mass production using PM manufacturing technology.

Where contact stress cannot be kept within the allowable stress levels, asymmetricgearing can also be introduced, with the challenge here being to balance stresses and

NVH (noise, vibration and harshness) when driving on the coast side of the gear.

Automotive transmission design using full potential of Powder Metal

A second paper, by Anders Flodin (Hgans AB) and Peter Karlsson (Vicura AB),described a particularly ambitious programme, in which the design of a specificautomotive transmission is being assessed in detail and the viability of incorporation ofgears, manufactured by PM, in this transmission without sacrificing performance is beingevaluated.

The transmission, chosen for this programme, was a 6-speed manual gearbox, used byGM in the Opel Insignia model, with a 4-cylinder turbocharged 2-litre engine delivering220hp/320Nm, and in other GM vehicles.

The 1st, 2nd and reverse drive gears are machined directly into the shaft of the gearboxand therefore could not be considered as candidates for replacement by PM. All othergears in the transmission the reverse idler, the 1st and 2nd driven gears and bothdrive and driven members for 3rd, 4th, 5th and 6th gear were, however, evaluated aspotential PM targets.

The methodology adopted in this programme began with a system analysis. This

comprised disassembly of the gearbox, while recording pull-off forces for gears andbearings and measuring axial play in the system.

The housing was scanned and imported into FE software. Shafts and gears weremeasured, modelled and assembled into the housing.

An essential part of a system analysis is the bearing stiffness. The bearingrepresentation in this system model was reduced to define the stiffness between twonodes, representing the inner ring and the outer ring, due to the fact that this bearingstiffness is strongly nonlinear and depends on both bearing design and loaddirection/magnitude.

Simplified modelling techniques, in order to save calculation time, were used for bolts,roller bearing contact between gears and shaft as well as gear to gear contacts in thesystem analysis where the focus is on deformation of housing, shafts and bearings.

The output from the system analysis was gear misalignment and transmissiondeflections, which were used as input to the gear analysis where the micro geometrywas adjusted to provide the best working behaviour of the gears, considering themisalignment and bending from shafts and bearings.


7/12

7

Fig. 3 Transmission error for first gear in the investigated M32 transmission [2]

The influence of these micro geometry adjustments on peak to peaktransmissions error (TE), a parameter that describes the quality of the mesh cycle of twogear flanks, is shown in Fig. 3. It is desirable to keep TE as low as possible. The greencurve is for the copied PM gear with the steel flank design. This curve is higher thanthe original machined steel gear (red curve) for all torques, because of the lowerstiffness of the PM material compared with the solid steel. The result from the designiterations to improve TE for the optimised PM gear is shown in the blue curve, whereTE is lower for every torque level and is likely to perform significantly better than the PMgear with the copied design.

A typical European consumer usage duty cycle was used to evaluate gear life. Misalignment data was taken from the system analysis and was accounted for in themicro geometry of the tooth flanks. Abuse load was 6500Nm on the differential cage,based on measured vehicle data.

The working behaviour of the gears in the system were modelled for 50%, 100%, 150%and 200% load and a range of temperatures, in order to assure the functionality underdifferent conditions.

Initially, all PM gears were modelled as being sintered and case hardened Astaloy85Moproducts at a density level of 7.25 g/cm 3, using the material data shown in Table 2.

Table 2 Material data for PM [2]


8/12

8

For this particular transmission, it has been demonstrated that the reverse idler gear andthe 3rd and 4th gear pairs can be made with the shortest possible manufacturing routethat gives 7.25 g/cm 3 density.

For the 5th and 6th gear pairs, it was identified that a double press/double sinter processto increase density to 7.4 g/cm 3 or the application of post-sintering operations, such asshot peening or super-finishing, would be necessary to increase performance.

Fig. 4 Loads on 6th gear pair with correlating S-n curves for case hardenedAstaloy85Mo PM gears with ISO 7 or better tolerances [2]

The durability of the 6th gear pair, manufactured using Astaloy85Mo at 7.25 g/cm 3, ispresented in Fig. 4. It can be seen from this figure that tooth root bending fatigue waswithin acceptable limits but that contact stress on the gear flank was a little too high.These gears, therefore, would require an increase in performance to qualify; hence, theneed for the processing variants proposed above.

The first and second driven gears would need either the application of surfacedensification or more radical redesign.

The gear redesign in the GM transmission has taken both micro- and macro-geometry

into account in order to reduce weight and inertia. Table 3 summarises the weight andinertia reduction benefits achievable for the driven gears in the transmission using


9/12

9

copied PM and optimised PM concepts. Optimised redesign can remove 1.1 kg ofmass.

Table 3 Weight and inertia reduction for the redesigned transmission [2]

The next step in this on-going initiative will be to redesign the first and second gear pairsusing the more advanced design philosophies such as non-involute gearing andasymmetric gear teeth to be able to prototype the gear box without using anyperformance enhancing technologies such as Hot Isostatic Pressing (HIP) or other

densification technologies.

There are a few unknown factors when moving away from the traditional involute curveshape. It is quite possible to reduce the contact and bending stress, but the difficulty lieswhen the transmission error has to be kept low for both drive and coast sides in order toavoid noise problems. This will be modelled to achieve good mesh properties beforegear manufacture.

A few transmissions will then be built according to the optimised design but employingdifferent PM technologies and will be installed in a car for everyday driving as a proof of

concept. The transmissions will also be put into test rigs to test durability, noise andefficiency according to specified drive cycles.


10/12

10

SUGGESTION

Good Housekeeping is Essential

There are several sources of gearbox contamination, including those that are built-in,

internally generated, ingressed and added during maintenance. Many gearboxes operate indirty environments. Therefore, good housekeeping methods should be used duringinspections. Areas around inspection ports and other openings should be cleaned beforethey are opened. Inspectors should take care not to drop anything into the gearbox. Shirtpockets should be empty, and tools should be stored in a tool belt. Ports should never be leftopen during breaks and should be closed and secured after the inspection is complete.

Walkaround Visual Inspection

You should perform a thorough external examination before the gearbox inspectionport is opened. Use an inspection form to record important data that would otherwise be lost

once cleaning is completed. For example, before cleaning the exterior of the gear housing,inspect it for signs of overheating, corrosion, contamination, oil leaks and damage. Measurethe tightening torque of structural fasteners that carry significant loads such as torque armbolts. Look for evidence of movement including cracked paint or fretting corrosion atstructural interfaces. Note the condition of the fasteners and inspect load-bearing surfaces ofcomponents for fretting corrosion or other evidence of movement.

Detecting Overheating

The following are signs of overheating:

Smoke from shafts, seals or breathers

Discolored or burnt paint on housings

Water sprayed on the housing or shafts evaporates quickly, boils or crackles

Temper colors on unpainted surfaces

Melted plastic components such as shipping plugs

Low oil level in sight glass or on dipstick

Dark oil in sight glass or on dipstick and

Metal chips on magnetic plugs, chip detectors or filters (may denote gear or bearingfailure caused by overheating)


11/12

11

CONCLUSION

Gearboxes are complex mechanical devices which allow cars to operate at differentroad speeds while remaining within the rev range of the engine

Many performance cars are now fitted with 'paddle shift' style switches behind the steeringwheel which are often marketed as sequential gearboxes, however these are often not truesequential mechanisms, but simple electronic manual controls to fairly standard automatictransmissions.

Below is an introduction to some of the different transmissions which can be fitted inperformance cars:

AUTOMATIC TRANSMISSIONS WITH MANUAL CONTROL

These 'Tiptronic' style systems allow the driver to have greater control of gear selection in acar with automatic transmission by offering a 'manual mode'. This mode can be controlledusing paddle switches behind the steering wheel or by selecting a dedicated slot on thetransmission control. The more advanced versions of this system are linked to the enginemanagement controls, automatically raising the engine speed in response to a downshift andachieving the same quick, smooth gear change as heel and toe shifting allows. Even whenin manual mode, certain failsafe controls are built into the system which will prevent. forexample, the engine stalling from the revs dropping below a set limit. Good Tiptronic

systems can reduce the shift time compared to a manual transmission, but many will not.

DIRECT SHIFT GEARBOXES (DSG)

DSG gearboxes are a recent addition to the suite of technology now becomingreadily available in production cars. The idea behind DSG is to provide fast gearchanges with the longevity of a conventional automatic gearbox.

DSG is essentially a computer controlled manual gearbox complete with twoclutches which each engage a different selection of gears. The first clutch engagesthe gears 1, 3, and 5 with the even gears engaged by clutch two. The beauty of thesystem is that the computer can predict which gear you're likely to select and pre-select this (as long as it's either one up or one down). When shifting to the pre-selected gear, all the system needs to do is release one clutch and engage theother. This can be done incredibly quickly and results in lightning changes.


12/12

12

REFERENCES

Arnaudov, K., Genova, P., and Dimitrov, L. (2005). For an unified and correctIFToMM terminology in the area of gearing. Mechanism and Machine Theory, 40(9):993 1001. Campos, A. (2004). Cinemtica Diferencial de Manipuladores empregando

Cadeias Virtuais. PhD thesis, Universidade Federal de Santa Catarina. Davidson, J. K. and Hunt, K. H. (2004). Robots and Screw Theory:

Applications of Kinematics and Statics to Robotics.(Oxford University PressInc., New York).

Davies, T. H. (1981). Kirchhoffs circulation law applied to multi -loop kinematic

chains. Mechanism and Machine. Theory, 16:171 183. Davies, T. H. (1995a). Circuit actions attributable to active couplings.Mechanism and Machine Theory, 30(7):1001 1012.

Davies, T. H. (1995b). Couplings, coupling network and their graphs.Mechanism and Machine Theory, 30(7):991 1000.

Davies, T. H. (2000). The 1887 committee meets again. subject: freedom andconstraint. In Hunt, H., editor, Ball 2000 Conference, pages 1 56, TrinityCollege. University of Cambridge, Cambridge University Press.

Hsu, C. and Lin, Y. (1994). Automatic analysis of the redundant gears in

planetary gear trains. International Journal of Vehicle Design, 15(3):402 15.

jabatan kejuruteraan mekanikal jj513

Documents