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Gear box icon stick shift template vector illustration. Then the loss in efficiency due to excess or inadequate lubrication is analysed. The final pages look at different types of lubricant used in gear drives. Chapter 4. This chapter is dedicated to all the various forms of gear failure that can be encountered by the engineer where gear trains are concerned. In the examination of the failures, the varying reasons or causes of failure, along with suggested remedies, are listed.
The factors which either individually or as a combination result in the above failures are listed, before the identification of the failures and their respective remedies.
Chapter 5. The different forms of crown wheel and pinion that are available to the designer are discussed in this chapter. The three forms are:. The differences between the three methods are discussed, together with a general description of the forces created when a pair of spiral bevel gears run together.
The movement of the tooth contact pattern as the load applied to the gear increases is also discussed. The final pages of the chapter give a brief description of, and the calculations for, the manufacturing and inspection dimensions for a pair of Klingelnberg palloid spiral bevel gears. Chapter 6. The design features, the production features and the calculation of the manufacturing and inspection dimensions for a pair of Oerlikon cycloid spiral bevel gears are given in the early part of this chapter.
The latter part advises the designer of the varying stages which are usually covered by the design, production and development departments prior to the introduction of a new transmission onto the market, and emphasizes the co-operation necessary between these departments if the product is to be successful.
Chapter 7. This final chapter covers the design of a racing-type rear engine mounted gearbox. The opening pages deal with the aims of the gearbox and the reasons for each of the aims.
Following this, the design procedures for the internal gear pack are discussed, along with the arrangements of the various shafts. This covers the location of the shafts, together with their supporting bearings.
Different layouts and bearing location methods for the crown wheel and differential are covered, as are the methods used to locate these assemblies and some of the problems that can be encountered with them. This is followed by a listing and brief description of the varying types of differential units that are used in racing gearboxes. Having discussed the in-line layout for the internal gear pack, the next few pages describe a transverse gearbox layout where the internal gear pack lies across the car chassis.
The problems of internal ratio changing with the transverse gearbox layout are discussed, along with the major problem which can affect the overall car performance, namely a simple and positive gear change system that can be fitted and adjusted so that the driver is able to make quick and totally reliable gear change movements. Following the section giving details of these problems, the advantages of using a transverse gearbox are listed, together with the practical reasons for these advantages.
This is followed by a description of the gear change systems tha t have been utilized in the past, along with the arrangements of the selector forks that give the quickest gear change movements.
As well as covering the positive location of the selector dog rings, various systems that have been used are listed. The later part of this chapter, having arrived at a preliminary design and layout for the gearbox internals, deals with the problems that can be encountered with the lubrication system and various methods that are used to cope with the high speeds and heavy tooth loads involved.
The design of the gearbox casings and the detailing of each component part ready for manufacture are given in the final pages, along with a guiding list of materials that the author used for the various components during his thirty or so years involvement in the design of Formula One racing gearboxes.
In all manual automotive gearboxes, except those designed specifically for motor racing or other uses where noise is not a problem, the crown wheel and pinion usually consists of either a pair of spiral or hypoid gears. Both the spiral and hypoid bevel gears have certain advantages over each other, all of which must be seriously taken into account when a new design of gearbox or transmission is being initiated. The ability to lap the entire tooth surface of a hypoid gear, as there is lengthwise sliding motion between the mating teeth at every point, generally results in smoother and consequently quieter running gears.
Due to the offset required in a pair of hypoid bevel gears, the crown wheel and the pinion have different spiral angles, which results in the two gears having the same normal pitches.
It is usual to design the pinion with a coarser transverse pitch than the crown wheel; this results in a larger pinion diameter than for the corresponding spiral bevel pinion.
The amount of the enlargement is dependent upon the amount of the pinion offset, and results in the following advantages:. But it must be realized that with low gear ratios, the use of hypoid gears may result in very large'diameter pinions and therefore it may prove advantageous to use a spiral bevel design in such situations.
These factors must be fully and carefully investigated at the initial design stages. The efficiency of both hypoid and spiral bevel gears can be very high, although the efficiency of hypoid gears is slightly less than that of the equivalent spiral bevel gears, due to the increase in the sliding motion between the mating teeth.
This efficiency is dependent upon the following:. Both spiral and hypoid bevel gears have sliding motion in the profile direction, but only the hypoid bevel gear has lengthwise sliding motion. This increase in sliding motion results in a rise in heat generated, with the resultant loss in efficiency.
The increase in heat generated means careful investigation into the problems created in the gear lubrication and cooling system in an attempt to reduce to and maintain reasonable operating temperatures. One result of the spiral bevel gear having no lengthwise sliding motion is that it is generally less susceptible to scoring than the hypoid gear.
However, the problem of scoring in hypoid bevel gears can usually be solved with the co-operation of the lubrication and tribology engineers. Due to the increased size of the hypoid pinion and its larger spiral angle, the relative radius of curvature between the mating teeth on a hypoid bevel gear pair is greater than that of a corresponding spiral bevel gear pair, resulting in lower contact stresses between the hypoid tooth surfaces with a similar reduction in the possibility of pitting.
In actual practice, loads up to 1. The subject of gear lubrication is more fully covered in Chapter 3, but the following points refer especially to spiral and hypoid bevel gears:. Both spiral and hypoid bevel gears have the same sensitivity to malalignment in mountings on assembly and under load while in operation. This problem can be controlled by the lengthwise curvature of the teeth, i. Rigid bearing mountings will obviously reduce the adverse effects of the gear sensitivity. The assembly of a hypoid bevel gear pair can be slightly more complicated than that of an equivalent spiral bevel gear pair, mainly due to the inclusion of the hypoid offset, which can create problems in measuring the mounting distance during assembly, thus requiring special gauging equipment.
Using a pair of spiral bevel or hypoid bevel gears of the same average spiral angle will result in the hypoid gearwheel having a lower spiral angle than the equivalent spiral gearwheel, and the hypoid pinion having a higher spiral angle than the equivalent spiral pinion. As a result of the above, the axial thrust on the hypoid pinion bearings will be greater, while the axial thrust on the hypoid gearwheel bearings will be less, than the axial thrust on the bearings of an equivalent spiral bevel gear pair.
The facility to use a larger shank or shaft diameter with a. The larger hypoid pinion diameter and its need for higher load-carrying capacity bearings can result in the casing for a pair of hypoid gears being larger than that for an equivalent pair of spiral bevel gears.
This also applies to the sue of the differential casing, which carries the hypoid gearwheel. As the offset of a pair of hypoid gears is increased, so the pinion face is displaced axially towards the centre-line of the hypoid gearwheel, thus reducing the diametral space available for the differential. For low gear ratios, the outside diameter of the hypoid pinion may become excessive and consequently reduce the clearance between the gearbox casing and the ground. This applies especially when ratios are 2: 1 or less.
The following rules can be used as a general guide:. The hypoid pinion, being larger, permits the use of larger pinion shaft diameters which can be advantageous. Either spiral or hypoid bevel gears will be satisfactory, but it should be noted that as the ratio decreases so the diameter of the hypoid pinion increases relative to the size of the corresponding spiral bevel pinion.
As both spiral and hypoid bevel gears are produced on the same machines, the manufacturing costs will be similar for either pair of gears, but the hypoid gears have two distinct advantages over spiral bevel gears from the production point of view:. The drive-line and the output drive are on the same horizontal plane when using spiral bevel gears, but with a pair of hypoid gears the output drive can be either above or elow the drive-line. Having made the decision which type of gear is most advantageous to the design, the hand of spiral to be used remains to be decided.
In both spiral and hypoid bevel gears, the hand of spiral is denoted by the. In a left-hand spiral, the teeth incline in a counter-clockwise direction away from the axis when looking at the face of a gearwheel or from the small end of the pinion, whereas in a right-hand spiral, the teeth incline away from the axis of the gear in a clockwise direction. The hand of spiral of any one member of the gear pair is always opposite to the hand of spiral of its mating gear in both hypoid and spiral bevel gears; therefore, when identifying the hand of a pair of either hypoid or spiral bevels it is usual to quote the hand of spiral of.
The hand of spiral dictates the direction of the thrust loads when the gears are loaded, and the hand of spiral should where possible be selected so that the thrust provides the motion for the pinion and gearwheel to move out of mesh when the gears are running under load in normal drive rotation, whenever this is permitted by the combination of the gear ratio, the pressure angle and the spiral angle.
Where this is not possible, the hand of spiral should be selected to give an outward direction thrust at the pinion. From the notes on the previous pages of this chapter, it can be seen that the prime factor in the design of spiral or hypoid bevel gears must be the load capacity of the gears.
The resistance to tooth breakage normally depends on the bending stress occurring in the root area of the tooth and resistance to surface failure from the contact stress occurring at the tooth surface. Finally, the scoring resistance can be assessed by the critical temperature at the point of contact of the gear teeth. To aid the checking of these stresses, the Gleason Gear Co. Rochester, New York, USA have produced the following Empirical formulae and calculation procedures which closely reflect the design philosophy in a majority of current car designs.
Class I road. Cement concrete, brick, asphalt block good 1. Second-grade bitumin macadam, tar, oiled macadam, treated gravel : in poor condition 2. Sandy clay, gravel, crushed stone, cobbles: in good condition 1. Earth, sand: in good condition 2. This torque is based on normal loads and overall car performance, and provides an estimated value from which the minimum gear or crown wheel size can be calculated.
For high-performance sports or racing cars fitted with manually operated transmissions, the crown wheel diameter cannot safely be estimated on the basis of performance torque alone, because it has been positively established that, with this type of vehicle, gear torques ranging from two to five times the maximum calculated torque can be produced in the lower gear ratios, as a result of snapping the clutch.
This force, along with the additional weight transfer to the driving wheels and the higher coefficient of friction between the tyres and the road surface, results in slip torques almost equal to the full engine torque.
Therefore, it is essential for these types of vehicle that the crown wheel and pinion sizes are checked using these higher torque values in the stressing design formulae. When not available, use 0. Dynamic weight transfer give the proportion of load transferred to driving axle due to acceleration.
When not available, use:. Checking the strength of the gears, using the new higher torques, should be carried out by checking the pair of gears for their resistance to tooth breakage and surface failure. Resistance to tooth breakage is normally dependent upon the bending stress occurring in the root area of the tooth, and the resistance to surface failure usually depends on contact stress occurring on the tooth surfaces, while the scoring resistance is measured by the critical temperature at the point of contact of the gear teeth.
These values can be obtained using the appropriate Gleason formulae. Modified versions of such formulae are given in detail in the following pages. The dynamic bending stresses in straight, spiral or hypoid bevel crown wheels and pinions manufactured in steel are calculated using the following formulae:. OO where torque T is in kg. Using the formulae given and the relevant torque values, the dynamic tensile stress should always be calculated for both the crown wheel and pinion in each application.
In the same way, a modified equation for the contact stress in straight, spiral or hypoid bevel, crown wheels and pinions manufactured in steel has also been arrived at and is given in the following pages. P denotes the use of stresses and torque values relevant to the pinion: since the contact stress is equal on crown wheel and pinion, it is only necessary to calculate the value for the pinion. The formula for the calculated contact stress assumes that the tooth contact pattern covers the full working profile without concentration at any point under full load.
The values required to solve the equations for Q and Zp can be calculated using the following data and formulae:. Subscripts P and G refer to pinion and gear, respectively, and mate refers to required for both gear and pinion. For straight bevel and Zero1 bevel gears, the transverse contact ratio must be greater than 1.
With the preceding values calculated, it is now possible to determine the values required to calculate the equations for the geometry factors for strength and contact stress. The contact stress value is at an assumed distance 'f' from the mid-point of the tooth to the line of contact. The value of 'f' should be chosen to produce the minimum value of Z,, which corresponds to the point of maximum contact stress, and may be found by trial.
For straight bevel and Zero1 bevel gears, this line of contact will pass close to the lowest point of single tooth contact, in which case distance. The remaining values are calculated from the following formulae before the calculations for the geometry factors for strength and contact stress can be completed:. Within the tooth form factor are incorporated the components for both the radial and tangential loads and the combined stress concentration and stress correction factor.
Since the tooth form factor must be determined for the weakest section, an initial assumptipn must be made and by trial a final solution obtained. This factor determines what proportion of the total load is carried on the most heavily loaded tooth.
Note: Use the positive sign for the concave side of the pinion tooth and mating convex side of the gear tooth. Use the negative sign for the convex side of the pinion tooth and mating concave side of the gear tooth. That is, use the positive sign for a left-hand pinion, driving clockwise when viewed from the back, or a right-hand pinion, driving anti-clockwise. Use the negative sign for a right-hand pinion, driving clockwise, or a left-hand pinion, driving anti-clockwise.
This quantity evaluates the effectiveness of the tooth in distributing the load over the root cross-section. This factor expresses the relative radius of profile curvature at the point of contact when the contact stress is a maximum.
This method of calculating this factor determines what proportion of the total load is carried on the tooth being analysed at the given instant. From the foregoing formulae it is possible to calculate the size of crown wheel and pinion necessary to withstand the loads to be applied. With the size of crown wheel and pinion fixed, the next problem in the transmission design to be solved is to finalize the crown wheel and pinion ratio.
This must ensure that the maximum road speed or output shaft speed required can be achieved for a given number of engine revolutions per minute.
The crown wheel and pinion ratio can be calculated using the following formulae: Crown wheel and pinion ratio. The second formula assumes that the internal ratio in the gearbox is a 1 : 1 ratio or a direct drive from the engine. Therefore, when using any other ratio the necessary modification must be incorporated into the formula. Having fixed the crown wheel and pinion ratio and subsequently the number of teeth on both components, the final factor in finalizing the size of the crown wheel and pinion must be the choice of material and the heat treatment to be used.
This will have a large effect on the strength and surface durability of the two mating gears. Having finalized the size of both the crown wheel and pinion, the first lines of the transmission or gearbox layout can be drawn. The guidelines usually given to the transmission designer include the relative position of the engine crankshaft centre-line to the gearbox output shaft centre-line.
From these dimensions the centre-lines of the gearbox input shaft, the pinion shaft and the crown wheel, together with the output shaft, can be arrived at. This position can be rigidly tied down in a two-shaft gearbox, given the engine installation location relative to the gearbox output shaft or axle drive shaft centre-line, the ground clearance required and the necessary clearances between the engine, gearbox and other surrounding components.
Using this dimension and given the gearbox input torque, the tooth size - either diametral pitch or module, which is dictated by the gear tooth strength, the number of teeth and the gear ratios - can be calculated.
In an automobile application, the internal ratios in a gearbox, usually four, five or six, are selected to suit the required vehicle performance matched to the engine output torque, and in some instances, particularly high-performance sports cars and racing cars, to suit the drivers individual technique and the type of circuits which they are to be used upon. The size of the gear tooth, both the diametral pitch or module and the tooth width, will depend on the material used in the manufacture of the gears and any heat treatment incorporated, plus the required life expectation.
At this stage of the design, it is essential that a preliminary stressing programme is carried out to decide the size of the following gearbox components required to cope with the maximum gearbox input torque and allowing for the requisite safety factor:. The cross-sectional area should be checked both for shear and torsional stress, as well as the amount of deflection under full load. The cross-sectional area should also be checked both for shear and torsional stress, and if as in some gearboxes a gear ratio is included between the input and intermediate shafts, then the torque input must be calculated to suit.
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Transmission manual. The driver is manually selecting a drive mode on a touch screen display in a car. Car safety handle. Closeup shot of a handle of automatic transmission in a car. Closeup of businesswoman driving car and shifting automatic transmission.
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