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In current competitive automobile sector, gear shift quality has become significant factor for vehicle evaluation. OEMs are sensibly focusing on improving gear shift quality to meet customer’s expectations. Though there are different gear shifting habits in different drivers, diagonal shifting is the fastest way of shifting gears in manual transmission vehicle. So the components linked with shift system should be designed to facilitate smooth diagonal gear shift pattern. This paper enlightens the process of defining chamfers on internal gear shifting components for smooth diagonal shifting movement of gear shift lever. It is hard to define chamfers by analytical or practical approach. Creo-mechanism is very useful simulation tool which can be used to understand diagonal shift patterns and to define the chamfers.

This paper takes a review of fretting phenomenon on splines of the engaging gears and corresponding splines on shaft of automotive transmission and how it leads to failure of other components in the gearbox. Fretting is a special wear process which occurs at the contact area of two mating metal surfaces when subject to minute relative oscillating motion under vibration. In automotive gearbox, which is subjected to torsional vibrations of the powertrain, the splines of engaging gears and corresponding shaft may experience fretting, especially when the subject gear pair is not engaged. The wear debris formed under fretting process when oxidizes becomes very hard and more abrasive than base metal. These oxidized wear particles when comes in mesh contact with nearby components like bearings, gears etc. may damage these parts during operation and eventually lead to failure.

With the advent of BS VI regulations, automotive manufacturers are required to innovate the powertrains, fuel systems, exhaust and its after treatment systems to meet the regulatory requirements. The exhaust regulations can be met either by reducing the exhaust gases being generated by the engine (attacking the source) or by treating the exhaust gases in after treatment devices. The choice of the opted system varies with the manufacturer. The after-treatment devices such as catalytic converters are generally mounted in the engine compartment to take advantage of high temperature of exhaust gases to yield the reactions. Such an arrangement imposes a lot of thermal load on the peripheral components such as gearshift cables, bearings, oil seals, driveshafts etc. Thermal shields or thermal sleeve are used to address thermal issue and to protect transmission components.

In modern automotive vehicles, there is a major concern for noise and vibrations generating from drivetrain. These noise and vibrations affect the passenger comfort and drivetrain parts life. Engine generates fluctuating torque and causes angular acceleration that results into torsional vibrations. These vibrations are transmitted to powertrain. Clutch disc consists damper springs and hysteresis which aids reducing these torsional vibrations. Based on the damper spring stiffness, one can control the resonance speed range and shift the resonance rpm out of driving speed range of engine. The resonance should not happen within driving speed range of vehicle to avoid large amplitude torsional vibration. But here limitation is put on the torque transmission capability of clutch for meeting vehicle requirements. As, low stiffness of damper spring requires large wind-up angle so, it is critical to decide its stiffness.

Exhaust Noise attenuation is one of the important functions of exhaust muffler. Transmission Loss (TL) is a measure of noise attenuation used in designing exhaust mufflers for NVH. TL is a logarithmic difference between inlet and outlet pressures for unit velocity input at inlet of the muffler and anechoic termination at outlet of the muffler as boundary conditions. TL amplitude and its frequency tuning depends on a combination of various muffler design parameters like volume, length, muffler cross section, pipe cross sections, pipe perforations, number of chambers, baffle perforations, etc. Achieving the desired TL performance with no valleys over a wide frequency range is very challenging. Manual design iterations with large numbers of permutations and combinations of design variables are difficult and time-consuming. It also needs a highly experienced professional to balance TL performance, design variables and design constraints.

Passenger utility vehicles like car, SUVs, MPVs are used in wide application all over the world. Luxuries are becoming essential features of product mix along with comfort and ergonomics. Customer desires best shift quality with emerging technologies like AT, DCT, CVT, etc. and every OEM is working hard to achieve it. It is very difficult to satisfy the customer desire because of diversities in demographics and geographic. Gear shift quality (GSQ) is very crucial touch point in overall drive feel of vehicle. It consist of various parameters like mode selection feel, precision, comfort, select Noise, etc. It demands tradeoff practices among various parameters as stated. In this paper, external mode selection system of automatic transmission is explained. Various contributing parameters are explained with practical design approach for detent profile, mode selection mechanism, cable & dampers, etc.

Gear rattle is due to impact noise of unloaded gears in transmission having freedom to move in backlash region. Engine order vibrations in the presence of backlash in meshing pairs induce the problem. It is a system behavior wherein flywheel torsional vibrations, the pre-damper characteristics and transmission drag torque plays a vital role in an engine idle condition (hot & cold). Idle rattle is a severe issue, which is highly noticeable in cold condition or after 1st engine crank. Gear rattling observed in idle condition is idle gear rattle or neutral gear rattle, specifically in cold condition is a “Cold idle rattle” and this is one of the critical noise parameters considered for entire vehicle NVH. Damper mechanism in the clutch, is used to serve better isolation (by reducing the input excitation to transmission parts) of vibrations between engine and transmission their by reducing gear rattle intensity.

Gearbox and driveline durability is always been a sensitive subject from both end user and manufacturer’s point of view. Since powertrain is heart of vehicle, naturally it is expected to long last and perform satisfactorily for the entire vehicle life. Sometimes the driveline aggregates especially gearbox might face some issues because of various factors, but this is distinctively noted by the driver since it is one of the important touch point of the vehicle. The gear slippage is a very typical phenomenon observed in automotive gearbox. The issue of gear slippage is very sensitive because it leads to compromising safety of the driver, also it deteriorates gear shift quality and thereby performance of the vehicle. Generally, gear slippage is not observed during end of line testing or during early kilometers of vehicle. It is observed after some thousand kilometers, that to initially gear slippage is not observed consistently and that’s why it is difficult to identify at early stage.

Normal engine mounting system is designed to carry loads of powertrain in all driving conditions and also isolate the vibrations of powertrain. Softer mounts are good for vibration isolation but it is not recommended to have softer mounts because durability will be affected adversely. Optimum stiffness needs to be finalized which will have balance between durability and performance. In addition to durability many performance parameters needs to be checked during the time of development. This study includes the development of engine mounting system for elimination of drive away judder in first gear. Maximum peak torque value for the drive-away event is in the range of 80Nm - 120Nm. In the worst case, this peak torque can reach to maximum 170Nm depending on maneuver, engine rpm is around 1100-1200. Steering wheel, instrument panel and whole vehicle cabin will vibrate for few seconds and then vehicle will run smoothly.

The clutch is the connecting link between engine and the power train. It connects and disconnects the engine to the gearbox as per the wish of the driver. Clutch has a friction disc which acts like a fuse wire which wears in the process of the connection. This paper tries to calculate the clutch life analytically (In terms of Kms. run by vehicle), of automotive vehicles having manual transmission. As the clutch engages and disengages the engine to the gearbox, during this time due to slippage, energy is dissipated which results in the wear of the clutch disc. It calculates life based on the volumetric wear of the clutch disc and wear allowance available. The work done by other people in this domain include the empirical estimation of clutch life based on the past data, effect of the surface topography on the friction characteristics of the wet clutches, modeling of clutch housing and facing temperature for the estimation of the clutch life of a manual transmission etc.

As we are moving towards complete electrification from combustion engine to electric motor, the system design approach also changes due to application. For a range of 100-150 kg EV powertrain weight, number of mounts as well as mount locations, orientations and stiffnesses plays a significant role during system design. The electric powertrains are usually lighter and their mounts are usually stiffer than the mounts for typical combustion engines, the static displacements at dead load are usually lower. However, currently it seems like there is no common direction of all OEM’s regarding the question of how stiff an e-motor mounting system should actually be. Due to the high torque of the EV’s one could even think about switching to a four point mounting instead of a pendulum mounting.

Rubber hose and metallic pipe with crimped joints are extensively used in steering system assembly, transmission oil cooler system, brake system etc. to carry hydraulic fluid or lubricants from one place to another. The pipe and rubber hose assembly provides necessary flexibility for complex routing on the vehicle level. Design of hose and pipe assembly for this application are different due to difference in operating pressure and temperature requirement for vehicle application. This paper defines the criteria for design and validation of hose & pipe assembly used to connect automatic transmission with the cooler. Crimped joints are validated for their separation force, leakages, ability to withstand pressure pulsations, burst test etc. Parameters which influence the hose & pipe assembly durability are pipe end flaring dimensions, type of crimping, reinforcement type, its size, material and pattern, rubber material properties, crimping force, effective crimping diameter etc.

Single plate dry clutch is one of the most abuse components in the vehicle. With the growing population of traffic in cities, useful life of clutch is affected drastically which is evident from the rise in complaints on clutch from metropolitan cities. The governing design parameter, which affects the life of clutch, is the energy dissipated in clutch per unit area of friction lining of clutch disc. The life of clutch is affected by many factors like vehicle weight, engine torque, driveline ratios, friction lining, size of clutch, which are taken into consideration during design stage of the clutch. Apart from these factors, one more factor, engine calibration, affects the clutch life drastically. However, it is not taken into consideration during design stage owing to its inherent nature as it gets matured over the vehicle development program.

Clutch engagement judder is a phenomenon wherein the driver experiences vibrations on seat during the clutch engagement process for the vehicle launch. Clutch engagement judder is one of the critical vehicle attributes as a part of overall vehicle NHV. Torsional oscillations, specifically originating from clutch in the driveline during clutch engagement, are referred as clutch engagement judder. Judder is a phenomenon wherein friction induced torsional vibrations are generated in the driveline because of sliding contact between clutch and flywheel, during engagement. These resulting oscillations inherit the first resonance frequency of the driveline. The engagement judder not only affects the dynamics of transmission system but also the vehicle, because of excitations being transferred to body via suspensions and mounts. Passengers experience these oscillations as vibrations during vehicle launch. If excitation level is high then it may cause discomfort to passengers.

Gearshift quality is a perceived quality parameter. Hence, is getting much importance because of the increased awareness about comfortable and refined driving experience, especially in the case of passenger cars. When the topic of gearshift feeling is broached in manual transmission vehicles, synchronizer pack (shifter sleeve, engaging gear, strut, synchronizer and gear synchro ring assembly) have been the focus point for optimization. Synchronizer type (single, double or triple cone), lining material, datch chamfer angle of shifter sleeve/synchro ring of gear/synchronizer, all of these have been extensively studied in the past to improve the gearshift quality. With stringent timelines for vehicle development, OEMs prefer to use off-the-shelf powertrain systems developed by powertrain manufacturers. Due to this, avenues to refine gearshift feel gets reduced to a large extent and hence refinement becomes difficult.

Breather assembly is mounted on transmission to maintain the pressure equilibrium inside transmission. Breather allows the transmission to breathe air when the air inside transmission expands or contracts due to heating and cooling of lubricating oil during vehicle running. Breather allows the hot air to escape and cool air to enter into the transmission to prevent overheating issue. Failure of breather assembly can lead to pressure buildup inside transmission and further leading to leakage from transmission oil seals. Oil leakage through the breather assembly is governed by parameters such as opening pressure, location and orientation of breather etc. The transmission undergoes different operating conditions of input speed, load, temperature, inclination etc. Also, breather assembly is designed and positioned in such a way that there is no leakage through breather due to oil splash inside the transmission.

In today’s manual transmissions of car, gearshift system requires high performance with particular emphasis on low effort, minimal travel and positive feel. To meet these targets, a high capacity multi cone synchronizers along with higher co-efficient of friction material used for lower gears. The design of synchronizer with these specifications is influenced by torsional fluctuations from engine. Excessive torsional vibrations leads to wobbling of synchro rings within the peripheral clearances with surrounding parts. Wobbling leads to abrasion wear of frictional area of synchro ring causing grating or crashing noise of gears during shifting. This paper presents the optimization of the multiple cone synchronizer design exposed to excessive torsional vibrations and validation of the same on test bench during development stage instead vehicle level validation.

During every clutch engagement energy is dissipated in clutch assembly because of relative slippage of clutch disc w.r.t. flywheel and pressure plate. Energy dissipated in clutch is governed by many design parameters like driveline configuration of the vehicle vis-a-vis vehicle mass, and operational parameters like road conditions, traffic conditions. Clutch burning failure, which is the major failure mode of clutch assembly, is governed by energy dissipation phenomenon during clutch engagement. Clutch undergoes different duty cycles during usage in city traffic, highways or hilly regions during its lifetime. A test schedule was derived using energy dissipated during every clutch engagement event as a base and using road load data collected on the vehicle. Road load data was collected in different road mix conditions comprised of city traffic, highway, hilly region, rough road for few hundred kilometers.

In today’s automobile market, most OEMs use manual transmission for cars. Gear Shifting is a crucial customer touch point. Any issue or inconvenience caused while shifting gears can result into customer dissatisfaction and will affect the brand image. Synchronizer is a vital subsystem for precise gear shifting mechanism. Based on vehicle application selection of synchronizer for given inertia and speed difference is a key factor which decides overall shift quality of gearbox. For more demanding driver abuse conditions like skip shifting, conventional brass synchronizers have proved inadequate for required speed difference and gear inertia, which eventually results into synchronizer crashing and affects driving performance. To increase synchronizer performance of multi-cone compact brass synchronizer, a ‘Grit blasting process’ has been added. These components tested with an accelerated test plan successfully.

Electrical and Series Hybrid Vehicles are generally provided with single speed reduction gearbox. To improve performance and drive range, a two-speed gearbox with coordinated control of traction motor and gearshift actuator is proposed. For a two-speed gearbox, gearshift without clutch would increase the shifting effort. Active Synchronization is introduced for a smoother gearshift even without clutch. The quality of gearshift is considered as a function of applied shift force and time taken. To enhance the quality of the gearshift further, the location of the synchronizer in the transmission system is optimized. To validate the improvement in the quality of the gearshift, a mathematical model of the two-speed gearbox incorporating proposed location of synchronizer assembly along with active synchronization is developed. The qualitative and quantitative analysis of the results achieved is presented.