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Contribution of the Mechanical Linkage in Gear Shift Feel of North-South Transmission.

Introduction

The globalization has driven quest and thirst of being superior among passenger vehicle manufacturers because of cutthroat competition.

The car manufacturers are trying to differentiate their products by inventing new features and technologies in their product mix, at the same time they are controlling costs to face the immense competition.

Customer's opinion about the product is the most crucial factor in today&'s passenger vehicle market because it has a dominant role in sales and thereby revenues. Hence it has gained prime most importance and new product development is mainly concentrated around customer demands, needs, perceptions and desires. What customer thinks or feels about the product? What are his perceptions and beliefs? What are his desires and is it possible to make them reality? Nowadays these questions are also important for designers and they are designing their respective aggregate by keeping customer in mind. How customer makes his opinion about the car is very important and one must understand which factors are contributing in the opinion making. Customer makes his opinion based on overall ergonomics, ambience, comfort and response offered by tangible entities of the product, these entities mainly include aesthetics of product and customer touch points. Aesthetics includes shape, color, styling of exteriors as well as interiors of the car which gives pleasant experience by virtue of its visibility whereas touch points are those entities which are handled by the customer while driving the vehicle. Customer touch points include all controls like gear shift lever, steering, brake, clutch, infotainment system buttons etc. These touch points contribute in both performance and handling of the car and hence play most crucial role in making customer's opinion about the product because they are frequently handled by customer while driving [1,2,10,11].

Gear shift lever is the most crucial touch point because it contributes in both handling and performance of the car. Gear shifting contributes in handling of vehicle by means of smooth shifting, light selection and shifting forces, touch feel of GSL (Gear Shift Lever) knob etc. Gear shifting has a major role in performance of vehicle i.e. speed of vehicle, its acceleration as well as the overall fuel efficiency is governed by transmission [1,2,7,5,9].

Gear shifting is very subjective matter, the experience, expectations and desires of drivers related to gear shifting differ from person to person, also geographic and demographic diversities add more complexities in this context. Thus, it is impossible to define ideal gearshift feel but we can find patterns in the expected gearshift feel e.g. European drivers may like high shift forces and click shift feel while Asian drivers may like very smooth and light shift feel etc. Therefore, by identifying these common demands and desires of certain demographic and geographic drivers, we can define certain entities, which will help us to obtain expected gear-shift feel. We refer these entities as Gear Shift Quality (GSQ) parameters and the desired gearshift feel can be objectively expressed with help of these Gear Shift Quality parameters. GSQ parameters are further classified as Static GSQ parameters and Dynamic GSQ parameters. Static GSQ parameters are those parameters which are measured when vehicle is stationary and engine is not running; dynamic GSQ parameters are those parameters which are measured when vehicle is in running condition i.e. both in driving and coasting mode [5,7,8,9].

Gear shift feel is affected by various factors, many factors are directly linked to gearbox and some factors are outside the gearbox. Factors linked to gearbox include synchronizers, inertia of gears, dog teeth geometry, step ratio, oil drag, GSL leverage, aspect ratio, dampening bushes, detent spring stiffness, mechanical linkage resistance and stiffness, profile for guiding rails detent etc., whereas external factors are clutch inertia, driveline stiffness, shifting rpm, driving condition etc. Though many factors are affecting GSQ it is important to see their intensity or contribution in GSQ parameters, synchronizers influences dynamics parameters whereas static GSQ parameters are mainly influenced by shift system peripherals [1,2,5_,7,8,9].

In his paper a discussion is made on how Mechanical Linkage affects the gear shift quality parameters. The paper explains learning's about mechanical linkage kinematics, force calculations and transformations, mechanism models we worked on, the interrelations between linkage parameters and how these help to improvise gear shift feel. Discussion is made on noise, vibrations, shift lever rattle cause and effects, the role of mechanical linkage in all these. Optimization of linkage stiffness, weight, inertia and angles between links with help of Creo-simulation model is described and the conclusion is drawn in the end.

General Overview of the Topic

Gear Shift Quality Analysis (GSQA) is the crucial factor in case of manual gearbox, the gear shift quality can be affected by gearbox related issues as well as some factors which are not related to gearbox. Gear Shift Quality (GSQ) is defined in terms of GSQ parameters and these parameters are controlled in certain limits. GSQ also scatters because of GSQ parameters are controlled in certain bands. It is important to understand types of vehicle layouts and gearbox construction before going in the discussion.

Based on orientation of transmission, two types of layouts used in automotive transmission, North South (N-S) layout and East West (E-W) layout. Generally E-W layout uses a transaxle. Transaxle is integration of transmission and differential and it has lateral layout. In case of N-S layout, transmission and differential are connected through propeller shaft. E-W layouts are low power low torque system, where ground clearance and space are the constraints. On other hand, N-S layout are used for high torque and high power application where ground clearance and space constraints are not too much stringent [1,2].

East-West transmissions have limitation of torque ratings and gross vehicle weight. Due to these limitations of East-West layouts, North-South transmission layout is preferred for bigger sports utility vehicles. Nowadays customers using sports utility vehicles and similar automotive are demanding luxury shift feels like cars. Massive torque ratings make it difficult to achieve and maintain GSQ standards in case of these vehicles that have N-S layout [7,8,9].

Shift systems of the vehicle also play vital role in GSQ.

Two popular shift systems used in vehicles are rod shift mechanical linkage system and cable shift system, these systems have their inherent advantages and disadvantages and are adapted as per demand of the vehicle layout. Generally rod shift mechanical linkage shift system is used for N-S transmission. We will discuss the importance of mechanical linkage and how it affects GSQ in later part of the paper, let us go thru the background of the case study and the theoretical aspects of the topic.

Background

During development of 6-Speed UV North-South transmission it was observed that GSQ is inconsistent. The inconsistency observed was more in static GSQ parameters like gear selection travel (both total and gate to gate), gear shifting travel (both total and gate to gate), leftt/right stop force, leftt/right stiffness, neutral free play box@10/5N, in to gear play box@10/5N, in to gear/neutral/swallow forces during gear shifting in static condition etc.

This is not acceptable because this will affect customer&'s opinion about the product. Hence, it is necessary to obtain consistency in GSQ parameters of all manufactured gearboxes on production line. To do so, it was decided to sort out the causes of the spread in GSQ parameters.

During this process we observe that mechanical shift linkage also contributes in gear shift quality especially gear shift lever free play, selection and shifting travels, stiffness during shifting and selection etc. Hence, we decided to do some experiments on mechanical linkage so that GSQ issues gets resolved.

Before going in detail discussion on GSQ problems and there solution, let's have a quick look on the vehicle and gearbox construction and theoretical aspects of the topic.

Layout of North-South Transmission

Figure 1 represents the schematic of North- South transmission layout, in this layout gearbox and engine are longitudinally aliened.

In case of North-South layout, lateral vibrations are more because of longitudinal crankshaft and main shaft construction. North-South layout have advantage of handling high torque and power with relatively higher efficiency than the East-West layout with same configuration [1,2].

North-south layouts have many disadvantages from noise and vibrations point of view. North-South layouts have more vibrations because they have longitudinal Gearbox and Engine mounting. In this layout, engine crankshaft and transmission output shaft are in line with each other. Thus along with torsional vibrations, engine rocking will add up the vibrations. Driver sitting position is close to gearbox in N-S layout therefore cable type shift system cannot be used because cable type shift system is less efficient when Gearbox position and driver position are very close to each other. In such constraint layout, cable routing is difficult and results into less efficient operation and inferior GSQ. In case cable shift systems these vibrations will not be transferred to gear knob because of the position of gearbox is relatively away from driver and conduits used to hold flexible cables acts as damper.

North-South transmission generally uses rod shift mechanical linkage shift system. In this case, because its close vicinity to the driver, vibrations at GSL are relatively more, use of dampener at GSL will help to reduce these vibrations but still some vibration will be transferred to GSL knob. However, rod shift mechanical linkage system has some advantages over cable shift system. Rod shift mechanical linkage system has greater efficiency, because of rigidity of linkage loss of force is lesser also linkage system is facing very less friction compared to cable shift system. Rod shift mechanical linkage systems are simple in construction, are easy to maintain and has very less cost of manufacturing as well as maintenance[1,2,5,7,9].

Gearbox Construction Schema of 4X2 and 4X4 Gearbox

It is important to understand the construction of the gearbox whose GSQ is to be controlled before going to see problem definition, methodology and experimentation carried out. Fig. 2 and fig. 3 represents construction scheme of 4X2 and 4X4 gearboxes respectively.

The gearbox construction schema of 4X2 gearbox is shown in fig.2. In this gearbox rod shift mechanical linkage shift system is used along with three bushes for dampening vibrations. Bush-1 is bush between extension arm and mounting bracket, Bush-2 is at gear shift lever and Bush-3 is in between gearbox and extension arm. Rail type shift system is connected to gear shift lever through top cover and linkage.

In 4X4 layout, similar system is used like 4X2 gearbox except the mounting bracket. In 4X4 layout, a small sheet metal bracket used to connect TOD/transfer case and extension arm through dampening bush.

Gear Shift Quality (GSQ)

Gear Shift Quality (GSQ) is the gearshift feel desired by majority population of drivers of certain demographic and geographic area and is expressed in terms of certain measurable entities referred as gearshift quality parameters.

While looking for the best-fit solution for gearshift quality that can satisfy majority population of drivers of a demographic and a geographic area, it was observed that there are many factors which has some impact on GSQ. Many of those parameters, if not optimized can give inferior GSQ. For example, higher linkage stiffness will improve firmness of GSL but will transfer relatively more vibrations to gear knob. On the other hand, comparatively less stiff linkage with damper will reduce firmness of GSL, but will dampen vibrations and prevent there transfer to gear knob. Hence, as a first step, it is important to identify the major factors that affect GSQ and optimize them so that we can achieve the desired consistency in GSQ [1,2,7,8,9].

GSQ Parameters

Gear shift quality of a gearbox is one of the most important factor that contributes in overall driving comfort. Subjective evaluation of shift quality has limitation for expressing it in quantifying terms, hence objective evaluation of gear shift quality is necessary. Therefore, by identifying the common demands and desires of certain demographic and geographic drivers, we can define certain entities, which are measurable and will help us to obtain expected gearshift feel. We refer these entities as Gear Shift Quality parameters [5,6,7,8,9,10,11].

Based on operating conditions, GSQ parameters are classified as static GSQ parameters and dynamic GSQ parameters. In this case we are focusing only on static parameters which can be explained as,

1. Static GSQ Parameters These GSQ parameters are measured in static condition i.e. when vehicle is stationary and engine is not running.

Some of the main static parameters are listed as, (refer fig. 4)

* Left/Right Travel: - Measured movement of Gear Shift Lever (GSL) from neutral to lateral ends (either towards codriver side or towards driver side).

* Neutral to Gear Travel: - Measured movement of GSL from neutral position to shift gear position.

* Neutral void box: - Free play of GSL measured when in neutral when force of 5N/10N is applied at knob.

* Into Gear void box: - Free play of GSL measured when in shifted into gear when force of 5N/10 N is applied at knob.

* Cross Gate Travel: - This parameter defines the travel of gear knob in Y-direction of vehicle. This travel mainly covers the displacement of knob in Y- direction.

* Cross gate over travel: - This parameter defines the displacement of gear knob in Y- direction after crossing the detent springs till the end stop.

* Left/right stop force: - It is the force applied at GSL such that its movement is stopped after it completes the selection travel in particular leftt/right direction.

* Selection force (neutral to gate or cross gate) Static: - This is minimum force required to select the desired gate in static condition i.e. when vehicle is stationary and engine is not running.

* Shifting force (neutral to gear or gear to gear) Static: - This is minimum force required to shift the desired gear in static condition i.e. when vehicle is stationary and engine is not running.

* Gate Precession: - Gate precession represents how much precisely gate is selected by the driver. Gate precession is concluded after observing no. of shifts of a particular gear. Fig. 5 shows typical h-plot of gate precession, this graph is plotted by measuring no. of shifts of gears with help of GSQA software. During gate selection the zone in which GSL lies is represented by H-plot graph.

Problem Definition

During drive trials of 6-speed UV transmission we received feedbacks from drivers mentioning issues in GSQ, these feedbacks were of subjective nature and also differ from person to person. Hence we decided to do the GSQA of those cars on which GSQ issues were reported and also those cars on which no GSQ issue was reported. During the GSQ testing of 6-Speed UV transmission we found that static GSQ parameters measured on gearboxes are showing scattering, since the project was in final stage of development scope for design change was very limited. In order to resolve this issue we decided to segregate the main or major issues observed and resolve them considering all limitations and scopes. For more detail description we formed a vehicle batch of 10 vehicles in which few gearboxes was with ok GSQ and few gearboxes was with not ok GSQ. This batch was offered to a jury panel that consist of skilled drivers, unskilled drivers and subject matter experts. This was done for checking the opinion of everybody so that we can find patterns.

We collected feedbacks from each and every individual jury member and segregated that data for the subjective conclusion of the issue. From the jury trials we found following issues were reported,

* Drivers reported that they find it difficult to identify the gate to shift the gear.

* Drivers reported that in some vehicles, GSL is dancing/shaking in gear shifted condition.

* It was also observed that some GSL have excessive vibrations transferred to GSL knob.

* Drivers reported that they don&'t feel firmness while shifting gears and they experience some kind of rubbery feeling while shifting gears.

* It was reported by drivers that during selection of gears GSL travel is not even for all gates.

It is necessary to translate this collective information in to problem definition. Complaints received from drivers indicate that there is inconsistency in static GSQ parameters. When we measured GSL free play of a problematic vehicle we found it in range of 25-30 mm, thus we decided to focus on static parameters and work on rod shift linkage mechanism. Following targets were decided to achieve in order to resolve this issue.

1. Free play in neutral (@5N) [less than or equal to] 6 mm.

2. Free play in into gear (@5N) [less than or equal to] 4 mm.

3. Selection travel (gate to gate) [less than or equal to] 39-45 mm.

4. Selection travel (Cross gate) [less than or equal to] 78-84 mm.

5. Selection travel (Total) [less than or equal to] 117-125 mm.

6. Shifting travel (N to gear) [less than or equal to] 50-60 mm.

The above targets were set to resolve the following issues of GSQ.

1. Fumbling while gate selection.

2. GSL is shaking after gear selection.

3. Excessive vibrations at GSL knob.

4. Uneven selection travel of GSL.

5. Into gear and end to end stiffness.

It is important to understand the construction and working of mechanical linkage of the gearbox before we see methodology.

Rod Shift Mechanical Linkage Construction

Fig. 6 and fig. 7 represents the construction and exploded view of the rod shit mechanical linkage. The gear shift lever is connected to link rod through a pin joint, the other end of the link rod is connected to universal joint. Selector shifter shaft is connected to universal joint at the end and shifter finger is mounted on selector shifter shaft.

From the exploded view we can see that there are total three pin joints which allows two degrees of freedom one translational and one rotational, thus the linkage can transfer motion of GSL intended to select or shift the gear to the shifting finger.

In the existing design the plastic bushes are used for minimizing friction at pin joints, but this has also increased no. of parts and thereby possibility of excessive clearance within the linkage. Clearance at each joint will lead to free play, hence it is important to control free play at all joints.

Methodology

The iterative method was selected for resolution of the issues. This was done for ensuring quick and easy solution, too much design changes may lead in delays and increased cost.

The detail analysis and measurement of forces transferred by the linkage was completed first in order to understand the linkage efficiency. When we measured forces at GSL and Shifter finger we found that approximately 86% force is utilized effectively Fig. 8 represents the points of force measurement and respective distances, formulae for force calculations are as below.

[mathematical expression not reproducible]

[mathematical expression not reproducible]

It is observed that following factors are affecting linkage performance.

1. Clearances at joints resulting in free play at GSL.

2. Friction between joints.

3. Line of action through which force is transferred.

4. Linkage Stiffness i.e. its resistance to twisting.

We decided to target above four factors for improving the linkage performance, before starting iteration we done tolerance stack analysis for finding the contribution of each joint in maximum possible clearance.

Let us see the significance of all factors before going to discuss iterations.

1. Clearances at joints resulting in free play at GSL:-

The clearance is provided for smooth working of joints, radial clearance provided at joints results in to free play.

The contribution of each clearance in GSL free play is calculated by following formula.

Contribution of perticular joint clearance in GSL free play = GSL leverage x Clearance of perticular joint

GSL free play will increase with increase in no. of joints, also it is observed that the clearances in these joints increases with usage because bushes used at these joints get worn out. It is important to note that we cannot eliminate bushes because they are necessary for reducing friction between joints but we can minimize no. of bushes in mechanism [3,4,6].

2. Friction between joints:-

The friction between joints reduces linkage efficiency, as forces applied will face resistance before they are transferred. The friction increases when two adjacent parts come in contact under load, hence bushes or soft bearing surfaces are provided to minimize the resistance created due to rubbing of parts. Tight clearances at joints lead to higher friction because of higher contact area. When linkage is operated with excessive force or when it faces abusive loading conditions pins used in linkages get bend, the holes in clamps become oval, this ultimately results in increased friction. Force lost in Friction is calculated by following formula [3,6].

Force lost in Friction=Force at joint x Coefficient of friction

3. Line of action of force: -

Line of action of force affects linkage efficiency Ideally line of action of force should be coincident, if angle is formed between line of action of force of two adjacent links it reduces linkage efficiency because the applied force get resolve in to components and one component will be lost in friction. Hence it is important to keep this effective line of action as straight as possible and if angle is unavoidable keep it as minimum as possible [3,4,6].

4. Linkage Stiffness:-

Linkage stiffness is also important. In rod shift mechanical linkage system linkage has to deal with rotational and linear movement hence its torsional rigidity is equally important. The linkage should have high resistance to twisting at the same time weight of linkage should be kept optimum. We can calculate twisting angle by following equation [3,4].

[mathematical expression not reproducible]

Where,

[theta] - Twist angle.

T - Torque applied on linkage.

L - Length of linkage.

G - Modulus of rigidity.

J - Polar moment of inertia.

Set Up for Measurements

The experiment is carried on gearbox for measuring the free plays, selection travel, shifting travel, selection forces and shifting forces. Fig. 9 represents a schematic of test set up. The construction of the setup is very simple, it consist of a base stand on which gearbox is mounted with help of bolts and clamping plate. The purpose is to hold gearbox firmly so that measurements can be done with ease.

The scale stand has provision such that scale can be mounted and adjusted in both selection and shifting direction. Two push pull gauges used for measurement of force. Mainly one push pull gauge is used for measuring the selection and shifting forces. Second push pull gauge is used to cross check linkage efficiency.

We used the same gear-shifting knob for the entire exercise; this knob has special marking on it where the push-pull gauge pin has to apply the force. A pointer-pin was fixed on knob so that free play can be measured easily.

Before Start of Iterations

We measured values of free plays, selection travels, shifting travels, section forces and shifting forces before start of iterations. The measurements were taken on randomly selected production gearboxes. It is observed that there is inconsistency in values measured. The initial readings are as below,

Free play in at neutral (@5N) = 12-25 mm (in problematic vehicles it was observed 25-30 mm).

Free play in into gear (@5N) = 12-25 mm.

Selection travel (gate to gate) = 55-67 mm.

Selection travel (Cross gate) = 92-102 mm.

Selection travel (Total) = 135-171 mm.

Shifting travel (N to gear) = 54-64 mm.

Selection force (Static) = 22-28 mm.

Shifting Force (Static) = 25-30 mm.

Iteration 1: Changing Assembling Method of the Spiral Pin

From tolerance stack analysis we come to know that two spiral pins used at selector shifter shaft contribute about 40% clearance in selection direction hence we carry some initial trials to check the validity of stack.

In ordered to do so we changed only direction of spiral pin assembly as shown in fig. 10. This initial solution was implemented on 12 problematic gearboxes and we found that direction of assembling spiral pin reduces free play up to 30-40% in selection direction, whereas even if some play is increased in shifting direction it is not showing major effect. In addition, joint clearances are having there major contribution in selection direction thus by reducing clearances in selection direction we can reduce GSL free play. Fig. 10 shows how the direction of assembling spiral pin can change the clearances direction and thereby helps to reduce GSL free play.

When we implement this change on all problematic gearboxes we found that GSL free play is effectively reduced by 30-40% hence we decided to implement this change before we proceed for further iterations. In next stage of experiment we carried out few more iterations and checked their effects.

The summary of iteration 1 is mentioned in table1.

Apart from the objective evaluation we also noted down the subjective feedback about the gear shifting which is summarized as below.

a. Gate selection precession is improved significantly.

b. Shaking of GSL lever is minimized effectively

c. Vibrations at GSL observed were quite lesser than problematic gearbox.

d. Gate selection travels unevenness felt earlier is reduced.

e. Gear selection and shifting feel is not changed much.

Iterarion 2: Changing Assembling Method of the Spiral Pin and Welding One Pin Joint of Universal Joint

In the next iteration we decided to weld one pin joint of universal joint. Fig. 11 represents the weld location where a spot welding was done. This was done because line of action of linkage has a small angle of 13.6[degrees], we decided to lock one degree of freedom so that we can minimize the free play further. When we took trial on gearbox it was observed that free play is further reduced hardly by 1 mm but there is significant increase in selection effort, shifting effort is also increased.

Though we face the failure in this iteration, we come to know that even if there is slight change in line of action use of universal joint is mandatory. Mechanism can work without UJ but selection force increases due to resistance created by the angle between line of action of linkage and selector shifter shaft.

Summary of iteration 2 is represented in table2.

Apart from increase in selection and shifting force, we observed that GSL tilts and twists at the damper location, which may lead to GSL failure. Thus, welding pin joint of UJ is not a good option. We also noted down the subjective feedback about the gear shifting which can be summarized as below,

a. Gate selection precession is improved.

b. Shaking of GSL lever is minimized effectively.

c. Vibrations at GSL were reduced.

d. Gate selection travels unevenness felt earlier is reduced.

e. Gear selection and shifting feel is worse than original condition.

Iteration 3: Changing Assembling Method of the Spiral Pin and Adding Shims at all Joints

If we want to reduce free play further, we must attack on all pin joint clearances. Thus, we added shims at six locations of all three pin joints in the mechanism. Fig. 12 represents the locations where we added these shims. The shim thickness was 0.1 and 0.05 mm, this helped us to reduce clearances of all joints below 0.1 mm. When we checked the free play with the above arrangement we found that free play is effectively reduced up to 6 mm, but selection force is increased and return of GSL has became sluggish. This is not desirable output but this helped us to understand up to which extent free play can be minimized with existing design.

Summary of iteration 3 is presented in table 3.

We also reversed direction of spiral pin assembly and implement only shims and all joints to see effect of tightening joint clearances on GSL free play. We observed that GSL free play can be reduced up to 5 mm by tightening of joints and it was also observed that selection force increases up to 40 N. Thus for further reduction of GSL free play we should do some design changes.

Apart from the objective evaluation we also noted down the subjective feedback about the gear shifting which is summarized as below,

a. Gate selection precession is improved.

b. Shaking of GSL lever is minimized effectively.

c. Vibrations at GSL observed were quite lesser than problematic gearbox.

d. Gate selection travels unevenness felt earlier is reduced.

e. Gear selection and shifting feel is worse than original condition.

Iteration 4: Changing the Link Design and Elimination of Universal Joint from Linkage

After conducting three iterations on existing linkage design we come know that the GSL free play cannot be controlled beyond 6-8 mm even if components are assembled with certain care. It is also observed that even if we want to add shims at joints of existing linkage it is a tedious and time consuming job. Thus we decided to made some changes in linkage such that it can be easy and quickly implemented.

We kept all four aspects in mind while modifying the design of new linkage. The universal joint is removed from design and line of action of linkage and selector shifter shaft made coincident, also no. of pin joints were reduced to two joints and box circlip implemented so that shims can be easily assembled. Fig. 13 shows the new linkage details.

In the modified design instead of rigid rod we used a 3.2 mm thick heavy pipe of 21 mm diameter which has same modulus of rigidity. The pipe was flattened at both ends and holes were drilled so that pins can be located and welded to the new link pipe. Since line of action of selector shifter shaft and new link is same universal joint is removed and only one pin joint is kept at top cover side of the mechanism. Extra clearance is provided at this joint to compensate the resistance while transferring swing motion of GSL to rotational motion of selector shifter shaft. In new design total no. of pin joints reduced to 2 (existing design has 3 pin joints) and no. of bushes reduced to 4 (existing design has 8 bushes) and total linkage stiffness is increased by 10%. Comparatively less no. of joints and bushes will help to reduce the net clearance.

Creo Simulation Model Creo simulation and mechanism are the modules offered by the PTC Ltd. along with the 3D modeling software. In order to save time and cost it is better to simulate the model before we go for the actual manufacturing. We created a 3D simulation model of the concept linkage for cross checking its smooth working before we build physical prototype. It took 3 working days for the 3D modeling and simulation.

Creo simulation helps to check following

1. Check interference and helps to find fouling of parts.

2. Software predicts whether the expected motion of linkage can be possible.

3. Can find resistance to the motion.

4. Software helps to find out problematic areas i.e. which joint is critical etc.

5. It helps to predict the mechanical strengths of parts are ok or not ok.

The new concept linkage is evaluated in Creo simulation and was found ok.

Proto-building and its Implementation on Gearbox The prototype linkages were manufactured after this and we conducted trials with the new design linkage on existing problematic gearboxes. During gearbox linkage assembly, spiral pins were also assembled in preferred directions. We found that free play is consistently reduced in range of 5-6 mm in neutral as well as in to gear, selection and shifting travels were also improved. The selection and shift feel with this linkage is better as compared to existing designs used in previous iterations; selection and shifting forces were also found lesser. Summary of iteration 4 is mentioned in table 4.

Apart from the objective evaluation we also noted down the subjective feedback about the gear shifting which is summarized as below,

a. Gate selection precession is significantly improved.

b. Shaking of GSL lever is minimized effectively

c. Vibrations at GSL observed were quite lesser than problematic gearbox.

d. Gate selection travel unevenness felt earlier is reduced significantly.

e. Gear selection and shift feel is significantly improved compared to original gear shift feel.

Results

The results obtained from the above iterations needs to be plotted graphically for better comparison so that conclusion can be drawn. For plotting graphs, average value of the range is considered.

Fig. 14 represents graphical comparison of free play in neutral and free play into gear. Measurement of free play is taken with 5 N force applied on GSL knob. We observe that free play is significantly reduced in all iterations but it is observed lowest in iteration 4. Apart from reduction in free play, its variation is also controlled within narrow band of 1 mm. This helps to control neutral void box with precision.

Figure 15 represents graphical comparison of selection travel and shifting travel in various conditions. Selection travel is effectively reduced in iteration 3 and iteration 4. This will help driver to quickly identify gates which will reduce fumbling while gate selection, hence gate selection precision will improve. In case of shifting travel, though significant difference is not observed in all iterations but it is slightly reduced as compared to earlier condition.

In fig. 16, graphical comparison of selection force and shifting force is shown. It can be seen that selection force is significantly increased in iteration 2 and iteration 3; this is because of increased friction. It is observe that selection effort is negligibly reduced in iteration 1 and it is observed lowest in iteration 4 showing reduction of 4-5 N. Shifting effort also noticeably increased during iteration 2 and iteration 3 due to the increased friction between joints. We observe that shifting effort is negligibly reduced in iteration 1 and it is observed lowest in iteration 4 showing minute reduction of 2 N.

Conclusion

Following conclusions can be derived from the experimentation done on mechanical linkage.

1. We successfully resolved the GSQ complaints reported by drivers regarding static GSQ parameters.

* GSL free play effectively reduced from range of 12-25 mm to 5-6 mm.

* Shaking of GSL is eliminated.

* Vibrations at gear shift knob reduced effectively

* Gate selection precision is significantly improved and selection travels are controlled in narrow tolerance band of 5-10 mm.

* Gear selection force is controlled in narrow band of 3-5 N and gear shifting force is controlled within narrow band of 4-6 N.

* Gear selection feel is also significantly improved in case of modified linkage.

From the experiment it is understood that in case of rod shift mechanical linkage gearbox, mechanical linkage plays a significant role in obtaining appropriate gear shift quality.

2. GSL free play should be kept as minimum as possible because higher GSL free play affects neutral void, into gear void, gate selection travel, cross-gate selection travel, total selection travel and gate precession.

3. Stiffness of linkage and line of action of force are also important factors, they contribute in linkage efficiency and thereby gear shift feel. Hence it is important to keep stiffness of linkage and line of action under control.

Contact Information

Onkar Prabhakar Gurav

Tata Technologies Ltd., Phase-I Rajiv Gandhi Infotech Park,

Hinjewadi, Pune-411057

onkar.gurav@tatatechnologies.com

+91 8975210500

Acknowledgments

I am very grateful to Mr. M. V. Kher for the support and guideline in this activity.

I am thankful to my team for providing me guidelines and support for conducting these tryouts. I am thankful to Mr. R. Samson and Mr. Onkar Gangvekar for helping me, involving me in this activity, sharing observations and for team spirit we showed while working on this activity.

Definitions/Abbreviations

etc. - et cetera

i.e. - that is

no. - number

GSL - gear shift lever

GSQ - gear shift quality

GSQA - gear shift quality analysis

N-S - north-south

E-W - east-west

Fig. - figure

UV - Utility Vehicle

TOD - Torque on demand

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Santosh Deshmane, Tata Motors Ltd.

Onkar P. Gurav, Tata Technologies, Ltd.

Vipul Sahu, Tata Motors Ltd.

History

Received: 12 Jan 2018

Published: 08 Oct 2017

e-Available: 08 Oct 2017

Citation

Deshmane, S., Gurav, O., and Sahu, V., "Contribution of the Mechanical Linkage in Gear Shift Feel of North-South Transmission," SAE Int. J. Passeng. Cars - Mech. Syst. 10(1):2018, doi: 10.4271/06-11-01-0008.

doi:10.4271/06-11-01-0008
TABLE 1 Summary of iteration 1.

                                                      Achieved
Sr. No.  Parameter                        Target      (Range)

1        Free play in neutral (@5N)         6 mm        8-10 mm
2        Free play in into gear (@5N)       4 mm        8-10 mm
3        Selection travel (gate to gate)   39-45 mm    50-52 mm
4        Selection travel (Cross gate)     78-84 mm    86-94 mm
5        Selection travel (Total)         117-125 mm  125-140 mm
6        Shifting travel (N to gear)       50-60 mm    50-60 mm
7        Selection force (Static)          20 N        21-25 N
8        Shifting force (Static)           25 N        25-28 N

TABLE 2 Summary of iteration 2.

                                                      Achieved
Sr. No.  Parameter                        Target      (Range)

1        Free play in neutral (@5N)         6 mm        8-10 mm
2        Free play in into gear (@5N)       4 mm        8-10 mm
3        Selection travel (gate to gate)   39-45 mm    50-52 mm
4        Selection travel (Cross gate)     78-84 mm    86-94 mm
5        Selection travel (Total)         117-125 mm  125-140 mm
6        Shifting travel (N to gear)       50-60 mm.   50-60 mm
7        Selection force (Static)          20 N        35-40 N
8        Shifting force (Static)           25 N        28-32 N

TABLE 3 Summary of iteration 3.

                                                  Achieved
Sr. No.  Parameter                    Target      (Range)

1        Free play in at neutral        6 mm        6-8 mm
         (@5N)
2        Free play in into gear         4 mm        6-8 mm
         (@5N)
3        Selection travel (gate to     39-45 mm    45-50 mm
         gate)
4        Selection travel (Cross       78-84 mm.   82-90 mm
         gate)
5        Selection travel (Total)     117-125 mm  125-135 mm
6        Shifting travel (N to gear)   50-60 mm.   50-60 mm
7        Selection force (Static)      20 N        30-40 N
8        Shifting force (Static)       25 N        28-32 N

TABLE 4 Summary of iteration 4.

                                                      Achieved
Sr. No.  Parameter                        Target      (Range)

1        Free play in neutral (@5N)         6 mm        5-6 mm
2        Free play in into gear (@5N)       4 mm        5-6 mm
3        Selection travel (gate to gate)   39-45 mm    45-48 mm
4        Selection travel (Cross gate)     78-84 mm.   82-88 mm
5        Selection travel (Total)         117-125 mm  125-133 mm
6        Shifting travel (N to gear)       50-60 mm    50-60 mm
7        Selection force (Static)          20 N        18-21 N
8        Shifting force (Static)           25 N        23-27 N
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Author:Deshmane, Santosh; Gurav, Onkar P.; Sahu, Vipul
Publication:SAE International Journal of Passenger Cars - Mechanical Systems
Article Type:Report
Date:Jan 1, 2018
Words:6657
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