APTE 551 Vehicle Power Transmissions Manual Transmissions & Gear Ratios © Unitec New Zealand1

APTE 551 Vehicle Power Transmissions

Manual Transmissions &

Gear Ratios

© Unitec New Zealand 1

Purpose of TransmissionA running engine will need to produce a torque

that will enable it to move from stationary to the desired.

The transmission provides a range of gearing which allows the engine to operate at various speeds to

suit different driving conditions.

(Source: Ed May’s 7th Ed)


Design of Gear box ratios

• Vehicle motion in different conditions is governed by the power is transmitted from its source to the wheels.

• For IC engines – for good overall performance due to its diverse conditions it is important to proper gear ratios.

• Low gear is used when: at low speed, provide higher traction for acceleration, road climbing with high load.

• High gears is used for higher speed and must allow proper matching between engine torque and speed characteristics with vehicle acceleration and speed.


GradabilityMaximum grade a vehicle can negotiate depends on two factors:

• The limitation of road adhesion and• The limitation of the engine torque.


Transmission flow

Although some what crude by today’s standards, this early automotive drive train contained the components needed to

transfer the torque from the engine to the drive wheels. These included most of the components that are used in

modern vehicles.

(Source: Tom Birch, 8/02 5


4 x 4’s :

Full-time Four Wheel Drive

SUV ( Sport Utility Vehicles- example: Subaru

OutBack)

Heavy Duty AWD ( Dedicated off-roaders –

example Toyota Land Cruiser)

http://www.subaru.co.nz/New_Vehicles/Outback/3.0R_LTD/


Types of Gear Boxes

Passenger Vehicle Manual ( No. of speeds: 3,4,5,6 + R)

Commercial Vehicle Manual ( No. of speeds up to 12 using Low-Hi range selection)

Semi Automatic ( Manual gearbox with vacuum operated clutch release: example early 70’s VW Beetle semi- automatic gearbox) ( Other example: Commercial Semi-Automatics)

Automatics ( 3, 3 + OD, 4 + OD, 5 + OD)Planetary ( power flow through coaxial shafting) ( example: Majority of Automatics)

Non- Planetary (power flow through parallel shafting) ( example Honda Matic)

Continuously Variable Transmissions (CVT) ( example Nissan March)

Introduction: Different Gear Wheel Designs

These are the main types of gear wheel designs implemented in gearboxes and final drive assemblies:

8© Unitec New Zealand(Source: Ed May’s Sixth Ed)

Helical gear cut on slant


5 Speed Manual Gearbox(Source: Ed May’s, Holden Australia)


16-Speed Commercial Manual Gearbox( Source: Bosch, ZF )

Introduction: Different Gear Wheel Designs

• Spur Gears: These are the simplest gear designs, and their teeth are cut straight parallel to the rotation axis.

• Helical Gears: These are similar to spur gears, except that the teeth are cut on an angle ( helix ) with respect to the rotation axis.

• Internal Gear and Pinion: This design is mostly used in automatic transmissions. Also is called by other names like “epicyclical” or “planetary” gears. The combination comprises of internal annular gear ( ring), a central external pinion gear, and may include also a carrier with its pinions ( planet gears).

• Bevel Gears: These are cone-shaped rather than disc form like the previous three types. They are configured whenever the input & output shaft lines are not parallel like in the above three types.


Gear Ratio Calculations

To calculate gear ratio ( or speed ratio) of a particular gearing setup, it is very important to identify which wheel is the input member (that receives power inflow), and which one is the output member( that transfers power outflow), have available the data of gear teeth count or geometrical diameters ( or radiuses) of both gears in mesh.

12© Unitec New Zealand

Simple gear train in mesh to produce speed conversion(Source: Ed May’s Sixth Ed)

Gear Ratio = number of teeth of output gear / number of teeth of input gear = diameter ( or radius) of output/ diameter ( or radius) of input

Gear Ratio Calculations

Gear Ratio can also be calculated if information about input/ output rotational speeds or transmitted torques are available as follows:


Gear Ratio = rotational speed of input gear / rotational speed of output gear = transferred torque of output gear / transferred torque of input gear

Gear Ratio Calculations : Simple Gearing


This illustration shows three gears in mesh in a “simple” gearing arrangement, where gear A and C are terminal gears and gear B is an idler. To calculate gear ratio we apply the previous formulas over input & output gears ( terminal gears), using number of teeth ( A: 10 teeth, C: 20) :

Gear Ratio (A>>C) = 20/10 = 2 : 1

Gear Ratio ( C>>A) = 10/ 20 = 0.5 : 1

Gear Ratio Calculations : Compound Gearing


This illustration shows a 2 stage compound gearing, where terminal gears are A & B . To calculate the overall gear ratio, we subdivide the compound into simple gear trains and then multiply their gear ratios to get to overall gear ratio. For example if A is input and B is output, then :

Gear Ratio (A>>B) = (24 x 30) / (12 x 10) = 6 : 1

Gear Ratio

• A numerical value of gear ratio > 1 signifies a gearing resulting in speed reduction ( torque multiplication)

• A numerical value of gear ratio < 1 signifies a gearing resulting in speed stepping ( torque reduction)

• A numerical value of gear ratio = 1 signifies a direct-drive gearing

• It is important to include a minus sign in front of numerical gear ratio to signify that direction of rotation of power flow becomes reversed across the gearing setup.


Different Configurations of Manual Transmissions meshing mechanisms

• Sliding mesh: This is an old technology, where two ( or three) gear wheels are brought into mesh-interface by sliding a gear wheel along its shaft. This technology is now limited to engagement of reverse gear only, due to its disadvantages ( let’s think of some those disadvantages?? )


(Source: Ed May’s Sixth Ed)

Different Configurations of Manual Transmissions meshing mechanisms

• Synchro-mesh: This is the mostly used meshing technology in vehicle’s manual transmissions. It was developed to make gear changes smoother, easier, and quicker than with sliding mesh with longer assembly service life.



Componentry of a Synchroniser Assembly



Functionality of the Synchroniser• By design, synchronisers have a hub splined to slide axially along a shaft, so that

synchroniser interfaces on either side to a gear wheel riding on a roller bearing supported by same shaft. The mechanism was developed from sliding-mesh historical design. Simply, the synchroniser matches speeds of the shaft and the respective gear wheel at the moment of engagement by providing a “ blocking” and “ speed synchronising” actions to ensure smoother and timely gear shifting.

20© Unitec New Zealand(Source: Ed May’s Sixth Ed)

Transaxles• The term “ Transaxle” refers to a combination

transmission assembly of a a multi-speed gearbox unit and a final drive unit in one case.

• Transaxles are implemented in various vehicle drive configurations:

Front wheel Driven. Rear Engined & Driven. In some All Wheel Driven, to transfer drive to front

axle.• The final drive part composes of a suitable reduction

gear train and a differential gear unit.


Configuration of 5-speed manual Transaxle

• The following 6 diagrams illustrate power flow in all engaged gear positions of a typical 5-speed manual transaxle shown on right.




S Tronic System…Audi model• Accommodate 2 set of clutches• 2 sets of main shafts• Bottom gear connected to bottom shaft rotate on

bearings.• Top gears fixed to top shaft rotates with shaft.• Outside shaft accommodate odd number

(1,3,5,7) gears• Inner shaft accommodate even number gears

(2,4,6)


http://www.bing.com/videos/search?q=youtube-+double+clutch+systems&docid=608055236190143170&mid=EF17D83B9FBD8FE65469EF17D83B9FBD8FE65469&view=detail&FORM=VIRE3#view=detail&mid=EF17D83B9F

BD8FE65469EF17D83B9FBD8FE65469

• http://www.bing.com/videos/search?q=Video animation for the S Tronic

• system:http://www.youtube.com/watch?v=UUrvlQyo2fU


Failure Analysis – Gear box

© Unitec New Zealand 26(Source: Tom Birch, 8/02

This transaxle with a broken case from an internal failure:

What could be the probable cause?

What would be the impact on cost?

Failure Analysis – Gear box

27

This speed gear has 2 completely broken teeth and one that is half gone.

1 What could be the cause of the problem?

2The black colour of the gears can tell us some that the gear was very hot – briefly explain how could this had occurred>

(Source: Tom Birch, 8/02

Worn Clutch Tooth Plate

© Unitec New Zealand 28(Source: Tom Birch, 8/02

The clutch teeth on this plate are nearly gone.

Can you explain why?

( refer to your eng material experience)

Hot Main Drive Gear


This main drive gear shows deformed teeth and a black color from overheating.

What could be the cause of failure and why?


Synchronizer Sleeve


The teeth at this end of the sleeve are worn and rounded (red circle) with upset metal.

Determine the cause of the problem.


• http://www.bing.com/images/search?q=Dual-Clutch+Transmission+Animation&Form=IQFRDR#view=detail&id=577161442828A28F099467CD4050AACDFAD91AD8&selectedIndex=2


Documents

APTE 551 Vehicle Power Transmissions Manual Transmissions & Gear Ratios © Unitec New Zealand1