Chain Drive

Due (10/18/22)

• Update this page with current information

• chain vs flat belt vs v belt

3.1.2. Chain Drive

• In this concept, a chain that passes over a sprocket transfers power from the rear axle of the vehicle to the front axle to engage a four wheel drive.

• The rear sprocket is attached to the output shaft of the gearbox

• The front sprocket is attached to the front axle of the car

• Drive reduction of 0.7:1 will be accomplished by sizing the front sprocket to be larger than the smaller sprocket

  • This is done because a larger diameter for the front sprocket means, when the rear sprocket finishes a revolution, the front sprocket will still be progressing through its first revolution and thus cause underdrive

    • Underdriving is good because it increases engine output

• The chain can be tensioned with a tensioning device

• Commonly used in bicycles and motorcycles

• Basic components of chain drives:

  • Larger sprocket(Front sprocket)

  • Smaller sprocket (Rear Sprocket)

  • Chain Link

• Advantages:

  • Applicable for a variety of distances

  • Compact and have overall small dimensions

  • Lightweight when compared to a driveshaft

  • Initial tension is not required

  • Very high efficiency (98%)

  • Easy to install

  • Low maintenance cost

  • Withstand abrasive conditions

  • Operate in wet conditions

• Disadvantages:

  • Requires frequent lubrication

  • Requires precise alignment when compared to belt drives

  • Load capacity is less than gear drives

  • Requires adjustments for slack (i.e. why a tensioning device is needed

Weight:

40 series chain: .41 lb/ft

3.1.3. Driveshaft

• A tubular component that is connected that is connected to the gearbox(in the rear of the vehicle) in order to transmit torque from the transmission to the differential in the front of the vehicle; differential delivers torque to the front wheels which runs the vehicle

• Components of a driveshaft:

  • Flanges

  • Slip yoke and tube yoke

  • End yoke

  • Midship shaft

  • Universal joint

  • Center bearing

  • Tube

• Gears used in the final drive axle/differential are ring and pinion gears

  • Pinion gear is the small gear at the end of the drive shaft and connects to a larger ring gear which rotates the drive axle

• In order to achieve the final drive ratio to underdrive the vehicle, one must lower the number of drive shaft rotations (pinion gear) for every tire rotation (ring gear)

• Advantages of driveshaft:

  • Drive system is less likely to get jammed

  • Lower maintenance than chain and belt system

  • High durability

  • Simple construction

  • Low noise even at high torque

  • Is not jammed easily

• Disadvantages of driveshaft:

  • High weight, especially when compared to other options

  • Less efficiency than a chain driven system

  • The shaft can be damaged when the speed is very high

  • Advantages of a driveshaft can often be done with a chain driven system

3.1.4 V-Belt Drive

• A trapezoidal shaped belt is looped over pulleys in order to transmit power between two or more rotating shafts, shafts that often have parallel axes of rotation

• Pulleys would be placed at a measured distance to cause tension on the belt

  • The rotation of the rear pulley would increase the tension on one side of the belt and those create a tight side

  • Tight side applies tangential force to front pulley

  • Opposite side is the slack side

• Performance of a V-belt is determined by how tightly it fits into the groove of the sheave

• In order to get the appropriate drive reduction, the front pulley would larger than the rear pulley

• Components of a V-belt drive system:

  • Front pulley

  • Rear pulley

  • V-belt

• Advantages of V-belt drive system:

  • Less chance of slippage when compared with other belts

  • Fairly high efficiency when compared to driveshafts

  • Lubrication free

  • Smooth operation

  • Easy installation and maintenance

  • Low noise when operating

• Disadvantages of V-belt drive system:

  • Limited speed range

  • Susceptible to wear and tear

  • Still prone to slippage and can be difficult to adjust

  • High cost when compared to flat belt

  • Cannot transfer power at a longer distance

3.1.5 Flat Belt Drive

• A flat rectangular cross section belt that is run over a drive pulley(connect to input) to a driven pulley

• Components of a Flat Belt

  • Front pulley

  • Rear pulley

  • V-belt

• Advantages of a Flat-Belt System

  • Can be used for transmitting power to a long center distance (even up to 15m)

  • Comparatively higher efficiency than V-belts

  • Relatively cheap

  • Elasticity of belt allows for good dampening characteristics

• Disadvantages of a Flat-Belt System

  • High Slippage

  • High noise

  • Low mechanical efficiency

  • Cannot achieve constant velocity ratio between driver and driven pulley

Gates GT3 5mm (20mm width 95.5mm pitch) timing belt

What is a chain drive?- A chain drive is a means of transferring mechanical power from one place to another. On a vehicle this is used to transmit power from the engine to the axles of the car. Thus achieving four wheel drive. Chain drives are most common on motorcycles and bikes but some automobiles have used them. A chain drive is mainly composed of three main parts, the chain, a rear sprocket and a front sprocket.

• The rear sprocket is attached to the output shaft of the gearbox

• The front sprocket is attached to the front axle of the car

• Drive reduction of 0.7:1 will be accomplished by sizing the front sprocket to be larger than the smaller sprocket

  • This is done because a larger diameter for the front sprocket means, when the rear sprocket finishes a revolution, the front sprocket will still be progressing through its first revolution and thus cause underdrive

    • Under driving is good because it increases engine output

Gear Ratio- The gear ratio is the ratio of the number of turns the output shaft makes when the input shaft turns once. In the scenario where output shaft is turning slower than the input shaft the output shaft will be be turning but will be outputting more torque.

Chain Tensioning "The engineering standard for chain tension is to have between 1%-3% of the distance between the front and rear shafts in total up-and-down chain movement" https://xladv.com/articles/how-to-properly-adjust-your-drive-chain-r19/:~:text=The%20engineering%20standard%20for%20chain%20tension%20is%20to,when%20the%20chain%20is%20at%20it's%20tightest%20point

3.2. Governing Principles

The drive system of a vehicle is governed by:

• Kinematics/dynamics (slider-crank mechanism, valvetrain)

• Solid mechanics/FEA (component stresses)

• Tribology (bearings and lubrication)

• Manufacturability (casting, machining, forging)

Chain Sizing- For our chain calculations we had to make some assumptions in our calculations. We assumed that the torque coming out of the gearbox as 100ft-lb. From there we also had to make an initial assumption of the rear sprocket diameter, we chose various diameters over 2 inches as to not interfere with our CV's. Then we were able to calculate our tension in the chain as the input torque divide by the radius of the sprocket. From there we obtained the tension in the chain and where able to look at McMaster-Carr and match-up a chain that would be able to withstand that tension.

Sprocket Sizing- From our obtained chain we where then able to get the correct sprockets on McMaster-Carr to comply with our .7 under-driven ratio.

Weight

• Weight was determined to be the most critical factor when choosing our choice of drive chain. Minimizing unnecessary weight is vital to building a fast and competitive car in Baja SAE competitions.

Reliability

• Reliability was determined to be our second most important factor to think about. This year's Baja team’s main priority is performing well in the Endurance event. To perform well at this event our car must remain on the track for as long as possible during this 4 hour race. This means we have to choose components that can withstand the grueling challenges of this race that can put intense strain on the car.

Power Efficiency

• While it is important to be able to have high power efficiency to transmit engine torque. Based on our design torque is not always being transmitted, and all options have a high efficiency. So power efficiency is not our top priority.

Maintenance

• While options like the chain drive require much more maintenance than the drive belts such as needing to lubricate the chain. Maintenance is already standard practice for our Baja team so extra maintenance requirements are not a problem.

Cost

• While our baja team does strive to be cost efficient and effective we have adequate fundraising and cash reverses to buy any part that we need.

Other Considerations

Based on the previous information we have picked the chain drive to be the most suitable application for our drive train. But now there are many decisions to make that will maximize the potential of our choice. One area of refinement is to add idler sprockets to our chain drive system. This will allow us to reduce the overall packaging size of the drivetrain allowing more space for other components of the car. Another decision to make is whether or not our chain and sprockets are strong enough or if we needed to manufacture special heat treated or other special manufacturing to increase the strength of these components. A big area to look into with chain drives is proper chain tensioning. Chain tensioning can make or break a chain drive system. A chain that is too tightly tensioned will wear down on the sprockets and will eventually lead to failure. While a chain that is too loosely tensioned will slip and jam.