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Power transmission - Coggle Diagram
Power transmission
Clutches
- Main clutch (in drive train)
- Between engine and manual transmission and they are needed for:
- Starting phase to bridge the speed difference from zero to the lowest engine speed (=idle speed)
- Interrupting the load, while changing the gear (shifting) in mechanical transmission
- All-wheel drive for connection of a drive axle
- Shifting clutch (in transmission): Shifting in gear train (manual transmission, gear step in automatic transmissions).
Caloric energy equals to integral of variation of mechanical power which is equal to torque times velocity variation
Variations
Friction clutch
Common main clutch. Force F presses the clutch plates agains a friction disk. Therefore the Torque the clutch makes is equal to the force times the friction coefficient times the mean friction radius times the number of friction pairs.Clutch pressure:
- Dry clutch passenger vehicle: p < 20 [N/cm2]
- Dry clutch heavy vehicle: p < 8
- Wet clutch heavy vehicle: p < 5
Dimensioning
ƒ(transferable torque, thermal strain)
Design of clutch to have Mc max ~ 1.5 x Me maxTypes:
- Wet clutch - friction coefficient decreases, therefore we need more pressure and more friction pairing
- Dry clutch - higher friction coefficient, therefore less presure
Flow clutch (hydraulic rotation converter)
- Input shaft connected to pump which rotates and, due to the centrifugal forces, throw the oil in it outwards. This oil will make the turbine rotate, transmitting the torque to the output shaft. The pump spins faster than the turbine.
- Starting clutch for heavy vehicle
- For automatic transmission
- Used as a retarder - like a hydrodynamic brake used for trucks to brake just using the shear stress on the fluid because it will heat up. Needs to cool the oil and put it again on the clutch
Equation Mc = ke' x n^2 x d^5Clutch factor K'e
Geometries:
- Routing torus (highest)
- Bulging disk
- Storage room (lowest)
PROS
- Low space requirement
- Diamater adjusted to aplication
- Good damping from ICE speed oscilations
CONS:
- low efficiency
- high torque at stand still —> need to cool the oil
- continuous operation —> slip of 3%
Haldex Clutch
- Only for AWD placed behind the transmission and the rear
- Further development of the viscous clutch
- A bunch of lamellas connected via toothing. The end of one of the shafts is tilted, so that when the shafts are spinning in different velocities, it presses a hydraulic piston that presses all the plates and connects the shafts and transmit the torque to the other axle.
During curves, is not good to have a haldex clutch becase one axle will be turning with different velocities on purpose, that's why there is a valve to regulate it
Motivation:
Combustion engine can't transmit torque without any velocity, therefore we need a starting clutch. If we did not have any transmission, there would not have any efficiency loss and we would always be at the highest gear —> direct connection between motor and shaft. Transmission has at least 4 gears, but there is always a speed gap.
Also useful for electric motors since permanent magnet electric motors should be disconnected from the DT to increase overall efficiency. In order to shift the maximum efficiency driving point to another velocity.
Construction
When someone presses the pedal, it will move the ejector onwards, which actuates the disk spring. The disk spring is connected to the pressure plate, making it release the friction lining. This will cut the transmission of power from the motor to the power train, making it possible to 1- start the motor since there will not have any load, 2- change gears
- High energy consumption in clutch during coupling (sliding), equal to the energy needed to accelerate the inertial mass at start.
- Temperature difference between friction side and back side of pressure plate and flywheel → conical deformation → Effective friction surface is reduced
- THERE IS NO CONVERSION OF TORQUE
- Load capacity
- Start on level plane: 36 Nm/cm2
- Start on drive up-hill: 300 Nm/cm2
- Diameter
- Small diameter
- (+) build size
- (+) costs
- (+) inertia of clutch plate
- (+) weight
- Large diameter
- (+) torsion damping curve
- (+) fading stability
- (+) coating durability
- (+) pedal force.
Dynamics
- Idle operation
- oscillation of motor pistons excites the springs installed within the clutch
- model it with a spring and a friction damper
- motor torque accelerates the inertia times acceleration of delta + damping times the deformation (turning angle) + stiffness times the difference of the turning angle
- assuming a oscillation of the deformation angle or the torque takes place, just multiply the initial by e^jwt. Derive it twice and then j^2 = 1 (complex numbers)
- Driving elasticity
switches the operation zone to the resonance line (around 40-70Hz) —> it has a tradeoff of resonance and transmitting high frequency excitations
- Principle of operation for driving elasticity:
- allows for a rotational angle between transmission input shaft and clutch plate
- allows the generation of friction energy from oscillation angle
- friction dampens the vibrations from the drive train (rumbling, rattling)
Using dual mass flywheel
more comfortable, increase of dampimp
Gearbox
Mechanical stepped GB
- FD - driving force at max power for gear i
- Gap need to be bridged by the friction clutch. If too big, then too much heat and losses
- trasmission ratio i = i[gx] x i[d] (typical value for id is 4 and for ig of 1st gear is also 4)
Normal driving gear: tangent point of Fd and gear before 0%
Top speed gear: tangent point where it intersects with 0%
Resting gear or eco gear: tangent point after. 0%Truck: up to 16 gears
passangers: up to 9 gears -> automatic
Input/output/counter shaft with cog wheelsSelecting gears
- Geometric gear factor: dividing each consecutive gear ratio you always get the same value= gear step factor (see formula)
- Progressive gear factor: i increases from last to 1st gear (see formula)
Planetary transmission
- Planet gears
- Sun gear
- Sun gear shaft
- Planet carrier
- Ring gear
Kutzbach plan
- lines from the center and edges of the planet gears, assume velocity and than connect the points. 2 speed given (input and fixed) and one resulting. conect the h of the points to the origin and extend these lines until the radius. this will give the sizes for determining i
PROS:
- Compact
- Teeth are in continuous interaction (but this brings friction and splashing, reducing efficiency)
- Shifting under load with the main clutch but this requires a brake for each gear
- Shifting without torque disruption (good for automatic transmission)
CONS:
- expensive and lower efficiency
Speed manual transmission with fixed countershaft
- has dog clutches
- needs shifting clutches
- drive shaft moves
cog wheels
Speed manual transmission without fixed countershaft
- needs shifting clutches
- differential on the right side
- escadinha
- FWD
- Throughput from the countershaft
With fixed countershaft for coaxial throughput
- escadinha reversa
- RWD with engine in the front
Unsynchronized transmission
- needs a synchronizing element
- needs sliding shift sleeves
- selector fork moves the sleeves back and forth
- blocker ring guarantees everything is rotating with the same velocity and teeth are in position for coupling.
Phase 1 - bring synchronize ring to position
Phase 2 - start sync with some friction until its locked
Phase 3 - bring back the sync ring
Flow trasmission
Hydrodynamic torque converter
- Pump
- Turbine
- Idler brings back the fluid to the pump. Idler is fixed to housing
Mo = Mi + ML
i = input
o = output
L - idlerconverter factor k Mi = ki x ni^2 x di^5SLIP OF AROUND 10%, design point around 30%Graphs - Efficiency depends on the ratio of po/pi=(kono/kini). As Ko decreases with lower slips, efficiency decreases.
Trilok transmission
- Idler no longer fixed, but connected to transmission housing over a free-wheel F
- with friction clutch
PROS:
- At low engine rotations, the transferred torque is very small, so stalling the engine is not possible.
- Raising the engine rotations for startup brings at start rotations nI highest torque MO atnO =0!
- No wear, no sliding friction.
CONS:
- Price and efficiency.
- Inferior braking effect compared to rigid engine–transmission connection. - Push-start (without additional technical effort) not possible.
-
Stepless mechanical transmission - continuous variable transmission CVT
no need to change gear because the transmission is done via a belt that allows every combination of velocity and torque below the curve
- variator 2 plate sets
- pressing/releasing plates to move the belt/chain
- it can run in 3 modes, compromise, consumption efficiency and performance
- planetary gear + clutch to lock ring gear for reverse
- push link belt or tension link chain
PROS
- infinit choice of gear ratio
CONS
- limited torque due to belt
Differentials
Bevel gear drive axle differential
velocities are different, but torque is equal
- trasmission sends torque to housing
- shafts from wheels: suns
- top and bottom are planets
Locking differential
deltaF is limited by friction in transmission, not by miu,max !
- Partial self-locking
- Full self-locking
Centre differentials - Power divider
Torques are not equal
- as a bevel gear transmission
- one planet for both drive shafts
- torsen
Casdan Shafts
- Between differentials and wheels
- avoid opperation around critical speed range - 1 at gaussian. frequency equal to sqr stiffness/mass
- hollow shaft
actual resonance around 0.6-0.8 theoretical
Joints
- single universal joint
- Avoid cardan error: Possible by using two joints
- double joint
- attainable, enough for the turning angle of driven wheels.
- homokinetic joint
- Torque transfer through balls in symmetry plane.
- Choose guide surface of balls so, that they are in symmetry plane for every bending angle.
- homokinetic tripod-type
- special designs (rubber)
- Rzeppa type