AT414
Transmission line systems in vehicles
Lecture 4
• Hydromechanics
• Hydromechanics
• hydrostatics
• hydrodynamics
• hydrostatics
• Dynamic effect through pressure times area
• hydrodynamics
• Dynamic effect through mass times acceleration
• The hydraulic coupling
• A device used for transmitting power from driving shaft to driven shaft with the help of fluid
• Oil is used as the working fluid because of its salability, non-corrosive nature and lubricating
properties
• There is no mechanical connection between the two shafts
• Consists of a radial pump impeller mounted on a driving shaft and a radial flow reaction turbine
mounted on the driven shaft
• Both the impeller and runner are identical in shape and together form a casing which is
completely enclosed and filled with oil
• The hydraulic coupling
• When the driving shaft is rotated, the oil starts moving from the inner radius to the outer radius
of the pump impeller
• The pressure energy and kinetic energy of the oil increase at the outer radius of the pump
impeller
• The energy-increased oil enters the runner of the reaction turbine at the outer radius and flows
from the outer radius to the inner radius of the turbine runner
• The oil while flowing through the runner, transfers its energy to the blades of the runner and
makes the runner to rotate
• Finally, the driven shaft rotates, the oil then flows back into the pump impeller
• Thus, a continuous circulation of oil occurs, and hence continuous rotation of both shafts are
maintained
• The hydraulic coupling
• The power is transmitted hydraulically from the driving shaft to the driven shaft and the driven
shaft is free from engine vibrations
• The speed of the driven shaft is always less than the speed of the driving shaft by about 2 percent
• The efficiency or the power transmission by hydraulic coupling is about 98 %
• The efficiency of hydraulic coupling
• The hydraulic coupling
• The hydraulic coupling
• Slip of fluid coupling is defined as the ratio of the difference of the speeds of the driving and
driven shafts to the speed of the driving shaft
• At high engine speeds, the coupling is very efficient
• It gives one to one ratio between driven and driving members
• At medium speeds, the coupling is not quite as effective
• At low engine speeds, there is little power transfer
• When the engine speed is low, there is no power transfer
• The hydraulic coupling
• Slip of fluid coupling is defined as the ratio of the difference of the speeds of the driving and
driven shafts to the speed ur the driving shaft
• At high engine speeds, the coupling is very efficient
• It gives one to one ratio between driven and driving members
• At medium speeds, the coupling is not quite as effective
• At low engine speeds, there is little power transfer
• When the engine speed is low, there is no power transfer
• The fluid coupling cannot increase the torque above that produced by the crank shaft
• Torque converter
• Hydrodynamic transmissions use the inertia of a fluid flow
• An engineer Hermann Föttinger who combined the impeller pump, turbine wheel and a reactor
to absorb the reaction torque together in one housing
• A device used to transmit, increased or decreased power from one shaft to another
• The torque transmitted at the driven shaft may be more or less than the torque available at the
driving shaft
• The torque at the driven shaft may be increased by about five times the torque available at the
driving shaft with an efficiency of about 90 %
• Torque converter
• Component
• A hydrodynamic clutch with the two main components impeller and turbine wheel permits no
torque conversion, since no torque can act against the housing
• A torque converter must have in addition at least one reactor to provide reaction forces
• Torque converter
• Function
• Acts as a fluid coupling to smoothly connect engine power through oil to the transmission gear
train
• Multiplies the torque or twisting effort from the engine when additional performance is desired
• Provides direct drive through the torque converter
• Components
• The pump or impeller (driving member)
• The turbine or runner (driven or output member)
• The stator (reaction member)
• The converter cover is welded to the pump to seal all three members in an oil filled housing
• The converter cover is bolted to the engine flexplate which is bolted directly to the engine
crankshaft
• The converter pump is therefore mechanically connected to the engine and turns at engine speed
whenever the engine is operating
• Torque converter
• Friction Clutches
• Operation
• When the engine is running and the converter pump is spinning, it acts as a centrifugal pump,
picking up oil at its center and discharging this oil at its rim between the blades
• The shape of the converter pump shell and blades cause this oil to leave the pump spinning in a
clockwise direction toward the blades of the turbine
• As the oil strikes the turbine blades, it imparts a force to the turbine causing it to turn
• When the engine is idling and the converter pump is not spinning fast, the force of the oil leaving
the pump is not great enough to turn the turbine with great torque
• This allows the vehicle to stand in gear with the
engine idling. As the throttle is opened and
pump speed increases, the force of the oil
increases and more engine power is
transmitted to the turbine member and the
gear train
• Torque Converter
• Torque converter
• Oil flowing from the pump impeller to the turbine exerts a torque on the stationary vanes
• These vanes change the direction of flow of oil making a possible torque and speed
transformation
• The torque relationship
• Torque converter
• Torque converter
• At low speed ratios, torque converters are more economical than fluid coupling
• Conversely, when the speed ratio approaches unity, the fluid coupling is economical
• Far optimum advantages in a system, the transmission system is designed that the unit acts as a
converter allow speed ratios and as a coupling at high speed ratios
• The characteristics or fluid coupling and Torque convertor
• Torque converter
• At low speed ratios, torque converters are more economical than fluid coupling
• Conversely, when the speed ratio approaches unity, the fluid coupling is economical
• Far optimum advantages in a system, the transmission system is designed that the unit acts as a
converter allow speed ratios and as a coupling at high speed ratios
• The characteristics or fluid coupling and Torque convertor
• The torque ratio of a torque convertor falls with increasing speed ratios, while at the same
time the efficiency increases
• At a speed ratio between 0.65 and 0.7 (design value), the transmission efficiency reaches its
maximum value of about 85%
• If the speed ratio exceeds the design value, the efficiency decreases rapidly
• However, the efficiency of the fluid coupling increases continuously with speed ratio
• It reaches a maximum value of about 95% when the speed ratio is 0.95
• The rise in efficiency of the fluid coupling is not as fast as that of the torque convertor during
initial stages
• The torque convertor, running at its design ratio (0.65 - 0.7), has a higher efficiency than that
of the fluid coupling at the same speed ratio
• Thus the torque convertor is a more efficient power transmitting device at low speed ratios
while the fluid coupling is more efficient device at speed ratio nearer to 0.95 or 0.98
• Torque converter
• For automobiles, the speed ratio varies between 0 and 0.98
• Therefore, it is usual to have a combination of fluid coupling and hydraulic convertor so as to
avoid the inefficient range of operation of each device
• At low speed ratios, the unit acts as a torque convertor while at high speed ratios, the same unit
works as a fluid coupling with torque ratio of unity and its efficiency increases to about 0.98 with
an increasing speed ratio
• Torque converter
• The individual torque values can be determined using Euler’s turbine equation
They depend on the flow rate Q, the fluid density 𝜌 and the angular momentum difference Δ(𝑟 𝑐𝑢 )
• The angular momentum is the product of the radius r and the circumferential component 𝑐𝑢 of the
absolute speed
• Torque converter
• principles
• hydrodynamic transmissions use the inertia of a fluid flow
• An engineer Hermann Föttinger who combined the impeller pump, turbine wheel and a reactor
to absorb the reaction torque together in one housing
• The advantages of the hydrodynamic transmission
• Load-dependent, continuously variable ratio changing: Adapting the ratio to the load on the
output shaft
• Virtually non-wearing: No abrasion
• Elastic connection between engine and powertrain: Vibration and torque shock loads are damped
since input and output are not positively engaged
• Reaction effect can be eliminated: No stalling of the engine
• The disadvantages of the hydrodynamic transmission
• Low efficiency over broad operating ranges: Requires a rear-mounted gearbox
• Complexity of the rear-mounted gearbox: The gearbox must be power-shiftable (conventional
automatic transmission, CVT) or have an additional gear shifting clutch (torque converter clutch
transmission)
• Torque converter
• The efficiency 𝜂 𝑇𝐶 of the torque converter
𝑇𝑇 𝜔𝑇
Where the torque ratio 𝜇 = and the speed ratio 𝜈 =
𝑇𝑃 𝜔𝑃
• Torque can only be transmitted where there is a speed difference between the impeller and the
turbine
• The pressure difference arising from differing centrifugal forces circulates the fluid, enabling
momentum exchange between the two wheels
• The speed difference relative to the speed of the pump is referred to as slip S
• Torque converter
• The interaction between the active wheel blade and working liquid is used to realize the
interconversion of mechanical energy and liquid energy
• The impeller continuously absorbs the power the internal combustion engine and transfers it to the
turbine
• The transmitted torque is changed through the change of the liquid moment of momentum
engine crankshaft 1
Hydraulic torque converter 2
housing
turbine 3
impeller 4
fixed guide wheel 5
guide wheel fixing casing 6
driven shaft 7
starting gear ring 8
• Torque converter
• The impeller 4 is integrated with the hydraulic torque converter housing 2 and bolted to the flange at
the rear end of the engine crankshaft 1
• The hydraulic torque converter housing 2 is made into two halves and welded into one after assembly
(some are bolted)
• The starting gear ring 8 is provided outside the housing
• The turbine 3 is connected with other parts of the powertrain through the driven shaft 7
• The guide wheel 5 is fixed on the guide wheel fixing casing 6
• Torque converter
• Transferring torque
• The working fluid stored in the ring cavity not only has circular motion around the hydraulic torque
converter shaft, but also has the circular flow in the circulation circle along the direction indicated by
the arrow so that the torque can be transferred from the impeller to the turbine
• The hydraulic torque converter can transfer the torque, and change the torque value output by the
turbine with the turbine speed (reflecting the driving speed of the vehicle) when the impeller torque is
unchanged
• During the circular flow, the fixed guide wheel gives a moment of reaction to the turbine, so that the
output torque of the turbine is different from the input torque of the impeller
• Torque converter
• Transferring torque
engine crankshaft 1
Hydraulic torque converter housing 2
turbine 3
impeller 4
fixed guide wheel 5
guide wheel fixing casing 6
driven shaft 7
starting gear ring 8
• Torque converter
• The working principle of the hydraulic torque converter
• The center lines of flow paths of all circulation circles are expanded into a straight line on the same
plane
• In the expanded view, the impeller B, turbine W and guide wheel D form three annular planes
• Torque converter
Roller 1
Pourable resin chock 2
turbine hub 3
flange 4
Turbine 5
starting gear ring 6
torque converter housing 7
Impeller 8
Guide wheel 9
OWC outer race 10
OWC inner race 11
Impeller hub 12
torque converter output shaft 13
guide wheel fixing casing 14
thrust washer 15
OWC cover 16
• Torque converter
• The torque converter housing 7 is welded by the front and rear halves. The front end of the housing is
connected to a tray fitted with a starting gear ring 6 and screwed to flange 4 at the rear end of the
crankshaft
• The impeller 8 is equipped with radial flat blades
• The impeller hub 12 welded on the impeller housing can rotate freely
• The turbine 5 has sloping curved blades
• The turbine hub 3 riveted with the turbine housing is splined with the output shaft 13 of the torque
converter
• The impeller and turbine blades and housing are steel plate stamping parts
• The blade and inner ring are spot-welded and brazed to the housing
• The guide wheel is cast in aluminum alloy and is fixedly connected to the OWC outer race 10
• Torque converter
• The roller type one-way clutch of the torque converter
• The guide wheel 3 is riveted on the outer race 2 with rivet 4 (or with spline)
• The inner race 1 is splined with the fixing casing 14 so the inner race is fixed
• The inner surface of the outer race 2 has several eccentric arc surfaces
• The roller 5 is often pressed by the laminated spring 6 to the narrower end of the raceway between
the inner and outer races, so as to wedge inner and outer races
inner race 1
outer race 2
guide wheel 3
rivet 4
roller 5
laminated spring 6
• Torque converter
• In case of low turbine speed and large difference from the impeller speed, the fluid from the turbine
impacts on the guide wheel blade, trying to make the guide wheel 3 rotate clockwise
• Since the roller 5 is wedged at the narrow end of the raceway, the guide wheel and the OWC outer
race 2 are clamped and fixed together on the inner race 1
• At this point, the hydraulic torque converter plays the role of increasing the torque
• When the turbine speed rises to a certain degree, the impact force of the fluid on the guide wheel is
reversed, so the guide wheel rotates freely in the same direction with respect to the inner race and the
turbine
