Automatic_transmission

1. q
Dr. Mohamed Essam
February 2024
Automatic Transmission
Autotronics Program
Lec. 1
‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

2. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

3. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
• An automatic transmission or transaxle selects gear ratios according to:
• Engine speed
• Powertrain load
• Vehicle speed, and other operating factors.
• Little effort is needed on the part of the driver, because both upshifts and downshifts occur
automatically.
• A driver-operated clutch is not needed to change gears, and the vehicle can be brought to a stop
without shifting to neutral.
• The driver can also manually select a lower forward gear, reverse, neutral, or park.
• The number of available forward gears in current vehicles varies from four to eight. Some have
zero fixed ratios and use a constantly variable design, where the ratio changes according to
conditions.
• Most new automatics also feature a lockup torque converter. Some automatic transmissions are
fitted with a transfer case that sends torque to additional drive axles to allow for four-wheel or all-
wheel drive.
• Until recently, all automatic transmissions were controlled by hydraulics only. However, most
systems now feature computer-controlled operation of the torque converter and transmission.

4. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
Automatic Transmission
• The most widely used automatic transmissions and transaxles are four-speed units with an
overdrive fourth gear. Five- and six-speed transmissions are also used. Many older cars had three
speeds and a select group of newer cars have five speeds. Most new automatics also feature a
lockup torque converter.
• Seven- and eight-speed units are mostly found in luxury vehicles. Today’s transmissions have at
least one overdrive gear to reduce fuel consumption, lower emission levels, and reduce noise
while the vehicle is cruising. Today’s transmissions also have a lockup torque converter that
eliminates loss of power through the torque converter. The torque converter lockup clutch and
shifting of the transmission are computer controlled.

5. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
Automatic Transmission
• Hydraulic clutches and hydraulic (hydrodynamic) torque converters are widely used in
transporting machines. They are combined into a class of devices called hydraulic transmissions
and have many features in common: the energy from the driven to the driving shaft is transmitted
by a fluid circulating in a circulation loop (cycle) and there are vanes on the driven and driving
wheels. But there is also a basic difference between hydraulic clutches and hydraulic torque
converters.
• Hydraulic torque converter is a device that contains an impeller (pump), a runner (turbine), and at
least one guide apparatus (a reactor). It is fully justifiable to call the driving wheel in a hydraulic
torque converter an impeller and the driven wheel a turbine runner because it is precisely how
the energy is transmitted from the driving to the driven shaft. The torque in a pump impeller Mp
and in a turbine runner Mt is unequal.
• Hydraulic clutch is a device where there is no reactor and the vanes are made in the form of
straight plates perpendicular to the surface of a torus (cylindrical ring) where they are located.

6. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
Automatic Transmission
• Hydraulic clutches and hydraulic (hydrodynamic) torque converters are widely used in
transporting machines. They are combined into a class of devices called hydraulic transmissions
and have many features in common: the energy from the driven to the driving shaft is transmitted
by a fluid circulating in a circulation loop (cycle) and there are vanes on the driven and driving
wheels. But there is also a basic difference between hydraulic clutches and hydraulic torque
converters.
• Hydraulic torque converter is a device that contains an impeller (pump), a runner (turbine), and at
least one guide apparatus (a reactor). It is fully justifiable to call the driving wheel in a hydraulic
torque converter an impeller and the driven wheel a turbine runner because it is precisely how
the energy is transmitted from the driving to the driven shaft. The torque in a pump impeller Mp
and in a turbine runner Mt (dash line) is unequal (Fig. 1).

7. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
Hydraulic Torque Converter
• The torque converter is located between the engine and the transmission/transaxle and performs
the following functions.
1. Transmits and multiplies engine torque
2. Acts as a clutch between the engine and the transmission/transaxle
3. Allows slippage, which makes it possible for the transmission to be engaged in gear even
when the vehicle and wheels are stopped
• The three major parts of the torque converter include:
• Impeller. The impeller is the driving member and rotates with the engine, and is located on
the transmission side of the converter. The impeller inside the torque converter is also called
the pump (not to be confused with the pressure pump).
• Turbine. The turbine is located on the engine side of the converter. The impeller vanes pick up
fluid in the converter housing and direct it toward the turbine. Fluid flow drives the turbine,
and when the flow between the impeller and the turbine is adequate, the turbine rotates and
turns the transmission input shaft.
• Stator. A torque converter also contains the stator, or reactor, which is a reaction member
mounted on a one-way clutch.

8. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

9. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
Hydraulic Torque Converter
• The vanes used in each of the three elements of a torque converter are curved to increase the
angle of the fluid flow. This also increases the force exerted by the fluid and improves the
hydraulic advantage. The outlet side of the impeller vanes accelerates the fluid as it leaves the
impeller to increase torque transfer to the turbine.
• The impeller and the turbine contain a curved shelf known as split rings to more efficiently move
the fluid.
OPERATION
• A torque converter acts like two fans pointing toward each other. Air pushed by the powered fan
causes the blades of the nonpowered fan to rotate. In the case of a torque converter, the two fans
are the turbine and the impeller. The transmission fluid is the air that is being forced to turn the
nonpowered fan. The fluid only connection between the impeller and the turbine allows for
absorption of sudden and harsh shocks in speed and/or torque. The curve of the stator vanes is
opposite to the curve of the impeller and turbine vanes.
• Since the stator is located between the impeller and turbine, it changes the direction of the fluid
as it leaves the turbine, and thereby multiplies the torque from the impeller. Torque converters
are single-piece, welded and balanced assemblies that cannot be disassembled or easily repaired.
Although they can be rebuilt using specialized equipment, most shops simply replace converters
as a unit if they fail.

10. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

11. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
TORQUE CONVERTER FLEXPLATE
• The torque converter is typically bolted to a thin metal disc called a flex plate.
The center of the flex plate often has a pilot indention for the nose of the
converter, and the flex plate itself is bolted to the rear flange of the engine.
• The flex plate replaces the heavy flywheel used with a manual transmission.
An important function of a flywheel is to smooth out engine pulsations and
dampen vibrations. An automatic transmission does not require a conventional
flywheel because the weight of the torque converter provides enough mass to
dampen engine vibrations.
• An external ring gear generally attaches to the outer rim of the flex plate,
while on some applications the ring gear may be welded to the outside of the
torque converter cover. This ring gear engages the starter motor pinion gear to
turn the engine during starting. Some manufacturers also place the crankshaft
position sensor tone ring in the outer lip of the flex plate.
• TORQUE CONVERTER DRIVES THE PUMP Oil pump drive shafts generally pass
through the converter inside a hollow input or transfer shaft and internally
connect to the converter housing by splines or a hexagon-shape shaft. The
torque converter is also responsible for driving the transmission oil pump.

12. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

13. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
TRANSMISSION INPUT SHAFT
• Most rear-wheel-drive transmissions use an inline method to drive the converter and provide a
direct mechanical connection between the turbine and the transmission input shaft. In a typical
design, splines on the turbine connect it to the transmission input shaft and the stator hub
mounts on a one-way overrunning clutch. The one-way clutch mounts on splines to a stationary
extension of the oil pump called the stator support, or reaction shaft.
TORQUE CONVERTER OPERATION
• Fluid sent to the torque converter from the transmission oil pump is picked up by the rotating
vanes of the impeller and transferred to the turbine vanes. The two types of fluid flow inside a
torque converter are rotary flow and vortex flow.
1. Rotary flow is created by the rotation of the torque converter and causes the oil (ATF) to flow
around the circumference of the torque converter.
2. Vortex flow is the flow of the fluid from the impeller to the turbine and back to the impeller.

14. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

15. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
TORQUE MULTIPLICATION PHASE
• Torque multiplication in a torque converter occurs due to the following series of events inside the
torque converter.
1. Fluid leaving the turbine vanes strikes the concave, or front side, of the stator vanes.
2. The stator vanes change the direction of the fluid so that it pushes the back side of the impeller
vanes.
3. The stator redirects fluid flow because it remains stationary during the torque multiplication
phase.
4. The stator hub mounts on a one-way clutch, freewheeling in a clockwise direction, but locking
when driven in a counterclockwise direction.
5. The stator redirects fluid flow because it remains stationary during the torque multiplication
phase.
6. When fluid from the turbine strikes the concave face of the stator vanes, it tries to drive the
stator counterclockwise. By locking the stator, it can redirect the fluid back to the impeller.
7. The force of the fluid redirected from the stator adds to the force of the fluid flowing to the
impeller, to increase the overall torque being transferred from the impeller to the turbine. This
is called the torque multiplication phase.

16. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

17. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
TORQUE MULTIPLICATION PHASE
• Torque multiplication occurs whenever the vortex flow makes a full cycle
from impeller to turbine, through the stator and back to the impeller. A
torque converter multiplies torque in relation to the speed ratio.
• At low speed ratios, the impeller (engine speed) is turning much faster than
the turbine (transmission input shaft speed), so vortex flow is high and
torque multiplication occurs.
• As turbine speed increases and approaches impeller speed, rotary flow
increases, which reduces both vortex flow and torque multiplication.
• As the speed ratio approaches 90%, torque multiplication becomes minimal
and a torque converter functions like a fluid coupling.
• The stator hub mounts on a one-way clutch, freewheeling in a clockwise
direction, but locking when driven in a counterclockwise direction. When
fluid from the turbine strikes the concave face of the stator vanes, it tries to
drive the stator counterclockwise. By locking the stator it can redirect the
fluid back to the impeller.

18. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
COUPLING PHASE
• When the speed ratio is 90° or more, fluid flow in the torque converter is mostly rotary flow and
the angle of flow from turbine to stator increases. This is called the coupling phase. When the
torque converter reaches this phase, the turbine is traveling at nearly the same speed as the
impeller, rotary flow is much greater than vortex flow, and the torque multiplication drops.
• During this phase, fluid from the turbine strikes the convex side, or backside, of the stator vanes
rather than the concave side. As the force of fluid striking the backside becomes great enough to
drive the stator clockwise, the stator one-way clutch overruns. With the clutch overrunning the
turbine, impeller, and stator, all rotate in the same direction and at approximately the same
speed. The stator unlocks and freewheels once the angle of fluid flow changes enough to strike
the opposite side of the stator vanes and rotate the stator clockwise.
• Torque multiplication drops as the torque converter approaches the coupling phase because the
stator no longer redirects fluid to increase the flow from impeller to turbine. When the torque
converter reaches coupling speed, the turbine is traveling at nearly the same speed as the
impeller, rotary flow is much greater than vortex flow, and the torque converter simply transmits
torque like a fluid coupling. During the coupling phase, most converters lose about 10% coupling
efficiency, which means that there is a 10% speed difference between the impeller and turbine.

19. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
STALL SPEED
• Stall speed is the engine speed when the engine drives the impeller at the maximum speed
possible without moving the turbine. The engine speed at which this occurs is called the torque
converter stall speed. When the impeller rotates but the turbine does not, the speed ratio is zero.
This is the lowest possible speed ratio and the greatest possible torque multiplication. Most
modern torque converters multiply torque in the range of 2:1 to 2.5:1 at the stall speed. Typical
stall speeds are designed to match the needs of individual vehicles and engines and range from a
low of about 1,450 RPM to as high in some stock vehicles as 2,500 RPM or even higher for high-
performance torque converters.
NORMAL OPERATION
• When the transmission selector is moved from park (P) or neutral (N) into a drive gear, some
engine torque is transferred to the input shaft of the transmission or transaxle. The vehicle will
move slightly if the brakes are released. This slight movement of the vehicle when the engine is at
idle speed and the brakes are released is called creep. Therefore, a slight movement is normal for
a vehicle equipped with an automatic transmission.
• NOTE: Vehicle creep is more noticeable when the engine is cold due to the higher idle speed.

20. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
TORQUE CONVERTER DIAMETER
• The outside diameter of a torque converter and the angle of its stator blades determine the stall
speed of the converter. When both a small and large diameter converter share the same stator
blade angle and turn at the same speed, the smaller converter creates less centrifugal force to
move the fluid inside.
• As a result, the small diameter converter has a higher stall speed, multiplies torque at higher
engine speeds, and will not couple until the engine reaches high speeds. In comparison, the large
diameter converter has a lower stall speed, multiplies torque at lower engine speeds, and also
couples at a lower engine speed.
• Vehicle manufacturers select torque converters to match the powertrain requirements and
operating demands of each vehicle application.
• A vehicle with a large engine that produces a lot of torque at low RPM will often use a torque
converter that couples at low speeds for greater fuel economy and lowest possible exhaust
emissions.
• Vehicles with smaller engines that produce less torque at low RPM will use a torque converter
that allows the engine to operate higher in its torque curve, where more power is available. High-
performance vehicles with automatic transmissions use small diameter converters for the same
reason. Therefore, the vehicle manufacturer selects the best stall speed based on the power band
of the engine and the weight of the vehicle.

21. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
Multi-stage converter
• When greater torque multiplication is required, a
multistage converter is often used. This type uses a series
of turbines and stators, and the shown Figure shows its
main features.
• When the converter is placed under conditions of low
pump and low turbine speeds, the fluid will follow the
path. The energy in the fluid is gradually extracted as it
passes through each turbine and stator stage.

22. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
LOCKUP TORQUE CONVERTER
PURPOSE AND FUNCTION
• Even the most efficient torque converters slip 8% to 12% during operation, because the fluid that
transmits torque exhibits a type of slippage known as fluid shear.
• Fluid shear creates friction heat but performs no work when the different layers of fluid slide past each
other. Eliminating torque converter slippage can improve fuel economy approximately 4% to 5% during
freeway cruising. With the increased emphasis on fuel economy and low exhaust emissions for late
model vehicles, this became an important goal for automotive engineers.
• An additional benefit to reducing slippage is a reduction of transmission operating temperature, which
increases transmission life expectancy. Lockup torque converters reduce slippage by using a torque
converter clutch (TCC) to lock the impeller to the cover (shell). Similar to a clutch for a manual
transmission, a TCC uses a friction disc operated by a hydraulic piston to mechanically couple the
turbine to the converter (cover /shell). Engaging the clutch creates mechanical connection between the
engine and transmission, resulting in a direct 1:1 drive ratio without slippage.

23. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

24. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
CONVERTER CLUTCH CONTROL
• The first hydraulic lockup converters were controlled entirely by hydraulic pressure and spool valves in
the transmission valve body. Some older designs added simple electric switches and solenoids to
control pressure to the converter clutch. Since the early 1990s, the powertrain control module (PCM)
or the transmission control module (TCM) regulates the timing and application of the clutch. The
torque converter clutch operates under the following conditions.
• Lockup may also be limited to specific vehicle speeds or operating conditions. For most vehicles,
lockup can occur at speeds over 25 to 30 mph (40 to 48 km/h) but can occur sooner in many newer
transmissions/transaxles. Once lockup occurs, the clutch may disengage automatically during certain
operating conditions such as part- or full-throttle downshift. At these times, the increased acceleration
requirements generally override the need for better fuel economy.
• Most computer systems can lock and unlock or modulate a converter clutch hundreds of times per
minute to meet the vehicle demands of the moment and some recent systems also allow partial lockup
of the torque converter. Traditional lockup torque converters operate either locked or unlocked. Partial
lockup converters allow a regulated amount of slippage at the clutch. Each type of torque converter
requires a certain type of friction material.
• This allows the converter to lock up smoothly, improving fuel economy and performance, without the
drawback of shock to the driveline. Using the wrong type of automatic transmission fluid (ATF) can
alter the frictional properties of the lockup clutch, leading to shudder or other similar customer
complaints.

25. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

26. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
Lockup Piston Clutch
• The lockup piston clutch has a piston-type clutch located between the front
of the turbine and the interior front face of the shell (Shown Figure). Its
main components are a piston plate and damper assembly and a clutch
friction plate.
• The damper assembly is made of several coil springs and is designed to
transmit driving torque and absorb shock.
• The clutch is controlled by hydraulic valves, which are controlled by the
PCM. The PCM monitors operating conditions and controls lockup according
to those conditions.
• To understand how this system works, consider this example. To provide for
clutch control, Chrysler adds a three-valve module to its standard
transmission valve body. The three valves are the lockup valve, fail-safe
valve, and switch valve.
• The lockup valve actually controls the clutch. The fail-safe valve prevents
lockup until the transmission is in third gear. The switch valve directs fluid
through the turbine shaft to fill the torque converter.

27. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

28. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

29. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
Lockup Piston Clutch
• When the converter is not locked, fluid enters the converter and moves to
the front side of the piston, keeping it away from the shell or cover. Fluid
flow continues around the piston to the rear side and exits between the
neck of the torque converter and the stator support.
• During the lockup mode, the switch valve moves and reverses the fluid
path. This causes the fluid to move to the rear of the piston, pushing it
forward to apply the clutch to the shell and allowing for lockup.
• Fluid from the front side of the piston exits through the turbine shaft that is
now vented at the switch valve.
• During acceleration, system fluid pressure increases. If the converter is in its
lockup mode, the higher pressure moves the fail-safe valve to block fluid
pressure to the lockup valve. Spring tension moves the switch valve,
directing fluid pressure to the front side of the piston. The torque converter
then returns to its non-lockup mode.

30. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
PLANETARY GEARS
• Nearly all automatic transmissions rely on planetary gear sets to transfer
power and multiply engine torque to the drive axle. Compound gear sets
combine two simple planetary gear sets so load can be spread over a
greater number of teeth for strength and also to obtain the largest number
of gear ratios possible in a compact area.
• A simple planetary gear set consists of three parts: a sun gear, a carrier with
planetary pinions mounted to it, and an internally toothed ring gear or
annulus.
• The sun gear is located in the center of the assembly. It can be either a spur
or helical gear design. It meshes with the teeth of the planetary pinion
gears.
• Planetary pinion gears are small gears fitted into a framework called the
planetary carrier. The planetary carrier can be made of cast iron,
aluminum, or steel plate and is designed with a shaft for each of the
planetary pinion gears. (For simplicity, planetary pinion gears are called
planetary pinions.)
• Planetary pinions rotate on needle bearings positioned between the
planetary carrier shaft and the planetary pinions. The carrier and pinions
are considered one unit—the midsize gear member.

31. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬
PLANETARY GEARS
• The planetary pinions surround the sun gear’s center axis and they are
surrounded by the annulus or ring gear, which is the largest part of the
simple gear set. The ring gear acts like a band to hold the entire gear set
together and provide great strength to the unit. To help remember the
design of a simple planetary gearset, use the solar system as an example.
• The sun is the center of the solar system with the planets rotating around it;
hence, the name planetary gear set.

32. ‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬

33. q
Thank you
‫والطاقة‬ ‫الصناعة‬ ‫تكنولوجيا‬ ‫كلية‬