Actuators and optical speed sensor and application in automatic transmission
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An actuator is a kind of motor that controls or moves mechanisms or
Actuators are extremely useful devices and have diverse range of uses in
It is operated from a source of energy usually from electric current
,hydraulic fluid pressure , pneumatic pressure.
An actuator is a mechanism by which a control system acts on
The control system can be an electronic system , software based..
Type of medium
Hydraulic pneumatic electrical
“Pressure exerted anywhere in a confined incompressible fluid is
transmitted equally in all directions throughout the fluid, acts upon every
part of the confining vessel at right angles to its interior surfaces”.
F = P x A
Hydraulic refers to means and mechanisms of transfer of power
Hydraulic systems convert mechanical power to fluid power , transmit
the fluid power to some location , convert back this fluid power to
mechanical power to do useful work.
Hydraulic systems are used when large force are required.
CYLINDER AND PISTON
DIRECTION CONTROL VALVE
PRESSURE RELIEF VALVE
WORKING OF HYDRAULIC ACTUATION SYSTEM
Α directional control valve controls the direction of oil flow in the system
and, therefore, the direction of motion of the cylinder piston.
The valve has four ports, labeled Ρ, Τ, Α, and Β. Ρ and Τ stand for pressure
and tank (or reservoir), and Α and Β are output ports. The valve can be operated
in three different positions.
Case 1: Lever is moved away
from valve body
case 2 Lever is moving towards
• The oil from the pump flows through path Ρ-Α of the valve to the upper end of the
• The oil pushes the piston downward, which lowers the attached load. At the same time,
the oil at the lower end of the cylinder flows back to the reservoir through path Β-Τ of the
directional control valve.
case 3 : Lever is idle in position
• When the directional control valve lever is released, the valve automatically returns
to the center (neutral) position.
•In this position, all four ports are blocked and oil cannot escape from either side of
•. This stops the movement of the piston and causes oil to flow from the pump back to
the reservoir through the pressure relief valve.
ADVANTAGES and DISADVANTAGES
Actuation of large control surface with minimal input.
Variable speed and direction.
Greater load carrying capacity.
Leakage may occur
High fire risk
Temperature changes alters the viscosity of the fluid.
A pneumatic actuator converts energy (typically in the form
of compressed Air) into motion. The motion can be rotary or linear,
depending on the type of actuator.
A Pneumatic actuator mainly consists of a piston, a cylinder, and valves or
Pneumatic systems are very common, and have much in common with
hydraulic systems with a few key differences
ADVANTAGES AND DISADVANTAGES
Infinite availability of source
Safe and clean
Easy to leak
•The physical principle of all
electric motors is that when an
electric current is passed
through a conductor (usually a
coil of wire) placed within a
magnetic field, a force is exerted
on the wire causing it to move.
COMPONENTS OF AN ELECTRIC MOTOR
The principle components of an electric motor are:
The classic DC motor has a rotating armature in the form of an
A rotary switch called a commutator reverses the direction of
the electric current twice every cycle, to flow through the
armature so that the poles of the electromagnet push and pull
against the permanent magnets on the outside of the motor
As the poles of the armature electromagnet pass the poles of
the permanent magnets, the commutator reverses the polarity of
the armature electromagnet.
During that instant of switching polarity, inertia keeps the
motor going in the proper direction
What is a stepper motor?
1. Motor that moves one step at a time
2. Brushless motor
3. each step is defined by a step angle
4. Rotation of the angle is proportional to the input impulse
Internal components of a Stepper Motor
OPTICAL SPEED SENSORS
• First appeared in general motor vehicles
• It uses photocell , light emitting diode(LED) and two blade mirrored
reflector to generate electrical signal
• More fast and accurate
• Located inside the speedometer head at the back of the control panel
When the vehicle is in motion the speedometer cable spins the two
Each time the reflector rotates through the LED beam , the light is
reflected to the photocell
This generates an electric signal and also electric pulses
the computer is programmed to convert the pulses to the electronic
measurement of vehicle speed
Application in automatic
Since the optical speed sensors are fast and accurate ,they have wide
application in automatic transmission.
Using the data from the optical speed sensors the ,the gear can be shift
automatically at the desired speed.
Thus the vehicle can be operated at optimal efficiency without much
skill of driver.
For the torque converter clutch operation speed sensor data is
Actuators have wide application in our daily life
Hydraulic ,electric and pneumatic actuators are used I
almost all automobiles.
Optical speed sensors are necessary for automatic
Erylmaz B, Wilson BH (2000). Combining leakage and
orifice flows in a hydraulic servo valve model. J.
Dynamic Systems Measurement Control, 122: 576-579