Compressor clutch pulley
Drag coe cient
is a dimensionless quantity that is used to quantify the drag or resistance of an object in a
uid environment, such as air or water. It is used in the drag equation in which a lower drag
coe cient indicates the object will have less aerodynamic or hydrodynamic drag. The drag
coe cient is always associated with a particular surface area.
Reducing the drag coe cient in an automobile improves the performance of the vehicle as it
pertains to speed and fuel e ciency.
0.3-0.35 best cars cd → should be less than 0.3
Design:
• Stator
• Three coil systems
• Multiples of three coils
Rotor:
• Rotor
• Synchronous motor with permanent magnet:
• Rotor = permanent magnet with north pole and south pole
• Several poles
• Other rotor designs also possible
Operation:
• Stator coils connected to three alternating voltages with o set oscillations
• Magnetic rotary eld
• Drives the rotor
• Actuated by power electronics (= inverter, frequency converter)
Observations:
- Higher frequency
Faster rotation of the magnetic eld
Faster rotor rotation
• Higher voltage
Higher coil current
Higher rotor torque
Disadvantages of a synchronous motor with permanent magnet:
1. Powerful permanent magnets
• Require rare earth elements
• Very scarce, costly
2. Permanent magnetic eld of the permanent magnets
• High torque only by increasing the stator coil current
• Reaches torque limit
Synchronous motor with permanent magnet for small vehicles or hybrid drives
Rotor with solenoid:
• Coil current can be adapted to requirements
• Output limited by thermal load on coils only
Disadvantage:
• Current transferred using brushes and slip
rings
• Wear
• Rotor consumes energy
• Less e cient
Asynchronous motor:
• No slip rings and power supply
• Rotor with cage
• Cage features several current loops = coil with one coil winding
Stator supplied with three-phase current:
• Magnetic rotary eld of the stator
• Induction generates current in the cage
• Rotor with individual magnetic eld
• Correlation of magnetic elds results in rotational movement
Advantages of asynchronous motors:
• Robust
• Output restricted by heat development only
• Suitable for powerful drives
Disadvantage of the asynchronous motor:
• Low e ciency
Which type of electric motor is used in the drive of these vehicles?
Direct current motor
Stepper motor
Synchronous motor
Asynchronous motor
Direct current motor
Stepper motor
Synchronous motor
Asynchronous motor
Three phase AC motor
Alternator concept
Voltage generation:
Magnetic eld of the permanent magnet
Electric circuit
• Consisting of conductor loop, sliding contacts, and bulb
Conductor loop rotation:
Bulb
Lights up permanently
Does not light up
Lights up according to the rotation cycle
How bright is the bulb if the conductor loop assumes the following positions?
Variation with time of the induced voltage
Wave-type curve:
• Constant change from positive to negative and vice versa
• Alternating voltage
Voltage curve at various rotational speeds
Low rpm
• Slow change to voltage
• Low maximum voltage
Medium rpm
• Voltage changes at average speed
• Average maximum voltage
High rpm
• Fast voltage change
• High maximum voltage
Alternating voltage
• Must be recti ed
• With diodes ( ow valve)
What do you notice about the voltage curve?
The alternating voltage remains unchanged.
exclusively the positive part of the wave appears at the bulb.
Exclusively the negative part of the wave appears at the bulb.
The alternating voltage has dropped.
Half-wave recti cation
Voltage values
• Mean value: 12 V
• Voltage peaks: brie y 42 V
Puts some electronic circuits at risk
Do not use chargers with half-wave recti cation!
Which voltage curve do you expect if the recti er diode is connected in a circuit like this?
Positive half-waves
Negative half-waves
No recti cation
In which arrangement does the bulb more frequently light up very brightly?
Without recti cation
If the positive half-wave is allowed to pass through
If the negative half-wave is allowed to pass through
Identical for both recti er circuits and most frequent actuation
Alternator concept
Three - phase alternator
Compact alternator structure
Generating the magnetic eld:
• Using solenoids
• In the rotor
• Excitation winding
Generating the alternator voltage
• Coil winding
• In the stator
• Three coils (stator coil)
left
WDD 222082 ← baumuster 1A
rightproduction
WDB
engine type 000792 car number
WDC
A = sindel ngen Stuttgart
F = Bremen → SL
G - class: Graz x
Induction:
Change of a magnetic eld
• Change strength (solenoid on/o )
• Change position (move magnet)
