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Electric Motors for Electric cars and Hybrids

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Presentation on theme: "Electric Motors for Electric cars and Hybrids"— Presentation transcript:

1 Electric Motors for Electric cars and Hybrids
Image courtesy of Tesla Corp.

2 High Voltage Safety Contact with voltage of less than 50 volts is unlikely to cause injury. Voltages above 50 volts are potentially deadly. Anytime you work on and around electrical systems that have voltages above 50 volts proper safety procedures must be observed to avoid injury. Danger High Voltage

3 High Voltage Safety Its not the voltage that kills – it’s the current [Amps] The human body conducts electricity – when the voltage is increased, the amount of current passing through the body increases proportionally High Voltage

4 High Voltage Safety 1 milliamp – slight tingle
5 milliamps – mild shock – not painful 6 to 30 milliamps – painful shock – muscle control is lost 50 to 150 milliamps – extreme pain – respiratory arrest - you can’t let go of anything in your grasp – potentially fatal 1 to 4.3 amps – ventricular fibrillation [heart attack] – nerve damage – probably fatal 10 amps – Cardiac arrest – Severe burns – Electrocution

5 High Voltage Safety Orange wires contain high voltage conductors.
Before doing any work that requires disconnecting an orange cable the service plug must be removed.

6 Inverter Capacitors can Kill
Drain Resistor The Inverter contains 3 large capacitors that can hold a charge for up to 5 minutes after the service plug is removed Wait at least 5 minutes before beginning work

7 Class 0 Gloves High voltage rubber gloves with leather covers are required when working on BEV and Hybrid vehicles

8 CAT III DVOM A CAT III rated meter with CAT III rated test leads is needed when working on any high voltage automotive system

9 Remove service plug The service plug disconnects the high voltage battery array from the inverter when removed When working on a high voltage system put the service plug in your toolbox so that a coworker cannot reinstall it to move the vehicle

10 Electric Traction Motors
Electric motors are very compact and are highly efficient A typical gasoline ICE engine has an efficiency rating of a little over 25% Electric motors typically operate between 95% to 98% efficiency 3 phase electrical terminals Resolver terminals Drive spline Coolant tubes Image courtesy of Tesla Corp. Image courtesy of Robert Bosch GMBH

11 Torque - Electric vs. ICE
lbs/ft An electric motor can produce torque at 0 RPM and it’s torque output remains nearly constant – up to about 5000 rpm Because it produces constant torque at nearly all RPMs electric cars do not require multiple speed transmissions 200 Electric Motor 100 ICE Motor 1000 2000 3000 4000 5000 6000 RPM

12 Motor generators The electric motor used to power a BEV or hybrid also functions as a generator When the brakes are applied the electric motor becomes a generator that converts the kinetic energy of the vehicle into electricity that is then stored in the battery This process is called ‘regenerative braking’ Hybrid vehicles also generate electricity when the ICE engine is running and the batteries are discharged

13 3 Types of Electric Motor Generators
Brush type Not suitable for electric vehicles Permanent Magnet Used by all manufactures except Tesla Inductive Used only by Tesla and Toyota RAV-4 EV Image courtesy of General Motors Corp.

14 Brush type electric motors
Stationary field coil Rotating Armature Nearly all of the DC motors used in non-hybrid automobiles use electric motors similar to starter motors A set of graphite brushes conduct electricity to the armature windings at the commutator Brushes are located deep inside the motor and require periodic replacement This type of motor is an efficient motor but it makes a very poor generator Power + Brush Commutator

15 Brushless motors BEV and Hybrid vehicles use 3 phase AC brushless motors There are two types: Permanent Magnet Inductive Nearly all manufactures use the permanent magnet type All Tesla vehicles use the Inductive type The Toyota RAV-4 EV uses an electric driveline/battery system built by Tesla so it also has in inductive motor

16 Permanent magnet motors
Image courtesy of General Motors Corp

17 Permanent magnet rotor
Instead of an armature the permanent magnet motor has a rotor with 6, 8, 12 or 16 or more permanent magnets attached to it’s outer circumference N S

18 Permanent rare earth magnets
The permanent magnets are made of iron alloyed with small amounts of rare earth materials such neodymium or samarium–cobalt mixed with boron 2.2 pounds of neodymium are used in the manufacture of every Toyota Prius

19 Permanent Magnet Motor
The magnets are normally encased in a non-magnetic metal shell to prevent the them from being ripped out of the rotor by centrifugal force at high RPM Permanent Magnet Motor Image courtesy of General Motors Corp

20 Stator coil The permanent magnet rotor is located inside a stator coil
To inverter The permanent magnet rotor is located inside a stator coil The stator coil is a stationary set of electromagnets that surrounds the rotor The stator’s three electromagnetic coils windings are connected to an inverter The inverter is a series of solid state switches that connects the stator coils to the high voltage battery terminals as needed

21 Image courtesy of General Motors Corp
Induction motors Image courtesy of General Motors Corp

22 Copper or aluminum bars
Inductive Motors Copper or aluminum bars Inductive motors have a ‘squirrel cage’ type rotor Copper or aluminum [non magnetic materials] bars are mounted between two rings. Instead of running parallel to the motor shaft they are skewed slightly

23 Rotor for inductive motor
Conductor bars The conductor bars are supported by laminated iron plates that intensify the magnetic fields

24 Inductive motor + The stator coils’ magnetic field induces an electric current into the copper strips on the conductor The electric current will in turn have it’s own magnetic field surrounding it The magnetic field surrounding the copper strip is repelled from the stator’s magnetic field causing the rotor to turn away from the stator coil -

25 Stators for inductive motors
The stator coils for inductive are almost identical to the stator coils in permanent magnet type motors They generally have thicker wires and the wires are often square in cross section to allow more current flow Inductive motors are generally less efficient than permanent magnet motors at low rpm and more efficient at high rpm Cooling fins The Tesla BEV is designed for a top speed of 130 mph so inductive motors were chosen for their high speed advantage The inductive motor was invented by Nickolas Tesla, hence the name of the car company Image courtesy Tesla corp.

26 Stator Assembly The stator coils are wrapped around a laminated iron frame The stator assembly is nearly identical in construction to a conventional alternator stator The power requirements of the traction motor require the stator assembly to be larger and wider

27 Stator windings U V W If the stator windings were removed from the stator frame and then flattened out they would look like this

28 Stator windings U U V V W W Each winding is offset 20 from its neighbor in a 6 pole motor Each winding is called a phase The 3 phases are labeled ‘U’, ‘V’ and ‘W’

29 Stator coil U V W The stator coil is made up of 3 interconnected windings [Phases] 6 poles The each branch is wrapped around laminated iron poles This stator has six poles but there can be many more

30 Stator coil U + V W N S - If a positive voltage is applied to the ‘V’ terminal and negative is applied to ‘W’, the poles shown here in blue become magnetized with the north pole toward the center and the yellow poles are magnetized with the south pole toward the center N S S N

31 Stator coil + U - V S N W When you change the positive voltage to the ‘U’ terminal and negative is applied to the ‘V’, the poles shown here in green become magnetized with the north pole toward the center and the blue poles are magnetized with the south pole toward the center

32 Stator coil U - V S N + W When positive voltage is applied to the ‘W’ terminal and negative is the ‘U’, the poles shown here in yellow become magnetized with the north pole toward the center and the green poles are magnetized with the south pole toward the center

33 Permanent magnet rotor
S The rotor is attached the motor shaft and has a set of permanent magnets embedded near the outer circumference

34 Rotor with permanent magnets
The rotor has a set of permanent magnets bonded to an iron disc In some designs two permanent magnets are arraigned in a ‘V’

35 Magnetic field surrounding the rotor
Lines of magnetic force extend outward from the rotor The magnets will be attracted to stator poles with the opposite polarity and repelled from stator poles with the same polarity N S

36 Motor operation Red = North Pole [inside] + U Green = South Pole - V Blue = not Magnetized W When the stator coils are energized the north poles on the rotor will be attracted to the stator’s south poles and repelled from the north poles

37 Motor operation Red = North Pole [inside] For rotation to continue the polarity of the stator coils must change By applying + positive voltage to terminal ‘V’ and negative to terminal ‘W’ the stator poles move 20 counter clockwise U + Green = South Pole V - Blue = not Magnetized W

38 Motor operation Red = North Pole [inside] - Changing the polarity of the stator coils by changing the electrical polarity at the stator terminals will cause the rotor to move another 20 counterclockwise U Green = South Pole V + Blue = not Magnetized W

39 Motor operation Red = North Pole [inside] + - + - Continuously alternating the polarity of the voltage applied to the stator terminals will produce a rotating magnetic field that will drive the rotor and apply torque to the drive wheels U V + - W

40 Generator Operation The rotor is surrounded by intense magnetic fields.

41 Generator Operation When lines of magnetic force move through a conductor an electric current is induced in the conductor When the lines of magnetic force are approaching the conductor the electrons flow in one direction When the lines of magnetic force move away from the conductor the electrons move in the opposite direction A rotating magnetic field will produce an AC current in the conductor as the field moves toward and away from the conductor

42 Generator Operation during braking
The inverter converts this AC current to DC and sends it back to the HV batteries The current flowing through the stator windings has it’s own magnetic field The magnetic field created by current flowing through the stator windings repels the magnetic field of the rotor magnets This magnetic repulsion puts a load [drag] on the rotor that causes the vehicle to slow down

43 Generator Operation No current flow When the batteries are maximum charge [80% SOC] the inverter will the shut down the flow of current to the batteries. With no current flowing through the stator windings there will be no magnetic resistance applied to the rotor The hydraulic brakes will be needed to slow the vehicle when the batteries are fully charged

44 Hybrid motor location There are three locations for hybrid electric motor[s] BAS [Belt-Alternator-Starter] hybrid systems have a small electric motor / generator bolted to the engine in place of an alternator IMA systems have a single motor / generator sandwiched between the engine and the transmission Two motor hybrids have 2 motor /generators located inside the transmission

45 Image courtesy of General Motors Corp
BAS Systems The GM BAS [Belt-Alternator-Starter] system uses an intermediate voltage motor [42 volts] that is driven by the multi-rib belt The hybrid motor supplies additional torque to the crankshaft when operating under load and functions as a starter during start-stop operation Note: three phase AC cables are not orange – 42 volts max Motor / Generator Image courtesy of General Motors Corp

46 IMA type motor location
Honda introduced the IMA [Integrated Motor Assist] on the 1999 Insight. Stator windings The IMA motor is sandwiched between the back of the engine block and the transmission case CVT Transmission Rotor

47 Honda IMA Motor Stator windings U, V & W electrical cables Since the stator assembly is bolted directly to the engine block heat is removed through the engine cooling jackets Rotor Image courtesy American Honda Motor Corp

48 The rotor in the IMA system is bolted directly to the crankshaft
The flywheel and damper assembly is bolted to the rotor Rotor location Stator windings Rotor

49 Stator and Rotor Assembly
Stator Leads Coolant Inlet Coolant Outlet Porsche also uses an IMA system where the rotor attached to the crankshaft. The stator coils are cooled by engine coolant Image courtesy of Robert Bosch GMBH

50 This special tool is needed to remove the Honda rotor from the crankshaft
The rotor must be removed to service the rear main seal Rotor removal

51 Honda rotor removal/installation tool
Rotor storage Honda rotor removal/installation tool The permanent magnets on the rotor are so powerful it can cause injury if your fingers were to get caught between the rotor and a steel work bench or vise It takes about 100 pounds of pulling force to lift the rotor shown here away from the vice

52 IMA System limitations
The problem with the IMA system is that the crankshaft of the ICE engine is directly coupled to the electric motor This prevents the vehicle from running in electric mode This limits the efficiency of the system as the engine must always be running when the vehicle is in motion Image courtesy of Robert Bosch GMBH

53 Two motor – Single Mode Toyota, Ford and Nissan hybrids use two electric motors located inside the transmission Planetary gearset MG1 MG2

54 Motor / Generators for Prius
By placing 2 electric motors inside the transmission the vehicle can be driven solely by electric power at road speeds up to 30 MPH The planetary gearset allows the torque from the ICE engine to be combined with the torque of the two electric motors Having two electric motors allows the transmission to operate as a CVT MG1 Planetary gearset MG2 Stator temperature sensor connector Image courtesy of Toyota Motors Corp

55 Electric motors located inside the transmission
The stator windings and rotor are exposed to transmission fluid Oil pickup tube Coolant passages inside the transmission case remove excess heat from the stator coils

56 Dual mode transmissions
Dual mode transmissions also have two traction motors Clutch packs Rotor for Motor #2 Clutch packs Rotor for Motor #1 Electric oil pump The dual mode transmission also has conventional clutches that allow engine torque to be applied directly to the drive wheels at highway speeds Image courtesy of General Motors Corp

57 Dual mode transmission
Motor #1 Clutch packs Motor #2 Clutch packs A dual mode system can run: Under electric power with the ICE engine shut down Under a combination of ICE and electric power Under mechanical drive with the electric motors essentially shut down

58 Cooling electric motors
Although the electric motor [permanent magnet or inductive] is up to 98% efficient that 2% of the electrical energy that is not converted to mechanical power is converted into heat Excess heat is normally removed by a liquid cooling system but some motors use air cooling Coolant passage for MG2 Coolant passage for MG1

59 Prius coolant passages
The Prius has coolant inlet and outlet tubes for each of the electric motors inside the transaxle Prius coolant passages Coolant inlet Coolant outlet

60 Liquid cooling systems
Two motor hybrid systems use liquid cooling systems to remove excess heat from the electric motor/generator and inverter This cooling system is completely separate from the ICE engine’s cooling system and has it’s own radiator and water pump The high temperatures of the ICE cooling system would damage the electronics inside the inverter Coolant is long life antifreeze and water An electric water pump circulates coolant through the inverter and motor generator housing [transmission]

61 Two coolant reservoirs
Two motor hybrids have two coolant reservoir tanks One for the ICE engine typically located an the radiator support A second reservoir for the inverter is typically bolted to the side of the inverter case A coolant level sensor is located inside the reservoir for the inverter/motor Most manufactures recommend that the fluid level in the inverter reservoir should never be ‘topped off’ Topping off the fluid level will mask a slow leak in the system – preventing the warning light from turning on

62 Two coolant reservoirs
Reservoir for ICE engine coolant Reservoir for electric motors and inverter

63 Bracket for A/C compressor
BEV motor cooling This Nissan Leaf traction motor has cooling passages similar to an ICE engine – Note the freeze out plugs an the outside of the housing Bracket for A/C compressor Coolant outlet Coolant inlet Freeze-out plugs

64 Motor Cooling Gear reduction fill/level plug Earth brush cover
Gear reduction unit drain plug Coolant drain plugs Radiator Freeze-out plugs Coolant hose 2012 Nissan Leaf

65 BEV Cooling System Inverter An electrically driven water pump circulates coolant through the inverter, traction motor and radiator. To Batteries Electric Water Pump Radiator Motor The PCM monitors the motor temperature The PCM increases the water pump speed as temperature increases

66 Electric Water Pump Pump speed can be controlled by the PCM by pulse width modulation In a PWM system the computer varies the on time – vs. off time to control the flow of electrical current through the motor The electric motors that drive the A/C compressor will use a 3 phase permanent magnet motor who’s speed is controlled by an inverter

67 Resolver Resolver coil The Resolver is a sensor that sends rotor position data to the Hybrid or EV control module Elliptical disc

68 Resolver The PCM needs to know where the rotor is before it can determine the proper stator phase coils to energize Unlike a crankshaft position sensor that generates an electrical pulse as the engine rotates the resolver can determine the position of the rotor when the electric motor is not turning

69 Resolver Circuit The resolver provides the Hybrid Control Module with rotor position information AC Signal The AC signal in coil ‘A’ creates a pulsating magnetic field that is carried into the resolver disc If the resolver disc is close to an output coil a high amplitude return signal is sent back to the hybrid control module The Hybrid Control Module compares the difference in amplitude between coil ‘B’ and coil ‘C’ to determine the exact position of the rotor Coil ‘A’ Input Coil ‘B’ Output Elliptical disc on rotor Shaft Coil ‘C’ Output

70 Prius resolver The Prius has two resolvers
The resolver contains a set of three electromagnetic coils Prius resolver Pigtail lead connects to hybrid control module The Prius has two resolvers One for each electric motor inside the transaxle The resolver is bolted to the case cover and should never be removed Resolver timing is critical – resetting the resolver timing can only be done by the factory

71 Prius resolver An eccentric disc is attached to the rotor shaft
This disc rotates inside the electromagnet coils in the resolver Prius resolver Rotor Resolver eccentric

72 Gear reduction units for BEVs
Battery electric vehicles require a gear reduction unit to reduce the speed produced by the electric motor down to a speed that the wheels normally rotate Electric motors produce nearly constant torque so a multi-speed transmission is not needed At 60 MPH a 24” high tire [P R 14] is rotating at only 841 RPM The electric motor operates a peak efficiency at speeds of 3500 to 5500 RPM Gear reduction unit Image courtesy of Robert Bosch GMBH

73 Gear Reduction Units To bring the RPM of the electric motor down to the speed that wheels turn in normal driving requires a gear reduction of about 5 to 1 The gear reduction unit also includes a differential gearset that allows the wheels on either side of the vehicle to turn at different speeds Electric motor and gear reduction unit for Toyota Highlander Hybrid

74 BEV Gear reduction unit
Parking pawl actuator motor The gear reduction unit shown here uses a conventional 2 stage spur type gearset

75 Reduction gears First stage ratio = 32 22 = 1.64 Spur type reduction gears are used when the electric motor is mounted ahead of or behind the axle centerline Second stage ratio = 62 22 = 3.1 Overall gear ratio = x 3.1 = 5.07 Input = 22 Idler - driven = 32 Idler - driving = 20 Final drive = 62

76 Gear reduction using Planetary gears
Ring gear If the traction motor is to be located on the axle centerline a set of planetary gears is used to provide gear reduction This helps place the weight of the motor lower to the ground for better handling and allows for more cabin room Planet gear Sun gear Image courtesy of Robert Bosch GMBH

77 Electric Motor/Transmission/Differential
Secondary electric motor Primary electric motor CVT torque combining gearset Planetary gearset type differential To help improve efficiency at highway speeds a second electric motor can be coupled to the primary motor to provide continuously variable gear ratios [CVT] Image courtesy FAG GMBH

78 Hub Mounted Motors 3 Phase AC Current Stator Mitsubishi – BEV Hub Motor Coolant Alternatively motors can be mounted in the wheel hubs Motors larger than 20 KW generally require liquid cooling Coolant Rotor

79 Hub Mounted Rotor Advantages Disadvantages
Simplicity – no gears, differentials or axle shafts. Increases interior volume – no engine compartment needed. In four wheel drive configuration - allows regenerative braking from all 4 wheels. Ideal power train for 4WD and automatic traction control. Using differential power [More torque to one side] eliminates the need for power steering. Very high unsprung weight has negative effect on handling. No torque multiplication . If one motor fails the torque of the working motor will create a severe torque steer condition. Difficult to cool . Motor is exposed to dirt, water and vibration.

80 Image courtesy American Honda Motor Corp
Hub Motors Honda’s Experimental Air Cooled Hub Motor Image courtesy American Honda Motor Corp

81 Prototype Hub Motor Stator Conventional alloy rim and tire
Wheel Bearing Steering Knuckle Stator coils, power electronics and micro-inverter Rotor Image courtesy Protean Corp

82 Service and repair The only service that the electric motor requires is coolant replacement at typically 5 year / 100,000 mile intervals There are very few replaceable parts Most manufacturers will provide only remanufactured motor assemblies[BEV] or transmissions Aftermarket remanufactured stator and rotor kits are becoming available for the gen 2 & 3 Prius

83 Scan Tool Diagnosis Diagnostic trouble codes for most hybrid and BEV drive systems using the Snap-On Modis or Verus DTCs will be manufacturer’s specific codes normally in the P3xxx range The look at serial data you will need to determine module label for the Hybrid control module – it may have a cryptic designation so look at data from all modules until you see PIDs related to he hybrid system

84 Motor/Generator PID data
Problems with the electric traction motors will normally be visible in the serial data stream Each stator coil has a temperature sensor Motor overheating could be caused by a loss of coolant, water pump failure or a restricted coolant hose

85 Motor / Generator PID data
In addition to stator core temperature PID data also includes the motor rpm and amount of torque produced Negative torque values indicates the motor/generator is operating in regenerative braking mode Rr Motor refers to the rear traction motor on the Toyota Highlander hybrid

86 Stator Test Connect three 12 volt test lights between each of the stator leads Turn the rotor by hand Turn the crankshaft for IMA and MG1 – turn one drive wheel while holding the other stationary to test MG2 All three light bulbs should flash with equal intensity as the rotor turns Test connections can be made at the transaxle or inverter terminals after removing the service plug

87 Review The three basic components of a hybrid or BEV traction motor are: Rotor Stator Resolver An IMA system has a single electric motor located at the back of the engine block Two motor hybrid systems have the electric motors located inside the transmission

88 Review Most hybrid and BEV motors are liquid cooled and share their cooling system with the inverter An electric water pump circulates coolant through the traction motor and inverter BEVs require a gear reduction unit to allow the electric motor to run at peak efficiency while the wheels turn at a much lower speed

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