Objectives At the completion of this session, the delegates will understand and will be able to

Hybrid Vehicles An overview Lecture delivered by: Prof. Ashok.C.Meti MSRSAS-Bangalore 1 Objectives At the completion of this session, the delegates will understand and will be able to appreciate- The need for Hybrid automobiles The working principles of hybrid vehicles. Advantages and limitation and related issues 2 1

Topics Hybrid vehicles Introduction Hybrid system design Potential areas for efficiency improvement Types of Hybrid Vehicles Hybrid Vehicle Components Control Systems in Hybrids 3 Stanley Steam Car -1905 Ford Model T (1909) Hybrid Vehicles Background: In early days of automobiles - competition between vehicles powered dby IC engines and vehicles powered by electricity. IC engine powered vehicles, electricity powered vehicles and steam cars were sold in the US - (1890-1905) Work of the pioneers like Edison, Tesla and Westinghouse contributed to electric vehicle development. Limited range of EVs was not an issue for the small cities of that period 4 2

Limitations of batteries - range and utility of EVs. Some developers went straight to IC engine powered vehicles. Some tried to marry the advantages of EVs and dthe internal combustion engine into Hybrid vehicle First hybrid vehicle was built in 1898 and several vehicles were sold in 1900s Hybrid vehicles had significant problems: Require two propulsion systems consumes more space, add weight and greatly increases cost. Careful coordination of the engine and motor was necessary for achieving much of the efficiency benefits and tackle drivability problems (mechanical systems). Thus, the EVs did not survive the continued development of IC engines. (early 1900s) What happened next? 5 What is wrong with IC engine powered automobiles? Main concerns: Fuel efficiency Environmental pollution One of the solutions Hybrid powertrain approach IC Engine - Energy balance Pollutants from an automobile 6 3

Example of a typical hybrid automobile GM Hybrid System - Aura Green Line s hybrid powertrain is rated at 164 horsepower (122 kw) at 6400 rpm and 159 lb.-ft. (215 Nm) of peak torque at 5000 rpm. 7 GM Hybrid system - Aura Green Line s hybrid powertrain is rated at 164 horsepower (122 kw) at 6400 rpm and 159 lb.-ft. (215 Nm) of peak torque at 5000 rpm. While maintaining the vehicle s sporty feel, the GM Hybrid system seamlessly reduces fuel consumption by: Shutting off the engine when the vehicle is stopped, to minimize idling Restarting the engine promptly when the brake pedal is released Enabling early fuel shut-off during vehicle deceleration Capturing vehicle kinetic energy during deceleration through regenerative braking to charge the advanced nickel metal hydride battery Performing intelligent battery charging when it is most efficient 8 4

Hybrid System Design Introduction: There are virtually a large number of ways to design a hybrid system and many different methods of achieving similar fuel consumption benefits. These methods have different tradeoffs on cost and customer acceptance, which will influence market acceptance and future hybrid design. Most hybrid systems combine an electric motor and IC engine to improve overall efficiency and recapture regenerative braking energy. 9 Efficiency benefits: The average efficiency of a gasoline IC engine driven automobile in a typical use: Only about 15 % Other 85% is lost to Engine heat Heated exhaust gases Aerodynamic drag Tire rolling resistance Driveline losses Braking Combining electric motor and energy storage to the IC engine significantly improves efficiency in several ways depending upon the system design 10 5

Potential areas for efficiency improvement Idle-off (Stop-Start Systems) IC Engine Engine downsizing Engine Efficiency New Technologies Regenerative Braking Electrical Accessories Others Aerodynamics Weigh reduction 11 Idle-off Average vehicle idles approximately 18-20% of the time in a city driving condition Stopping the engine at idle can reduce fuel consumption by about 5-8 %. [ time to restart ] More fuel can be saved by cutting of the fuel during deceleration More powerful motor can restart the engine much more rapidly than a conventional starter motor and modern computers and fuel injection have solved the startup problems. A 3-5 kw motor can spin the engine up to normal idle speed in less than 500 ms Fuel control can eliminate i un-burnt tfuel and dits hydrocarbon emissions. Idle-off systems need little energy storage and can be implemented with relatively small, low cost battery packs 12 6

Regenerative Braking When the vehicles slowdown or stops, a large amount of kinetic energy is lost mainly in the form of heat The energy is lost to friction Primarily in the brakes To Mechanical friction losses in the engine An electric motor can be used as a generator to capture some of this energy. This mode of operation of the motor is used to recharge the energy storage device. Most accelerations and decelerations are relatively mild and relatively of small duration. An electric motor of about 10 20 kw, depending on the size of the vehicle is sufficient for this purpose 13 Large regenerative braking rates must be coordinated properly with friction brakes of the vehicle to avoid large deceleration or jerk in the forwards and backwards Other issues: Cost of the system and incremental efficiency benefits [ motor and storage system]. Location of the electric motor Cost and complexity desirable to bolt the motor directly to the engine Losses are more as engine consumes some energy due to friction. Alternative is to use a clutch. But this adds to cost and adds to packaging problem.[front wheel drive vehicles] 14 7

Engine Downsizing The power required for a vehicle is mainly dependent on: Vehicle speed Load Operating condition The peak power is required infrequently In hybrid systems, the electric motor can provide a power boost when appropriate, enabling the use of a smaller engine without degrading performance 15 Usually a smaller engine is more efficient for a given load because it has- Lower frictional losses Less heat loss to engine block and cylinder Lesser pumping losses [WOT operations] Incremental efficiency benefit from the engine downsizing is roughly proportional to the incremental cost of the energy storage and electric motor (need for a trade off) But this does not translate into proportional costeffectiveness of the entire system. 16 8

Engine Efficiency Engines are least efficient when operating at low loads or part loads A hybrid system can be designed to help keep the engine at higher loads and minimize engine operation during less efficient modes. Some examples: Motor supplying power at low vehicle speeds and loads, engine shut-off. The high torque of the motor allows the engine to turn slower, and hence more efficiently, during the highway driving while maintaining adequate acceleration Careful integration of the electric motor and transmission can allow the engine to operate at higher efficiency speed and load points. If additional charging of the battery pack is needed beyond that provided d by regenerative braking, the engine could be controlled to supply the additional energy under higher engine efficiency modes. There are trade-offs with all of the potential efficiency benefits 17 Electrical accessories The additional power in hybrid vehicles can be used to improve the efficiency of engine accessories, such as Air conditioning compressor Power steering pump Water circulation pump and so on. Currently all these are generally driven by engine (speed dependency) Using electric motors to power accessories allows them to be operated independently of the engine and only as needed The increase in overall vehicle efficiency could be in the range of 5 10 % 18 9

Types of Hybrid Vehicles Many different types of hybrids have been built Though they are generally called as hybrids but they differ greatly in design and purpose Categories based on features and purpose: p Conventional vehicle (IC engine) Mild Hybrid Stop-start, regenerative braking, electric motor assist, operating voltage more than 60V Full Hybrid Stop-start, regenerative braking, electric motor assist, OV more than 60V, can be powered by only electricity Performance Hybrid designed for improved acceleration rather than fuel economy Plug-in Hybrid Full hybrid, can use external electricity for charging batteries, extending the range 19 20 10

Micro Hybrid Systems Under this category, normally, the stop-start systems are covered. Some OEMs use conventional starter system with conventional IC engine combined with Stop-Start Start ECU. Some of the vehicles are fitted with integrated alternator and motor units (or BAS units) In certain designs, Integrated Starter Alternator (ISA), or Integrated Starter Generator (ISG), is built, or integrated, into the existing hybrid structure, rather than hung on the engine as an accessory 21 Series Hybrid System Battery Inverter Inverter IC Engine Generator Motor Electric motor a single source of power for traction The engine drives a generator; never drives the vehicle The generator in turn generates electricity The energy storage device may be charged by the generator output or by using the regenerative braking The configuration usually is set up with a small engine that provides a range-booster to a large battery pack 22 11

This system optimizes the engine operation The engine can be run at its most efficient point and shut off when it is not needed Eliminates the need for clutches and conventional transmissions Low on emissions and has excellent efficiency during stopand-go driving (minimizes inefficient engine operation and maximizes energy recaptured from regenerative braking) If the engine is used as primary source of power, double conversion increases the inefficiencies Many hybrids use combination of series and parallel hybrid 23 Parallel Hybrid System Battery Inverter Engine Transmission Motor Both engine and motor are connected directly to the drivetrain Highest efficiency range of each is selected and used, depending upon the operating conditions 24 12

Parallel hybrid system is more complicated as it poses more challenges in integration of two power sources The major advantage is that large efficiency gains can be derived with even a relatively small energy storage (weight reduction) Minimizes cost of energy storage and performance penalty from additional weight. There are two other variations of series and parallel configurations: Through-the-road h h dhybrid bid Fuel Cell Hybrid 25 Through-the-road Hybrid An interesting configuration: one set of wheels are powered by the engine Another set of wheels powered by electric motor This system is called as Through-theroad Parallel Hybrid because the two power sources are run in parallel by independently driving different wheels The interaction between the IC engine and electric drive is completely done by wire and either of the systems can be turned off to drive the vehicle as an electric or ICE system The main advantage - it adds part-time all-wheel-drive (AWD) capability. It also allows more flexibility in mounting locations of the motor But, it adds considerable complexity and cost Motor IC Engine 26 13

Plug-in Hybrids (PHEVs) Plug-in hybrid electric vehicles are full hybrids with larger batteries and the ability to recharge from an electric power grid The batteries can be charged using a power socket over night from the grid When the batteries run low, the engine starts and powers the vehicle and the generator to charge the batteries They have a larger range in electric only mode 27 Hybrid Vehicle Components Electric Motors There are two basic types: Induction AC Motor Uses part of the electric current to generate the magnetic field. Simpler and cheaper than DC motor Used in low power systems such as- simple idle-off systems with integrated starter/generators Permanent magnet DC Motor Uses 3-phase windings and switching modules to sequentially control the flow of electricity to each phase. BLDC permanent magnet motors are more efficient. DC motors are more expensive. BLDC motors use magnets sintered with rare earth metals such as Neodymium. Electric motor technology is a mature technology 28 14

Examples of Electric Motors: BLDC Motor 100 kw, oil cooled BLDC motor for automotive application. Weight is 21 kg Honda Civic Motor The electric drive motors used in hybrids are hightorque heavy-duty permanent magnet motors. These compact, but powerful, dynamos operate on power raging up to about 650 volts. Toyota Prius pancake motor/generator (M/G) set 29 Energy Storage Battery packs are the primary type of energy storage for hybrid vehicles Usually designed for hybrid vehicles- With higher power density and Sized to deliver sufficient power without overheating. Ultra Capacitors are high power versions of electrolytic capacitors - Store energy as an electrostatic charge. They have features like Rapid transfer of power Potential for better durability Lower cooling requirement They are likely to be considered for hybrids in near future. 30 15

Example of an Ultra-capacitor Honda uses an Ultra-capacitor in its Fuel Cell powered vehicle FCX. The ultra-capacitor serves as a supplementary power source to the main power source for more powerful performance under various driving conditions. It stores energy produced during deceleration and braking and provides powerful drive assist during startup, acceleration and at other times when an extra boost is required. HONDA Ultra Capacitor Module 31 Batteries Various types of batteries are developed based on different technologies. The lead acid battery is the most well known rechargeable type. Types of batteries include: Lead acid Nickel metal hydride Nickel ion Nickel cadmium Lithium polymer Lithium ion Sodium sulfur Sodium metal chloride and so on. 32 16

From the designer s point of view the battery can be treated as a black box which has a range of performance criteria These criteria will include: Specific energy (Wh.kg 1 ) Energy density (Wh.m 3 ) Specific power (W.kg 1 ) Typical voltages Amp-hour efficiency (charging efficiency is less than 100%) Energy efficiency Commercial availability Cost Operating temperatures Self-discharge rates number of life cycles Recharge rates, and so on.. 33 Nickel-Metal Hydride (NiMH) batteries Have higher power densities Longer life cycle than lead-acid batteries Have safe characteristics and their power output is not affected by battery state of charge. Very expensive High self-discharge rates Low-temperature operation Higher cooling requirements NiMH Hybrid Battery System [Ford Escape] 34 17

Lithium-Ion batteries Higher power and energy level than NiMH battery Better low-temperature performance Low self-discharge rate Need improvement in Cycle life Durability Cost Toyota Li-Ion Battery Hyundai Li-Polymer Battery 35 Regenerative Brakes Regenerative braking allows a motor to act as a generator when coasting or braking Kinetic energy that normally would be wasted during braking is converted into electrical energy to recharge the battery The energy conversion is achieved within the integrated motor / generator units. While the brake pads and rotors stop the wheels at high speed or in emergency situations, the regenerative braking system slows the vehicle in normal driving 36 18

Gasoline engines The hybrid car has a IC engine much like the one found on conventional cars However, the engine on a hybrid will be smaller and will use advanced technologies to reduce emissions and increase efficiency These are matched with efficient, electronically controlled transmissions Epicyclic gear train CVT and so on 37 Some of the advanced features of IC engines: Lighter and compact designs Electronically controlled operations- ease of control in synch with motor control, if necessary MPFI or GDI systems for- Better fuel efficiency and control Reduced emission levels Coil-on spark plug or waste spark ignition system ETC (drive-by-wire)- better control of engine operation Variable valve timing and lift mechanisms- improved performance at wide operating range Exhaust after treatment system for further reduction in emissions Engine Honda Civic Power-plant [IMA] Motor Transmission 38 19

Variable Valve Timing and Lift Mechanisms 39 Electronic Throttle Control Van Doorne Type CVT Throttle Body 40 20

Belt Alternator System (BAS) The motor/alternator of the Belt Alternator Starter (BAS) hybrid system [GM] is driven by a high-tension belt from the engine crankshaft. It boosts power under acceleration, charges the battery, and restarts the engine after stopping the engine in auto mode 41 Stop-Start System For a conventional vehicle, it is possible to implement to Stop-Start system (micro hybrid, Idle off) The system uses a redesigned conventional starter motor, and ECU, couple of sensor and CAN interface with the vehicle CAN bus. The ECU monitors various parameters like the battery condition, transmission status, clutch pedal travel sensor, Ignition key position and other safety interlock signals. 42 21

Start-Stop System - Typical Configuration Accelerator Pedal Sensor Power from Battery Clutch Pedal Position Sensor Battery Sensor ECU Starter Motor Indicator Lamp Engine Speed Sensor Enable / Disable Gear Position Sensor.. CAN Interface* (Optional) 43 Power Electronics and Control DC motors generally use 3-phase motor windings. 3 switching modules control the current flow to the proper windings as the motor turns. The switches must be able to rapidly and accurately turn large amounts of current on and off as well as the controlling the direction and phase of the current. Produces a large amount of heat thus needs a cooling system. Size and cost is substantial 44 22

Converters Converters (DC-to-DC) alter voltage up or down as needed for various components. This may require changing the battery voltage which may range from 144V to 488V to as low as 12V to power the lights, accessories and convenience systems, or step it up to as high as 650V to power drive motors. Inverters Inverters convert DC to AC for the purpose of driving AC motors Cooling Systems Battery pack and power electronics produces large amount of heat that needs to be cooled. Charging gand discharging ga battery involves chemical reactions that generate heat as a byproduct. This heat degrades performance and shortens life. Efficient cooling system is required to cool both 45 Control Systems in Hybrids The control systems in a hybrid vehicle have to perform very complex tasks of managing two different types of power plants IC engine and electric motor The control systems have fast operating speeds and real-time capabilities Different modules are put together to achieve the required control actions The controllers talk to each other through CAN Ex: Electric motor controller, engine controller, battery management controller, transmission controller, brake system controller and so on These controllers have to decide the most efficient mode of vehicle operation depending on the prevalent driving conditions and energy resources. This action has to be transparent to the driver 46 23

Electronics that controls the Honda s IMA The HONDA Civic is one of the popular HEVs Uses Integrated Motor Assist (IMA) hybrid system The engine is a 1.3 ltr i-vtec with the i-dsi system engine (63kW) coupled to a transmission through an ultra thin (58mm) motor (VCM Variable Cylinder Management) The motor is a three phase, synchronous AC motor, gets it power from a NiMH battery pack (158V) and is rated 5.5 Ah It also works as a generator with a max output of 15kW The IMA system is controlled by the components housed in a single unit called Intelligent Power Unit (IPU) EPA estimated fuel economy rating of 49/51 mpg city / highway 47 Electronics that make the IMA system work Battery Module-(BM), Battery Condition Monitor-(BCM), Motor Control Module-(MCM), Power Control Module- (PCU), Motor drive Module-(MDM), Voltage Converter Module, DC/DC Converter 48 24

Modes of operation of the IMA and i-vtec 49 Summary The historical background of Hybrid vehicles and need for hybrid vehicles have been studied Various configurations of hybrid vehicles have been explained Main components of hybrids, their use have been discussed with examples in a vehicle 50 25