“ADVANCED ‘ISA’ SYSTEM FOR IC ENGINES & HYBRID ELECTRIC VEHICLE.”

ABSTRACT  

The advanced ISAD system for internal combustion engines & hybrid electric vehicle applications to reduce emissions, fuel consumption and enhance energy efficiency. The new starter-alternator combination provides a more efficient and higher output platform, which will provide the vehicle designer unique ways to reengineer many functions under the hood. Virtually any accessory, which is presently belted driven, may be converted to an electrically powered counterpart with the ready availability of more electrical power from the larger alternator component of the system. Hydraulic power steering units, belt driven air conditioning compressors, various fluid pumps and their components could be replaced with more efficient electric motor-driven system powered by the ISAD. Starting motor advents of the new ISAD system include a quite start feature because the gears and whine of the traditional starter will be eliminated. This system will be able to increase the starting speed and it also supports the acceleration phase. The total system weight is nearly the same. The ISAD system provides all the functions of the engines starter motor and alternator in one electric system installed between the engine and gearbox without significantly increasingly weight and volume of the vehicle. The system has been demonstrated for passenger’s cars and it can be used in commercial vehicles as well.

During starting, the induction machine cranks the engine with high starting torque. In the generation mode, the power is input to the ISA from automotive engine, which is emulated using permanent magnet DC motor, while the DC bus voltage is maintained at 42V.

This paper includes the comparison between conventional starter, ISG, and ISA. Also this paper contains the principle of ISA mild hybridization and one case study of Valeo and Ricardo for 42V diesel vehicle.

At last we conclude that, the ISAD system is the first step to HEV (Hybrid electric vehicle) technology.

1. INTRODUCTION

1.1 NEED OF ELECTRIFICATION

In last years, the automotive electrical load has increased, by replacing of different mechanical equipments with servomotors, by using electrical equipments that improve the internal combustion engine (ICE) performances, in parallel with the comfort and safety (e.g. positioning and regulation systems, navigation and control systems). Today, the average electrical power load on the automotive alternator is between 750 W and 1 kW. It is expected to increase to 4 – 6 kW, in the next decade. Since, the present automotive 12V System didn’t cover this power. It is likely to adopt the 42 V systems for the new-generation auto vehicles. The changing of this voltage level will be a good opportunity for substituting the automotive starter and alternator, by a single equipment, the integrated starter-alternator (ISA). The conventional Lund ell (claw-pole) alternator is coupled to ICE, by a transmission belt (typically 3:1 ratio), and the starter, a DC brushed motor, accelerates the ICE to cranking speed, due to a large mechanical gear (typically 10:1)

1.2 DEVELOPMENT TARGETS

1. Achieve fuel economy twice as good as or better than that of gasoline-powered vehicle in the same class.

2. Secure driving performance equivalent to that of gasoline-powered vehicles in the same class.

3.  Achieve a 10% exhaust emission levels of current Japanese standard

4. Achieve other performance characteristics comparable to those of conventional models.

1.3 FEATURES

1. “Start-Stop” is a fuel saving function that automatically cuts off the engine when the                             vehicle comes to a stop and restarts it when the driver engages a gear or releases the                  brake (automatic transmissions).

2. “Green-Boost” is the alternator motor mode ability to deliver up to 10 kW more mechanical power to the transmission.

3. Regenerative braking is a feature that makes it possible to regenerate the energy of                 braking phases into useful electric energy.

4. High electrical output: up to 12 kW at 42 Volt.

5. Noiseless and rapid engine starting.

6. Compatible with future 42 Volt electrical networks.

1.4 HYBRID ELECTRIC VEHICLE

A type of vehicle that may address many of the problems associated with electric vehicles is a hybrid electric vehicle (HEV). HEVs combine an electric motor and battery pack with an internal combustion engine to improve efficiency. In some HEVs, the batteries are recharged during operation, eliminating the need for an external charger. In other cases, the vehicle must still be plugged in at the end of the day. Either way, range and performance can be significantly improved over electric vehicles.

The combustion and electric systems of HEVs are combined in various configurations. In one configuration (series hybrid), the electric motor supplies power to move the wheels, while the combustion engine is connected to a generator which powers the motor and recharges the batteries. In another configuration(parallel hybrid), the combustion engine provides primary power, while the electric motor adds extra power for acceleration and climbing, or the electric motor is the primary power source, with extra power provided by the engine. In some parallel hybrid systems, the engine and electric motor work in tandem, with either system providing primary or secondary power depending on driving conditions.

The hybrid drive train allows the combustion engine to operate at or near peak efficiency most of the time. This can lead to significantly higher levels of overall vehicle system efficiency. The higher efficiency of these vehicles allows them to achieve very high fuel economy and lower emissions. For example, the hybrid Honda Insight is rated at 61 miles per gallon (mpg) in the city, and 70 mpg on the highway. A gasoline-fueled Honda Civic Hatchback, by comparison, achieves a rating of 32 mpg city and 37 mpg highway.24 Fuel economy improvements can help cut demand for foreign petroleum, and the higher efficiency enables hybrid vehicles to attain, and even surpass, the range of conventional vehicles, even with a smaller fuel tank. Furthermore, since these vehicles utilize conventional fuel, the fueling infrastructure problems associated with electric vehicles can be eliminated.

The only hybrid vehicles currently available in the U.S. market are the Honda Insight, the Honda Civic Hybrid, and the Toyota Prius. Over the next few years, however, most major manufacturers plan to introduce hybrid passenger vehicles. Further, while the currently available hybrids are smaller cars, manufacturers are also developing larger hybrids such as mini-vans and sport utility vehicles.25

Until recently, HEVs were treated as conventional vehicles because they run on gasoline or diesel fuel. However, the Internal Revenue Service announced on May21, 2002, that it will allow taxpayers to claim a clean-burning fuel vehicle tax deduction of $2,000.26

2. ELECTRIC MOTOR TECHNOLOGIES

In this section, the three most common electric motor technologies and the power electronic devices with control circuits in vehicle applications are discussed. The three motors are the permanent magnet (brushed and brushless type) motors, induction motors, and switched reluctance motors. Among those three motor configurations, the permanent magnet motor type is more widely applied in the vehicles because of its merits. An electric motor is a well-known device that converts electrical energy to mechanical energy using magnetic field linkage. An electric motor consists of two major elements: (1) a fixed stator with current-carrying windings or permanent magnets, (2) a rotating rotor which provides a magnetic field produced by additional current carrying windings or attached permanent magnets between the rotor and stator magnetic fields. Modern electric motor advances have resulted from developments and refinements in magnetic materials, integrated circuits, power electronic switching devices, computer modeling and simulation, and manufacturing technology, rather than by fundamental changes in operating and control principles. The dramatic improvements in permanent magnet materials and power electronic devices over the last two decades have led to the development of brushless permanent magnet motors that offer significant improvements in power density, efficiency, and noise/vibration reduction. Also, because there is no electrical Sparks, there is less radiated noise.

2.1 PERMANENT MAGNET MOTORS

The permanent magnet machine is highly coveted for its high power density and high efficiency.  This is mainly due to the high energy density NdFeB and SmCo magnets, which are commercially available today. In other words, advancements in high-energy permanent magnet materials and magnet manufacturing technologies enabled the manufacturing of high power density and high efficiency permanent magnet motors at a reasonable cost. Also, the availability of fast switching high power semiconductor devices with low on-state voltage drop such as MOSFETs and IGBTs. Ever increasing high-speed microprocessors/digital signal processors have contributed to permanent magnet electric motors. While the cost for semiconductors and the permanent magnets is still high at the present time, trends for cost reduction are continuing and encouraging.

2.1.1 BRUSH TYPE PERMANENT MAGNETIC MOTOR

There are two types of permanent magnet motors: brush and brushless. Today’s vehicle applications almost exclusively use brush type permanent magnet motors.

The brush permanent magnet motors have four general characteristics that cause them to be useful for vehicle application:

1)      Desirable torque versus speed,

2)      Simple control of torque and speed,

3)      High electromagnetic power density, and

4)      Inverters are not required.

Nevertheless, there are six general characteristics that detract from more wide applications in the automotive industry:

1)      friction between the brushes and the commutator,

2)      brushes and commutators require maintenance,

3)      current is supplied to the armature through the brushes and commutator,

4)      brushes and commutators are open and produce sparking,

5)      cooling of a DC motor is difficult, and

6)      Switching of large currents is required for control of DC motors.

The brushless motors are becoming stronger candidates over traditional brush type motors for the following reasons: higher efficiency, higher power density, better heat dissipation, and increased motor life. In addition, brushless motors experience no losses due to brush friction and they deliver higher torque compared to a brushed type motor of equal size and weight.

2.1.2 BRUSHLESS TYPE PERMANENT MAGNET MOTOR

Electronically commutated, brushless permanent magnet motors are however, becoming prime movers in vehicle propulsion, industrial drives, and actuators as a result of improvements in permanent magnet materials, advances in the power electronic devices, and power integrated circuits in the last two decades. Not only have there been gradual improvements in Alnico and Ferrite (ceramic) alloys, but the rapid development of rare-earth magnets, such as samarium-cobalt (Sm -Co) and neodymium-boron-iron (Nd B Fe) around 1980, have provided designers with a significant increase in available field strength. This new high density, brushless, permanent magnet motor system provides a very high torque to inertia ratio.

2.1.3 PERMANENT MAGNET MATERIAL

Figure 4 summarizes the four most common permanent magnet materials used today by motor manufacturers. In most cases, the higher remanence with higher coercivity in a permanent magnet is desired by motor designers. The alnico magnet provides a fairly high remanence flux density but a low coercive force. When the coercive force is low and two opposing magnetic poles are in proximity of each other, the magnetic poles can weaken each other and there is a possibility of permanent demagnetization by the opposing field.

Unlike an alnico magnet, the ferrite magnet has a low flux density, but a high coercive force. It is possible to magnetize the ferrite magnet across its width as a result of this high coercive force. Ferrite magnets are most widely used in electric motors because their material and production costs are low. The cost of a typical ferrite magnet material at this time is about 6-8 times lower than the Nd B Fe. Nonetheless, output power to weight ratio is 1.22, ferrite, vs. 1.36, Nd B Fe. This means that the ferrite magnet motor will be about 20% heavier for the same output compared with the Nd B Fe magnet motor. Another measurement is an output power per unit cost of active material. It is predicted that the output power per unit cost is about 4 times lower for ferrite magnet motor compared to the Nd B Fe magnet motor. Delco Remy uses the ferrite and Nd B Fe magnets for different starter motor applications. Rare-earth magnets have both high magnetic remanence, and high coercive force. Since the initial cost is high, these permanent magnets are used in applications such as high performance and high-energy density motor applications. For a given volume, the flux density is twice that of the ferrite, leading to a larger torque production. Nd B Fe magnetic materials are superior to any other magnetic material now on the market. The only disadvantage of using an Nd B Fe magnet, as opposed to an Sm Co magnet, is that the high-energy density Nd B Fe permanent magnet has a maximum operating temperature of 100 to 150 degrees C, as compared to 200-300 degrees C for Sm Co, alnico, and ferrite.

2.2 INDUCTION MOTORS

Alternating current (AC) induction motors are the most common of all types of electric motors manufactured for the general use in household applications, industrial drives, and electric propulsion. These motors are rugged, relatively inexpensive, and require very little maintenance. They range in size from a few watts to about 15,000 hp. The induction motors have certain inherent disadvantages including speed which, is not easily controlled, plus it runs at low lagging power factors when lightly loaded, and the starting current is usually five to seven times full-loaded current.

Induction motors have relatively low manufacturing cost and are mechanically rugged because they can be built without slip rings or brush and commutators. Consequently much attention has been given to induction motors for automotive applications in the areas of vehicle propulsion, engine starting, braking, electricity generating, speed reversal, speed change, etc. In spite of many interests in vehicle applications, the costs of the power electronic components are still relatively high, especially in the low power region. Furthermore, in many automotive applications it is either not possible or not desirable to use a mechanical sensor for speed or angle, etc. This means, a simple and affordable control system, using only the voltage and the current of the induction motor as measured quantities, is necessary. A sensor less controller technology has been demonstrated using a switched reluctance motor by many academia and industrial teams.

3. CONVENTIONAL STARTER, ISG & ISA.

3.1 STARTER AND GENERATOR: -

Fig3.1: - Delco self starter generator unit

The automotive starter (sometimes called a cranking motor) dates back to the early part of the automotive industry. In 1912 the Cadillac Motor Car Company introduced the electric self- starter to replace the hand crank. Frank and Perry Remy of the Remy Electric Company were also early innovators in the automotive industry. Remy Electric also developed and introduced starting motors in the same time period. This innovation in essence broadened the accessibility of the automobile from those strong enough to hand crank to virtually everyone. There have been many developments and refinements in the starting motor since its introduction in 1912 (see Figure 7). The primary innovations focused on the engagement method, changing from six to 12 volts, and gear reduction. From the 1980s to today the industry has focused on size and weight reduction as well as reliability and durability improvement.

3.2 INTEGRATED STARTER GENERATOR

An integrated starter-generator can be used in conventional vehicles to reduce fuel consumption and improve acceleration. As with a hybrid vehicle, using the high-torque device allows the engine to shut off when the vehicle is stopped. When power is applied, the engine can restart in less than one second.45 It is believed that the integrated starter-generator could improve fuel economy of conventional vehicles by as much as 20%. However, because the integrated starter-generator requires considerable amount of electrical power, it is being developed concurrently with 42-volt electrical systems.

3.3 ISA SYSTEM DISCRIPTION

A block diagram of the overall system is illustrated in the figure. As indicated in the figure, the system is based on an induction machine mechanically coupled to an engine, and it is fed by a 36V battery through a three phase IGBT inverter. The controller has been implemented using dSACE 1104 control card. The control algorithm derives PWM signals for the three phase inverter by taking speed, IM line currents and DC voltage as inputs.

1.1kW/22V Induction machine has been used for the prototype hardware. The induction machine line to line voltage of 22V is chosen because of the 42V DC bus voltage and to ensure that the inverter operates in boost mode, so that motor current is in continuous conduction at all times.

3.4 SPECIFICATIONS

In practice, the available 30-36V battery voltage at motoring and required 30-36V charging voltage at generating is the main problem during electric machine design. Besides the dilemma from voltage specifications, the requirement of a wide speed range and the high temperature of cooling media in the ISA system. The ambient temperature range from -40°C to 125°C, which is a typical for an air cooled ISA machine. If the machine cooled by liquid, the available engine coolant temperature will be up to 135-140°C, unless a separate liquid cooling loop is introduced. The speed of electric cool machine runs from 0-6000 r/min for the crankshaft mounted ISA system, which is the same as engine speed. The maximum operating speed electric machine run as high as 13,800-19,200 r/min for the belt driven ISA system with the belt transfer ratio of 2.3-3.2.

In the 42V DC electric system, the motoring performance specifications should met over at lower voltage level of 30-33V dc, although the maximum available battery voltage is 36V at the dc input of the electric machine drive. If the 14V electric system is used for the ISA system onboard vehicle, the motoring operations of the machine have to be fully functional at 10-11V dc voltage in spite of the battery voltage of 12V. the low available voltage is caused by a low battery charge state and internal resistance as well as ambient temperature. If a three phase induction machine is used for ISA machine and the space vector control is introduced for its control, it needs to meet all motoring specifications at the minimum available line to line voltage of 21-23V ac and 7-8V ac in rms value for the 42V dc and the 14V dc systems, respectively.

2. Automotive direct-drive integrated starter-alternator requirements and selection

The proposed solution is represented by a direct-drive, where the electrical machine of ISA is coaxial with the shaft of the ICE and the transmission (clutch and gear box).

(Figure 2)

The integration of the starter and alternator in just one electrical machine will make more efficient the use of electrical equipment, and eliminate the space and weight problems, improving in the same time the performances and reducing the generator and starting noises. Another advantage is that ISA eliminates mechanical elements, such as transmission belt, pulleys and flywheel.

ISA allows at start the operation in motor regime, as a starter, and after that, will work in generator regime, providing electrical energy as an alternator. In motor regime, the ISA system should reach 500 rpm in maximum 3-5 s, overcoming a load torque of 80 – 150 Nm. In generator regime, the ISA system transforms the mechanical energy in a.c. electrical energy, which after rectification recharges the automotive battery. Table 1

Table:-Automotive starter/alternator performance requirement

Summarizes the automotive starter and alternator performance requirements, for both, conventional and integrated system. The interior permanent-magnet synchronous machine (IPMSM) has been selected to fulfill the above-stated performance requirements for an automotive ISA (Figure 3).

The associated electronic power converter is considered of bi-directional AC-DC three-phase bridge type in IGBT technology (Fig. 4).

The control of ISA system means the current control by hysteresis regulators, in function of the motor speed error. The main challenge in the selection of an ISA direct-drive is the fulfillment of performance at the lowest possible system cost.

The main data and parameters of the IPMSM designed for automotive direct-drive ISA are the

following:

- Rated voltage: U = 42 V;

- Output power: P = 6 KW;

- Stator phase resistance: Rs = 0,0103;

- d – axis inductance: Ld = 0,06497 * 10-3 H;

- q – axis inductance: Lq = 0,30505 * 10-3 H;

=0,063 Wb;

- Permanent magnet excitation flux: PM

- Number of poles pairs: p = 12;

4. PRINCIPLE OF ISA MILD HYBRIDIZATION

Vehicle speed is controlled by the driver through either the accelerator pedal or the brake pedal. Depending on the driving mode, either a positive or a negative torque is requested from the engine; however, in case of braking, if the negative torque provided by the engine is insufficient, friction torque in the wheels provides an additional braking torque which results in energy loss. The engine speed is determined by the transmission and the gear ratio between the engine crankshaft and the wheel. Consequently, the engine torque is the only available variable that can be adjusted in order to operate the engine in efficient BSFC regimes. For a parallel hybrid configuration, power can be provided for propulsion by both the thermal and electrical paths. The ISA is mechanically coupled to the engine, as depicted in Figure.

Figure 4.1: Schematic diagram of the HMMWV power train incorporating the ISA

(T-Turbine, C-Compressor, D-F- Front Differential, D-Rear Differential, EM- Exhaust Manifold, IM- Intake Manifold, ISA-Integrated Starter Alternator, T/C- Torque Coupler, Trans-Transmission)

Hence, the ISA speed is determined by the engine speed by means of a constant ratio. As a consequence, the additional power available by the ISA can only be regulated by adjusting the ISA torque. The latter can be either positive or negative contingent upon the mode in which the ISA is operating, as designated by the power management algorithm. In the motor mode, the ISA contributes power to the driveline by drawing electrical energy from the battery. In the generator mode, the ISA absorbs power from the driveline and charges the battery.

In cruising, the power requested from the power train by the driver is expressed by positive amount of torque, TDRIVER, given a fixed engine speed:

Tdriver = TISA + TEngine

The power management algorithm comes to a decision regarding the ISA torque, TISA, based on the current SOC, in order to utilize the most proper engine operating point as far as fuel consumption is concerned. Conversely, when braking is demanded by the driver, the power is expressed by a negative torque TDRIVER:

T Driver= T Engine+ T ISA+ T Brake

A fraction of this torque is absorbed by the engine, ENGINE, whereas the ISA absorbs the maximum absolute amount within the constraints imposed by the battery and the ISA. If a residual amount remains, this must be handled by the friction brakes, TBRAKE. Consequently, the ISA can recover the energy that otherwise would be lost by means of friction brakes so as to charge the battery.

5. CASE STUDY

Valeo and Ricardo team for 42-V diesel vehicle

Valeo's high-efficiency integrated starter-alternator system, which will be mounted on the crankshaft between the engine and the transmission, performs a number of key functions. The integrated unit uses electronic control to crank the engine, providing stop-and-go capability. When a driver stops at a traffic light, for example, the engine is automatically cut, both saving fuel and reducing emissions. As soon as the driver engages a gear again, the engine automatically and quietly restarts. NVH improvements are inherent when at standstill because of the absence of engine noise. The quiet starting is realized through the use of the integrated starter-alternator in motor mode. Since this unit is fully integrated into the powertrain and replaces the traditional starter motor, engaging the starter's gear on the ring gear is no longer. The starting time is 0.3 s as opposed to 1 s with a conventional starter motor, leading to further reduction in emissions.

.

The special design of the Valeo integrated starter-alternator means it can provide additional torque into the powertrain over the full range of engine speeds. During acceleration, the starter-alternator is used as an electric motor to give an extra boost to the engine; despite the smaller engine size, the i-MoGen powertrain can supply similar torque to the much larger and heavier 2.0-L diesel engine.

In a conventional vehicle, the kinetic energy of a vehicle is lost as heat when the driver applies the brakes. With the high-output starter-alternator, a part of this energy can be saved, using the alternator to generate electric energy. As soon as the driver presses the brake pedal, an electronic communication is sent to the integrated starter-alternator that immediately converts kinetic energy from the vehicle to electrical energy that can be stored in the battery. It is then possible to re-use this energy, which is the basic principle behind regenerative braking.

The maximum electrical output power from the Valeo integrated starter-alternator unit—when running in alternator mode—is 6 kW, which is three times higher than conventional alternators. This high output is necessary to allow the operation of high- power electrical components such as the electrical HVAC compressor or the electrically heated diesel particulate filter, a Ricardo solution that efficiently destroys harmful diesel particulate.

As part of the integrated starter-alternator system, Valeo will integrate a dc/dc converter to supply 14 V to the low-power electrical components that are not converted to 42 V. Such a high capacity dc/dc converter is expected to be a requirement in future 42-V vehicles where specific components will require lower voltage.

A key requirement for 42-V systems is the reliability of available power. Valeo is collaborating with a battery expert to develop and integrate fault-tolerant batteries with a battery state-of-charge function to guarantee the reliability of all its 42-V systems.

 

 

6. ADVANTAGES, DISADVANTAGES & APPLICATIONS

6.1 ADVANTAGES

1. Reduce fuel consumption.
2. Reduce emission.
3. Enhance energy efficiency.
4. Weight is less
5. High power generation.
6. Quick start & stop.
7. Well engine performance.
8. Big cities getting more advantage.

6.2 DISVANTAGES

1.        Requirement of mass production.

2.        Audible normally associated with engine cranking.

3.        Battery required is of high voltage.

6.3 APPLICATIONS

      1.    Vehicle magnetic air conditioner

      2.    Camless electromagnetic valve  System.

      3.    Turbocharger generator

      4.    Permanent magnet traction wheel motor

      5.    Electric variable transmission

7. CONCLUSION

The automotive industry trends and prediction of the future electrical system was presented. Today’s 2 kw platforms need to be replace with 20 kw or even 50 kw platforms on which host of electrically generated functions will be enabled -some of which we have not even conceived .The three major motor configuration and enabling technologies that support more electrical system to vehicle application were presented. Some devices on the vehicle that are now driven mechanically could be driven electrically, since the needed power will be availed by ISA system. Component such as air conditioner compressor, the water pump and the power steering system can then be operated only on demand, instead of remaining a continuous parasitic load on the engine when they are in the “off” part of their operating cycle. This will further reduce fuel consumption and emission. The ISA system is the first step to HEV technology.

8. REFERENCES

1. www.indiacar.com
2. www.automotiveengineering.com
3. www.automobile.com
4. www.google.com
5. IEEE industry applications magazine.
6. Automotive Research Center, The University of Michigan() SAE technical paper series-by Andreas Malikopoulos, Zoran Filipi and Dennis Assanis)