The Widespread Introduction of the TOYOTA Mild Hybrid Cars(HEV) May Promote
an Earlier Introduction of 42V Cars
Introduced into low-priced sedans following the 2001 Crown Royal

Toyota Motor Corporation launched the Crown Sedan with the newly established specification, TOYOTA Hybrid System-Mild (THS-M), in October 2002. This car is in the range known as the Mild Hybrid (Mild Hybrid Car) after the Crown Royal Saloon launched in August 2001. "Mild" is the designation used by Toyota. Hybrid cars such as the Prius and Estima can select a mode whereby they are driven only by the electric motor (EV drive) and are known as the Strong Hybrids, while the Mild Hybrid Cars have no option of only selecting EV drive. The function of their motors is limited only to drive assist, and the restart of the vehicle after an idling stop. Improvement in fuel efficiency for the Mild Hybrid is not as significant as that of the Strong Hybrid. However, the conventional type of engine/transmission systems needs no significant change with the THS-M, which means that it might be adopted in Toyota's wide range of vehicle types.

Another feature of the Mild Hybrid Cars is to employ a 42V power source system (the 42V-charging voltage/36V-open-circuit voltage system using a 36V battery) in commercially available cars for the first time worldwide. The 42V power source system is considered to be the next generation of in-vehicle power source systems. The 42V power source system has been already recognized as a future direction in the automotive industry in Japan, the US and Europe. However, working toward establishing global standardization is still underway, therefore, it is considered that the adoption of the new system will be carried out largely after 2005.

A total of 102,967 units of Toyota's hybrid cars were sold worldwide up until March 2002 since the launch of the Prius in 1997. Toyota projects 300,000-unit production of the hybrid cars per year including the Mild Hybrid Cars in 2005. It is essential to expand the hybrid car market to achieve this project. The world's first car with a 42V power source system, the Crown Royal, is a high-end vehicle that has a 3,000cc direct-injection engine, in which the basic model price is 3.82 million yen. On the other hand, the basic model price of the Crown Sedan with the newly established specification, THS-M, which has a 2,000 cc engine, is 2.44 million yen. These hybrid cars have been introduced into the market in the price range where increased demand is expected. Most of the projected 300,000-unit production for 2005 is quite likely to be the Mild Hybrid.

Accordingly, the number of cars with a 42V power source system (the 42V car) will also increase ahead of all other manufacturers worldwide. It is said that the 42V car has many electrical parts and circuit components that are required to be newly developed so as to be compatible with 42V. That means that the parts manufacturers supplying to Toyota for its Mild Hybrid Cars will develop the new generation of parts ahead of the competition.

■The World's First 42V Car, TOYOTA Mild Hybrid Car

The world first 42V power source system was incorporated into the THS-M used in the Crown Royal Saloon, which was then introduced into the market in August 2001. The Mild Hybrid has an automatic engine idling stop function used when the vehicle is stopped and a regenerative braking system used during deceleration/braking to reduce fuel consumption. They bring approximately a 15% improvement in fuel consumption when measured using the method 10-15 mode, and a 30% improvement when the urban traffic mode of the Toyota standard when compared to the basic model. In addition, the Crown Royal achieved a 50% decrease in emissions when compared to the 2000 standard so that it obtained a ☆☆ rating certified by the Land, Infrastructure and Transportation Ministry as an excellent low emission vehicle. The Crown Sedan also achieved a 75% decrease and was awarded a ☆☆☆ rating, as an ultra low emission vehicle.

The major concern about idling stop was the air conditioner operation. However, the use of 36V battery to drive the compressor causes no problems in its operation even when the engine stops. The electric power generated by storing the braking energy is utilized to restart the engine after idling stop, so that the vehicle can smoothly start. Furthermore, the hybrid system can be employed in existing models with conventional engine/transmission rather than the power train designed for the hybrid vehicles.

Toyota said that the Mild Hybrid system is expected to bring about significant advantages to decrease the total amount of CO2 and emission as the system can apply to a wide range of vehicle types due to the following factors; (1) Simple system design so that conventional engines can be compatible with the hybrid system without major changes. (2) Use of the next generation of 42 V power and the high-technology 36V lead type battery for motor drive.

■Major Features, Operating Conditions and Major Specifications of the THS-M

■Toyota's Model Lineup With the THS-M

■Resolving the Problems Associated with Idling Stop that Brings a Significant Increase in Fuel Efficiency when Driving in Urban Areas.

There is a huge difference in improved fuel efficiency of the Mild Hybrid between the 10-15 mode and the urban traffic mode of the Toyota standard, resulting in approximately a 15% and 30% improvement respectively. These results show the idling stop effect considered to be an effective method to improve fuel efficiency and reduce emission in urban areas. Many fuel-efficient cars introduced by the Japanese automotive manufacturers have the idling stop function.

Toyota's hybrid cars, such as the Prius and Estima also have the automatic idling stop function. In addition to these hybrid cars, the idling stop system called the TOYOTA STOP AND GO SYSTEM is employed in the Vitz (MT) and the Crown Comfort (AT, LPG vehicle).

However, the specification with the idling stop system has not been widely applied to the various models. This is due to several disadvantages including a need to operate the shift lever, a jolt effect when the engine stops, rough starting and an inactive air conditioner while stopping in heavy traffic. In addition, the Prius for example, the possibility exists that the engine might start if the air conditioner operates even during an idling stop.

Such problems have been solved by the Mild Hybrid idling stop system using a 36V battery, which may be widely employed in Toyota's various vehicles and therefore allows a substantial improvement in fuel efficiency when driving in urban areas.

■Toyota's Idling Stop System and THS-M

It is said that Toyota first started developing the THS-M as a hybrid system to be used in FR vehicles. The high voltage range (100-400V) is used in hybrid cars such as the Prius while the low voltage of 42V was used in Mild Hybrid cars. The THS-M mainly consists of the motor/generator (ISG: Integrated Starter Generator or ISA: Integrated Starter Alternator) having the two functions of integrated starter and alternator, the inverter unit incorporating a DC/DC converter and ECU, and a 36V battery.

The motor/generator is connected to the crankshaft of the engine via the drive belt for the auxiliary devices. After the automatic idling stop, the vehicle starts via belt drive through power supply from the 36V battery. The engine restarts in 0.4-0.5 seconds and then the belt drive stops, as the auxiliary drive is no longer required. In addition, the 36V battery is charged from the power regenerated by storing the deceleration energy when decelerating and braking. During an idling stop, the electromagnetic clutch interposed between the crankshaft of the engine and the pulley is disengaged. The motor/generator supplied with power from the 36V battery drives the air conditioner compressor via the belt so that the air conditioner operation continues even if the engine stops. Furthermore, as soon as the engine stops, the electrically-operated oil pump for the AT is driven by the 12V battery to maintain the optimum hydraulic pressure, which allows the vehicle to smoothly restart.

■System Construction of THS-M

■The Mild Hybrid Car Using the 14V/42V Double Power Source System

The 42V power source system (the 42V-charging voltage/36V-open-circuit voltage system using a 36V battery) is considered as a basis for the next generation of in-vehicle power sources. The research for the system started in Europe, the US and Japan in the middle of the 1990's. The discussions about global standardization have been promoted in 2002. It was during the last half of the 1950's when the in-vehicle battery system was changed from the 6V battery type to the existing 12V battery type (the 14V-charging voltage/12V-open-circuit voltage system). That means this is the first time that the standard has been changed in 50 years.

It is expected that the 42V power source system will become widespread as a package that includes the technology to improve fuel efficiency or the new technology to enhance safety, comfort and convenience in the immediate future. A combination of a system for improving fuel efficiency and a system for enhancing safety, comfort and convenience is another option. This combined system enables a model to have excellent fuel efficiency while being a well-equipped luxury car with high performance.

It is difficult for the Toyota Crown Mild Hybrid Car with the world's first 42V power source system to have all its electrical system parts modified to be compatible with 42V in such a short time. Therefore, a 14V/42V double power source system has been adopted, in which the DC/DC converter and two batteries, 12V/36V, are used.

Many new parts are required to be developed in order to shift to the 42V system. The parts industry is expected to be invigorated by this change. However, modifying the existing electronics to be compatible with the 42V system may involve a large-scale development and capital investment to be carried out by the parts manufacturers, which is a hurdle for smooth shifting to the 42V system. Therefore, the adoption of the double power source system can be considered as a realistic solution while cost increase is unavoidable. Shifting to the 42V system does not bring about any advantage that appeals to consumers. Thus, it matters that what sort of technology can be employed by shifting to the 42V system.

■The Adoption of the 42V Power Source System Brings About the Possibility That Enhanced Safety, Comfort and Convenience, and Significant Improvement in Fuel Efficiency Will Go Hand in Hand

Shifting to the 42V vehicle power source system is required for the high-value-added technology to enhance safety, comfort and convenience, and the technology for significant improvement in fuel efficiency.

It is expected that the scope to adopt the new technology to enhance safety, comfort and convenience will be expanded by shifting to the 42V system. It includes steer-by-wire, brake-by-wire, active roll control, electrically-operated 4WD, catalytic heater, front defroster and seat heater.

Mid-range and large vehicles have difficulties with improving fuel efficiency. However, it is expected that the improvement will be attained, for example through switching the driving mode for the air conditioner compressor, power steering and water pump from the engine drive to the battery drive to reduce the engine load. The THS-M includes the system for smooth automatic idling stop and start, and engine restarting, which allows improvement in fuel efficiency when driving in urban areas. Furthermore, the electrically-operated engine valve technology, considered to be under development by the major manufacturers, is expected to allow a 30-35% improvement in fuel efficiency when compared to the cam drive.

If these technologies are employed, power consumption of their respective functions may exceed 1kW. It is assumed that the peak power consumption in the whole vehicle will reach 10kW or higher in the future. Common generators can supply only 2.5kW electric power through the existing 14V system and the maximum power available from those with the most advanced technology is assumed to be still only 5kW. It seems difficult to comply with these technologies. Even if these can be employed, larger and more massive parts, which cause fuel efficiency to deteriorate, as well as a voltage drop and an increase in heat loss during power distribution are unavoidable, resulting in inefficient operation.

Considering the factors described above, there is a consensus in the automotive industry that it is essential to shift to a high voltage system in the range equal to, or lower than DC60V/AC25V in which there is no concern about electric shock hazard, more specifically to the 42V system.

■Examples of Beneficial and Adoptable Technologies for the 42V Power Source System (Source: Delphi)

■High Evaluation Made by JSAE on the Industrial Invigoration Resulting from New Parts Development.

In 2000, the research was carried out by the Society of Automotive Engineers of Japan (JSAE) regarding the influences caused by the introduction of products completely compatible with the 42V power source system rather than the complicated and expensive 14V/42V double power source system.

The report of the research shows that shifting the existing electronics to the 42V system brings about advantages to the following product fields; Starter motor, Power window motor, Solenoid, Wire harness, Connector, Fuse/fuse box, Window heater/seat heater.
For example, it is expected that the mass of the wire harness can be reduced by approximately 25% through the use of thinner wires and the volume of the alternator, motor and solenoid can be reduced by approximately 20%.

The report from JSAE concludes that no significant advantage can be expected in parts areas other than those which are described above. More specifically, it judges that it is difficult or impossible for headlamps/low-power lamps to be compatible with the 42V system. The parts cost is likely to increase in most product fields due to additional compatible parts, part changes, increasing man-hour and longer work hours while expecting a modest cost increase of the wire harness as well as a cost decrease of the fuse box because of their possible downsizing. Semiconductor switches are widely employed, therefore, it can be expected that fuses will be no longer be required and circuitry will be simplified.

Automotive manufacturers have said that they are ready to make a capital investment to the extent that a large-scale complete changeover will be carried out. On the other hand, the parts manufacturers expect that the suppliers of the major components for the 42V system including alternators, starters and batteries, and those which deal with circuit components including switches, relays and fuses, will have to develop many products, substantially modify or completely renew their production facilities. This will require a significant capital investment by each company. Taking a broad view, however, such an investment can be regarded as an effective method to bring about the following various advantages; Invigoration of the economy, Good opportunities for the electrical and electronic engineers to be actively involved and A chance to create new value to automotive parts through the introduction of new technologies and products

■Influences Caused by Shifting to the 42V System Upon the Existing Electronics (Disclosed by the JSAE Research)

■Denso and Japan Storage Battery Supply the Major Components for the THS-M.

Denso supplies the motor/generator, one of the major components for the THS-M. Denso developed the world's first small belt type ISG(Integrated Starter Generator) in June 2001 for mass-production cars, in which the starter and alternator are integrated into one unit, to be used in the Toyota Estima Hybrid. That was followed by the Crown Mild Hybrid. The inverter for the Mild Hybrid is also supplied by Denso.

The 36V battery (sealed lead battery) was jointly developed between Toyota and Japan Storage Battery and then the latter started its mass production for the first time world wide. As the 36V battery alternately supplies power to the motor/generator and charges the battery in the regenerative braking system at frequent intervals, new positive and negative polar plates were developed and a production facility specific to the 36V battery was also newly established.

■The Major Unit Suppliers for the THS-M