The high-voltage power circuit is a new technology that supports the new THS II system. By providing a newly developed high-voltage power circuit inside the power control unit, the voltage of the motor and the generator has been increased from 274V in THS to a maximum of 500V in THS II. As a result, electrical power can be supplied to the motor using a smaller current, thus contributing to an increase in efficiency.
Power, which expresses the work performed by electricity within syiven amount of time, is calculated by multiplying voltage by current. If the power necessary for driving the motor is held constant, the above formula indicates that doubling the voltage reduces the current by 1/2. Next, by following Joule's Law (Calorie = Current2 x Resistance), the power loss in terms of calories is reduced to 1/4 (1/2 Current x 1/2 Current) if the resistance is held constant. The high-voltage power circuit in THS II increases power by increasing the voltage while keeping the current constant. Furthermore, for the same power level, increasing the voltage and reducing the current reduces energy loss, resulting in higher efficiency.
The motor has been developed based on the technologies that Toyota has nurtured while working on electric vehicles. THS II uses an AC synchronous-type motor, which is a high-efficiency DC brushless motor with AC current. Neodymium magnets (permanent magnets) and a rotor made of stacked electromagnetic steel plates form a high-performance motor.
Furthermore, by arranging the permanent magnets in an optimum V-shape, the drive torque is improved and the output is increased. This, combined with a larger power supply achieved by an increase in the power supply voltage, has increased power output by approximately 1.5 times from THS, i.e.
, to 50 kW from 33 kW, even with a motor of the same size, producing the highest output per unit of weight and volume in the world. For motor control, a newly developed over-modulation control system has been added to the medium-speed range, in addition to the existing low- and high-speed control methods. By improving the pulse width modification method, the output in the medium-speed range has been increased by a maximum of approximately 30%.
Like the motor, the generator is also an AC synchronous type. In order to supply sufficient power to the high-output motor, the generator is rotated at high speeds, increasing its output. Measures such as rotor strength enhancement have increased the rpm range for the maximum possible output from 6,500 (in the conventional type) to 10,000 rpm. This high rpm has significantly increased the power supply up to the medium-speed range, improving the acceleration performance in the low/medium-speed.
As a result, an optimum combination of a high-output motor and an engine has been achieved. The power control unit contains an inverter that converts the DC from the battery into an AC for driving the motor and a DC/DC converter for conversion to 12V. In THS II, a high-voltage power circuit that can increase the voltage from the power supply to 500V, has been added. Based on the relationship of Power = Voltage x Current, increasing the voltage makes it possible to reduce the current, which in turn makes it possible to reduce the size of the inverter. Also, because the control circuits have been integrated, the size of the power control unit itself has remained almost the same as before.
This semiconductor switching device (IGBT: Insulated Gate Bipolar Transistor) boosts the voltage from the battery and converts the boosted DC power into AC power for driving the motor. Since the current that must be switched is large, minimizing heat generation is important. Therefore, Toyota has developed a unique transistor finely tuned down to the crystal level. This device is 20% smaller than the similar device used in THS and has achieved low heat generation and high efficiency. In THS II, further enhancements have been made to the compact, high-performance nickel-metal hydride battery developed for THS. Having reduced the battery's internal resistance by improving the electrode material and by using an entirely new connection structure between (battery) cells, the new battery's input/output density is 35% better than the battery used in THS, achieving the highest output density (output per unit of weight) in the world.
To maintain a constant charge, the new battery is discharged or receives charging energy from the generator and the motor, and therefore does not require external charging, as do electric vehicles. A regenerative braking system is used which, during engine braking and braking using the foot brake, operates the electric motor as a generator, converting the vehicle's kinetic energy into electrical energy, which is used to charge the battery. The system is particularly effective in recovering energy during city driving, where driving patterns of repeated acceleration and deceleration are common. When the footbrake is being used, the system controls the coordination between the hydraulic brake of the ECB and the regenerative brake and preferentially uses the regenerative brake, thereby recovering energy even at lower vehicle speeds. Furthermore, by improving the battery input performance, more energy is recovered.
Additionally, by reducing the friction loss in the drive system, such as in the transmission, the energy that used to be lost as driving system loss during deceleration is now recovered, significantly increasing the total amount of recovered energy.
Melih ("may-lee") Oztalay, CEO SmartFinds Internet Marketing Web: www.toyotaofbedford.com EMail: firstname.lastname@example.org Toyota Ohio state customers now have an online showroom built with Toyota Cleveland Ohio shoppers in mind.