TOYOTA ADVANCES NEW ELECTRIC CAR DEVELOPMENT

TOKYO―Toyota Motor Company, working in close cooperation with the academic world, has since 1971 made considerable progress in the second stage of its program to develop a new electric car.

The problems to be overcome are immense, but all the targets set to date have been met or exceeded, and a second-stage experimental electric car is due for final tests by the end of this year (1975).

The main thrust of the company's efforts is being sponsored and subsidized by the Ministry of International Trade and Industry, which recognizes the need for developing such a vehicle in Japan.

Toyota management believes that the reciprocating engine vehicles of today will stay in the future mainstream of automotive development and that electrically powered vehicles will serve as auxiliary or supplemental transportation. For this reason, the company has been developing a small electric car for urban and suburban use.

The main obstacle to the successful development of an electric car in the past has been the bulkiness of the batteries and their need for frequent recharging.

New Batteries

Toyota is currently working on seven different types of battery: three lead ones, three metal-air ones, and a sodium-sulfur one.

The company's first experimental vehicle is powered by sixteen 192V lead batteries, with a capacity of 158.5 ah/5 hr, in order to give both adequate power for the motor and a reasonable interval between recharging.

Among the targets set and achieved were a top speed of over 80 kph (the Toyota car reached 94 kph), a driving range on one battery charge of 180-200 km, a maximum of three seconds for acceleration from zero to 30 kph, and the ability to ascend a 6 degree gradient at a minimum speed of 40 kph

High Efficiency Motor

The motor control system needs to combine low voltage, high amperage, maximum efficiency and minimum weight and size. There are three major possibilities: an inverter-controlled induction motor, a transistor-controlled thyristor motor, or a thyristor chopper-controlled DC compound motor.

The thyristor chopper-controlled motor used in the first Toyota experimental car has four poles and an efficiency of 80%. The output power is 19.1 kw (one hour rating), the voltage is 145V, the amperage is 162A, and the weight/power ratio is 2.46 kg/kw/hr. It weighs 46.9 kg, and is capable of up to 10,000 rpm. Its newly developed transistor has the extremely high capacity of 300V, 400A.

The thyristor motor is of the revolving-armature type, which provides better overload resistance. Consequently the motor can be both smaller and lighter.

Computer Control System

The Toyota electric car features a remarkably versatile computer control system, which oversees the vehicle's battery, acceleration, braking, gear selection and safety protection circuit.

With the three speed electronic automatic transmission (EAT), the computer continuously checks the speed of the car and the electric power flowing into the motor. According to the signals which it receives, it automatically selects the most suitable gear, giving rapid jerk-free acceleration, and a high cruising speed.

The computer also automatically evaluates the angle of depression of the accelerator and compares it with the current passing to the main motor. It then decides whether the thyristor motor should be switched on or off, thereby controlling the power flow from the battery to the motor, and the vehicle's speed.

When the car is in use, the computer registers the battery level and informs the driver how much power he has left. It also checks and controls the charging process, ensuring full charging and protecting the battery from overcharging.

Many Other Features

Toyota has also developed a new hybrid electric vehicle braking system, which combines the hydraulic braking of gasoline-powered cars with computer- controlled braking of the motor. The result is more efficient and safer braking.

Another highly sophisticated feature is the built-in safety circuit. It collects information from all parts of the car and detects any malfunction, whether mechanical or stemming from a computer error. It locates the fault, warns the driver of the problem and, if there is any danger, it cuts off the motor current.

The first stage Toyota electric car's unladen weight is 1,375 kg and the laden weight is 1,650 kg. It is 3.35 m long, 1.58 m wide and 1.54 m high. There is sufficient power in the engine and space inside for five passengers, or for three passengers plus 300 kg of luggage.

In designing a body to contain five people and a large number of batteries, Toyota had to rethink the conventional car design, and came up with a vehicle that combines fully adequate passenger seating with a great degree of driving safety. It has a steel-frame chassis and FRP panels. This makes the upper part of the body light and strong, puts the center of gravity low on the road, and improves road holding and safety.

Plastic is preferable to metal for the non-structural sections of the body. It is light, easily-mouldable and corrosion-proof, and needs less tooling up for commercial production, making it economically feasible to turn out limited quantities of any given model. Toyota's research has produced an unsaturated polyester for use in the car that is superior to presently available plastics. It also has better resistance to corrosion and shock.