Building on the innovations introduced in the Toyota Prius, the HV-M4 is
the first hybrid four-wheel drive in the world. The THS-C hybrid system
links a high-performance engine with a pair of electric motors and a
continuously variable transmission (CVT) to form a powertrain that never
requires external charging. The HV-M4 also acts as a "generator on
wheels," supplying household electrical current via several 100V
outlets. The vehicle embodies the latest advances in styling and
information-age functionality. The body design is intelligent and
futuristic. The interior is spacious, comfortably seating six. And
multiple MONET multimedia consoles transform the interior into a
media-rich living space. The HV-M4 is a true next-century vehicle.
The HV-M4 mid-sized minivan was developed to demonstrate the type of
vehicle we could expect in the future. "We have designed the HV-M4 to
exceed all expectations," explains Chief Engineer Shigeru Matsuhashi.
"Our primary development concept was to extract maximum performance
from minimal resources."
The vehicle tail lamps, for example, use neon and LED, significantly
cutting energy use. The next-generation propulsion system fully embodies
this minimalist principle. The THS-C hybrid system combines a 2.4-liter
gasoline engine with two electric motors and a continuously variable
transmission (CVT). Only the absolute minimum of energy is used to move
the vehicle, so the HV-M4 has a fuel efficiency double that of vans of the
same class (in Japan's 10-15 test mode). The HV-M4 also meets the
requirements of Japan's forthcoming cleanest emissions category: J-ULEV.
Why a Hybrid System?
The combination of a gasoline engine with an electric motor can radically
improve fuel efficiency and lower emissions to J-ULEV levels, while
eliminating the problem associated with electric vehicles--the need to
recharge the battery overnight. The hybrid system simply charges the
battery during normal driving as required.
How the System
Works
The THS-C hybrid system comprises a high-efficiency gasoline engine, which
provides the primary power, plus two electric motors--one of which drives
the front wheels, the other the rear. The transmission includes a power
split device that allocates power from the engine, diverting a portion of
it to the electric motor or to the battery via inverters, depending on
operating conditions . This system, working in concert with the
regenerative braking system, achieves large improvements in fuel economy,
while also producing smooth acceleration and deceleration under all loads.
And it does all this while automatically charging the battery when needed.
Normal Driving/Battery-Charging
The power provided by the engine is transmitted directly to the front
wheels via the CVT (path A). An electronic control unit (ECU) controls the
level of charge in the battery. When this falls below a certain value, a
portion of the engine power is diverted to the battery as determined by
instructions from the ECU. By using the front motor as a generator and
pushing the torque in reverse, the batteries can be charged (path B).
Full-Throttle
Acceleration
During full-throttle acceleration, the battery supplies electricity to
drive the front motor, thereby providing additional power to the front
wheels (path C). If a further power boost is required, the rear motor can
also be used for short periods (path D).
Light Load
When the vehicle is operating on a light load--for instance, moving at
very low speeds or going down a gentle incline--the engine cannot run at
peak efficiency. At these times, the engine is not engaged. The vehicle is
driven by the front motor using power supplied by the battery (paths C,
D).
Deceleration/Braking
As the vehicle slows, both sets of wheels drive the respective motors in
reverse. Acting as generators, the front and rear motors convert the
vehicle's kinetic energy into electricity, and send it through the
inverters to be stored in the battery (paths C', D').
4WD Mode
On low-friction road surfaces, if any front wheel slippage is detected,
the power to the front axle is reduced by diverting power received from
the engine. The front motor is then used as a generator to absorb engine
power and produce electricity to drive the rear motor (path E). The net
effect is a transfer of power from the front to the rear wheels to combat
the slippage. If the power generated by the front motor is insufficient,
it can be augmented by the battery.
Through these various systems, the HV-M4 has a fuel efficiency double that
of vans of the same class (in Japan's 10-15 test mode). It also meets the
extremely strict requirements of the J-ULEV category of vehicles.
Mobile Power Source
The HV-M4's hybrid system can supply electric power to appliances outside
of the powertrain circuit. It is equipped with three AC 100V sockets on
the inside and one on the outside that allow occupants to use electrical
devices freely. It can be connected up to power-hungry goods such as hair
dryers, microwave ovens and televisions--and still never need any external
charging. In essence, this makes it a convenient "generator on
wheels."
The power supply is approximately 1.5 kW. This makes the HV-M4 useful not
only for camping or other leisure activities, but also for powering
electric wheelchairs or medical devices. It could be used as an ambulance,
or as a camper. Even when supplying maximum power, the engine only turns
over at low revolutions, so users do not need to suffer any of the noise
usually produced by an oil-powered general-purpose generator.
Packaging
The HV-M4 embodies the advances in styling and information-age functions
that characterize the latest minivans. The external body design is
deliberately futuristic and intelligent.
One notable feature is the innovative choices of exterior vehicle
lighting. The low-beam head lamps use fiber optic cables to deliver light
from a remote light source. Because fiber optics are flexible and can
transfer light waves without loss, the head lamp light source can be
placed literally anywhere within the vehicle, maximizing space efficiency.
Moreover, rather than using lens to create separate beams which are
targeted at areas in front of the vehicle, the HV-M4 uses fiber optics to
create individual beams that can be aimed separately. The low-beams are
encased in a stack of four rhomboid lamps, adding to the hi-tech feel of
the front end.
The lighting on the vehicle's rear is just as futuristic. The red loop
encircling the center of the rear end of the vehicle contains a neon tube
light. The poles of this red strip function as the tail lamp. On either
side of the rear end, eight LEDs are clustered. The five outermost LEDs
glow orange and function as the turn signals. The innermost stack of three
LEDs glow red, functioning as both the stop and tail lamps. Altogether,
these eco-friendly exterior lighting innovations make this one vehicle
that you will notice.
Inside the HV-M4, the cabin will comfortably seat six, with plenty of
space for everybody to have a good time, either individually or as a
group. The second seat is equipped with a MONET multimedia monitor, while
the third seat features an overhead console, allowing passengers to relax
on their own in peace. "It's designed to be a kind of multimedia
living space," comments Mr. Matsuhashi.
A dashboard-mounted multi-purpose display panel provides a wealth of
information to the driver and front passenger, and acts as the interface
for the HV-M4's various intelligent transport systems (ITS).
The HV-M4's human-machine interface is well suited to the demands of the
information age. Navigation functions can be controlled by voice commands,
and frequently used audio switches are readily accessible on the steering
wheel. Instrumentation is easy to read, and controls are grouped together
for maximum ease of use.
An added benefit of the hybrid system is that the drive shaft tunnel down
the center of the vehicle can be made extremely small. This frees up space
usually reserved for hidden mechanical parts and lets you make the most of
the cabin.
The HV-M4 contains a number of ITS features designed to give the driver
and other occupants extra help and to perform communications functions.
These include millimeter-wave radar cruise control and an auto-follow
function for traffic jams. A newly-developed guidance function helps the
driver back into tight parking spaces. The HV-M4 even has an onboard PC to
facilitate Internet access.
The vehicle is also equipped with a card interface to use at electronic
toll collection (ETC) booths on expressways, which are due to begin
operation in Japan during the coming year. In addition, the HV-M4 will be
able to receive wireless broadcasts of audio and video material, which
Mobile Broadcasting Corporation, a Toyota affiliate, is planning to start
in 2001.
