The Ultimate Technology

Today, the plug-in hybrid electric vehicle (PHEV) model of the Outlander has become the flagship model of Mitsubishi Motors. When originally released in 2013, it established the new category of a PHEV crossed with an SUV, which was unlike anything before in the automotive world.

How did the development team eventually arrive at the PHEV? Together with Kazunori Handa, a member of the EV and Powertrain Advanced Engineering Development Department and the development team of EVs at Mitsubishi Motors since 1994, this series looks back on the development of the PHEV. Part 2 is "PHEV: The Ultimate Technology."

PHEVs are vastly different from battery EVs in that they are equipped with engines. If the electricity charged in the battery runs low, PHEVs start the engine which then recharges the battery. In situations which require more power such as quick acceleration or hill climbing, electricity is generated by the engine in addition to the battery in order to supply electricity to the motors. The engine can also serve as the power source when driving at high speeds.

Mitsubishi Motors' PHEVs also feature three different drive modes. In EV Mode, only the electric motors are used to power the vehicle; in Series Hybrid Mode, the engine is used to generate power that is stored in the battery and utilized to power the electric motors; and in Parallel Hybrid Mode, the vehicle is powered mainly by the engine with assistance from the electric motors. The car automatically switches between these three modes, with EV Mode usable for most normal driving situations, Series Hybrid Mode in higher power consumption scenarios such as hill climbing and acceleration, and Parallel Hybrid Mode when driving continuously at high speeds.

The challenge that arose during development was figuring out how to have the car make the decisions to switch between these modes. In other words, when the driver steps on the accelerator, the car has to decide instantaneously whether to supply power from the battery or to supply power generated by the engine. It also requires a system for appropriate power charging according to remaining battery. The development of a PHEV drive system was a challenge unlike anything before in the automotive industry.

Looking back on that time, Kazunori Handa reflects:

It became imperative to develop a controller that could comprehensively control the engine, motors, and battery. We fundamentally want the car to drive as much as possible without using the engine, so we had the car run on only the drive battery when normal acceleration is applied. When the driver steps hard on the accelerator, the controller determines that strong acceleration is desired and generates additional power from the engine, driving the motors as much as possible.

However, when the driver first steps lightly on the accelerator and then steps harder mid-acceleration, the car first accelerates only with electric power and then activates the engine for supporting power, so the timing of the acceleration is inevitably delayed. The controller would be useless if it makes the driver feel uncomfortable every time the engine is activated. We had a hard time developing controls that could switch as quickly and smoothly as possible between multiple power sources.

The controller decides whether to accelerate or decelerate based on the accelerator operation of the driver. In the process of developing the drive technology, the development team focused attentively on responding to the driver's intent that are put into the accelerator operation. Realizing that the only way to succeed at this unprecedented challenge was to conduct repeated trials, they conducted repeated test drives while thoroughly analyzing the relationship between the accelerator operation of the driver and driving speed. Having sought to deliver controls that precisely reflected the intention of the driver, they eventually perfected a revolutionary PHEV drive system that automatically selects the optimal driving mode according to driving conditions and remaining battery.

The key to the development of the PHEV is the powertrain specific to electric vehicles, comprised of a lithium-ion battery and electric motors (the unit that generates the power needed for driving, which is the engine in a gasoline-powered car). Having launched the i-MiEV ahead of the competition gave Mitsubishi Motors the advantage of having developed batteries with sufficient capacity for normal everyday driving, along with electric motors that can deliver the comfortable ride of an EV. While some people internally were saying that PHEVs might not need batteries as large as those in EVs, the development team was convinced that the battery technology developed for the i-MiEV can also be used in a PHEV and can become Mitsubishi Motors' strength. Handa comments:

When you activate the engine for city driving, you cannot enjoy the smooth, powerful acceleration of an EV. The engine produces audible sound and emits CO2. We believed that the ability to drive an SUV on the battery (electricity) alone in everyday driving situations would be highly appealing to our customers.

Mitsubishi Motors' high-capacity drive battery (12.0 kWh*) which improved upon the battery in the i-MiEV achieved a driving range of approximately 60km* even when installed in an SUV with a larger body than the i-MiEV. Offering enough range for daily driving, no other PHEV had ever been equipped with such a high capacity battery.

*At the time the Outlander PHEV was launched in 2013. JC08 mode in Japan.

"The common conception before was that PHEVs are nothing more than hybrids and electric motor driving is for nothing but support, so small batteries are fine," says Handa. "Our insistence on a high-capacity battery overturned that common conception."

unique technologies established over the years have also gone into Mitsubishi Motors' PHEVs. One of them is the four-wheel control technology. Mitsubishi Motors has emphasized the development concept of All Wheel Control (AWC) that achieves precise handling and superior vehicle stability by maximizing the performance of all four tires in a balanced manner. Super-All Wheel Control (S-AWC) is the very embodiment of that ideal. This system drastically improves car handling and stability by seamlessly, continuously controlling vehicle movements while accelerating, cornering, and braking without any discomfort for the driver. In addition to rigorous tests anticipating various weather and road conditions, we also honed this technology in grueling motorsports competitions such as the Dakar Rally and the World Rally Championship. Handa comments:

The motor was originally used for the i-MiEV kei-car, so it lacks the driving force to power an SUV. To overcome that, we put motors in both the front and rear for additional power. Rather than the conventional four-wheel drive which uses the propeller shaft to transmit driving force from the engine to the four wheels, we made the front and rear motors totally independent and made it possible to control driving force in both the front and the rear. Since both front and rear motors can be freely controlled, it takes expertise to properly control front and rear driving force according to the road surface conditions. This has been a major challenge for other companies, but Mitsubishi Motors had already established a plethora of technology to deliver the full potential of four-wheel drive with the Pajero and the Lancer Evolution.

When the decision to go with four-wheel drive was made, the S-AWC development team came together and put the finishing touches on a distinctively Mitsubishi Motors' four-wheel control system. Handa comments:

Internal combustion controls driving force in increments of one-tenth of a second, but electric motors can exert control in increments of 1/10,000 of a second. Highly responsive motors are able to control torque (driving force) in a sophisticated manner with excellent response. We were able to achieve precisely the ideal type of control that the S-AWC development team wanted.

The utility of an SUV that fuses the road handling of four-wheel drive with the comfort of a passenger vehicle is another technology that Mitsubishi Motors has been building upon in the development of vehicles such as the Pajero.

Making an SUV-type PHEV meant that the large capacity drive battery needed to be installed in just the right position. Installing it in the cargo space would make it impossible to offer customers the roomy interior space they desire, and would not allow the vehicle to carry large amounts of cargo. The decision was made to install the battery in the floor of the passenger cabin. However, the vehicle also needed to offer roughly the same amount of interior space for five passengers as a similarly-sized gasoline-powered vehicle. Furthermore, since the vehicle might be driven on rough roads, the battery also cannot be placed in a location where it will hit the ground. Its location was adjusted repeatedly down to the millimeter for the optimal balance. The body was also reinforced to ensure a high level of impact safety and steering stability.

And while the vehicle is very quiet while driving on the motors, noises that had not previously been of any concern became noticeable. Therefore, the development team implemented measures for vibration suppression, sound insulation, sound absorption, and also tuned the front and rear suspension to accommodate the increased weight of the battery while reducing road noise. "Installing the drive battery under the floor lowered the vehicle's center of gravity, improving both steering stability and ride comfort relative to internal combustion SUVs," says Handa.

This is how Mitsubishi Motors completed the Outlander PHEV, a fusion of the company's EV technology established with the i-MiEV, four-wheel control technology refined with the Lancer Evolution, and SUV expertise honed with the Pajero. It was first launched in the Japanese market under the catch phrase "Spread a new pair of wings, with the electric vehicle that charges itself to take you even farther." That was the moment when Mitsubishi Motors' EVs took one step closer toward the ideal.