|North American spec i-MiEV. Click to enlarge.|
Mitsubishi’s North American-spec i-MiEV battery electric vehicle (earlier post)—available in either an ES base model or upgrade SE trim package —will be available to test drive at US dealerships beginning in November 2011 with the first scheduled customer vehicle deliveries set to commence in early 2012.
Mitsubishi is positioning the North American i-MiEV electric vehicle as the most affordably-priced mass-produced EV available in the US. Manufacturer’s Suggested Retail Price (MSRP) is $29,125—$6,075 less than electric vehicles produced by other mainstream automobile manufacturers—for the base ES model before a federal tax credit of $7,500 and available state financial incentives (subject to availability of funding).
Compared to the original Japan/EU-spec i-MiEV, this new US-spec electric vehicle features a roomier interior and improved safety features, due to a 110mm (4.3-inch) wider track and redesigned front and rear bumpers, a Tire Pressure Monitoring System (TPMS) and an Acoustic Vehicle Alerting System (AVAS) to warn pedestrians of the approaching EV. A redesigned center console featuring improved materials will also feature prominently on the new North American Mitsubishi i-MiEV.
Background. First shown as a concept vehicle at the 2003 Frankfurt Motor Show, the production car version of Mitsubishi i was introduced to the Japanese public in January 2006. In its home market, the Mitsubishi i was a keijidōsha—a light vehicle class or kei car—powered by a 12-valve, 659cc DOHC inline-3-cylinder engine that featured the MIVEC (Mitsubishi Innovative Valve timing Electronic Control system) for maximum power output and fuel efficiency.
The engine placement is just forward of the rear axle and behind the rear seat. Positioned low and toward the center of the chassis, it gives the car a low center of gravity for excellent handling and stability while also maximizing interior volume. It is this concept of optimal packaging of the drivetrain components that made the i the logical choice when Mitsubishi decided to make a 100% electric-powered vehicle as it was relatively easy for engineers to swap the gasoline engine for an electric motor and stow the lithium-ion battery pack beneath the sub-floor.
i-MiEV, Japan-spec. Mitsubishi launched the i-MiEV (Mitsubishi innovative Electric Vehicle) in Japan in mid-2009. With a 16 kWh lithium-ion battery pack, 47 kW (63 horsepower) electric motor and single-speed reduction gear transmission, the Mitsubishi i-MiEV has an approximate range of 160 kilometers (99 miles) in the Japanese 10-15 mode urban driving pattern and a top speed of approximately 130 km/h (81 mph).
Following its launch at home, the i-MiEV entered into the Hong Kong and Australian markets in 2010. By the end of that year, the EU version of the Mitsubishi i-MiEV was launched in Germany, followed by the United Kingdom at the beginning of 2011.
Mitsubishi i-MiEV, North American-Spec. The North American production vehicle features a more powerful 49 kW AC synchronous electric motor (66 bhp), an 88-cell 16 kWh lithium-ion battery pack and includes an onboard battery charger. The N.A. Mitsubishi i is rated by the EPA to attain 126 mpg equivalency in city driving and 99 mpg in highway driving and achieves a “real world” EPA driving range of 62 miles (98 miles in the EPA LA4 city unadjusted).
The vehicle’s batteries can be recharged in approximately 22 hours by the included 120V Level 1 portable charging cable, 7 hours by a dedicated 240v Level 2 EVSE charger (available for home installation by select retailers or utility companies), and receive an 80% charge in under 30 minutes from a public Level 3 quick charging station via the optional charging port (a separate port on the opposite flank of the car). The 2012 Mitsubishi i-MiEV uses the CHAdeMO protocol for high-speed EV charging.
Standard appointments on all Mitsubishi i models include a 4 speaker, 100-watt AM/FM/CD audio system with MP3/WMA playback capability; speed-sensitive Electric Power Steering (EPS); LED tail lamps; a driver’s seat heater; an electric manual air conditioning system with micron filter; and a vehicle security and immobilizer anti-theft system. An advanced airbag system consisting of dual-stage front airbags, driver and front-passenger seat-mounted side-impact supplemental airbags and roof-mounted curtain side-impact supplemental air bags; 4-wheel anti-lock brakes (ABS) with Electronic Brake-force Distribution (EBD); and Active Stability Control (ASC) with Traction Control Logic (TCL) are also included as standard equipment.
Vehicle options include a Cold Zone package that includes heated outside mirrors and a battery warming system for the main lithium-ion battery pack ($150 MSRP) and a Premium Package available with the upgrade SE trim level that includes an HDD navigation system with rear view camera, DC quick charging port and the FUSE Hands-free Link System with USB port and steering wheel-mounted audio controls ($2,790 MSRP).
|Location of the battery pack. Click to enlarge.|
Battery pack. The 16 kWh battery pack is located beneath the vehicle’s interior floor (sub-floor) and the chassis (body frame) inside a specially-designed stainless-steel protective battery case. This design not only helps to protect the battery pack in an accident but also minimizes penetration of objects/debris that can be picked up from the road surface while driving. Additionally, this stout support structure also aids the vehicle’s structural rigidity as it is bolted directly onto the chassis.
Components that form a protective barrier to the main drive lithium-ion battery pack include the battery protector (a thick skid plate located aft of the front wheels and in front of the battery pack), the undercover (a protective covering over the entire battery pack) and the supporting frame system (several fortified braces that rests between the battery pack and the undercover that hold the latter item in place). The lithium-ion battery pack encasement structure is completely waterproof.
Mitsubishi estimates that after 5 years, the capacity of the Main Drive Lithium-ion battery will be approximately 80% of its original capacity. After 10 years, the capacity should be approximately 70%. Other factors that can adversely affect battery capacity over time include frequent driving using aggressive acceleration/deceleration, repeated frequent use of the quick charger, and vehicle operation/storage in extreme temperature environments.
|Batteries (blue), Battery Tray (purple), Battery Ventilation Fan (in green at top of image). Click to enlarge.|
The 2012 Mitsubishi i includes a battery temperature conditioning system to ensure optimal performance, reliability and longevity of the advanced lithium-ion battery pack. This system performs two critical functions: to cool the battery pack during Level 3 quick charging so that it does not get excessively hot, and to warm up the battery pack when it is undergoing Level I or Level II charging in case the battery temperature is too low.
This is accomplished by a forced air ventilation system that makes use of the HVAC blower forces to flow heated or cooled air around the battery pack via a special battery ventilation fan.
The battery temperature conditioning system is composed of the following components:
- HVAC. Heating, ventilating and air-conditioning system
- Switching damper. Redirecting heated/cooled air from the passenger compartment to the battery pack
- Floor duct. Ducting connecting the HVAC system and battery pack
- Air duct. Specialized ducting for air distribution to battery pack
- Battery ventilation fan. To exhaust the conditioned air that circulates around the battery pack
When the vehicle’s ECU detects that a Level 3 DC quick charging connector has been plugged into the vehicle, it then determines whether the battery pack requires cooling based on battery temperature information from the BMU (Battery Management Unit). If it deems that cooling is necessary, the ECU then signals the compressor heater control unit that controls the compressor, A/C control unit and the HVAC system while communicating simultaneously with the battery management unit (BMU) to engage the battery ventilation fan.
The cooling system only becomes operational when it detects that the battery temperature is above 68 °F (20 °C); in this initial phase the HVAC blower fan and the battery ventilation fan are engaged. If the ECU determines that the battery temperature exceeds 86 °F (30 °C), then the HVAC blower fan and the battery ventilation fan are supplemented by the air conditioner.
When the vehicle’s ECU determines that a Level 1 or Level 2 charging connector is plugged into the Mitsubishi i, it then determines whether or not battery heating is necessary based on battery temperature information from the battery management unit (BMU). If the system deems battery heating necessary, it then starts the compressor heater control unit which controls the heater, the A/C control unit and the HVAC system while concurrently telling the BMU to turn on the battery ventilation fan.
MiEV OS - Mitsubishi innovative Electric Vehicle Operating System. Mitsubishi Motors has more than four decades of experience in developing battery-electric vehicles. This is reflected in the Mitsubishi EV operating system, MiEV OS. The MiEV OS oversees and monitors the function of these components:
- Electric Vehicle motor
- Main Drive Lithium-ion battery pack
- Battery Management Unit (BMU)
- Inverter – Motor Control Unit
- On-board vehicle charger & DC/DC converter
- Driver inputs (throttle, brake, gear selection, etc.)
- Safety systems (traction control, ABS, air bags, etc.)
- Electric motor unit cooling system
The management of all of these components are overseen by the vehicle integration controller (EV-ECU). The EV-ECU utilizes information from each of these components to control a wide range of systems including:
Battery management system. The Battery Management System consists of the battery management unit (BMU); cell monitoring units (CMU) that monitor the state of each individual lithium-ion battery cells (one CMU per battery cell; a total of 88 cells in each vehicle battery pack); a leakage sensor to determine if there is any leakage from the high voltage system; and an electric current monitor to constantly watch over the battery pack’s amperage.
High voltage control system. If the 2012 Mitsubishi i should be in a collision, the main drive lithium-ion battery pack fails or if failsafe systems detect any battery leakage, the High Voltage Control System instantly triggers the high voltage circuit to shut off from the main battery to help protect the driver, vehicle occupants and/or rescue personnel.
If an impact is detected by the conventional G-sensors utilized in the air bag, the High Voltage Control System deactivates the circuitry. As a special precaution, Mitsubishi engineers have added a specialized supplemental G-sensor that automatically shuts off the high voltage circuit should the impact level in the collision be so great that it damages the High Voltage Control System. Additionally, if the on-board diagnostics receives any information that it deems may lead to a serious failure of the vehicle’s operation, the High Voltage Control System will perform a high voltage system shut off.
Cruising range estimation. The cruising range of the Mitsubishi i is estimated continuously by determining electric power consumption and the capacity level of the battery. The system estimates the average electrical power consumption from data supplied by the battery management unit (BMU) and the inverter-Motor Control Unit while simultaneously factoring in information relayed to it from the HVAC system and the onboard charger. The cruising range control unit takes this information, along with the actual switchgear positions over the air conditioning/heater controls that have been selected by either the driver or the front passenger, to determine the estimated driving range of the vehicle.
Traction control. Traction control on the 2012 Mitsubishi i not only controls vehicle stability under braking but at the same time maximizing the amount of energy produced and fed back into the Main Drive Lithium-ion battery pack by the regenerative braking system.
Smooth start control. The Smooth Start Control technology developed on the Mitsubishi i restrains electric motor torque at the start which helps to reduce drivetrain vibration. The result is smooth and quick acceleration.
Battery energy level estimation. The Battery Energy Level Estimation system takes a variety of technical criteria into account including an estimation of the state of charge (SOC) and energy capacity of the battery pack, along with battery current and cell voltage information as well as driving conditions. The system also looks at an historical behavior to examine usage and charging patterns to intelligently make an ongoing estimation of the battery pack’s capacity to provide the most accurate picture of how much energy the main drive lithium-ion battery is actually capable of storing.
Regenerative brake control. The Regenerative Brake Control system’s goal is to provide the maximum amount of regenerative energy back into the lithium-ion battery pack in the most controlled and efficient manner. The system calculates the torque level from the electric motor based on the shift lever position (D, Eco, or B), and the accelerator and brake pedal positions. Data from the anti-lock braking system (ABS), the battery management unit (BMU) and the inverter-Motor Control Unit (MCU) are also factored into the equation to help optimize torque levels.
Power save control. Power Save Control takes in driver input data including accelerator and brake pedal positioning, along with air conditioning or heater settings, as well as information from the inverter-Motor Control Unit, the vehicle’s Main Drive Lithium-ion battery capacity level and torque production from the electric motor to determine whether or not the car should go into a power saving mode by automatically reducing the output from the HVAC system and/or slightly restricting available torque levels from the electric motor. The Power Save Control system operates from the conventional “D” drive setting gear selection on the shift gate.
|Inner structure of motor. Click to enlarge.|
Motor and transmission. The main components that make up the drivetrain for the North American-spec Mitsubishi i include the electric motor; fixed reduction gear transmission; and Motor Control Unit (MCU).
The synchronous permanent magnetic motor with neodymium magnet weighs 108 lb (49 kg) and is water-cooled. Mitsubishi engineers used computer-aided design and analysis to reduce noise, vibration and harshness (NVH) produced by the electric motor (placement of the motor in the rear also reduces the electric motor noise for the cabin occupants).
Designed specifically for the 2012 Mitsubishi i, the mounting system for the electric motor also makes a significant contribution in the reduction of unwanted noise, vibration and harshness (NVH). The front of the motor mount (located in the rear of the vehicle) features a pair of dual insulators that have been developed by Mitsubishi engineers for optimal minimization of vibration where the mount connects to the chassis by cutting off high-frequency noise produced by the electric motor. The rear motor mount accomplishes the identical goals (noise and vibration reduction) as the front mount but is smaller and features a single insulator due to packaging requirements.
The electric motor in the Mitsubishi i is completely maintenance-free and backed by a 5-year / 60,000 mile power train warranty.
The North American-spec motor produces nearly 49 kW (66 bhp) at 3000 to 6000 rpm and 196 Nm (145 lb-ft) of torque from 1 to 300 rpm. Because all 145 lb-ft of torque are available at any rpm, standing start acceleration is ideal for stop-and-go urban (city) driving conditions. Maximum rotation speed of the electric motor is 9900 rpm.
|Cutaway of the fixed gear transmission. Click to enlarge.|
The fixed gear ratio transmission of the 2012 North American-spec Mitsubishi i is engineered to make the most of the electric motor’s high torque output and a wide power band. The 7.065 gear ratio has been selected for use in this transmission as Mitsubishi research and testing determined this to be the best ratio for optimum dynamic performance from the electric motor. This fixed gear ratio, along with a simplified two-stage parallel shaft reduction and a conventional differential unit, distribute motor torque to the vehicle’s rear wheels.
Other technical highlights include a single open-type ball bearing that helps to reduce drag and an output shaft layout position that helps to reduce friction of the transmission. The transmission measures less than 7 inches in length and weighs less than 42 lbs. When mated to the electric motor, the combined transmission/motor measures less than 19 inches long and weighs 143 lbs.
The Motor Control Unit (MCU) manages and regulates the electrical power supply to the electric motor to generate the necessary level of torque to power the vehicle by converting the battery packs DC voltage into three-phase AC. Conversely, the MCU is responsible managing the electrical energy that is produced by the regenerative braking system and is fed back into the lithium-ion battery pack.
In propulsion mode (drive), the MCU generates the three-phase AC current dataset into the coil of the electric motor to generate a magnetic field. The motor is rotated by synchronizing the magnetic-field of magnets with the magnetic-field of coil current and with speed sensing position of the rotor. The MCU controls motor torque by adjusting the magnetic-field of the coil current. The attraction and repulsion that takes place between the rotating magnetic field and the magnets within the electric motor generates the acceleration torque.
In regeneration mode (braking), the MCU generates deceleration torque by adjusting the phase of electrical current and feeding the regenerative energy back into the main drive lithium-ion battery pack. In this phase, the electric motor essentially becomes a generator.
|Structure of MCU. Click to enlarge.|
The critical electrical components housed within the Motor Control Unit are a smoothing condenser to help stabilize the DC current; several insulated-gate bipolar transistors (IGBT) that convert the DC electrical current into AC;a heatsink to provide cooling/heat dissipation and a control board that supervises the electric motor. The control board is located in a separate area within the MCU from the smoothing condenser, the IGBTs and the heatsink to protect it from the heat generated by these components.
The Motor Control Unit measures 11.3 inches wide, 12.2 inches long and 6.7 inches tall and weighs 33 lbs. and, like the vehicle’s electric motor, is housed a completely waterproof and dust-proof structure and makes use of water-cooling for temperature control.
Electric Vehicle Braking System. When developing the braking system, engineers paid particular attention to making sure that the system would offer the driver very good braking feel. This has been achieved by hours of testing and tweaking of the regenerative braking system and by also incorporating a specially-designed electric vacuum pump that acts as a power source for the brake booster.
The Brake Assist (BA) and Active Stability Control (ASC) systems are standard equipment on all units sold in the United States and Canada. The brake assist mechanism is integrated directly into the brake booster. This enhances vehicle safety in panic braking situations because, when the system detects that the driver is depressing the brake pedal in a quick and abrupt manner, the brake booster and the brake assist mechanism reach full power instantaneously without the additional force required from the driver’s foot as is the case with a conventional hydraulic braking system.
The braking system equipped on the North American-spec 2012 Mitsubishi i is identical to the setup found on both the Japanese and European-spec models.
Another distinctive design element to the braking system of the Mitsubishi i is an electric brake vacuum pump as the power source of the vacuum brake booster that takes the place of the design common in internal combustion engine powered vehicles —one that relies on intake manifold vacuum pressure to power a brake booster.
The electric brake vacuum pump does not operate full-time but activates on-demand when necessary. The electric brake vacuum pump is attached to a bracket that makes use of a dual isolation structure that helps to decrease pumping vibration from entering the cabin. Additionally, noise produced by the pump itself has been lessened by the design of its intake and venting structures.
The Brake Vacuum Pressure System includes the electric brake vacuum pump; MiEV Operating System (EV- ECU); vacuum sensor; relay; and brake warning lamp (instrument display)/brake audible warning buzzer. The vacuum sensor measures the vacuum pressure in the brake booster. The MiEV operating system EV-ECU receives this information and controls the electric brake vacuum pump accordingly. If this system fails or it detects a brake vacuum pressure shortage, this will automatically illuminate a brake warning light on the instrument display and an audible brake warning buzzer will sound to alert the driver.
Depressing the brake pedal repeatedly may activate the brake warning system (audible alert and illuminated warning light). If the system determines that everything is normal with the brake vacuum pressure, then the buzzer stops sounding and the warning light will deactivate after a few seconds, signaling to the driver that the vehicle is okay and that they may resume normal driving.
Driving. The electric i offers three drive modes: “D” is the standard mode and provides full power access and normal regenerative braking effort. “Eco” slightly reduces overall power output, thus conserving energy and slightly increases the regenerative braking capability. “B” provides full power with the strongest calibration of regenerative braking capability.
|Click to enlarge.|
Subjective impressions. Mitsubishi recently hosted a media Ride & Drive attended by GCC using production prototypes of the North American spec i-MiEV recently in Portland, Oregon—one of the company’s key initial target markets due to the city’s aggressive moves to encourage the adoption of electric vehicles. Media attending had the opportunity for a brief driving exposure over the course of an afternoon to the i-MiEV under different conditions.
Mitsubishi has made the interior of the N.A.-spec vehicle much roomier than the Japan/EU spec version—the contrast between the two for occupants is significant. With a 50/50-split fold-down and reclining rear seats, the i-MiEV also has more than 50 cubic feet of rear cargo volume.
The i-MiEV handles extremely well in traffic, although the ride is not always the gentlest, depending upon the road condition. Mitsubishi engineers did a very good job of noise reduction—the faint whine that can accompany an electric motor wasn’t detectable by two of us in the front seats.
The difference between the responsiveness of the vehicle in the different drive modes is quite clear. As Mitsubishi suggests, D mode will likely remain the standard for regular drivers; in D mode, the i-MiEV is peppy, with good performance up-hill. B mode delivers very noticeable regen, which, if one is focused on recapturing as much of the energy as possible is a great feeling, but might prove a bit unsettling for an average driver. Eco mode, outside of the city, makes the i-MiEV feel sluggish and a bit mushy. For city traffic, however (where presumably you’re not blasting off of the line or charging up a hill), it makes a great deal of sense.