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Prius v chief engineer Hiroshi Kayukawa spent five years sweating the details, but now can’t help but smile or talk in detail about his teams’ accomplishments when asked.
The panoramic sunroof is a lightweight polycarbonate sheet, not the expected glass. Weight control was a key aspect of the development.
Hiroshi Kayukawa is the chief engineer for the Prius v. Though not always certain of his English, the Japanese native is willing to suffer the delays necessary with the translation of questions from English to Japanese—often asking for more detail or clarification of terms—before giving his response. His eagerness is palpable. This is his vehicle, and he is proud of what he and the 1,500 people on the “v Team” have created over the past five years: the first line extension for the Prius brand, one that gives buyers a place to move when they begin to outgrow the original sedan.
“We went to shopping malls and ‘box stores’ to see what vehicles were being used, and how people used them,” says Kayukawa. His target customer was someone who had a growing family, which meant they were spending time making trips to Costco and Home Depot, which put them beyond the cargo capacities of the Prius. This lead to questions including: How much room is enough? What is the proper division between people space and cargo space? What changes would have to be made to the powertrain to give the new Prius model acceleration on par with the current one? These were just some of the questions Kayukawa and his team had to answer.
Bigger, stronger & still aerodynamic. It took little time to realize that the new model had to be larger, but then they had to figure out how big was big enough. Compared to the current third-generation Prius, the length of the new car increased 6.0 in. to 181.7 in., width grew 1.1 in. to a still slim 69.9 in., and height swelled 3.3 in. to 62 in. Overall, the Prius v (for “versatility”) is larger, but not so large that it casts an oversize shadow. “Most of the increase in wheelbase,” says Kayukawa, “is behind the B-pillar.” (The 109.4-in.wheelbase is 3.0-in. longer.) The v sits on a heavily modified (lengthened, widened) version of the MC platform found under the regular Prius, fitted with a new top hat and upper structure. Toyota says the new Prius has 58% more cargo room than the sedan (a hatchback), and more cargo space than the Chevrolet Equinox, Ford Escape and Nissan Rogue, small SUVs that are its direct competitors.
Body rigidity is improved through greater use of high-strength and ultra-high-strength steels, as well as by paying close attention to load paths. For the front suspension this meant separating the inputs for the MacPherson struts’ springs and dampers to improve road isolation, reduce NVH and enhance handling without adding weight to the structure or requiring increased use of sound deadening. Because the Prius v is a cargo carrier (Japan market versions also offer a third row that Kayukawa says “is much too small and narrow for North America”), a modified version of the torsion beam rear suspension from the third–generation Prius is used. Its design allows the damper and spring to be placed near the tire on separate mounts, and takes up little underfloor space.
During the vehicle development, it was a given that the new Prius “would have to look like a member of the family, but have its own personality.” Getting a low drag coefficient from a taller, blockier shape meant spending long hours in the wind tunnel. Consequently, the difference in coefficient of drag for the v is a still-respectable 0.29, a 0.05-Cd increase over the original. This was accomplished by:
• Emphasizing the lower leading edge of the front bumper and filling the gap behind it with an underbody shield.
• Using the side skirts to manage lower body airflow.
• Combining sharp-edged front bumper corners and flat wheel flare surfaces to improve airflow around the wheels.
• Adding “eyebrows” to the front lights to direct and control the flow of air over the large side mirrors,
• Gently curving the roof to keep the boundary layer of air attached before funneling it to the rear spoiler that directs air into the gap behind the car.
• Using the outside corners of the rear bumper to reduce turbulence created by the rotating rear wheels.
• Adding shields to smooth underbody airflow.
• Using the lower edge of the rear bumper to create a larger “pocket” for the air coming off the body to flow into, further reducing turbulence.
Weight saving. Control of weight was another priority for Kayukawa and his team. In addition to the lightweight high-tensile steels, the Prius v features aluminum in key body panels; a resin panoramic sunroof that is 40% lighter than a comparable glass panel and offers greater ability to block UV rays; polypropylene door panels injected around a foam core; and a cargo area deck board with a lightweight urethane foam center.
The top-of-the -line Prius v Five (there are three trim levels, Two, Three and Five) features SofTex material for the heated six-way adjustable driver’s seat and four-way adjustable front passenger’s seats. This premium seat trim has the texture and grain of real leather, is 28% lighter and is easily cleaned with
soap and water. In addition, it has 99% fewer VOC emissions and its manufact-uring process produces fewer CO2 emissions than other synthetic leathers.
This thought process extended to the premium JBL GreenEdge sound system. JBL says the system provides twice the performance of a standard design while using half the energy at maximum volume, and it weighs 4.18-lb. less. The door-mounted speakers use injection-molded carbon-impregnated supports instead of plastic or metal. These not only reduce weight of the individual part, they become part of the door panels’ structure. By delivering higher sound pressure levels with dramatically lower power consumption, JBL engineers were able to remove four speakers with no loss of performance. This saves Toyota approximately $50 per speaker. In addition, the amplifier is smaller and lighter, the acoustic lenses on the 180 x 250-mm front and 170-mm rear high-efficiency door-mounted speakers also eliminate the need for a subwoofer. The technology behind this audio system was developed for the Lexus LFA, and will be finding its way into the Camry, Tundra, Tacoma and other Toyotas as they are redesigned.
Under the hood. The drive system is carried over from the regular Prius. Toyota’s Atkinson-cycle 2ZR-FXE 1.8-liter inline four-cylinder produces 98 hp at 5,200 rpm, 105 lb-ft at 4,000 rpm, and has both variable valve timing and an electronic throttle. There are no accessory drive belts as the air conditioning compressor and water pump are electrically driven to reduce parasitic losses. One benefit is that this also allows cabin heating and cooling to continue when the engine isn’t running. A new exhaust heat recirculation system reduces the time needed to bring the engine coolant to operating temperature by one minute, improving both heater performance and shortening the time the engine needs to operate when cold.
As before, the hybrid system uses two motor-generator units, the second of which is water-cooled and operates at a maximum voltage of 650 V. Surprisingly, Toyota has not switched to a more power-
dense battery technology like lithium-ion because, as Kayukawa says, the nickel-metal hydride batteries currently in use are “bulletproof.” The Prius v uses the same number of cells (168) and modules (28) as the Prius hatchback and draws cool outside air through a snorkel located under the rear seat. Total hybrid system power output is 134 hp.
One addition to the Prius v’s repertoire is Pitch and Bounce Control. This software trick adds or subtracts torque through the hybrid system’s electric motor to dampen body oscillations. It is not speed dependent, and responds to an approximate 1.5 Hz frequency. The idea is to make the Prius v feel more stable and controlled. In addition, Kayukawa’s team changed the final drive ratio from the Prius hatchback’s 3.268:1 to a steeper 3.704:1 to match the acceleration curves of the standard car, despite the fact that the v is about 300 lb. heavier and has a maximum carrying capacity of 1,056 lb. As a result of this and its greater size, the Prius v carries a preliminary EPA mileage rating of 44 city/40 highway/42 combined. This is significantly lower than the 51/48/50 rating of the Prius hatchback, but the highest combined mileage rating in its competitive set.