Little more than two years after the first announcement of the unique collaboration between Toyota and Tesla Motors, members of the media were taking to the streets of Newport Beach, CA, in August to drive the all-new, all-electric SUV. The vehicle combines a Tesla designed and produced battery and electric powertrain with Toyota’s most popular SUV model to create an EV capable of achieving an EPA-estimated 92 or 113 mi of driving range, depending on the selected charge mode—standard or extended, respectively.
“A typical product planning cycle is more than four years; the RAV4 EV moved from conception to production in less than two,” said Bob Carter, Group Vice President and General Manager, Toyota Division, at the vehicle’s reveal at the 2012 Electric Vehicle Symposium in May. “There was no template for this project, no guidelines, just a challenge to bring a premium EV to the market.”
Toyota and Tesla engineers rose to the challenge, employing a fast and flexible development and evaluation program—dubbed eFAST (early field and suitability testing)—to validate and confirm vehicle performance.
Many different approaches were employed during the collaborative build process between the two parties and much was learned through the partnership of the two disproportionately sized companies.
“They were available at TTC during our Obeya activities during development. There were weekly TV and telephone conferences between both sides of engineering, as well as many business trips to the Palo Alto area,” said Greg Bernas, Chief Engineer, Toyota Technical Center (TTC) in Ann Arbor, MI. “Currently, all groups are creating reflection documents that will be reviewed, and from these documents a main report will be generated to provide the lessons learned from the program.”
Don’t be a drag
One of the first objectives during development was to reduce the coefficient of drag of the gas-powered RAV4 from 0.35 Cd. Toyota redesigned the front bumper, upper and lower grille, side mirrors, rear spoiler, and underbody design to optimize airflow.
Rear spats were extended from the current vehicle by about 1.6 in (41 mm), helping to move more air out and around the tire, and a new front spat fairing was added and designed to help start to route the air sooner so that it would hit the outer portion of the front existing spat.
On the back is a much larger rear spoiler, which has been extended in both the vertical and the horizontal surfaces compared to the current vehicle, making it 4.7 in (119 mm) larger and stretching 4.9 in (124 mm) farther down the back side of the window.
“What we’re doing is reshaping the way the air comes off the back of the vehicle,” said Sheldon Brown, Executive Program Manager, TTC. “In effect, we’re trying to reduce that low-pressure wake by tapering down that wake by holding the air on the body longer and allowing that air to change into a smaller pocket. This is a 2.5% drag reduction and makes the vehicle much more efficient.”
With a large, flat battery beneath the vehicle, underbody airflow is also greatly enhanced.
“That flat surface in effect can reduce about 2% of our drag,” Brown said. “In addition, we buttoned up our motor compartment and between the motor compartment and battery put in an extension. All of those covers serve to protect some of the high-voltage cabling, but more importantly for us from an efficiency standpoint they give us about 2.5% drag reduction.”
A spat at the back of the battery was also added to help prevent the air from colliding with the rear suspension members. The spat redirects the air, forcing it smoothly over and increasing performance by 1.4%.
In total, the aerodynamic coefficient of drag was reduced from 0.35 Cd to 0.30, making it what the company claims to be the most aerodynamic SUV in its class in the world and comparable with a number of sedans in terms of overall aero performance.
“That’s extremely meaningful in range, especially when talking about highway range, where as velocity increases obviously our drag goes up significantly and the force against the vehicle has to be offset by power,” Brown said.
The front-wheel-drive RAV4 EV is powered by an ac induction motor with a fixed-gear open differential transaxle gear ratio of 9.73:1 and features two drive modes—Normal and Sport. In Sport mode, the vehicle reaches 0-60 mph (0-97 km/h) in 7.0 s and has a maximum speed of 100 mph (161 km/h). In Normal mode, 0-60 time dips to 8.6 s and the max speed is 85 mph (137 km/h). Max output from the electric powertrain is 154 hp and peak torque is 218 lb·ft (296 N·m) in Normal and 274 lb·ft (371 N·m) in Sport.
“The torque difference is achieved by software changes in the motor ECU,” Bernas said. “The max torque and max speed are modified via software changes when the Sport mode button is selected.”
Two charge modes are also offered—Standard and Extended. In Standard mode, the battery charges up to 35 kW·h, providing an EPA-estimated 92 mi (148 km) of driving range. Extended mode allows the battery to charge to full capacity of 41.8 kW·h for an estimated driving range of 113 mi (182 km).
“Having two charge modes serves multiple purposes,” Bernas said. “From our field data and customer surveys, 96% of the commuting distances are covered by Standard charge mode. Standard charge mode also creates the best practice to optimize battery life. For the customer that has longer commute distances, or for the occasional longer planned trip the Extended charge mode utilizes 41.8 kW·h of the battery energy.”
The charging system supplier is Leviton, which offers a 240-V (Level 2), 40-A, 9.6-kW output charging station. The vehicle also comes equipped with a 120-V (Level 1) 12-A charging cable for instances when the recommended 240-V charging is not available.
“Charging time with 240 V, 40 A is anywhere from 5 to 6 h, depending on which mode you are in; if you’re in a normal mode it’ll probably take around 5 h, if you’re in extended mode 6 h,” Bernas said.
A dc fast-charge option is not available on this model.
“We felt that at this point in time, based on customer usage, or lack thereof, we didn’t think it was relevant to put on this vehicle,” Bernas said. “They’re still trying to come up with standards, and we want to make sure there’s a specific standard put in place first. If we do continue on a next phase, that’ll be something that we strongly consider and see how the infrastructure and the customer acceptance is to it.”
The liquid-cooled battery is a first for Toyota and provides advantages for vehicles in a wide range of environmental climates. A two-tier packaging design was selected that used the most available space in the underbody.
“In our thermal system, we use a water/glycol [mix] basically like using a radiator,” Brown said. “The battery cooling system is integrated with the cabin system so we actually share some components, including the A/C compressor. We also have a chiller and expansion valve that’s used in an emergency when battery and cabin heat exceed the radiator’s capability.”
The climate system plays a key factor in the EV driving range, and Toyota has responded to this fact by three climate control modes: Normal, Eco Lo, and Eco Hi. Each level progressively reduces power consumption of the blower, compressor, and electric heater, and seat heaters are automatically activated in Eco Lo and Eco Hi. Eco Lo can reduce climate control system power consumption by up to 18% compared to Normal, and Eco Hi offers up to 40% reduction vs. Normal.
Remote climate control is also provided for pre-cool and pre-heat capability prior to driving while the vehicle is plugged in. The system can be set by a timer on the navigation display or via a smartphone.
A cooperative regenerative braking system minimizes kinetic energy lost during stopping, recovering it and converting it to electrical energy, while recharging the battery and extending driving range. The system shares the same engineering philosophy as other Toyota hybrid vehicles; however, “the one difference is the necessary communication between Telsa’s EV motor and Toyota’s brake system,” Bernas said.
“With this cooperative regen braking, we are able to increase range by approximately 20% compared to, for example, a vehicle that does not have this function,” Brown said. “We use a blended system that works with the brake to determine to slow the vehicle which is the best methodology, increasing the motor resistance vs. using the friction brakes.”
Protecting the pack
Several unique safety features have been incorporated into this vehicle. The battery modules are encased in a structural pack surrounded by a four-sided extruded aluminum enclosure. Large aluminum rocker extrusions act as a structural attachment between the enclosure and the body, as well as provide further impact protection.
“Battery protection is paramount, especially with a large-format battery like we have,” Brown said. “We had to consider battery protection for the front, side, and rear impacts and make sure that we always maintain high-voltage insulation. To date, we’ve run well over 50 actual crash tests and in every single case battery electrical isolation, coolant line integrity, and module integrity was achieved.”
A steel floor is used to protect the battery and inverter assemblies in the event of a collision or road-surface clearance obstruction. In addition, skids have been added to ensure that the battery force is distributed through the crossmembers inside. A rigid inverter protection brace bridges the gap between the body front crossmember and the front suspension member to mitigate inverter damage. Special steel ramps built into the front of the undercarriage serve to deflect intrusion into the battery enclosure. In a rear impact, the battery’s rear mounting brackets can separate the battery from the body, further protecting the battery enclosure from intrusion.
Multiple redundant systems are also in place to automatically prevent the unintentional discharge of energy. In the event of an accident, electrical contacts automatically open, isolating the battery from the rest of the high-voltage system. After the contacts open, active and passive discharge strategies are employed to remove any remaining energy from the high-voltage system within 5 s, in accordance with U.S. federal motor vehicle safety standards.
Tesla builds the electric powertrains at its production facility in Palo Alto, CA, and then ships them to Toyota Motor Manufacturing Canada for final assembly into the vehicle.
“Our main goal was to minimize the production impact for assembly between the RAV4 and the RAV4 EV,” Bernas said. “Currently both vehicles are run off the same line. One difference is that the RAV4 EV has to go off-line for the necessary filling of the coolant for the motor and battery loops.”
The RAV 4 EV goes on sale in late summer 2012 at select California dealers, and sales volume is planned for about 2600 units through 2014.