Toyota has built hybrids for over a quarter-century now, but only recently started electrifying its trucks. It’s a big deal, because the automakers' trucks have always been defined by their absolute dependability. Consequently, they’ve always lagged behind the market in terms of powertrain technology. For trucks, Toyota likes to stick with what it knows works, rather than coming up with something new for newness sake.
Now, Toyota has two hybrid truck powertrains, one with a twin-turbo V-6 for the Tundra and Sequoia, and one with a single-turbo four-cylinder for the Tacoma, 4Runner, and Land Cruiser. At the first drive for the Land Cruiser and Tacoma hybrid, we took a deep dive into the four-cylinder setup.
“For environmental concerns, America obviously has strict regulations, so for us, to ensure that as many customers as possible can enjoy the vehicle… there was a need for us to take on the challenge to improve the environmental friendliness and also the fuel efficiency,” said Ketia Moritsu, chief engineer for the new 4Runner and Land Cruiser, through an interpreter.
It’s called i-Force Max, and it’s not really like Toyota’s long-running Prius hybrid system. In fact, it’s a lot simpler to understand. Here, you have a 2.4-liter turbocharged four-cylinder, an eight-speed automatic, and a 48-horsepower electric motor-generator sandwiched in between. The motor is powered by (and charges up) a 1.9-kilowatt-hour Nickel-Metal-Hydride battery mounted under the rear seats. Total system output is 326 hp and 465 pound-feet of torque.
“[The motor] is fundamentally designed to really support that part of the torque ramp and power ramp where you know the turbos are coming up to speed,” said Sheldon Brown, chief engineer for the Tacoma. “It helps us with our peak torque and then of course, when our turbo efficiency starts to fall off, it can come back in and assist.”
Because of the small battery, the Tacoma Hybrid doesn’t have a dedicated EV mode. It can drive around on pure electricity at the ECU’s discretion, briefly, at low speeds, and the system can shut off the engine for coasting on the highway. Fuel economy isn’t the priority either. Compared with their gas-only equivalents, hybrid Tacomas get around 2 mpg more in the city, 1 mpg more on the highway, and 1 mpg more combined. Really, this is about performance.
“We didn’t follow the path of just a hybrid system that focuses on fuel economy,” Moritsu explained. “So powerful, torquey, agile, maneuverability, and performance, those were the priorities. And we were able to balance that with the environmental performance of the vehicle as well. That was the biggest challenge for development.”
In terms of reliability, the hybrid system itself shouldn’t prove too problematic. Moritsu assured us of this. Toyota’s used Nickel-Metal-Hydride battery chemistry since the beginning, and while this isn’t the most energy dense, it's a well-proven technology. “We love it for its durability,” Brown said.
The electric motor itself is a fairly simple device, too. Really, the big concern for reliability in a truck is the engine.
“First and foremost, a lot of the truck duty cycle is really happening on the engine side,” Brown explained.
The 2.4-liter in the Tacoma is shared with many other Toyota products, notably the Highlander and Grand Highlander. But it’s very different for the trucks.
“There are internal components to the engine that are also specced up, maybe bearing coatings as an example, something that are going to see a longer or higher duty cycle,” Brown said. “Specifically when we start to think about things like the turbo, for example, it's really important that we think about truck duty cycles, they're gonna be towing, which means you're gonna be in the boost mode a lot more. You might be lugging in a reduction gear, which means your RPMs are up. Especially on these trucks, you're going to be giving it the beans, running through the desert. So we go to our commercial grade in terms of design requirements as well as our testing protocols for those.”
That means designing for a 50-percent longer duty cycle, and for more truck-specific scenarios. “We take the time to really consider how the truck is used,” Brown said “These trucks are going to be crawling up big hills, going down. We take a look at how the oil is actually moving throughout the engine, making sure that you're not starving the engine for oil when you're crawling up a 30-percent grade.”
Using a conventional automatic transmission enables a good tow rating and the inclusion of a low-range transfer case, an off-roading essential. Though this actually did present a problem. In the Tacoma, for example, the low-range gear is 2.57:1, which is a big torque multiplier when you’ve got 465 pound-feet on tap. Brown told us Toyota actually had to change the throttle map for 4-Low, to make sure drivers can manage all that torque when precise control is needed.
We tested the four-cylinder hybrid powertrain earlier this month in both the Land Cruiser and Tacoma. Off-road, the calibration is such that you don’t even really notice the hybrid powertrain at work. Which was the goal.
“We were in a review one time, and I said to [the engineering teams], ‘The highest compliment I can give you is this was unremarkable because it just did everything I wanted to do when I wanted it to,’” Brown said.
On the road, the torque of the hybrid system is noticeable compared with the standard gas-only Tacoma, but again, it all works seamlessly. You don’t think about the fact that it’s a hybrid.
Only time can reveal if this powertrain ranks up there with Toyota’s best, but know that these are nameplates the company takes very seriously. If Toyota is going to go hybrid for trucks, it can’t miss. On early exposure, it seems they haven’t.
