2016 Prius: The Fourth Generation
The little car that could still can. And this time as a car that not only gets great fuel economy, but which
has ride and handling that makes it more
than an econo-box (and its styling is
anything but boxy).
#Toyota #HP #engineer
There probably isn’t a single car in the world that has the same ownership or identification with a category as the Prius does.
Arguably, the word hybrid is as closely associated with Prius as tissue is with Kleenex or Styrofoam is with a closed-cell extruded polystyrene foam from Dow Chemical.
Sports car. . .?
Muscle car. . . ?
Sedan. . .?
Coupe. . .?
Crossover. . .?
In any of these cases there are numerous vehicles that could be cited. But “hybrid car” pretty much goes straight to Prius, and with good reason.
That is, the first generation vehicle went on sale in Japan in 1997. Remember that one of the fundamentals of a hybrid powertrain is that it is really good in stop-and-go traffic (the regenerative braking recharges the battery), but not as good on highway rides. Traffic in Tokyo was congested in 1997, and that hasn’t changed.
That’s one key reason behind the development of what has become known as Toyota’s “Hybrid Synergy Drive.”
The Prius went on sale elsewhere in the world in 2000.
The first-generation car had a somewhat poky design, so it was probably a good thing that in 2003 the second generation Prius was launched with the hatchback flowing roofline that is now characteristic of the car. Or was characteristic of the car, but more on that shortly.
Generation three came out in 2009, and while changed inside and out, the interior design was changed far more substantially, with the exterior still being unmistakably Prius.
Through July 2015 from the initial launch, Toyota sold 3,527,200 Prius models (not including the v and c variants) globally.
The thing about the Prius has always been fuel economy. The third generation car in the U.S. was to achieve EPA-estimated 51 mpg city/48 mpg highway/50 mpg combined, yet have seating for five.
Yet the Prius was to come under fire because its ride and handling weren’t the stuff of exhilaration.
So when the engineering team went to work on what was to become the fourth generation Prius, that was one of the targets they focused on.
Back in March 2015, Toyota revealed what it calls the “Toyota New Global Architecture” (TNGA). This is an approach to vehicle development and production that is predicated on sharing across models such that taking into account both powertrain and platforms, there is a reduction in required resources of as much as 20 percent or more.
In terms of the platforms, Toyota is looking to achieve vehicles that have a lower center of gravity and a lower overall stance. Additionally, TNGA-based vehicles would have a significantly increased body rigidity, on the order of a 30 to 60 percent improvement. (There is also a production aspect to this approach. Toyota wants to reduce the capital investment required for new model production. The target is to spend 50 percent less to do so compared to what the corporation spent in 2008. What’s more, they intend that the investments made would be to provide more of a mixed-model capability, driven, in part, by common vehicle architectures. This would not only provide flexibility to address changes in model demand, but also help reduce overall investments. Another objective is to develop production lines that are “simple and slim,” equipping them with equipment that is compact so as to lend itself to locations that the typical massive equipment can’t be accommodated by.)
One of the things that the lower center of gravity and the increase in body rigidity results in: improved ride and handling.
And the first Toyota vehicle to be based on TNGA is the fourth-generation Prius.
The first thing to know is that the 2016 Prius is at the upper end of the torsional rigidity goal: 60 percent. One part of this comes from the increased use of high-tensile strength steel. The last-generation vehicle (internal code: CG) has 3 percent of that material; the fourth-generation (internal code: NG) has 19 percent, including hot-stamped steel, >1400 MPa. Also is the use of laser screw welding to supplement spot welding (this is a robotic laser scanning process that provides the ability to produce welds where there is clearance or no clearance between sheets as well as on different types of materials (i.e., ferrous and non-ferrous). And they’ve also used structural adhesives in strategic areas to supplement the welds. Not only does this stronger base facilitate better ride and handling, but also structural safety.
And while on the subject of the body structure, another area that the previous Prius came into some criticism was on cabin noise. So while a more well-assembled structure certainly provides benefits as regards noise, vibration and harshness (NVH), the engineering team went at the NG with an array of noise countermeasures, ranging from a new two-point engine mount and torque rod system to the use of silencers around the front seats, dash, and cowl panels.
To improve the ride and handling, the suspension of the fourth-generation car is different than the previous. The front suspension is a revised version of the MacPherson struts used on generation three. However, in the rear there is a newly designed trailing arm-type double wishbone setup in place of the torsion beam suspension that had been used. The torsion beam is lighter than the double wishbone setup (which explains, in part, why the new car is approximately the same weight as the previous model, weight reduction efforts notwithstanding), but it doesn’t handle uneven road surfaces as well.
Not surprisingly, there is electric power steering.
Of course, the most significant aspect of this or any hybrid system is the powertrain. There is a 1.8-liter, DOHC, 16-valve Atkinson Cycle four cylinder engine that produces 95 hp @ 5,200 rpm and 105 lb-ft of torque. One of the key areas of focus was to improve the thermal efficiency of the engine. The thermal efficiency of the third-generation Prius engine is 30 percent. The thermal efficiency of this fourth generation is 40 percent, which Toyota claims makes it the most thermally efficient, mass produced engine in the world.
Then there are the electromechanical portions of the system. There are two main motor generators (MGs), with MG2 being the one that drives the front wheels. There is a hybrid transaxle (i.e., an electronically controlled variable transmission). The system is redesigned so that the MG2 is mounted on a parallel shaft in relation to the engine crankshaft; previously it was a coaxial setup. One of the benefits of this approach is a more compact design. There are also improvements in terms of fiction loss, which is on the order of 20 percent. (MG1 and the planetary gear set are still coaxially located with the engine crankshaft.)
The power control unit (PCU) has been repositioned so that it is bolted on top of the transmission, which means that there is now a direct high-voltage connection, so the number of orange cables that once snaked under the hood has been reduced. The size of the PCU is reduced by 33 percent, the mass is down by 11% and there is a 20% reduction in parasitic losses, so it is more efficient.
Historically, the Prius has used a nickel-metal hydride (NiMH) battery. The fourth-generation Prius still does. At least one of the models does. There are three grade levels, Two, Three and Four, or Entry, Mid-Grade and Premium. There is a NiMH battery pack that provides 201.6-Volts standard on the Two models. There is a 207.2-Volt lithium-ion battery pack standard on the other models. A key difference between the batteries is that the lithium-ion has greater energy density than the NiMH, which means that it can store more energy by volume. That said, the Prius Two Eco model has the greatest estimated fuel economy of all of the vehicles: 58 city/53 highway/56 combined miles per gallon.
The batteries in both cases are located under the rear seat. This provides greater storage space below the rear hatch.
Of course, before anyone gets to the platform or under the hood, there is the exterior sheet metal of the 2016, which is quite simply a radical departure from certainly the last two generations.
The theme for the stylists was “Yu-bi-shin,” or “Ingenious Beauty.” The car is lower, longer and wider than the previous model:
GEN 3 GEN 4
Height: 58.7 in. 58.1 in.
Length: 176.4 in. 178.7 in.
Width: 68.7 in. 69.3 in.
The roof peak has been shifted forward by 6.7 in., so there is still the triangular silhouette that has long been characteristic of the Prius, but given the shapes of the front bi-LED and LED rear lights, chances are one would have to look exceedingly hard at the profile to see the familiar resemblance.
A key aspect of the shape of the car is to reduce drag as much as possible. The coefficient of drag for the 2016 Prius is 0.24. Contributing to this are such things as automatic grille shutters, underbody panels with stabilizing fins, and front spats and covers on the sides of the fuel tank.
Although the structure of the car, as mentioned, is designed to assure safety, the Prius is nothing if not a high-technology car, so the vehicle is available with an array of technologies meant to enhance safety.
The package is called “Toyota Safety Sense (P)” and it includes pre-collision with pedestrian detection, lane departure alert with steering assist, automatic high beams and dynamic radar cruise control.
In addition to which, there are sonar-based “Intelligent Parking Assist” and blind spot monitoring with rear cross traffic alert.
There are dual 4.2-in. full-color thin-film transistor (TFT) displays in the car that provide a variety of information about the vehicle and its operation on one (e.g., vehicle speed, fuel, driving mode, odometer), and driving support (e.g., status of the radar cruise control, climate control, audio, navigation) on the other. In addition to which there is a 6.1-in. color touch screen in the center console for infotainment purposes. There is also an available color head-up display that shows the speed, navigation information, and indication of the hybrid system status.
The Prius has come—and gone—a long way since that first-generation model. Early on, the argument against it was that no one wanted a car with such a complex powertrain, although for regular drivers it was pretty much transparent, they just put gas in the car just like they did for their non-hybrid. The remarkable fuel economy of the Prius trumped that argument. Now, when gas prices are far lower than has been the case for quite some time, the knock on the Prius is that no one will buy a car that has such phenomenal fuel efficiency. And arguably, the response to that is the ride and handling that the TNGA provides the car.