Hybrid Synergy Drive
Of course, the 2012 Camry Hybrid XLE's big selling point is Toyota’s Hybrid Synergy Drive (HSD) that promises an EPA-rated 40 MPG in the city and 38 MPG on the highway, which is a bump up from the standard four-cylinder engine's 25 MPG and 35 MPG in the city and highway. Toyota’s HSD is a series-parallel hybrid system that lets the gasoline and electric motors to drive the wheels individually or together.
HSD combines a traditional four-cylinder engine with an electric motor to boost city mileage, in particular, beyond conventional gasoline-only configurations. But unlike Toyota's Prius, which is tuned explicitly for fuel economy, the 2012 Camry Hybrid XLE can get up and move when it needs to. Reviewers from MotorWeek cite a 0-60 MPH time of 7.2 seconds, and a quarter-mile pass in 15.5 seconds. That's not too shabby for a mid-size hybrid sedan.
The Gasoline Motor
The same 2AR-series 2.5-liter four-cylinder engine offered in the Camry's non-hybrid trim serves as the base for our car. Toyota tweaks the 2AR by changing the standard Otto thermodynamic cycle to a modern Atkinson cycle design capable of better efficiency. This allows the motor to hold its intake valves open longer, extracting maximum mechanical energy from the combustion process.
Although the Atkinson cycle yields greater efficiency, it sacrifices low-end torque in the process. The result is a drop from 178 hp and 170 ft-lbs of torque to 156 hp and 156 ft-lbs of torque. This is where the electric motors step in.
The Electric Motors
Toyota mates its 2AR-FXE engine to a pair of electric motors capable of a combined 140 hp with 199 ft-lbs of torque, maximum. Together, the car receives a 200 hp rating, while torque is unspecified due to the complications of combining both subsystems.
The two electric motors work together to distribute power, and they have built-in generators to recharge the battery pack. Or, energy from braking can be used to help replenish the battery. Unlike traditional motors, the HSD system lacks a starter and alternator; it instead leverages the electric motors.
Combining The Power
Toyota employs a power split device to blend power from the engine and electric motors. A complicated set of gears lets the two power sources work together or on their own. The power split device also functions as an electronic continuously variable transmission, or eCVT, that confers optimal gearing for the driving task at hand. CVTs differ from standard automatic and manual transmissions by enabling an infinite number of effective gear ratios between the first and final drives, rather than fixed ratios. The benefit of a CVT is its ability to either keep an engine running as efficiently as possible or to deliver as much power as possible. Though, in this case, it's used to maximize gas mileage.
The Battery Pack
Toyota's 2012 Camry Hybrid XLE uses traditional nickel-metal hydride (Ni-MH) batteries instead of lithium-ion (the new hotness).
The electrical power source delivers 6.5 A per hour with a nominal voltage of 244.8 V. It consists of 204 cells that output 1.2 V each. Although the battery pack is located in the Camry's trunk, there's still quite a bit of space back there. Toyota did have to sacrifice the folding rear seats to make everything fit.
The power control unit, or PCU, is a box in the engine bay composed of an inverter, a voltage-boosting converter, and an AC/DC converter. Since the motors run on AC power, the PCU's job is to convert DC power from the batteries. The PCU also converts power from the generators back into DC for charging. Additionally it steps voltage up and down based on the motors' needs.
Many hybrid vehicles employ regenerative braking, using electrical resistance to provide a majority of a car's stopping power. The rest comes from a conventional mechanical system, whereby pads squeeze rotors. Heat generated during that process is captured and turned back into energy that charges the battery pack, extending its operation.
The 2012 Toyota Camry Hybrid XLE can run on battery power exclusively for up to 1.6 miles at speeds under 25 MPH. Toyota even exposes a button to engage EV mode when the right conditions are available. For the most part, however, the EV mode button is quite useless, since the vehicle intelligently switches to EV mode when it can.
The End Result
During our week with the 2012 Toyota Camry Hybrid XLE, we found that aggressive driving from stoplight to stoplight was actually quite a bit of fun. We stepped into the car thinking it'd be painfully dull, but were proven wrong right away; the car has more pick-up than you might expect. Only about half of a tank of gas was consumed in seven days of driving, and the computer tells us we averaged about 37 MPG through a mix of stop-and-go traffic with a couple of freeway trips.
Driving a hybrid is different than a petrol-powered vehicle. You and I are used to our engines firing up when we turn our keys. A hybrid, on the other hand, turns on electrically, but the motor doesn't turn on every time you take the car out. This results in an eerily silent start-up until the engine engages.