Toyota Debuts First-ever 2020 Corolla Hybrid
Corolla hybrid promises over 50 MPG combined city/highway.
The hybrid powertrain and battery were a natural fit for the new Corolla because of the Toyota New Global Architecture (TNGA) platform. There’s no compromise in cabin roominess, for example, when choosing the Corolla Hybrid versus a gas model.
The new hybrid system combines a 1.8-liter four-cylinder gasoline engine with two motor/generators through an electronically controlled planetary-type continuously variable transmission (CVT) transaxle. Combined system output of 121 horsepower yields decidedly responsive performance.
The nickel-metal hydride (Ni-MH) battery pack employs a newly developed technology called Hyper-Prime Nickel™ to boost battery performance in a smaller and lighter package. The battery’s smaller size and flatter shape allow it to be packaged under the rear seat, rather than taking up trunk space, and also allowing a 60/40 split folding rear seatback to expand cargo capacity. The battery location also contributes to the vehicle’s lower center of gravity, a boon to agility.
The engine, working in concert with the electric motor (MG2), assures responsive performance, while exemplary energy efficiency is achieved by using both electric motors (MG1 and MG2) for hybrid battery charging.
Driving the Corolla Hybrid
The Corolla Hybrid’s linear acceleration response may take some by surprise. When pulling away, the battery provides a subtle power boost in order to put less strain on the engine and eliminate the “rubber band” effect experienced with some hybrids.
A preload differential adds to the confident acceleration feel. During low loads and low differential rotation, differential-limited torque is distributed to the left and right wheels, yielding excellent handling stability. At mid-range and high engine loads, the preload differential functions as an open differential.
Corolla Hybrid has EV mode, which allows the vehicle to be operated as a pure electric vehicle for short distances, depending upon certain conditions, such as battery charge level. This mode is useful for operating the vehicle in parking lots or indoor parking garages, for example. The Vehicle Proximity Notification feature alerts pedestrians of the vehicle’s presence when running in battery mode.
Along with the expected NORMAL and ECO drive modes, a SPORT drive mode setting allows for an increase in power for stronger acceleration response when desired.
- NORMAL mode: Allows the hybrid system to achieve an ideal combination of fuel economy and vehicle acceleration. The accelerator opening amount changes linearly in response to accelerator pedal operation.
- ECO mode: Improves hybrid system efficiency by limiting power in response to light to moderate accelerator pedal input.
- SPORT mode: Available power is increased, allowing for improved acceleration response.
Stopping the Corolla Hybrid
Another boost to efficiency comes from the Electronically Controlled Brake (ECB) system, which coordinates operation between the regenerative braking force of the electric motors and the hydraulic braking system force to provide optimal stopping power. By proactively using the electric motors to recover as much electrical energy as possible from the regenerative braking system, this extremely efficient cooperative control helps to maximize fuel economy.
An active hydraulic booster on the conventional (non-regenerative) braking system improves pedal feel and feedback for the driver. Critically, should there ever be a malfunction in the ECB system, the conventional hydraulic braking system can stop the vehicle.
Brake Hold, when engaged, is a convenient technology that reduces driver effort while waiting at a traffic light or while driving in heavy traffic. When the driver presses the accelerator, Brake Hold releases instantly.
How the Other Half Works
The other half of the Hybrid Synergy Drive team, the gas engine, is no less impressive than the electric side. The 2ZR-FXE 1.8-liter inline four-cylinder engine was designed specifically for a hybrid application. The long-stroke configuration employs the Atkinson cycle, which uses a very high compression ratio (13.0:1) along with a shorter intake stroke and longer expansion stroke than the Otto cycle. The Atkinson cycle extracts more energy from the fuel, and the electric motors compensate for reduced low-end power (versus the Otto cycle).
Friction created by the piston skirts, rotating parts and oil pump is reduced, and an electric water pump eliminates the parasitic losses with a conventional belt-driven pump. Toyota sought efficiency gains in every system. The highly-efficient air conditioning system, for example, uses S-FLOW control, which automatically optimizes airflow throughout the cabin according to the temperature setting, actual cabin and outside temperatures, sunlight intensity, and occupied seats.
Getting the engine up to operating temperature quickly is critical to conserving fuel and reducing emissions at start-up. In the Corolla Hybrid, an exhaust heat recirculation system speeds up engine coolant warm-up. That in turn allows the hybrid system to stop the gas engine earlier and more often in the driving cycle when it’s not needed, for example in low-power-demand city driving conditions.
The PTC (Positive Temperature Coefficient) heater quickly provides cabin heat electrically in cold temperatures.
The Corolla Hybrid rolls on 15-inch aluminum alloy wheels with low-rolling resistance tires. As on the Corolla gas models, the new multi-link rear suspension improves both handling agility and ride comfort compared to the previous-generation Corolla Sedan.
The instrument panel uses a high-grade meter with a 7-inch Multi-Information Display (MID). The MID shows the speedometer, as well as a hybrid system indicator/real-time battery charge status indicator. ECO accelerator guidance, also shown in the MID, can provide a guideline for maximizing fuel efficiency by coaching the driver on optimal accelerator pedal operation to match driving conditions.