Toyota engineers put a shine into the 2014 Corolla

  • 09-Sep-2013 02:20 EDT
2014_Corolla_LE_Eco_008.jpg

The all-new Toyota Corolla shares DNA with the Furia Concept, which debuted at NAIAS, and offers LED headlamps as standard on all trims.

Considering past incarnations, the most obvious feature of the new Toyota Corolla is that it doesn’t look like an old Corolla, with an exterior design that borrows from the Furia concept car that debuted at NAIAS in January. One of the benefits of the redesign that Chief Engineer Shinichi Yasui and his team of 300 engineers brought to the consumer is that all models of the Corolla come standard with LED headlamps.

Much of the motivation behind such a typically high-end feature being standard on a compact car entailed the need for Toyota to offer a vehicle that it hoped would excite customers, especially considering the ever-increasing competition in that market. Indeed, designers wanted to change the basic shape and drive experience of an aesthetically non-exciting 47-year-old vehicle into one that was the opposite.

Looking ahead and under

To make a front end that would grab attention with more rounded corners and yet a more aggressive, sculpted look, designers did away with “the thick structure” of conventional headlamps.

The more compact LED headlamps reduced corner mass, allowing for more tapering in the exterior and enabling engineers to “accentuate the Corolla’s rounded-corner, front-end design theme.” The reduced mass was at least partly the result of a lighter weight PES resin lens being able to be used instead of conventional glass due to the lower heat inherently generated by LED lights.

Much attention was paid to the aerodynamics and NVH of the vehicle during exterior design, with its 0.28 drag coefficient being a stand-out for its class. The underbody, in particular, was targeted with strategic under-cover placement for a flatter design that would refine airflow and reduce turbulence. Its unibody body design makes extensive use of high-strength steel for improved rigidity while enabling the curb weight of the vehicle (all trims) to stay below 2900 lb (1315 kg).

Overall, the 2014 Corolla is longer, lower, and wider, riding on a wheelbase that is 3.93 in (100 mm) longer than the model it replaces. Its width was increased by 0.63 in (16 mm) and its height reduced by 0.39 in (10 mm) for an overall sportier look while simultaneously increasing interior space.

Variable valve control

While not doing much to the core 1.8-L I4 engine to excite potential buyers, there is a version of the Corolla, the LE Eco, which offers an engine equipped with what Toyota has branded as Valvematic. The computer-controlled system operates only on the intake valves for optimized continuously variable timing (lift and phasing).

Under light-load conditions, the throttle butterfly valve can be held open while the Valvematic system controls engine air intake with the intake valves, increasing intake manifold air pressure for reduced pumping losses and improved efficiency.

It is said to increase fuel economy by 5.3% (up to 42 mpg) and provide 140 hp (104 kW) at 6100 rpm and 126 lb·ft (170 N·m) at 4000 rpm vs. the standard engine’s 132 hp (98 kW) at 6000 rpm and 128 lb·ft (173 N·m) at 4400 rpm.

That said, even with improved fuel economy and power, and limited price difference, Toyota is projecting only 10% of its initial Corollas to be offered with the Valvematic system, mainly due to “limitations on some of the supplier parts” from Japan, particularly the system's actuator.

Belt-and-pulley CVT

Three different transmissions are available on the new Corolla: a six-speed manual, a four-speed automatic, and an all-new continuously variable transmission with intelligent shifting (CVTi-S) that Toyota says is the first application of such a transmission on a high-production vehicle. The transmission is a belt-and-two-pulley design and features what Toyota says is a “world’s first” two discharge-port oil pump to operate the pulleys while also providing lubrication to other transmission parts.

Driven by the engine, the pump works more efficiently compared to conventional single output pumps, as one of the two output ports automatically switches from high to low pressure when operating at high engine speeds. The pressure range for the new oil pump is optimized to provide adequate pressure for proper clamping of the belt by the pulleys without causing loss of efficiency by over-pressuring at high speeds.

Toyota says its CVTi-S was specifically tuned to the preferences of the North American driving market, with features such as discrete, stepped shift points being programmed into the transmission’s acceleration and deceleration curves. The CVTi-S, which offers a more linear connection between pedal effort and acceleration feel compared to "rubber band" CVTs, hunts for the optimum point to shift, creating for the driver a sensation similar to a traditional automatic transmission. On the Corolla S trim, up to seven shift points can also be manually actuated from the shift gate or steering wheel paddle shifters.

To arrive at an improvement of 3 mpg per CVTi-S-equipped vehicle vs. the old Corolla, Toyota engineers had to conquer challenges such as the high level of hydraulic pressure required for traditional CVTs and the optimization of the pulley ratio range.

CVT hydraulic-fluid pumps are typically driven at the same rate as engine speed, wasting energy at higher engine speeds as more fluid is pumped than necessary to lubricate and sandwich the CVT’s belt. With the CVTi-S, Toyota says engineers reduced hydraulic pressure to an optimal point to protect against belt slippage, while conserving drive effort to limit excess pumping losses. The co-axial two-port design enables a 25% reduction in pump drive torque and results in reduced parasitic engine loss.

For a belt-driven CVT such as the CVTi-S, the range of speed ratios is determined by the diameters of the input and output pulleys. The greater the difference in size between these two pulleys, the greater the range of gear ratios the transmission can offer. The clearances within the Corolla’s CVTi-S exterior casing and between internal components have been enhanced to better accommodate the pulley sizes within the compact transmission case.

The CVTi-S offers a forward gear ratio range of 0.396: to 2.480:1, which works well for acceleration, cruising speeds, and economical driving with a 4.761:1 final drive ratio. It includes a transmission fluid warmer to help get fluid to optimal temperature faster. It also uses a lower viscosity CVT fluid that protects all of the transmission’s internal parts while helping reduce parasitic loss. Its compact case design uses reinforcing ribs to help suppress vibration and noise.

Assembly of the Corolla for the North American market will be in both Mississippi and Ontario. Toyota is expecting to sell 330,000 Corollas in 2014, with 60% of the growth projected to be by conquest buyers.

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