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Advanced CVT redesigned for VTEC TURBO application

The CVT automatic transmission has been newly designed especially for its integration with the new VTEC TURBO engines. It is the result of a two-year development programme based at Honda’s R&D Centre in Frankfurt that incorporated a large number of driving scenarios, including congested urban traffic, open rural roads and high-speed German autobahns.

Mitsuru Kariya, Chief Engineer and Global Project Leader explains: “We faced numerous major challenges in redeveloping the CVT for the new Civic, but the highest priority was given to driveability. To ensure we achieved our objective to give the new Civic ‘soulful performance’, we set out to ensure drivers would feel utterly confident in the CVT’s ability to engage them, and we were determined to deliver this dynamic, exciting feel.”

To achieve this engaging driveability, the most significant new design feature is the turbine twin damper torque converter, which is exclusively employed for this new application with the VTEC TURBO engines.

Compared to traditional CVT systems which exhibit a ‘rubber band’ feel under more demanding acceleration, the new unit delivers a totally different, more direct delivery of engine speed, which in turn results in a more linear response. It exhibits characteristics similar to those of current-generation dual-clutch automatic transmissions.

The CVT delivers its more natural drivability via a ‘multi-gear’ feel thanks to control software that is exclusive to Europe. This simulates seven speeds through the rev range, with optimised ‘gear change’ mapping providing the driver with the familiar feel of gear changes. Steering wheel-mounted gear shift paddles offer the driver the opportunity to take more control both in automatic and in ‘manual’ mode.

Honda’s CVT features two additional programmes that provide situation-specific safety and driveability enhancements.

Early Downshift During Braking (EDDB) uses the engine to assist the driver during braking. When the system recognises a deceleration, downhill, or cornering situation initiated by the braking system, EDDB automatically increases the engine speed to provide engine braking. This then allows for quick re-acceleration after slowing or quick acceleration after cornering.

Fast Off measures how quickly the driver releases the accelerator pedal and maintains engine revs to provide engine braking in situations where the driver has released the pedal quickly. This system has been extensively tested for Europe’s high speed, multi-lane roads. For example, Fast Off recognises when the driver has prepared to pass a vehicle in front, but is unable to complete the manoeuvre due to a vehicle in the next lane. As the driver quickly releases the accelerator pedal to let the vehicle behind pass by, Fast Off maintains a high engine speed in preparation for completing the overtaking manoeuvre.

Efficiency of the 1.0 litre VTEC TURBO with CVT exceeds that of most 1.0 litre class competitors with automatic transmissions, while maintaining similar performance. It also exceeds the acceleration performance of the previous 1.8 litre five-speed automatic Civic. The performance of the 1.5 litre VTEC TURBO with the CVT was assessed by Honda engineers as class-leading, with fuel efficiency still among the class best. (Internal Honda Data)
 
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