A Transmission Contributing to Outstanding Fuel Efficiency and Smooth Driving
Manual transmissions and stepped automatic transmissions shift gears by switching between multiple gearsets. A continuously variable transmission (CVT) shifts through gear ratios in a continuous manner, enabling a smooth acceleration or deceleration feel, without any shift shock. A CVT also contributes to higher fuel efficiency as there is greater freedom in gear ratio settings, allowing effective use of engine speed ranges where combustion efficiency is highest.
A CVT mechanism consists of two pulleys—a drive (input) pulley and a driven (output) pulley—and a metal belt. The two pulleys are hydraulically controlled according to driving parameters, such as accelerator position and vehicle speed, to adjust the widths of the grooves where the belt sits. This alters the diameters of the pitch circles along which the metal belt is conveyed, continuously changing the gear ratio.
CVT Operation
Gear Ratio Variability
Low-Speed Gear Ratio (e.g. for Starting from Standstill) to High-Speed Gear
Ratio (e.g. for High-Speed Cruising)
In Pursuit of Both Fuel Efficiency and Enhanced Drivability
A CVT can heighten fuel efficiency by mainly running at engine speed ranges where combustion efficiency is highest. Initially, however, there was a time lag between the accelerator operation and perception of the vehicle accelerating. This is known as a “rubber band feel” and is the result of the sound of engine revs mounting with engine speed while the increase in vehicle speed comes after.
This feels awkward, especially to people who used to drive vehicles with a manual or stepped automatic transmission. Committed to dispelling this discomfort to bring CVT-equipped vehicles, and therefore greater fuel efficiency, to more people, Honda set about improving, and achieving greater compatibility between, hardware and software.
Increasing acceleration G-force when starting from standstill or accelerating as a way of resolving the time lag between engine speed and the perceived acceleration is usually incompatible with fuel efficiency, which would typically worsen. Honda instead took steps to improve the efficiency and responsiveness of the hardware, for example by reducing the friction between parts and optimizing hydraulic pathways. In addition, control technology was developed to improve drivability in a range of scenarios, including acceleration, deceleration, and cornering, enabling both outstanding fuel efficiency and an exhilarating driving experience.
Honda’s Original CVT Shift Control in Sync with Driver Intentions
G-Design Shift
Pulley hydraulics are controlled with high precision in sync with engine control, improving shift response to the driver’s accelerator operation. This realizes a quick build-up of acceleration G-force when starting from standstill or kicking down and a sustained acceleration feel from a constant G-force. Additionally, engine speed increases in a linear relationship with vehicle speed. The sound of the engine during acceleration and the increase in vehicle speed are therefore aligned with human sensitivities and produce a highly satisfying acceleration feel.
G-Design Shift Control
Full Throttle Acceleration Step-Up Shift Control
When the driver steps on the accelerator pedal to elicit powerful acceleration, the gear ratio and engine speed are controlled in steps, realizing stepped transmission-like shifting. The rhythmical change in engine speed and engine sound produces a comfortable and exhilarating driving experience synchronized with the perceived acceleration.
Step-Up Shift Control
Braking Step-Down Shift Control
When the vehicle decelerates after the driver steps on the brake pedal with more than a certain degree of force, engine braking is engaged by downshifting in steps with the engine speed remaining high. This provides reassurance during deceleration. When lateral G-force is detected during cornering, engine speed remains high to assist smooth acceleration out of the corner.
Step-Down Shift Control Activation Scenario (Descent)
Step-Down Shift Control Activation Scenario (Expressway Exit)
Step-Down Control Activation Scenario (Cornering)
Optimization for Regional Characteristics
To realize the right drivability to match user tendencies, road environments, and climates of different regions, Honda develops software that is optimized for each region. For example, Snow mode for cold regions prevents wheel spinning when starting from standstill or during acceleration by controlling driving force characteristics relative to the accelerator application. During deceleration, CVT shift characteristics are controlled to elicit powerful deceleration, helping deliver a highly dependable smooth ride even on slippery surfaces.
