Thanks. So if I do not switch to HV engine mode...the gear symbol will come back??? I only switch to HV engine mode because salesman said it best to do that since I do travel on highway. I don't switch when on backroads.
HV Mode works together with ECON Mode, NORMAL Mode, or SPORT Mode. I believe HV stands for Hybrid Vehicle, but cannot document that belief. Honda's non-plug-in hybrid vehicles work to maintain a charge in the battery so that battery power is always available to provide extra power for acceleration or hill-climbing.
The Clarity is much more pleasant to drive when there is a decent charge in the battery because the car weighs 4,059 lbs and the engine maxes out at a paltry 103 horsepower. Without battery power, the Clarity cannot accelerate or climb hills easily, hence HV Mode is there to preserve battery power for tasks such as driving on the expressway, when higher aerodynamic forces will drain the battery more quickly.
When you switch the Clarity to HV Mode, regardless of which of the other 3 modes is in effect, the Intelligent Multi-Mode Drive (i-MMD) system will try to maintain the battery at its current state of charge (SOC) and use the internal combustion engine (ICE) to power the car and recharge the battery as necessary. When you select HV Mode, you're indicating you want to switch from primarily battery-powered travel to primarily ICE-powered travel.
However, HV Mode doesn't use the ICE all the time. It picks from any of the three basic "drive modes," according to which it decides is the most efficient at any given moment.
The three basic drive modes are EV drive mode, HV drive mode, and Engine drive mode. You don't get to select these modes, the i-MMD system does that. EV drive mode is when the battery and traction motor are powering the car. HV drive mode is when the battery and the ICE-powered starter motor/generator combine to feed electricity to the traction motor. Engine drive mode is when the gear icon appears to indicate the i-MMD system has engaged the Engine-drive clutch so that the ICE is mechanically connected through gears to drive the front wheels. It turns out that this direct connection is the most efficient method of powering the car in some instances, such as when the load is light at expressway speeds.
Only in Engine drive mode is the speed of the engine proportional to the road speed. In other modes the i-MMD system runs the engine at whatever speed it deems necessary to charge the battery and respond to the accelerator pedal. When the battery charge is depleted, people on this forum report hearing the engine revs go uncomfortably high, which they call the "angry bees."
In my experience with HV Mode, the i-MMD system doesn't manage to maintain the original SOC on long drives. The number of bars in the battery charge gauge decreases, which I find disappointing. I believe the i-MMD system should burn as much gasoline as necessary after each acceleration or hill-climb to bring the SOC back to what it was when I pressed the HV button. Rather than burn gas unnecessarily, Honda's engineers count on regenerative braking opportunities to restore the battery's SOC to its original level. That may work when coming down a long hill, but it never seems to work for me.
HV Charge Mode is the least-efficient way to drive a Clarity PHEV because it runs the engine at high RPMs to propel the car and recharge the battery at the same time. It's main purpose is to get a charge back into the battery before the next mountain if you just used up most of the charge on the previous mountain. Honda decided to limit HV Charge Mode to charging the battery to 58% of full charge. When the battery reaches 58% of full charge, HV Charge Mode switches to HV Mode.
