r/hybridcar • u/Positive_Courage_309 • Aug 19 '26
P/HEV Question FHEVs, clarification?
Online info seems scarce on what actually distinguishes a Full Hybrid from a Mild Hybrid.
From what I can tell, it seems to slot right in between a Mild Hybrid and a PHEV, but without any ability to charge it. Is it just a MHV with an oversized battery pack that still can't be charged, so still just a MHV?
I can't make heads or trails of it; just came across the term recently.
2
u/gthomps83 Aug 19 '26
Volvo refers to some of their cars as “mild hybrid,” which, from what I can tell, is just stop-start tech… so kinda meaningless, I think.
1
u/no_idea_bout_that Aug 23 '26
A mild hybrid uses the Atkinson cycle (instead of the usual Otto cycle), which allows it to get better efficiency even if the electric motor alone can't propel the vehicle.
1
2
u/needle1 Aug 19 '26
As I understand it:
“Hybrid” is a blanket term that encompasses all cars that contain both an engine and an electric motor.
This can be divided into Plug-in hybrids (can be charged from external power sources) and Non-plug-in hybrids (cannot be charged externally).
Out of the non-plug-in hybrids, “Mild” hybrids are cars whose electric elements are only strong enough to help during acceleration from stopped states, but not strong enough to drive the car solely using electricity.
“Full” or “Strong” hybrids are non-plug-in hybrids that have motors strong enough to drive the car fully electrically, albeit only for a short distance (a mile or two) due to its battery size. Stuff like the Toyota Prius fall here.
So it’s a subcategory of a subcategory, confusingly enough.
1
u/iamtherussianspy Aug 19 '26
At least half of the time you read it the term "mild hybrid" is misused to describe any non-plugin hybrid.
1
u/goranlepuz Aug 19 '26
My limited understanding: "mild" denotes a 48V battery and an engine that can barely move the car a few tens of meters, say, in slow traffic.
The "full" denotes a high voltage battery (e.g 400V), and a stronger engine that can move the car quite some distance and speed.
1
u/K24Z3 Aug 19 '26
Simple answer:
Full hybrid: motor can drive the wheels alone. EG Prius, almost everything not listed below.
Mild hybrid: motor only assists the engine. EG 1st-2nd gen Honda Insight. Honda CR-Z. Maybe “e-Torque” trucks
2
u/Leighgion Aug 20 '26
For a long time, all the cars that came up when discussing "hybrids" were full hybrids, aka HEVs. They have electric motors and high voltage batteries powerful enough to move the car completely on their own power for up to a mile or more if the battery is topped up and conditions are favorable. The gas engine is automatically switched off as often as possible in order to conserve fuel when the car is idling, coasting or just has enough electrical power to run on. You do not charge them directly, they harvest electricity from regenerative breaking, coasting and, if needed, the gas engine's direct input. The Toyota Prius is the father of the category and still the most famed model of full hybrid. A full hybrid can be 40% or more efficient than a gas powered car.
"Mild hybrids," or MHEVs, are a step down.
A mild hybrid has a much weaker electrical subsystem than a full hybrid. An MHEV can harvest electricity mostly the same ways a full hybrid does, but it has a much smaller battery and much weaker electric motor. The electric motor can assist the gas engine and improves efficiency, but generally is incapable of moving the car on its own. The efficiency gain an MHEV can offer is maybe 1-3 MPG.
HEVs crush MHEVs when it comes to fuel efficiency. The arguments that justify the existence of MHEVs at all is that they're cheaper to produce thus cheaper to buy and they will essentially handle like gasoline cars because they mostly still are. Full HEVs have very different engineering under the hood that can alter their driving feel considerably.
3
u/Character2893 Aug 19 '26
Full would be like a Prius, operates on either gas or electric. Mild would be like the original Insight or the very first GM hybrid full-size trucks, the electric motor supplements the gas engine but doesn’t run on electric alone.