Direct drive mode

[Downsizer]

During journeys up and down the A1 from Peterborough to Tyneside this week I generally had the cruise control set at 65-68 mph. I was surprised how often the car reverted to EV mode on flat sections, as I had assumed that at those speeds direct drive was almost permanent, apart from travelling downhill. Average fuel consumption was shown as 62-64 mpg, so the true figure was no doubt a bit lower. The external temperature was around 20C so no heating or cooling was needed.

[NetworkMan]

I've had that happen when the car needed to accelerate in order to close the rather large gap which had opened up due to a car in front going off left or me pulling out into a faster lane.  It accelerated more rapidly than I would have done myself and presumably needed more power than was available in the rather high cruising gear.  It can always use the motor to provide extra power in engine drive mode but perhaps not enough or not enough battery charge available.

[jasonevans]

This chart may help.
It shows on aveage how often the hybrid is  active.
It's a great system.
 

[jasonevans]

Ignore my typo on 50mph as I put 50mpg - Doh !
It's a great system though. If your light on the throttle it's suprising how fast you can go on electric only before engine kicks in to recharge the battery .

[stani]

This chart may help.
It shows on aveage how often the hybrid is  active.
It's a great system.

That's an interesting chart... I have the best consumption on a longer trip at 80km/h - that is, when supposedly in "Engine drive"...

[coldstart]

... I was surprised how often the car reverted to EV mode on flat sections, as I had assumed that at those speeds direct drive was almost permanent ...

The Honda drive train is quite cleverly thought out! Its main design goal is fuel efficency.
This is accomplished by keeping the ICE in one of several preconfigured load levels.

During direct (or engine) drive a clutch gets engaged that connects the ICE "directly" to the wheels and thus eliminating the losses of going through the generator - electric motor cycle.

The surplus energy at any speed is fed into the battery until it reaches a charge level of about seven bars on the HV-battery gauge. Upon reaching this charge level the drive train switches to pure electric until the charge level falls to three or less bars.
Then the ICE gets started again and the cycle begins anew.

[NetworkMan]

I find that Honda graphic rather strange.  It shows that at speeds of over 120 km/h the car is back in hybrid mode presumably because the engine can't produce enough power in engine drive and hybrid mode will enable it to run faster and produce more power. It is strange because there is a video on youtube of a 2022 Crosstar running at 130 km/h. in direct drive mode and doing about 42 mpg - not bad for 81 mph.

If you look closely at the graphic you can see the engine drive mode symbol and see energy being fed to and taken from the battery as the gradient changes.  The constant noise level seems to confirm that the engine is indeed running at constant speed

The more I study this car the more interesting it becomes!

By the way, if you see poor petrol consumption figures on the motorway remember headwinds.  Since mpg goes down at roughly the square of the speed, hitting a 10 mph head wind at 70 mph will take the consumption from (say) 60 mpg to about 46 mpg if you maintain the 70 mph. [(80/70)^2 = 1.3].

 

[NetworkMan]

BTW the power flow graphic appears at about 1' 37" into the video.

[Downsizer]

In addition to wind speed and direction, the system responds to almost imperceptible changes in road inclination. All very logical!

[ahavoja]

I once towed a trailer at 100 km/h (62 mph). The engine was constantly revving higher than usual, being so loud that I could hear it over the road noise. Usually, without a trailer, I wouldn't hear the engine at that speed.

The car was using the hybrid mode the whole time and did not engage the direct drive. Apparently the added air drag + rolling resistance from the trailer required so much extra power that the engine needed to rev higher than what would have been possible when in direct drive mode. I think the fuel consumption was roughly 7 l/100km (40 mpg).

[Lord Voltermore]

I once averaged about 65 mpg heading east  but  only about 52 mpg  on the same stretch of motorway when heading west.   I began to think there was a problem with the car.   

  I  then noticed that all the power generating windmills were   orientated in a way that showed  I had been assisted by a tailwind when driving  east  but against a constant  headwind   driving west.    Windspeed was enough to turn the windmill sails   but not noticeably strong .

I think this wind drag affect is enough to explain why the  Yaris  has a slightly better mpg figure than the  more boxy styling of the (much roomier)  Jazz.   Not  IMO due to any superiority in the  Yaris drive mode. system.         

[NetworkMan]

I once averaged about 65 mpg heading east  but  only about 52 mpg  on the same stretch of motorway when heading west.   I began to think there was a problem with the car.   

  I  then noticed that all the power generating windmills were   orientated in a way that showed  I had been assisted by a tailwind when driving  east  but against a constant  headwind   driving west.    Windspeed was enough to turn the windmill sails   but not noticeably strong .

I think this wind drag affect is enough to explain why the  Yaris  has a slightly better mpg figure than the  more boxy styling of the (much roomier)  Jazz.   Not  IMO due to any superiority in the  Yaris drive mode. system.       

Just back from a short holiday 250 miles each way involving mostly M5, M6 and M54.  We were unlucky and had a slight headwind both ways.  With the ACC set to 70 mph but often slowed down we averaged about 56 mpg both ways which is much what we would have got in our old 2016 Polo with 4 cylinder 1.2 litre turbo petrol and GDI engine. Not a bad result for the Honda with probably similar gearing and NA engine with port injection.  The Honda recuperation will have helped and of course overall the Honda mpg is about 10-15 mpg better.

The Yaris is bound to be better on the motorway.  The clever planetary gearbox enables the engine to be run at the most efficient engine speed for any particular road speed whereas the Honda direct drive will be optimised for one specific road speed.  The Yaris has a 3 cylinder engine - more efficiency and less refinement.  I think it is port injection too so no GDI gain there. The Jazz is narrower but taller and we don't know about the Cd of either car so who knows which is the better car aero-wise.

[John Ratsey]

The Yaris is bound to be better on the motorway.  The clever planetary gearbox enables the engine to be run at the most efficient engine speed for any particular road speed whereas the Honda direct drive will be optimised for one specific road speed.

I think the Jazz's engine is optimised for best efficiency between about 1,500 and 3,000rpm. Over that range the engine power increases in proportion to the rpm. The power needed to move the vehicle increases disproportionally with speed so the system has to switch out of direct drive to enable the engine to provide enough power.

Back in 2020 I used a smartphone app + bluetooth OBDII reader to see the engine rpm at different vehicle speeds. IIRC, direct drive was used between about 40 and 60mph on level road and constant speed. I assume that above about 3k rpm the second set of inlet valves opens to help increase the power output but at lower efficiency (this was the behaviour of older Jazz engines) which contributes to the big drop in fuel economy at motorway speeds. The appears to be one of the issues that Honda is addressing in the next generation e:HEV drivetrain https://global.honda/en/tech/Honda_eHEV_next_generation/.

[NetworkMan]

John,
Do you recall the mph/1000rpm in direct drive?  I estimated that at about 25 mph/1000 rpm since that is pretty common for cars of about that weight, engine size and available torque. I guessed too that there must be a shift from a high efficiency regime to a high power one, perhaps from Atkinson cycle to Otto cycle since that can be done by the i-VTEC system changing cams, though not necessarily by switching from 8 valves to 16.
I have an OBD->bluetooth plug-in and the 'torque-pro'  app but haven't got around to trying it on the Jazz.

My 2015 car is definitely in direct drive at 70 mph and the video above shows a pre facelift car in direct drive at 130 km/h, about 81 mph., presumably without a tailwind!

[zdan]

Nice topic, wanted to post something similar about this for a while.

In my 2014 CT/Prius I can do up to 30mph EV only if I press the "EV" button. After 30mph it will disengage EV but I could still use the EV if I feather the gas to about half of the "ECO" range in my dash. It never goes in only EV over 45mph.

How's on the 2020+ Jazz? I'm planning to get one soon.