Higher speed returns better mpg than low speed?

[nielshm]

What's the optimal speed for Toyota hybrids? I don't like the fuel prices these days, and still rising towards the sky. 

So I try the best I can to stretch the golden drops. 50 mph (80 km/h) is pretty slow, low drag in the wind etc, but hydrid does'nt really kick in. A lot of charging again and again, but very little Battery assist to boost the mpg. 

A bit faster, like 56 mph (90 km/h) seems to work put much better. The cycle between charging, Battery assist, and regenerative braking seems be much more smooth. And often returns better mpg. 

It just does'nt make sense, in a world with economy and inflation going wild, and we all try the best to save a penny if possible. 

 

[Stopeter44]

Round here, the local speed limit is 80 km/h, I haven't had a chance to try 90 km/h on similar roads - some roads a bit further away are 90 km/h. Maybe what you find 80 vs 90 km/h is linked to the DNF 2.0 litre engine.

On my usual diet of 80 km/h country roads I haven't noticed what you say. I get a good 55%-60% EV time, a mix of country roads and village streets. The My T app is giving me 3.9l/100. Coming from more like 6.8l/100 I'm happy, even if a litre of E10 is 1,74€, E5 (95) can be had for just 0,04€ more and should be 4% +/- more efficient, but I have to drive 25km to get it, so any advantage is wiped out by the 50 km round trip.

[nielshm]

E5 is not an option. Additional cost is at least 7%, Shell V-power is 11% (danish prices). So in terms of overall economy, E10 is the only choice. 

[Catlover]

You will get better mpg when the engine is throughly warm.  It’s a bit milder weather, except for the winds, but winter 5-10 mpg worse then summer. Everything will be a fine line. You maybe “chasing after the Wind” finding an optimum speed. Better looking at you driving style, plenty YouTube videos showing “pace and glide”, anticipation at traffic light and more.

[Stopeter44]

20 minutes ago, nielshm said:

E5 is not an option. Additional cost is at least 7%, Shell V-power is 11% (danish prices). So in terms of overall economy, E10 is the only choice. 

Even E5 (98) is only 0,6€ more these days, around here, so that's getting close to break even. Mind you, it is ridiculous discussing the possible economy of 0.25€ for a fill up, compared with depreciation, insurance, w.h.y. in the overall cost of a car !

[nielshm]

It's not about summer or winter. It's not about my driving style. It's all about changing one simple parameter, and seeing a different result. A bit faster very often translates into better economy, it just don't make sense. Maybe the hybrid system does have some limitations or sweet spots the optimal performance. 

[Stopeter44]

On 2/17/2022 at 12:03 PM, nielshm said:

A bit faster very often translates into better economy, it just don't make sense.

I think it can make sense, but I expect that there's a "super optimal" speed for cruising, where all the planets line up and you get maximum efficiency from the ICE, and perfect reutilisation of the excess energy pumped into the traction Battery. As @Catlover is implying, I suspect over any given stretch of road, you are never going to have the exact same conditions from one day to another. There's wind speed, temperature and the coffee you drank that morning/afternoon, whatever, all make a difference !

Edited February 19, 2022 by Stopeter44

[nielshm]

4 minutes ago, Stopeter44 said:

Even E5 (98) is only 0,6€ more these days, around here, so that's getting close to break even. Mind you, it is ridiculous discussing the possible economy of 0.25€ for a fill up, compared with depreciation, insurance, w.h.y. in the overall cost of a car !

In Denmark that would be 4£ more for a fill up with E5 and 6£ for V-power or 98/100 octane. 

I fill the car once a week, so it does make a difference. 

[AndrueC]

Very difficult to say. However I am of the opinion that 50 mph is not optimal. I think that because it seems like the HSD struggles to keep the Battery charged at 50 mph. If you're doing a mostly steady 60 mph there will often be moments when the ICE stops charging the Battery but it's rare to see that if you're only doing 50 mph. On the other hand that's complicated by why the ICE might be doing a better job.

I think that the ECU has a complicated algorithm for choosing how/when it charges the Battery. It will always charge it if it thinks it's low but otherwise I assume it looks as the difference in ICE efficiency between 'maintaining speed' and 'maintaining speed and charging' then considers the losses involved in using the battery to move the vehicle (it's the difference between the two that is responsible for the overall lower fuel consumption that we enjoy). ICE efficiency isn't linear so it's possible that making the ICE work harder can make it more efficient (more fuel burnt per distance travelled but more energy extracted from the fuel). Maybe at 50 it's just that much better to 'overrun' the ICE whereas at 60 charging the battery actually makes the ICE less efficient.

[Stopeter44]

@nielshm Sorry, I wasn't referring to you specifically, it does depend on your mileage, etc. I was referring to myself.

[Stopeter44]

3 minutes ago, AndrueC said:

I think that the ECU has a complicated algorithm for choosing how/when it charges the battery. It will always charge it if it thinks it's low but otherwise I assume it looks as the difference in ICE efficiency between 'maintaining speed' and 'maintaining speed and charging' then considers the losses involved in using the battery to move the vehicle (it's the difference between the two that is responsible for the overall lower fuel consumption that we enjoy). ICE efficiency isn't linear so it's possible that making the ICE work harder can make it more efficient (more fuel burnt per distance travelled but more energy extracted from the fuel). Maybe at 50 it's just that much better to 'overrun' the ICE whereas at 60 charging the battery actually makes the ICE less efficient.

Yes, that's what I was getting at, if there's not enough juice in the Battery to move the car, then ICE kicks in, and will tend to operate at maximum efficiency, which shows as ICE driving wheels and charging Battery at the same time, then some the stored energy will be moved used for traction.

[nielshm]

33 minutes ago, Stopeter44 said:

@nielshm Sorry, I wasn't referring to you specifically, it does depend on your mileage, etc. I was referring to myself.

I do 23K miles a year. 60% is the exact same route to/from work every single day. Same amount of traffic, no jams or slowing down, always the same. Of course wind and rain makes a difference, but most days are just like all the others. 

So with small changes in speed, it’s easy to see a difference right away. 

[TonyHSD]

The efficiency will depend of how much the internal combustion engine is loaded, since the ice works to propel the car and also to recharge the Battery at slightly higher speeds the inertia of the car is greater and therefore it’s easier on the fuel because the high rotational speed of the wheels can help the ice turn the MG1 using less energy (fuel). Basically your Toyota hybrid is most efficient when your engine is quieter. There is also one more thing, when you drive with 50mph the car switches to ev more often and drains the Battery faster then recharging again where if you drive with 60mph the ice will be the major power source with little help from e motor and longer Battery drain intervals. Speeds of around 60-65mph are the most suitable for our hybrids.

[Roy124]

  From my early piston engine training 60 years ago it is all to do with power curves. 

The sweet points IIRC were at 40% and 60%. 

At 40% you get maximum economy but you don't get anywhere.  At 60% you get the best compromise between speed and time. 

The first is economy and the latter range.  These are of course based on rpm, not speed. 

[Red_Corolla]

For long distance at sustained high speeds, I feel that diesel is still hard to beat. But any plain ICE powered car drops off significantly in slower conditions and this is where the real advantage of a hybrid lies. On motorway runs, my 2.0 Corolla only gets similar economy to my old BMW straight six, which was a substantially more powerful car. My previous Skoda 2.0 diesel was less powerful than a 2.0 Corolla but still better than a 1.8 whilst being able to produce similar mpg on a run (high 60s - low 70s). It was also a big, heavy car. Town, country and heavy traffic is where hybrid is in its element.

[Roy124]

Stuart, that is certainly true. When we first got a petrol E Class Mercedes we thought we had made a big mistake with mpg well below 30.  Later, with a similar diesel we were getting just under 40 rising to 49 on a long run, never managed 50 😁. 

However if you factor in the weight there is no contest.  It really is a question of picking the best car to meet your criteria.  There is even a powerful argument for hiring a car for rare journeys.  Typically this means a large car for family holidays but it could also be for a small car a city holiday. 

[TonyHSD]

Last two days even in a heavy winds I am rocking 53mpg, slightly more than my typical average for that time of the year., I didn’t kept the car in ready mode for heating as it wasn’t that cold at least and been driving  mostly at around 60mph with more only when the wind was helping 😉👌 btw my dash displays dead on accurate 👍

[Cyker]

I know what you mean about speed; I think around 56mph seems to be a general mpg peak in most of the cars I've driven for some reason. (This may be partly due to the fact that, at that speed, you're almost certainly behind a lorry  )

In my Mk4 I find it doesn't matter so much what speed I'm going at - The biggest effect is acceleration: If I accelerate but keep it in ECO/ECO+, just below the PWR zone, it tends to keep the mpgs higher, but going even 2 blocks into the PWR zone for more than brief periods tends to drop the mpg very quickly (I nearly got it up to 70mpg on the way home but dropped it back to 68 when I hit the motorway because I kept blasting past a dawdling middle-lane hoggers, and up hills too! But man it's satisfyingly fun to do in the Mk4    ... Oh well, still got 3/4 of a tank to try and make that up...!)

I have found the cruise control returns worse mpg than I can when I'm driving tho' - For some reason the CC tends to not use the Battery as much, and gets it quite highly charged, whereas when I'm driving it is able to go into electric-only much more often.

I found in my old Mk1 D4D, 56mph was the most efficient speed too - I reckon it could do 800+ miles easily on a single tank if it could hold that speed! I tended to drive at 60mph, but interestingly I discovered that for some bizarre reason it could get higher mpgs at a constant 70mph! However, driving at that speed for extended periods became quite alarming in the Mk1 due to how the steering became noticeably more light and skittish (esp. if there was a side wind!!  ) so I tended to stick to the mid 60's...

 

[Arita]

Mind you some of the cars are designed and tuned to be most optimal at 90kmh. Years ago I had a BMW E90 2.0d and the consumption at 70kmh was crazy... Get up to 90 and it was sometimes 2L/100 less!!

[Kental]

16 hours ago, Cyker said:

I know what you mean about speed; I think around 56mph seems to be a general mpg peak in most of the cars I've driven for some reason. (This may be partly due to the fact that, at that speed, you're almost certainly behind a lorry  )

In my Mk4 I find it doesn't matter so much what speed I'm going at - The biggest effect is acceleration: If I accelerate but keep it in ECO/ECO+, just below the PWR zone, it tends to keep the mpgs higher, but going even 2 blocks into the PWR zone for more than brief periods tends to drop the mpg very quickly (I nearly got it up to 70mpg on the way home but dropped it back to 68 when I hit the motorway because I kept blasting past a dawdling middle-lane hoggers, and up hills too! But man it's satisfyingly fun to do in the Mk4    ... Oh well, still got 3/4 of a tank to try and make that up...!)

I have found the cruise control returns worse mpg than I can when I'm driving tho' - For some reason the CC tends to not use the battery as much, and gets it quite highly charged, whereas when I'm driving it is able to go into electric-only much more often.

I found in my old Mk1 D4D, 56mph was the most efficient speed too - I reckon it could do 800+ miles easily on a single tank if it could hold that speed! I tended to drive at 60mph, but interestingly I discovered that for some bizarre reason it could get higher mpgs at a constant 70mph! However, driving at that speed for extended periods became quite alarming in the Mk1 due to how the steering became noticeably more light and skittish (esp. if there was a side wind!!  ) so I tended to stick to the mid 60's...

 

Before the NDEC tests, economy figures used to be quoted at (from memory) a town cycle, constant 56 mph (90kph) and 75 mph (120kph). Cars would often be programmed to flat spot at these speeds to improve the official figures.

[Chriss27]

Around mid 50s mpg being optimal has always been around since the oil crisis in the early 70s when USA made freeways a maximum speed of 55mph

[Saxmaniac]

I think as stated above, just drive as you would any other car when you don't want to waste fuel. Light acceleration, brake early. Economy drops with speed as wind drag rises exponentially, 55 - 60mph seems good compromise. Let the computer do all the thinking, you can't out guess it, some clever oriental gentleman spent 20 years developing it🤪

[Bozz]

22 hours ago, Saxmaniac said:

Let the computer do all the thinking, you can't out guess it, some clever oriental gentleman spent 20 years developing it

Absolutely. It is a marvel of automotive engineering and fascinates me.