Optimal Motorway Speed

[user 258]

Speaking as an ex-Prius owner, I'm coming to the conclusion that the Outlander is really two cars sharing a single body shell.

The hybrid systems in the Prius are tightly integrated - they have to be because the battery pack only has a range of a couple of miles. The car is continually playing the petrol engine and the electrical drive off against each other to get best fuel economy - the battery is more a temporary store for excess power coming out of the petrol engine and the electric motor is more akin to a turbocharger, allowing the car to turn in decent acceleration from an engine which is objectively lacking on power and has a terrible power curve.

The Outlander is less tightly integrated. You have an electrical transmission which can receive its power from either the battery pack or from the generator attached to the engine - with a special case at high speed where the engine can be physically coupled to the wheels. The car's default behaviour is to run as pure electrical till the battery goes flat, then fall back to pure petrol with an electrical transmission until you recharge the battery. You have a limited ability to modify this behaviour with the "Save" and "Charge" buttons, but it is never going to be the tightly integrated hybrid system that the Prius is. I guess that you might slightly improve the fuel economy by playing with those buttons, but I doubt that the overall impact will be very high.

Also as an ex Prius driver I think that is a pretty accurate description. Is also add, for other readers, that the Prius ALWAYS runs in parallel hybrid mode when the engine runs so is always as economical as possible. I think the patents on the Toyota hybrid system are about to expire so there may be a more cars using their system which is probably the best system available bar none.

Kind regards
Mark

 

[maby]

I'm not convinced that the Prius system is better than the Outlander - it just solves a different problem. The Prius is not an electric vehicle - it has an electric range of no more than a couple of miles. Fuel consumption on the Prius is relatively independent of patterns of usage or driving conditions - I've never seen mine do less than 45mpg or more than 60mpg.

The Outlander, on the other hand, is far more dependent on usage and driving conditions. If you want to drive a significant distance at high speed, you will inevitably do most of it burning petrol- and your fuel consumption is going to tend towards 40mpg almost irrespective of what you do. Equally, if you do a lot of short journeys, you can probably avoid burning any petrol at all with the potential for amazing fuel consumption figures.

 

[user 258]

I'm not convinced that the Prius system is better than the Outlander - it just solves a different problem. The Prius is not an electric vehicle - it has an electric range of no more than a couple of miles. Fuel consumption on the Prius is relatively independent of patterns of usage or driving conditions - I've never seen mine do less than 45mpg or more than 60mpg.

The Outlander, on the other hand, is far more dependent on usage and driving conditions. If you want to drive a significant distance at high speed, you will inevitably do most of it burning petrol- and your fuel consumption is going to tend towards 40mpg almost irrespective of what you do. Equally, if you do a lot of short journeys, you can probably avoid burning any petrol at all with the potential for amazing fuel consumption figures.

I beg to differ. The issue is how effiiciently does the engine move the car forward when the battery isn't in use (save mode or depleted). The Toyota system is ALWAYS in parrallel hybrid mode so is ALWAYS at its most effiecient. Even more efficient than the Outlander PHEV's parrallel hybrid mode as the Toyota can spin the engine at any speed it needs to in order to produce the needed power as efficiently as possible whereas the PHEV can only spin the engine according to road speed (2100rpm @ 50mph) and series hybrid mode is inherently inefficient due to the additional energy conversion process.

I think you are mixing up the design of the Prius that Toyota went for as compared to how it works. For example, you are referring to the standard Prius with a 1.3KWh battery that can do a mile or two in EV mode at speeds upto 30mph. The plug-in Prius enhanced this by using a more powerful electric motor (upto 53mph) and a bigger battery (4.4KWh) giving 15.5 claimed miles. There is nothing (except space in the chassis and cost) to stop Toyota using an even more powerful electric motor and an even bigger battery to improve all these figures further. The big difference comes when the engine starts though as the Toyota hybrid system is simply more efficient than the PHEV.

Kind regards,
Mark

 

[maby]

I'm not convinced that the Prius system is better than the Outlander - it just solves a different problem. The Prius is not an electric vehicle - it has an electric range of no more than a couple of miles. Fuel consumption on the Prius is relatively independent of patterns of usage or driving conditions - I've never seen mine do less than 45mpg or more than 60mpg.

The Outlander, on the other hand, is far more dependent on usage and driving conditions. If you want to drive a significant distance at high speed, you will inevitably do most of it burning petrol- and your fuel consumption is going to tend towards 40mpg almost irrespective of what you do. Equally, if you do a lot of short journeys, you can probably avoid burning any petrol at all with the potential for amazing fuel consumption figures.

I beg to differ. The issue is how effiiciently does the engine move the car forward when the battery isn't in use (save mode or depleted). The Toyota system is ALWAYS in parrallel hybrid mode so is ALWAYS at its most effiecient. Even more efficient than the ...

I think you are mixing up the design of the Prius that Toyota went for as compared to how it works. For example, you are referring to the standard Prius with a 1.3KWh battery that can do a mile or two in EV mode at speeds upto 30mph. The plug-in Prius enhanced this by using a more powerful electric motor (upto 53mph) and a bigger battery (4.4KWh) giving 15.5 claimed miles. There is nothing (except space in the chassis and cost) to stop Toyota using an even more powerful electric motor and an even bigger battery to improve all these figures further. The big difference comes when the engine starts though as the Toyota hybrid system is simply more efficient than the PHEV.

Kind regards,
Mark

I know that is the theory, but I'm not convinced it really works in practice (speaking as an owner of a MK2 Prius and my son drives a MK3). I've never seen a Prius turn in better than 60mpg and 50 is more typical. The Outlander is a substantially larger and heavier car but apparently is able to return 45mpg on a flat battery - little, if any, benefit from a significantly more complex system.

Don't get me wrong - I loved my Prius, but for its handling, not its fuel consumption - there are plenty of modern non-hybrid cars that can return similar or better.

 

[user 258]

I'm not convinced that the Prius system is better than the Outlander - it just solves a different problem. The Prius is not an electric vehicle - it has an electric range of no more than a couple of miles. Fuel consumption on the Prius is relatively independent of patterns of usage or driving conditions - I've never seen mine do less than 45mpg or more than 60mpg.

The Outlander, on the other hand, is far more dependent on usage and driving conditions. If you want to drive a significant distance at high speed, you will inevitably do most of it burning petrol- and your fuel consumption is going to tend towards 40mpg almost irrespective of what you do. Equally, if you do a lot of short journeys, you can probably avoid burning any petrol at all with the potential for amazing fuel consumption figures.

I beg to differ. The issue is how effiiciently does the engine move the car forward when the battery isn't in use (save mode or depleted). The Toyota system is ALWAYS in parrallel hybrid mode so is ALWAYS at its most effiecient. Even more efficient than the ...

I think you are mixing up the design of the Prius that Toyota went for as compared to how it works. For example, you are referring to the standard Prius with a 1.3KWh battery that can do a mile or two in EV mode at speeds upto 30mph. The plug-in Prius enhanced this by using a more powerful electric motor (upto 53mph) and a bigger battery (4.4KWh) giving 15.5 claimed miles. There is nothing (except space in the chassis and cost) to stop Toyota using an even more powerful electric motor and an even bigger battery to improve all these figures further. The big difference comes when the engine starts though as the Toyota hybrid system is simply more efficient than the PHEV.

Kind regards,
Mark

I know that is the theory, but I'm not convinced it really works in practice (speaking as an owner of a MK2 Prius and my son drives a MK3). I've never seen a Prius turn in better than 60mpg and 50 is more typical. The Outlander is a substantially larger and heavier car but apparently is able to return 45mpg on a flat battery - little, if any, benefit from a significantly more complex system.

Don't get me wrong - I loved my Prius, but for its handling, not its fuel consumption - there are plenty of modern non-hybrid cars that can return similar or better.

Clearly the PHEV is larger and heavier with a larger, less efficient engine (Otto cycle rather than the Atkinson cycle of the Prius) so will always be less economical than a Prius. However, that is compounded further with the even less efficient series hybrid mode which probably loses an additional 15-20% efficiency.

The standard Prius gives the best results in urban driving because it can switch the engine off when not needed AND recover some of the lost kinetic energy which conventional cars can't. On the motorway is is a different equation when most "normal" diesel cars can match or beat the Prius. However, that's because diesel fuel is about 25% (I think) more energy dense than petrol.

The PHEV will return about 40mpg under ideal motorway conditions (65-70mph). I would bet that with a depleted battery you'd be lucky to get much over 30mpg in urban driving as you have the weight, series hybrid inefficiency, AND the Otto cycle enging working against you. The standard petrol Outlander is rated at 22mpg on the urban cycle. I'm sure the PHEV could better this by switching off the engine but that is a rough starting point.

In a nutshell, if you could transplant the Prius hybrid system (sized up of course) into the Outlander I would almost gurantee a 10-25% improvement in mpg when the engine is running.

kind regards,
Mark

 

[Hypermiler]

Maby - I've not worked out how to quote on here, sorry!

Re you not seeing a Prius doing more than 60mpg - we have regularly got more than 60 out of ours when just pootling round country lanes on a summer holiday, and we actually got over 70mpg on the way back from Scotland along A66 (perhaps slightly downhill all the way?!) once when we were running out of petrol! I know you will know this, but for people new to this type of vehicle - the key is to glide as much as possible - the engine needs to be off as much as possible: in a Prius you can use "pulse and glide" if no one is behind you- accelerate to around 45 mph, foot off gas till regen, then foot lightly back on so no arrows at all. (It is a bit easier to do this in the PHEV since you can use B0.) There are whole websites devoted to getting the most out of a Prius - there is also "warp stealth" (which I forget, but I think is doing motorway speeds without engine, given the Prius normally goes to engine at just over 30mph).

Just wanted to give the Prius its due. Oh, and I am told we get around 50mpg on a combined cycle in the Prius which includes around 50% motorway at 80mph+ (note this is 2006 non plug-in model).
Cheers
H

 

[user 258]

Hi,

Just for reference I got 50-55mpg in winter and 55-60mpg out of my gen 2 prius and roughly 75mpg out of my plug-in Prius when on long runs when the battery made almost no difference since it only had a 12 mile range.

Before buying the PHEV I completed a test drive of about 10 miles (4 miles 50mph motorway and 6 miles 65mph motorway) and got 42mpg. The same route in my Prius gave 79mpg. Both cars in save mode for a fair comparison.

Just completed a return trip of 55 miles in the PHEV and averaged 97mpg. The journey was roughly 20 miles urban (max 40mph) and the remainder motorway where I drove steadily at 60-65mph being in no hurry. I calculated this worked out at 32 miles on battery and the remainder at 40mpg to equate to about 97mpg. I completed the trip with --.- EV range.

Kind regards,
Mark

 

[jayfdee]

An earlier comment suggested that Diesel fuel was perhaps 25% more energy dense than petrol and hence the better mileage per litre.
In fact both fuels have a very similar calorific value,and SG.
The reason for diesels better economy is the much higher compression ratio used,and also CI (compression ignition) can burn the fuel at Stoichiometric conditions,and IC(internal combustion) cannot and needs to burn a richer mixture. A spark plug will not ignite a stoichiometric mixture and has to have a richer mix to ignite.Sorry to get all technical.
However I am getting my PHEV soon and look forward to learning all about its technical abilities.

 

[jayfdee]

Forget my previous comment,Petrol is lighter than diesel so a litre of diesel even with similar CV will provide more energy.
Sorry for the error,but the stoichiometric stuff is correct.

 

[ian4x4]

If you really want to understand how a Prius works then there are some very good explanations on the internet.

This is one example.
https://www.youtube.com/watch?v=ZmHpSyTsfm0

The Prius uses some very clever differential gearing to mix the electric motors and the engine.

Its main limitation is that it is forced to start up the engine because it's electric motors will overspeed as the road speed rises.

If you explore the electrical side
https://www.youtube.com/watch?v=UxuqHcUbSQ0

You will see Toyota have been very clever in their energy recovery and heating/cooling systems.

As the Prius is smaller, lighter and much more aerodynamic it should go further on a gallon of petrol.

The PHEV is basically a larger, mainly electrically driven SUV, which is more practical, and 4 wheel drive.

I'm waiting with interest for someone to produce some equally good instruction videos on the PHEV.