PHEV economy observations

[Flatcoat]

Towed the caravan (1550kg) from south of Huddersfield to Edinburgh via the M1/A1 today. Using Shell Vpower and keeping the cruise set at 63mph (on the premise it will probably be a true 60). Economy was 29.5 mpg in sport save for last 25 mile stint when I also put into ‘charge’ mode. I had forgotten to charge the car before setting off so decided to charge en route, the dropped to 19.4mpg…. Tomorrow towing to Loch Ness via A9 and will update on the economy on that stretch. 

[Oscarmax]

Last September Tesco E10 driving solo around the New Forest  with its advised 40mph restrictions used Charge mode from memory it dropped from 50 + mpg to mid 30's, so I not surprised. 

[ernieb]

It’s an expensive way to charge the traction Battery, I rarely if ever use this feature. Typically, I either use EV or HEV mode. I believe it was designed so that the car could be used in low emission zones?

[AJones]

I'm not sure there's much benefit from 'charge mode', it's running the engine harder and burning more fuel to charge the Battery, to then use that stored electricity at some point later. Whereas you could just use the engine (in HEV mode) to directly drive the car when you need it, avoiding the losses from converting that energy to electricity, putting it into the Battery, taking it out again and back through the motor to the wheels.

It has some niche uses - for short trips, if you can't plug in, you can top-up the Battery when the engine is hot and avoid having to start and warm up the engine for every short trip. There's an emissions argument, run the engine on the motorway or country roads to then drop into EV mode when your driving around town or city centres.

[Flatcoat]

3 hours ago, AJones said:

I'm not sure there's much benefit from 'charge mode', it's running the engine harder and burning more fuel to charge the battery, to then use that stored electricity at some point later. Whereas you could just use the engine (in HEV mode) to directly drive the car when you need it, avoiding the losses from converting that energy to electricity, putting it into the battery, taking it out again and back through the motor to the wheels.

It has some niche uses - for short trips, if you can't plug in, you can top-up the battery when the engine is hot and avoid having to start and warm up the engine for every short trip. There's an emissions argument, run the engine on the motorway or country roads to then drop into EV mode when your driving around town or city centres.

I am not using the ICE generated charge in the Battery at home. I am away on holiday and for a variety of reasons simply needed more charge in the traction Battery. I am well aware of the pros and cons hence I very very rarely charge from any source while on the go! 

[Flatcoat]

4 hours ago, ernieb said:

It’s an expensive way to charge the traction battery, I rarely if ever use this feature. Typically, I either use EV or HEV mode. I believe it was designed so that the car could be used in low emission zones?

As above. 

[Nick72]

6 hours ago, ernieb said:

It’s an expensive way to charge the traction battery, I rarely if ever use this feature. Typically, I either use EV or HEV mode. I believe it was designed so that the car could be used in low emission zones?

I'm guessing now Ernie but I suspect the Charge mode was really designed to allow folks to run power off the traction Battery through the 1.5kW (or whatever it is) mains adapter in the boot when out camping in the middle of nowhere. For all the markets like North America that got this high power outlet feature. That's truly useful in that case. I'd definitely use it for then once I'd depleted the traction Battery on route or just need to top it up for the next night of camping out. 

[Nick72]

Normal driving 30mph to 50mph roads with light traffic and a medium weight foot I'm seeing 50 to 54mpg without the EV effect. Just off the odometer and doing the maths. Not towing anything of course. 

Caning it on the motorway and it's more like 45 mpg.

Either way it's hugely impressive for a large car with the drag coefficient of a brick.

[ernieb]

4 minutes ago, Nick72 said:

I'm guessing now Ernie but I suspect the Charge mode was really designed to allow folks to run power off the traction battery through the 1.5kW (or whatever it is) mains adapter in the boot when out camping in the middle of nowhere. For all the markets like North America that got this high power outlet feature. That's truly useful in that case. I'd definitely use it for then once I'd depleted the traction battery on route or just need to top it up for the next night of camping out. 

Good call, not thought of that. Certainly could be useful even in the UK to charge a laptop/iPad etc., if you were remote.

[Nick72]

1 minute ago, ernieb said:

Good call, not thought of that. Certainly could be useful even in the UK to charge a laptop/iPad etc., if you were remote.

It's basically a huge camping Battery which if there's 14kWhrs available that could power a lot of stuff on a campsite or caravan for a couple of nights. Then just run the engine in charge mode to recharge the Battery for another 2 nights. 

I really really wish we got this feature. I can't do much off 150W.

[AJones]

9 minutes ago, Nick72 said:

I'm guessing now Ernie but I suspect the Charge mode was really designed to allow folks to run power off the traction battery through the 1.5kW (or whatever it is) mains adapter in the boot when out camping in the middle of nowhere.

Sounds plausible. The Prius PHEV came out before the RAV4 PHEV and it has charge mode as well, the Japanese version of the Prius PHEV had options for a power outlet inside the vehicle and an accessory that plugged into the charging socket to give a 1.5kW power outlet for plugging in appliances. It also supported a power to home system.

See page 24 onwards.

https://toyota.jp/pages/contents/request/webcatalog/priusphv/priusphv_main_202007.pdf

[Nick72]

5 hours ago, AJones said:

Sounds plausible. The Prius PHEV came out before the RAV4 PHEV and it has charge mode as well, the Japanese version of the Prius PHEV had options for a power outlet inside the vehicle and an accessory that plugged into the charging socket to give a 1.5kW power outlet for plugging in appliances. It also supported a power to home system.

See page 24 onwards.

https://toyota.jp/pages/contents/request/webcatalog/priusphv/priusphv_main_202007.pdf

That would have been perfect. Some US owners of the R4P have used the traction Battery to power their homes in California when the grid power goes off. 

[Flatcoat]

For comparison of computer accuracy I did a brim to brim over the first part of the journey and which gave 30mpg, pretty accurate. 

[Oscarmax]

16 hours ago, Nick72 said:

Normal driving 30mph to 50mph roads with light traffic and a medium weight foot I'm seeing 50 to 54mpg without the EV effect. Just off the odometer and doing the maths. Not towing anything of course. 

Caning it on the motorway and it's more like 45 mpg.

Either way it's hugely impressive for a large car with the drag coefficient of a brick.

Similar figures for us, charge mode on the RAV4 is a real killer, strangely our previous Mitsubishi 2020 Outlander 2.4 PHEV towing in charge mode would achieve approximately 30mpg over a 178 mile journey, but solo just using the ICE unit would achieve 35/36mpg ?

 

[Oscarmax]

10 hours ago, Flatcoat said:

For comparison of computer accuracy I did a brim to brim over the first part of the journey and which gave 30mpg, pretty accurate. 

Yes the computer we have found the computer to be very accurate.

[AndrueC]

22 hours ago, AJones said:

I'm not sure there's much benefit from 'charge mode', it's running the engine harder and burning more fuel to charge the battery, to then use that stored electricity at some point later.

If the ICE had a linear fuel consumption and power curve you'd be right but they don't. It's possible (even likely I'd say knowing Toyota) that by making the ICE work harder you're also allowing it to extract more energy from the fuel being burnt.

The only question then is whether the increase in energy extracted per litre of petrol is greater than the losses incurred in moving electricity around.

When you take your foot off you are throttling a petrol engine and they don't work very efficiently that way. A petrol ICE is typically most efficient at or slightly below wide open throttle.

We don't drive around at wide open throttle (well petrol engines don't) because it'd be dangerous and because wind and tyre resistance more than negate the advantage. However in this case none of that applies so the car is free to let the engine work harder and potentially get more out of the fuel being burnt.

This is the main reason why 'pulse and glide' works so well.

[ernieb]

The PHEV ICE, like others who use this engine, is optimised to run at a round 2k rpm at this operating zone it is capable of around 41% efficiency. Many of us who drive the PHEV version will know that it will go full beans if you hit the right peddle but most of the time it appears to sit at it’s optimum rpm. My guess is that at a steady speed, without hills up or down, in traction Battery charge mode the ICE is still likely to be running around the 2k rpm mark. 

[Nick72]

8 hours ago, ernieb said:

The PHEV ICE, like others who use this engine, is optimised to run at a round 2k rpm at this operating zone it is capable of around 41% efficiency. Many of us who drive the PHEV version will know that it will go full beans if you hit the right peddle but most of the time it appears to sit at it’s optimum rpm. My guess is that at a steady speed, without hills up or down, in traction battery charge mode the ICE is still likely to be running around the 2k rpm mark. 

I think that's spot on Ernie. And the CVT helps here. 

[Flatcoat]

11 hours ago, AndrueC said:

If the ICE had a linear fuel consumption and power curve you'd be right but they don't. It's possible (even likely I'd say knowing Toyota) that by making the ICE work harder you're also allowing it to extract more energy from the fuel being burnt.

The only question then is whether the increase in energy extracted per litre of petrol is greater than the losses incurred in moving electricity around.

When you take your foot off you are throttling a petrol engine and they don't work very efficiently that way. A petrol ICE is typically most efficient at or slightly below wide open throttle.

We don't drive around at wide open throttle (well petrol engines don't) because it'd be dangerous and because wind and tyre resistance more than negate the advantage. However in this case none of that applies so the car is free to let the engine work harder and potentially get more out of the fuel being burnt.

This is the main reason why 'pulse and glide' works so well.

That may apply with a car with a conventional ICE and gearbox, however as other point out, not in a RAV Hybrid nor many other Toyota hybrid products. 

[AJones]

10 hours ago, AndrueC said:

If the ICE had a linear fuel consumption and power curve you'd be right but they don't. It's possible (even likely I'd say knowing Toyota) that by making the ICE work harder you're also allowing it to extract more energy from the fuel being burnt.

Quite likely, but I would expect that Toyota will already know this and incorporate it into the design of the hybrid engine control. If it is more efficient to run the engine at higher revs and/or higher torque and use the extra power to charge the Battery then the hybrid control will likely be optimising this already in HEV mode when it is running the engine.

In HEV mode, the engine is generally off at lower speeds/torques, the engine starts up when more power is required and while it is running it is used to charge the Battery, so presumably running at a speed/torque combination optimal for efficiency.

10 hours ago, AndrueC said:

The only question then is whether the increase in energy extracted per litre of petrol is greater than the losses incurred in moving electricity around.

No it's more complicated because in HEV mode there will be periods when the engine is not running at all because there's little demand for torque to the wheels. Putting it into 'charge mode' forces the engine to run continually, so there's a question of how efficient is the engine during those periods when it's running mostly or purely to charge the Battery, during those periods when it would otherwise have been shut off.

The battery will likely have charging power limits to protect it, along with other possible limits in the transmission system, limiting the power input, so there's a separate question of can the engine still run at decent efficiency if all or most of the power is going to the battery? 

Or is it more efficient to charge the battery at times when the engine is running to also supply torque to the wheels, so at a higher total power, as in HEV mode.

[AndrueC]

1 hour ago, Flatcoat said:

That may apply with a car with a conventional ICE and gearbox, however as other point out, not in a RAV Hybrid nor many other Toyota hybrid products. 

The transmission has nothing to do with it. It's the ICE itself that has a Specific Fuel Consumption curve. All internal combustion engines do.

Toyota's HSD gives the ECU a lot more options that's all. In a PHEV presumably it completely disassociates the ICE output from the road wheel torque so the ECU can run the ICE any way it wants regardless of what the driver is requiring from the drivetrain.

Whether using the ICE to charge your Battery is expensive or not will of course depend on the cost of fuel and the cost of electricity. But there are plenty of series-hybrid vehicles on the market so it's clearly not a stupid idea.

And during the recent energy crisis the cost of electricity actually meant that my 1.8 Corolla Hybrid was cheaper to run than your PHEV so perhaps at that time using your ICE to charge your Battery would also have been cheaper 😉

[Flatcoat]

On 5/6/2024 at 9:42 PM, AndrueC said:

The transmission has nothing to do with it. It's the ICE itself that has a Specific Fuel Consumption curve. All internal combustion engines do.

Toyota's HSD gives the ECU a lot more options that's all. In a PHEV presumably it completely disassociates the ICE output from the road wheel torque so the ECU can run the ICE any way it wants regardless of what the driver is requiring from the drivetrain.

Whether using the ICE to charge your battery is expensive or not will of course depend on the cost of fuel and the cost of electricity. But there are plenty of series-hybrid vehicles on the market so it's clearly not a stupid idea.

And during the recent energy crisis the cost of electricity actually meant that my 1.8 Corolla Hybrid was cheaper to run than your PHEV so perhaps at that time using your ICE to charge your battery would also have been cheaper 😉

In respect of the RAV eCVT the transmission is precisely part of the reason why the economy is so good. I know it can’t change the efficiency of the engine per se, but it does help with the efficacy of the drivetrain. 
 

To update the second part of the journey north gave around 25.5mpg. Not unduly surprised given the long climbs on that stretch of M9/A9. Tomorrow we head south to Glenrothes so will see how the economy fares heading downhill as we return south! 😁

[Nick72]

9 hours ago, Flatcoat said:

In respect of the RAV eCVT the transmission is precisely part of the reason why the economy is so good. I know it can’t change the efficiency of the engine per se, but it does help with the efficacy of the drivetrain. 
 

To update the second part of the journey north gave around 25.5mpg. Not unduly surprised given the long climbs on that stretch of M9/A9. Tomorrow we head south to Glenrothes so will see how the economy fares heading downhill as we return south! 😁

Still pretty reasonable.

All the best and keep on trucking. 

[Oscarmax]

22 hours ago, Flatcoat said:

In respect of the RAV eCVT the transmission is precisely part of the reason why the economy is so good. I know it can’t change the efficiency of the engine per se, but it does help with the efficacy of the drivetrain. 
 

To update the second part of the journey north gave around 25.5mpg. Not unduly surprised given the long climbs on that stretch of M9/A9. Tomorrow we head south to Glenrothes so will see how the economy fares heading downhill as we return south! 😁

It a bit like the hilly terrain of the Cornwall A30 fuel consumption goes out of the window

[GBgraham]

22 hours ago, Oscarmax said:

It a bit like the hilly terrain of the Cornwall A30 fuel consumption goes out of the window

Horses for courses me thinks. I'm based in quite a mountainous terrain and my trips are nearly always a case of A to B and return on the same route and what goes up must come down.

As today I did 44miles on electric and returned back to base showing 10 miles in reserve so there's no complaints from me with the workings of the RAV4 PHEV