Criticism of motorway performance

[Dod101]

I was about to agree with you but you mentioned diesel! I have had a diesel car and hated it!

IMHO a bit of an outdated generalisation . Mine is as quiet inside as the equivalent petrol model which it leaves for dead on economy and performance on any journey, and the old bugbear of slow cabin heating a thing of the past with its supplementary electric one for short cold-weather journeys. Sadly the name’s now likely forever unfairly tarnished by reference to its smoky forebears.

Yes I too wondered if Dod had perhaps had a pre-common rail diesel as yes, they are horrid.

A common rail diesel is a completely different animal and for performance and driver experience, is indistinguishable from a petrol engine. From outside the car, the engine still sounds rather diesel-like though quieter and that's about it.

And getting back to the original topic, my Mercedes van is the most comfortable motorway vehicle I've ever driven. So quiet it's hard to tell the difference between 30mph and 80, blistering performance that catches out many a sports car and the most comfortable driving seat I've ever had. The only downside is, oddly, fuel consumption is appalling.


(Edit to fiddle with html - still not quite right!)

My diesel engined car was a long time ago I will admit, but I went from a 6 cylinder petrol Audi A6 saloon to a very ordinary diesel which sounded like a tractor and performed not much differently. It has put me off diesels for life. My petrol Q5 Sport is wonderful for me anyway, although petrolheads will obviously believe that it leaves something to be desired. (They always do)

Dod

[raybarrow]

Hi Folks,

It's Christmas Eve, full of a cold (typical!) so a question.

I started this prior to my New Year search for a Honda Jazz CVT and because I was feeling sorry for my self with yet another 'Dad's Christmas cold'. It's now officially Covid, Merry bl00dy Christmas!

Looking at the complexity of screens for controlling everything, I think they are to be avoided. You cannot control the car and use a touch screen. Screens have their place but not for the uses to which they are put.

This is interesting as I am looking at the 2014/2016 age which is about when the touch screen appeared, and I have the same misgivings. I don't have to look at any of the knobs and switches in our present cars when driving, I know or can feel where they all are. I don't use the phone when driving but I do use the radio, (Radio 4 not the 'thump, thump' stuff). So i need to check if any of the major controls are 'hidden' in the touch screen, I would hope not. I'm excluding Sat Nav as I use a smartphone with What Three Words and Here. Updated in minutes at home. The touch screen software and Sat Nav updates seem to be at first glance a major computer driven procedure last a few hours. I am happy to be proven wrong? I've only looked at two cars.
Anyway back to Covid, so much NHS and Track&Trace online form filling, I no time to search for cars at the moment!! Looking forward to trip to the rubbish bin.
Hey Ho,
Ray.

[Mike4]

That's interesting. I submitted this reply yesterday and it didn't appear. Did it again today and now have it twice.
Ray.

I saw it yesterday. Very surprised to see it repeated. No idea why you didn't see it, unless you got a cached page.

TJH

Same here, I saw Ray's reply yesterday too, and like you was surprised and puzzled to see it again as a new post today as I'd already read it.

[jackdaww]

.

what about diesel particulates emissions ?

[tjh290633]

.

what about diesel particulates emissions ?

What about exhaust filters? What about tyre and brake dust?

TJH

[XFool]

You cannot beat the laws of physics. Both cars require the same amount of energy to move at a constant speed. The only source of energy which a hybrid has is the fuel input to the engine. You cannot create energy by having a battery. You can use braking energy to charge up the battery, or when descending hills, but that energy has only come from accelerating or climbing the hill.

No skin in this game wrt cars and motorway driving...

However: "You cannot beat the laws of physics." Indeed. So... "You cannot create energy by having a battery. You can use braking energy to charge up the battery, or when descending hills, but that energy has only come from accelerating or climbing the hill."

No? But, if you do have regenerative braking, you must be at least partially recovering the kinetic energy stored in the car to the battery; as opposed to dissipating it as heat in a vehicle without regenerative breaking.

Isn't that also one of "the laws of physics." ?

[tjh290633]

You cannot beat the laws of physics. Both cars require the same amount of energy to move at a constant speed. The only source of energy which a hybrid has is the fuel input to the engine. You cannot create energy by having a battery. You can use braking energy to charge up the battery, or when descending hills, but that energy has only come from accelerating or climbing the hill.

No skin in this game wrt cars and motorway driving...

However: "You cannot beat the laws of physics." Indeed. So... "You cannot create energy by having a battery. You can use braking energy to charge up the battery, or when descending hills, but that energy has only come from accelerating or climbing the hill."

No? But, if you do have regenerative braking, you must be at least partially recovering the kinetic energy stored in the car to the battery; as opposed to dissipating it as heat in a vehicle without regenerative breaking.

Isn't that also one of "the laws of physics." ?

You are assuming braking. Brakes are not applied on every hill. Very seldom applied on a constant speed run on a motorway. The steepest that I know is the M62 descending into Lancashire. You do not need to apply brakes as you descend, if you lift off the accelerator the car will slow on the descent. The A23 at Handcross going south will lead to an slight increase in speed on the descent without power, but only 1 or 2 mph. On neither of these will you get regenerative braking unless you delibeerately slow the car down.

TJH

[redsturgeon]

You cannot beat the laws of physics. Both cars require the same amount of energy to move at a constant speed. The only source of energy which a hybrid has is the fuel input to the engine. You cannot create energy by having a battery. You can use braking energy to charge up the battery, or when descending hills, but that energy has only come from accelerating or climbing the hill.

No skin in this game wrt cars and motorway driving...

However: "You cannot beat the laws of physics." Indeed. So... "You cannot create energy by having a battery. You can use braking energy to charge up the battery, or when descending hills, but that energy has only come from accelerating or climbing the hill."

No? But, if you do have regenerative braking, you must be at least partially recovering the kinetic energy stored in the car to the battery; as opposed to dissipating it as heat in a vehicle without regenerative breaking.

Isn't that also one of "the laws of physics." ?

You are assuming braking. Brakes are not applied on every hill. Very seldom applied on a constant speed run on a motorway. The steepest that I know is the M62 descending into Lancashire. You do not need to apply brakes as you descend, if you lift off the accelerator the car will slow on the descent. The A23 at Handcross going south will lead to an slight increase in speed on the descent without power, but only 1 or 2 mph. On neither of these will you get regenerative braking unless you delibeerately slow the car down.

TJH

I have a PHEV and it has an indicator telling me when I am drawing battery power and when I am regenerating. On the motorway today I can tell you that it was frequently regenerating when I lifted my foot off the accelerator without braking.

John

[9873210]

You cannot beat the laws of physics. Both cars require the same amount of energy to move at a constant speed. The only source of energy which a hybrid has is the fuel input to the engine. You cannot create energy by having a battery. You can use braking energy to charge up the battery, or when descending hills, but that energy has only come from accelerating or climbing the hill.

No skin in this game wrt cars and motorway driving...

However: "You cannot beat the laws of physics." Indeed. So... "You cannot create energy by having a battery. You can use braking energy to charge up the battery, or when descending hills, but that energy has only come from accelerating or climbing the hill."

No? But, if you do have regenerative braking, you must be at least partially recovering the kinetic energy stored in the car to the battery; as opposed to dissipating it as heat in a vehicle without regenerative breaking.

Isn't that also one of "the laws of physics." ?

You are being sucked in.

Regenerative braking is a red herring here. It's a minor effect in motorway driving. The main advantage is that the hybrid decouples the operation of the engine from the movement of the vehicle. This allows the engine to operate more efficiently, producing the same useful energy with less fuel.

There are apparently two arguments from physics being alluded to here. The first is conservation of energy. In this context it merely tells you that the energy of the fuel is equal to the useful work plus the waste, it tells you nothing about how much is wasted. The second argument would be from thermodynamics, the engine has a maximum efficiency that cannot be improved on. But engines on actual motorways rarely operate anywhere near the limit, so the existence of a limit does not mean fuel efficiency cannot be improved.

Consider the follow comparing a car with overdrive with one without: "You cannot beat the laws of physics. Both cars require the same amount of energy to move at a constant speed. The only source of energy is the fuel input to the engine. You cannot create energy by having overdrive. You cannot use overdrive to recover braking energy." Every sentence is true, but strung together it is utter tosh and it's equally utter tosh when applied to hybrids.

[tjh290633]

I have a PHEV and it has an indicator telling me when I am drawing battery power and when I am regenerating. On the motorway today I can tell you that it was frequently regenerating when I lifted my foot off the accelerator without braking.

John

Yes, you are then getting regenerative braking. It is slowing the car down. You then have to use that energy to regain speed.

TJH

[tjh290633]

You are being sucked in.

Regenerative braking is a red herring here. It's a minor effect in motorway driving. The main advantage is that the hybrid decouples the operation of the engine from the movement of the vehicle. This allows the engine to operate more efficiently, producing the same useful energy with less fuel.

There are apparently two arguments from physics being alluded to here. The first is conservation of energy. In this context it merely tells you that the energy of the fuel is equal to the useful work plus the waste, it tells you nothing about how much is wasted. The second argument would be from thermodynamics, the engine has a maximum efficiency that cannot be improved on. But engines on actual motorways rarely operate anywhere near the limit, so the existence of a limit does not mean fuel efficiency cannot be improved.

Consider the follow comparing a car with overdrive with one without: "You cannot beat the laws of physics. Both cars require the same amount of energy to move at a constant speed. The only source of energy is the fuel input to the engine. You cannot create energy by having overdrive. You cannot use overdrive to recover braking energy." Every sentence is true, but strung together it is utter tosh and it's equally utter tosh when applied to hybrids.

An overdrive reduces the mechanical resistance in the drive train. The speed of the engine is reduced. That is why it reduces the fuel consumption. You get a similar effect with a higher axle ratio.

Your argument depends on whether you have a series or a parallel hybrid.

TJH

[redsturgeon]

I have a PHEV and it has an indicator telling me when I am drawing battery power and when I am regenerating. On the motorway today I can tell you that it was frequently regenerating when I lifted my foot off the accelerator without braking.

John

Yes, you are then getting regenerative braking. It is slowing the car down. You then have to use that energy to regain speed.

TJH

I was answering specifically the post where you said

On neither of these will you get regenerative braking unless you delibeerately slow the car down.

I was not deliberately slowing down.

John

[DrFfybes]

On neither of these will you get regenerative braking unless you delibeerately slow the car down.

I was not deliberately slowing down.

John

Not deliberately, but you must have been slowing down more than if you were just coasting (which would be a zero net energy consumtion). In the Avensis, going up an incline in top at 70mph, the readout often drops to 20 mph, going downhill it is often 99 (or more except the readout only has 2 digits). However unless I lift off the throttle completely to consciously slow the vehicle down using engine braking, I'm not losing any efficiency.

As 9873210 says, on the motorway the regeneration is (largely) irrelevant. The big factors are air resistance and engine efficiency. An engine is most efficient at certain rpm (ISTR being told it is at peak torque) so if your cruising rpm is below this then you lose efficiency. Most cars are designed to be comfortable at motorway speeds, so often this means overgearing for reduced noise and vibration. A Ford engine engineer friend says they design for best driveability over a range of conditions, whilst meeting emissions limits. Fuel efficiency is a secondary consideration. With a hybrid the engine can be designed for efficiency rather than performance, the peak torque and maximum efficiency can be lower down the rev range at the expense of peak power output as the batteries fill in any holes in the power curve.

In the Avensis peak torque is around 1850 rpm, which is (I think) about 80-85 mph, so I'm always below maximum efficiency on a motorway. However a hybrid can run at a higher efficiency and use the battery as a buffer, so going downhill or slowing slightly it uses more fuel to recharge the battery, energy it uses up again to climb a hiill or regain speed whilst leaving the petrol component still at max efficiency.

Paul

[Lanark]

This is what Which say

However, in our own independent lab fuel economy tests, we found that average fuel economy (over the 22 models we examined) was 61% less than official manufacturer claims. Based on driving 9,000 miles each year, that could add £400 a year to your annual fuel bills.*
... our own independent tests are more stringent and include tougher test cycles – including our unique motorway test – to better replicate the strain put on cars by real owners.
...
Without a full battery, each of the models we tested performed worse in terms of fuel economy (when they operate as a regular ‘full’ hybrid). So if you don’t have convenient access to charging facilities, you may want to consider a normal hybrid car.

That said, if you do have access to regular charging, and plan to run the car mainly on its battery, you may find you’re better off going straight for an electric car (EV). Some of the PHEV models we tested consume electricity at an enormous rate, compared to comparable EV cars.

Their weight (particularly in large SUVs) and overall smaller electric motors combining to sap power quickly, which could prove uneconomical, especially if you rely on the public charging network.

https://www.which.co.uk/news/2021/03/pl ... res-claim/

So I think a lot of this will depend on the battery range of the car

If the hybrid has a battery range which is a significant proportion of your motorway drive, AND you can fully charge it at home, then it may perform well.
However most hybrids have a much smaller range than pure electric cars.

[ReformedCharacter]

An overdrive reduces the mechanical resistance in the drive train. The speed of the engine is reduced. That is why it reduces the fuel consumption. You get a similar effect with a higher axle ratio.

TJH

I'm confused about the reference to an overdrive reducing mechanical resistance in the drive train. An overdrive passes energy through additional components - quite a few - so I don't see how passing power through additional components can reduce mechanical resistance. Of course I agree that higher gearing can reduce fuel consumption and improve engine efficiency but that comes from reducing engine speed and by allowing the engine to operate at a speed which is most efficient.

RC

[9873210]

This is what Which say
[quote"Which magazine"]
...
you may want to consider a normal hybrid car.
...

The title of the article is Plug-in hybrid cars use more fuel than official figures claim

There is a big difference between HEV and PHEV.

In a HEV all the energy comes from the engine, and hence from the fuel (petrol or diesel). The motors, batteries and motor controllers function as a transmission. They can perform the normal gearbox operation that trades off rpm and torque.* The small amount of storage in the battery allows additional trades offs across a few minutes of time, trading peak power for average power and average efficiency for peak efficiency. If the car is designed to do these things well it will get higher fuel efficiency.

A PHEV on the other hand is all about the badge. Most are designed simply to get the badge; many are designed as extra-marital aids.

But a bigger problem is lumping all PHEV or HEV together. As with anything automotive there are good designs and bad designs. The Prius is a good design, there are a few other good designs and many bad designs. You should discuss the good designs and ridicule anything from BMW. Lumping all HEV or PHEV together is like calling any car with go faster stripes and a spoiler a "sports car" and complaining about the lame average acceleration of sports cars.

Notably in the Which article the PHEV that comes closest to the claims is the Prius PHEV. Toyota designed the HEV to get high fuel economy and this carries through to the plug-in.


* In theory you could run a Prius drive train without a battery. It would require completely different programming to make sure the engine power varied to match drive power and ensure one motors consumption matched the other motors generation. It would not work well with the existing components (particularly the engine), but it could work.