Prius Engine Variants

[PoulStaugaard]

I find it somewhat disappointing that Toyota doesn't offer more than one engine version for the Prius. For starters, there must be several parameter values, starting with valve lift and timing that could have been chosen differently, prioritizing performance somewhat at the expense of efficiency. But I suppose the reason they chose not to do so was to avoid confusing the message of what the Prius is about.

One thing that they could have done without confusing the message, would be to offer a diesel version. I'm aware that you Americans consider diesel engines to be dirtier than gasoline engines, but with their improved mileage and the addition of particle filters, some argue that the opposite is true. The diesel engines are intrinsically more efficient than gasoline engines, and in urban trafic they would benefit even more from the optimization of engine load, that HSD offers. To my knowledge, only Peugeot has announced having a diesel-electric hybrid on the way, promising a 38% reduction in fuel consumption relative to the current diesel generation with the aid of a 16kW electric motor. As for CO2 emission, they claim to achieve just 90g/km. But Peugeot uses a conventional 6-speed transmission, nothing like the Prius PSD. It is not that Peugeot and Toyota aren't working together already (they produce the minimalistic Peugeot 107 / Toyota Aygo in a joint venture), but I suppose the cost of licensing Toyotas patents dissuaded Peugeot from taking that route.

Any thoughts on this ? Does anyone know if Toyota or anyone is working on a diesel version of the HSD design ?

[patsparks]

Toyota considered with the additional cost of the HSD and the additional cost of diesel would be too high a price for potential buyers.
Also could you imagine the diesel shuddering to a stop each time you lift your foot off the accelerator then shuddering back to life each time you put your foot down? Some people don't like the petrol engine doing it!

I guess with variable valve timing it may be possible to spin the diesel up to speed before injecting fuel, not sure how the Atkinson cycle would work with diesel.

Diesel also releases more carbon per litre than petrol so even if you scrub the particulates from the exhaust you still have a higher release of carbon into the atmosphere. I'm no expert on this side of things but there is plenty of information if you use the search function.

[donee]

Hi All,

Its been mentioned by a Toyota engineer in a public talk that the HSD system is a $2K cost in comparison to traditional cars. Even though the battery is like $2.4 K . This is because there is no starter, alternator, egr valve, or power steering pump and asociated mounting hardware in the HSD system.

In order to get good mileage with a diesel, a variable geometery turbo charger is usually installed. This and the heavy engine block, which is harder to machine and the extra emissions device(s), results in about a $1.5 K . Diesels can idle at extremely low fuel consumption, so there is not a synergy with a stop/start hybrid system and a diesel engine. Additionally, diesels have good low-end torque, again poor synergy with an electric motor in a parallel hybrid configuration. Diesels also have good fuel efficiency at partial loads. Parallel Hybrid systems are primarily a way to increase engine load for the time the engine is running, and turn it off when loads are too low for the engine to be efficient. Again, not a good match. Hybrids are more optimum for stoichiometric engines that have pumping losses, or Brayton (Turbine) cycle engines which tend to have high efficiency only at high powers for other reasons.

Diesels are more appropriate for series hybrid vehicles. The cost of the diesel is offset by the lower cost of the generator, in comparison to the shaft driven transmission. But the size of such an engine would be so small, that some of the diesel efficiencies might be lost in air flow inefficiency. Something like a 2 cylinder diesel might be appropriate for the Chevy/Opel Volt/? concept. This would keep the cylinders and air pasages large. As this is not a standard engine configuration, the extra cost of the custom engine might not work economically. One of the things that has made the Prius an economic success is the use of standard engine blocks that are shared with other cars (Echo, Yaris, others?).

Additonally, continuous cruise power would be traded off. GM is proabably not willing to do yet. Although, with a 40 mile electric range, it would be very practical for them to do. The engine would be running after the car was parked if its not plugged in, to make up for battery drainage. But in continuous driving, in conditions that bring the battery to low state of charge, the power would be limited to that of the 2 cylinder diesel (50 hp). Which with an aerodynamic shape such as the Opel Eflex concept would probably be a 90 mph cruising speed maximum. Hill climbing after a long high speed run on flat roads would be misrable, however. Unless one took a lunch break and let the car recharge in the parking lot before hitting the hills.

So, I think that diesel hybrid is not a practical buisness/engineering solution presently in a HSD car. With the impact of the HSD waining over time, and fuel increasing further, this may turn-around. At present, and has been mentioned in this thread, the Prius does not recover any exhaust energy. Add that into the mix, achieving either a full Miller Cycle engine, or Atkinson Cycle / Miller Valve train with turbo-generator and the Prius engine will be as effiicient as diesels in a car with a $2.8 K price increase over standard car, and able to get 70 mpgUS (due to the operational advantages of the HSD, besides diesel-like engine efficiency) in real-world mixed service.


In which case the only thing that could beat them in CO2 reduction is the PHEV or EV being driven half the batery capacity range between rechargings. A thru-road diesel parallel hybrid has shown this level of fuel economy (GM Precept concept). But, there is probably concern about that idea in slipery road conditions.

As to the American dislike for diesel, there is also the European subsidy (lower tax rates) of diesel that may be prompting Poul's questions. Maybe its time for that to go away? Just like the Post-Katrina hybrid car subsidy is phasing out in the US?

[Tchou]

<div class='quotetop'>QUOTE(PoulStaugaard @ Nov 4 2007, 12:28 PM) [snapback]534585[/snapback]</div>

I find it somewhat disappointing that Toyota doesn't offer more than one engine version for the Prius. For starters, there must be several parameter values, starting with valve lift and timing that could have been chosen differently, prioritizing performance somewhat at the expense of efficiency. But I suppose the reason they chose not to do so was to avoid confusing the message of what the Prius is about.

One thing that they could have done without confusing the message, would be to offer a diesel version. I'm aware that you Americans consider diesel engines to be dirtier than gasoline engines, but with their improved mileage and the addition of particle filters, some argue that the opposite is true. The diesel engines are intrinsically more efficient than gasoline engines, and in urban trafic they would benefit even more from the optimization of engine load, that HSD offers. To my knowledge, only Peugeot has announced having a diesel-electric hybrid on the way, promising a 38% reduction in fuel consumption relative to the current diesel generation with the aid of a 16kW electric motor. As for CO2 emission, they claim to achieve just 90g/km. But Peugeot uses a conventional 6-speed transmission, nothing like the Prius PSD. It is not that Peugeot and Toyota aren't working together already (they produce the minimalistic Peugeot 107 / Toyota Aygo in a joint venture), but I suppose the cost of licensing Toyotas patents dissuaded Peugeot from taking that route.

Any thoughts on this ? Does anyone know if Toyota or anyone is working on a diesel version of the HSD design ?
[/b]

They are not doing it because diesel pollutes more than gasoline engines...
Diesel makes less CO2 it's true but they also make particules, and even with a particules filter the smaller and more dangerous ones manage to pass through...
Also diesel produce Nox a lot more than gasoline engines (Nox cause acid rains...)...
Peugeot would have a lot of problems saying that diesel pollutes more after years taken to make people believe the other way...
The only way to make a diesel pollute less is to ad a denox catalyser, like in D-Cat toyotas or blue motion VW s or bluetec Mercedes... Peugeot is behind on this... and even if the diesel reject less Co2 it still reject other kinds of bad stuff...

[Tchou]

<div class='quotetop'>QUOTE(PoulStaugaard @ Nov 4 2007, 12:28 PM) [snapback]534585[/snapback]</div>

I find it somewhat disappointing that Toyota doesn't offer more than one engine version for the Prius. For starters, there must be several parameter values, starting with valve lift and timing that could have been chosen differently, prioritizing performance somewhat at the expense of efficiency. But I suppose the reason they chose not to do so was to avoid confusing the message of what the Prius is about.

One thing that they could have done without confusing the message, would be to offer a diesel version. I'm aware that you Americans consider diesel engines to be dirtier than gasoline engines, but with their improved mileage and the addition of particle filters, some argue that the opposite is true. The diesel engines are intrinsically more efficient than gasoline engines, and in urban trafic they would benefit even more from the optimization of engine load, that HSD offers. To my knowledge, only Peugeot has announced having a diesel-electric hybrid on the way, promising a 38% reduction in fuel consumption relative to the current diesel generation with the aid of a 16kW electric motor. As for CO2 emission, they claim to achieve just 90g/km. But Peugeot uses a conventional 6-speed transmission, nothing like the Prius PSD. It is not that Peugeot and Toyota aren't working together already (they produce the minimalistic Peugeot 107 / Toyota Aygo in a joint venture), but I suppose the cost of licensing Toyotas patents dissuaded Peugeot from taking that route.

Any thoughts on this ? Does anyone know if Toyota or anyone is working on a diesel version of the HSD design ?
[/b]

They are not doing it because diesel pollutes more than gasoline engines...
Diesel makes less CO2 it's true but they also make particules, and even with a particules filter the smaller and more dangerous ones manage to pass through...
Also diesel produce Nox a lot more than gasoline engines (Nox cause acid rains...)...
Peugeot would have a lot of problems saying that diesel pollutes more after years taken to make people believe the other way...
The only way to make a diesel pollute less is to ad a denox catalyser, like in D-Cat toyotas or blue motion VW s or bluetec Mercedes... Peugeot is behind on this... and even if the diesel reject less Co2 it still reject other kinds of bad stuff...

[bwilson4web]

Hi,

Good friend 'donee' has pretty well surveyed some of the engineering issues but I'd like to offer some facts and data to make sure we're all using the same set of data:
<div class='quotetop'>QUOTE(PoulStaugaard @ Nov 4 2007, 06:28 AM) [snapback]534585[/snapback]</div>

I find it somewhat disappointing that Toyota doesn't offer more than one engine version for the Prius. For starters, there must be several parameter values, starting with valve lift and timing that could have been chosen differently, prioritizing performance somewhat at the expense of efficiency. But I suppose the reason they chose not to do so was to avoid confusing the message of what the Prius is about.[/b]

Toyota makes a Camry, Highlander and via Lexus, three models of hybrids. In Japan, they also sell a hybrid minivan. There are subtle differences between the different models and the hybrid transaxles but more importantly, a spectrum of vehicles that meet different user profiles and transportation needs. For a new technology, this broad based approach is a much better answer than having only one hybrid model with many variants. Not everyone wants or can use a Prius model for their transportation needs.

<div class='quotetop'>QUOTE(PoulStaugaard @ Nov 4 2007, 06:28 AM) [snapback]534585[/snapback]</div>

One thing that they could have done without confusing the message, would be to offer a diesel version. I'm aware that you Americans consider diesel engines to be dirtier than gasoline engines, but with their improved mileage and the addition of particle filters, some argue that the opposite is true. The diesel engines are intrinsically more efficient than gasoline engines, and in urban trafic they would benefit even more from the optimization of engine load, that HSD offers. To my knowledge, only Peugeot has announced having a diesel-electric hybrid on the way, promising a 38% reduction in fuel consumption relative to the current diesel generation with the aid of a 16kW electric motor. As for CO2 emission, they claim to achieve just 90g/km. But Peugeot uses a conventional 6-speed transmission, nothing like the Prius PSD. It is not that Peugeot and Toyota aren't working together already (they produce the minimalistic Peugeot 107 / Toyota Aygo in a joint venture), but I suppose the cost of licensing Toyotas patents dissuaded Peugeot from taking that route.

Any thoughts on this ? Does anyone know if Toyota or anyone is working on a diesel version of the HSD design ?[/b]

As 'donee' pointed out, diesels have implementation problems to which I would add that diesels aren't the only form of 'lean burn' or high efficiency engine. Sterling cycle and turbine technology have distinct advantages. Furthermore, we're still tossing 1/3 of the usable heat out the exhaust pipe and heat management needs improved materials.

One thing hybrid technology has taught is it is the system, not just the individual parts, are key. Hybrid technology needs to be applied across the whole spectrum of transportation from motorcycles through construction and utility and interstate trucks. There is a broad spectrum of challenges and rather than try to make a rainbow of 3,000 lb passenger vehicles, let's see a broad range of hybrids at all weights, speeds and driving profiles.

IMHO, there are Prius being forced into driving profiles that don't match the vehicle design. For example, attempts to use it on rough, unpaged roads or 80+ mph cruisers. Heck, one good ole boy made a 'stretch' Prius when they needed an 8 seat station wagon or minivan. A good builder has more than one hammer to have the right tool for the right job.

Bob Wilson

[prius2go]

80mph cruiser.....
It is good for this too,
the ICE can run at constand load, avoiding inefficient changes in fuel input
the electric motor boosts on uphill gradients, regens on downhill
typical average 55mpg at 80mph

I'm not sure of the figures for an equivalent diesel

Couldnt the diesel be pitched at the minimum for the size of vehicle,
the electric motor being used for accelaration when needed

[donee]

<div class='quotetop'>QUOTE(prius2go @ Nov 4 2007, 06:25 PM) [snapback]534673[/snapback]</div>

80mph cruiser.....
It is good for this too,
the ICE can run at constand load, avoiding inefficient changes in fuel input
the electric motor boosts on uphill gradients, regens on downhill
typical average 55mpg at 80mph

I'm not sure of the figures for an equivalent diesel

Couldnt the diesel be pitched at the minimum for the size of vehicle,
the electric motor being used for accelaration when needed
[/b]

That s probably 55 mpgUK at 80 mph most likely. We do not see that here with US gallons. The coversion comes out to 42 mpgUS, which is sounds about right.

[Bebopp]

<div class='quotetop'>QUOTE(donee @ Nov 4 2007, 08:29 AM) [snapback]534594[/snapback]</div>

[/b]

Good post donee, certainly some technical points worth considering there. Of course there has always been the inherent diesel engine efficiency issue that requires relatively high cylinder temperatures for ignition that will be affected by the electric motor augmentation, unless the diesel engine is kept running at all times, in which case isolating it from the electric motor (in accelerations, e.g.) will be problematic. The Atkins cycle will not be conducive to a diesel engine, and therefore there will have to be a major re-design.

[PoulStaugaard]

<div class='quotetop'>QUOTE(donee @ Nov 4 2007, 02:29 PM) [snapback]534594[/snapback]</div>

Hi All,

Diesels are more appropriate for series hybrid vehicles. The cost of the diesel is offset by the lower cost of the generator, in comparison to the shaft driven transmission. But the size of such an engine would be so small, that some of the diesel efficiencies might be lost in air flow inefficiency. Something like a 2 cylinder diesel might be appropriate for the Chevy/Opel Volt/? concept. This would keep the cylinders and air pasages large. As this is not a standard engine configuration, the extra cost of the custom engine might not work economically. One of the things that has made the Prius an economic success is the use of standard engine blocks that are shared with other cars (Echo, Yaris, others?).

Additonally, continuous cruise power would be traded off. GM is proabably not willing to do yet. Although, with a 40 mile electric range, it would be very practical for them to do. The engine would be running after the car was parked if its not plugged in, to make up for battery drainage. But in continuous driving, in conditions that bring the battery to low state of charge, the power would be limited to that of the 2 cylinder diesel (50 hp). Which with an aerodynamic shape such as the Opel Eflex concept would probably be a 90 mph cruising speed maximum. Hill climbing after a long high speed run on flat roads would be misrable, however. Unless one took a lunch break and let the car recharge in the parking lot before hitting the hills.

So, I think that diesel hybrid is not a practical buisness/engineering solution presently in a HSD car. With the impact of the HSD waining over time, and fuel increasing further, this may turn-around. At present, and has been mentioned in this thread, the Prius does not recover any exhaust energy. Add that into the mix, achieving either a full Miller Cycle engine, or Atkinson Cycle / Miller Valve train with turbo-generator and the Prius engine will be as effiicient as diesels in a car with a $2.8 K price increase over standard car, and able to get 70 mpgUS (due to the operational advantages of the HSD, besides diesel-like engine efficiency) in real-world mixed service.
In which case the only thing that could beat them in CO2 reduction is the PHEV or EV being driven half the batery capacity range between rechargings. A thru-road diesel parallel hybrid has shown this level of fuel economy (GM Precept concept). But, there is probably concern about that idea in slipery road conditions.

As to the American dislike for diesel, there is also the European subsidy (lower tax rates) of diesel that may be prompting Poul's questions. Maybe its time for that to go away? Just like the Post-Katrina hybrid car subsidy is phasing out in the US?
[/b]

I'm aware that series hybrid diesel designs have been used for trains, probably due to a mechanical torque converter being even less efficient, but let's get a few facts straight:

The Prius does use series hybrid together with the PSD as an alternative to a conventional gearbox, not because it is more efficient in itself (it certainly isn't), but because it helps the gasoline ICE operate as efficiently and cleanly as possible.

Peugeot's HybridHDI uses a diesel with a conventional transmission in parallel with a smaller electric motor, despite the fact that this must be way expensive to manufacture than Toyotas HSD design (they probably save on development cost and component sharing).

Peugeots claims 25% better mileage and 15% less CO2 for the HybridHDI 308 than the Prius achieves despite the fact that the Prius has a 10% advantage on aerodynamic drag and a small advantage on weight. They are probably not lying; their conventional diesel is very close to the Prius on mileage. As oil prices will continue to go up, you cannot argue with those figures, at least not for long distance transport.

With Toyota already having the HSD transmission in production, they should be able to produce a HSD diesel much more cheaply than Peugeot's solution.