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XL1 dive and drive: Volkswagen aggressively optimizes for efficiency in its sleek diesel plug-in hybrid

24 June 2013

2013-06-21 13.58.02
XL1s ready to roll. Click to enlarge.

During a media event in Wolfsburg, Germany, Volkswagen provided a medium dive into details of its two-seater XL1 Super Efficient Vehicle diesel plug-in hybrid (earlier post) as well as some driving time on local roads and highways.

The XL1 is aggressively optimized for efficiency in all areas of its design and technology—from materials (carbon fiber reinforced polymer monocoque); to powertrain (0.8L two-cylinder diesel, 20 kW electric motor and 5.5 kWh Li-ion pack with efficiency-optimized control and brake regeneration strategies); to lightweighting (little baffling to shield the driver from engine, chassis and road noises); to aerodynamics (with a Cd of 0.189, the XL1 bests the only other production vehicle that has come close, the GM EV1’s 0.19; the original Honda Insight hybrid had a Cd of 0.25). It reflects, the Volkswagen team members said, an effort by the company to deliver the most efficient vehicle they could—but one that could still be series-produced, homologated and sold—with current technologies.

2013-06-21 14.45.00
Rear view, with engine compartment with air intake labeled. Click to enlarge.

The lightweight XL1 (795 kg, 1,753 lbs) delivers NEDC fuel consumption of 261 mpg (0.9 l/100 km) with CO2 emissions of 21 g/km and an all-electric range of 31 miles (50 km) as well as a total range of 310 miles (499 km). The XL1 has a top speed (electronically controlled) of 160 km/h (99 mph); cruising at a constant 100 km/h the XL1 uses only 8.3 hp (6.2 kW). In all-electric mode, the XL1 requires less than 0.1 kWh to cover more than 0.6 miles (one kilometer), based on the NEDC.

0.1 kWh per km equates to 0.161 kWh/mile, or 16 kWh/100 miles. Even accounting for differences resulting from variations in drive cycles, XL1 appears to deliver significantly better electric fuel consumption than the EPA-rated electric or plug-in vehicles on the US market.

XL1M
Comparison of electric drive fuel consumption (kWh/100 miles). Data: Volkswagen, US EPA and DOE. Click to enlarge.

Volkswagen has begun limited production of the XL1; 50 units are being built initially, with 250 slated for build.

Initial visual impressions. XL1 is visually striking; 153.1 inches long, 65.6 inches wide, and only 45.4 inches tall. By comparison, a Volkswagen Polo is slightly longer (156.3 in) and wider (66.2 in), but is significantly taller (57.6 in). Even a sportscar like the Porsche Boxster is 5.1 inches taller than XL1. (When you scoot alongside a heavy-duty truck and trailer combo, you realize how low to the ground you are.) Its aerodynamic shape appears bio-inspired by aerodynamic swimmers—similar to a dolphin, as Volkswagen says, or to a boxfish. (Earlier post.)

2013-06-21 14.46.08
The XL1 with door-mounted camera clearly visible. Click to enlarge.

XL1 represents the third evolutionary stage of Volkswagen’s 1-liter car strategy, referring to the goal set by Prof. Dr. Ferdinand Piëch—currently Chairman of the Supervisory Board of Volkswagen AG—more than 10 years ago to produce a practical car that had a combined fuel consumption of one liter per 100 km (235 mpg).

With XL1, the engineers and designers successfully came up with a body design that delivers more everyday utility than the two previous prototypes. In the L1, the 1-liter car that was shown in 2002 and 2009, the driver and passenger sat behind each other for optimal aerodynamics; in the XL1, the two occupants sit slightly offset, side by side, almost as in a conventional vehicle.

The XL1 uses scissor doors; hinged low on the A-pillars and just above the windshield in the roof frame, they swivel upwards and slightly forwards as well. The doors also extend far into the roof. When they are opened, they create an large amount of entry and exit space.

XL1A
The offset seating in the XL1 not only enables shoulder room for the driver and passenger, but also provides the location for the placement of the 5.5 kWh Li-ion battery pack—which is sited in front of the passenger area. Click to enlarge.

In profile, the roofline traces an arc from the A-pillar back to the rear. The rear wheels are fully covered to prevent turbulence, while airflow around the wheel arches is optimized by small spoilers in front of and behind the wheels. There are no door mirrors: these are replaced by small cameras known as e-mirrors (digital outside mirrors) that send images to two displays, one in each door.

Despite its aggressive design, the XL1 can still be considered a practical car. It is roomy and pleasant for two passengers; entry is convenient—despite the low body—due to the large door openings; it offers an adjustable driver’s seat and steering wheel; comes with the expected full range of multimedia devices with radio, navigation, Internet; offers air conditioning and PTC auxiliary heating; and has a cargo capacity of approximately 4.2 cubic feet. Cruise control, ABS and electronic stabilization program, and a parking assistant all contribute to a “modern” level of driver assistance.

Driving—initial impressions. The XL1 is not a sprinter (0-100 km/h in 12.7 seconds), but it doesn’t feel as though it lacks for power or struggles at its higher speed range. Attaining cruise speed or overtaking on the highway just takes a bit longer. XL1 has no power steering, but is very nimble and easy to control due to its aerodynamic shape and light weight.

Coasting at higher speeds is noticeably different than in other vehicles—with its very low coefficient of drag, the XL1 feels as if it is slipping through the air, not battering its way ahead.

The brake regeneration strategy is very aggressive. Unlike the e-Golf, for example, which uses its paddle shifters to allow the driver to click through three different settings for regen (earlier post), XL1 goes for as much energy as it can get, every time.

It is relatively easy to become accustomed to the position of the e-mirror screens in the doors and the lack of outside mirrors. It’s a bit more difficult not to have a central rear-view. Since the engine compartment is behind the driver and passenger’s head, there is no rear window, but a central rear-view camera display would be helpful, especially with backing up.

Occupants of the XL1 cabin will experience more noise than the level to which they are likely accustomed. Sound baffling brings extra weight, and the VW engineering team was determined the break the upward spiral of weight gains in vehicles (e.g., more features makes a heavier car, which requires more power, which requires a larger engine, etc.). As a result, there is minimal shielding of the noise that accompanies any car when it is driving.

The two-cylinder diesel is very audible when it runs. Braking too yields its own sound with which drivers will be largely unfamiliar. The ceramic brakes make a sound similar to sliding out on gravel, or swooshing through water. Until the driver becomes accustomed to the noise, in other words, it sounds as if something might be amiss. Nor is there much cushioning from road noise. Rolling over a manhole cover, for example, is initially a bit startling.

However, those design decisions contributed to the extreme fuel efficiency of the XL1, the engineers point out.

Powertrain. The XL1 is a rear wheel-drive plug-in parallel hybrid, using a 48 hp 0.83L, two-cylinder TDI common-rail turbodiesel with aluminum block; a weight-optimized magnesium seven-speed DSG dual-clutch automatic transmission; a 27 hp traction motor; and a water-cooled 5.5 kWh Li-ion battery pack. The entire hybrid unit is housed between the driven rear wheels. The hybrid module, which incorporates the electric motor and the clutch, is positioned between the TDI engine and the seven-speed DSG transmission.

XL1B
The hybrid power unit. Click to enlarge.

 

XL1C
Layout of the XL1 powertrain. Note the position of the battery pack on the passenger side, which also helps with weight distribution in the car (with one driver). Click to enlarge.

The XL1 is not a product of any of Volkswagen’s modular Baukästen (assembly kits such as the MQB, MLB or MSB, earlier post). Nonetheless, some of the learnings from the XL1 will flow back to inform the evolution of the different kits, such as to the MQB which has its own plug-in hybrid powertrain, to make its debut in the A3.

XL1D
XL1E
Components of the XL1 plug-in power unit. Click to enlarge.   Components of MQB plug-in hybrid power unit. Click to enlarge.

The 5.5 kWh lithium-ion battery—integrated in the front section of the XL1—supplies the electric motor with 220 volts of electrical energy. The battery comprises 60 25Ah cells, with a carbon-fiber case. The power electronics system manages the flow of high voltage energy to and from the battery or electric motor and converts direct current to alternating current. The XL1’s 12-volt electrical system is supplied via a DC/DC converter and a small auxiliary battery.

The TDI delivers 89 lb-ft (120 N·m) of torque from its 830 cc. The electric motor, which generates up to 103 lb-ft (140 N·m) of torque from a standstill, works as a booster to support the TDI engine when full system power is required. Together, the TDI engine and electric motor deliver maximum torque of 103 lb-ft along with 68 hp in boosting mode.

XL1F
Comparing the rear-wheel drive XL1 plug-in hybrid powertrain layout to that of the front-wheel drive MQB plug-in hybrid powertrain layout. Click to enlarge.

As well as boosting the TDI engine under hard acceleration, the electric motor can also power the XL1 on its own for a distance of up to 31 miles. In this mode, the TDI engine is decoupled from the drivetrain by disengaging a clutch, and is shut down.

Meanwhile, the clutch on the gearbox side remains closed, so the DSG is fully engaged with the electric motor. The driver can choose to drive the XL1 in pure electric mode, provided that the battery is sufficiently charged, by pressing a button on the instrument panel.

Restarting the TDI engine is a smooth process. While driving, the electric motor’s rotor is sped up and is very quickly coupled to the clutch in a process known as “pulse starting”. This accelerates the diesel engine to the required speed and starts it, so the driver hardly notices the transition. In certain operating conditions, the load of the TDI engine can be shifted so that it operates at its most favorable efficiency level.

The XLI can be also be put into a charging mode, which runs the engine at a slightly higher point that required, using the excess power to generate electricity to recharge the battery.

XL1G
Power and torque curves for the XL1. Click to enlarge.

(In our brief driving experience, whenever the TDI kicked in, it went straight to 2,000 rpm (according to the tachometer). Volkswagen engineers said that seemed a bit high.)

Some of the parameters used to realize the optimum propulsion mode for the given conditions are accelerator pedal position and demanded engine load, as well as the energy supply and mix of kinetic and electrical energy at any given time. The already complex control strategy is made even more complex by the requirements of the diesel engine, as well as emissions control (e.g., DPF regen events, etc.)

The gears in the DSG transmission are also always selected with the aim of minimizing energy usage.

The 0.8-liter two-cylinder TDI engine was derived from a 1.6-liter four-cylinder engine, so it shares the 88-mm bore spacing and a bore and stroke of 81.0 mm x 80.5 mm. The XL1’s engine also shares key internal modifications for reducing emissions, which include specially formed piston recesses for multiple injection and individual orientation of the injection jets. The common-rail diesel’s smooth running properties were transferred to the two-cylinder engine, aided by a balancer shaft that is driven by and turns at the same speed as the crankshaft.

The TDI’s aluminum crankcase is constructed with extremely low tolerances, which in turn leads to very low frictional losses. Exhaust gas recirculation, an oxidation catalytic converter, and a diesel particulate filter are used in order to minimize emissions: the XL1’s engine is already compliant with the Euro-6 emissions standard.

The vehicle’s cooling system is also designed to maximize efficiency. The mechanical water pump actively cools the engine only when operating conditions require it. The system includes automatically controlled air intakes at the front of the vehicle to reduce drag. A second electric water pump, used only when needed, circulates a separate lower temperature loop to cool the starter generator and the power electronics. This thermal management strategy also contributes towards reduced fuel consumption.

Materials and weight. The XL1 utilizes lightweight and extremely strong carbon fiber reinforced polymer (CFRP) construction for the monocoque, all exterior body parts, and components such as the anti-roll bars. Produced using the Resin Transfer Molding process (RTM), the density/specific gravity of the CFRP is around 20% of a comparable steel exterior structure’s. The CFRP parts are as strong as comparable steel or aluminum parts, yet the exterior skin of the XL1 is just 0.05 inches thick.

XL1H
XL1I
CFRP monocoque. Click to enlarge.   Assembly of front structure. Click to enlarge.

 

XL1J
XL1K
Assembly of rear structure. Click to enlarge.   Manufacturing and installing swivel door (CFRP – Prepreg). Click to enlarge.

Compared to manufacturing CFRP in a pre-preg process, the RTM process is more economical—with lower costs at higher volumes—because it can be automated. The RTM parts are produced in multi-shell heated and vacuum-sealed molds. This involves injecting liquid resin at high pressure into the tool which contains the semi-finished carbon material. The part is then cured in the mold.

The XL1 weighs just 1753 pounds (795 kg), consisting of:

  • 501 lb (227 kg) for the drive unit including battery (231 lb, 105 kg);
  • 337 lb (153 kg) for the running gear;
  • 176 lb (80 kg) for the interior;
  • 232 lb (105 kg) for the electrical system; and
  • 507 lb (230 kg) for the body, including crash structure and windshield.

A total of 21.3% of the new XL1, or 373 lb (169 kg), consists of CFRP. In addition, Volkswagen uses lightweight metals for 22.5% of all the parts (395 lb, (179 kg), with just 23.2% (406 lb, 184 kg) of the car being constructed from steel and iron.

As an example, the seats are made from CFRP and weigh 25.6 lb (11.6 kg) each, or about half the mass of a normal car seat. The seats are also very comfortable.

As another example of the use of lightweight materials, polycarbonate side windows weigh about a third less than conventional windows: a pane of glass on XL1 would weigh 16.5 lb (7.5 kg), whereas the polycarbonate ones weigh 11.5 lb (5.2 kg) each.

(Volkswagen purchased an 8.18% stake in SGL Group—one of the world’s leading manufacturers of carbon-based products with a portfolio ranging from carbon and graphite products to carbon fibers and composites. (Earlier post.) SGL is partnering with BMW in a joint venture to produce carbon fiber for automotive applications; BMW owns 15.6% of SGL.)

The weight of the running gear is also reduced by the use of many lightweight components. Aluminum is used for parts such as the suspension arms, brake calipers, dampers, and steering gear housing; the anti-roll bars are made from CFRP; the brake discs are ceramic; the wheels are case in magnesium alloy; and the steering wheel body is plastic.

The car is also designed to reducing rolling resistance, with friction-optimized wheel bearings and driveshafts, as well as ultra-low rolling resistance Michelin tires, sized 115/80 up front and 145/55 R16 at the back.

Safety. The CFRP monocoque is not only light weight, but provides a survival cell for the driver and passenger. This is achieved by the intelligent design of load paths, including the use of sandwich structures in the monocoque, while the front and rear aluminum crush structures absorb a large share of energy in frontal and rear collisions.

Frontal crash protection measures include aluminum crash tubes with crossmembers, a sandwich structure (CFRP / PMI foam) in the firewall, and an airbag in the steering wheel.

The CFRP doors have aluminum impact beams to absorb crash energy and the door frame also minimizes intrusions into the safety cell. A great deal of attention was also paid to extricating occupants in the event of a rollover collision: pyrotechnic separating screws are used to simplify opening of the doors, which ordinarily open upwards.

Rear crash protection measures also include aluminum crash tubes with cross members.

XL1L
Click to enlarge.

Volkswagen hosted Green Car Congress at the Wolfsburg event.

June 24, 2013 in Diesel, Hybrids, Plug-ins | Permalink | Comments (19) | TrackBack (0)

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Will they ever sell it, or is it just for journalists and shows and a bit of trickle down to the golf ?
OK, they plan to make 300 of them.
They should have 2 versions - a "pure" version as described, and a "domesticated" version with better soundproofing, etc. to make it easier to live with.
The "pure" would get the headlines, the "domestic" would sell.
Lots of people would like this - all the prius early adopters without any kids could use it, or use it as an commuter car and us the Prius as a family wagon.

However, it may be worth it in technology development alone - it is such a full on economy vehicle that they learn a lot without being polluted by considerations such as comfort.

they should drop this complicated transmission and makes it a pure EV with 200Kg of battery that could have a 300miles range instead

Agreed, VW recently admitted that they are buying automotive grade LiIon for under 200 Euros per kWh. Give one of these a 35 kWh pack (175 kg) and you've got >180 miles EV range for 7,000 Euros. Half the weight and cost again should Envia make good on their claims.

This is what the Volt was supposed to do (235/mpg) but it ended up being about 89/mpge.

The Prius (IV+) will be improved to 70/mpg with 2+ kWh of lithium batteries but would require 10+ kWh of ultra light batteries and lighter body to do 120+/mpge.

I've been following the development of this car ever since the prototype VW-L1 and yet this is the most detailed article I've ever seen. Thanks Mike.

Diesel hybrid is the future of green cars. 261 mpg (0.9L)/100km is fantastic. This car is an excellent technology showcase, and even a practical car.

But the most important point is the following:

The VW XL emits less CO2 when driven as a hybrid than when driven as a plug-in, by a factor of 2.5. The numbers tell the truth:

0.1 kWh / 1km * 522g / kWh = 52g / km ~= 2.47 times 21g / km

The average grix mix in the US in 2010 was 522 gCO2/kWh (*). Until we get the grix mix number down to less than 200g/kWh, it is better to drive an XL than an electric car, and use any incremental supply of non-fossile electricty (solar, wind, etc) to dial down the coal plants.

Reference: See page 113 of the following document

http://www.iea.org/co2highlights/co2highlights.pdf

When you have a vehicle as efficient as this, it barely matters what you power it by.
For instance, a pure diesel would work very well, as would a diesel (or gas) hybrid.

What is important is to get them out in volumes and at prices that people will pay.

(I still think they will need more sound insulation - it doesn't matter how efficient a vehicle is if it horrible to be in.)

It is great to see VW really sticking with this for over 10 years, I suppose it can come from both engineering and marketing budgets.

0.16 kWh/mile vs. 0.3 for more "normal" EVs.

13,000 annual miles at $0.11/kWh. A normal EV would cost about $16 per month in additional electricity costs. And since we're seeing special off-peak charging rates of around $0.04/kWh that difference drops to about $6 per month.

That small a difference is not likely to pay for expensive vehicle efficiency. Much cheaper to just add more wind or solar capacity to the grid.

@Bob,
I think the point is that you can go twice as far with the same size battery.
The cost of the electricity is already tiny.

“The cost of the electricity is already tiny. ”

Energy is a very cheap commodity in all its forms. For most people is is a small fraction of the cost of living. That is why BEV are MIA. If you do not drive very far on a daily basis, a BEV is practical but will not save much because you do not use much fuel.

If you spend a lot of time in your car saving money gets old. I had a friend who commuted long distances to save money in a GEO metro. He traded it in on a Suburban.

“13,000 annual miles ”

That works out to a 50 mile a day commute. That works out 500 hours a year driving to work assuming you are not stuck in traffic. Who does that?

“The average grix mix in the US in 2010 was ..”

BEV in the US re not powered by the average but the specific power plant loading following at that time the BEV is charging. In the US that would be a coal plant.

Sure you can make up a scenario where you save money or reduce ghg but the actual case is that actual case for actual people is that you d not save money or reduce environmental impact.

That is bad choice.

"you can go twice as far with the same size battery"

Yes. And that might make the 'cost of efficiency' work.

Higher energy efficiency vehicles, i.e. moving from A to Z with less energy) is what many car manufacturers will have to learn to do.

VW has proven that it is possible to move a better designed vehicle for 100 Km with less than 1 liter of fuel (about 235 miles/gal)

With appropriate efforts, others could do the same or even much better.

Those cars could be fully electrified for 500+ Km between recharge with current best performance batteries and up to 1000+ Km per charge by 2020 or so?

This excellent and record-setting ultra-efficient vehicle is an excercise in high-efficiency technology, including the extensive use of light-weight material. The choice of a 2-seater configuration and a diesel engine is simmply to allow the vehicle to set record as a 1-liter vehicle, capable of traveling 100km using 1 liter of fuel. Valuable information and experience learned from this excercise will be applied to mainstream 4-5-seater vehicles.

A more practical higher-volume production model would have to have at least 4 seats. For a practical PHEV version, a light-weight and low-cost gasoline engine like those used in motor cycle can be used. A 2-cylinder 500cc 50-hp motorcycle engine would suffice as a range extender, having half the weight and a fraction of the cost of the diesel engine, while the battery and motor can supply 20-30-mi range on electricity. With more powerful motor and battery, the geared transmission can be eliminated, and the vehicle can have purely electric transmission. This electric transmission can have two-motor-generator set, which can act in parallel as a very powerful electric boost to the ICE's torque, or in series at low speeds in charge-sustaining mode when the engine must turn faster than the drivetrain's speed. This will allow far better acceleration than the current XL1 can do right now, while eliminating transmission friction during cruise that can improve efficiency a bit more.

With more manufacturing experience gain from the use of light-weight components, a light-weight PHEV will not necessarily cost more than a heavier PHEV made from conventional heavier components, because the weight and cost of the battery pack, motor, controller can all be saved, balancing out the higher cost of light-weight materials used. This XL1 here is certainly a step, or rather a big milestone, in the right direction.

CFRP cost 40 times as much as aluminium, according to a VW engineer (said at the Qatar motor show).

A 2-stoke 50 hp engine will be noisy and inefficient. The current choice of diesel engine ensures high fuel efficiency in the relevant load scenarios.

A stronger gear box will solve the XL1's acceleration issues, since there is plenty of torque to go around from the two motors. The combined torque of the two power plants is essentially double of what the gearbox limits. This brings the XL1 down into the 7-8 sec range 0-100 km/h.

I say, put a stronger gearbox in it. Allow it to gain 1-200 kg from said gearbox, cheaper materials, a bit of sound insulation and you have got yourself a sweet one-person long-distance commuter car.

I have heard many people say this car should have just a diesel engine to make it cheaper. But an aerodynamic car like this would have a (non-limited) top speed of 250+ km/h with a diesel strong enough to give it decent acceleration. That is why it needs to be a hybrid, plug-in or not. But with enough e-motor torque assist for acceleration that may require a battery large enough to warrant plug-in. Anyway, the plug-in feature itself is not expensive. The battery has to be large enough to support that kind of power draw.

Even in the current configuration, the power of the diesel is enough to sustain almost 200 km/t, which should be 'entertaining' in a car with bicycle front wheels ;-)

Comment on regeneration: I would prefer strong 'engine brakes' when you let go of the gas. Most of the time you take the foot off the gas, it is because you want to reduce the speed, preferably without engaging the brakes. And seeing as this car has near-zero wind resistance, it would go on forever coasting, which is never a realistic nor useful scenario.

Sorry, Thomas, but I cannot understand many of your points!

CFRP is not more expensive than aluminum! Many gun frames are now made of CFRP, for example, the Bushmaster Carbon 15, the whold Glock line up, S&W polymer frames, Kahr 9 and 10 SW, CZ-7P, etc...the list is too long...and these polymer framed versions cost LESS than the aluminum counterparts. The Bushmaster Carbon 15 (knock off of the Colt AR-15) sold for hundreds of dollars less than the XM-15 used in the alledged Sandy Hook shooting.
In the field of R/C helicopter, aluminum alloy rotor heads cost more than CFRP heads! Machining costs more than injection molding.

The Ninja 500-cc 2-cylinder engine is a FOUR stroker, not a two-stroker, and can be made quiet with exhaust emission system and adequate muffling. A motorcycle engine is purposely made with little muffling for the enjoyment of motoring. The engine sound is music to the ears of the motorheads, myself included.

Putting a stronger gear box and incurring more weight, friction, and cost? For what? In a PHEV, you'll need a strong electric motor anyway, to provide adequate acceleration. IMHO, it is counterproductive to put a gear-shift transmission on a PHEV!

Strong engine brakes? LOL...Hello, this is a PHEV...You actually meant strong electric motor energy recuperation, didn't you? Engine braking has no role in a PHEV!

Roger,

I do not know about the guns that you are referring to. I am merely quoting Dr Harald Ludanek of VW. I do not know about those prices myself. But I imagine that it matters how many parts you can put into one curing oven at the same time.

Sorry about misreading 2/4 stoke. My point still stands that motorcycle ICEs are very inefficient at part load. All experience here in Europe is that diesel are quieter than gas engines due to the lower rpm. And the 'diesel rumble' only occurs at high load.

You will notice that the e-motor delivers 140 Nm and the ICE 120 Nm but the gearbox only allows 140 Nm in total. That is why acceleration is so poor.

I do agree with you that a PHEV should not need a gearbox at all, but only run the ICE 'in the highest gear', as I believe we have discussed before (if my memory serves me. This car certainly have the electric capability to run without the ICE below highway speeds. But VW chose this configuration - most likely to test the configuration that will still be the most likely on their real production cars.

Yes, of course I meant electric motor energy recuperation! DUH! Do you take me for an idiot?

But I was referring to the feel of engine braking. Many manufacturers are now advertising the gliding capability of their automatic transmissions. I hate gliding! I find it useless, whereas engine brakes/electric recuperation helps slow the car down and reduce energy consumption when approaching a corner/red light/stop sign.

@Thomas,
Motorcycle engine is not as efficient as a diesel, however, when used only at its peak efficiency, and only occasionally, not daily, perhaps the weight and cost saving of the motorcycle engine may outweight the heavier and more expensive diesel engine.
The PHEV should have at least 20-30 mile range on battery, such that is charged once or twice daily, will cover daily driving needs for most of the time. Eventually, most malls or business parking will have charging receptacle for quick juice-up, thus further extending the electric range of the PHEV. Thus, the ICE will only be rarely used, thus should be as small, light, and low-cost as possible.

I think that automatic regen braking should be optional and adjustable via a knob on the dashboard or steering wheel. I hate automatic regen braking,and has to step on the gas pedal slightly for coasting, to remove automatic regen, when dring the Prius. I wish I can dial that out, and only regen when the brakes is pressed gently. I like power and glide, use the ICE to accelerate the vehicle, and coasting it as much as possible.

Have no mechanical gear train, just electrical, with a genset optimized for efficiency buffering through the battery pack. A lightweight, air-cooled Hatz B40 single-cylinder diesel would work as a genset engine and be much less expensive than the VW setup.

Hello All,
In the discussion of diesel versus gasoline engines keep in mind that the differences are shrinking. The compression ratios of gasoline engines are now commonly 11-12:1 with Mazdas 13-14:1 being the highest. Mazdas diesel is also 14:1, so weight and cost ranges will begin to narrow. Homogenous Charge Compression Ignition maybe the future! Also, maybe someday two stroke direct injection will be environmentally friendly enough for on road use.

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