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Volkswagen combines XL1 powertrain with up! for the twin up! concept plug-in diesel hybrid; 214 mpg

Introducing the twin up! Click to enlarge.

Volkswagen presented the twin up! concept car at the Tokyo Motor Show. Equipped with a plug-in hybrid system from the super-efficient XL1 (earlier post), the four-seater based on the up! city car achieves combined fuel consumption of 1.1 liters per 100 km (214 mpgUS) (NEDC), with corresponding CO2 emissions of 27 g/km.

All new Volkswagen vehicles are configured to accept alternative drive systems as well as conventional ones, making installation of the compact XL1 plug-in hybrid system in the twin up! relatively easy. The only modification made in the production version was to lengthen the up!’s extremely short front overhang by 30 mm. The drive unit of the twin up! (system power: 55 kW) is mounted at the front of the car. It comprises a two-cylinder 0.8L TDI (35 kW); electric motor (35 kW); a 7-speed DSG (DQ200E) and the power electronics.

From XL1 to twin up! Click to enlarge.

The two-cylinder TDI was derived from a common rail four-cylinder (1.6-liter displacement). The 0.8-liter TDI has a cylinder spacing of 88 mm; its bore is 81.0 mm, and its stroke is 80.5 mm. Besides reduced engine displacement, other emissions-reducing measures were implemented such as specially formed piston recesses, multipoint fuel injection and controlled orientation of individual injection sprays. Smooth running of the small engine is ensured thanks to a balancer shaft. An exhaust gas recirculation system, oxidation catalytic converter and diesel particulate filter are used to reduce emissions values.

Located between the TDI and the 7-speed DSG is the hybrid module with an electric motor and decoupling clutch; this module was integrated in the DSG housing in place of the usual flywheel. The electric motor is supplied with energy from the 8.6 kWh lithium-ion battery that can be charged by the TDI. The power electronics, which operate at 308V, manage the bidirectional flow of high-voltage energy between the battery and the electric motor and convert direct current to alternating current.

The engine compartment of the twin up! is completely covered. All service access points are in maintenance-friendly locations. A matt black engine compartment cover with acoustic insulating effect organises all recognizable components, providing for better organisation. The power electronics, and the service access located across from it, are integrated in a high-gloss black band, which also functionally partitions the engine compartment. A central acoustic capsule unites design themes from the world of combustion engines and electric motors; the electric elements are coded in the color blue.

Phantom views of the twin up! Click to enlarge.

The two “tank systems” are located in the back, underneath the rear bench seat and the luggage compartment: the lithium-ion battery as well as a 12 V battery for the vehicle’s electrical system and a 33-liter (8.7 gallon) fuel tank.

In all-electric operation the twin up! can cover a range of 50 km (31 miles). The twin up! accelerates up to 60 km/h (37 mph) in 8.8 seconds and has an all-electric top speed of 125 km/h (78 mph). The components of the plug-in drive system give the concept car a top speed in hybrid operation of 140 km/h (87 mph) and at the same time provide a high torque for a small car of 215 N·m (159 lb-ft).

In electric mode, the TDI is decoupled from the drivetrain by opening the decoupling clutch and is shut off. Meanwhile, the driving clutch on the gearbox side remains closed, and the 7-speed DSG is fully engaged. Provided that the battery has a sufficiently high state of charge, the driver can choose when and where the twin up! should be driven all-electrically by simply pressing the e-mode button.

Later, the process of restarting the two-cylinder engine is a very smooth process. When a "pulse start" of the TDI is performed while driving, the rotor of the electric motor is revved, and the engine-side clutch is engaged very quickly. This turns the TDI, accelerating it to the necessary engine speed, and starts it.

When the twin up! is braked, the electric motor operates as a generator; its braking energy is used to charge the battery. Load point shifting of the TDI, which can be performed under certain operating conditions, has a positive effect on engine fuel efficiency, including energy usage in the hybrid system. Load point shifting makes the turbodiesel operate at more favorable efficiency levels, and excess energy can be fed to the battery.

Another method for improving fuel efficiency is in gear selection of the automatic 7-speed DSG. The engine controller regulates the entire energy and drive management system based on the specific load demanded by the driver. Parameters flowing into this control system include the accelerator or e-pedal position, engine load, energy supply and mix of kinetic and electric energy, so that the system always uses the optimal type of propulsive power.

Controls and display components were redesigned for the twin up!, and user control, status display and climate control functions on the concept car were implemented entirely in digital form.


Freddy Torres

Exactly the correct approach! Now VW can continue increasing the power output of the electric motor and battery while keeping the size of the diesel engine the same. Notice that at 214 mpg, the price of electricity and the diesel per mile travelled is nearly the same! This means you no longer feel restricted to use liquid fuel. Instead, you would only feel compelled to charge up when electricity is produced from clean sources.


This is almost the same mpg indicated by New GM for the Volt PHEV before it was reduced by 70+% to something like 89 mpge.

Will the same thing happen to this small PHEV.

If (probably) not, this small PHEV may be the answer for and all around vehicle for students, to go to work and drive around town etc.


This shows that there is no need for a conventional EV. The need for rare elements/metals, which would limit the use of EVs in the foreseeable future, must be substantially reduced in this PHEV compared with the EV version of the same car.

As a remark, it should be noted that the current EU regulations to calculate fuel and electricity consumption for PHEVs and EVs is very, very favourable. Therefore, the figures provided by VW (according to these regulations) are not at all realistic compared to normal traffic and average EU electricity generation. Of course, this bias applies to both PHEVs and EVs in comparison to conventional vehicles. This can just be considered as another incentive from the EU.

Furthermore, when comparing cost for fuel and electricity, one should note that the tax on electricity in EU (and Germany, as in the e-up! example by VW in previous GCC article) is far lower than on fuel. In addition, both taxes are applied at the “sales point” and does not take into account the poor efficiency of electricity generation and distribution (~30% from fossil/nuclear resources) in comparison to fuel production and distribution (>80%). Cost comparisons on a neutral basis (i.e. without taxes and incentives) would give quite different results for the operating cost.

Nick Lyons

Interesting concept, but too slow as currently configured--a practical car where I drive (California) has to be able to get out of its own way. I wouldn't feel safe driving something like this on our freeways--simply merging with traffic would be hair-raising. They need to get the 0-60 time down to 10 seconds or so.


Peter XX:
Perhaps you would be specific and list the rare earth elements/metals which are needed in BEV and PHEV cars and are not in conventional cars, as I am not aware of any which are essential to them which are not needed in an ICE.


I might be interrested to buy in 2025 or so when i gonna need a replacement. Slow acceleration is not a big problem as i often drive alone in the car. With this car the advantage is that you can measure the outside wind velocity as it impede or help accelarations. Can we remove the ice for added mpg when we know that we are not going far ?


The ICe is built in, and you won't want to be pulling it out and putting it back again - unless you regularly do that for your conventional car!

Roger Pham

This is Smart! Very Smart. A very logical follow up to the XL1. But it can be yet further improved for even better mpg and much better acceleration!

For better mpg, adopt a more aerodynamic body. Also, eliminate the 7-speed DSG with its associated weight and internal friction. Downsize the fuel tank to 3 gallons for about 600-mi of range. Who needs 1600 mi of range while exposed to increase risk of fuel fire? (More fuel on board, higher risk of fuel fire damage due to higher fuel volume, plus because the smaller fuel tank can be built much stronger to prevent rupture in the case of a survivable crash)

How can the fairly bulky 7-speed DSG (according to the photo shown) be eliminated while having better mpg and acceleration? By adding another Generator/motor right next to the drive motor, connected via a clutch. No gear-change transmission!

Adding another e-motor will significantly boost all-electric acceleration and top speed. The anemic 7-speed DSG is limited to 55 kW! By adding another e-motor/generator of 35 kW, we now have 35 kW of ICE + 35 kW of drive motor + 35 kW of gen/motor = 95 kW of raw power! You can see that the 35 kW motor is fairly small in comparison to the bulky and anemic 7-speed DSG. Even adding another 35 kW motor, one will still have significant space saving.

In engine-only acceleration at slow speeds, the two motors will simulate gear-change transmission by having he engine driving the gen/motor while using the current generated to drive the drive motor. Acceleration in this mode will be slow, but only necessary when the batter is damaged or weak. Normally, the 8-kWh battery, if capable of 10 C max discharge, can provide 80 kW of power to supplement the coupled torque of the engine, for a very spirited acceleration, using 70 kW of combined motors power PLUS the engine's direct torque. Acceleration will be in the sport-car range. Top speed will be much better as well...until the battery runs out of juice, then one will be down to the anemic torque of the 35 kW engine...but enjoy the top speed while battery lasts, which will be quite many minutes of thrill, especially in a much more aerodynamic body! A PHEV should not need gear-change transmission.

Roger Pham

Correction to above: 35 kW of engine + 35 kW of gen/motor + 35 kW of drive motor = 105 kW of raw power! (not 95 kW of raw power as I erroneously posted) This should nearly double the power available for acceleration and top speed!

Roger Pham

Furthermore, having only a 35-kW motor would make for efficient cruise on electric power alone, but not for efficient acceleration by lead-footed driver, because the motor will be pushed to its limit and suffer from high ohmic loss. By adding the 35-kW motor/gen, acceleration will be more efficient when kept at the same acceleration force generated by the single 35 kW motor. During cruise, the motor/gen can be de-coupled to maintain electric-mode cruise efficiency as before.


This is quite a tech-fest but you wonder how much it would cost, and how many could be sold ?

It is a great idea, but the Up is very small.

I wonder what would happen if you but the package into a Polo or a Golf.
If you are going to spend that much on a car, you want a reasonably sized one. The problem then is how to get enough power to handle the weight.
Does VW have a 3 cylinder version of that engine ?

Roger Pham

Yet furthermore, with 105 kW of total power on tap (189 hp) why limit this power train to the diminutive and unaerodynamic up! body? Mate it to the voluptous, curvaceous and aerodynamic VW CC lineup and enjoy much higher sales and profit margin! See:

Of course, the CC-line body should undergo some form of weight reduction by making lighter chassis and lighter body panels, now with lighter power train, to maintain the high efficiency of the PHEV power train, and this is totally doable. The end result is a 5-seat PHEV that is very desirable to have by all segments of consumers, yet having high profit margin and reasonable purchasing cost while using only a dimunitive ICE of 0.8 liter and having plenty of cargo space and passenger space, having only a 4-gallon fuel tank. This combination will usher into a new age of PHEV's, with price and internal space competitive with a comparable ICE, yet with very low energy cost and maintenance and repair costs.


RP. . would you also make it an AWD while at it or would that be restricted to the CC-line only?

Roger Pham

Good point, HD, since AWD will give more value to the car, while in a PHEV, AWD is much easier and cheaper to make than in a conventional AWD ICEV. An AWD vehicle would give better traction in poor road condition and in hilly area, and an electrically motivated AWD can result in better automatic stability control system.

However, AWD should be an option only and only in larger vehicles like the CC line or Jetta line. AWD is more complicated in that you'll need a second set of differential gears, more complex rear-wheel suspension, and that the rear wheel drive motor can intefere with the mounting of the battery pack and the fuel tank. However, with only a 4-gallon fuel tank, the packaging should be much easier. The battery pack can be split in half, with some battery capacity in the front under the hood, in order to maximize trunk (boot) space, in the AWD version.

I'd like to make a small correction to the hp number, though. 105 kW is equivalent to 141 hp, not the 189 hp I stated above. However, instead of using the diesel engine for the PHEV version, VW can use 1/2 of the 2-liter SOHC gasoline engine in the VW Jetta instead, that should be good for 40 kW. Then, adding a 40 kW drive motor and 40 kW generator/motor2, will boost power to 120 kW, or 161 hp, and that should be good enough for a larger compact size vehicle like the CC line.

Ford can do the same for their PHEV line, by using 1/2 of the 2-liter 142-hp gasoline engine, that should be good for 53 kW, and that is quite a bit more powerful than the VW Jetta 2-liter gasoline engine 115-hp of the same displacement.





Replacing the ICE genset with a small (30 KW), 3+KW per liter FC and using improved batteries could power an AWD CC-line unit for up to 300,000 miles without using liquid fuels?

Roger Pham

The problem w/ FC and H2 is that H2 is a much bulkier fuel than gasoline, requiring volumes 3-6x as much, as well as much heavier container that is also much more expensive (10 folds) than a gasoline tank. A PHEV already has a heavy and bulky and expensive battery pack. Adding another very bulky, heavy and expensive H2 tank would be too much!

Also, H2 is much less available than gasoline. A PHEV-40 charged once daily, or a PHEV-20 charged twice daily, can cut fuel consumption by 80%, or a 5-fold reduction in fuel usage. At that low rate of fuel usage, they can use future synthetic liquid fuel that will be entirely CO2-free.


Diesel Hybrid is the way to go, as I have been saying for 5+ years now, and VW has just put the last nail in the coffin of the naysayers.

It is amusing how HarveyD and others are contorting themselves to hide their past errors by suggesting that the TDI engine should be replaced by hydrogen fuel cells and other such nonsense. It must be difficult to be so wrong all the time.

VW now just needs to create a regular Golf or Jetta with a twin-drive system. The Golf TwinDrive prototype of ~2011 already got 70+mpg. Now make a Golf/Jetta/SportWagen that gets 100 mpg EPA and we can cut oil consumption to 1/4 the current average. BOOM, done. That will buy us much needed time for the next quantum leap in automobile efficiency.

Do it VW, and do it NOW!


>>All new Volkswagen vehicles are configured to accept alternative drive systems as well as conventional ones, making installation of the compact XL1 plug-in hybrid system in the twin up! relatively easy.

This sounds VERY promising. When do we get a GOlf or Jetta with TwinDrive?


You may not see the attraction of making the vehicle all electric with the addition of a fuel cell RE, that does not mean that it is not a good idea.
A drastically reduced part count, and the elimination of whole systems such as the gearbox and high temperature exhaust to name just two, together with the zero pollution at point of use of a fuel cell RE make it a fundamentally more advanced system.



I agree, a PHEV with a fuel cell instead of an engine makes sense. Reform methanol and use an HT PEM, the cost per mile should be very good.


@HD, @RP,
To further lighten the vehicle, provide for AWD and improve fuel economy why not move to wheel hub electric motors, decoupling the TDI from the drive train all together. Instead have the TDI drive a generator geared to allow the TDI to always operate at its highest efficiency. The TDI would then only operate to recharge the batteries or if juice was needed for acceleration. This would drop the transmission, drive train, axels and other mass, allow for downsizing of the fuel tank and permit installation of a higher capacity battery pack for extended EV range. With the elimination of the drivetrain and reduced complexity, the cost should be further reduced. This platform would be very easy to install in virtually any vehicle configuration.

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