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Innas and NOAX to Show Hydraulic Series Hybrid Drivetrain at Hannover Messe

The Hydrid drivetrain. Click to enlarge.

At the Hannover Messe, 20-24 April, Innas BV and NOAX BV will introduce the latest design of the Innas hydraulic transformer (IHT) and the “Hydrid”, a hydraulic series hybrid drive train for passenger cars and off-road equipment. With this new design, the fuel consumption of a vehicle can be more than halved, with a corresponding reduction in CO2 emissions of 50%, without compromise on weight, size, traction or top speed, according to the companies.

In a Hydrid, the complete mechanical drive train of a car is replaced by a full hydrostatic transmission, allowing energy recuperation and more efficient operation of the engine operation. The backbone of the Hydrid is the hydraulic common pressure rail (CPR) system, which collects and distributes the power inside the vehicle. The accumulators determine the pressure levels in the system. On the high pressure side, the pressure varies between 200 and 400 bar (20 to 40 MPa).

The internal combustion engine powers a constant displacement pump. The engine torque is directly related to the pressure in the high pressure accumulator and can consequently only vary between 50% (at 200 bar) and 100% (at 400 bar) of the maximum torque. Operation of the engine at low loads is therefore completely avoided.

Each wheel has its own hydraulic motor. These motors act as a pump when braking. The recuperated brake energy is stored in the high pressure accumulator. The torque of the in-wheel motors is controlled with the hydraulic transformers, one for each axis. The system has a variable traction control for the front and rear axis. The Hydrid uses floating cup type pumps, motors and hydraulic transformers developed by Innas.

The Floating Cup is an axial piston principle for hydrostatic pumps, motors and transformers. “Floating Cup” refers to the cylinders—each piston gets its own cup-like cylinder, which are free-floating on a barrel plate. Floating cup machines typically have 24 pistons, compared to the 7 or 9 pistons of other axial piston pumps and motors. The pistons are pressed into a central rotor in a double, mirrored configuration.

Fcmachine VarFCPump
Components of a floating cup machine.
Click to enlarge.
The new Innas variable floating cup pump.
Click to enlarge.

The floating cup principle has an extremely high torque efficiency, even at low speed—more than 95% at 0.1 rpm and 350 bar. The principle has almost no torque losses at low-speed driving or during start-up when accelerating from standstill. The multi-piston design creates a smooth, almost constant torque output which is necessary for low noise, vibrations and harshness (NVH).

Compared to electric machines, or even to other hydraulic pumps and motors, the floating cup principle has a very high power and torque density. This is especially important for the in-wheel motors in order to minimize the unsuspended weight of the wheels.

The floating cup principle is designed for deep drawing, sintering and other production technologies which are familiar in the automotive world but relatively new for the production of hydrostatic machines, Innas says.

Comparing transmission efficiencies. Click to enlarge.

Transmission efficiency. The German Institute for Fluid Power Drives and Controls (IFAS) at RWTH Aachen University has built a simulation model of the Hydrid. In this model, the efficiencies of the hydrostatic components are derived from measurements on existing floating cup machines. Although the cycle analysis shows that the hydraulic components themselves create more losses than a comparable mechanical transmission applied in a mid-sized sedan, these losses are more than compensated for by the energy which is recuperated during braking.

Including the recuperated brake energy, the total efficiency of the Hydrid transmission is in the end somewhat better than the estimated efficiency of an all-wheel drive mechanical transmission.

Engine efficiency. Click to enlarge.

Engine efficiency. Comparing a conventional diesel-engined car with a hydrid car using the same engine (100 kW), the Hydrid delivered a specific fuel consumption of 3.1 L/100km (76 mpg US)—less than half the fuel consumption of the conventional vehicle.

For some 80% of the NEDC, the power demand of the vehicle is less than 10 kW. At these low power conditions, the engine coupled to a conventional mechanical drivetrain can only run in an area with poor efficiency. In the vehicle with the Hydrid transmission, the high-pressure accumulator forces the engine to run between the loads Tmin and Tmax (diagram at right). In this area the engine has the highest efficiency.

The engine is now in on/off operation and is only in operation during 11% of the cycle. For the other 89%, the engine is switched off, thereby completely eliminating idle losses. The hydraulic pump can be used as a starter to enable the frequent on-off operation of the engine.

Innas is an independent engineering company specializing in the fields of hydraulic components, hydraulic drives and combustion engines. Key technologies are the Floating Cup technology for hydraulic pumps and motors, the Innas hydraulic transformer, the Chiron free piston engine and the Hydraulic Common Pressure Rail. NOAX is responsible for the marketing and further development of the Innas technology. NOAX has the exclusive right to exploit the industrial rights and know-how of the Chiron Free Piston Engine, the Innas Hydraulic Transformer and the Floating Cup technology.




If the engine is going to be off 89% of the time why not make it radically smaller?
Maybe a small rotary engine or single cylinder turbo diesel.

Then you would have an even lighter, cheaper car with even lower fuel consumption.

I would love to see this power train in a light aerodynamic carbon fibre body, it would probably be able to out accelerate and brake a conventional sports car.


3PeaceSweet: Check out the Lightning
According to a local TV spot last night, they will be ready for sale in 2011.


I would like to see hydraulic hybrids in trash trucks. There is so much stop and go that a good efficient quiet hybrid would be great. Maybe with twice the mileage they can make is happen. Power the engine off natural gas and make them even cleaner too.

Nick Lyons

Great drivetrain for delivery vehicles, also utility trucks (e.g. cherry picker) which can leverage the hydraulic infrastructure.

I wonder how it will compare at steady highway speeds. This drivetrain has significantly lower mechanical efficiency under steady load.


I prefer that scottish company's concept for hydraulic motors.. they dont use a hydraulic "tranformer" for each motor, instead they drive valves in each motor electronically. Seems simpler and with less hardware.

This part is disturbing:
Although the cycle analysis shows that the hydraulic components themselves create more losses than a comparable mechanical transmission applied in a mid-sized sedan, these losses are more than compensated for by the energy which is recuperated during braking.

So they are saying you will get a hit in highway mileage but very high city mileage due to braking energy capture.

This seems fairly complex to me, compared to the simplicity of a Prius.

Probably would be very practical for 4WD vehicles and large stop/go heavy vehicles such as a bus or trash truck.


An electric hybrid with a supercapacitor would be better. Hydraulics store more brake energy because they are not limited by battery chemistry. Converting electricity to chemistry and back again costs you energy. A capacitor stores electricity without converting it so there's no loss.


I don't particularly care which system is optimal; being able to build a drivetrain which cuts fuel consumption in half using processes already familiar and probably equipment already available (and sitting idle) in auto plants, this could and should be pushed into production as fast as possible.

This may be feasible for a retrofit to existing vehicles as a through-the-road hybrid on the non-drive axle, a la the Poulsen hybrid.  If the USA is to deal with our balance of payments problem and vulnerability to new oil price spikes (which ARE coming), we need measures like this.


Good point poet.. we do have the ability to manufacture these systems today, and probably with high reliability.. on the other hand we dont have lithium battery production capability for electric hybrids.


We have some interesting observations that show up the inefficiencies of conventional drive trains.
I don't see any particular merit in the hydraulic answer (beyond some present manufacturing ability) that gives a leveraged advantage in applications where hydraulic systems are a major part of the vehicles operations.
The best transmission efficiency is described as:
"the hydraulic components themselves create more losses than a comparable mechanical transmission"
"Including the recuperated brake energy, the total efficiency of the Hybrid transmission is in the end somewhat better than the estimated efficiency of an all-wheel drive mechanical transmission."

Shows that the hydraulic hybrid uses the recuperated braking energy to bring the transmission up to he efficiency of mechanical 4WD trans - that presumably without braking Regen.

So the 76% improvement in fuel efficiency is down to operation of a smaller 100KW diesel motor operating in
high efficiency torque zone with stop start.

That concept applied to an electric hybrid should give similar figures.
While we all wait for battery technology to prove itself over time, so this is a less model able, For the majority of vehicles that have no need for hydraulics beyond the odd oil pump, It makes little sense to apply this technology with the whole extra 'specialist diagnostics, workshop and maintenance issues.

It would be wrong to link the efficiency savings from system design to the technology ?IE hydraulics when there may be (are) other applicable options (battery capacitor). .
The trash trucks, mining and various plant with substantial hydraulic systems would find the same applies that simplifying systems inventories will be an economical and logistical advantage.

I find these claims between apples and oranges with claims of fuel savings, that press all the right buttons to get the gullible jumping up and down test the limits of credibility.


Arnold, I can substantially increase my fuel economy using boost-and-coast driving; when the engine is turning at road speed it is pushing the car at full torque, and the rest of the time it's running at idle, with much lower friction and pumping losses.  If my car had a transmission that let the engine shut off when it wasn't going at max, I'm sure my 5-passenger 4-door would get 50+ MPG highway instead of 38-40.  A few percent extra losses in the drivetrain wouldn't come close to offsetting the gains, even in a car with a 1.9 liter diesel.


As per HEV the ice is off at low loads, current draw is negligible on overrun depending on drivetrain and the recovered energy supplements acceleration.
I think this is an area that the ev may be slightly behind but not much again this would depend on the drive arrangement.
You could say then that eliminating transmission losses by disconnect will give eficiency gains. That is true but such arrangement would be possible with IE. electric wheel motors or other low friction trans.

This would leave the energy storage losses that are likely lowest with a capacitor buffer.
The hydraulic accumulator has not comparable energy density a battery.

The electrical - hydraulic analogy works well so far but an ev doesn't require hydraulics whereas a hydraulic needs ECU,s for ICE and probably transmission? To my mind this means extra complication through more systems.

If CPU's are already a challenging necessity in a consumer? appliance, we will simply need to get better at it.
If the hydraulics perform a comparable job without any other merit, it would seem that arrangement 'schizophrenic' if not required for other operations.


The problem with the eHEV drivetrain is that the batteries are costly, and we don't have the facilities to scale up the production of motors and electronics rapidly.  If we can bypass some of these limits with a hHEV drivetrain, exactly what is the problem?  You could even retrofit such a system into a plug-in by adding a battery pack, motor and hydraulic pump.

Suppose for a moment that such a package was available for e.g. the Ford Crown Victoria.  I imagine that these cars get around 15 MPG in taxi service in large cities (figuring increased idling over EPA city cycle).  If the taxi does 100,000 miles a year and fuel consumption can be cut in half, that's 3,300 gallons/year saved.  Even at today's prices of about $2/gallon for regular, a $10,000 hydraulic retrofit would pay for itself in 18 months; a $3000 factory hydraulic drivetrain option would pay for itself in 5 months.

There is no reason not to be building these things by the hundreds of thousands, if not millions.


We will need all solutions to move things in a good direction. If 20% of the cars sold today were hybrid, would we have enough motors and batteries? Maybe not. Hydraulic motors may not be off the shelf items either. Taxis, trash trucks and whatever may be better suited to this. Other applications to different solutions. Whatever fits should be applied, but all I know is we need to use less importd oil NOW.

Henry Gibson

INNAS-NOAX built an efficient good, perhaps great, free piston engine that could pump hydraulic fluids. Perhaps they are not using it in their hybrid concept car because no one could be persuaded to buy a single cylinder car no matter what. ..HG..

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