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Artemis Intelligent Power Unveils New Hydraulic Hybrid Powertrain

Three different configurations of the HEDDAT-based series hybrid system with increasing hybrid functionality leading to up to 30% reduction in CO2. Click to enlarge.

Artemis Intelligent Power has unveiled a new hydraulic hybrid powertrain for vehicles based on its Digital Displacement (DD) technology, which replaces the port plates and swash plates in conventional hydraulic machines with computer-controlled high-speed solenoid valves.

The UK Energy Saving Trust confirmed that a prototype BMW 530i hydraulic series hybrid, retrofitted with the HEDDAT (High Efficiency Digital Displacement Automotive Transmission), showed double the fuel economy in city driving compared to the same car with a manual transmission. Overall, including highway driving, the prototype had 30% lower carbon emissions than it had before the company fitted its hydraulic system. The development costs for the prototype were shared by the UK Department for Transport, through a technology program run by the Energy Saving Trust.

An earlier phase of the HEDDAT work was selected in 2003 as one of five proposals to participate in the UK Department for Transport’s Ultra Low Carbon Car Challenge. (Earlier post.)

The Artemis hydraulic hybrid uses a series configuration—a Digital Displacement hydraulic pump and DD motors drive the wheels and compress gas (held in an accumulator) to store energy. The HEDDAT-based system can be configured to deliver a range of hybrid functions, including regenerative braking and start-stop (using a small hydraulic starter motor).

The hydraulic transmission is potentially much more durable, lighter and cheaper than electric hybrids. The company expects the hydraulic system to deliver substantially better fuel savings than electric hybrids in most vehicle applications.

In the just-completed 22-month project, Artemis developed new transmission components and technology, then switched them with the standard manual transmission. The new transmission is automatic, but apart from this the new components fit in the same space as before so the car looks and feels the same as it did before.

Rendering of the DD system. Click to enlarge.

The Digital Displacement technology. The core component of a Digital Displacement system is a hydraulic piston pump/motor with actively controlled poppet valves which rectify the flow into, and out of, each cylinder. The cylinders are generally disposed radially around an eccentric with valving around the periphery.

Each cylinder has two of the actively controlled poppet valves, one to each of the high and low pressure manifolds. When idling, the fluid flows in and out around the low pressure valve. The high pressure valve remains closed and isolates the reciprocating cylinder from the high pressure fluid. When pumping, the microprocessor closes the low pressure valve to send fluid to the high pressure service. It is also possible to hold the high pressure valve open, taking fluid from the high pressure output.

The valves are each operated by a small electro-magnetic latch so that they can be opened and closed on a stroke-by-stroke basis. The solenoid coil in each latch is activated by a power FET, which is in turn connected directly to the digital output of an embedded controller.

The rapid sequenced valve actuation allows each cylinder, at the end of each stroke, to be reconfigured to either pump, motor or idle. By controlling the sequence of cylinder enablings, the machine can pump fluid to a hydraulic service or accept it back (while the returning fluid actually helps to drive the crankshaft of the machine) at infinitely variable flow-rates.

Banks of cylinders can be assembled along a common crankshaft to allow multiple independent outputs.

Comparison of efficiencies. Click to enlarge.

While many types of hydraulic pumps achieve efficiency similar to Artemis’s Digital Displacement technology at their full flow rates, none can match DD’s efficiency at partial displacements, according to Artemis. DD machines lose so little energy efficiency at partial flow rates that they are close to uniformly efficient over the whole displacement range.

Artemis suggests that commercial vehicles rather than passenger cars will be the first on-highway vehicles to be fitted with the new transmissions. Bosch Rexroth, the global supplier of components and systems for industrial and factory automation and mobile applications, has purchased the worldwide rights to use the company’s Digital Displacement technology in on-highway vehicles.

Sauer-Danfoss APS, a major global supplier of hydraulic systems to the construction, agricultural and handling machinery industry, has also signed up to use Artemis’ technology. Sauer-Danfoss has transferred engineers from the USA and Europe to Edinburgh to work closely with Artemis.

Artemis’ technology emerged from the University of Edinburgh as part of the Wave Power research program led by Professor Stephen Salter. Digital Displacement technology, embeds patented computer control into proven and robust hydraulic pump and motor designs. The novel computer control makes the machines dramatically more efficient than traditional hydraulics, while maintaining their inherent reliability, low cost and high power density.

Artemis also plans to replace wind turbine mechanical gearboxes with its hydraulic technology. Independent studies show that 30% of wind turbine downtime is due to mechanical gearbox failures. The increasing demand for wind turbines to be sited offshore is encouraging wind farm developers to look ever harder at gearbox reliability as maintenance costs are much higher offshore. Artemis has already begun developing the components for full size wind turbines.

Some of the initial wind turbine work is being supported by the Carbon Trust, and Artemis says the progress they are making is already getting the attention of some of the larger turbine manufacturers and purchasers.



problem for this technology is that a lot of the car manufacturers are already committed to the battery-electric route. so even if it does deliver on its potential (lighter, cheaper, better), we won't be seeing this in hybrids any time soon.

Wow a 30% improvement in efficiency and mileage.
If they can scrounge up another 20% they will hit BEV territory.

However, on long haul transport trucks, it should have a payback.


Sounds interesting. What drives the FEAD during engine-off?


Can it be combined with an electric system or is that getting too complicated?


Based on what physics is a mechanical system more robust than a electromagnetic system? With mechanical pistons, pumps, and other gear wearing against each other, there is inheritent inefficiency and limited lifetime.

There is no combustion engine which has been demonstrated to be in continous operation for 100+ years without any major overhaul; However, there exist electric generators (hydro power) where except the bearings (mechanical system...) nothing needed to be swapped in the past 120 years, and still providing power....


This outfit will make a fortune on the wind turbine gearboxes - forget the other stuff.


The accumulator contains compressed air?

It should be heated with the exhaust. That would do wonders to the efficiency.


The Artemis system as all hydraulic systems have some flow that are difficult to eliminated. One of the problem is loss off efficiency due to temperature differential. What you do if you will get -20C?

Instead of hydraulic transmission better solution is wave transmission or to be exact four phase wave transmission that was develop by George Constantinesco in 1920.
See the picture on the figure 3.


@Helen: sweet idea

I wonder, how difficult it would be to retrofit this type of system?

Also, for new vehicles:

-is a transmission such as this significantly more expensive than traditional automatic units? I would have a hard time believing that it would cost more than the DCTs being developed by VW/Audi/BMW
-what sort of losses are experienced at low temperatures? Is there any way to compensate for this?
-Perhaps such a design paradigm (hydraulic power transmission) would be well suited to a free-piston engine design whereby the engine and transmission are one in the same. This would help to alleviate mechanical losses within the ICE.


These are quite outstanind results indeed, It can seriously compete with HEV especially on truck or even light truck where the battery cost and size can be a serious issue. It can also be a nice solution for 4WD.


To answer some of the questions above.
EPA, UPS, and Eaton did an analog hydraulic hybrid. They achieved over 40% in fuel savings. But did so; by replacing the standard UPS truck engine with a VW Rabbit engine. I suspect if they applied this digital system to a BMW 525 it would have similar or better performance (0-60) as the standard 530.
It is less costly than a a battery hybrid
It could and should be offered as an after market retrofit and would be ideally suited for the SUV driving soccer mom crowd. After market retrofits have been applied to garbage trucks in some areas.
Hydraulic energy losses are generally thought to be less than electrical losses. Electric hybrid's recover energy from the heat of breaking. Hydraulic hybrids recover the energy mechanically from the drive train.
I suspect temperature issues can be address by using the correct additives to the hydraulic fluids.


CVT/IVT offers an acceleration advantage, right? (rhetorical)

This advantage would allow for engine downsizing while maintaining comparable performance.

I suppose a low temp workaround would be using the exhaust heat (plenty of it available) to bring the hydraulic fluid up to a working temperature.

Take a vehicle like the current VW Passat-

Stock form: 19mpg city, 28mpg highway, 23.5mpg combined.
w/ Artmeis digital displacement transmission~30.5mpg combined
w/ 25% engine downsizing~32mpg (?)
w/ aero improvements due to smaller engine/smaller cooling load~33mpg

Its kinda like a vicious circle of improvement. A better transmission improves acceleration which, to hold performance constant, reduces the size of the engine needed. This in turn reduces the size of periphery components (radiator, battery, transmission, etc) which further reduces the vehicle weight/frontal surface area hence further reducing the necessary engine size....

Sorry. I got a little excited there. End Ramble.


One more question:

Aren't CVTs particularly well suited to diesels as they can keep the engine in a very small RPM range over a wide range of speeds thus minimizing engine-out NOx and PM?


The cool thing about hydraulic hybrids is that they're not too much more expensive than traditional transmissions, which means that diesels, HCCI, RandCams, turbines, Atkinson cycle motors, 2-strokes, downsized high-compression turbos, and other nontraditional combustion strategies become viable. Sure, you're gaining 30% efficiency...but when you pile on, say, 15% efficiency gains from HCCI or more for diesel, it immediately becomes extremely compelling.

The other cool thing is that, due to their durability, simplicity, and cost, this type of hybrid becomes very viable for taxis, livery, and other service vehicles. I bet you could retrofit a Crown Vic taxi with this sort of system and realize some extremely significant efficiency gains.


I'm surprized they only got a 30% improvement. Other prototype hydraulic hybrids have gotten 60-70% and flywheel hybrids even more.

I don't know what's wrong here but maybe their hydraulic storage accumulators are too small or the car itself wasn't optimized to take full advantage of the system's benefits.



Read it again. The 30% improvement was in combined cycle driving. City driving saw a 100% improvement in fuel economy.

Also, the stock 3.0L I6 was kept in place. A downsized engine was not used to take advantage of the performance benefits of an IVT. Other demonstration units have used downsized engines, e.g. the EPA, Eaton, UPS project.


The website for has been updated with some more information regarding the BMW 530i modified with the hydraulic hybrid transmission.

Henry Gibson

Hydraulic hybrids are probably the cheapest way of getting fuel efficiency. Micro-controllers and transistors allow for rapid automatic control. Steam locomotives were optimised for high performance in their last days with large pipes and efficient valves, and hydraulic drives can be also optimized. A locomotive in Algeria had electric valves. Electric valves are available for diesel engines. It would be bad to ignore the INNAS NOAX hydraulic engine pump which is also computer controlled and very efficient and long lived; although, Innas is trying to ignore it with their hydraulic hybrid. To obtain the best efficiency, small engines must be used that operate mostly in their most efficient range. No matter how much fluid needs to be pumped, the NOAX engine can be programmed to pump it efficiently.

Parry People movers is finishing two, already sold, hydraulic hybrid rail trolleys with large flywheels for more efficient passenger service. The service was already tested with a prototype.

It is now very easy to create a plug in hydraulic hybrid with a ZEBRA battery and a simple low power DC motor-hydraulic-pump that needs no expensive electric high power drive electronics.

It is important also not to ignore the work of Constantinesco, with modern materials and designs the ratchet drive required might be made long lived, but there is no energy storage in his system. He did invent a successfully used system to send sound waves though pipes of fluid so that the machine gun could be synchronised with the propellor blades in British WWI aircraft. Such aircraft were mentioned by the dog Snoopy in the cartoon series Peanuts, "Synchronised Vickers Machine Guns Firing Through The Airscrew Arc".


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