|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.