A Scottish company has developed a new transmission technology that it claims doubles in-town fuel efficiency. Artemis Intelligent Power's hydraulic hybrid powertrain replaces the traditional port and swash plates in its hydraulic system with computer-controlled solenoid valves.

The transmission, called the HEDDAT (High Efficiency Digital Displacement Automotive Transmission), yielded twice the fuel efficiency of a standard manual transmission-equipped BMW 530i in a start-stop traffic environment, reports CleanTech. The technology stores energy in hydraulic, rather than electric, form, but the system's engineers note that the harder a hydraulic hybrid is driven, the more its advantage over electric hybrid systems grows. The BMW used in the tests achieved 41.1mpg in the European city cycle, 39.6mpg in the European combined cycle and 42.1mpg in the US combined cycle. Those results amount to reductions of 30-50% in CO2 output.

Because the hydraulic system is able to store energy at a faster rate than the regenerative systems in electric hybrids, it can recapture more of the kinetic energy that would otherwise be lost. This means the HEDDAT could achieve significant gains no matter the driving style of the person behind the wheel.

The technology underlying the system isn't new. Hydraulic hybrids have been around for years, but it hasn't advanced at the same rate that electricity-based systems have. The breakthrough by Artemis could be the step that makes hydraulic hybrids commercially viable. If the licensing contracts with Bosch Rexroth and Sauer-Danfoss APS are any indication, it already is. It will likely be several years before production-level automotive applications are available, however.