Apparently, this is because both machines have sensors that send the motors into overdrive when they're actually sucking up dust. In this way, Dyson claims Siemens and Bosch are capitalizing on "flawed" European regulations that allow vacuum cleaners to be tested while empty, and deceiving consumers with stellar ratings that can only be achieved in perfect lab conditions. BSH Group, which is responsible for both home appliance brands being targeted, is obviously unhappy with Dyson's accusations.

"We do not understand these assertions by Dyson and we strenuously reject them. All Bosch & Siemens vacuum cleaners are measured in compliance with European energy regulations. Appliance performance at home is consistent with laboratory performance – and any suggestion to the contrary is grossly misleading."

The statement from BSH goes on to praise its own commitment to "stringent testing," and even calls Dyson out for not being as transparent with its energy ratings and performance metrics. While Dyson has begun legal proceedings against Bosch and Siemens specifically, it's all part of a broader agenda the company has been pushing for some time. Even before the newest rating system for vacuum cleaners was brought in last year, Dyson instigated a judicial review with the European Court, the outcome of which is due before the end of this year. According to the legal challenge, the rating standard fails in two areas: it doesn't recognize real-world performance, and the energy label doesn't take into account the environmental impact of replacement bags and filters. James Dyson himself also argued that German competitors had too much say in the drafting of European regulations, allowing them to devise tests that would yield favorable energy ratings.

It's in Dyson's interests to shape the rating system as it sees fit, of course, giving its energy-efficient products greater exposure. And what better time to make the grand gesture of legal action, when efficiency ratings are a hot topic in the aftermath of the Volkswagen emissions scandal? (Coincidentally, Bosch is also implicated in that mess, having supplied software to VW for use in testing.) James Dyson used the uproar against VW as an opportunity to criticize the "murky world on regulations," and this campaign against Bosch and Siemens appears to be an extension of that. Commenting on the vacuum cleaner situation, he said:

"Bosch has installed control electronics into some of its machines to wrongfully increase energy consumption when in use – to cheat the EU energy label. Their behaviour is akin to that seen in the Volkswagen scandal. It seems that industry is rife with manufacturers engineering to find their way around tests, rather than engineering better, more efficient technology. This behaviour is seriously misleading customers."

While there's no arguing that efficiency standards should actually mean something, the question remains: do consumers actually look at the energy rating of a vacuum cleaner before buying it, and do they even care? Dyson certainly does -- especially when it's calling out competitors to benefit its own image.