Dyson Appliances Limited v Hoover Limited

Patent claims must be construed purposively, between strict literalism and treating the claims as mere guidelines. The construction must provide fair protection for the patentee and reasonable certainty for third parties.

Prior art anticipates a claim only where it gives clear and unmistakable directions which inevitably produce the claimed invention. Obviousness is assessed through the skilled but unimaginative addressee. That person's technical outlook may reflect an established industry mindset, including commercial conditions which shape the perceived need for innovation. Commercial success or motivation is neither necessary nor sufficient to establish inventive step.

Dyson held a patent for a vacuum-cleaning appliance in which dirty air passed through cyclone units of successively higher efficiency. A cylindrical or reverse-tapered cyclone first removed larger particles. A frusto-conical cyclone then removed finer particles.

A deputy judge of the Chancery Division held the patent valid and infringed by Hoover's upright vacuum cleaner. Hoover appealed, alleging anticipation and obviousness in light of the Campbell and Donaldson prior art. It also disputed whether its cyclones were connected “in series” and whether its trumpet-shaped high-efficiency cyclone was “frusto-conical” within the claims.

The central issues were the proper construction of the patent, whether the prior art destroyed novelty or inventive step, and whether Hoover's appliance fell within the claims.

1. Appeal dismissed unanimously. Aldous LJ delivered the leading judgment. Sedley LJ and Arden LJ agreed, adding observations about obviousness. The patent remained valid and infringed.

2. Under section 125 of the Patents Act 1977 and the Protocol on the Interpretation of article 69 EPC, patent claims require a purposive construction. The court must avoid both strict literalism and treating the claims as guidelines. It must combine fair protection for the patentee with reasonable certainty for third parties. “Vacuum cleaning appliance” therefore meant an appliance which cleaned a surface, rather than every apparatus which separated particles from air.

3. Campbell did not anticipate the patent. Its disclosure did not make it inevitable that the outer chamber would operate as a lower-efficiency separating cyclone. Its operation depended materially on inlet velocity, and some methods of operation would fall outside the claims. Donaldson was not anticipatory because its mine-drilling dust collector was not a vacuum-cleaning appliance as properly construed.

4. The invention was not obvious. Applying the four-stage Windsurfing approach, the material difference from Campbell was the provision of a lower-efficiency circular cyclone. The skilled person would not have understood Campbell's outer chamber as a separating cyclone and had no apparent reason to modify it in that way. Donaldson belonged to the different context of dust removal in mines and became relevant only through hindsight.

5. Aldous LJ held that the skilled person's mantle includes the attitudes and perceptions of an actual skilled worker. Sedley LJ agreed that commercial realities may shape the person's technical horizon and perception of need. Arden LJ stressed that the ultimate comparison remains technical. Commercial motivation or later commercial success is neither a necessary nor a sufficient answer to obviousness.

6. Hoover infringed. Cyclones may be “in series connection” where air reaching the higher-efficiency cyclone has first been cleaned by the lower-efficiency cyclone. The claim did not require every part of the lower cyclone's output to pass through the higher cyclone. Hoover's intermediate unit did not alter the invention's functional sequence. It could also be combined with the final cyclone and treated as one cyclone unit.

7. “Frusto-conical” did not require mathematical exactitude. It encompassed a generally frusto-conical shape which concentrated the vortex and separated fine particles. Hoover's trumpet-shaped cyclone performed that function and fell within the claim.

The appeal was dismissed with costs. No order was made on the respondent's notice, and permission to appeal to the House of Lords was refused.

1. Court of Appeal (Civil Division): By [2001] EWCA Civ 1440, dismissed Hoover's appeal, upheld the findings that the patent was valid and infringed, and made no order on Dyson's respondent's notice.
2. Chancery Division: On 13 October 2000, Mr R M Fysh QC, sitting as a deputy judge, held the patent valid and infringed. No neutral or report citation is stated.