Research and development (Details) (USD $)	3 Months Ended	9 Months Ended
Jun. 28, 2014	Jun. 29, 2013	Jun. 28, 2014	Jun. 29, 2013
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense, net of grants receivable	$ 1,045,000	$ 970,000	$ 3,058,000	$ 3,057,000
Percentage of sales (in hundredths)	10.80%	11.20%	11.00%	13.10%
Cummins Generator Technologies and Newcastle University [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Grant income recorded	28,000	39,000	61,000	76,000
Research and development expense on projects	83,000	114,000	180,000	225,000
Technology Strategy Board Project Grant in 2013 [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Grant income recorded	1,000	1,000	4,000	1,000
Research and development expense on projects	8,000	3,000	18,000	3,000
Low Emission Transport Collaborative Projects Fund [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Grant income recorded	103,000		339,000	0
Research and development expense on projects	423,000		1,392,000	0
Total grants awarded			$ 480,000

- Definition

The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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