Two pinions (2, 3) are rotatably mounted on a drive shaft (5) and mesh with respective gear wheels (6, 7) which are fixed to the output shaft. The pinions can be alternatively coupled to the drive shaft by hydraulic clamping sleeves (10) of two friction clutches (8, 9) to produce different transmission ratios. …??The clutches (8, 9) are preferably double walled with a jacket chamber (12) connectable to a hydraulic fluid pressure source (11) and an outer jacket (14) for engaging an inner surface of the pinions (2, 3). …??There is preferably an overload cutout arrangement which releases the clutches by means of a safety valve (41) operating on excessive hydraulic pressure. …IMAGE…
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