Image Number 4 for United States Patent #4712631.
In a bridging circuit (6.sub.a, 6.sub.b) connecting the two opposing chambers ( V.sub.1 V.sub.2) of the hydraulic assistance actuator (5), a valve seat (11) is interposed which may be closed selectively by a valve member which is biased by an electromagnetic actuator (14) having two states, energized and unenergized, which is controlled by at least one switch (18.sub.a, 18.sub.b) actuatable by the lever (19) of the gear changing mechanism of the vehicle so as to close the bridging circuit (6.sub.a, 6.sub.b) when the parking gears are engaged (first and reverse) in order to obtain maximum hydraulic assistance power, the assistance power being reduced during other conditions of use of the vehicle (driving along the road).
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