Pivotal implement

A pivotal implement, such as a pivotal plow, comprising:

• an implement frame having an axle extending generally longitudinally in the direction of travel about which said frame may pivot;
• an undercarriage on which said implement frame is pivotably supported for movement relative to said undercarriage about said longitudinal axle, said undercarriage including at least one pair of spaced-apart wheels and at least one pair of transversely-extending wheel axles, each of which supports one of said wheels and each of which is coupled to said undercarriage for independent movement in a substantially vertical direction, relative to the longitudinal axis of said undercarriage, between an upper limiting position and a lower limiting position;
• blocking means associated with said wheel axles for preventing a tipping movement of said undercarriage relative to said implement frame about said longitudinal axle, said blocking means being movable between a blocking position and an unblocking position for respectively preventing and permitting movement of said wheel axles;
• and
• sensor means associated with each of said wheel axles which are responsive to a change in position of its associated wheel axle relative to said longitudinal axle and which are coupled to said blocking means and which move said blocking means into a blocking position when the associated wheel axles moves from said upper limiting position downwardly relative to said longitudinal axle.