Abstract: The control device comprises a motor (5) having a shaft (7a) provided at one end with a worm (8a) to drive a nut-wheel (9a), the set of the worm (8a) and of the nut-wheel (9a) forming part of a reduction gear (R). A screw (12a) cooperates with the nut (11a). This screw (12a) is fixed in rotation around its axis. The reduction gear (R) comprises a stirrup (26a) comprising two intersecting cylindrical sleeves (30a, 31a) communicating through an opening (W). One (30a) of these sleeves receives the nut-wheel (9a). The worm (8a) is accommodated in a tube (10a), connected to the casing (6) of the motor (5), which comprises a window (32a) on its cylindrical wall at one end intended to be engaged in the other sleeve. For the assembly of the reduction gear, the above mentioned end of the tube (10a) is fitted in the other sleeve (31a) of the stirrup (26a) so that the above mentioned window should come to be opposite the above mentioned opening (W).

Abstract: Pinging in an internal combustion engine is avoided by reducing the ignition advance angle, whenever pinging is detected, by a given angular retardation to arrive at a corrected advance angle. In the absence of pinging at said corrected advance angle, the angle of advance is progressively increased again stepwise at a first incremental rate of increase which is being maintained so long as the absence of pinging is maintained, up to a maximum cumulative increase; if this cumulative increase is attained without again detecting pinging the advance angle is increased stepwise at a second incremental rate until the normal advance angle value or the recurrence of pinging. At the time of transition from said first to said second incremental rate, said second incremental rate of increase is greater than or equal to said first incremental rate.

Abstract: A motor-reduction gearbox combination has the driven shaft output gear on the floor of the casing and below the driving shaft which is perpendicular to the driven shaft. The drive shaft has two multi-start corner screw portions of opposite hand and preferably of equal arithmetic pitch, to be engaged by respective pinions. Each pinion forms part of a respective double gear unit by being fixed to, or more preferably formed integrally with, a gearwheel meshing with the driven shaft output gear. For each double gear unit, the ratio of the number of teeth on the gearwheel to the number of teeth on the pinion is equal to the number of thread starts of the associated worm screw portion of the driving shaft, and in the preferred case the double gear units both have the same such ratio.