Abstract: A crankshaft drive in an internal combustion engine, which comprises at least one cylinder having a cylinder head, and a crankcase housing a crankshaft rotating at a predetermined direction and at a predetermined speed, and a balance shaft extending parallel to the crankshaft and rotating at the predetermined speed of the crankshaft in a direction opposite to the predetermined rotating direction of the crankshaft, the crankshaft and the balance shaft carrying balance weight means for balancing a mass of first order. An auxiliary shaft extends parallel to the crankshaft and rotates at the predetermined speed of the crankshaft in the predetermined rotating direction of the crankshaft, the auxiliary shaft carrying a counterweight for balancing a residual moment resulting from the rotating balance shaft with respect to the rotating crankshaft.

Abstract: A variable ratio drive pulley of the type employed in snowmobiles to transmit a drive from the snowmobile engine to a variable ratio belt drive transmission has a fixed flange and an opposed movable flange which cooperate to drive the belt. The drive pulley is coupled to rotate with the engine crankshaft and the movable flange incorporates a centrifugal means that operates to advance it towards the fixed flange, with a force that increases with speed of rotation, to grip the transmission belt between the flanges and apply a driving torque thereto, this torque being applied by both the flanges. To reduce the effects of engine induced vibrations on the centrifugal means and on the movable flange, a damping structure is incorporated in the torque path between the engine crankshaft and the centrifugal means and movable flange.

Abstract: A system for reversing the direction of a two-stroke, internal combustion engine provided with a spark ignition system, the engine having at least one cylinder and a piston reciprocating therein and connected to drive a rotary crankshaft, the system comprising: a manually operable inverse command button; trigger means located proximate a rotary member driven by the crankshaft, a cooperating member carried on the rotary member and cooperating with the trigger means as the rotary member rotates to generate a train of pulses; means detecting the direction of rotation of the crankshaft and generating a direction signal indicative of direction of rotation; a microprocessor control unit receiving the train of pulses, the direction signal and an output from the inverse command button and connected to control the spark ignition system, the microprocessor monitoring the speed and direction of rotation of the rotary member on the basis of the train of pulses and the direction signal, the microprocessor operable when th

Abstract: A variable ratio drive pulley of the type employed in snowmobiles to transmit a drive from the snowmobile engine to a variable ratio belt drive transmission has a fixed flange and an opposed movable flange which cooperate to drive the belt. The drive pulley is coupled to rotate with the engine crankshaft and the movable flange incorporates centrifugal weights that operate to advance it towards the fixed flange, with a force that increases with speed of rotation to grip the transmission belt between the flanges and apply a driving torque thereto, this torque being applied by both the flanges. To reduce the effects of engine induced vibrations on the centrifugal weights and on the movable flange, a damping structure is incorporated in the torque path between the engine crankshaft and the centrifugal weights and movable flange.

Abstract: This invention relates to an improved snowmobile drive train configuration arrangement that incorporates a fixed ratio speed reduction mechanism directly coupled to the engine crankshaft. This mechanism is in turn coupled to the driving pulley of a variable ratio belt drive system, the driven pulley of which is mounted on the axle of the sprocket wheels that drive the snowmobile track. Interposing the reduction drive between the engine and the belt drive system reduces the operational speed of both the pulleys and the belt, which proves beneficial from several aspects: the mechanical efficiency of the global system is increased, the dynamic response of the transmission to throttle modulation is improved; aerodynamic losses are reduced; the bending vibrations of the crankshaft are no longer transmitted to the drive clutch; and the engine can be run at higher RPM without decreasing the efficiency of the belt drive system.

Abstract: In a snowmobile drive train the variable ratio belt drive is not directly coupled to the engine crankshaft as in the prior art, but rather the driving pulley of the variable ratio belt drive is carried on one end of a jackshaft and the engine power is applied to the opposite end of the jackshaft. The jackshaft is supported in a fixed bearing in the vehicle frame, this bearing being immediately adjacent to the driving pulley so that the influence on the belt drive of vibrations generated by the engine is vastly diminished. Therefore the engine mounts can be arranged to fully absorb vibrations of the engine. Previously, when the driving pulley was directly coupled to the engine crankshaft it was necessary to include a tie restraint to limit movements of the engine housing in the direction of separation between the axes of the driving and driven pulleys.

Abstract: In order to provide for advantageous adjustment possibilities for an infinitely variable drive pulley for a belt drive transmission with two flanges arranged on a shaft and which accommodate a V-belt. One flange is fixed axially on the shaft and the other is moveable in the axial direction against the force of at least one return spring by centrifugal weights in the form of adjusting levers. The adjusting levers each acts on an abutment cam surface, and is supported so as to be able to pivot out about a pin that extends transversely to the shaft, spaced radially therefrom. The adjusting levers can be moved relative to their pivot pins through an adjustment eccentric.

Abstract: In order to ensure correction for altitude for the carburetor used on a internal combustion engine, a control system for the pressure within the fuel bowl (8) is incorporated. This control system consists of a pressure splitter (11) that is connected, on the one hand, with the lower pressure of the venturi throat (4) in the area in which the fuel delivery line (7) opens out and, on the other hand, with the induction pressure in the area of the inlet end (10) of the air flow passage (4), said pressure splitter incorporating a pressure line (12) with two chokes (13, 14) that are connected in series, between which the fuel bowl (8) is connected to the pressure line (12). One or both of the two chokes (13, 14) can be controlled as a function of specific air density.

Abstract: In a two-stroke cycle internal combustion engine, cylinder structure has an inside peripheral surface which defines a cylinder bore and is formed with an exhaust port, which has an axial extent along the axis of said cylinder bore and communicates with said exhaust system. A piston is axially reciprocable in said cylinder bore and adapted to open and close said port. A restricting member is mounted in said cylinder structure adjacent to said port and adjustable between a full-flow position, in which said restricting member exposes said exhaust port throughout its axial extent, and a restricting position, in which said restricting member restricts the axial extent of said exhaust port. A positioning drive is operatively connected to said restricting member and operable to adjust said restricting member between said full-flow and restricting positions. The positioning drive is adapted to be controlled in dependence on the exhaust gas pressure in said exhaust gas system.