fly-wheel revclves. Attached to the driving shaft is a flanged member which carries a number of bell cranks spaced equidistantly or 120 degrees apart. This driven member also carries a plate which is keyed to it and which must revolve with the driven shaft. This plate can move back and forth on its key so the two clutch-driven plates are in contact with the driving plate only when the clutch lever has moved the clutch-link actuator to the

FIG. 97.-Clutch of Avery Tractor is Provided With Three Clutch Shoes.

position shown, where the toggle links are approximately vertical and the bell cranks are holding the driven and driving plates of the clutch into firm engagement.

When the clutch-link actuator is moved back the bell crank is pulled away from the outer clutch-driven plate, and as there is no pressure to maintain frictional contact

between the driven and driving members, the fly-wheel of the motor may continue to revolve while the mechanism attached to the drive shaft becomes stationary. Wear between the clutch plates may be taken up by an adjustable contact member carried by the bell crank. A clutch of this type may be applied gradually and may

be allowed to slip to some extent while getting the tractor under way without doing any injury. When the clutch lever is operated to the limit of its movement in one direction the clutch is firmly engaged, while moving

it to the other extreme position will insure complete dis

engagement.

Clutches shown at Figs. 97 and 98 are similar in construction. In these a series of contact blocks are carried at the end of counter-balanced, pivoted levers. The blocks are pushed out by means of a toggle linkage actuated by a clutch-shifting bell crank, in much the same manner as has been previously described. One member is attached to the crank shaft while the other rotates with the driving shaft. The clutch shown at Fig. 97 is used to bring a belt pulley into engagement with the engine shaft, though the principle may be reversed and the belt pulley represent a member attached to the engine fly-wheel while the spider which carries the clutch blocks and actuating mechanism would be attached to the independent transmission shaft.

Friction Disk and Roll Clutches. Some tractor designers employ friction-wheel clutches instead of the types described. These operate on a different principle as the members are not locked together so that they revolve as a unit, but the driven member rotates the driving member which turns on a different plane. A double friction disk clutch such as used on the Heider is shown at Fig. 99, and its relation to the engine may be clearly ascertained. The fly-wheel has a fiber ring attached to it which serves as a driving member, while two disks are attached to the cross shaft which is placed at right angles to the crank shaft of the motor. These disks are adapted to be brought into contact with the fiber friction ring with a considerable degree of pressure.

The sketch at Fig. 100 shows the principle of operation. If the engine fly-wheel is turning in the direction indicated by the arrow and the friction disk A is brought in contact with it, the cross shaft to which the disk A is

attached will turn in the same direction, and as this carries a driving pinion which is in mesh with a driving gear on the differential casing of the counter shaft it will turn it in the opposite direction. As the connection from the counter shaft to the rear wheels is by chain and sprockets the rear wheels will turn in the same direction as the counter shaft does and the entire machine will move in the direction of the large arrow or forward. If conditions are reversed and the friction disk A is pulled out of engagement with the fly-wheel, while friction disk B is brought in contact with that member, the tractor will move backward because friction disk B will be revolved in a direction opposite to that friction member A turns in.

Another form of friction clutch in which a friction wheel is employed is shown at Figs. 101 and 102. The view of the mechanism at Fig. 101 shows clearly the mounting of the friction wheels for driving a movable cross shaft, which in this case is parallel with the engine crank shaft. This main driving shaft, which extends across the frame, is provided with a friction driving wheel at each end and carries a pair of sliding gears which may be engaged with either one or two gears on the transmission cross shaft placed immediately back of the main driving shaft that carries the friction wheels. The gears on the transmission cross shaft are of different diameters, one being smaller than the other, as is true of the sliding gears on the squared main shaft. Before discussing the method of obtaining speed changes or final drive it will be well to consider the action of the friction rollers.

The engine carries two large fly-wheel members, which are so arranged, one at each side of the frame, that the friction wheels employed for driving fit in an annular