Abstract: A vehicle, such as a single truck or a truck-and-trailer combination, having a power plant, has primary ground-engaging wheels driven by the power plant and a hydraulic pump, also driven by the plant and connected by ducts to a variable-displacement motor which is mechanically coupled to drive secondary driving wheels, e.g., tandem wheels on the truck or wheels on a trailer, there being first and second ducts between the pump and motor, and the displacement of the motor can be altered to equalize substantially the pressures within the two ducts when the vehicle moves ahead on straight road affording good traction. Substantially no power is transmitted through the ducts while the vehicle moves on said road, but when one of, e.g., the primary driving wheels slips, either forwardly or backwards, hydraulic fluid is transmitted through the ducts to retard or speed-up the primary driving wheel through the pump.

Abstract: A metering pump for determining the quantity of a fluid flowing at an externally-determined rate, e.g., for measuring the volume of a gas, such as air, flowing through a flow-restrictive element, such as a filter, has a variable-volume chamber (e.g., a bellows) including a movable wall which is urged in one direction (e.g., toward expansion if an inspirator) by resilient means and is driven in the opposite direction by mechanical means, such as a reciprocable lever arm which engages the wall but leaves it during a part of its movement, said means having electrical contacts in a circuit which powers an electrical motor driving the mechanical means, the contacts being open when the mechanical means leaves the wall, permitting the wall to move at a rate determined by the fluid flow rate. Counting means, such as a counter, are coupled to the electric motor or circuit for counting the movements of the wall.