A new transmission uses a hydraulic motor that selectively engages separate cylinders under differing conditions and could help agricultural vehicles achieve higher ground speeds and greater mechanical efficiencies.
The motor, developed by Poclain Hydraulics, Inc. of Sturtevant, WI (http://rbi.ims.ca/3848-518), and known as the MW24, works in conjunction with a hydrostatic pump made by the company. It serves as part of a vehicle transmission known as the Speed+. Poclain's engineers claim the motor could help sprayers and other large agricultural machines achieve ground speeds greater than 60 kph (approximately 37 mph).
The key to the transmission's greater speed capabilities lies in the variable operation of its MW24 cam lobe motor. The motor contains a single cylinder block incorporating two rows of pistons—one row containing larger pistons, and another row containing smaller ones. During operation, four distinct motor torques and speeds can be achieved by operating a combination of the larger pistons, smaller pistons, and the unit's power-transmitting cams. The system, for example, can generate low speeds by engaging both rows of pistons while keeping all cams active. Or it can change the torque and speed outputs by employing the following combinations: operating both rows of pistons and half of the motor's cams, disengaging the large row of pistons while keeping all cams active, or employing the small pistons in conjunction with half of the cams. In general, it increases vehicle speed by disengaging pistons and decreasing displacement.
Using the motor pistons in this way endows the product with a transmission ratio of as much as 1:6, which is "significantly higher than that of conventional hydrostatic transmissions using cam lobe motors," says Vincent Siquier, applications engineering manager for Poclain. "Partially disengaging the motor allows us to increase the transmission opening," Siquier says. "And that results in twice the speed."
Designed for large, off-highway vehicles, the Speed+ transmission typically employs four of the MW24 motors–one at each wheel. During operation, power passes from the vehicle's engine to the transmission's hydrostatic pump, which delivers pressurized oil to the four hydraulic wheel motors. A hydraulic valve, located external to the motors, engages and disengages the separate rows of pistons.
An electronic control unit, known as the SmartDrive, sends control signals
that manage the hydraulic motor's displacement, as well as the pump's swash
plate and the vehicle's engine operation. The SmartDrive reportedly can provide
automatic "speed shift" across continuously variable speeds from 0 to 65 kph. It
can also switch the transmission between a work mode and higher-speed automotive
mode, and can even provide cruise and traction control, as well.
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Motorized Brain: An electronic control
unit, which works in conjunction wiht the Speed+ transmission, governs the
swash plate of the hydrostatic pump, as well as the operation of the four
hydraulic motors.
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