A directly operated valve with optimized flow capacity
Powershift transmissions require powerful clutch actuation if their hydraulic engaging process is to be gentle yet quick. Thomas has developed the PPCD08 (Proportional Pressure Control Direct-Operated) to achieve this using a directly operated pressure control valve. It is ideally suited to clutch control tasks in powershift transmissions for tractors, earthmovers, and crawlers in particular.
Herdorf; Las Vegas, March 7, 2017 – Depending on the number of clutches, between six and eight of these valves are usually assembled onto an aluminum die-cast manifold and mounted to the interface of the transmission housing. The valves are then actuated via a separate control unit, with the valves controlling the pressure in proportion to the current applied. The valve spool controls the equivalent pressure in the clutch quickly and precisely, generating traction between the clutch plates and causing several shafts to engage. If the actuating current decreases, e.g., when changing gear, the valve gently empties the clutch and causes the friction pairings to separate (disengage).
With a flow rate of between 18 and 25 liters per minute, the PPCD08 is the first directly operated pressure control valve to offer such a high flow capacity so far unique to this compact installation space. This ensures that the clutch is filled quickly and pressure levels are kept stable regardless of the flow rate. The valve also boasts faster switching times (< 45 ms) than its pre-operated counterparts. In directly operated valves, the electromagnetic force is transmitted directly to the valve spool and does not need to pass through a pressure stage, a technically complex process required in pre-operated models.
The direct mechanical contact with the valve spool also means better dynamics, fewer pressure overshoots during regulation, and a low susceptibility to fluctuations within the system in terms of all the influencing factors (low/high temperatures, oil viscosity, vibrations, pressure fluctuations, etc.).
The vehicle operator does not lose any traction or experience any juddering when changing gear. Despite this high performance density, the valve nevertheless boasts an unparalleled compactness, fitting into a space measuring less than 30 mm in the outer diameter of the housing. Featuring a high proportion of tried-and-tested carry-over parts (COPs) and a simple valve design with only a few individual components, the Thomas PPCD08 also represents unbeatable value for money.
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Thomas_PPCD08.jpg: Thomas has developed its directly operated PPCD08 (Proportional Pressure Control Direct-Operated) pressure control valve to provide powerful clutch actuation in powershift transmissions.
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