Positive infinitely variable
Positive Infinitely Variable (PIV) is the English name that the Englishman GJ Abott introduced for the mechanically adjustable continuously variable transmission he invented in 1924. The German Werner Reimers (1888–1965) bought the patent and founded an English- German gear company in Bad Homburg vor der Höhe in 1928 , which - since 1931 he has owned completely - was renamed PIV Antrieb Werner Reimers KG in 1936 . Since 1960 the company has been called PIV Antrieb Werner Reimers GmbH & Co. KG before it was renamed PIV Drives GmbH on November 1st, 2001 after the takeover by the Italian gear manufacturer Brevini .
The PIV gearbox basically consists of two toothed pairs of cone pulleys, which are located on the shafts arranged in parallel (input and output shaft). They are connected by a chain of packages with steel lamellas that can be moved within the individual packages. The end faces of the lamellas engage in radially machined flat recesses in the conical disks and thus transmit the torque . One of the disks is arranged to be displaceable on the respective shaft. A mechanically or hydraulically adjustable rocker can be used to continuously vary the spacing between the pairs of pulleys, causing the slat chain to move. This changes the effective transmission diameter of the chain and thus the transmission ratio.
PIV as the manufacturer's name has long been a prototype and synonym for CVT transmissions. The multi-disc chain drives are characterized by their simple and robust construction, high reliability, low maintenance and simple control with high precision. They can be operated during operation at full load and have no slip during normal operation . This makes them suitable for stepless torque and speed conversion and - with the appropriate control - for automatic compensation of speed fluctuations, as is necessary, for example, when driving generators . In the event of overload or blockage, the slats jump over. In this way, the gearbox also takes on the function of a safety or slip clutch , with increased wear . Their disadvantages are great weight, high space requirements and mechanical wear on the chain and pulleys. A further development of these lamellar chain transmissions are so-called roller chain transmissions, whereby the conical disks are no longer toothed and the power is transmitted through chains with lateral rollers. The advantage of this further development is that if the chain is overloaded, the chain will not slip. There are also types of gears with smooth disks and chains in which the frictional connection is achieved by rocker pressure pieces instead of lamellae or rollers. These chains are also used in the CVT transmissions that are already in use.
PIV gearboxes have long been used as a standard solution in special machines in general mechanical engineering and in construction machinery. The modern electronically controlled transmissions that are used in automobiles today were developed from them.