| 摘要 |
<p>The header of a harvester is raised and lowered by a hydraulic cylinder controlled by solenoid valves when a raise circuit (170) or a lower circuit (172) is energised, in order to maintain a predetermined ground clearance. The header carries a rotary switch (72) in a sealed housing (74) with a wiper arm (80) having an integral bush (126) extending in sealed manner out of the housing and keyed by a pin (140) on to a transverse shah (58) carrying one or more ground engaging feelers. The wiper arm moves a make before break brush across a row of contacts (98) to bridge these selectively to a common contact (100). A manually operable selector switch (182, 184, 186) has an off position in which the raise and lower circuits cannot be energised and three further positions each corresponding to a predetermined range of header-to-ground clearance. In each such further position a first group of the contacts (98) consisting of at least one end contact (108) is connected to the raise circuit (170) and a second group of contacts comprising at least the other end contact (110) is connected to the lower circuit (172). One of the intervening contacts (102, 104, 106) is not included in either group so as to establish a dead band and the "dead" contact is selected by the position of the manual selector switch to select the clearance height range. The end contacts (108) and (110) are of greater arcuate extent than the intervening contacts and allow the housing (74) to be adjusted on the header about the axis of the shaft (58) for joint adjustment of the clearance height ranges. Connections to the contacts (98) and (100) are by way of an external plug connector so that the sealing of the housing (74) is maintained. The switch (72) can accordingly withstand the harsh environment of a harvester header.</p> |
