Device for electrohydraulically lifting agricultural implements

In an electrohydraulic device for lifting agricultural implements, said device comprising a hydraulic lifting jack having a hydraulic fluid reservoir, a constant stroke-volume pump connected to said reservoir,

• a stepless distributor with a valve body and a slide valve therein and connected to said pump and to said jack via a check valve, a pressure regulator piloted by the pressure at the lifting jack and connected to said pump to regulate its fluid discharge, a downstroke return valve for descent of the implements, connecting said distributor to said reservoir, and a relay valve means for connecting the piloting pressure of the regulator to the reservoir during downward movement of the implements, an improvement comprising the combination therewith of:
• a flow reducing valve fed by said pump in parallel with said distributor and said regulator,
• piloting electrovalve means for determining the position of the stepless distributor and fed by the reducing valve,
• said distributor having first and second control chambers at the opposite ends of the slide valve,
• said first control chamber having a cross-sectional area substantially equal to one-half of that of the second said control chamber,
• said first control chamber being directly connected to said reducing valve, and
• said slide valve having means for alternately isolating said second control chamber from said reservoir, for placing in communication with said reservoir, and for placing it in communication with the first chamber, depending on the condition of said electrovalve,
• a first electronic pickup for detecting and signalling the desired position of said implements,
• a second electronic pickup for detecting and signalling the actual position of said implements,
• a third electronic pickup for detecting and signalling the desired tractive stress on the implements,
• a fourth electronic pickup for detecting and signalling the actual stress on said implements,
• a fifth electronic pickup detecting and signalling the position of the slide valve of the distributor, and
• electronic control means for controlling said device and comprising
• a first comparator which compares the signals of said first and second pickups and puts out a difference signal,
• a second comparator which compares the signals of said third and fourth pickups and puts out a difference signal,
• a third comparator which determines between the difference signals of said first and second comparators that signal for indicating the larger amount of lift of the implements,
• a fourth comparator comparing the signal from the fifth pickup with the output signal of the third comparator, and
• actuating means actuated by said fourth comparator to actuate the electrovalve to cause the difference between the signal of the fifth pickup and that of the third comparator to approach zero.

A device for hydraulically lifting agricultural implements, comprising:

• a lifting jack,
• a pump with constant stroke volume connected by a fluid passageway to a stepless distributor,
• a flow pressure regulator of the pump piloted by the pressure of the lifting jack,
• downstroke valve means adapted to connect the distributor to a reservoir for lowering the implements,
• a relay valve means for connecting to the reservoir the piloting pressure of the regulator in the downward movement of the implements,
• a reducing valve fed by the flow circuit of the pump, and
• at least one pilot electrovalve of the stepless distributor fed by the reducing valve.