Blade rotating, blade tripping and shock absorbing hydraulic cylinder for scraper-type snow plows

Claim 1

In a vehicle carried snow scraper having a blade rotatable in one direction to a raised position out of contact with the road and rotatable in a reverse direction to a lowered position in contact with the road, motor means for rotating the blade, comprising: a fluid reservoir and a source of fluid under pressure, at least one hydraulic cylinder oscillatably secured to a scraper portion fixed to the vehicle, the cylinder having a piston therein fixed to one end of a piston rod, a second floating piston through which the rod is slideable, the pistons being resiliently spaced by a compression coil spring around the rod, passages into the cylinder at the fixed piston end and at the floating piston end, the blade having ear means projecting therefrom, the other end of the rod being pivotally secured to the ear means, a four way pilot valve; tubular lines from the pilot valve connected respectively to the source of pressure fluid, the fixed piston end passage, the reservoir, and the floating piston end passage; the pilot valve having a first position for connecting fluid under pressure to the fixed piston end passage by one valve passage for raising the blade and connecting the floating piston end passage to the reservoir by another valve passage, the pilot valve having a second position for connecting fluid under pressure to the floating piston end passage by one valve passage for lowering the blade and connecting the fixed piston end passage to the reservoir by another valve passage, the line from the pilot valve to the floating piston end passage including a hydraulic relief valve and a pilot operated check valve in that order connected therein, the relief valve having a cracking pressure chosen to turn the blade into contact with the road and to apply sufficient pressure to the road so as to compress the cylinder spring to substantially half its free length, a tubular line leading from the relief valve to the reservoir for carrying off fluid when the relief valve is cracked, the check valve having a chamber therein and a piston in the chamber adapted to open the check valve when the chamber is subjected to pressure, and a tubular line from the chamber connected to the line from the pilot valve to the fixed piston end passage for opening the check valve when the blade is raised, whereby the blade is raised when the pilot valve is moved to its first position and the blade is lowered and spring loaded when the pilot valve is moved to its second position and the cylinder acts as a shock absorbing trip for the blade when it meets an obstruction thereby further compressing the cylinder spring.