Electrohydraulic control apparatus

• US 4,316,486 A
• Filed: 02/28/1980
• Issued: 02/23/1982
• Est. Priority Date: 10/09/1976
• Status: Expired due to Term

• Current Assignee: Danfoss A/S
• Original Assignee: Danfoss A/S
• Inventors: Petersen, Alex, Tandrup, Niels
• Primary Examiner(s): Cohen, Irwin C.
• Application Number:
  US06/125,502
• Time in Patent Office: 726 Days
• Field of Search: 91/454, 91/459, 91/442, 91/461, 137/625.64, 137/625.62, 137/625.63, 137/596.16, 137/596.14, 137/596.15, 251/86, 251/88
• US Class Current: 137/625.64
• CPC Class Codes: F15B 11/006 Hydraulic "Wheatstone bridge" circuits, i.e. with four nodes, P-A-T-B, and on-off or proportional valves in each link
• CPC Class Codes: F15B 13/043 with electrically-controlled pilot valves
• CPC Class Codes: F15B 2211/20538 constant capacity
• CPC Class Codes: F15B 2211/30525 Directional control valves, e.g. 4/3-directional control valve
• CPC Class Codes: F15B 2211/3116 the pump port being open in the centre position, e.g. so-called open centre
• CPC Class Codes: F15B 2211/3144 the positions being continuously variable, e.g. as realised by proportional valves
• CPC Class Codes: F15B 2211/31576 having a single pressure source and a single output member
• CPC Class Codes: F15B 2211/329 actuated by fluid pressure
• CPC Class Codes: F15B 2211/6355 having valve means
• CPC Class Codes: Y10T 137/86614 Electric
• CPC Class Codes: Y10T 137/87209 Electric

Abstract

The invention relates to an electrohydraulic control assembly of the type having a slide valve unit for controlling the operating direction of a hydraulic servomotor. The assembly includes a bridge circuit between the pressure source and the drain tank which has a pressure operated valve in each of its four branches. Diagonally opposite bridge terminals between the supply and exhaust branches of the bridge circuit are connected operating chambers on opposite sides of the slide valve unit. The bridge circuit valves are operated by solenoid valves to achieve selective directional operation of the slide valve unit.

Claims

1. An electrohydraulic control assembly for controlling the operating direction of a bidirectional hydraulic work motor, comprising, a control valve unit including a motor controlling slide valve with pressure chambers on opposite sides thereof, neutral position springs and means in said chambers for maintaining said slide valve in a neutral position in the absence of unequal pressures in said chambers, said slide valve being selectively movable in opposite directions from a neutral position in response to pressure in either of said chambers for motor controlling purposes, a source of pressurized fluid and an exhaust tank, a hydraulic bridge circuit between said source and said tank having two supply branches connected to said source and two exhaust branches connected to said tank, pressure holding means between said exhaust branches and said tank for holding the bridge outlet pressure above atmospheric pressure, said bridge circuit having diagonally opposite ports between said supply and exhaust branches connected to said slide valve pressure chambers, valves having pressure operated chambers including a pressure operated supply valve in each supply branch and a pressure operated exhaust valve in each exhaust branch, said supply and exhaust valves being pressure operable to closed positions, pressure dissipation means between said pressure operated chambers of said exhaust valves and said tank to effect unloading of said exhaust valves in the absence of loading pressures, said exhaust valves having ball type closure elements, solenoid pilot valve means connected to respective pairs of said pressure operated chambers of said supply and exhaust valves to effect selective closing of said valves to selectively pressurize and exhaust said control valve unit chambers to cause said slide valve to move in a selected direction, said slide valve having rapid movement to a neutral position upon the deenergization of a respective pair of solenoid pilot valve means and the subsequent release of operating pressures in said bridge valves by the action of one of said neutral position springs causing said slide valve to move and force fluid from one of said chambers to the other through said bridge valves in said exhaust branches, and valve opening spring biasing means for each of said exhaust valves for rapidly overcoming said pressure holding and dissipation means to rapidly open said ball type closure elements thereof in the absence of a closing control pressure to avoid a cavitational action by preventing the closing of an exhaust valve due to a strong suction developed in one of said chambers as a result of said rapid movement of said slide valve.

2. A control assembly according to claim 1 wherein said bridge valves on the supply side of said bridge circuit have ball type closure elements which are biased in the closing direction by valve springs.

3. A control assembly according to claim 2 wherein said bridge valves include differential pistons of which the larger piston area is subjected to control pressure.

4. A control assembly according to claim 1 wherein said pressure holding means is formed by a counterpressure valve.

5. A control assembly according to claim 6 wherein each of said bridge valves has a cylindrical portion with first and second ports being axially and circumferentially located respectively, each of said bridge valves being adapted to close said first port of the corresponding one of said valves, and all of said bridge valves being arranged relative to said control valve pressure chambers so that said axially located ports of said bridge valves have direct fluid communication with said pressure chambers.