Application of Damping Hole Half – bridge in Variable – load – sensitive Pump Control

February 6, 2017 · Posted in Uncategorised 

Application of Damping Hole Half – bridge in Variable – load – sensitive Pump Control

Pressure control valve principle chart [1]

Pressure control valve principle chart [1]

1, three schematics triggered thinking
Damping holes are widely used in hydraulic systems, of course, do not miss the pump control valve. Small damping holes in different occasions to play a different role: stable pressure; slow shock; delay response and so on. But with the realization of the pressure flow control function of the three pump control Drilling Machine for Sieve Plate valve schematic diagram, causing a small series of i interest. Interested to Xiaobian: from Parker, Rexroth and Danfoss control valves are load-sensitive and pressure cut off (compensation) function, but the location of the orifice layout has its own characteristics.

P2 Pump L1 Control Valve Schematic [2]

P2 Pump L1 Control Valve Schematic [2]

Rexroth A10VO Pump DFR Control Valve Schematic [3]

Rexroth A10VO Pump DFR Control Valve Schematic [3]

Danfoss S45 Pump LS Control Valve Schematic [4]

Danfoss S45 Pump LS Control Valve Schematic [4]

From the above schematic, it can be seen that Parker and Rexroth control valves are in the form of independent dampers (A and B in the diagram), and Danfoss’ dampers (A and B) are integrated into the control spool. Although the design is different, but the final realization of the pressure and flow control tube punching machine, it shows that the three schematics in the A, B damping holes follow the same basic principles?
2, structure vs. principle
Before we get to the basics, it may be helpful to discuss how each of these schematics is implemented in a different structure, perhaps to help us understand how it cnc drilling machine works.

Parker P2 pump pressure control valve structure diagram [5]

Parker P2 pump pressure control valve structure diagram [5]

Parker’s pressure-control valves mount the damping hole A by increasing the parallel bypass. 【I small series as the collection of materials is limited, can not find the right pressure and flow control valve structure diagram】

Rexroth A10VO pump DFR control valve structure [6]

Rexroth A10VO pump DFR control valve structure [6]

Rexroth A, B damping holes are processed in the same damping plug, the left and right side of the thin-walled holes corresponding to the schematic of the B-damping and A damping.

Danfoss S45 pump LS control valve structure diagram [4]

Danfoss S45 pump LS control valve structure diagram [4]

Danfoss A, B damping is not through the additional form of damping holes to achieve, but through the special processing of the spool shoulder to achieve the role of damping holes. This design reduces the type of parts, more simple.
3, the principle behind the schematic
In a lot of information, we can see some explanations of the above-mentioned damping holes, but mainly focus on the structure size and the role of the introduction, but rarely mentioned behind the theory CNC Angle Line. In this issue i small series to Parker’s pressure control valve, for example, to summarize the principle behind the schematic. The pump control system is simplified, you can abstract the structure diagram is as follows:

Parker with pressure control valve pump structure diagram [1]

Parker with pressure control valve pump structure diagram [1]

Through analysis of the above structural principle diagram, it is not difficult to find that the valve port controlled between the valve core and the valve hole is essentially a variable damping, and the DB fixed damping of the rear end together forms the C type hydraulic half-bridge. P0 is the input pressure of the C-type hydraulic half-bridge, PA is the output pressure side, used to change the servo piston chamber pressure, thus controlling the servo piston movement.
Pump of any control, and ultimately to change the pump swashplate angle to achieve their own control purposes, and the servo cavity pressure is an important factor to change the angle of the swashplate. Effective control of the servo chamber pressure has become the design of the points.

C-type hydraulic half-bridge structure of the pressure control valve pump diagram [1]

C-type hydraulic half-bridge structure of the pressure control valve pump diagram [1]

Based on the diagram of the pressure control valve and related dimensions, the sensitivity parameter of the spool can be obtained: Sx = Av / Cv Av – spool cavity area; Cv – spring stiffness. That is, the change in the unit pressure P0 caused by the displacement of the valve core [1].

C-type hydraulic half-bridge dimensionless pressure curve [1]

C-type hydraulic half-bridge dimensionless pressure curve [1]

Based on the C-type half-bridge dimensionless pressure curve, it can be seen that the slope of the curve at 0.25P0 is the largest, that is, the pressure gain E0 is maximum. At this point the servo chamber pressure changes the most sensitive [1]. According to the structural parameters of a control valve, you can calculate:
Sx = 0.0162 mm / bar
E0 ≈ 1300 bar / mm [at P0 = 200 bar]
A change in outlet pressure P0 of 1 bar results in a change in servo-chamber pressure PA of 21 bar [1] at K = 21 bar / bar [at P0 = 200 bar].
4, hydraulic half-bridge
In addition to the C-type hydraulic half-bridge, there are A-and B-type half-bridge structure. The main difference is that A-type half-bridge on both sides are variable damping structure; B-type is the C-type image, the input damping is a fixed damping structure.
A-type half-bridge has good symmetry, high linearity and gain a little bit, but to control the bilateral axial dimensional accuracy, process requirements are higher; B / C half-bridge gain moderate, large margin, Lower requirements, so this is why such a half-bridge structure commonly used in a variety of control valve reasons [7].

A-type and B-type hydraulic half-bridge structure principle [1]

A-type and B-type hydraulic half-bridge structure principle [1]

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