Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
  • G05D16/00—Control of fluid pressure
  • G05D16/20—Control of fluid pressure characterised by the use of electric means
  • G05D16/2006—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means
  • G05D16/2013—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means
  • G05D16/2024—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means the throttling means being a multiple-way valve

Definitions

• the invention relates to a directly controlled, self-adjusting, three-way proportional pressure magnet valve
• a valve housing having a boring, an inlet port, an outlet port and a load port, a sliding piston having control edges and a solenoid magnet providing a force on the piston in a direction corresponding to an opening of the inlet port and a closing of the outlet port, the piston being biased in the opposite direction by the pressure in the load port.
• the valve can be used in systems involving relatively high pressures of 30 to 150 bar or even higher for applications where high accuracy, small hysteresis, quick response and small leakage are required.
• Hydraulic proportional pressure magnet valves are valves in which the hydraulic pressure in the load port can be adjusted approximately proportional to a control value, such as the power of an electric current to a solenoid magnet.
• pilot valve which controls the piston of the main proportional valve.
• All these pilot controlled valves which exist in various embodiments in the market, have disadvantages in that they have either poor accuracy, large hysteresis (in a graph of magnetic current against pressure) , slow response or too high leakage. Additionally, many embodiments are vulnerable with respect to dirt.
• a directly controlled proportional valve having a piston.
• one end of the piston is biased by an armature and the other end by a mechanical spring.
• the pressure in the load port may be transmitted to the end of the piston in order to act thereon in the same direction as the spring, i.e. in the direction corresponding to a closing of the inlet port.
• This hydraulic pressure and the spring force counteracts the force from the armature on the other side, so that the piston is balanced and the valve becomes self-adjusting.
• All previously known solutions employ at least one spring stabilizing the main piston.
• the advantage of a spring is that already prior to an increase in the pressure a certain current in the solenoid windings is required, whereby a stable pressure characteristic from zero is obtained.
• By replacing the spring with another spring having a different characte ⁇ ristic curve it is furthermore possible to obtain an adap ⁇ tation to various ranges of pressure control.
• On the other side either a larger hysteresis (in the graph for the magnet current versus pressure) or a larger leakage is obtained.
• the heat development in the magnet is also increased, which in turn adversely influences the hysteresis.
• valve must be tuned in accordance with the actual charac ⁇ teristic curve of the spring, which increases the production costs. Further, the characteristic curve of the spring varies with the temperature. Other disadvantages are based on the fact that a spring involves a slower response and instability problems (mass oscillations) and consumes part of the magnet force. Another reason that a spring has been regarded as indispensable, may be that the hydraulic counter-force co ⁇ operating with the spring can only be obtained with a certain delay which depends on the volume of the hydraulic fluid on the load side. Without a spring too large amplitudes of the control piston may therefore easily occur.
• the object of the invention is to provide a proportional pressure magnet valve which is devoid of the disadvantages referred to above, for use in an operational range which makes the characteristic curve of the valve in the lower part of the pressure range of no concern.
• the proportional pressure magnet valve according to the invention is characterized in that the characteristic curve of the solenoid magnet, i.e. the force exerted versus the position of the armature at constant current, is declining in the direction of positive force over the entire effective operational area in order to provide a stable balance with the counter-force from the load pressure and thus a self- adjusting valve without the assistance of mechanical springs.
• the movements of the control piston may be kept within reasonable limits in spite of the fact that the counter-pressure requires some time to develop.
• the characteristic curve must be distinctly declining.
• a preferred minimum value for the decline over the operational area used is 1 N/mm.
• the decline should not be too steep, since the return forces can then be too strong and cause over- steering and oscillation phenomena.
• a suitable maximum value for the decline in the force is 5 N/mm.
• Another important feature of the invention is the use of a positive overlapping of the outlet port (reservoir port) and the inlet port (pump port) by the control edges of the piston. This involves that the distance between the control edges of the piston is smaller than the distance between the inlet port and the outlet port.
• the positive overlapping reduces leakage through the valve, which allows use of smaller pressure pumps.
• Previously known proportional pressure magnet valves have a distance between the control edges corresponding with very close tolerances to the distance between the ports.
• the positive overlap is rather small, preferably smaller than 1 mm, which is still suffi ⁇ cient to make it unnecessary " for the tolerance of the distance between the control edges of the piston to be kept so small as to create problems in the machining of the piston or the ports.
• the advantages achieved according to the invention specifi ⁇ cally consist in that the valve reacts with a minimum time lag and has a great accuracy and small leakage or consumption, respectively.
• the production costs of the valve are reduced because the positive overlapping of the control edges allows the manu ⁇ facture to take place with larger tolerances without the hysteresis becoming unduly large.
• valve according to the invention has good stability margins at pressures up to 200 bar.
• An adaptation of the valve to different pressure ranges is effected in a simple manner, in fact merely by changing the piston diameter on which the load port pressure acts.
• Fig. 1 illustrates an axial section through a proportional valve according to the invention.
• Fig. 2 illustrates magnet force characteristic curves, showing the magnet force versus the armature position with the current as a parameter.
• a piston 2 which has two control edges 4 and an extension 5, can reciprocate in a boring in a valve housing 1 and is activated by a solenoid magnet 3 through an armature rod 6.
• the valve housing has an inlet port 9 (pump port) and an outlet port 10 (reservoir port) as well as a load port 11 which leads to the device (not shown) the pressure load of which is to be adjusted.
• a passage 7 from the load port 11 to the end of the boring in the valve housing into which the extension 5 extends.
• this connection may be provided by a passage 8 through the piston 2.
• the pressure in the load port will thereby provide a counter-force to the force from the solenoid magnet 3.
• the solenoid magnet 3 which operates in conjunction with the counter-pressure on the piston extension 5, has a charac ⁇ teristic force curve as shown in Fig. 2.
• the proportional valve is completely without mechanical springs, which means that disturbing mass oscillations are largely avoided. This is possible because the characteristic curve is declining in the direction of a positive force.
• Pressure medium is supplied through the inlet port 9 when the magnet current and thereby the magnet force increases, so that the piston is shifted to the right in the Figure. The pressure in the load port 11 will then increase. When the magnet forces are reduced the piston will be shifted to the left, and pressure medium will then be discharged through the outlet port 10, thus reducing the pressure in the load port 11.
• valve according to the invention is rather insensitive to temperature changes.
• the piston diameter can be chosen without having to provide room for a spring. Pro ⁇ blems with mass oscillations are reduced, and the hysteresis is improved, which provides a quick response.
• valve according to the invention solves tasks which no prior valve has solved, and opens for completely new applications of such valves for precision control.

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• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Automation & Control Theory (AREA)
• Magnetically Actuated Valves (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=19890032

Family Applications (1)

Country Status (4)

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Family Cites Families (4)

• 1987
  • 1987-06-17 NO NO872525A patent/NO163341C/no not_active IP Right Cessation
• 1988
  • 1988-06-17 EP EP88905243A patent/EP0318552A1/en not_active Withdrawn
  • 1988-06-17 JP JP63504889A patent/JPH01503818A/ja active Pending
  • 1988-06-17 WO PCT/NO1988/000054 patent/WO1988010461A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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