JPS5929127B2 - dc solenoid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC solenoid in which a plunger is returned to its original position by the internal magnetic force of the solenoid itself, without requiring an external restoring force such as a spring.

DC solenoids that use permanent magnets to attract and hold a plunger are already widely used.

It is called a monostable solenoid. Since the plunger is held in the retracted position by the magnetic force of the magnet, there is no need to constantly energize the coil.

It is effective in reducing electricity costs. A spring force is always applied to the plunger forward, and the return force is generated by the elastic force of the spring. 5. It is possible to transition between two states simply by applying instantaneous current to the excitation coil.

Attraction and return operations are performed by energizing the excitation coil to enhance or cancel the magnetic flux created by the permanent magnet. The reason why a spring is used in this way is probably because the conventional DC solenoid, which did not have a permanent magnet and consisted only of a coil and a plunger, always had a spring for return purposes.

Even when a permanent magnet was added to the simplest DC solenoid to create a self-holding solenoid, a spring was used continuously. However, adding a spring requires an extra number of man-hours.

If you want to store the spring inside the yoke,
The effective volume within the yoke is reduced, and space for coils, etc. is limited 20. If the spring were to be attached to the outside of the yoke, the plunger and push rod would have to be extended, making them bulky. This prevents miniaturization of solenoids. Furthermore, the spring becomes fatigued due to repeated expansion and contraction operations.

It may break. The amount of displacement and elastic force of a spring are directly proportional.

When the plunger is attracted and held by the fixed iron core, the spring displacement is at its maximum, and therefore the elastic force is also at its maximum.
n Therefore, the attractive force of the permanent magnet had to be set to exceed the sum of the force required to pull the load and the elastic force of the spring.

The present invention overcomes these drawbacks.

Does not require a spring and uses plastic 35 instead of magnetic force itself.
Njia can be brought back. There already exists a DC solenoid that combines a permanent magnet and an excitation coil to move a plunger forward and backward without using a spring force.

This is a so-called bistable self-holding solenoid. this is,
A permanent magnet is provided in the middle, and two excitation coils of equal size are provided before and after this.

The plunger can be stopped in two stable states: a forward position and a rearward position. To change the state, the excitation coil on the stationary side of the plunger is momentarily energized to produce a magnetic flux in the opposite direction to that of the permanent magnet. A bistable solenoid is completely symmetrical around a permanent magnet. Therefore, the holding force is also equal in the front and rear directions. Furthermore, a fixed iron core is provided before and after the plunger to restrict the range of movement of the plunger.
At the same time, it has increased holding power. Bistable solenoids are
In this way, the plunger can be moved forward and backward without a spring force.

However, in many cases, the movement characteristics required of a solenoid do not need to be symmetrical.

There is not much requirement for the front and rear holding forces to be equal. In many cases, the holding force during suction is as large as several kilograms, but the force applied to the plunger upon return is only about 1/10 to 1/100.
For this reason, spring return type solenoids have been widely used. Furthermore, if a fixed iron core is provided at the front and back, as in a bistable solenoid, the plunger will not come out.

If dirt or small sand gets inside and deteriorates the sliding characteristics of the plunger, it cannot be removed. Furthermore, the stroke required of the solenoid is often as short as several micrometers.

For bistable solenoids, the stroke is only slightly less than the thickness of the excitation coil. This is because if the stroke is made significantly smaller than the thickness of the excitation coil, the magnetic resistance of the magnetic path on the opposite side will decrease, and the holding force will be reduced. For this reason, many bistable solenoids are small. Due to the limited dimensions, permanent magnets must be made of rare earth metals that produce a small but strong magnetic field. This is significantly more expensive than ferrite magnets. The present invention is different from either the monostable solenoid or the bistable solenoid and overcomes these drawbacks.

The DC solenoid of the present invention has an excitation coil at the rear of a permanent magnet, a magnetic front yoke in front with a spacer in between, and the whole body is surrounded by the magnetic yoke.

A new continuous magnetic path from the permanent magnet to the plunger to the front yoke applies the return force of the plunger.

EMBODIMENT OF THE INVENTION Hereinafter, the structure, operation, and effect of the present invention will be explained in detail with reference to drawings showing examples.

FIG. 1 is a vertical cross-sectional view of the DC solenoid according to the embodiment of the present invention when it returns to normal.

FIG. 2 shows a longitudinal sectional view of the suction holder. The yoke 1 is made of magnetic metal and is cut into a cross shape and then bent at four sides to form a case with a U-shaped cross section.

Four permanent magnets 2 are fixed in front of the yoke 1 so that the same poles face each other.

The plunger 3 is a round bar made of magnetic material and can move in the axial direction around the center of the yoke.

The fixed iron core 4 is a magnetic body fixed to the rear center of the yoke 1.

It is on the same axis as the plunger 3 and attracts the plunger. It also has the role of a stopper. The excitation coil 5 is provided immediately behind the permanent magnet 2 and between it and the rear end surface of the yoke.

The number of windings may be one system or two systems. The guide pipe 6 is made of a non-magnetic metal such as brass or a synthetic resin with excellent sliding properties such as polytetrafluoroethylene (PTFE).

This holds the plunger 3 so that it can move back and forth. Further in front of the permanent magnet 2, a front yoke 8 made of a magnetic material is provided with a spacer 7 in between.

The front yoke 8 is fixed to the front end of the yoke 1 by six caulks 7. The spacer is made of a non-magnetic material such as a baked plate.

The thickness is determined by the desired stroke. The tip of the non-magnetic push rod 9 has a male thread 10, which is screwed into a female thread hole 11 at the rear end of the plunger. The push rod passes through the core hole 12 of the fixed core 4. This is useful when removing the plunger. The opposing surfaces of the fixed core 4 and the plunger 3 are conical inclined surfaces 14 and 15.

This is to lengthen the stroke. In the arrangement shown in FIG. 1 at the time of return, the magnetic flux emitted from the permanent magnet 2
It passes through the front yoke 8 and returns from the yoke 1 to the permanent magnet.

Magnetic flux circulates in a short magnetic path that occurs in the front. plunger 3
When the front end of the front yoke 8 and the inner surface 16 of the front yoke 8 face each other with a minimum distance from each other, the thermal stress energy is the smallest. The illustrated state corresponds to this. In other words, this state is stable. A part of the magnetic flux of the permanent magnet detours backward and passes through the plunger 3 from the fixed iron core 4 through the air gap 17.

However, this is small. This is because the magnetic resistance of the air gap is large. Let x be the length of the gap 17, that is, the amount of advance of the plunger.

When the plunger is pushed back from the state shown in Figure 1, a forward reaction force appears at first.

As the plunger is pushed in further, the direction of the force changes, and a force is applied to the plunger in the direction of suction. The state shown in FIG. 2 shows the state in which the air is sucked in this way (x=0).

The suction power is strong. The magnetic flux of the permanent magnet is plunger 3,
It goes around the fixed iron core 4 and the yoke 1. Most of the magnetic flux crosses the ramps 14, 15, which creates a force that attracts the plunger backwards. On the other hand, since a gap 18 is formed between the front yoke 8 and the front end of the plunger 3, the magnetic flux is interrupted here. As described above, both FIG. 1 and FIG. 2 are stable states, but the degree of stability is completely different.

FIG. 3 is a graph showing an example of the relationship between the displacement x of the plunger and the backward thrust F that the plunger receives at this time.

The horizontal axis is in units of fins, and the vertical axis is in grams (9). The thrust force during suction, that is, the suction holding force is 32209, which is extremely large.

Once you get 1WIL, this will drastically decrease to 225g.

At about 1.411, the direction of the thrust is reversed and becomes a forward thrust.

Forward thrust is small.

411 takes the minimum value -210g.

When X=611, the thrust becomes O.

In fact, it is preferable to provide a stopper (not shown) in order to stop the plunger at a position where a certain amount of forward thrust remains.

This example can therefore be used as a solenoid with a stroke of 3-4u. The above are the static characteristics of the solenoid.
The small thrust force upon return is similar to a spring-type monostable solenoid. They also have a common feature in that they have a large holding power during suction. Therefore, the solenoid of the present invention can be used in place of a conventional self-retaining monostable solenoid. Next, regarding dynamic characteristics, in order to attract the plunger, the excitation coil is energized to generate new magnetic flux in the magnetic path surrounding the excitation coil.

This cancels the magnetic flux Φf circulating around the front yoke formed by the permanent magnet in front, and conversely generates a new magnetic flux 1r circulating around the fixed iron core. FIG. 4 schematically shows the state of the magnetic flux within the solenoid at the moment the transition begins.

Due to the magnetomotive force generated by applying the pulse current, a new magnetic flux F'r flows forward inside the yoke 1, but this
Fr passing through the permanent magnet 2, and Vr passing through the front yoke
It is divided into 2.

The front yoke flow F'R cancels the magnetic flux Φf caused by the permanent magnet and eliminates the attractive force between the plunger 3 and the front yoke.

Fr=Fr, +F2 (1) However, the total magnetic flux Fr produced by the solenoid passes through the air gap 17 between the plunger and the fixed iron core 4.

The plunger is attracted to the fixed core because a Maxwell stress is generated that is proportional to the square of the magnetic flux passing through the air gap.
The magnetic flux F'r at the time of attraction must be large to some extent.

Since the magnetic reluctance of the air gap is large, a large magnetomotive force (ampere turns) is required. In other words, a relatively large current is required. When I return, it's the exact opposite.

Since the plunger is attracted to the fixed iron core 4, there is a static magnetic flux Φg circulating around the permanent magnet, the plunger, the fixed iron core, and the yoke, which strongly holds the plunger by itself. FIG. 5 is a schematic diagram showing the magnetic flux distribution upon return. The excitation coil is energized in the opposite direction. This generates a new magnetic flux Vq that circulates backward in the yoke and forward in the plunger. A part becomes the magnetic flux Fql that passes through the permanent magnet 2 in the opposite direction to the magnetization. The remainder becomes the magnetic flux V/'Q, which flows across the air gap 18 to the front yoke. The total magnetic flux Vq is
This cancels the magnetic flux Vg previously formed by the permanent magnet.

The attractive force between the plunger and the fixed core disappears. Fq=F'q
1+Fq, (2) However, Vq2 has the effect of attracting the plunger to the front yoke 8.

The attractive force between the plunger and the fixed iron core disappears, and an attractive force is generated between the front yoke and the plunger, so that the plunger moves forward.

In this way, the return state shown in FIG. 1 is achieved. The current for return is smaller than the current for attraction.

This is because the magnetic resistance in the initial state is small and the magnetomotive force is small. There is a significant asymmetry between the suction and return movements.

It is not just that the current at the time of suction is larger than the current at the time of return. The permissible range also differs. From the above explanation,
The condition for magnetic flux cancellation during attraction operation is Vr2-Φr
(3) It follows that.

However, this condition is not strict. The voltage applied to the excitation coil is excessive, the magnetomotive force is too high, and Fr2>Fr(
4) It will operate without any problem even if

The case where the magnetic flux due to the magnetomotive force of the excitation coil exceeds the magnetic flux preliminarily formed by the permanent magnet is tentatively referred to as excessive cancellation. During suction (Figure 4), is the force that pulls the plunger toward the fixed core equal to the total magnetic flux? Due to Fr, part of the force that pulls the plunger back to the front yoke becomes magnetic flux Fr2.

The front yoke and the plunger face each other on the side, and the plunger and the fixed bolt face face each other on the end face. Even if the same magnetic flux passes through the front yoke, plunger, and fixed core, the force of attraction between the plunger and fixed core is greater. When attracting, is the magnetic flux always larger than the magnetic flux (Fr2Φr) passing through the front yoke? Fr passes between the plunger and the fixed iron core.

This is because Fr>Vr,>(v/'R2-Φr) (5).

Of course, at the beginning of suction, the front yoke and plunger are close together, and the plunger and fixed core are far apart.

Therefore, even if the same magnetic flux passes through a set of these members, the attractive force of the closer members should be greater. However, this is not a big difference. As shown in Figure 6, three
Two magnetic bodies A, B, and C are placed, and a constant magnetic flux in the axial direction is A.
, B, and C.

The attractive force between A and B and the attractive force between B and C are proportional to the ratio of the solid angles Ω1 and Ω at which B looks at A and C. The solid angle between the plunger and the fixed core is not many times smaller than 2π due to the short air gap 17.

Therefore, during suction, even if there is excess cancellation, the plunger is drawn toward the fixed iron core. This is because the force with which the front yoke pulls back the plunger due to the excess magnetic flux is extremely weak. However, at the time of return in Figure 5, in the case of excess cancellation,
This creates a rather difficult problem.

The conditions for magnetic flux cancellation are Fq=Φg (6).

Moreover, is the force of the front yoke pulling back the plunger a magnetic flux? According to Fq. What if there is excess cancellation? Fq〉Φg (7), but
The magnetic flux (Vq-Φg) produces an attractive force between the fixed iron core and the plunger.

Unless the suction force of the front yoke exceeds this suction force, the return operation will not proceed. Further, the front yoke and the plunger are separated, and the plunger and the fixed core are in contact with each other.

Even if the same amount of magnetic flux passes through the three members, the attractive force between the plunger and the fixed iron core is greater. How large it is depends on geometric conditions such as the angle of the inclined surfaces 14 and 15 and the distance between the front end of the plunger and the front yoke during suction. This ratio is m
shall be. This will be around 1-10. Furthermore, the total magnetic flux? Assume that only 1/n of Fq becomes Vq2.

n depends on the differential coefficient of the hysteresis curve of the permanent magnet, the magnetic permeability of the front yoke, etc. It is considered that n is a value close to 1 and never exceeds 2. Since the attractive force acting between two members is proportional to the square of the magnetic flux passing through them, the attractive force between the plunger and the fixed iron core is canceled by the excess (?Fq-Φg
) is written as (Fq-Φg)2 (8), then the attractive force between the plunger and front yoke can be written as Vql (1)2- (9) nm.

The conditions under which the return operation is possible can be found as (9)>(8). From these, it is necessary that the magnetic flux Fq for return by the excitation coil be between.

It can thus be seen that the current in the excitation coil upon return is limited to a narrow range.

However, it can also be seen that this range is not 0 and always exists. Since the DC resistance of the excitation coil is fixed, the applied voltage is limited within a certain range. Although such limiting conditions are imposed compared to a conventional DC solenoid that returns using a spring, both the return and suction operations are almost the same in other respects.

Since the solenoid of the present invention does not require a spring,
Spring installation work can be omitted.

Compared to the case where the spring is housed in the yoke, the volume occupied by the excitation coil and magnet can be increased. Therefore, if the volume is the same, a solenoid with excellent holding power and suction power can be manufactured. The stroke depends on the length of the forward gap 18 in FIG.

This depends on how far the front end of the plunger protrudes from the permanent magnet during suction and how thick the e1 spacer is. The stroke s is approximately equal to s=d-EOl).

The larger the stroke, the more power is required to drive the plunger.

In the case of a bistable solenoid, the stroke cannot be much smaller than the thickness of the excitation coil, so the entire solenoid has become smaller. Even this requires a sufficient holding force, so strong rare earth metal-based permanent magnets are often used. Unlike the bistable type, the present invention requires only one excitation coil.

Furthermore, the stroke is not limited by the thickness of the coil. Furthermore, the plunger cannot be removed from the bistable type. The DC solenoid of the present invention allows the plunger to be easily removed. It can also be replaced freely. The solenoid of the present invention is superior to conventional monostable and bistable self-retaining solenoids in these respects.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a DC solenoid in a restored state according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view in the suction state. FIG. 3 is a graph showing the relationship between the displacement x of the plunger from the suction position and the thrust force F received by the plunger. FIG. 4 is a schematic diagram showing magnetic flux distribution during suction operation. FIG. 5 is a schematic diagram showing magnetic flux distribution during return operation. FIG. 6 is an explanatory diagram showing the magnitude of attractive force when the same magnetic flux passes through three magnetic bodies in a cylinder. 1... York, 2.
...Permanent magnet, 3...Plunger, 4.
... Fixed iron core, 5 ... Excitation coil, 6.
...Guide pipe, 7...Spacer, 8
・・・・・・Front yoke, 9・・・・・・Pushing rod.

Claims (1)

[Claims] 1 A magnetic yoke 1, a permanent magnet 2 provided at the front of the yoke 1 and facing the same polarity, an excitation coil 5 provided at the rear of the permanent magnet 2, and a magnetic magnet provided movably in the center of the yoke. It consists of a plunger 3 and a front yoke 8 made of a magnetic material, which is provided in front of and separated from the permanent magnet 2 and has an inner surface 16 through which the plunger passes. A DC solenoid characterized by being spaced further back than 8.