JPH0232472B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the manufacture of a magneto flywheel comprising a non-magnetic rotor having a stator coaxial with the rotor and at least one arcuate permanent magnet cooperating across an air gap. Regarding the method.

Rotating permanent magnets are used in magneto flywheels for generating ignition panels for internal combustion engines in conjunction with a stator. The magnet has a radial magnetic flux associated with the air gap that provides the necessary current pulses in the stator windings. For effective operation, the magnets must be as close as possible to the air gap, and keeping in mind air circulation and manufacturing possibilities to obtain the stator and flywheel concentrically with each other, the air gap should be narrow. is optimal.

The permanent magnets of magneto flywheels are typically constructed in an arcuate shape with a concave or convex cylindrical surface in close proximity to the cylindrical surface that defines the air gap. In the former case the flywheel cooperates with the inner stator and in the latter case with the outer stator. The flywheel is made of non-magnetic material,
For example, it includes a rotor made of aluminum alloy and permanent magnets that are fitted into recesses of the rotor and fixed thereto. The flywheel can be provided with permanent magnets that cooperate with the ignition stator as well as with another stator to operate as a generator.

Permanent magnets currently used are usually so-called ceramic magnets. Although these ceramic magnets are capable of very high saturation and are therefore effective, ceramic magnets are also very brittle and
It can only be machined by grinding. The attachment of the magnets to the flywheel must be carried out with great care so that there is no risk of the magnets being exposed to stress and breaking during this process.

To obtain maximum magnetic flux across the air gap,
It is advantageous to fix the magnets in recesses in the cylindrical surface delimiting the air gap of the rotor, so that the magnetic poles are in direct contact with the air gap. however,
The requirements for this are that both the rotor and magnet surfaces are
It is pre-machined prior to installation, which means that relatively complex measures are required during the installation process to achieve the necessary uniform concentric section surfaces for the air gap.
However, in practice it is not possible to first mount the magnets on the rotor and subsequently machine the air gap section to its final shape and dimensions. This is because the magnets and rotors each require different machining operations. Advantageously, the magnets can only be machined by grinding, whereas the rotor can only be machined by turning. In an attempt to solve this problem, magnets were equipped with ferromagnetic pole pieces. Unfortunately, ferromagnetic turning chips stick to the pole piece and are rarely removed, making turning (or other cutting tool machining operations) impossible or extremely difficult. There is a serious drawback.

It is an object of the present invention to provide a flywheel magneto without significantly affecting the effectiveness of the flywheel magneto.
The object of the present invention is to provide a method for manufacturing a magneto flywheel of the type described in the introduction, in which ceramic permanent magnets are provided in an arrangement that substantially facilitates the manufacture of the magneto.

To achieve the above object, the method for manufacturing a magneto flywheel according to the present invention comprises a rotor blank having at least one recess delimited by a cylindrical surface for engaging a permanent magnet, delimiting an air gap. The rotor surface is manufactured by die-casting with allowance for machining, the cylindrical surface of the permanent magnet is placed against the cylindrical surface of the rotor, the permanent magnet is fitted into the recess, and the backing plate is attached to the permanent magnet facing the opposite side from the air gap. The air gap is sectioned by inserting it into the recess against the arched surface of the magnet and filling the remaining space in the recess with stabilizing plastic material, leaving a thin wall of rotor material between the permanent magnet and the air gap. This consists of machining and removing the estimated machining allowance on the rotor surface.

In this way, the invention takes advantage of the fact that flywheel magnetrotor blanks can be die-cast according to known techniques, with support surfaces precisely shaped to provide complementary support surfaces for the magnets. For assembly, the magnets are simply and precisely inserted into their correct position and stabilized by molding the magnets in a plastic compound without applying mechanical effects to the magnets. Subsequent machining of the rotor section facing the air gap is performed only on the rotor material and does not cause any problems.
It has been discovered that the remaining wall of rotor material between the air gap and the magnets can be made very thin. because,
This is because the wall facing the magnet is supported by the molded magnet through a very thin molded plastic material between the magnet and the wall. The magnets are very tightly moored to the rotor, but this applies to both inwardly and outwardly facing magnets.

In particular, if the magneto flywheel is an outwardly facing magnet surrounded by an outer stator,
In an advantageous embodiment, the magnet can be further anchored in the recess by anchoring a backing plate connected to the back side of the magnet to the wall of the recess of the magnet. Thus, the centrifugal force acting on the magnets is substantially transmitted to the rotor via the backing plate, so that the thin wall of rotor material left towards the air gap is not exposed to any significant stress.

Since the wall of rotor material left towards the air gap can have a thickness of several tenths of a millimeter, no significant attenuation of the magnetic flux occurs.

Hereinafter, embodiments of a magnetic flywheel manufactured by the method of the present invention will be described with reference to the accompanying drawings.

The magneto flywheel shown in FIGS. 1 and 2 consists of a cylindrical annular flange 2 and a rotor plate 3.
It includes a rotor 1 having a hub 4 and a hub 4. A plurality of fan blades 5 are arranged along the outer circumference of the flange. The blades in the diagram are oriented radially,
Advantageously, it is curved in the circumferential direction of the rotor, ie in the direction of rotation. The rotor is suitably formed by die-casting of an aluminum alloy, the said parts being integral or having a separate hub 4, for example made of steel, as shown in FIG.

An inner cylindrical surface 6 coaxial with the axis A-A of the rotor,
It forms the radially outer ring of the air gap between the flywheel and the cooperating stator (not shown). As can be seen in FIG. 1, the cylindrical surface 6 extends only partially around its circumference, i.e. along two symmetrically opposed circumferential sections, each circumferential section having a central angle of approximately 90°. spread across the country.
Between these two parts, an annular flange 2 is internally delimited by a cylindrical part of a slightly larger radius,
These cylindrical sections form relief surfaces during the final machining of surface 6, as will be explained in detail below. The die-cast rotor blank has a machining allowance 17 shown in dashed lines in the figure.

A recess 11 is arranged in alignment with each cylindrical surface 6. An axial cross-section of the recess can be seen in FIG. The recess is open towards the rotor end face shown and has an inner cylindrical wall 12 coaxial with the outer wall to the rotor axis A--A. There is also a side wall 1 in the recess.
3 and 13 are provided.

The rotor blanks described above are made with regular die-casting tolerances for details of the kind in question, with particular care being taken on the cylindrical surface 12 so that the total radial tolerances are within ±0.1 mm with respect to the rotor axis.
This tolerance can be maintained without difficulty using means conventional in the art.

The ceramic permanent magnet 7 shown in FIG.
It is embedded in 1. This magnet is arch-shaped,
The radially inner cylindrical surface 8 is coaxial with the outer cylindrical surface 9. The magnet is partitioned by two end faces 10,10. The inner cylindrical surface 8 is ground to a complementary radius to the surface 12 of the recess 11. The distance between the substantially parallel end faces 10,10 of the magnet is slightly smaller than the distance between the end faces 13,13 of the recess 11 parallel to the faces 10,10. The ends of the magnet have north and south poles with radially directed magnetic flux, and these poles are reversed at each end of the magnet. A ferromagnetic backing plate 15 is connected to the arched outer surface 9 of the magnet. Between the poles at each end is a non-magnetized portion indicated by O. Place the magnet at end face 1 in the direction of rotation of the flywheel (as indicated by the arrow in Figure 1).
It is fitted into the recess 11 so that the cylindrical surface 8 engages with the inner cylindrical surface 12 of the recess.
As can be seen in FIG. 1, the radial width of the magnet with the backing plate is smaller than the radial width of the recess 11.
A backing plate 15 is joined to the magnet 8 and both are molded into the indicated positions of the recess 11 using a suitable stabilizing plastic material 16, such as urethane plastic or epoxy resin containing talcum powder. Ru. A plastic material fills the space between the recess and the magnet with backing plate and forms a thin bonding layer between the contact surfaces 8 and 12 of the magnet and the recess, respectively.

Between the cylindrical contact surface 12 and the cylindrical surface 6 delimiting the air gap, a thin cylindrical wall 14 of rotor material is formed after final machining. This wall should be between 0.2 and 1.0 mm, preferably 0.3 and 0.5 according to normal conditions
With a thickness between mm.

An embodiment of a magneto flywheel manufactured by the method according to the invention is shown in FIG. 1, in which there are point-symmetrically opposed permanent magnets, but only one magnet is shown in detail. do not have. The opposite side, on the other hand, is shown in dash-dotted lines with respect to the hoops of the associated recesses. however,
The flywheel often has only one permanent magnet, of course without the symmetrically opposed cylindrical part surfaces 6 and the associated recesses 11;
It is then replaced by a counterweight or other shaped rotor to allow static and dynamic balance.

The above magnet is manufactured as follows.

A blank for the rotor 1 is manufactured by die casting of a suitable aluminum alloy. The blank has conventional machining allowances, such as on the hub portion, in accordance with common practice, but otherwise has prefinished surfaces. This applies in particular to the recess 11 which has an inner cylindrical surface 12, said surface being made with a radial tolerance of ±0.1 mm. A special machining allowance 17 is provided for the cylindrical surface 6 delimiting the air gap. A conditioned, magnetized permanent magnet 7 having a polished inner cylindrical surface 8 and an attached backing plate 15 is mounted such that surface 8 engages recessed surface 12 and one end surface 1
0 is fitted into each recess 11 so that it engages with the end surface 13 of the recess. At this time, these engaging surfaces should be located at the front end of the magnet in the direction of rotation.
To ensure good contact between surfaces 8 and 12,
An elastomagnetic arcuate holder or full ring is applied to the free surface of the machining allowance 17. then,
The magnet is pressed against the surface 12 by its own magnetic attraction force. At this location, the stabilized plastic material is molded into the space around the magnet with the backing plate. After the plastic material (urethane plastic or epoxy resin may be used) hardens, the magnet 7
is rigidly moored in its definite final position, with its inner cylinder and pole faces coaxial with the rotor axis A-A within the given tolerances and with its front end face 10 at a precisely determined position in the circumferential direction. , thereby precisely determining the angular position of the transmitted ignition pulse. Since the length between the end faces of the magnet is smaller than the corresponding length 12 of the recess 11, care is taken of possible length variations of the magnet. The magnet can thus be accommodated within the length tolerances that are unavoidable when manufacturing ceramic magnets, without the need for adjustment by grinding.

The stabilizing plastic material is injected hot in a narrow strip so that it lies between the polished contact surface 8 of the magnet and the die-cast contact surface 12 of the recess at a point where the magnet does not directly engage the surface 12 of the recess. , filling a very narrow space is unavoidable. After the plastic material has hardened, the rotor surface 6 is finally machined, for example by turning. Due to the stabilizing effect of the plastic layer and the magnet support surface 8, the rotor material can be machined so close to the recess 11 that only a thin wall with a thickness of approximately several tenths of a millimeter remains. . This thickness is usually between 0.3 and 0.5 mm, but may exceed or fall below this interval, and thus may vary between 0.2 and 1.0 mm as appropriate. can.

3 and 4 show another embodiment of a flywheel manufactured by the method according to the invention. In this case too, the main part of the flywheel consists of a rotor comprising a cylindrical annular flange 21, a rotor plate 22 and a hub section 23. The rotor is provided with a plurality of fan blades 24 having radial extensions as shown in FIG. 2, but these blades may also be curved in the direction of rotation of the flywheel. In this case, the flange 21 is formed with two symmetrically opposed projections 25, each of which contains a permanent magnet 27, an outer coaxial ridge with a winding in order to generate an ignition pulse in the passage of the magnet. Rotor (not shown)
We are starting to collaborate with The protruding portion 25 is
The air gap between the rotor and the stator is radially bounded by a cylindrical surface 26. magnet 2
7 has an outer polished cylindrical surface 28 in contact with the radially outer cylindrical surface 32 of the recess 31 in the projection 25. As before, this recess is open towards the illustrated end face of the rotor and is delimited by the other two end faces 33, 33 and an arcuate inner face. A recess 31 is separated from the cylindrical surface 26 delimiting the air gap by a thin wall 34. A backing plate 35 is attached to the inner arcuate surface 29 of the magnet. As in the previous embodiment,
The distance between the end faces 30, 30 of the magnet is smaller than the distance between the end faces 33, 33 of the recess 31. magnet 27
is placed in the recess 31 with its end surface 30 engaged with the end surface 33 of the recess, and at this time, the surface 30 is
at the front end of the magnet in the direction of rotation (indicated by the arrow in the figure). As in the previously described embodiment, the radial width of the recess 31 is greater than the radial width of the magnet with the backing plate 35, so that the radial width of the recess 31 extends between the backing plate and the radially inner cylindrical surface of the recess. There is space left.

As for the nature of the magnet and the rest of the performance,
Permanent magnet 27 corresponds to the magnet in FIG. As in the previous embodiment, the permanent magnet 27 is molded into the recess 31 using a suitable hardened plastic material 16. It will be noted, however, that the backing plate 35 of the magnet 27 according to FIG. 3 projects onto the end face 33 of the recess 31. This performance stabilizes the magnet in its position in the recess. This is because the magnets are glued to a backing plate that meshes with the rotor. As the flywheel rotates, the centrifugal force acting on the magnets is mostly transmitted to the rotor projections 25 through the backing plate, so that the thin walls 35 are not exposed to significant centrifugal forces from the magnets.

Although only one permanent magnet 27 is shown in detail in FIG. 3, the symmetrically opposed magnets are indicated by the dotted outline of the associated recess 31. In certain cases, if the rotor is provided with only one magnet, then the symmetrically opposed magnet shown in FIG. .

As can be seen from FIG. 3, a plurality of permanent magnets 41
are arranged in a ring around an inner cylindrical surface 40 defining an air gap with respect to the stator (not shown). In cooperation with the stator, these magnets form a generator for providing generator current. Magnet 41 is constructed in the same way as magnet 7 in FIG. Therefore, the magnet 41 has a cylindrical surface 4
an inner, polished cylindrical surface 4 for engaging 5;
2, which cylindrical surface constitutes a continuous cylindrical surface radially inside the annular slot 44 in the rotor 20. This slot is separated by a thin wall 46 from the cylindrical surface 40 defining the air gap. The annular slot thus constitutes a continuous extension of the magnet recess in the recess embodiment described above. Along their outer arched surfaces 43,
A magnet 41 is connected to a common annular backing plate 47. This backing plate engages the radially outer wall of the groove 44. The magnets are stabilized in their position by being molded with plastic material 16 of the type described above.

The magneto flywheel according to FIGS. 3 and 4 is manufactured in a manner similar to that described in connection with FIGS. 1 and 2. For that purpose, the rotor 20 is
The outer cylindrical surface 26 defining the air gap for the outer stator and the inner cylindrical surface 40 defining the air gap for the inner stator are die cast with machining allowances 17. The permanent magnet 27 for generating the ignition pulse is arranged in exactly the same manner as described above in its precise radial and circumferential position by contact with the respective faces 32 and 30 of the recess 31. During die casting, the backing plate 35
is inserted into the slot provided in the rotor portion 25 in advance. To assemble the generator magnet 41, the magnet is attracted to the cylindrical surface 45 of the annular slot by mounting a ferromagnetic ring against the free surface of the inner machined allowance 17.

[Brief explanation of drawings]

1 is an end view of a magneto flywheel manufactured by the method according to the invention, capable of cooperating with an inner stator for generating ignition pulses; FIG. 2 is a cut along the line - of FIG. 1; 3 is a partial sectional view, FIG. 3 is an end view of a flywheel manufactured by the method according to the invention, capable of cooperating with an outer stator for generating ignition pulses and an inner stator for generating electric current; FIG. FIG. 3 is a partial cross-sectional view taken along line - of FIG. 3, and FIG. 5 is an end view of the permanent magnet of the flywheel of FIG. 1 with a backing plate connected thereto. 1... Rotor, 1, 20... Rotor recess,
7, 27, 11... Arch-shaped permanent magnet, 12, 3
2, 45... Cylindrical support surface, 14, 34, 44...
...Thin walls of rotor material.

Claims (1)

[Scope of Claims] 1. A die-cast rotor of non-magnetic material with at least one ceramic permanent magnet disposed across an air gap and cooperating with a stator;
and said permanent magnet is adapted to engage with a complementary cylindrical surface coaxial with the axis of the rotor with its cylindrical surface, for engaging the permanent magnets 7, 27, 41; A rotor blank having at least one recess 11, 31, 44 delimited by a cylindrical surface 12, 32, 45 of the rotor surface 6 delimiting the air gap,
26, 40 are manufactured by die casting with a machining allowance of 17, and the cylindrical surfaces 8, 28, 42 of the permanent magnets are attached to the rotor 1,
The permanent magnet is fitted into the recess by leaning against the cylindrical surface 12, 32, 45 of 20, and the backing plate 15, 35, 47 is placed against the arched surface 9, 29, 4 of the permanent magnet facing away from the air gap.
Insert the plastic material 1 into the recess leaning against 3, and stabilize the remaining space in the recess.
6, and the machining allowance 17 of the rotor face delimiting the air gap is machined away so that a thin wall 14, 34, 46 of rotor material remains between the permanent magnet and the air gap. Method. 2. A method as claimed in claim 1, in which an arch-shaped holder of magnetic material is placed against the free surface of the machining allowance when the permanent magnet is fitted. 3. The method according to claim 1, wherein the permanent magnets 7, 27, 41 are joined to the backing plates 15, 35, 47 when they are fitted into the recesses.