Method of grinding half toroidal CVT disk

A half toroidal CVT disk having an inner surface portion, an outer surface portion and a toroidal surface having a given machining allowance is centered with said inner surface portion worked prior to the heat treatment of said half toroidal CVT disk as the standard thereof, and then is chucked by a chuck mechanism. The toroidal surface of the chucked half toroidal CVT disk is ground by a grinding mechanism with the grinding wheel for grinding the half toroidal CVT disk in a state that one of said half toroidal CVT disk and said tool is inclined at a given angle with respect to the other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of grinding a half toroidal CVT disk used as a continuously variable transmission in an automobile.

2. Description of the Related Art

A half toroidal CVT disk includes a disk-shaped disk main body1; and, as shown inFIG. 5, the disk main body1has an inner surface portion2consisting of a through hole formed in the central portion thereof, an outer surface portion3, and a toroidal surface4formed on one surface of the disk main body1. On one end side of the inner surface portion2, there is formed an inner surface involute spline portion5; and, on the other end side thereof, there is formed an inside diameter surface6. And, the toroidal surface4, inner surface involute spline portion5and inside diameter surface6, except for the outer surface portion3, must be respectively ground so as to have concentricity accuracy of a given value or higher.

For this reason, conventionally, for example, as disclosed in JP-A-2000-271844, in a state where the outer surface portion3is centered with the inner surface involute spline portion5as the standard thereof and is chucked in the thus centered state, the outer surface portion3is ground; and, with the thus ground outer surface portion3as the standard thereof, the toroidal surface4and inner surface portion2are respectively ground in separate steps.

Also, as a compound grinding machine, conventionally, there is known a compound grinding machine which, as disclosed in JP-A-10-235545, comprises a plurality of spindle devices each including a work chuck for chucking a work, while these spindle devices are carried on a swing table which is capable of indexingly swinging in such a manner to be able to correspond to a plurality of operation positions. At these operation positions, there are disposed two or more kinds of grinding devices and, using the grinding devices, the works chucked by the work chucks are respectively ground to thereby shorten the grinding time.

In case where the toroidal surface and inner surface portion of the half toroidal CVT disk are ground in separate steps, it is necessary to grind the outer surface portion as the common standard surface for securing the concentricity of these grinding surfaces. However, to grind the outer surface portion is not necessary for the function of the half toroidal CVT disk and thus the step of grinding the outer surface portion provides a great factor in the increased cost of the half toroidal CVT disk.

Also, there must be secured concentricity between the inner surface involute spline portion to be worked prior to the heat treatment of the half toroidal CVT disk and the toroidal surface and inner surface portion to be ground.

Further, in case where the outer surface, inner surface portion and toroidal surface are ground sequentially in separate steps, the half toroidal CVT disk not only must be mounted onto and removed from the grinding machines but also must be delivered between the grinding machines in these respective grinding steps, which makes it troublesome to grind the half toroidal CVT disk and thus provides an important factor in the increased cost thereof.

Still further, in the case of the toroidal surface grinding operation, there is a limit on the diameter of a grinding wheel and the direction of the rotary shaft of the grinding wheel must be set at an angle of 58°-65° (±15°) with respect to the direction of the rotary shaft of the work.

SUMMARY OF THE INVENTION

The present invention aims at eliminating the drawbacks found in the above-mentioned conventional half toroidal CVT disk grinding methods. Accordingly, it is a main object of the invention to provide a half toroidal CVT disk grinding method which can secure concentricity between the inner surface portion and toroidal surface of the half toroidal CVT disk while omitting the step of grinding the outer surface portion thereof, whereby the inner surface portion is smoother than the outer surface portion, thereby being able to reduce the number of manufacturing steps of the half toroidal CVT disks and thus the manufacturing cost thereof.

Also, it is a second object of the invention to provide a half toroidal CVT disk grinding method which is capable of not only grinding the inner surface portion and toroidal surface of the half toroidal CVT disk simultaneously using a compound grinding machine while they remain chucked by the same chuck mechanism but also securing concentricity between the inner surface portion and toroidal surface.

Further, it is a third object of the invention to provide a half toroidal CVT disk grinding method which, in case where the inner surface portion of the half toroidal CVT disk is hard broached after the half toroidal CVT disk is thermally treated, can grind the toroidal surface of the half toroidal CVT disk with the thus hard broached inner surface portion as the standard thereof to omit the step of grinding the outer surface portion the half toroidal CVT disk, thereby being able to reduce the number of manufacturing steps of the half toroidal CVT disk and thus the manufacturing cost thereof.

In attaining the above objects, according to a first aspect of the invention, there is provided a method of grinding a half toroidal CVT disk by a grinding mechanism with a tool for grinding the half toroidal CVT disk, the half toroidal CVT disk having an inner surface portion, an outer surface portion and a toroidal surface having a given machining allowance, the method including the steps of: centering the half toroidal CVT disk with a first part of the inner surface portion worked prior to the heat treatment of the half toroidal CVT disk as the standard thereof; chucking the centered half toroidal CVT disk by a chuck mechanism; grinding the toroidal surface of the chucked half toroidal CVT disk in a state that one of the half toroidal CVT disk and the tool is inclined at a given angle with respect to the other; and grinding a second part of the inner surface portion simultaneously with the toroidal surface in a compound manner.

Further, according to a second aspect of the invention, there is provided a method of grinding a half toroidal CVT disk by a grinding mechanism with a tool for grinding the half toroidal CVT disk, the half toroidal CVT disk having an inner surface portion, an outer surface portion and a toroidal surface having a given machining allowance, the method comprising the steps of: hard-broaching the inner surface portion after the heat treatment of the half toroidal CVT disk; centering the half toroidal CVT disk with the hard broached inner surface portion as the standard thereof; chucking the centered half toroidal CVT disk by a chucking mechanism; and grinding the toroidal surface of the chucked half toroidal CVT disk in a state that one of the half toroidal CVT disk and the tool is inclined at a given angle with respect to the other.

Now, according to the first aspect of the invention, the half toroidal CVT disk is centered with the inner surface portion worked prior to the heat treatment of the half toroidal CVT disk as the standard thereof and is chucked in the thus centered state by the chuck mechanism and, in the centered state, the toroidal surface is ground. Thanks to this, even in case where the step of grinding the outer surface portion of the half toroidal CVT disk is omitted, there can be secured concentricity between the inner surface portion and toroidal surface of the half toroidal CVT disk. This can decrease the number of manufacturing steps of the half toroidal CVT disk, so that the manufacturing cost of the half toroidal CVT disk can be reduced. Further, when the toroidal surface is ground, the inner surface portion is ground simultaneously in a compound manner. This makes it possible not only to secure concentricity between the inner surface portion and toroidal surface of the half toroidal CVT disk but also to shorten the grinding operation time, thereby being able to reduce the manufacturing cost of the half toroidal CVT disk.

Further, according to the second aspect of the invention, in case where the inner surface portion is hard broached after the heat treatment of the half toroidal CVT disk, in a state where the half toroidal CVT disk is centered with the thus hard broached inner surface portion and is chucked in the thus centered state by the chuck mechanism, the toroidal surface is ground. Due to this, there is eliminated the step of grinding the outer surface portion of the half toroidal CVT disk to thereby decrease the number of manufacturing steps of the half toroidal CVT disk, so that the manufacturing cost of the half toroidal CVT disk can be reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, description will be given below of the preferred embodiments of a method for grinding a half toroidal CVT disk according to the invention with reference to the accompanying drawings.

FIGS. 1 to 3show a first embodiment of a method for grinding a half toroidal CVT disk according to the invention. As shown inFIG. 1, a grinding machine10includes a grinding mechanism11, a drive mechanism12and an inner surface grinding unit13. The grinding mechanism11includes a cutting table14, while the cutting table14can be driven in the direction of an arrow mark A shown inFIG. 1through a ball screw15by a servo motor16.

The cutting table14includes a drive motor (not shown) which can drive and rotate a grinding wheel17, that is, the rotational force of this drive motor can be transmitted to the grinding wheel17through a spindle18. The grinding surface of the outer peripheral surface of the grinding wheel17is formed in a curved shape having a radius corresponding to the toroidal surface19aof a half toroidal CVT disk (which is hereinafter referred to as a work19) which is a finished product with the grinding operation thereof completed. Therefore, since the work19has a machining allowance in a state before it is ground, the radius of the surface to be ground of the work19is set smaller than the diameter of the grinding surface of the outer peripheral surface of the grinding wheel17. Here, an angle α between the rotation center axis a of the work19and the center axis b of the grinding wheel is set in the range of 58°-65° (∓15°).

The drive mechanism12includes a drive motor (not shown), while this drive motor includes a chuck mechanism20for chucking the work19. The chuck mechanism20is structured as shown inFIGS. 2 and 3. That is, a chuck main body21includes a work receiving portion22formed in the front portion thereof and, in the central portion of the work receiving portion22, there is disposed a collect24which is connected to a draw bar23.

And, in case where the work19is set on the work receiving portion22, the collect24is inserted into the inner surface involute spline portion19bof the work19. In this state, in case where the draw bar23is pulled in the direction of an arrow mark B shown inFIG. 3, the collect24is allowed to spread, thereby being able to hold the inner surface involute spline portion19bof the work19. At the then time, the work19is also pulled in the same direction and is thereby butted against the standard surface of the work receiving portion22.

Further, on the outer periphery of the work receiving portion22of the chuck main body21, there is disposed a floating chuck mechanism25. The floating chuck mechanism25includes three pawls26so that the outer periphery of the work19can be held at three positions spaced at regular intervals of 120° by these three pawls26, while the three pawls26are respectively connected to their associated cylinders29through their associated levers28which can be rotated about their associated pivots27.

And, in case where the levers28are pulled by the cylinders29respectively, the levers28can be respectively rotated about their pivots27and the pawls26can be respectively moved toward the work19, thereby holding the outer surface portion19cof the work19. At the then time, even in case where the inner surface portion19dand outer surface portion19cof the work19happen to be out of concentricity with each other, due to the action of the floating chuck mechanism25, there is eliminated the possibility that the pawls26can be made free or can be strongly pressed against the outer surface portion19cof the work19in part.

Now, the inner surface grinding unit13, as shown inFIG. 1, includes an inner surface grinding cutting table31and an inner surface grinding traverse table32which is carried on the inner surface grinding cutting table31. The inner surface grinding cutting table31can be driven in the direction of an arrow mark c shown inFIG. 1through a ball screw33by a servo motor34, while the inner surface grinding traverse table32can be driven in the direction of an arrow mark d shown inFIG. 1through a ball screw35by a servo motor36.

The inner surface grinding traverse table32carries an inner surface grinding spindle37thereon and, on the inner surface grinding spindle37, there is mounted an inner surface grinding wheel30. And, the inner surface grinding wheel30is used to grind the inner surface portion19dof the work19.

Next, description will be given below of the operation of the above-described first embodiment of a half toroidal CVT disk according to the invention.

That is, the work19chucked by the chuck mechanism20is rotated using the drive motor (not shown) of the drive mechanism12and, at the same time, the grinding wheel17of the grinding mechanism11is rotated using the drive motor (not shown). In this state, in case where the cutting table14is moved in the A direction using the servo motor16, the grinding wheel17moves forward in the radial direction C shown inFIG. 3with respect to the toroidal surface19aof the work19and thus cuts the toroidal surface19ato thereby grind the same.

On the other hand, at the then time, since not only the inner surface grinding wheel30mounted on the inner surface grinding spindle37is rotated but also the inner surface grinding cutting table31is moved in the arrow mark c direction by the servo motor34to execute a cutting operation, the inner surface portion19dof the work19is ground simultaneously by the inner surface grinding wheel30, that is, the inner surface portion19dis ground in a compound manner.

In this manner, in a state where the toroidal surface19ais centered with the inner surface involute spline portion19bworked prior to execution of the heat treatment of the half toroidal CVT disk serving as the work19as the standard thereof and is chucked by the chuck mechanism20, the toroidal surface19ais ground. Thanks to this, even in case where the step of grinding the outer surface portion19cis omitted, concentricity between the inner surface portion19dand toroidal surface19acan be secured. This can reduce the number of the manufacturing steps of the half toroidal CVT disk, which in turn makes it possible to reduce the manufacturing cost thereof.

By the way, in the case of a light grinding operation, only the collet chucking function of the chuck mechanism20can provide sufficient holding rigidity for the work19. However, in the case of a grinding operation to be executed in the present embodiment, the toroidal surface19amust be ground in a wide range and, in some cases, the grinding resistance in the radial direction can range up to 40 kgf. In such case, there is a possibility that the work19can be moved or shifted in position, which lowers the grinding accuracy (roundness and chatter). Therefore, in order to obtain more sufficient holding rigidity, the outer surface portion19cof the work19is held by the floating chuck mechanism25. However, it should be noted here that the floating chuck mechanism25is not always necessary.

Also, in the above-mentioned first embodiment, when the toroidal surface19ais ground in a state where it is centered with a part of the inner surface involute spline portion19bof the half toroidal CVT disk serving as the work19as the standard thereof and is chucked by the chuck mechanism20, the inner surface portion19dis ground simultaneously with the grinding of the toroidal surface19a, that is, in a compound manner by the inner surface grinding wheel30. Thanks to this, concentricity between the inner surface portion19dand toroidal surface19acan be secured as well as the grinding operation time can be shortened, thereby being able to reduce the manufacturing cost of the half toroidal CVT disk.

Now,FIG. 4shows a second embodiment of a method for grinding a half toroidal CVT disk according to the invention. In the second embodiment, in the inner surface portion of a work19which consists of a different half toroidal CVT disk from the disk19employed in the first embodiment, there is formed an inner surface ball spline groove19e. In the case of the work19having such inner surface ball spline groove19e, after it is thermally treated, the inner surface ball spline groove19emust also be worked.

For example, the inner surface ball spline groove19eand inner surface portion19dcan be worked integrally by hard broaching. In this case, in a state where the thus hard broached inner surface portion19dis chucked by the chuck mechanism20according to the first embodiment and the concentricity of the toroidal surface19awith the hard broached inner surface portion19dis secured, the toroidal surface19ais ground using the grinding wheel17.

In case where only the inner surface ball spline groove19eis hard broached but the inner surface portion19dis not hard broached after the disk19is thermally treated, after the inner surface ball spline groove19eis received by its associated ball and is then centered, in order to secure the rigidity and holding force of the disk19, the outer surface portion19cis chucked by a floating chuck mechanism25similar to that of the first embodiment and the toroidal surface19ais then ground.

In this manner, in case where the inner surface portion of the work is hard broached after the work is thermally treated, the toroidal surface of the work is ground with the thus hard broached inner surface as the standard thereof. This eliminates the need to grind the outer surface portion of the work, thereby being able to reduce the number of manufacturing steps of the half toroidal CVT disk. As a result of this, the manufacturing cost of the half toroidal CVT disk can be reduced.

While only certain embodiments of the invention have been specifically described herein, it will apparent that numerous modifications may be mede thereto without departing from the spirit and scope of the invention.

As has been described heretofore, according to the first aspect of the invention, even in case where the step of grinding the outer surface of a half toroidal CVT disk is omitted, whereby the inner surface is smoother than the outer surface, concentricity between the inner surface portion and toroidal surface of the half toroidal CVT disk can be secured. This can decrease the number of manufacturing steps of the half toroidal CVT disk, so that the manufacturing cost of the half toroidal CVT disk can be reduced. Further, the inner surface portion and toroidal surface of the half toroidal CVT disk can be ground simultaneously in a compound manner by a compound grinding machine while they remain chucked simultaneously by the same chucking mechanism. This makes it possible not only to secure concentricity between the inner surface portion and toroidal surface of the half toroidal CVT disk but also to shorten the grinding operation time, thereby being able to enhance the productivity of the half toroidal CVT disk.

According to the second aspect of the invention, in case where the inner surface portion of the half toroidal CVT disk is hard broached after the disk is thermally treated, the toroidal surface of the half toroidal CVT disk can be ground with the thus hard broached inner surface portion as the standard thereof.

This eliminates the step of grinding the outer surface of the half toroidal CVT disk and thus decreases the number of manufacturing steps of the half toroidal CVT disk, thereby being able to reduce the manufacturing cost of the half toroidal CVT disk.