Crankshaft machining system and crankshaft machining method

A crankshaft machining system includes a center hole boring device, a post-centering balance meter and a cutting device. The post-centering balance meter is configured to measure the shape of a post-centering crankshaft blank on the basis of a pair of center holes. Additionally, the post-centering balance meter is configured to set a principal axis of inertia on the basis of the shape of the post-centering crankshaft blank and generate center hole positional information for correction that indicates intersections between the principal axis of inertia and both end surfaces of the post-centering crankshaft blank. The center hole boring device is configured to bore a pair of center holes on both end surfaces of another crankshaft blank to be loaded next on the basis of the center hole positional information for correction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of International Application No. PCT/JP2014/050277, filed on Jan. 10, 2014. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2013-016765, filed in Japan on Jan. 31, 2013, the entire contents of which are hereby incorporated herein by reference.

BACKGROUND

Field of the Invention

The present invention relates to a crankshaft machining system for machining a crankshaft and a crankshaft machining method of machining a crankshaft.

Background Art

In general, a crankshaft is fabricated by machining a crankshaft of a material state (hereinafter referred to as “a crankshaft blank”) with reference to a pair of center holes. For example, according to a method described in Japan Laid-open Patent Application Publication No. 2010-29994, a crankshaft is formed as follows. First, a balance center axis of a crankshaft blank is found out by rotating the crankshaft blank and measuring its shape with a balance meter. Next, using a center hole boring device, center holes are bored in the crankshaft blank at intersections between both end surfaces of the crankshaft blank and the balance center axis. Thereafter, using one or more types of cutting devices, main journals and pin journals of the crankshaft blank are cut with reference to the center holes.

In a step described in Japan Laid-open Patent Application Publication No. 2010-29994, the positions of the center holes can be corrected by the center hole boring device through the feedback of the rotational imbalance amount of a finished crankshaft to the center hole boring device.

However, even when the positions of center holes can be corrected by the center hole boring device with respect to a crankshaft in which the center holes have been already bored and for which cutting has been done, the crankshaft is inevitably handled as a defective product unless the rotational imbalance amount thereof falls in an allowable range after the balance correction. Furthermore, the condition of unevenness in thickness of a crankshaft blank tends to vary in accordance with the manufacturing lot of the crankshaft blanks. Hence, every time the manufacturing lot of the crankshaft blanks is changed, a large number of deficit products are inevitably produced.

The present invention has been produced in view of the aforementioned situation. It is an object of the present invention to provide a crankshaft machining system and a crankshaft machining method whereby the number of deficit products can be reduced.

Solution to Problems

A crankshaft machining system according to a first aspect includes a center hole boring device, a post-centering balance meter and a cutting device. The center hole boring device is configured to bore a pair of center holes on both end surfaces of a crankshaft blank. The post-centering balance meter is configured to measure a shape of a post-centering crankshaft blank with reference to the pair of center holes, and the post-centering crankshaft blank is the crankshaft blank having the pair of center holes bored. The cutting device is configured to cut a main journal and a pin journal of the post-centering crankshaft blank. The post-centering balance meter is configured to set a principal axis of inertia on the basis of the shape of the post-centering crankshaft blank and transmit information indicating intersections between the principal axis of inertia and both end surfaces of the post-centering crankshaft blank to the center hole boring device. The center hole boring device is configured to bore a pair of center holes on both end surfaces of another crankshaft blank to be loaded next on the basis of the information that indicates the intersections and is transmitted thereto from the post-centering balance meter.

According to the crankshaft machining system of the first aspect, prior to cutting of the main journal and the pin journal of the post-centering crankshaft blank, ideal center hole positions can be comprehended on the basis of the principal axis of inertia with reference to the pair of center holes. Hence, a pair of center holes can be accurately bored in respective crankshaft blanks to be loaded thereafter. Consequently, the number of crankshafts to be handled as deficit products can be reduced.

In the crankshaft machining system according to the first aspect, the post-centering balance meter may be configured to transmit additional machining information to the cutting device, and the additional machining information indicates a machining position on and a machining amount of a counterweight of the post-centering crankshaft blank, which are required for matching a straight line connecting the pair of center holes with the principal axis of inertia on the basis of the shape of the post-centering crankshaft blank. The cutting device is herein configured to machine the counterweight on the basis of the additional machining information. With the configuration, imbalance can be removed from the post-centering crankshaft blank by matching a center hole reference axis with the principal axis of inertia. Hence, the post-centering crankshaft blank used for generating center hole positional information for correction can be also utilized as a non-defective product.

A crankshaft machining method according to a second aspect includes the steps of boring a pair of center holes on both end surfaces of a crankshaft blank; measuring a shape of a post-centering crankshaft blank with respect to the pair of center holes, the post-centering crankshaft blank being the crankshaft blank having the pair of center holes bored therein; setting a principal axis of inertia on the basis of the shape of the post-centering crankshaft blank; and boring a pair of center holes on both end surfaces of another crankshaft blank to be loaded next on the basis of information indicating intersections between the principal axis of inertia and both end surfaces of the post-centering crankshaft blank.

According to aspects of the present invention, it is possible to provide a crankshaft machining system and a crankshaft machining method whereby the number of deficit products can be reduced.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

First, a crankshaft1of a material state (hereinafter referred to as “a crankshaft blank1”) as a machining object of a crankshaft machining system to be described will be explained. In the following explanation, the crankshaft blank1for an inline-four engine will be described, but the engine type for which the crankshaft blank1is used is not limited to this.

FIG. 1is an external perspective view of the crankshaft blank1.

The crankshaft blank1has main journals J (J1to J5), pin journals P (P1to P4) and counterweights CW (CW1to CW8). In the crankshaft blank1, the main journal J1, the counterweight CW1, the pin journal P1, the counterweight CW2, the main journal J2, the counterweight CW3, the pin journal P2, the counterweight CW4, the main journal J3, the counterweight CW5, the pin journal P3, the counterweight CW6, the main journal J4, the counterweight CW7, the pin journal P4, the counterweight CW8and the main journal J5are aligned in this order. For example, the crankshaft blank1is fabricated by casting with casting dies or by forging with forging dies.

Next, a crankshaft machining system100according to an exemplary embodiment will be explained.

FIG. 2is a block diagram of a construction of the crankshaft machining system100.FIG. 3is a schematic diagram of a construction of a post-centering balance meter20.

As shown inFIG. 2, the crankshaft machining system100includes a center hole boring device10, the post-centering balance meter20and a cutting device30.

Center Hole Boring Device10

The center hole boring device10is configured to bore a pair of center holes on both end surfaces of the crankshaft blank1in the condition that the main journals J1and J5of the crankshaft blank1are clamped.

Specifically, the center hole boring device10is firstly configured to clamp the main journals J1and J5of the crankshaft blank1with a work clamper. Next, the center hole boring device10is configured to mill both end surfaces of the crankshaft blank1with milling cutters.

Next, the center hole boring device10is configured to set the geometric centers of both end surfaces as the positions of center holes. Subsequently, the center hole boring device10is configured to drive a pair of center drills to bore a pair of center holes CH (seeFIG. 3) in the positions of the geometric centers on both end surfaces.

Thereafter, a crankshaft blank1ain which the pair of center holes CH has been bored (hereinafter referred to as “a post-centering crankshaft blank1a”) is configured to be transported from the center hole boring device10to the post-centering balance meter20.

Additionally, when receiving center hole positional information for correction (to be described) from the post-centering balance meter20, the center hole boring device10is configured to bore a pair of center holes in center hole positions for correction on both end surfaces of another crankshaft blank1to be loaded next. Specifically, the center hole boring device10is configured to bore a pair of center holes CH in positions on both end surfaces, which are displaced from the geometric centers of both end surfaces by the displacement amount indicated by the center hole positional information for correction.

Moreover, every time receiving anew the center hole positional information for correction, the center hole boring device10is configured to store the cumulative amount of displacement amounts. When the crankshaft blank1is a newly loaded one, the center hole boring device10is configured to bore a pair of center holes CH on both end surfaces of the crankshaft blank1in positions displaced from the geometric centers of both end surfaces by the cumulative amount.

Thus, by the feedback of the center hole positional information for correction from the post-centering balance meter20to center hole positional setting, the post-centering crankshaft blank1ato be fabricated thereafter can be reduced in rotational imbalance amount.

The post-centering balance meter20is configured to measure the shape of the post-centering crankshaft blank1aon the basis of the pair of center holes CH and set a principal axis of inertia of the post-centering crankshaft blank1a. As shown inFIG. 3, the post-centering balance meter20includes a machine base31, a first center base32, a second center base33, a first center34, a second center35, a motor36, a sensor37and a controller38.

The first and second center bases32and33are fixed onto the machine base31. The first center34is supported by the first center base32, whereas the second center35is supported by the second center base33. Each of the first and second centers34and35is movable along and also rotatable about an axis AX. The motor36is configured to rotate the second center35about the axis AX. At this time, the first and second centers34and35are being pressed into the pair of center holes CH of the post-centering crankshaft blank1a. Hence, the first center34is configured to be rotated together with the second center35through the post-centering crankshaft blank1a.

The sensor37is a displacement meter for measuring the entire circumferential shapes of the counterweights CW1to CW8of the post-centering crankshaft blank1a. For example, a non-contact displacement meter (a laser displacement meter, an infrared displacement meter, an LED displacement sensor, etc.) or a contact displacement meter (a differential transformer, etc.) can be used as the sensor37.

When the post-centering crankshaft blank1ais loaded to the post-centering balance meter20, the controller38is configured to drive and control the first and second centers34and35to insert the tip ends of the first and second centers34and35into the pair of center holes CH bored on both end surfaces of the post-centering crankshaft blank1a. The controller38is configured to drive and control the motor36to rotate the second center35, and is simultaneously configured to drive and control the sensor37to sequentially measure the entire circumferential shapes of the counterweights CW1to CW8. Specifically, the controller38is configured to simultaneously obtain values measured by an encoder mounted in association with a rotary table for rotating the second center35and values measured by the sensor37, and is configured to calculate polar coordinates of the entire circumferences (i.e., shape measurement data) on the basis of the obtained values. One rotation is only required for the shape data calculation of each of the counterweights CW1to CW8.

The controller38is configured to compare the shape measurement data of the counterweights CW1to CW8and shape design data of the counterweights CW1to CW8and calculate numeric values that indicate differences therebetween (e.g., size differences, vertical and horizontal directional displacements, angular displacements, etc.).

Next, the controller38is configured to modify the shape design data of the counterweights CW1to CW8with use of the calculated numeric values. Then, the controller38is configured to generate three-dimensional shape data of the post-centering crankshaft blank1aby adding the shape design data of the main journals J (J1to J5) and the pin journals P (P1to P4) to the modified shape design data of the counterweights CW1to CW8. Thereafter, the controller38is configured to set the principal axis of inertia with reference to the pair of center holes CH on the basis of the three-dimensional shape data of the post-centering crankshaft blank1a. It should be noted that PCT International Patent Application Publication No. WO2009/016988 explains an exemplary method of calculating a principal axis of inertia.

Next, the controller38is configured to set intersections between the principal axis of inertia with reference to the pair of center holes CH and both end surfaces of the post-centering crankshaft blank1aas positions in which the pair of center holes CH should have been originally bored (hereinafter referred to as “center hole positions for correction”). The center hole positions for correction are positions ideal for boring a pair of center holes on both end surfaces of the crankshaft blank1.

Then, the controller38is configured to calculate the displacement amount between the center hole positions for correction and the positions in which the pair of center holes CH has been actually bored. The controller38is configured to transmit the calculated displacement amount to the center hole boring device10as the information that indicates the center hole positions for correction (hereinafter referred to as “center hole positional information for correction”). It should be noted that in the present exemplary embodiment, the controller38is configured to calculate the displacement amount and also transmit the center hole positional information for correction to the center hole boring device10every time the post-centering crankshaft blank1ais loaded anew.

Moreover, the controller38is configured to set the machining position(s) on and the machining amount(s) of the counterweight(s) CW1to CW8, which are required for matching a straight line connecting the pair of center holes CH (hereinafter referred to as “a center hole reference axis”) with the principal axis of inertia. Specifically, the controller38is configured to calculate in which part(s) of the counterweight(s) CW1to CW8, and to what extent(s), imbalance should be removed to match the center hole reference axis with the principal axis of inertia on the basis of the shape balance of the post-centering crankshaft blank1ato be calculated from the three-dimensional shape data.

When the post-centering crankshaft blank1ais transported to the cutting device30, the controller38is configured to transmit, to the cutting device30, information that is required for imbalance removal and indicates the machining position(s) on and the machining amount(s) of the counterweight(s) CW1to CW8(hereinafter referred to as “additional machining information”).

The cutting device30is configured to cut the main journal(s) J and the pin journals) P of the post-centering crankshaft blank1a.

Moreover, when receiving the additional machining information in loading of the post-centering crankshaft blank1a, the cutting device30is configured to machine the counterweight(s) CW (CW1to CW8) on the basis of the additional machining information. As types of machining to be performed at this time, cutting and/or boring are/is performed for the outer peripheral surface and/or the lateral surface of at least one of the counterweights CW (CW1to CW8). Thus, rotational imbalance in a finished crankshaft can be reduced by the feed-forward of the additional machining information.

After cutting of the counterweight(s) CW, the cutting device30is configured to cut the main journal(s) J and the pin journal(s) P with reference to the pair of center holes CH.

It should be noted that the cutting device30may include a plurality of machining devices for performing various steps such as cutting of the counterweight(s) CW, rough machining of the main journal(s) J, rough machining of the pin journal(s) P, precision machining of the main journal(s) J and precision machining of the pin journal(s) P. Put differently, the cutting device30may be a multifunctional device for cutting of the post-centering crankshaft blank1a.

Crankshaft Machining Method

Next, a crankshaft machining method will be explained.FIG. 4is a flowchart for explaining the crankshaft machining method.

In Step S10, the center hole boring device10sets geometric centers of both end surfaces of the crankshaft blank1as center hole positions.

In Step S20, the center hole boring device10bores a pair of center holes CH in the center hole positions on both end surfaces of the crankshaft blank1.

In Step S30, the post-centering balance meter20measures the shape of the post-centering crankshaft blank1awith reference to the pair of center holes CH and sets a principal axis of inertia of the post-centering crankshaft blank1a.

In Step S40, the post-centering balance meter20sets center hole positions for correction from the principal axis of inertia and generates center hole positional information for correction. Simultaneously, the post-centering balance meter20sets the machining position(s) on and the machining amount(s) of the counterweight(s) CW (CW1to CW8), both of which are required for imbalance removal, and generates additional machining information.

In Step S50, the post-centering balance meter20transmits the center hole positional information for correction to the center hole boring device10, and simultaneously, transmits the additional machining information to the cutting device30.

In Step S60, the center hole boring device10bores a pair of center holes CH in the center hole positions for correction of another crankshaft blank1to be loaded anew.

In Step S70, on the other hand, the cutting device30cuts the counterweight(s) CW on the basis of the additional machining information. After Steps S60and S70, the cutting device30cuts the main journal(s) J and the pin journal(s) P in Step S80.

The crankshaft machining system100includes the center hole boring device10, the post-centering balance meter20and the cutting device30. The post-centering balance meter20is configured to measure the shape of the post-centering crankshaft blank1awith reference to a pair of the center holes CH. Additionally, the post-centering balance meter20is configured to set the principal axis of inertia on the basis of the shape of the post-centering crankshaft blank1a, and is configured to generate the center hole positional information for correction that indicates intersections between the principal axis of inertia and both end surfaces of the post-centering crankshaft blank1a. The center hole boring device10is configured to bore a pair of center holes CH on both end surfaces of another crankshaft blank1to be loaded next on the basis of the center hole positional information for correction.

Therefore, prior to cutting of the main journals) J and the pin journal(s) P of the post-centering crankshaft blank1a, ideal center hole positions can be comprehended on the basis of the principal axis of inertia set with reference to the pair of the center holes CH. Hence, a pair of the center holes CH can be accurately bored in the respective crankshaft blanks1to be loaded thereafter. Consequently, the number of crankshafts to be handled as deficit products can be reduced.

The cutting device30is configured to machine the counterweight(s) CW of the post-centering crankshaft blank1aon the basis of the additional machining information.

With the configuration, imbalance can be removed from the post-centering crankshaft blank1aby matching the center hole reference axis with the principal axis of inertia. Hence, the post-centering crankshaft blank1aused for generating the center hole positional information for correction can be also utilized as a non-deficit product.

Other Exemplary Embodiments

The crankshaft machining system100may include a pre-centering balance meter40shown inFIG. 5, although not described in the aforementioned exemplary embodiment. The pre-centering balance meter40is a device configured to measure the rotational balance of the crankshaft blank1and set ideal center hole positions in the crankshaft blank1on the basis of the measured rotational balance.

Specifically, as shown inFIG. 5, the pre-centering balance meter40includes a machine base11, a stationary base12, a drive base13, a first chuck14, a second chuck15, a motor16, a sensor17and a controller18. When the crankshaft blank1is loaded, the controller18is configured to drive and control the first and second chucks14and15to cause them to hold parts of the crankshaft blank1that are configured to be clamped by the center hole boring device10(i.e., the main journals J1and J5). Next, the controller18is configured to drive the motor16to rotate the second chuck15, and simultaneously drive the sensor17to sequentially measure the entire circumferential shapes of the counterweights CW1to CW8. Next, the controller18is configured to set the principal axis of inertia of the crankshaft blank1by performing processing similar to that performed by the controller38of the post-centering balance meter20, and is configured to set intersections between the principal axis of inertia and both end surfaces of the crankshaft blank1as center hole positions.

Where the crankshaft machining system100includes the pre-centering balance meter40as described above, the center hole boring device10is only required to bore a pair of center holes in the center hole positions to be notified from the pre-centering balance meter40. On the other hand, the post-centering balance meter20is capable of checking whether or not centering is properly performed in machining of the center hole boring device10by comparing the positions of a pair of actually bored center holes CH and the center hole positions for correction in the post-centering crankshaft blank1a. For example, when the positions of actually bored center holes and the center hole positions for correction are different from each other, it is possible to find out malfunctions such as displacement of the clamp positions of the crankshaft blank1in the center hole boring device10.

In the aforementioned exemplary embodiment, the controller38of the post-centering balance meter20is configured to transmit the additional machining information to the cutting device30in every blank loading. However, the controller38may be configured to transmit the additional machining information only when the machining amount is greater than or equal to a predetermined threshold. With the configuration, additional machining is configured not to be performed for the counterweight(s) CW as long as the rotational imbalance amount of the post-centering crankshaft blank1afalls within an allowable range. Hence, work time required for finishing the crankshaft can be reduced.

In the aforementioned exemplary embodiment, the post-centering balance meter20is configured to generate the additional machining information of the post-centering crankshaft blank1a. However, the additional machining information is not required to be generated. In this configuration, although the post-centering crankshaft blank1ato be firstly produced has chances of being handled as a deficit product, but additional machining can be omitted in the cutting device30.

Although not particularly described in the aforementioned exemplary embodiment, when the manufacturing lot of the crankshaft blanks1is changed, the post-centering balance meter20may be configured to set the center hole positions for correction only for the post-centering crankshaft blank1ato be produced first in the new manufacturing lot. In this configuration, the center hole boring device10is supposed to use the same center hole positions for correction with respect to all the crankshaft blanks1in the same manufacturing lot. Even in this configuration, the crankshaft blanks exhibit the same tendency of unevenness in thickness on a manufacturing lot basis. Hence, reduction in rotational imbalance amount can be expected for the post-centering crankshaft blanks1ain the same manufacturing lot.

In the aforementioned exemplary embodiment, the post-centering balance meter20is configured to transmit the center hole positions for correction of only a single post-centering crankshaft blank1ato the center hole boring device10. However, the post-centering balance meter20may be configured to transmit the average of the center hole positions for correction of a plurality of crankshaft blanks. With the configuration, variation among single measurements can be averaged and stable feedback is enabled.