CA2089244A1

CA2089244A1 - Broaching bearings in an engine block

Info

Publication number: CA2089244A1
Application number: CA002089244A
Authority: CA
Inventors: Harvey J. Yera; Donald W. Mast
Original assignee: National Broach and Machine Co
Current assignee: Nachi Machining Technology Co
Priority date: 1992-10-27
Filing date: 1993-02-10
Publication date: 1994-04-28
Also published as: GB9306372D0; GB2271949B; ITRM930262A1; DE4328272A1; FR2697186A1; GB2271949A; IT1262363B; JPH06143024A; ITRM930262A0

Abstract

ABSTRACT OF THE DISCLOSURE

An elongated broach for broaching a plurality of axially aligned bearing bores, having a front piloting section and a rear piloting section. Between the front and rear piloting sections, the broach has alternate broaching sections and piloting sections. While one broaching section is broaching one bearing bore, the adjacent piloting section is guiding the broach in the next bearing bore. This provides a guided movement of the broach and prevents the broach from straying off line.

Description

20~9'~

TITLE: BROACHING BEARINGS IN AN ENGINE B~OC~

This invention relates generally to broaching and refers more particularly toa broach for, and method of,broaching the aligned crankshaft bearings in an engine block.

~ACKGROUND AND SUMMARY
When broaching a ~eries of aligned bearing~, such as the crankshaft bearing bores of an engine block, care must be taken to insure that the bores are cut true, that is, that they are rosnd and in line. The problem is particularly troublesome when the bearings are formed of different materials having different machining characteristics. As an exa~ple, the cran~shaft bearings of a cast aluminum engine bloc~ may have ductile iron bearing caps, 80 that one half of each bearing i8 aluminum and one half i- iron. The aluminum portion of each bearing is softer and gummier and prone to tearing, wherea~ the ductile iron bearing cap~ are abrasive and have a higher cutting force con~tant. Thi~ causes the broach to stray off line ana pu~h into the softer aluminum material. As a result, the broach may cut holes that are off line and egg-shaped rather than round. Also, the forces generated by the broaching process may cause the bearing caps to deflect during broaching, causing an out-of-round condition in the final bore~.

20~92~

In accordance with the present invention, the broach has a front piloting section to guide the block over the broach.
This front piloting section preferably is completely in the block before cutting begin~. The broach is designed with alternate cutting and piloting section~, 80 that no two ad~acent bearing ~ournals are broached at the same time. While one broaching section is broaching one bearing bore, the ad~acent piloting section is guiding the broach in the next bearing bore.
This provide~ 8 gu~ded movement of the broach and prevents the broach from straying off line.
Each piloting section which follows a broa~hing section is desiqned to guide behind that particular broaching section. Therefore, each piloting section is slightly larger in diameter based on the stock removal of the broaching ~ection which precedes it. $his a~ures that the broach will not drift away from the iron bearing caps and into the aluminum engine block.
Preferably the broaching sections are de~igned with spiral gullets to obtain a continuous engagement throughout the part. The broach may be rotated 360 while lt is broaching ~o that every point on the cutting edge~ will engage in the aluminum for half a stroke and in the ductile iron the other half.
Rotating the broach will apply uniform wear pattern~ on the cutting edge~. This will al~o aid in minimizing drifting of the tool.

2~924~

The last broaching section may be a burnishlng shell to improve the finish of the broached holes.
It is an object of this invention to provide a broach, and a method of broaching, having the foregoing features and capable of achieving the results indicated.
Another ob~ect is to provide a broach which i~ rugged and durable, composed of a relatively few ~imple parts, capable of being inexpens~vely manufactured, and well designed for the accomplishment of it~ intended function.
These and other ob~ects, features and advantages of the invention will become more apparent as the following description proceeds, especially when considered in con~unction with the accompanying drawings.

BRIEF DESCRIPTION OF THF DRAWINGS
Figure lisan elevational view of a broach constructed ln accordance with the invention.
Figure 2 i~ a fragmentary elevatlonal view showing the retriever end of the broach connected to a lead bar.
Figure 3 is a sectional view taken on the line 3--3 in Figure 1.
Figure 4 is a sectional view taken on the line 4--~in Figure 1.

20~2'1~

Fiqure~ SA - 5D show the broach in several posltions as it is pulled through the aligned bearing bore~ for the crankshaft of an engine block to broach the bore~ in sequence.
Pigure 6 is an elevational view showing one of the pilot ~hell~ of the broach.
Figure 7 i8 an end view of the pilot shell a~ viewed fro~ the left in Figure 6.
Figure 8 is an end view of the pilot shell as viewed from the right in Figure 6.
Figure 9 is an elevational view of one of the broaching shells of the broach.
; Figure 10 is an end view of the broaching shell as viewed from the left in Figure 9.
Fiqure 11 i~ an end view of the broaching ~hell as viewed from the right in Figure 9.
Figure 12 i~ an enlarged fragmentar,v view of a portion of the broaching shell showing the cutting teeth.
Figure 13 is an elevational view of the burnishing shell of the broach.
Figure 14 i~ an enlarged frag~entary view ~howing a portion of the burni~hing ~hell.

DETAILED DESCRIPTION
Referring now more particularly to the drawinq~, the broach 10 is used to broach the bearing bores for the crankshaft 2~9~

of an engine block 12. The engine block 12 comprises in this instance an aluminum casting 14 havinq a plurality of spaced bearing formations 15, 16, 18, 20 and 22 each shaped with a semi-circular recess 24 forming one-half of a bearing bore.
Secured to each bearing formation by fastener~ 26 1~ a bearing cap 28 of ductile lron having a 3emi-cyllndrical reces~ 27 providing the other half of the bearing bore. The bearlng bores are numbered 29, 30, 32, 34 and 36 snd are cylindrical, axi~lly spaced, and aligned, and each 1~ formed one-half of aluminum and one-half of ductile iron.
The broach comprises an elongated, solid, unitary draw bar 40 having a pull bead 42 for connection to a power device such as a hydraulic piston-cylinder assembly (not shown) and at the other end having a retriever 44 which can be attached to a lead bar ~6 by any sultable coupllng 48.
The broach has a front piloting section 50 and a rear ~iloting section 52. Between the front and rear pllotlng sectlons are a plurality of axially spaced broachlng sect~on~
54, 56, 58, 60 and 62 with lntermediate pllotinq sectlons 64, 66, 68 and 70 in the spaces between the broaching sectlons.
The front pilotinq section 50 18 formed of a plurality of cyllndrical ~hell~ 72 sleeved on the draw bar whlch are stacked together end-to-end. The shells are all of the same outside diameter and may be of the came or differing lengths, but together form the front piloting section 50 which is of 2~1~92~

greater length than the overall distance between the five bearings. The diameter of the shells 72 is designed to provide a close guiding fit in the bearing bores before broaching.
The rear piloting section 52 is in this instance an integral cylindrical portion of the draw bar and iQ of uniform diameter throughout its length. The diameter of the rear piloting section 52 is designed to provide a clo~e guiding fit in the bearing bores after broaching.
The broaching section~ 54 - 62 are in the form of cylindrical shells sleeved on the draw bar and preferably having spiral gullets 73 between the continuous spiral cutting teeth.
Spiral cutting teeth are preferable on a finishing broach, but not necessary on a roughing broach. The teeth are preferably formed with spaced flats 75 to break up the chips. These flats are non-aligned when the broach rotates, so that the next tooth ~ill not have a flat at the same location. The broaching sect$ons, starting with the ~ection 54 nearest to the front end of the broach, are progres ively larger in diameter ~o that each takes a cut in the gradual removal of stock and the broaching of the bores to a predetermined final dlameter.
The rearmost broaching section 62 in this instance is burnishing shell in which the teeth have rounded crest 63 to pack or compress the material forming the bores in a finishing operation. A burnishing shell improve~ the finish and quality of the broached bores. How~ver, a burnishing shell is not 20892~4 always required, and usually is not employed for rough cutting~
In those instances where a burnishing shell is not needed, the rearmost section 62 will be replaced by a broaching shell with the same type of cutting teeth as shells 54, 56, 58 and 60.
The piloting sections 64 - 70 are in the form of cylindrical sbells sleeved on the draw bar and with smooth cylindrical radially outer surfaces. Each plloting section is designed to guide specifically behind the broaching section immedlately ahead of it. The diameter of the pilotinj sections is based on the stock removal of the broaching section whlch precedes it and, therefore, the piloting sections, starting with section 64 nearest the front end, are progressively larger in diameter. Thus after a hole is broached by one broaching section, the piloting section immediately to the rear thereof guides in that hole and is dimensioned to have a close fit therein in order to guide properly.
The broaching sections 54 - 62 and piloting sections 64 - 70 are interlocked to prevent them frQm rotating on the draw bar 40. Thus the burnishing shell 62 has a slot 7~ cut across one end which receives a central projection 76 on the ad~acent end of the rear piloting section 52. The parallel sides 78 and 80 of the ~lot 74 engage the parallel sides of the pro~ection 76 so that the burnishing shell is held from rotation.
~he opposite end of the burnishing shell 62 has a pro~ection similar to the projection 76 on the rear piloting section 2 ~ 9t~

S2 which engages in a slot in the piloting shell 70 to prevent the latter from rotating. There is a ~imilar pro~ection/slot interengagement between the ends of the other broaching and piloting shells so that they are all interlocked with the draw bar and prevented from rotating. The shells 72 making up the front piloting section 70 may or may not be interlocked to prevent rotation. In thls instance, tbe shells 72 are not ~nterlocked and thus are free to rotate.
The lead bar ~6 has helical grooves 84 in which one or more stationary pins 86 engage so that the lead bar, and hence the broach, rotate in the direction of the arrow 85 as the broach is pulled through the bearings of the engine block in the direction of the arrow 87. Preferably the broach is thus rotated 360 or one full revolution when broaching while pulled through the engine block 80 that every point on the cutting edges will engage in the aluminum of the block for half a ~troke and in the ductile iron of the bearing cap for the other half of the stroke. Rotating the broach will apply unlform wear patterns on the cutting edges of the broaching sections, further alding in minimizing drifting of the broach. The spiral gullets also achieve a re continuous engagement with the bearing bores throughout the broaching action.
A nut 77 is threaded on the front end of the draw bar 40 and packs the various shells sleeved on the draw bar into tight end-to-end contact, holdinq the slot and pro~ection 2~8~2~

interengagement between the broaching shells and intermed$ste piloting shells so they are not free to rotate on the draw bar.
A set screw 79 carried by the nut is advanced into engagement with an annular groove 81 in the draw bar to hold the nut clamped against the shells.
Figures 5A - 5D ~how the broach a~ it i~ pulled through the bearing bores of the engine block. It will be noted in Figure 5A that initlally the front piloting section 50 i8 completely within all five bearing bores. Figures 5B and 5C
show the alternate broaching of the bearing bores and guiding in the broached bores as the broach advances. Figure 5D shows the position of the broach after broaching has been completed and the rear piloting section 52 extends through all of the broached bearing bores.
A~ noted in Figures 5B and 5C, the broach is designed in relation to the spacing of the bearing bores so that no two ad~acent bearing ~ournal~ are broached at the same time. While one broaching section i8 broaching one bearing bore,the ad~acent piloting section is guiding the broach in the ne~t bearing bore.
Thus a guidea movement of the broach is provided, preventing the broach from ~traying off line.
Although the broach 10 is described and illu~trated as composed of an assembly of separable part3 in which the front piloting ~ection 50 is formed of a plurality of shells 72 sleeved on the draw bar 40, and the broaching sections 54 - 62 and 2~92~4 intermediate piloting sections 64 - 70 are Also formed of cylindrical shells sleeved on the draw bar, it ~hould be understood that the broach may, if desired, be formed 89 one solid piece in which all parts, including the draw bar, front piloting section50,rearpiloting section 52, broachlng sectlon~
S4 - 62 and intermediate piloting sections 64 - 70 ~re manufactured as a single integral unit.

Claims

1. An elongated broach for broaching first and second axially aligned and spaced bores, said broach having axially spaced leading and trailing piloting sections and a broaching section between said leading and trailing piloting sections, said leading piloting section being adapted to guide said broach in said second bore while said broaching section is broaching said first bore and said trailing piloting section being adapted to guide said broach in said first bore while said broaching section is broaching said second bore.

2. An elongated broach for broaching a plurality of axially aligned and spaced bores, said broach having front and rear ends, a front piloting section adjacent said front end of said broach and a rear piloting section adjacent said rear end of said broach, said broach having between said front and rear piloting sections a plurality of axially spaced broaching sections and an intermediate piloting section in each space between said broaching sections, said broach being adapted to be advanced front end first through said bores in sequence with said broaching sections broaching said bores in sequence and said piloting sections guiding said broach in said bores in sequence.

3. An elongated broach as defined in Claim 2, wherein the diameter of each intermediate piloting section is based upon the stock removal of the broaching section immediately in front of it to effectively guide in said bores after they are broached.

4. An elongated broach as defined in Claim 2, wherein means are provided to axially advance said broach, and means are provided to rotate said broach as it is advanced.

5. An elongated broach as defined in Claim 2, wherein means are provided to axially advance said broach, and means are provided to rotate said broach one full revolution as it is advanced.

6. An elongated broach as defined in Claim 2, wherein said broach has cutting elements provided with chip-clearing flats.

7. An elongated broach as defined in Claim 2, comprising an elongated draw bar, and said broaching sections and intermediate piloting sections are shells sleeved on said draw bar.

8. A method of broaching first and second axially aligned and spaced bores, comprising providing an elongated broach having axially spaced leading and trailing piloting sections and a broaching section between said leading and trailing piloting sections, axially advancing said broach through said first and second bores in sequence, and during the axial advance of said broach guiding said broach by engagement of said leading piloting section in said second bore while broaching said first bore by said broaching section and guiding said broach by engagement of said trailing piloting section in said first bore while broaching said second bore by said broaching section.

9. A method of broaching a plurality of axially aligned and spaced bores, comprising providing an elongated broach having a front piloting section adjacent the front end thereof and a rear piloting section adjacent the rear end thereof with a plurality of axially spaced broaching sections between said front and rear piloting sections and an intermediate piloting section in each space between said broaching sections, and axially advancing said broach front end first through said bores in sequence with said broaching sections broaching said bores in sequence and said piloting sections guiding said broach in said bores in sequence.

10. A method as defined in Claim 9, wherein the diameter of each intermediate piloting section is based upon the stock removal of the broaching section immediately in front of it to effectively guide in said bores after they are broached.

11. A method as defined in Claim 9, and further including rotating the broach as it is advanced.

12. A method as defined in Claim 9, and further including rotating said broach one full revolution as it is advanced.

13. A method as defined in Claim 9, wherein the spacing of said bores and said broaching and piloting sections is such that no two adjacent bores are broached by the broaching sections at the same time.

14. A method as defined in Claim 9, wherein the length of said front piloting section of the broach is greater than distance between the endmost ones of said plurality of bores so that said front piloting section passes through all of said bores before the forwardmost broaching section enters any of said bores.

15. A method of broaching a plurality of axially aligned and spaced crankshaft bearing bores of an engine block in which the bearings are formed in part of a first material and in part of a second material having different machining characteristics, comprising providing an elongated broach having a front piloting section adjacent the front end thereof and a rear piloting section adjacent the rear end thereof with a plurality of axially spaced broaching sections between said front and rear piloting sections and an intermediate piloting section in each space between said broaching sections, and axially advancing said broach front end first through said bores in sequence with said broaching sections broaching said bores in sequence and said piloting sections guiding said broach in said bores in sequence, the diameter of each intermediate piloting section being based upon stock removal of the broaching section immediately in front of it to effectively guide in said bores after they are broached, the diameter of said front piloting section being based upon the initial diameter of said bores before they are broached by said broaching sections to effectively guide in said bores.

16. A method as defined in Claim 15, wherein the length of said front piloting section of the broach is greater than distance between the endmost ones of said plurality of bores so that said front piloting section passes through all of said bores before the forwardmost broaching section enters any of said bores.

17. A method as defined in Claim 15, including rotating said broach one full revolution as it is advanced.

18. A method as defined in Claim 15, wherein the spacing of said bores and said broaching and piloting sections is such that no two adjacent bores are broached by the broaching sections at the same time.