US2325836A - Gear crowning - Google Patents

Description

ug- 3, 1943 VR. s. DRUMMOND 2,325,836

GEAR CROWNING Filed May 5, 1941 4 sheets-sheet 1 L -al ROBERT SDRUMMO D BY WW,M42L

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Aug. 3, 1943. R. s. DRUMMOND GEAR CROWNING Filed May 5, 1941v 4 Sheets-Sheet 2 FIGB).7

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A TTORNE YS.

Aug. 3, 1943. R. s. DRUMMOND GEAR CROWNING Filed May 5, 1941 4 Sheets-Sheet 5 FIGA;

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INVENTOR ROBERT s oRuMMoND BY W ATToRNEYs Aug.` 3, 1943. R. s. DRUMMOND GEAR CROWN ING Filed May 5, 1941 4 Sheets-Sheet 4 INVENTOR ROBER BY W ,l n Ts URUMMND ATTORNEYS Paieiiiee aug. s, reta entran stares mmh? pagina osait @nomma Robert S. Drummond, Detroit, Mich. y

application May 5, 1an, seriai No. 391,99?

3 Claims.

grinding wheel is employed. A grinding wheel of this type is adapted to be passed along the tooth spaces of a gear being ground, the working surfaces of the grinding wheel being trimmed in accordance with the profile to be imparted to the teeth of the gear. When a grinding wheel is used, it is rotated at relatively high speed and according to the present invention, during the` relative traverse between the gear and tool, an additional relative motion is superimposed which causes the grinding wheel to approach the gear radially as the contact between the teeth of the gear and the grinding wheel approaches either end of the gear teeth. The composite relative motion thus produced may be regarded as a relative motion in a curved path, extending generally along a tooth space of the gear, the curvature being such that the path is concave toward the gear being crowned. The result of this is the formation of crowned or bowed gear teeth. The direction of curvature may, of course, be reversed, in which case the teeth of the gear are thicker at the ends than centrally thereof so as to present a hollow longitudinal prole.

It is accordingly an object of the present invention to provide a method and machine for grinding gears which results in a relative motion between the grinding wheel and gear in a curved path extending generally along a tooth space oi the gear. l

It is a further objectvof the present invention to provide a machine and method for crowning 40 gears, which results in a relative motion extending generally along a tooth space of the gear in a curved path, the curvature of which is concave toward the gear. l

. Itis a further object of the invention to provide 4 a method and machine for crown grinding gears, i

' i which results in a relative motionbetween the grinding wheel and'gear equivalent to a motion composed of a. straight-linereciprocation of the gear past the grinding wheel, in combination with a timed movement of the grinding wheel toward and away from the path of translationof the gear.

(Cl. Sil-33) having cam means for moving the grinding wheel toward and away from the path of reciprocation of' the gear in timed relation thereto.

Y It is a further object of the invention to provide, in a grinding machine, an eccentric bushing operatively associated with a cam for moving the gear grinding wheel support toward and away from the path of traverse of the gear in timed relation thereto.

It is a further object of the invention to provide a crowning mechanism on a form-grinding machine in which camV means are provided for moving the grinding wheel toward and away from the path of traverse of the gear, and in which resilient means urge the camming means into contact.

Other objects of the invention will be apparent n asthe description proceeds,l and when taken i'n conjunction with the-accompanying drawings, wherein:

Figure 1 is a front elevation of my improved grinding machine;

Figure 2 is a, fragmentary side elevation of the attachment, partly in section;

Figure v3 is a fragmentary front elevation of the camming attachment;

Figure 4 is a front elevation, with parts broken away, of a somewhat different embodiment of my invention; y

Figure 5 is a fragmentary side elevation of the structure shown in Figure 4, with parts in section;

Figure 6 is a vertical section through the tool spindle of the structure shown in Figures d and 5;

` Figure '7 is a fragmentary section on theline 1 1, Figure l; and

Figure 8 is a diagram illustrating the type of crowned teeth resulting from the practice disclosed herein.

Referring nrsi to Figure 1, I'have illustrated a gear grinding machine which is modified in accordance with two embodiments of my invention, one of which is shown in'Figures 2 and 3, and the other of which is` shown in Figures 4 to 7. The .machine comprises abase I on which a work carriage' il is mounted for reciprocation from right to left, as seen in this gure. Suitable means, either manual or automatic, may be provided for reciprocting the carriage I l, but in Figurei I have illustrated a handwheel I2 which is adapted to perform this function by conventional means. y

Mounted on the carriage il is a headstock i3, having a center it adapted to be advanced or retracted by a handwheel |5. Opposite the headstock I3 is an indexing mechanism l 8 which may be of conventional type and which includes a second center l1 adapted to engage the end of a gear supporting xture or shaft I8 for supporting a gear G. A driving dog indicated generally at |9 is provided for preventing rotation between the gear G and an index plate (not shown) received within the housing of the indexing device I6.

For spur gears the index plate is held against rotation, and accordingly the gear G, after indexing, is held against rotation. It is within the contemplation of the present invention, however, that conventional means may be provided for rotating the index plate and hence the gear G in accordance with the helix angle of the gear G in order to crown grind helical gears. Mechanism of this sort is now well-known for the grind- 'ing of unmodified helical gears, and will not be described in detail. y

Carried by the base l0, at the rear of the machine as shown in Figure 1, is a column havling suitable vertical ways 2| therein for the re ception of a tool slide 22 mounted therein for vertical reciprocation. The tool slide 22 has horizontal ways therein indicated at 23, and slidably mounted in these ways is a block 24 which provides for adjustment of the grinding wheel W in a horizontal direction. v

Mounted on the work carriage is a trimmer l indicated generally at which is adapted to trim the working surface of the grinding wheel W to the desired profile. rlhe grinding Wheel W is a form-grinding wheel in which the working {prorile is accurately trimmed to the desired profile to be imparted to the teeth of the gear G.

As thus far described, machines of this type have been well-known in the art, and the gear grinding operation performed thereby has been carried out by first aligning a tooth space of the gear G with the wheel W and `traversing the work carriage to the right or left past the wheel W. Contact between the wheel W and the gear Gis limited to a small area directly beneath the axis of the wheel W, and as the translation of the carriage moves the gear past the grinding wheel, the profiles of the gear teeth are ground to the same prole as the trimmed working surfaces of the grinding wheel W.

The column 20 is mounted for adjustment about a vertical axis passing through the axis determined by the centers |4 and This is to permit the grinding of helical gears, for which purpose the column 20 will be set around at an angle in accordance with the helix angle of the gear, and suitable means, previously referred to but not illustrated, will impart a rotation to the gear being ground in accordance with its helix angle.

According to` the present invention I have modiied the construction of these well-known types of grinding machines by providing means for raising and lowering the spindle of the grinding wheel W in timed relation to relative traverse between the grinding wheel and the gear G.

One embodiment of this means is illustrated in detail in Figures 2 and 3.

Essentially the crowning mechanism comprises a cylindrically bored sleeve formed on the block 24 which is adapted to receive an eccentric bushing 4| the eccentricity of which is indicated in Figure 3 by the spacing between vertical lines as indicated at 42. The eccentric bushing 4| is mounted for rotation in the sleeve 40 and is retained therein in accurately centered relation by means of a ring 43 which is bolted or otherwise secured to the sleeve 40 as indicated at 44. The eccentric bushing 4| is provided with a cylindrical bore for the reception of a grinding wheel spindle housing 45, which is adapted to be locked in accurately centered position and against longitudinal shifting by means of a tapered ring 46, held in place by a ring 41 threaded into bushing 4|.

The grinding wheel W has a spindle 48 rotatable within the housing 45, and the housing at the opposite end from the grinding wheel carries a bracket on which is mounted a motor (not shown) for rotating the grinding wheel. The motor, together With suitable reduction gearing as desired, the spindle, the grinding wheel, and the grinding wheel spindle housing all form a subassembly which is rigidly clamped in the bushing 4| by the means just described.

Due to the eccentricity of the bushing 4|, rotation of this bushing in the sleeve 40 results in arcuate movement of the grinding wheel assembly. Since, however, `in the ypresent device it is contemplated that the arc of movement of the eccentric bushing shall be very small, the arrangement is such that the effect of oscillation of the bushing A4| through the arc referred to will be substantially vertical straight movement of the grinding Wheel subassembly.

The sleeve 4U is provided with a lateral opening 5U. Bolted or otherwise secured to a flat surface 5| of the bushing 4|, as indicated generally at 52, is an operating arm 53 which extends through the opening 50 with sufficient clearance to permit oscillation of arm 53 in a vertical plane to the extent desired.

Mounted on the carriage as indicated in Figure 1, is a cam 55, the construction of which is shown in detail in Figures 2 and 3. Mounted on the tool slide 22 is a guide bracket 56 which is apertured as indicated at 5l to receive a vertical post 58, terminating at its lower end ina bifurcated member 59 which receives a cam follower 60. A second apertured bracket 6| is mountedon the column 20 and receives the cam follower E0 in accurately guided relation. The cam follower is pivoted as indicated at 62 to the bifurcated bracket 59.

Mounted on the exterior of the vertical post 58 and beneath the bracket 56 is a compression spring which is adapted to seat at its upper end against the bracket 56, and at its lower end against a spring seat 66, adapted to be locked in adjusted position by means of set screw 61, By this arrangement, the effective force applied by the spring 65 may be varied.

Threaded into the upper end of the post 58 is a rod 68. The bifurcated member 59 previously referred to is also threaded within the post 58. This provides for variation in length of the connection between the cam follower 60 and the eccentric bushing in accordance with the setting of the tool slide 22. It will be appreciated that the tool slide 22 is adjustable vertically in accordance with the diameter of the gear G. The threaded connections between the post 58, the bifurcated member 59, and the rod 68 permit a corresponding adjustment to be made in the connections.

The upper end of the rod 63 is provided with a pivot pin 10, having a portion 7| received in a correspondingly shaped recess in the arm 53.

As a result of the construction just described, translation of the carriage to the right or left basically the same as that ssseenmnmeawmrenntma'mmsnd lowering of the cam follower il, and hence automatically of the pivot pin 1|. Movement of the pinliwilibeinanarcuatepathaboutthecenter of the external cylindrical snrfaceaof the eccentrie bushing 4|, and will impart a corresponding oscillation to the bushing about the center of its external cylindrical surface. Due to the eccentricity of the bushing, this will result in a corresponding movement of the grinding wheel subassembly, which for all practical purposes will be substantially in a vertical straight-line path.-

When it is desired to employ the grinding machine without imparting modified or crowned characteristics to the teeth of the gears being ground, the cam attachment is disconnected and bushing 4| is small, being on the order of .200 of an inch or less, and the axis of the bushing during Operation will move from a position spaced horizontally from, the axisof the sleeve Il to a position slightly above and slightly below this axis. The result of this isto impart an arcuate movement to the tool spindle housing 45, but due to the small angularity of this movement, it is in eilect a substantially straight-line vertical movement. This eccentricity is shown in Figure 4 by the dimension a.

As best seen in Figures 4 and 5, the bushing 4| has a flattened portion adjacent its lower surface to whichis secured a plate 88 having depending therefrom a finger 8|.- As shown in Figure 5 the linger 8| is relatively wide to pertne bushing u may be locked against rotation in the sleeve 48 by means of clamping screw 12.

The position of the cam 55 will be in predetermined relation to the gear G so as to accomplish a desired result. As illustrated in Figure 3, the cam 55 is upwardly convex, When the cam `follower 6U is in intermediate position as shown in Figure 3, the gear being ground will be cen- 'tered with respect to the grinding wheel W so that the contact between the grinding wheel and the gear G will be at the mid portion as measured from end to end of the teeth of the gear being ground. Traverse of the carriage in either direction from this mid position will result in the cam follower moving to a lower vportion of the cam 55, which will result in the grinding wheel moving correspondingly toward the gear or in a direction to increase the depth of grind. It will be observed that the grinding wheel is not positively moved downward upon traverse of the carriage, but instead is biased downward by the spring 65. 'I'his is a desirable feature since it permits the grinding to be carried out at a pressure controllable by the compression of the spring 85. 'Ihe traverse of the 'carriage will be at a slow rate, suillcient to permit removal of .the excess stock adjacent the ends of the gear mit operation of the device with the block 24 moved to diierent positions. A plunger l2 engages a rounded portion of the linger 8i and imparts rotation to the bushing 4|. Plunger 82 is provided with rack teeth`,`shown at Bland is adaptedvto he reciprocated by means of a pinion 84 mounted on a vertical shaft 85 which'extends downwardly in the column 2l to a position at the rear of the carriage il, as shown in Figure 1. Suitable bearing and securing means indicated generally at 85 are provided for mounting the shaft 85 so that it partakes of the vertical adjusting movement of the slide 22. Adjacent the follower 98 is mounted in an so as to form longitudinally concave or hollow teeth. It will be readily apparent that other longitudinally modiled gear teeth will be provided by modcations in the cam 55.

According to a second and preferred embodiment of my invention, equivalent results are accomplished by mechanism differing in detail from that previously described. While theoperation of this embodiment of my invention is previously described,

it diiers therefrom specifically in that it permits raising and lowering of the slide 22 without dis-l Also, the

turbing the crowning adjustment. camming means, which raises and lowers the wheel spindle, is positive acting rather than spring pressed.

lower surface of the shaft is a sleeve 81 which is splined thereto to' permit yrelative vertical movement, the sleeve 81 having formed thereon a pinion 88. The pinion 88 meshes with rack teeth indicated at 89 in Figure I formed on a. cam follower 90. As best seen inv Figure 7, the cam frame of the machine. 'i y Asbest seen in Figure 7, the carriage' has a't its rear-,surface adjacent the cam follower 90 a cam structure indicated generally at 92 which iscomposed of two separate velements 92a and' 92h. These elements are relatively adjustable so as to modify the camming action in a manner which will be readily apparent. For example, by separating elements 92a and 92h a certain distance, fiat portions 93 'of the elements are effective during middle traverse of the carriage Il, and the result will be'gear teeth-which are unmodied throughout a predetermined central portion but which arecrowned for a similarly predetermined corresponding distance from their ends.

As best seen in Figure 5, the sleeve 81 which carries the pinion 88 is mounted in bearings 94 and is retained against vertical movement in an opening-95 of the framev by means of a closure ring 98 which accurately centers the bushing 4| Referring speciiically to Figures 4 to 7, I show I the tool slide 22 which is mounted for vertical adjustment and the block 24 which carries the tool spindle housing 45. The -block 24 is provided with a cylindrically bored sleeve 40 for the reception of an eccentric bushing 4| which, in turn, carries the tool spindle housing 45.

The amount of eccentriclty of the eccentric in the sleeve 40-while atthefsametime permitting the limited rotation thereof necessary for .the crowning motion previously described.

In order to retain the flnger'8l firmly against the plunger 82, I employ the structure illustrated in Figure 4. In this figure I show a lever |08 pivoted as indicated .at IUI, having a linger por-v tion engaging the nger 8|. The levervlilll also has a short arm |02 extending therefrom, which opening 9| in the several seen in Figure 4, by a compression spring indicated at |011. This constantly biasesl the eccentric sleeve 4U in a direction to cause rm engagement between the finger 8l and the` plunger 82.

As seen in Figure 4, uponthe translation cf is engaged by a plunger H33 urged upwardly, as

done solely to enable those skilled in the art to practice the invention, thek scope of which is indicated by the appended claims.

What I claim as my invention is:

l. In a gear grinding machine having aframe,

l a work carriage mounted for translation on said the carriage I l to the right or left (as seen in Figure l), the cam follower 9D will move axially, The cam follower 9D is in its extreme for- Ward position, contacting the low portion of the cam structure 92 when the grinding wheel contacts the teeth ofthe gear midway between their ends. -Motion -of the work carriage il in either direction from this mid position will result in moving the cam followerI 90 tothe rear and will upward movement is effected by means of compression spring iiil and associated parts. 'Ihis results in positive removal of material from the teeth of the gear Ain a single stroke. rIhis has been found satisfactory since the amount of stock removal is relatively small.

The type of crowning which results from the use of the machines illustrated imparts desirable properties to the gear. Since the teeth surfaces are normally involute, it will be understood that a relative down-set to the wheel will result in the removal of more stock from adjacent the tip of the tooth than from adjacent its root. This results in lowering the profile of the teeth throughout the crowned portions in a manner which will eifect an increase in pressure angle ofthe teeth adjacent their end crowned surfaces. It is particularly desirable to avoid limited contact between meshing -gears adjacent the top corners, and the practice of this method results in providing the maximum clearance at the point where contact is most undesirable and destructive;

In Figure 8 I have illustrated this condition diagrammatically. The profile of the uncrowned tooth, adjacent an end, is indicated at HU. The profile of the crowned tooth, adjacent an end, is indi;ated at IH. parent that more material is removed from adjacent the tip of the crowned portion of the tooth than is removed from adjacent the root, as particularly evident by comparisons of depths of stock removal indicated by arrows H2, H3 and H4. Thus the crowned portions of the tooth is provided with tip relief, thereby adding to the elimination of interference. Furthermore, this tip relief will be uniform on all four corners,

vgiving a symmetrical tooth.

The present type of grinding of gear teeth has specic advantages over previously known types. In the rst place, the crowning operation is carried out simultaneously on two tooth surfaces, which contributes to rapidity in production. In the second place, the profile of the vground and modiiied gear teeth will be the same in any place along the gear tooth, being at Y all points determined solely by the trimmed curvature of the working surface of the grinding wheel W.

While I have illustrated two specifically different machines for carrying outJ .my improved method, it will be understood that this has been frame, a column adjacent said carriage, and a tool slide mounted for vertical adjustment on said column: an eccentric bushing on said slide, a tool spindle housing in said bushing, means for rotating said bushing in accordance with translation of said carriagecomprising a vertical shaft secured to said slide ,for verticalmovement therewith, a pinion splined to said shaft adjacent said carriage, a rack carried by said frame in mesh with said pinion, a cam on said carriage engaging said rack, and means operatively interconnecting said shaft and said bushing.

2. In a gear grinding machine having a frame, a work carriage mounted for translation on said frame, a column adjacent said carriage, and a tool slide mounted for vertical adjustment on said column: an eccentric bushing on said slide, a tool spindle housing in said bushing, means for rotating said bushing in accordance with translation of said carriage comprising a vertical shaft secured to said slide for vertical movement therewith, a pinion splined to said shaft adjacent said carriage, a rack carried by said frame in From this figure it is ap- Y mesh with said pinion, a cam on said carriage engaging said rack, a second pinion on said shaft, and a second rack in mesh therewith operatively interconnecting said shaft and said bushing.

3.` In a gear grinding machine having a frame, a work carriage mounted for translation on said frame, a column adjacent said carriage, and a tool slide mounted for vertical adjustment on said column; an eccentricbushing on said slide, a tool spindle housing in-said bushing, means for rotating said bushing in accordance with translation of said carriage comprising a vertical shaft secured to said slide for vertical movement therewith, a pinion splined to said shaft adjacent said carriage, a rack carried by said frame in mesh with said pinion, a cam on said carriage engaging said rack, a second pinion on said shaft, and a second rack in mesh therewith, said bushing having a lateral arm engageable by said second rack and spring.

4. In a gear grinding machine having a reciprocable work carriage, a tool supporting sleeve adjacent said carriage, an eccentric bushing in said sleeve, means in said bushing for supporting a grinding wheel spindle, a cam on said carriage, a cam follower engageable with said cam and connected to said bushingv to oscillate the same in said sleeveupon reciprocation of said carriage.

5. In a gear grinding machine having a reciprocable Work carriage, a tool supporting sleeve adjacent said carriage, an eccentric bushing in said sleeve, means Yin said bushing for support- -rocable work carriage, a tool supporting sleeve adjacent said carriage, an eccentric bushing in said sleeve, means in said bushing for supporting a grinding wheel spindle, a cam on said carriage, a cam follower engageable with said cam and connected to said bushing to oscillate the same in said sleeve upon reciprocation of said carriage, and releasable means for `locking said bushing against rotation in said spindle.

7. In a gear grinding machine having a reciprocable` work carriage, a tool supporting sleeve adjacent said carriage, an eccentric bushing in said sleeve, means in said bushing for supporting a grinding wheel spindle, said sleeve having a lateral opening therein, an arm rigidly secured to said bushing and extending through said opening, a cam on said carriage, a cam follower engagea-ble with said cam and connected to said arm to oscillate said bushing in said sleeve upon reciprocation of said carriage.

8. In a gear grinding machine having a reciprocable work carriage, a tool supporting sleeve adjacent said carriage, an eccentric bushing in said sleeve, means in said bushing for supporting a grinding wheel spindle. and means for rotating said bushing in accordance with the reciprocation of said carriage comprising a cam on said carriage and a cam follower engageable with said cam and operatively connected to said bushing.

ROBERT S. DRUMMOND.

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