Timing belt adjustment mechanism

A belt tension and timing adjustment mechanism particularly for the timing belt of a lawn mower or the like having a plurality of rotary cutting blades. One rotary blade is mounted to the mower deck by a mounting plate having a plurality of bolts. The deck includes an aperture which closely receives one of the bolts, which defines a pivot axis, and the remaining bolts are received in elongated slots for pivotal movement of the rotary blade assembly to adjust the tension in the belt. The plate is rotated on the pivot axis by an adjustment bolt assembly having a bolt received through integral tabs on the adjustment plate and deck. The plate is spring biased by a spring and spacer assembly on the bolt against the tension of the belt, wherein the correct belt tension is indicated by the space between the adjustment bolt head and the plate tab, making belt tension adjustments simple and accurate.

FIELD OF THE INVENTION 
The present invention relates to improvements in timing belt adjustment 
mechanisms, particularly adjustment mechanisms for the timing belt of a 
rotary mower having a plurality of blades with overlapping cutting paths. 
The timing belt adjustment mechanism of this invention pivotally adjusts 
the blade and spindle assembly of one blade relative to the other to 
adjust the tension in the timing belt. 
DESCRIPTION OF THE PRIOR ART 
Tractor mounted mowers of the general type disclosed herein are now common 
in the industry. The mower assembly is generally suspended beneath the 
tractor on a linkage which permits vertical adjustment of the mower to 
adjust the cutting height of the rotary blades. In a belt driven mower of 
this type, an endless drive belt is received around the power take-off 
pulley of the tractor and a driven pulley of the mower. Drive belt tension 
may be maintained by a spring actuated idler sheave assembly which 
receives the drive belt. 
The prior art includes mower assemblies having a plurality of spaced 
horizontal rotary blades which rotate on vertical axes having overlapping 
cutting paths to provide a uniform cutting swath. The blades are rotatably 
mounted in a bearing housing on a shaft. The bearing housings are usually 
mounted on a horizontal mower deck with the shafts extending vertically 
through the deck in parallel relation. Each shaft includes an annular 
sprocket mounted thereon and a flexible timing belt is received around the 
sprockets to rotate the blades in timed relation. The drive sprocket of 
the rotary blades is generally mounted on the same shaft as the driven 
pulley of the mower which receives the drive belt. The mower may include 
three or more rotary blades, wherein each blade in addition to the first 
blade on the drive shaft is connected to the first blade by a timing belt. 
As described above, the blades must rotate in timed relation to avoi 
contact of the blades in their overlapping rotational paths. Further, the 
tension of the timing belt is particularly important to avoid wear or 
slippage, which may result in blade to blade contact. It is often 
difficult to adjust the tension in the timing belt of the rotary mowers of 
the prior art. Generally, belt tension is adjusted by loosening the blade 
bearing housing mounting bolts, then attempting to hold the blade housing 
against the tension of the belt, while tightening the mounting bolts. More 
importantly, it is not possible to accurately gage the tension in the 
timing belt, except by "feel", which requires an experienced mechanic. 
Where the belt is too tight, the belt may wear excessively. 
It is thus an object of the present invention to provide a simple and 
reliable timing belt adjustment mechanism, wherein the tension in the 
timing belt may be easily and accurately gaged and easily adjusted to the 
optimum tension. 
SUMMARY OF THE INVENTION 
As described above, the timing and tension adjustment mechanism of this 
invention is particularly adapted for adjustment of the timing belt of a 
lawn mower having a plurality of rotary cutting blades with overlapping 
cutting paths. The blades are rotatably mounted on generally vertical 
shafts each having a bearing housing mounted on the mower deck. The shafts 
extend through the deck, in generally parallel relation. An annular 
sprocket is mounted on each shaft and a flexible timing belt is received 
around the sprockets for rotating the blades in timed relation. The 
adjustment mechanism of this invention releases the tension in the timing 
belt for timing adjustment and accurately adjusts the tension in the belt 
to a predetermined optimum tension. 
The timing and tension adjustment mechanism includes an adjustment plate 
overlying the mower deck and mounting one rotary blade assembly on the 
deck. In the disclosed embodiment, one of the blade bearing housings is 
attached to the mower deck by a plurality of mounting bolts. The mower 
deck includes a pivot aperture which closely receives one of the bearing 
housing mounting bolts and the deck includes a plurality of arcuate or 
elongated slots which receive the remaining mounting bolts. The deck 
aperture thus provides a pivot axis for rotation of the bearing housing 
around one of the bolts to adjust the tension in the timing belt. 
In the preferred embodiment of the adjustment mechanism, the mower deck and 
the adjustment plate have integral opposed tabs having generally coaxially 
aligned apertures. An adjustment bolt having an enlarged head portion and 
a threaded shank is received through the aligned apertures in the tabs. A 
stop is provided on the bolt shank, between the tabs, and a tubular spacer 
is telescopically received on the adjustment bolt shank which engages the 
stop and is located between the bolt stop and the adjustment plate tab. 
The aperture in the adjustment plate tab permits the tubular spacer to 
pass freely therethrough, around the bolt shank and a compression coil 
spring is telescopically received around the spacer having opposed ends 
engaging the adjustment plate tab and the stop. A bolt adjustment means, 
such as a threaded nut, is received on the bolt and threadably biased 
against the deck tab to incrementally adjust the adjustment bolt 
longitudinally against the force of the compression spring. The 
compression spring thereby maintains the tension in the belt and the 
tension in the belt may be adjusted by rotating the nut on the adjustment 
bolt against the deck tab. 
In the preferred embodiment, the tension in the timing belt is indicated by 
the space between the bolt head and the adjustment plate tab. When the 
tension in the belt is properly adjusted, the bolt head will be slightly 
spaced from the adjustment bolt tab. This space or gap may be accurately 
adjusted to the thickness of the ignition key or any convenient 
measurement. The gap is easily measured and maintained by adjustment of 
the nut or nuts on the adjustment bolt bearing against the deck tab. The 
tension in the belt is released for adjustment of the timing of the rotary 
blades by adjustment of the stop means, which may also be provided by a 
nut threadably received on the bolt shank and located between the 
adjustment plate and deck tab. 
The timing and tension adjustment mechanism of this invention is thus 
simple in construction, yet reliable and accomodates a plurality of rotary 
cutting blades. Other advantages and meritorious features of the timing 
belt adjustment mechanism of this invention will be more fully understood 
from the following description of the preferred embodiments, the appended 
claims and the drawings, a brief description of which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the disclosed embodiment, the lawn mower assembly 20 is mounted beneath 
a tractor, not shown, on a drawbar suspension. The tractor may be a 
conventional lawn or garden type tractor having a horsepower range from 
about 5 to 20 HP, such as disclosed in the prior art. The tractor in the 
disclosed embodiment includes a C-shaped carriage hitch 22 and a power 
take-off pulley 24 which is mounted on the forward output shaft of the 
tractor, not shown. An endless drive belt 26 is received on the power 
take-off pulley 24 of the tractor, around the idler sheaves of the idler 
sheave assembly 28, and around the mower driven pulley 30, to drive the 
rotary mower blade 32. The tractor, which does not form a part of this 
invention, may be any conventional tractor. The details of the mower 
drawbar suspension and idler sheave assembly 28, which do not for a part 
of this invention, are more fully described in copending applications, Ser 
Nos. 217,617 and 217,718 filed Dec. 18, 1980, which are incorporated 
herein by reference. 
The forward end of the mower assembly 20 is supported on a drawbar 
suspension, which includes two pair of parallel links. The power parallel 
links 36 and 38, are pivotally connected to the carriage hitch 22 at 40 
and 42, respectively. The carriage hitch is attached to the forward end of 
the tractor by bolts or the like through apertures 34 in the carriage 
hitch. The rearward ends of the lower links 36 and 38 are pivotally 
connected to the mower frame 49 by pivotal connections 44 and 46, 
respectively. In the disclosed embodiment, the pivotal connections are 
provided by metal pins, which are received through apertures in the links 
and the tractor chassis or mower frame, and which are retained by cotter 
pins, not shown. The linkage may thus be easily disassembled, as required. 
The parallel upper links 48 and 50 are pivotally connected to the tractor 
chassis at their forward ends by pins received through pivot aperture 52 
and 54, respectively. The rearward ends of the upper parallel links are 
pivotally connected to mower frame member 60 by pivotal connections 56 and 
58, respectively. As shown, the upper parallel links 48 and 50 are 
generally parallel to the lower parallel links 36 and 38, forming two 
pairs of parallelograms about which the forward end of the mower assembly 
may be raised or lowered. 
The rearward end of the mower assembly is supported on gage wheels 64. The 
gage wheels are rotatably supported on wheel support arms 66 by 
conventional bolt and bearing assemblies 68. The wheel support arms are 
connected to rock shaft 70, which is rotatably supported at the rearward 
end of the mower by brackets 72. The brackets are welded or otherwise 
secured to the mower frame, as best shown in FIG. 2. A lift arm 74 is 
connected to the rock shaft to form a bellcrank lever with the rock shaft 
and wheel support arms, such that rotation of the wheel support arms 66, 
about rock shaft 70, rotates the lift arm 74. 
The lift arm 74 is operably connected to the drawbar linkage by a tie rod 
78. The tie rod includes a rear clevis 80 which is threadably received on 
the rearward end of the tie rod and retained by nut 82. The clevis is 
pivotally connected to the upper free end of the lift arm 74 by pivot pin 
84, which is received in an arcuate slot 86 to accomodate the rotational 
motion of the lift arm about rock shaft 70. The forward end of the tie rod 
is pivotally connected to a bellcrank lever 90 by clevis 92, which is 
threadably received on the forward end of the tie rod and retained by nut 
94. The clevis is pivotally connected to the upper free end of the 
bellcrank by pivot pin 96. As described, above, the pivot pins in the 
disclosed embodiment are retained by cotter pins, not shown. The bellcrank 
lever 90 is pivotally connected to one of the upper parallel links 48 and 
one of the lower parallel links 36 to raise the forward end of the mower 
in parallel relation to the rearward mower end and maintain the rotary 
blades level for an even cut. 
The bellcrank lever is connected by a leveler link 100 to the pivotal 
connection 44 between the lower link 36 and the mower frame member 49. The 
upper end of the leveler link is pivotally connected to the bellcrank 
lever by pin 102, which is received in a lost motion slot 104 in the 
leveler link. The lost motion slot will accomodate the arcuate motion of 
the bellcrank lever. The bellcrank lever is connected to one of the upper 
links 48 by a rectangular tab 106, which is welded or otherwise secured to 
the upper link 48. A pivot pin 108 is rotatably received in a bearing 
sleeve 110, which is secured to or integral with the tab 106. The 
bellcrank lever 90 is thus pivotally connected to one of the upper and 
lower parallel links, 48 and 36, respectively, and to the tie rod 78 at 
its free end. Longitudinal movement of the tie rod 78 will thus rotate the 
bellcrank lever to adjust the height of the forward end of the mower. 
The mower is retained at one of five predetermined heights by height 
adjustment arm 116, which is secured to rock shaft 70. The free end of the 
height adjustment arm 116 is U-shaped, as shown in FIG. 2, and includes a 
spring biased lock pin 118 which is receiveable in one of the vertically 
spaced apertures 120 in the sector plate 122 attached to the mower 
chassis. The mower is raised or lowered by rotating wheel support arms 66 
about rock shaft 70 to swing the gage wheels 64 beneath the rearward end 
of the mower to raise or lower the rearward end of the mower. As described 
more fully in the above referenced copending application, rotation of the 
wheel support arms 66 rotates the lift arm 74 and moves the tie rod 78 
longitudinally to rotate bellcrank 90 and simultaneously raise or lower 
the forward end of the the mower, in parallel relation. The mower is 
retained at the desired height by the spring bolt 118. 
As shown in FIGS. 1 and 2 and described more fully in the above referenced 
copending application filed concurrently herewith, the idler sheave 
assembly 28 maintains a constant tension in the drive belt 26 as the mower 
is raised or lowered. The idler sheave assembly is supported on a U-shaped 
bracket 130 and includes a fixed mule sheave 132 and a spring actuated 
rock sheave 134. The U-shaped idler sheave bracket is pivotally supported 
on the upper parallel links, 48 and 50, by pivot bolts 136, such that the 
idler sheave assembly moves vertically with the mower as the mower is 
raised or lowered. The tension in the drive belt is adjusted by rotation 
of adjustment screw 138 having a handle portion 140 at the forward end of 
the carriage hitch 22. 
It will be understood that the lawn mower assembly 20 shown in FIGS. 1 and 
2, including the drawbar suspension and idler sheave assembly, is merely 
illustrative of the type of rotary lawn mower suitable for the timing belt 
adjustment mechanism of this invention, which is disclosed in FIGS. 3 and 
4. Further, the drawbar suspension and idler sheave assembly are more 
fully disclosed and claimed in separate copending applications, which are 
incorporated herein by reference. 
The adjustment mechanism of this invention is adapted to adjust the timing 
and tension in a timing belt of a lawn mower having two or more rotary 
cutting blades. The disclosed embodiment of the lawn mower assembly 
includes two driven rotary blades 32 and a center blade 150. The blades 
are mounted on shafts 156 and 162 in spindle housings 152 and 154, 
respectively. Driven sprockets 158 are mounted on the outer rotary blade 
shafts and aligned with drive sprockets 160 mounted on the center blade 
shaft 162. The center blade shaft includes the driven pulley 30, which 
receives the drive belt 26 of the mower. The shafts 156 and 162 are 
splined and received in splined openings in the sprockets, such that the 
rotary blades 32 and 150 accurately rotate with the sprockets. The timing 
belts 164 are received around the sprockets and include ribs, as shown in 
FIG. 4, which are received in grooves in the sprockets, such that the 
outer sprockets 158 are accurately controlled by the center or drive 
sprockets 160. 
The rotary blade assemblies are mounted on the generally horizontal mower 
deck 166. In the disclosed embodiment, the spindle housings 152 and 156 
include an annular collar 168 and 170, respectively, which are attached to 
the mower deck by threaded bolts and nuts 172. The bolts, which are 
integral with adjustment plate 178, are received through openings in the 
mower deck 166 and the collars 168 and 170 of the spindle housings and 
secured by nuts 172. 
In the preferred embodiment of the adjustment mechanism, the openings in 
the mower deck which receive the mounting bolts include a pivot aperture 
174, which closely receives the mounting bolt, and a plurality of slots 
176 which receive the remainder of the mounting bolts. The outer spindle 
housings 152 are thus permitted to rotate about pivot axes provided by 
apertures 174 to adjust the tension in the timing belt 164. For example, 
when the blade spindle housing 152 shown in FIG. 4 is rotated in a 
counter-clockwise direction about pivot aperture 174, the tension in the 
timing belt will be increased. The rotary blade assembly including the 
blade and spindle housing are retained in the set position by adjustment 
mechanism 200. 
The adjustment mechanism includes the adjustment plate 178 and an integral 
tab 180 which is formed from an upturned portion of the adjustment plate. 
A generally parallel deck tab 182 is integrally struck from the upper 
plate of the mower deck 166. The tabs 180 and 182 include generally 
coaxially aligned apertures which receive an adjustment bolt 184 having an 
enlarged head portion 186 and a threaded shank portion 188. The adjustment 
bolt 180 includes and adjustable stop member, between the tabs, including 
a threaded nut 194 received on the threaded shank portion and an enlarged 
washer 196. A tubular spacer 198 is received on the threaded shank portion 
of the bolt between the washer 196 of the stop member and the enlarged 
head 186 of the shank. A coil spring 202 is compressed between the washer 
196 of the stop member and the adjustment plate tab 180. As shown in FIG. 
4, the diameter of the aperture 190 in the adjustment plate tab is large 
enough to permit the tubular spacer 198 to pass freely therethrough. The 
diameter of the spring 202 is greater than the aperture 190. The coil 
spring 202 is thus compressed between the adjustment plate tab 180 and the 
washer 196 of the stop member as the plate 180 is rotated. 
The timing belt adjustment mechanism of this invention may be utilized to 
either release the tension in the timing belt 164, to adjust the timing 
between either of the outer rotary blades 32 and the center blade 150 and 
accurately adjust the tension in the timing belt. Further, the adjustment 
mechanism indicates the tension in the belt, as now described. The 
"timing" of the blades 32 and 150 is adjusted by loosening the blades 
spindle housing mounting bolts 172 and turning the nut 204 towards the 
compression of spring 202. The nut 204 will allow movement of the 
adjustment bolt to the right in FIG. 4 which permits rotation of 
adjustment plate 178 clockwise to loosen the tension in the timing belt 
164. The blades 32 and 150 may then be rotated and adjusted, such that the 
blades extend at right angles, as shown, which will avoid any contact 
between the blades in their overlapping cutting paths. 
The tension in the timing belt 164 is adjusted by threading nuts 204 and 
206 which are threadably received on the threaded shank portion 188 of the 
adjustment bolt on opposite sides of the mower deck tab 182. The correct 
or preferred timing belt tension is indicated by the location of the 
adjustment bolt head 186 relative to the adjustment plate tab 180. When 
the bolt head is spaced from the tab 180, the compression of spring 202 
biases the adjustment plate tab 180 to rotate the plate 178 in a 
counter-clockwise direction, against the tension in the timing belt 164, 
increasing the tension in the belt. When the bolt head 186 is correctly 
spaced from the tab 180, as shown in FIG. 4, the spring pressure equals or 
offsets the preferred belt tension. The preferred predetermined space may 
be set at any convenient or desired distance. For example, in the 
disclosed embodiment, the preferred distance between the bolt head and the 
tab is equal to the thickness of an ignition key. 
When there is no gap between the bolt head 186 and tab 180 or when the gap 
is insufficient, the gap is set or increased by loosening nut 206 and 
threading nut 204 against tab 182. The nut moves bolt 188 to the left in 
FIG. 4, rotating adjustment plate 178 in a counter-clockwise direction, 
increasing the tension in the belt. When the gap is greater than desired, 
nut 204 is threaded toward nut 194, moving adjustment bolt 188 to the 
right in FIG. 4, reducting the tension in the belt. When the desired gap 
is set, nut 206 is tightened against tab 182, locking the bolt in the 
correct position. The tension in the belt may thereafter be easily 
determined by gaging the distance between the bolt head 186 and tab 180. 
The belt tension is adjusted by threading nuts 204 and 206, as described 
above. When the proper timing belt tension is set, the nuts 172 are 
tightened and the spindle housings are locked on the mower deck. 
The timing belt adjustment mechanism of this invention thus provides an 
indicator of belt tension and permits easy adjustment of the belt tension 
to avoid slippage or excessive wear in the timing belt. The adjustment 
mechanism is relatively simple in construction, yet reliable and 
accomodates three or more rotary cutting blades. It will be understood 
that various modifications may be made to the adjustment mechanism of this 
invention without departing from the preview of the appended claims.