Tensioning device for power transfer assembly

A belt-type power transfer assembly for driving the separating mechanism of a rotary combine harvester is disclosed wherein the assembly includes spaced apart driving and driven pulleys, an endless flexible belt interengaged between the pulleys to transfer rotational power therebetween and spring-loaded tensioning means operably engaged with the flexible belt to take up the slack thereof and to maintain proper tension therein when transferring rotational power. Stop means are associated with the spring-loaded tensioning means for restricting biasing movement thereof in the direction of the flexible belt, causing the tensioning means to act as fixedly positioned tensioning means after an initial belt tensioning movement thereof. The power transfer assembly according to the invention may be used to drive the separating mechanism of a rotary combine harvester.

BACKGROUND OF THE INVENTION 
The present invention relates to belt-type power transfer assemblies and 
has particular reference to such power transfer assemblies having belt 
tensioning devices and to the use of such power transfer assemblies on 
rotary type combine harvesters. 
In known combine harvesters, crop material is threshed and separated in a 
threshing and separating mechanism and the separated grain, together with 
impurities is fed to a cleaning mechanism for cleaning. In conventional 
combine harvesters final grain separation is accomplished by straw 
walkers. In rotary combine harvesters the crop material is subjected to a 
much more aggressive and positive separating action during a relatively 
prolonged period of time, whereby the efficiency of a rotary combine 
harvester usually is greater than that of a conventional machine. 
In one type of rotary combine harvester a conventional transversely 
extending threshing mechanism having a threshing cylinder and a cooperable 
concave is combined with a rotary separating mechanism having a rotor of a 
width greater than that of the threshing mechanism and disposed parallel 
thereto with its ends extending transversely past the respective ends of 
the threshing mechanism. The rotary separating mechanism operates spirally 
to convey the crop material received from the threshing mechanism towards 
each of its ends, while submitting the crop to a separating action. 
It has been experienced that in rotary combine harvesters of the type 
described, irregular feeding of crop material to the separating mechanism 
may cause plugging which eventually may result in a so-called "kill-stop" 
of said mechanism. Provided the drive train to the separating mechanism 
does not comprise other safety devices, such a "kill-stop" often would 
result in a major breakdown, such as the drive belt and/or pulleys 
breaking and/or shafts bending. 
spring-loaded tensioning devices for belt-type power transfer assemblies 
maintain belt tension to provide a positive drive under a wide range of 
load conditions, including the aforesaid "kill-stop" conditions; however, 
such tensioning devices improve the operative life of the belt. On the 
other hand, fixedly positioned belt tensioning devices will not provide a 
positive drive under "kill-stop" conditions, but do significantly shorten 
belt life. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to overcome the aforementioned 
disadvantages of the prior art. More particularly, it is an object of the 
invention to combine in a belt-type power transfer assembly the advantages 
of spring-loaded and fixedly positioned belt tensioning devices, while 
eliminating the respective disadvantages thereof. In other words, the 
invention provides a belt-type power transfer assembly comprising a 
spring-loaded belt tensioning device which guarantees not only a longer 
belt life and a positive drive under normal load conditions, but also a 
substantial belt slip as a safety precaution under excessive load 
conditions so that extra safety devices are no longer needed to cope with 
such excessive load conditions. 
It is a further object of this invention to apply such an improved power 
transfer assembly on a rotary combine for driving the rotary separating 
mechanism thereof. 
According to the invention, a belt-type power transfer assembly comprises 
driving and driven pulleys, an endless flexible belt interengaged between 
said driving and driven pulleys to transfer rotational power therebetween, 
spring-loaded tensioning means operably engaged with the flexible belt to 
take up the slack thereof and to maintain proper tension therein when 
transferring rotational power and stop means associated with the 
spring-loaded tensioning means for restricting movement thereof in the 
direction of the flexible belt. 
Preferably, the spring-loaded tensioning means comprise a tension pulley 
rotatably mounted on a pivot arm and biasing means acting between a fixed 
support on the machine chassis and the pivot arm to urge the latter with 
the tension pulley thereon in the direction of the flexible belt. The stop 
means are associated with the biasing means and restrict biasing movement 
thereof. The biasing means may comprise a rod pivotally coupled at one end 
to the pivot arm and supporting at a distance therefrom abutting means. A 
compression spring may be provided in the pre-compressed condition between 
the abutting means on the rod and the fixed support on the machine 
chassis. The stop means may be associated with the compression spring for 
restricting extension thereof. 
The stop means preferably are in the form of a generally U-shaped bracket, 
one leg of the U-shape being held in fixed position relative to one end of 
the compression spring and the other leg of the U-shape being positioned 
in the vicinity of the other end of the compression spring for engagement, 
upon extension of the compression spring, with the fixed support, 
respectively the abutting means on the rod at the side thereof facing away 
from said compression spring for restricting extension of said compression 
spring. 
According to a further aspect of the invention, the belt-type power 
transfer assembly identified above is applied on a combine harvester 
comprising a threshing mechanism and a rotary separating mechanism for 
driving said separating mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to the drawings, particularly FIG. 1, a side elevational 
view of a harvester incorporating the principles of the instant invention 
can be seen. Any left and right references are used as a matter of 
convenience and are determined by standing at the rear of the machine, 
facing the forward end, the direction of travel. The combine, generally 
indicated at 1, comprises a main chassis or frame 2 supported on a front 
pair of drive wheels 3 and a rear pair of steerable wheels 4. Supported on 
the main chassis 2 are an operator's platform 5 with a driver's seat 6 and 
a steering wheel 7, a grain tank 8, a threshing and separating mechanism 
indicated generally at 9, a grain cleaning mechanism 11 and an engine 12. 
A conventional header 13 and straw elevator 14 extend forwardly of the 
main chassis 2. 
As the combine harvester 1 is propelled forwardly over a field with 
standing crop, the latter is severed from the stubble by a sickle bar 10 
on the header 12, whereafter a reel 15 and a header auger 16 convey the 
cut crop to the straw elevator 14 which supplies it to the threshing and 
separating mechanism 9. The crop received within the threshing and 
separating mechanism 9 is threshed and repeated; that is to say the crop 
is rubbed and beaten, whereby the grain, seed or the like, is loosened and 
separated from the straw, stalks, coils or other discardable part of the 
crop. 
Grain which has been separated from the straw falls onto the grain cleaning 
mechanism 11 which comprised means to separate chaff and other impurities 
from the grain and means to separate unthreshed materials (tailings). 
Clean grain is then elevated into the grain tank 8 and the tailings are 
reprocessed in separate tailings rethreshers (not shown) and returned to 
the cleaning mechanism 11 for repeat cleaning action. 
A threshing portion 17 of the threshing and separating mechanism 9 
comprises a rotatable threshing cylinder 18 cooperable with a stationary 
threshing concave (not shown). Rearwardly of the threshing mechanism 17, a 
deflector beater, or so-called straw beater 19 with an associated beater 
grate (again not shown) is provided. 
A separating portion 20 of the threshing and separating mechanism 9 
comprises a first separator rotor or cylinder 21 and a second rotor or 
cylinder 22 cooperable with respective concaves (also not shown). The 
second rotor 22 is mounted within a separating housing (not shown) and 
both of these components have a width substantially exceeding the width of 
the first rotor 21 which, like the straw beater 19, has the same width as 
the threshing mechanism 17. 
Drive means are provided for driving the threshing cylinder 18, the straw 
beater 19, the first separating rotor 21 and the second separating rotor 
22 in the counter clockwise direction 38 as viewed in FIG. 1. The drive 
means to the threshing cylinder 18 and straw beater 19 are conventional 
and are therefore not shown in the drawings. The power transfer assembly 
to the separating rotors 21 and 22 basically comprises a first belt 
transmission 31 between the engine shaft 32 and an intermediate shaft 33, 
a second belt transmission 34 between said intermediate shaft 33 and the 
first separating rotor 21 and finally a third belt transmission 35 between 
the first and second separating rotors 21 and 22. The invention is 
concerned with the second belt transmission 34 and will be described in 
greater detail below. 
A conventional rpm monitor (not shown) may be associated with, for example, 
the shaft of the second separating rotor 22 for warning the operator when 
the speed thereof drops below a nominal value and so that the operator can 
take appropriate corrective action. 
In operation, the mat of crop material issuing from the threshing mechanism 
is deflected by the straw beater 19 to the separating mechanism 20 where 
it is first conveyed in a generally rearward direction between the first 
separating rotor 21 and the associated concave and then received by the 
second separating rotor 22, where it is divided into two portions (by 
means not shown). The resulting two portions are moved spirally around the 
rotor 22 to respective ends thereof to complete the separating action. On 
reaching the ends of the rotor 22, the mats of crop material (straw) are 
propelled by the rotor through respective discharge channels and the straw 
hood 23 for discharge from the machine. 
The threshing and separating components of the combine harvester so far 
described are disclosed in greater detail in British Specification No. 
2,063,039, the contents of which are incorporated herein by reference. 
With reference to FIGS. 2 and 3, the power transfer assembly according to 
the invention and for the separating mechanism 20 will be seen in greater 
detail. The intermediate shaft 33 is provided with a V-pulley 36 for 
receiving V-belt 37 of the first belt transmission 31 and which drives the 
intermediate shaft 33 in the direction as shown at 38 in FIG. 2. The 
second belt transmission 34 comprises a first V-pulley 41 on the 
intermediate shaft 33, a further V-pulley 42 on the shaft 43 of the first 
separating rotor 21 and a V-belt 44 interengaged therebetween for 
transferring rotational power from the intermediate shaft 33 to the 
separating mechanism 20 in general and to the first separating rotor 21 in 
particular. 
The third belt transmission 35 comprises again a first V-pulley 46 on the 
shaft 43 of the first separating rotor 21, a further V-pulley 47 on the 
shaft 48 of the second rotor 22 and a V-belt 49 interengaged therebetween. 
spring-loaded tension pulleys 51,52 operably engage with the so-called 
slack portions of the respective V-belts 44 and 49 to take up the slack 
thereof and to maintain proper tension therein when transferring 
rotational power. 
The tension pulley 51, which is part of the belt tensioning device 50, is 
rotatably supported on one end of a pivot arm 53 which is pivotally 
mounted at 54 on the combine chassis 2. The pivot arm 53 is pivotaly 
coupled at its other end to a tension rod 55 of a biasing means generally 
indicated at 56. The tension rod 55 extends through an aperture in one leg 
57 of a fixed and generally L-shaped support 58 on the chassis. An 
adjustable stop 61 in the form of an abutment nut 62 and an associated 
lock nut 63 is provided adjacent the threaded free end of the tension rod 
55. A compression spring 64 extends coaxially with the tension rod 55 
between the fixed support 58 and the adjustable stop 61. The compression 
spring is dimensioned and pre-compressed to urge the tension pulley 51 
with a pre-determined force against the slack portion 39 of the belt 44. 
To facilitate adjustment of the degree of pre-compression of the spring 
64, a so-called spring indicator 65 is provided. As is conventional, the 
spring indicator 65 is generally L-shaped and is positioned with its 
shorter leg 66 in engagement with the support 58 on the chassis 2. The 
longer leg 69 has a length corresponding to the length of the compression 
spring 64 when compressed to the degree as desired. Thus, to pre-compress 
the spring to the pre-determined amount, it is sufficient to adjust the 
stop 61 on the tension rod 55 until its surface abutting the compression 
spring 64 is aligned with the free end of the longer leg 69 of the spring 
indicator 65. Such adjustment is done when the drive is interrupted. As 
the belt 44 stretches during its lifetime readjustment is necessary from 
time to time. 
According to the invention, stop means 67 are associated with the biasing 
means 56 for restricting the extension of the compression spring 64 as the 
drive belt 44 lengthens during operation and thus permits the compression 
spring 64 to urge the tension pulley 51 further in the direction of the 
drive belt 44 for taking up the increased slack therein. 
The stop means 67 are in the form of a generally U-shaped bracket 68 having 
both legs 71,72 apertured for sliding over the tension rod 55. The bracket 
68 is positioned with one leg 71 in engagement with the abutment nut 62 on 
the tension rod 55. The compression spring 64 may be arranged to urge said 
leg 71 in continuous contact with said abutment nut 62. 
The bracket 68 further also comprises between the base portion 73 and the 
leg 72, a bent portion 74, which is hooked around the leg 59 of the 
support 58. When the compression spring 64 is pre-compressed to the 
pre-determined amount and when the drive is disengaged, the hooked portion 
74 is positioned at a short distance from the leg 59 of the support 58 
thus providing therebetween a clearance 75, which typically may be in the 
range of 10 mm. However, this clearance is, of course, dependent upon, 
among other things, belt characteristics such as length and strength, 
maximum load to be transferred and the positioning of idler pulley 
relative to the driving and driven pulleys. As the compression spring 64 
extends, the bent portion 74 approaches and eventually engages the support 
58 whereafter further extension of the compression spring 64 is 
impossible. The hooked portion 74 overlying the leg 59 of the support 58 
equally prevents angular displacement of the stop means 67 around the 
tension rod 55. 
Prior to turning to the operation of the structure according to the 
invention, and for enabling a better understanding of the characteristics 
of the invention, some consideration will be made hereafter with respect 
to belt-type power transmission assemblies, in general, and with respect 
to such assemblies having either spring-loaded or fixedly positioned belt 
tensioning devices, in particular. 
It is generally known in the art of belt-type power transfer assemblies 
that the so-called slack portion of the belt appears to lengthen when 
transferring power. This is partly due to actual stretching of mainly the 
so-called tight portion of the belt as a result of the tension therein 
while transmitting power. However this lengthening in part also may be 
fictive and result from the driving and driven shafts bending toward each 
other under load conditions, especially when the pulleys are provided at a 
substantial distance from the nearest bearing means supporting the shafts 
on the chassis. Further, the chassis may be caused to bend, whereby the 
bearing means, supporting the shafts, no longer extend perfectly parallel 
to each other and thus the spacing between driving and driven pulleys 
decreases. 
For the sake of convenience, this apparent lengthening of a belt under load 
conditions and consisting of fictive stretching as a result of the 
aforementioned deformations, as well as of actual stretching, will be 
called herein dynamic belt stretch. This dynamic belt stretch increases 
with incresing power being transferred. 
Of course belt tensioning devices are used in combination with these 
belt-type power transfer assemblies. These belt tensioning devices are 
either spring-loaded or fixedly positioned. spring-loaded belt tensioning 
devices are advantageous for several reasons. One such reason is the fact 
that they take up the dynamic belt stretch under loading conditions. 
Another such reason is the fact that spring-loaded belt tensioning devices 
provide a longer belt life as the nominal force with which tensioning 
devices are set to act on the slack portion of the belts may be kept lower 
than in case of fixedly positioned tensioning devices. 
However, under certain conditions spring-loaded tensioning devices equally 
may have a disadvantage. If the belt of a belt-type power transmission 
could be arranged to slip to a substantial degree under excessive load 
and/or peak load conditions, such slip could reduce and/or eliminate the 
danger for breakdowns resulting therefrom and thus, in fact, act as a kind 
of safety slip clutch. Typically, a spring-loaded tensioning device 
prevents such substantial belt slip under the conditions described and 
thus the belt type power transmission assembly comprising a spring-loaded 
tensioning device cannot normally act as a safety device. 
Of course prolonged belt slip would burn the belt and thus the safety 
characteristics aimed at and resulting from such belt slip are really 
useful only when this belt slip is, or otherwise can be kept very short in 
time. 
Fixedly positioned belt tensioning devices do not take up the dynamic belt 
stretch in a belt-type power transfer assembly. As a result thereof, this 
type of belt tensioning devices must be set to exert a substantially 
larger initial force on the so-called slack portion of the belt (when no 
power is being transferred) to guarantee transmission of a nominal power. 
Hence, the belt in such a transmission assembly, is always highly 
tensioned, even when transmitting an actual power which is smaller than 
the nominal power for which the assembly is adjusted. This causes faster 
belt wear in comparison with an assembly having a spring-loaded belt 
tensioning device. 
However, as the fixedly positioned tensioning device is unable to take up 
dynamic belt stretch, substantial belt slip will occur when the power 
being transferred exceeds the nominal power, for which the assembly is 
set, with a certain amount. Thus the belt assembly with fixedly positioned 
tensioning device acts as a kind of safety slip clutch protecting the 
assembly against excessive and/or extreme peak loads. 
It has been experienced that, in rotary combine harvesters of the type 
described, irregular feeding of crop material to the separating mechanism 
may cause plugging, which eventually may result in a so-called "kill-stop" 
of said mechanism. In case the separating mechanism would be belt driven 
with a drive assembly comprising a conventional spring-loaded tensioning 
device, and provided the drive train does not comprise other safety 
devices, such a "kill-stop" often would result in a major break-down such 
as the belt and/or pulleys breaking and/or shafts bending. Under these 
circumstances, the rpm monitor associated with the separator mechanism is 
often unable to produce a timely warning to the operator, as a "kill-stop" 
may occur very suddenly. 
Coming back to the structure according to the invention, it will be 
appreciated that, prior to starting operation of the combine harvester 1, 
the belt tensioning device 50 of the power transfer assembly 34 for 
driving the separator mechanism 20 is set for a nominal power transmission 
as is required for driving the separator mechanism 20 under normal load 
conditions. This means that, prior to starting the drive, the compression 
spring 64 is pre-compressed to a pre-set amount by adjusting the stop 
means 61 on the tension rod 55 until the length of the spring 64 
corresponds to the length of the longer leg 69 of the spring indicator 65. 
In this condition, the tension pulley 51 is pressed with a pre-determined 
and rather reduced force against the slack portion 39 of the belt 44, thus 
taking up the slack thereof. Under these conditions, the hooked portion 74 
of the stop means 67 is at a clearance 75 from the leg 59 of the support 
58 on the chassis 2. 
When driven and transferring power to the separating mechanism 20, dynamic 
stretch occurs in the drive belt 44. This dynamic stretch is taken up by 
the spring-loaded tensioning device 50 as the compression spring estends 
to a certain amount for urging the tension pulley 51 further in the 
direction of the slack portion 39 of the belt 44. The clearance 75 is 
thereby reduced but not yet eliminated, provided the load is not 
excessive. Thus the tensioning device 50 continues to operate as a 
spring-loaded tensioning device and thus has the advantages of 
conventional belt tensioning devices as described above. 
However, an excessively large lump or an excessively thick layer of crop 
material fed to the separating mechanism 20, produces a peak load 
respectively a continuously high load. In both cases these loads 
substantially exceed the nominal load for which the drive assembly is set. 
This results in additional dynamic belt stretch and thus permits the 
compression spring 64 to extend further for urging the tension pulley 51 
even further in the direction of the slack portion 39 of the belt 44 and 
until the hooked portion 74 of the stop means 67 engages the support 58. 
From that moment onwards, the tensioning device 50 according to the 
invention acts as a fixedly positioned tensioning device and thus, further 
dynamic belt stretch soon results in substantial belt slip, which provides 
protection against damage which otherwise might be caused. 
This belt slip also results in the rpm of the separating rotors 21,22 
dropping substantially and eventually becoming zero. The rpm monitor 
associated with the separating mechanism 20 immediately triggers an alarm, 
whereby the operator is warned to immediately stop operation and interrupt 
the drive, thus avoiding not only the type of damage already described, 
but also avoiding burning of the drive belt. 
It thus will be appreciated that the structure according to the invention 
combines the advantages of a belt-type power transfer assembly having a 
spring-loaded tensioning device and a belt-type power transfer assembly 
having a fixedly positioned tensioning device while eliminating the 
disadvantages of these respective assemblies. Indeed, a longer belt life 
together with a reduced loading (bending) of the driving and driven shafts 
is obtained on the one hand as well as a protection against excessive 
loads and/or peak loads and against the threats of major breakdowns which 
may result therefrom on the other hand. This arrangement also eliminates 
the need for a separate safety clutch in the drive line to the separating 
mechanism of a rotary combine and thus, the cost of the combine is reduced 
accordingly. 
Also, the stop means according to the above-described embodiment of the 
invention, do not require any special adjustment as indeed, the U-shaped 
bracket 67 is automatically correctly positioned as soon as the 
pre-compression of the spring 64 is accurately adjusted by means of the 
nuts 62,63 and with reference to the spring indicator 65. Such adjustment 
of the pre-compression of the spring 64 is necessary from time to time to 
take into account the permanent belt stretch (other than the dynamic belt 
stretch defined above) resulting from belt wear. 
It will be understood that various changes in the details may be made to 
the arrangement as described with reference to the FIGS. 2, 3 and without 
departing from the scope of the invention. One such change is shown in 
FIG. 4. Components in the arrangement according to FIG. 4 which are 
identical to corresponding components in the arrangement according to 
FIGS. 2, 3, have been indicated by the same reference numerals. 
The U-shaped bracket 68, which is in the arrangement according to FIGS. 2, 
3 is movable in unison with the tension rod 55 for abutting against the 
support 58, has been replaced by a fixedly positioned U-shaped bracket 81. 
This bracket 81 again has two apertured legs 82,83 for positioning the 
same on the tension rod 55. A first leg 82 is disposed to seat together 
with the shorter leg 66 of the spring indicator 65 against the fixed 
support 58 on the chassis 2 and to be held thereagainst by the compression 
spring 64. Said spring 64 engages at its other end a washer 84 abutting 
against the abutment nut 62 of the stop 61 on the tension rod 55. The 
other leg 83 of the bracket 81 is positioned in the no-load condition at a 
distance 75 from the lock nut 63. 
Extension of the compression spring 64 causing the tnesion pulley 51 to 
take up dynamic stretch, also causes the tension rod 55 and the stop 61 
thereon to move relative to the fixed support 58 and to the now stationary 
second leg 83 of the U-shaped bracket 81. Such relative movement is 
limited by the lock nut 62 engaging said second leg 83 whereafter the 
tensioning device, using the components shown in FIG. 4, operates as if it 
were a fixedly positioned tensioning device. 
In the arrangement shown in FIG. 5, the stop means in the form of a 
U-shaped bracket, have been replaced by other stop means, which, this time 
are in the form of a simple abutment nut 91 and an associated lock nut 92 
provided on the tension rod 55 in the vicinity of the fixed support 58 and 
at the side thereof opposite to the side facing the compression spring 64. 
The abutment nut 91 is positioned, in the no-load condition, at a distance 
75 from the fixed support 58. When excessive load is applied to the power 
transfer assembly, the extension of the compression spring 64 causes the 
abutment nut 91 to engage the support 58, whereafter again the tensioning 
device using the components of FIG. 5, operates as if it were a fixedly 
positioned tensioning device. It will be understood however that, contrary 
to the arrangements according to FIGS. 2, 3 and 4, the arrangement 
according to FIG. 5 requires additional adjustment of the stop means 61 
any time the pre-compression of the compression spring 64 is readjusted. 
Clearly, other amendments to arrangements already shown and described are 
still possible. According to one such further amendment, the leg 72 and 
the hooked portion 74 of the U-shaped bracket 67 according to FIG. 3 may 
be replaced by a generally elongate aperture in the base portion 73 of the 
stop means 67 and generally in the vicinity of the fixed support 58 on the 
one hand and by a finger fixedly coupled to said support 58 and extending 
within said elongate aperture on the other hand. 
It will be understood that changes in the details, material, steps and 
arrangment of parts which have been described and illustrated to explain 
the nature of the invention will occur to and may be made by those skilled 
in the art upon a reading of this disclosure within the principles and 
scope of this invention. The foregoing description illustrates the 
preferred embodiment of the invention; however, concepts, as based upon 
the description, may be employed in other embodiments without departing 
from the scope of the invention. Accordingly, the following claims are 
intended to protect the invention broadly as well as in the specific form 
shown.