Chisel plow release mechanisms

This invention relates to an automatic release mechanism for a cultivator which provides good resistance to release of the shank holder and which upon release causes the shank holder to rise to a good height to clear obstacles encountered during operation of the cultivator. The shank holder is mounted so as to pivot about an axis and is retained in the working position by a pair of springs under tension, the forward end of the springs being mounted in front of and beneath the position of the pivot axis of the shank holder, and the moment arm of the springs is such that, as the shank holder pivots, the moment arm decreases resulting in the tangential force applied by the springs to the ground engaging tool about the pivot axis remaining substantially constant during pivoting of the shank holder to clear an obstacle.

This invention relates to an automatic release mechanism for a cultivator. 
It has specific application to chisel plows but is not limited thereto 
being useful also for other types of field cultivators. 
Various release mechanisms for cultivators are already known. These usually 
fit into two classes which will be designated herein as "spring cushions" 
and "automatic trips". 
Spring cushion mechanisms are normally designed with two compression 
springs positioned vertically in front of the mounting bar. Any release 
mechanism in which the point pressure increases as the shank releases may 
be considered to be a spring cushion type. When the pressure at the 
forward point of the earth working tool increases to a certain value the 
unit begins to lift by backward rotation of the shank and shank holder, 
the pressure increasing with the amount of lift. 
An advantage of spring cushion mechanisms is that they are economical, 
having few moving parts to wear out and to maintain. Also, when they 
release they return with a pressure approaching that at which they 
release. However, they have the disadvantage that they start to release at 
relatively low pressures so that heavy soil resistance causes them to drag 
back until the increased point pressure is higher than the soil 
resistance. This can cause ridging and rapid sweep wear. Another drawback 
is their normally low tripping height which means that in some cases they 
may not clear the obstruction. 
Automatic trips normally employ an over-centre locking mechanism which 
requires considerable force to release. After release the force, required 
to raise the shank is reduced, providing relatively easy lift and greater 
upward movement than spring cushion mechanisms. Hence they provide much 
more protection for the shanks than do spring cushion mechanisms because 
of their reducing release pressure and increased trip height. They also 
have a fairly definite high pressure break point. This results in the 
sweeps being held quite stiffly in the working position with improved wear 
and working characteristics. Automatic trip mechanisms, however, have 
several disadvantages. They are complicated and expensive and usually have 
several moving parts which increase the wear possibilities. A major 
disadvantage is that they reset at considerably less pressure than that at 
which they release. This is because they use a lock-up mechanism which 
carries a high pressure only when it is locked. The result is that in 
heavy soils there is a very definite possibility that they will not reset. 
The ground engaging tool of a cultivator in operation is subject to two 
forces, viz., horizontal force and tangential force. The horizontal force 
is measured in the horizontal plane and is produced by the soil flowing 
past and by initial impact with obstructions. The tangential force is 
measured in the direction in which the sweep is pointing. In normal 
operation it is the same as the horizontal force. However, when the sweep 
is released the tangential force moves more and more toward the vertical 
as the sweep rises. When the sweep is sliding over an obstacle such as a 
rock the point of the sweep exerts a tangential force on the obstacle. The 
tangential force is also important to consider when the ground engaging 
tool has to reset after releasing. It is the value of the tangential force 
which determines whether or not the ground engaging tool will reset into 
the soil. 
Canadian Patent No. 946,676 issued May 7, 1974 to Sherman H. Quanbeck 
describes a chisel plow clamp and shank holder comprising a spring cushion 
mechanism which is preferable to other such prior art mechanisms in that 
it allows the shank and shank holder to pivot upwards providing a good 
clearance for obstacles. However, the force exerted by the tool does 
increase with increased pivoting of the shank and shank holder. 
The present invention seeks to maintain the advantages of both of the 
spring cushion and automatic trip mechanisms while avoiding in large 
measure their disadvantages. Apparatus constructed in accordance with the 
invention releases at a relatively high pressure and yet is of a 
relatively simple construction. It is distinctly superior to the prior art 
spring cushion mechanisms in that the tangential force remains 
substantially constant as the shank and shank holder pivot to ride over 
obstacles. Moreover it has a good clearance height and a return force 
which is nearly equal to the release force. 
The shank and shank holder are held in place in the normal earth-working 
position by a pair of springs under tension. Upon contact with an obstacle 
which applies sufficient force to the earth working tool to cause release 
of the mechanism the shank and shank holder pivot backwards about a pivot 
axis thus elevating the earth working tool. It is a very important feature 
of the invention that during pivoting the tangential force remains 
substantially constant rather than increasing as it does in the known 
spring cushion mechanisms. The springs pivot during release so that their 
moment arms about the pivot axis of the shank holder decrease as the 
holder pivots upward. Also, it is important that the forward pivot points 
of the springs are located forward of and below the pivot axis of the 
shank holder in order to prevent the tangential force from increasing as 
the shank holder pivots. 
It is an object of the present invention to provide a cultivator release 
mechanism which releases at relatively high pressure on the earth working 
tool. 
It is another object of the invention to provide a cultivator release 
mechanism which is simple in construction and which pivots to a relatively 
high clearance to override obstructions. 
It is a further object of the invention to provide a cultivator release 
mechanism which exerts a return force on the release mechanism of a 
magnitude near to that of the release force. 
It is a more specific object of the invention to provide a cultivator 
release mechanism which exerts a substantially constant tangential force 
on the earth working tool during release to rise over an obstruction. 
In accordance with a broad aspect of the invention there is provided a 
release mechanism for an earth working tool comprising: 
mounting bracket means; 
means fixedly attaching said mounting bracket means to a frame member of an 
earth cultivator; 
a shank holder; 
shank pivot means, said shank pivot means mounting said shank holder to 
said mounting bracket means for pivotal movement in a vertical plane about 
a pivot axis; 
a shank affixed to said shank holder at an upper portion of said shank and 
the earth working tool being affixed to the lower end of said shank; 
spring means exerting a predetermined force maintaining said earth working 
tool in a lower position for earth working, said spring means extending 
when said earth working tool impacts an obstruction permitting said shank 
holder to pivot upwards so that said earth working tool rises over the 
obstruction, the arrangement being such that as said shank holder pivots 
upward said spring means pivots so that the moment arm of the force 
exerted by said spring means about said pivot axis decreases whereby the 
tangential force exerted by said earth working tool remains substantially 
constant. 
There is also provided in accordance with the invention a cultivator 
release mechanism comprising: 
a mounting plate extending along one side of a frame member of a 
cultivator; 
a pair of back plates extending along a second side of said frame member; 
means clamping said mounting plate and back plates to said frame member; 
said mounting plate and said back plates extending downward beneath said 
frame member and converging so that each of said back plates lies adjacent 
said mounting plate over a lower portion thereof; 
a mounting bracket integral with the upper portion of said mounting plate; 
shank pivot means mounted on said bracket; 
a shank holder pivotally attached to said bracket by said pivot means; 
a shank affixed to said shank holder and having an earth working tool 
located on the lower end thereof; 
a pair of springs under tension mounted on opposite sides of said shank 
holder and each having a front end and a rear end, the rear end of each 
spring being attached to said shank holder; 
spring pivot means fixed to the lower portion of said back plates and 
mounting plate, the front end of each of said springs being attached at a 
pivot point to said spring pivot means, said spring pivot point being 
located lower than and forwardly of said shank pivot means, the 
arrangement being such that when, in operation, said ground working tool 
contacts an obstruction causing said shank and shank holder to pivot 
upwards, the tangential force exerted on said earth working tool is 
substantially constant over the full range of pivoting of said shank 
holder.

The cultivator shank release mechanism illustrated in FIGS. 1 and 2 has as 
its main components base plate or mounting bracket means 1, shank holder 
2, back plates 3 and 4 and tension springs 5 and 6. When assembled to the 
cultivator as illustrated in FIG. 1 a portion of the cultivator frame (not 
shown) is clamped in the rectangular space between the upper opposed 
portions of base plate 1 on one side and back plates 3 and 4 on the other 
side by means of four bolts. One of these bolts 9 and the associated 
washer 7 and nut 8 are shown in FIG. 2. 
Base plate 1 has a pair of apertured base eyes 26 and 27 to which shank 
holder 2 is pivotally attached by means of shoulder bolt 10. The upper 
portion of shank 16 is mounted to the shank holder 2 and an earth-working 
tool 21 is fixedly attached to the lower end of shank 16. 
As best illustrated in FIG. 1 the lower portions of the base plate 1 and 
back plates 3 and 4 are bent toward each other to produce together with 
the lower portion of the cultivator frame a triangular shape in 
cross-section. A pair of eye bolts 13 with associated washers 14 and nuts 
15, one of each of which is shown in FIG. 2, are employed to clamp the 
lower portions of the back plates 3 and 4 to base plate 1 thereby 
providing a rigid anchor point for the forward ends of tension springs 5 
and 6. The forward ends of the springs are hooked into the eyes of bolts 
13. 
The rear ends of springs 5 and 6 are hooked into apertures in cross-bar 28 
which forms part of shank holder 2. 
In the normal working position illustrated in FIG. 1 in solid lines springs 
5 and 6 are under preset tension. This tension retains shank holder 2 
together with shank 16 and working tool 21 firmly in the normal working 
position. When the working tool encounters an obstacle which exerts a 
sufficient backward force to overcome the force exerted by the springs the 
shank holder is pivoted backwards and upwards as illustrated by the 
phantom lines in FIG. 1. 
As is clearly illustrated in FIG. 1 eyebolts are located well beneath and 
in front of shoulder bolt 10 about the axis of which the shank holder 
pivots. It is also apparent from FIG. 1 that when the shank holder pivots 
backward the rear ends of springs 5 and 6 pivot upwards to cause the 
distance between the axial centrelines of the springs and the pivot axis 
of the shank holder to decrease. Thus the moment arm of the force exerted 
by the springs decreases as the shank holder pivots. The arrangement is 
such that the tangential force, shown in FIG. 1 by the arrow denoted "T", 
remains substantially constant during pivoting of the shank holder. It is 
important to recognize that in order to achieve this result the front 
pivot points of the springs must be located both forwardly of and beneath 
the pivot axis of the shank holder. 
When an obstacle is encountered the working tool rides over it by reason of 
the pivoting of the shank holder, and the earth-working tool exerts a 
force in the tangential direction against the obstacle. Having cleared the 
obstacle the earth-working tool resets to the normal operating position 
with a force nearly equal to the force which caused it to be released to 
pivot upwards. It is the tangential force which is most important to 
consider when the earth-working tool has to reset after releasing. 
As shown in FIG. 3 the base plate 1 includes a stop block 30 the purpose of 
which is to limit the pivoting of the shank holder as explained hereunder. 
The base plate also includes a plate 52 which is positioned so that one 
face of shoulder bolt 10 rests against it to prevent the shoulder bolt 
from turning and causing wear on the base plate. 
The shank holder 2 is illustrated in FIGS. 2 and 4. It comprises a main bar 
32, bearing support 34, web 36, brace 38, channel 40, bushing sheath 42 
and, as previously noted, cross-bar 28 to which the rear ends of springs 5 
and 6 are attached. The parts of the shank holder are rigidly affixed to 
one another as by welding. The extent of the pivoting of the shank holder 
is limited by the end 44 of brace 38 abutting against stop block 30 of 
base plate 1. 
Four hardened self-lubricating bushings 22, 23, 24 and 25 are located in 
bushing sheath 42 to receive shoulder bolt 10 which is retained in place 
by washer 11 and nut 12. This provides a low-friction pivot for the shank 
holder enabling it to reset with nearly the same force as that at which it 
released. The shank 16 is attached to shank holder 2 by sliding it through 
hollow rectangular channel 40 on the bottom of the holder and securing it 
with bolt 17, washers 18, lockwasher 19 and nut 20. 
FIG. 5 illustrates the characteristics of a known spring cushion mechanism. 
In this figure the solid curve shows the vertical jump height or rise of 
the shank holder versus force exerted. It is evident that the force upon 
release (lower portion of curve) increases very substantially as the shank 
holder rises. The reset force (upper portion of curve) is somewhat but not 
too greatly lower than the release force. 
FIG. 6 illustrates the characteristics of a known automatic trip mechanism. 
Here it is seen that the force decreases quite rapidly as the shank holder 
rises and also that the reset force is much lower than the force upon 
release. Thus there is the disadvantage with this type of mechanism that 
the reset force may be insufficient to cause the earth-working tool to 
re-penetrate the ground after clearing an obstacle. 
FIG. 7 illustrates the characteristics of a shank release mechanism in 
accordance with the invention. In this case it is seen that a very 
substantial force is required to effect release and consequent pivoting of 
the shank holder. However, after release the tangential force remains 
substantially constant as the shank holder pivots upward to clear an 
obstacle. Moreover, the reset force is only slightly less than the release 
force and also remains substantially constant upon resetting. 
Although only a single embodiment of the invention has been described many 
modifications and variants may be devised by those skilled in the art. 
Accordingly, the foregoing embodiment is to be considered as illustrative 
only rather than restrictive of the invention and all such modifications 
and variants as come within the meaning and range of equivalency of the 
appended claims are to be included.