The present invention relates to a rotor reversing mechanism
for a feeder in an agricultural harvesting machine and can be used with both round
and square balers or any other rotor type in-feed system.
The rotor of a baler is the part used to propel the straw
picked up from the ground into the baling chamber of a baler where it is compacted
and formed into bales. The rotor can also be part of an in-feed or transport element
for other processing means. In use, a blockage of the rotor may occur from time
to time resulting in activation of the overload safety device in the drive line.
Hence the drive is interrupted and, in such an event, the operator has to switch
off the drive to the baler and rotate the rotor in the reverse sense to release
For this purpose, it is known to provide a baler rotor
with a reversing mechanism which comprises a ratchet mounted on the rotor and a
pawl carried on a reversing arm that is reciprocated by means of a double acting
hydraulic cylinder. When the reversing arm is extended fully into a park position,
the pawl is disengaged from the ratchet to allow the drive to rotate the rotor in
its normal forward direction.
A problem that arises when using such a reversing mechanism,
is that the operator can accidentally re-engage the drive to the baler before the
reversing arm has reached its park position, that is to say while forward rotation
of the rotor is being opposed by engagement between the pawl and the ratchet. Such
premature re-engagement of the drive to the baler can result in serious and possibly
irreparable damage to the reversing mechanism.
With a view to mitigating the foregoing disadvantage of
the prior art, the present invention provides a reversing mechanism for a rotor
of an in-feed system of an agricultural harvesting machine, comprising a ratchet
mounted for rotation with the rotor, a pawl carried by a reversing arm for engaging
the ratchet, a double acting hydraulic cylinder for reciprocating the reversing
arm to cause the rotor to rotate in a reverse direction and means for disengaging
the pawl from the ratchet when the reversing arm is in a park position, characterised
in that a spring is provided for urging the reversing arm towards the park position
and the working chambers of the double acting hydraulic cylinder are permanently
connected to one another by way of a throttled passage.
The agricultural harvesting machine may be a baler, such
as a round or a rectangular baler, a loading wagon, a forage harvester, or some
other type of machinery collecting crop material from a field.
In a baler intended to be towed by a tractor, the hydraulic
supply to the double acting hydraulic cylinder is normally derived from a four port
three position valve on the tractor. The ports include two input ports and two output
ports. The input ports are connected to a high pressure and a drain, respectively,
while the two output ports lead to the working chambers on the opposite sides of
the piston of the hydraulic cylinder. In a neutral central position of the valve,
all the ports are isolated. In a first end position of the valve, the high pressure
input port is connected to a first of the working chambers and the drain is connected
to the second. Last, in the opposite end position of the valve, the connections
to the working chambers are reversed, that is to say the first working chamber is
connected to drain while the second is connected to the high pressure input port.
In the present invention, as in the prior art, moving the valve to one end position
results in the rotor being cranked in a reverse direction and moving the valve to
the opposite end position returns the reversing arm towards the park position. The
reversing mechanism of the invention, however, differs from the prior art in its
operation when the valve is in the neutral position. In the prior art, both of the
working chambers of the double acting hydraulic cylinder were blocked and hydraulic
fluid could not flow into nor out of either working chamber. As a result, the position
of the reversing arm was hydraulically locked. Consequently, if the neutral position
was engaged before the reversing arm had reached its park position, the pawl would
still be engaged with ratchet and re-engaging the drive to the rotor would result
in damage to the reversing mechanism, as earlier mentioned. By contrast, in the
present invention, in the neutral position of the valve, the two working chambers
of the double acting cylinder are connected to one another through the throttled
passage. Consequently, there is no hydraulic lock and instead the spring acting
on the reversing arm will move it to the park position where the pawl is disengaged
and any fluid displaced from one of the working chambers during this movement will
simply be pumped into the other through the throttled passage.
The passage connecting the two working chambers creates
a short circuit in parallel with the hydraulic cylinder. The degree of throttling
provided in the passage is necessarily a compromise in that the greater the throttling
the higher the pressure developed across the passage to operate the hydraulic cylinder.
On the other hand, as the throttling also acts to damp the movement of the reversing
arm towards the park position, reducing the degree of throttling enables the reversing
arm to return to the park position more quickly.
The faces of the piston of the double acting cylinder may
have an equal surface area but this makes for a more expensive construction of the
cylinder. More usually, because the piston rod projects from only one end of the
cylinder, the piston faces are of unequal area and the piston acts as a differential
In the preferred embodiment of the invention, the piston
is a differential piston and the pressure acting on the larger face of the piston
acts to move the reversing arm towards the park position. In this case, the volume
of fluid discharged from the working chamber with the smaller cross sectional area
is always less than the volume available in the chamber on the opposite side of
the piston to accommodate the discharge fluid. Consequently, the risk of hydraulic
lock does not arise, though a void (filled with a Torricellian vacuum) will be developed
in the working chamber with the larger cross sectional area.
The use of a differential piston also affects the speed
of movement of the reversing arm, causing it to move more rapidly towards the park
position than away from the park position. This is advantageous in that it reduces
the risk of the drive to the rotor being re-engaged before the pawl has been disengaged
from the ratchet.
The reversing arm is preferably mounted for rotation about
the axis of the rotor and the pawl is pivotably mounted on the reversing arm in
such a manner as to engage with the ratchet teeth under the action of a spring,
the pawl being pivoted against the action of the spring when it comes into a contact
with a stationary abutment in the park position of the reversing arm.
Though the spring may act directly on the reversing arm,
it is preferred for the spring to act on the reversing arm by way of a lever system
designed to increase the spring force acting on the reversing arm as it approaches
the park position.
The spring lever system may conveniently comprise a first
lever rotatable at one end about an axis that is fixed in relation to the rotor
axis and carrying at its opposite end a two-armed lever, one arm of the two-armed
lever being connected to the reversing arm and the other to a spring of which the
opposite end is anchored to a point that is fixed relative to the axis of the rotor.
Advantageously, the two-armed lever is a bell crank lever
and the anchoring point of the spring coincides with the pivot axis of the first
The invention will now be described further, by way of
example, with reference to the accompanying drawings, in which:
- Fig. 1 is a perspective view of a reversing mechanism of the invention,
- Fig. 2 is a front view of the mechanism shown in Fig. 1,
- Fig. 3 is a plan view from above of the mechanism shown in Fig. 1,
- Fig. 4 is a section through a detail of the reversing mechanism of Fig. 1, and
Fig. 5 is a schematic representation of the hydraulic circuit of the reversing mechanism
in Fig. 1.
In the drawings, the sprocket 10 is used to drive the rotor
of a baler, the rotor not being shown in the drawings. A ratchet 12 is mounted on
the same axis for rotation with the rotor as is a second sprocket 14 which is used
to transmit drive to a pickup. As earlier explained, blockages develop from time
to time within the baler and these are freed by rotating the rotor in the reverse
The present invention is concerned only with the reversing
mechanism and only the parts concerned with driving the rotor in the reverse direction
will now be described in detail.
The reversing mechanism comprises a reversing arm 16 rotatable
about the axis of the rotor and carrying a head 18 which is shown in section in
Fig. 4. The head 18 can pivot relative to the reversing arm 16 about a pivot bolt
20 and it carries a pawl 22 which engages the teeth of the ratchet 12. At a point
24 above the pivot 20, the head 18 is pivotably connected to the end of the rod
30 of a double acting hydraulic jack 32 of which the cylinder is pivotably mounted
about a fixed pivot bolt 34.
When the rotor is to be reversed for the purpose of clearing
a blockage, the rod 30 of the hydraulic jack 32 is retracted from the park position
shown in Fig. 2. Pulling on the pivot point 24 causes of the head 18 to pivot about
the bolt 20 so that the pawl 22 engages in the teeth of the ratchet 12. This locks
the reversing arm 18 to the rotor and as the rod 30 is retracted the rotor is caused
to rotate in the reverse direction. To continue to turn the rotor after the rod
of 30 has reached the limits of its stroke, the rod 30 is first extended towards
the illustrated position in Fig. 2. While doing so, the pawl 22 will ride over the
teeth of the ratchet 12 against the action of a spring 44 which biases the pawl
22 in a direction to engage with the ratchet teeth. Several cycles of operation
of the hydraulic jack 32 may be carried out until the rotor has been turned sufficiently
for the blockage to be cleared.
Once the blockage has been cleared, it is essential to
ensure that the pawl 22 has been disengaged from the teeth of the ratchet 12 before
the drive to the rotor through the sprocket 10 is re-engaged. This is effected by
extending the rod 30 to the position shown in Fig. 2 in which the reversing arm
16 abuts an adjustable stop 42. Further extension of the rod 30 will now cause the
head 18 to pivot clockwise, as viewed, about the bolt 20 and thereby disengage the
pawl 22 from the teeth of the ratchet 12. This is the position which is referred
to herein as the park position.
As so far described the reversing mechanism and its method
of operation are conventional. The problem that was encountered in the prior art
was that the drive to the rotor could be engaged while the pawl 22 was still engaged
with the teeth of the ratchet 12 with consequent damage to the reversing mechanism.
In the illustrated embodiment of the invention, the head
18 of the reversing arm is additionally pivotably connected at the point 24 to a
spring biased lever system that urges the reversing arm 16 towards the park position.
The lever system comprises a bell crank lever 26 which is itself pivoted at a central
fulcrum 38 about the free end of a lever 28. The lever 28 is pivoted about a fixed
axis 36 located near the pivot bolt 34. The end of one arm of the bell crank lever
26 is pivotably connected to the point 24 on the head 18 of the reversing arm 16
while the free end of the other arm of the bell crank lever 28 is connected by way
of a coil spring 40 to the pivot 36 of the lever 28.
Furthermore the circuit of the hydraulic jack is modified
in the manner illustrated in Fig. 5. In Fig. 5, the parts of the hydraulic circuit
shown to the left of the dotted line 50 form part of the tractor towing the baler.
Two connectors 52 and 54 lead to a manually controlled three position valve 56.
Two ports on the input side of the valve 56 are connected to a hydraulic pump 58
and a reservoir 60, respectively. In the central position of the valve, as illustrated
in Fig, 5, the pump 58 is connected to the reservoir 60 while both the output ports
are blocked off. In one end position, the valve connects one of the output ports
to the pump 58 and the other output port to the reservoir 60 while in the opposite
end position these connections are reversed.
The hydraulic jack 32 has two working chambers 62 and 64.
Because of the cross-sectional area of the rod 30, the piston 66 acts as a differential
piston and the cross sectional areas of the two working chambers 62 and 64 are unequal.
The working chamber 62 is connected by a pipe 70 to the connector 52 while the working
chamber 64 is connected by a pipe 72 to the connector 54. As so far described, the
hydraulic circuit is conventional. In the illustrated embodiment of the invention
there is an additional throttled passage 74 that connects the pipe 72 to the pipe
74, the throttle being formed by a hole having a diameter of about 1.5 mm.
Starting from the position shown in the drawing, the rod
30 is retracted by moving the valve 56 to the first end position in which the working
chamber 64 is connected to the pump 58 and the larger working chamber is connected
to the reservoir 60. In this position, fluid will also flow from the pump 58 to
the reservoir 60 through the throttled passage 74 but the size of the throttle ensures
that sufficient pressure difference exists between the two working chambers to retract
the rod 30 and rotate the rotor in the reverse direction.
To return the rod 30 to the park position, the valve 56
is moved to the other end position to connect the pump 58 to the larger working
chamber 62 and the smaller working chamber 62 to the reservoir. Once again, there
will be some leakage through the throttled passage 74 but despite this the return
movement will be more rapid, because it will not be opposed by the rotor, because
it will be assisted by the spring 40 and because the higher pressure of the pump
58 will be acting on the larger face of the piston 66.
Let it now be assumed that the operator after having oscillated
the valve between its two end positions to cause the rotor to reverse, inadvertently
returns the valve to the central neutral position before the rod 30 is fully retracted,
i.e., while the pawl 22 is still engaged in the teeth of the ratchet 12. In the
prior art and in the absence of the throttled bypass passage 74, the rod would be
hydraulically locked, but in the illustrated embodiment of the invention, even with
the working chambers 62 and 64 isolated by the valve 56 from the pump 58 and the
reservoir 60, the rod is extended by the action of the spring 40. The force applied
by the spring 40 is modified by the lever system 26 and 28 and increases as the
rod 30 reaches the fully extended position.
During this movement of the piston, fluid displaced from
the working chamber 64 is pumped through the passage 74 into the working chamber
62 and as the latter has the larger cross sectional area hydraulic lock cannot occur
because the increase in the volume of the chamber 62 will always exceed the decrease
in the volume of the working chamber 64. Any void that may appear in the chamber
62 as a result will contain a Torricellian vacuum but the force it generates is
insignificant in comparison with the other forces acting on the rod 30.
It would be possible to design the hydraulic jack so as
to have working chambers of equal cross sectional area but this increases the cost
of the jack unnecessarily.