Wood reducing apparatus having hydraulically controlled material feed system

A wood chipper or grinder includes counter rotating upper and lower feed drums driven by a hydraulic motor at variable fluid pressure to produce variable torque to the feed drums. Wood debris fed to a gap between the rollers is advanced toward a grinder or chipper to reduce the material. A hydraulic feed control system operates off the variable hydraulic pressure associated with the motor and, in an automatic mode, exerts more or less downward clamping pressure on the upper feed drum with changes in pressure to the motor. The system sets an upper limit on the clamping pressure in the automatic mode which can be overridden manually if necessary to apply greater downward force than that achievable in the automatic mode. The upper feed drum can also be manually raised if necessary.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to wood reducing apparatus of the type used to reduce trees, limbs, and other wood debris into chips or grindings by advancing the material into the path of a rotating chipping or grinding drum or disc, and more particularly to automated feed systems for such wood reducers which engage and advance the material for chipping or grinding.

2. Related Art

There are various devices known in the art used for reducing trees, tree limbs, and other scrap wood products such as wood pallets and the like into chips or grindings. The material is introduced into a feed chute and advanced against a rotating reducing drum or wheel driven within a chamber downstream of the feed chute, which carries a series of spaced knives or teeth that cut or shred the material into chips or grindings.

Such apparatus are typically equipped with a power driven feed system located in a throat of the feed chute upstream of the rotating reducing drum or wheel which operates to engage and advance the material toward the reducer. One such feed system11employed in various prior art wood chipping apparatus13(portable and stationary equipment) manufactured by the assignee of the present invention is illustrated inFIGS. 1 and 2, and includes a set of opposed feed drums15,17which are mounted in the throat19of the apparatus13. The drums15,17are counter rotating and power driven by hydraulic motors which operate to positively drive the upper and lower drums15,17in opposite directions away from the feed chute for drawing the wood feed material into a feed gap21between the upper and lower feed drums15,17. The upper feed drum15is mounted on a swing arm23which straddles the chipping chamber and is pivoted to the frame25of the apparatus13by pivot mount27, enabling the upper feed drum15to be displaced relative to the lower feed drum17in order to vary the gap21between the drums15,17to enable feed material of varying diameter and bulk to be fed to the gap21between the drums15,17. The enlarged fragmentary view ofFIG. 2shows the feed drum15in a fully lowered position (solid lines) and a fully-raised position (broken chain lines). Tension springs29(only one shown) are connected to the frame25of the apparatus13at their lower end on opposite sides of the chipping chamber and are coupled to the movable swing arm23at their upper ends outwardly of the pivot mount27. The springs29act to urge the swing arm23downwardly, and thus constantly bias the upper feed drum15to the fully lowered solid line position.

As feed material is presented to the gap21, the upper feed drum15rides on top of the material and thus widens the gap21to enable the material to pass between the drums15,17. The upward movement of the feed drum15is counteracted by the downward tension force exerted by the springs29. The tension springs29thus apply a certain compression load on the material being fed into the gap21. Under most conditions, the force applied by the tension springs29is sufficient to grip the material firmly enough to draw the material into the rotating chipper mechanism31. However, due to the inherent spring constant characteristic of a tension spring29, the closing compression force exerted by the springs29varies with the position of the swing arm23, such that the tension springs29provide far less compression force when the upper feed drum15is at or near the fully lowered solid line position and increases when the gap21is opened through movement of the feed drum15toward the broken line raised position ofFIG. 2. Consequently, when the material fed to the gap21is relatively small, such as small tree branches and the like, the tension springs29may not provide sufficient compression force to grip and draw the material into the rotating chipper31without slipping.

A pair of hydraulic cylinders33are connected at their lower end to the frame25on opposite sides of the chipping chamber (only one shown) and at their upper end to the swing arm23outwardly of the pivot mount27. The cylinders33have a set of upper and lower feed/return lines35,37which communicate with the upper and lower ends of the cylinders33and are coupled to a manually operable valve bank39. The valve bank operates manually via a lever41to position the cylinders33in either a neutral position in which hydraulic fluid is permitted to flow freely into and out of both ends of the cylinders such that the cylinders33do not exert any substantial resistance to the raising or lowering of the swing arm33, but go along for the ride, or hydraulic fluid under pressure may be pumped into the lower end of the cylinders33to manually raise the upper feed drum15in the event that the incoming feed material is awkwardly shaped or otherwise the upper feed drum15requires manual assistance from the hydraulic cylinders33to raise the feed drum15high enough to climb on top of the feed material, or to manually feed pressurized hydraulic fluid into the upper end of the cylinders33to urge the upper feed drum15downwardly. In normal operation, the cylinders33are maintained in the neutral position and thus do not play any role in applying a compressive gripping force to the incoming feed material, with the feed mechanism11being relied instead on the tension springs29. Accordingly, this prior art feed system11is reliant for automatic feed entirely upon the clamping force applied by the tension springs29for gripping the wood material fed to the gap21, and the hydraulic cylinder comes into play only with manual input from the operator to either raise or lower the upper feed drum15.

It is an object of the present invention to overcome the inherent limitations presented by the tension spring-type automatic feed mechanism for wood reducing apparatus while retaining the capability of manually raising the upper feed drum to accommodate the introduction of very large or awkward feed material to the gap between the feed drums.

SUMMARY OF THE INVENTION AND ADVANTAGES

According to the invention, a wood reducing apparatus for reducing wood scrap such as tree limbs, branches, wood pallets and the like to chips or grinding comprises a set of counter rotating feed drums mounted in a throat of a feed chute of the apparatus ahead of a wood reducing mechanism mounted within a chamber of the apparatus. The upper feed drum is supported for pivoting movement relative to the lower feed drum in order-to vary the size of a feed gap defined between the drums. The upper feed drum is coupled to a hydraulic motor driven by a supply of hydraulic fluid that varies in pressure with changing loads on the feed drum. At least one hydraulic cylinder is mounted on the frame of the apparatus and is operatively coupled to the upper feed drum. A hydraulic feed control system communicates with the cylinder and with the supply of hydraulic fluid and is operative in an automatic mode to supply pressurized hydraulic fluid to one end of the cylinder in order to effect application of a downward closing force on the upper feed drum of a predetermined constant load irrespective of the lateral position of the upper drum relative to the lower drum. The applied force to the cylinders increases with an increase in the fluid pressure to the motor.

One advantage of the present invention is that the hydraulic feed control system operates to apply a constant downward clamping pressure on the upper feed drum regardless of its position relative to the lower drum. Thus, unlike the prior tension spring systems, the same load is applied by the upper drum when the upper drum is in a substantially lowered position as when it is in a substantially raised position. This has the further advantage of applying the same compression load to small material fed to a small feed gap when the upper feed drum is only slightly spaced from the lower feed drum due to the size of the incoming material. The hydraulic feed control system thus does not suffer from the inherent limitations of a tension spring system whose applied load is governed by a spring constant which applies less load to the upper feed drum when the feed gap is small.

Another advantage of the invention is that the hydraulic feed control system operates off the line pressure to the feed drum motor. Under conditions where the motor of the feed drum has to work harder due to an increased load on the feed drum, the hydraulic feed control system automatically responds by applying corresponding greater pressure to the cylinder or cylinders and thus an increased downward clamping force of the upper feed drum on the material being fed through the gap. The increase in clamping pressure is not dependent on the pivot position of the feed drum, as with the prior tension springs, but on an increase of pressure of the fluid supplied to the feed drum motor.

According to a further aspect of the invention, the hydraulic feed control system is preferably controllable also in a manual mode through operator input in order to selectively actuate the cylinder to raise or lower the upper feed drum, if needed, to accommodate the introduction of large or awkward incoming feed material to the feed gap or to override the automatic mode to apply even greater downward pressure on the feed drum for enhanced gripping of adverse material. Once the manual control is released, the system is restorable to the automatic mode to apply the constant compression load to the feed material in order to grip and advance the material toward the reducing device within the apparatus.

Another advantage of the present invention is that it provides a simple solution to the inherent limitations of a tension spring and can be adapted to many chipping or grinding apparatus with little modification to the otherwise existing feed system.

DETAILED DESCRIPTION

One embodiment of a wood reducing apparatus50constructed according to the invention is shown inFIG. 3incorporating an automatic hydraulic feed mechanism52of the invention which is additionally shown inFIGS. 4 and 5. The apparatus50shown inFIG. 3in which the feed mechanism52is adapted happens to be, for purposes of illustration, a portable wood chipping apparatus of the usual type having a frame54supporting a set of wheels56and a tow hitch58, and having an onboard engine60which drives a rotatable chipping drum62mounted within a chipping chamber64which communicates with an infeed chute66at one end and a discharge chute68at a discharge end. The feed mechanism58is mounted in a throat70of the infeed chute66upstream of the chipping drum62. It will be appreciated that the subject feed system52is equally adaptable to other types of wood chipping or grinding apparatus where material is to be automatically fed to a rotating chipping or grinding mechanism to reduce the wood debris to chips or grindings, and such embodiments are incorporated herein by reference. Such additional embodiments include typically large stationary chipping and grinding apparatus which typically would not have wheels or a hitch and would be used, for example, to grind pallets and other scrap wood debris. The additional embodiments contemplated by the invention also include disc-type chippers and grinders.

Turning now more particularly toFIGS. 3 and 4, the feed mechanism52of the invention includes a set of upper and lower feed drums72,74which are each supported for rotation about generally horizontal, parallel axles76,78and having outer feed material gripping surfaces82,84which are preferably cleated for improved gripping of the wood feed material. The upper feed drum72is positively driven in a counterclockwise direction as viewed inFIGS. 3 and 4by a hydraulic motor. The hydraulic motor is shown in the schematic ofFIG. 5at108and is driven by a hydraulic constant displacement pump100which delivers a supply of hydraulic fluid to the motor108that is variable in pressure (e.g., between 200 and 2000 psi) through hydraulic line83with changes in load to the feed drum72to drive the upper feed drum72. The pump100may be powered by an engine60or other means of power. The lower feed drum74is likewise driven, but in the opposite direction. The invention is thus adapted for working with whatever hydraulic drive system is available to positively rotate the feed drums72,74.

The upper feed drum72is supported on a swing arm86mounted by pivot connection88to the frame54and straddling the chamber64which enables the upper feed drum72to be moved or displaced laterally relative to the lower feed drum74in order to vary the size of a feed gap90defined between the outer surfaces82,84of the feed drums72,74, respectively. As illustrated inFIG. 4, the upper feed drum72is movable between a fully lowered position shown in solid lines in which the outer surfaces82,84are very near to one another to provide a relatively small feed gap90, and a fully raised position illustrated by broken chain lines inFIG. 4in which the upper feed drum72is raised further away from the lower drum74while maintaining the parallel relationship between their axes of rotation so as to provide a relatively larger feed gap90.

At least one and preferably a pair of hydraulic cylinders92are mounted at their lower ends to the frame54by pivot mounts94and connected at their upper ends to the swing arms86by pivot mounts96. The cylinders92are coupled to a hydraulic feed control system98, the schematic of which is shown inFIG. 5.

The hydraulic feed control system98operates off the pressure of the hydraulic fluid delivered to the drum motor108, and is operative in an automatic mode to constantly supply fluid under pressure to the upper ends of the cylinders92in such manner as to constantly urge the swing arm86and thus the upper feed drum72downwardly toward the lower feed drum74to apply a constant load to material fed into the gap90, regardless of the position of the upper feed drum72relative to the lower feed drum74, and thus the size of the gap.

The system98is further operable in a manual mode to supply fluid under pressure to the lower end of the cylinder in order to selectively raise the swing arm86and thus the upper feed drum72away from the lower feed drum74to accommodate the introduction of large or awkward feed material into the gap90. The system98is further operable in a manual mode to supply fluid under pressure to the upper end of the cylinders in order to exert additional down pressure on the feed drums beyond that provided in the automatic mode of operation. It will be observed from comparingFIGS. 3 and 1that the apparatus50of the present invention lacks the usual pull down tension springs of the typical prior art device which normally acts to urge the feed drum downwardly. The tension spring and passive cylinder of the prior art are replaced according to the invention with the set of active cylinders92which operate in an automatic, dynamic mode to enable the upper feed drum72to be displaced relative to the lower feed drum74in order to vary the size of the gap90(i.e., variable position) while maintaining a constant, uniform downward load applied to feed material within the gap90, regardless of the size of the gap90. The system98is selectively operable in the manual mode as described above to widen the gap90if necessary to accommodate the initial infeeding of large or awkward materials, or to narrow the gap to apply added down pressure on the upper feed drum72.

A schematic of the hydraulic system is shown inFIG. 5. The hydraulic pump100is driven by an engine60, or the like, and draws hydraulic fluid from a reservoir102where it is pumped under pressure to a flow splitter104. One part of the flow goes through a control valve106and is delivered to a hydraulic motor108through hydraulic line110for driving the upper feed drum72. The pressure of the hydraulic fluid in line110is variable and depends upon the load on the feed drum72. The hydraulic fluid pressure required to simply rotate the feed drum may be on the order of about 200 psi without any material being fed to the feed gap90. Under load, the hydraulic pressure required to drive the feed drum72may vary greatly during the operation of the reducing device50up to a maximum hydraulic pressure of about 2000 psi. It will be understood that the range of 200 to 2000 psi is given by way of example in connection with the preferred embodiment, but those skilled in the art will appreciate that a larger or smaller range may be appropriate for a given application depending upon the requirement of the application, as might the value of the minimum and maximum operating pressures. Accordingly, the minimum pressure may be more or less than 200 psi and the maximum pressure may be more or less than 2000 psi.

The hydraulic feed control system98that operates the cylinders92in an automatic mode operates off the variable hydraulic fluid pressure delivered to the motor108. As illustrated inFIG. 5, the feed control system98is coupled through a hydraulic line114to the line110associated with the hydraulic motor108, and thus sees the same variation in pressure in line114as that in line110. The feed control system98may include a first pressure relief valve116to prevent overpressure of hydraulic fluid to the other components down line of the pressure relief valve116. However, not all applications of the hydraulic feed control system98require the pressure relief valve116and it is thus optional.

The hydraulic feed control system98includes a pressure reducing valve118that is exposed on its up line side to the variable pressure in lines110and114associated with the feed motor108(e.g., 200 to 2000 psi). The pressure reducing valve118operates as a pressure governor to set a maximum pressure limit of hydraulic fluid down line of the pressure reducing valve118coming from the infeed lines110,114to a set pressure above that of the minimum operating pressure of the motor108, but below the maximum operating pressure. For example, the pressure reducing valve118in the preferred embodiment is set to 800 psi, such that the hydraulic pressure in the system98down line of the pressure reducing valve118in the automatic mode which operates the feed wheel cylinders92to exert downward force on the feed drum72is in the range of the minimum operating pressure associated with the feed motor108up to a maximum of the set valve (e.g., 800 psi) of the pressure reducing valve118.

A check valve120is arranged in line between the pressure reducing valve118and the first or upper end of the cylinders92. The check valve120is arranged to prevent back pressure of hydraulic fluid from the cylinders92to the pressure reducing valve118. The invention contemplates that the check valve120may not be necessary in all applications, wherein the pressure reducing valve118operates to govern the maximum pressure into the system98and may also operate to check the back pressure from the system98back to the lines110,114. In the embodiment shown, the check valve120is present and serves as a primary check against back pressure from the system98back through the lines110,114.

The system98further includes another check valve124formed with a pilot bleed hole open to a reservoir dump through a manual control valve113and operates to relieve stored fluid pressure from the system98by bleeding hydraulic fluid as necessary to the reservoir when the system98transitions from a relatively higher pressure condition (high load on the feed drum72) to a relatively lower fluid pressure condition (reduced load on the feed drum). The system98further includes a pressure relief valve122which is disposed in line between the upper or first end of the feed drum cylinders92and the reservoir dump of the control valve113. The pressure relief valve122is set to a relief pressure greater than the set pressure of the pressure reducing valve118, but less than that of the maximum of the operating pressure of the feed motor108. In the preferred embodiment, the pressure relief valve is set at 900 psi, such that the hydraulic pressure downline of the pressure reducing valve up to the maximum of 800 psi is maintained in the system98and directed to the first end of the feed drum cylinders92to urge the feed drum72downwardly in the automatic mode at whatever pressure is present in the line110driving the motor108, up to a maximum of 800 psi associated with the pressure relief valve118.

The system98may further include diagnostic gauges126,128which may be used to set the desired pressure limits of the pressure reducing valve118and pressure relief valve122, respectively.

In the automatic mode of operation, the hydraulic pressure in line110needed to drive the feed motor108to rotate the feed drum72prior to the introduction of any material to the feed gap90is at the minimum (e.g., 200 psi). This 200 psi is likewise present in line114and thus in the top end of the cylinders92. As wood debris material is fed to the gap90, the feed drum72is caused to climb up onto the material, pivoting the swing arms86upwardly. This upward movement of the swing arms86draws the pistons of the cylinders92upwardly, pushing the hydraulic fluid out of the upper or first end of the cylinders92. As shown in the schematic ofFIG. 5, the fluid escaping the upper end of the cylinders92encounters the pressure relief valve122and, when the pressure exceeds 900 psi, the pressure relief valve122opens, dumping the excess fluid to the reservoir through the control valve113. Once the pressure drops below 900 psi, the pressure relief valve122closes.

As the load on the feed drum72increases, due to a variety of factors such as heavy or awkward wood debris fed to the gap90, the pressure of the hydraulic fluid delivered from the pump100to the motor108increases up to a maximum of 2000 psi to drive the drum72with increased torque. This increase in hydraulic fluid pressure in line110is likewise transmitted to line114and to the feed control system98. The pressure reducing valve118allows any increase, up to 800 psi, to be transmitted directly to the upper end of the cylinders92, forcing the swing arm86, and thus the feed drum72downwardly to effect an increase in clamping force on the debris present in the gap70between the upper and lower feed wheels72,74. It will thus be seen that the feed control system98operates in the automatic mode off the variable pressure, and is insensitive to the position of the drum72or the width of the feed gap90, unlike the prior spring tension system. As the load on the feed drum72drops back to a lower level, for example back to 200 psi, the elevated pressure present in the system98(up to 800 psi) is relieved through the metered leakage of the pressurized fluid through the bleed hole of the check valve124to the reservoir associated with the control valve113until such time as the pressure in the system98equals that present in the lines110and114.

If, when operating in the automatic mode, the operator desires to increase the downward pressure exerted by the upper feed drum72on the material above that available through the automatic mode of operation (i.e., exceeding 800 psi down pressure in the cylinders92), the operator can move a lever of the control valve113to a “down” position, whereby hydraulic fluid pressure in line112from the other side of the flow splitter104generated by the pump100directs hydraulic fluid pressure under an elevated pressure (e.g., 1500 psi) into the system98through the check valve124where it is applied to the first or upper end of the cylinders92to exert the increased downward force on the upper feed drum72. The control valve113may be fitted with a port relief valve which sets the manual down pressure exerted on the cylinders to a maximum below the maximum pressure delivered from the pump100(e.g., set at 1500 psi, below the 2000 psi available from the pump100) to prevent overpressurization of the cylinders92, if desired. Once the “down” lever is moved back to a neutral position, any excess pressure in the system98bleeds back through the pressure relief valve122until it equalized with the line pressure in lines110and114in the automatic mode.

If the operator wishes to manually raise the feed drum72in order to assist the drum in climbing up and over wood debris fed to the gap90, the operator may move a lever of the control valve113to a “up” position, which directs the hydraulic fluid from line112through control valve113under elevated pressure (e.g, 1500 psi) to the second or lower end of the cylinders92, forcing the pistons of the cylinder92upwardly. The upper movement of the pistons forces the fluid in the first or upper end of the cylinders92out of the cylinders where it is discharged through pressure relief valve122to the reservoir dump associated with the control valve113. Upon returning the lever from the “up” to a neutral position, the system98returns to the automatic mode of operation described above.

The disclosed embodiment is representative of a presently preferred form of the invention, but is intended to be illustrative rather than definitive thereof. The invention is defined in the claims.