Patent Application
20050132702
This invention relates to a hydraulic drive system for providing rotation to a shaft, particularly for single or multiple shaft shredders, grinders and other comminution equipment.
It is an object of the invention to provide an integrated drive system which is more economical to purchase and operate than known systems but which will provide the necessary output on an “as needed” basis only. This will lower the required power output of the prime mover used and also lower the structure and requirements on equipment to connect the prime mover to the hydraulic system.
In the invention, a prime mover provides input power to a hydraulic drive system comprising a variable displacement hydraulic pump; a directional hydraulic valve; a variable displacement hydraulic motor fed hydraulic fluid by the hydraulic pump, the hydraulic motor having internal torque control and speed modulation through a valve via the variable displacement; and a shaft driven by the hydraulic motor. The shaft is, for instance, a shredder shaft, a grinder shaft or a rotating shaft of other comminuting equipment.
The prime mover is either an electric motor or an internal combustion engine, advantageously a diesel engine.
The hydraulic pump provides constant and maximum horsepower control by torque control, modulating the pressure and volume output to reduce pump flow output as a function of pressure as maximum input horsepower is reached. To this end, the system has a system operating pressure sensor which sends a signal to a torque control valve spool means of the hydraulic pump to adjust a hydraulic pump swash plate for varying an output flow of the hydraulic pump to thereby provide the torque control.
The system is either an open loop hydraulic system or a closed loop hydraulic system.
Torque and horsepower control allow the use of small engines and electric motors to produce a final output at the shredder shaft selectively high speed with low torque or low speed with high torque, all variable without steps.
A particular advantage of the invention is that shaft speed and cutter tip force (torque) are a function of the feedstock material being processed, therefore optimizing processing production rates (see FIGS. 3 to 5). When encountering materials which are tough to process, the motor displacement continuously increases, effectively increasing torque and cutter tip force to break through materials. When encountering non-processable materials, the cutter tip stalls, the system produces a maximum preset operating pressure, holds that pressure for a certain time period (for example one second) as sensed by a pressure switch and programmable logic controller (PLC), which then reverses rotation direction of the shredder shaft by energizing a valve, to repeat the operation but in the opposite direction (see
The invention produces constant and maximum horsepower control by a variable displacement hydraulic pump which has torque control to reduce pump flow output as a function of pressure as maximum input horsepower is reached. Therefore once the maximum input horsepower is attained, and the operating pressure within the circuit increases, the flow of oil decreases at a ratio until a maximum horsepower is achieved, not allowing the engine or electric motor to exceed its capacity, yet producing an optimized flow as a function of pressure.
This occurs internally within the hydraulic pump circuit by monitoring the system operating pressure produced by the feedstock material being processed, sending this signal through a torque control valve spool with the hydraulic pump, and adjusting the hydraulic pump swash plate to vary the output flow of the hydraulic pump.
Further features of the invention will be described or will become apparent in the course of the following detailed description.
In order that the invention may be more clearly understood, the preferred embodiment thereof will now be described in detail by way of example, with reference to the accompanying drawings, in which:
Referring to FIGS. 1 to 2, a hydraulic drive system according to one embodiment of the invention has a prime mover 3, an electric engine E in
Further parts of the hydraulic drive system are standard features, such as a filter 9, a cooler 10 and check valve 11. An over pressure valve 7 is advantageously attached to the hydraulic motor 8, to provide oil backpressure to lubricate the hydraulic motor
The calculation for fluid power is HP=(PSI×GPM)/1714.
In one embodiment of the invention, a continuously variable torque shaft drive is used which has a variable displacement hydraulic motor connected through planetary reduction and directly to a shredder shaft having at least one cutter attached. Other shafts to be rotated are included in the invention, for example multiple shafts independently or mechanically linked together through a gear mechanism. A displacement control spool (not shown) within the hydraulic motor 8 adjusts the movable motor swash plate (not shown) angle within a motor housing (not shown) to increase or decrease motor displacement as a function of the system operating pressure. This is produced by the hydraulic fluid system operating pressure produced by the cutter tip resistance for the feedstock material being processed by the shredder (
The pump and motor work together as a system to optimize performance for the feedstock material being processed, i.e. the power output requirements to the rotating shaft 4. For a shredder, the material is fed into a hopper, the cutter teeth penetrate into the material and are met with resistance. This resistance translates into a hydraulic fluid system operating pressure, feeding a signal back to both the pump horsepower control spool and the motor displacement control spool within the hydraulic motor. As the resistance of the cutter increases, the operating pressure increases, which causes the pump torque control to reduce the pump displacement and limit the pump input horsepower, while at the same time the hydraulic motor displacement is increased, reducing the shaft speed and increasing the torque output of the motor and thus increasing the cutter tip force. This happens continuously and steplessly throughout the processing cycle of the shredder.
If the cutter contacts an item that is unshreddable, the pump develops maximum hydraulic fluid system pressure at minimum displacement, the hydraulic motor is adjusted to maximum displacement (thus torque) and the hydraulic fluid system operating pressure activates a pressure reversing switch and sends this electrical signal through to the PLC. If this signal is held for a specified interval, for example one second, the PLC sends a signal to the hydraulic valve to reverse the direction of the oil flow to the hydraulic motor. This reverses the shaft direction of rotation for processing in the other direction. If this pressure reversing occurs for a preset number of times within a programmed time period, the PLC will detect this and send a signal to the prime mover to shut down and shut the shredder off.
A further feature of one embodiment of the invention is a timed auto reversing cycle, allowing the PLC to activate the hydraulic valve for direction change automatically as a function of time (a change of rotation direction after a pre-set time interval). This improves agitation of material within the hopper.
It will be appreciated that the above description relates to the preferred embodiment by way of example only. Many variations on the invention will be obvious to those knowledgeable in the field, and such obvious variations are within the scope of the invention as described and claimed, whether or not expressly described. For example, multiple shafts can be driven independently or through a mechanical linkage (gears etc.). Both slow speed and high speed processing equipment can be driven by a drive according to the invention.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10170430 | Jun 2002 | US |
| Child | 10888644 | Jul 2004 | US |
