Gearbox Counterweight for Mower Blade Torque Compensation
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Solution Overview
Problem
Combine harvester cutterbars experience high stress and vibrations due to changing drive torques, which reduce the service life of drive train components and transmit vibrations throughout the harvesting machine.
Innovation Solution
A differential gear, designed as a cardan shaft drive with a balancing mass, is used to generate phase-shifted balancing torques that counteract the alternating torques, smoothing them out on the main shaft by maintaining a sinusoidal oscillation with the same frequency and amplitude as the blade drive, effectively reducing torsional vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a gearbox is used to convert rotary drive motion into crank motion for oscillating the cutter bar, then the cutting function is achieved, but high stress and vibrations occur due to alternating torques
Solution Approach 1:
A counterweight is arranged on the main shaft to compensate for the alternating torques resulting from the cutter bar oscillation. The counterweight generates balancing torques that counteract the varying drive torques, reducing stress on the drive train components and extending their service life.
Solution Approach 2:
The invention utilizes controlled mechanical vibration through the counterweight system to balance the alternating torques. The counterweight creates opposing vibrations that cancel out the harmful vibrations transmitted through the gearbox and drive train, reducing overall system stress.
2Ease of operation
If a gearbox is used to convert rotary drive motion into crank motion, then the cutter bar oscillation is achieved, but vibrations are transmitted throughout the harvesting machine
Solution Approach 1:
The counterweight on the main shaft generates balancing torques that counteract the alternating torques from the cutter bar. This compensation reduces the vibrations transmitted through the gearbox housing to the harvesting machine, isolating the oscillation to only the cutter bar.
Solution Approach 2:
The invention converts the harmful alternating torques and vibrations into a beneficial balancing effect. The counterweight system takes the harmful vibration energy and transforms it into a compensating force that reduces overall system vibrations, turning a negative effect into a positive solution.
3Speed
If the cutter bar is accelerated and decelerated translationally during oscillation, then the cutting motion is achieved, but varying torques cause high stress on the drivetrain
Solution Approach 1:
The counterweight compensates for the varying drive torques caused by the cutter bar's acceleration and deceleration during oscillation. By generating opposing balancing torques, the counterweight reduces the peak stress on drivetrain components during the high-acceleration phases of cutter bar motion.
Solution Approach 2:
The invention changes the torque parameter profile by introducing a counterweight that modifies the torque distribution in the drivetrain. The counterweight alters the instantaneous torque values to reduce peak stresses while maintaining the required cutter bar speed variations for effective cutting.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces the sum of torques to near zero, enhancing the durability of the drive train and minimizing vibrations transmitted to the harvesting machine by compensating for alternating torques directly at the transmission input.
Implementation Method 1
A compensating mass, used to generate variable compensating torques phase-shifted relative to the alternating torques, is driven via a compensating gear from the main shaft or the input shaft with a 90° phase shift relative to the movement of the knife drive pin.
Implementation Method 2
The variable drive of one of the balancing masses, via the compensating gear according to the invention, generates the balancing torque by means of which the sum of the kinetic energy of the system consisting of the oscillating cutter bar and the rotating balancing mass can be kept constant.
Implementation Method 3
The compensating gear is designed as a cardan shaft drive that forms part of the main shaft.
Implementation Method 4
The main shaft is designed, at least in sections, as a cardan shaft drive equipped with two universal joints spaced apart from each other in the axial direction
Implementation Method 5
This is achieved by the balancing mass exhibiting a high angular velocity in the two end positions of the cutter bar, where its speed and kinetic energy are zero. In the respective central position of the cutter bar, where it reaches its maximum speed and maximum kinetic energy, the angular velocity of the balancing mass should, on the other hand, be low.
Data Source
Figure 1~2
Figure 3
Figure 4a~5
AI summary
A gearbox (7) for driving a mower unit of a harvesting machine has a main shaft (20) arranged in a gearbox housing (17), which is driven by an input shaft and on which a crankpin (21) driven by a planetary gear drive (24, 25, 26) is eccentrically guided on the output side. The crankpin (21), which is at least indirectly connected to an oscillating mower blade, transmits alternating torques resulting from the blade torques to the main shaft (20) during operation of the mower unit. A counterweight is arranged on the main shaft (20) to compensate for the torsional vibrations resulting from the alternating torques. For effective compensation of the alternating drive torques, which is adapted to them, the counterweight (47) is driven by the main shaft (20) or the input shaft via a compensating gear (29) to generate variable counterweight torques phase-shifted by 90° relative to the alternating torques.