Abstract:
A power take-off unit (“PTO”) may include a damper to reduce noise while the PTO is operating at low torque or at low RPM. The damper may also be located in the transmission before the PTO driver gear. A method may be used to systematically measure the frequency and/or amplitude of the vibrations that cause noise and to adjust the damping constant of a damper to reduce the noise.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to transmissions that use power-take off units (“PTOs”). In particular, the invention relates to transmissions that interface with a PTO using a PTO drive gear. 
         [0003]    2. Related Art 
         [0004]    PTOs provide a convenient means to power accessories or secondary functions of a vehicle or other powered equipment. PTOs may be used with vehicles of all types, including, but not limited to, automobiles, trucks, marine vessels, or airplanes. A PTO may also be used with an industrial engine. A PTO may interface directly with an engine, or may interface with a transmission that is used with an engine. Generally, the output of a PTO is a shaft to which other devices or equipment can be attached and powered. For example, the output of a PTO may be used to power a hydraulic pump, winch, or dump truck bed lift. PTOs may be driven by any torque carrying shaft in the engine, transmission, or vehicle. 
         [0005]    A common arrangement is an engine-driven PTO arrangement where the PTO receives an input torque from the engine crankshaft, or a component connected to the engine crankshaft. A common connection point for engine-driven PTO applications is the torque converter impeller, which may be directly connected to the engine crankshaft through a connection to the engine flex-plate. 
         [0006]    Typically, in engine-driven PTO applications, excessive gear noises are generated at the interface between the drive gear, which may be a gear in a transmission, and the PTO input gear due to backlash. Backlash may be described as the amount of clearance or space between mating components such as gears. Components may generate noise due to their backlash, particularly when the components are unloaded. Noise typically occurs when the engine is operating at low revolutions per minute (“RPM”) due to torsional vibrations from the engine that excites the gear mesh of the drive gear and PTO input gear. Noise may also occur during PTO operation when the PTO is operating with a low torque load at the output side of PTO. This noise results in decreased efficiency and may be irritable or harmful to the operator of the vehicle or equipment that is driven by the PTO. Thus, there is a need for a PTO that offers reduced noise during operation, particularly when the PTO is operating with a low load or at low RPMs. 
       SUMMARY OF THE INVENTION 
       [0007]    The descriptions below include apparatuses and methods for reducing the operation noise of PTOs. A transmission may include a damper at a point along the torque path from the transmission PTO output gear to the PTO output. The damper absorbs vibrations and rattling in the PTO components and correspondingly may decrease the noise caused by the backlash of the gears or other components along the torque path. 
         [0008]    According to one embodiment of the invention, a damped system comprises a transmission; a damper; a drive gear; a first shaft configured to transmit torque from the transmission to the damper; and a second shaft configured to transmit torque from the damper to the drive gear. 
         [0009]    According to another embodiment of the invention, a power take-off unit comprises an input gear an input shaft connected to the input gear; an output shaft coupled to the input shaft; and a damper coupled between the input shaft and the output shaft. 
         [0010]    According to another embodiment of the invention, a method of operating a power take-off unit comprises the steps of receiving torque at an input shaft; and damping the PTO input shaft with a damper. 
         [0011]    Other systems, methods, features and advantages will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The embodiments described below may be more fully understood by reading the following description in conjunction with the drawings, in which 
           [0013]      FIG. 1  is a block diagram of a damped system according to one embodiment of the invention; 
           [0014]      FIG. 2  is a block diagram of a damped system according to one embodiment of the invention; 
           [0015]      FIG. 3  is a block diagram of a damped system according to one embodiment of the invention; 
           [0016]      FIG. 4  a schematic diagram of a transmission and a PTO that includes a damper according to another embodiment of the invention; 
           [0017]      FIG. 5  is a mechanical illustration of a PTO equipped with a damper according to another embodiment of the invention; and 
           [0018]      FIG. 6  is a flow diagram of a method for operating a PTO equipped with a damper according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The described embodiments may alleviate the excessive noise generated when operating a PTO, particularly at low torque loads and/or at low RPMs. A vehicle transmission that integrates or interfaces with a PTO may include a damper to reduce noise generated by the transmission/PTO interface or in the PTO due to low RPM operation of the PTO, or due to backlash. Alternatively, the damper may be located in the PTO. The disclosed embodiments may be used with engine- or rear-driven PTOs. 
         [0020]      FIG. 1  illustrates a block diagram of damped system  100  according to one embodiment of the invention. Drive source  110  may be an engine, e.g., an internal combustion or diesel engine. Drive source  110  is coupled to transmission  120 , which may be, for example, a manual or automotive transmission. Transmission  120  is coupled with damper  130 , which may be a fluid damper, spring damper, or another type of damper. 
         [0021]    Damper  130  may dampen the vibrations in damped system  100  by absorbing, for example, torsional or other mechanical vibrations at interface  145  between drive gear  140  and PTO unit  150 . Typically, interface  145  is a gear mesh. The damping effect of damper  130  may reduce the excessive noise that may result due to these vibrations. 
         [0022]    Damper  130  is coupled with drive gear  140 , which is further coupled with PTO unit  150 . PTO unit  150  may output a torque to drive a torque load (not shown). 
         [0023]      FIG. 2  illustrates a block diagram of damped system  200  according to another embodiment of the invention. Vibration sensor  260  has been added to damped system  100 . Vibration sensor  260  may be an electromechanical, piezoelectric, or mechanical device that detects vibrations and provides a signal that represents the frequency and/or amplitude of the mechanical vibrations at interface  245  or elsewhere in damped system  200 . 
         [0024]    The output of vibration sensor  260  is sent to damper  230 . Damper  230  may have an adjustable frequency at which it most efficiently dampens vibrations. For example, damper  230  may be a spring damper or fluid damper with an adjustable damping constant. The damping constant may be adjusted by the user of damped system  200 , or may be adjusted automatically by a processor based on a signal from vibration sensor  260 . Alternatively, damper  230  may be self-adjusting based on a signal from vibration sensor  260 . Damper  230  and vibration sensor  260  may form a regulation loop that may search for particular vibrations and dampen them. For example, the regulation loop may search for vibrations in the frequency range of human hearing, i.e., 10 Hz to 20 kHz. 
         [0025]      FIG. 3  illustrates a block diagram of damped system  300  according to another embodiment of the invention. In damped system  300 , damper  360  is a component of PTO  390 . Damper  360  may dampen the vibrations at interface  345  between drive gear  340  and PTO input gear  350 . Interface  345  is typically, but is not limited to, a gear mesh. Damper  360  transmits torque to PTO assembly  370 , which transmits torque to PTO output shaft  380 . PTO assembly  370  may comprise a combination of gears, clutches, and shafts, or any other components or combinations of components that transmit torque from damper  360  to PTO output shaft  380 . PTO output shaft  380  may interface with a torque load, such as a pump or lift. 
         [0026]      FIG. 4  illustrates a schematic diagram of system  400  according to one embodiment of the invention. System  400  includes transmission  405  and PTO  410 . Transmission  405  includes torque converter  415 , and may be an automatic transmission. Alternatively, transmission  405  may be a manual transmission. Transmission  405  further includes damper  440 , which may be, for example, a fluid or spring damper. Damper  440  may also be an adjustable damper with an adjustable damping constant. Damper  440  transmits torque from transmission  405  to drive gear  420 . Damper  440  may, however, dampen vibrations that are created when transmission  405  is operating at low RPMs, or due to backlash between drive gear  420  and input gear  425 . 
         [0027]    Drive gear  420  transmits torque to input gear  425 . Typically, the interface of drive gear  420  and input gear  425  is a gear mesh. Input gear  425  transmits torque to idler shaft  430 . Idler shaft  430  may advantageously transmit torque from one end of a vehicle to another, or may reverse the direction in which output shaft  455  rotates. Idler shaft  430  transmits torque to clutch pack  450  via gear  435 . If clutch pack  450  is not engaged, then torque is not transmitted to output shaft  455 . Damper  440  may provide for reduced noise while operating PTO  410  with a low torque load or while transmission  405  is operating at low RPMs. 
         [0028]      FIG. 5  depicts a mechanical illustration according to another embodiment of the invention. Shaft  502  may be the output shaft of a drive source or a shaft in a transmission that is directly or indirectly coupled to a drive source. Shaft  502  is connected to damper  536 , which may advantageously dampen the vibrations of the drive source. These vibrations may cause the gear mesh between drive gear  504  and input gear  506  to generate excessive noise, particularly when the transmission is operating at low RPMs or when PTO  538  is operating with a low torque load coupled to output shaft  534 . Damper  536  transmits torque to drive gear  504 , which transmits torque to input gear  506 . Input gear  506  is connected to shaft  508 , which is also connected to gear  510 . Idler gear  512  meshes with gear  510 . Idler gear  512  is connected with idler gear shaft  514 , which is also connected with gear  516 , which meshes with gear  518 . Gear  518  is connected to shaft  526 , which is connected to first side  528  of clutch  532 . Second side  530  selectively engages with first side  528  of clutch  532  to affect a torque transfer from shaft  526  to output shaft  534 . When first side  528  is not engaged with second side  530 , no torque is transferred from shaft  526  to output shaft  534 . The operator of PTO  538  may control the configuration of clutch  532  to selectively transmit torque to output shaft  534  when operating PTO  538 . Clutch  532  may be controlled electrically, mechanically, hydraulically, or pneumatically. PTO  538  may receive an input signal from a switch or user interface to provide the user of PTO  538  with a means of changing the configuration of clutch  532 . 
         [0029]    Output shaft  534  may optionally include splines as depicted in  FIG. 5  for interfacing with the PTO load (not shown). A splined output shaft may be used where the PTO load includes a hollow shaft with groves that may mesh with and engage the splines on output shaft  534 . 
         [0030]      FIG. 6  illustrates method  600  for damping vibrations according to one embodiment of the invention. Method  600  begins with step  605  in which a damping constant of an adjustable damper is set to a predetermined value. The predetermined value may be based on a value stored during a previous execution of method  600  or may be based on a vibration frequency known to result in noise. 
         [0031]    In step  610 , a measurement is made of the frequency and/or amplitude of the vibrations of one or more components of a transmission or PTO. In step  615 , the damping constant of the adjustable damper is adjusted based on the measurement of step  610 . A microprocessor located in a vibration sensor may record measurements of the vibration amplitude over a range of frequencies. The range of frequencies may be the range of human hearing, i.e., 10 Hz to 20 kHz, or may be a smaller or larger range of frequencies. The microprocessor, or some other component in communication with the vibration sensor, may adjust the damping constant of the adjustable damper to dampen the vibrations occurring at the frequency where the maximum amplitude vibrations are located. 
         [0032]    Method  600  returns to step  610 , and a new measurement is made. Method  600  may repeat in this manner to continuously dampen the vibrations that may cause the most irritation or harm, such as at frequencies within the range of human hearing, i.e., 10 Hz to 20 kHz. Steps  605 ,  610 , and  615  of method  600  may be implemented as software or firmware executable by a processor, or as hardware. 
         [0033]    Coupling of the components in the disclosed embodiments may be implemented by mechanical, electrical, hydraulic, or pneumatic means. The gears used in the disclosed embodiments may include spur gears, bevel gears, worm gears, hypoid gears, planetary gears, herringbone gears, and helical gears. The use of helical gears may be advantageous because of their high efficiency and low noise. Methods or processes may be implemented, for example, using a processor and/or instructions or programs stored in a memory. Specific components of the disclosed embodiments may include additional or different components. A processor may be implemented as a microprocessor, microcontroller, application specific integrated circuit (ASIC), discrete logic, or a combination of other types of circuits or logic. Similarly, memories may be DRAM, SRAM, Flash, or any other type of memory. Parameters, databases, and other data structures may be separately stored and managed, may be incorporated into a single memory or database, or may be logically and physically organized in many different ways. Programs or instruction sets may be parts of a single program, separate programs, or distributed across several memories and processors. 
         [0034]    While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.