Abstract:
An engine starter system is disclosed. The starter system includes an electric cranking motor having a shaft and configured to crank the engine. The starter system further includes a planetary-type reduction gear unit that has a starter motor ring gear. The starter system has a pinion mechanism mounted on the shaft and configured to selectively engage a ring gear of the engine. A clutch assembly is configured to transmit torque between the shaft and the pinion mechanism. The clutch assembly includes a current conducting material and the starter motor ring gear includes one or more permanent magnets. The starter system employs the principle of Lenz&#39;s law to reduce the overrunning rotational speed of the cranking motor upon disengagement of the pinion mechanism from the engine&#39;s ring gear after the engine has started.

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to internal combustion engines, and more particularly to a magnetic brake system for a starter motor of an internal combustion engine. 
     BACKGROUND 
     Generally, overrunning clutches are used in starter assemblies. The overrunning type clutch transmits torque in one direction and is freewheeling in the opposite direction. The starter utilizes a gear reduction of the output of the starter&#39;s cranking motor to produce the high starting torque necessary in some applications to start an engine. When the engine starts, it instantaneously accelerates towards its running speed forcing the clutch of the starter to overrun due to the clutch&#39;s output rotating slower than engine input rpm. In automotive engines, the starter is moved out of contact with the ring gear of the engine so that the starter only operates at the high engine speed for a very short period of time. 
     More specifically, the starter&#39;s pinion is clutched to drive shaft of the crank motor through the overrunning clutch, which permits the pinion to transmit drive in only one direction. In this manner, the drive is energized through the pinion to the engine flywheel ring gear. However, if the pinion remains engaged with the ring gear, for example, because an operator fails to release the key as soon as the engine starts, the running engine causes the crank motor to spin excessively. During such overrunning time a “coast down” noise occurs until the armature of the cranking motor stops rotating. This coast down noise is significantly undesirable, particularly in automotive engines. 
     The present disclosure is directed towards overcoming one or more of the problems set forth above. 
     SUMMARY 
     In one aspect, the present disclosure is directed to a starter assembly. The starter assembly includes a starter motor having a shaft and configured to crank an engine. The starter assembly further includes a planetary-type reduction gear unit having a starter motor ring gear. A pinion mechanism is mounted on the shaft and is configured to selectively engage a ring gear of the engine. A clutch assembly is configured to transmit torque between the shaft and the pinion mechanism. The clutch assembly includes a current conducting material and the starter motor ring gear includes one or more permanent magnets. 
     In another aspect, the present disclosure is directed to a method of slowing down overrunning of a starter system. The method includes mounting a pinion mechanism on a shaft of a starter motor configured to crank an engine. The method further includes engaging selectively, a ring gear of the starter motor, the ring gear of the starter motor including one or more permanent magnets. The method also includes transmitting torque between the shaft and the pinion mechanism by a clutch assembly that includes a current conducting material, and disengaging the pinion mechanism from engine cranking. 
     In another aspect, the present disclosure is directed to a machine having a combustion engine and configured to power operations of the machine. The machine includes an interface that is configured to receive an input from a machine operator to start the engine. The machine further includes a starter motor having a shaft and configured to crank the engine. The machine further includes a planetary-type reduction gear unit including a starter motor ring gear. The machine also includes a pinion mechanism mounted on the shaft and configured to selectively engage a ring gear of the engine, and a clutch assembly configured to transmit torque between the shaft and the pinion assembly. The clutch assembly includes a current conducting material and the starter motor ring gear includes one or more permanent magnets. 
     In a further aspect, the present disclosure is directed to a starter assembly. The starter assembly includes a starter motor having a shaft and configured to crank an engine. The starter assembly further includes a planetary-type reduction gear unit having a starter motor ring gear. The starter assembly also includes a pinion mechanism that is mounted on the shaft and configured to selectively engage a ring gear of the engine. A clutch assembly is configured to transmit torque between the shaft and the pinion mechanism. The clutch assembly includes a current conducting material and the starter motor ring gear includes one or more permanent magnets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of a machine, according to an exemplary disclosed embodiment. 
         FIG. 2  is a diagrammatic view of a drive system, according to an exemplary disclosed embodiment. 
         FIG. 3  is a diagrammatic view of a ring gear, according to an exemplary disclosed embodiment. 
         FIG. 4  is a diagrammatic view of a clutch assembly, according to an exemplary disclosed embodiment. 
         FIG. 5  is a diagrammatic view of a ring gear, according to another disclosed embodiment. 
         FIG. 6  is a diagrammatic view of a clutch assembly, according to another disclosed embodiment. 
         FIG. 7  is a flow diagram of a method, according to an exemplary disclosed embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  provides a diagrammatic view of a machine  10  according to an exemplary disclosed embodiment. Machine  10  may include a cab  12  and an engine  14 . While machine  10  may be an on-highway truck, it is contemplated that the present disclosure may be applicable to any other machine that has an engine. For example, machine  10  may include off-highway vehicles, passenger cars, construction equipment, earth-moving equipment, and generator sets. 
     Engine  14  may include an internal combustion engine that operates using diesel fuel, gasoline, gaseous fuels, or other types of fuel as well as hybrid engine systems that run on a combination of fuel and electrical power. It is contemplated that engine  14  may provide power for operation of machine  10 , including electrical power to run devices inside cab  12  and elsewhere on machine  10 . Engine  14  may have functional relationships with other machine components such as, for example, a starter system  19 . As shown in  FIG. 2 , starter system  19  may include a starter motor  20  and a planetary-type reduction gear unit  33 . 
     Starter motor  20  may include a shaft  22  and an armature  24 . The motor  20  may be a DC permanent magnet type motor or any type of motor appreciable to an ordinarily skilled artisan. Starter motor  20  may include a commutator with brushes  28 . The brushes  28  may be carbon brushes or any type of brush appreciable to one of ordinary skill in the art. 
     Planetary-type reduction gear unit  33  that includes a starter motor outer ring  34  may be mounted on shaft  22  and may be configured such that the torque of armature  24  is transmitted to the reduction gear. A pinion mechanism  30  and a clutch assembly  32  may also be mounted on shaft  22  of starter motor  20 . 
     Pinion mechanism  30  may be configured to mesh with a suitable gear, such as the ring gear  42  of engine  14 , to provide rotational power to start engine  14 . Although pinion mechanism  30  is shown to be in mesh with engine ring gear  42 , pinion mechanism  30  may rotate freely and does not have to be meshed with engine ring gear  42 . 
     Starter motor ring gear  34  may be constructed of low carbon steel or any suitable material. As shown in  FIG. 3 , permanent magnets  36  may be imbedded in starter motor ring gear  34 . One or more permanent magnets may be used, and the magnets may be located in any suitable location on starter motor ring gear  34  or any location on starter motor  20  as one of ordinary skill would appreciate. 
     Clutch assembly  32  may also be constructed from low carbon steel or any suitable material. The clutch assembly  32  may be any suitable clutch known in the art such as a roller type overrunning clutch. A current conducting material  38  such as copper may be included with overrunning clutch  32  as shown in  FIG. 4 . The current conducting material  38  may be located on an outer periphery of the clutch assembly  32  and form a band around the clutch assembly  32 . One of ordinary skill in the art would appreciate that any suitable current conducting material  38  may be used and the current conducting material may be located in any suitable location on the clutch assembly or any location on starter motor  20  as one of ordinary skill would appreciate. An ordinarily skilled artisan would appreciate that the entire clutch assembly may be constructed from a suitable current conducting material. 
     In an alternate embodiment, starter motor ring gear  34  may be constructed from a current conducting material such as low carbon steel and a current conducting material such as copper band  40  as shown on  FIG. 5 . One or more permanent magnets  36  may then be imbedded with the clutch assembly  32  in any suitable location, an example of which is shown in  FIG. 6  any suitable location on starter motor ring gear  34 . 
     Cab  12  may include an enclosed area of machine  10  configured to house the operator. Cab  12  may also include an operator interface  16  that may contain dials and/or controls for conveying information and for operating machine  10  and its various components and a controller  18  as shown in  FIG. 1 . Interface  16  may include a monitor, a touch-screen, a portable hand-held device, a keypad, a control panel, a keyboard, an off-board command and control system, and/or other suitable input devices. Interface  16  may receive input from a machine operator and generate corresponding command signals in response to the input, which may be communicated to controller  18  for processing and/or execution. In one aspect, interface  16  may include a starter mode selection device such as, for example, a knob, a dial, a selector switch, one or more buttons, etc., allowing the operator to select an automatic starter mode and a manual starter mode. In response to an operator&#39;s selection of a desired starter mode, interface  16  may communicate a corresponding selection signal to controller  18 . 
     Interface  16  may also include means for receiving a machine operator&#39;s request to start engine  14  and for generating a corresponding start request signal. The means for receiving and generating may include a magnetic switch configured to receive a coded key containing magnetic information, a memory chip embedded, a radio-frequency identification circuit (RFID), a keypad allowing the code to be manually entered by an operator, a data port allowing direct communication with a service tool or a computer having the code, an antenna allowing reception of the code from a remote location, a scanner configured to read coded indicia, or any other configuration that can receive the code and generate a signal indicative of the code. Interface  16  may also display data relating to machine and/or starter status in response to signals from controller  18 . 
     Starting of engine  14  may be regulated by controller  18 . Controller  18  may include, for example, an electronic control module (ECM) or another processor capable of executing, and/or or outputting command signals in response to received and/or stored data. Controller  18  may include computer-readable storage, such as read-only memories (ROM), random-access memories (RAM), and/or flash memory; one or more secondary storage devices, such as a tape-drive and/or magnetic disk drive; one or more microprocessor (CPU); and/or any other components for running an application and processing data. The microprocessor(s) may comprise any suitable combination of commercially-available or specially-constructed microprocessors for controlling system operations. As such, controller  18  may include instructions and/or data stored as hardware, software, and/or firmware within the memory, secondary storage device(s), and/or microprocessor(s). Alternatively or additionally, controller  18  may include and/or be associated with various other suitably arranged hardware and/or software components. For example, controller  18  may include power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, amplifier circuitry, timing circuitry, filtering circuitry, switches, and/or other types of circuitry, if desired. 
     Controller  18  may include one or more data storage structures in the computer-readable medium containing predetermined data to facilitate starter control determinations in connection with an algorithm of machine  10 . The data storage structures may include, for example, arrays matrices, tables, variable classes, etc. The predetermined data may be based on known machine and/or starter control system performance specifications, such as those of engine  14  and starter motor  20 . The predetermined data may be derived from performance test results, engineering knowledge, and/or other resources. For example, the data storage may include an appropriate engine speed at which ignition should take place, lookup tables defining the amounts of electrical current, fluid displacement rates, and/or pressures required to provide an appropriate torque to start engine  14 . 
     Controller  18  may also receive a signal from operator interface  16  indicating selection of an automatic start mode or selection of a manual start mode to initiate starting of engine  14 . Controller  18  may further receive a signal from operator interface  16  indicative of the operator&#39;s request to start engine  14  (e.g., turning a key and/or pressing a button). 
       FIG. 7  illustrates an exemplary method of slowing down drive system  19 .  FIG. 7  will be described in detail in the following section. 
     INDUSTRIAL APPLICABILITY 
     The disclosed starter system  19  may have wide application in a variety of engine types including, for example, diesel engines, gasoline engines, and gaseous fuel powered engines and may be implemented into any engine appreciable to an ordinarily skilled artisan. 
     The pinion mechanism  30  may be mounted onto the shaft  22  (step  100 ) and may be configured to selectively engage the ring gear  42  of engine  14  (step  120 ) to initiate cranking engine  14 . Starter motor ring gear  34 , including one or more permanent magnets may be selectively engaged (step  140 ). Torque may be transmitted between shaft  22  and the pinion mechanism  30  via a clutch assembly  32  (step  160 ). Once engine  14  starts, engine ring gear  42  may be disengaged from the pinion mechanism  30  (step  180 ) and rotation of starter motor  20  may come to a stop. 
     Braking of starter motor  20  is enhanced and overrunning speed is reduced because a portion of starter motor ring gear  34  or clutch assembly  32  includes either permanent magnets or a conducting material such as copper. Preferably, when a portion of the starter motor ring gear  34  includes permanent magnets, the clutch assembly  32  includes a conducting material. The conducting material may be located on an outer periphery of the clutch assembly  32 . It should be noted that the permanent magnets may be included with the clutch assembly  32  while the conducting material is included with the starter motor ring gear  34 . 
     Lenz&#39;s law provides that when an emf (voltage) is generated by a change in magnetic flux, the induced emf is such that it produces a current whose magnetic field opposes the change which produces it. Eddy currents are caused when a conductor is exposed to a changing magnetic field due to relative motion of the field source and conductor. According to Lenz&#39;s law, the current swirls in a plane perpendicular to the magnetic field and creates electromagnets with magnetic fields that oppose the change of the magnetic field. Eddy currents can generate strong repulsive forces between the conductor and the field source, which can provide a strong braking effect. 
     Because clutch assembly  32  may include a conducting material  38  while the ring gear  34  includes permanent magnets  36 , when the ring gear is disengaged from the pinion assembly (step  180 ), the conducting material  38  becomes exposed to the magnetic field from the permanent magnets  36  and eddy currents are generated within conducting material  38 . The eddy currents operate to slow down the starter system  19  as they oppose the rotational force of the drive system as described above and cause it to lose energy. The faster the overrunning drive spins, the stronger the effect of the eddy currents. Thus, armature  24  slows down, reducing coast down noise and enhancing brush  28  life. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and method without departing from the scope of the disclosure. Additionally, other embodiments of the disclosed system and methods will be apparent to those skilled in the art from consideration of the specification. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.