Patent Application
20130139645
The present disclosure relates generally to a starter motor for starting an internal combustion engine and particularly to a starter motor including a torque limiter.
Most automotive and heavy-duty vehicles use engine starter motors with internal gear trains. The internal gear trains are typically planetary configurations. Planetary gearing is a gear system that consists of an outer gear referred to as an annulus, one or more planet gears, and a central gear referred to as a sun gear. Typically, the planet gears are mounted on a planetary gear carrier and are configured to rotate around the sun gear. The planet gears are meshingly engaged with a geared opening of the annulus. The annulus is typically held in a stationary position within a housing of the starter motor.
The gear train transfers rotation of an electric motor of the starter motor to an overrun clutch of the starter motor and then to a pinion gear of the starter motor. In particular, an input of the gear train, which is typically the sun gear, is connected to an output shaft of the electric motor. An output of the gear train, which is typically the planetary gear carrier, is connected to an input of the overrun clutch. An output of the overrun clutch is connected to the pinion gear. Rotation of the output shaft of the electric motor results in rotation of the sun gear. The rotating sun gear causes the planet gears and the planetary gear carrier to rotate. The overrun clutch transfers rotation of the plenary gear carrier to the pinion gear. The pinion gear is slidably mounted on a pinion shaft, and is movable between an engaged position and a disengaged position.
To start an engine with the typical starter motor, the pinion gear is moved to the engaged position, in which the pinion gear becomes meshingly engaged with a geared portion of a flywheel of the engine. Next or at the same time, the electric motor is activated, which causes the pinion gear and the flywheel to rotate. The rotating flywheel puts the engine pistons into motion, which typically causes the engine to start. When the engine does start, the flywheel begins to rotate at a rotational rate that is greater than the rotational rate of the pinion gear, which causes the overrun clutch to decouple the pinion gear from the output of the gear train. This prevents damage to the gear train, which may occur as a result of the rapidly rotating flywheel. The pinion gear is moved to the disengaged position after the engine is started.
When the pinion gear is engaged with the flywheel and is rotating the flywheel, the engine loads the starter motor with a pulsating torque that is a result of the pistons moving within the engine cylinders, among other moving engine parts. The pulsating torque is typically less than the stall torque, a term that refers to the magnitude of torque that causes the output shaft of the electric motor to stop rotating. The engine, however, may load the starter motor with a torque that is much greater in magnitude than the stall torque during certain engine events. These engine events may include engine backfire, hydraulic lock-up, or engagement of the pinion gear with the flywheel after the engine is already started. For example, hydraulic lock-up may result in a torque that is about five hundred percent (500%) to six hundred percent (600%) of the stall torque. The high torque is primarily caused by kinetic energy stored in the output shaft of the electric motor, which is then converted to strain energy upon rapid deceleration of the output shaft.
Vehicle manufacturers require that the starter motor should not fail or cause failure of other engine components as a result of the high-torque engine events described above. To meet this requirement, starter motor manufacturers design starter motor components to withstand a torque in excess of the stall torque. This often results in starter motor components being larger, heavier, or made from more robust and expensive materials than if the components were only required to withstand the torque encountered during normal engine operation.
Therefore, it is desirable to provide a starter motor that limits the torque internal to the starter motor so that the starter motor can be smaller, lighter, and less expensive to manufacture.
According to one embodiment of the present disclosure, a starter motor includes a housing, a planetary gear assembly, and a plurality of detents. The housing defines an interior space. The planetary gear assembly is at least partially positioned in the interior space and includes a plurality of planetary gear components. The planetary gear components comprise a sun gear, an annulus, a plurality of planet gears, and a planetary gear carrier. The plurality of detents is configured to releasably retain a rotational position of a component of the planetary gear components relative to the housing. Each of the detents including a biasing member and a bearing member.
According to another embodiment of the present disclosure, a starter motor includes a housing and a planetary gear assembly. The housing defines an interior space. The planetary gear assembly is at least partially positioned in the interior space. The planetary gear assembly includes a plurality of planetary gear components. A component of the planetary gear components is configured to remain stationary relative to the housing when a component torque is less than a predetermined torque level. The component of the planetary gear components is configured to rotate relative to the housing when the component torque is greater than or equal to the predetermined torque level.
According to yet another embodiment of the present disclosure, a starter motor includes a housing, a planetary gear assembly, a plurality of biasing members, and a plurality of bearing balls. The housing defines an interior space and a plurality of bores. The planetary gear assembly is at least partially positioned in the interior space and includes a sun gear, an annulus defining a plurality of grooves, and a plurality of planet gears. Each of the biasing members is at least partially positioned in a respective one of the bores. The plurality of bearing balls are movable between a first position and a second position. Each of the bearing balls are biased toward the annulus by a respective one of the biasing members. In the first position the biasing members bias each of the bearing balls at least partially into a respective one of the grooves to prevent rotation of the annulus relative to the housing. In the second position the plurality of bearing balls are displaced from the plurality of grooves to enable rotation of the annulus relative to the housing.
The above-described features and advantages, as well as others, should become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying figures in which:
For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that the present disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the disclosure as would normally occur to one skilled in the art to which this disclosure pertains.
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The bore structure 108 is provided on the housing 104 and is positioned within the interior space 132. In particular, in the embodiment of
With continued reference to
With reference again to
The planetary gear assembly 116 is at least partially positioned in the interior space 132 defined by the housing 104. The planetary gear assembly 116 includes a plurality of planetary gear components. The planetary gear components include a sun gear 160, a plurality of planet gears 164, a planetary gear carrier 168, and an annulus 172. The planetary gear components are made of metal or another hard material such as plastic.
As shown in
The planet gears 164 are positioned to meshingly engage the sun gear 160. The planetary gear assembly 116 includes four (4) of the planet gears 164, although only two (2) of the planet gears are shown in
The planetary gear carrier 168 is connected to the planet gears 164. The planetary gear carrier 168 rotates about the axis of rotation 176 in response to the planet gears 164 revolving around the axis of rotation. Rotation of the planetary gear carrier 168 is coupled to the pinion gear 128 through the clutch assembly 124, in a manner known to those of ordinary skill in the art.
With continued reference to
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The bearing members 224 are bearing balls, which have a generally spherical shape. The bearing members 224 are biased toward the annulus 172 by the biasing members 220. The bearing members 224 are formed from steel; however, in other embodiments, the bearing members may be formed from other sufficiently hard materials. Additionally, in other embodiments, the bearing members 224 may be provided as generally cylindrical rollers (not shown).
The detents 120 are movable between an engaged position and a disengaged position. When the detents 120 are in the engaged position, the biasing members 220 bias the bearing members 224 at least partially into the grooves 188 of the annulus 172 (as shown in
The detents 120 are positioned in the engaged position when a torque load exerted on the output shaft 156 by the electric motor (referred to herein as the motor torque or a component torque) is below a predetermined torque level, which equals approximately one hundred thirty percent (130%) to two hundred percent (200%) of the stall torque of the electric motor. Accordingly, during most engine starting operations, the detents 120 remain in the engaged position and prevent rotation of the annulus 172 relative to the housing 104, such that rotation of the sun gear 160 by the output shaft 156 results in rotation of the planetary carrier 168 and the pinion gear 128.
The detents 120 move to the disengaged position when the motor torque is greater than or equal to the predetermined torque level, as may occur during engine events such as engine backfire, hydraulic lock-up, or if the pinion gear 128 is caused to engage the flywheel when the engine is already in operation. In particular, the detents 120 move to the disengaged position when less torque is required for the electric motor 112 to move the detents to the disengaged position and rotate the annulus 172 than is required for the electric motor to rotate the planetary gear carrier 168. Accordingly, by moving to the disengaged position the detents 120 direct the motor torque from the planetary gear carrier 168 to the annulus 172 to prevent damage to the starter motor 100.
The annulus 172 causes the detents 120 to move to the disengaged position by applying a force to the detents that compresses the biasing members 220 and moves the bearing members 224 away from the grooves 188. The force applied to the detents 120 by the annulus 172 is generated by the torque applied to the annulus by the electric motor 112. The torque applied to the annulus 172 is transmitted to the detents 120 by contact between the first side surface 204 and the second side surface 208 and the bearing member 224.
As shown in
The magnitude of the predetermined torque level is based on the spring constant of the biasing members 220, the angle α, the total number of the detents 120, as well as other factors. Increasing the spring constant increases the predetermined torque level by requiring a greater magnitude of the parallel force 232 to move the bearing members 224 from the engaged position within the grooves 188. Decreasing the spring constant decreases the predetermined torque level by requiring a lesser magnitude of the parallel force 232 to move the bearing members 224 from the engaged position. Increasing the angle α, decreases the predetermined torque level by directing a greater amount of the force applied to the bearing members 224 in the parallel direction and also causes less force to be applied in the perpendicular direction. Decreasing the angle α, increases the predetermined torque level by directing a lesser amount of the force applied to the bearing members 224 in the parallel direction and increases the amount of force being applied in the perpendicular direction. Increasing the total number of the detents 120 generally increases the predetermined torque level, and decreasing the total number of the detents generally decreases the predetermined torque level.
As described above, the typical starter motor is designed and manufactured to withstand a motor torque of about five hundred percent (500%) to six hundred percent (600%) of the stall torque. This requires the typical motor starter to be more robust than is necessary for most engine starting operations. The starter motor 100 described herein may be manufactured less robustly (i.e. smaller and lighter) without sacrificing its ability to withstand a high motor torque. In particular, the starter motor 100 need only be designed to withstand a motor torque that is slightly greater than the predetermined torque level, since the detents 120 prevent the electric motor 112 from being subject to torque levels in excess of the predetermined torque level. Being less robust than the typical starter motor may make the starter motor 100 less expensive to manufacture.
In operation, the detents 120 prevent damage to the starter motor 100 as a result of a motor torque in excess of the predetermined torque level. During an engine starting operation the pinion gear 128 is moved into position to engage the flywheel of the engine and the output shaft 156 rotates the sun gear 160. Since the detents 120 retain the rotational position of the annulus 172, the planet gears 164 revolve around the axis of rotation 176 and the planetary gear carrier 168 rotates about the axis of rotation. Rotation of the planetary gear carrier 168 rotates the pinion 128 and the flywheel. The rotation of the flywheel puts the pistons in motion and typically starts the engine.
During the engine starting operation an engine event may occur that generates a motor torque in excess of the predetermined torque level. In a conventional starter motor, the excessive torque is transmitted to the output shaft of the electric motor and may damage the electric motor and/or another part of the conventional starter motor. The starter motor 100 as described herein, however, diverts the excessive motor torque away from the electric motor 112 to prevent damage to the electric motor and/or the other parts of the starter motor.
The starter motor 100 diverts the excessive motor torque that may be generated during an engine event according to the following. The motor torque is transmitted from the pinion gear 128, to the overrun clutch 124, and then to the planetary gear carrier 168. The excessive torque may cause the pinion gear 128 and the planetary gear carrier 168 to stop rotating at a very high rate of deceleration. The outputs shaft 156, however, tends to continue to rotate since the electric motor 112 remains supplied with electrical energy and also due to the inertia of the output shaft 156 and the rotor 158. Since the motor torque exceeds the predetermined torque level, the electric motor 122 may more easily rotate the annulus 172 than the planarity gear carrier 168. Accordingly, the torque generated by the electric motor 112 is diverted to the annulus 172, which causes rotation of the annulus and moves the detents 120 to the disengaged position. The electric motor 112 continues to rotate the annulus 172 instead of the planetary gear carrier 168 until the motor torque is less than the predetermined torque level or until the electric motor is no longer supplied with electrical energy, at which point the detents 120 return to the engaged position.
When the annulus 172 is rotated relative to the housing 104, the grooves 188 rotate past the bearing members 224 and in doing so generate sound that is audible to most users. Upon hearing the sound a user may become alerted to the engine event and in response the user may halt the supply of electrical energy to the electric motor 112.
In an alternative embodiment of the starter motor 100 the detents 120 may be configured to releasably retain another component of the planetary gear assembly 116 (i.e. the planet gears 164 or the sun gear 160). For example, in an embodiment in which the detents 120 releasably retain the rotational position of the planet gears 164 and the planet gear carrier 168, the pinion gear 128 may be connected for rotation with the annulus 172 and the sun gear 160 is connected for rotation to the output shaft 156. In response to the motor torque exceeding the predetermined torque level, rotation of the sun gear 160 results in rotation of the planetary gear carrier 168 when the detents 120 move to the disengaged position. By way of another example, in an embodiment in which the detents 120 releasably retain the rotational position of the sun gear 160, the pinion gear 128 may be connected for rotation with the planetary gear carrier 168 and the annulus 172 may be connected for rotation with the output shaft 156. In response to the motor torque exceeding the predetermined torque level, rotation of the annulus 172 results in rotation of the sun gear 160 when the detents 120 move to the disengaged position. In these alternative embodiments, the grooves 188 are formed in the component of the planetary gear assembly 116 that is releasably retained.
While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.
