The present disclosure relates to the field of starter motor assemblies for starting an engine, and particularly to a clutch portion of the starter motor assembly, which includes a planetary gear assembly.
A starter motor assembly is typically used to start an internal combustion engine, such as an engine in a typical passenger vehicle. The conventional starter motor assembly broadly includes an electric motor coupled to a drive mechanism. The electric motor is electrically connectable to a battery, and the drive mechanism is mechanically coupled to the engine. The electric motor is energized by the battery upon the closing of an ignition switch. The drive mechanism transmits torque generated by the electric motor to a flywheel of the engine, thereby rotating the flywheel and causing the engine to start. After the engine is started, the ignition switch is opened and the electric motor becomes deenergized.
Typically, the drive mechanism includes a gear assembly having an input and an output. The input is mechanically connected to the electric motor and the output is mechanically connected to the engine (i.e. the flywheel of the engine). The gear ratio between the input and the output of the gear mechanism typically causes the output to rotate with less angular velocity than the input. Accordingly, one function of the gear mechanism is to reduce the angular velocity of the motor to an angular velocity that is suitable for rotating the flywheel.
During engine starting, torque form the engine is sometimes briefly transferred to the starter motor assembly (including the gear assembly) before decoupling of the gear assembly from the flywheel occurs. For at least this reason, it is desirable for the gear assembly to be sufficiently robust so as to withstand any brief pulses of torque from engine. As is typically the case, making an assembly robust increases manufacturing cost of the assembly due to increased material costs, among other reasons.
Therefore, it is advantageous to provide a starter motor assembly including a gear assembly that is sufficiently robust but that minimizes manufacturing costs.
In accordance with one embodiment of the disclosure, a starter motor for an engine 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 and includes a sun gear defining an axis of rotation, a ring gear, a planetary gear carrier configured to rotate about the axis of rotation, and no more than two planet gears rotatably connected to the planetary gear carrier and configured to mesh with the sun gear and the ring gear. A gear ratio (“GR”) between the sun gear and the ring gear is based on the following formula:
The variable “NR” is a number of gear teeth of the ring gear, and the variable “NS” is a number of gear teeth of the sun gear.
According to another embodiment of the disclosure, a starter motor for an engine 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 and includes (i) a sun gear having a first number of gear teeth equal to a pitch diameter of the sun gear, (ii) a ring gear having a second number of gear teeth equal to a pitch diameter of the ring gear, and (iii) no more than two planet gears each connected to a planetary gear carrier. Each planet gear of the no more than two planet gears has a third number of gear teeth equal to a pitch diameter of the no more than two planet gears.
According to yet another embodiment of the disclosure, a planetary gear assembly for a starter motor includes a sun gear, a ring gear, a planetary gear carrier, no more than two planet gears, and no more than two bearing members. The sun gear defines an axis of rotation. The planetary gear carrier is configured to rotate about the axis of rotation. Each planet gear is configured to mesh with the sun gear and the ring gear, and each planet gear includes a bearing surface defining a bearing passage. Each bearing member includes a tube structure and at least two ball bearings. The tube structure extends axially from the planetary gear carrier and includes an interior surface defining an axial cavity and an exterior surface. The tube structure defines at least two bearing passages extending between the interior surface and the exterior surface. Each ball bearing is at least partially positioned within one of the bearing passages, and at least a portion of each ball bearing extends radially away from the exterior surface. Each tube structure is configured to extend at least partially through one of the bearing passages. The at least two ball bearings are positioned against one of the bearing surfaces
The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. While it would be desirable to provide a starter motor and/or a planetary gear assembly that provides one or more of these or other advantageous features, the teachings disclosed herein extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned advantages.
As shown in
The solenoid 14 is at least partially positioned within the housing 12. When the solenoid 14 is electrically energized it is configured to cause a lever 38 to move the pinion 34 axially along the shaft 30 until gear teeth 42 on the pinion engage with gear teeth (not shown) on a flywheel of the engine. When electrical energy to the solenoid 14 is removed, a return spring 46 within the solenoid 14 is configured to return the pinion 34 and the lever 38 to their original positions, shown in
The rotor 18 is also at least partially positioned within the housing 12. The rotor 18 rotates relative to the housing 12 in response to the rotor 18 being supplied with electrical energy. The rotor 18 is provided as any rotor, as desired by those of ordinary skill in the art.
With reference to
The sun gear 50 is a generally circular gear having a plurality of external gear teeth 78. The sun gear 50 is mechanically coupled to the rotor 18 and is configured to rotate about an axis of rotation 79 (also shown in
The planet gears 54 are also generally circular gears that define a plurality of external gear teeth 82 and an axis of rotation 83. The gear teeth 82 of the planet gears 54 are configured to mesh with the gear teeth 78 of the sun gear 50. The gear assembly 22 includes no more than two of the planet gears 54. Specifically, in one embodiment, the gear assembly 22 includes only two of the planet gears 54. In another embodiment, the gear assembly 22 includes only one of the planet gears 54.
The planet gears 54 are rotatably connected to the planetary gear carrier 70 by the bearing members 74 (described in detailed below). To this end, the planet gears 54 include a bearing surface 91 that defines a bearing passage 93 (see also
The planetary gear carrier 70 is formed on an end (right end in
The ring gear 64 is a generally circular gear defining a plurality of internal gear teeth 84 that are configured to mesh with the gear teeth of the planet gears 54. A center point 92 of the ring gear 64 is aligned with the axis of rotation 79. The ring gear 64 is mechanically connected to the clutch 26.
With continued reference to
The clutch collar 62 is mechanically connected to the ring gear 64 so as to be non-rotatably relative to the ring gear. In other embodiments, however, the clutch collar 62 may be separate from the ring gear 64. The outer surface of clutch collar 62 defines a clutch surface 66.
One of the springs 76 and one of the rollers 80 are positioned in each of the pockets 72 defined by the outer clutch member 68. The springs 76 are oriented within the pockets 72 to bias the rollers 80 in a circumferential direction (i.e. clockwise as viewed in
The rollers 80 of the clutch 26 are generally cylindrical elements. The rollers 80 are at least partially positioned within the shell opening 86 and at least partially positioned within the pockets 72. Therefore, the rollers 80 are positioned between the clutch surface 66 and the shell 68.
The position of the rollers 80 within the pockets 72 determines if the clutch 26 is in a locked configuration or an unlocked configuration. When the rollers 80 are positioned toward the center of the pockets 72 (a position that is not shown in the figures) the rollers 80 are free to rotate and, consequently, the clutch collar 62 and the ring gear 64 are free to rotate relative to the shell 68. This “unlocked” configuration occurs when the ring gear 64 is rotated in a counterclockwise direction relative to the shell 68 in the view of
When there is no relative motion between the ring gear 64 and the shell 68, the springs 76 partially wedge the rollers 80 between the clutch surface 66 and the shell 68. With substantially any clockwise rotation of the clutch collar 62 relative to the shell 68, the rollers 80 become even further wedged between the clutch collar and the shell, thereby preventing any additional relative rotation therebetween. In this “locked” configuration, the clutch collar 62 and the ring gear 64 are locked into synchronous movement with the shell 68, and the ring gear is configured to resist rotation about the axis of rotation 79 in the clockwise direction (as shown in
When the clutch 26 is in the unlocked configuration, the gear assembly 22 exhibits a gear ratio between the sun gear 50 and the ring gear 64 based on the following formula:
In the above formula the gear ratio between the sun gear 50 and the ring gear 64 is represented by the variable “GR”, the number of gear teeth 84 of the ring gear 64 is represented by the variable “NR”, and the number of gear teeth 78 of the sun gear 50 is represented by the variable “NS”. Accordingly, the gear ratio “GR” equals the number of gear teeth of the ring gear “NR” divided by the number of gear teeth of the sun gear “NS” plus one. In one specific embodiment, the number of gear teeth 84 of the ring gear 64 equals sixty-one, the number of gear teeth 78 of the sun gear 50 equal nineteen, and the gear ratio equals approximately 4.2 (i.e. 61/19+1≈4.2). That is, for every 4.2 rotations of the sun gear 50, the ring gear 64 rotates approximately one time. In other embodiments, the sun gear 50 and the ring gear 64 have any number of gear teeth 78, 84 as desired by those of ordinary skill in the art.
The number of gear teeth 82 of the planet gears 54 (“NP”) does not contribute to determining the gear ratio (“GR”). In the specific embodiment described above, however, the number of gear teeth 82 of the planet gears 54 is equal to nineteen. In other embodiments, the planet gears 54 have any number of gear teeth 82 as desired by those of ordinary skill in the art.
As shown in
With regard to the gear assembly 22, the sun gear 50 defines a pitch circle 102 having a pitch diameter 106. The planet gears 54 each define a pitch circle 110 having a pitch diameter 114. And the ring gear 64 defines a pitch circle 118 having a pitch diameter 122. In one embodiment, the gears 50, 54, and 64 have pitch diameters with the following magnitudes. The pitch diameter 106 is of the sun gear 50 is equal to the number of gear teeth 78 of the sun gear 50 (i.e. “NS”). The pitch diameter 114 of the planet gears 54 is equal to the number of gear teeth 82 of the planet gears (i.e. “NP”). The pitch diameter 122 of the ring gear 64 is equal to the number of gear teeth 84 of the ring gear (i.e. “NR”). This configuration of pitch diameters results in a robust gear assembly 22, even when the gear assembly includes only two of the planet gears 54.
In one specific embodiment, the pitch diameter 106 of the sun gear 50 is equal to nineteen millimeters and NS equals nineteen, the pitch diameter 114 of the planet gears 54 equals nineteen millimeters and NP equals nineteen, and the pitch diameter 122 of the ring gear 64 equals sixty-one millimeters and NR equal sixty-one. Accordingly, each pitch diameter 106, 114, and 122 has the same unit of measurement; namely, millimeters in this exemplary embodiment. In other embodiments, the pitch diameters 106, 114, and 122 are any magnitude of any unit(s) of measurement, as desired by those of ordinary skill in the art.
As shown in
The tube structure 150 is generally cylindrical and is connected to the planetary gear carrier 70. The tube structure 150 includes an interior surface 162 and an exterior surface 168. The tube structure 150 is formed from steel. In another embodiment, the tube structure 150 is formed from any other material as desired by those of ordinary skill in the art.
The interior surface 162 defines an axial cavity 172 that extends through the tube structure 150 from an end of the tube structure connected to the planetary carrier 70 to an opposite end of the tube structure that is spaced apart from the planetary carrier. A center axis 176 of the tube structure 150 extends through the axial cavity 172 and is aligned with the axis of rotation 83 of the planet gear 54 that is associated with it.
The exterior surface 168 defines an exterior periphery 180 of the tube structure 150. The exterior periphery 180 is generally circular (see
The tube structure 150 further defines a plurality of passages 184 and a groove 188. In the embodiment illustrated in
The groove 188 is a circumferential groove around the tube structure 150. The groove 188 is spaced apart from the planetary gear carrier 70 by at least a thickness 192 (
The bearings 154 are spherical ball bearings formed from steel or any other desired material. The bearings 154 are partially positioned within the cavity 172 and are partially positioned within the passages 184. Additionally, each bearing 154 extends radially away from the exterior surface 168. The bearings 154 are sized larger than the passages 184 so that the bearings are prevented from passing through the passages. In particular, a diameter 200 (
As shown in
With reference to
In operation, the motor starter 10 is activated to start the engine to which it is connected. When the motor starter 10 is activated, typically by a user closing an ignition switch (not shown), the solenoid 14 is activated and causes the pinion 34 to move into engagement with the flywheel of the engine (not shown). Next or at the same time, the rotor 18 is supplied with electrical energy and begins to rotate.
With reference to
After the engine is started, the engine rotates the flywheel faster than the pinion 34 can drive it; therefore, the flywheel begins to drive the pinion in the clockwise direction. This driving action of the pinion 34 is communicated back to the planet gears 54 through the shaft 30 and the carrier 70. When this happens, the clutch 26 disengages the pinion 34 from the rotor 18 to prevent damage to the starter motor 10. In particular, the driving action of the flywheel causes the ring gear 64 and the clutch collar 62 to rotate in the counterclockwise direction, which causes the clutch 26 to enter the unlocked configuration. The rotation of the clutch collar 62 in the counterclockwise direction dislodges the rollers 80 from the wedged orientation against the biasing force of the springs 76 and enables the ring gear 64 to rotate. Therefore, when the clutch 26 is in the unlocked configuration the rotor 18 is not driven by the flywheel of the operating engine. The ring gear 64 is rotated by the flywheel until the pinion 34 is disengaged from the flywheel by removing the supply of electrical energy from solenoid 14.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that other implementations and adaptations are possible. For example, various changes may be made and equivalent elements may be substituted for elements thereof without departing from the scope of the invention. In addition to the foregoing examples, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Also, there are advantages to individual advancements described herein that may be obtained without incorporating other aspects described herein. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.