Patent Application
20190092374
The present disclosure relates to a steering control assembly for a vehicle steer-by-wire system.
Conventional vehicle steering systems require a mechanical linkage between a vehicle steering wheel and the road wheels. A force is needed to move the mechanical components and steer the vehicle. As the mechanical linkage is not required in steer-by-wire systems, there is a need to provide feedback to a driver that may be similar to the load on the steering system provided by the mechanical components in traditional steering systems.
In at least some implementations, a steering assembly includes a steering shaft rotatable in response to an input, an actuator having an output, a gear train and a housing. The gear train couples the steering shaft with the output so that the actuator can apply a force to the steering shaft via the output and gear train. The gear train provides a change in torque from the output to the steering shaft, such as to increase the torque provided from the actuator. The housing surrounds at least part of the gear train and includes gear teeth that define part of the gear train and are arranged to engage at least one other gear of the gear train.
In at least some implementations, the gear train includes a first planetary gear set having a first sun gear coupled to the output, a first planet carrier, and multiple first planet gears carried by the first planet carrier. Each first planet gear is meshed with the first sun gear and with the gear teeth of the housing, where the gear teeth formed in the housing define a ring gear located radially outwardly surrounding the first planet gears. In at least some implementations, the housing is not rotated as the first sun gear and first planet gears rotate. The first planet carrier may be coupled to the steering shaft for rotation with the steering shaft.
In at least some implementations, the gear train includes a second planetary gear set having a second sun gear coupled to the first planet carrier, a second planet carrier, and multiple second planet gears carried by the second planet carrier, each second planet gear being meshed with the second sun gear and with the gear teeth of the housing, wherein the gear teeth of the housing define a ring gear located radially outwardly surrounding the second planet gears. In such implementations, the second planet carrier may be coupled to the steering shaft for rotation with the steering shaft. In this way, the gear train may include a first gear set coupled to the output and a second gear set coupled to both the steering shaft and to the first gear set, where the second gear set is coupled to the first gear set either directly or via one or more intervening gears.
In at least some implementations, the actuator may include an electric motor and the output may be a drive shaft rotated by the motor, and the drive shaft may be coaxial with the steering shaft, and axially spaced from the steering shaft.
In at least some implementations, a steering assembly for a steer-by-wire steering system includes a first housing having an interior, a steering shaft having at least a portion within the interior of the first housing, a second housing coupled to the first housing and including inwardly extending gear teeth, at least one gear received within the second housing and having teeth meshed with the inwardly extending gear teeth of the second housing, and an actuator coupled to the second housing and having an output that drives said at least one gear for rotation relative to the second housing.
In at least some implementations, the second housing includes a main body and the inwardly extending teeth are formed directly in the main body. In at least some implementations, multiple gears are meshed with the inwardly extending gear teeth of the second housing. And the actuator may include a housing that is mounted to the second housing.
The following detailed description of representative implementations and best mode will be set forth with regard to the accompanying drawings, in which:
Referring in more detail to the drawings,
As will be explained in greater detail below, the steering assembly 12 includes a steering control assembly 24 which, in
As shown in
The control assembly 24 may include an actuator 56 that drives an output 58 (e.g. rotates the output) to provide a force to the steering shaft 30 to inhibit or assist rotation of the steering shaft. In at least some implementations, the control assembly 24 includes an electric motor 56 that has a drive shaft 58 (i.e. output shaft) that is coupled to the steering shaft 30 as set forth in more detail below. The electric motor 56 may be reversible to rotate the output shaft 58 in both directions about an axis 52 to provide a force to the steering shaft 30 when the motor 56 is actuated. The output shaft 58 may be coaxial with the steering shaft 30, axially spaced from the steering shaft and, as noted above, may be coupled to the steering shaft via a transmission 34. The actuator, e.g. motor, may include an outer casing or housing 26.
To facilitate use of a smaller and less powerful motor 56, which may weigh and cost less than a more powerful motor, the transmission 34 may include a gear train having multiple gears arranged to increase the torque provided by the motor 56 to the steering shaft 30. In at least some implementations, the gear train includes at least one planetary gear set and in the illustrated implementation, the gear train includes two planetary gear sets 62, 64 arranged in series to provide two stages of torque increase between the motor 56 and the steering shaft 30.
As shown in
The gear train also includes a ring gear 74 radially outwardly spaced from, surrounding and meshed with the planet gears 68. The ring gear 74 may be fixed against rotation so that the sun gear 66, planet gears 68 and planet carrier 70 rotate relative to the ring gear 74. In at least some implementations, the ring gear 74 is integrally formed in a portion of the first housing, and/or with a second housing 76 that is coupled to the first housing 38. As shown, the second housing 76 includes an inner surface and teeth 78 defining the ring gear 74, which may be formed in the inner surface of the second housing 76 so that the ring gear and corresponding portion of the housing 76 are formed in the same piece of material. This reduces the complexity and cost of having to secure a separate ring gear body to the housing, eliminates a tolerance that would be inherent in connection of a separate ring gear body to the housing and thus, reduces the tolerance stack-up within the gear train to increase the efficiency of the gear train and facilitate assembling the steering assembly. Of course, a ring gear may be formed separately from the housing(s) and coupled in any desired fashion (e.g. weld, adhesive, fastener, etc.) thereto, if desired. Providing the ring gear 74 integral with a second housing 76 that is coupled to the first housing 38 may facilitate use of different second housings 76 having a different ring gear arrangement that may be used with different planet gears (or with a different number of stages of gears—e.g. use of an axially shorter housing with fewer gear sets) without having to change the entire steering assembly housing. Further, the motor 56 may be coaxially coupled to the housing portion that defines the ring gear 74 (e.g. either the first or second housing) which as illustrated in the drawings, is the second housing 76. As shown in
In addition to the pins 72 for the planet gears 68, the planet carrier 70 of the first stage gear set 62 may include an oppositely facing coupler (e.g. a hub or pin 82) on which the sun gear 84 of the second stage gear set 64 is mounted. The second stage sun gear 84 may be fixed to the hub 82 (or integrally formed on or with the hub) of the first stage planet carrier 70 for co-rotation with the first stage planet carrier. The remainder of the second stage 64 may be the same as the first stage 62, including multiple second stage planet gears 86 meshed with the second stage sun gear 84, mounted to a second stage planet carrier 88 (on hubs or pins 89 fixed to the planet carrier) and meshed with the ring gear 74. The second stage planet carrier 88 may include a coupler 90 (e.g. a hub or pin) to which the steering shaft 30 is connected for co-rotation of the steering shaft and the second planet carrier. Hence, a torque path is defined between the steering shaft 30 and motor 56, through the second stage gear set 64 and the first stage gear set 62. Of course, only one gear stage may be used, or more than two gear stages may be used, as desired to achieve a desired torque in the steering assembly. Further, where a torsion bar 46 or some other component permits relative torsional rotation of portions of the steering shaft, it may be desirable in at least some implementations to provide the transmission 34 and motor 56 coupled to the steering shaft 30 on the opposite side of the torsion bar (or other torsion component) as the steering wheel 28.
As best shown in
Hence, the motor 56 is mechanically coupled to the steering shaft 30 and may be actuated to provide so-called ‘road-feel’ to the driver—e.g., a rotational resistance profile experienced by the driver which typically is associated with turning a steering wheel mechanically coupled to the vehicle wheels (e.g., in a non-steer-by-wire system). Thus, by selectively actuating the motor 56, the motor may provide rotational resistance to the steering shaft 30 and connected steering wheel 28 to simulate road-feel to the driver.
Further, the actuator output shaft 58 and the steering shaft 30 may each have ends that are radially overlapped by the housing 76 in which the ring gear teeth 78 are formed. In the illustrated embodiment, the second housing 76 overlaps ends of the steering and output shafts 30, 58, as well as the gears of the transmission 34. The gear train 34, steering shaft 30, output shaft 58 and motor 56 may all be coaxially aligned which may facilitate a balanced torque transmission between these components.
In at least some implementations, the extent to which the steering shaft 30 may be rotated may be limited by one or more end stops, which may, for example, be arranged so that the steering shaft and steering wheel 28 may rotate more than one full revolution in each direction from a centered position. In at least some implementations, the steering wheel 28 may rotate a total of 3.5 revolutions from engagement with an end stop in one direction to engagement with an end stop in the other direction of steering wheel rotation. To reduce the abruptness of the engagement of a portion of the steering assembly 12 with the end stop(s), the motor 56 may be actuated to provide a counterforce (i.e. a force in the opposite direction from the steering force) before the end stop will be encountered. To accomplish this, the steering position sensors may provide a signal to a controller 16 that controls actuation of the motor 56 when the steering wheel 28 has met or exceeded a threshold amount of rotation in either direction. For this purpose and/or for the purpose of providing road feel or other force profile to the steering shaft 30, the transmission 34 may provide a torque increase of 1.5:1 to 30:1 from the motor 56 to the steering shaft 30. In one non-limiting example, each of the planetary gear stages 62, 64 provides a 4:1 torque increase so both gear stages provide a torque increase of 16:1 from the output shaft 58 to the steering shaft 30. Of course, other torque values may be used as desired.
As shown in
In the example shown, the rotation limiting gear set 102 includes a planetary gear set having a third sun gear 112 that is fixed relative to the steering shaft 30 so that the third sun gear and steering shaft rotate together. As shown, the third sun gear 112 is fixed to the second end 40 of the steering shaft 32 and is hence, on the opposite side of the torsion bar 46 as the steering wheel 28. Also as shown, the third sun gear 112 and the steering shaft 30 are fixed to the hub 90 of the second planet carrier 88 so that the second planet carrier, third sun gear and steering shaft rotate together and are coaxial. This also places the rotation limiting gear set 102 in parallel with the second gear set 64 and not in series with it. The result is that the rotation limiting gear set 102 is not within the torque flow path between the motor 56 and steering shaft 30 and the rotation limiting gear set does not increase the torque that the motor provides to the steering shaft.
In the planetary gear set, the third sun gear 112 is meshed with multiple third planet gears 114 that are carried on pins 116 of a third planet carrier 118. The third planet gears 114 are each meshed with a ring gear 74 that is fixed against rotation (that is, it does not rotate due to rotation of the planet gears). The ring gear 74 may be separate from or the same ring gear(s) of the first and second gear sets 62, 64 (e.g. in the embodiment shown, the third planet gears may engage the same inwardly extending teeth 78 of the second housing 76). In this way, the teeth 78 of the second housing 76 may extend along an axial length sufficient to engage all three gear sets 62, 64, 102, or the teeth may be provided in discrete sections that are aligned with the planet gears of each gear set, with gaps or spaces between the discrete sets of teeth. Accordingly, as the steering shaft 30 rotates, the third sun gear 112 rotates and drives the third planet gears 114 for rotation relative to the ring gear 74, which causes rotation of the third planet carrier 118 relative to the steering shaft 30 at a reduced rotational rate that corresponds to the gear ratio of the rotation limiting gear set 102. To support and journal for rotation the third planet carrier 118, a bearing 120 (
In at least some implementations, the movable stop surfaces 104, 106 are carried by the planet carrier 118 and each is engageable with a respective one of the fixed stop surfaces 108, 110 to define the end points of steering shaft rotation in each direction of rotation (i.e. one end point in each direction of rotation). In the example shown in
In the example shown in
In the position of the planet carrier 118 shown in
In at least some implementations, the rotation limiting gear set 102 provides a gear ratio of between 1.5:1 and 8:1. In the example shown, the gear ratio of the rotation limiting gear set is 4:1, and the steering shaft 30 may rotate more than once in each direction from the centered position before the stop surfaces are engaged. In at least some implementations, the steering wheel 28 may rotate a total of more than three revolutions between its opposed rotational end points while the planet carrier 118 rotates less than one revolution (i.e. less than 360 degrees). In one non-limiting example, the steering wheel rotates 3.5 revolutions, from one end point to the other end point, or 1.75 revolutions from the center position to each end point, and the planet carrier rotates less than 180 degrees from the center position to each end point.
The mechanical stops (e.g. stop surfaces 104-110) operate even when electric power is not available which is not the case with electrically powered brakes or clutches that may be used in steering systems. Further, the mechanical stops are light weight, of simple design and durable, whereas electrically actuated brakes or clutches may be heavier, more complex and less reliable over time. Further, the steering wheel rotational limits are easy to control by placement of the opposed stops 104-110 and by choosing a gear ratio for the rotation limiting gear set 102.
While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention all the possible equivalent forms or ramifications of the invention. It is understood that the terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention.
