Patent Description:
A known vehicle steering apparatus includes a steering member which is linearly movable to effect turning movement of steerable vehicle wheels. A pinion is disposed in meshing engagement with a rack portion of the steering member. A steering column interconnects the pinion and a vehicle steering wheel.

In addition, this known steering apparatus includes a ball nut assembly which is connected with an externally threaded portion of the steering member. A motor is connected with the ball nut assembly. The motor is operable to effect rotation of the ball nut assembly relative to the steering member in order to provide steering assist. A steering apparatus having this general construction is disclosed in <CIT>. <CIT> discloses the preamble of claims <NUM> and <NUM>.

A first aspect, according to claim <NUM>, provides for an apparatus for use in turning steerable vehicle wheels includes a steering column having a pinion connected with a vehicle steering wheel such that rotation of the steering wheel results in rotation of the pinion. An electrically powered steering unit includes an electric motor having a first output shaft rotatable about an axis. A first planetary gear stage has a first gear reduction ratio and is driven by the first output shaft. A second planetary gear stage is driven by the first planetary gear stage and the pinion and has a second gear reduction ratio different from the first gear reduction ratio. A second output shaft is driven by the second planetary gear stage and coupled to the steerable wheels such that rotation of the second output shaft affects steering of the vehicle wheels.

A second aspect, according to claim <NUM>, provides for an apparatus for use in turning steerable vehicle wheels operably connected to a steering wheel by a pinion rotatable by the steering wheel includes an electrically powered steering unit having an electric motor with a first output shaft rotatable about an axis. A gearbox includes a first planetary gear stage having a first gear reduction ratio and driven by the first output shaft. A second planetary gear stage is driven by the first planetary gear stage and the pinion. The second planetary gear stage has a second gear reduction ratio different from the first gear reduction ratio. A second output shaft is driven by the second planetary gear stage and coupled to the steerable wheels such that rotation of the second output shaft affects steering of the vehicle wheels. A controller controls rotation of the first output shaft in response to rotation of the steering wheel.

The foregoing and other features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which:.

The present invention relates to an apparatus for use in turning steerable vehicle wheels. An example apparatus <NUM> for use in turning steerable vehicle wheels <NUM> is illustrated in <FIG>. The apparatus <NUM> can be used in commercial vehicles. The apparatus <NUM> includes a steering column <NUM> and an electrically powered steering unit (EPS unit) <NUM> for providing steering assist. The steering column <NUM> extends from a first end <NUM> to a second end <NUM>. A steering wheel <NUM> is connected to the first end <NUM>. A pinion <NUM> is connected to or provided on the second end <NUM>. Rotation of the steering wheel <NUM> transmits force through the steering column <NUM> to the pinion <NUM>. In other words, the pinion <NUM> rotates under the influence of force transmitted through the steering column <NUM>.

A steering linkage <NUM> is connected to the steerable vehicle wheels <NUM>. As shown, the steering linkage <NUM> includes a first, second, and third steering members <NUM>, <NUM>, <NUM>. The first steering member <NUM> is connected to an output shaft <NUM> of the EPS unit <NUM>. The first steering member <NUM> can be, for example, a pitman arm. The second steering member <NUM> is connected to the first steering member <NUM> and can be, for example, a drag link. The third steering member <NUM> is connected to the second steering member <NUM> and one of the steerable wheels <NUM>. The third steering member <NUM> can be, for example, a steering arm.

The EPS unit <NUM> provides steering assist by affecting movement of the steering linkage <NUM> - and therefore the steerable wheels <NUM> - in response to rotation of the steering wheel <NUM>. Referring further to <FIG>, the EPS unit <NUM> includes a reversible electric motor <NUM> and a gearbox <NUM> connected to the motor. The electric motor <NUM> has an output shaft <NUM> (see <FIG>) that extends into the gearbox <NUM>. The gearbox <NUM> includes a housing <NUM> having a passage <NUM> that extends generally along an axis <NUM> entirely through the housing. Teeth <NUM> are provided on the housing <NUM> along the length of the passage <NUM> and extend circumferentially about the axis <NUM>.

As shown in <FIG>, the pinion <NUM> is supported in the housing <NUM> by a pair of bearings <NUM>. A cap <NUM> is connected to the housing <NUM> and receives the second end <NUM> of the steering column <NUM> in a manner that allows for relative rotation therebetween. A torsion bar <NUM>, output shaft <NUM>, and coupling <NUM> help transfer rotation of the of the second end <NUM> of the steering column <NUM> (acting as the input shaft) to the pinion <NUM>. The components <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are coaxial with one another.

The torsion bar <NUM> extends within the second end <NUM> of the steering column <NUM> and the output shaft <NUM>. A first end <NUM> of the torsion bar <NUM> is fixed for rotation with the second end <NUM>. A second end <NUM> of the torsion bar <NUM> is fixed for rotation with the output shaft <NUM>. When the second end <NUM> is rotated by the steering wheel <NUM>, the torsion bar <NUM> permits a prescribed amount of relative rotation between the second end <NUM> and the output shaft <NUM> before second end and output shaft rotate together. The coupling <NUM> is connected to the output shaft <NUM> for transferring rotation of the output shaft to the pinion <NUM>.

Referring further to <FIG>, first and second planetary gear stages <NUM>, <NUM> are positioned within the housing <NUM> and aligned along the axis <NUM>. The first and second stages <NUM>, <NUM> are connected in series with one another. The output shaft <NUM> of the motor <NUM> extends along the axis <NUM> towards the first stage <NUM>.

The first planetary gear stage <NUM> includes a sun gear <NUM> secured to the output shaft <NUM> and rotatable therewith. Planetary gears <NUM> are in meshed engagement with the sun gear <NUM> and the teeth <NUM> on the housing <NUM>. Rotating the output shaft <NUM> in the manner R<NUM> rotates the sun gear <NUM>, causing the planetary gears <NUM> to rotate and orbit the sun gear while maintaining meshed engagement with the teeth <NUM>. Although three planetary gears <NUM> are shown, the first planetary gear stage <NUM> can include more or fewer planetary gears.

The planetary gears <NUM> are rotatably supported on a carrier <NUM> that rotates about the axis <NUM> in the manner R<NUM> as the planetary gears rotate and orbit the sun gear <NUM>. The carrier <NUM> is radially spaced from the housing <NUM>. The first planetary gear stage <NUM> can have a gear reduction ratio r<NUM> from the sun gear <NUM> to the carrier <NUM> of, for example, about <NUM>:<NUM> to about <NUM>:<NUM>.

The second planetary gear stage <NUM> includes a sun gear <NUM> secured to the carrier <NUM> of the first planetary gear stage <NUM>. The sun gear <NUM> is rotatable with the carrier <NUM> about the axis <NUM>. Planetary gears <NUM> are in meshed engagement with the sun gear <NUM> and the teeth <NUM> on the housing <NUM>. Rotating the sun gear <NUM> in the manner R<NUM> causes the planetary gears <NUM> to rotate and orbit the sun gear while maintaining meshed engagement with the teeth <NUM>. Although three planetary gears <NUM>, are shown the second planetary gear stage <NUM> can include more or fewer planetary gears.

The planetary gears <NUM> are rotatably supported on a carrier <NUM> that rotates about the axis <NUM> in the manner R<NUM> as the planetary gears rotate and orbit the sun gear <NUM>. The carrier <NUM> is radially spaced from the housing <NUM>. The second planetary gear stage <NUM> can have a gear reduction ratio r<NUM> from the sun gear <NUM> to the carrier <NUM> of, for example, about <NUM>:<NUM> to about <NUM>:<NUM>. It will be appreciated that the gearbox <NUM> can include additional planetary gear stages (not shown) to achieve a desired gear reduction ratio through the gearbox.

A bushing <NUM> is connected to the housing <NUM> and centered about the axis <NUM> at the end of the passage <NUM> opposite the motor <NUM>. A bearing <NUM> is mounted in the bushing <NUM> and is rotatable about the axis <NUM> relative to the bushing in the manner R<NUM>. An output shaft <NUM> is mounted in the bearing <NUM>. The output shaft <NUM> includes a smooth portion <NUM> fixed to the bearing <NUM>. A splined portion <NUM> is connected to the carrier <NUM> of the second planetary gear stage <NUM> such that the carrier and output shaft <NUM> rotate together about the axis <NUM> in the manner R<NUM>. The output shaft <NUM> also includes a projection <NUM> for connection to the steering linkage <NUM>.

A gear <NUM> is secured to the carrier <NUM> of the first planetary gear stage <NUM> and rotatable therewith in the manner R<NUM>. The gear <NUM> is also in meshed engagement with the pinion <NUM> (<FIG>) on the steering column <NUM>. As a result, rotation of the steering wheel <NUM> is transferred to the gear <NUM> by the pinion <NUM>. The pinion <NUM> and the gear <NUM> can have a gear reduction ratio r<NUM>.

The apparatus <NUM> (<FIG>) further includes a controller <NUM> and one or more vehicle condition sensors that cooperate to control the EPS unit <NUM> based on sensed vehicle conditions. In one example, the vehicle condition sensors can include a torque sensor <NUM> and a position sensor <NUM> connected to the controller <NUM>. The torque sensor <NUM> senses the torque applied to the steering wheel <NUM> and generates a signal indicative of the torque. The position sensor <NUM> senses the rotational position of the steering wheel <NUM> and generates a signal indicative of the steering wheel position. It will be appreciated that either or both sensors <NUM>, <NUM> can be positioned inside the cap <NUM> (see <FIG>) or along the steering column <NUM>.

The signals from the torque sensor <NUM> and the position sensor <NUM> are sent to the controller <NUM>. The controller <NUM> analyzes the outputs of the sensors <NUM>, <NUM> and affects operation of the motor <NUM> of the EPS unit <NUM> as a function of the output of the sensors. It is also contemplated that only the torque sensor <NUM> or only the position sensor <NUM> can be used to affect operation of the motor <NUM>. The controller <NUM> can also have inputs which vary as a function of sensed lateral acceleration of the vehicle (not shown) or other vehicle operating conditions. In any case, the signals received by the controller <NUM> dictate the speed and/or torque of the motor <NUM> and thereby dictate the speed and torque transferred by the output shaft <NUM> to the gearbox <NUM> to assist in turning of the steerable vehicle wheels <NUM>.

During operation, the operator rotates the steering wheel <NUM> to thereby rotate the pinion <NUM>. This, in turn, rotates the gear <NUM> about the axis <NUM> in the manner R<NUM> at a first speed S<NUM> and first torque T<NUM>. As noted, the gear reduction ratio r<NUM> dictates the relationship between steering wheel <NUM> rotation and gear <NUM> rotation.

At the same time, the controller <NUM>, in response to signals received by at least one of the sensors <NUM>, <NUM>, actuates the motor <NUM> to rotate the output shaft <NUM> in the manner R<NUM> with a desired second speed S<NUM> and second torque T<NUM>. The second speed S<NUM> of the output shaft <NUM> is reduced by the gear reduction ratio r<NUM> of the first planetary gear stage <NUM> to the first speed S<NUM> at the carrier <NUM>. In other words, the controller <NUM> ensures that the second speed S<NUM> is chosen based on the gear reduction ratio r<NUM> such that the carrier <NUM> rotates at the same first speed S<NUM> as the input gear <NUM> secured thereto. The controller <NUM> therefore coordinates rotation of the output shaft <NUM> with rotation of the steering wheel <NUM>.

The second torque T<NUM> of the output shaft <NUM> is increased by the gear reduction ratio r<NUM> to a third torque T<NUM> at the carrier <NUM>. As a result, the sun gear <NUM> of the second planetary gear stage <NUM> fixed to the carrier <NUM> and the input gear <NUM> rotates at the first speed S<NUM> in the manner R<NUM> with a fourth torque T<NUM> equal to the sum of the first torque T<NUM> and third torque T<NUM>.

The first speed S<NUM> of the sun gear <NUM> is reduced by the gear reduction ratio r<NUM> of the second planetary gear stage <NUM> to a third speed S<NUM> at the carrier <NUM>. The fourth torque T<NUM> of the sun gear <NUM> is increased by the gear reduction ratio r<NUM> to a fifth torque T<NUM> at the carrier <NUM>. As a result, the output shaft <NUM> secured to the carrier <NUM> rotates at the third speed S<NUM> in the manner R<NUM> with the fifth torque T<NUM>.

From the above, it is clear that the first speed S<NUM> delivered by the steering wheel <NUM> to the gearbox <NUM> via the pinion <NUM> is decreased by the product of the gear reduction ratios r<NUM> and r<NUM>. The first torque T<NUM> delivered by the steering wheel <NUM> to the gearbox <NUM> is increased by the product of the gear reduction ratios r<NUM> and r<NUM>. The second speed S<NUM> delivered by the output shaft <NUM> of the motor <NUM> to the gearbox <NUM> is decreased by the product of the gear reduction ratios r<NUM> and r<NUM>. The second torque T<NUM> delivered by the output shaft <NUM> of the motor <NUM> to the gearbox <NUM> is increased by the product of the gear reduction ratios r<NUM> and r<NUM>. Together, the gear reductions r<NUM>-r<NUM> produce the desired third speed S<NUM> and fifth torque T<NUM> at the output shaft <NUM>.

As shown in <FIG>, when the output shaft <NUM> rotates in the manner R<NUM> at the third speed S<NUM> and with the fifth torque T<NUM>, the first steering member <NUM> secured thereto likewise rotates in the manner R<NUM> at the third speed and with the fifth torque. The first steering member <NUM> moves the second steering member <NUM> in the manner L, which pivots the third steering member <NUM> in the manner R<NUM> to steer the vehicle wheels <NUM>. The EPS unit <NUM> therefore relies on the mechanical advantage of the gearbox <NUM> to reduce the speed of the motor <NUM> and steering wheel <NUM> while increasing the torque provided thereby to provide steering assist to the vehicle operator.

Due to this configuration of the gearbox <NUM> and gear <NUM>, the apparatus <NUM> is capable of providing feedback or steering feel to the operator. In other words, the gearbox <NUM> is capable of supplying a relatively lower gear reduction ratio r<NUM> to the steering wheel <NUM> while simultaneously providing steering assist to the steering linkage <NUM> through much higher reduction ratios r<NUM>, r<NUM>. To this end, the gear reduction ratio r<NUM> is configured such that turning of the steering wheel <NUM> by the operator, e.g., lock-to-lock rotation, is within a predetermined range.

In another example shown in <FIG>, multiple motors are connected to the gearbox for affecting steering assist of the steerable wheels. Components in <FIG> that are identical to the components in <FIG> are given the same reference number whereas components that are similar are given the suffix "a".

As shown in <FIG>, two reversible motors 62a are secured to opposite sides of the housing 72a of the gearbox 70a. The output shaft <NUM> of each motor 62a is connected to a drive belt <NUM>. The drive belt <NUM> is connected to an input shaft <NUM> fixed to the sun gear <NUM> of the first planetary gear stage <NUM>. When both motors 62a are actuated, the drive belt <NUM> transmits torque from each motor to the gearbox 70a. It will be appreciated that instead of both motors 62a acting simultaneously one of the motors can be deactivated and used only for redundancy/backup. In any case, the drive belt <NUM> can have meshed/toothed connections with the output shafts <NUM> and/or input shaft <NUM> to help mitigate slippage.

During operation, the operator rotates the steering wheel <NUM> to thereby rotate the pinion <NUM>. This, in turn, rotates the input gear <NUM> about the axis 74a in the manner R<NUM> at a first speed S<NUM> and first torque T<NUM>. The gear reduction ratio r<NUM> dictates the relationship between steering wheel <NUM> rotation and input gear <NUM> rotation.

At the same time, the controller <NUM>, in response to signals received by at least one of the sensors <NUM>, <NUM>, actuates both motors 62a to rotate about respective axes <NUM> with the second speed S<NUM> and second torque T<NUM>. The drive belt <NUM> transmits both motor 62a rotations to the input shaft <NUM> such that the input shaft - and the sun gear <NUM> secured thereto - rotates at the second speed S<NUM> at a sixth torque T<NUM> equal to twice the second torque T<NUM>.

The planetary gear stages <NUM>, <NUM> thereafter cooperate with the sun gear <NUM> and the gear <NUM> to adjust the speed and torque thereof as previously described to provide the output shaft <NUM> with a desired speed and torque for assisting steering of the vehicle wheels <NUM>. More specifically, the second speed S<NUM> of the sun gear <NUM> is reduced by the gear reduction ratio r<NUM> of the first planetary gear stage <NUM> to the first speed S<NUM> at the carrier <NUM>. The controller <NUM> ensures that the second speed S<NUM> is chosen based on the first speed S<NUM> and the gear reduction ratio r<NUM> such that the carrier <NUM> rotates in the manner R<NUM> at the same first speed S<NUM> as the input gear <NUM> secured thereto. The controller <NUM> therefore coordinates rotation of the input shaft <NUM> with rotation of the steering wheel <NUM>.

The sixth torque T<NUM> of the input shaft <NUM> is increased by the gear reduction ratio r<NUM> to a seventh torque T<NUM> at the carrier <NUM>. As a result, the sun gear <NUM> of the second planetary gear stage <NUM> fixed to the carrier <NUM> and the input gear <NUM> rotates at the first speed S<NUM> in the manner R<NUM> with an eighth torque T<NUM> equal to the sum of the sixth torque T<NUM> and seventh torque T7.

The first speed S<NUM> of the sun gear <NUM> is reduced by the gear reduction ratio r<NUM> of the second planetary gear stage <NUM> to the third speed S<NUM> at the carrier <NUM>. The eighth torque T<NUM> of the sun gear <NUM> is increased by the gear reduction ratio r<NUM> to a ninth torque T<NUM> at the carrier <NUM>. As a result, the output shaft <NUM> secured to the carrier <NUM> rotates at the third speed S<NUM> in the manner R<NUM> with the ninth torque T<NUM>. In one example, the ninth torque T<NUM> associated with the two motor 62a gearbox 70a is greater than the fifth torque T<NUM> associated with the single motor <NUM> gearbox <NUM>. Consequently, the gearbox 70a is capable of providing steering assist to larger vehicles than gearbox <NUM>.

Claim 1:
An apparatus (<NUM>) for use in turning steerable vehicle wheels (<NUM>), the apparatus (<NUM>) comprising:
a steering column (<NUM>) having a pinion (<NUM>) connected with a vehicle steering wheel (<NUM>) such that rotation of the steering wheel (<NUM>) results in rotation of the pinion (<NUM>);
an electrically powered steering unit (<NUM>) comprising:
an electric motor (<NUM>) having a first output shaft (<NUM>) rotatable about an axis (<NUM>);
a first planetary gear stage (<NUM>) having a first gear reduction ratio and driven by the first output shaft (<NUM>);
a second planetary gear stage (<NUM>) driven by the first planetary gear stage (<NUM>) and the pinion (<NUM>) and having a second gear reduction ratio different from the first gear reduction ratio; and
a second output shaft (<NUM>) driven by the second planetary gear stage (<NUM>) and coupled to the steerable wheels (<NUM>) such that rotation of the second output shaft (<NUM>) affects steering of the vehicle wheels (<NUM>), wherein each of the first and second planetary gear stages (<NUM>, <NUM>) comprises:
a sun gear (<NUM>, <NUM>) rotatable about the axis (<NUM>);
planetary gears (<NUM>, <NUM>) in meshed engagement with the sun gear (<NUM>, <NUM>) and orbiting the sun gear (<NUM>, <NUM>) while rotating in response to rotation of the sun gear; and
a carrier (<NUM>, <NUM>) connected to the planetary gears (<NUM>, <NUM>) and rotatable about the axis (<NUM>);
characterised in that the apparatus (<NUM>) further comprises a gear in meshed engagement with the pinion (<NUM>) and rotatable with the carrier (<NUM>) of the first planetary gear stage (<NUM>) for transferring torque from the steering wheel (<NUM>) to the carrier (<NUM>) of the first planetary gear stage (<NUM>).