SEMI-DECOUPLED STEERING SYSTEM

A steering system for a vehicle is disclosed. The steering system may have a steering linkage and a controller. When operation of the steering system is within a predefined relative rotational range, the controller may be programmed to translate steering motion to a steering gear box through a motor. Operation of the steering system outside the predefined rotational limit actuates the steering linkage. Once the steering linkage is actuated, steering motion is translated to the steering gear box directly through the steering linkage.

TECHNICAL FIELD

This disclosure relates to steering systems for a vehicle and specifically to steering systems with a decouplable steering mechanism.

BACKGROUND

Steering systems in vehicles may use a variety of shafts, gears, cables, and pulleys to transfer a steering input from a steering mechanism such as a steering wheel, yoke, stick, steering pedal, or tiller to a control component such as road wheels, ailerons, rudders, or other control surfaces, which may then steer the vehicle. Steering systems may incorporate systems which provide a mechanical advantage or power assistance between the steering mechanism and the control component. In automobiles, a gearbox may be used to transfer the rotational input of a steering wheel to road wheels and to provide a mechanical advantage, power assistance, and even variable ratio steering.

Common gearboxes used in automobiles include a rack and pinion, a recirculating ball, or a worm and sector mechanism to transfer the rotational movement of the steering wheel to the pivotal movement of the road wheels. Power steering systems help drivers steer vehicles by augmenting steering effort of the steering wheel. Hydraulic or electric actuators may add controlled energy to the steering mechanism, so the driver needs to provide only modest effort regardless of conditions. The actuators are often connected to the steering system through additional sets of gearing. A direct mechanical connection between the steering mechanism and the control component may provide a path for noise, vibration, and harshness to pass.

Steer-by-wire systems decouple the direct mechanical connection between the steering mechanism and the control component and replace the traditional mechanical control systems with electronic control systems. Safety can be improved by providing computer controlled intervention of steering with systems such as Electronic Stability Control (ESC), adaptive cruise control and Lane Assist Systems. Ergonomics can be improved by the amount of force and range of movement required by the driver and by greater flexibility in the location of controls. This flexibility also significantly expands the number of options for the vehicle's design.

To provide for a redundant back-up system in steer-by-wire systems, a backup clutch may be used. Clutches used in steer-by-wire systems are normally closed requiring power to be applied to disengage the clutch while in use. A clutch is a mechanical device that provides for the transmission of motion from one component (the driving member) to another (the driven member) when engaged, and allows for complete disengagement from one component to another when not engaged.

SUMMARY

In one aspect of the disclosure, a vehicular steering linkage is provided. The linkage has a first steering shaft with a first interaction surface, and a second steering shaft with a second interaction surface. The first and the second steering shafts rotate independently of each other within a predetermined relative rotational range provided between the two interaction surfaces of the shafts. Operation within the predetermined relative rotational range allows the steering linkage to decouple components within a vehicle steering system. The steering system may include a steering wheel and a steering gearbox. When the vehicle steering system is operated within the predetermined relative rotational range the steering linkage decouples the steering wheel and steering gearbox. When the predetermined relative rotational range is met, the interaction surfaces contact each other and couples the steering wheel and steering gearbox.

In another aspect of the disclosure, a steer-by-wire system is provided. The steering control system may include a controller and a steering linkage. The controller monitors the motion of a steering wheel and translates that motion to a steering gear box. The controller actuates a motor to assist in translating the motion of the steering wheel to the steering gear box. The motor may be an electric power assist motor. The controller may also be in communication with a steering wheel movement motor. Utilizing the steering wheel movement motor, the controller may be programmable to align steering wheel movement with steering gearbox movement resulting from a vehicle wheel movement.

A steering linkage is disposed between two steering shafts. The steering linkage may have a relative steering angle range within which the steering linkage provides decoupled rotation of the two steering shafts. The steering linkage further provides a relative rotational limit at which the steering linkage provides coupled rotation of the two steering shafts. Coupling the steering shafts translates the motion of a steering wheel directly to a steering gear box. This allows for a direct mechanical link from the steering wheel to the steering gear box.

In yet another aspect of the disclosure, a semi-decoupled steering system is provided. The semi-decoupled system includes a controller and a passive mechanical linkage. The controller may be programmable to monitor and align movement of a steering mechanism and a steering gearbox to provide a steer-by-wire effect. The passive mechanical linkage is disposed between the steering mechanism and the steering gear box and may provide a direct mechanical engagement from the steering mechanism to the steering gear box when a misalignment limit is met.

The steering system may further include a first steering shaft in coupled movement with the steering mechanism and a second steering shaft in coupled movement with the steering gearbox. The steering shafts may define the relative rotational range comprising the misalignment limit. The passive mechanical linkage couples the steering shafts at a rotational limit within the relative rotational range. For example, the relative rotational range comprising the misalignment limit may have a positive rotational direction limit and a negative rotational direction limit. When operating between the positive and negative rotational direction limits the first and second steering shafts are rotationally disengaged, and only engage when either the positive or negative rotational direction limits are met.

Embodiments according to the present disclosure provide a number of advantages. For example, the present steering linkage does not require power to remain decoupled and a predetermined rotational limit may also provide a backup in case of power steering lag. These embodiments are meant to be merely illustrative and not conclusive.

DETAILED DESCRIPTION

The illustrated embodiments are disclosed with reference to the drawings. It should be understood that the disclosed embodiments are intended to be merely examples that may be embodied in various and alternative forms. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to practice the disclosed concepts.

Referring toFIG. 1, a vehicle steering system10is provided with a steering mechanism12capable of receiving a steering input from a user and a steering gear box14capable of providing a steering output to a control component (not shown). The steering mechanism12may be a steering wheel18, as shown here, or any other device capable of receiving steering input from a user, such as, but not limited to, a yoke, steering pedal, stick, or tiller. The control component may be a wheel and tire20, as shown here, or any other device capable of steering a vehicle, such as, but not limited to, ailerons, rudders, skis, tracks, or other control surfaces.

In the case where the steering mechanism12is a steering wheel18, the system may have a steering angle sensor22connected to it to measure the rotational/angular movement of the steering mechanism12. A controller24may be in communication with the steering angle sensor22, and the steering angle sensor22may transmit the motion of the steering wheel18to the controller24. The controller24may then be programmed to actuate a motor26to translate the steering wheel18angular movements to the gearbox14. The motor26is configured to be actuated by the controller24to align movement of the steering gearbox14with a steering mechanism12, in this case a steering wheel18. In essence, the motor26translates steering wheel18angular movement to the steering gearbox14. The motor26may be an electric power assist motor.

Further, a second motor28, different from motor26, may be disposed on the steering mechanism12. The steering mechanism motor28may be in communication with the controller24, and the controller24may be further programmed to align steering mechanism12movement with the steering gearbox14movement. The controller24may be programmed to align steering gearbox14movements with steering mechanism12movements in both directions using both motors26,28simultaneously. The controller24may be further programmed to filter out noise, vibration, and harshness from the gearbox14and vehicle wheel20from being transmitted to the steering mechanism12. The steering mechanism motor28may be a steering wheel movement motor30.

For example, as the vehicle is being driven, a driver may turn the steering wheel18, as shown by arrow32, and the controller24would respond by energizing both motors26,30simultaneously. The controller24would energize motor26to move the steering gearbox14an appropriate distance to align with the angular rotation of the steering wheel18, while at the same time providing feedback resistance to the turning of the vehicle back to the driver through motor30. As the vehicle comes out of the turn, the driver may allow the steering wheel18to slip within their hands, moved by motor30, the controller recognizing the slip and responding by controlling each motor26,30as necessary to allow for the front wheels20to straighten back out. The controller24, in combination with at least the two motors26,30, and an array of sensors (not all shown, one of which being the steering angle sensor22), may provide the same level of input and response found in a traditional steering system. The concept of using a controller24to transfer rotational movement of a steering wheel18electronically via motors to steerable wheels and tires20is referred to as a steer-by-wire system.

The controller24may also be programmed to provide variable ratio steering with traditional gearboxes14by providing greater gearbox14translation as compared to steering mechanism12input at differing points in the motion of the steering mechanism12. Steer-by-wire systems require power to operate, as such it may be advantageous to provide a backup or redundant system in the case of power loss.

A steering linkage40, which may be a passive mechanical linkage, is disposed between the steering mechanism12and the steering gearbox14. The steering linkage40is configured to allow the steering mechanism12and the steering gearbox14move independently of each other within a predetermined alignment range, shown here as a predetermined relative rotational range θ. The steering linkage40provides a direct mechanical link between the steering mechanism12and the steering gearbox14when a predetermined misalignment limit42, shown here as a rotational limit42, of the two is met. When the predetermined misalignment limit42is met, the steering linkage40engages and translates the steering movement32of the steering mechanism12to the steering gearbox14.

Steering linkage40may be disposed between a first steering shaft44and a second steering shaft46. Alternatively, the steering linkage may include the first and second steering shafts44,46. The steering linkage40provides decoupled rotation of the two shafts44,46within a relative rotational range θ and coupled rotation of the two shafts at a relative rotational limit42. The first shaft44may be an input shaft44in coupled movement with the steering mechanism12, and the second shaft46may be an output shaft46in coupled movement with the steering gearbox14. The steering linkage40provides for a specified relative interaction between the first and second shafts44,46.

The interaction between the first shaft44and the second shaft46allows is decoupled within the predefined rotational range θ. The steering linkage16interacts with the two shafts44,46and is capable of coupling the two shafts44,46at a rotational limit42at one end of the relative rotational range θ. The predetermined rotational range θ typically does not exceed 15 degrees, but may be in the range of 1 to 5 degrees.

Referring toFIG. 2, a diagrammatic exploded example of the steering linkage40ofFIG. 1is shown. In this figure, the steering linkage40is shown with a first portion48pulled away from a second portion50illustrating that the steering linkage40decouples a direct connection between the first and second shafts44,46. As before, the first shaft44is in a coupled rotational movement with the steering mechanism12and the second shaft46is in coupled rotational movement with the steering gearbox14(seeFIG. 1). As the steering mechanism12moves, the first portion48moves, and as the steering gearbox14moves, the second portion50moves. So long as the movement between the steering mechanism12and the steering gearbox14remains aligned, the first and second portions48,50, and thus the first and second shafts44,46, move in unison.

Any misalignment in the movement of the steering mechanism12and steering gearbox14may occur within the predetermined relative rotational range θ of the first and second shafts44,46. The predetermined rotational range θ may be defined by a first interaction surface52on the first portion48of the steering linkage40and a second interaction surface54on the second portion50of the steering linkage40. When the relative rotation of the first and second shafts44,46meets the predetermined relative rotational range θ, the first interaction surface52contacts the second interaction surface54causing a direct linkage between the two shafts44,46. Contact between the first and second interaction surfaces52,54causes the first steering shaft44and the second steering shaft46to rotate jointly, or as one linkage. The occurrence of a misalignment meeting the predetermined relative rotational range θ such that the first interaction surface52contacts the second interaction surface54may also be understood as a positive relative rotational limit.

The steering linkage40may also include a third interaction surface56and a fourth interaction surface58. As with contact between the first and second interaction surfaces52,54, contact between the third and fourth interaction surfaces56,58may also cause joint rotation of the first and second steering shafts44,46, just in the opposite direction. The occurrence of a misalignment meeting the predetermined relative rotational range θ such that the third interaction surface56contacts the fourth interaction surface58may be understood as a negative relative rotational limit. The distance between these positive and negative relative rotational limits may be understood as the predetermined relative rotational range θ. For example, with a predetermined rotational range of 15 degrees, the first interaction surface52may contact the second interaction surface54at a positive relative rotational limit of +7.5 degrees and the third interaction surface56may contact the fourth interaction surface58at a negative relative rotational limit of −7.5 degrees.

Once either of the positive or negative rotational limits is reached, the predetermined rotational limit θ is met and steering shafts44,46are rotationally engaged. Being rotationally engaged, the first and second steering shafts44,46rotate together until disengagement occurs. The steering shafts44,46may remain rotationally engaged until the relative rotation of the two shafts changes direction to be within the relative rotational range θ again. This causes the two shafts44,46to become disengaged until either the positive rotational direction limit is re-met or the negative rotational direction limit is met in an opposite relative rotational direction of the shafts44,46.

When the steering shafts44,46are disengaged, operating within the predetermined relative rotational range θ, noise, vibration, and harshness are inhibited from being transferred from the steering gear box14, or other steering system components, to the steering mechanism12. The steering linkage40engages and translates the steering movement of the steering mechanism12to the gearbox14only when either the positive rotational limit or the negative rotational limit is reached. It should be noted thatFIG. 2is diagrammatic in showing a nearly 180 degree predetermined rotational range θ, however, as mentioned above, the predetermined rotational range θ typically does not exceed 15 degrees, and may even be in the range of 1 to 5 degrees. Changing the angular distance between the second interaction surface54and fourth interaction surface58can accomplish a reduced predetermined rotational range θ.

Referring toFIG. 3, an alternate diagrammatic exploded example of a steering linkage70is shown disposed between the first and second steering shafts44,46. In this example, the relative rotational range θ is provided by a pin72disposed in a slot74. Opposing sides of the pin72may provide first and third interaction surfaces76,78and opposing side walls of the slot74may provide second and fourth interaction surfaces80,82. As before, when the first surface76contacts the second surface80, which may also be referred to as a positive rotational direction limit84, the two shafts44,46will engage and rotate together. Similarly, when the third surface78contacts the fourth surface82, which may also be referred to as a negative rotational direction limit86, the two shafts44,46will also engage and rotate together. Relative rotation of the two shafts44,46within the predetermined rotational range θ allows for the two shafts44,46to rotate independently.FIG. 3clearly shows the rotational distance between the positive and negative rotational limits84,86as being the predetermined rotational range θ, and the range θ may be set by changing the length of the slot74. As with steering linkage40, steering linkage70may also have a predetermined rotational range θ of 15 degrees or less and may be in the range of 1 to 5 degrees.

Coupled rotation between the first steering shaft44and the second steering shaft46directly translates the steering mechanism12motion to the steering gearbox14. This is true even if the controller24is still communicating movements between the steering mechanism12and the steering gearbox14, thus the steering linkages40,70may provide a backup in case of power loss or in the case of any misalignment between two steering system components. A typical steer-by-wire system merely has a normally open clutch which may only engage in the case of power loss and provides no misalignment protection. The normally open clutch requires power to maintain the clutch open during operation. The steering linkages40,70, as disclosed here are passive mechanical linkages requiring no power to function. Even though the steering linkages40,70, as described above may replace typical steer-by-wire clutches, it is also envisioned that a control strategy may be employed to monitor the steering components for misalignment and engage a clutch when misalignment exists.

Referring toFIG. 4, an operational flow-chart for a semi-decoupled steering system is provided. At step100a steering input is received by the system. At step102, a controller attempts to translate all of the steering input to a steering gearbox via a motor. At step104, the semi-decoupled steering system monitors whether the steering input is within a rotational range in relation to the gearbox movement. If the steering input reaches a predetermined rotational limit, defining the boundaries of the rotational range, the steering input is not within the rotational limit and the process moves to step106.

At step106, a steering linkage translates the steering input to the steering gear box and the process moves to step108. This creates a direct mechanical linkage from the steering input to the steering gear box. However, if the steering input is within the predetermined rotational range, such that the controller actuated a motor translating all of the steering input to the steering gear box, maintaining the steering components within alignment, then the process proceeds directly to step108without the need to go to step106. At step108, all of the steering input from step100is translated to the steering gearbox, whether by motor, flowing directly through steps102,104to108, or through step106if the motor is unable to transfer all of the steering input. Once the steering input is translated to the steering gear box, either through a linkage, through a motor, or a combination of the two, the vehicle steers at step110.