Vehicle suspension systems are described herein. An example wheel steering apparatus includes a steering actuator to couple to a rear axle, a tie rod, and a transfer link to couple the steering actuator and the tie rod. The steering actuator is positioned on a first side of a first longitudinal axis of the rear axle and the tie rod positioned on a second side of the first longitudinal axis of the rear axle opposite the first side.
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This disclosure relates generally to vehicle suspensions and, more particularly, to rear wheel steering apparatus to generate positive rear Ackermann.
Ackermann steering geometry enables mechanically linked steerable wheels to move together simultaneously during turning and steering movements. However, in some instances, space constraints of a vehicle suspension prevent desired Ackermann geometry between steering components, thereby resulting in less than desired Ackermann (e.g., negative Ackermann) and reducing vehicle maneuverability, handling and/or performance. For example, solid axles with rear wheel steering capability often generate negative rear wheel Ackermann due to various components (e.g., driveshaft package, brake package, etc.) that interfere with a desired mounting location of rear wheel steering components.
FIG. 1 represents an example vehicle that may be implemented with an example wheel steering apparatus in accordance with the teachings of this disclosure.
FIG. 2 is a perspective, bottom view of an example vehicle suspension of the example vehicle of FIG. 1 implemented with the example wheel steering apparatus disclosed herein.
FIG. 3 is an assembled, perspective bottom view of an example axle and the example wheel steering apparatus of the example vehicle suspension of FIG. 2.
FIG. 4 is an exploded view of the example axle and wheel apparatus assembly of FIG. 3.
FIG. 5 is a partial, perspective front view of the example wheel steering apparatus of FIGS. 2-4.
FIG. 6 is a perspective view of the example axle and wheel steering apparatus of FIGS. 2-5.
FIG. 7 is a top, schematic view of a rear wheel of the example vehicle and the example wheel steering apparatus of FIGS. 1-6 showing the rear wheel in a straight position.
FIG. 8 is a top, schematic view of the rear wheel of the example vehicle and the example wheel steering apparatus of FIGS. 1-6 showing the rear wheel at a first steering angle.
FIG. 9 is a top, schematic view of the rear wheel of the example vehicle and the example wheel steering apparatus of FIGS. 1-6 showing the rear wheel at a second steering angle.
FIGS. 10A and 10B illustrate graphs representative of rear Ackermann produced by example wheel steering apparatus and/or the suspension apparatus disclosed herein.
FIG. 11 is a flowchart of an example method of assembling an example steering apparatus disclosed herein to a vehicle.
The figures are not to scale. Instead, to clarify multiple layers and regions, the thickness of the layers may be enlarged in the drawings. Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used in this patent, stating that any part (e.g., a layer, film, area, or plate) is in any way positioned on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, indicates that the referenced part is either in contact with the other part, or that the referenced part is above the other part with one or more intermediate part(s) located therebetween. Stating that any part is in contact with another part means that there is no intermediate part between the two parts. Stating that a part is coupled or connected to another part indicates that the parts are joined directly or through one or more intervening parts. Thus, physical contact is not required for two parts to be coupled or connected.
Ackerman geometry prevents tires of a vehicle from turning about different points during a vehicle turning event. When the tires of a vehicle turn relative to different points (e.g., different center points relative to a radius of curvature of a turning path of the vehicle), the wheels fight each other to force the vehicle to turn about the point about which each tire is turning. As a result, one or more of the tires drag in a direction slightly different from that in which the vehicle is steered, causing the tires to scrub against the ground and wear. Solid axle rear suspension systems typically include non-steerable wheels. For non-steerable rear wheel suspensions, Ackerman geometry is configured such that each of the front wheels and the rear wheels turn about a common turning point during a turning event.
To improve handling and/or vehicle performance, some vehicles utilize all-wheel steering functionality. Rear wheel steering enables rear wheels of a vehicle to provide steering in addition to front wheels to improve vehicle handling, vehicle maneuverability, and/or performance. Implementing a four-wheel steering system (e.g., front and rear wheel steerability) requires Ackermann accommodation for all four wheels to improve vehicle maneuverability (e.g., avoid or reduce tire scrubbing during turning).
Positive Ackermann prevents or reduces tire scrubbing during turning while negative Ackermann does not reduce (e.g., increases) tire scrubbing. Thus, positive Ackermann is typically desired. For example, positive Ackermann allows the front wheels and the rear wheels of a four-wheel steer vehicle to rotate around a common center point (e.g., located between a front axle and a rear axle) during turning to reduce (e.g., minimize or eliminate) tire scrubbing and/or tire wear and/or improve vehicle handling and/or maneuverability. Typically, 100 percent Ackermann is not desired, due to trade-offs relating to higher speed handling and/or steering. However, a moderate level of positive Ackermann is desired to reduce tire scrubbing and/or tire wear. For example, positive Ackermann of approximately between 40 percent and 60 percent significantly reduces tire scrubbing, tire wear and/or significantly improves vehicle maneuverability, handling and/or other characteristic(s).
Some vehicles employing rear-wheel steering generate negative Ackermann (e.g., negative Ackermann percentages) due to space constraints that prevent desired Ackerman geometry of steering components. In other words, a desired, positive Ackermann geometry cannot be achieved. For example, a driveshaft assembly (e.g., a rear differential housing or casing), a brake package, shock absorbers, and/or other vehicle components associated with a solid rear axle (e.g., a Hotchkiss solid rear axle) may interfere with a desired mounting location of a rear wheel steering apparatus (e.g., a steering actuator and tie rod/knuckle interface). As a result, such a rear suspension assembly can exhibit negative Ackermann. The negative Ackermann can cause excessive tire wear or scrubbing, turn diameter performance degradation, undesirable noise condition(s) and/or reduced vehicle maneuverability and/or performance characteristic(s). For example, negative Ackermann can cause excessive tire scrubbing and/or tire wear during a low-speed turning event, thereby providing unwanted or undesired steering influence degrading comfort and performance to vehicle passengers.
For example, due to Ackermann geometry restrictions, an inner rear wheel may have a steering angle that is less than a steering angle of an outer rear wheel, thereby delivering negative Ackermann during a turning event. Negative Ackermann, for example, may cause a front driver-side wheel and a rear driver-side wheel to rotate about a first common point and may cause a front passenger-side wheel and a rear passenger-side wheel to rotate about a second common point different than the first common point during a turning event (e.g., a left-handed turn).
An example wheel steering apparatus disclosed herein produces positive (e.g., rear) Ackermann for an all-wheel steering vehicle. Specifically, an example wheel steering apparatus disclosed herein may be employed with a solid rear axle (e.g., a Hotchkiss solid rear axle). For example, the example wheel steering apparatus disclosed herein enables rear wheel steering capability while generating positive Ackermann. In some examples, steering apparatus disclosed herein produce approximately between positive 40 percent and positive 60 percent Ackermann. In some examples, an example steering apparatus disclosed herein may be configured to generate less than positive 40 percent Ackermann (e.g., between zero percent and 40 percent (e.g., 30 percent)) or more than positive 60 percent Ackermann (e.g., between 60 percent and 100 percent (e.g., 75 percent)). Additionally, example steering wheel apparatus disclosed herein generate positive or improved Ackermann for vehicles having space constraints.
An example steering apparatus disclosed herein includes a steering actuator (e.g., a steering rack) positioned aft of an axle (and/or differential casing) and a tie rod/knuckle interface positioned forward of the axle. In other words, a longitudinal axis of the steering apparatus is positioned on a first side of a longitudinal axis of the rear axle (e.g., aft of the axle) and a tie rod/knuckle interface is positioned on a second side of the longitudinal axis of the rear axle (e.g., fore of the axle) opposite the first side. To this end, the rear axle is positioned between the steering actuator and the tie rod/knuckle interface. In some examples, the tie rod is positioned such that a longitudinal axis of the tie rod is substantially parallel (e.g., with 10 percent tolerance) relative to a longitudinal axis of the steering actuator and/or the longitudinal axis of the rear axle. To transfer translational motion of the steering actuator to translational motion of the tie rod, an example steering apparatus disclosed herein employs a transfer linkage assembly (e.g., a dual transfer linkage). The linkage assembly enables a tie rod/knuckle interface to be located or positioned forward of a wheel center while the steering actuator is positioned rear of the wheel center to generate positive Ackermann. The linkage assembly disclosed herein employs dual linkages to transfer translational movement of a steering actuator to respective ones of the rear wheels.
FIG. 1 is an example vehicle 100 that can implement the teachings of this disclosure. The vehicle 100 of the illustrated example includes front wheels 102, 104 supported by a front suspension and rear wheels 106, 108 supported by a rear suspension. The front suspension associated with the front wheels 102, 104 provides steerability to the front wheels 102, 104. Likewise, the rear suspension associated with the rear wheels 106, 108 provides steerability to the rear wheels 106, 108. The vehicle 100 may be a body-on-frame construction or unibody construction. In some examples, the vehicle 100 may be a truck as depicted in FIG. 1. The example teachings of this disclosure may be implemented with any type of suspension (e.g., a steerable suspension, a non-steerable suspension) and/or any other types of vehicles (e.g., passenger vehicles, military vehicles, etc.)
FIG. 2 is an example vehicle suspension 200 of the vehicle 100 of FIG. 1 implemented with an example steering apparatus 202 (e.g., a steering assembly) in accordance with teachings of this disclosure. The vehicle suspension 200 of the illustrated example can implement the rear suspension (e.g., a steerable solid axle, leaf spring suspension) associated with the rear wheels 106, 108 (FIG. 1) of the vehicle 100. To provide lateral stability to the vehicle 100 and provide an anti-roll stabilizer, the vehicle suspension 200 of the illustrated example includes a biasing element or leaf spring system 204. For example, the vehicle suspension 200 of the illustrated example is a steerable, solid axle suspension commonly referred to as a Hotchkiss suspension. Although the vehicle suspension 200 is described in connection with the rear suspension or a rear solid axle, leaf spring suspension (e.g., a Hotchkiss suspension), the teachings of the disclosure may also be applied to a front suspension (e.g., of the vehicle 100 associated with the front wheels 102, 104 (FIG. 1), a steer by wire suspension) and/or any other type of suspension(s) (e.g., solid axle suspensions having coil springs, air springs with multi-links and/or any other biasing element, suspensions of a vehicle that support steerable wheel assemblies and/or non-steerable wheel assemblies, etc.).