Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
1998-06-12
2001-09-04
Swann, J. J. (Department: 3611)
Motor vehicles
Steering gear
With fluid power assist
C074S422000
Reexamination Certificate
active
06283244
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to improvements in steering mechanism assemblies for automotive vehicles, particularly with the aim of solving problems of the mechanical design and alignment of housing elements for accommodating the various components of the steering mechanism, particularly the steering control linkage, and with the aim of improving the conditions, functioning, and engagement of the steering mechanism components, particularly those of the steering control linkage.
It is an object of the invention to provide structural improvements in housings conventionally used for steering control linkage assemblies, which improvements are aimed at simplifying the fabrication, structure, and angular alignment (skew angular alignment), of housing elements for a steering control linkage employing rack-and-pinion steering wherein rotational movement of the steering wheel is converted into reciprocable linear movement of the rack.
A further object of the invention is to improve the steering control linkage such that correct frictional contact is maintained between the interengaged dentations (those of the rack and pinion), within the established limits of tolerance, in response to axial stresses present in the articulations of the housing which tend to urge the rack into a position distant from and out of proper engagement with the pinion and back into tighter engagement, which stresses thereby result in generation of undesirable noise.
The principal end product of the invention is a steering control linkage housing of simple structure for control linkages for unassisted (manual) mechanical steering or power steering, which control linkages employ a rack and pinion, wherewith the subject housing incorporates means to improve the conditions of engagement of the rack and pinion in the face of axial stresses present in the housing, which stresses cause undesirable noise during the operation of the vehicle.
BACKGROUND OF THE INVENTION
Conventional steering control linkage housings are fabricated by casting of molten aluminum or other materials. A valve housing comprised generally of cast iron is also used in the case of power steering. The fabrication of such components is attended by various problems. Complex and precise procedures are required for assembly and alignment of a cast iron valve housing with a cast aluminum steering control linkage housing, to ensure correct skew angular positioning of the components of the steering control linkage.
One reason why it is difficult to achieve proper alignment of conventional steering control linkage housings comprised of cast material is that there are two subassemblies which must be aligned:
the rack and its housing, and
the pinion, the valve system, and their housings.
The parts of the housing must be in correct skew angular alignment in order to achieve good operating characteristics of the steering system, and particularly the steering control linkage.
The alignment procedures may require different skew angular alignments depending on the particular variant of the steering system used, and necessitate the use of different casting molds for fabricating the elements of the steering control linkage housings and for adapting the power-assisted steering valve housing. For each situation, a specific skew angular alignment of the steering column shaft (pinion shaft) and the rack housing is required, in order for the steering system to function properly.
Another problem which occurs with steering systems is the undesirable noise generated by excessive frictional play between the dentation of the pinion and the dentation of the rack. Such noise is a problem in power-assisted steering systems as well as manual systems. In some cases, the vibration is absorbed by elasticity in the steering system. Otherwise it must be reduced to acceptable limits in order to avoid noise which is disagreeable to the driver and which signals improper functioning of the engaged components.
This noise problem may be due to incorrect alignment of the contoured openings in the housing, but the main cause of steering system noise is axial stresses in the joints between the housing and the chassis, which stresses give rise to a force component perpendicular to the rack bar and tending to distance the rack bar from the pinion, thereby acting counter to the means integrated in the steering assembly which are intended to regulate the relative positions of the rack and pinion.
The said axial stresses also act axially on the rack, which rack is generally mounted with releasable support means on an end bearing in the steering control linkage housing, wherewith in addition to the component of said stresses which act perpendicularly to the rack, the axial stresses give rise to an undesirable axial movement of the rack which interferes with correct interengagement of the rack and the pinion, again tending to cause the respective dentations to separate, wherewith when, in alleviation of this separation, the rack tends to return to its initial position. The result is noise, in an intensity and frequency which depend exclusively on the intensity of the abovementioned axial stresses.
The conventional means used by automobile manufacturers to address these drawbacks in steering control linkages is to use high precision molds for fabricating the housings, in order to achieve the correct alignment of the steering control linkage components. The concept is that substantial improvement in operation will result from improvements in such alignment. In addition, the known technique of providing devices which periodically regulate the position of the rack bar has been used. The general such device comprises a manually adjustable thrust bearing which is elastically urged counter to the direction of the axial stresses. These devices function well, but when over-adjusted (which is always a possibility) the result is that the rack bar is not properly re-engaged, which is detrimental to the mechanism because the re-engagement force is too great or too small, either momentarily (dynamically) or on a sustained basis.
SUMMARY OF THE INVENTION
In order to solve the problems mentioned in the foregoing, according to the invention there is proposed a housing for steering control linkages which housing has a particular structure which enables correct mutual alignment—which may be selected from a range of possible mutual alignments—of housing elements for the rack bar and the pinion (which pinion is fixed to the steering column shaft), wherewith if power-assisted steering is to be employed the housing elements may further comprise a structure for adapting to a power steering valve housing.
The inventive housing is comprised of a pair of tubular housing elements formed from steel tubes, which elements are readily machinable over their entire length. These two tubular elements are joined together in a precise skew angular arrangement as required by the particular steering control linkage.
The steel tubular elements are joined with the aid of contoured openings cut into the tube walls which openings have suitably coordinating shapes, such that when the tubular elements are superposed in the precise prescribed skew angular orientation, they can be joined together by welding or brazing at the superposed borders of the contoured openings.
The described structure of the steering control linkage housing is simple in design. It eliminates the problems of porosity which cast housings present, facilitates the mechanical alignment of the parts of the housing in coordination with the rack bar and pinion which the housing accommodates, eliminates the need for tooling in the nature of molds which would need to be re-tooled for each variation in the skew angular alignment of the housing elements, facilitates the provision of support means for support bearings for the rack bar (e.g. because the inventive housing is readily machinable), and facilitates the exact positioning of elements of the housing which are differently positioned in different versions of conventional housings. The alignment and positionin
Bottorff Christopher
Kajander John
Swann J. J.
Visteon Global Technologies Inc.
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