Abstract:
A wheeled vehicle includes a solid vehicle frame and a solid front axle including wheels movable to change the direction of the vehicle, a steering assembly including a steering wheel, a steering shaft coupled with the steering wheel, and a rotary output member having an end selectively movable in response to an input to the steering wheel, the solid front axle vehicle includes an electric power assist steering (EPAS) system for selectively steering the vehicle separately from any input to the steering wheel. The EPAS system includes a motor having a rotary output coupled to a steering gear and a steering rack having a longitudinal extent defining an axis having an end coupled a tie rod of the steering assembly. The longitudinal axis of the EPAS assembly is aligned with or transverse to the forward vehicle direction so its output is coupled to the output of the steering wheel and can be actuated independently.

Description:
BACKGROUND 
       [0001]    It is generally known to provide a vehicle with a steering mechanism. It is generally known to provide a vehicle, such as a passenger vehicle, with a steering assembly that is operated by a steering wheel. For quite some time it has also been generally known to provide a vehicle with power assisted steering as well as electric power assisted steering. However, such electric power assisted steering (EPAS) have been limited to column-based systems for relatively small vehicles and relatively lowly rated front gross axle weights. Further, such generally known EPAS systems are only implemented in rack and pinion type steering architectures where an electric motor is directly driving a pinion on the gear rack. One known alternative to the above is a column-mounted EPAS where an electric motor directly drives the I-shaft or steering column. The column-mounted EPAS is a relatively very expensive solution, particularly in a vehicle architecture including a solid front axle and cab on frame design. 
         [0002]    However, despite such power assisted steering system assemblies being known for quite some time, none have been successfully integrated into vehicles having a solid (or monobeam) front axle. In particular, the generally known power assisted steering system assemblies have not been successfully integrated into a vehicle having a significant gross axle weight rating (GAWR) being steered, such as a heavy duty pickup having a cab on frame architecture and including a solid front axle, because such generally known mechanisms are not currently commercially available and capable of proper operation in such applications. Accordingly, their long remains a significant need to develop an electronically controlled, power assisted steering system that can be used in a vehicle having a solid front axle and having a significant gross vehicle weight over the wheels being steered. 
     
    
     
       DRAWINGS 
         [0003]      FIG. 1  is a perspective graphic view of a vehicle frame having a solid front axle and including a power assist steering apparatus according to an exemplary embodiment of the present disclosure; 
           [0004]      FIG. 2  is an alternate perspective graphic view of the exemplary embodiment of  FIG. 1 ; 
           [0005]      FIG. 3  is a bottom graphic view of the exemplary embodiment of  FIG. 1 ; 
           [0006]      FIG. 4  is a front plan graphic view of the exemplary embodiment of  FIG. 1 ; 
           [0007]      FIG. 5  is a bottom plan graphic view of the exemplary embodiment of  FIG. 1 ; 
           [0008]      FIG. 6  is a top plan graphic view of the exemplary embodiment of  FIG. 1 ; 
           [0009]      FIG. 7  is a partial, bottom view detailing the mounting of the rack mechanism of the exemplary embodiment of  FIG. 1 ; 
           [0010]      FIG. 8  is a partial, perspective graphic view of the exemplary embodiment of  FIG. 7  detailing one end mount of the rack mechanism; 
           [0011]      FIG. 9  is a partial, perspective graphic view of the exemplary embodiment of  FIG. 7  detailing the other end mount of the rack mechanism; 
           [0012]      FIG. 10  is a perspective graphic view of a vehicle frame having a solid front axle and including a power assist steering apparatus according to an alternate exemplary embodiment of the present disclosure; 
           [0013]      FIG. 11  is an alternate bottom perspective graphic view of the exemplary embodiment of  FIG. 10 ; 
           [0014]      FIG. 12  is a partial, perspective graphic view of the exemplary embodiment of  FIG. 10 ; 
           [0015]      FIG. 13  is a front plan graphic view of the exemplary embodiment of  FIG. 10 ; 
           [0016]      FIG. 14  is a bottom plan graphic view of the exemplary embodiment of  FIG. 10 ; and 
           [0017]      FIG. 15  is a top plan graphic view of the exemplary embodiment of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring in general to all of the Figures and in particular to  FIGS. 1 through 9 , an exemplary embodiment of an electronic power assist steering assembly according to the present disclosure and teachings is provided for a vehicle having a solid front axle capable of supporting a relatively significant front gross axle weight rating (GAWR). One such exemplary vehicle is, but is not limited to, a pickup truck, such as a heavy duty pickup truck. Typically, some pickup trucks have a front GAWR of greater than approximately 3000 pounds. It is possible for such vehicles to have a maximum front GAWR in the range of between approximately 5000 pounds and approximately 7000 pounds. Further, it is known that the maximum front GAWR for such vehicles can be as high as approximately 10,000 pounds or more. 
         [0019]    Typically, such a vehicle may include a vehicle frame  10  having any generally known or appropriate construction. In particular the vehicle frame  10  includes right-hand and left-hand beams as is generally known for a cab on frame vehicle. The vehicle frame  10  may include a front axle  11  coupled to the vehicle frame  10  in any known or appropriate manner. The front axle  11  may be a solid or monobeam member and may include a differential  12 . The front axle  11  is preferably supported on the left-hand and right-hand sides by wheels as is generally known. Front axle  11  may include other known and appropriate left hand and or right hand functioning components such as steering knuckles, bushings, bearings, rotors and brake mechanisms as are all generally known. Further, the vehicle may include a steering assembly  20  including a steering wheel  21  coupled indirectly to rotate a first end  22  of an I-shaft or steering column  23 . The I-shaft  23  may be of a general or appropriate construction and may have a second or opposite end  24  coupled to rotate an input  25  to a recirculating ball nut mechanism  50 . The steering wheel  21  may be of any generally known or appropriate type and may include other devices and mechanisms as may be desired and/or appropriate. 
         [0020]    The recirculating ball nut mechanism  50  may be of a general or appropriate construction and may include an output or link member  55  that rotates between at least a first position in which the wheels are turned all the way to the left and a second position in which the wheels are turned all the way to the right. The ball nut mechanism  50  may include an electric motor coupled to a gear train for rotating within the mechanism  50 . The ball nut may be coupled to the output  50  disposed through the ball nut on the axis thereof such that rotation of the ball nut may cause the rack shaft to move axially (or translate) with respect to the housing of the ball nut mechanism  50 . The ratio of turns of the steering wheel  21  to the rotation angle of the output member  55  is consistent with traditional steering mechanisms of the type. Traditionally, the known steering assemblies in such a vehicle would include a hydraulic power assist system (HPAS) which is unexpectedly absent in the vehicle of the present disclosure. 
         [0021]    In the steering assembly  20  according to the exemplary embodiment, the output member  55  of the mechanism  50  includes an end  56  which may be coupled to a first end  61  of a drag link  60 . The drag link  60  further includes a second end  62  which may be coupled to a steering knuckle of the right-hand wheel of the vehicle such that movement of the end  56  of the output member  55  of the mechanism  50  moves the drag link  60  causing the steering knuckle to move the wheel. The steering knuckle of the right-hand wheel of the vehicle of the exemplary embodiment may also be coupled to a first end  71  of a tie rod or crossover or parallel link  70 . The tie rod link  70  may include a second end  72  that may be coupled to the steering knuckle of the left-hand wheel of the vehicle such that movement of the steering knuckle of the right-hand wheel may be directly transferred to movement of the left-hand wheel by the tie rod  70  as is understood in the vehicle steering art and is best shown in  FIGS. 2 and 3 . While the present exemplary embodiment is disclosed as including a drag link steering geometry as part of the steering assembly  20 , it should be understood that the exemplary embodiment may also include a Haltenberger or a parallel link steering system or any other steering system that may be usable or appropriate in a vehicle according to the exemplary embodiment. 
         [0022]    The steering assembly  20  according to the exemplary embodiment further includes an electric power assist steering (EPAS) device  100  as best shown in  FIGS. 7 through 9 . The output of the EPAS device  100  may be provided as an input to the first end  61  of the drag link  60  of the steering assembly  20  for assisting in steering the front wheels of the vehicle having a solid front axle. The EPAS device  100  may generally extend longitudinally and include it in a longitudinal axis. The EPAS device  100  may be coupled to and supported on a crossbeam support or cross member  115  that may extend between the left-hand and right-hand beams of the solid vehicle frame  10  as best shown in  FIGS. 1 through 9 . The cross number  115  may include a first end  116  coupled to the right-hand frame member and a second end  117  coupled to the left-hand frame member of the vehicle frame  10 . The cross member  115  may be a generally tubular member made from an appropriate material (typically similar to that of vehicle frame) sufficient for fixedly supporting the EPAS device  100  longitudinally between the right-hand and left-hand frame members and transferring the forces generated by the EPAS device  100  to the drag link  60  using the vehicle frame  10  as a base. The cross member  115  may have a generally round or circular cross-section and may have any known or appropriate shaped cross-section including square, rectangular, round, elliptical or any other known or appropriate shape and may be tubular or solid. 
         [0023]    Referring to  FIG. 8 , the first end  116  of the cross member  115  may be coupled to the right-hand vehicle frame member using a bracket  118 . Referring to  FIG. 9 , the second end  117  of the cross member  115  may be coupled to the left-hand vehicle frame member using a bracket  119 . Referring now to  FIG. 7 , the EPAS device  100  may be coupled to a bracket  120  that may be coupled directly to the cross member  115 . Alternatively, the EPAS device  100  may be directly coupled to the cross member  115  in an embodiment not shown in the figures. The bracket  120  may include a first extension tab  121  located at a first end of the racket  120  and may further include a second extension tab  122  located at a second end of the bracket  120 . Each of the first and second extension tabs  121  and  122 , respectively, include a passage or hole therein for coupling the bracket member  120  to the cross member  115 . The cross member  115  may be located in the holes in the first and second extension tabs  121  and  122 , respectively, and may then be coupled, connected or fixed, such as by welding, in any known or appropriate manner. Bracket member  120  may further include a base  123  extending between the first and second extension tabs  121  and  122 , respectively. The base  123  preferably may have a generally planar and rectangular shape and may include a plurality of holes for directly coupling the EPAS device  100  to the base  123  using a plurality of fasteners, such as bolts, or any other known or appropriate coupling device or attaching method. 
         [0024]    The EPAS device  100 , according to the exemplary embodiment, may further include an electric motor  140  having a rotating output that may be coupled to a recirculating ball nut device  150 . The recirculating ball nut device  150  may be of a general or appropriate construction and may include a steering gear and rack  170  and a cover or bellows  180  for covering at least a portion of an output or link member  185  of the rack  170  as best shown in  FIG. 7 . The motor  140  of the EPAS device  100  may be supplied with electrical power from the electrical system of the vehicle. The motor  140  of the EPAS device  100  may preferably be controlled using an appropriate electric controller such as the electrical controller of the steering assembly  20 . The motor  140  generates a rotary output that may be coupled to the input of the ball nut device  150 . 
         [0025]    In the EPAS device  100  according to the exemplary embodiment, the ball nut device  150  may include a gear train for rotating the ball nut within the device  150  and transferring the rotary motion of the ball nut (not shown) to the steering gear for translating or axial movement of the rack  170  and the output end  185  for supplying an additional steering input to the wheels of the vehicle separate from the input to steering wheel  21 . The output of the end  185  of the EPAS device  100  may be coupled to the output end  55  of the mechanism  50  and the end  61  of the drag link  60  using any known or appropriate coupling structure. In the exemplary embodiment shown, the end  185  may be coupled to the end  55  and the end  61  using a pin or stud  190  to form a double joint such that the output of the EPAS device  100  may be used to control the steering of the front wheels of the vehicle which are driven using power from the powertrain and supplied to the front wheels through the solid front axle. 
         [0026]    The device  150  preferably may further be designed such that back driving of the rack  170  from the operation of the steering assembly  20  through the steering wheel  21  and the mechanism  50  and its output member  55  may have as little resistance from the device  150  as possible. In one exemplary embodiment as disclosed, this may be accomplished by including a one-way driving clutch mechanism within the device  150 . Similarly, the mechanism  50  may preferably include a one-way driving clutch mechanism there in such that output of the EPAS device  100  may be used for driving the drag link  60  and the driving assembly  20  and not against resistance forces of the mechanism  50 . 
         [0027]    As should be apparent from the exemplary embodiment as disclosed, the steering assembly  20  no longer includes a hydraulic assist which has been eliminated from the steering gear mechanism  50  and thereby eliminating the need for a power steering pump which reduces the overall power consumption of the vehicle and thereby improving its efficiency and ultimately it&#39;s fuel economy. The EPAS device  100  of the exemplary embodiment may be controlled as desired or necessary to provide steering assist during operation of the vehicle. The ball nut mechanism may be coupled to the output  50  disposed through the ball nut on the axis thereof such that rotation of the ball nut may cause the rack shaft to move axially (or translate) with respect to the housing of the ball nut mechanism  50 . 
         [0028]    Referring now to the exemplary embodiment disclosed in  FIGS. 10 through 15 , there is disclosed a steering assembly for a vehicle including an EPAS device  200 . Similar to the exemplary embodiment disclosed in  FIGS. 1 through 9 , the EPAS device  200  includes many carryover components which are labeled the same in the exemplary embodiment of  FIGS. 10 through 15 . It should be noted that the vehicle frame  10  is of similar cab on frame design for a heavy duty vehicle and includes right-hand and left-hand frame members and cross frame members. Similarly, the heavy duty vehicle of  FIGS. 10 through 15  includes a solid or monobeam front axle  11  including the differential  12 . 
         [0029]    In the present exemplary embodiment, the frame  10  includes a cross member  14  which is moved forward with respect to the front axle  11  providing additional clearance and space proximate the end  24  of the I-shaft  23  for locating the EPAS device  200  along the left-hand rail of the solid frame of the vehicle. In the present exemplary embodiment, the EPAS device  200  may be directly coupled to the left-hand rail of the solid frame of the vehicle or may alternatively be coupled to a bracket that is coupled to the left-hand rail of the frame of the vehicle. While the EPAS device  200  of the present exemplary embodiment is generally operable in a manner similar to the EPAS device  100  of the prior exemplary embodiment, it provides improved optional packaging opportunities and related efficiencies. The opportunity to package the EPAS device  200  longitudinally aligned with the left-hand frame member and the I-shaft  23  (or alternatively with the right-hand frame member in a right-handed driving vehicle) provides additional significant benefits for an EPAS solution for a solid front axle vehicle. 
         [0030]    In the present exemplary embodiment, the vehicle may include an EPAS device  200  including a motor  240  having a rotary output coupled to a single-sided rack and pinion EPAS gear device  250  including a rack  270  that may be linearly translated by the gear device  250  in response to the motor  240 . Since the present exemplary embodiment no longer requires, but may still optionally include, the mechanism  50 , the end  285  of the rack  270  of the EPAS device  200  may be coupled to the end  24  of the I-shaft  23  may be coupled to a first end  231  of a lower steering linkage  230  which may have its other end coupled to a gearbox  235  integrated with the steering gear of the rack  270  of the device  250  to directly drive the rack  270  to translate to engage the steering linkage of the steering assembly  20  and steer the wheels of the vehicle in response to an input applied to the steering wheel  21 . In the exemplary embodiment where the mechanism  50  remains coupled to the I-shaft  23 , the mechanism  50  will be a non-assist type recirculating ball nut gear (i.e., a manual drive). 
         [0031]    In the present exemplary embodiment shown, the I-shaft  23  is directly coupled to the EPAS device  200  which reduces or minimizes the amount of lash within the steering assembly  20  to provide improved steering compliance when a steering input is applied to the steering wheel  21 . Additionally, while the present exemplary embodiments show the EPAS devices  100  and  200 , having a longitudinal axis located either perpendicular or aligned with the axis (or plane) of the I-shaft  23 , it should be understood that it may be possible to adjust the longitudinal axis of the EPAS devices  100  and  200 , respectively to be located at any angle with respect to the longitudinal axis of the I-shaft  23  as may be desired for the packaging of the steering assembly  20  in a vehicle according to the present disclosure. 
         [0032]    In the present exemplary embodiment of  FIGS. 10-15 , the steering linkage of the steering assembly  20  may include the output link member or pitman arm  255  having a first end coupled to the base member  284  of the frame  10  and a second or output end  256 . Similar to the prior exemplary embodiment, the end  256  of the link member  255  may be coupled to an end  261  of a drag link  260 . To utilize the existing steering linkage members of the steering assembly  20 , a lever  288  may be coupled at one end to the end  285  of the rack member  270  and may be coupled at a second and to the first end of the link member  255  and supported there with on the base  284  so that rotation of the lever  288  caused by movement of the end  285  of the rack  270  may be directly transferred to cause rotation of the link member  255  and thereby may cause movement of the drag link  260  to cause the wheels of the vehicle to turn. As best shown in  FIG. 12 , the ends of the lever  288  and the link member  255  share a common pivot supported by the base  284  and it may be coupled there with using any known or appropriate device such as a fastener or stud. A second end  262  of the drag link  260  may be coupled to a steering knuckle on the end of the solid front axle similar to the prior exemplary embodiment and as is understood in the art. 
         [0033]    The steering assembly  20  of the present embodiment may further include a steering link member  290  having a first and coupled near the middle of the lever member  255  and a second end coupled to the right-hand frame member  10 . The steering link member  290  includes a pair of telescoping link members and provides stability to the steering assembly  20  during operation. The steering assembly  20  of the present exemplary embodiment may further include a parallel or tie rod or link member  267  having a first end coupled to the knuckle member proximal the second end  262  of the drag link  260  and a second and coupled to the knuckle member of the left-hand wheel. 
         [0034]    In operation, the steering assembly  20  of the present exemplary embodiment may be operated by an in input applied a rotational force to the steering wheel  21  which is transmitted to rotate the I-shaft  23  which transmits the rotational force to the lower steering linkage  230  which provides an input to the steering gear of the rack and pinion device  250  thereby translating the rack  270 , the end  285  of which rotates the lever  288  and output member  255  about the base  284  providing an input to the drag link  260  and thereby steering the wheels of the vehicle. Rotation of the steering wheel  21  in an opposite direction is similarly translated to cause the rack member  270  to move in an opposite direction and to thereby cause the drag link  260  to move in opposite direction and to also move the link member  267  and thereby steer the wheels of the vehicle in an opposite direction. 
         [0035]    Any numerical values recited herein or in the figures are intended to include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner. As can be seen, the teaching of amounts expressed as “parts by weight” herein also contemplates the same ranges expressed in terms of percent by weight. Thus, an expression in the Detailed Description of the Invention of a range in terms of at “‘x’ parts by weight of the resulting polymeric blend composition” also contemplates a teaching of ranges of same recited amount of “x” in percent by weight of the resulting polymeric blend composition.” 
         [0036]    Unless expressly stated, all ranges are intended to include both endpoints and all numbers between the endpoints. The use of “about” or “approximately” in connection with a range applies to both ends of the range. Thus, “about 20 to 30” is intended to cover “about 20 to about 30”, inclusive of at least the specified endpoints. 
         [0037]    The use of the term “consisting essentially of” to describe a combination shall include the elements, ingredients, components or steps identified, and such other elements ingredients, components or steps that do not materially affect the basic and novel characteristics of the combination. The use of the terms “comprising” or “including” to describe combinations of elements, ingredients, components or steps herein also contemplates embodiments that consist essentially of the elements, ingredients, components or steps. By use of the term “may” herein, it is intended that any described attributes that “may” be included are optional. 
         [0038]    The disclosure of “a” or “one” to describe an element, ingredient, component or step is not intended to foreclose additional elements, ingredients, components or steps. Plural elements, ingredients, components or steps can be provided by a single integrated element, ingredient, component or step. Alternatively, a single integrated element, ingredient, component or step might be divided into separate plural elements, ingredients, components or steps. 
         [0039]    It is understood that the present description is intended to be illustrative and not restrictive. Many embodiments as well as many applications besides the examples provided will be apparent to those of skill in the art upon understanding the present disclosure. The scope of the claimed invention should, therefore, not be determined with limiting reference to the description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. Any disclosure of an article or reference, including patent applications and publications, is incorporated by reference herein for all purposes. Any omission in the following claims of any aspect of subject matter disclosed herein is not a disclaimer of such subject matter.