Abstract:
A side rail made of sheet steel includes a first region which underwent heat treatment, a second region which is not heat-treated, and a transition zone between the first and second regions. The transition zone is hereby defined by a width which is smaller than or equal to 50 mm. An additional component can be coupled to the side rail to form a side rail assembly.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of German Patent Application, Serial No. 10 2010 012 833.3-21, filed Mar. 25, 2010, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein. 
         [0002]    This is one of five applications all filed on the same day. These applications deal with related inventions. They are commonly owned and have the same inventive entity. These applications are unique, but incorporate the others by reference. Accordingly, the following U.S. patent applications are hereby expressly incorporated by reference: “CROSS MEMBER”, representative&#39;s docket no.: PELLMANN-2; “TRANSMISSION TUNNEL”, representative&#39;s docket no.: PELLMANN-4″; “AUTOMOBILE COLUMN”, representative&#39;s docket no.: PELLMANN-5; and “METHOD FOR PRODUCING A MOTOR VEHICLE COMPONENT, AND A BODY COMPONENT”, representative&#39;s docket no.: PELLMANN-6. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to a side rail, and more particularly to a side rail for installation in a motor vehicle. 
         [0004]    It would be desirable and advantageous to provide an improved a side rail which obviates prior art shortcomings and can be produced at low cost in industrial-scale production while still being reliable in operation. 
       SUMMARY OF THE INVENTION 
       [0005]    According to one aspect of the present invention, a side rail is made of sheet steel and includes a first region which underwent heat treatment, a second region which is not heat-treated, and a transition zone between the first and second regions. The transition zone is defined by a width which is smaller than or equal to 50 mm. 
         [0006]    In accordance with the present invention, the material property in certain regions of the side rail of the invention can be produced with a reliable process and with desired properties. After hot-forming and press-hardening of a steel sheet blank made from high-strength hardenable steel, a particular area of the side rail is targeted to undergo a heat treatment. Heat-treating a particular area of a component, such as the cross member, will hereinafter also be referred to a “partially” heat-treating or “partial” heat treatment of a component or an area of a component. By the partial heat treatment below the austenitic transition temperature, ductile material structures are produced in the heat-treated regions of the side rail. 
         [0007]    According to an advantageous feature of the present invention, in the targeted heat-traded regions an intentional deformation may be facilitated in the event of a crash, without causing cracks to form in these regions or elements to be torn off. The energy dissipation capability of the side rail is hence increased with simultaneously high stiffness. As a result, a large amount of energy is absorbed in a motor vehicle equipped with a side rail according to the invention by converting kinetic energy from the impact into deformation energy, with simultaneously high stiffness of the passenger compartment. The side rail can conceivably also used be as an engine support or in the region of the luggage compartment, where possibly a higher energy absorption capacity is required than in the region of the passenger compartment. By targeted adjustment of the heat-treated region, the heat-treated regions may be applied, for example, in form of zebra stripes which are oriented in the direction of the vehicle over the length of the side rail. In this way, the side rail can fold much like an accordion in the event of a crash. 
         [0008]    According to another advantageous feature of the present invention, the width of the transition zone may be less than 30 mm, currently preferred less than 20 mm. Within the context of the present invention, the transition zone from a heat-treated region to a non-heat-treated region is comparable to a zone affected by heat from a weld seam. Moreover, the material structure is changed in the transition zone which may not always be desirable. 
         [0009]    According to another advantageous feature of the present invention, a small-size transition zone may be created in the side rail according to the invention. A transition zone of less than 15 mm may advantageously be realized on the side rail. Accordingly, those regions on the individual components, in particular on the side rail, which are designed to deform in the event of a crash and those regions which can essentially retain their shape in the event of a crash, can be clearly assigned during the manufacture of a crash-optimized motor vehicle body. 
         [0010]    According to another advantageous feature of the present invention, the width of the heat-treated region may correspond to 0.2-times to 3.0-times the width and/or the height of the heat-treated region. In relation to the distribution of the total stress inside the component, a particularly advantageous embodiment for the crash and stiffness structure of the motor vehicle body is attained. 
         [0011]    According to another advantageous feature of the present invention, joining flanges may be partially heat-treated. The heat-treated region, suitably embodied as joining flange, is advantageous for the crash property and stiffness of the body, such as an exemplary integral body-frame body. A joining flange of a side rail is the region that is coupled with other components. 
         [0012]    A joining flange refers to, for example, the attachment region to the vehicle roof and/or the splash guard, but also to a rocker panel. The coupling can be produced by gluing, riveting, welding, brazing or similar coupling processes. 
         [0013]    The region which has been partially heat-treated does not have a tendency to tear or detach in the event of the accident and therefore holds the surrounding connected structural and safety components together. This particular advantageous for protecting occupants in a passenger compartment. 
         [0014]    Another advantage relates to regions subjected to an intentional deformation in the event of an accident. The regions defined for intentional deformation can be deformed without cracking. This also increases the overall energy absorption capability of the entire motor vehicle body accompanied by a small penetration depth into the passenger compartment. 
         [0015]    Another application is, for example, the intentional deformation of individual regions to reduce the repair costs after an accident. This deformation is intended to transfer energy to be dissipated into the body, thereby once more improving the safety for the vehicle occupants in the event of a crash. 
         [0016]    The regions heat-treated with the method of the invention can deform in the event of a crash so as to produce intentional wrinkles accompanied by absorption of energy. Additionally, the heat-treated regions tend to form less cracks due to their ductile structure compared to the hot-formed and press-hardened, hard and brittle structure. 
         [0017]    The partial heat treatment of joining flanges has the additional advantage that the joining flanges have ductile material properties. With a material connection produced by thermal joining, a structural change takes place in a subsequent process in the zone affected by heat generated by the joining method. A ductile section of the side rail is particularly advantageous for the welding process and the material structure created in the zone affected by heat of the welding process. This is particularly advantageous for the durability of the connected weld seams of the motor vehicle in the event of an accident. 
         [0018]    According to another advantageous feature of the present invention, openings in the side rail may be partially heat-treated. These openings may be incorporated in the component, for example, to reduce weight or for passing through other components, for example a door hinge or wiring harness and the like. Cracks can form in an accident particularly in the region of the openings and also in the end region of openings due to stress in the components, in particular surface stress, which can extend over the entire component. By reducing the surface stress, a ductile material structure is obtained in this region. This counters the formation of cracks and hence also an accidental deformation of the side rail. 
         [0019]    According to another advantageous feature of the present invention, an end region of the side rail may be partially heat-treated, whereas a joining flange arranged on the end region is not heat-treated. This has the advantage that by incorporating the side rail in a motor vehicle body, the heat-treated regions can attenuate loads caused by reverse bending stresses, which may be introduced into the body by, for example, body torsion or other driving parameters, for example drive train vibrations and the like. This has a beneficial effect particularly with respect to the durability of the motor vehicle body by reducing the surface stress in the end regions, positively affecting the required crash properties of the joining flanges connected to the motor vehicle body that are not heat-treated. 
         [0020]    According to another advantageous feature of the present invention, spot-shaped regions of the side rail may be partially heat-treated, wherein the spot-shaped regions have dimensions of less than 50 mm, suitably less than 30 mm. For connecting the side rail to a motor vehicle body, these spot-shaped regions may advantageously be intentionally heat-treated, thereby allowing spot welding or other local laser welding in the spot-shaped regions, as frequently performed in the production of motor vehicles. In the event of a motor vehicle crash, the side rail with the coupled components has again high connection strength in these connected spot-shaped regions. Crack formation or tearing and/or detachment are significantly reduced with the heat-treated spot-shaped regions. 
         [0021]    According to another advantageous feature of the present invention, the heat-treated regions may have a yield strength between 300 N/mm 2  and 1300 N/mm 2 , suitably 400 N/mm 2  to 800 N/mm 2 , currently preferred 400 N/mm 2  to 600 N/mm 2 . In addition, the heat-treated regions may advantageously have a tensile strength between 400 N/mm 2  and 1600 N/mm 2 , suitably 500 N/mm 2  to 1000 N/mm 2 . Currently preferred is a tensile strength of 550 N/mm 2  to 800 N/mm 2 , and advantageously a durability between 10% and 20%, and currently preferred 14% to 20%. The material still has the required high-strength mechanical properties; however, due to the reduced tensile strength, elongation limit and the increased durability the material is sufficiently ductile to produce wrinkles, instead of breaking or tearing, under a suitable load. This advantageously counters potential crack formation in the heat-treated region of the material. 
         [0022]    According to another advantageous feature of the present invention, the yield strength and/or tensile strength may decrease in the transition zone from heat-treated region to non-heat-treated region with a gradient of more than 100 N/mm 2  per 1 cm, suitably of more than 200 N/mm 2  per 1 cm. Currently preferred, the gradient is more than 400 N/mm 2  per  1  cm. Advantageously, very small local regions may be heat-treated, whereas the transition zones are kept smaller in relation thereto. The transition zone resulting from the gradient between the hot-formed and press-hardened, non-heat-treated region and the partially heat-treated region has a therefore a dimension of less than 50 mm, particularly preferred between 1 mm and 20 mm. This produces small local heat-treated regions with sharp edges and smaller transition zones compared to the heat-treated regions. 
         [0023]    According to another advantageous feature of the present invention, the side rail may be partially heat treated by heating the region to be heat-treated to a heat-up temperature, holding the heat-up temperature during a holding time, and cooling down from the heat-up temperature in at least two phases. 
         [0024]    According to another advantageous feature of the present invention, the component may be heated up to and in held at the heat-up temperature in a temperature range between 500° C. and 900° C. The temperature range between 500° C. and 900° C. for heat-up and holding the heat-up temperature intentionally and reliably reduces stress in the heat-treated regions during production. 
         [0025]    According to another advantageous feature of the present invention, heat-up may occur over a time period of up to 30 seconds, suitably of up to 20 seconds or of up to 10 seconds. Currently preferred is a time period of up to 5 seconds. The short heat-up phase for reaching the heat-up temperature is, in combination with a subsequent holding phase, particularly advantageous for the process reliability of the produced component. 
         [0026]    According to another advantageous feature of the present invention, the holding time may extend over a time period of up to 30 seconds. Advantageously, the holding time may extend over a time period of up to 20 seconds, suitably of up to 10 seconds. Currently preferred is a time period of up to 5 seconds. Within the context of the invention, the hardening and tempering process can be particularly reliably performed by intentionally controlling the material structure transformation at a constant temperature and is only affected by the duration of the holding time. The attained heat-up temperature is held substantially constant. 
         [0027]    According to another advantageous feature of the present invention, the first cooldown phase may have a longer duration than the second cooldown phase. This is particularly advantageous for the material structure to be produced and for the related processing steps. The side rail according to the invention can be post-processed immediately following processing. It is therefore feasible within the context of the invention that the heat-treated regions as well as the side rail have a component temperature of 200° C. when transferred to a post-processing process. 
         [0028]    Moreover, the second phase may advantageously be performed in a time period of up to 120 seconds, suitably of up to 60 seconds. 
         [0029]    According to another aspect of the invention, a side rail assembly has a side rail made of a sheet steel. The side rail has a first region which underwent heat treatment, a second region which is not heat-treated, and a transition zone between the first and second regions. The transition zone is defined by a width which is smaller than or equal to 50 mm. The side rail assembly further includes an additional component coupled to the side rail. 
         [0030]    According to another advantageous feature of the present invention, the side rail assembly with the side rail and the coupled component may be partially heat-treated in the coupling regions. This has the particular advantage that the side rail with the coupled regions does not tend to tear off or detach in the event of a vehicle crash. The components coupled to the side rail may include, for example, engine support components. This may be, for example, milled, cast or welded components. 
         [0031]    Another advantage is that engine support components have a longer service life because the coupled regions between the side rail and the motor mount component better attenuate vibrations originating at the engine due to a partial heat treatment. The susceptibility for fatigue cracks at the coupling locations is hereby significantly reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0032]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
           [0033]      FIG. 1  shows a detail of a side rail according to the invention; 
           [0034]      FIG. 2  shows a side rail according to the invention; 
           [0035]      FIG. 3  shows a side rail assembly according to the invention; and 
           [0036]      FIGS. 4   a ),  b ),  c ) show different temperature curves during manufacture of the side rail. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0037]    Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
         [0038]    Turning now to the drawing, and in particular to  FIG. 1 , there is shown a detail of a side rail. As can be seen, a heat-treated region WB according to the present invention is formed in a non-heat-treated region NWB. A transition zone UB is disposed between the non-heat-treated region NWB and the heat-treated region WB. A material structure having the tendency to be ductile is created in the heat-treated region WB, whereas the material structure in the non-heat-treated region NWB is hard and brittle. The transition zone UB is inherently created during treatment of the heat-treated region WB. In the context of the present invention, the transition zone UB has essentially a width a, which extends from the heat-treated region WB to the non-heat-treated region NWB, which is particularly small in relation to the heat-treated region WB and which has substantially sharp edges. 
         [0039]      FIG. 2  shows a side rail  1  according to the invention. The side rail  1  has beads  2 , openings  3  and recesses  4 . The side rail  1  according to the invention has joining flanges  5  in its marginal regions. Depending on the requirements, the beads  2 , openings  3  and recesses  4  and the joining flanges  5  are each partially heat-treated after hot-forming and press-hardening of the side rail  1  according to the invention. 
         [0040]      FIG. 3  shows a side rail assembly  6 . The side rail assembly  6  consists of an upper hot-formed, press-hardened side rail  1  which is partially heat-treated after press-hardening, and a lower hot-formed, press hardened component  7  which is also partially heat-treated after press-hardening. The side rail  1  and the component  7  are coupled to one another at their side regions by way of joining flanges  5 . The coupling locations  8  are, according to the invention, partially heat-treated after the joining process, for example a thermal joining process. 
         [0041]      FIG. 4   a  shows a temperature curve as a function of time, with the time intervals heat-up time (t 1 ), holding time (t 2 ), cooldown time first phase (t 3 ) and cooldown time second phase (t 4 ). Also shown on the temperature axis are the heat-up temperature (T 1 ) and a first cooldown temperature (T 2 ). 
         [0042]    Starting with a blank of sheet steel which is hot-formed and press-hardened to produce a side rail which is essentially at a temperature below 200° C., this vehicle component is heated during the heat-up time to the heat-up temperature (T 1 ). With a starting temperature of below 200° C., but still above room temperature, the residual thermal energy from the hot-forming and press-hardening process is used for the partial heat treatment within the context of the invention. 
         [0043]    Heat-up includes a linear temperature increase as a function of time. After the heat-up time (t 1 ), the heat-up temperature (T 1 ) is maintained during a holding time (t 2 ). The heat-up temperature (T 1 ) is held essentially constant during the entire holding time (t 2 ). Temperature variations in form of a temperature increase or a temperature decrease are not illustrated, but may be implemented within the context of the invention during the holding time (t 2 ) to affect the desired changes in the material structure, but also for cost reasons of the production process. 
         [0044]    At the end of the holding time (t 2 ), a first cooldown to a cooldown temperature (T 2 ) occurs. The temperature hereby decreases linearly during the cooldown time of the first phase (t 3 ) to the cooldown temperature (T 2 ). The cooldown temperature (T 2 ) may be in a range between 100° C. and a heat-up temperature (T 1 ). 
         [0045]    In an immediately following second cooldown phase, an additional linear temperature decrease takes place during the cooldown time of the second phase (t 4 ). The temperature can hereby essentially be lowered to room temperature or to a desired (unillustrated) target temperature. It would also be feasible within the context of the invention to include additional cooldown phases, which are not illustrated. 
         [0046]      FIG. 4   b  shows a substantially similar temporal arrangement of the heat treatment, with the difference to  FIG. 4   a  that the temperature increases progressively during the heat-up time (t 1 ), whereas the temperature steadily decreases with time (t 3 , t 4 ) during the first and second phase of the cooldown. 
         [0047]      FIG. 4   c  shows, in addition to  FIGS. 4   a  and  4   b , that the temperature curve has a diminishing temperature increase during the heat-up time (t 1 ) and that the functional dependence of the temperature decrease over time (t 3 , t 4 ) is progressive during each of the various cooldown phases. 
         [0048]    In the context of the invention, it would also be feasible to combine the temperature dependence over time in mixed forms, such as progressive, linear and diminishing, and to realize a temperature change with progressive, diminishing or linear functional dependence during the holding time (t 2 ). 
         [0049]    While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 
         [0050]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: