Abstract:
Disclosed is a method for manufacturing a crash pad for vehicles. In the method, a surface material is inserted into an upper mold. A base material of a liquefied resin is supplied through a loading aperture of a lower mold. A shape of a molded product of the crash pad including the surface material and the base material is maintained by combining the upper mold and the lower mold together and then cooling thereafter. The molded product is taken out from a mold after separating the upper mold from the lower mold.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2011-0088747 filed Sep. 1, 2011, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    (a) Technical Field 
         [0003]    The present invention relates to a method for manufacturing a crash pad for vehicles. More particularly, it relates to a method for manufacturing a crash pad for vehicles through rear low-pressure injection-molding. 
         [0004]    (b) Background Art 
         [0005]    Generally, a vacuum molding process and a powder molding process (e.g., powder slush molding) are widely used in manufacturing of crash pads for vehicles to which soft foam skin is applied. However, the above processes are costly due to expensive manufacturing processes and numerous process steps thereof. Therefore, it is difficult to economically justify their application low-cost vehicles. 
         [0006]    Accordingly, a hard plastic type crash pad is being applied to low-priced vehicles. However, since this type of crash pad has little texture, and has much need for improvement in quality, especially seeing that soft foam is so effective 
         [0007]    In order to improve the quality of the hard-type crash pad, as shown in  FIG. 1 , a process has been developed in which polypropylene foam  3  is laminated on thermoplastic olefin skin  2  to form a surface material  1 , and then the surface material  1  and a polypropylene base material are bonded to and laminated on each other. 
         [0008]    Referring to  FIG. 2 , in a method for manufacturing a crash pad using soft foam skin, the surface material  1  is inserted into a mold, and is pre-heated for vacuum molding, and then a base material  5  is injection-molded at a lower temperature from a separate mold  6 . Thereafter, an adhesive is coated on the base material  5 , and then the surface material  1  and the base material  5  are bonded to each other. Finally, products are taken out of the mold through a piercing process. 
         [0009]    However, in the above process, a bonding process between the surface material  1  and the base material  5  is necessary and takes quite a long time to complete. Furthermore, the bonding process is harmful to environment due to the use of a separate oil-based adhesive. To overcome the above limitation, it is possible to insert a surface material in which polypropylene foam is laminated on thermoplastic olefin skin into a mold and then integrally form a base material. 
         [0010]    Hereinafter, a method for manufacturing a crash pad through rear low-pressure injection molding according to a related art will be described with reference to  FIG. 3 . 
         [0011]    The surface material  1  is inserted into the mold  6 , and, when the mold  6  is opened, a molten resin  5 , having a temperature of about 150° C. and including compositions such as polypropylene and thermoplastic olefin, is injected onto the rear side of the surface material  1  at a low temperature. Thereafter, when the mold  6  is closed, the molten resin  5  that has been injection-molded at a low temperature is compressed on the polypropylene foam  3  of the surface material  1  to integrally form the base material  5  and the surface material  1 . However, when the heat-resistance of the polypropylene foam  3  of the surface material  1  to which the molten resin  5  is injection-molded is low, rupture, depression, and bending may occur on the surface material  1 , deteriorating the exterior of the surface material  1 . On the other hand, when the heat-resistance of the polypropylene foam  3  is high, there is no rupture or depression but the surface quality such as its cushion or softness may be reduced. 
         [0012]    In addition, as shown in  FIG. 4 , the polypropylene foam  3  may be melted and compressed by the heat and injection pressure of the molten resin  5 . Accordingly, the thickness of the polypropylene foam  3  may be reduced to a ratio of about 0.6 or less after the molding than before the molding, and the recovery rate of the foam may be reduced. Generally, since two or more gates  7  are dispersedly disposed to injection-mold these large parts (e.g., a crash pad, gas generated from the molten resin  5  as shown in  FIG. 5  may concentrate between the gates  7  during compression by the mold  6 . In this case, surface swelling such as bending may occur at an interface between the surface material  1  and the base material  5 . 
         [0013]    For this reason, polyethylene foam or thermoplastic olefin foam may be used in a foam layer instead of polypropylene foam to improve the surface quality (e.g., cushion and softness). In this case, however, rupture or depression may increase. Also, cloth can be used in the foam layer instead of polypropylene foam. However, the structure of the surface cloth may be transcribed on the surface after the molding, deteriorating the exterior and reducing the perceived quality. When a thermoplastic olefin protection film is laminated on an injection surface of foam to prevent the rupture or bending of foam of good surface quality, the flow of high-temperature resin from the injection gate part may be deteriorated, increasing surface bending after the rear low-pressure injection molding. 
         [0014]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE DISCLOSURE 
       [0015]    The present invention provides a method for manufacturing a crash pad for vehicles, which reduces manufacturing time and complexity by integrally forming a base material through low pressure injection molding without a separate bonding process after inserting a surface material into a mold. 
         [0016]    The present invention also provides a method for manufacturing a crash pad for vehicles, which minimizes the damage of a surface material and maximizes the recovery rate of the surface material by minimizing the pressure and heat applied to a polypropylene foam (soft foam) during integral formation of a base material and the surface material using a high-density foam layer under the soft foam of the surface material, and prevents swelling of the exterior of a surface material by absorbing gas generated from a molten resin of the base material. 
         [0017]    In one aspect, the present invention provides a method for manufacturing a crash pad for vehicles, including: inserting a surface material into an upper mold; supplying a base material of a liquefied resin through a loading aperture of a lower mold; maintaining a shape of a molded product of the crash pad including the surface material and the base material by combining the upper mold and the lower mold together and then cooling thereafter; and removing the molded product from a mold after separating the upper mold from the lower mold. 
         [0018]    In an exemplary embodiment, the method may further include vacuum-compressing the surface material on an internal surface of the upper mold by releasing air inside the upper mold through an air outlet of the upper mold before supplying the base material after inserting the surface material. 
         [0019]    In another exemplary embodiment, the surface material may include a surface layer and a foam layer laminated on a rear surface of the surface layer. The foam layer may include an upper layer contacting the real surface of the surface layer and having a low-density structure, and a lower layer of a high-density structure to which a molten resin is injected. The lower layer may block heat and pressure of the molten resin. 
         [0020]    Other aspects and exemplary embodiments of the invention are discussed infra. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present invention, and wherein: 
           [0022]      FIG. 1  is a cross-sectional view illustrating a surface material of a crash pad for vehicles according to a related art; 
           [0023]      FIG. 2  is a schematic view illustrating an exemplary method for manufacturing a crash pad for vehicles according to a related art; 
           [0024]      FIG. 3  is a schematic view illustrating another exemplary method for manufacturing a crash pad for vehicles according to a related art; 
           [0025]      FIG. 4  is a photograph illustrating a surface material compressed by pressure and heat of a molten resin in the related art; 
           [0026]      FIG. 5  is a schematic view illustrating swelling of a surface material caused gas concentration in a related art; 
           [0027]      FIG. 6  is a schematic view illustrating a method for manufacturing a crash pad for vehicles according to an exemplary embodiment of the present invention; 
           [0028]      FIG. 7  is a cross-sectional view illustrating a structure of a crash pad for vehicles according to an exemplary embodiment of the present invention; 
           [0029]      FIG. 8  is a view illustrating a method for manufacturing a crash pad for vehicle according to an exemplary embodiment of the present invention; and 
           [0030]      FIG. 9  is a cross-sectional view illustrating absorption of gas generated from a molten resin at a lower layer of a foam layer during molding compression. 
       
    
    
       [0031]    Reference numerals set forth in the Drawings includes reference to the following elements as further discussed below:
         10 : surface material     11 : surface layer     12 : upper layer     13 : lower layer     14 : mold     14   a : upper mold     14   b : lower mold     15 : gate     16 : base material     17 : air outlet     18 : foam layer       
 
         [0043]    It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various exemplary features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
         [0044]    In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
       DETAILED DESCRIPTION 
       [0045]    Hereinafter reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0046]    It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles. 
         [0047]      FIG. 6  is a schematic view illustrating a method/process for manufacturing a crash pad for vehicles according to an embodiment of the present invention.  FIG. 7  is a cross-sectional view illustrating a structure of a crash pad for vehicles according to an embodiment of the present invention. The present invention relates to a method for manufacturing a crash pad for vehicles, which improves heat-resistance of a surface material  10  and satisfies both the exterior quality and the perceived quality by manufacturing a crash pad through rear low-pressure injection-molding. By perceived quality it is meant the degree of cushion or softness which a surface exhibits or the degree to which a material yields to pressure or weight. 
         [0048]    The method for manufacturing a crash pad may include inserting a surface material  10  into a mold, injection-molding a base material  16  at a low pressure, and removing a product. First, the surface material  10  may be inserted into an upper mold  14   a . In this case, the surface material  10  may be pre-heated if necessary. The surface material  10  of the crash pad may include a surface layer  11  and a foam layer  18 . The foam layer  18  may be formed to have a multi-layer structure, thereby overcoming depression, bending, and rupture of the surface during injection molding and improving the surface perceived quality (e.g., degree of cushion or softness) even after the injection molding. Thus, the surface material  10  is both heat-resistive and of high perceived quality, both of which are problems in the previous designs discussed above. 
         [0049]    For this, the foam layer  18  disposed on the other side of the surface layer  11  may include two or more types of olefin polymer-based foam that have different foaming ratios or types and are stacked on each other. The types of olefin polymer-based foam may include olefin-based thermoplastic elastomer (TPE) including at least one of polypropylene, polyethylene, polypropylene copolymer or terpolymer including C 2  or C 4 ˜C 12 -α-olefins, and polyethylene copolymer or terpolymer including C 2  or C 4 ˜C 12 -α-olefins. Also, the olefin polymer-based foam may include at least one of styrene-based TPE, urethane-based TPE, ester-based TPE, amide-based TPE, and vinyl acetate-based TPE at a content of 50% or less to improve the physical properties of a sheet. 
         [0050]    When the foam layer  18  is configured to have a multi-layer including an upper layer  12  and a lower layer  13 , the lower layer  13  contacting an injection resin  16  may include foam having a high heat-resistance, and the upper layer  12  combined with the surface material  10  to thereby affect the perceived quality may include foam having a better perceived quality such as increased cushion characteristics. 
         [0051]    As shown in  FIG. 7 , the surface material  10  of the crash pad for vehicles according to the embodiment may include the surface layer  11  and the foam layer  18 . In this case, the surface layer  11  may include one of thermoplastic olefin sheet, polyvinyl chloride sheet, PVC alloy sheet, and polyurethane sheet, which are commonly used as interior materials for vehicles. 
         [0052]    The TPO sheet may include olefin-based thermoplastic elastomer (TPE) including at least one of polypropylene, polyethylene, polypropylene copolymer or terpolymer including C 2  or C 4 ˜C 12 -α-olefins, and polyethylene copolymer or terpolymer including C 2  or C 4 ˜C 12 -α-olefins. The TPO sheet may include at least one of styrene-based TPE, urethane-based TPE, ester-based TPE, amide-based TPE, and vinyl acetate-based TPE at a content of about 0.1 wt % to about 50 wt % to improve the physical properties of a sheet, and may further include an irradiation cross linking process to improve the emboss maintenance and the surface abrasion characteristics. In this case, scratch-resistance, durability, chemical-resistance, and abrasion-resistance can be further improved by further coating chlorinated polypropylene-based resin, acryl-based resin, and urethane-based resin on the surface of the surface layer  11 . 
         [0053]    The foam layer  18  may be formed in a multi-layer, and in this embodiment, may have a multi-layer structure including an upper layer  12  and a lower layer  13 . However, the foam layer  18  may have three layers including an upper layer  12 , an intermediate layer, and a lower layer  13 , or more. Particularly, when the foam layer  18  is formed in a multilayer, foams having different foaming ratios or types may be used. Since the upper layer  12  is combined with the surface material  10  constituting the surface layer  11  and the affects the perceived quality, the upper layer  12  may be formed using PP/PE/TPO foam for vacuum molding. 
         [0054]    Also, since the lower layer  13  comes in contact with a high-temperature injection resin  16 , the lower layer  13  may be formed using PP foam for injection-molding, which has an excellent heat-resistance. For this, TPE foam may be used as the foam layer  18 . Particularly, the foam may include olefin-based thermoplastic elastomer (TPE) including at least one of polypropylene, polyethylene, polypropylene copolymer or terpolymer including C 2  or C 4 ˜C 12 -α-olefins, and polyethylene copolymer or terpolymer including C 2  or C 4 ˜C 12 -α-olefins. Also, the foam may include at least one of styrene-based TPE, urethane-based TPE, ester-based TPE, amide-based TPE, and vinyl acetate-based TPE at a content of 50% or less to improve the physical properties of a sheet. 
         [0055]    Also, the upper layer  12  may be foamed at a ratio of about 5 to about 50 to improve the perceived quality during injection-molding, and the lower layer  13  may be foamed at a ratio of about 1 to about 30 to improve the heat-resistance. 
         [0056]      FIG. 8  is a view illustrating a method for manufacturing a crash pad for vehicle according to an exemplary embodiment of the present invention.  FIG. 9  is a cross-sectional view illustrating absorption of gas generated from a molten resin at a lower layer of a foam layer during molding compression. Here, the foaming ratio relates to the density of the foam. The foaming ratio is in inverse proportion to the density. 
         [0057]    The upper layer  12  may be formed with a low-density foam structure to increase the surface perceived quality of a crash pad. The lower layer may be formed with a high-density foam structure to block heat and pressure of a molten resin  16  injected onto the surface material  10  during injection-molding. Thus, the thickness of the foam layer  18  can be preserved, and the deviation of the thickness according to locations of the foam layer  18  can be minimized. Also, the recovery rate of the foam can be increased due to the high-density foam layer  18 . For example, the improvement of the recovery rate of the foam layer  18  due to the lower layer  13  of the high-density structure shows that the thickness of the foam layer  18  after molding increases about 0.8% or more compared to that before molding. 
         [0058]    The lower layer  13  of the high-density structure may absorb gas generated from the molten resin  16  to prevent swelling and bending of the surface material  10  due to gas concentration between existing gates. The material of the high-density foam may include a PP foam material or a polar polymer material identical to the base material  16  for smooth joining with the base material  16 , and may include a material containing homo-PP by about 10 wt % or more to improve the heat-resistant effect of the product. In addition, the foaming thickness of the upper layer  12  may range from about 0.5 mm to about 9.5 mm so as not to affect the surface perceived quality, and the lower layer  13  may also range from about 0.5 mm to about 9.5 mm to endure the temperature of injected resin. 
         [0059]    The foaming ratio, material type, and thickness may vary according to the molding conditions of the injected resin and the surface perceived quality satisfaction. Particularly, the thickness of the foaming layer  18  including the upper layer  12  and the lower layer  13  may range from about 1 mm to about 10 mm. The reason why the thickness of the foam layer  18  is limited to the above range is that when the thickness of one layer becomes 0.5 mm that is the minimum maintenance condition of the foam layer  18 . For example, if the upper layer  12  is maintained under about 0.5 mm, the surface perceived quality may be reduced when combined with the surface material  10 . Additionally, if the lower layer  13  is maintained under about 0.5 mm, it cannot endure the temperature (about 150° C. to about 250° C.) of the injected resin  16 , which may incur bending, depression, and rupture during the injection-molding. Accordingly, the foam layer  18  must have a thickness of about 1 mm or more. More specifically, in the above example, the 1 mm range relates to the thickness of the foam layer  18 , which consists of two layers (i.e., the upper layer  12  and the lower layer  13 ). Therefore, one half of 1 mm, i.e., 0.5 mm becomes the new range for the upper layer or the lower layer individually. 
         [0060]    When the thickness of the foam layer  18  exceeds about 10 mm, reduction of sharpness of a corner part after molding, deviation from other assemblies, and rises in costs may occur. Accordingly, the foam layer  18  must have a thickness of about 10 mm or less. 
         [0061]    The injected resin (molten resin  16  for base material) may be injected onto an undersurface of the lower surface layer  13 , i.e., the foam layer  18  of the surface material  10  through the gate  15  of an injection machine in a state where the injected resin is melted at a temperature of about 150° C. to about 250° C. Furthermore, since the foam cannot be injected in different foam ratios and materials at the same time, a separate combining process is required to laminate different foams. The laminating method may include thermal laminating, adhesive laminating, and hot-melt-type laminating, most preferably, thermal laminating. 
         [0062]    When the surface layer  11  is combined with the upper layer  12  of the foam layer  18  through thermal laminating, the temperature of the surface layer  11  directly before the laminating has to be maintained at least about 50° C. to about 300° C. to prevent foliation after molding. The surface material  10  may be inserted into an upper mold  14   a , and then, if necessary, the internal air of the upper mold  14   a  may be exhausted to allow the surface material  10  to be vacuum-compressed on a target surface inside the upper mold  14   a  and simultaneously supply the base material  16  of a liquefied resin state to an upper surface through a lower mold  14   b . When the mold  14  is in an open state, the liquefied resin  16  may be injected onto the surface material  10  through the gate  15 . Here, an air outlet  17  may be formed in the upper mold  14   a  to exhaust air. When air inside the upper mold  14   a  is exhausted by a vacuum pump (not shown), the surface material  10  may be vacuum-compressed on the undersurface of the upper mold  14   a.    
         [0063]    Also, a hot runner nozzle is disposed in the lower mold  14   b  to supply the base material  16  of a liquefied resin, and the base material  16  of the liquefied resin supplied from the hot runner nozzle may include PP or TPO resin that is olefin resin, but embodiments are not limited thereto. 
         [0064]    Next, the upper mold  14   a  may be downwardly combined with the lower mold  14   b . Here, the liquefied resin  16  supplied to the lower mold  14   b  may be formed into a mold shape of the mold  14  to form the base material  16 , and also integrally formed with the surface material  10  that is not yet cooled, without a separate adhesive. 
         [0065]    Thereafter, the upper mold  14   a  may rise and the formed crash pad part may be separated from the lower mold  14   b . The crash pad part may be processed through piercing so as to have a proper size, thereby taking out an interior material that has been completely molded. Here, the piercing process may be identical to a typical piercing process used for molding of an interior material for vehicles, and detailed description thereof will be omitted. 
         [0066]    Hereinafter, the present invention will be described in more detail based on the following embodiment, but the present invention is not limited thereto. 
       EXAMPLE 
       [0067]    The following examples illustrate the invention and are not intended to limit the same. A crash pad for vehicles according to an embodiment may include a surface layer  11  and a foam layer  18 . The surface layer  11  may be configured by the same method as a typical method, and the foam layer  18  may be manufactured in a structure in which the upper layer  12  formed of PP/PE/TPO foam material for vacuum molding, having a high foaming ratio (e.g., about 15 or more) is laminated on the lower layer  13  formed of PP foam material for injection molding, having a lower ratio (e.g., about 15 or less) and a high heat-resistance. 
       Test Example 1 
       [0068]    The lower layer of the foam layer is formed with the same multilayer structure as Embodiment 1 except that the lower layer is formed of TPO/PP/PE sheets. 
       Test Example 2 
       [0069]    The foam layer is formed in a single layer structure of PP foam for injection molding, and the surface layer is formed using the same configuration as a typical one. 
       Test Example 3 
       [0070]    The foam layer is formed in a single layer structure of PP/PE/TPO foam for vacuum molding, and the surface layer is formed using the same configuration as a typical one. 
       Test Example 4 
       [0071]    The foam layer is formed in a single layer of cloth (e.g., nonwoven, fabric, etc), and the surface layer is formed using the same configuration as a typical one. 
         [0072]    In order to check the rupture, depression, bending, thickness deviation, and surface perceived quality characteristics after injection molding, a sample of the same size and condition was manufactured, and the characteristics were verified during the above process, and the result thereof is expressed as Table 1. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 Surface exterior 
                   
               
               
                   
                   
                   
                 after injection 
                 Surface perceived 
               
               
                   
                   
                 Rupture/depression 
                 molding (surface 
                 quality after 
               
               
                   
                 Type of foam 
                 during injection 
                 bending, thickness 
                 injection molding 
               
               
                 Division 
                 layer 
                 molding 
                 deviation) 
                 (cushion/softness) 
               
               
                   
               
             
             
               
                 Example 
                 Upper layer: 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                   
                 PP/PE/TPO foam 
               
               
                   
                 for vacuum 
               
               
                   
                 molding 
               
               
                 Test Example 1 
                 Upper layer: 
                 ◯ 
                 X 
                 ◯ 
               
               
                   
                 PP/PE/TPO foam 
               
               
                   
                 for vacuum 
               
               
                   
                 molding 
               
               
                 Test Example 2 
                 PP foam for 
                 ◯ 
                 ◯ 
                 X 
               
               
                   
                 injection molding 
               
               
                   
                 (high 
               
               
                   
                 heat-resistance, 
               
               
                   
                 low ratio: 15 or 
               
               
                   
                 less) 
               
               
                 Test Example 3 
                 PP/PE/TPO foam 
                 X 
                 X 
                 ◯ 
               
               
                   
                 for vacuum 
               
               
                   
                 molding (high 
               
               
                   
                 ratio: 15 or more) 
               
               
                 Test Example 4 
                 Cloth (nonwoven, 
                 ◯ 
                 X 
                 X 
               
               
                   
                 fabric, etc.) 
               
               
                   
               
             
          
         
       
     
         [0073]    In Table 1, O represents that there are no rupture, depression, surface bending and thickness deviation, and the surface perceived quality is excellent. X means the opposite of O. 
         [0074]    As shown in Table 1, the embodiments of the present invention complemented limitations of typical foam layers  18 , and verified injection-molding (no rupture and depression), the exterior surface after the injection molding, and the surface perceived quality after the injection molding are good. 
         [0075]    In light of the above method, the present invention advantageously reduces manufacturing costs and complexity of the overall process since the surface material and the base material can be bonded without a separate bonding process by integrally forming the base material on the surface material by a rear low-pressure injection-molding method. Furthermore, since a high-density foam layer is inserted between a base material and a surface material of a crash pad to which soft foam is applied, and the high-density foam layer blocks pressure and heat of resin during injection molding, the thickness of the surface material can be preserved, and the deviation of the thickness according to its location can be minimized, thereby improving the recovery rate of the foam. In addition, the high-density foam layer can prevent swelling and bending of the surface material caused by gas concentration between gates in a related art, by absorbing gas generated from a molten resin. Thud, it is possible to improve the exterior of the surface by preventing depression, rupture, and bending of the surface material, and also improve the surface perceived quality such as cushion or softness even after injection molding. 
         [0076]    The invention has been described in detail with reference to exemplary embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.