Description:PLASTIC ROOF FRONT HEADER FOR REDUCTION OF BOOMING NOISE IN PASSENGER VEHICLE
FIELD OF INVENTION:
[001] The present subject matter described herein, relates to structure of roof front header of a vehicle, and, in particular, to a plastic embedded roof front header structure for reducing booming noise in passenger cabin of the vehicle. BACKGROUND AND PRIOR ART:
[002] In four wheel vehicles, wind shield is positioned in between roof panel and cowl top panel. While upper part of wind shield is mounted with roof front header or roof front cross member and lower part of wind shield glass is mounted on the cowl top panel of the vehicle. The roof front header is provided below the roof panel on which windshield is mounted. The roof front header is connected with front pillar i.e., pillar A of the vehicle from both the ends. Further, the roof front header extends along width direction of the vehicle. The roof front header provides stiffness to the roof panel and support to the windshield.
[003] Common problem in the passenger compartment/cabin is low frequency (30Hz-100Hz) booming noise. The natural frequency of the roof front header usually falls in the driving range, i.e., 40 Hz to 50Hz/ 1200rpm to 1500 rpm.The booming noise is caused due to resonance of cabin acoustic cavity with vehicle body panel. Low frequency structure borne noise generated by powertrain travels thru engine and suspension mounting and excite the body panels like roof, windshield etc. When this engine excitation frequency matches with any of the structure panel’s natural frequency, resonance occurs. These structure panels start vibrating due to which the cabin air gets compressed/decompressed, which cause booming noise. Windshield is one of the major source which causes booming noise, mainly due to vibrations of its mounting region at roof front header. Since the windshield is connected to the front sides of the roof front header, it is necessarily transmitting its vibration to windshield. Further, the natural frequency of the roof front header usually falls in the driving range (40 Hz to 50 Hz/ 1200 rpm to 1500 rpm), it is observed that when engine excitation at matches with natural frequency of roof header, it start vibrating and in-turn windshield start vibrating under resonance. Windshield being a large panel transmits the vibration to air cavity inside cabin. This creates booming noise which is oppressive to occupants.
[004] Japanese Patent Publication 2015003701A titled “Structure of Roof Cross Member Part” relates to a roof front cross member which supports the upper part of wind shield glass which is placed ahead and provided along a vehicle width direction. Further, roof cross member has a hat shaped cross section. An upper edge part of the cross member is formed into an arc shape protruding upward in a vehicle front view and a front edge part of the cross member 6 is formed into an arc shape protruding forward in a vehicle lower view. Left and right end parts of the cross member are joined to a front piller 4 and front and rear end parts of the cross member are joined to the roof panel. In a vehicle width direction center portion of the cross member, a lower edge part is formed into a linear shape in the vehicle front view and a rear edge part is formed into a linear shape in the vehicle lower view. Since the present Japanese patent document provides a hat shaped cross section to the roof front header. It increases the structural complexity and rigidity through change in cross section of roof front header.
[005] Fig. 1, 2, and 3 illustrates addition of mass damper in roof front cross member to reduce booming noise problem as known in the art. In the fig.1, roof front cross member 104 is positioned below the roof panel 102 and windshield 106 is mounted on top of roof panel 102. Hereinafter, the combination of roof front cross member, roof panel, and windshield may be referred as system. In order to reduce the booming noise, an additional mass 108 is added on the roof front cross member 104. By addition of the additional mass 108, the additional mass 108 shifts the natural frequency of the system to a lower value. Generally, natural frequency of any system follows the below relation:
--------------------------------------------------------------(1)
[006] Where fn is natural frequency, k is stiffness, and m is mass. The natural frequency lowers when stiffness is low and mass is more. When the natural frequency of the roof front cross member is shifted to a lower value due to mass addition, the vibration of roof front header is decoupled from the problem/excitation frequency (excitation frequency is the frequency at which the engine/suspension vibrates with high amplitude resulting in transfer of vibrations to structural panels through engine/suspension mounting paths). It results in the reduction of booming noise in the passenger cabin. However addition of mass leads to reduction of fuel efficiency in the vehicle. Further it increases the manufacturing and tooling cost.
[007] Another method for reduction of booming noise in the passenger cabin is addition of reinforcement in the cowl panel. In this method, an additional reinforcement is added in the cowl panel of the vehicle. By application of the reinforcement on the cowl panel, stiffness of the system can be changed. Based on the equation 1, by changing the stiffness, natural frequency of the system can be increased or decreased. Thus by changing the stiffness of the system the natural frequency is shifted to a higher/lower value and results in decoupling from excitation frequency. This results in reduction in booming noise. The addition of reinforcement increases the cost and weight of the vehicle which reduces the fuel efficiency of the vehicle.
[008] Though the above mentioned prior art reduces the booming noise in the passenger cabin as they are intended for, but each has its own drawbacks and limitations. The disadvantage in the above mentioned prior arts is that it increases weight and cost of the system. Therefore, the known systems do not provide degree of freedom for reduction of booming noise without effecting the fuel efficiency and cost in the vehicle. Accordingly, it is desirable to provide a roof front header that is effectively tuned at a frequency which is not in the excitation frequency range in order to reduce booming noise. Therefore, a simple, inexpensive, and effective roof front cross member is required for reduction in booming noise while maintaining the weight and stiffness of the roof front cross member.
OBJECTS OF THE INVENTION:
[009] The principal objective of the present invention is to provide a bolted plastic roof front header for reducing booming noise.
[0010] Another object of the present subject matter is to provide molded plastic roof front header for reducing the booming noise.
[0011] Another object of the present subject matter is to provide a plastic roof front header which is light in weight for reducing the booming noise.
[0012] Yet another object of the present invention is to provide a plastic roof front header which is simple, inexpensive, and efficient to reduce booming noise without increasing weight of the vehicle.
SUMMARY OF THE INVENTION:
[0013] The subject matter disclosed herein relates to a roof front header which is positioned below the roof panel and windshield. The present roof front header is made from plastic material. The present roof front header is of two types 1) bolted type plastic roof front header, and 2) molded type plastic roof front header. In the bolted type plastic roof front header, outer periphery of the roof front header is kept of steel material while inner part of the roof front header is made of plastic. The outer periphery is kept of steel material because it is the place which is used for spot welding of the plastic roof front header with the metal roof panel of the vehicle. The inner part which is made of plastic material is connected with the steel outer periphery by using bolt connections. The plastic part is bolted with the steel part to make complete roof front header.
[0014] In another embodiment of the present subject matter, molded type plastic roof front header reduces the booming noise in passenger cabin. In the molded type plastic roof front header, roof front header is assembled by using the plastic metal hybrid technique (PMH). Through PMH technique, molten plastic is poured over the steel part using injection molding, and the plastic forms an outer envelope which surrounds the steel part and bind the steel part after getting cooled. The present molded type plastic roof front header has plastic around steel at the front periphery (flange). The steel part is provided at front periphery (flange) in the plastic roof front header for spot welding of the plastic roof front header with the roof panel of the vehicle. In the molded type plastic roof front header, the front flange or front periphery is made up of plastic-steel hybrid whereas the rest of the roof header structure is made of only plastic. The front flange or front periphery is kept of hybrid (plastic + steel) due to the requirement of spot welding at that location with the roof panel. The plastic structure of roof front header reduces the stiffness of the roof front header. Due to reduction in the stiffness, the natural frequency of the roof front header shifts to lower value which reduces the amplitude of the vibrations of the roof front header and decouples its natural frequency from problem frequency zone. Due to decoupling of the natural frequency, overall windshield vibrations are reduced and it results in reduction of booming noise levels inside the passenger cabin.
[0015] In order to further understand the characteristics and technical contents of the present subject matter, a description relating thereto will be made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to limit scope of the present subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0017] Fig. 1, 2, & 3 illustrate addition of mass, addition of reinforcements and cross section reduction of roof header respectively, to reduce booming noise problem as known in the art;
[0018] Fig. 4a illustrate structure of bolted type plastic roof front header to reduce booming noise, in accordance with an embodiment of the present subject matter;
[0019] Fig. 4b illustrates cross section of the bolted type plastic roof front header, in accordance with an embodiment of the present subject matter;
[0020] Fig. 4c illustrates structure and construction of the bolted type plastic roof front header, in accordance with an embodiment of the present subject matter;
[0021] Fig. 5a illustrates structure of molded type plastic roof front header to reduce booming noise, in accordance with an embodiment of the present subject matter;
[0022] Fig. 5b illustrates structure and construction of the molded type plastic roof front header, in accordance with an embodiment of the present subject matter;
[0023] Fig. 5c illustrates cross sections of the molded type plastic roof front header, in accordance with an embodiment of the present subject;
[0024] Fig. 6 illustrates graph shows test result which indicates reduction in booming noise in front cabin of vehicle after applying the present plastic roof front header, in accordance with an embodiment of the present subject matter;
[0025] Fig.7 illustrates graph shows test result which indicates reduction in booming noise in rear cabin of vehicle after applying the present plastic roof front header, in accordance with an embodiment of the present subject matter; and
[0026] Fig. 8 illustrates analysis of the natural frequency for roof front header, in accordance with an embodiment of the present subject matter.
[0027] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0028] The subject matter disclosed herein relates to a roof front header which is positioned below the roof panel and windshield. The present roof front header is made from plastic material. The present roof front header is of two types 1) bolted type plastic roof front header and 2) molded type plastic roof front header. In the bolted type plastic roof front header, outer periphery of the roof front header is kept of steel material while inner part of the roof front header is made of plastic. The outer periphery is kept of steel material because it is the place which is used for spot welding of the plastic roof front header with the metal roof panel of the vehicle. The inner part which is made of plastic material is connected with the steel periphery by using bolt connections. The plastic part is bolted with the steel part to make complete roof front header.
[0029] In another embodiment of the present subject matter, molded type plastic roof front header reduces the booming noise in passenger cabin. In the molded type plastic roof front header, roof front header is assembled by using the plastic metal hybrid technique (PMH). Through PMH technique, molten plastic is poured over the steel part using injection molding and the plastic forms an outer envelope around the steel part and bind the steel part after getting cold. The present molded type plastic roof front header has plastic around steel. The steel part is provided in the plastic roof front header for spot welding of the plastic roof front header with the roof panel of the vehicle. In the molded type plastic roof front header, plastic encloses the steel flange from three sides i.e. top, bottom, and rear side. The steel part is extended in the front side at those regions where spot welding of roof header is done with roof panel. Combination of steel and plastic in the roof front header reduces the stiffness of the roof front header. Due to reduction in the stiffness, the natural frequency of the roof front header shifts to lower value and hence gets decoupled from the original excitation frequency or problem frequency. This results in reduction of booming noise levels inside the passenger cabin.
[0030] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0031] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0032] The natural frequency of the roof front header usually falls in the driving range (40 Hz to 50 Hz, 1200 rpm to 1500 rpm) where the excitation forces from the engine are high. In order reduce the booming noise levels in the driving range of vehicle, it is required to shift the natural frequency of the roof front header to a lower value. Natural frequency of a system follows the below relation:
--------------------------------------------------------------(1)
[0033] Where fn is natural frequency, k is stiffness, and m is mass. The natural frequency lowers when stiffness is low and mass is more. The natural frequency of the roof front header couples with the excitation force frequency of the engine due to which resonance occurs. Since the windshield is mounted on top of roof panel under which roof front header is present, the vibration of roof front header causes the windshield to vibrate along with it. Windshield having a large surface area, compresses and decompresses the air cavity inside the cabin. This in turn causes pressure difference which generates booming noise in the passenger cabin, i.e., front cabin and rear cabin.
[0034] In the present invention, the material of the roof front cross member is changed from steel to plastic. The plastic is selected from different range of plastics like NoryIGTX_979, techno_polymer, polypropylene, polyethylene etc.. The stiffness of plastic material is almost 100 times lesser than that of steel due to which the natural frequency of roof front header with plastic material comes to lower than that of steel material. This results in the resonance decoupling of roof front header and in turn the windshield panel from excitation force at that frequency. There are several structural issues which prohibits construction of roof front header with plastic material. The present structure of plastic roof front header is optimized to achieve a structure with stability and lower natural frequency value. The present subject matter illustrate two types of plastic roof front header, i.e., 1) Bolted type roof front header and 2) molded type roof front header.
[0035] Fig. 4a illustrates structure of bolted type plastic roof front header to reduce booming noise, in accordance with an embodiment of the present subject matter. The bolted plastic roof front header 403 is positioned below the roof panel 401 and windshield 402. The bolted plastic roof front header 403 has plastic part 403a and steel part 403b (as illustrated in fig. 4c). The steel part 403b is provided on outer periphery of the bolted plastic roof front header 403. Where the plastic part 403a is provided inside the outer steel periphery of the bolted plastic roof front header 403. The outer steel periphery 403b is used for spot welding of the bolted plastic roof front header 403 with metal sheet of the roof panel 401 of the vehicle. The plastic part 403a is connected with the steel part 403b using bolt connections 404. The plastic part 403a is bolted with the steel part 403b to make complete bolted plastic roof front header 403 and to achieve resonance lesser stiffness which help in shifting the natural frequency of the roof front header to a lower value. Further, the steel part 403b of the bolted plastic roof front header 403 is spot welded with the roof panel 401.
[0036] Fig. 4b illustrates cross section AA of the bolted plastic roof front header 403, in accordance with an embodiment of the present subject matter. From the cross section AA, the complete structure and mounting of the bolted plastic roof header 403 with the roof panel 401 is illustrated. The steel part 403b of the bolted plastic roof front header 403 is mounted on the roof panel 401 through spot welding and plastic part 403a is bolted with the steel part 403b. The windshield 402 is mounted on the roof panel 401.
[0037] Fig. 4c illustrates structure and construction of the bolted plastic roof front header 403, in accordance with an embodiment of the present subject matter. Fig. 4c illustrates exploded view of the bolted plastic roof front header 403. Fig. 4c illustrates combination of the steel part 403b with the plastic part 403a and forms the complete bolted plastic roof front header 403.
[0038] Fig. 5a illustrates structure of molded type plastic roof front header to reduce booming noise, in accordance with an embodiment of the present subject matter. Fig. 5a illustrates another embodiment of the plastic roof front header which can be made using Plastic Metal Hybrid technique (PMH). Similar to the bolted plastic roof front header 403, the molded plastic roof front header 503 is also provided below the roof panel and the windshield. The present molded plastic roof front header 503 has two parts, i.e., plastic part 503a and steel part 503b. Both the steel part 503b and the plastic part 503a are assembled by using the plastic metal hybrid technique (PMH). The plastic part 503a encloses the steel part 503b completely from three sides. The plastic part 503a has cut outs at the front flange which represent the patch at which the spot welding is to be done with roof panel 401. The steel part 503b overlaps with the plastic part 503a over the front flange region. At junction, on the front flange there is a steel part 503b over which the plastic part 503a is poured in molten form and upon cooling solidifies and covers the steel part from top and bottom creating a sandwich section. In the front flange region of molder roof front header 503, there are patches where only steel portion is present. Those are the patches at which spot welding is done. The remaining portion of the front flange of molded type roof front header 503 is hybrid type having a steel and plastic joined together through plastic metal hybrid technique.
[0039] Fig. 5b illustrates structure and construction of the molded type plastic roof front header, in accordance with an embodiment of the present subject matter. Fig. 5b illustrates exploded view of the molded plastic roof front header 503. Fig. 5b illustrates combination of the steel part 503b with the plastic part 503a and forms the complete molded plastic roof front header 503. The molded plastic roof front header 503 is made through PMH technique as explained above. In the PMH technique, molten plastic is poured over the steel part 503b using injection molding and the plastic forms an outer envelope around the steel part 503b and binds the steel part after getting cold. The molded plastic roof front header 503 has plastic around steel part 503b. The steel part 503b is provided in the molded plastic roof front header 503 for spot welding of the molded plastic roof front header 503 with the roof panel of the vehicle.
[0040] Fig. 5c illustrates two cross sections BB and CC of the molded plastic roof front header, in accordance with an embodiment of the present subject. Cross section CC illustrates the area where steel part is connected with the roof panel. Cross section BB illustrates the area where hybrid part (i.e., steel part covered by plastic part) is available. The area where hybrid part is present there is not spot welding of the molded plastic roof front header 503 with the roof panel. In the cross section BB, steel part 503a overlaps by the plastic part 503a and not connection with the roof panel is present. In the cross section CC, plastic part 503a does not cover the steel part 503b which is used for spot welding of the molded plastic roof front header with the roof panel of the vehicle.
[0041] Combination of steel and plastic in the roof front header reduces the stiffness of the roof front header. The stiffness of the plastic material is almost 100 times lesser than that of steel material. Therefore, the plastic roof front header has low stiffness. Due to reduction in the stiffness, the natural frequency of the roof front header shifts to lower value which results in the resonance decoupling of the roof front header from the excitation force at the driving frequency, i.e., 40Hz to 50Hz/1200rpm to 1500 rpm. Reduction in the natural frequency of the roof front header avoids the vibrations in the roof front header at the problem frequency (frequency at which excitation forces from engine are high) which in turn avoids the vibration of windshield at the problem frequency. Therefore, contribution of both roof front header and windshield is reduced and results in reduction of booming noise levels inside the passenger cabin.
[0042] Steel Roof front header has following characteristics:
Young’s modulus = 210 Gpa
Poison’s ratio = 0.3
Density = 7850 kg/mm3
[0043] Plastic Roof front header has following characteristics:
Young’s modulus = 1.8 GPa
Poison’s ratio = 0.46
Density = 950 kg/mm3
[0044] Several tests are conducted to check the impact of the plastic roof front header on booming noise in the cabins of the vehicle. Fig. 6 illustrates a graph indicating reduction in booming noise in front cabin of vehicle after applying the present plastic roof front header, in accordance with an embodiment of the present subject matter. The noise analysis was carried out with roof front header of steel material and roof front header of plastic material. The Computer Aided Engineering (CAE) results for the same are shown in the figure 6 and 7 for front cabin and rear cabin in a vehicle respectively. As shown by the graph of figure 6 and 7, the incorporation of plastic roof front header in place of steel roof front header reduces the booming noise by 4.5 dB(A) to 5 dB(A) in the frequency range of 40 Hz to 50 Hz.
[0045] Further, the operation deflection shape analysis for both the models was done. The results clearly shows that at the problem frequency the roof front cross member with steel material is having higher amplitude of vibration than that of plastic roof front cross member.
[0046] Fig. 8 illustrates analysis of the natural frequency for roof front header, in accordance with an embodiment of the present subject matter. Natural frequency analysis was also done for the roof front header in both steel and plastic model. It was found that the natural frequency of roof front cross member shifts from 44 Hz to 40 Hz which is clearly illustrates in the graph of figure 8.
[0047] By the implementation of plastic material in the roof front header, the natural frequency of the roof front header shifts to a lower value, which can be seen from the natural frequency analysis as shown in figure 8. The amplitude of vibration of roof front cross member is reduced at the problem frequency zone (40 Hz to 45 Hz). Due to this the overall windshield vibration is also reduced and it results in reduction of booming noise levels inside vehicle cabins.
[0048] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.

Claims:We claim:
1. A plastic roof front header (403) for reducing booming noise in passenger cabin of vehicle, the plastic roof front header (403) comprising:
a steel part (403b), wherein the steel part (403b) is provided on outer periphery of the plastic roof front header (403); and
a plastic part (403a) provided in inside the outer periphery of the steel part (403b).
2. The plastic roof front header (403) as claimed in claim 1, wherein plastic has less stiffness as compared to steel.

3. The plastic roof front header (403) as claimed in claim 1, wherein the plastic part (403a) is mounted inside the outer periphery of the steel part (403b).

4. The plastic roof front header (403) as claimed in claim 1, wherein the steel part (403b) is spot welded on roof panel (401) of vehicle.

5. The plastic roof front header (403) as claimed in claim 1, wherein the plastic roof front header (403) material has 1.8 GPa Young’s Modulus.

6. A plastic roof front header (503) for reducing booming noise in passenger cabin of vehicle, the plastic roof front header (403) comprising:
a steel part (503b); and
a plastic part (503a) encloses the steel part (503b) completely from three sides, top, front and rear.

7. The plastic roof front header (503) as claimed in claim 6, wherein the plastic part (503a) has an extended flange at plurality of locations for joining and forming of steel and plastic hybrid section.

8. The plastic roof front header (503) as claimed in claim 6, wherein the plastic part (503a) has front flange which is left un-extended in order to have only the steel part (503b) patch for spot welding with the roof panel (401).

9. The plastic roof front header (503) as claimed in claim 6, wherein the plastic roof front header (503) is assembled using Plastic Metal Hybrid (PMH) Technique.

10. The plastic roof front header (503) as claimed in claim 6, wherein the plastic roof front header (503) reduces booming noise by 4.5 dB(A) to 5 dB(A).

11. The plastic roof front header (503) as claimed in claim 6, wherein the plastic roof front header (503) material has a Poison’s ratio 0.46.