Title of Invention

AN ASSEMBLY FOR STIFFNESS MEASUREMENTS AND A METHOD FOR TORSIONAL AND BENDING STIFFNESS MEASUREMENTS ON A VEHICLE STRUCTURE.

Abstract

The invention provides an asembly for stiffness measurement on a vehicle structure and novel methods to measure pure torsional and pure bending stiffness on the BIW. The assembly and method of this invention incorporates flexibility in adjusting wheelbase and wheel track as per vehicle demand and hence offers liberty to mount vehicle structes of various dimensions. No hydraulic, electrical power packs, control valves are used for rig operations. The assembly according to the instant invention comprises a base frame with a first beam and a second beam mounted at a distance above the frame. The vehicle structure is mounted on the beams. The said beams are independently piovted in the middle and can be fixed or set free as per the required boundry conditions for loading. This provides freedom to change loading and restrained planes in order to take up torsion followed with bending stiffness measurement without altering the test setup and just locking one of the beams and setting the other beam free.

Full Text

FORM 2 THE PATENTS ACT 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION (See Section 10; rule 13) TITLE OF THE INVENTION AN ASSEMBLY FOR STIFFNESS MEASUREMENTS AND A METHOD FOR TORSIONAL AND BENDING STIFFNESS MEASUREMENTS ON A VEHICLE APPLICANTS TATA MOTORS LIMITED, an Indian company having its registered office at Bombay House, 24 Homi Mody Street, Hutatma Chowk, Mumbai 400 001 Maharashtra, India INVENTORS Nitin Harish and Sanjeev Annigeri both Indian nationals of TATA MOTORS LIMITED, an Indian company having its registered office at Bombay House, 24 Homi Mody Street, Hutatma Chowk, Mumbai 400 001 Maharashtra, India PREAMBLE TO THE DESCRIPTION The following complete specification particularly describes the invention and the manner in which it is to be performed. FIELD OF THE INVENTION The present invention relates to an assembly for stiffness measurements on a vehicle structure. The invention also relates to a method of performing stiffness measurements, especially torsional and bending stiffness measurements on the vehicle structure. BACKGROLfND OF THE INVENTION Stiffness (such as torsional and bending) of vehicle structure plays critical role in vehicle's durability, ride and handling and NVH response. Vehicle structure stiffness should be optimized along the wheelbase and wheel track in order to have desired vehicle behavior. Moreover over-design causes the structure to strengthen unnecessarily thereby increasing the cost and on the other hand under-design makes the structure susceptible to warping leading to uncomfortable driving conditions. Torsion and bending stiffness of vehicle structure are significant for the following parameters: a) Road disturbances traverse through suspension as loads and they eventually transfer to the BIW (Body in White) of a passenger car for a monocoque type construction. b) The car structure or body shell must be stiff enough to take up road loads without yielding and at the same time should not be unnecessarily stiff causing an increase in cost. c) From ride and handling point of view in order to have better comfort, the front and rear stiffness values of BIW should be in tune with each other and with respect to suspension stiffness also. 2 d) For better anti-diving and anti-squatting response from the car, total front and rear stiffness must be in good tune with each other. Since major chunk of front and rear stiffness is due to vehicle structure, it becomes mandatory for evaluating it for better handling. e) BIW of a car should not be soft because in that case parking on uneven grounds will affect door opening and closing. f) Car paint durability on BIW is also greatly influenced by the torsional and bending stiffness values of the structure. At present stiffness measurements of vehicle structure are performed along with solid bars replacing suspension or with vehicle suspension components, which are solidified in order to eliminate suspension stiffness addition to the stiffness of the structure. However, the addition of vehicle suspension stiffness to the structure is never fully eliminated because of the local stiffening of the structure between suspension and hard points. Since suspensions change from vehicle to vehicle, using suspension for evaluating stiffness of structure makes it impossible to compare stiffness of two different vehicles. Moreover, for torsional stiffness measurements loading vehicle structure at suspension points induces bending load in the structure thereby adversely affecting the desired pure torsional loading. Further, no dedicated test rig is present for measuring torsion and bending stiffness consecutively. The usual practice is to have a test rig setup for measuring torsional 3 stiffness and then changeover to setup for bending stiffness. Thus lot of time goes waste in aligning the vehicle structure with respect to the test rig. Stiffness measurements for structure (BIW) if done for in-house production vehicles have the location of measurement points (as per vehicle coordinate system) fixed as they can be taken up from CAD data but reporting stiffness values for benchmark vehicles at various structural locations is not possible because of unavailability of CAD data. This lacuna makes comparison of new design with current market designs literally impossible. SUMMARY OF THE INVENTION The present invention provides a novel solution to overcome the disadvantages of the current rig setups in evaluating pure torsional and bending stiffness of vehicle structure (usually called as BIW - Body in White). The invention provides an assembly for stiffness measurement on a vehicle structure and novel methods to measure pure torsional and pure bending stiffness on the BIW. The assembly and method developed according to this invention incorporates flexibility in adjusting wheelbase and wheel track as per vehicle demand and hence offers liberty to mount vehicle structures of various dimensions. Most importantly, no hydraulic, electrical power packs, control valves are used for rig operations. The assembly according to the instant invention comprises a base frame with a first beam and a second beam mounted at a distance above the base frame. The said beams are identical to each other and the vehicle structure is mounted on the beams. The said beams are adjustably spaced apart from each other and are independently gripped by a beam holding plate, such that, depending on the wheelbase of the vehicle under test, 4 the said beams can be brought closer to each other or further away from each other by adjusting the beam holding plate. The said beams are independently pivoted in the middle and can be fixed or set free as per the required boundary conditions for loading. This provides freedom to change loading and restrained planes in order to take up torsion followed with bending stiffness measurement without altering the test setup and just locking one of the beams and setting the other beam free. Another embodiment of the invention is the provision of universal joints provided in the beams used for loading the BIW thereby eliminating the problem of the bending load getting induced in the BIW and thereby ensuring pure torsion to the structure under torsional test. A further embodiment is the provision of slotted plates on the beams. Depending on the wheel track of the vehicle under test, slotted plates are provided on the beams to adjust the assembly, which provides the added advantage of determining the stiffness measurements of various types of vehicles by accommodating a wide range of vehicle structures on just one rig set up. A further embodiment of this invention is the turnbuckle loading arrangement employed to apply load in clockwise or anticlockwise direction with respect to the torsional stiffness measurement test. The turnbuckle is a known device that consists of two threaded eyelets, one screwed into each of a small metal loop, one with a left-handed thread and the other with a right-handed thread. The load can be applied onto the vehicle structure by rotating the loop, which causes both eyelets to be screwed in or out depending on the load required. Thus the provision of the turnbuckle based loading mechanism is simple to operate and avoids the use of any electrical power. 5 Load cells are either provided in or very close to the turnbuckle to record the corresponding loads as applied by rotating the turnbuckle. Further, two cross scales are provided along with laser pointer to mark locations for measurements on BIWs. The laser pointer perpendicular to the slider moves on the Y-scale to locate the required point on the BIW above which it can be marked. This feature gives independence of common reference for comparing BIW stiffness on like-to-like basis at any point on different vehicle structures. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the assembly for mounting vehicle structures according to the invention to perform stiffness measurements. Figure 2 shows the assembly of the invention, setup for the torsional stiffness measurement of the vehicle structure. Figure 3 shows the vehicle structure undergoing torsional stiffness measurement and the corresponding graph of thfftwist angle distribution over the length of the vehicle structure. Figure 4 shows the assembly of the invention, setup for the bending stiffness measurement of the vehicle structure. Figure 5 shows the vehicle structure undergoing bending stiffness measurement and the corresponding graph of the deflection verses wheelbase of the vehicle structure. 6 DETAILED DESCRIPTION OF THE INVENTION The assembly for mounting vehicle structure as per the instant invention will be discussed in the following paragraphs with reference to Figure 1. (Like parts will be referred with like numerals in all figures) The assembly comprises a base frame (B) that is leveled and grouted on concrete ground using rest pads, grouting bolts, shims, spirit level etc. Two base channels (C), parallel to each other are provided within the base frame (B), said base channels comprising either slots or stepped holes to enable adjustment for different wheel base requirements. Two Beam holding plates (IB, IB') are provided, one on each end of the base channels (C). One of the beam holding plates (IB) is slidably attached to the base channels (C) thereby facilitating adjustment of the length of the setup as per the wheelbase of the vehicle. The other beam holding plate (IB') remains fixed at the opposite end of the adjustable beam holding plate (IB). Two loading beams (2A, 2B) independently pivoted at their centers are held in place by the beam holding plates (IB, IB') respectively as shown clearly in figure 1. Slotted plates (1A) are provided on the top of the pivoted beams as shown in figure 1 to provide flexibility in accommodating various vehicle structures having different wheel tracks. The loading beam (2A) is designed such that it is free at one end and the other end is connected to a turnbuckle device (3) so that for the torsional stiffness measurement, torsion can be applied to the vehicle structure with the said device and for the bending stiffness measurement, the said beam (2A) can be locked so as to not move at all. This setup therefore provides two pivoted beams (2A, 2B) that are identical and which can either be fixed or set free as per the required boundary conditions for loading. It is to be noted that the provision of such independent pivoted beams as described above allows torsion and bending stiffness measurements to be performed in succession with 7 minimal time loss for setup change or turning the entire BIW from front to rear. Load sensors (4) are optionally provided on or adjacent the turnbuckle to record the corresponding loads as applied by rotating the turnbuckle. Two Measurement scales (5 A, 5B) are provided to measure the co-ordinates of points on the vehicle structure where stiffness valves are required. The measurement scale (5A) is provided to run alongside the length of the vehicle structure and it measures the distance along the X-axis and the measurement scale (5B) is provided to run along the width of the vehicle and it measures the distance along the Y-axis. A laser pointer (5C) is adapted to locate the above said X and Y distances on the vehicle structure. The assembly according to the present invention is designed in order to make it vehicle BIW independent and the fixtures such as universal joints (6), as per the vehicle suspension mounting location, can be developed and mounted on the setup for measuring different vehicle's stiffness. The assembly for torsional stiffness measurement on the vehicle structure will now be discussed with respect to figure 2. The vehicle structure is represented with the numeral (10) with the vehicle structure's front referred with numeral (10A) and the vehicle structure's rear referred with numeral (10B). The vehicle front (10A) is mounted by means of universal joints (6) on the slotted plates (1A) provided on the loading beam (2A) and the vehicle rear (10B) is fixedly mounted by means of fixed links (7) on the slotted plates (1 A) provided on the restraining beam (2B) The restraining beam (2B) is held fixed by locking the turnbuckles and no torsion is transmitted to this restrained beam. The vehicle structure is therefore held fixed at one end at suspension mounting points and torque is applied at the other end though suspension mounting points by means of turning the 8 turnbuckle arrangement either in the clockwise or anticlockwise direction. This setup of the vehicle structure generally simulates a cantilever beam with torque applied at the free end. Vertical displacements occurring at different points on vehicle structure along the wheelbase are measured using the dial gages (not shown). In broad spectrum, the graph of the twist angle distribution over length of the vehicle structure looks as shown in figure 3. Minimum torsional stiffness Kimm is calculated as follows: From the graph in figure 3 it is clear that the angle of twist for certain torque is changing along the longitudinal axis of the BIW. Hence, torsional stiffness will also vary such that the torsional stiffness will be the least where twist angle is the highest (generally at loading plane). The assembly for bending stiffness measurement on the vehicle structure will now be discussed with respect to figure 4. As mentioned above, the vehicle structure is represented with the numeral (10) with the vehicle structure's front referred with numeral (10A) and the vehicle structure's rear referred with numeral (10B). For the bending stiffness measurement, the front end of the vehicle structure (10A) is mounted on universal joints (6) thereby simulating mounting on a roller-supported beam (2A') and the rear end of the vehicle structure (10B) is mounted on a rear beam (2B') with the help of fixed links thereby simulating mounting on a hinged beam. The turnbuckle arrangement is not turned in this case and is held stationary throughout the experiment. The loads (11, 12, 13 and 14) represent or simulate the weight of the driver, weight of the co-driver, weight of the rear passenger behind the driver and weight of the rear passenger behind the co-driver respectively. Load cells (4) are provided to record the load acting when dead weights 9 (11, 12, 13 and 14) are applied on the vehicle structure. The front end (10A) and the rear end (10B) of the structure are held fixed by locking the turnbuckles at both the ends of the beam. The setup of the vehicle structure in this case is such that the boundary conditions simulate a simply supported beam. The displacements are measured using the dial gages (not shown) at predefined points on the vehicle structure. The graph of the deflection verses wheelbase is shown in Figure 5. Minimum bending stiffness is calculated as follows: From the graph it is clear that the deflection for certain loading pattern is changing along the longitudinal axis of BIW. Hence bending stiffness will also vary. It will be least where deflection is highest, which is generally at the center of the wheelbase. 10 We Claim: 1. An assembly for stiffness measurements on a vehicle structure comprising: a base frame grouted on concrete ground said base frame having at least two base channels parallel to each other disposed within the base frame; an independently pivoted first beam and an independently pivoted second beam on which beams a vehicle structure under test is mounted, said first beam being mounted at a distance above the base frame and said second beam mounted at a distance above the base frame and at an adjustable distance horizontally parallel to the first beam such that the distance between the first and second beam is adjustable depending on the wheelbase of the vehicle; means (1A) to adjust the assembly depending on the wheel track of the vehicle said means being provided on the top surface of the beams; and a loading arrangement to apply load on the vehicle structure depending on the stiffness to be measured. 2. The assembly as claimed in claim 1, wherein the first beam and the second beam are independently gripped by beam holding plates. 3. The assembly as claimed in claim 1 and 2, wherein the base channels comprise slots or stepped holes at least partially along the length of the base channels; one of the said beam holding plate being slidably attached to the base channels by means of said slots or stepped holes and the other beam holding plate being fixedly attached to the base channels, to facilitate adjustment of the length of the assembly depending on the wheelbase of the vehicle structure. 4. The assembly as claimed in claim 1, wherein the means to adjust the assembly depending on the wheel track of the vehicle comprises slotted plates. 11 5. The assembly as claimed in claim 1, wherein the loading arrangement is a turnbuckle loading arrangement employed to apply load at one end of the beam in clockwise and/or anticlockwise direction when the vehicle structure is under torsional stiffness measurement test and is provided to remain stationary and locked when the vehicle is under bending stiffness measurement test. 6. The assembly as claimed in any one of the preceding claims, wherein it comprises universal joints on the first beam for loading the vehicle structure. 7. The assembly as claimed in claim 5, wherein load cells are provided in the vicinity of the loading arrangement to record the corresponding loads applied on the vehicle structure. 8. The assembly as claimed in any one of the preceding claims, wherein two cross scales are provided along with a laser pointer to mark the locations for deflection measurements on vehicle structures due to the torsional or bending load. 9. A method for measuring the torsional stiffness of a vehicle structure, said vehicle structure comprising a front end and a rear end and said method comprising the steps of: mounting the front end of the vehicle structure by means of universal joints on the slotted plates provided on the first beam; fixedly mounting the rear end of the vehicle structure by means of fixed links on the slotted beams provided on the second beam; locking the turnbuckle so that no torsion is transmitted to the rear end through the second beam; 12 applying torque by means of the turnbuckle on the front end of the vehicle structure by turning the turnbuckle arrangement either in the clockwise or anticlockwise direction; recording the load acting when the said torque load applied to the vehicle structure using load cells; determining the minimum torsional stiffness based on the torque load recorded by the load cells. 10. The method as claimed in claim 9, wherein the minimum torsional stiffness is determined by the following relation (units - KNm/deg): where, KTmin is the minimum torsional stiffness; T is the torque load applied on the structure 0L is the twisting angle at the loading plane (front end) 9R is the twisting angle at the restrained plane (rear end) 11. A method for measuring the bending stiffness of a vehicle structure, said vehicle structure comprising a front end and a rear end and said method comprising the steps of: mounting the front end of the vehicle structure by means of universal joints on the slotted plates provided on the first beam such that the front end is envisaged to be mounted on a roller-supported beam; mounting the rear end of the vehicle structure with fixed links on the second beam such that the rear end is envisaged to be mounted on a hinged beam; 13 locking the turnbuckle arrangement at both ends of the beam such that the front end and the rear end of the structure remain fixed; applying loads at predetermined points in the vehicle structure such that the loads simulate at least the weight of the driver, the weight of the co-driver, the weight of the rear passenger behind the driver and the weight of the rear passenger behind the co-driver; recording the load acting when the said weights are applied to the vehicle structure using load cells; determining the minimum bending stiffness based on the load recorded by the load cells. 12. The method as claimed in claim 11, wherein the minimum bending stiffness is determined by the following relation (units - (N/mm): Dated this 3 day of A uqusy 2006. where, KBmin is the minimum bending stiffness L is the load applied to the vehicle structure Z„,„ is the maximum deflection. TATA MOTORS LIMITED By their Agent & Attorney (Karuna Goleria) of DePENNING & DePENNING

Documents:

1226-mum-2006-abstract(22-07-2008).doc

1226-mum-2006-abstract(22-07-2008).pdf

1226-mum-2006-cancelled pages(22-07-2008).pdf

1226-mum-2006-claims(granted)-(22-07-2008).doc

1226-mum-2006-claims(granted)-(22-07-2008).pdf

1226-mum-2006-claims.doc

1226-mum-2006-claims.pdf

1226-mum-2006-correspondence(22-07-2008).pdf

1226-mum-2006-correspondence(ipo)-(19-09-2008).pdf

1226-mum-2006-correspondence-received.pdf

1226-mum-2006-description (complete).pdf

1226-mum-2006-drawing(22-07-2008).pdf

1226-mum-2006-drawings.pdf

1226-mum-2006-form 1(03-08-2006).pdf

1226-MUM-2006-FORM 1(23-7-2008).pdf

1226-mum-2006-form 2(granted)-(22-07-2008).doc

1226-mum-2006-form 2(granted)-(22-07-2008).pdf

1226-mum-2006-form 3(03-08-2006).pdf

1226-mum-2006-form 5(03-08-2006).pdf

1226-mum-2006-form 8(22-07-2008).pdf

1226-mum-2006-form-1.pdf

1226-mum-2006-form-2.doc

1226-mum-2006-form-2.pdf

1226-mum-2006-form-26.pdf

1226-mum-2006-form-3.pdf

1226-mum-2006-form-5.pdf

1226-mum-2006-power of attorney(03-08-2006).pdf

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