Apparatus for a test of passing a wheel comprising a rim and a tyre over an obstacle

Abstract: An apparatus for a test of passing over an obstacle of a wheel (2) provided with a tyre (4) comprises a road-wheel (1) supporting a relief (100), a steering knuckle (6) capable of rotatably supporting a hub (5) and the wheel (2), and two suspension arms (8, 9) supporting the steering knuckle (6). The apparatus also comprises a first, second, third and fourth leaf spring (10, 11, 12, 13) connected to the suspension arms (8, 9) and to a supporting frame (15), a fifth leaf spring (14) connected to the steering knuckle (6) and to the supporting frame (15) and a pneumatic spring (40) in engagement with the steering knuckle (6) and with the supporting frame (15). First and second acceleration transducer means (48, 49) associated with the hub (5) provide measurements of natural frequencies and dampenings of the tyre (4) in a radial and in a longitudinal direction. The apparatus can be used both in the movable-hub mode and in the fixed-hub mode.

Description: The present invention relates to an apparatus for a test of passing over an obstacle of a wheel comprising a rim and a tyre. A test used to determine the characteristics of a tyre is that of passing over an obstacle. Such test is used to detect natural frequencies and dampenings of a tyre in a vertical direction and in a horizontal direction, that is to say in the plane of the wheel. To this day, the used test of passing over an obstacle used is of the indoor type, with a fixed hub on a road wheel. The tests consists in mounting the wheel on a dynamometric hub and squeezing it, with an imposed vertical load, against a road-wheel rotating at preselected speeds having a relief of a preselected shape that constitutes the obstacle. The excitation to which the tyre is subjected, in the fixed-hub test, is the deformation imposed by the obstacle when the tyre passes over it at a certain speed. The obstacle, in relation to the forward speed of the wheel, excites the natural motions of the tyre (excitation of the impulsive type), that starts to vibrate with its natural frequencies. After a more or less short time these vibrations are dampened. The methodology consists, then, in the analysis of the free dampened oscillations of the tyre at different forward speeds. The signals variable over time, detected at the fixed hub, are those of the longitudinal and vertical force, that are depending on the excitation provided by the obstacle, on the forward speed of the wheel and on the natural frequencies of the tyre in the plane of the wheel. Four natural modes of the tyre, known as "rigid" modes, are highlighted by the fixed-hub test of passing over an obstacle. During the test the signals of force, longitudinal and vertical, after the obstacle has abandoned the tyre are analyzed over time, and the natural frequencies and the dampenings are identified with techniques of analysis or mathematical models (for example the Prony or Ibrahim model) for signals of the impulsive type. The final results are the curves of the natural frequencies and of the dampenings of the four vibration modes of the tyre (that is, those modes ranging from 30 Hz to 130 Hz) against the forward speed. Thus, overall, eight experimental curves are obtained against the speed: four of the natural frequencies and four of the dampenings. In the traditional test of passing over an obstacle, the condition of constraint of the wheel of the fixed hub (equivalent to a hinge in the plane of the wheel) does not allow the highlighting of the natural modes of the wheel wherein the hub is free to oscillate in the vertical and longitudinal direction. Such natural modes, on the other hand, are present in a motor car under 30 Hz (≈ 14 Hz in a vertical direction, ≈ 20 Hz in the longitudinal direction). The object of the present invention is an apparatus that allows the analysis of the natural modes of a tyre in a range of frequencies from 0 Hz to 130 Hz. The above mentioned object is achieved, according to the invention, with an apparatus for a test of passing over an obstacle of a wheel comprising a rim and a tyre, said apparatus being usable under the condition of movable hub and comprising a road-wheel rotating at preselected speeds, supporting a relief with a preselected shape forming said obstacle, a hub to which said rim of said wheel is fastened, a steering knuckle capable of rotatably supporting said hub and said wheel, first and second acceleration transducer means associated with said hub capable of measuring natural frequencies and dampenings of said tyre in a radial and in a longitudinal direction, characterized in that it comprises two suspension arms supporting said steering knuckle, a first, second, third and fourth leaf spring having respective first ends fastened to a respective suspension arm and respective second ends connected to a supporting frame by means of respective adjustable first, second, third and fourth fastening means capable of varying the length of each leaf spring to adjust its stiffness and to change the longitudinal stiffness of said suspension arms, a fifth leaf spring having a first end fastened to said steering knuckle and a second end connected to a shoe by means of fifth adjustable fastening means capable of varying the length of said fifth leaf spring to adjust its stiffness and to change the radial stiffness of said suspension arms, and a pneumatic spring in engagement with said steering knuckle and with said supporting frame, said pneumatic spring being capable of giving an initial radial preload to said tyre, said preload being equivalent to a share of weight of a vehicle that bears upon a wheel. According to a preferred embodiment, said apparatus comprises clamping elements capable of being engaged with said first ends of said first, second, third and fourth leaf springs to clamp said suspension arms in a longitudinal direction, said fifth leaf spring being shortenable so as to clamp said suspension arms in a radial direction so as to attain a condition of fixed hub. The apparatus according to the invention acts like a "passive suspension" and simulates the behaviour of the suspension of a vehicle, wherein the excitation at the hub of the wheel is given by an obstacle placed on the road wheel, that transmits the forces to the hub through the tyre. In the apparatus it is possible to adjust the stiffness of the suspension in a vertical and longitudinal direction, and thus the two values of the natural frequencies of the suspension (radial and longitudinal) by varying the stiffness of the leaf springs through displacements of the point at which the leaf springs engage the supporting frame so that the frequencies of the unsuspended masses of the "simulator" (passive suspension) coincide with those of the vehicle under examination. Thus, the apparatus allows to have values of the frequencies of the suspension equal to those of the vehicle under examination (of which the comfort is to be optimized). While with the traditional test of passing over an obstacle performed with the condition of constraint of the fixed-hub wheel four natural modes of the tyre are highlighted, called "rigid" modes, with the test with a hub that is movable, in a longitudinal and a radial direction, it is possible to highlight two more natural modes, one in a radial direction, the other in a longitudinal one, that are those so-called of "suspension", that fall in the frequency interval of 0 - 30 Hz. From the movable-hub test of passing over an obstacle are thus obtained six natural modes of the tyre, that translate into six curves of the natural frequencies and of the corresponding dampenings against the forward speed. Features and advantages of the invention will now be illustrated with reference to an embodiment represented as a non-limiting example in the enclosed drawings, wherein: Fig. 1 is a front view of an apparatus for a test of passing over an obstacle of a wheel, made according to the invention; Fig. 2 is a side view of the apparatus of Fig. 1, Fig. 3 is a rear view of the apparatus of Fig. 1. There is shown in Figs. 1, 2 and 3 an apparatus for a test of passing over an obstacle of a wheel, made according to the invention. The apparatus comprises a road-wheel 1 provided with a relief 100 of a preselected shape, forming an obstacle. A wheel 2, comprising a rim 3 and a tyre 4, is fastened to a hub 5, rotatably supported by a steering knuckle 6, so that its tyre 4 remains in contact with the road-wheel 1. The road-wheel 1 rotates thanks to an electric motor, not shown, and causes the tyre 4 to rotate. The steering knuckle 6 is connected by means of pins 7 to two superimposed suspension arms 8 and 9, substantially triangular that form a quadrilateral suspension. The suspension arms 8 and 9 are supported by sleeves 150 and 151 in a supporting frame 15 by means of pins 80 and 90. Four leaf springs 10, 11, 12 and 13 connect the arms 8 and 9 to the supporting frame 15. The leaf springs 10, 11, 12 and 13 are formed by laminas substantially parallel to the sides of the suspension arms 8 and 9. The leaf springs 10, 11, 12 and 13 have one end 101, 111, 121 and 131, respectively, fastened to the arms 8 and 9 by means of threaded stems of the pins 80 and 90 and respective nuts 16. The leaf springs 10, 11, 12 and 13 have another end 102, 112, 122 and 132, respectively, connected to walls 152 and 153 of the frame 15 by means of a spacer 18, 19, 20 and 21, respectively, and an adjustable bolt 22, 23, 24 and 25, respectively. When the bolts 22, 23 24 and 25 are loosened, their threaded stems can slide in respective slots 26, 27, 28 and 29, obtained in the walls 152 and 153 and extending in a direction orthogonal to the plane of the wheel 2, to adjust the anchoring point of the leaf springs 10, 11, 12 and 13 with respect to the frame 15. This way, it is possible to vary the stiffness K2 of the leaf springs 10, 11, 12 and 13 and, thus, the longitudinal stiffness (arrow 64) of the suspension arms 8 and 9. The two arms 8 and 9 are the same and the respective pairs of leaf springs 10, 11 and 12, 13 are also the same and connected in the same way to the arms 8 and 9 and to the frame 15. A leaf spring 14 is interposed between the steering knuckle 6 and the frame 15. The leaf spring 14 is formed by a lamina substantially parallel to the plane of the suspension arms 8 and 9. The spring 14 has one end 141 fastened to a support 30, integral with the steering knuckle 6, by means of a bolt 31 and has another end 142 connected to a shoe 32 by means of a spacer 33 and an adjustable bolt 34. By loosening the bolt 34, its threaded stem can slide in a slot 35 obtained in the shoe 32 and extending in a direction orthogonal to the plane of the wheel 2 to adjust the point of anchoring of the leaf spring 14 with respect to the frame 15. This way, it is possible to vary the stiffness K1 of the leaf spring 14 and, thus, the radial stiffness of the suspension arms 8 and 9. The shoe 32 is fitted in a slot 36 obtained in a wall 154 of the frame 15 and extending parallel to the plane of the wheel 2 by means of a spacer 37 and an adjustable bolt 38. When the bolt 38 is loosened, its threaded stem can slide in the slot 36 in a radial direction (arrow 65) so as to align the leaf spring 14 with the axis of rotation 50 of the wheel 2. A pneumatic spring 40 is interposed between the support 30 and a wall 155 of the frame 15. The spring 40 can be adjusted and is used to give an initial radial preload to the tyre 4 of a value equivalent to a share of weight of a vehicle that bears upon the wheel. The frame 15 is slidably supported in a base 41 by means of swallow-tailed slide guides 42 extending in a radial direction. The frame 15 is driven to slide along the guides 42 by a forward actuator 47 comprising a forward shaft 43, provided with a worm thread, that engages with a corresponding threaded hole 44 of the frame 15. The shaft 43 is rotatably supported in a bracket 45 that prevents its axial translations and is driven to rotate by means of a driving handwheel 46 (arrow 60). While the shaft 43 rotates, the frame 15 slides in a radial direction to adjust the position of the wheel 2 with respect to the road-wheel 1. It is thus possible to move the tyre 4 toward the road-wheel 1 and away from it (double arrow 61) in order to carry out the removal of the tyre and to move it up against the road wheel before giving the radial preload with the pneumatic spring 40. To the hub 3 of the wheel 2 there are fastened two radial and longitudinal acceleration transducers 48 and 49, consisting of linear accelerometers. The accelerometer 48 measures the accelerations in a longitudinal direction (parallel to the peripheral velocity vector of the tyre), the accelerometer 49 measures the accelerations in a radial direction (perpendicular to the axis of rotation of the road wheel and of the wheel with the tyre). The frame 15 is provided with four bolts 51 that are used to clamp the ends 101, 111, 121 and 131 of the leaf springs 10, 11, 12 and 13, fastening the arms 8 and 9 with respect to the frame 15 in a longitudinal direction. This allows to obtain the condition of a hub fixed in the longitudinal direction. When the length of the leaf spring 14 is shortened to its maximum extent it is possible to have a high stiffness of the suspension in the radial direction so as to obtain the condition of a hub fixed in that direction as well. During the movable-hub test of passing over an obstacle, the road-wheel 1 drives the wheel 2 to rotate (arrow 62) and the obstacle 100, depending the forward speed of the wheel 2, excites the natural motions of the tyre 4 that starts to vibrate with its natural frequencies, oscillating on the axis 50 (double arrow 63). The vibrations of the tyre 4 are dampened after a more or less short time and at the hub 3, by means of accelerometers 52 and 53 the signals are detected, variable over time, of the longitudinal and vertical forces. These signals are depending on the excitation given by the obstacle, on the forward speed of the wheel and on the natural frequencies of the tyre in the plane of the wheel. The dampened free oscillations of the tyre are analyzed at different forward speeds and six natural motions of the tyre are highlighted, in a field of frequencies ranging from 0 Hz to 130 Hz. These natural motions are translated into six experimental curves of the natural frequencies and of the corresponding dampenings with the forward speed.

Claims: An apparatus for a test of passing a wheel over an obstacle, the wheel (2) comprising a rim (3) and a tyre (4), said apparatus being usable under the condition of movable hub and comprising a road-wheel (1) rotating at preselected speeds, supporting a relief (100) with a preselected shape forming said obstacle, a hub (5) to which said rim (3) of said wheel (2) is fastened, a steering knuckle (6) capable of rotatably supporting said hub (5) and said wheel (2), first and second acceleration transducer means (48, 49) associated with said hub (5) capable of measuring natural frequencies and dampenings of said tyre (4) in a radial and in a longitudinal direction, characterized in that the apparatus further comprises two suspension arms (8, 9) supporting said steering knuckle (6), first, second, third and fourth leaf springs (10, 11, 12, 13) having respective first ends (101, 111, 121, 131) fastened to a respective suspension arm (8, 9) and respective second ends (102, 112, 122, 132) connected to a supporting frame (15) by means of respective adjustable first, second, third and fourth fastening means (22; 23; 24; 25) capable of varying the length of each leaf spring (10, 11, 12, 13) to adjust its stiffness and to change the longitudinal stiffness of said suspension arms (8, 9), a fifth leaf spring (14) having a first end (141) fastened to said steering knuckle (6) and a second end (142) connected to a shoe (32) by means of fifth adjustable fastening means (34) capable of varying the length of said fifth leaf spring (14) to adjust its stiffness and to change the radial stiffness of said suspension arms (8, 9), and a pneumatic spring (40) in engagement with said steering knuckle (6) and with said supporting frame (15), said pneumatic spring (40) being capable of giving an initial radial preload to said tyre (4), said preload being equivalent to a share of weight of a vehicle that bears upon a wheel, so as to attain a condition of movable hub. An apparatus according to claim 1, characterized in that it comprises clamping elements (51) capable of being engaged with said first ends (101, 111, 121, 131) of said first, second, third and fourth leaf springs (10, 11, 12, 13) for clamping said suspension arms (8, 9) in a longitudinal direction, said fifth leaf spring (14) being shortenable so as to clamp said suspension arms (8, 9) in a radial direction so as to attain a condition of fixed hub. An apparatus according to claim 1, characterized in that said shoe (32) is mounted in said supporting frame (15) in a manner slidable in the radial direction so as to position said fifth leaf spring (14) coaxial with said wheel (2), further adjustable fastening means (38) being associated with said shoe (32) so as to fasten it with respect to said supporting frame (15). An apparatus according to claim 1, characterized in that said supporting frame (15) is slidably supported in a base (41) by means of sliding guides (42) having radial direction and is in engagement with forward actuator means (47) capable of changing the position of said supporting frame (15) in said radial direction and of adjusting the position of said wheel (2) with respect to said road-wheel (1).

Inventors: DI BERNARDO CARLO, MANCOSU FEDERICO, MATRASCIA GIUSEPPE, DI BERNARDO, CARLO, MANCOSU, FEDERICO, MATRASCIA, GIUSEPPE
Applicants: PIRELLI, PIRELLI PNEUMATICI
Application year: 1996
Main classification: G01M17
IPC codes: G01M7, B60C19, G01M17