Automatically regulated belt stretching device

Abstract: An engine (11) equipped with driving belts (13) is provided with an automatically regulated belt stretching device (10), arranged in the vicinity of one belt (13), mounted on a support (12) fixed to the engine (11). The device (10) comprises a pin (16) extending from the support (12) and defining a longitudinal axis (17), said pin (16) being provided with a pair of shoulders (21,22) at a distance from one another, between which two bushings (23) are inserted, said bushings (23) being adapted to define, together with the pin (16), a pair of housings (27), springs (28) capable of displacing the bushings (23) relative to the shoulders (21,22) and to the longitudinal axis (17) of the pin (16) being housed therein. A bearing which (25) rotates in contact with one belt (13) is provided on the outer surface of each bushing (23).

Description: This invention relates to an automatically regulated belt stretching device. It is known that the transmission of motion from the drive shaft to the cam shafts is effected by means of cogged belts manufactured in such a way that after an initial permanent set, they become virtually non-deformable. The engine casings produced today are manufactured from light aluminium alloys having a high coefficient of thermal expansion. Consequently, during the operation of an engine and as a result of the variations in temperature to which said engine is subjected, there are considerable variations in the distance between the centres of the shafts on which the belt operates. These variations occur as the engine passes from a heating phase to a temperature control phase and then to the cooling phase following stoppage of said engine. These variations then lead to substantial changes with respect to the initial tension of the belt and thus to disadvantages during the operation thereof, such as noise and excessive or insufficient tension. FR-A-2 058 815 describes a tensioning device for belt transmission, having the features indicated in the preamble of claim 1. This known belt stretching device is not destined particularly to be used in an engine and it does not take into account changes of the belt tension due to temperature variation. Hydraulically operated stretchers using the engine oil are also known, which, in spite of the accuracy of assembly and construction, may have operating defects, such as oil losses, noise, possible seizure and high costs. The object of this invention is to propose a belt stretching device of a simple construction, the operation of which does not require pressurised fluids and complex moving components, such as levers and springs, but which can nevertheless obviate the disadvantages of the known prior art. This problem is solved in the case of an engine equipped with driving belts provided with an automatically regulated belt stretching device as claimed in claim 1. According to this invention, said device is thermally coupled to said engine by means of said support, said support transmitting heat to said elastic means. In particular, the elastic means consist of a plurality of leaf springs forming a group in each of said housings. The leaf springs according to this invention are of the type having form storage as a function of the temperature reached. In a preferred embodiment according to this invention, each group of leaf springs consists of four springs. Sealing means are provided in an end portion of said shoulders, between these shoulders and said bushings. The said pin, between said shoulders and in correspondence with said bushings, has a square section and said shoulders, said bushings and said elastic means are held on said pin by means of a nut engaged in a threaded end portion of said pin. The features and further advantages of this invention will be clear from the following description, which is given by way of a non-limiting example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a device according to the invention in contact with part of the driving belt of an engine; Figure 2 is a section along the line II-II of Figure 1, and Figures 3, 4 & 5 show details from Figure 2 in different arrangements. With reference to the drawings, a belt stretching device according to the invention is designated in general by the reference numeral 10, said device 10 being fixed to an engine 11 by means of a support 12. The device 10 is mounted in the vicinity of a belt 13 driven by pulleys 14. The belt can be of the type having a V-shaped or cogged section and in any case defines its one smooth surface 13a. As already stated, the device 10 consists of the support 12, fixed to the engine by means of appropriate bolts 15, a pin 16 extending vertically from said support and defining a longitudinal axis 17, a first portion 18, an intermediate portion having a square section 19 and an end threaded portion 20 on to which a nut 31 can be screwed. The pin 16 is provided with a pair of shoulders 21 and 22, spaced at a distance from the intermediate portion 19 of said pin. Two bushings 23 are inserted between this pair of shoulders on opposite sides of the intermediate portion of the pin 16 having a square section 19, in such a way that they can be displaced. Sealing elements 24 are provided between the bushings 23 and the shoulders 21 and 22, both at the top and at the bottom. The bushings 23 have a bearing 25, the outer surface 26 of which is smooth and is in contact with the flat surface of the belt 13. In addition to defining the section of Figure 2, the line II-II of Figure 1 represents an axis 35 along which the centre of rotation of the bearing 25 is displaced. The belt 13 is preferably in contact with the bearing tangentially in correspondence with or in the vicinity of this axis 35. The shoulders 21 and 22 and the bushings 23 define at either side housings 27 between which springs 28 having substantially the shape of a plate and being of the type having form storage as a function of the temperature reached are inserted. The elements are held on the pin by the nut 21 and the pin is fixed to the support 12. The device 10 according to this invention can be thermally coupled to the engine by means of the support 12 and can transmit heat from the engine to the form storage springs 28. Depending on the temperature reached, said springs assume various configurations, shown in Figures 3, 4 and 5. In a preferred embodiment according to this invention, four springs having form storage are inserted into each housing 27, Figure 3 showing an arrangement with hypothetical temperatures of less than 0 o C, Figure 4 showing an arrangement with hypothetical temperatures of between 0 and 20 o , and Figure 5 showing the arrangement of the same springs at the operative temperature (warm engine 60 - 100 o C). By virtue of this belt stretcher, which is completely free of any hydraulic connections and which therefore does not use any pressurised fluid, the displacement of the bearing 25 can be effected by means of the stresses applied to one or both of the bushings 23 by the springs 28 having form storage. According to the changes in the arrangement of the form storage springs, the centre of rotation of the bearing 25 is displaced along the axis 35 and with respect to the longitudinal axis 17 (normal to the axis 35) of the pin 16, thereby allowing said bearing to transmit more or less stress to the flat surface 13a of the belt according to the temperature reached by the engine and therefore according to the expansion it undergoes. The elastic characteristics of the form storage springs according to this invention are in any case sufficient to apply satisfactory tension to the belts used at present, resulting overall in a device which is reliable, of simple construction and economically advantageous.

Claims: An engine (11) equipped with driving belts provided with an automatically regulated belt stretching device (10) arranged in the vicinity of one belt (13) and mounted on a support (12) fixed to said engine (11), said device (10) comprising a pin (16) extending from said support (12) and defining a longitudinal axis (17), said pin (16) being provided with a pair of shoulders (21,22) at a distance from one another and bushing means (23) which are adapted to define, together with said pin (16), a pair of housings (27), elastic means (28) capable of displacing said bushing means (23) relative to said shoulders (21,22) and to said longitudinal axis (17) of said pin (16) being housed therein, said bushing means (23), moreover, on their outer surfaces with respect to said housings (27), having a bearing (25) in contact with a flat surface (13a) of said one belt (13), characterised in that said bushing means (23) comprise two bushings which are inserted between said shoulders (21,22), said device (10) being thermally coupled to said engine (11) by means of said support (12), said support (12) transmitting heat to said elastic means (28) which are of the type having form storage as a function of the temperature reached. Belt stretching device (10) according to claim 1, characterised in that said elastic means (28) consist of a plurality of leaf springs (28) forming a group in each of said housings (27). Belt stretching device (10) according to claim 2, characterised in that each group of leaf springs (28) consists of four springs (28). Belt stretching device (10) according to claim 1, characterised in that sealing means (24) are provided in an end portion of said shoulders (21,22), between these shoulders (21,22) and said bushings (23). Belt stretching device (10) according to claim 1, characterised in that the said pin (16), between said shoulders (21,22) and in correspondence with said bushings (23), has a square section (19) and said shoulders (21,22), said bushings (23) and said elastic means (28), are held on said pin (16) by means of a nut (31) engaged in a threaded end portion (20) of said pin (16). Belt stretching device (10) according to claim 1, characterised in that said flat surface (13a) of said belt (13) is in contact with said bearing (25) tangentially and in the vicinity of an axis (35) along which said bearing (25) is displaced by the action of said elastic means (28).

Inventors: PATTANO PIETRO, PATTANO, PIETRO
Applicants: FIAT AUTO SPA, FIAT AUTO S.P.A.
Application year: 1991
Main classification: F16H7
IPC codes: F16H7