WO2012143219A1 - Belt tensioner - Google Patents

Abstract

The invention relates to a belt drive having a driving belt pulley (6), one or more driven belt pulleys (7, 8, 9, 10), a driving belt (13) entwining the belt pulleys with pre-tension and a belt tensioner (14) having a tensioning roller (17), a housing (18), a piston (19) mounted in a longitudinally movable manner therein and a threaded compression spring (20) generating the belt pre-tension by means of the belt tensioner, the spring characteristics thereof being coordinated to the length change of the belt tensioner within an operating range of the tension roller, wherein the nominal first outer operating position (A₁) and the nominal second outer operating position (A₂) of the tension roller are predetermined in consideration of dimensional component tolerances and thermally dependent dimension changes in the belt drive. For the purpose of improved wear resistance of the belt tensioner, according to the invention the operating range of the tension roller should comprise a predetermined center operating position (A_M) in which the coils of the screw compression spring are twisted against each other so that the number of effective spring coils substantially equals n=i+0.5, wherein i is a natural number.

Description

 tensioner

The invention relates to a belt drive, comprising a driving pulley, one or more driven pulleys, a belt tensioned with belt pulleys and a belt tensioner with a tensioning pulley, a housing, a longitudinally movably mounted in the housing piston and the belt prestressing by means of the tensioning roller generating A helical compression spring, the force applied to the housing and the piston in the direction of extension of the belt tensioner and whose spring characteristic is tuned to the change in length of the belt tensioner within an operating range of the tension roller. The nominal first external working position and the nominal second external working position of the tensioning roller are predetermined under consideration of dimensional component tolerances and thermally induced dimensional changes in the belt drive.

Background of the Invention A belt tensioner to be considered in the context of the invention is composed of a linear tensioner and typically a roller lever which converts the longitudinal force resulting from the helical compression spring of the linear tensioner into belt tension via the tensioning roller mounted on the roller lever. Generic linear tensioner for ancillary belt drives of internal combustion engines, as they are basically known from WO2009 / 074566 and DE 10 2008 057 041 A1, consist to a large extent of plastic parts, to which the housing and the longitudinally movably mounted piston and expediently also between Include housing and piston arranged slide bearing. In some belt drive specific layouts, however, after a short period of operation, severe wear on these contact partners can be observed, which is due to the oscillating longitudinal movement of the piston in the housing in conjunction with excessive transverse forces in the linear adjuster. Object of the invention

The present invention has for its object to improve a belt drive of the type mentioned in view of the required wear resistance of the bearings in the belt tensioner. Summary of the invention

The solution of this problem arises from the characterizing features of claim 1, while advantageous developments and refinements of the invention, the dependent claims can be removed. Accordingly, the working range of the tension roller should comprise a predetermined average working position, in which the turns of the helical compression spring are twisted against each other so that the number of effective spring turns is substantially n = i + 0.5. Where i is a natural number. In other words, in this working position, the number of effective spring turns should be half-integer, so that the two ends of the effective turns and consequently the effective support points of the spring are offset by (ideally exactly) 180 °. Due to the then correspondingly offset longitudinal force introduction into the piston and the housing, the resulting torques have the same direction of rotation and, given correspondingly low transverse bearing forces, do not cause any appreciable deflection of the linear tensioner in the region of the longitudinal mounting. Behavior of the helical compression spring: Investigations by the applicant have shown that the initial and the final turn of the spring-loaded helical compression spring against the immediately adjacent turns, the so-called transition turns twist. During spring deflection, the contact points between the start and end turns and the associated transition winding twist, and at the same time, the mutual contact angles of these turns increase, so that the actual number of intermediate effective turns depends on the instantaneous clamping length of the spring and spring length , ie decreases with increasingly tense spring. In this respect, the inventive design of the belt drive applies, according to which the ends the effective spring coils are opposed by about 180 °, strictly speaking, only for the predetermined mean working position of the tension roller, while the spring has a different number of effective turns in the other working positions of the tension roller. Conversely, an integer number of effective spring coils, ie n = i, would result in the effective support points of the spring ends facing each other without angular offset, with their eccentricity from the spring longitudinal axis to torques with opposite direction of rotation and wear-promoting lateral bearing forces at the then correspondingly longitudinal deflection would lead the piston in the housing. However, this effect could also be exploited in accordance with wear-resistant design of the bearings and the sliding bearing to increase the transverse force-induced bearing friction in the linear clamp targeted. Thus, the overall damping of the belt tensioner could be maximized either with unchanged pivot point friction of the roller lever or modified with adapted pivot point friction.

In an advantageous embodiment of the invention, the average working position of the tensioning roller should be spaced symmetrically on the one hand to a nominal installation position of the tension roller and on the other hand to the first outer working position. The nominal installation position corresponds to the component nominal dimensions or mean dimensions of the belt drive relative to room temperature (20 ° C.), and the first external working position corresponds to the maximum permissible component tolerance position of the belt tensioner in conjunction with the hot operation of the belt drive. The selected average working position corresponds to a mean operating position of the tensioning roller (and thus a clamping length of the helical compression spring), in which rather the belt drive is operated most frequently when new. The there due to the tightly tensioned helical compression spring comparatively high stress on the belt tensioner decreases with increasing operating time of the belt drive, since the belt tensioner extends with increasing permanent elongation of the belt and accordingly adjusting tensioner in the direction of smaller spring force. Although the number of effective spring turns increases and leaves the ideal value of n = i + 0.5, this will accordingly compensating bending moment on the longitudinal positioning of the piston in the housing compensated by the simultaneously decreasing force level of the relaxing spring. Ideally, therefore, the wear-causing stress of the contact points in the longitudinal storage over the service life of the belt drive decreases overall.

An advantageous spring characteristic of the helical compression spring can be chosen such that the number of effective spring coils between the two outer working positions increases by a maximum Δη = 0.5 when the helical compression spring moves from the first external working position towards the second external working position their operational travel expands. In this case, the second outer working position of the tension roller corresponds to the maximum length of the belt tensioner component tolerance position in conjunction with the cold operation of the belt drive.

Another torque source that can stress the longitudinal bearing wear-generating transverse forces, the accuracy of the transverse guidance of the helical compression spring on the spring supports of the housing and piston. Consequently, these are in connection with the Federmaßen and their dimensional tolerances as possible to make so that the helical compression spring is centered at least approximately free of play and coaxial to the longitudinal axis of the belt tensioner. Brief description of the drawings

An embodiment of the invention is illustrated in the figures and described below. Show it:

Figure 1 shows the layout of a belt drive to drive the ancillaries of a

 Internal combustion engine; the belt tensioner according to Figure 1 in a perspective view;

Figure 3 is a known spring diagram of a helical compression spring; Figure 4 shows the torsional behavior of a helical compression spring under load;

Figure 5 shows the spring forces on the belt tensioner in not inventive design of the belt drive and

Figure 6 shows the spring forces on the belt tensioner in the inventive design of the belt drive.

Detailed description of the drawings

Figure 1 shows an accessory belt drive of an internal combustion engine, not shown. The belt drive comprises a driving pulley 6, which is arranged on the crankshaft of the internal combustion engine, and driven pulleys 7 to 10, which are arranged on the ancillaries (generator, air compressor, power steering pump, coolant pump), pulleys 1 1, 12 and one of the pulleys. 6 to 10 and the pulleys 1 1, 12 with bias winding belt 13 and a belt tensioner 14 to generate the belt pretension. The principle known in its structural design belt tensioner 14 is shown in an enlarged view of Figure 2. The belt tensioner 14 is composed of a linear tensioner 15 and a roller lever 16 with tensioning roller 17 mounted thereon. The linear tensioner 15 comprises a housing 18, a piston 19 mounted longitudinally movably therein, and a cylindrical helical compression spring 20 clamped between the housing 18 and the piston 19 and acting in the direction of extension of the linear tensioner 15. The housing 18 and the piston 19 are provided with fastening eyes 21, 22, wherein the first eye 21 on the housing 18 for stationary pivotal mounting of the linear tensioner 15 on the internal combustion engine is used and wherein the second eye 22 on the piston 19 (see Figure 6) for pivotal pivotal connection of the linear tensioner 15 with the roller lever 16 is used. The stationary by the internal combustion engine pivot point 23 of the roller lever 16 is provided with a friction bushing which dampens the vibrations in the belt drive during pivotal movements of the roller lever 16. For longitudinal storage of the piston 19 in the housing 18 is an axially supported on the piston 19 slide bushing 24 (see sectional view of Figure 6). As further shown in Figure 2, the spring-loaded linear tensioner 15 is axially held together outside of the belt drive by a pin 25 which is mounted in the piston 19 and movably disposed in an axial pin stop forming slot 26 of the housing 18. The piston 19, the housing 18 and the pin 25 are made of glass fiber reinforced polyamide and the sliding bush 24 made of temperature-resistant polyamide.

The wear resistance of the longitudinal bearing now depends essentially on the directions in which the helical compression spring 20 forces - and consequently torques - in the spring supports 27, 28 of the housing 18 and the piston 19 in the different operating positions of the tension roller 17 initiates and how strong the case are to be supported transverse forces / deformation in the longitudinal storage. A spring characteristic according to the invention will be explained starting from FIGS. 3 and 4. FIG. 3 shows, for a cylindrical helical compression spring 20, the wire height above the spring seat (ordinate) as a function of the wire length coordinate zeta (ζ) which runs along the spring turns (abscissa) according to the right-hand spring sketch. This typical course of the wire height results from the different pitches of the individual turns: with 1 and 5, the initial and the final turn are designated;

- with 2 and 4, the respective subsequent transition turns are designated and

- with 3, the mean turns between the transition turns are designated. As is indicated in FIG. 4 for a real helical compression spring 20 by means of arrows, the spring 20 exciting shortening (ie in FIG. 3, the wire height would decrease at ζ = L _D ) results in a torsion of the start and end turns 1 and 5 with respect to FIG respectively associated transition winding 2 or 4. Die Long arrows symbolize the shortening of the spring 20, while the curved arrows each mark the circumferentially wandering contact point 29, 30 between the spring ends 1, 5 and the associated transition winding 2 and 4 respectively. Since these contact points 29, 30 not only travel, but also form with increasing spring travel at the same time to an increasing line contact, the number of momentarily resilient, ie effective turns is variable and decreases with increasing deflection. Concomitantly causes the wandering in the circumferential direction of the contact of the start and end turns 1 and 5 to the associated transition winding 2 and 4, a longitudinal force support of the helical compression spring 20 with varying circumferential angles to the spring supports 27, 28 of the housing and piston.

Figure 5 shows the internal forces and the resulting internal torques in the linear tensioner 15 ', with which the helical compression spring 20' acts on the piston 19 and the housing 18 in a non-inventive tuning of the spring characteristic. Shown is the responsible for heavy wear of the longitudinal mounting installation extreme of the helical compression spring 20 ', in which the number of effective turns is integer and, for example, n = 5. Accordingly, the contact and support points of the spring ends at the same circumferential angles on the spring supports 27, 28, and designated with F ' _L Auflagerlängskräfte the spring 20' are on the same line of action eccentric to the longitudinal axis 31 of the linear tensioner 15 '. The eccentricity is additionally increased by a measure which results from a centering of the helical compression spring 20 'on the two spring supports 27, 28 carried out with a large radial play. The eccentric Auflagerlängskräfte F ' _L lead in conjunction with the Auflagerquerkräften F' _Q to the designated M ' _L torques, due to their opposite direction of rotation as a longitudinal storage of the piston 19 in the housing 18 comparatively strongly deforming and oscillating in the high-frequency operation of the linear tensioner 15 'quickly wear the bending moment. A linear tensioner 15 with inventive tuning of the helical compression spring 20 is shown in FIG. An essential first difference is here selected number of effective spring coils in a predetermined operating position of the tension roller 17, as explained below with reference to Figure 1. According to the invention, the number of effective spring coils in a predetermined nominal working position of the tensioning roller 17 is half-payable and, for example, n = 5.5. In this case, the contact and support points of the spring ends extend at 180 ° offset circumferential angles on the spring supports 27, 28, and designated with F _L Auflagerlängskräfte the spring 20 are on two maximum spaced lines of action and also eccentric to the longitudinal axis 31 of the linear tensioner 15. A second difference relates to the clear and here to zero reduced radial clearance in the spring centering on the two spring supports 27, 28. The opposite 180 ° and not additionally eccentric lack of radial play Auflagerlängskräfte F _L lead in conjunction with the here oppositely directed Auflagerquererkäften F _{Q to} the with M _L designated torques. These act due to their now same direction of rotation as a longitudinal deformation of the piston 19 in the housing 18 barely deforming bending moment, so that the linear tensioner 15 remains wear-resistant even with operationally high-frequency oscillation.

FIG. 1 illustrates the different positions that the tensioning roller 17 can nominally assume at the time of mounting the belt tensioner 14 and during operation of the belt drive:

- M denotes the (external) mounting position in which the tension roller 17 must be pivoted sufficiently far out of the belt drive to apply the belt 13;

- N indicates the nominal installation position of the belt tensioner 14. All component dimensions of the belt drive are based on room temperature (20 ° C)

Nominal dimensions or median dimensions;

- Ai refers to the first external working position of the operational work area of the tension roller 17. Here are all the component dimensions of the belt drive in the belt tensioner 14 and thus the helical compression spring 20th maximum shortening tolerance position in conjunction with the dimensionally equivalent hot operation of the belt drive;

- A ₂ denotes the second outer working position of the operational work area of the tensioning roller 17. In this case, all the component dimensions of the belt drive are in the belt tensioner 14 and thus the helical compression spring 20 maximum lengthening tolerance position in conjunction with the dimensionally equivalent cold operation of the belt drive;

- A _M denotes an inventively predetermined average operating position of the tension roller 17. The intermediate working position, which lies exactly in the middle between the first outer working position A1 and the nominal mounting position N, is in the new state of the belt drive especially frequently started up and is therefore suitable for the wear rate of the longitudinal bearing in the Linear tensioner 15 decisive. The helical compression spring 20 is compressed in this working position to such a length that their number of effective turns nominally half-integer, ie n = i + 0.5, and thus the inner bearing forces correspond to the load case of the linear tensioner 15 shown in FIG.

The characteristic of the helical compression spring 20 is also chosen such that the number of effective spring turns by just Δη = 0.5 increases when the belt tensioner 14 with tensioning roller 17 starting from the first outer working position Ai into the second outer working position A ₂ and the Spring 20 expands by the corresponding spring travel.

LIST OF REFERENCE NUMBERS

1 initial turn

 2 transition winding

3 mean turns

 4 transition winding

 5 final turn

6 driving pulley 7 driven pulley

8 driven pulley

9 driven pulley

10 driven pulley

1 1 pulley

 12 pulley

 13 straps

 14 belt tensioner

 15 linear clamps

 16 roller levers

 17 tension roller

 18 housing

 19 pistons

 20 helical compression spring

21 first fastening eye

22 second fastening eye

23 pivot point of the roller lever

24 sliding bush

 25 pen

 26 long hole

 27 Spring support of the housing

28 spring support of the piston

29 contact point

 30 contact point

 31 longitudinal axis

Claims

claims 1 . A belt drive comprising a driving pulley (6), one or more driven pulleys (7, 8, 9, 10), a belt (13) biasing the pulleys (6, 7, 8, 9, 10) and a belt tensioner ( 14) with a tensioning roller (17), a housing (18), a longitudinally movable in the housing (18) mounted piston (19) and a belt tension by means of the tension roller (17) generating the helical compression spring (20), the housing (18) and the piston (19) is subjected to force in the direction of extension of the belt tensioner (14) and whose spring characteristic is adapted to the change in length of the belt tensioner (14) within an operational working range of the tensioning roller (17), the nominal first outer working position (A 1 and the Nominal second outer working position (A ₂ ) of the tensioning roller (17), taking into account dimensional component tolerances and thermal dimensional changes in the belt drive are predetermined, characterized gekennzei that the working area of the tensioning roller (17) comprises a predetermined average working position (A _M ) in which the turns of the helical compression spring (20) are torqued against each other such that the number of effective spring turns is substantially n = i + 0, 5, where i is a natural number. 2. A belt drive according to claim 1, characterized in that the average working position (A _M ) on the one hand to a nominal mounting position (N) of the tension roller (17) and on the other hand to the first outer working position (Ai) is symmetrically spaced, the nominal mounting position (A) N) corresponds to the component nominal dimensions or mean dimensions of the belt drive, and wherein the first outer working position (A) corresponds to the maximum possible shortening of the belt tensioner (14) component tolerance position in conjunction with the hot operation of the belt drive. 3. belt drive according to claim 1, characterized in that the spring characteristic of the helical compression spring (20) is such that the number of effective spring coils between the two outer working positions (Ai, A ₂ ) by a maximum Δη = 0.5 increases when the helical compression spring (20) from the first outer working position (A ^ starting towards the second outer working position (A ₂ ) expands to its operational travel, the second outer Working position (A ₂ ) of the belt tensioner (14) maximum lengthening component tolerance position in conjunction with the cold operation of the belt drive corresponds. Belt drive according to Claim 1, characterized in that the spring supports (27, 28) running on the housing (18) and on the piston (19) coaxially center the helical compression spring (20) at least approximately free of play and to the longitudinal axis (31) of the belt tensioner (14).