DE102019105235B4 - Belt drive of an internal combustion engine - Google Patents

Abstract

Belt drive of an internal combustion engine, comprising a generator (8) and a decoupler (5) driving its generator shaft with: - a belt pulley (4) wrapped around the belt (1) with a first inner lateral surface (19), - one rotatable with respect to the belt pulley (4) Driver (22) with a second inner lateral surface (20), - a hub (9) which can be rotated with respect to the belt pulley (4) and the driver (22) and is attached to the generator shaft, - and one in the drive torque flow between the belt pulley (4) and the hub (9) arranged in series of a loop strap (15) and a torsion spring (16), the loop strap (15) with its outer circumferential surface (18) in one of the or both inner circumferential surfaces (19, 20) with oversize (P1, P2 ) is clamped, characterized in that the oversize (P1, P2) is so large that for the maximum transferable drive torque T from the loop tape (15) to the torsion spring (16) and for the maximum operating torque M of the torsion spring (16) the f The following ratio, depending on the speed n of the internal combustion engine, applies: T (n = 0) <M (n = ni) <T (n = ni) with ni: idling speed.

Description

• - einer vom Riemen umschlungenen Riemenscheibe mit einer ersten Innenmantelfläche,
• - einem gegenüber der Riemenscheibe verdrehbaren Mitnehmer mit einer zweiten Innenmantelfläche,
• - einer gegenüber der Riemenscheibe und dem Mitnehmer verdrehbaren Nabe, die auf der Generatorwelle befestigt ist,
• - und einer im Antriebsmomentfluss zwischen der Riemenscheibe und der Nabe angeordneten Reihenschaltung aus einem Schlingband und einer Drehfeder,

wobei das Schlingband mit dessen Außenmantelfläche in einer der oder beiden Innenmantelflächen mit Übermaß eingespannt ist.The invention relates to a belt drive of an internal combustion engine. The belt drive comprises a generator and a decoupler driving its generator shaft with:

• - a belt pulley with a first inner circumferential surface wrapped around by the belt,
• - a driver that can be rotated with respect to the pulley and has a second inner circumferential surface,
• - a hub that can be rotated with respect to the belt pulley and the driver and is attached to the generator shaft,
• - and a series connection of a loop band and a torsion spring arranged in the drive torque flow between the belt pulley and the hub,

wherein the loop tape is clamped with its outer circumferential surface in one of the or both inner circumferential surfaces with an oversize.

Torsional vibrations and irregularities that are introduced from the crankshaft of an internal combustion engine into its belt drive for ancillary units can, as is known, be compensated for by decouplers, which are usually referred to as decouplers or isolators and are typically designed as generator pulleys. The loop is used as a one-way clutch that, when closed, transfers the drive torque from the belt pulley to the hub, whereby the elasticity of the torsion spring connected in series with the loop smooths the rotational irregularities from the crankshaft and introduced into the belt drive. When the belt pulley rotates with a delay, the loop belt opens, whereby - then vice versa - no significant torque can be transmitted from the hub to the belt pulley, so that the generator shaft, which is subject to high inertia, can overtake the belt pulley.

Belt drives with generic decouplers are from numerous publications and, for example, from DE 10 2015 224 608 A1 , DE 10 2016 211 558 A1 and DE 10 2017 004 974 A1 famous. Also known are the torsional vibrations in the belt drive that occur during the starting process of the internal combustion engine and in particular are caused by resonance and that - without further countermeasures - can cause particularly high angles of rotation of the torsion spring with consequently excessive material stresses in the spring wire. To reduce the spring load it is, for example, in the US 2004/0014540 A1 proposed to limit the torsional amplitudes of the torsion spring by an inner sleeve which fills the (inner) annular space between the torsion spring and the hub. the EP 1 844 245 B1 proposes a torque limiter as overload protection for the torsion spring, which fills the (outer) annular space between the torsion spring and the loop tape and limits the maximum angle of rotation of the torsion spring, which widens radially under load.

the WO 2013/067 621 A1 discloses a belt drive with a decoupler which comprises an actively controllable loop belt coupling.

Proceeding from this, the present invention is based on the object of structurally improving a belt drive of the type mentioned at the outset by limiting the mechanical tension load on the torsion spring by the lowest possible torsional amplitudes of the spring when the internal combustion engine is started.

The solution for this results from the features of claim 1. Accordingly, the loop tape should be pressed in with such an oversize that for the maximum drive torque T that can be transmitted from the loop tape to the torsion spring and for the maximum operating torque M of the torsion spring, the following ratio is dependent on the Speed n of the combustion engine applies:
T (n = 0) <M (n = n _i ) <T (n = n _i ) with n _i : idle speed.

The maximum operating torque M (n = n _i ) of the torsion spring, hereinafter referred to as M _{i for} short, results from the maximum generator load plus the torque amplitude with which the torsion spring compensates for the rotational irregularities in the belt drive when the internal combustion engine is idling. The drive torque T that can be transmitted from the loop belt to the torsion spring is greater, so that from the idling speed, ie in the entire operating speed range of the internal combustion engine, the drive torque is transmitted to the generator essentially without slippage.

The overload protection of the torsion spring according to the invention results from the fact that the maximum drive torque that can be transmitted to the torsion spring in a speed range below idling is less than M _i , so that within this speed range the excessive torsional vibrations of the belt drive caused by the engine start process are not transmitted to the torsion spring in full, but rather be cut off, as it were. This drive torque limitation is made possible by the property of the loop belt to want to expand radially due to centrifugal force and to exert more static friction generating contact pressure on the input and output-side inner circumferential surfaces of the pulley or the driver with increasing speed. Consequently the slip limit and accordingly the maximum transferable drive torque decrease with decreasing speed of the loop belt. The present invention makes use of this characteristic by dimensioning the oversize with which the loop belt is clamped on the drive and / or driven side: this oversize is so great that when the internal combustion engine is at a standstill, ie n = 0, the maximum drive torque that can be transmitted by the loop belt is less than M _i is. Thus, below idle speed, torsional vibrations, the amplitudes of _{which would lead to the limit torque M i being} exceeded, are not transmitted to the torsion spring as a result of (intermittent) slippage of the loop.

This overload protection works at least within a part of the starting speed range, this sub-range being maximized in that ideally T _i (short for T (n = n _i )) is only slightly larger than M _i or, in the borderline case, practically the same size. With regard to the effect of the overload protection, it can also be advantageous that the slip limit of the loop belt in the range of the average starting speed n _s and consequently T _s = T (n = n _s ) are comparatively low. Then the torque difference between T _i and M _{i is} very much smaller than between T _i and T _s : T _i - M _i << T _i - T _s .

A first outer circumferential surface section of the loop tape with a first oversize P ₁ in the first inner circumferential surface and a second outer circumferential surface section of the loop tape with a second oversize P ₂ in the second inner circumferential surface are preferably clamped. The first oversize P ₁ is larger than the second oversize P ₂ . The ratio P ₁ > P _{2 has the} effect that the loop belt first slips in relation to the (driven) driver and, on the other hand, is carried along with little slip by the (driving) pulley. This ensures that the speed of the hub and the generator shaft with the belt pulley is essentially synchronized when the engine is started.

The first oversize P ₁ can be so large with regard to the synchronous speed run-up that for the maximum static friction torque F ₁ that can be transmitted from the first inner circumferential surface to the first outer circumferential surface section and for the maximum drive torque T that can be transmitted _{from the loop belt to the torsion spring, the ratio applies: F 1} (n = 0)> T _i .

The second oversize P _{2 can be so large that the following applies to the maximum static friction torque F 2} that can be transferred from the second outer jacket surface section to the second inner jacket surface: F ₂ (n = 0) ~ 0 does not engage in drive torque transferring engagement with the driver, but slips completely at 100% slip.

A favorable producibility of the decoupler is given with regard to the oversize setting in that the two inner circumferential surfaces have the same diameter and that for the diameters d ₁ , d _{2 of} the two outer circumferential surface sections in the untensioned state of the loop the relationship applies: d ₁ > d ₂ . Alternatively, the loop tape can be wound with a constant outer diameter, in which case the respective oversize is set over - if necessary - differently sized diameters of the inner circumferential surfaces.

In principle, the invention can also be used in other belt pulleys of a belt drive, for example in a crankshaft decoupler.

• 1 den Riementrieb in schematischer Darstellung;
• 2 den Entkoppler im Längsschnitt;
• 3 den Entkoppler in perspektivischer Explosion;
• 4 das Schlingband des Entkopplers als perspektivisches Einzelteil;
• 5 ein charakteristisches Drehmoment / Drehzahl - Diagramm des Entkopplers.

Further features of the invention emerge from the following description and from the drawings, in which an exemplary embodiment of a belt drive of an internal combustion engine with a decoupler according to the invention is shown. Show it:

• 1 the belt drive in a schematic representation;
• 2 the decoupler in longitudinal section;
• 3 the decoupler in perspective explosion;
• 4th the loop tape of the decoupler as a perspective item;
• 5 a characteristic torque / speed diagram of the decoupler.

1 shows an accessory belt drive of an internal combustion engine. The belt running in the direction of the arrow 1 wraps around the pulley 2 the crankshaft, the pulley 3 a water pump and the pulley 4th of a decoupler 5 as well as a pulley 6th . A belt tensioner 7th tightens the belt 1 before. The decoupler explained below 5 drives the generator shaft of a generator 8th at.

The structural design of the decoupler 5 goes out of the 2 until 4th emerged. The one from the belt 1 wrapped outer circumferential surface of the belt pulley 4th is the poly-V shape of the belt 1 profiled accordingly. The pulley 4th is hollow-cylindrical and rotatable on a hub 9 stored, which is firmly screwed to the generator shaft. To do this, the hub 9 an internal thread in the middle section 10 and on the front end section remote from the generator an internal multi-tooth 11 as an engagement contour for the screwdriver. The bearing of the pulley 4th on the hub 9 takes place on the generator side Radial and axial end by means of a roller bearing 12th and at the end remote from the generator, radially by means of a plain bearing 13th . The roller bearing 12th is a single-row ball bearing sealed on both sides, and the plain bearing 13th is a radial bearing ring made of polyamide that connects to the pulley 4th is in direct sliding contact. Into the end of the pulley remote from the generator 4th is after screwing the hub 9 a sealing protective cap on the generator shaft 14th snapped.

The one for the function of the decoupler 5 essential components are one as a loop tape 15th trained one-way clutch and one - with respect to the drive torque flow from the pulley 4th on the hub 9 - with the loop tape 15th torsion spring connected in series 16 that the torsional vibrations in the belt drive compared to the hub 9 and consequently towards the generator 8th decoupled. The loop tape 15th and the torsion spring 16 extend coaxially to one another in the direction of the axis of rotation 17th of the decoupler 5 , with the loop tape 15th radially between the pulley 4th and the torsion spring 16 is arranged and the torsion spring 16 encloses.

The loop tape 15th is with its cylindrical outer jacket surface 18th in a cylindrical first inner lateral surface 19th and in a cylindrical second inner lateral surface 20th clamped. The first inner lateral surface 19th is through one in the pulley 4th pressed-in sleeve 21 formed, and the second inner circumferential surface 20th is by a (also sleeve-shaped) driver 22nd formed in the sleeve 21 is rotatably mounted.

The loop tape wound on the right 15th and the torsion spring wound on the left 16 each have legless ends that form the loop tape 15th or the torsion spring 16 Expand radially when transmitting the drive torque. In the process, the loop band is tensed 15th with a first outer circumferential surface section 18-1 that is in the drive torque flow from the pulley 4th runs against the first inner lateral surface 19th . The second outer circumferential surface section 18-2 , which is in the drive torque flow on the part of the torsion spring 16 runs, braces itself against the second inner lateral surface 20th so that's from the pulley 4th Introduced drive torque through static friction between the sleeve 21 and the loop tape 15th on the one hand and between the loop tape 15th and the driver 22nd on the other hand in the torsion spring 16 initiated and from there in a smoothed form onto the hub 9 is transmitted. The one on the driver 22nd acting axial forces of the torsion spring 16 are via a plain bearing ring 23 on the inner ring of the rolling bearing 12th supported.

The introduction of the drive torque into the torsion spring 16 takes place via one on the driver 22nd molded spring plate 24 with a rotary stop that covers the circumferential face 25th of the spring end on the drive side in the one on the pulley 4th the direction of rotation shown. The transmission of the drive torque into the hub 9 takes place via an integrally formed, output-side spring plate 26th with a rotary stop on the circumferential face 27 of the spring end on the output side takes along in the direction of rotation shown. The introduced torsional vibrations are smoothed out by elastic relative rotations of the spring plate on the drive side 24 compared to the spring plate on the output side 26th .

The loop tape 15th enables the hub to be overtaken when the torque is reversed 9 and thus an overtaking of the generator shaft in relation to the pulley 4th . The loop tape slips 15th in the sleeve 21 and / or in the driver 22nd through, and that from the loop tape 15th The torque that can be transmitted is reduced to the moment of sliding friction between the contact partners slipping through each other.

The inventive construction of the decoupler 5 In addition, it enables the loop belt to slip through depending on the speed 15th in such a way that the comparatively large torsional vibrations of the belt drive during the starting process of the internal combustion engine, their amplitudes lead to excessive twisting and consequently torque peaks of the torsion spring 16 would result by limiting the looping belt 15th transferable drive torque at speeds below the idle speed of the internal combustion engine not on the torsion spring 16 transferred, but as a result of intermittent slipping of the loop tape 15th be cut off, as it were. This (speed-dependent) overload protection of the torsion spring 16 is adjusted by the excess with which the loop tape 15th in the sleeve 21 and in the carrier 22nd is clamped. The transferable drive torque decreases as the excess becomes smaller, so that below the idling speed even comparatively small rotational irregularities of the belt drive cause the loop belt to slip through 15th cause.

• Drahtquerschnitt des Schlingbands 15: 1,2 mm • 1,2 mm
• Anzahl der Schlingbandwindungen: 20
• Windungsanzahl des ersten Außenmantelflächenabschnitts 18-1: 10
• Windungsanzahl des zweiten Außenmantelflächenabschnitts 18-2: 10
• Übermaß P₁ = 0,5 mm
• Übermaß P₂ = 0,05 mm
• mittlerer Windungsdurchmesser im eingespannten Zustand des Schlingbands: 38,5 mm

In the present exemplary embodiment, the two inner lateral surfaces have 19th and 20th the same diameter. How it looks 4th becomes clear, is the unstressed diameter d _{1 of} the first outer circumferential surface section 18-1 greater than the unstressed diameter d _{2 of} the second outer circumferential surface section 18-2 , so that for the oversize P _{1 of} the first outer circumferential surface section 18-1 opposite the first inner lateral surface 19th and for the oversize P _{2 of} the second outer circumferential surface section 18-2 opposite the second inner lateral surface 20th the relationship is: P ₁ > P ₂ . The illustrated embodiment has the following design data:

• Wire cross section of the loop tape 15th : 1.2mm • 1.2mm
• Number of loop tape turns: 20
• Number of turns of the first outer lateral surface section 18-1 : 10
• Number of turns of the second outer circumferential surface section 18-2 : 10
• Oversize P ₁ = 0.5 mm
• Oversize P ₂ = 0.05 mm
• Average coil diameter in the clamped state of the loop tape: 38.5 mm

Das Diagramm zeigt im Einzelnen:

• - die mit F₁ bezeichnete Drehmomentkurve stellt das an der Schlupfgrenze von der ersten Innenmantelfläche 19 der Hülse 21 auf den ersten Außenmantelflächenabschnitt 18-1 des Schlingbands 15 übertragbare Haftreibmoment in Abhängigkeit von n' dar.
• - die mit F₂ bezeichnete Drehmomentkurve stellt das an der Schlupfgrenze vom zweiten Außenmantelflächenabschnitt 18-2 auf die zweite Innenmantelfläche 20 übertragbare Haftreibmoment in Abhängigkeit von n' dar.
• - das mit G_i bezeichnete Drehmoment ist die mittlere Generatorlast bei Leerlaufdrehzahl $$\text{n}\text{'}={\text{n'}}_{\text{i}}\left({\text{n}}_{\text{i}}\text{ des Verbrennungsmotors}=750\text{ rpm}\right)$$
  
• - das maximale Betriebsmoment M_i der Drehfeder 16 ergibt sich aus der mittleren Generatorlast G_i zuzüglich der durch die Drehungleichförmigkeiten des Riementriebs bei Leerlaufdrehzahl n'_i erzeugten Drehmomentamplituden der Drehfeder 16.
• - die mit n'_s bezeichnete Drehzahl entspricht der - vom Startermotor erzeugten - mittleren Drehzahl n_s des Verbrennungsmotors während des Startvorgangs.

These data lead to the in 5 shown torque / speed diagram of the decoupler 5 . The speed of the pulley 4th is denoted by n ', and according to the present transmission ratio ü = 2.7 applies to the speed ratio between n' and the speed n of the pulley 2 , i.e. the speed of the combustion engine: $$\text{n}\text{'}:\text{n}=2.7$$

The diagram shows in detail:

• - The _{torque curve denoted by F 1} represents that at the slip limit of the first inner lateral surface 19th the sleeve 21 on the first outer circumferential surface section 18-1 of the loop tape 15th transferable static friction torque as a function of n '.
• - The _{torque curve labeled F 2} represents that at the slip limit of the second outer circumferential surface section 18-2 on the second inner lateral surface 20th transferable static friction torque as a function of n '.
• - The _{torque designated by G i} is the mean generator load at idling speed $$\text{n}\text{'}={\text{n '}}_{\text{i}}\left({\text{n}}_{\text{i}}\text{of the internal combustion engine}=750\text{rpm}\right)$$
  
• - The maximum operating _{torque M i of} the torsion spring 16 results from the mean generator _{load G i} plus the torque amplitudes of the torsion spring generated by the rotational irregularities of the belt drive at idle speed n ' _i 16 .
• - The speed designated by n ' _s corresponds to the mean speed n _{s of} the internal combustion engine generated by the starter motor during the starting process.

The one from the noose 15th on the torsion spring 16 The maximum transferable drive torque T (n ') is of course the smaller static friction torque of F ₁ and F ₂ , i.e. in the present case F ₂ . In a simulation calculation with the above construction data, the following static friction torques F ₁ (n ') and F ₂ (n') were determined at the slip limit of the two outer surface sections 18-1 or. 18-2 determined: n '= 0 rpm: F ₁ = 80 Nm F ₂ = 0 Nm n '= 2500 rpm: F ₁ = 115 Nm F ₂ = 36 Nm n '= 5000 rpm: F ₁ = 218 Nm F ₂ = 143 Nm

• - für das bei Leerlaufdrehzahl n'_i maximal übertragbare Antriebsmoment T_i = F₂ (n'i) gilt das Verhältnis: T_i > M_i. Dieses Verhältnis besagt, dass bei Leerlaufdrehzahl n'_i das zugehörige Generatorlastmoment G_i zuzüglich der Drehmomentamplituden der Drehfeder 16 im Wesentlichen schlupffrei von der Riemenscheibe 4 auf die Nabe 9 übertragbar sind.
• - für das bei Motorstillstand (n' = n = 0) maximal übertragbare Antriebsmoment T (n' = 0) = T₀ gilt das Verhältnis: T₀ < M_i. Dieses Verhältnis besagt, dass es unterhalb der Leerlaufdrehzahl n'_i einen Drehzahlbereich gibt, in dem die erfindungsgemäße Beschränkung des übertragbaren Antriebsmoments T wirksam ist.
• - für T (n' = n'_s) = T_s gilt weiterhin die Beziehung: T_i - M_i << T_i - T_s. Aus dieser Beziehung folgt, dass die erfindungsgemäße Beschränkung des übertragbaren Antriebsmoments T im nahezu gesamten Drehzahlbereich zwischen der mittleren Startdrehzahl n'_s und der Leerlaufdrehzahl n'_i wirkt.
• - für T (n' = 0) gilt weiterhin: T (n' = 0) = F₂ (n' = 0) ~ 0. Das bedeutet, dass bei Motorstillstand kein nennenswertes Antriebsmoment T vom Schlingband 15 auf die Drehfeder 16 übertragbar ist.
• - für F₁ gilt die Beziehung: F₁ (n' = 0) > T_i als Voraussetzung für einen schlupfarmen und damit im Wesentlichen synchronen Drehzahlhochlauf des Schlingbands 15 und folglich der Nabe 9 und der Generatorwelle mit der Riemenscheibe 4.

The diagram shows the following:

• - For the maximum transferable drive torque T _i = F ₂ (n'i) at idling speed n ' _i , the ratio: T _i > M _i applies. This ratio means that at idling speed n ' _i the associated generator _{load torque G i} plus the torque amplitudes of the torsion spring 16 essentially slip-free from the pulley 4th on the hub 9 are transferable.
• - For the maximum transferable drive torque T (n '= 0) = T ₀ when the engine is at a standstill (n' = n = 0), the ratio: T ₀ <M _i applies. This ratio means that there is _{a speed range below the idling speed n 'i} in which the inventive restriction of the transmittable drive torque T is effective.
• - for T (n '= n' _s ) = T _s the relationship continues to apply: T _i - M _i << T _i - T _s . It follows from this relationship that the inventive restriction of the transmittable drive torque T acts _{in almost the entire speed range between the mean starting speed n 's} and the idling speed n' _i.
• - For T (n '= 0) the following still applies: T (n' = 0) = F ₂ (n '= 0) ~ 0. This means that when the motor is at a standstill, there is no significant drive torque T from the loop belt 15th on the torsion spring 16 is transferable.
• - For F ₁ the relationship applies: F ₁ (n '= 0)> T _i as a prerequisite for a low-slip and thus essentially synchronous speed run-up of the loop belt 15th and consequently the hub 9 and the generator shaft with the pulley 4th .

Claims (5)

Belt drive of an internal combustion engine, comprising a generator (8) and a decoupler (5) driving its generator shaft with: - a belt pulley (4) wrapped around the belt (1) with a first inner lateral surface (19), - one rotatable with respect to the belt pulley (4) Driver (22) with a second inner circumferential surface (20), - a hub (9) which can be rotated with respect to the belt pulley (4) and the driver (22) and which is attached to the generator shaft, - and a series connection of a loop strap (15) and a torsion spring (16) arranged in the drive torque flow between the belt pulley (4) and the hub (9), the loop strap (15) with its outer circumferential surface (18) in one of the or both inner circumferential surfaces ( 19, 20) is clamped _{with oversize (P 1} , P ₂ ), characterized in that the oversize (P ₁ , P ₂ ) is so large that for the maximum transferable drive torque from the loop tape (15) to the torsion spring (16) T and for the maximum operating torque M of the torsion spring (16) the following ratio applies as a function of the speed n of the internal combustion engine: T (n = 0) <M (n = n _i ) <T (n = n _i ) with n _i : Idle speed. Belt drive after Claim 1 , characterized in that a first outer _{circumferential surface section (18-1) of the loop tape (15) is clamped with a first oversize P 1} in the first inner circumferential surface (19) and that a second outer circumferential surface section (18-2) of the loop tape (15) with a second oversize P ₂ is clamped in the second inner circumferential surface (20), the relationship being: P ₁ > P ₂ . Belt drive after Claim 2 , characterized in that the first oversize P _{1 is so large that for the maximum static friction torque F 1} that can be transferred from the first inner jacket surface (19) to the first outer jacket surface section (18-1) and for that from the loop band (15) to the torsion spring ( 16) maximum transferable drive torque T the ratio applies: F ₁ (n = 0)> T (n = n _i ). Belt drive after Claim 2 or 3 , characterized in that the second oversize P _{2 is so large that the maximum static friction torque F 2} that can be transmitted from the second outer lateral surface section (18-2) to the second inner lateral surface (20) _{applies: F 2} (n = 0) ~ 0. Belt drive according to one of the Claims 2 until 4th , characterized in that the two inner lateral surfaces (19, 20) have the same diameter and that for the diameter d _{1 of} the first outer lateral surface section (18-1) and for the diameter d _{2 of} the second outer lateral surface section (18-2) in the untensioned state of the loop tape ( 15) the relationship applies: d ₁ > d ₂ .

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