Europaisches Patentamt (19) European Patent Office Office europeenpeen des brevets EP 0 676 537 B1 (12) EUROPEAN PATENT SPECIFICATION (45) Date of publication and mention (51) Intel e F02B 67/06 of the grant of the patent: 02.12.1998 Bulletin 1998/49 (21) Application number: 95301889.2 (22) Date of filing: 21.03.1995 (54) Belt tensioning device for internal combustion engine Treibriemenspannvorrichtung fur Brennkraftmaschine Dispositif tendeur de courroie pour moteur a combustion interne (84) Designated Contracting States: (72) Inventors: DE ES GB • Meckstroth, Richard J. Northville, Michigan 48167 (US) (30) Priority: 04.04.1994 US 223250 • Toth, Gerard S. Belleville, Michigan 48111 (US) (43) Date of publication of application: 11.10.1995 Bulletin 1995/41 (74) Representative: Messulam, Alec Moses A. Messulam & Co. (73) Proprietors: 24 Broadway • FORD MOTOR COMPANY LIMITED Leigh-on-Sea Essex SS9 1BN (GB) Brentwood Essex (GB) Designated Contracting States: (56) References cited: GB WO-A-90/10805 DE-A- 3 609 232 • FORD-WERKE AKTIENGESELLSCHAFT DE-A-4 114 716 US-A- 4 277 240 50735 Koln (DE) US-A- 4 299 584 US-A- 4 355 991 Designated Contracting States: DE • Ford Motor Company Dearborn, Ml 48126 (US) Designated Contracting States: ES DO Is- CO lO CO Is- CO Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice the Patent Office of the Notice of shall be filed in o to European opposition to European patent granted. opposition a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. a. 99(1) European Patent Convention). LU Printed by Jouve, 75001 PARIS (FR) 1 EP 0 676 537 B1 2 Description objectionable squealing noise which will be audible to the driver of the vehicle. The squealing noise produced The present invention relates to a belt -driven auto- by the loose drivebelt slipping on the crank pulley is motive engine accessory drive system and means for caused by an overrunning effect of the alternator. Fig- tensioning such a system. Drive systems for the front s ures 10 and 11 show rotational speed data produced end accessories of automotive engines typically include during tests in which an instrumented engine was rap- a belt having a tensioning device for maintaining the belt idly decelerated from a high rate of speed. Figure 10 in contact with all the pulleys of the system, including illustrates the behaviour of a prior art system; Figure 11 the drive pulley, which is usually attached to the crank- illustrates a system according to the present invention. shaft of the engine, as well as with a plurality of driven 10 As shown in Figure 1 0, alternator speed tails off to zero pulleys, with at least one driven pulley attached to each at about 300 msec, after the crankshaft stops. Similarly, rotating accessory. Such accessories frequently include the idler rpm and drivebelt speed tail off to zero at about an alternator, a power steering pump, an air conditioning 200 milliseconds following the stopping of the crank- compressor, a secondary air pump for emission con- shaft. This occurs because once the crankshaft stops, trols, as well as other types of rotating devices. 15 the high rotational inertia of the alternator causes it to Conventional tensioners utilise elastic force provid- remain rotating and causes the alternator to pull the ten- ed by, for example, a flat wire spring for maintaining a sioner in a direction so as to loosen the belt. In turn, this tensioning pulley in contact with the drive belt. Such a causes a "bubble" of belt to extend from the alternator pulley is shown as item No. 34 in Figure 1 of the present to the crankshaft pulley, and as a result the drivebelt application. Although damped tensioners have been 20 slips on the crankshaft pulley. The resultant squeal may used to some extent in automotive front end accessory be very audible. In contrast with the operation according drive systems, such tensioners typically are symmetri- to the conventional tensioner at Figure 10, Figure 11 cal in their damping characteristics. In other words, the shows the results of the use of a tensioner and control motion of the tensioner is damped in the direction tend- system according to the present invention. In essence, ing to increase the tension of the belt, as well as in the 25 the tensioner has a governor for controlling the rotation- direction tending to decrease the tension in the belt. Un- al motion of the tensioner arm such that the tensioner's fortunately, if the tensioner is set up with a fairly low arm will be freely able to rotate in the direction in which damping rate so as to allow the tensioner wheel to be the tension in the drivebelt is increased, while move- compliantly in contact with the belt in a direction tending ment of the arm in the direction in which tension in the to tighten the belt, the tensioner will be allowed to pull 30 drivebelt is decreased, is resisted. Because the tension- back in a direction allowing the belt to loosen in the event er cannot move readily in the direction in which the ten- that the following series of events occurs within the ac- sion in the drivebelt is decreased, the tension within the cessory drive system. belt is maintained and, as a result, the deceleration rates Figure 10 illustrates a problem with conventional of the drivebelt, the alternator and the crankshaft con- tensioners which is solved by a tensioner according to 35 verge. This is shown graphically in Figure 11 . Note that the present invention. Operation of a front end acces- the three plots for alternator, idler and crankshaft all con- sory drive system with a corrective tensioner according verge at a about 1 1 00 msec. This means effectively that to the present invention is shown in Figure 11 . Both plots the alternator is no longer permitted to pull the tensioner illustrate the rotational speed or angular velocity of an in a direction tending to decrease the tension in the belt, engine's alternator, idler pulley, and crankshaft pulley. 40 and as a result, the alternator is decelerated in close The rotational speed of the idler pulley is a direct indi- congruence with the crankshaft's deceleration. This has cator of the speed of the drivebelt because it is assumed the beneficial effect of preventing squeal of the drivebelt for the purpose of this discussion that minimal slip oc- at the crank pulley, because with the tension maintained curs between the idler pulley and the drivebelt; this is a at a proper level in the drivebelt, the belt will not slip at good assumption because the rotating inertia of the idler 45 the crankshaft pulley. pulley is relatively slight as compared with the rotational United States Patent 4,299,584 describes a belt inertia of the other components of the engine's front end tensioning device for an endless drive belt for a vehicle accessory drive system, particularly the alternator. As accessories drive system. A bracket is mounted on the shown in both plots, crankshaft rpm decreases at a very engine adjacent the drive belt and a lever plate is pivot- high rate in the situation being considered. It has been so ally mounted thereon. An idler pulley is rotatably mount- determined that during wide open throttle transmission ed on the lever plate and is adapted to be moved in a upshifts at lower gear speeds, such as the upshift from belt tensioning direction for engagement with the drive first to second gear with an automatic transmission and belt. A coil spring is mounted on the bracket and is en- an engine speed of, for example 4500 rpm, the crank- gaged with the lever plate and pulley in the belt tension- shaft may decelerate at a rate approaching 20,000 rpm 55 ing direction. The device is provided with a spring steel per second. These high deceleration rates cause the detent which engages ratchet teeth to retard movement front end accessory drivebelt to slip on one or more pul- of the lever plate in a direction opposite to belt tensioning leys, particularly the crankshaft pulley, thereby giving an direction. 2 3 EP 0 676 537 B1 4 United States Patent 4,277,240 describes a hy- strut having a connecting rod portion being able to draulic tensioning device for maintaining a predeter- move freely in the direction in which tension in the mined amount of tensioning force on an endless drive drive belt is increased, while resisting movement in belt for a vehicle accessories drive system. The drive the direction in which tension in the drive belt is de- belt rotates an idler pulley which hydraulically actuates 5 creased; a piston by driving the pump which supplies hydraulic and an electric controller for operating the governor fluid to the piston. The piston pivots a lever toward the in response to at least one sensed engine parame- belt whereupon the idler pulley engages the belt and ex- ter indicative of a period of rapid engine decelera- erts the desired tensioning force on the belt. tion. DE 4114716 is also concerned with a belt drive for 10 an internal combustion engine in which the belt drives The hydraulic strut preferably comprises a piston the generator and, for example, an air conditioning unit. reciprocably mounted within a cylinder mounted upon The belt is tensioned by a tensioning pulley which is the connecting rod, with the connecting rod having a free mounted on a pivoted lever which can be positioned by end attached to the tensioner arm such that the piston an electromagnetic actuator to vary the tension of the is slides within the cylinder as the tensioner arm rotates, belt.