192 clutches and power-stop control – Clutches – Automatic
Reexamination Certificate
2000-05-31
2002-05-28
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Clutches
Automatic
C192S055610, C192S08100C
Reexamination Certificate
active
06394248
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to pulleys. More particularly, the present invention relates to an over-running clutch pulley which has particular application within an engine accessory system including an automotive alternator.
2. Description of the Prior Art
During operation of an engine, a belt drive system is sometimes used to power and operate the various accessory devices including, but not limited to, an alternator which provides electrical power to the vehicle. While several type of belt drive systems are in use, the system which is currently in favor is known as a serpentine drive system. Serpentine drive systems generally include a drive pulley connected to the crankshaft of the automobile's internal combustion (I.C.) engine and a ribbed belt trained about the drive pulley. The belt is also trained about one or more driven pulleys which are in turn connected to the input shafts of the various accessories. An automatic belt tensioner is also provided to maintain the tension of the belt within the proper range. Most driven pulleys are provided in a one-piece design. These pulleys have no over-running capabilities, meaning that the pulley is rigidly mounted to rotate with the accessory input shaft.
When the input shaft of the accessory device is running at high speed (up to 22,000 rpm for an alternator), a significant amount of inertia is built up within the accessory device. As a result of the combined inertia and the lack of over-running capabilities, relative slipping between the pulley and the belt can occur if the belt decelerates too quickly. If significant slipping of the belt occurs, an audible squeal will be produced. Not only is a squealing belt annoying from an auditory standpoint, but it also undesirable from a mechanical standpoint since it produces undue wear on the belt itself.
In a typical driving situation, the accessory belt will experience instances of large deceleration, such as during in a
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upshift during wide-open throttle acceleration. The situation is made even worse if the throttle is closed or “backed out” immediately after the transmission has been shifted. In these situations, the belt decelerates very quickly while the pulley, with the high inertia from the accessory, keeps rotating very quickly in spite of the friction between the pulley and the belt.
Another major problem with the front end accessory drive is the torsional vibrations caused by the engine pulsations. Each cylinder in the internal combustion engine fires, a torsional pulsation is produced, causing a sinusoidal variation in the overall torque produced by the engine. In most operating conditions, the engine is rotating quickly enough that these torsional vibrations are smoothed out, and little if any vibration can be felt by the driver. The front end accessory drive is designed so that under most operating conditions, there is no resonant vibration in any part of the system, so the belt spans between the accessories usually operate smoothly with little if any vibration. However, resonant conditions can exist under certain accessory loads and engine speeds. Examples of this problem are when “lugging” or sub-idle speed is encountered in a manual transmission vehicle, or when high loads are experienced when the A/C and power steering are operating simultaneously at maximum output. During these conditions, one or more belt spans between the accessories can begin vibrating uncontrollably, producing noise, belt wear and the potential for the belt being thrown off the pulleys.
In attempting to cure the slipping and resonant vibration of the belt, and associated problems, various design proposals have been put forward. One proposed design includes the use of higher belt tensions. However, in these designs the belt tends to wear even more quickly. Additionally, the bearings associated with the input shaft of the accessory also have shown greater wear and a shortened useful life. Various other tensioner constructions have been proposed, but those tensioners have generally exhibited poor performance and were costly to implement.
Attempts to cure the belt slippage, vibration and squeal problem have also proceeded in another direction. While early driven pulleys were constructed in a one-piece design, newer pulley designs have been proposed where the driven pulley itself exhibits an “over-running” capability. This allows the driven pulley to rotate relative to the input shaft of the accessory and therefore accommodate the inertia built up within the accessory.
U.S. Pat. No. 4,725,259 issued to Miyata discloses a construction where the driven pulley is mounted to the input shaft via a one-way clutch. The clutch only engages when the angular velocity of the pulley is accelerating. Otherwise, the clutch slips relative to the input shaft of the accessory. This design is intended to smooth out the recurring fluctuations of instantaneous velocity in the belt that is typical of an I.C. engine. The design smoothes out the corresponding recurrent instantaneous slipping of the belt relative to the driven pulley. No specific constructions for the Miyata one-way clutch are given in the disclosure of this patent.
U.S. Pat. Nos. 5,139,463 and 5,156,573, issued to Butzek et al., disclose alternator pulley constructions in which a coil spring is disposed in a space between a hub attached directly to the accessory input shaft and a pulley mounted for relative movement exteriorly of the hub.
In the '463 patent, the two ends of the coil spring are respectively bent radially inward and radially outward so that one will engage the hub and the other will engage the pulley. In this patent, the spring is wound so that when a positive torque is applied from the belt to the pulley, the rotational movement of the pulley will be transferred to the input shaft of the accessory as a result of the spring “winding-up” and the tangs engaging both the hub and pulley. Whenever negative torque is provided from the belt to the pulley, the spring enables the input shaft to disengage from the accessory and the hub to rotate relative to the pulley.
In the '573 patent, the coil spring has one end bent radially outward. Additionally, the spring includes two sets of volutes, an intermediate set located between the other set and the bent end of the spring. The diameter of the hub and the inner diameter of the non-intermediate volutes are such that the volutes engage the hub when the pulley is being driven by the belt. When a negative torque is established between the alternator pulley and the input shaft, the volutes loosen with respect to the hub and allow slipping to occur. Importantly, the Butzek design of the intermediate volutes allows for a “resilient rotational motion” to ease the shock loading between the pulley and the hub but can cause fatigue problems in the spring.
U.S. Pat. No. 5,598,913 discloses a one way over-running clutch pulley in which a coil spring engages a composite cylindrical surface which is defined by both the sheave and hub. The spring is oriented so that torque is transferred from the sheave to the hub when the sheave is driving the hub. The spring allows slip to occur between these two components during deceleration of the drive belt's recurring speed and torque fluctuations.
While the clutch pulleys of these patents may operate adequately in some respects, they have drawbacks in others. First, some prior art pulleys have experienced resonant vibration problems, especially during idle and sub-idle conditions. Another problem in over-running pulleys is hard lock-up. During engine idle, the large torque fluctuations which are characteristic of the internal combustion engine are smoothed out by an over-running pulley such as the pulley disclosed in the '913 patent. During the brief periods of deceleration, the pulley over-runs. Because of its stiff nature in the drive direction, the hub would over (theoretically) rotate slower than the sheave's input speed of the alternator and pulley (or sheave and hub) are equal.
Adler Jonathan M.
Frayer Robert
Houtman Thomas W.
King Randall K.
Monahan Russell E.
Brinks Hofer Gilson & Lione
Lorence Richard M.
NTN Corporation
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