Abstract:
A motorized tensioner that is controllable for adjusting a belt tension. The tensioner comprises a tensioner arm and a spring. One end of the spring is connected to a moveable member that is connected to a gearbox driven by an electric motor, whereby a spring position is adjustable. The other spring end is connected to a damping mechanism, which is in turn engaged with the tensioner arm. The motor and gearbox position the moveable member, and thereby a spring end, according to a control signal received from a controller. The spring end position determines the spring force and thereby the belt tension in the system. The damping mechanism frictionally interacts with a tensioner body to damp oscillatory movements of the tensioner arm.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a tensioner, and more particularly to a motorized tensioner that is electrically controlled in order to adjust a belt tension in a belt drive.  
       BACKGROUND OF THE INVENTION  
       [0002]     Vehicle engines include among other things, accessories that are driven by the engine. Accessories may include a power steering pump, an air conditioning compressor, alternator and so on. Each of these accessories usually has a pulley that is connected by a belt to an engine crankshaft pulley. Each accessory is driven by the belt as the crankshaft rotates.  
         [0003]     In order to operate efficiently it is necessary for the belt to be placed under a certain amount of preload or tension. This may be accomplished using known methods. A moveable shaft on one of the accessories may be mechanically adjusted to tension a belt. Another method includes use of a belt tensioner.  
         [0004]     A belt tensioner comprises a spring imparting a force upon a lever arm. The lever arm typically comprises a pulley journaled thereto. The pulley is in contact with a belt to be tensioned. A biasing member such as a spring in the tensioner is used to impart and maintain a belt tension load. The belt load is a function of the geometry of the tensioner and drive, as well as the spring rate of the tensioner spring.  
         [0005]     Actuators have been used to control a tensioner position, and thereby a belt tension. For example they are used to adjust a phase difference between a driver and driven pulley. The control signal is derived from the relative rotational phase of a driver pulley as compared to a driven pulley.  
         [0006]     Representative of the art is U.S. Pat. No. 5,733,214(1998) to Shiki et al. which discloses a system for adjusting the tension of an endless transmitting belt in an internal combustion engine comprising a control system for adjusting a tension to be applied from a tensioner to an endless belt based upon a phase angle between a driver and a driven pulley.  
         [0007]     Reference is also made to copending U.S. Pat. application Ser. No. 10/147,032 filed May 15, 2002.  
         [0008]     What is needed is a motorized tensioner that is controllable in order to adjust a belt tension on a belt drive. What is needed is a motorized tensioner having an adjustable biasing member position. What is needed is a motorized tensioner having an asymmetric damping mechanism. The present invention meets these needs.  
       SUMMARY OF THE INVENTION  
       [0009]     The primary aspect of the invention is to provide a motorized tensioner that is controllable in order to adjust a belt tension on a belt drive.  
         [0010]     Another aspect of the invention is to provide a motorized tensioner having an adjustable biasing member position.  
         [0011]     Another aspect of the invention is to provide a motorized tensioner having an asymmetric damping mechanism.  
         [0012]     Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.  
         [0013]     The invention comprises a motorized tensioner that is controllable for adjusting a belt tension. The tensioner comprises a tensioner arm and a spring. One end of the spring is connected to a moveable member that is connected to a gearbox driven by an electric motor, whereby a spring position is adjustable. The other spring end is connected to a damping mechanism, which is in turn engaged with the tensioner arm. The motor and gearbox position the moveable member, and thereby a spring end, according to a control signal received from a controller. The spring end position determines the spring force and thereby the belt tension in the system. The damping mechanism frictionally interacts with a tensioner body to damp oscillatory movements of the tensioner arm. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention.  
         [0015]      FIG. 1  is a front perspective view of an engine with an inventive tensioner.  
         [0016]      FIG. 2  is a diagram of the belt drive system layout with an inventive tensioner.  
         [0017]      FIG. 3  is a control logic diagram.  
         [0018]      FIG. 4  is a front side perspective view of an inventive tensioner.  
         [0019]      FIG. 5  is a rear side perspective view of an inventive tensioner.  
         [0020]      FIG. 6  partial cut-away view of an inventive tensioner.  
         [0021]      FIG. 7  is a front perspective partial cut-way view of an inventive tensioner.  
         [0022]      FIG. 8  is a side partial cut-away view of the inventive tensioner.  
         [0023]      FIG. 9  is a partial front perspective view of the moveable spring attachment member.  
         [0024]      FIG. 10  is a partial front perspective view of the tensioner base and the moveable spring attachment member.  
         [0025]      FIG. 11  is a partial front perspective view of a spring and tensioner base.  
         [0026]      FIG. 12  is a partial cut-away view of the inventive tensioner.  
         [0027]      FIG. 13  is a detail of a damping mechanism.  
         [0028]      FIG. 14  is a cross-section of  FIG. 13  at line  14 - 14 .  
         [0029]      FIG. 15  is a detail of a damping mechanism.  
         [0030]      FIG. 16  is a cross-section of  FIG. 15  at line  16 - 16 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]      FIG. 1  is a front perspective view of an engine with an inventive tensioner. Tensioner  100  is a component part of a front end accessory drive (FEAD) for an engine E. An FEAD generally comprises one or more accessories driven by a belt. Belt B is trained about a number of pulleys  1 ,  2 ,  4 ,  5 ,  6 . Each pulley is connected by a rotating shaft to an engine accessory component. For example, in  FIG. 1, 1  is connected to the crankshaft,  2  is connected to an alternator or starter-generator,  4  is connected to a power steering pump,  5  is connected to a vaporous refrigerant compressor, and  6  is connected to a water pump. Pulley  3  is connected to the arm of the inventive tensioner  100 .  
         [0032]      FIG. 2  is a diagram of the belt drive system layout with an inventive tensioner. Each of the components described for  FIG. 1  are shown schematically in  FIG. 2 . Arm  101  of tensioner  100  has a movement M in order to control a belt tension.  
         [0033]     The inventive tensioner can be installed in any span of a belt system. The tensioner&#39;s position in the FEAD system depends upon the number and type of accessories included in the particular FEAD system. For example, in a particularly demanding system such as a starter-generator system, the inventive tensioner can be installed on the immediate adjacent span ‘downstream’of the starter-generator  2  as shown in  FIG. 2 . Of course, the inventive tensioner can be installed in any span of the FEAD system and its position will depend upon the number and type of components.  
         [0034]     When a prior art tensioner is used in the described position, a very high belt tension must be maintained at all times in order to assure proper system operation in the worst case load situation, that is, during generator/starter load under high engine acceleration.  
         [0035]     Unlike the prior art, the inventive tensioner continuously adjusts belt tension so as to provide only the tension needed for proper system operation at any given time. The inventive tensioner can operate at a low belt tension during most operating conditions, for example 350N, only applying a proper high belt tension during conditions such as described above, i.e., during generator-starter load under high engine acceleration or when all of the accessories are loaded. This allows a high belt tension to be applied only when needed. The inventive tensioner keeps the belt tension low when the engine is off as well. Operating in this manner results in an increase in operating life of the belt, bearings, and other system components since peak tensions are only applied as needed for a short period of time.  
         [0036]      FIG. 3  is a control logic diagram. Inputs shown in box (A) include exemplary control parameters that may be established by a user or set automatically by a control system. For example, a mode of operation can include engine following which means that the biasing member position, and thereby belt load or tension, is set according to an engine operating parameter, for example, engine speed or load. Another input useful for setting a tensioner load is the load condition for each accessory. Of course, other parameters or variables may be selected such as a combination of accessory loads coupled with ambient temperature, throttle position, engine speed, brake position, On-Off air conditioner signals, and so on.  
         [0037]     Belt slip may also be measured as a direct means of determining a belt operating tension. A “low” tension will allow a belt to slip on a pulley. A proper belt tension prevents belt slip on a pulley. Belt slip may be detected by noise emission, or by a differential rotational speed between two or more accessories. In the later case the rotating shaft for each accessory is instrumented in order to detect the shaft speed of each.  
         [0038]     In an FEAD system where only one belt drives all accessories, there is only a single instance where maximum belt tension is needed to transmit power to all system components. This occurs when all accessory components are operating at full load and the engine is experiencing high acceleration. This also corresponds to the maximum belt tension requirement for the FEAD system. This condition requires the maximum belt tension and the tensioner is adjusted accordingly. As each component is loaded, the belt tension is incrementally increased to prevent belt slip and maintain a proper torque carrying capacity. The belt tension is incrementally reduced for each accessory component that is not loaded, or as each is unloaded.  
         [0039]     In box (B) the input variables are analyzed by the system control logic. An exemplary control module used to implement the control logic comprises a Micro LYNX  4  ™ processor. The control module is programmable by a user and comprises a processor and memory capability. An encoder at the motor shaft generates 256 pulses per shaft revolution which is sufficient for setting a belt tension, although a higher or lower number of pulses per revolution may be used depending on a system design.  
         [0040]     The processor (B) uses the inputs from (A) to calculate a desired belt tension. Once the belt tension is calculated, the processor calculates a required position for one end of the biasing member which corresponds to the desired belt tension. In general, the belt tension is increased as accessories are turned on and is decreased as accessories are turned off, and/or, as engine accelerations and deccelerations occur.  
         [0041]     The control logic then sends a signal to the tensioner actuator, in this case, electric motor (C) . The electric motor is operated in order to properly position the end of the biasing member connected to the gearbox (D). The electric motor is stopped once the appropriate feedback variable is received from the sensors, for example motor current (E) or arm position (F).  
         [0042]     System control is accomplished by use of feedback from a motor current monitor or sensor (E), and from an arm position monitor or sensor (F). The current sensor and the arm position sensor are each electrically connected to the controller processor. Arm position sensor may be any one of a number of such position sensors known in the art.  
         [0043]     The current sensor detects a motor amperage. An increase in motor amperage over a prior or steady state value reflects an increase in arm load and a commensurate increase in belt tension. A decrease in motor amperage from a prior or steady state value reflects a decrease in load on the tensioner arm and a decrease in belt tension. Each of these signals is provided to the controller (B). The processor compares the values for current sensor and arm position against an over/under look-up table stored in a processor memory in order to stop operation of the motor once the required value is received. Should the values be exceeded, the motor may be shut down to avoid damaging the system.  
         [0044]     By way of example and not of limitation, the inventive tensioner and system operates in a belt tension range of approximately 300N to 700N. This corresponds to a spring attachment member  106  angular rotation a, see  FIG. 9 , of approximately 40° based upon a tensioner arm length of 75 mm and a pulley diameter of 76 mm. These values are presented as examples and not by way of limitation. By moving member  106 , the gearbox ‘winds’ or ‘unwinds’ the spring  109 , thereby increasing or decreasing a spring force exerted on the tensioner arm and the belt. More particularly, the 300 N position is a function of the spring rate and corresponds approximately to the α=0° position. The 700N position corresponds approximately to the α=40° position. The spring rate may be adjusted up or down to vary the angular rotation α needed for member  106  as well.  
         [0045]     In operation the tensioner provides a belt tension as well as damping. The tensioner has a damping coefficient as required by the system. An exemplary value of approximately 23% is utilized in the instant system, and it is asymmetric. of course, other damping coefficients may be realized by changing a coefficient of friction of the damping mechanism surfaces  108   a , see  FIG. 8 . Asymmetric refers to a damping coefficient being greater in a tensioner arm loading direction as compared to a tensioner arm unloading direction during operation of the FEAD system. A loading direction is the direction opposite that of a spring force and has the effect of increasing a load on the tensioner arm. An unloading direction is opposite that of a loading direction. The system may also be operated using damping that is not asymmetric, wherein the damping is approximately equal in the loading and unloading directions.  
         [0046]      FIG. 4  is a front side perspective view of an inventive tensioner. Tensioner  100  comprises tensioner body  102  and tensioner arm  101 . Pulley  105  is journaled to an end of tensioner arm  101 . Pulley  105  engages a belt B as shown in  FIG. 2 . Electric motor  103  is attached to one end of gearbox  104 . Tensioner body  102  is connected to the other end of gearbox  104 .  
         [0047]     Electric motor  103  comprises a DC stepper motor having a voltage range of 12-50 V. By way of example and not of limitation, the motor has a continuous torque of 0.6 Nm and a peak transient torque of 4.3 Nm. The gearbox has a reduction ratio of 100:1 and a torque capacity of 75 Nm. The electrical requirements of the electric motor are provided by the engine electrical system, for example, by an engine alternator or generator or battery.  
         [0048]      FIG. 5  is a rear side perspective view of an inventive tensioner. Pulley  105  is shown underhung but may also be overhung on the opposing surface of tensioner arm  101  as well to accommodate an FEAD system layout.  
         [0049]      FIG. 6  partial cut-away view of an inventive tensioner. Spring attachment member  106  is connected to gearbox output shaft  107 . Gearbox output. shaft  107  determines a position of spring attachment member  106 . Post  101   a  on arm  101  engages the damping mechanism  108 , see  FIG. 13  and  FIG. 15 . A spring force is transmitted to arm  101  through contact of the damping member  108  with post  101   a . Arm  101  is co-axially aligned with, and has an axis of rotation about shaft  107 . However, arm  101  is not mechanically constrained to rotate simultaneously with shaft  107 .  
         [0050]      FIG. 7  is a front perspective partial cut-way view of an inventive tensioner. One end of spring  109  is engaged with spring attachment member  106 , see  FIGS. 6 and 12 . The other end of spring  109  is engaged with damping mechanism  108 , see  FIG. 13  and  FIG. 14 .  
         [0051]     Spring  109  comprises a torsional spring having a predetermined spring rate. The spring rate may be selected depending upon the system belt tension needs. Pivot  110  is connected to tensioner base  102 . Tensioner arm  101  is rotatably engaged with pivot  110  to transmit a belt load to the base.  
         [0052]      FIG. 8  is a side partial cut-away view of the inventive tensioner. The orientation of spring  109  with respect to spring attachment member  106  is shown. Spring end  109   b  is engaged with member  106 . Spring end  109   a  is also engaged with damping mechanism  108 . Damping mechanism  108  is engaged with arm  101  at post  101   a , see  FIG. 6 . Damping mechanism surfaces  108   a  frictionally engage a cooperating arcuate inner surface  102   a  of tensioner body  102 , see  FIG. 7 .  
         [0053]      FIG. 9  is a partial front perspective view of the moveable spring attachment member. Spring attachment member  106  comprises a spring end receiving portion  106   a . Receiving portion  106   a  comprises a slot or groove  106   b  which engages spring end  109   b . Gearbox output shaft  107  is connected to rotatable member  112 , to which member spring attachment member  106  is connected. Spring attachment member  106  is rotatable with an angular movement a by a rotation of shaft  107 . Shaft  107  is rotatable in either a clockwise or counterclockwise direction, depending upon a spring wind direction. Shaft bushing  111  rotates in a corresponding recess  113  in tensioner body  102 , see  FIG. 10 . The angular movement of member  106  adjusts or changes a position of spring  109 . Movement in a first direction increases a force on the arm and thereby a belt tension. A movement of member  106  in a direction opposite the first direction decreases a belt tension. The first direction may either be clockwise or counterclockwise depending upon the wind direction of the spring  109 . The range of angular movement a can be up to 3600 or more.  
         [0054]      FIG. 10  is a partial front perspective view of the tensioner base and the moveable spring attachment member. Spring receiving portion  106   a  projects into tensioner base  102  through arcuate slot  114  in a bottom of tensioner base  102 . Spring receiving portion  106   a  is therefore moveable relative to the tensioner body  102  within arcuate slot  114 . Such movability of spring receiving member  106  allows a spring end position and spring force to be set. This determines a tensioner arm position, which in turn determines a belt tension. Tensioner  100  is attached to an engine surface using threaded fasteners applied through mounting brackets  115 .  
         [0055]      FIG. 11  is a partial front perspective view of a spring and tensioner base. Spring  109  is shown installed in the tensioner body  102  with end  109   b  engaged with spring receiving portion  106   a . Spring end  109   a  engages damping mechanism  108 , see  FIGS. 13 and 15 .  
         [0056]      FIG. 12  is a partial cut-away view of the inventive tensioner. End  109   b  of spring  109  is shown engaged with spring receiving portion  106   a . End  109   a  of spring  109  is engaged with an alternate damping mechanism  2000 , see  FIGS. 15, 16 . Spring receiving member  106  is connected to member  112  and thereby to gearbox output shaft  107 . The damping mechanism shown in this  FIG. 12 , and  FIG. 15  and  FIG. 16 , is an alternate embodiment to that depicted in  FIG. 7 ,  FIG. 13  and  FIG. 14 .  
         [0057]      FIG. 13  is a detail of a damping mechanism. Damping mechanism  108  comprises damping band  1020 . Damping band  1020  is connected to an outer arcuate surface  1040  of damping shoe  1010 . Spring, or biasing member, receiving portion comprises a slot  1030  in damping shoe  1010 . Receiving portion or slot  1030  receives spring end  109   a , see  FIG. 11 , of spring  109 . Surface  1050  engages a portion of a coil of a spring to provide support during operation. Damping band  1020  comprises a plastic such as nylon, PA and PPA, and their equivalents. Post l 0 l a  shown in  FIG. 6  contacts damping mechanism  108  at either  1060  or  1070  depending upon the direction or spring wind or of movement of arm  100 . A spring force by which the belt tension is created is transmitted from spring  109  to arm  101  through contact between the damping mechanism  108  and post l 0 l a . Frictional surface  108   a  engages an inner cooperating surface  102   a  of tensioner base  102 . This embodiment comprises an asymmetric damping characteristic as described elsewhere in this specification. The damping mechanism described herein is also described in co-pending U.S. patent application Ser. No. 10/147,183 filed May 15, 2002, which description is incorporate herein by reference.  
         [0058]      FIG. 14  is a cross-section of  FIG. 13  at line  14 - 14 . Ring cut  1060  extends about an outer perimeter of outer arcuate surface  1040 . Rim or protrusion  1070  extends about a partial circumference of damping shoe  1010 . Ring cut  1060  in combination with protrusion  1070  serve to mechanically attach damping band  1020  to damping shoe  1010 .  
         [0059]      FIG. 15  is a detail of a damping mechanism. Damping mechanism  2000  comprises a first arcuate member  2100  and a second arcuate member  2200 . First arcuate member  2100  has a spring end receiving portion or slot  2110  into which a spring end  109   a  is engaged. Spring end  109   a  engages slot  2110  in two points, namely at  2501  and  2502 . This results in a normal force N being created to press damping mechanism arcuate member  2100  against the base inner surface  102   a . This embodiment comprises an asymmetric damping characteristic as described elsewhere in this specification.  
         [0060]     With respect to spring end l 09   a , referring to  FIG. 13 , spring end  109   a  engages slot  1030  in the same manner as described in this  FIG. 15 .  
         [0061]     A wall of the spring receiving portion has maximum thickness  2110   a  at the spring contact area for increased strength. Wall  2110   a  may be tapered from the contact area in one direction or in both directions as it extends in both directions. The damping mechanism described herein is also described in co-pending U.S. patent application Ser. No. 10/147,183 filed May 15, 2002, which description is incorporate herein by reference.  
         [0062]     First arcuate member  2100  comprises a damping band  2130  attached to a damping shoe  2120 . Second arcuate member  2200  comprises a damping band  2150  attached to a damping shoe  2140 .  
         [0063]     First arcuate member  2100  is in pivotal contact with the second arcuate member  2200  at a point of contact  2160 . Point of contact  2160  comprises end  2280  of damping shoe  2120  and end  2190  of damping shoe  2140 . Point of contact  2160  may be varied from a minimum radius (r) to a maximum radius across a width W of each damping shoe according to the needs of a user.  
         [0064]     End  2170  of arcuate member  2200  is in contact with post  101   a  on arm  101 , see  FIG. 12  and  FIG. 6 . This arrangement results in arcuate member  2200  being subjected to a greater load than arcuate member  2100 .  
         [0065]     In order to achieve a desired asymmetric damping factor, point of contact  2160  between the arcuate members is located at a predetermined radial distance, r, from a lever arm axis of rotation R-R. A minimum radius location (r) for point of contact  2160  results in the highest asymmetric damping factor for the damping mechanism. Point of contact  2160  may be disposed at a maximum outer radius ( 2880 ) which produces a lesser asymmetric damping factor as compared to a foregoing minimum radius location, (r).  
         [0066]     In an alternate embodiment end  2180  of first arcuate member  2100  is in contact with the second arcuate member end  2170 . Post l 0 l a  is then in contact with arcuate member  2200  at point  2160 . In this alternate embodiment, a spring having a coil wind direction opposite that used for the embodiment shown in  FIG. 12  and  FIG. 15  is used. Therefore, by switching the point of contact between the arcuate members from one end of the first arcuate member ( 2180 ) and second arcuate member to the other end ( 2160 ), a torsional spring having an opposite wind can be used.  
         [0067]     Damping band  2130 ,  2150  are made of frictional material such as plastics, phenolics and metallics. A working surface  2300 ,  2310  of damping band  2300 ,  2150  respectively is slideably engaged under pressure with a tensioner base surface  102   a , see  FIG. 12 . A frictional damping force is generated as the damping band slides on the tensioner base surface.  
         [0068]     Damping shoes  2120 ,  2130  are each made of structural material such as steel, molded plastic or equivalents thereof. Each damping shoe can be manufactured by utilizing a powder metal process, a die cast process, injection molding or similar processes. Materials that can be used include steel, aluminum (for low load parts), thermoplastics with various fillers, and equivalents thereof.  
         [0069]     Damping band  2150  of the second arcuate member has a material thickness greater than the damping band  2130  of the first portion. This has two advantages, first, increased spring hook-up size (and spring thickness) can be realized, therefore a spring having a greater spring rate can be used. The greater spring rate spring results in the ability to generate a greater belt tension. Second, since the second portion  2200  of the damping mechanism has higher load than the first portion  2100 , a reduced thickness of the first damping band  2130  will equalize durability and wear life of both parts.  
         [0070]      FIG. 16  is a cross-section of  FIG. 15  at line  16 - 16 . Ring cut  2210  extends about an outer perimeter of damping shoe  2120 . Protrusion  2220  extends about a partial circumference of damping shoe  2120 . Ring cut  2230  extends about an outer perimeter of damping shoe  2140 . Protrusion  2240  extends about a partial circumference of damping shoe  2140 . Each ring cut  2210 ,  2230  in combination with each protrusion  2220 ,  2240  serve to mechanically attached each damping band  2130 ,  2150  to each damping shoe  2120 ,  2140  respectively.  
         [0071]     Although forms of the invention have been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.