Abstract:
A device for detecting the speed of an endless torque-transmitting member that passes around a pair of spaced conical pulley pairs of a continuously variable transmission. The device includes a sensor that is positioned adjacent the endless torque-transmitting member and that detects the speed of the endless torque-transmitting member at a point that is located relative to the movement course of the endless torque-transmitting member that is independent of the rotational speed relationship of the pulley pairs.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to apparatus for determining the speed of an endless torque-transmitting member of a continuously variable transmission.  
           [0003]    2. Description of the Related Art  
           [0004]    Conical pulley transmissions having an endless torque-transmitting means and for providing a continuous change of the transmission ratio are increasingly utilized as automatic transmissions in motor vehicles. FIG. 1 of the drawings is a schematic representation showing the basic structure of such a transmission.  
           [0005]    A continuously variable transmission of the type shown in FIG. 1 includes two conical pulley pairs  4  and  6 . One conical pulley disc  4   1  of conical pulley pair  4  is rigidly connected with a drive shaft  8  that is driven by, for example, an internal combustion engine. The other conical pulley disc  4   2  of conical pulley pair  4  is non-rotatably connected with but is axially moveable relative to drive shaft  8 . One conical pulley disc  6   1  of conical pulley pair  6  is rigidly connected with an output shaft  10  that drives the vehicle. The other conical pulley disc  6   2  of conical pulley pair  6  is non-rotatably connected with but is axially moveable relative to output shaft  10 . An endless torque-transmitting means  12  passes around the two conical pulley pairs  4  and  6  and is in frictional engagement with the opposed two conical surfaces of the respective conical pulley pairs. By means of opposite adjustment of the axial spacing between the two conical pulleys of each conical pulley pair, the rotational speed relationship between the two conical pulley pairs, and therefore the transmission ratio of the transmission, can be changed.  
           [0006]    Pressure chambers  14  and  16  that are connected by way of hydraulic conduits  18  and  20  with a control valve  22  serve, for example, for the adjustment of the transmission ratio by the application to pressure chambers  14  and  16  of pressurized hydraulic fluid pressure, by which the transmission ratio can be controlled. A control unit  23  serves for the actuation of the control valve  22  and includes a microprocessor with associated storage means. Inputs for the control unit are connected, for example, with a selection lever unit that serves for operating the transmission, an accelerator pedal, rotational speed sensors, and the like. The outputs of the control unit are connected, for example, with a clutch, a power output stage of the engine (not shown) and control valve  22 . The construction and function of a continuously variable transmission are known and are therefore not further explained.  
           [0007]    For many applications it is advantageous to know the speed of endless torque-transmitting means  12 , for example in order to precisely establish the contact pressure applied by the conical surfaces of the conical pulleys with which the endless torque-transmitting means is in contact, and which is controllable by the pressure in pressure chambers  14  and  16 . That contact pressure should only be as large as necessary for acceptable frictional engagement or power flow between the endless torque-transmitting means and the conical pulleys, so that the transmission is not unnecessarily stressed and so that no unnecessary hydraulic pumping capacity is utilized.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of the invention is to provide apparatus having a simple structure and that works reliably to determine the speed of the endless torque-transmitting means of a continuously variable transmission.  
           [0009]    That object is achieved with apparatus for the determination of the speed of the endless torque-transmitting means of a continuously variable transmission, which continuously variable transmission includes two conical pulley pairs rotatably situated on separate axes that are parallel to each other and having two spaced conical discs. The axial spacing of the conical discs can be changed in opposite directions for the purpose of changing the rotational speed relationship of the conical pulley pairs, so that an endless torque-transmitting means that passes around the conical pulley pairs moves independently of the respective transmission ratio and in frictional engagement with the conical surfaces of the conical pulleys. The apparatus includes a sensor that detects the speed of the endless torque-transmitting means in a position whose location relative to the movement path of the endless torque-transmitting means is independent of the rotational speed relationship of the conical pulley pairs.  
           [0010]    The sensor is advantageously guided and brought into contact with a slack strand of the endless torque-transmitting means by a guide bar that is tiltable about an axis that is parallel to the axes of the conical pulley pairs.  
           [0011]    The guide bar is advantageously located on an oil pipe that extends between the conical pulley pairs so that it is displaceable in a direction that is substantially perpendicular to the direction of movement of the endless torque-transmitting means and is stationary in the direction of movement of that element.  
           [0012]    If the endless torque-transmitting means is a plate-link chain, the sensor advantageously detects the moving pins that interconnect individual links, the end faces of which pins are in frictional engagement with the conical surfaces. Preferably, the sensor is a proximity sensor that detects the end faces of the pins.  
           [0013]    In a preferred embodiment of the apparatus in accordance with the invention the sensor is connected to an control unit in which data relative to the plate-link chain are stored, and which determines the speed of the plate-link chain by the number of the detected pins and by the time intervals between successive pins. Advantageously, the number of plate links of the plate-link chain and their lengths are stored in the control unit.  
           [0014]    If the plate-link chain has different spacings between the pins, the control unit stores at least one of the different spacing between the pins and at least a number of equal, successive spacings, and the control unit determines the speed of the plate-link chain after detecting a number of equal, successive spacings.  
           [0015]    The invention can be installed in all types of continuously variable transmissions having continuously variable transmission ratios. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The structure, operation, and advantages of the present invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings in which:  
         [0017]    [0017]FIG. 1 is a schematic representation of a previously-described, known continuously variable transmission with an associated control unit.  
         [0018]    [0018]FIG. 2 is a cross-sectional view through the middle of a continuously variable transmission, perpendicular to the axes of the shafts;  
         [0019]    [0019]FIG. 3 is a side view of a portion of a plate-link chain; and  
         [0020]    [0020]FIG. 4 is an enlarged, cross-sectional view taken along the line IV-IV of FIG. 2. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    [0021]FIG. 2 shows a cross-sectional view through the middle of a continuously variable transmission, perpendicular to the axes of the shafts  8  and  10 . The slack strand of endless torque-transmitting means  12  is guided by a guide bar  24  which prevents undulations of the slack strand. In the illustrated embodiment, the rotational direction of the pulley pairs  4  and  6  is counterclockwise, and shaft  8  is the drive shaft that is driven by the motor. The continuously variable transmission or its endless torque-transmitting means  12 , which are completely represented by dashed lines, are shown in two different positions. In position A, the spacing between the conical pulleys of conical pulley pair  4  is at a minimum and that between the conical pulleys of conical pulley pair  6  is at a maximum, so that the transmission operates at the highest possible gear ratio. In the other position B, the transmission operates at the smallest possible gear ratio, which means that the radius at which the endless torque-transmitting means travels on the conical pulley pair  6  is at a maximum.  
         [0022]    As is apparent, the movement path of endless torque-transmitting means  12  changes continuously with the transmission ratio change, whereby the straight parts of the movement paths generally do not intersect at an intersection point S as shown, the position of which is fixed and independent of the rotational speed relationship or the transmission ratio (in FIG. 2 only the lower intersection point S is identified).  
         [0023]    Guide bar  24  that guides endless torque-transmitting means  12  between an outer guideway  28  and an inner guideway  26  is carried on a fixed pivot in the form of a pin that is fastened to the transmission housing (not shown) or on an oil pipe  30 . Guide rail  24  includes a U-shaped recess  32  whose opposite sidewalls are approximately perpendicular to the movement direction of the endless torque-transmitting means, or to the longitudinal direction of the guide bar, and is supported in such a way that it follows a change of the movement path of the endless torque-transmitting means  12  by pivoting on the outer surface of oil pipe  30  and by the shifting of the opposed walls of recess  32  relative to the oil pipe outer surface, so that its slack strand is continuously securely guided and is secured against any undulations. Oil pipe  30  has radial openings through which, and through corresponding openings at the bottom of recess  32 , guide bar  24  is supplied with lubricant so that the endless torque-transmitting means is lubricated and is moveable along guide bar  24  with reduced friction.  
         [0024]    Endless torque-transmitting means  12  is advantageously shown in the illustrated embodiment as a known plate-link chain, of which a portion is shown in FIG. 3. Such a plate-link chain is composed of several side-by-side rows of plate links  34  arranged in the movement direction of the plate-link chain, in which links  34  are arranged one behind another in the movement direction of the plate-link chain. The connection of the plate links is effected by pins  36  that pass laterally through the plate-link chain or through inner openings of the plate links, wherein the pins are composed of two rocker members the facing surfaces of which roll against each other when the chain assumes a curved form, and whose oppositely-facing surfaces serve as bearing surfaces for neighboring rows of the links and serve for longitudinally connecting the rows. Outer end faces  38  of pins  36 , or the rocker member pairs, form the surfaces with which the plate-link chain is in a frictional engagement with the conical surfaces of the conical disk pairs.  
         [0025]    A sensor  40  is securely fastened on guide bar  24  so that it detects end faces  38  of pins  36 , or the rocker member pairs, that pass by, for detecting the linear speed of plate-link chain  12 . Because guide bar  24  moves in correspondence with the change of the movement path of the plate-link chain, without moving along the movement direction of the chain, the position of the sensor remains constant relative to the movement path of the plate-link chain and is independent of the transmission ratio, so that the linear speed of the plate-link chain is reliably detected.  
         [0026]    Advantageously, sensor  40  is mounted in the middle region of the guide bar, from which a connection conduit can be passed between the conical pulleys to the outside.  
         [0027]    In FIG. 4, which shows a cross-section taken along line IV-IV of FIG. 2, sensor  40  is mounted on the side of guide bar  24  and extends into the interior thereof, where end faces  38  move along a sensor surface of sensor  40 . Sensor  40  is, for example, an inductively functioning distance sensor, the inductance of which changes from time to time when the end faces move by, so that the time lapse or the number of the passing pins  36  can be detected. It is sufficient for resolution accuracy if the two end faces of a pair of rocker members are not detected individually, but are detected together as end faces of a single pin. If the distance between pins  36  and the time duration of the passing movement of two pins passing sensor  40  are known, the speed of the plate-link chain can be determined.  
         [0028]    In order to determine the speed of a so-called “random pitch” chain whose links have different lengths, so that the spacing between pins  36  varies, an algorithm for the detection of the pattern at which the spacing between pins  36  changes can be stored in an control unit connected with sensor  40 , for example in control unit  23 . For example, the pattern in which long and short links follow one another, or the quantity, is stored in control unit  23 , so that by counting the number of successively following same pin spacings can be determined, whether it is a matter of short or long spacings. It should be understood that at least one more additional pin spacing must be evaluated than actually present equal pin spacings. After identifying whether it is a short or a long pin spacing, the speed of the plate-link chain can in turn be determined by forming a simple ratio from the pin spacing and the time interval in which the pins follow one another.  
         [0029]    According to another evaluation type, as many pins can be counted as are contained in the chain, so that the speed can be determined from the length of the time needed and the chain length.  
         [0030]    It should be understood that the algorithm can be changed in various ways.  
         [0031]    The described structural arrangement can be changed in various ways. Sensor  40  can be cast in an opening in the guide bar, or can be glued. Sensor  40  can work in any suitable physical fashion. Sensor  40  can be fastened on a transmission housing of belt-driven transmissions whose conical surfaces have a form by which the junction S is stationary and independent of the transmission ratio, and the movement of the plate-link chain at point S can be determined through an opening in the guide bar. The data transmission from the sensor to an control unit can occur without contact.  
         [0032]    Guide bar  24  does not necessarily have to guide the endless torque-transmitting means along its inner or outer side, but can, for example, guide it only along its inner side, and it can be urged outward elastically at its bearing.  
         [0033]    In a further changed design, a touching wheel, for example a gear wheel or a friction wheel, can be arranged in such a way that it detects the movement of the endless torque-transmitting means about at the junction S, so that a direct mechanical sensing of the endless torque-transmitting means can take place at the stationary location of its movement path. This is especially advantageous if the endless torque-transmitting means is not formed as a plate-link chain, but is in the form of a band with a substantially level front- or backside. It should be understood that a plate-link chain can also be sensed from the outer or inner side.  
         [0034]    In an advantageous way it is common to all embodiments of the invention that the endless torque-transmitting means is detected by the sensor at one position, the location of which is approximately constant relative to the endless torque-transmitting means and independent of the respective transmission ratio.