Patent Document

FIELD OF THE INVENTION 
     This invention relates to preventing slippage in the belt of a belt-type continuously variable transmission for use in a vehicle. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 5,820,514 discloses a belt-type continuously variable transmission (hereinafter referred to as belt CVT) for use in a vehicle. 
     The belt CVT comprises a primary pulley for inputting the drive force of an engine, a secondary pulley for outputting the drive force to a drive wheel, and a V-belt that is wrapped around the primary pulley and secondary pulley. In the primary pulley and secondary pulley, pulley grooves for accepting the belt are each varied in width by oil pressure. Changes in the width of the pulley grooves change the contact radius between the V-belt and the pulley, which results in changing the rotation speed ratio of the primary pulley and the secondary pulley, or in other words the speed ratio of the transmission. 
     The output rotation of the engine is transmitted to the primary pulley via a torque converter and a forward/reverse change-over mechanism. 
     The forward/reverse change-over mechanism comprises a forward clutch that is engaged during forward travel of the vehicle, or in other words when the driver places a shift lever in a drive range (D), and a reverse clutch that is engaged during reverse travel, or in other words when the driver places the shift lever in the reverse range (R). When the shift lever is in the neutral range (N), both of these clutches are released, and the output rotation of the engine is not transmitted to the primary pulley. These clutches are engaged by means of oil pressure, and the clutches are released from an engaged state by the release of oil pressure into a drain. 
     SUMMARY OF THE INVENTION 
     In this type of belt CVT, when the shift lever is moved from the drive range (D) to the neutral range (N) and then back to the drive range (D) during vehicle travel, the oil pressure engaging the forward clutch is released all at once into the drain and is thus reduced, and oil pressure is subsequently re-supplied to the forward clutch for the engagement thereof. 
     Meanwhile, the primary pulley and secondary pulley of the belt CVT require a constant oil pressure in order to prevent slippage in the V-belt while maintaining the present groove width, regardless of whether a change in speed ratio has been directed. 
     Because oil pressure is usually supplied by the same oil pressure supply unit, the oil pressure supplied to the belt CVT temporarily decreases due to the effect of supplying oil pressure to the forward clutch when an operation is performed whereby the shift lever is moved from the drive range (D) to the neutral range (N), and then back to the drive range (D) during vehicle travel. As a result, the power by which the pulley holds the V-belt can be insufficient for the rotation torque of the engine that is input to the primary pulley during the change-over from the neutral range (N) to the drive range (D), and slippage can occur between the pulley and the V-belt. V-belt slippage is especially likely to occur when the accelerator pedal is depressed following re-selection of the drive range (D) since the input torque to the primary pulley suddenly increases. This type of slippage in a V-belt consisting of a metal member contributes to impaired durability of the V-belt. 
     It is therefore an object of this invention to prevent slippage in a belt-type continuously variable transmission accompanying an operation of a shift lever during vehicle travel. 
     In order to achieve the above object, this invention provides a vehicle drive train comprising an engine, a continuously variable transmission comprising a pair of pulleys that are mutually connected via a belt wherein the continuously variable transmission varies torque transmitted between the pulleys via the belt according to a supplied oil pressure, a clutch which connects the engine to one of the pair of pulleys by engaging in accordance with a supplied oil pressure wherein the oil pressure is supplied to the clutch and continuously variable transmission from an identical oil pressure source, a drive wheel connected to the other of the pair of pulleys, and an engine output regulating mechanism which reduces an output torque of the engine when the clutch is engaged. 
     The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a drive train control device for a vehicle according to this invention. 
         FIGS. 2A and 2B  are block diagrams depicting the configuration of a controller according to this invention. 
         FIG. 3  is a flow chart describing an engine output torque regulation routine executed by the controller. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1  of the drawings, a belt CVT  1  for use in a vehicle comprises a primary pulley  41 , a secondary pulley  42 , and a V-belt  43  wrapped around the pulleys  41  and  42 . 
     The primary pulley  41  comprises a fixed conical plate  41   a  and a movable conical plate  41   b  disposed facing each other. The V-belt  43  catches in a pulley groove that is V-shaped in cross-section and is formed between the fixed conical plate  41   a  and the movable conical plate  41   b . The movable conical plate  41   b  moves in response to a primary pressure supplied via a primary pressure regulating unit  44  to vary the width of the pulley groove and the contact radius between the V-belt  43  and the primary pulley  41 . The movable conical plate  41   b  is fixed to an input shaft  41   c . The output rotation of an engine  70  mounted in the vehicle is input to the input shaft  41   c  via a torque converter  20  and a forward/reverse change-over mechanism  30 . 
     The secondary pulley  42  comprises a movable conical plate  42   a  and a fixed conical plate  42   b  disposed facing each other. The V-belt  43  catches in a pulley groove that is V-shaped in cross-section and is formed between the movable conical plate  42   a  and the fixed conical plate  42   b . The movable conical plate  42   a  moves in response to a secondary pressure supplied via a secondary pressure regulating unit  45  to vary the width of the pulley groove and the contact radius between the V-belt  43  and the secondary pulley  42 . The rotation of the fixed conical plate  42   b  is transmitted to a drive wheel  80  of the vehicle. The pressure-receiving surface area of the movable conical plate  41   b  and movable conical plate  42   a  are set to be substantially equal. 
     The torque converter  20  is a publicly known mechanism for transmitting the rotation of the engine  70  by means of the flow of oil between a pump impeller and a turbine liner. The torque converter  20  comprises a lockup device for causing the pump impeller to rotate in integrated fashion with the turbine liner. 
     The forward/reverse change-over mechanism  30  comprises a planetary gear set  31 , a forward clutch  32 , and a reverse clutch  33 . The planetary gear set  31  comprises an external sun gear  31   a , and an internal ring gear  31   d  disposed on the outside thereof. A plurality of pinions  31   b  that mesh with the outside perimeter of the sun gear  31   a  and the inside perimeter of the ring gear  31   d  and a carrier  31   c  for supporting the pinions  31   b  are furthermore comprised therein. The sun gear  31   a  is connected to an output shaft of the torque converter  20 , and the carriers  31   c  are connected to the input shaft  41   c  of the primary pulley  41 . 
     The forward clutch  32  connects the carrier  31   c  with the sun gear  31   a  according to oil pressure supplied to a clutch piston chamber  32   a  from a clutch pressure regulating unit  35 . As a result, the output rotation of the torque converter  20  is transmitted as is to the input shaft  41   c  of the primary pulley  41  via the sun gear  31   a  and carrier  31   c.    
     The reverse clutch  33  locks the rotation of the ring gear  31   d  according to the oil pressure supplied to a clutch piston chamber  33   a  from the clutch pressure regulating unit  35 . As a result, the sun gear  31   a  and carrier  31   c  rotate in opposite directions, and the output rotation of the torque converter  20  is transmitted to the input shaft  41   c  of the primary pulley  41  in reverse. 
     The forward clutch  32  and reverse clutch  33  are engaged exclusively. Specifically, the reverse clutch  33  is invariably released when the forward clutch  32  is engaged, and the forward clutch  32  is invariably released when the reverse clutch  33  is engaged. In a state in which the forward clutch  32  and reverse clutch  33  are both released, the sun gear  31   a  and carrier  31   c  rotate relative to each other in arbitrary fashion. 
     Oil pressure is supplied to the primary pressure regulating unit  44 , secondary pressure regulating unit  45 , and clutch pressure regulating unit  35  from an oil pressure pump  10  driven by the engine  70 . The discharge pressure of the oil pressure pump  10  is regulated to a predetermined line pressure by means of a line pressure regulating unit  46 , and is distributed to the primary pressure regulating unit  44 , secondary pressure regulating unit  45 , and clutch pressure regulating unit  35 . The primary pressure regulating unit  44  furthermore regulates the line pressure to a predetermined primary pressure to operate the movable conical plate  41   b  of the primary pulley  41 . The secondary pressure regulating unit  45  furthermore regulates the line pressure to a predetermined secondary pressure to operate the movable conical plate  42   a  of the secondary pulley  42 . The line pressure of the clutch pressure regulating unit  35  is regulated to a predetermined clutch pressure, and is selectively supplied to the forward clutch  32  and reverse clutch  33 . 
     The primary pressure regulating unit  44 , secondary pressure regulating unit  45 , and line pressure regulating unit  46  respectively regulate the primary pressure, secondary pressure, and line pressure according to command signals from a controller  60 . 
     The clutch pressure regulating unit  35  supplies the oil pressure used for engaging a particular clutch according to the command signal from the controller  60 . 
     The controller  60  is composed of a microcomputer that comprises a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and an input/output interface (I/O interface). The controller may also be composed of a plurality of microcomputers. 
     The controller  60  controls the primary pressure, secondary pressure, and line pressure, and engages and releases the forward clutch  32  and reverse clutch  33 . The controller  60  also controls the output torque of the engine  70  by outputting an engine control signal to an electronic throttle  61  provided in the engine  70 . 
     Detected data from a rotation speed sensor  47  for detecting the rotation speed of the engine  70 , a rotation speed sensor  51  for detecting the rotation speed of the primary pulley  41 , a rotation speed sensor  52  for detecting the rotation speed of the secondary pulley  42 , a pressure sensor  53  for detecting the primary pressure, a pressure sensor  54  for detecting the secondary pressure, an inhibitor switch  56  for detecting the selected position of the shift lever provided to the vehicle, and an accelerator pedal depression sensor  57  for detecting the amount of depression of the accelerator pedal provided in the vehicle are input as signals to the controller  60  to serve as parameters for controlling these actions. The shift lever is provided with a drive range (D) used for forward travel, a reverse range (R) used for reverse travel, and a neutral range (N) in which the rotation torque of the engine  70  is not transmitted to the drive wheel. 
     Because the secondary pulley  42  is connected with drive wheel  80 , the rotation speed of the secondary pulley  42  detected by the rotation speed sensor  52  is utilized as a parameter for indicating the vehicle speed. 
     The controller  60  performs publicly known control relating to the operation of the forward clutch  32  and reverse clutch  33  of the forward/reverse change-over mechanism  30  according to the range selection of the shift lever, and relating to the speed ratio of the publicly known belt CVT  1 , which is controlled by the primary pressure and secondary pressure. Furthermore, the controller  60  limits the output torque of the engine  70  so that no slippage occurs in the V-belt  43  when the shift lever is operated from the drive range (D) to the neutral range (N) and from the neutral range (N) to the drive range (D) within a short amount of time during vehicle travel, as previously described. 
     Referring to  FIGS. 2A and 2B , the functioning of the controller  60  for limiting the output torque will now be described. 
     The controller  60  comprises a transmission control unit  61  and an engine control unit  62 . 
     The transmission control unit  61  is composed of a torque-limiting condition determining block  61   a , an oil pressure controlling block  61   b , a torque limiting initiation/termination determining block  61   c , a torque capacity calculating block  61   d , an input torque calculating block  61   e , a torque limit determining block  61   f , a torque limit value calculating block  61   g , and a torque limit value output block  61   h.    
     The engine control unit  62  is composed of an engine torque calculating block  62   a , a torque-down amount calculating block  62   b , and an electronic throttle opening regulating block  62   c.    
     The units and blocks depicted in the drawings are hypothetical units/blocks depicting functions of the controller  60 , and do not exist physically. 
     The torque-limiting condition determining block  61   a  determines whether torque-limiting conditions are established based on the selected range input from the inhibitor switch  56  and on the rotation speed of the secondary pulley  42  input from the rotation speed sensor  52 . Torque limiting conditions are established when the selected range of the shift lever shifts from the neutral range to the drive range at a vehicle speed that is at or above a set vehicle speed. The set vehicle speed is set in this case at ten kilometers per hour. The torque-limiting condition is not satisfied when the vehicle speed is less than ten kilometers per hour, because the vehicle start-up performance will be adversely affected, if the output torque of the engine  70  is limited to a vehicle speed less than ten kilometers per hour. 
     The oil pressure controlling block  61   b  limits the line pressure and secondary pressure over a predetermined time period to pressures that the oil pressure pump  10  is capable of generating. The line pressure is limited in order to maintain the engaging pressure of the forward clutch  32 , and the secondary pressure is limited so as to prevent the speed ratio of the belt CVT  1  from increasing, or in other words to prevent the output rotation of the belt CVT  1  from decreasing. Limiting the line pressure results in limiting the primary pressure. As a result, the primary pressure is maintained at a low pressure over a predetermined time period after the selected range of the shift lever is changed over from the neutral range to the drive range, as depicted in the drawing of the torque limit determining block  61   f.    
     The torque limiting initiation/termination determining block  61   c  sets a torque limit flag to unity when torque limiting conditions are established based on the determination results of the torque limiting-condition determining block  61   a , and resets the torque limit flag to zero when torque limiting conditions are not established. The initial value of the torque limit flag is zero. 
     The torque capacity calculating block  61   d  calculates the speed ratio of the belt CVT  1  from the rotation speed of the primary pulley  41  and rotation speed of the secondary pulley  42 . Furthermore, the maximum torque that would not cause the belt  43  to slip against the primary pulley  41  and secondary pulley  42  is calculated based on the speed ratio and the secondary pressure detected by the pressure sensor  54 . This value is labeled as the torque capacity Tc. 
     The input torque calculating block  61   e  sets the actual engine torque Te input from the engine control unit  62  as the input torque Ti of the belt CVT  1 . 
     The torque limit determining block  61   f  compares the input torque Ti and torque capacity Tc of the belt CVT  1 , and determines that torque limiting is necessary for the input torque Ti when the torque capacity Tc falls below the input torque Ti, as shown by the shaded area in the figure. 
     The torque limit value calculating block  61   g  limits the input torque Ti to the torque capacity Tc when it is necessary to limit the input torque. 
     The torque limit value output block  61   h  outputs a torque limit requirement value that is in accordance with the torque limit flag to the torque-down amount calculating block  62   b . When the torque limit flag is at zero, a maximum value for the torque limit requirement value is output to the torque-down amount calculating block  62   b  as the torque limit requirement value. Herein the maximum value denotes that no torque limitation is required. When the torque limit flag is at unity, the input torque Ti calculated by the torque limit value calculating block  61   g  is output as the torque limit requirement value to the torque-down amount calculating block  62   b.    
     The engine torque calculating block  62   a  of the engine control unit  62  calculates the throttle valve opening TVO of the engine  70  from the amount of depression of the accelerator pedal, and calculates the output torque of the engine  70  from the throttle valve opening TVO, fuel injection amount of the engine  70 , and rotation speed of the engine  70 , with reference to a map having characteristics such as those shown in the figure. If the controller  60  also controls the fuel injection amount of the engine  70 , the controller  60  is capable of obtaining the fuel injection amount from data that are stored therein. 
     The torque-down amount calculating block  62   b  calculates a torque-down amount on the basis of the torque limit requirement value that is input from the torque limit value output block  61   h  and the output torque of the engine  70  calculated by the engine torque calculating block  62   a.    
     The electronic throttle valve opening regulating block  62   c  narrows the valve opening of the electronic throttle  61  according to the torque-down amount. 
     Next, referring to  FIG. 3 , a routine executed according to the above configuration whereby the controller  60  prevents belt slippage in the belt CVT  1  will be described. This routine is executed at intervals of ten milliseconds during operation of the engine  70 . 
     First, in a step S 1 , the controller  60  determines whether the vehicle speed is at or above the previously described set vehicle speed of ten kilometers per hour on the basis of the rotation speed of the secondary pulley  42  detected by the rotation speed sensor  52 . When the vehicle speed is under ten kilometers per hour, the controller  60  determines that limiting of the output torque of the engine  70  will not be performed in a step S 8 , and the routine is terminated. 
     When the vehicle speed is at or above ten kilometers per hour, the controller  60  determines in a step S 2  whether the torque limit flag is at unity. When the torque limit flag is not at unity, the controller  60  performs the processing of a step S 3 . 
     In the step S 3 , the controller  60  determines whether the shift lever has been changed over from the neutral range (N) to the drive range (D). This determination is performed by comparing the input signal from the inhibitor switch  56  with the previous input signal at fixed time intervals. If the shift lever has not been changed over from the neutral range (N) to the drive range (D), the controller  60  determines that limiting of the output torque of the engine  70  will not be performed in the step S 8 , and the routine is terminated. 
     When the shift lever has been changed over from the neutral range (N) to the drive range (D), the controller  60  sets the torque limit flag to unity in a step S 4 . 
     Next, in a step S 5 , the controller  60  limits the line pressure and secondary pressure to pressures that the oil pressure pump  10  is capable of generating. 
     The controller  60  furthermore calculates the torque-down amount in a subsequent step S 6 . 
     In a subsequent step S 7 , the controller  60  limits the output torque of the engine  70  on the basis of the torque-down amount. The controller  60  terminates the routine after the process in the step S 7 . 
     On the other hand, in the step S 2 , when the torque limit flag is at unity, the controller  60  determines whether a predetermined period of time has elapsed since the torque limit flag was set to unity in a step S 9 . If the predetermined period of time has not elapsed, the controller  60  executes the processing beginning in the step S 5 . 
     When the predetermined period of time has elapsed, the controller  60  stops limiting the output torque of the engine  70  in a step S 10 , the torque limit flag is set to zero, and the routine is terminated. The predetermined period of time corresponds to the time required for torque limiting to become unnecessary after changing over from the neutral range (N) to the drive range (D), and is determined experientially in advance. 
     By executing this routine, the output torque of the engine  70  is limited over the predetermined period of time when the shift lever is changed over from the neutral range (N) to the drive range (D) while the vehicle is traveling at or above the predetermined vehicle speed. 
     In the routine described above, the steps S 1  through S 3  and the step S 9  correspond to the functioning of the torque-limiting condition determining block  61   a , the step S 4  corresponds to the functioning of the torque limiting initiation/termination determining block  61   c , the step S 5  corresponds to the functioning of the oil pressure controlling block  61   b , and the step S 6  corresponds to the functioning of the torque capacity calculating block  61   d , input torque calculating block  61   e , torque limit determining block  61   f , torque limit value calculating block  61   g , engine torque calculating block  62   a , and torque-down amount calculating block  62   b . The step S 7  corresponds to the functioning of the throttle valve opening regulating block  62   c , and the steps S 8  and S 10  correspond to the functioning of the torque limit value output block  61   h.    
     During changing over from the neutral range (N) to the drive range (D), the oil pressure which acts upon the primary pulley  41  and secondary pulley  42  is reduced in order to maintain the engaging pressure of the forward clutch  32 . However, the primary pulley  41  and secondary pulley  42  are able even in this case to maintain the necessary holding force to prevent the input torque Ti input to the belt CVT  1  from the engine  70  from exceeding the torque capacity Tc, and the belt  43  from slipping. Also, when the accelerator pedal is depressed during changing over from the neutral range (N) to the drive range (D), the belt  43  does not slip because the torque Ti that is input to the belt CVT  1  from the engine  70  is controlled so as not to exceed the torque capacity Tc. 
     Also, because the output torque of the engine  70  is limited only for the predetermined period of time based on the torque capacity that is calculated based on the actual speed ratio and primary pressure, limiting of the output torque of the engine can be kept to the required minimum. 
     The contents of Tokugan 2002-256463, with a filing date of Sep. 2, 2002 in Japan, are hereby incorporated by reference. 
     Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. 
     For example, the predetermined vehicle speed is set to ten kilometers per hour in this embodiment, but can be changed to any speed according to the specifications of the engine or belt CVT to which the invention is applied. 
     In the embodiment thus described, changing over of the shift lever from the neutral range to the drive range is detected by the inhibitor switch  56 , and the vehicle speed is detected by the rotation speed sensor  54  in order to determine whether the torque limiting condition is established. The speed ratio calculated from the speed detected by the rotation speed sensors  53  and  54 , and the secondary pressure detected by the pressure sensor  54  are used to calculate the torque capacity of the belt CVT  1 . The engine rotation speed is detected by the rotation speed sensor  47 , the valve opening of the electronic throttle  61  is detected from the accelerator pedal depression amount sensor  57 , and the fuel injection amount of the engine  70  is obtained from data stored within the controller  60  in order to calculate the output torque of the engine  70 . The parameters for these controls can, however, be detected or calculated by various other means. This invention can be applied to any vehicle drive train device that uses the above parameters to control the claimed engine output torque, independent of the method used to acquire the parameters. 
     The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows:

Technology Category: b