Abstract:
In control apparatus and method for an automotive vehicle, the vehicle having a continuously variable transmission associated with a vehicular engine and including a belt that transmits a revolution of a primary pulley to a secondary pulley that is enabled to make a gear shift by modifying a pulley ratio between the primary and secondary pulleys with a hydraulic, a determination is made as to whether a belt slip between at least one of the primary and the secondary pulleys occurs and an output section outputs a signal to command an engine control unit to increase an engine speed by a predetermined engine speed when the belt slip is determined to occur.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to shift hydraulic system of a belt-type continuously variable transmission. More particularly, the present invention relates to control apparatus and method for preventing an occurrence of a belt slip of the belt-type continuously variable transmission (so called, CVT).  
           [0003]    2. Description of the Related Art  
           [0004]    A Japanese Patent Application First Publication No. Heisei 9-250370 published on Sep. 22, 1997 exemplifies a previously proposed shift hydraulic system for a belt-type continuously variable transmission. In the above-described Japanese Patent Application First Publication, when an electromagnetic hydraulic control valve has failed to control a line pressure, a technique to prevent an excessive rise in the line pressure is disclosed. That is to say, if the electromagnetic hydraulic control valve has failed, the hydraulic valve becomes an open state such that the hydraulic of an oil pump is disabled to be drained and an excessive rise in the line pressure causes a clamp pressure to clamp a belt of the continuously variable transmission to be excessively high. Hence, the frictional load of the belt becomes large, a fuel consumption becomes wasteful, and a durability of the belt becomes worsened.  
         SUMMARY OF THE INVENTION  
         [0005]    However, if a (waste or dust) is invaded into a hydraulic circuit disclosed in the above-described Japanese Patent Application Publication, the valve constituting the electromagnetic hydraulic control valve becomes sticky due to a clogging of the waste or dust so that the line pressure becomes lowered. If the line pressure is lowered, the clamp pressure for the belt is not sufficiently supplied. Thus, a slip of the belt occurs. The durability of the belt becomes reduced. Especially, when the vehicle is started, the large torque is inputted. On the contrary, there is a possibility that the belt slips when an engine speed is slow and the line pressure becomes lowered.  
           [0006]    It is, therefore, an object of the present invention to provide control apparatus and method for the belt continuously variable transmission associated with an engine which are capable of preventing the occurrence of the belt slip and improving the durability of the belt even if the waste or dust is invaded into the hydraulic circuit to reduce the line pressure.  
           [0007]    According to one aspect of the present invention, there is provided a control apparatus for an automotive vehicle, comprising: a continuously variable transmission associated with a vehicular engine and including a belt that transmits a revolution of a primary pulley to a secondary pulley that is enabled to make a gear shift by modifying a pulley ratio between the primary and secondary pulleys with a hydraulic; a belt slip determining section that determines if a slip between at least one of the primary and the secondary pulleys occurs; and an output section that outputs a signal to command an engine control unit to increase an engine speed by a predetermined engine speed when the belt slip determining section determines that the slip therebetween occurs.  
           [0008]    According to another aspect of the present invention, there is provided a control apparatus for an automotive vehicle, comprising: an engine control unit; an oil pump driven by an engine; a continuously variable transmission associated with a vehicular engine and including a belt that transmits a revolution of a primary pulley to a secondary pulley that is enabled to make a gear shift by modifying a pulley ratio between the primary and secondary pulleys with a hydraulic, continuously variable transmission including a belt to transmit a revolution of a primary pulley to a secondary pulley driven by a revolution of the engine; an original hydraulic supplying section that supplies an original hydraulic of a control hydraulic to control the pulley ratio with the oil pump as a hydraulic source; a gear shift actuator that supplies an original hydraulic for the control hydraulic that controls a pulley ratio with the oil pump as a hydraulic source; a gear shift actuator that supplies the control hydraulic to each pulley; and a gear shift controlling section that outputs a control command to the gear shift actuator; and an original hydraulic determining section that determines whether the original hydraulic of the original hydraulic supplying section is equal to or below a predetermined hydraulic when an engine idling is carried out during a vehicular stop; and an output section that outputs a signal to command the engine control unit to increase the engine idling speed by a predetermined engine speed.  
           [0009]    According to a still another aspect of the present invention, there is provided a control method for an automotive vehicle, the vehicle comprising: a continuously variable transmission associated with a vehicular engine and including a belt that transmits a revolution of a primary pulley to a secondary pulley that is enabled to make a gear shift by modifying a pulley ratio between the primary and secondary pulleys with a hydraulic, and the method comprising: a belt slip determining section that determines if a belt slip between at least one of the primary and the secondary pulleys occurs; and outputting a signal to command an engine control unit to increase an engine speed by a predetermined engine speed at a time of determining that the slip therebetween occurs.  
           [0010]    This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a circuit block diagram of an essential unit of a vehicle equipped with a belt continuously variable transmission to which a control apparatus for the belt continuously variable transmission is applicable.  
         [0012]    [0012]FIG. 2 is a hydraulic circuit block diagram of the control apparatus shown in FIG. 1.  
         [0013]    [0013]FIG. 3 is an operational flowchart representing a belt slip detection control procedure in the first embodiment of the control apparatus for the belt continuously variable transmission.  
         [0014]    [0014]FIG. 4 is an operational flowchart representing a belt slip preventive control procedure in the first embodiment shown in FIG. 1.  
         [0015]    [0015]FIG. 5 is an operational flowchart representing a belt slip detection and preventive control procedure in a second preferred embodiment of the control apparatus according to the present invention.  
         [0016]    [0016]FIG. 6 is an operational flowchart representing a belt slip preventive procedure in a third preferred embodiment of the control apparatus in a third preferred embodiment according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    Reference will hereinafter be made to the drawings in order to facilitate a better understanding of the present invention.  
       First Embodiment  
       [0018]    [0018]FIG. 1 shows a control system of an engine and a belt(-type) continuously variable transmission  3  (hereinafter, described as CVT) to which a first preferred embodiment of a control apparatus according to the present invention is applicable.  
         [0019]    Reference numeral  1  denotes a torque converter, reference numeral  2  denotes a lock-up clutch, reference numeral  3  denotes a CVT (Continuously Variable Transmission), reference numeral  4  denotes a primary pulley revolution speed sensor, reference numeral  5  denotes a secondary pulley revolution speed sensor, reference numeral  6  denotes a hydraulic control valve unit, reference numeral  8  denotes an oil pump driven with an engine, reference numeral  9  denotes a CVT control unit, reference numeral  10  denotes an accelerator opening angle sensor, reference numeral  11  denotes an oil temperature sensor, reference numeral  18  denotes an engine, reference numeral  19  denotes an engine control unit (hereinafter, also abbreviated as ECU), reference numeral  16  denotes an engine speed sensor, and a reference numeral  17  denotes a throttle valve opening angle sensor. Engine  18  is provided with a plurality of fuel injectors to inject fuel and with an electronically controlled throttle valve which is operated in response to a command of an electronically driven actuator. ECU  21  outputs a command to inject fuel to each fuel injector and a command to open an angle to electronically controlled throttle valve.  
         [0020]    ECU  21  basically receives signals from engine speed sensor  16  detecting the engine speed Ne, from accelerator opening angle sensor  10  to detect a manipulated variable of an accelerator pedal by a vehicle driver, and from throttle opening angle sensor  17  to detect a throttle opening angle TVO corresponding to an engine load and outputs commands such as to command engine  18  to control an engine output torque, to command engine  18  to control an idling speed of engine  18  during a vehicle stop, and to command engine  18  to control a fuel cut-off to improve a fuel economy by cutting off the fuel injection until an engine speed Ne is reduced to a predetermined engine speed during a vehicular deceleration. Torque converter  1  is linked to an engine output axle as a revolution transmission mechanism and lock-up clutch  2  is disposed to directly couple engine  18  to CVT  3 . An output end of torque converter  1  is linked to a ring gear  21  of forward-and-rearward switching mechanism  20 . Forward-and-rearward switching mechanism  20  is constituted by a planetary gear mechanism having a ring gear  21  linked to an engine output axle  12 , a pinion carrier  22 , and a sun gear  23  linked to an input axle  13  of the transmission. Pinion carrier  22  is provided with a backward drive brake  24  to fix pinion carrier  22  to a transmission casing and a forward drive clutch  25  to integrally link input axle  13  of the transmission and the pinion carrier  22 .  
         [0021]    Primary pulley  30   a  of CVT  3  is disposed on an end of transmission input axle  13 . CVT  3  is constituted by primary pulley  30   a , secondary pulley  30   b , and a belt  34  which transmits a revolution force of primary pulley  30   a  to a secondary pulley  30   b . Primary pulley  30   a  includes a fixed truncated cone shaped plate  31 , and a movable truncated cone shaped plate  32  which is movable in an axial direction of the input axle  13  of transmission by means of a hydraulic acted upon a primary pulley cylinder chamber  33 , a letter V-shaped pulley groove being formed together with an oppositely arranged fixed truncated cone shaped plate  31 .  
         [0022]    A secondary pulley  30   b  is disposed on a driven axle  38 . Secondary pulley  30   b  includes a fixed truncated cone shaped plate  35  integrally revolved to driven axle  38  and a movable truncated cone shaped plate  36  which is formed with a letter V-shaped pulley groove together with the opposing fixed truncated cone plate  35  is movable in the axial direction of driven axle  38  by means of the hydraulic acted upon a secondary pulley cylinder chamber  37 .  
         [0023]    A drive gear (not shown) is fixed onto driven axle  38  and drive gear drives a drive shaft from pinion disposed on an idler axle, a final gear, and differential mechanism to the road wheels (not shown).  
         [0024]    The revolving force inputted from engine output axle  12  to CVT  3  is transmitted to CVT  3  via torque converter  1  and forward-and-rearward switching mechanism  20 . The revolving force of transmission input axle  13  is transmitted to a differential gear unit via primary pulley  30   a , belt  34 , secondary pulley  30   b , a driven axle  38 , drive gear, an idler gear, an idler axle, a pinion, and a final gear.  
         [0025]    During a power transmission as described above, a contact position radius of belt  34  is varied by displacing the contact position radius by moving movable truncated cone plate  36  in the axial direction and the movable truncated cone plate  32  of primary pulley  30   a  in the axial direction. Thus, a revolution ratio, viz., a gear ratio between primary pulley  30   a  and secondary pulley  30   b  can be changed. Such a control as a V-shaped pulley groove width described above is carried out by means of the hydraulic control via CVT control unit  9  to be supplied to primary pulley cylinder chamber  33  or secondary pulley cylinder chamber  37 .  
         [0026]    CVT control unit  9  receives primary revolution speed Npri from primary pulley revolution speed sensor  4 , a secondary pulley revolution speed N SEC  from secondary pulley revolution speed sensor  5 , a primary pulley pressure Ppri from primary pressure sensor  14 , and a secondary pulley Psec from secondary pressure sensor  15 . In addition, CVT control unit  9  is communicated with ECU  21  to transmit and receive each sensor value information therebetween. Based on these input signals control signals are calculated. Control signals are outputted to hydraulic control valve units  6 .  
         [0027]    Hydraulic control valve unit  6  drives respective electronic control valves and stepping motor  54  as will be described later on the basis of the control signals calculated in CVT control unit  9 . The shift control is carried out by supplying a control pressure to primary pulley cylinder chamber  33  and secondary pulley cylinder chamber  37 .  
         [0028]    [0028]FIG. 2 shows a circuit block diagram representing the hydraulic circuit of the belt (type) continuously variable transmission in the first embodiment according to the present invention.  
         [0029]    In FIG. 2, reference numeral  40  denotes a pressure regulator valve to adjust a delivery pressure of an oil pump  8  supplied from an oil passage  41  as a line pressure (viz., a pulley clamp pressure). An oil passage  42  is communicated with an oil passage  41 . Oil passage  42  is connected to a shift control valve  50  which supplied a control hydraulic to primary pulley cylinder chamber  33  of CVT  3 . A pulley pressure supply oil passage  48  which supplies a clamp pressure to clamp belt  34  is connected to secondary pulley cylinder. In addition, oil passage  43  connected to oil passage  42  supplies an original pressure of a pilot valve  55 . Shift control valve  50  includes a suction port  50   a  connected to oil passage  42 , a supply port  50   b  which supplies the hydraulic with primary pulley cylinder  33 , a drain port  50   c  which drains the hydraulic, and a link  52  to which a stepping motor (S/M)  54  which is operated in response to a control signal from CVT control unit  9 . Shift control valve  50  constitutes a mechanical feedback mechanism. An activation of stepping motor  52  moves spool  50   d . When the hydraulic is supplied to primary pulley cylinder chamber  33 , a variation in a gear (shift) ratio causes movable pulley (secondary pulley) to be moved. This movement drives spool  50   d  in a direction opposite to the drive of stepping motor  54  so that the supply of hydraulic is stopped. Thus, a desired gear (shift) ratio can be achieved. On the other hand, when the hydraulic of primary pulley cylinder chamber  33  is drained (exhausted), the variation in the gear ratio causes the movable pulley to be moved. This movement drives spool  50   d  in the opposite direction to the previous drive so that the drainage of the hydraulic is stopped. Thus, the desired gear ratio can be achieved.  
         [0030]    Hydraulic drained from pressure regulator valve  40  is supplied to a clutch regulator valve  60  via an oil passage  46 . As described above, a clutch regulator valve  60  adjusts the hydraulic lower than that developed by pressure regulator valve  40  so that the hydraulic supplied as a clutch pressure of a forward clutch  25  is not higher than a pulley clamp pressure. This oil passage  46  is communicated with oil passage  42  and with an orifice  45 . Clutch regulator valve  60  adjusts the hydraulic in oil passage  46  and oil passage  61 . The hydraulic of oil passage  46  and oil passage  61 . The hydraulic of oil passage  61  is supplied to a select switching valve  80  and select control valve  90 .  
         [0031]    Pilot valve  55  sets a constant supply pressure to a lock-up solenoid  71  to a select switching solenoid  70 . An output pressure of select switching solenoid  70  is supplied from oil passage  73  to select switching valve  80  to control an operation of a select switching valve  80 . An output pressure of lock-up solenoid  71  is supplied from oil passage  72  to select switching valve  80 .  
         [0032]    Select switching valve  80  is operated by select switching solenoid  70 . An oil passage  72  which supplies a signal pressure from lock-up solenoid  71  is connected as an input port of select switching valve  80 , an oil passage  61  at which clutch regulator valve  60  serves to adjust the hydraulic is connected to the select switching valve  80 , and an oil passage  93  at which select control valve  90  serves to adjust the hydraulic is connected to select switching valve  80 . An oil passage  83  to supply the hydraulic to operate a spool  92  of a select control valve  90  is connected to select switching valve  80 . A drain oil passage  84  to drain the hydraulic is connected to select switching valve  80 .  
         [0033]    Select control valve  90  is operated by means of lock-up solenoid  71  supplied from hydraulic passage  83 . A hydraulic passage  62  at which the hydraulic is adjusted by means of clutch regulator valve  60  is connected to an input port of select control valve  90 . An oil passage  83  to supply a signal pressure of lock-up solenoid  71  is connected to select control valve  90 . Then, a control over a communication state between the oil passage  62  and the oil passage  93  causes the hydraulic to be adjusted.  
         [0034]    [0034]FIG. 3 shows an operational flowchart representing a belt slip detection control procedure executed in the first embodiment of the control apparatus.  
         [0035]    At a step S 101 , CVT control unit  9  determines whether engine speed Ne is higher than a predetermined engine speed Ne1. If Ne&gt;Ne1 (Yes) at step S 101 , the routine goes to a step S 102 . That is to say, in a case where the hydraulic is not secured irrespective of the drive of the engine, there is a possibility of failure in the hydraulic circuit. At step S 102 , CVT control unit  9  determines whether a difference (P* sec −P 1 ) between a target secondary pulley cylinder hydraulic P*sec and a first set hydraulic P 1  (for example, 0.05 MPa) is larger than a (second) set hydraulic P 0  (for example, 1 MPa). If the difference (P*sec−P 1 ) is larger than set hydraulic P 0  (Yes), the routine goes to a step S 103 . If (P*sec−P 1 )≦P 1  (No) at step S 102 , the routine goes to a step S 104 . At step S 103 , CVT control unit  9  sets (P*sec−P 1 ) as a set value Pmin. At step S 104 , CVT control unit  9  sets the set value to Pmin. At step S 102  through S 104 , CVT control unit  9  selects set value Pmin to determine if a difference between a target secondary pulley hydraulic P*sec and an actual secondary pulley hydraulic Psec is too large. If target secondary pulley hydraulic P*sec is low and placed in the vicinity to set hydraulic value P 0 , there is no possibility that the deviation is in excess of set hydraulic P 0 . Hence, as a determination criterion, a subtraction of first set value P 1  from target secondary pulley hydraulic P*sec is used. When a target secondary pulley P*sec is high, set hydraulic P 0  is used as the deviation determination criterion. At a step S 105 , CVT control unit  9  determines whether a difference between target secondary pulley hydraulic P*sec and actual secondary pulley hydraulic Psec is larger than set value Pmin, CVT control unit  9  can determine that the hydraulic is sufficiently secured. At a step S 106 , CVT control unit  9  determines if actual secondary pulley hydraulic Psec is smaller than first set hydraulic P 1 . If Psec&lt;P 1  (Yes) at step S 106 , the routine goes to a step S 107 . If Psec≦P 1  (No) at step S 106 , the routine goes to step S 111 . At step S 107 , CVT control unit  9  determines if shift ratio G (=Npri(or Nin)/Nsec (or Nout) revolution speed of the primary pulley with respect to the secondary pulley) is larger than a predetermined shift ratio G 0 . If G&gt;G 0  (yes) at step S 107 , the routine goes to a step S 110 . If G≦G 0  (No) at step S 107 , the routine goes to step S 111 . That is to say, if the secondary pulley is not almost revolved against the revolution of the primary pulley, CVT control unit  9  can determine that the belt is being slipped. At step S 108 , a belt slip (occurrence) flag F is set to “1”. At step S 111 , a belt slip (occurrence) flag F is reset.  
         [0036]    [0036]FIG. 4 shows an operational flowchart representing a belt slip preventive control when the belt slip is detected. At step S 201 , CVT control unit  9  determines whether a belt slip flag F is set to “1”. If set to “1” (F=1) (Yes) at step S 201 , the routine goes to a step S 202 . If F=0, the routine in FIG. 5 is ended. At step S 202 , CVT control unit  9  determines if CVT falls in an over-drive mode (OD, namely, the shift ratio control is small). If OD (Yes) at step S 202 , the routine goes to a step S 203 . If Not, the routine goes to a step S 204 . At step S 203 , CVT control unit  9  transmits a torque limitation demanded value T1 to ECU  31 . At step S 204 , CVT control unit  9  transmits a torque limitation demanded value T 2  to ECU  31 . It is noted that T1&gt;T2. That is to say, since, when the gear ratio is small, no deceleration is carried out (or a speed increase side), a torque applied to the secondary pulley is small and even if an upper limit of the input torque is made higher, the belt is not easy to be slipped. While securing a smooth running ability, the belt slip can be prevented. On the other hand, when the gear (shift) ratio is large, the deceleration occurs. The torque applied to the secondary pulley becomes large. If torque limitation demanded value T2 is set to be low due to the large torque applied to the secondary pulley, the torque limitation demanded value T2 is set to be low to prevent the recurrence of the slip. Then, at a step S 206 , CVT control unit  9  transmits to ECU  31  a fuel cut-off recovery speed increase demand signal which indicates a resumption of fuel injection when the engine speed is decreased by a predetermined speed. That is to say, if the engine idling speed is increased, there is a possibility that the fuel injection is resumed at an engine speed lower than the idling speed. Hence, an engine stability may occur. For example, in a case where, during the normal operation the idling speed is 550 rpm and the fuel cut-off recovery engine speed is 1200 rpm, the idling speed is increased to 750 rpm. In this case, fuel cut-off recovery speed is also increased from 1200 rpm to 1350 rpm.  
       Second Embodiment  
       [0037]    Next, a second preferred embodiment of the control apparatus will be described. A basic structure of the second embodiment is generally the same as described in the first embodiment. Hence, only a difference point will be described below. FIG. 5 shows an operational flowchart representing a belt slip preventive control when the belt slip is detected. Since steps S 201  through S 206  are the same as described in the first embodiment, different steps will be explained below. That is to say, at a step S 301 , CVT control unit  9  determines whether the velocity of the vehicle in which the control apparatus according to the present invention is mounted (VSP) is zero. If the vehicle is stopped (VSP=0), the routine goes to a step S 302 . If VSP≠0 at step S 301  (No), the routine goes to step S 201 . The contents of step S 201  has been described. At step S 302 , CVT control unit  9  determines whether a line pressure P L  is larger than a predetermined line pressure P PL . If P L &gt;P PL  (Yes) at step S 302 , the routine is ended. If P L ≦P PL  (No) at step S 302 , CVT control unit  9  transmits an idle speed increase demand ECU  31  to increase the present engine idle speed. That is to say, if line pressure PL during the vehicle stop is smaller than predetermined line pressure P PL , there is a possibility of the belt slip. Immediately, the idle speed is raised. It is possible to secure the line pressure. Then, the belt slip during the vehicular stop can be prevented.  
       Third Embodiment  
       [0038]    Next, a third preferred embodiment of the control apparatus according to the present invention will be described. The basic structure of the third embodiment is generally the same or described in the first embodiment. Hence, the difference points will be described below. FIG. 6 shows an operational flowchart representing the belt slip preventive control when the belt slip is detected. Steps S 201  through S 206  are generally the same as those described in the first embodiment. The difference points will only be described below. At step S 401 , CVT control unit  9  determines if the vehicle speed VSP, viz., the vehicle is stopped.  
         [0039]    At a step S 402 , CVT control unit  9  determines if line pressure PL is larger than a predetermined line pressure P PL . If PL&gt;P PL  (Yes) at step S 402 , the routine goes to a step S 403 . At step S 403 , a line pressure decrease flag f is set to “0”. At step S 404 , line pressure decrease flag f is set to “1”. At a step S 405 , CVT control unit  9  determines whether a belt slip decrease flag F=1 and line pressure decrease flag f=1. If F=1 and f=1 (Yes) at step S 405 , the routine goes to a step S 205 . If F≠1 or f≠1 (No) at step S 405 , the routine is ended. That is to say, if the line pressure at the idling speed during the vehicular stop is equal to or smaller than the predetermined line pressure and the belt slip is determined to occur under a state in which the torque during the vehicular start is largely applied, the idling speed at the next vehicular stop is increased. Hence, it is not necessary to increase the idle speed with no belt slip. While preventing the belt slip, the fuel consumption can be improved.  
         [0040]    The contents of a Japanese Patent Application No. 2002-280749 (filed in Japan on Sep. 26, 2002) are herein incorporated by reference. Various changes and modifications may be made without departing from the sprit and scope of the present invention which is to be defined in the appended claims.