Patent Document

BACKGROUND OF THE INVENTION 
   The present invention relates to a hydraulic control apparatus for a vehicle with a belt-drive continuously variable transmission (CVT). 
     FIG. 4A  illustrates a hydraulic control apparatus of a related art. As illustrated in  FIG. 4A , primary pulley  300  of a belt-drive CVT includes fixed disk  301  making a unitary rotation with input rotation transmitted from an engine, and moveable disk  302  axially moveable corresponding to an oil pressure supplied to cylinder chamber  303 . Transmission control valve  100  includes spool  101 , port  102  communicated with a pressure regulator valve, not shown, port  103  communicated with cylinder chamber  303 , and drain port  104  through which an oil pressure in cylinder chamber  303  is drained when communicated with port  103 . Spool  101  is connected with stepping motor  200  via link  400 . Link  400  is coupled to stepping motor  200  at one end thereof and an outer circumferential periphery of moveable disk  302  at an opposite end thereof. Thus, spool is also connected with moveable disk  302  via link  400 . As moveable disk  302  moves, spool  101  is displaced. Stepping motor  200 , spool  101  of transmission control valve  100 , moveable disk  302  of primary pulley  300  and link  400  constitute a mechanical feedback mechanism for controlling the movement of spool  101 . 
   Referring to  FIGS. 4A and 4B , an operation of the mechanical feedback mechanism upon changing a transmission ratio of the belt-drive CVT to the Low speed side, namely, upon increasing the transmission ratio, is explained. Here, in other words, the transmission ratio of the belt-drive CVT is a pulley speed ratio between a rotational speed of primary pulley  300  and a rotational speed of a secondary pulley, not shown.  FIG. 4B  shows, at upper, middle and lower parts thereof, relationships between stepping motor  200 , spool  101  of transmission control valve  100  and the pulley speed ratio in an initial state of the mechanical feedback mechanism, in a driven state of stepping motor  200 , and in a transmission ratio change completed state, respectively. In the initial state, spool  101  is in a neutral position where the communication between ports  102 ,  103  and  104  are blocked. When a drive command for controlling the transmission ratio to the Low speed side is outputted to stepping motor  200  as shown in the middle part of  FIG. 4B , stepping motor  200  drives spool  101  to upward move from the neutral position shown in the upper part of  FIG. 4B  to a drain position shown in the middle part of  FIG. 4B . In the drain position of spool  101 , port  103  is communicated with port  104  to thereby allow drain of the oil within cylinder chamber  303  from port  104 . Owing to the drain of the oil within cylinder chamber  303 , moveable disk  302  is moved downward as indicated by arrow in  FIG. 4A . This causes the opposite end portion of link  400  which is coupled with moveable disk  302  to move downward. As a result, spool  101  is downward moved and return to the neutral position as shown in the lower part of  FIG. 4B . In the neutral position, the communication between ports  103  and  104  are prevented so that drain of the oil pressure is stopped. The change of the transmission ratio to the Low speed side is thus completed. Japanese Patent Application First Publication No. 09-032898 discloses a hydraulic control apparatus having such a mechanical feedback mechanism. 
   SUMMARY OF THE INVENTION 
   However, in the related art described above, even in a case where the engine is restarted after the vehicle is stopped while the transmission ratio is kept on the High speed side, stepping motor  200  will be controlled so as to change the transmission ratio to the Low speed side in order to ensure a sufficient driving force of the engine. In such a case, ports  303  and  304  are communicated with each other so that the oil within cylinder chamber  303  is drained from port  104  as explained above. The amount of the oil within cylinder chamber  303  becomes insufficient in amount, whereby there will occur slippage of the belt of the CVT. 
   It is an object of the present invention to eliminate the above-described disadvantage and provide a hydraulic control apparatus for a vehicle with a belt-drive continuously variable transmission (CVT), which is capable of ensuring a transmittable torque capacity of the belt even when the vehicle is stopped while the transmission ratio is kept on the High speed side. 
   In one aspect of the present invention, there is provided a hydraulic control apparatus for a vehicle having an engine, the hydraulic control apparatus comprising: 
   a belt-drive continuously variable transmission (CVT) including a primary pulley and a secondary pulley, each of the primary and secondary pulleys having a cylinder chamber to which an oil pressure is supplied and defining a groove variable in width corresponding to the oil pressure, and a belt engaged with the groove to transmit rotation of the primary pulley to the secondary pulley, the belt-drive CVT being operative to continuously vary a transmission ratio by changing the width of the groove; 
   an oil pressure source operative to produce an oil pressure supplied to the belt-drive CVT, the oil pressure source being adapted to be driven by the engine; 
   a pressure regulator valve operative to regulate the oil pressure produced by the oil pressure source; 
   a controller programmed to develop a transmission control signal, the transmission control signal including a high speed transmission control signal for changing the transmission ratio to a high speed side and a low speed transmission control signal for changing the transmission ratio to a low speed side; 
   a transmission actuator operative to be driven based on the transmission control signal; 
   a first oil passage for supplying the oil pressure regulated by the pressure regulator valve; 
   a second oil passage for supplying the oil pressure regulated to the cylinder chamber of the primary pulley and draining the oil pressure from the cylinder chamber of the primary pulley; 
   a third oil passage for draining the oil pressure within the cylinder chamber of the primary pulley; 
   a fourth oil passage downstream of the pressure regulator valve; and 
   a transmission control valve operative to be actuated by the transmission actuator for controlling the oil pressure within the cylinder chamber of the primary pulley, the transmission control valve including a first port communicated with the first oil passage, a second port communicated with the second oil passage, a third port communicated with the third oil passage, and a spool having a block position where fluid communication between the first, second and third ports is prevented, a high speed side transmission position where the first port is fluidly communicated with the second port when the transmission actuator is driven in response to the high speed transmission control signal, and a low speed side transmission position where the second port is fluidly communicated with the third port when the transmission actuator is driven in response to the low speed transmission control signal, the spool cooperating with the transmission actuator and the primary pulley to form a mechanical feedback mechanism for returning the spool to the block position in response to change in the width of the groove of the primary pulley, 
   wherein the third oil passage is connected with the fourth oil passage to supply an oil pressure to the cylinder chamber of the primary pulley and establish a minimum oil pressure required for clamping the belt depending on reduction of the oil pressure within the cylinder chamber of the primary pulley. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram illustrating a control apparatus of a vehicle having a belt-drive continuously variable transmission (CVT), according to an embodiment of the present invention. 
       FIG. 2  is a hydraulic circuit diagram of the embodiment shown in  FIG. 1 , with modifications of the embodiment. 
       FIG. 3  is a diagram showing a relationship between a stepping motor, a transmission control valve and a primary pulley width. 
       FIGS. 4A and 4B  are diagrams showing a relationship between a stepping motor, a transmission control valve and a primary pulley width in the related art. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , there is shown a hydraulic control apparatus for a vehicle having an engine and an automatic transmission coupled to the engine, according to an embodiment of the present invention. The automatic transmission is equipped with belt-drive continuously variable transmission (hereinafter referred to as CVT)  3 . As illustrated in  FIG. 1 , CVT  3  is coupled to the engine via lockup clutch  2  for direct connection between CVT  3  and the engine. Torque converter  1  is connected to output shaft  12  of the engine. Forward-reverse switching mechanism  20  is disposed on an output side of torque converter  1 . Forward-reverse switching mechanism  20  includes a planetary gear train, reverse brake  24  and forward clutch  25 . The planetary gear train includes ring gear  21  coupled to output shaft  12  of the engine, pinion carrier  22 , and sun gear  23  coupled to input shaft  13  of CVT  3 . Reverse brake  24  is operative to fix pinion carrier  22  to a transmission case. Forward clutch  25  is operative to couple input shaft  13  of CVT  3  and pinion carrier  22  with each other and acts as a start clutch. Oil pump  8  acting as an oil pressure source is mechanically coupled to the engine and directly driven by the engine. 
   CVT  3  includes primary pulley  30   a , secondary pulley  30   b  and belt  34  connecting primary and secondary pulleys  30   a  and  30   b  to thereby transmit the rotation force of primary pulley  30   a  to secondary pulley  30   b . Primary pulley  30   a  is disposed on a rear side portion of input shaft  13 . Primary pulley  30   a  includes fixed disk  31  rotatable together with input shaft  13 , and moveable disk  32  opposed to fixed disk  31  in an axial direction of input shaft  13 . Fixed and moveable disks  31  and  32  have generally conical shapes and cooperate with each other to form a V-groove in which belt  34  is engaged. Moveable disk  32  is axially moved on input shaft  13  by an oil pressure supplied to primary pulley cylinder chamber  33 . Secondary pulley  30   b  is disposed on driven shaft  38 . Secondary pulley  30   b  includes fixed conical disk  35  rotatable together with driven shaft  38 , and moveable disk  36  opposed to fixed disk  35  in an axial direction of driven shaft  38 . Fixed and moveable disks  35  and  36  have generally conical shapes and cooperate with each other to form a V-groove in which belt  34  is engaged. Moveable disk  36  is axially moved on driven shaft  38  by an oil pressure supplied to secondary pulley cylinder chamber  37 . A driving gear, not shown, is fixed onto driven shaft  38 . The driving gear is operative to drive a driving shaft connected to a wheel via a pinion on an idler shaft, a final gear and a differential gear. 
   The rotation force outputted from output shaft  12  of the engine is transmitted to input shaft  13  of CVT  3  via torque converter  1  and forward-reverse switching mechanism  20 . The rotation force of input shaft  13  is successively transmitted to primary pulley  30   a , belt  34 , secondary pulley  30   b , driven shaft  38 , the driving gear, an idler gear, the idler shaft, the pinion, the final gear and the differential gear. Upon thus transmitting the rotation force, moveable disk  32  of primary pulley  30   a  and moveable disk  36  of secondary pulley  30   b  are axially moved on input and driven shafts  13  and  38 , respectively, to change a width of the V-groove which extends in the axial direction of input and driven shafts  13  and  38 . A radius of curvature of a circular arc formed by V-belt  34  contacted with pulleys  30   a  and  30   b  is continuously varied by changing the V-groove width. A pulley speed ratio between the rotational speed of primary pulley  30   a  and the rotational speed of secondary pulley  30   b , namely, a transmission ratio of CVT  3 , can be thus changed. The change of the V-groove width is conducted by controlling the oil pressure supplied to primary pulley cylinder chamber  33  or secondary pulley cylinder chamber  37 . The hydraulic control is performed by CVT controller or control unit  9 . 
   A plurality of sensors are electronically connected to CVT controller  9  to detect engine operating conditions. The sensors includes primary pulley speed sensor  4 , secondary pulley speed sensor  5 , throttle position sensor  10  and pulley clamping pressure sensor  14 . Primary pulley speed sensor  4  detects the rotational speed of primary pulley  30   a  and generates signal Np indicative of the detected primary pulley speed. Secondary pulley speed sensor  5  detects the rotational speed of secondary pulley  30   b  and generates signal Ns indicative of the detected secondary pulley speed. Throttle position sensor  10  detects an opening degree of a throttle valve and generates signal TVO indicative of the detected throttle opening degree. Pulley clamping pressure sensor  14  detects a pulley clamping pressure supplied to each of primary and secondary pulley cylinder chambers  33  and  37  for clamping belt  34 , and generates signal CP indicative of the detected pulley clamping pressure. 
   CVT controller  9  receives the signals generated from these sensors, processes the signals, and develops and transmits control signal CS to hydraulic control valve unit  6 . CVT controller  9  may be a microcomputer including central processing unit (CPU), input and output ports (I/O), read-only memory (ROM), random access memory (RAM) and a common data bus. 
   Hydraulic control valve unit  6  receives a plurality of signals indicative of an accelerator opening degree, the transmission ratio of CVT  3 , the rotational number of input shaft  13 , a primary pulley pressure, and the like. Hydraulic control valve unit  6  controls the transmission ratio of CVT  3  by supplying pulley clamping pressure CP to primary and secondary pulley cylinder chambers  33  and  37  based on the input signals. 
     FIG. 2  shows a hydraulic circuit used in the embodiment of the hydraulic control apparatus. As illustrated in  FIG. 2 , pressure regulator valve  40  is connected to oil pump  8  via oil passage  41 . Pressure regulator valve  40  regulates a discharge pressure produced from oil pump  8  and outputs the regulated pressure as line pressure (pulley clamping pressure). Oil passage  43  is communicated with oil passage  41  and supplies pulley clamping pressure CP to secondary pulley cylinder chamber  37 . Oil passage  42  as a line pressure supply passage is communicated with oil passage  41  and supplies primary pulley cylinder chamber  33  with pulley clamping pressure CP for clamping belt  34  and a transmission control pressure for controlling the transmission ratio of CVT  3 . 
   Transmission control valve  50  is disposed on oil passage  42  and controls an oil pressure within primary pulley cylinder chamber  33 . Namely, transmission control valve  50  controls supply and drain of an oil pressure relative to primary pulley cylinder chamber  33 . Specifically, transmission control valve  50  has port  51  connected to oil passage  42 , port  52  connected to oil passage  52   a  which is communicated with primary pulley cylinder chamber  33 , and port  53  connected to oil passage  72  which is communicated with oil cooler  80 . Transmission control valve  50  also has spool  50   a  moveable to switch fluid communication between ports  51 ,  52  and  53 . Spool  50   a  has a block position where the fluid communication between ports  51 ,  52  and  53  is prevented, a high speed side transmission position where ports  51  and  52  are fluidly communicated with each other to change the transmission ratio to a smaller value, namely, to the High speed side, and a low speed side transmission position where ports  52  and  53  are fluidly communicated with each other to change the transmission ratio to a larger value, namely, to the Low speed side. 
   Spool  50   a  is connected with stepping motor  90  and moveable disk  32  of primary pulley  30   a  via link  91 . Spool  50   a , stepping motor  90  and moveable disk  32  form a mechanical feedback mechanism for controlling the movement of spool  50   a . Stepping motor  90  which acts as a transmission actuator for actuating spool  50   a , is driven based on a transmission control signal transmitted from CVT controller  9 . The transmission control signal includes a high speed transmission control signal for changing the transmission ratio to the High speed side and a low speed transmission control signal for changing the transmission ratio to the Low speed side. Stepping motor  90  actuates spool  50   a  to shift between the high speed side transmission position and the low speed side transmission position in response to the high speed transmission control signal and the low speed transmission control signal. Depending on these positions of spool  50   a , the oil pressure is supplied to primary pulley cylinder chamber  33  and discharged therefrom. This causes moveable disk  32  to axially move to change the width of the V-groove of primary pulley  30   a . In response to the change in the V-groove width, spool  50   a  connected with moveable disk  32  via link  91  is returned to the block position. In the block position, the supply of the oil pressure and the discharge thereof are stopped and thus the transmission operation is completed. The operation of the mechanical feedback mechanism will be in detail explained later. 
   An oil pressure drained from pressure regulator valve  40  is supplied to clutch regulator valve  60  downstream of pressure regulator valve  40  via oil passage  46 . Oil passage  46  is communicated with oil passage  44  which is communicated with oil passage  42  and has orifice  45 . Clutch regulator valve  60  regulates the oil pressure in oil passage  46  and the oil pressure in oil passage  61  to produce forward clutch applying pressure CAP. Forward clutch applying pressure CAP is supplied to forward clutch  25  of forward-reverse switching mechanism  20  via oil passage  61 , a select switching valve, not shown, and a select control valve, not shown. With this arrangement, forward clutch applying pressure CAP is regulated smaller than pulley clamping pressure CP. 
   An oil pressure drained from clutch regulator valve  60  is supplied to torque converter regulator valve  70  downstream of clutch regulator valve  60  via oil passage  62 . Torque converter regulator valve  70  regulates the oil pressure in oil passage  62  to produce a torque converter pressure and a lockup clutch applying pressure and a lockup clutch releasing pressure. The lockup clutch applying pressure and the lockup clutch releasing pressure are supplied to a lockup control valve via oil passage  63  communicated with oil passage  62 . An oil drained from torque converter regulator valve  70  is supplied to oil cooler  80  via oil passage  71 . The oil passing through oil cooler  80  is cooled and supplied to lubrication parts of CVT  3  to be lubricated. Oil passage  71  is connected with oil passage  72  communicated with port  53  of transmission control valve  50 . 
     FIG. 3  illustrates the mechanical feedback mechanism for controlling spool  50   a  of transmission control valve  50 . Referring to  FIG. 3 , the operation of the feedback mechanism is explained. First, an operation of changing the transmission ratio to the Low speed side, namely, an operation of increasing the transmission ratio, is described. In this case, the width of the V-groove of primary pulley  30   a  must be increased by draining the oil pressure within primary pulley cylinder chamber  33 . First, stepping motor  90  is moved upward as viewed in  FIG. 3 . Following the movement of stepping motor  90 , spool  50   a  is also upward moved to the low speed side transmission position where port  52  is fluidly communicated with port  53  to thereby allow drain of the oil pressure within primary pulley cylinder chamber  33  from port  53 . The oil pressure drained is then supplied to oil cooler  80  via oil passage  72  as shown in  FIG. 2 . Owing to the drain of the oil pressure within primary pulley cylinder chamber  33 , moveable disk  32  is moved downward as viewed in  FIG. 3 , to thereby increase the width of the V-groove. The transmission ratio is shifted to the Low speed side. The downward movement of moveable disk  32  causes spool  50   a  to move downward to the block position where the fluid communication between port  52  and port  53  is prevented. As a result, the drain of the oil pressure within primary pulley cylinder chamber  33  is stopped and the change of the transmission ratio to the Low speed side is completed. 
   Next, an operation of changing the transmission ratio to the High speed side, namely, an operation of decreasing the transmission ratio, is explained. In this case, the width of the V-groove of primary pulley  30   a  must be decreased by supplying an oil pressure to primary pulley cylinder chamber  33 . When stepping motor  90  is moved downward as viewed in  FIG. 3 , spool  50   a  is also moved downward to the high speed side transmission position where port  51  is fluidly communicated with port  52  to thereby allow supply of the oil pressure from pressure regulator valve  40  to primary pulley cylinder chamber  33 . This causes moveable disk  32  to move upward as viewed in  FIG. 3 , to thereby decrease the width of the V-groove. Thus, the transmission ratio is shifted to the High speed side. The upward movement of moveable disk  32  causes spool  50   a  to move upward to the block position where the fluid communication between port  51  and port  52  is prevented. As a result, the supply of the oil pressure to primary pulley cylinder chamber  33  is stopped and the change of the transmission ratio to the High speed side is completed. 
   When the vehicle is stopped while the transmission ratio is kept on the High speed side, spool  50   a  is placed in the block position where port  52  is prevented from fluid communication with port  51  and port  53 . In this condition, when the engine is restarted and stepping motor  90  is actuated to drive spool  50   a  for changing the transmission ratio to the Low speed side, port  52  and port  53  are communicated with each other. Therefore, the oil pressure to be supplied from torque converter regulator valve  70  toward oil cooler  80  via oil passage  71  is supplied to primary pulley cylinder chamber  33  via oil passages  71  and  72 , ports  53  and  52 , and oil passage  52   a . This can establish the oil pressure, namely, pulley clamping pressure CP, within primary pulley cylinder chamber  33 , which is required to clamp belt  34 , to thereby prevent occurrence of slippage of belt  34 . This serves for improving durability of belt  34 . 
   Further, the oil pressure regulated by clutch regulator valve  60  is smaller than the oil pressure regulated by pressure regulator valve  40 . The oil pressure regulated by torque converter regulator valve  70  is smaller than the oil pressure regulated by clutch regulator valve  60 . Port  53  is connected with oil passage  72  connected with the downstream side of pressure regulator valve  40 . Specifically, oil passage  72  is connected with oil passage  71  for supplying the oil pressure from torque converter regulator valve  70  to oil cooler  80 . With the arrangement, in an ordinary case where the transmission ratio is on the Low speed side, the oil can be discharged from port  53  without adversely influencing other hydraulic control circuits. On the other hand, in a case where the oil pressure within primary cylinder chamber  33  becomes lower than a minimum oil pressure required for clamping belt  34 , for instance, upon the vehicle stopping while the transmission ratio being kept on the High speed side, upon the occurrence of failure of transmission actuator  90 , and the like, the oil discharged from torque converter regulator valve  70  toward oil cooler  80  and the lubrication parts can be bypassed and supplied to primary cylinder chamber  33  via oil passages  71  and  72  and ports  53  and  52 . This can establish the oil pressure within primary cylinder chamber  33  which is sufficient to clamp belt  34  and prevent slippage of belt  34 . 
   Further, the connection between port  53  and the oil passage downstream of pressure regulator valve  40  is not limited to the above embodiment. Port  53  may be connected with other oil passages downstream of pressure regulator valve  40  in which the oil pressure smaller than the line pressure produced by pressure regulator valve  40  but larger than the minimum oil pressure required for clamping belt  34  is established. For example, as illustrated by broken lines in  FIG. 2 , port  53  may be connected with oil passage  63  via oil passage  172  or may be connected with oil passage  61  via oil passage  272 . In such a case, the same effect as described above can be performed. 
   This application is based on a prior Japanese Patent Application No. 2002-285499 filed on Sep. 30, 2002. The entire contents of the Japanese Patent Application No. 2002-285499 is hereby incorporated by reference. 
   Although the invention has been described above by reference to a certain embodiment of the invention and the modifications, the invention is not limited to the embodiment and modifications described above. Modifications and variations of the embodiment and modifications described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims.

Technology Category: 2