Abstract:
A range switching device for performing switching the range of a transmission includes first control valve, a second control valve having a characteristic opposite to the first control, and first, second, third and fourth switching valves for controlling the transmission of oil pressures. The first and second switching valves cooperatively control the transmission of the oil pressure from the first control valve to a forward or reverse driving element (R). The third and fourth switching valve cooperatively control the transmission of the oil pressure from the second control valve to the forward or reverse driving element (R). The third and fourth switching valves each perform a substantially same oil pressure transmission when the state of the second and third actuators is reversed with respect to the first switching and second switching valves, respectively.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from Japanese Patent Application No. 2012-043283 filed on Feb. 29, 2012, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to range switching devices that perform switching of drive, reverse, and neutral ranges in an automatic transmission of a vehicle such as an automobile, and more particularly to a range switching device that can switch the ranges even when one or some valves fail. 
         [0004]    2. Description of the Related Art 
         [0005]    In an automatic transmission such as a CVT or a planetary gear step AT provided in an automobile or the like, the drive, reverse, and neutral ranges are switched by controlling the oil pressure supplied to engagement elements such as a forward clutch and a reverse clutch. 
         [0006]    Switching of such drive, reverse, and neutral ranges has conventionally been performed by a manual valve connected by a mechanical linkage to an operation lever operated by the driver. 
         [0007]    Recently, there has been proposed a technology so-called shift-by-wire system in which switching of running ranges is performed only by eclectic signals, without providing a mechanical linkage between the operation lever and the transmission. 
         [0008]    As an example of a conventional technique relating to shift-by-wire systems of automatic transmission, Japanese Unexamined Patent Application Publication (JP-A) No. 2008-128475 describes a range switching device in which spool valves are actuated by three solenoid valves to switch the oil pressure supplied to drive and reverse hydraulic servos. 
         [0009]    Further, JP-A No. 2008-128473 describes a range switching device in which running ranges are switched by two solenoid valves and the running range can be maintained even when either one of the solenoid valves fails in the running range. 
         [0010]    However, when one or some of solenoid valves fail, the technique described in JP-A No. 2008-128475 cannot switch the ranges, and thus the vehicle cannot run. 
         [0011]    The technique described in JP-A No. 2008-128473 ensures minimal failsafe capability, thereby maintaining the running range during running and switching to the neutral range even when either one of the solenoid valves has failed. However, the neutral range is selected in this state, the range pressure cannot be supplied again, and thus the vehicle cannot run. 
       SUMMARY OF THE INVENTION 
       [0012]    In view of the above, it is an object of the present invention to provide a range switching device that is capable of switching among the drive, reverse, and neutral ranges even when one or some valves fail. 
         [0013]    A first aspect of the present invention provides a range switching device that performs switching among a drive range in which an oil pressure is transmitted to a forward fastening element of a transmission, a reverse range in which an oil pressure is transmitted to a reverse fastening element, and a neutral range in which an oil pressure is substantially not transmitted to either one of the forward fastening element and the reverse fastening element. The range switching device includes: a first control valve that is driven by a first actuator and controls an oil pressure transmitted from an oil pressure supply source to a downstream; a first switching valve that is driven by a second actuator and can select an oil channel for transmitting the oil pressure transmitted from the first control valve to the downstream; a second switching valve that is driven by a third actuator and can transmit the oil pressure transmitted from the first switching valve to either one of the forward fastening element and the reverse fastening element; a second control valve that is driven by the first actuator and controls the oil pressure from the oil pressure supply source to the downstream so as to deliver a characteristic opposite to that of the first control valve; a third switching valve that is driven by the second actuator and can select an oil channel for transmitting the oil pressure transmitted from the second control valve to the downstream; and a fourth switching valve that is driven by the third actuator and can transmit the oil pressure transmitted from the third switching valve to either one of the forward fastening element and the reverse fastening element. The first switching valve and the second switching valve can cooperatively switch to any one of a state for transmitting the oil pressure transmitted from the first control valve to the forward fastening element, a state for transmitting the oil pressure to the reverse fastening element, and a state without transmitting the oil pressure. The third switching valve and the fourth switching valve can cooperatively switch to any one of a state for transmitting the oil pressure transmitted from the second control valve to the forward fastening element, a state for transmitting the oil pressure to the reverse fastening element, and a state without transmitting the oil pressure. The third switching valve and the fourth switching valve each perform a substantially same oil pressure transmission when a state of the second actuator and a state of the third actuator are reversed with respect to the first switching valve and the second switching valve, respectively. 
         [0014]    With such a configuration, even when one or some of the first to third actuators and the control valves and switching valves driven thereby fail, range switching same as that of a normal state can be performed by switching other normal actuators, control valves and switching valves to a state opposite to the normal state. 
         [0015]    Preferably, the first switching valve and the third switching valve can be switched among running ranges including the drive range and the reverse range and the neutral range. The second switching valve and the fourth switching valve can be switched between the drive range and the reverse range. 
         [0016]    With such a configuration, since the characteristic of the first switching valve is opposite to that of the third switching valve and the characteristic of the second switching valve is opposite to that of the fourth switching valves, switching among the running ranges and the neutral range and between the drive range and the reverse range can be performed in the same manner as in the normal state even during a failure. 
         [0017]    Preferably, at least one of three pairs of the first control valve and the second control valve, the first switching valve and the third switching valve, and the second switching valve and the fourth switching valve is configured as a spool valve having a common spool. 
         [0018]    With such a configuration, it is possible to reduce the number of parts, simplify the device configuration, decrease weight, and reduce the size. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a schematic block diagram of a transmission control system including a range switching device of Embodiment 1 according to the present invention; 
           [0020]      FIG. 2  shows a hydraulic circuit of the range switching device of Embodiment 1 and illustrates a N range in a normal state; 
           [0021]      FIG. 3  shows the hydraulic circuit of the range switching device shown in  FIG. 2  and illustrates another example of the N range in a normal state; 
           [0022]      FIG. 4  shows the hydraulic circuit of the range switching device shown in  FIG. 2  and illustrates a D range in a normal state; 
           [0023]      FIG. 5  shows the hydraulic circuit of the range switching device shown in  FIG. 2  and illustrates an R range in a normal state; 
           [0024]      FIG. 6  shows the hydraulic circuit of the range switching device shown in  FIG. 2  and illustrates the state of the N range during the ON failure of an FR clutch linear solenoid; 
           [0025]      FIG. 7  shows the hydraulic circuit of the range switching device shown in  FIG. 2  and illustrates the state of the D range during the OFF failure of the FR clutch linear solenoid; 
           [0026]      FIG. 8  shows the hydraulic circuit of the range switching device shown in  FIG. 2  and illustrates the state of the R range during the OFF failure of the FR clutch linear solenoid; 
           [0027]      FIG. 9  shows the hydraulic circuit of the range switching device shown in  FIG. 2  and illustrates the state of the D range during the ON failure of a first DNR solenoid; 
           [0028]      FIG. 10  is a schematic block diagram of a transmission control system including a range switching device of Embodiment 2 according to the present invention; and 
           [0029]      FIG. 11  is a schematic block diagram of a transmission control system including a range switching device of Embodiment 3 according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    The present invention provides a range switching device that can switch among the drive, reverse, and neutral ranges even when one or some valves fail by forming ports ensuring opposite characteristics in spool valves driven by the respective first to third solenoids and selecting ranges by combinations of logical patterns of the valves. 
       Embodiment 1 
       [0031]    Embodiment 1 of a range switching device according to the present invention is explained below. 
         [0032]    The range switching device of Embodiment 1 is provided, for example, at a continuously variable transmission (CVT) that is installed on an automobile such as a passenger car and transmits the output of an engine. 
         [0033]      FIG. 1  is a schematic block diagram of a transmission control system including the range switching device of Embodiment 1. 
         [0034]    As shown in  FIG. 1 , a transmission control system  1  has a CVT control unit  10 , a shift-by-wire control unit  20 , and an inhibit relay  30 . The transmission control system  1  controls a secondary linear solenoid L 1 , an FR clutch linear solenoid L 2 , a first DNR solenoid S 1 , and a second DNR solenoid S 2 . 
         [0035]    The CVT control unit  10  performs integral control of the CVT and auxiliary device thereof. The CVT control unit  10  includes an information processing device such as a CPU, a memory device such as a ROM or a RAM, an input/output interface, and a bus connecting these devices. 
         [0036]    The CVT control unit  10  performs the shifting control of the CVT and the control of a lock-up clutch (not shown in the figure). 
         [0037]    A P range switch  11 , a brake switch  12 , a shift sensor  13 , and a back lamp relay  14  are connected to the CVT control unit  10 . 
         [0038]    The P range switch  11  is provided in a shift operation unit (not shown in the figure) that is used by a driver for shifting and serves to detect that the operation of selecting a P range has been performed in the shift operation unit. 
         [0039]    The brake switch  12  detects whether or not a brake operation is performed by the driver. The brake switch  12  is turned ON when the driver depresses a brake pedal (not shown in the figure). 
         [0040]    The shift sensor  13  detects whether the driver has selected a range such as D (drive), N (neutral), or R (rear) at the shift operation unit. 
         [0041]    The back lamp relay  14  lights back lamps on the rear side of the vehicle when the R range is selected. 
         [0042]    The outputs of the P range switch  11  and the shift sensor  13  are both also transmitted to the shift-by-wire control unit  20 . 
         [0043]    The CVT control unit  10  determines the range required by the driver on the basis of the outputs of the P range shift  11  and the shift sensor  13 , controls the FR clutch linear solenoid L 2 , the first DNR solenoid S 1 , and the second DNR solenoid S 2 , switches among the D range, N range, and R range, and outputs a switching request relating to a P lock system  21  to the shift-by-wire control unit  20 . 
         [0044]    The shift-by-wire control unit  20  switches the P lock system  21  to the P range or a state other than the P range on the basis of the switching request output relating to the P lock system  21  from the CVT control unit  10 . 
         [0045]    The shift-by-wire control unit  20  includes an information processing device such as a CPU, a memory device such as a ROM or a RAM, an input/output interface, and a bus connecting these devices. 
         [0046]    The secondary linear solenoid L 1  adjusts the oil pressure supplied from an oil pump (not shown in the figure) and supplies the adjusted pressure to the range switching device. 
         [0047]    The FR clutch linear solenoid L 2 , the first DNR solenoid S 1 , and the second DNR solenoid S 2  supply the oil pressure to later-described spool valves  100 ,  200 , and  300  to control these spool valves. 
         [0048]    In this embodiment, a linear solenoid is used that adjusts the oil pressure according to an electric current, but the present invention is not limited to such configuration. Alternatively, for example, a duty solenoid may be used that adjusts the oil pressure according to a duty ratio. 
         [0049]    The P lock system  21  mechanically locks the rotation of the output shaft of the transmission when the P range is selected, and releases the mechanical lock of the rotation of the output shaft of the transmission when a state other than the P range is selected. 
         [0050]    The inhibit relay  30  is provided in a power supply system that supplies power to a starter motor (not shown in the figure). When a range other than the P range and the N range is selected, the inhibit relay inhibits the drive of the starter motor, except for the case of an automatic start of the engine from the idle stop control state. 
         [0051]    Further, an engine control unit  40  and a behavior control unit  50  are connected to the CVT control unit  10  and the shift-by-wire control unit  20  through a CAN communication system C, which is a vehicle LAN. 
         [0052]    The engine control unit  40  performs the integral control of the engine and the auxiliary device thereof (not shown in the figure). 
         [0053]    The behavior control unit  50  performs a vehicle behavior control and an antilock brake control. The vehicle behavior control creates a difference in a brake force between the left and right wheels according to the occurrence of vehicle behavior such as understeering or oversteering, thereby generating a moment in the direction of inhibiting such a behavior. 
         [0054]    The hydraulic system of the range switching device of Embodiment 1 is explained below. 
         [0055]      FIG. 2  shows the hydraulic circuit of the range switching device and illustrates the N range in a normal state (no-failure state). 
         [0056]    In  FIGS. 2 to 11 , hydraulic paths in which a high pressure is supplied are shown by bold black lines. 
         [0057]    The range switching device switches the supply of oil pressure to a forward clutch D and a reverse clutch R and has the spool valves  100 ,  200 , and  300 . 
         [0058]    The spool valve  100  is configured by inserting a round rod-like spool  130  into a cylindrical sleeve  110 . 
         [0059]    The spool  130  is operated by switching the pressure supplied from the FR clutch linear solenoid L 2  to one end of the sleeve  110 . 
         [0060]    Small-diameter portions  131  and  132  constituting the oil channels are formed in the spool  130  in the order of description from one end side thereof. 
         [0061]    When the FR clutch linear solenoid L 2  is switched ON (a discharge pressure is high), the spool  130  is moved to the right in  FIG. 2  by the oil pressure. 
         [0062]    When the FR clutch linear solenoid L 2  is switched OFF (the discharge pressure is low), the spool  130  is moved to the left in  FIG. 2  by a biasing force of a spring. 
         [0063]    Ports  111 ,  112 ,  113 ,  114 ,  115 , and  116  are formed in the sleeve  110 . 
         [0064]    The ports  111  and  112  supply a line pressure into the sleeve  110 . 
         [0065]    The port  111  communicates with the port  113  via the small-diameter portion  131  when the FR clutch linear solenoid L 2  is ON, and is closed when the solenoid is OFF. 
         [0066]    The port  112  communicates with the port  114  via the small-diameter portion  132  when the FR clutch linear solenoid L 2  is OFF, and is closed when the solenoid is ON. 
         [0067]    The ports  113  and  114  supply an oil pressure from the sleeve  110  to the spool valve  200 . 
         [0068]    Further, the oil pressure line from the port  113  is branched to supply an oil pressure to the end of the sleeve  110  on the opposite side of the FR clutch linear solenoid L 2 , whereby the oil pressure applied to the ports  113  and  114  can be continuously controlled according to the electric current flowing in the FR clutch linear solenoid L 2 . 
         [0069]    The ports  113  and  114  communicate respectively with the small-diameter portions  131  and  132  of the spool  130 , regardless of whether the FR clutch linear solenoid L 2  is ON or OFF. 
         [0070]    The ports  115  and  116  drain the oil pressure from the sleeve  110 . 
         [0071]    The port  115  is closed when the FR clutch linear solenoid L 2  is ON, and communicates with the small-diameter portion  131  of the spool  130  when the solenoid is OFF. 
         [0072]    The port  116  is closed when the FR clutch linear solenoid L 2  is OFF, and communicates with the small-diameter portion  132  of the spool  130  when the solenoid is ON. 
         [0073]    In the spool valve  100 , a portion receiving the supply of oil pressure from the port  111  functions as the first control valve according to the present invention, and a portion receiving the supply of oil pressure from the port  112  functions as the second control valve according to the present invention. 
         [0074]    The spool valve  200  is configured by inserting a round rod-shaped spool  230  into the cylindrical sleeve  210 . 
         [0075]    In a normal state, the spool valve  200  mainly performs the selection from running ranges including the D range and the R range, and the N range. 
         [0076]    The spool  230  is driven by switching the pressure supplied from the first DNR solenoid S 1  to one end of the sleeve  210 . 
         [0077]    Small-diameter portions  231 ,  232 ,  233 , and  234  constituting the oil channels are formed in the spool  230  in the order of description from one end side thereof. 
         [0078]    When the first DNR solenoid S 1  is switched ON (the discharge pressure is high), the spool  230  is moved by the oil pressure to the left in  FIG. 2 . 
         [0079]    Where the first DNR solenoid S 1  is switched OFF (the discharge pressure is low), the spool  230  is moved by the biasing force of a spring to the right in  FIG. 2 . 
         [0080]    Ports  211 ,  212 ,  213 ,  214 ,  215 ,  216 ,  217 ,  218 , and  219  are formed in the sleeve  210 . 
         [0081]    The ports  211  and  212  introduce an oil pressure supplied from the spool valve  100  into the sleeve  210 . 
         [0082]    The port  211  communicates with the port  113 , and also communicates with the small-diameter portion  232  of the spool  230 , regardless of whether the first DNR solenoid S 1  is ON or OFF. 
         [0083]    The port  212  communicates with the port  114 , and also communicates with the small-diameter portion  234  of the spool  230 , regardless of whether the first DNR solenoid S 1  is ON or OFF. 
         [0084]    The port  213  supplies the oil pressure introduced from the port  113  via the port  211  and the small-diameter portion  232  to the spool valve  300 . 
         [0085]    The port  213  communicates with the port  211  via the small-diameter portion  232  when the first DNR solenoid S 1  is ON, and is closed when the solenoid is OFF. 
         [0086]    The port  214  supplies the oil pressure introduced from the port  113  via the port  211  and the small-diameter portion  232  to the spool valve  300 . 
         [0087]    The port  214  communicates with the port  211  via the small-diameter portion  232  when the first DNR solenoid S 1  is OFF, and is closed when the solenoid is ON. 
         [0088]    The port  215  supplies the oil pressure introduced from the port  114  via the port  212  and the small-diameter portion  234  to the spool valve  300 . 
         [0089]    The port  215  communicates with the port  212  via the small-diameter portion  234  when the first DNR solenoid S 1  is ON, and is closed when the solenoid is OFF. 
         [0090]    The port  216  drains the oil pressure returned from the port  321  of the spool valve  300  from the port  218  via the small-diameter portion  231  when the oil pressure is unnecessary. 
         [0091]    The port  216  communicates with the small-diameter portion  231  when the first DNR solenoid S 1  is OFF, and is closed when the solenoid is ON. 
         [0092]    The port  217  communicates with the oil channel leading from the port  214  to the spool valve  300 , and drains the oil pressure supplied from the port  214  from the port  219  via the small-diameter portion  233  when the oil pressure is unnecessary. 
         [0093]    The port  217  communicates with the small-diameter portion  233  when the first DNR solenoid S 1  is ON, and is closed when the solenoid is OFF. 
         [0094]    The ports  218  and  219  drain the oil pressure from the small-diameter portions  231  and  233  respectively. 
         [0095]    The ports  218  and  219  communicate with the small-diameter portions  231  and  233  respectively, regardless of whether the first DNR solenoid S 1  is ON or OFF. 
         [0096]    In the spool valve  200 , a portion receiving the supply of oil pressure from the port  113  functions as the first switching valve according to the present invention, and a portion receiving the supply of oil pressure from the port  114  functions as the third switching valve according to the present invention. 
         [0097]    The spool valve  300  is configured by inserting a round rod-shaped spool  330  into the cylindrical sleeve  310 . 
         [0098]    In a normal state, the spool valve  300  mainly performs switching between the D range and the R range. 
         [0099]    The spool  330  is driven by switching the pressure supplied from the second DNR solenoid S 2  to one end of the sleeve  310 . 
         [0100]    Small-diameter portions  331 ,  332 ,  333 , and  334  constituting the oil channels are formed in the spool  330  in the order of description from one end side thereof. 
         [0101]    When the second DNR solenoid S 2  is switched ON (the discharge pressure is high), the spool  330  is moved by the oil pressure to the right in  FIG. 2 . 
         [0102]    When the second DNR solenoid S 2  is switched OFF (the discharge pressure is low), the spool  330  is moved by the biasing force of a spring to the left in  FIG. 2 . 
         [0103]    Ports  311 ,  312 ,  313 ,  314 ,  315 ,  316 ,  317 ,  318 ,  319 ,  320 , and  321  are formed in the sleeve  310 . 
         [0104]    The port  311  introduces the oil pressure supplied from the port  213  into the sleeve  310 . 
         [0105]    The port  311  communicates with the small-diameter portion  331  when the second DNR solenoid S 2  is OFF, and is closed when the solenoid is ON. 
         [0106]    The port  312  introduces the oil pressure supplied from the port  214  into the sleeve  310 . 
         [0107]    The port  312  communicates with the small-diameter portion  333  regardless of whether the second DNR solenoid S 2  is ON or OFF. 
         [0108]    The port  313  introduces the oil pressure supplied from the port  215  into the sleeve  310 . 
         [0109]    The port  313  communicates with the small-diameter portion  334  regardless of whether the second DNR solenoid S 2  is ON or OFF. 
         [0110]    The port  314  supplies the oil pressure introduced from the port  311  via the small-diameter portion  331  to the forward clutch D. 
         [0111]    The port  314  communicates with the small-diameter portion  331  regardless of whether the second DNR solenoid S 2  is ON or OFF. 
         [0112]    The port  315  supplies the oil pressure introduced from the port  312  via the small-diameter portion  333  to the forward clutch D. 
         [0113]    The port  315  communicates with the small-diameter portion  333  when the second DNR solenoid S 2  is ON, and is closed when the solenoid is OFF. 
         [0114]    The oil channels from the ports  314  and  315  merge and are connected through a shuttle valve V 1  to the forward clutch D. 
         [0115]    The port  316  supplies the oil pressure introduced from the port  312  via the small-diameter portion  333  to the reverse clutch R. 
         [0116]    The port  316  communicates with the small-diameter portion  333  when the second DNR solenoid S 2  is OFF, and is closed when the solenoid is ON. 
         [0117]    The port  317  supplies the oil pressure introduced from the port  313  via the small-diameter portion  334  to the forward clutch D. 
         [0118]    The port  317  communicates with the small-diameter portion  334  when the second DNR solenoid S 2  is OFF, and is closed when the solenoid is ON. 
         [0119]    The port  318  supplies the oil pressure introduced from the port  313  via the small-diameter portion  334  to the reverse clutch R. 
         [0120]    The port  318  communicates with the small-diameter portion  334  when the second DNR solenoid S 2  is ON, and is closed when the solenoid is OFF. 
         [0121]    The port  319  communicates with the oil channels from the ports  314  and  315  and drains the oil pressure through the small-diameter portion  332 , port  321 , port  216 , and small-diameter portion  231  from the port  218  when the oil pressure is unnecessary. 
         [0122]    The port  319  communicates with the small-diameter portion  332  when the second DNR solenoid S 2  is OFF, and is closed when the solenoid is ON. 
         [0123]    The port  320  communicates with the oil channel from the port  316  and drains the oil pressure through the small-diameter portion  332 , port  321 , port  216 , and small-diameter portion  231  from the port  218  when the oil pressure is unnecessary. 
         [0124]    The port  320  communicates with the small-diameter portion  332  when the second DNR solenoid S 2  is ON, and is closed when the solenoid is OFF. 
         [0125]    The port  321  communicates with the port  216  and also communicates with the small-diameter portion  332 , regardless of whether the second DNR solenoid S 2  is ON or OFF. 
         [0126]    In the spool valve  300 , a portion receiving the supply of oil pressure from the port  113  through the spool valve  200  functions as the second switching valve according to the present invention, and the portion receiving the supply of oil pressure from the port  114  through the spool valve  200  functions as the fourth switching valve according to the present invention. 
         [0127]    The shuttle valve V 1  is provided on the inlet side of the forward clutch D. 
         [0128]    The shuttle valve V 1  has two inlets and communicates one thereof which is at a relatively high pressure side with the forward clutch D. 
         [0129]    One inlet of the shuttle valve V 1  communicates with the ports  314 ,  315 , and  319 . 
         [0130]    The other inlet of the shuttle valve V 1  communicates with the port  317 . 
         [0131]    A shuttle valve V 2  is provided on the inlet side of the reverse clutch R. 
         [0132]    The shuttle valve V 2  has two inlets and communicates one thereof which is at a relatively high pressure side with the reverse clutch R. 
         [0133]    One inlet of the shuttle valve V 2  communicates with the ports  316  and  320 . 
         [0134]    The other inlet of the shuttle valve V 2  communicates with the port  318 . 
         [0135]    In the case of a vehicle equipped with an idle stop system that stops the engine when the vehicle is stopped, the biasing force of the spring in each spool valve is preferably set such that the running range can be maintained by the discharge pressure of the electric pump. 
         [0136]    The operation of the above-described range switching device is explained below. 
       &lt;N Range in Normal State&gt; 
       [0137]    In a normal state shown in  FIG. 2  and in an N range, the FR clutch linear solenoid L 2  is OFF, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is OFF. 
         [0138]    As a result, the line pressure reaches the small-diameter portion  234  through the port  112 , small-diameter portion  132 , and ports  114  and  212 , in the order of description. Since the port  215  is closed, the line pressure is not supplied to the forward clutch D or the reverse clutch R. 
         [0139]    The N range can be also selected in the state shown in  FIG. 3 , instead of the state shown in  FIG. 2 . 
         [0140]      FIG. 3  shows a hydraulic circuit of the range switching device of Embodiment 1 and illustrates another example of the N range in a normal state. 
         [0141]    In the state shown in  FIG. 3 , the second DNR solenoid S 2  is ON and the spool  330  of the spool valve  300  moves to the right. In this case, however, the line pressure also reaches only the small-diameter portion  234 , as in the case illustrated by  FIG. 2 , and therefore the line pressure is not supplied to the forward clutch D or the reverse clutch R. 
         [0142]    &lt;D Range in Normal State&gt; 
         [0143]      FIG. 4  shows the hydraulic circuit of the range switching device of Embodiment 1 and illustrates the D range in a normal state. 
         [0144]    In the state shown in  FIG. 4 , the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is ON. 
         [0145]    As a result, the line pressure is supplied to the forward clutch D through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , port  214 , port  312 , small-diameter portion  333 , port  315 , and shuttle valve V 1  in the order of description. 
         [0146]    &lt;R Range in Normal State&gt; 
         [0147]      FIG. 5  shows the hydraulic circuit of the range switching device of Embodiment 1 and illustrates the R range in a normal state. 
         [0148]    In the state shown in  FIG. 5 , the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is OFF. 
         [0149]    As a result, the line pressure is supplied to the reverse clutch R through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , port  214 , port  312 , small-diameter portion  333 , port  316 , and shuttle valve V 2  in the order of description. 
         [0150]    The range switching performed when a failure occurs in which the FR clutch linear solenoid L 2  is fixed in the ON state is explained below. 
         [0151]    &lt;N Range During ON Failure of FR Clutch Linear Solenoid&gt; 
         [0152]      FIG. 6  shows the hydraulic circuit of the range switching device of Embodiment 1 and illustrates the state of the N range during an ON failure of the FR clutch linear solenoid. 
         [0153]    In the state shown in  FIG. 6 , the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is ON, and the second DNR solenoid S 2  is ON. 
         [0154]    As a result, the line pressure reaches the port  311  through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , and port  213  in the order of description. However, since the port  311  is closed, the line pressure is not supplied to the forward clutch D or the reverse clutch R. 
         [0155]    &lt;D Range During ON Failure of FR Clutch Linear Solenoid&gt; 
         [0156]    Similarly to the state shown in  FIG. 4  described hereinabove, the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is ON. 
         [0157]    As a result, the line pressure is supplied to the forward clutch D through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , port  214 , port  312 , small-diameter portion  333 , port  315 , and shuttle valve V 1  in the order of description. 
         [0158]    &lt;R Range During ON Failure of FR Clutch Linear Solenoid&gt; 
         [0159]    Similarly to the state shown in  FIG. 5  described hereinabove, the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is OFF. 
         [0160]    As a result, the line pressure is supplied to the reverse clutch R through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , port  214 , port  312 , small-diameter portion  333 , port  316 , and shuttle valve V 2  in the order of description. 
         [0161]    The range switching performed when a failure occurs in which the FR clutch linear solenoid L 2  is fixed in the OFF state is explained below. 
         [0162]    &lt;N Range During OFF Failure of FR Clutch Linear Solenoid&gt; 
         [0163]    Similarly to the state shown in  FIG. 2  described hereinabove, the FR clutch linear solenoid L 2  is OFF, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is OFF. 
         [0164]    As a result, the line pressure reaches the small-diameter portion  234  through the port  112 , small-diameter portion  132 , port  114 , and port  212 . However, since the port  215  is closed, the line pressure is not supplied to the forward clutch D or the reverse clutch R. 
         [0165]    &lt;D Range During OFF Failure of FR Clutch Linear Solenoid&gt; 
         [0166]      FIG. 7  shows the hydraulic circuit of the range switching device of Embodiment 1 and illustrates the state of the D range during the OFF failure of the FR clutch linear solenoid. 
         [0167]    In the state shown in  FIG. 7 , the FR clutch linear solenoid L 2  is OFF, the first DNR solenoid S 1  is ON, and the second DNR solenoid S 2  is OFF. 
         [0168]    As a result, the line pressure is supplied to the forward clutch D through the port  112 , small-diameter portion  132 , port  114 , port  212 , small-diameter portion  234 , port  215 , port  313 , small-diameter portion  334 , port  317 , and shuttle valve V 1  in the order of description. 
         [0169]    &lt;R Range During OFF Failure of FR Clutch Linear Solenoid&gt; 
         [0170]      FIG. 8  shows the hydraulic circuit of the range switching device of Embodiment 1 and illustrates the state of the R range during the OFF failure of the FR clutch linear solenoid. 
         [0171]    In the state shown in  FIG. 8 , the FR clutch linear solenoid L 2  is OFF, the first DNR solenoid S 1  is ON, and the second DNR solenoid S 2  is ON. 
         [0172]    As a result, the line pressure is supplied to the reverse clutch R through the port  112 , small-diameter portion  132 , port  114 , port  212 , small-diameter portion  234 , port  215 , port  313 , small-diameter portion  334 , port  318 , and shuttle valve V 2  in the order of description. 
         [0173]    The range switching performed when a failure occurs in which the first DNR solenoid S 1  is fixed in the ON state is explained below. 
         [0174]    &lt;N Range During ON Failure of First DNR Solenoid&gt; 
         [0175]    Similarly to the state shown in  FIG. 6  described hereinabove, the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is ON, and the second DNR solenoid S 2  is ON. 
         [0176]    As a result, the line pressure reaches the port  311  through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , and port  213  in the order of description. However, since the port  311  is closed, the line pressure is not supplied to the forward clutch D or the reverse clutch R. 
         [0177]    &lt;D Range During ON Failure of First DNR Solenoid&gt; 
         [0178]      FIG. 9  shows the hydraulic circuit of the range switching device of Embodiment 1 and illustrates the state of the D range during the ON failure of the first DNR solenoid. 
         [0179]    In the state shown in  FIG. 9 , the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is ON, and the second DNR solenoid S 2  is OFF. 
         [0180]    As a result, the line pressure is supplied to the forward clutch D through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , port  213 , port  311 , small-diameter portion  331 , port  314 , and shuttle valve V 1  in the order of description. 
         [0181]    &lt;R Range During ON Failure of First DNR Solenoid&gt; 
         [0182]    Similarly to the state shown in  FIG. 8  described hereinabove, the FR clutch linear solenoid L 2  is OFF, the first DNR solenoid S 1  is ON, and the second DNR solenoid S 2  is ON. 
         [0183]    As a result, the line pressure is supplied to the reverse clutch R through the port  112 , small-diameter portion  132 , port  114 , port  212 , small-diameter portion  234 , port  215 , port  313 , small-diameter portion  334 , port  318 , and shuttle valve V 2  in the order of description. 
         [0184]    The range switching performed when a failure occurs in which the first DNR solenoid S 1  is fixed in the OFF state is explained below. 
         [0185]    &lt;N Range During OFF Failure of First DNR Solenoid&gt; 
         [0186]    Similarly to the state shown in  FIG. 2  described hereinabove, the FR clutch linear solenoid L 2  is OFF, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is OFF. 
         [0187]    As a result, the line pressure reaches the small-diameter portion  234  through the port  112 , small-diameter portion  132 , and ports  114  and  212 . However, since the port  215  is closed, the line pressure is not supplied to the forward clutch D or the reverse clutch R. 
         [0188]    &lt;D Range During OFF Failure of First DNR Solenoid&gt; 
         [0189]    Similarly to the state shown in  FIG. 4  described hereinabove, the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is ON. 
         [0190]    As a result, the line pressure is supplied to the forward clutch D through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , port  214 , port  312 , small-diameter portion  333 , port  315 , and shuttle valve V 1  in the order of description. 
         [0191]    &lt;R Range During OFF Failure of First DNR Solenoid&gt; 
         [0192]    Similarly to the state shown in  FIG. 5  described hereinabove, the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is OFF. 
         [0193]    As a result, the line pressure is supplied to the reverse clutch R through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , port  214 , port  312 , small-diameter portion  333 , port  316 , and shuttle valve V 2  in the order of description. 
         [0194]    The range switching performed when a failure occurs in which the second DNR solenoid S 2  is fixed in the ON state is explained below. 
         [0195]    &lt;N Range During ON Failure of Second DNR Solenoid&gt; 
         [0196]    Similarly to the state shown in  FIG. 6  described hereinabove, the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is ON, and the second DNR solenoid S 2  is ON. 
         [0197]    As a result, the line pressure reaches the port  311  through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , and port  213  in the order of description. However, since the port  311  is closed, the line pressure is not supplied to the forward clutch D or the reverse clutch R. 
         [0198]    &lt;D Range During ON Failure of Second DNR Solenoid&gt; 
         [0199]    Similarly to the state shown in  FIG. 4  described hereinabove, the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is ON. 
         [0200]    As a result, the line pressure is supplied to the forward clutch D through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , port  214 , port  312 , small-diameter portion  333 , port  315 , and shuttle valve V 1  in the order of description. 
         [0201]    &lt;R Range During ON Failure of Second DNR Solenoid&gt; 
         [0202]    Similarly to the state shown in  FIG. 8  described hereinabove, the FR clutch linear solenoid L 2  is OFF, the first DNR solenoid S 1  is ON, and the second DNR solenoid S 2  is ON. 
         [0203]    As a result, the line pressure is supplied to the reverse clutch R through the port  112 , small-diameter portion  132 , port  114 , port  212 , small-diameter portion  234 , port  215 , port  313 , small-diameter portion  334 , port  318 , and shuttle valve V 2  in the order of description. 
         [0204]    The range switching performed when a failure occurs in which the second DNR solenoid S 2  is fixed in the OFF state is explained below. 
         [0205]    &lt;N Range During OFF Failure of Second DNR Solenoid&gt; 
         [0206]    Similarly to the state shown in  FIG. 2  described hereinabove, the FR clutch linear solenoid L 2  is OFF, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is OFF. 
         [0207]    As a result, the line pressure reaches the small-diameter portion  234  through the port  112 , small-diameter portion  132 , and ports  114  and  212 . However, since the port  215  is closed, the line pressure is not supplied to the forward clutch D or the reverse clutch R. 
         [0208]    &lt;D Range During OFF Failure of Second DNR Solenoid&gt; 
         [0209]    Similarly to the state shown in  FIG. 9  described hereinabove, the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is ON, and the second DNR solenoid S 2  is OFF. 
         [0210]    As a result, the line pressure is supplied to the forward clutch D through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , port  213 , port  311 , small-diameter portion  331 , port  314 , and shuttle valve V 1  in the order of description. 
         [0211]    &lt;R Range During OFF Failure of Second DNR Solenoid&gt; 
         [0212]    Similarly to the state shown in  FIG. 5  described hereinabove, the FR clutch linear solenoid L 2  is ON, the first DNR solenoid S 1  is OFF, and the second DNR solenoid S 2  is OFF. 
         [0213]    As a result, the line pressure is supplied to the reverse clutch R through the port  111 , small-diameter portion  131 , port  113 , port  211 , small-diameter portion  232 , port  214 , port  312 , small-diameter portion  333 , port  316 , and shuttle valve V 2  in the order of description. 
         [0214]    The relationship between each of the above-described solenoid states and the range to be selected is presented in Table 1 below. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 FR clutch 
                   
                   
                   
               
               
                   
                 linear 
                 First DNR 
                 Second DNR 
                   
               
               
                   
                 solenoid 
                 solenoid 
                 solenoid 
                 Range 
               
               
                   
                   
               
             
             
               
                   
                 OFF 
                 ON 
                 OFF 
                 D 
               
               
                   
                   
                   
                 ON 
                 R 
               
               
                   
                   
                 OFF 
                 OFF 
                 N 
               
               
                   
                   
                   
                 ON 
                 N 
               
               
                   
                 ON 
                 ON 
                 OFF 
                 D 
               
               
                   
                   
                   
                 ON 
                 N 
               
               
                   
                   
                 OFF 
                 OFF 
                 R 
               
               
                   
                   
                   
                 ON 
                 D 
               
               
                   
                   
               
             
          
         
       
     
         [0215]    As described hereinabove, the range switching device of Embodiment 1 can switch among the D range, N range, and R range and maintain the running capacity of the vehicle even when any one of the FR clutch linear solenoid L 2 , first DNR solenoid S 1 , and second DNR solenoid S 2  or any one of the spool valves  100 ,  200 , and  300  fails. 
       Embodiment 2 
       [0216]    Embodiment 2 of the range switching device according to the present invention is described below. 
         [0217]    In Embodiments 2 and 3, the components substantially identical to those of the preceding embodiment are assigned with the same reference numerals and the explanation thereof is herein omitted. Thus, mainly the differences among the embodiments are explained. 
         [0218]      FIG. 10  shows a hydraulic circuit of the range switching device of Embodiment 2 and illustrates the D range in a normal state. 
         [0219]    In the range switching device of Embodiment 2, the spool valve  100  of Embodiment 1 is divided into below-described spool valves  100 A and  100 B. The spool valves  100 A and  100 B are together driven by the FR clutch linear solenoid L 2 . 
         [0220]    A sleeve  110 A of the spool valve  100 A is provided with ports  111 ,  113 , and  115 . 
         [0221]    A spool  130 A inserted into the sleeve  110 A is provided with a small-diameter portion  131 . 
         [0222]    A sleeve  110 B of the spool valve  100 B is provided with ports  112 ,  114 , and  116 . 
         [0223]    A line pressure is supplied to each of the ports  111  and  112  from a common modulator valve  400 . 
         [0224]    A spool  130 B inserted into the sleeve  110 B is provided with a small-diameter portion  132 . 
         [0225]    Embodiment 2 can achieve an effect substantially identical to that of the above-described Embodiment 1. 
       Embodiment 3 
       [0226]    Embodiment 3 of the range switching device according to the present invention is explained below. 
         [0227]      FIG. 11  shows a hydraulic circuit of the range switching device of Embodiment 3 and illustrates the D range in a normal state. 
         [0228]    As shown in  FIG. 11 , in the range switching device of Embodiment 3, the side where an oil pressure is supplied from the spool valve  200  to the first DNR solenoid S 1  and the side where the spring is provided are inverted with respect to those in Embodiment 2. 
         [0229]    As a result, with respect to the spool valve  200 , the relationship between the ON/OFF switching of the first DNR solenoid S 1  and the state of the spool valve  200  has the characteristics opposite to those of Embodiment 1 and Embodiment 2. 
         [0230]    Embodiment 3 can achieve an effect substantially identical to that of the above-described Embodiment 1 and Embodiment 2. 
         [0231]    The spool valves  100  and  300  can be also configured to obtain such opposite characteristics. 
       [Modifications] 
       [0232]    The present invention is not limited to the above-described examples and various changes and modifications are possible. Those changes and modifications are also included in the technical scope of the present invention. 
         [0000]    (1) The range switching devices in the embodiments are provided, for example, at a continuously variable transmission (CVT), but the present invention may be also applied to transmissions of other types in which shifting between drive and reverse directions is performed by hydraulic engagement elements or fastening elements, such as a step AT using planetary gears.
 
(2) The shape, structure, and disposition of the elements constituting the range switching device are not limited to those of the embodiments and may be changed as appropriate. For example, the configuration of oil channels that communicate the ports of the spool valves and the disposition of the solenoid valves may be changed as appropriate.