Abstract:
Provided is a range switching device for performing switching among drive, reverse, and neutral ranges of a transmission. The device includes a first switching valve driven by a first actuator and a second switching valve driven by a second actuator. The valves switch an oil channel to transmit the oil pressure from an oil pressure supply source between first state and second states. When the first and second switching valves are in the first and second states respectively, the oil pressure is transmitted to the forward fastening element. When the first and second switching valves are in the second state and first states respectively, the oil pressure is transmitted to the reverse fastening element. When both the valves are in the first or second state, oil pressure transmission to the forward and reverse fastening elements is substantially blocked.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2012-051584 filed on Mar. 8, 2012, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to range switching devices that perform switching among 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 prevents reverse running and ensures safety even in the case of a failure. 
     2. Description of the Related Art 
     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. 
     Switching among 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. 
     Recently, there has been proposed a technology so-called shift-by-wire system in which switching of running ranges is performed only by electric signals, without providing a mechanical linkage between the operation lever and the transmission. 
     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. 
     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. 
     However, with the technique described in JP-A No. 2008-128475, when switching between drive and reverse is performed using a drive/reverse switching valve, where a failure mode occurs such that the state of the valve is reversed, abrupt switching can take place from drive to reverse or from reverse to drive. 
     To resolve this problem, it is possible to increase the failsafe ability by detecting the failure state and creating different combinations of control states of a plurality of valves, but in this case where the failure detection speed is low, the designed combination is not obtained and the vehicle might run in reverse. 
     SUMMARY OF THE INVENTION 
     In view of the above, it is an object of the present invention to provide a range switching device that ensures safety even when a failure occurs. 
     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 the oil pressure is transmitted to a reverse fastening element, and a neutral range in which the oil pressure is substantially not transmitted to either of the forward fastening element and the reverse fastening element. The range switching device includes: a first switching valve that is driven by a first actuator and can switch an oil channel by which the oil pressure from an oil pressure supply source is transmitted, between a first state and a second state; and a second switching valve that is driven by a second actuator and can switch an oil channel by which the oil pressure from an oil pressure supply source is transmitted, between a first state and a second state. When the first switching valve is in the first state and the second switching valve is in the second state, the oil pressure is transmitted to the forward fastening element. When the first switching valve is in the second state and the second switching valve is in the first state, the oil pressure is transmitted to the reverse fastening element. When the first switching valve and the second switching valve are both in the first state or in the second state, oil pressure transmission to the forward fastening element and the reverse fastening element is substantially blocked. 
     With such a configuration, as a result of performing the switching among the drive range, reverse range, and neutral range by combinations of logical patterns of states of the first and second switching valve, even when a single switching valve or actuator fails, no transition is made from the drive range to the reverse range or from the reverse range to the drive range, and safety can be ensured even when a failure occurs. 
     Preferably, the oil channel by which the oil pressure is transmitted from the oil pressure supply source to the forward fastening element is constituted by connecting the oil pressure supply source, the first switching valve, the second switching valve, and the forward fastening element in this order, and the oil channel by which the oil pressure is transmitted from the oil pressure supply source to the reverse fastening element is constituted by connecting the oil pressure supply source, the second switching valve, the first switching valve, and the reverse fastening element in this order. 
     With such a configuration, the above-described effect can be reliably obtained. 
     Preferably, when the energizing of the first actuator and the energizing of the second actuator are both blocked, the oil pressure transmission to the forward fastening element and to the reverse fastening element is substantially blocked. 
     With such a configuration, where power supply is interrupted for any reason, the neutral range is assumed, thereby making it possible to increase safety further. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         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; 
         FIG. 2  shows a hydraulic circuit of the range switching device of Embodiment 1; 
         FIG. 3  shows a D range state in the hydraulic circuit shown in  FIG. 2 ; 
         FIG. 4  shows an R range state in the hydraulic circuit shown in  FIG. 2 ; 
         FIG. 5  shows an N range state in the hydraulic circuit shown in  FIG. 2 ; 
         FIG. 6  shows another embodiment of the N range state in the hydraulic circuit shown in  FIG. 2 ; and 
         FIG. 7  is a diagram showing a hydraulic circuit of a range switching device of Embodiment 2 according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a range switching device that ensures safety even when a failure occurs is attained by a configuration in which the switching of ranges is performed by combinations of logical patterns of states of two switching valves, and the neutral range is assumed when one switching valve in the drive range or reverse range is reversed. 
     Embodiment 1 
     Embodiment 1 of a range switching device according to the present invention is explained below. 
     The range switching device of according to 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. 
       FIG. 1  is a schematic block diagram of a transmission control system including the range switching device of according to 1. 
     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  and controls a secondary linear solenoid L 1 , a FR clutch linear solenoid L 2 , a first DNR solenoid S 1 , and a second DNR solenoid S 2 . 
     The CVT control unit  10  performs integral control of the CVT and auxiliary device thereof and is constituted by 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 the aforementioned devices. 
     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). 
     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 . 
     The P range switch  11  is provided in a shift operation unit (not shown in the figure) that is used by the driver for shifting and serves to detect that the operation of selecting a P range has been performed in the shift operation unit. 
     The brake switch  12  detects whether a brake operation is performed by the driver. The brake switch is ON when the driver steps on a brake pedal (not shown in the figure). 
     The shift sensor  13  detects whether the driver has selected a range such as D (drive), N (neutral), R (rear), or P (parking) in the shift operation unit. 
     The back lamp relay  14  lights back lamps on the rear side of the vehicle when the R range is selected. 
     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 . 
     The shift-by-wire unit  20  controls the secondary solenoid L 1 , FR clutch linear solenoid L 2 , first DNR solenoid S 1 , and second DNR solenoid S 2  through the CVT control unit  10  on the basis of the output of the shifter sensor  13  and switches the D range, N range, and R range. 
     The shift-by-wire control unit  20  is constituted by 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 the aforementioned devices. 
     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. 
     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 the below-described spool valves  100 ,  200 , and  300  to control the spool valves. 
     In this case, a linear solenoid is used that adjusts the oil pressure according to an electric current, but such configuration is not limiting and, for example, a duty solenoid may be used that adjusts the oil pressure according to a duty ratio. 
     Further, a P lock system  21  is connected to the shift-by-wire control unit  20 . 
     The P lock system  21  mechanically locks the rotation of the output shaft of the transmission when the P range is selected. 
     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 or N range is selected, the inhibit relay inhibits the drive of the starter motor, except for the case of automatic start of the engine from the idle stop state. 
     Further, an engine control unit  40  and a behavior control unit  50  are connected through a CAN communication system C, which is a vehicle LAN, to the CVT control unit  10  and the shift-by-wire control unit  20 . 
     The engine control unit  40  performs the integral control of the engine (not shown in the figure) and the auxiliary device thereof. 
     The behavior control unit  50  performs a vehicle behavior control by which a difference in a brake force is created between the left and right wheels according to the occurrence of vehicle behavior such as understeering or oversteering, and a moment is generated in the direction of inhibiting such a behavior, or performs an antilock brake control. 
     The hydraulic circuit of the range switching device of Embodiment 1 is explained below. 
       FIG. 2  shows the hydraulic circuit of the range switching device. 
     In  FIG. 2 , the ON and OFF positions of the valve elements of the spool valves are shown together to facilitate the understanding. 
     The range switching device switches the applied oil pressure to a forward clutch (Fwd) and a reverse clutch (Rvs) (not shown in the figure) and is constituted by spool valves  100 ,  200 , and  300 . 
     In the spool valves  100 ,  200 , and  300 , a spool is inserted into a cylindrical sleeve provided with a plurality of ports, and the oil channels are switched by controlling the oil pressure supplied from the solenoids and moving the spools. 
     More specifically, where an oil pressure is supplied from the solenoids, the valve elements of the spool valves  100 ,  200 , and  300  are set to the ON positions shown in  FIG. 2 , and where the supply of oil pressure is blocked, the valve elements are set by the biasing force of the springs to the OFF positions shown in  FIG. 2 . 
     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 springs in the spool valves  100 ,  200 , and  300  may be set such that the running range can be maintained by the discharge pressure of the electric pump. 
     The spool valve  100  supplies the adjusted line pressure to the spool valves  200  and  300  and is driven by switching the oil pressure supplied from the FR clutch linear solenoid L 2 . 
     The spool valve  100  has ports  101 ,  102 ,  103 , and  104 . 
     The port  101  serves to introduce the line pressure into the spool valve  100 . 
     The port  102  serves to supply an oil pressure from the spool valve  100  to the spool valves  200  and  300 . 
     The port  103  serves to communicate with the port  102  and drain the oil pressure from the port  104  through the interior of the spool valve  100  when the oil pressure is not necessary. 
     The port  104  serves to drain the oil pressure introduced from the port  103  into the spool valve  100 . 
     In the spool valve  100 , when the FR clutch linear solenoid L 2  is OFF, the port  101  and the port  102  communicate with each other, and the port  103  and the port  104  are closed. 
     The spool valve  200  supplies the oil pressure supplied from the port  102  of the spool valve  100  to the spool valve  300  and supplies the oil pressure supplied from the spool valve  300  to the forward clutch. 
     The spool valve  200  is driven by switching the oil pressure supplied from the first DNR solenoid S 1 . 
     The spool valve  200  has ports  201 ,  202 ,  203 ,  204 ,  205 ,  206 ,  207 , and  208 . 
     The port  201  serves to introduce the oil pressure supplied from the port  102  into the spool valve  200 . 
     The port  202  serves to supply the oil pressure from the spool valve  200  to the spool valve  300 . 
     The port  203  serves to communicate with the port  202  and drain the oil pressure from the port  204  through the interior of the spool valve  200  when the oil pressure is not necessary. 
     The port  204  serves to drain the oil pressure introduced from the port  203  into the spool valve  200 . 
     The port  205  serves to introduce the oil pressure supplied from the port  302  of the spool valve  300  into the spool valve  200 . 
     The port  206  serves to supply the oil pressure supplied from the port  205  to the forward clutch  210 . 
     The port  207  serves to communicate with the port  206  and drain the oil pressure from the port  208  through the interior of the spool valve  200  when the oil pressure is not necessary. 
     The port  208  serves to drain the oil pressure introduced from the port  207  into the spool valve  200 . 
     In the spool valve  200 , when the first DNR solenoid S 1  is ON, the port  201  and the port  202  communicate with each other, the port  207  and the port  208  communicate with each other, and the ports  203 ,  204 ,  205 , and  206  are closed. 
     Further, when the first DNR solenoid S 1  is OFF, the port  203  and the port  204  communicate with each other, the port  205  and the port  206  communicate with each other, and the ports  201 ,  202 ,  207 , and  208  are closed. 
     The spool valve  300  supplies the oil pressure supplied from the port  102  of the spool valve  100  to the spool valve  200  and also supplies the oil pressure supplied from the spool valve  200  to the reverse clutch. 
     The spool vale  300  is driven by switching the oil pressure supplied from the second DNR solenoid S 2 . 
     The spool valve  300  has ports  301 ,  302 ,  303 ,  304 ,  305 ,  306 ,  307 , and  308 . 
     The port  301  serves to introduce the oil pressure supplied from the port  102  into the spool valve  300 . 
     The port  302  serves to supply the oil pressure from the spool valve  300  to the spool valve  200 . 
     The port  303  serves to communicate with the port  302  and drain the oil pressure from the port  304  through the interior of the spool valve  300  when the oil pressure is not necessary. 
     The port  304  serves to drain the oil pressure introduced from the port  303  into the spool valve  300 . 
     The port  305  serves to introduce the oil pressure supplied from the port  202  of the spool valve  200  into the spool valve  300 . 
     The port  306  serves to supply the oil pressure supplied from the port  305  to the reverse clutch  310 . 
     The port  307  serves to communicate with the port  306  and drain the oil pressure from the port  308  through the interior of the spool valve  300  when the oil pressure is not necessary. 
     The port  308  serves to drain the oil pressure introduced from the port  307  into the spool valve  200 . 
     In the spool valve  300 , when the second DNR solenoid S 2  is ON, the port  301  and the port  302  communicate with each other, the port  307  and the port  308  communicate with each other, and the ports  303 ,  304 ,  305 , and  306  are closed. 
     Further, when the second DNR solenoid S 2  is OFF, the port  303  and the port  304  communicate with each other, the port  305  and the port  306  communicate with each other, and the ports  301 ,  302 ,  307 , and  308  are closed. 
     The range switching operation performed in the range switching device of Example 1 is explained below. 
     &lt;D Range&gt; 
       FIG. 3  illustrates the D range state in the hydraulic circuit of Example 1. 
     In the state shown in  FIG. 3 , 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 ON. 
     As a result, the line pressure is supplied to the forward clutch through the port  101 , spool valve  100 , port  102 , port  301 , spool valve  300 , port  302 , port  205 , spool valve  200 , and port  206  in this order. 
     Since the port  201  is closed, the oil pressure from the port  102  is not directly introduced into the spool valve  200 . 
     &lt;R Range&gt; 
       FIG. 4  illustrates the R range state in the hydraulic circuit of Example 1. 
     In the state shown in  FIG. 4 , 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. 
     As a result, the line pressure is supplied to the reverse clutch through the port  101 , spool valve  100 , port  102 , port  201 , spool valve  200 , port  202 , port  305 , spool valve  300 , and port  306  in this order. 
     Since the port  301  is closed, the oil pressure from the port  102  is not directly introduced into the spool valve  300 . 
     &lt;N Range&gt; 
       FIG. 5  illustrates the N range state in the hydraulic circuit of Example 1. 
     In the N range, the FR clutch linear solenoid L 2  is actually controlled to a low-pressure state, but it is shown fixed to a high pressure to facilitate the understanding. 
     In the state shown in  FIG. 5 , 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. 
     As a result, the line pressure is supplied from the port  102  of the spool valve  100  to the port  201  of the spool valve  200  and to the port  301  of the spool valve  300 , but since the ports  201  and  301  are both closed, the oil pressure is not supplied to the forward clutch and the reverse clutch. 
     In Example 1, the N range can be obtained also in the state shown in  FIG. 6 . 
       FIG. 6  shows another example of the N range state in the hydraulic circuit of Example 1. 
     In the state shown in  FIG. 6 , the line pressure is transmitted from the port  101 , spool valve  100 , and port  102  to the port  301 , the spool valve  300 , port  302 , and port  205  in this order, and from the port  102  to the port  201 , spool valve  200 , port  202 , and port  305  in this order, but since the ports  205  and  305  are both closed, the oil pressure is not supplied to the forward clutch and the reverse clutch. 
     As described hereinabove, in Example 1, as a result of switching the D range, R range, and N range by combinations of logical patterns of the states of the spool valves  200  and  300 , the switching to the N range is performed even when the state of either of the spool valves  200  and  300  is reversed due to a failure or the like during running in the D range or R range. Therefore, reverse running cannot occur and safety is increased. 
     Embodiment 2 
     Embodiment 2 of the range switching device according to the present invention is explained below. 
     In Embodiment 2, the components substantially identical to those of Embodiment 1 are assigned with the same reference numerals and the explanation thereof is herein omitted. Thus, mainly the differences between the examples are explained. 
       FIG. 7  shows the hydraulic circuit of the range switching device of Embodiment 2. 
     In Embodiment 2, the state of the spool valve  300  in relation to the ON/OFF switching of the second DNR solenoid S 2  is reversed with respect to that of Example 1. 
     The effect substantially identical to that of the above-described Embodiment 1 can be also obtained in Example 2. 
     MODIFICATIONS 
     The present invention is not limited to the above-described embodiments and various changes and modifications are possible. Those changes and modifications are also included in the technical scope of the present invention. 
     (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, for example, 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 connect the ports of the spool valves and the disposition of the solenoid valves may be changed as appropriate. 
     (3) In Embodiment 2, the characteristic of the spool valve driven by the second DNR solenoid is reversed with respect to that of Example 1, but the characteristics of other spool valves may be also reversed.