Abstract:
A headrest height adjusting apparatus includes: a basal member attached to a seatback and supporting a driving member; a movable member linked to a headrest and lifted up and down relative to the basal member; a transmitting member transmitting a driving force of the driving member to the movable member and lifting up and down the headrest linked to the movable member. The transmitting member having a frangible portion that leads a collapse of the transmitting member against an impact applied in a vertical direction between the driving member and the movable member and absorbs energy of the impact.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 U.S.C. §119 with respect to Japanese Patent Application 2006-086161, filed on Mar. 27, 2006 the entire content of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a hydraulic pressure control apparatus for an automatic transmission for simultaneously controlling engaging elements to be in an engaged state or in a disengaged state by means of, for example, a solenoid valve operated by hydraulic pressure from a hydraulic pressure source, and specifically, to a hydraulic pressure control apparatus that can achieve at least seven forward shift stages. 
       BACKGROUND 
       [0003]    A known hydraulic pressure control apparatus for an automatic transmission employs a so called clutch-to-clutch control system by which each engaging element is simultaneously controlled to be in an engaged state or in a disengaged state, by means of a solenoid valve (linear solenoid valve) directly operated by hydraulic pressure from the hydraulic pressure source, in order to provide a smooth and high level response shift feeling. JP2005-163916A (Reference 1) discloses a hydraulic pressure control apparatus having a failsafe valve for the purpose of avoiding an interlock of a shifting mechanism at an event of failure. 
         [0004]    In Reference 1, the automatic transmission incorporates, therein, three engaging elements C-3, B-1 and C-4. According to the hydraulic pressure control apparatus disclosed in JP2005-163916A, a failsafe valve is arranged between a hydraulic servo ( 53 ,  55  and  54  in  FIG. 4  of Reference 1) for each engaging element and a hydraulic pressure source ( 20  in  FIG. 4  thereof). Hydraulic pressure supply to the hydraulic servo ( 53 ) is established or interrupted by the first failsafe valve ( 43  in  FIG. 4  thereof) that is selectively operated by a first solenoid valve ( 36 ) arranged so as to correspond to the first failsafe valve. Likewise, hydraulic pressure supply to the hydraulic servo ( 55 ) is established or interrupted by the second failsafe valve ( 45 ) that is selectively operated by a second solenoid valve ( 37 ). The third failsafe valve ( 44 ) is selectively operated via both of the first and second failsafe valves by a third failsafe valve switching hydraulic pressure applied. Therefore, the failsafe valves are firmly switched by the solenoid valves, which is less in quantity than the failsafe valves, respectively. In the event of an off-failure for a solenoid signal, because the solenoid valves for a clutch C 1 , a clutch C 2  and a clutch C 4  (a corresponding engaging element) is a normally high type (NH; outputs hydraulic pressure at the maximum pressure level in the de-energized state), a cutoff valve ( 41 , failsafe valve) discontinues supply of the pressure C 1  during one of the fifth, seventh and eighth shift stage being selected with the pressure C 2  being supplied. In this case, a vehicle can drive at the sixth shift stage with the clutches C 4  and C 4  engaged. During any of the first, second third and fourth shift stages with the pressure C 2  being supplied, a vehicle can drive at the fourth shift stage with the clutches C 1  and C 4 . 
         [0005]    According to a hydraulic pressure control apparatus for an automatic transmission having failsafe valves, the failsafe valve is not operated during the shift mode and is operated during a fixed shift stage mode. Here, the hydraulic pressure supplied to the engaging element to be engaged (output pressure of control valve) is not switched by a hydraulic balance that is delicate as a signal pressure and is turned on or off by an on-off solenoid valve, so that the switching of the failsafe valve is assured. Further, an operation condition of other failsafe valve can be switched in accordance with a combination of operations of the on-off solenoid valves. Therefore, it is possible to reduce the number of on-off solenoid valves. However, according to an embodiment disclosed in Reference 1, control valves ( 24 ,  31 - 35  in  FIG. 4  of Reference 1) is a direct pressure type valve that is not structured with a combination of a linear solenoid valve and a control valve and does not use a modulator pressure. From the view of the current development of such direct pressure type valve, a normally high-type and direct pressure type valve (NH) has not been utilized yet. A normally low-type (NL; not outputs hydraulic pressure in the de-energized state) valve depends on electromagnetic force and hydraulic pressure. A normally high-type valve (NH) depends on electromagnetic force only, and hydraulic pressure is less outputted in response to an increase in electric current. Therefore, in order to drive a vehicle during an off failure, it is necessary to change an oil passage or add another valves (at least another two or three valves) by use of a method disclosed in JP2005-24059A. Further, in Reference 1, the failsafe valve is operated even during a fixed shift stage mode. Therefore, there is a possibility of interlock due to a primary failure of a failsafe valve. 
         [0006]    A need thus exist to provide a hydraulic pressure control apparatus which shows improved safety and can achieve at least seventh shift stage only with minor changes of the oil passage structure for the sixth shift stage. 
       SUMMARY OF THE INVENTION 
       [0007]    According to an aspect of the present invention, a hydraulic pressure control apparatus for an automatic transmission has a plurality of engaging elements. By the apparatus, a shift stage is switched in accordance with a combination of supplying hydraulic pressure to at least one of the engaging elements and draining hydraulic pressure from at least one of the engaging elements. The apparatus includes: a plurality of control valves each generating control hydraulic pressure from line pressure in response to an amount of electric power supplied thereto and controlling engagement or disengagement of at least one corresponding engaging element from among the engaging elements by use of the control hydraulic pressure; a plurality of shift valves each responsive to be actuated by a signal pressure and selectively establishing an oil passage for supplying the line pressure to each control valve in response to the signal pressure; a plurality of on-off solenoid valves each controlled in an energized state or in a de-energized state and each switching the signal pressure for a corresponding shift valve from among the plurality of shift valves in response the energized or de-energized state; a shift mode under which the plural shift valves are actuated to open the oil passages for supplying the line pressure to all of the corresponding control valves in accordance with a combination of the on-off solenoid valves in the energized or de-energized state: a fixed shift mode under which the plural shift valves are actuated to open at least one of the oil passages for supplying the line pressure to the corresponding control valve so that at least one corresponding engaging element from among the engaging elements is engaged and a shift stage is established in the automatic transmission; and an additional control valve provided to increase the number of shift stages achievable in the automatic transmission. The plural shift valves each supply the line pressure to the additional control valve only during the fixed shift mode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawings, wherein: 
           [0009]      FIG. 1  is a view illustrating an entire structure of a hydraulic pressure control apparatus for an automatic transmission according to a first embodiment of the present invention; 
           [0010]      FIG. 2  is a schematic view of the automatic transmission according to the first embodiment. 
           [0011]      FIG. 3  is a table explaining relationships between combinations of the engaging elements C 1 , C 2 , C 3 , C 4 , B 1  and B 2  to be engaged or disengaged and shifts stage corresponding to each combination according to the first embodiment; 
           [0012]      FIG. 4  is a hydraulic circuit diagram partially schematically illustrating a structure of the hydraulic pressure control unit according to the first embodiment of the present invention; 
           [0013]      FIG. 5  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the first embodiment; 
           [0014]      FIG. 6  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to a second embodiment of the present invention; 
           [0015]      FIG. 7  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the second embodiment; 
           [0016]      FIG. 8  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to the third embodiment of the present invention; 
           [0017]      FIG. 9  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the third embodiment; 
           [0018]      FIG. 10  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to a fourth embodiment of the present invention; 
           [0019]      FIG. 11  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the fourth embodiment; 
           [0020]      FIG. 12  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to a fifth embodiment of the present invention; 
           [0021]      FIG. 13  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the fifth embodiment; 
           [0022]      FIG. 14  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to a sixth embodiment of the present invention; 
           [0023]      FIG. 15  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the sixth embodiment; 
           [0024]      FIG. 16  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to a seventh embodiment of the present invention; 
           [0025]      FIG. 17  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the seventh embodiment; 
           [0026]      FIG. 18  is a hydraulic circuit diagram schematically illustrating a hydraulic pressure control unit according to an example 1; 
           [0027]      FIG. 19  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the seventh embodiment; 
           [0028]      FIG. 20A  is a shift operation diagram for a 6-speed AT according to the example 1; 
           [0029]      FIG. 20B  is a shift operation diagram for an 8-speed AT for an 8-speed AT according to the first embodiment; 
           [0030]      FIG. 21A  is a shift operation diagram for a 6-speed AT according to an example 2; and 
           [0031]      FIG. 21B  is a shift operation diagram for an 8-speed AT according to Reference 1. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Embodiments of the present invention will be described below with reference to the attached drawings. 
       First Embodiment 
       [0033]    Described below is a hydraulic pressure control apparatus for an automatic transmission according to the first embodiment of the present invention, with reference to the attached drawings.  FIG. 1  is a view illustrating an entire structure of the hydraulic pressure control apparatus for an automatic transmission according to the first embodiment of the present invention. The hydraulic pressure control apparatus for an automatic transmission includes: an automatic transmission  1 ; a hydraulic pressure control unit  3  and an electronic control unit  4 . The automatic transmission  1  is connected to an output shaft (not illustrated) of an engine  2 . The hydraulic pressure control unit  3  controls supply of hydraulic pressure to hydraulically driven type engaging elements (not illustrated) housed in the automatic transmission  1 . The electronic control unit  4  controls actuation of solenoid valves (not illustrated) housed in the hydraulic pressure control unit  3 . 
         [0034]    The electronic control unit  4  incorporates, therein, a microcomputer and is connected to an engine rotational speed sensor (Ne sensor)  5 , an input shaft rotational speed sensor (Nt sensor)  6 , an output shaft rotational speed sensor (No sensor)  7 , an opening degree sensor (θ sensor)  8  and a position sensor  9 . The engine rotational speed sensor (Ne sensor)  5  detects a rotational speed Ne of the output shaft of an engine  2 . The input shaft rotational speed sensor (Nt sensor)  6  detects a rotational speed Nt of an input shaft  11  of the automatic transmission  1 . The output shaft rotational speed sensor (No sensor)  7  detects a rotational speed No of an output shaft  12  of the automatic transmission  1 . The rotational speed No of an output shaft  12  corresponds to a speed of a vehicle. The opening degree sensor (θ sensor)  8  detects an opening degree θ of a throttle valve of the engine  2 . The opening degree θ of the throttle valve of the engine  2  corresponds to a load applied to the engine  2 . The position sensor  9  detects a position (driving range) of a shift lever operated by a driver. The electronic control unit  4  controls, based upon outputs of the sensors  5 ,  6 ,  7 ,  8  and  9 , electric power supply (energizing or de-energizing) to control valve units (control valves) SL 1 , SL 2 , SL 3  and SL 4  and on-off solenoid valves S 1 , S 2  and S 3 . Accordingly, a desired shift stage is achieved (see  FIG. 3 ). 
         [0035]      FIG. 2  is a schematic view of the automatic transmission  1  according to the first embodiment. The automatic transmission  1  enables to achieve eight forward shift stages and includes a torque converter  10 , the input shaft  11 , the output shaft  12 , a first double-pinion planetary gear train G 1 , a second single-pinion planetary gear train G 2 , and a third double-pinion planetary gear train G 3 . The torque converter  10  is connected to the output shaft of the engine  2  and includes a pump impeller  10   b  at its input side, a turbine runner  10   a  at its output side, and a lock-up clutch LU frictionally engaged by a pressure difference. In case where a rotational speed difference between the pump impeller  10   b  and the turbine runner  10   a  is small, the lock-up clutch LU is engaged and aids transmitting the input torque of the torque converter  10  to the gear box. The input shaft  11  is an output shaft of the torque converter  10 . The output shaft  12  is connected to an axis via a differential gear (not illustrated). The first double-pinion planetary gear train G 1 , the second single-pinion planetary gear train G 2  and the third double-pinion planetary gear train G 3  are mutually connected between the input shaft  11  and the output shaft  11  as illustrated in  FIG. 2 . The automatic transmission  1  incorporates, therein, plural engaging elements. According to the first embodiment, there are seven engaging elements: a first frictional clutch C 1 , a second frictional clutch C 2 , a third frictional clutch C 3 , a fourth frictional clutch C 4 , a first frictional brake B 1 , a second frictional brake B 2  and the lock-up clutch LU. The hydraulic pressure control unit  3  and the electronic control unit  4  selectively control engagements and disengagements of the frictional clutches C 1 , C 2 , C 3  and C 4  and the frictional brakes B 1  and B 2 , and thus a shift stage and a shift pattern is selectively established in the automatic transmission  1 . The hydraulic pressure control unit  3  and the electronic control unit  4  further control the engagement and disengagement of the lock-up clutch LU. The lock-up clutch LU is frictionally engaged when a rotational speed difference between the pump impeller  10   b  and the turbine runner  10   a  of the torque converter  10  is small during the vehicle driving at the forward shift stage. The second single-pinion planetary gear train G 2  can be provided with a one-way clutch OWC arranged in parallel with the second frictional brake B 2 . The frictional clutches C 1 , C 2 , C 3  and C 4 , the frictional brake B 1  and B 2  and the lock-up clutch LU are frictionally engaged when being applied with a high-leveled hydraulic pressure by the hydraulic pressure control unit  3 , while they are frictionally disengaged when being applied with a low-leveled hydraulic pressure thereby. The second frictional brake B 2  can be structured with mechanically separated brakes B 2 S and B 2 L. 
         [0036]      FIG. 3  is a table explaining relationships between combinations of the engaging elements C 1 , C 2 , C 3 , C 4 , B 1  and B 2  to be engaged or disengaged and shifts stage corresponding to each combination according to the first embodiment. The automatic transmission  1  is applicable to effect eight forward and single reverse shift stages. The eight forward shift stages is represented by under-drive shift stages, which are 1st, 2nd, 3rd, 4th and 5th shift stages, and over-drive shift stages, which are 6th, 7th and 8th shift stages. It is obvious that the automatic transmission  1  is applicable to achieve a neutral shift stage as well. More specifically, the output shaft  12  is rotated in an opposite direction of the input shaft  11  when only the third frictional clutch C 3  and the second frictional brake B 2  are frictionally engaged. In this case, the vehicle drives rearward. The neutral shift stage is established when only the second frictional brake B 2  is engaged. The 1st shift stage is established when only the first frictional clutch C 1  is engaged. The 1 st shift stage can be established when the second frictional brake B 2  is also engaged. The 2nd shift stage is established only with the first frictional clutch C 1  and the first frictional brake B 1  frictionally engaged. The 3rd shift stage is established only with the 1 st frictional clutch C  1  and the 3rd frictional clutch C 3  frictionally engaged. The 4th shift stage is established only with the first frictional clutch C 1  and the fourth frictional clutch C 4  frictionally engaged. The 5th shift stage is established only with the first frictional clutch C 1  and the second frictional clutch C 2  frictionally engaged. The 6th shift stage is established only with the second frictional clutch C 2  and the fourth frictional clutch C 4  frictionally engaged. The 7th shift stage is established only with the second frictional clutch C 2  and the third frictional clutch C 3  frictionally engaged. The 8th shift stage is established only with the second frictional clutch C 2  and the first frictional brake B 1  frictionally engaged. The table in  FIG. 3  also explains a relationship between the shift stage and a driving range (R range, N range, D range) selected in response to an operation of a manual lever (not illustrated) by a driver. 
         [0037]    Described below is a structure and controlling of the hydraulic pressure control unit according to the first embodiment with reference to the attached drawings.  FIG. 4  is a hydraulic circuit diagram partially schematically illustrating a structure of the hydraulic pressure control unit according to the first embodiment of the present invention. 
         [0038]    The hydraulic pressure control unit  3  includes control valve units SL 1 , SL 2 , SL 3 , SL 4 , SL 5  and SLU, a manual valve  21 , shift valves  22 ,  23  and  24 , on-off solenoid valves S 1 , S 2  and S 3 , a D-N accumulator  25 , a N-D accumulator  26 , a N-R accumulator  27 , hydraulic switches SW 1 , SW 2 , SW 3 , SW 4  and SW 5 , an LU relay valve  28 , and shuttle valves SB 1 , SB 2  and SB 3 . 
         [0039]    The first control valve unit (control valve) SL 1  is a control valve unit for the first frictional clutch C 1  and is integrated with a linear solenoid valve and a spool valve. The first control valve unit SL 1  can be structured with a linear solenoid valve and a spool valve, which are mechanically isolated from each other. The spool valve of the first control valve unit SL 1  is selectively movable in response to an amount of electric power supplied to the linear solenoid valve of the first control valve unit SL 1 . The spool valve of the first control valve unit SL 1  is formed with a supply port through which an output pressure (pressure D) of the first switching circuit  23   g  of the second shift valve  23  is introduced. In the first control valve unit SL 1 , a control hydraulic pressure is generated in response to an amount of electric power supplied to the linear solenoid valve of the first control valve unit SL 1 . The control hydraulic pressure is generated from the output pressure (pressure D) of the first switching circuit  23   g  of the second shift valve  23 , which is introduced to the spool valve the first control valve unit SL 1 . The control hydraulic pressure is outputted via an output port of the spool valve. In the situation where the first control valve unit SL 1  is supplied with: 1) the output pressure (pressure D) of the first switching circuit  23   g  of the second shift valve  23  introduced via the supply port; and 2) an output pressure (pressure D) of a fourth switching circuit  24   h  of the third shift valve  24  introduced via a drain port thereof, the pressure D is outputted from the output port, regardless if the linear solenoid valve is energized or de-energized. The output pressure (pressure SL 1 ) of the first control valve unit SL 1  is supplied to the first frictional clutch C 1  and the first hydraulic switch SW 1 . The first control valve unit SL 1  is a normally low-type valve unit (NL), which doest not output the pressure SL 1  in the de-energized state and incrementally outputs the pressure SL 1  in response to an increase in the amount of electric power supplied in the energized state. The output port of the first control valve unit SL 1  fluidly communicates with the drain port thereof in the de-energized state. 
         [0040]    The second control valve unit (control valve) SL 2  is a control valve unit for the second frictional clutch C 2  and the second frictional brake B 2 L and is integrated with a linear solenoid valve and a spool valve. The second control valve unit SL 2  can be structured with a linear solenoid valve and a spool valve, which are mechanically isolated from each other. The spool valve of the second control valve unit SL 2  is selectively movable in response to an amount of electric power supplied to the linear solenoid valve of the second control valve unit SL 2 . The spool valve of the second control valve unit SL 2  is formed with a supply port through which an output pressure (pressure D) of the manual valve  21  is introduced. In the second control valve unit SL 2 , a control hydraulic pressure is generated in response to an amount of electric power supplied to the linear solenoid valve of the second control valve unit SL 2 . The control hydraulic pressure is generated from the output pressure (pressure D) of the manual valve  21 , which is introduced to the spool valve the second control valve unit SL 2 . The control hydraulic pressure is outputted via an output port of the spool valve. In the situation where the second control valve unit SL 2  is supplied with: 1) the output pressure (pressure D) of the manual valve  21  introduced via the supply port; and 2) an output pressure (pressure D) of a sixth switching circuit  221  of the first shift valve  22  introduced via a drain port thereof, the pressure D is outputted from the output port, regardless if the linear solenoid valve is energized or de-energized. The output pressure (pressure SL 2 ) of the second control valve unit SL 2  is supplied to the second hydraulic switch SW 2 . The output pressure (pressure SL 2 ) of the second control valve unit SL 2  is further supplied to the second frictional clutch C 2  via a fifth switching circuit  22   k  of the first shift valve  22  in the case where a spool of the first shift valve  22  is positioned as denoted with a symbol “∘”. The output pressure (pressure SL 2 ) of the second control valve unit SL 2  is still further supplied to the second frictional brake B 2 L via a third switching circuit  22   i  of the first shift valve  22 , a sixth switching circuit  231  of the second shift valve  23  and a third shuttle valve SB 3  in case where a spool of the first shift valve  22  is positioned as denoted with a symbol “x” and a spool of the second shift valve  23  is positioned as denoted with a symbol “∘”. The second control valve unit SL 2  is a normally low-type valve unit (NL), which doest not output the pressure SL 2  in the de-energized state and incrementally outputs the pressure SL 2  in response to an increase in the amount of electric power supplied to the linear solenoid thereof in the energized state. The output port of the second control valve unit SL 2  fluidly communicates with the drain port thereof in the de-energized state. 
         [0041]    The third control valve unit (control valve) SL 3  is a control valve unit for the third frictional clutch C 3  and is integrated with a linear solenoid valve and a spool valve. The third control valve unit SL 3  can be structured with a linear solenoid valve and a spool valve, which are mechanically isolated from each other. The spool valve of the third control valve unit SL 3  is selectively movable in response to an amount of electric power supplied to the linear solenoid valve of the third control valve unit SL 3 . The spool valve of the third control valve unit SL 3  is formed with a supply port through which an output pressure (pressure PL or R) of a third switching circuit  23   i  of the second shift valve  23  is introduced. In the third control valve unit SL 3 , a control hydraulic pressure is generated in response to an amount of electric power supplied to the linear solenoid valve of the third control valve unit SL 3 . The control hydraulic pressure is generated from the output pressure (pressure PL or R) of the third switching circuit  23   i  of the second shift valve  23 , which is introduced to the spool valve the third control valve unit SL 3 . The control hydraulic pressure is outputted via an output port of the spool valve. In the situation where the third control valve unit SL 3  is supplied with: 1) the output pressure (pressure PL or R) of the third switching circuit  23   i  of the second shift valve  23  introduced via the supply port; and 2) an output pressure (pressure D or R) of a third switching circuit  24   g  of the third shift valve  24  introduced via a drain port thereof, the line pressure is outputted from the output port, regardless if the linear solenoid valve of the third control valve unit SL 3  is energized or de-energized. The output pressure (pressure SL 3 ) of the third control valve unit SL 3  is supplied to the third frictional clutch C 3  and the third hydraulic switch SW 3 . The third control valve unit SL 3  is a normally low-type valve unit (NL), which doest not output the pressure SL 3  in the de-energized state and incrementally outputs the pressure SL 3  in response to an increase in the amount of electric power supplied in the energized state. The output port of the third control valve unit SL 3  fluidly communicates with the drain port thereof in the de-energized state. 
         [0042]    The fourth control valve unit (control valve) SL 4  is a control valve unit for the first frictional brake B 1  and is integrated with a linear solenoid valve and a spool valve. The fourth control valve unit SL 4  can be structured with a linear solenoid valve and a spool valve, which are mechanically isolated from each other. The spool valve of the fourth control valve unit SL 4  is selectively movable in response to an amount of electric power supplied to the linear solenoid valve of the fourth control valve unit SL 4 . The spool valve of the fourth control valve unit SL 4  is formed with a supply port through which an output pressure (pressure D) of the fifth switching circuit  24   i  of the third shift valve  24  is introduced. In the fourth control valve unit SL 4 , a control hydraulic pressure (pressure SL 4 ) is generated in response to an amount of electric power supplied to the linear solenoid valve of the fourth control valve unit SL 4 . The control hydraulic pressure (pressure SL 4 ) is generated from the output pressure (pressure D) of the fifth switching circuit  24   i  of the third shift valve  24 , which is introduced to the spool valve the fourth control valve unit SL 4 . The control hydraulic pressure is outputted via an output port of the spool valve. The drain port of the fourth control valve unit SL 4  communicates with an exhaust circuit (EX). The pressure SL 4  is supplied to the first frictional brake B 1  and the fourth hydraulic switch SW 4 . The fourth control valve unit SL 4  is a normally low-type valve unit (NL), which doest not output the pressure SL 4  in the de-energized state and incrementally outputs the pressure SL 4  in response to an increase in the amount of electric power supplied in the energized state. The output port of the fourth control valve unit SL 4  fluidly communicates with the drain port thereof in the de-energized state. 
         [0043]    The fifth control valve unit (additional control valve) SL 5  is a control valve unit for the fourth frictional clutch C 4  and is integrated with a linear solenoid valve and a spool valve. The fifth control valve unit SL 5  can be structured with a linear solenoid valve and a spool valve, which are mechanically isolated from each other. The spool valve of the fifth control valve unit SL 5  is selectively movable in response to an amount of electric power supplied to the linear solenoid valve of the fifth control valve unit SL 5 . The spool valve of the fifth control valve unit SL 5  is formed with a supply port through which an output pressure (pressure D) of a second switching circuit  22   h  of the first shift valve  22  is introduced. In the fifth control valve unit SL 5 , a control hydraulic pressure (pressure SL 5 ) is generated in response to an amount of electric power supplied to the linear solenoid valve of the fifth control valve unit SL 5 . The control hydraulic pressure (pressure SL 5 ) is generated from the output pressure (pressure D) of the second switching circuit  22   h  of the first shift valve  22 , which is introduced to the spool valve the fifth control valve unit SL 5 . The control hydraulic pressure (pressure SL 5 ) is outputted via an output port of the spool valve. The drain port of the fifth control valve unit SL 5  communicates with an exhaust circuit (EX). The pressure SL 5  is supplied to the fourth frictional clutch C 4  and the fifth hydraulic switch SW 5 . The fifth control valve unit SL 5  is a normally low-type valve unit (NL), which doest not output the pressure SL 5  in the de-energized state and incrementally outputs the pressure SL 5  in response to an increase in the amount of electric power supplied in the energized state. The output port of the fifth control valve unit SL 5  fluidly communicates with the drain port thereof in the de-energized state. 
         [0044]    The LU control valve unit (control valve) SLU is a control valve unit for the lockup clutch LU and is integrated with a linear solenoid valve and a spool valve. The LU control valve unit SLU can be structured with a linear solenoid valve and a spool valve, which are mechanically isolated from each other. The spool valve of the LU control valve unit SLU is selectively movable in response to an amount of electric power supplied to the linear solenoid valve of the LU control valve unit SLU. The spool valve of the LU control valve unit SLU is formed with a supply port through which an output pressure (pressure PL) of a second switching circuit  24   f  of the third shift valve  24  is introduced. In the LU control valve unit SLU, a control hydraulic pressure (pressure SLU) is generated in response to an amount of electric power supplied to the linear solenoid valve of the LU control valve unit SLU. The control hydraulic pressure (pressure SLU) is generated from the output pressure (pressure D) of the second switching circuit  24   f  of the third shift valve  24 , which is introduced to the spool valve the fifth control valve unit SLU. The control hydraulic pressure (pressure SLU) is outputted via an output port of the spool valve. The pressure SLU is supplied to the lockup clutch LU and the LU relay valve  28 . The LU control valve unit SLU is a normally low-type valve unit (NL), which doest not output the pressure SLU in the de-energized state and incrementally outputs the pressure SLU in response to an increase in the amount of electric power supplied in the energized state. The output port of the LU control valve unit SLU fluidly communicates with the drain port (exhaust circuit; EX) thereof in the de-energized state. 
         [0045]    The manual valve  21  switches a hydraulic circuit in association with a driving range selected based upon an operation of a manual lever (not illustrated). The manual valve  21  incorporates therein a spool  21   a  slidably movable in a casing in association with an operation of the manual lever. When the D range is selected, the pressure PL, which is inputted thereinto via its pressure PL port, is outputted via its pressure D port as the pressure D. When the R range is selected, the pressure PL, which is inputted thereinto via its pressure PL port, is outputted via its pressure R port as the pressure R. The output pressure (pressure D) outputted from the pressure D port of the manual valve  21  is supplied to the supply port of the second control valve unit SL 2 , the first switching circuit  22   g  of the first shift valve  22 , the first switching circuit  23   g  and a fifth switching circuit  23 K of the second shift valve  23 , and the fifth switching circuit  24   i  of the third shift valve  24 . The output pressure (pressure R) outputted from the pressure R port of the manual valve  21  is supplied to the third switching circuit  22   i  of the first shift valve  22 , the second hydraulic chamber  23   e  of the second shift valve  23 , the second shuttle valve SB 2  and the third shuttle valve SB 3 . 
         [0046]    The first shift valve  22  is a switching valve for selectively establishing an oil passage and incorporates, in its valve body, a first spool  22   a , a second spool  22   b , a spring  22   c , a first hydraulic chamber  22   d , a second hydraulic chamber  22   e , and a third hydraulic chamber  22   f . The first spool  22   a  is arranged to be slidable within the valve body (not illustrated). The second spool  22   b  is arranged at an opposite side to the first spool  22   a  relative to the spring  22   c  in the valve body (not illustrated) and is slidably positioned in the valve body. The spring  22   c , which is arranged in the second hydraulic chamber  22   e , biases the first spool  22   a  towards the first hydraulic chamber  22   d  and the second spool  22   b  towards the third hydraulic chamber  22   f . When the first shift valve  22  is inputted with a signal pressure of the first on-off solenoid valve S 1 , the first hydraulic chamber  22   d  is actuated so as to bias the first spool  22   a  towards the third hydraulic chamber  22   f . The second hydraulic chamber  22   e  is a hydraulic chamber communicating with an exhaust port (exhaust circuit; EX) of the first shift valve  22 . When an hydraulic pressure (pressure C 2 ) for the second frictional clutch C 2  is introduced to the first shift valve  22 , the third hydraulic chamber  22   f  is actuated so as to bias the second spool  22   b  towards the first hydraulic chamber  22   d . In case where a force level of the hydraulic pressure applied by the first hydraulic chamber  22   d  is higher than the sum of the biasing force of the spring  22   c  and the hydraulic pressure applied by the third hydraulic chamber  22   f , the first spool  22   a  is slidably moved towards the third hydraulic chamber  22   f (“x” in  FIG. 4 ). In an opposite case thereto, the first spool  22   a  is slidably moved towards the first hydraulic chamber  22   d  (“∘”). The first spool  22   a  of the first shift valve  22  is formed with a first switching circuit  22   g . Because of this structure having the first switching circuit  22   g , when the first spool  22   a  is positioned as denoted with “x” in  FIG. 4 , a fluid communication is established among the first switching circuit  23   g  and the second switching circuit  23   h  of the second shift valve  23 , the fourth switching circuit  24   h  of the third shift valve  24  and the pressure D port of the manual valve  21 . On the other hand, when the first spool  22   a  is positioned as denoted with “∘” in  FIG. 4 , a fluid communication is established among the first switching circuit  23   g  and the second switching circuit  23   h  of the second shift valve  23 , the fourth switching circuit  24   h  and an exhaust port (EX) of the first shift valve  22 . The first shift valve  22  further includes the second switching circuit  22   h . Because of this structure having the second switching circuit  22   h , when the first spool  22   a  is positioned as denoted with “x” in  FIG. 4 , the supply port of the fifth control valve unit SL 5  fluidly communicates with the exhaust port (EX) of the first shift valve  22 . On the other hand, when the first spool  22   a  is positioned as denoted with “∘” in  FIG. 4 , the supply port of the fifth control valve unit SL 5  fluidly communicates with the fourth switching circuit  23   j  of the second shift valve  23 . The first shift valve  22  still further includes the third switching circuit  22   i . Because of this structure having the third switching circuit  22   i , when the first spool  22   a  is positioned as denoted with “x” in  FIG. 4 , the third switching circuit  23   i  of the second shift valve  23  fluidly communicates with the pressure R port of the manual valve  21 . On the other hand, when the first spool  22   a  is positioned as denoted with “∘” in  FIG. 4 , the supply port of the fifth control valve unit SL 5  fluidly communicates with the third switching circuit  23   i  of the second shift valve  23 . The first shift valve  22  still further includes a fourth switching circuit  22   j . Because of this structure having the fourth switching circuit  22   j , when the first spool  22   a  is positioned as denoted with “∘” in  FIG. 4 , the sixth switching circuit  231  of the second shift valve  23  fluidly communicates with an exhaust port (EX) of the first shift valve  22 . On the other hand, when the first spool  22   a  is positioned as denoted with “x” in  FIG. 4 , a fluid communication is established among the sixth switching circuit  231  of the second shift valve  23 , the output port of the second control valve unit SL 2  and the second hydraulic switch SW 2 . The first shift valve  22  still further includes the fifth switching circuit  22   k . Because of this structure having the fifth switching circuit  22   k , when the first spool  22   a  is positioned as denoted with “x” in  FIG. 4 , a fluid communication is established among the second frictional clutch C 2 , the third hydraulic chamber  22   f  and an exhaust port (EX) of the first shift valve  22 . On the other hand, when the first spool  22   a  is positioned as denoted with “∘” in  FIG. 4 , a fluid communication is established among the second frictional clutch C 2 , the third hydraulic chamber  22   f  of the first shift valve  22 , the output port of the second control valve unit SL 2  and the second hydraulic switch SW 2 . The first shift valve  22  still further includes the sixth switching circuit  221 . Because of this structure having the sixth switching circuit  221 , when the first spool  22   a  is positioned as denoted with “∘” in  FIG. 4 , a fluid communication is established among a drain port of the second control valve unit SL 2 , the fifth switching circuit  23   k  of the second shift valve  23  and the second shuttle valve SB 2 . On the other hand, when the first spool  22   a  is positioned as denoted with “x” in  FIG. 4 , the drain port of the second control valve unit SL 2  fluidly communicates with an exhaust port (EX) of the first shift valve  22 . There is an orifice and a check valve mounted on an oil passage extending between the third switching circuit  22   i  of the first shift valve  22  and the third switching circuit  23   i  of the second shift valve  23 . 
         [0047]    The second shift valve  23  is a switching valve for selectively establishing an oil passage and incorporates, in its valve body, a first spool  23   a , a second spool  23   b , a spring  23   c , a first hydraulic chamber  23   d , a second hydraulic chamber  23   e , and a third hydraulic chamber  23   f . The first spool  23   a  is arranged to be slidable within the valve body (not illustrated). The second spool  23   b  is arranged at an opposite side to the first spool  23   a  relative to the spring  23   c  in the valve body (not illustrated) and is slidably positioned in the valve body. The spring  23   c , which is arranged in the second hydraulic chamber  23   e , biases the first spool  23   a  towards the first hydraulic chamber  23   d  and the second spool  23   b  towards the third hydraulic chamber  23   f . When the second shift valve  23  is inputted with a signal pressure of the second on-off solenoid valve S 2 , the first hydraulic chamber  23   d  is actuated so as to bias the first spool  23   a  towards the third hydraulic chamber  23   f . When the second shift valve  23  is inputted with the pressure R of the pressure R port of the manual valve  21 , the second hydraulic chamber  23   e  is actuated so as to bias the first spool  23   a  towards the first hydraulic chamber  23   d  and the second spool  23   b  towards the third hydraulic chamber  23   f . When the second shift valve  23  is inputted with an hydraulic pressure via the sixth switching circuit  231  of the second shift valve  23 , the third hydraulic chamber  23   f  is actuated so as to bias the second spool  23   b  towards the first hydraulic chamber  23   d . In case where a force level of the hydraulic pressure applied by the first hydraulic chamber  23   d  is higher than the sum of the biasing force of the spring  23   c  and the hydraulic pressure applied by the second hydraulic chamber  23   e  or is higher than the sum of the biasing force of the spring  23   c  and the hydraulic pressure applied by the third hydraulic chamber  23   f , the first spool  23   a  is slidably moved towards the third hydraulic chamber  23   f  (“x” in  FIG. 4 ). In an opposite case thereto, the first spool  23   a  is slidably moved towards the first hydraulic chamber  23   d  (“∘”). The first spool  23   a  of the second shift valve  23  is formed with a first switching circuit  23   g . Because of this structure having the first switching circuit  23   g , when the first spool  23   a  is positioned as denoted with “x” in  FIG. 4 , a fluid communication is established among the supply port of the first control valve unit SL 1 , the D-N accumulator  25 , the first switching circuit  22   g  of the first shift valve  22  and the fourth switching circuit  24   h  of the third shift valve  24 . On the other hand, when the first spool  23   a  is positioned as denoted with “∘” in  FIG. 4 , a fluid communication is established among the supply port of the first control valve unit SL 1 , the D-N accumulator  25  and the pressure D port of the manual valve  21 . The second shift valve  23  further includes a second switching circuit  23   h . Because of this structure having the second switching circuit  23   h , when the first spool  23   a  is positioned as denoted with “∘” in  FIG. 4 , a fluid communication is established among the first shuttle valve SB 1 , the first switching circuit  22   g  of the first shift valve  22  and a fourth switching circuit  24   h  of the third shift valve  24 . On the other hand, when the first spool  23   a  is positioned as denoted with “x” in  FIG. 4 , the first shuttle valve SB 1  fluidly communicates with an exhaust port (EX) of the second shift valve  23 . The second shift valve  23  still further includes the third switching circuit  23   i . Because of this structure having the third switching circuit  23   i , when the first spool  23   a  is positioned as denoted with “x” in  FIG. 4 , the supply port of the third control valve unit SL 3  fluidly communicates with the first switching circuit  24   e  of the third shift valve  24 . On the other hand, when the first spool  23   a  is positioned as denoted with “∘” in  FIG. 4 , the supply port of the third control valve unit SL 3  fluidly communicates with the third switching circuit  22   i  of the first shift valve  22 . The second shift valve  23  still further includes a fourth switching circuit  23   j . Because of this structure having the fourth switching circuit  23   j , when the first spool  23   a  is positioned as denoted with “∘” in  FIG. 4 , a fluid communication is established among the second switching circuit  22   h  of the first shift valve  22 , the fifth switching circuit  24   i  of the third shift valve  24  and the supply port of the fourth control valve unit SL 4 . On the other hand, when the first spool  23   a  is positioned as denoted with “x” in  FIG. 4 , the second switching circuit  22   h  of the first shift valve  22  fluidly communicates with an exhaust port (EX) of the second shift valve  23 . The second shift valve  23  still further includes the fifth switching circuit  23   k . Because of this structure having the fifth switching circuit  23   k , when the first spool  23   a  is positioned as denoted with “x” in  FIG. 4 , a fluid communication is established among the sixth switching circuit  221  of the first shift valve  22 , the second shuttle valve SB 2  and the pressure D port of the manual valve  21 . On the other hand, when the first spool  23   a  is positioned as denoted with “∘” in  FIG. 4 , a fluid communication is established among the sixth switching circuit  221  of the first shift valve  22 , the second shuttle valve SB 2  and an exhaust port (EX) of the second shift valve  23 . The second shift valve  23  still further includes the sixth switching circuit  231 . Because of this structure having the sixth switching circuit  231 , when the first spool  23   a  is positioned as denoted with “∘” in  FIG. 4 , a fluid communication is established among the third hydraulic chamber  23   f  of the second shift valve  23 , the third shuttle valve SB 3  and the fourth switching circuit  22   j  of the first shift valve  22 . On the other hand, when the first spool  23   a  is positioned as denoted with “x” in  FIG. 4 , a fluid communication is established among the third hydraulic chamber  23   f  of the second shift valve  23 , the third shuttle valve SB 3  and an exhaust port (EX) of the second shift valve  23 . There is an orifice and check valve mounted on an oil passage extending between the third switching circuit  23   g  of the second shift valve  23  and the pressure D port of the manual valve  21 . 
         [0048]    The third shift valve  24  is a switching valve for selectively establishing an oil passage and incorporates, in its valve body, a spool  24   a , a spring  24   b , a first hydraulic chamber  24   c  and a second hydraulic chamber  24   d . The spool  24   a  is arranged to be slidable within the valve body (not illustrated). The spring  24   b  is arranged in the second hydraulic chamber  24   d  and biases the spool  24   a  towards the first hydraulic chamber  24   c . When the third shift valve  24  is inputted with a signal pressure of the third on-off solenoid valve S 3 , the first hydraulic chamber  24   c  is actuated so as to bias the spool  24   a  towards the second hydraulic chamber  24   d . The second hydraulic chamber  24   d  fluidly communicates with an exhaust port (exhaust circuit; EX). In case where a force level of the hydraulic pressure applied by the first hydraulic chamber  24   c  is higher than the biasing force of the spring  24   b , the spool  24   a  is slidably moved towards the second hydraulic chamber  24   d  (“x” in  FIG. 4 ). In an opposite case thereto, the spool  24   a  is slidably moved towards the first hydraulic chamber  24   c  (“∘” in  FIG. 4 ). The spool  24   a  of the third shift valve  24  is formed with the first switching circuit  24   e . Because of this structure having the first switching circuit  24   e , when the spool  24   a  is positioned as denoted with “x” in  FIG. 4 , the third switching circuit  23   i  of the second shift valve  23  fluidly communicates with the pressure PL port. On the other hand, when the spool  24   a  is positioned as denoted with “∘” in  FIG. 4 , the third switching circuit  23   i  of the second shift valve  23  fluidly communicates with an exhaust port (EX) of the third shift valve  24 . The third shift valve  24  further includes the second switching circuit  24   f . Because of this structure having the second switching circuit  24   f , when the spool  24   a  is positioned as denoted with “x” in  FIG. 4 , the supply port of the LU control valve unit SLU fluidly communicates with an exhaust port (EX) of the third shift valve  24 . On the other hand, when the spool  24   a  is positioned as denoted with “∘” in  FIG. 4 , the supply port of the LU control valve unit SLU fluidly communicates with the pressure PL port. The third shift valve  24  still further includes the third switching circuit  24   g . Because of this structure having the third switching circuit  24   g , when the spool  24   a  is positioned as denoted with “x” in  FIG. 4 , a fluid communication is established among the drain port of the third control valve unit SL 3 , the N-R accumulator  27  and the second shuttle valve SB 2 . On the other hand, when the spool  24   a  is positioned as denoted with “∘” in  FIG. 4 , the drain port of the third control valve unit SL 3 , the N-R accumulator  27  and an exhaust port (EX) of the third shift valve  24 . The third shift valve  24  still further includes the fourth switching circuit  24   h . Because of this structure having the fourth switching circuit  24   h , when the spool  24   a  is positioned as denoted with “x” in  FIG. 4 , a fluid communication is established among the drain port of the first control valve unit SL 1 , the N-D accumulator  26 , the first switching circuit  23   g  of the second shift valve  23  and the second switching circuit  23   h . On the other hand, when the spool  24   a  is positioned as denoted with “∘” in  FIG. 4 , a fluid communication is established among the drain port of the first control valve unit SL 1 , the N-D accumulator  26  and an exhaust port (EX) of the third shift valve  24 . The third shift valve  24  still further includes the fifth switching circuit  24   i . Because of this structure having the fifth switching circuit  24   i , when the spool  24   a  is positioned as denoted with “∘” in  FIG. 4 , a fluid communication is established among the fourth switching circuit  23   j  of the second shift valve  23 , the supply port of the fourth control valve unit SL 4  and the pressure D port of the manual valve  21 . On the other hand, when the spool  24   a  is positioned as denoted with “x” in  FIG. 4 , a fluid communication is established among the fourth switching circuit  23   j  of the second shift valve  23 , the supply port of the fourth control valve unit SL 4  and an exhaust port (EX) of the third shift valve  24 . The third shift valve  24  still further includes the sixth switching circuit  24   j . Because of this structure having the sixth switching circuit  24   j , when the spool  24   a  is positioned as denoted with “x” in  FIG. 4 , the second frictional brake B 2 S fluidly communicates with the first shuttle valve SB 1 . On the other hand, when the spool  24   a  is positioned as denoted with “∘” in  FIG. 4 , the second frictional brake B 2 S fluidly communicates with the pressure R port of the manual valve  21 . There is an orifice and a check valve mounted on an oil passage extending between the third switching circuit  24   g  of the third shift valve  24  and the drain port of the third control valve unit SL 3 . There is an orifice and a check valve mounted on an oil passage extending between the fourth switching circuit  24   h  of the third shift valve  24  and the drain port of the first control valve unit SL 1 . There is an orifice and a check valve mounted on an oil passage extending between the sixth switching circuit  24   j  of the third shift valve  24  and the first shuttle valve SB 1 . There is an orifice and a check valve mounted on an oil passage extending between the sixth switching circuit  24   j  of the third shift valve  24  and the second frictional brake B 2 S. 
         [0049]    The first on-off solenoid valve S 1  switches an operated condition of the first spool  22   a  of the first shift valve  22  in response to energizing or de-energizing thereto. The first on-off solenoid valve S 1  is a normally high-type solenoid valve (NH), which supplies a signal pressure to the first shift valve  22  in the de-energized state and does not supply in the energized state. 
         [0050]    The second on-off solenoid valve S 2  switches an operated condition of the first spool  23   a  of the second shift valve  23  in response to energizing or de-energizing thereto. The second on-off solenoid valve S 2  is a normally high-type solenoid valve (NH), which supplies a signal pressure to the second shift valve  23  in the de-energized state and does not supply in the energized state. 
         [0051]    The third on-off solenoid valve S 3  switches an operated condition of the spool  24   a  of the third shift valve  24  in response to energizing or de-energizing thereto. The third on-off solenoid valve S 3  is a normally high-type solenoid valve (NH), which supplies a signal pressure to the third shift valve  24  in the de-energized state and does not supply in the energized state. 
         [0052]    The D-N accumulator  25  is mounted on an oil passage extending between the supply port of the first control valve unit SL 1  and the first switching circuit  23   g  of the second shift valve  23  and is actuated to absorb hydraulic shock that may occur at a time of a shift operation from the D range to the N range. 
         [0053]    The N-D accumulator  26  is mounted on an oil passage extending between the drain port of the first control valve unit SL 1  and the fourth switching circuit  24   h  of the third shift valve  24  and is actuated to absorb hydraulic shock that may occur at a time of a shift operation from the N range to the D range. 
         [0054]    The N-R accumulator  27  is mounted on an oil passage extending between the drain port of the third control valve unit SL 3  and the third switching circuit  24   g  of the third shift valve  24  and is actuated to absorb hydraulic shock that may occur at a time of a shift operation from the N range to the R range. 
         [0055]    The first hydraulic switch SW 1  is a hydraulic switch that is turned on when being supplied with the output pressure of the first control valve unit SL 1 . 
         [0056]    The second hydraulic switch SW 2  is a hydraulic switch that is turned on when being supplied with the output pressure of the second control valve unit SL 2 . 
         [0057]    The third hydraulic switch SW 3  is a hydraulic switch that is turned on when being supplied with the output pressure of the third control valve unit SL 3 . 
         [0058]    The fourth hydraulic switch SW 4  is a hydraulic switch that is turned on when being supplied with the output pressure of the fourth control valve unit SL 4 . 
         [0059]    The fifth hydraulic switch SW 5  is a hydraulic switch that is turned on when being supplied with the output pressure of the fifth control valve unit SL 5 . 
         [0060]    The LU relay valve  28  is a switching valve that switches an oil passage when being supplied with the output pressure of the LU control valve unit SLU. 
         [0061]    The first shuttle valve SB 1  can be supplied with the output pressure (pressure D) of the second switching circuit  23   h  of the second shift valve  23  and the pressure R of the manual valve  21 . When the output pressure (pressure D) of the second switching circuit  23   h  of the second shift valve  23  is higher than the pressure R, the sixth switching circuit  24   j  of the third shift valve  24  is supplied with the output pressure (pressure D) of the second switching circuit  23   h . In an opposite case thereto, the sixth switching circuit  24   j  of the third shift valve  24  is supplied with the pressure R. 
         [0062]    The second shuttle valve SB 2  can be supplied with the output pressure (pressure D) of the fifth switching circuit  23   k  of the second shift valve  23  and the pressure R of the manual valve  21 . When the output pressure (pressure D) of the fifth switching circuit  23   k  of the second shift valve  23  is higher than the pressure R, the third switching circuit  24   g  of the third shift valve  24  is supplied with the output pressure (pressure D) of the fifth switching circuit  23   k . In an opposite case thereto, the third switching circuit  24   g  of the third shift valve  24  is supplied with the pressure R. 
         [0063]    The third shuttle valve SB 3  can be supplied with the output pressure (pressure D) of the sixth switching circuit  231  of the second shift valve  23  and the pressure R of the manual valve  21 . When the output pressure (pressure D) of the sixth switching circuit  231  of the second shift valve  23  is higher than the pressure R, the second frictional brake B 2 L is supplied with the output pressure (pressure D) of the sixth switching circuit  231  of the second shift valve  23 . In an opposite case thereto, the second frictional brake B 2 L is supplied with the pressure R. 
         [0064]    Described blow is a shift pattern selected in response to a control state of the hydraulic pressure control unit according to the first embodiment of the present invention.  FIG. 5  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the first embodiment. 
         [0065]    In  FIG. 5 , the D range is denoted with “D”, the R range is denoted with “R”. There are forward shift stages inscribed at the right side of the “D” column. At the columns of the on-off solenoid valves (NH) S 1 , S 2  and S 3 , “On” represents that the NH-type on-off solenoid valve is in the energized state, and “Off” represents that the NH-type on-off solenoid valve is in the de-energized state. 
         [0066]    In each column for the frictional engagement element, “SL 1  (NL)” represents that the corresponding frictional engagement element can be controlled by the NL-type first control valve unit SL 1 . “SL 2  (NL)” represents that the corresponding frictional engagement element can be controlled by the NL-type second control valve unit SL 2 . “SL 3  (NL)” represents that the corresponding frictional engagement element can be controlled by the NL-type third control valve unit SL 3 . “SL 4  (NL)” represents that the corresponding frictional engagement element can be controlled by the NL-type fourth control valve unit SL 4 . “SL 5  (NL)” represents that the corresponding frictional engagement element can be controlled by the NL-type fifth control valve unit SL 5 . “SLU (NL)” represents that the corresponding frictional engagement element can be controlled by the NL-type LU control valve unit SLU. “SL 1 ↑”, “SL 2 ↑” and “SL 3 ↑” each represents that the corresponding frictional engagement element can be frictionally engaged by the line pressure from the corresponding control valve unit. 
         [0067]    “All SL Disconnected” represents a state where all of the solenoid valves SL 1 , SL 2 , SL 3 , SL 4  and SLU are electrically disconnected (electrically fail). “N” represents that all of the engaging elements are in the disengaged states and are positioned neutrally. “N (C 2 )” represents that a neutral shift stage is established in the transmission with only the second frictional clutch C 2  engaged. “N (B 2 )” represents that a neutral shift stage is established in the transmission with only the second frictional brakes B 2 S and B 2 L engaged. 
         [0068]    In the first embodiment, the 8-speed automatic transmission  1  is achieved only by adding the fifth control valve unit SL 5  and without any changes to a basic hydraulic circuit of the hydraulic pressure control unit  3 , which leads to reduction in manufacturing cost and development hours. Further, because there is no fail-safe valve mounted in the hydraulic pressure control unit  3 , there is no possibility for a double engagement to occur during a fixed shift stage mode due to a primary failure of the fail-safe valve. Therefore, even in the event of a failure during a shift mode, a safe driving of a vehicle is assured by changing the shift mode to the fixed shift stage mode. 
         [0069]    Further, as described above, the first shift valve  22  includes the second switching circuit  22   h , and the second shift valve  23  includes the fourth switching circuit  23   j . Therefore, only when all the on-off solenoid valves S 1 , S 2  and S 3  are electrically energized, the fifth control valve unit SL 5  is supplied with the output pressure (pressure D) of the fifth switching circuit  24   i  of the third shift valve  24  via the second switching circuit  22   h  of the first shift valve  22  and the fourth switching circuit  23   j  of the second shift valve  23 . Therefore, the oil passage, which extends to the fifth control valve unit SL 5  from the fifth switching circuit  24   i  of the third shift valve  24 , does not have to bypass the first shift valve  22  and the second shift valve  23  and is firmly wire-connected between the fifth control valve unit SL 5  and the fifth switching circuit  24   i  of the third shift valve  24 . 
       Second Embodiment 
       [0070]    Described below is a hydraulic pressure control apparatus for an automatic transmission according to a second embodiment of the present invention, with reference to the attached drawings.  FIG. 6  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to the second embodiment of the present invention.  FIG. 7  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the second embodiment. 
         [0071]    The configuration of the oil passage of the second embodiment is substantially the same as that of the first embodiment. However, the second and third control valve units SL 2  and SL  3  herein are not the normally low-type control valve units (NL) but the normally high-type control valve units (NH) on the premise that a normally high-type control valve unit can be developed so as to be mounted on the apparatus. 
         [0072]    In the second embodiment, the same effect as that of the first embodiment can be exerted, and the NH-type control valve unit contributes to enhance a driving performance of a vehicle. That is, as illustrated in  FIG. 7 , even when electric disconnection occurs for all of the control valve units in the situation where the on-off solenoid valve S 1  is in a de-energized state, the on-off solenoid valve S 2  is in an energized state and the on-off solenoid valve S 3  is in a de-energized state, the vehicle can start at the 1st shift stage. Further, even when electric disconnection occurs for all of the control valve units in the situation where the on-off solenoid valves S 1 , S 2  and S 3  are all in the energized state, the vehicle can drive at the 5th shift stage. Still further, the change from the NL-type to the NH-type for the control valve unit, does not cause any changes in the hydraulic circuit of the hydraulic pressure control unit  3 , and does not require any other additional valves against an off-failure of the control valve unit. 
       Third Embodiment 
       [0073]    Described below is a hydraulic pressure control apparatus for an automatic transmission according to a third embodiment of the present invention, with reference to the attached drawings.  FIG. 8  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to the third embodiment of the present invention.  FIG. 9  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the third embodiment. 
         [0074]    In the second embodiment, the second control valve unit SL 2  is shared by the second frictional clutch C 2  and the second frictional brake B 2 . In the third embodiment, however, the second control valve unit SL 2  is exclusively used for the second frictional clutch C 2 , and a sixth control valve unit SL 6  (additional control valve) is added as an exclusive unit for the second frictional brake B 2 . With the addition of the sixth control valve unit SL 6 , the use of the third shuttle valve (SB 3  in  FIG. 6  of the second embodiment) for the second frictional brake B 2 L is avoided, therefore but a fourth shuttle valve SB 4  is required to selectively supply the pressure D or the pressure R to the sixth control valve unit SL 6 . Further, in the third embodiment, a first shift valve  32  is provided with a fourth switching circuit  32   j , which prohibits the flow of the output pressure of the second control valve unit SL 2  from the fourth switching circuit ( 22   j  in  FIG. 6 ) of the first shift valve ( 22  in  FIG. 6 ) to the sixth switching circuit ( 231  in  FIG. 6  of the second embodiment) of the second shift valve ( 23  in  FIG. 6  of the second embodiment). The fourth switching circuit  32   j  allows the supply of the output pressure of the sixth control valve unit SL 6  to the sixth switching circuit  231  of the second shift valve  23 . Moreover, in the third embodiment, the sixth switching circuit ( 24   j  in  FIG. 6 ) of the third shift valve ( 24  in  FIG. 6  of the second embodiment) is no longer connected, via its inlet port, to the pressure R port of the manual valve ( 21  in  FIG. 6  of the second embodiment). The inlet port of the sixth switching circuit  24   j  of the third shift valve  24  of the third embodiment communicates with an exhaust circuit (EX). Described below are main structures that are different from the second embodiment. 
         [0075]    The sixth control valve unit (control valve) SL 6  is a control valve unit for the second frictional brake B 2 L and is integrated with a linear solenoid valve and a spool valve. The sixth control valve unit SL 6  can be structured with a linear solenoid valve and a spool valve, which are mechanically isolated from each other. The spool valve of sixth control valve unit SL 6  is selectively movable in response to an amount of electric power supplied to the linear solenoid valve of the sixth control valve unit SL 6 . The spool valve of the sixth control valve unit SL 6  is formed with a supply port through which an output pressure (pressure D or R) of the fourth shuttle valve SB 4  is introduced. In the sixth control valve unit SL 6 , a control hydraulic pressure is generated in response to an amount of electric power supplied to the linear solenoid valve of the sixth control valve unit SL 6 . The control hydraulic pressure is generated from the output pressure (pressure D or R) of the fourth shuttle valve SB 4 , which is introduced to the spool valve the sixth control valve unit SL 6 . The control hydraulic pressure is outputted via an output port of the spool valve. A drain port of the sixth control valve unit SL 6  fluidly communicates with an exhaust circuit (EX). The output pressure (pressure SL 6 ) of the sixth control valve unit SL 6  is supplied to a sixth hydraulic switch SW 6 . The output pressure (pressure C 2 ) of the sixth control valve unit SL 6  is further supplied to the second frictional brake B 2 L via the fourth switching circuit  32   j  of the first shift valve  32  and the sixth switching circuit  231  of the second shift valve  23  in the situation where the first spool  32   a  of the first shift valve  32  is positioned as illustrated with “x” in  FIG. 8  and the first spool  23   a  of the second shift valve  23  is positioned as illustrated in “∘” in  FIG. 8 . The sixth control valve unit SL 6  is a normally high-type valve unit (NH), which outputs the pressure C 2  at the maximum level in the de-energized state and decrementally outputs the pressure C 2  in response to an increase in the amount of electric power supplied to the linear solenoid thereof in the energized state. The output port of the sixth control valve unit SL 6  fluidly communicates with the supply port thereof in the de-energized state. 
         [0076]    The first shift valve  32  is a switching valve for selectively establishing an oil passage and incorporates, in its valve body, a first spool  32   a , a second spool  32   b , a spring  32   c , a first hydraulic chamber  32   d , a second hydraulic chamber  32   e , and a third hydraulic chamber  32   f . The first spool  32   a  is arranged to be slidable within the valve body (not illustrated). The second spool  32   b  is arranged at an opposite side to the first spool  32   a  relative to the spring  32   c  in the valve body (not illustrated) and is slidably positioned in the valve body. The spring  32   c , which is arranged in the second hydraulic chamber  32   e , biases the first spool  32   a  towards the first hydraulic chamber  32   d  and the second spool  32   b  towards the third hydraulic chamber  32   f . When the first shift valve  32  is inputted with a signal pressure of the first on-off solenoid valve S 1 , the first hydraulic chamber  32   d  is actuated so as to bias the first spool  32   a  towards the third hydraulic chamber  32   f . The second hydraulic chamber  32   e  is a hydraulic chamber communicating with an exhaust port (exhaust circuit; EX). When an hydraulic pressure (pressure C 2 ) for the second frictional clutch C 2  is introduced to the first shift valve  32 , the third hydraulic chamber  32   f  is actuated so as to bias the second spool  32   b  towards the first hydraulic chamber  32   d . In case where a force level of the hydraulic pressure applied by the first hydraulic chamber  32   d  is higher than the sum of the biasing force of the spring  32   c  and the hydraulic pressure applied by the third hydraulic chamber  32   f , the first spool  32   a  is slidably moved towards the third hydraulic chamber  32   f (“x” in  FIG. 8 ). In an opposite case thereto, the first spool  32   a  is slidably moved towards the first hydraulic chamber  32   d  (“∘”). The first spool  32   a  of the first shift valve  32  is formed with a first switching circuit  32   g . Because of this structure having the first switching circuit  32   g , when the first spool  32   a  is positioned as denoted with “x” in  FIG. 8 , a fluid communication is established among the first switching circuit  23   g  and the second switching circuit  23   h  of the second shift valve  23 , and the pressure D port of the manual valve  21 . On the other hand, when the first spool  32   a  is positioned as denoted with “∘” in  FIG. 8 , a fluid communication is established among the first switching circuit  23   g  and the second switching circuit  23   h  of the second shift valve  23 , and an exhaust port (EX) of the first shift valve  32 . The first shift valve  32  further includes the second switching circuit  32   h . Because of this structure having the second switching circuit  32   h , when the first spool  32   a  is positioned as denoted with “x” in  FIG. 8 , the supply port of the fifth control valve unit SL 5  fluidly communicates with an exhaust port (EX) of the first shift valve  32 . On the other hand, when the first spool  32   a  is positioned as denoted with “∘” in  FIG. 8 , the supply port of the fifth control valve unit SL 5  fluidly communicates with the fourth switching circuit  23   j  of the second shift valve  23 . The first shift valve  32  still further includes the third switching circuit  32   i . Because of this structure having the third switching circuit  32   i , when the first spool  32   a  is positioned as denoted with “x” in  FIG. 8 , the third switching circuit  23   i  of the second shift valve  23  fluidly communicates with the pressure R port of the manual valve  21 . On the other hand, when the first spool  32   a  is positioned as denoted with “∘” in  FIG. 8 , a fluid communication is established among the third switching circuit  23   i  of the second shift valve  23 , the second switching circuit  32   h  of the first shift valve  32  and the supply port of the fifth control valve unit SL 5 . The first shift valve  32  still further includes a fourth switching circuit  32   j . Because of this structure having the fourth switching circuit  32   j , when the first spool  32   a  is positioned as denoted with “x” in  FIG. 8 , a fluid communication is established among the sixth switching circuit  231  of the second shift valve  23 , the output port of the sixth control valve unit SL 6  and the sixth hydraulic switch SW 6 . On the other hand, when the first spool  32   a  is positioned as denoted with “∘” in  FIG. 8 , the sixth switching circuit  231  of the second shift valve  23  fluidly communicates with an exhaust port (EX) of the first shift valve  32 . The first shift valve  32  still further includes the fifth switching circuit  32   k . Because of this structure having the fifth switching circuit  32   k , when the first spool  32   a  is positioned as denoted with “∘” in  FIG. 8 , a fluid communication is established among the second frictional clutch C 2 , the third hydraulic chamber  32   f  of the first shift valve  32 , the output port of the second control valve unit SL 2  and the hydraulic switch SW 2 . On the other hand, when the first spool  32   a  is positioned as denoted with “x” in  FIG. 8 , a fluid communication is established among the second frictional clutch C 2 , the third hydraulic chamber  32   f  and the exhaust port (EX) of the first shift valve  32 . The first shift valve  32  still further includes the sixth switching circuit  321 . Because of this structure having the sixth switching circuit  321 , when the first spool  32   a  is positioned as denoted with “∘” in  FIG. 8 , the drain port of the second control valve unit SL 2  fluidly communicates with the fifth switching circuit  23  of the second shift valve  23 . On the other hand, when the first spool  32   a  is positioned as denoted with “x” in  FIG. 8 , the drain port of the second control valve unit SL 2  fluidly communicates with an exhaust port (EX) of the first shift valve  32 . There is an orifice and a check valve mounted on an oil passage extending between the third switching circuit  32   i  of the first shift valve  32  and the third switching circuit  23   i  of the second shift valve  23 . 
         [0077]    The fourth shuttle valve SB 4  can be supplied with the pressure D and the pressure R of the manual valve  21 . When the pressure D is higher than the pressure R, the supply port of the sixth control valve unit SL 6  is supplied with the pressure D. In an opposite case thereto, the supply port of the sixth control valve unit SL 6  is supplied with the pressure R. 
         [0078]    The sixth hydraulic switch SW 6  is a hydraulic switch that is turned on when being supplied with the output pressure of the sixth control valve unit SL 6 . 
         [0079]    In the third embodiment, the same effect as the first and second embodiment can be effected. 
       Fourth Embodiment 
       [0080]    Described below is a hydraulic pressure control apparatus for an automatic transmission according to a fourth embodiment of the present invention, with reference to the attached drawings.  FIG. 10  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to the fourth embodiment of the present invention.  FIG. 11  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the fourth embodiment. 
         [0081]    In the third embodiment, the input port of the sixth switching circuit ( 24   j  in  FIG. 8 ) of the third shift valve ( 24  in  FIG. 8 ) fluidly communicates with the exhaust port of the third shift valve  24 . In the fourth embodiment, however, a sixth switching circuit  24   j  of a third shift valve  24  is mounted on an oil passage extending between the sixth switching circuit  231  of the second shift valve  23  and the second frictional brake B 2 L. The other configuration of the hydraulic circuit and the apparatus of the fourth embodiment is the same as that of the third embodiment. 
         [0082]    In the fourth embodiment, the same effect as the first and second embodiments is yielded. As illustrated in  FIG. 11 , with the on-off solenoid valve S 1  in the de-energized state, the on-off solenoid valve S 2  in the energized state and the on-off solenoid valve S 3  in the energized state during the D range being selected, the second frictional brake B 2 S is also supplied with the pressure C 2  and is controlled for engagement. Therefore, an amount of torque is assured reliably. This is also applied to the case with the on-off solenoid valve S 1  in the de-energized state, the on-off solenoid valve S 2  in the energized or de-energized state and the on-off solenoid valve S 3  in the energized state during the R range being selected. The second hydraulic chamber  23   e  is supplied with the pressure R so that the first spool  23   a  of the second shift valve  23  is positioned at the side of “∘” in  FIG. 10  regardless if the on-off solenoid valve S 2  is in the energized or de-energized state. 
       Fifth Embodiment 
       [0083]    Described below is a hydraulic pressure control apparatus for an automatic transmission according to a fifth embodiment of the present invention, with reference to the attached drawings.  FIG. 12  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to the fifth embodiment of the present invention.  FIG. 13  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the fifth embodiment. 
         [0084]    In the fourth embodiment, a piston chamber for the second frictional brake is structured with two chambers of B 2 S and B 2 L. In the fifth embodiment, the piston chamber thereof is a single chamber B 2  (second frictional brake). Abolished in the fifth embodiment are: the second switching circuit ( 23   h  in  FIG. 10  of the fourth embodiment) of the second shift valve ( 23  in  FIG. 10 ); the sixth switching circuit ( 24   j  in  FIG. 10 ) of the third shift valve ( 24  in  FIG. 10 ); and the first shuttle valve (SB 1  in  FIG. 10 ), and the orifice and the check valve mounted on the oil passage between the first shuttle valve (SB  1  in  FIG. 10 ) and the sixth switching circuit ( 24   j  in  FIG. 10 ) of the third shift valve ( 24  in  FIG. 10 ) is relocated onto an oil passage extending between the fourth switching circuit  32   j  of the first shift valve  32  and the fifth switching circuit  33   k  of the second shift valve  33 . Described below are main structures that are different from the fourth embodiment. 
         [0085]    The second shift valve  33  is a switching valve for selectively establishing an oil passage and incorporates, in its valve body, a first spool  33   a , a second spool  33   b , a spring  33   c , a first hydraulic chamber  33   d , a second hydraulic chamber  33   e , and a third hydraulic chamber  33   f . The first spool  33   a  is arranged to be slidable within the valve body (not illustrated). The second spool  33   b  is arranged at an opposite side to the first spool  33   a  relative to the spring  33   c  in the valve body (not illustrated) and is slidably positioned in the valve body. The spring  33   c , which is arranged in the second hydraulic chamber  33   e , biases the first spool  33   a  towards the first hydraulic chamber  33   d  and the second spool  33   b  towards the third hydraulic chamber  33   f . When the second shift valve  33  is inputted with a signal pressure of the second on-off solenoid valve S 2 , the first hydraulic chamber  33   d  is actuated so as to bias the first spool  33   a  towards the third hydraulic chamber  33   f . When the second shift valve  33  is inputted with the pressure R of the pressure R port of the manual valve  21 , the second hydraulic chamber  33   e  is actuated so as to bias the first spool  33   a  towards the first hydraulic chamber  33   d  and the second spool  33   b  towards the third hydraulic chamber  33   f . When the second shift valve  33  is inputted with an hydraulic pressure via the fifth switching circuit  33   k  of the second shift valve  33 , the third hydraulic chamber  33   f  is actuated so as to bias the second spool  33   b  towards the first hydraulic chamber  33   d . In case where a force level of the hydraulic pressure applied by the first hydraulic chamber  33   d  is higher than the sum of the biasing force of the spring  33   c  and the hydraulic pressure applied by the second hydraulic chamber  33   e  or is higher than the sum of the biasing force of the spring  33   c  and the hydraulic pressure applied by the third hydraulic chamber  33   f , the first spool  33   a  is slidably moved towards the third hydraulic chamber  33   f  (“x” in  FIG. 12 ). In an opposite case thereto, the first spool  33   a  is slidably moved towards the first hydraulic chamber  33   d  (“∘”). The first spool  33   a  of the second shift valve  33  is formed with a first switching circuit  33   g . Because of this structure having the first switching circuit  33   g , when the first spool  33   a  is positioned as denoted with “x” in  FIG. 12 , a fluid communication is established among the supply port of the first control valve unit SL 1 , the D-N accumulator  25 , the first switching circuit  32   g  of the first shift valve  32  and the fourth switching circuit  34   h  of the third shift valve  34 . On the other hand, when the first spool  33   a  is positioned as denoted with “∘” in  FIG. 12 , a fluid communication is established among the supply port of the first control valve unit SL 1 , the D-N accumulator  25  and the pressure D port of the manual valve  21 . The second shift valve  33  further includes a second switching circuit  33   h . Because of this structure having the second switching circuit  33   h , when the first spool  33   a  is positioned as denoted with “x” in  FIG. 12 , the supply port of the third control valve unit SL 3  fluidly communicates with the first switching circuit  34   e  of the third shift valve  34 . On the other hand, when the first spool  33   a  is positioned as denoted with “∘” in  FIG. 12 , the supply port of the third control valve unit SL 3  fluidly communicates with the third switching circuit  32   i  of the first shift valve  32 . The second shift valve  33  still further includes a third switching circuit  33   i . Because of this structure having the third switching circuit  33   i , when the first spool  33   a  is positioned as denoted with “∘” in  FIG. 12 , a fluid communication is established among the second switching circuit  32   h  of the first shift valve  32 , the fifth switching circuit  34   i  of the third shift valve  34  and the supply port of the fourth control valve unit SL 4 . On the other hand, when the first spool  33   a  is positioned as denoted with “x” in  FIG. 12 , the second switching circuit  32   h  of the first shift valve  32  fluidly communicates with an exhaust port (EX) of the second shift valve  33 . The second shift valve  33  still further includes a fourth switching circuit  33   j . Because of this structure having the fourth switching circuit  33   j , when the first spool  33   a  is positioned as denoted with “x” in  FIG. 12 , a fluid communication is established among the sixth switching circuit  321  of the first shift valve  32 , the second shuttle valve SB 2  and the pressure D port of the manual valve  21 . On the other hand, when the first spool  33   a  is positioned as denoted with “∘” in  FIG. 12 , a fluid communication is established among the sixth switching circuit  321  of the first shift valve  32 , the second shuttle valve SB 2  and an exhaust port (EX) of the second shift valve  33 . The second shift valve  33  still further includes the fifth switching circuit  33   k . Because of this structure having the fifth switching circuit  33   k , when the first spool  33   a  is positioned as denoted with “x” in  FIG. 12 , a fluid communication is established among a third hydraulic chamber  33   f  of the second shift valve  33 , the second frictional brake B 2  and an exhaust port (EX) of the second shift valve  33 . On the other hand, when the first spool  33   a  is positioned as denoted with “∘” in  FIG. 12 , a fluid communication is established among the third hydraulic chamber  33   f  of the second shift valve  33 , the second frictional brake B 2  and the fourth switching circuit  32   j  of the first shift valve  32 . There are an orifice and a check valve mounted on an oil passage extending between the first switching circuit  33   g  of the second shift valve  33  and the pressure D port of the manual valve  21 . There are an orifice and a check valve mounted on an oil passage extending between the fifth switching circuit  33   k  of the second shift valve  33  and the fourth switching circuit  32   j  of the first shift valve  32 . There are an orifice and a check valve mounted on an oil passage extending between the fifth switching circuit  33   k  of the second shift valve  33  and the second frictional brake B 2 . 
         [0086]    The third shift valve  34  is a switching valve for selectively establishing an oil passage and incorporates, in its valve body, a spool  34   a , a spring  34   b , a first hydraulic chamber  34   c  and a second hydraulic chamber  34   d . The spool  34   a  is arranged to be slidable within the valve body (not illustrated). The spring  34   b  is arranged in the second hydraulic chamber  34   d  and biases the spool  34   a  towards the first hydraulic chamber  34   c . When the third shift valve  34  is inputted with a signal pressure of the third on-off solenoid valve S 3 , the first hydraulic chamber  34   c  is actuated so as to bias the spool  34   a  towards the second hydraulic chamber  34   d . The second hydraulic chamber  34   d  fluidly communicates with an exhaust port (exhaust circuit; EX). In case where a force level of the hydraulic pressure applied by the first hydraulic chamber  34   c  is higher than the biasing force of the spring  34   b , the spool  34   a  is slidably moved towards the second hydraulic chamber  34   d  (“x” in  FIG. 12 ). In an opposite case thereto, the spool  34   a  is slidably moved towards the first hydraulic chamber  34   c  (“∘” in  FIG. 12 ). The spool  34   a  of the third shift valve  34  is formed with the first switching circuit  34   e . Because of this structure having the first switching circuit  34   e , when the spool  34   a  is positioned as denoted with “x” in  FIG. 12 , the second switching circuit  33   h  of the second shift valve  33  fluidly communicates with the pressure PL port. On the other hand, when the spool  34   a  is positioned as denoted with “∘” in  FIG. 12 , the second switching circuit  33   h  of the second shift valve  33  fluidly communicates with an exhaust port of the third shift valve  34 . The third shift valve  34  further includes the second switching circuit  44   f . Because of this structure having the second switching circuit  44   f , when the spool  34   a  is positioned as denoted with “x” in  FIG. 12 , the supply port of the LU control valve unit SLU fluidly communicates with an exhaust port (EX) of the third shift valve  34 . On the other hand, when the spool  34   a  is positioned as denoted with “∘” in  FIG. 12 , the supply port of the LU control valve unit SLU fluidly communicates with the pressure PL port. The third shift valve  34  still further includes the third switching circuit  34   g . Because of this structure having the third switching circuit  34   g , when the spool  34   a  is positioned as denoted with “x” in  FIG. 12 , a fluid communication is established among the drain port of the third control valve unit SL 3 , the N-R accumulator  27  and the second shuttle valve SB 2 . On the other hand, when the spool  34   a  is positioned as denoted with “∘” in  FIG. 12 , a fluid communication is established among the drain port of the third control valve unit SL 3 , the N-R accumulator  27  and an exhaust port (EX) of the third shift valve  34 . The third shift valve  34  still further includes the fourth switching circuit  34   h . Because of this structure having the fourth switching circuit  34   h , when the spool  34   a  is positioned as denoted with “x” in  FIG. 12 , a fluid communication is established among the drain port of the first control valve unit SL 1 , the N-D accumulator  26 , the first switching circuit  33   g  of the second shift valve  33  and the first switching circuit  32   f  of the first shift valve  32 . On the other hand, when the spool  34   a  is positioned as denoted with “∘” in  FIG. 12 , a fluid communication is established among the drain port of the first control valve unit SL 1 , the N-D accumulator  26  and an exhaust port (EX) of the third shift valve  34 . The third shift valve  34  still further includes the fifth switching circuit  34   i . Because of this structure having the fifth switching circuit  34   i , when the spool  34   a  is positioned as denoted with “∘” in  FIG. 12 , a fluid communication is established among the third switching circuit  33   i  of the second shift valve  33 , the supply port of the fourth control valve unit SL 4  and the pressure D port of the manual valve  21 . On the other hand, when the spool  34   a  is positioned as denoted with “x” in  FIG. 12 , a fluid communication is established among the third switching circuit  33   i  of the second shift valve  33 , the supply port of the fourth control valve unit SL 4  and an exhaust port (EX) of the third shift valve  34 . There is an orifice and a check valve mounted on an oil passage extending between the third switching circuit  34   g  of the third shift valve  34  and the drain port of the third control valve unit SL 3 . There is an orifice and a check valve mounted on an oil passage extending between the fourth switching circuit  34   h  of the third shift valve  34  and the drain port of the first control valve unit SL 1 . In the fifth embodiment, the same effects are yielded as the first, second, third and fourth embodiments. 
       Sixth Embodiment 
       [0087]    Described below is a hydraulic pressure control apparatus for an automatic transmission according to a sixth embodiment of the present invention, with reference to the attached drawings.  FIG. 14  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to the sixth embodiment of the present invention.  FIG. 15  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the sixth embodiment. 
         [0088]    In the fifth embodiment, the output pressure of the sixth control valve unit SL 5  is supplied to the sixth switching circuit ( 32   j  in  FIG. 12 ) of the first shift valve ( 32  in  FIG. 12 ). In the sixth embodiment, however, the output pressure of the sixth control valve unit SL 6  is supplied to the second frictional brake B 2  and the third hydraulic chamber  33   f  of the second shift valve  33 . With this hydraulic circuit, the fourth shuttle valve SB 4  is connected to the fourth switching circuit  23   j  of the first shift valve  32 , and the supply port of the sixth control valve unit SL 6  is connected to the fifth switching circuit  33   k  of the second shift valve  33 . 
         [0089]    In the sixth embodiment, the same effects are yielded as the first, second, third and fourth embodiments. 
       Seventh Embodiment 
       [0090]    Described below is a hydraulic pressure control apparatus for an automatic transmission according to a seventh embodiment of the present invention, with reference to the attached drawings.  FIG. 16  is a hydraulic circuit diagram partially schematically illustrating a structure of a hydraulic pressure control unit according to the seventh embodiment of the present invention.  FIG. 17  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the seventh embodiment. 
         [0091]    In the seventh embodiment, as illustrated in  FIG. 16 , the third shift valve  44  is additionally provided with a fifth switching circuit  44   i  for the purpose of enhancing a driving performance at a reverse shift stage. When the third shift valve  44 , i.e., the fifth switching circuit  44   i  is positioned as denoted with “x” in  FIG. 16 , the pressure R can be supplied to the drain port of the sixth control valve unit SL 6  via the sixth switching circuit  44   j.    
         [0092]    In the seventh embodiment, the same effect is yielded as the first, second, third and fourth embodiment. As being summarized in  FIG. 17 , with the on-off solenoid valve S 1  in the de-energized state, the on-off solenoid valve S 2  in the energized or de-energized state and the on-off solenoid valve S 3  in the de-energized state during the R range selected, the vehicle start at the reverse shift stage is enabled even when wire disconnection occurs for all of the control valve units. 
         [0093]    In any of the first to seventh embodiments, an oil passage connection and/or an increase or decrease in the number of switching circuits of each shift valve is provided, but there is no other additional component apart from a control valve unit. As a result, a hydraulic apparatus for an 8-speed automatic transmission is structured with a hydraulic apparatus for a 6-speed automatic transmission as a basic structure and with minor changes thereto. Accordingly, even for a farther increase in the number of shift stages to be achieved in an automatic transmission, such increase in the number of shift stages can be achieved by supplying, to the additional control valve unit, the pressure D for the case of the on-off solenoid valves S 1 , S 2  and S 3  all in the energized state. 
         [0094]    In any of the first to seventh embodiments, the line pressure is supplied to the fifth control valve unit SL 5  that controls the fourth frictional clutch C 4  only when all of the on-off solenoid valves are in the energized state. Therefore, a fixed shift stage mode for the 4th shift stage and a fixed shift stage mode for the 6th shift stage are not present. As described above, in each first to seventh embodiment, although eight fixed shift stage modes for all of the eight shift stages are not set. Meanwhile, as disclosed in JP2005-163916A, in the case where a fixed shift stage mode is selected during a steady running of a vehicle and a shift mode is selected during a shift operation, the shift valves are required to selectively change oil passages in response to the changes from the steady running to the shift operation and vice versa. Further, it is necessary to consider a time, where a supply of hydraulic pressure to linear solenoid valves, and/or a period of time, where hydraulic pressure supply is cut off. In such circumstances, because the frequency of shift operations is increased in response to the increase in the number of shift stages, a response may be deteriorated. Rather than that, it is preferable that a steady running of a vehicle is maintained under a shift mode so that there is no need to have all fixed shift stages. 
         [0095]    Provided that a possible shift stage during electric disconnection failure, is to be set the same as that disclosed in JP2005-163916A, the output pressure of the fifth linear solenoid valve SL 5  can be supplied to the third frictional clutch C 3  and the output pressure of the third linear solenoid valve SL 3  can be supplied to the fourth frictional clutch C 4 . On the other hand, if a possible shift stage achievable during electric disconnection failure according to the embodiments of the present invention is to be set different from that disclosed therein, it is achieved by slightly increasing the oil passage connections and the switching circuits. For example, a vehicle can run at any of the fixed shift stages regardless of the control valve unit. 
       EXAMPLE 1 
       [0096]    Described below is the basis of the hydraulic pressure control apparatus for an automatic transmission of the present invention with reference to the attached drawings. 
         [0097]      FIG. 18  is a hydraulic circuit diagram schematically illustrating a hydraulic pressure control unit according to an example 1.  FIG. 19  is a table for explaining a shift pattern at each driving range selected in accordance with a control state of the hydraulic pressure control unit according to the example 1. 
         [0098]    According to a hydraulic circuit of the example 1, the third control valve unit SL 3  for the third frictional clutch C 3  is controllable during the N range for reduction in the number of accumulator against a conventional work. In the example 1, the hydraulic pressure control apparatus is applicable for a 6-speed automatic transmission (AT) that can establish six forward and single reverse shift stages with five engaging elements. In this case, there is no need to change oil passages even in the situation where all of the control valve units are normally-low type valve units (NL). However, the first shift stage cannot be maintained in the event that all electric disconnections occur while the vehicle is driving at the first shift stage. According to the first embodiment of the present invention, the automatic transmission  1  can establish eight forward shift stages based upon the example 1. 
         [0099]      FIG. 20A  is a shift operation diagram for a 6-speed AT according to the example 1.  FIG. 20B  is a shift operation diagram for an 8-speed AT for an 8-speed AT according to the first embodiment.  FIG. 21A  is a shift operation diagram for a 6-speed AT according to an example 2. In the example 2, the 6-speed AT is achieved based upon Reference 1.  FIG. 21B  is a shift operation diagram for an 8-speed AT according to Reference 1. 
         [0100]    Basically, an 8-speed AT is structured by adding one more engaging element into a 6-speed AT. An AT for further higher shift stages than the 8th shift stage can be structured by adding more engaging elements to a 6-speed AT. That is, comparing with a 6-speed AT that is a basis, a shift stage at a time of higher shift stage or lower shift stage failure is not changed that much. 
         [0101]    According to the hydraulic pressure control apparatus for an automatic transmission of the present invention, it is preferable that the line pressure is supplied to at least one of the control valves only when a shift pattern is selected, in which shift pattern all of the on-off solenoid valves are in the energized states. 
         [0102]    It is preferable that each shift valve includes a switching circuit which supplies the line pressure via all of the shift valves to at least one of the control valves only when a shift pattern is selected, which shift pattern structures a shift mode having higher shift stages in response to the on-off solenoid valves in the energized or de-energized states. 
         [0103]    It is preferable that the automatic transmission includes at least three shift valves, at least three on-off solenoid valves, at least five control valves and at least six engaging elements. 
         [0104]    As described above, it is possible to supply a hydraulic pressure apparatus for seven or more shift stages with the components in the same quantity as an apparatus for six shift stages, an additional control valve, and minor changes in the structure of an oil passage for the hydraulic apparatus for six shift stages. That is, with adding a control valve, there is no need to change the basic structure of the hydraulic pressure apparatus, which enables to reduce manufacturing cost and development hours. Further, being different from conventional works, the type of linear solenoid valves for control valves, whether it is NL-type or NH-type, does not affect the structure of the hydraulic pressure apparatus. Still further, there is no possibility that interlock may occur during a fixed shift stage mode due to a primary failure of a failsafe valve, because no failsafe valve is mounted in the apparatus. 
         [0105]    The present invention is applicable to a seat for a vehicle in which a seatback is fixed to a seat cushion at a predetermined angle. The principles, of the preferred embodiments and mode of operation of the present invention have been described in the foregoing specification. However, the invention, which is intended to be protected, is not to be construed as limited to the particular embodiment disclosed. Further, the embodiment described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents that fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.