K312 CVT SYSTEM


  1. FUNCTION OF MAIN COMPONENTS


    1. The main components of the K312 CVT system are as follows:

      Component Function
      Continuously Variable Transaxle Assembly Shift Solenoid Valve SC Used to switch control of the shift solenoid valve SLU between forward and reverse clutch control and lock-up clutch control.
      Shift Solenoid Valve SL
      Shift Solenoid Valve SLU Performs forward and reverse clutch control or lock-up clutch control depending on the state of the shift solenoid valves SC and SL.
      Shift Solenoid Valve SLP Controls the oil pressure of the primary pulley.
      Shift Solenoid Valve SLS Controls the oil pressure of the secondary pulley.
      Transmission Revolution Sensor (NIN) Detects the primary pulley speed.
      Transmission Revolution Sensor (NOUT) Detects the secondary pulley speed.
      Transmission Revolution Sensor (NT) Detects the input turbine speed.
      CVT Fluid Temperature Sensor Detects the CVT fluid temperature.
      Oil Pressure Sensor Detects the oil pressure for belt clamping force.
      Transmission Oil Cooler Helps warm up the CVT fluid immediately after the engine is started and then performs as a oil cooler during normal driving.
      E. F. I. Engine Coolant Temperature Sensor Detects the engine coolant temperature.
      Accelerator Pedal Sensor Assembly Detects the accelerator pedal opening angle.
      Throttle Position Sensor Detects the opening angle of the throttle valve.
      Stop Light Switch Assembly Detects the brake pedal depressing signal.
      Park/Neutral Position Switch Assembly Detects the shift lever position.
      Transmission Control Switch

      • Detects that the shift lever is in M.

      • Detects the driver's shift-up and shift-down operations when the shift lever is in M.
      Shift Paddle Switch (Transmission Shift Switch Assembly)* Detects the driver's upshift or downshift request.
      Pattern Select Switch Assembly Detects that the driving mode is in the sport mode.
      Combination Meter Assembly Shift Position Indicator Indicates the shift lever position and shift range.
      Sport Mode Indicator Illuminates when the pattern select switch assembly is pressed and informs the driver that sport mode is active.
      MIL Illuminates or blinks to alert the driver that the ECM has detected a malfunction.
      Buzzer Sounds when shift-down operation is rejected in M mode.
      ECM

      • Controls the electronic control of the CVT system.

      • When the ECM detects a malfunction, the ECM makes a diagnosis and memorizes the failed section.
      Deceleration Sensor Detects the angle of inclination of the vehicle.
      Brake Actuator Assembly Skid Control ECU

      • Transmits the vehicle speed and the longitudinal acceleration signal to the ECM.

      • Transmits the operating states of the ABS to the ECM.
      Air Conditioning Amplifier Assembly Transmits the operating state of the air conditioning system to the ECM.

      • *: Models with shift paddle switch (transmission shift switch assembly).

    2. The main components of the shift lock system are as follows:

      Component Function
      Shift Lock Control Unit Shift Lock Solenoid Locks the shift lever in P.
      P Detection Switch Detects if the shift lever is in P.
      Stop Light Switch Assembly Detects if the brake pedal is depressed.
      Shift Lock Control ECU Assembly Controls the shift lock solenoid based on signals from each switch.

  2. SYSTEM CONTROL


    1. Control List


      1. The electronic control system of the K312 CVT consists of the controls listed below.

        Control Outline
        Engine - CVT Integrated Control Effects coordinate control of the CVT system and engine control system to ensure both smooth and powerful driving that excels in shift response and fuel economy.
        Automatic Shift Control Optimally controls the pulley ratio and shifting speed to suit the driver's intentions and driving conditions based on signals from various sensors and switches.
        Acceleration Improvement Control
        7-speed Sport Sequential Shiftmatic
        Neutral Control When the vehicle is stopped, the driving force to the transaxle is shut off to improve fuel economy.
        Shift Control in Uphill/Downhill Traveling Controls to restrict the upshifts or to provide appropriate engine braking by using the ECM to determine whether the vehicle is traveling uphill or downhill.
        Lock-up Control The ECM sends a current to shift solenoid valve SC, SL, and SLU based on the throttle position sensor signal and vehicle speed signal, and engages or disengages the lock-up clutch.
        Flex Lock-up Control

    2. Engine - CVT Integrated Control


      1. To effect fine-tuned control in accordance with driving conditions, various signals are exchanged between the engine control system and the CVT system. As a result, both smooth and powerful driving that excels in shift response and fuel economy has been achieved.

        A005G33E02

    3. Speed Ratio Control (Shift Control)


      1. The ECM calculates the target primary pulley revolution speed in accordance with the accelerator pedal position signal, vehicle speed signal, and stop light switch signal, in order to attain an optimal pulley ratio and shifting speed. To allow the actual primary pulley speed (acquired from the primary speed sensor) to match the target primary pulley speed, the ECM actuates shift solenoid valves SLP and SLS in order to control the pressure of primary pulley and secondary pulley. As a result, optimal pulley ratio and shifting speed have been achieved.

        A005FURE02

      2. When the shift lever is in D, the system effects engine integrated control to optimize fuel economy characteristics and driving performance.

        A005FUOE05

      3. The sport mode limits the shift range for the acceleration side and maintains the primary pulley speed at high speeds. This produces a moderate engine braking force and provides an excellent shift response.

        A005G3JE09

      4. When the shift lever is in M, the shift characteristic is as shown below. The system will upshift automatically when the vehicle reaches the set speed during acceleration.

        A005FXOE15

    4. Acceleration Improvement Control


      1. The driver's acceleration demand is judged from the change of vehicle speed and change of accelerator pedal input.

      2. When starting off or accelerating, the engine speed and the vehicle speed are controlled to produce a linear feeling, improving the acceleration feeling. In addition, during acceleration, upshifts are performed. These upshifts prevent a stagnant feeling during acceleration as well as enabling the linear acceleration feeling.

        A005FSBE01

    5. Shift Control in Uphill/Downhill Traveling


      1. The ECM determines that the vehicle is driving uphill or downhill based on the accelerator pedal position sensor signal and the vehicle speed signal. During uphill driving, it limits upshifting to achieve smooth driving. During downhill driving, it downshifts upon detecting brake pedal operation, in order to provide moderate engine braking.

        A005FYZE04

      2. The actual acceleration calculated from the vehicle speed signal is compared with the reference acceleration (based on level road travel) stored in the ECM to determine uphill or downhill travel.

        A005FX2E03
        Text in Illustration
        *a Uphill *b Downhill
        *c Smaller *d Greater
        A005G4O Reference acceleration A005G6H Actual acceleration

    6. Lock-up Control


      1. The lock-up operation range has been expanded from that of the previous continuously variable transaxle, thus enabling control to start from low speeds.

      2. The lock-up operation range during deceleration has been expanded to the low-speed range. This expands the fuel cut range and achieves excellent fuel economy.

        A005G2DE05
        *1 Lock-up Off
        *2 Throttle Opening Angle
        *3 Lock-up On
        *4 Vehicle Speed

    7. Flex lock-up Control


      1. In order to improve the transmission efficiency and also the fuel economy, the linear solenoid (SLU) for lock-up engagement pressure control is employed to deliver flex lock-up control that can provide more precise control than that of the conventional lock-up clutch mechanism.

      2. The flex lock-up control consists of flex start control and flex lock-up control at deceleration.

      3. The flex start control aggressively operates the lock-up clutch during start-off to increase the transmission efficiency, as a result, the engine can run in its most efficient operating range.

        A005FQXE07

      4. Flex lock-up control during deceleration is used to expand the fuel-cut range. It operates the lock-up clutch over the low vehicle speed range when the vehicle decelerates so that minimal speed difference between the engine speed and turbine speed can be maintained.

    8. Neutral Control


      1. While the vehicle is stopped with the shift lever in D, by disconnecting the engine and CVT (releasing the forward clutch halfway), engine load is reduced. This improves fuel economy. However, if a certain gradient or higher is detected by forward and backward acceleration signals , the neutral control will not be implemented.

        A005G95E07

    9. Fail-safe


      1. This fail-safe function minimizes the loss of operability when an abnormality occurs in a sensor or shift solenoid valve. For details, refer to the Repair Manual.

    10. Diagnosis


      1. When the ECM detects a malfunction, the ECM records the malfunction and memorizes the information related to the fault. Furthermore, the ECM illuminates or blinks the Malfunction Indicator Lamp (MIL) in the combination meter assembly to inform the driver.

      2. The ECM will also store the Diagnostic Trouble Codes (DTCs) of the malfunctions. The DTCs stored in the ECM are output to the Global TechStream (GTS) via the ECM and the DLC3. For details, refer to the Repair Manual.

        Tech Tips

        To clear a DTC that is stored in the ECM, use the Global TechStream (GTS) or disconnect the cable from the battery terminal for 1 minute or longer.

  3. FUNCTION


    1. 7-speed Sport Sequential Shiftmatic


      1. The driver can select the desired shift range by moving the shift lever to "+" (forwards) or to "-" (backwards) while shift lever is in M (M mode). Also, the shift paddle switch (transmission shift switch assembly) is used*, which enable changing the shift range while the driver is holding the steering wheel. Thus, the driver is able to shift gears with a manual-like feel.

        *: Models with shift paddle switch (transmission shift switch assembly)

      2. When the shift lever is in D (D mode), the driver can momentarily select a desired shift range (M mode) by operating the shift paddle switch (transmission shift switch assembly). *

        Automatic shifting (D mode) will be reinstated under the following conditions:


        • The driver continues to push the shift paddle switch (transmission shift switch assembly) in the "+" direction longer than a predetermined length of time.

        • The driver depresses the accelerator pedal longer than a predetermined length of time while the transmission remains in the same shift range.

        • The vehicle has stopped.

        *: Models with shift paddle switch (transmission shift switch assembly)

        A005FVJE03
        *a 5th in M Mode
        *b 5th in D Mode
        *c M Mode

      3. In M mode, the transmission automatically upshifts or downshifts under the following conditions:

        Condition System Control
        Engine is under-revving. 1 step downshift
        Engine is over-revving. 1 step upshift

      4. The ECM will restrict the changing of the shift range if it detects a malfunction in the CVT system.

      5. If the vehicle speed and engine speed exceeds or goes below a preset level in response to the driver's downshift operation request, changing the shift range will be prohibited. In this case, the buzzer in the combination meter will sound to alert the driver.

    2. Shift Lock System


      1. A shift lock system consisting of a key interlock device* and a shift lock mechanism is used.


        • *: Models without entry and start system

      2. On the models without the entry and start system, the key interlock device prevents the key from being pulled out after the ignition switch is turned off, unless the shift lever is moved to P. Thus, the driver is urged to park the vehicle with the shift lever in P.

      3. The shift lock mechanism prevents the shift lever from being moved to a position other than P, unless the ignition switch is turned to ON, and brake pedal is depressed. It prevents the vehicle from starting off suddenly.

      4. A shift lock release button, vehicle manually overrides the shift lock mechanism, is used.

        A005FPME07

  4. CONSTRUCTION


    1. Torque Converter Assembly


      1. A compact, lightweight and high-capacity torque converter is used.

      2. A damper structure, which can perform lock-up operation starting in the low-speed range, is used. This absorbs engine torque fluctuations and provides excellent ride comfort.

        A005G4EE02
        Text in Illustration
        *1 Pump Impeller *2 Turbine Runner
        *3 Lock-up Clutch *4 Stator
        *5 Damper *6 1-way Clutch

    2. Oil Pump Assembly


      1. A trochoid gear type oil pump is used.

      2. The oil pump assembly has 1 inlet port and 2 outlet ports.

        A005G36E03
        Text in Illustration
        *a Conventional Models *b K312
        *c Outlet Port *d Outlet Port 1
        *e Outlet Port 2 *f Inlet Port

      3. When oil pressure exceeds a preset value, which is determined in accordance with the engine speed, the oil pump assembly discharges oil through 2 outlet ports, reducing the driving torque.

    3. Forward/Reverse Switching Unit


      1. The forward/reverse switching unit consists of a planetary gear, a forward clutch, and a reverse brake.

      2. The forward clutch, which acts during a forward movement, connects the input shaft with the planetary carrier.

      3. The reverse brake, which acts during reverse movement, keeps the ring gear stationary.

        A005G30E02
        Text in Illustration
        *1 Reverse Brake *2 Forward Clutch
        *3 Ring Gear *4 No. 1 Pinion Gear
        *5 Sun Gear *6 No. 2 Pinion Gear
        *7 Planetary Carrier - -
        *a Forward/Reverse Switching Unit - -

    4. Pulley and Steel Belt Unit


      1. The widths of the grooves of the pulleys are changed through hydraulic control.

      2. During acceleration, the action of shift solenoid valve SLP increases the oil pressure of the primary pulley, thus narrowing the width of the pulley groove.

      3. During deceleration, the action of shift solenoid valve SLP decreases the oil pressure of the primary pulley, thus widening the width of the pulley groove.

      4. The secondary pulley is hydraulically controlled by the shift solenoid valve SLS. It controls the belt clamping pressure to ensure the proper power transmission efficiency.

        A005FYIE02
        Text in Illustration
        *1 Secondary Pulley *2 Steel Belt
        *3 Primary Pulley - -
        *a Pulley Ratio (Low) *b Pulley Ratio (High)
        *c Groove Width (Large) *d Groove Width (Small)

      5. The primary pulley uses a single piston construction.

        A005G8AE02
        Text in Illustration
        *a Pulley Ratio (Low) *b Pulley Ratio (High)
        *c Chamber - -

      6. The steel belt consists of elements and 2 rows of steel rings. In contrast to chains and V-belts, which transmit power through the use of tensile force, the steel belt uses the compressive action (pushing force) of the elements to transmit power.

        A005FYJE05
        Text in Illustration
        *1 Steel Ring *2 Element

    5. Reduction Gear and Differential


      1. The reduction gear reduces the power output from the secondary pulley and transmits it to the differential.

      2. A 2 pinion type differential is used.

        A005FTGE02
        Text in Illustration
        *1 Reduction Drive Gear *2 Reduction Driven Gear
        *3 Front Differential - -

    6. Transmission Valve Body Assembly


      1. The transmission valve body assembly consists of the upper and lower valve bodies and 5 shift solenoid valves.

        A005G39E02
        Text in Illustration
        *1 Upper Valve Body *2 Lower Valve Body
        *3 Shift Solenoid Valve SLP *4 Shift Solenoid Valve SC
        *5 Shift Solenoid Valve SLS *6 Shift Solenoid Valve SLU
        *7 Shift Solenoid Valve SL - -
        A005FW8E02
        Text in Illustration
        *1 Primary Pulley *2 Secondary Pulley
        *3 Lock-up Clutch *4 Brake
        *5 Clutch *6 Valve Body
        *7 Manual Valve *8 Speed Ratio Control
        *9 Belt Clamping Pressure Control *10 ON-OFF and Back Pressure Control
        *11 Clutch Pressure Control *12 Shift Solenoid Valve SLP
        *13 Shift Solenoid Valve SLS *14 Shift Solenoid Valve SLU
        *15 Shift Solenoid Valve SL *16 Shift Solenoid Valve SC
        *17 ECM - -

      2. To ensure the proper control of the belt clamping pressure necessary for transmitting torque, the system controls the hydraulic pressure applied to the secondary pulley. The transmission valve body assembly is provided with a dedicated hydraulic pressure circuit for belt clamping pressure control. This circuit optimally controls the hydraulic pressure applied to the secondary pulley, thus achieving superior torque transmission performance.

        A005G9JE02
        Text in Illustration
        *1 Oil Pump Assembly *2 Primary Regulator Valve
        *3 Shift Solenoid Valve SLS *4 Shift Solenoid Valve SLP
        *5 No. 1 Line Pressure Modulator Valve *6 No. 2 Line Pressure Modulator Valve
        *7 Primary Pulley *8 Secondary Pulley

      3. Pulley ratio control is effected by controlling the hydraulic pressure applied to the primary pulley in order to provide fine-tuned control and a high level of reliability.

        A005G71E02
        Text in Illustration
        *1 Oil Pump Assembly *2 Primary Regulator Valve
        *3 Shift Solenoid Valve SLS *4 Shift Solenoid Valve SLP
        *5 No. 1 Line Pressure Modulator Valve *6 No. 2 Line Pressure Modulator Valve
        *7 Primary Pulley *8 Secondary Pulley

    7. Shift Solenoid Valves SC and SL


      1. The functions of each solenoid valve are outlined in the table below.

        Shift Solenoid Valve Type Function
        SC 2-way Used to switch control of the shift solenoid valve SLU between forward and reverse clutch control and lock-up clutch control.
        SL 2-way

    8. Shift Solenoid Valves SLS, SLP and SLU


      1. The functions of each solenoid valve are outlined in the table below.

        Shift Solenoid Valve Type Function
        SLS Linear Controls the oil pressure of the secondary pulley.
        SLP Linear Controls the oil pressure of the primary pulley.
        SLU Linear Performs forward and reverse clutch control or lock-up clutch control depending on the state of the shift solenoid valves SC and SL.

    9. Parking Lock Mechanism


      1. A parking lock mechanism is used on the secondary pulley. The engagement of the parking lock pawl with the parking lock gear integrated with the secondary pulley locks the movement of the vehicle.

        A005FN2E02
        Text in Illustration
        *1 Parking Lock Pawl *2 Parking Lock Gear

    10. Transmission Revolution Sensors and Oil Pressure Sensor


      1. The transmission revolution sensor (NIN) detects the input shaft speed and assists in shift control.

      2. The transmission revolution sensor (NOUT) detects the output shaft speed and assists in shift control.

      3. The transmission revolution sensor (NT) detects the forward clutch turbine speed and assists in lock-up clutch pressure control and forward clutch pressure control.

      4. The oil pressure sensor detects the hydraulic pressure applied to the secondary pulley and assists in belt clamping pressure control, which optimally controls the clamping pressure of the steel belt necessary for transmitting torque.

        A005FZCE02
        Text in Illustration
        *1 Transmission Revolution Sensor (NIN) *2 Transmission Revolution Sensor (NOUT)
        *3 Oil Pressure Sensor *4 Transmission Revolution Sensor (NT)

    11. CVT Fluid Temperature Sensor


      1. The CVT fluid temperature sensor detects the fluid temperature, effects shift control in accordance with the fluid temperature, and assists in lock-up clutch pressure control, forward clutch pressure control, and belt clamping pressure control.

        A005FZQE02
        Text in Illustration
        *1 CVT Fluid Temperature Sensor *2 Transmission Valve Body Assembly

    12. Park/Neutral Position Switch Assembly


      1. The park/neutral position switch assembly sends the P, R, N, D and M position signals to the ECM.

      2. The ECM controls the CVT system in accordance with the shift lever position signals.

      3. The ECM transmits signals to the combination meter assembly for the shift position indicator (P, R, N, D and M) in response to the signals received from the switches.

        A005FV5E02

    13. Transmission Oil Cooler


      1. The transmission oil cooler uses engine coolant to warm up the CVT fluid quickly. Consequently, the friction losses of the CVT are quickly reduced, thus improving fuel economy.

      2. After warming up the CVT fluid, the engine coolant flows into the transmission oil cooler to cool down the CVT fluid.

        A005G8JE02
        Text in Illustration
        *1 Transmission Oil Cooler - -
        *a Engine Coolant Inlet *b Engine Coolant Outlet
        *c CVT Fluid Outlet *d CVT Fluid Inlet
        A005G4O CVT Fluid Flow A005G6H Engine Coolant Flow

    14. Shift Control Mechanism


      1. A gate type shift lever that uses a transmission control cable is used.

      2. The shift control mechanism consists of a shift lock control unit assembly and a transmission control cable assembly.

        A005G5DE05
        Text in Illustration
        *1 Transmission Control Cable Assembly *2 Shift Lock Control Unit Assembly
        *a Shift Pattern - -

  5. OPERATION


    1. Forward/Reverse Switching Unit


      1. The forward clutch is connected when advancing, and engine torque is input from the input shaft to the planetary carrier and is output to the primary pulley.

        A005G1DE03
        Text in Illustration
        *1 Reverse Brake *2 Ring Gear
        *3 No. 2 Pinion Gear *4 Forward Clutch
        *5 No. 1 Pinion Gear *6 Sun Gear
        *a Input *b Output

      2. Engine torque is input to the sun gear when reversing. The ring gear is fixed by the reverse brake to transmit engine torque to the stepless shift transmission mechanism with inverse rotation.

        A005FPIE02
        Text in Illustration
        *1 Reverse Brake *2 Ring Gear
        *3 No. 2 Pinion Gear *4 Forward Clutch
        *5 No. 1 Pinion Gear *6 Sun Gear
        *a Input *b Output

    2. CVT Power Flow


      1. The changing of the pulley ratio is accomplished in a continuously variable manner by varying the widths of the grooves of the primary and secondary pulleys.

        A005FNEE08
        Text in Illustration
        *1 Primary Pulley *2 Secondary Pulley
        *3 Reverse Brake *4 Forward Clutch
        *5 Input Shaft *6 Reduction Drive Gear
        *7 Reduction Driven Gear *8 Differential Ring Gear

      2. Shift Lever in D (Pulley Ratio Low)

        A005GA4E04
        Text in Illustration
        *1 Primary Pulley *2 Secondary Pulley
        *3 Input Shaft - -
        *a Groove Width (Large) *b Groove Width (Small)
        *c Reverse Brake (Off) *d Forward Clutch (On)

      3. Shift Lever in D (Pulley Ratio High)

        A005G6CE03
        Text in Illustration
        *1 Primary Pulley *2 Secondary Pulley
        *3 Input Shaft - -
        *a Groove Width (Small) *b Groove Width (Large)
        *c Reverse Brake (Off) *d Forward Clutch (On)

      4. Shift Lever in N

        A005G8IE03
        Text in Illustration
        *1 Primary Pulley *2 Secondary Pulley
        *3 Input Shaft - -
        *a Groove Width (Large) *b Groove Width (Small)
        *c Reverse Brake (Off) *d Forward Clutch (Off)

      5. Shift Lever in R

        A005FRAE04
        Text in Illustration
        *1 Primary Pulley *2 Secondary Pulley
        *3 Input Shaft - -
        *a Groove Width (Large) *b Groove Width (Small)
        *c Reverse Brake (On) *d Forward Clutch (Off)