Automatic Transmission (Cvt): Overview Nissan Quest IV

COMPONENT DESCRIPTION

Scheme 1

TRANSAXLE: Component Description

Scheme 2

CVT Fluid Cooler

Scheme 3

1. The CVT fluid cooler (1) is installed in the radiator side tank (left side).
2. When engine is started while engine and CVT are cold, engine coolant temperature rises more quickly than CVT fluid temperature. CVT oil warmer is provided with two circuits for CVT and engine coolant respectively so that warmed engine coolant warms CVT quickly. This helps shorten CVT warming up time, improving fuel economy.
3. A cooling effect is obtained when A/T fluid temperature is high.

CVT Oil Warmer

Scheme 4

1. The CVT oil warmer (1) is installed on the front part of transaxle assembly.
2. When engine is started while engine and CVT are cold, engine coolant temperature rises more quickly than CVT fluid temperature. CVT oil warmer is provided with two circuits for CVT and engine coolant respectively so that warmed engine coolant warms CVT quickly. This helps shorten CVT warming up time, improving fuel economy.
3. A cooling effect is obtained when A/T fluid temperature is high.

Heater Thermostat

Scheme 5

1. The heater thermostat (1) is installed on the front part of transaxle assembly.
2. The heater thermostat open and close with set temperature.

Scheme 6

Scheme 7

DESCRIPTION

1. The TCM senses vehicle operating conditions through various sensors or signals. It always controls the optimum shift position and reduces shifting and lock-up shocks.
2. Receive input signals transmitted from various switches and sensors.
3. Determine required line pressure, shifting point, lock-up operation, etc.
4. If malfunction is detected, the system enters fail-safe mode. Refer to " «FAIL-SAFE»(ref-672632-S39559846692014112400000) ". Sensor (or signal) ==> TCM ==> Actuator Transmission range switch CVT fluid temperature sensor Secondary pressure sensor Primary pressure sensor Secondary speed sensor Primary speed sensor Engine speed signal Accelerator pedal position signal Closed throttle position signal Stop lamp switch signal Vehicle speed signal Overdrive control switch Shift control ( «SHIFT CONTROL SYSTEM»(ref-672632-S07792242902014112400000) ) Oil pressure control ( «OIL PRESSURE CONTROL SYSTEM»(ref-672632-S27019627342014112400000) ) Lock-up and select control ( «LOCK-UP AND SELECT CONTROL SYSTEM»(ref-672632-S06762794002014112400000) ) Fail-safe ( «FAIL-SAFE»(ref-672632-S39559846692014112400000) ) Self-diagnosis ( «DIAGNOSIS DESCRIPTION»(ref-672632-S19743844512014112400000) ) CONSULT communication line ( «DIAGNOSIS DESCRIPTION»(ref-672632-S19743844512014112400000) ) CAN communication line ( «U1000 CAN COMM CIRCUIT»(ref-672632-S11516281942014112400000) ) Line pressure solenoid valve Secondary pressure solenoid valve Torque converter clutch solenoid valve Lock-up select solenoid valve Step motor Shift position indicator O/D OFF indicator lamp

Scheme 8

TCM has a fail-safe mode. The mode functions so that operation can be continued even if the signal circuit of the main electronically controlled input/output parts is damaged.

Scheme 9

OIL PRESSURE CONTROL SYSTEM: System Description

The hydraulic control mechanism consists of the oil pump directly driven by the engine, the hydraulic control valve that controls line pressure and transmission, and the input signal line.

Scheme 10

1. When an input torque signal equivalent to the engine driving force is transmitted from the ECM to the TCM, the TCM controls the line pressure solenoid valve and secondary pressure solenoid valve.
2. Highly accurate line pressure control and secondary pressure control reduces friction for improvement of fuel economy.

Normal Oil Pressure Control

Appropriate line pressure and secondary pressure suitable for driving condition are determined based on the accelerator pedal position, engine speed, primary pulley (input) speed, secondary pulley (output) speed, input torque, stop lamp switch signal, transmission range switch signal, lock-up signal, power voltage, target shift ratio, oil temperature and oil pressure.

Secondary Pressure Feedback Control

In normal oil pressure control and oil pressure control in shifting, highly accurate secondary pressure is determined by detecting the secondary pressure using an oil pressure sensor and by feedback control.

Scheme 11

Scheme 12

1. The torque converter clutch piston in the torque converter is engaged to eliminate torque converter slip to increase power transmission efficiency.
2. The torque converter clutch control valve operation is controlled by the torque converter clutch solenoid valve, which is controlled by a signal from TCM. The torque converter clutch control valve engages or releases the torque converter clutch piston.
3. When shifting between "N" ("P") ==> "D" ("R"), torque converter clutch solenoid valve controls engagement power of forward clutch and reverse brake.
4. The lock-up applied gear range was expanded by locking up the torque converter at a lower vehicle speed than conventional A/T models.
5. If the CVT fluid temperature is low or the vehicle is in fail-safe mode due to malfunction, lock-up control is prohibited.

SHIFT CONTROL SYSTEM: System Description

In order to select the gear ratio that can obtain the driving force in accordance with driver's intention and the vehicle condition, TCM monitors the driving conditions, such as the vehicle speed and the throttle position, selects the optimum gear ratio, and determines the gear change steps to the gear ratio. Then TCM sends the command to the step motor, controls the inflow/outflow of line pressure from the primary pulley to determine the position of the moving-pulley and controls the gear ratio.

SHIFT LOCK SYSTEM: System Description

The selector lever cannot be shifted from the "P" position unless the brake pedal is depressed while the ignition switch is set to ON. The shift lock is unlocked by turning the shift lock solenoid ON when the ignition switch is set to ON, the park position switch is turned ON (selector lever is in "P" position), and the stop lamp switch is turned ON (brake pedal is depressed) as shown in the operation chart in the figure. Therefore, the shift lock solenoid receives no ON signal and the shift lock remains locked if all of the above conditions are not fulfilled. (However, selector operation is allowed if the shift lock release button is pressed.)

Scheme 13

SHIFT LOCK OPERATION AT "P" POSITION

When Brake Pedal Is Not Depressed (No Selector Operation Allowed)

The shift lock solenoid (1) is turned OFF (not energized) and the solenoid rod (A) is extended with the spring when the brake pedal is not depressed (no selector operation allowed) with the ignition switch ON.

The connecting lock lever (B) is located at the position shown in the figure when the solenoid rod is extended. It prevents the movement of the detent rod (C). For these reasons, the selector lever cannot be shifted from the "P" position.

Scheme 14

When Brake Pedal Is Depressed (Shift Operation Allowed)

The shift lock solenoid (1) is turned ON (energized) when the brake pedal is depressed with the ignition switch ON. The solenoid rod (A) is compressed by the electromagnetic force. The connecting lock lever (B) rotates when the solenoid is activated. Therefore, the detent rod (C) can be moved. For these reasons, the selector lever can be shifted to other positions.

Scheme 15

Diagnosis Description

This system is an on board diagnostic system that records exhaust emission-related diagnostic information and detects a sensors/actuator-related malfunction. A malfunction is indicated by the malfunction indicator lamp (MIL) and stored in ECU memory as a DTC. The diagnostic information can be obtained with the diagnostic tool (GST: Generic Scan Tool).

DIAGNOSIS DESCRIPTION: System Description

This is an on-board trouble diagnosis system which automatically detects malfunction. Detected malfunction is memorized in TCM as DTC. Diagnosis information can be confirmed using CONSULT.

DIAGNOSIS DESCRIPTION: DTC

1. DTC (P0703, P0710, P0840, etc.) is specified by SAE J2012/ISO 15031-6.
2. TCM memorizes DTC when malfunction is detected. It can memorize plural DTCs.

DIAGNOSIS DESCRIPTION: Malfunction Indicator Lamp (MIL)

1. TCM not only detects DTC, but also sends the CVT self-diagnosis signal to ECM through CAN communication. ECM sends the malfunctioning indicator lamp signal to the combination meter through CAN communication according to the signal, and illuminates MIL.
2. For malfunction indicator lamp (MIL) description, refer to " «DIAGNOSIS DESCRIPTION: MALFUNCTION INDICATOR LAMP (MIL)»(ref-672625-S26205845582014112400000) ".

TCM has a fail-safe mode. The mode functions so that operation can be continued even if the signal circuit of the main electronically controlled input/output parts is damaged.

There are many operating conditions that may cause a malfunction of the transmission parts. By understanding those conditions properly, a quick and exact diagnosis can be achieved.

In general, perception of a problem varies depending on individuals. Ask the customer about his/her concerns carefully. It is important to understand the phenomenon or status. To systemize all the information for the diagnosis, prepare the question sheet referring to the question points.

In some cases, multiple conditions that appear simultaneously may cause a DTC to be detected.

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When replacing the TCM, perform the following work.

When replacing the transaxle assembly, perform the following work.

1. The purpose of the test is to determine the overall performance of CVT and analyze causes of problems.
2. The road test consists of the following three parts: " «CHECK BEFORE ENGINE IS STARTED»(ref-672632-S01300150792014112400000) " " «CHECK AT IDLE»(ref-672632-S18586402142014112400000) " " «CRUISE TEST»(ref-672632-S16999367572014112400000) "
3. Before the road test, familiarize yourself with all test procedures and items to check.
4. Perform tests for all the check items until a malfunction phenomenon is detected. Perform diagnosis for NG items after the completion of road tests.

CAN (Controller Area Network) is a serial communication line for real time application. It is an on-vehicle multiplex communication line with high data communication speed and excellent malfunction detection ability. Many electronic control units are equipped onto a vehicle, and each control unit shares information and links with other control units during operation (not independent). In CAN communication, control units are connected with 2 communication lines (CAN-H and CAN-L) allowing a high rate of information transmission with less wiring. Each control unit transmits/receives data but selectively reads required data only.

The engine speed signal is transmitted from ECM to TCM via CAN communication line.

This malfunction is detected when the torque converter clutch does not lock-up as instructed by the TCM. This is not only caused by electrical malfunctions (circuits open or shorted), but also by mechanical malfunctions such as control valve sticking, improper solenoid valve operation, etc.

1. When line pressure solenoid valve is under electrically normal condition, if unusual gear change ratio at LOW side is detected due to low line pressure, it is judged as malfunction.
2. This DTC is not caused by electrical malfunction (circuit is open or shorted), but caused by mechanical malfunction (control valve clogging, solenoid valve sticking, etc.).

1. When secondary pressure solenoid valve is under electrically normal condition, the DTC is detected if secondary pressure is low.
2. This DTC is not caused by electrical malfunction (circuit is open or shorted), but caused by mechanical malfunction (control valve clogging, solenoid valve sticking, etc.).

Detects oil sensor function malfunction based on the mutual relation between primary pressure sensor and secondary pressure sensor.

Secondary pressure solenoid valve controls input and output of secondary pressure to secondary pulley according to driving condition, following the command by TCM.

Detects malfunction when power source (backup) is not supplied to TCM and learning function is stopped.

When TCM does not store calibration data (individual characteristic value) of each solenoid valve that is stored in the ROM assembly (in the control valve), a malfunction is detected.

The vehicle speed signal is transmitted from ABS actuator and electric unit (control unit) to TCM via CAN communication line.

Judges it as malfunction when it detects noise (pulse) generated by irregular contact of harness etc. of primary speed sensor and secondary speed sensor.

The electric throttle control actuator consists of throttle control motor, accelerator pedal position sensor, throttle position sensor, etc. The actuator sends a signal to the ECM, and ECM sends the signal to TCM via CAN communication.

1. The step motor changes the step by turning 4 coils ON/OFF according to the signal from TCM. As a result, the flow of line pressure to primary pulley is changed and pulley ratio is controlled.
2. This diagnosis item is detected when the electrical system is OK, but the mechanical system is NG.
3. This diagnosis item is detected when the state of the changing of the speed mechanism in the unit does not operate normally.