Not Just Another CVT LET'S PLAY BALL Not Just Another CVT by Lance Wiggins members.atra.com Apair of new transmissions were introduced in the 2014 Chevrolet Spark (C Body): The CVT-7 and 1ET35. We ll take a look at the details of each of them. The CVT-7 (RPO M4M) is manufactured by Jatco Corporation (known as a model APO by Jatco) and it s also used in some Nissan models (JF015E). Unlike most other CVTs on the market, the CVT-7 is a two-step unit, designed to provide improvements in fuel economy and performance when compared to a conventional CVT. The gear ratio of the CVT is expanded with an auxiliary gearbox, which is a planetary gearset attached to the output pulley. The two forward gear ratios are 1.821:1 and 1.000:1 and the reverse gear ratio is 1.714:1. The two-step gear ratio is controlled by the addition of the auxiliary portion of the transmission. This allows for using smaller pulleys, reducing the overall length by 10% and the weight by 13%. The new pulley size allows the pulleys and belt to be repositioned in the case, reducing friction loss by 30% because the oil isn t being agitated as much. A dedicated transmission controller sits under the driver s side of the dash, near the brake pedal. Like other TCMs, it must be programmed if replaced. The inputs to the controller are carried on the CAN data bus (engine RPM, torque, load, ABS, etc.) Sensors include: engine primary, secondary, and output speeds line pressure transmission oil temperature and an inhibitor switch. Outputs include pressure control and engine torque request via CAN. Fluid Level and Type The transmission has a stand pipe for checking fluid level; there s no dipstick even though it has a dipstick tube. The dipstick tube provides a fill point for the transmission. Check the fluid level at 122ºF (50ºC) with the engine running, in park, 4 GEARS January/February 2015
Not Just Another CVT Figure 1 on level ground. Remove the stand pipe plug and look for ATF to drip from the stand pipe: If nothing comes out, you ll need to add fluid. If fluid rushes out, the unit is overfilled: Allow the excess fluid to drain. When the fluid level is correct the fluid should drip from the stand pipe. The fluid is CVTF I Green Fluid, GM part number 19260800. Fluid capacity is 6.21 qts (5.88L). Line Pressure This unit doesn t have a pressure tap. The only way to check line pressure is with a scan tool. Normal line pressure: 1.2L engine 72.5 PSI at idle; 652-725 PSI at stall. 1.0L engine 72.5 PSI at idle; 620-693 PSI at stall. Pulleys Each pulley consists of one fixed sheave and one moveable sheave. The pressure applied to the primary and secondary pulley pistons determines the ratio and torque capacity by varying the size of the two pulleys. Pulley size and the ratio available from the auxiliary gear box planetary system determine the over-operational 7.3 ratio spread (figure 1). Figure 2 Clutches and Brakes One drive clutch and two brake clutches are used. The low brake and high clutch apply in D and M ranges and are controlled based on the gear ratio required. The reverse brake only applies in reverse. Oil Pump The CVT-7 uses an off-axis, chaindriven, vane-style pump. Auxiliary Gear Box The gear box consists of a planetary gearset, and the high, low, and reverse clutches/brakes. 6 GEARS January/February 2015
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Not Just Another CVT Reduction Gearset (Counter Gears) Like other transmissions, the reduction gearset transmits power from the transmission section to the final drive. The counter gear ratio varies depending on the engine. The 1.0L engine uses a 1.178:1 ratio while the 1.2L engine uses a 0.967:1 ratio. Both applications use a 3.882:1 final drive ratio. Valve Body, Solenoids, Sensors, and Valves The valves, solenoids, and sensors used by the CVT-7 include (figure 2 and 3): Control Valve: Controls oil pressure from the pump to feed the rest of the valve body and control systems Pressure Regulator: Controls line pressure Torque Converter Regulator: Controls the pressure within the torque converter Torque Converter Clutch Control Valve: Controls the pressure to the TCC solenoid Pilot Valve: Controls pressure feeding each solenoid High Clutch/Reverse Brake Switching Valve: Controls when pressure goes to the high clutch or reverse brake Manual Valve: Determines gear range based on shifter position Primary Pressure Control Valve: Controls pressure to the primary pulley to control primary pulley operation Primary Solenoid: Controls the primary pressure control valve (N/H solenoid) Low Brake Solenoid: Controls the operation of the Low Brake (N/L solenoid) High Clutch and Reverse Brake Solenoid: Controls the operation of the high clutch and reverse brake. (N/H solenoid) TCC Solenoid: Controls the TCC control valve (N/L solenoid) Line Pressure Solenoid: Controls the pressure regulator valve (N/H solenoid) Fluid Temp Sensor: A thermistor that creates a signal based on transmission fluid temperature Figure 3 Secondary Pressure Sensor: A variable pressure sensor that creates a signal based on the pressure applied to the secondary pulley piston High Clutch Oil Pressure Switch: Signals whether oil pressure is being fed to the high clutch ROM The CVT-7 uses a ROM (Read Only Memory) box mounted to the valve body area. It stores baseline calibration comparative data for the solenoids and can only be replaced with the valve body assembly. Figure 4 8 GEARS January/February 2015
Not Just Another CVT Adaptive Learning Reset Like other transmissions, the CVT-7 uses adaptive learning to improve transmission operation. The reset process synchronizes the transmission ROM to the TCM calibration. You ll need to reset the adaptive learning values during any of these conditions: TCM was replaced or reprogrammed Internal repairs that could affect transmission operation Transmission was replaced To reset the adapts, use a scan tool and select the Transmission Adaptive Pressure Reset function. This process will take about 10 seconds (figure 4). Another transmission available for the Chevrolet Spark (C Body) is known as the 1ET35 (RPO MME). It s an electric drive transmission. The 1ET35 is a fully automatic, front wheel drive, variable-speed, electronically-controlled transmission. It consists of one 85kW, 360-volt, 3-phase electric drive motor; one planetary/differential gearset; an internal Figure 5 mode switch (IMS); a temperature sensor; a high-voltage electric auxiliary fluid pump; and the housing (figure 5). The hydraulic system uses an electric auxiliary fluid pump motor assembly located inside the transmission for cooling and lubricating rotating components. This system consists of a gerotortype pump; an electric, 3 -phase, 360- volt, high voltage pump motor; a wiring harness; and a control module. The control module is located under the hood, inside the drive motor generator power inverter module. The transmission fluid pump operates under low pressure and will only run when the transmission is out of park or neutral and the module detects vehicle speed. The drive motor is a permanent magnet, 85 kw peak-power AC motor, and is controlled by the power inverter module. Drive motor speed is controlled and monitored by a resolver-type position sensor (like the 2ML70). The drive motor generator power inverter module monitors the angular position, speed, and direction of the drive motor based on the signals from the position sensor to the drive motor generator power inverter module. The drive motor position sensor, or resolver, contains a drive coil, two driven coils, and an irregularly shaped metallic rotor. The metallic rotor is mechanically attached to the shaft of the drive motor generator. When the vehicle is on, the drive motor generator power inverter module outputs a 5 VAC, 10 khz excitation signal to the drive coil. The drive coil excitation signal creates a magnetic field surrounding the two driven coils and the irregularly shaped rotor. The drive motor generator power inverter module then monitors the two driven coil circuits for a return signal. The position of the irregular shaped metallic rotor causes the magnetically-induced return signals of the driven coils to vary in size and shape. A comparison of the two driven coils signals allows the motor control module to determine the exact angle, speed, and direction of the drive motor. Fluid The 1ET35 uses Dexron VI HP, GM part number 19300536. The fluid capacity is 4.4 qts (4.2L). Lately it seems as though there s a new transmission being introduced every day. But a careful examination of the details shows that these new transmission aren t all that different than those you ve already seen. Once you identify the details, the rest isn t all that difficult to understand or repair. Portions of materials contained herein have been reprinted with permission of General Motors Corporation, Service Technology Group Agreement # 061O228. 10 GEARS January/February 2015