Control Module: Description and Operation

ECVT Control Unit Wiring Schematic:

ECVT Clutch Current Control Block Diagram:

ECVT CONTROL UNIT
The ECVT control unit is an 8-bit 16K byte microcomputer.

ECVT Output Modes:

OUTPUT MODES
The five output modes shown in the table are provided for smooth electromagnetic power clutch operation.

Starting mode
This mode controls the clutch torque at starting by increasing the clutch current in proportion to the engine speed and its rate of increase when the accelerator pedal is pressed.

When the vehicle is started by pressing the accelerator pedal lightly at a high idling speed, such as when the choke is used, the engine speed rises at a comparatively low rate and, therefore, the increase in clutch torque is also small and the vehicle starts slowly and smoothly.

When the stall speed is in the 1,900 to 2,500 rpm range, the starting characteristic is stable.

Clutch torque characteristic is also modified to compensate for low engine output during high-altitude operation. This enables the engine to start easily at high altitude as it does at low altitude.

When releasing and applying the accelerator pedal at a vehicle speed of 20 km/h (12 mph) or slower immediately after starting, the shock is absorbed so that the clutch is applied after its output side (pulley input shaft) speed almost coincides with engine speed.

Direct-coupling mode
This mode directly-couples the clutch by passing the rated current through it when the vehicle has reached a preset speed.

The rated current is divided into three steps, according to how the accelerator pedal Is pressed.

Accelerator pedal released: 0.4 - 1.8 amp

Accelerator pedal pressed lightly: 3.0 amp *1

Accelerator pedal press heavily: 3.51 amp *2

*1: Only accelerator switch operated

*2: Accelerator switch and throttle-position switch operated

Drag mode
To maintain good operating characteristics when starting and when driving siowly at a speed of 7 km/h (4 mph) or less, including stopping, in a running ("D", "Ds", "P") position, a drag torque is applied by passing a small current (approximately O.2 amp) through the clutch when the accelerator pedal is released.

To prevent a lowering of the idling speed by dispersion in the drag torque and to prevent the vehicle from creeping, the idling speed (ignition pulse) is fed back to control unit.

Reverse excitation mode
For demagnetization, the clutch enters the reverse excitation mode under the following four conditions:

^ Selector lever in "N" or "P" position - The reverse excitation mode is entered to turn off the clutch. When the selector lever is Set to the "D", "Ds", or "R" position, current does not flow in the starter and the engine does not start, even if the ignition key is turned to the "START" position.

^ Engine speed is 300 rpm or less - The reverse excitation mode is entered to prevent starting the engine by pushing the vehicle.

^ For 0.4 to 0.8 seconds after selector lever set to "D" or "P" position - The reverse excitation mode is entered to make selector lever operation easier.

^ For approximately one second when accelerator is released at low vehicle speed - The reverse excitation mode is entered to remove the residual magnetism.

Zero mode
This mode de-energizes the clutch while the output mode is being shifted from the direct-coupled mode to the drag mode when the accelerator is released in "D", "Ds", or position.

Transition response control
This mode controls the clutch torque transition response for smooth coupling of the clutch when the clutch is directly coupled, the selector lever is set to the "Ds" position, and when accelerating and decelerating at a very low speed.

SELF-DIAGNOSIS FUNCTION
The self-diagnosis function includes four modes; a U-check mode, read-memory mode, D-check mode and memory-clear mode. With these control modes, various systems are diagnosed and problems are identified when the "CHECK ECVT" (FWD model) or the "CLUTCH TEMP" (4WD model) warning indicator light is illuminated.

FAIL-SAFE FUNCTION
When sensor trouble occurs, the following fail-safe functions are performed:

^ When clutch current does not flow because of accelerator switch trouble, throttle-position switch and engine speed 1,000 rpm are sensed and the clutch is energized.

^ When the vehicle speed pulse is not input because of speedometer trouble, engine speed 1,200 rpm or higher is sensed and the clutch is energized with the accelerator released.

^ In the 2-phase line pressure control, when line pressure is not properly shifted due to a faulty torque signal circuit, high line pressure will be maintained.