VVTi 1UZ Comparison

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LS400 — NEW FEATURES
Engine Control System
General
The engine control system has been changed from that of the ’97 LS400 in the areas described below.The VVT-i, ETCS-i, and ACIS systems have been adopted.
The cruise control system and the engine immobiliser system have been integrated with the ECM.
A function to communicate with the multiplex communication system has been added.
The engine control system of the 1UZ-FE engine in the ’98 LS400 and ’97 LS400 are compared below.
Main Components of Engine Control System
1) General
The following table compares the main components of the 1UZ-FE engine in the ’98 LS400 and ’97 LS400.
2) Mass Air Flow Meter
The hot wire type mass air flow meter has been changed to the plug-in type. Its basic operation is the same as that of the previous type.
3) Crankshaft Position Sensor
The timing rotor of the crankshaft position sensor has been changed from the previous 12 teeth tom 34 teeth, with 2 teeth missing. It detects the crankshaft angle at 10 intervals.
4) Camshaft Position Sensor
The camshaft position sensor is mounted on the left bank cylinder head. To detect the camshaft position, a protrusion that is provided on the timing pulley is used to generate 1 pulse for every 2 revolutions of the crankshaft.
5) VVT Sensor
A VVT sensor is mounted on the intake side of each cylinder head. To detect the camshaft position, a timing rotor that is provided on the intake camshaft is used to generate 3 pulses for every 2 revolutions of the crankshaft.
VVT-i (Valiable Valve Timing-intelligent) System
1) General
The VVT-i system is designed to control the intake camshaft within a wide range of 50° (of crankshaft angle) to provide a valve timing that is optimally suited to the engine condition, thus realizing improved torque in all the speed ranges and fuel economy, and exhust emissions.
2) Construction and Operation
a. VVT-i Controller
The VVT-i Controller comprises the outer gear that is driven by the timing belt, the inner gear that is affixed to the camshaft and a movable piston that is placed between the outer gear and inner gear.
Having helical splines (twisted, vertical grooves) on its inner and outer periphery, the piston moves in the axial direction to shift the phase of the outer gear and inner gear, thus causing the valve timing to change continuously.
b. Camshaft Timing Oil Control Valve
The camshaft timing oil control valve controls the spool valve position in accordance with the command of the ECM thus allocating the hydraulic pressure that is applied to the intake camshaft timing pulley to the advance and the retard side. When the engine is stopped, thecamshaft timing oil control valve is in the most retarded state.
By the command of the ECM, when the camshaft timing oil control valve is in the position given in Fig. 1, hydraulic pressure is applied from the left side of the piston, which causes the piston to move to the right. Because of the twist in the helical splines that are cut out in the piston, the intake camshaft rotates in the advance direction in relation to the camshaft timing pulley. When the camshaft timing oil control valve is in the position given in Fig. 2, the piston moves to the left and rotates in the retard direction. Furthermore, the camshaft timing oil control valve shuts off the oil passages to maintain the hydraulic pressure at both sides of the piston, thus maintaining the phase at that position. This enables the phase to be set to a desired position.
c. ECM
In proportion to the engine speed, intake air volume, throttle position and coolant temperature, the ECM searches an optimal valve timing under each driving condition and control the camshaft timing oil control valve. In addition, the ECM uses signal from the VVT sensors and the crankshaft position sensor to detect the actual valve timing, thus performing feedback control to achieve the target valve timing.
ETCS-i (Electronic Throttle Control System-intelligent)
1) General
The ETCS-i system, which realizes excellent throttle control in all the operating ranges, has been adopted.
In the conventional throttle body, the throttle valve opening is determined invariably by the amount of the accelerator pedal effort. In contrast, the ETCS-i uses the ECM to calculate the optimal throttle valve opening that is appropriate for the respective driving condition and uses a throttle control motor to control the opening.
The ETCS-i controls the ISC (Idle Speed Control) system, the cruise control system, and the VSC (Vehicle Skid Control).
A duplicate system is provided to ensure a high level of reliability, and the system shuts off in case of an abnormal condition. Even when the system is shut off, the accelerator pedal can be used to operate the vehicle in the limp mode.
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