12/02/2000

SONIC TECH NOTE SERIES:

Injection Drive Modes for Toyota

Information provided is given free of charge in good faith without prejudice

I thought I would take the time to put together a little tech note on this topic. This tech note based on info from my experience as well as some information learned from books published by Toyota Motor Co.

The 7M-GTE uses what Toyota calls Grouped Injection, (some injector makers call this drive mode peak and hold). See pictures at link below for application chart.

INJECTOR OPERATING MODES:
Toyota TCCS uses two injection operating modes, this depends on the engine operating conditions, and is ultimately determined by the TCCS.  These modes are called; 
*synchronous and 
*asynchronous.

Synchronous Injection simply means that the injection events are synchronized with ignition events at specific crankshaft angles.  Synchronous injection is used most of the time by the TCCS.

Asynchronous injection is only used during acceleration, deceleration, and starting. It is not related to the ignition events and runs independently of ignition events based on change in idle contact (IDL) or start switch STA status without regard to crankshaft angle
 

INJECTOR TIMING/DRIVE SYSTEMS USED BY TOYOTA

GROUPED INJECTION
Injectors are grouped into pairs. The pairs consist of two consecutive cylinders in the firing order, and each pair is driven by a separate driver circuit. Four cylinder engines in this group use two groups of injectors, six cylinder engines three groups, and the early Lexus v8ís use four groups of injectors.
Injection is timed to deliver fuel immediately preceding the intake stroke for the leading cylinder in the pair. One group is pulsed once per engine cycle, delivering the entire calculated charge of fuel. This timing method ensures that the fuel does not linger behind the intake valve, thereby, reducing emissions, improving fuel economy and throttle response. Toyota uses two different TCCS drive circuits, voltage controlled and current controlled, along with low or high impedance injectors on the Grouped Injection family.

SIMULTANEOUS INJECTION
Toyota also uses Simultaneous Injection. With this system all the injectors are pulsed simultaneously by a common driver circuit.  Injection occurs once per crankshaft revolution, just prior to the crankshaft reaching TDC #1 cylinder.  This means that the injectors fire twice per cycle, one half of the calculated fuel is delivered by the injectors. This is the simplest and most common injection timing method in use but it is not used on the 7M-GTE the 7m-GTE uses Grouped injection described above.

INDEPENDENT INJECTION
Injectors are driven independently and sequentially by separate driver circuits for each cylinder.  Injection is timed to deliver the entire fuel charge just prior to each intake valve opening. This is the best method available and is utilized on the 2JZ-GTE engine. It offers the best performance, emissions, and fuel economy.  This drive system on Toyota always uses low impedance P&H style injectors.

HIGH & LOW RESISTANCE INJECTORS:
Toyota uses two different types of injector coil windings, they are used depending on the type of drive circuit used in the ECM and the design objective of the engine family.

DUTY CYCLE
Injector duty cycle is a ratio of the injectors on time to the total time.  As the engine rpm is increased, the total cycle time shrinks. If the on time remained the same then the duty cycle would rise.  If the engine PRM stayed the same and the on time decreased, then the duty cycle would drop. Duty cycle is a way of measuring the output time of the control unit that also factors in the speed of the engine. Whenever we read duty cycles above 85% the injector is essentially full open, and we can not expect any enrichment unless an injector with a larger volume is use. Furthermore should the injector enter a static or collapsed condition a very lean condition can result.
 

Best Regards
 

Reg Riemer
 

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