Control device for hybrid vehicle and method thereof

A control system for a hybrid vehicle having an internal combustion engine mounted on said vehicle for outputting a driving force via an output shaft, a lockup clutch mechanically and coaxially connected to said engine for connecting and disconnecting said driving force to a driving wheel, a transmission rotatably connected to said lockup clutch for changing a rotating speed thereof, a battery mounted on said hybrid vehicle for storing and providing an electric energy therefrom to various electric equipment, an accelerator pedal sensor provided in vicinity of an accelerator pedal for detecting a depressed amount thereof and for producing an accelerator signal, a brake switch provided near a brake pedal for detecting whether or not a driver steps thereon and for generating a brake signal when said driver steps thereof, and an inhibitor switch attached on a gear select mechanism for detecting whether a select lever is set in a drive range (D) and a rear range (R) or not and for outputting an ON signal when said lever is set in at least either one of said ranges, comprising:

• a first motor (A) interposed between said output shaft and said lockup clutch and electrically connected to said battery for generating an auxiliary electric energy and for returning thereof to said battery when said lockup clutch is released while said vehicle is running in a series running mode;
• a second motor (B) interposed between said first motor (A) and said transmission and electrically connected to said battery for assisting said engine when said lockup clutch is connected while said vehicle is running in a parallel running mode;
• a planetary gear interposed between said lockup clutch and said second motor (B) for alternatively and effectively using said motors (A) and (B) so as to be changeable to a motor or a generator as required;
• and
• electronic hybrid engine control means responsive to said accelerator signal, said brake signal, said ON signal for connecting said lockup clutch after setting said driving force to substantially zero in addition to making an r.p.m. of said first motor (A) to coincide with an r.p.m. of said secondmotor (B) when a driving condition is transiting from said series running mode to said parallel running mode and for disconnecting said lockup clutch after making said r.p.m. of said first motor (A) to coincide with said r.p.m. of said second motor by gradually increasing said r.p.m. of said second motor (B) at the time of when said driving force becomes substantially zero by incrementally adding a driving torque of said second motor (B) as much as a decreased torque of said engine when said driving condition is transiting from said parallel running mode to said series running mode in addition to gradually decreasing said driving force.