This invention relates to a vehicle drive force control device using an infinite speed ratio transmission (IVT).
Tokkai Hei 11-78619 published by the Japanese Patent office in 1999 describes a combination of an engine controlled according to a target output shaft torque with a continuously variable transmission whereof a speed ratio can be continuously varied. In this construction, a target engine torque is computed from a target output shaft torque according to a vehicle running state and a speed ratio of the continuously variable transmission. Further, an electronically controlled engine throttle is driven so as to achieve an optimum fuel-cost performance.
Tokkai Hei 9-210175 published by the Japanese Patent office in 1999 describes an IVT which combines a continuously variable transmission with a reducing gear unit and a planetary gear set so as to control a speed ratio region of a continuously variable transmission up to infinity.
When the IVT of the aforesaid Tokkai Hei 9-210175 is combined with the drive controller of the aforesaid Tokkai Hei 11-78619, the following problem arises. The IVT selectively applies a power recirculation mode and a direct mode according to the speed ratio, but in the power recirculation mode wherein torque is recirculated from the continuously variable transmission to a reducing gear unit, the transmission efficiency of the IVT is less than in the direct mode.
Also, in the IVT, when the rotation speed of the IVT output shaft is zero, for example when the vehicle is in the stationary state, the IVT speed ratio becomes infinite. Herein, the IVT speed ratio is represented by 1/speed ratio factor, and the speed ratio factor is given by IVT output shaft rotation speed/IVT input shaft rotation speed. The case when the speed ratio=0, i.e. when the IVT speed ratio is infinite, is referred to as the geared neutral point (GNP). Therefore, it is possible to treat the infinite number when the target engine torque is computed using a microcomputer. For this reason, a special calculating routine is built into the microcomputer to handle the case when the IVT output shaft rotation speed is zero. As a result, in some cases, the computational load increases and the precision of the computation declines.
It is therefore an object of this invention to efficiently perform drive force control using an infinite speed ratio transmission. It is a further object of this invention to rapidly and precisely perform computational processing at the GNP.
In order to achieve above object, this invention provides a vehicle drive force control device. The vehicle drive force control device comprises: an infinite speed ratio transmission permitting continuous variation of a speed ratio up to infinity and is joined to a motor, running state detection sensors which detect a vehicle running state, an input shaft rotation speed sensor which detects a rotation speed of an input shaft of the infinite speed ratio transmission, an output shaft rotation speed sensor which detects a rotation speed of an output shaft of the infinite speed ratio transmission, and a microprocessor which controls the infinite speed ratio transmission and motor, wherein this microprocessor is programmed to: calculate a target output shaft torque based on a detection value of the running state detection sensors, compute a speed ratio factor of an input shaft rotation speed and an output shaft rotation speed as output shaft rotation speed/input shaft rotation speed, from the detection values of the input shaft rotation speed sensor and output shaft rotation speed sensor, compute a torque ratio of the infinite speed ratio transmission from this speed ratio factor, compute a target torque of the motor from the target output shaft torque of the infinite speed ratio transmission and the torque ratio, control the output of the motor according to this target torque, and compute a target input shaft rotation speed of the infinite speed ratio transmission based on a vehicle speed, and thereby control the speed ratio.
According to another aspect of this invention, a vehicle drive force control device comprises: an infinite speed ratio transmission permitting continuous variation of a speed ratio up to infinity and is joined to a motor, running state detection means for detecting a vehicle running state, means for detecting a rotation speed of an input shaft of the infinite speed ratio transmission, means for detecting a rotation speed of an output shaft of the infinite speed ratio transmission, means for calculating a target output shaft torque based on a detection value of the running state detection sensor, means for computing a speed ratio factor of an input shaft rotation speed and an output shaft rotation speed as an output shaft rotation speed/input shaft rotation speed, from the detection values of the input shaft rotation speed sensor and output shaft rotation speed sensor, means for computing a torque ratio of the infinite speed ratio transmission from this speed ratio factor, means for computing a target torque of the motor from the target output shaft torque of the infinite speed ratio transmission and the torque ratio, means for controlling the output of the motor according to this target torque, and means for computing a target input shaft rotation speed of the infinite speed ratio transmission based on a vehicle speed, and thereby control the speed ratio.