US 5,961,421 AGranted

Power on skip downshift using three clutches

AssigneeToyota Jidosha Kabushiki Kaisha

InventorsKazumi Hoshiya, Hidehiro Oba

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Abstract

In an automatic transmission of the type wherein a stage intermediate between a higher speed stage and a lower speed stage is achieved through a clutch-to-clutch operation, a power-ON skip downshift is executed via the intermediate stage. First, when the skip downshift has been judged, the hydraulic pressure of the clutch (C4) of the higher speed stage is lowered. Next, when the input speed(r.p.m.) of the transmission have reached the synchronous r.p.m. (SS3) of the intermediate stage, the hydraulic pressure (P3) of the clutch (C3) of the intermediate stage is raised and adjusted so that the rise rate of the input r.p.m. may become a specific value d/dt(NT1). When the input r.p.m. have exceeded the synchronous r.p.m. (SS2) of the lower speed stage, the hydraulic pressure of the intermediate-stage clutch (C3) is adjusted so that the input r.p.m. may keep specific r.p.m. higher than the synchronous r.p.m. (SS2) of the lower speed stage, and simultaneously, the hydraulic pressure of the clutch (C2) of the lower speed stage is gradually raised. Finally, when a predetermined time period has lapsed since the start of the operation of raising the hydraulic pressure (P2) of the clutch (C2), the hydraulic pressure (P3) of the clutch (C3) is gradually lowered till the end of the gearshift.

A gearshift control apparatus for an automatic transmission wherein a skip downshift from a higher speed stage to a lower speed stage in a power-ON state is executed via a stage intermediate between the higher and lower speed stages, and wherein each of a gearshift from the higher speed stage to the intermediate stage, a gearshift from the intermediate stage to the lower speed stage, and a gearshift from the higher speed stage to the lower speed stage is done through a clutch to-clutch operation based on releasing and engaging a plurality of clutches, comprising:

first detection means for detecting a judgement that the power ON skip downshift from said higher speed stage to said lower speed stage is to be executed;
first control means for operating after the detection by said first detection means to lower a hydraulic pressure of the higher speed-stage clutch and thereby to raise input speed of said transmission;
second detection means for detecting a fact that the input speed of said transmission have reached synchronous speed of said intermediate stage owing to the operation of said first control means;
second control means for operating after the detection by said second detection means to raise and adjust a hydraulic pressure of the intermediate-stage clutch so that a rise rate of said input speed of said transmission may become a specific value;
third detection means for detecting a fact that said input speed of said transmission have exceeded synchronous speed of said lower speed stage owing to the operation of said second control means;
third control means for operating after the detection by said third detection means to adjust the hydraulic pressure of said intermediate-stage clutch so that said input speed of said transmission may keep specific speed higher than the synchronous speed of said lower speed stage, and simultaneously to gradually raise a hydraulic pressure of the lower-speed-stage clutch;
and
fourth control means for gradually lowering said hydraulic pressure of said intermediate-stage clutch after lapse of a predetermined time period since start of the operation of said third control means.

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Abstract

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