Control system for automatic transmission

Claim 2

An automatic transmission of a motor vehicle, comprising: a source of hydraulic pressure, a friction element; a conduit fluidly connecting said friction element and said hydraulic pressure source; an accumulator fluidly communicated with said conduit; a first valve fluidly interposed in said conduit at a position upstream of said accumulator; a selectively operable arrangement connected with said first valve for selectively conditioning said first valve to supply hydraulic fluid to said friction element; a fixed orifice interposed in said conduit at a position between said accumulator and said first valve; a one-way valve arranged in parallel with said fixed orifice, said one-way valve being arranged to close when hydraulic fluid is being supplied through said conduit toward said friction element and to open when fluid is being drained from said friction element; a by-pass device bypassing said fixed orifice, said by-pass device being responsive to said selectively operable arrangement for by-passing said fixed orifice for a given period of time following said first valve being conditioned to supply hydraulic fluid to said friction element; and electric control means for varying said given period of time in accordance with operation modes of an engine mounted on said motor vehicle.

Claim 3

An automatic transmission as claimed in claim 1, in which said by-pass device comprises: a by-pass passage by-passing said fixed orifice; and a solenoid valve which is arranged to fully open said by-pass passage when electrically energized and to fully close said by-pass passage when deenergized.

Claim 4

An automatic transmission as claimed in claim 2, in which said solenoid valve includes: a plunger projectable into said by-pass passage; a biasing spring biasing said plunger toward said by-pass passage; and a solenoid attracting said plunger against said spring when electrically energized.

Claim 5

An automatic transmission as claimed in claim 3, in which said electric control means varies said given period of time in accordance with an information as to whether said engine of the motor vehicle is loaded or unloaded.

Claim 6

An automatic transmission as claimed in claim 4, in which said electric control means is so arranged that the given period of time provided when the engine is loaded is made longer than that provided when the engine is non-loaded.

Claim 7

An automatic transmission as claimed in claim 5, in which said electric control means comprises a microprocessor which receives information data from a first sensor by which the position of a shift lever of the transmission is detected, a second sensor by which a speed of the motor vehicle is detected, a third sensor by which a temperature of oil of the transmission and a fourth sensor by which an opening angle of a throttle valve of the engine is detected.

Claim 8

An automatic transmission as claimed in claim 6, in which said electric control means is so arranged that the given period of time is gradually decreased with an increase of temperature of the transmission oil.

Claim 9

An automatic transmission of a motor vehicle, comprising: a source of hydraulic pressure; a friction element; a conduit fluidly connecting said friction element and said hydraulic pressure source; an accumulator fluidly communicated with said conduit; a first valve fluidly interposed in said conduit at a position upstream of said accumulator; a selectively operable arrangement connected with said first valve for selectively conditioning said first valve to supply hydraulic fluid to said friction element; a flow restricting means defined by said conduit at a position between said accumulator and said first valve; a one-way valve arranged in parallel with said flow restricting means of said conduit, said one-way valve being arranged to close when hydraulic fluid is being supplied through said conduit toward said friction element and to open when fluid is being drained from said friction element; and a flow control device incorporated with said flow restricting means, said flow control device being responsive to said selectively operable arrangement to control flow of hydraulic fluid from said hydraulic pressure source toward said friction element; and electric control means for controlling said flow control device in a manner to make said flow restricting means substantially inoperative for a first given period of time following said first valve being conditioned to supply hydraulic fluid to said friction element and to make said flow restricting means gradually operative for a second given period of time following said first given period of time.

Claim 10

An automatic transmission of a motor vehicle, comprising: a source of hydraulic pressure; a friction element; a conduit fluidly connecting said friction element and said hydraulic pressure source; an accumulator fluidly communicated with said conduit; a first valve fluidly interposed in said conduit at a position upstream of said accumulator; a selectively operable arrangement connected with said first valve for selectively conditioning said first valve to supply hydraulic fluid to said friction element; a flow restricting means defined by said conduit at a position between said accumulator and said first valve; a one-way valve arranged in parallel with said flow restricting means of said conduit, said one-way valve being arranged to close when hydraulic fluid is being supplied through said conduit toward said friction element and to open when fluid is being drained from said friction element; and a flow control device incorporated with said flow restricting means, said flow control device being responsive to said selectively operable arrangement to control flow of hydraulic fluid from said hydraulic pressure source toward said friction element; and electric control means for controlling said flow control device in a manner to make said flow restricting means substantially inoperative for a first given period of time following said first valve being conditioned to supply hydraulic fluid to said friction element and to make said flow restricting means gradually operative for a second given period of time following said first given period of time.

Claim 11

An automatic transmission as claimed in claim 8, in which said electric control means is so arranged that upon expiration of said second given period of time, said flow restricting means becomes completely operative.

Claim 12

An automatic transmission as claimed in claim 9, in which said flow restricting means comprises a fixed orifice which is operatively disposed in said conduit, and in which said flow control device comprises a by-pass passage bypassing said fixed orifice and a solenoid valve of an electromagnetic proportional type which continuously varies the sectional area of said bypass passage in accordance with a magnitude of electric current applied thereto.

Claim 13

An automatic transmission as claimed in claim 10, in which said solenoid valve comprises a plunger projectable into said by-pass passage, a biasing spring biasing said plunger toward said by-pass passage and a solenoid attracting said plunger against said biasing spring upon electric energization thereof.

Claim 14

An automatic transmission as claimed in claim 11, in which said electric control means receives information data from a sensor by which the position of a shift lever of the transmission is detected.

Claim 15

An automatic transmission as claimed in claim 12, in which said electric control means is so arranged as to supply said solenoid with a maximum current until said first given period of time expires and to gradually reduce the magnitude of current following the expiration of the first given period of time.

Claim 16

An automatic transmission as claimed in claim 13, in which said electric control means is so arranged as to reduce the magnitude of current to zero upon expiration of said second period of time.

Claim 17

An automatic transmission as claimed in claim 14, in which the distance by which said plunger of the solenoid valve is moved against said biasing spring is proportional to the magnitude of current applied to said solenoid.

Claim 18

An automatic transmission as claimed in claim 9, in which said flow restricting means comprises a given portion of said conduit, and in which said flow control device comprises a solenoid valve of electromagnetic proportional type which continuously varies the sectional area of said given portion of said conduit in accordance with a magnitude of electric current applied thereto.

Claim 19

An automatic transmission as claimed in claim 16, in which said solenoid valve comprises a plunger projectable into said given portion of the conduit, a biasing spring biasing said plunger toward said given portion and a solenoid attracting said plunger against said biasing spring upon electric energization thereof.

Claim 20

An automatic transmission as claimed in claim 17, in which said electric control means receives information data from a sensor by which the position of a shift lever of the transmission is detected.

Claim 21

An automatic transmission as claimed in claim 18, in which said electric control means is so arranged as to supply said solenoid with a maximum current until said first given period of time expires and to gradually reduce the magnitude of current following the expiration of the first given period of time.

Claim 22

An automatic transmission as claimed in claim 19, in which said electric control means is so arranged as to reduce the magnitude of current to zero upon expiration of said second period of time.

Claim 23

An automatic transmission as claimed in claim 20, in which the distance by which said plunger of the solenoid valve is moved against said biasing spring is proportional to the magnitude of current applied to said solenoid.