GB2132710A

GB2132710A - Torque converter lock-up clutch control

Info

Publication number: GB2132710A
Application number: GB8329947A
Authority: GB
Inventors: Masao Nishikawa; Yoshimi Sakurai; Takashi Aoki; Yoichi Sato
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1982-11-12
Filing date: 1983-11-10
Publication date: 1984-07-11
Also published as: DE3341160A1; GB2132710B; GB2166818A; GB2166818B; DE3341160C2; GB2166504A; GB8329947D0; FR2550140A1; GB8529289D0; GB2166504B; GB8529288D0; FR2550140B1

Abstract

A lock-up control device for a torque converter in an automatic transmission for a vehicle comprises a modulator valve Mv disposed in an oil passage for connecting an oil pressure cylinder 14 of the lock-up clutch with an oil pressure source, the modulator valve being composed of a valve body 86 for opening and closing said oil passage, a spring for biasing said valve body in a valve-opening direction, a first oil pressure chamber in which oil pressure biases the valve body in a valve-closing direction and a second oil pressure chamber in which speed-responsive oil pressure biases said valve body in the valve-opening direction. A solenoid valve 96, 97 releases pressure in said second oil pressure chamber to disengage the lock-up clutch when the throttle is released. A timer valve Tv disengages the clutch during a ratio shift. The lock-up clutch slips when speed is low and torque is high. <IMAGE>

Description

SPECIFICATION Lock-up control devicefortorque converter in auto matictransmission for vehicle In an automatic transmission comprising a fluid typetorque converter having an input member including a pump vane wheel and an output member including a turbine wheel, and an auxiliarytransmission having one or more stages of geartrains, through which the torque of the output member is transmitted to a driving wheel, a lock-up control device for a torque converter in which a direct coupling clutch capable of mechanically coupling said input and output members is interposed therebetween to control the slip loss ofthetorque converterto the minimum.

When an accelerator pedal is released during the operation of the vehicle with the torque converter placed in a lock-up state by actuation of the direct coupling clutch, a sudden change in reaction applied to a power plant including the engine is transmitted to the vehicle bodythroughthe power plant and as a consequence, unpleasant surging tends to occur. It is effective to release the actuation ofthe direct coupling clutch atan idle position of an engine throttle valve in orderto avoid the unpleasant surging. Various devices for that purpose have already been proposed.

Afurthermeansforsolving this problem has already been proposed, in which means, a unidirectional clutch is interposed in series with the direct coupling clutch between the input and output members ofthetorque converter, said unidirectional clutch being designed so that at the time of operation ofthe direct coupling clutch, onlytheoutputtorque of the engine may be transmitted towards the output member. In the idle condition of the engine throttle valve, vibration noises and wear due to the slip of the unidirectional clutch somewhat occur. If prevention of such occurence ofthe noises orthe like is taken into consideration, it is desirable to release the direct coupling clutch.

On the other hand, the applicant has already proposed an arrangement wherein forthe purpose of maintaining the power performance during the operation of the direct coupling clutch, the slip characteristic is imparted to the direct coupling clutch and the engaging force ofthe direct coupling clutch is controlled in accordance with the change in vehicle speed whereby during the maximum power output operation of the engine in a lowvehicle speed zone, the slip is purposely created in the direct coupling clutch to thereby allotthe transmission of output torque ofthe engine to a mechanical transmission system including the direct coupling clutch and a fluid transmission system including a fluid of the torque converter, thus suitably restoring a torque amplifying function of the torque converter, and in other words, power division of one kind is effected.

If an attempt is made to simultaneously effect the lock-up controls of different kinds, two valves are required, one valve for releasing the direct coupling clutch in the idle state ofthe engine throttle valve and the other for controlling the coupling force of the direct coupling clutch in accordance with the change in vehicle speed. Ifthese can be controlled efficiently by a single valve, the device is materially simplified, and a leak loss of pressure oil from the valve is minimized, which is extremely advantageous in practical use.

It is therefore a first object ofthe present invention to provide a lock-up control device for said torque converterwhich is simple in construction and in which the lock-up controls of different kinds may be carried out buy a single valve.

To achieve this object, the present invention is characterized by comprising a hydraulic direct coupling clutch having a slip characteristic provided between input and output members of a torque converter and capable of mechanically coupling said both members and a modulatorvalve disposed in an oil passage for connecting a hydraulic cylinder of said direct coupling clutch with an oil pressure source, said modulatorvalve being composed of a valve body for opening and closing said oil passage, a spring for biasing said valve body in a valve-opening direction, a first oil pressure chamber for introducing pilot oil pressure for biasing said valve body in a valve-closing direction from an input port side of said modulator valve, and a second pilot oil pressurechamberfor introducing pilot oil pressure for biasing said valve body in the valve-opening direction, wherein an output side of a device for generating oil pressure proportional to vehicle speed for releasing oil pressure which is changed proportional to the vehicle speed is connected through a throttle to said second pilot oil pressure chamber and a valve device for detecting the idle state of an engine throttlevalve to release said second pilot oil pressure chamber to atmosphere is connected to said second pilot oil pressure chamber.It is a second object of the present invention to provide a lock-up control deviceforsaid torque converter which is simple in construction and positive in operation and in which the torque convertercan be locked up overthree speed ratios adjacent to one another by a common control device, and at the time of speed change, said lock-up can be temporarily released to alleviate a shock atthe time of speed change.

To achieve this second object, the present invention is characterized bythe provision of an automatic transmission comprising a fluid type torque converter, a hydraulic direct coupling clutch provided between input and output members and capable of being actuated to mechanically coupling said both members, an auxilarytransmission connected to said torque converter and having plural stages of gear trains, said auxiliary transmission capable of being changed in speed to a plurality of speed ratios by selection of said gear trains, and a control mechanism for automatically effecting the selection of geartrains of said auxiliary transmission in accordance with the running condition ofthe vehicle, said automatic transmission comprising signal pressure which is The drawing(s) originally filed was (were) informal and the print here reproduced is taken from a iater filed formal copy. increased or reduced when one of said gear trains is selected so asto assume a certain speed ratio and which is conversely reduced or increased when the other ofgeartrains is selected so as to assume a speed ratio adjacent to the first-mentioned speed ratio, a lock-up actuating means for actuating said direct coupling clutch by common oil pressure even when eithergeartrain is selected, and a release means for detecting a variation in said signal pressure to release the lock-up of said direct coupling clutch during a period of said variation.

Accordingly, ifthe oil presure for establishing an intermediate speed stage gear train is used as a reference oil pressure of the lock-up actuating means, the actuation and release of the direct coupling clutch can be controlled bytheoil pressureforestablishing a low-speed stage and high-speed stage geartrain adjacent thereto, the torque converter can be locked up overthree speed ratios, and the releasing can be effected at the time of twice of speed change therebetween. Of course, this can be also applied to the transmission which is provided with onlytwo speed ratios.

Incidentally, where an actual control device for an automatictransmission is designed, it is advantageous, in terms of installation space and cost, to use an output of a speed-changing governor valve heretofore used,that is, governor pressure Pg, as signal pressure proportional tothevehicle speed. However, the characteristic of the governor pressure Pg is generally determined by a combination ofthesecondary parabola, and the rising speed ofthe governor pressure in a low-speed zone is high as shown in Fig.

11 This means that in the low-speed zone, as the vehicle speed lowers, the lock-up engaging force rapidly weakens. This is convenient because the lock-up state ofthetorque converter is released before the vehicle stops to avoid the engine stop (so-called "enst"). On the other hand, however, the characteristic ofthe governor pressure Pg has its own limitation for determining the speed change characteristic, and the characteristic ofthe governor pressure Pg cannot be determined freely in view ofthefact that the torque converter is locked up. Accordingly, if a release point ofthe lock-up is brought to the low-speed state as much as possible, there was a problem in that in the vehicle speed region above the release point, the engaging force ofthe direct coupling clutch is excessively strong to increase the vehicle vibrations.

That is, in Fig. 1, where the governor pressure Pg is increased to form lock-up pressure PL, if the amount of said increment is increased to PL' in order to lock-up the torque converterfrom a lower speed, the lock-up start point determined by a point crossed with internal pressure Pcofthetorqueconverteris shifted from vehicle speed Ato vehicle speed B to be shifted to the lowerspeedside. However, in vehiclespeedCwhich is the middle-speed zone, the engaging force of the torque converter increases and therefore, the vehicle vibraton increases and poor power feeling results.

It is therefore a third object ofthe present invention to provide a lock-up control deviceforsaidtorque converter which can considerably improve practical fuel costwithout making sacrifices for others while solving the problem of vibration in the middle-speed zone and being made to be able to maintain the lock-up engaging force down to the low-speed zone, underthe restriction that the existing speed-changing governor pressure is utilized.

To achieve this third object,the present invention is characterized by the provision of an automatic trans- mission comprising a fluid type torque converter having an input member and an output memberto which the output ofthe engine is transmitted; a hydraulic direct coupling clutch provided between said input and output members and capable of being actuated to mechanically engage said both members; an auxiliarytransmission connected to the output memberof said torque converter and having plural stages of geartrains, said auxiliarytransmission capable of being changed in speed to a plurality of speed ratios by selection of said geartrains; and a control mechanism having a governorvalvefor releasing governor pressure proportional to thevehicle speed and automatically selecting the geartrain of said auxiliarytransmission in accordance with the running condition ofthe vehicle; said automatic transmission comprising an oil pressure generating meansforgenerating oil pressure at a substantially given level at all times during the operation ofthe engine; and a selection means for comparing the governor pressure from said governorvalve with the generated oil pressure of said oil pressure generating means to select higher one of oil pressure, output pressure of said selection means being used as an index for controlling the engaging force of said direct coupling clutch.

Where the lock-up engaging force is madeto be maintained down to a lower speed zone in accordance with the aforesaid third object, if said system is applied even to the speed change ratio (the first speed) ofthe low-speed stage, a switching valve for releasing the lock-up state becomes necessary in a level below a certain vehicle speed. Otherwise,the locking-up ofthe torque converter is effected even during the stoppage of the vehicle, and therefore, the engine is not operated smoothly and for the worst, the engine stop possibly occurs (in case of the powerdivisiontype,the engine stop does not always occurcompletely).

It is therefore a fourth object ofthe present invention to provide a lock-up control device for said torque converter in which in the state of speed change ratio of a low-speed stage, pressure with the governor pressure increased is used as the lock-up engaging pressure, and the characteristicwherein said governor pressure rapidly lowers as the vehicle speed lowers is utilized, whereby possible occurence ofthe engine stop is eliminated even in the low-speed stage and the torque converter can be locked up without newly installing an exclusive-use switching valve which changes in switching mode in accordance with the vehicle speed.

To achieve this fourth object, the present invention is characterized by the provision of an automatic transmission comprising afluid type torque converter having an input member and an output memberto which the output of the engine is transmitted; a hydraulic direct coupling clutch provided between said input and output members and capable of being actuated to mechanically engage said both members; an auxiliary transmission connected to the output member of said torque converter and having plural stages of geartrains, said auxiliary transmission capable of being changed in speed to a plurality of speed ratios by selection of said gear trains; and a control mechanism having a governorvalvefor releasing governor pressure proportional to the vehicle speed and automatically selecting the geartrain of said auxiliarytransmission in accordance with the running condition ofthevehicle; said automatic transmission comprising an oil pressure generating meansforgenerating oil pressure ata substantially given level at all times during the operation ofthe engine; a selection means for comparing the governor pressure from said governor valve with the generated oil pressure of said oil pressure generating means to select higheroneofoil pressure; and an interruption means interposed between said selection means and said oil pressure generating means to cut-off a connection between said selection means and said oil pressure generating means when the speed ratio of the low-speed stage is established, output pressure of said selection means being used as an index for controlling the engaging force of said directcoupling clutch.

The above and other objects, characteristics and advantages of the present invention will be further apparentfrom the description of preferred embodimentswhich will be explained in detail with reference to the accompanying drawings in which: Figs. 1 to 4 show a first embodiment ofthe present invention, in which Fig. lisa schematic view as a whole of a transmission for an automobile with three stages offorward movement and one stage of backward movement, Fig. 2 is an oil pressure control circuit view of said automatictransmission including the device ofthe present invention, Fig. 2A is a developed view showing essential parts of a direct coupling clutch of Fig. 2, Fig. 3 is a characteristic curve of working oil pressure ofthedirectcoupling clutch, Fig. 4 is a view showing the relation between the speed change characteristic and the zones showing the strength ofthe engaging force of the direct coupling clutch; Fig. 5 is an oil pressure circuitview showing a second embodiment ofthe present invention; Fig. 6 is an oil presssure circuit view showing a third embodiment of the present invention; Figs. 7A-D are explanatoryviews showing the operation of a timing valve in Fig. 6 in order; Fig. 8 is a characteristic curve showing the change in working oil pressure ofthe direct coupling clutch in Fig . 6 when the speed change is made; Fig. 9 is an oil pressure circuit view showing a fourth embodimentofthe present invention;; Fig. 10 isan oil pressure circuitview showing a fifth embodiment of the present invention; Fig 11 is an oil pressure characteristic curve for explanation of problems; Fig. 12 is an oil pressure circuit view showing a sixth embodimentofthe present invention; Fig. 13 is a curve showing the engaging pressure of the direct coupling clutch in Fig. 12; Fig. 14 is a view for explanation of a zone capable of engaged driving of the direct coupling clutch; Fig. 15 is an oil pressure circuit view showing essential parts in a modified example of the timing valve in Fig. 12; and Figs. 16,17 and 18areoil pressurecircuitviews showing essential parts of a seventh embodiment, an eighth embodiment and a ninth embodiment, respectively, ofthe present invention.

Hereinafter, preferred embodiments of the present will be described in detail with reference to the accompanying drawings.

Priorto the explanation of a first embodiment of the present invention, Fig. lisa schematic view of an automatic transmission for a vehicle with three stages offorward movement and one stage of backward movement to which the present invention is applied.

Referring to Fig . 1, the output of the engine E is transmitted, via a torque converterT, an auxiliary transmission M and a differential device Df in said order, from a crank shaft 1 to driving wheels, W' to drive the latter.

The torque converterT comprises a pump vane wheel 2 connected to the crankshaft 1, a turbine vane wheel 3 connected to an input shaft 5 of the auxiliary transmission M, and a statorvane wheel 4 connected through a unidirectional clutch 7 to a statorshaft 4a relatively rotatably supported on the input shaft 5. The torque transmitted from the crank shaft 1 to the pump vane wheel 2 is transmitted to the turbine vane wheel 3 hydrodynamically, and when amplifying action of torque is effected during that period, the statorvane wheel 4bearsthe reaction thereof.

A pump driving gear8fordriving an oil pressure pump P shown in Fig. 2 is provided on the right end of the pump vane wheel 2, and a stator arm 4bfor controlling a regulatorvalve Vr shown in Fig. 2 is fixedly mounted on the right end ofthe stator shaft4a.

Between the pumpvanewheel 2 and the turbine vane wheel 3 is provided a rollertype direct coupling clutch Cd capable of mechanically coupling the former. This will be described in detail with reference to Fig. 2 and Fig. 2A. An annular driving member 10 having a driving conical surface 9 in the inner circumference thereof is secured to the innercircum- ferential wall 2a of the pump vane wheel 2. A driven member 12 having a driven conical surface 11 parallel to and facing to said driving conical surface 9 in the outer circumference thereof is axially slidably splinefitted in the inner circumferential wall 3a oftheturbine vane wheel 3. The driven member 12 informed at its one end integrally with a piston 13.The piston 13 is fitted into an oil pressure cylinder 14 provided on the inner circumferential wall 3a ofthe turbine vane wheel 3 to simultaneously receive internal pressure ofthe cylinder 14 and internal pressure ofthetorque converterT at both left and right ends thereof.

A colt mar clutch roller 15 is interposed between the driving and driven conical surfaces 9,11. The clutch roller 15 is retained byan annular retainer 16 in such a mannerthatthe centeraxis othereof is inclined by a fixed angle 6 with respectto the center line g of a phantom conical surface Ic extending through the central portion between boththe conical surfaces9 and 11, as shown in Fig. 2A.

Accordingly, when oil pressure higherthan internal pressure of the torque converter T is introduced into the oil pressure cylinder 14 at the stage wherein the torque amplifying function ofthe torque converter T becomes unnecessary, the piston 13, namely, the driven member 12 is urged towards the driving member 10. Thereby the clutch roller 15 is pressed against both the conical surfaces 9, 11 but when the driving member 10 is rotated by the output torque of the engine E in a direction as indicated by X in Fig. 2A with respectto the driven member 12, the clutch roller 15 revolves accordingly.However, this clutch roller 15 has its center axis inclined as previously mentioned, and therefore, said revolution imparts both the members 10,12 a relative axial displacementto move them close to each other. As a consequence, the clutch roller 15 is cut into and between both the conical surfaces 9,11 to mechanically couple between both members 10, 12, that is, between the pump vane wheel 2 and turbine vane wheel 3. If the output torque ofthe engine above the coupling force is applied between both the vane wheels 2,3 even when the direct coupling clutch Cd is operated as described above, the clutch roller 15 produces a slip with respect to each ofthe conical surfaces 9, 11.Thereby said torque is divided into two parts, one torque being transmitted mechanically through the direct coupling clutch Cd, and the other being transmitted hydrodynamicallythrough both the vane wheels 2,3, to form a variable rate power divisional system wherein the ratio oftheformertorqueto the lattertorque varies with a slip degree of the clutch roller 15.

When a reverse load is applied to thetorque converterT during the operation of the direct coupling clutch Cd, the rotational speed of the driven member 12 exceeds the rotational speed ofthe driving member 10, and therefore, relatively, the driving member 10 is rotated in a direction as indicated byYwith respect to the driven member 12, as a consequence of which the clutch roller 15 revolves in a direction opposite the formerto impart both the members 10, a relative axial displacement for moving them apart from each other. As a result, the clutch roller 15 is released from its cutting into and between both the conical surfaces 9, 11, assuming the idle state.Thus, the transmission ofthe reverse load from theturbine vane wheel 3 to the pump vane wheel 2 is effected onlyhydrodynami- cally.

If oil pressure ofthe oil pressure cylinder 14 is released, the piston 13 receives the internal pressure ofthetorque converterT and then moves back to its original position, whereby the direct coupling clutch Cd assumes an inoperative state.

Turning again to Fig. 1, a low-speed stage gear train G1, a middle-speed gear train G2, a high-speed stage geartrain G3 and a backward-movement geartrain Gr are provided in parallel between the input and output shafts 5,6 parallel to each other of the auxiliary transmission M. The low-speed stage gear train G1, comprises a driving gear 17 connected to the input shaft 5through a low-speed stage clutch C1 and a driven gear 18 connected to the output shaft 6 through a unidirectional clutch Co and meshed with said gear 17.The middle-speed stage geartrain G2comprises a driving gear 19 connected to the input shaft through a middle-speed stage clutch C2 and a driven gear 20 connected to the output shaft 6through a switching clutch Cs and meshed with said gear 19. The high-speed stage geartrain G3 comprises a driving gear 21 fixedly mounted on the input shaft 5 and a driven gear 22 connected to the output shaft 6 through a high-speed stage clutch C3.The backward-movement geartrain Gr comprises a driving gear 23 formed integrally with the driving gear 19 ofthe middle-speed stage gear train G2, a driven gear 24 connected to the output shaft 6 through the switching clutch Cs and an idle gear 25 meshed with both the gears 23,24. The switching clutch Cs is disposed between the driven gears 20,24, and the driven gears 20,24 can be selectively connected to the output shaft 6 by shifting a selector sleeve 26 ofthe clutch Cs to a forward position on the lefthand orto a backward-movement position on the righthand inthefigure.

Ifonlythe low-speed stage clutch Cz is engaged when the selector sleeve 26 is retained attheforward position as shown, the driving gear 17 is connected to the input shaft 5 to establish the low-speed stage gear train G1, through which geartrain G1, the torque is transmitted from the input shaft 5 to the output shaft 6.

Next, when the middle-speed stage clutch C2 is engaged while the low-speed stage clutch C1 remains engaged, the driving gear 19 is connected to the input shaft 5 to establish the middle-speed stage geartrain G2,through which gear train G2, the torque is transmitted from the input shaft 5 to the output shaft 6.

Duringthatperiod,theoutputshaft6 rotates at a higher speed than that of the driven gear 18 ofthe low-speed geartrain G1 due to a difference in change gear ratio between the low-speed and middle-speed stage gear trains G1, G2, and therefore, the unidirectional clutch Co slips to renderthe low-speed stage geartrain G1 substantially outofoperation. If the middle-speed stage clutch C2 is interrupted and high-speed stage clutch C3 is engaged while the low-speed stage clutch C1 is engaged, the driven gear 22 is connected to the output shaft 6 to establish the high-speed stage gear train G3, through which gear train G3, the torque is transmitted from the input shaft 5 to the output shaft 6.Also in this case,the unidirectional clutch Co slips to render the low-speed stage geartrain G1 out of operation, similarto the time when the middle-speed stage geartrain G2 is established. Next, if the selector sleeve 26 is switched to the backward-movement position on the righthand and only the middle-speed stage clutch C2 is engaged, the driving gear23 and driven gear 24 are connectedto the input shaft 5 and output shaft 6, respectively, to establish the backward-movement gear train G r, through which gear train Gr, the torque is transmitted from the input shaft5to the the output shaft 6.

The torque transmitted to the output shaft 6 is transmitted from an output gear 27 provided on the end of said shaft 6to a large-diameter gear 28 ofthe differential device Df.

Fig shows a combination of one example of an oil pressure circuitfor controlling the operation ofthe low-speed, middle-speed and high-speed stage clutches C1, C2 and C3 in Fig. 1 and one example of a control device Dc ofthe direct coupling clutch Cd in accordance with the present invention. In the figure, the oil pressure pump P sucks the oil from an oil tank R and feeds the oil under pressure into an operating oil passage 29. This pressure oil is regulated in pressure to a predetermined level by a regulatorvalve Vr, and thereafterfed to a manual valve Vm. This oil pressure is termed as the line pressure PI.

The regulatorvalve Vr has a pressure regulating spring 30 and a spring receiving cylinder 31 for carrying an outer end thereof, and this spring receiving cylinder 31 can be moved to left and right to adjust the set load of the pressure regulating spring 30. The stator arm 4b comes into contact with the outer surface of the spring receiving cylinder31 so as to applythe reaction force acting on the statorvane wheel 4, that is, the stator reaction force thereto.A statorspring 32forcarrying the stator reaction force is connected to the spring receiving cylinder3l.Accor- dingly, if the stator reaction force increases, the stator spring 32 is compressed, as a consequence of which the spring receiving cylinder 31 is moved leftwards to increase the set load of the pressure regulating spring 30 with the result that the oil pressure ofthe operating oil passage 29 is increased.

A part of pressure oil regulated bythe regulator valve Vr is introduced into the torque converter Tvia an inlet oil passage 34 having a throttle 33 to pressurize the interiorthereofto prevent a cavitation, said internal pressure being determined by the magnitude ofthe throttle 33, the strength of a spring 37 of a check valve 36 provided on an outlet oil passage 35 of thetorque converterT, and the like.

The oil having passed through the checkvalve 36 is returned to the oil tank R via an oil cooler not shown.

The surplus portion of pressure il discharged from the oil pressure pump P is introduced to a lubricating oil pasage 38 from the regulator valve Vr and fed to various lubricating portions. A pressure regulating valve 39 is connected to the lubricating oil passage 38 in orderto secure the oil pressure required to the minimum.

When the valve Vm is in a neutral position N as shown, the pressure oil fed to the manual valve Vm is not fed to any ofsaid clutches C1, C2, C3 and various other oil pressure operating portions. When the valve Vm is moved leftwards by one step from the illustrated position andshiftedto a drive position D,the operating oil passage 29 from the oil pressure pump P is communicated with an operating oil passage 411 leading to an oil pressure cylinder 401 ofthe lowspeed stage clutch C1 and with an operating oil passage 43 leading to a spring chamber42 of an oil pressure servo-motor Sm for shifting the selector sleeve 26, and therefore, the low-speed stage clutch C1 is actuated (engaged) to establish the low-speed stage geartrain G1.And a piston 44 ofthe servo-motor Sm remains ata position moved leftwards as shown to hold the selector sleeve 26 atthe forward position as shown in Fig. 1 through a shiftfork45 thereby placing the backward-movement geartrain Grin an inoperative state.

An inlet oil passage 46 in communication with an input port of a device for generating oil pressure proportional to vehicle speed, that is, a governor valve Vg is branched from the operating oil passage 43 leading to the spring chamber42 of the servo-motor Sm, and a first signal oil passage 471 extends from an outputportofthevalveVg.

The governorvalveVg,which is well known, is rotated about a rotational shaft 49 by a gear 48 meshed with the large-diameter gear 28 ofthe differential device Df. Thus, the rotational speed is proportional to the vehicle speed, and therefore, the governorvalve Vg can release the oil pressure proportional to the vehicle speed, that is, a governor pressure Pg, to the first signal oil passage 471 by the action ofthe centrifugal force acting on a weight 51 of a spool valve body 50.

An inlet oil passage 53 in communication with an input port of a throttle valve Vt is branched from the operating oil passage 43, and a second signal oil passage 472 extends from an output port ofthe valve Vt. A modulator valve 54 for determini ng an upper limitvalue of the inlet pressure ofthethrottle valve Vt is disposed halfway of the inlet oil passage 53.

Thethrottle valve Vt, which is well known, comprises a spool valve body 55, a control spring 58 for biasing the valve body 55 leftwards, a return spring 57 for biasing the valve body 55 rightwards, a control spring 59 for carrying the outer end ofthe control spring 58, a control cam 60 rotated in association with an increase in opening degree ofthethrottlevalve of the engine E to move the control piston 59 leftwards, an adjusting bolt 61 capable of adjusting the set load ofthe return spring 57 and the like. When the control piston 59 is moved leftwards, the displacement thereof causes the spool valve body 55 to be pushed leftwardsthrough the control spring 58.With this Ieftward movement, the oil pressure released to the second signal oil passage 472 acts on a left shoulder 55a of the spool valve body 55 so asto push backthe spool valve body 55 rightwards, and therefore, after all, the throttle valve Vtcan release the oil pressure proportional to the opening degree of the throttle valve of the engine E, that is, throttle pressure Pt, to the second signal oil passage 472.

The first and second signal oil passages 471, 472 are connected to pilot oil pressure chambers 62,62'; 63, 63', respectively, on both ends of a low-middle speed shift valve V1 and a middle-high speed shift valve V2.

Thereby, spool valve bodies 64,65 of these shift valves V1, V2 receive at both end surfaces thereof said governor pressu re Pg and th rottle pressure Pt and are operated as follows: That is, the spool valve body 64 ofthe low-middle speed shift valve V1 initially remains at a position moved rightwards as shown by the force of a spring 66 but when the vehicle speed increases to increase the governor pressure Pg and the force for moving the spool valve body 64 leftwards bythe governor pressure Pg overcomes the force for moving the valve body 64 rightwards bytheth rottle pressure Pt and spring 66, a click ball 68 moving together with the valve body 64 in a click motion mechanism 67 provided on the right end ofthevalve body 64 gets over a fixed locating projection 69 and the valve body 64 is rapidly switched to a Ieftwardly moved position, whereby the oil pressure from the oil pressure pump P, which has been so farfed only to the oil pressure cylinder401 ofthe low-speed stage clutch C1, is also fed to the oil pressure cylinder 402 ofthe middle-speed stage clutch C2through operating oil passages 70,71 and 412to place both the clutches C1, C2 in an engaged state, thus establishing the middle-speed stage gear train2.

When the vehicle speed further increases, the similar operation occurs also in the middle-high speed shift valve V2, whereby the spool valve body 65 of the valve V2 is moved leftwards due to the increasing governor pressure Pg to open the operating oil passages 412,71 to the oil tank Rand on the other hand,the operating oil passage 70 is then brought into communication with the operating oil passage413 leading to the oil pressure chamber 403 of the high-speed stage clutch C3, and therefore, the middle speed stage clutch C2 assumes the interrupted stated and the low-speed stage clutch C1 and high-speed stage clutch C3 assume the engaged state to establish the high-speed stage gear train G3 as previously mentioned.

Accumulators 72,73, a unidirectional valve 74, an orifice control valve 75 and the like are provided to alleviate the gearchange shock.

As is well known, a gear change map divided by the solid line can be depicted as shown in Fig. 4 Actually, the change gear map differs betweentheshift-uptime and shift-down time duetothe click motion mechan ism 67 provided on each of the shift valves V1, V2. This is well known and is not significant.Therefore, only "the mapfortheshift-up time will be given When the manual valve Vm is shifted to a position otherthan the drive position D,for example, to a middle-speed stage retaining position II or backward movement position Re, the middle-speed stage gear train G2 or backward-movement geartrain Gr is established, which has no particularly important relation with the present invention. No further ex planation will be made. Among the shift positions of the manual valve Vm, a reference character Pk designates a parking position.

The aforementioned oil pressure circuit is well known.

Now,the control device Dc ofthe direct coupling clutch Cd will befurther explained with referenceto Fig. 2. The control device De com prises a timing valve Tv and a modulator valve Mv.

The timing valve Tv comprises a spool valve body 20 which is moved between a rightfirstswitching position and a left second switching position, a first pilot oil pressure chamber 81 to which a left end surface ofthe valve body 80faces, a second pilot oil pressure chamber 81 to which a right end surface of the valve body 80 faces, a first input port 83 which is always communicated with the first pilot oil pressure chamber 81 through a throttle 82 provided on the valve body 80, a second input port 83' which is always communicated with a second pilot oil pressure chamber81 ' and an output port 84, wherein when the valve body 80 is in the rightfirst switching position, the first input port 83 is placed in communication with the output port 84 and when the valve body 80 is moved to the left second switching position, the second input port 83' is placed in communication with the output port 84. An oil passage 412' branched from the operating oil passage 412 of the middle-speed stage clutch C2 is connected to the first input port 83, and an oil passage 413 branched from the operating oil passage 413 of the high-speed stage clutch Cais connected to the second input port 83', the output port 84 being connected to the later-appearing input port 89 ofthe modulator valve Mv through an output oil passage 85.

The modulator valve Mv comprises a spool valve body 86 which is moved between a right closed position and a left open position, a spring 87 for biasing the valve body 86 towards the open position, a first pilot oil pressure chamber 88 to which a left end surface of the valve body 86 faces, a second pilot oil pressure chamber 88' to which a right end surface of the valve body 86 faces, and input and output ports 89, 90, the output port 90 being connected to the oil pressure cylinder 14 of the direct coupling clutch Cd through an output oil passage 91.The first pilot oil pressure chamber 88 is always communicated with the input port 89 through a throttle 92 provided on the valve body 86, a signal oil passage 47' branched from the first signal oil passage 471 is connected to the second pilot oil pressure chamber 88', and a throttle 93 is provided halfway of the oil passage 471'. A discharge oil passage 95 in communication with the oil tank R is connected to the second pilot oil pressure chamber 88' through athrottle 94, and an electro magnetic valve 96 as a valve device for opening and closing thethrottle 94 is provided adjacent the modulatorvalve Mv.The electromagnetic valve 96 comprises a needle valve 97 for opening and closing the throttle 94, a valve spring 98 for biasing the needle valve 97 toward the closed side and a solenoid 99for encircling the needle valve 97, the solenoid 99 being connectedtoapowersource 101 through an idle position detecting switch 100. The idle position detecting switch 100 is interlocked with an accelerator pedal 102 for opening and closing thethrottle valve of the engine E and the switch 100 is closed when the throttle valve is returned to the idle opening zone.The throttle 94 ofthe discharge oil passage 95 is set to an opening degreesmallerthan thethrottle 93 ofthe signal oil passage471'.

The operation of the control device Dcwill be explained hereinafter.

First, wherethe vehicle is running with the establishment of the low-speed stage geartrain G1, in this case, the low-speed stage clutch C1 is operating, and therefore,the operating oil passages4l2,4l3ofthe middle and high-speed stage clutches C2, C3 are communicated with the oil tank Rand thus the first and second input ports 83,83' and output port 84 of the timing valve Tv and the first pilot oil pressure chamber 88 ofthe modulatorvalve Mv are also communicated with the oil tank R, and the valve body 86 ofthe modulator valve Mvis held in the open position as shown bythe spring force ofthe spring 87 and the pressing force resulting from the governor pressure Pg introduced into the second pilot oil pressure chamber 88' through the signal oil passage 471' and therefore, the interior of the oil pressure chamber 14 ofthe direct coupling clutch Cd has atmospheric pressure.

On the other hand, since a part of the line pressure Pl is introduced into the torque converter through the throttle 33, the piston 13 ofthe direct coupling clutch Cd is movedleftwards bythe internal pressure ofthe torque converterTto place the clutch Cd in a released state.

When the vehicle speed increases from said condition and the middle-speed stage clutch C2 is actuated by being supplied with the operating oil pressure from the operating oil passage 412, said oil pressure is simulataneously introduced into the first pilot oil pressure chamber 81 ofthetiming valve Tv via the oil passage 412' and the first input port 83. The valve body 80 is shifted to the right first switching position by said introduced oil pressure, and therefore, the oil pressure ofthefirst input port 83 passes through the output port 84, then passes through the input and output ports 89,90 of the modulator valve Mv in the open position from the output oil passage 85 and then is introduced into the oil pressure cylinder 14 of the direct coupling clutch Cd via the output oil passage 91.

At the same time, in the modulatorvalve Mv, the oil pressure of the input port 89 acts even on the first pilot oil pressure chamber 88 through the throttle 92, and said oil pressure imparts the rightwardly moving force to the valve body 86. When said rightwardly moving force overcomes the leftwardly moving force ofthe spring 87 and the governor pressure Pg introduced into the second pilot oil pressure chamber 88' with respectto the valve body86, the valve body 86 is moved rightwards so as to close the output port 90.

When the relation of these forces is reversed, the valve body 86 is operated so asto open the output port 90.

As a consequence, the output oil pressure ofthe output port 90, that is, the operating oil pressure ofthe direct coupling clutch Cd is controlled from the governor pressure Pg proportional to the vehicle speed to the modulator pressure Pm (see Fig. 3) increased to a given level, said level of increment being determined by the set load of the spring 87.

Accordingly, in Fig. 3, since the modulator pressure Pm is lower than the internal pressure ofthetorque converterT at a level below the vehicle speed v1, the direct coupling clutch Cd cannot be operated (engaged) even if the modulator pressure Pm is introduced into the oil pressure cylinder 14, thus not imparing the torque amplifying function of the torque converterT. It can be understood from the abovedescribed factthatfor example, in Fig. 2, even if the manual valveVm is set to the backward-movement position Re orthe middle-speed stage retaining position II and the middle-speed stage clutch C2 is initially in the operating (engaging) condition, the torque converterT is operated as usual to render possible to start the vehicle.

Also, in Fig. 3, when the vehicle speed v is in the zone of v, < v c v2, the modulator pressure Pm increases as the vehicle speed increases to gradually strengthen the engaging force of the direct coupling clutch Cd to thereby obtain the weak engaging zone of the direct coupling clutch Cd as shown by the sand-like ground in Fig. 4.Thus, when in this zone, the output torque ofthe engine E increases beyond the engaging force of the direct coupling clutch Cd, the direct coupling clutch Cd slips andthetorqueofa part corresponding to the engaging force ofthe direct coupling clutch Cd is subjectto torque amplification via a mechanical transmission system including the clutch Cd andthetorqueofa part abovethe engaging force ofthe direct coupling clutch Cd is subject to torque amplification via a fluid transmission system including a fluid within the torque converterT.

Therefore, after all, under the fixed vehicle speed, the power divisional driving of a variable rate wherein the torque bearing rate of the fluid transmission system increases as the output torque of the engine increases is effected.

When the vehicle speed v enters the high-speed zone of v < v2,the governor pressure Pg introduced into the second pilot oil pressure chamber 88' of the modulator valve Mv increases enough to fully open the valve body86, and therefore, the modulator pressure Pm is increased up to the operating oil pressure ofthe middle-speed stage clutch C2, that is, to the line pressure PI to augment the engaging force ofthe direct coupling clutch Cd to the maximum whereby the strong engaging zone ofthe direct coupling clutch Cd shown by the oblique lines in Fig. 4 is obtained. Thus, in this zone, the direct coupling clutch Cd will not slip and all the outputtorque ofthe engine E can be transmitted efficiently.

When the vehicle speed increases from said state, the operating oil pressure of the middle-speed stage clutch C2 is released to the oil tank Rand the high-speed stage clutch C3 in place of the clutch C2 receives the operating oil pressure from the operating oil pressure 413for operation, that is, when the shift-up is made, said oil pressure is simultaneously introduced into the second pilot oil pressure chamber 81 ' of the timing valve Tv via the oil passage 413' and second input port 83', and the valve body 80 is shifted to the left second switching position by said introduced oil pressure. However, the switching operation of the valve body 80 is slowly controlled by the delayed action ofthethrottle 82to impartthevalve body 80 a given switching time.Since the operating oil pressure of the direct coupling clutch Cd is once released through the oil passage 412' already communicated with the oil tank R during that period, the operation of the direct coupling clutch Cd istemporarily released to prevent occurrence of change gear shock.

When the valve body 80 ofthe timing valve Tv is shifted to the left first switching position, the oil pressure of the second input port 83' is then supplied to the oil pressure cylinder 14 ofthe direct coupling clutch Cd through the modulatorvalve Mv similarto the time when the middle-speed stage geartrain G2 is established as previously described, and the oil pressure is also controlled by the modulator valve Mv in a manner similarto that as previously described.

Such an operation is likewise carried out even at the time of down-shift wherein the operation is switched from the high-speed stage geartrain G3 to the middle-speed stage geartrain G2.

Next, when the operating force is released from the accelerator pedal 102 to decelerate the vehicle, the idle position detecting switch 100 is closed to excite the solenoid 99 to open the needle valve 97, and therefore, the pressure oil within the second pilot oil pressure chamber 88' ofthe modulatorvalve My flows into the discharge oil passage 95 through thethrottle 94.On the other hand, the oil pressu re is supplid to the second pilot oil pressure chamber 88' through the throttle 93 from the signal oil passage 47, '. However, the quantity of oil discharged to the discharge oil passage 95 is greaterthan the quantity of oil supplied to the second pilot oil pressure chamber 88' due to the difference in size between both the throttles 93 and 94 as previously described, and after all, the pressure of the second pilot oil pressure 88' assumes substantially atmospheric pressure.Thus, the modulatorvalve Mv releases the low modulator pressure Pm as indicated by the phantom outlines in Fig. 3, and since the pressure at this time is lower than the internal pressureofthetorque converterTas indicated bythe dotted lines,the direct coupling clutch Cd causes the piston 13to be withdrawn and is placed in a released state. For this reason, the idle zone of the opening degree ofthethrottlevalve is shown in white in Fig. 4.

In this manner, the reverse load generated with the deceleration driving ofthevehicle is transmitted hydrodynamicallytothe engine Ethrough the torque converterTwithout depending on the idle operation ofthe roller 15 of the direct coupling clutch Cd and therefore, the noises and vibrations are alleviated.

Fig. 5 shows a second embodiment of the present invention. In this embodiment, a throttle valve Vt orVt' interlocked with the accelerator pedal 102 is utilized as a means for releasing oil pressure from the second pilot oil pressure chamber 88' ofthe modulatorvalve Mv in the idle zone ofthe opening degree of the throttle valve. That is, an opening and closing valve 103 as a valve device which is opened when the throttlevalve Vt orVt' is returned to the illustrated idle position is provided on the throttle valve, and said opening and closing valve 103 is incorporated in the discharge oil passage 95 branched from the signal oil passage 471,associated with the second pilot oil pressure chamber 88' of the modulatorvalve Mv.A throttle 93 is provided on the signal oil passage 471' at an upstream from the branched portion of the discharge oil passage 95 and a throttle 94 larger in opening degree than that ofthethrottle 93 is provided on the oil passage 95. Otherconstructionsarethe same as those shown in the previous embodiment. In Fig. 5, parts having the same function as that ofthe previous embodiment are given the same reference characters. It is noted that the throttle 94 of the discharge oil passage 95 can be omitted.

Inthis manner,when thethrottlevalvevtorVt' is returned to the idle position, the opening and closing valve 103 is opened, and therefore, the oil pressure of the second pilot oil pressure chamber 88' ofthe modulator valve Mv is discharged to the discharge oil passage 85. Thus, the output oil pressure ofthe modulator valve Mv lowers similarly to the previous embodiment and the direct coupling clutch Cd assumes a released state.

As described above, in accordance with the present invention, a single modulator valve can performs two modes of lock-up control, one wherein the engaging force ofthe direct coupling clutch is controlled in accordance with the variation in vehicle speed, and the other wherein the direct coupling clutch is released underthe idle condition of the engine throttle valve. As a consequence, the present invention has effects inthatthe device can be materially simplified and that a loss of leakage of pressure oil from the valve can be minimized.

Fig. 6 shows a third embodiment of the present invention.Thisembodiment is differentfromthe previous embodiment in a timing valve Tv in the lock-up control device Dc. That is, the timing valve Tv comprises a spool valve body 80 which is moved between a right first switching position and a left second switching position, a first pilot oil pressure chamber 81 to which a left end surface ofthe valve body 80 faces, a second pilot oil pressure chamber ' to which a right end surface of the valve body 80 faces, and a spring 105 for biasing the valve body 80 rightwards,wherein an oil passage412' branched from an operating oil passage 412 of a middle-speed stage clutch C2 is connected to the second pilot oil pressure chamber 81 ', the first pilot oil pressure chamber 81 being communicated with an oiltank R through an oil passage 104. The valve body 80 is provided in a circumferential surfacethereofwith two annular grooves 106,107. When the valve body 80 is in thefirstswitching position as shown, the input oil passage 411' branched from the operating oil passage 411 ofthe low-speed stage clutch C1 and led to the timing valve Tv is communicated with an output oil passage 85 ofthe timing valvi ievthrnugh the annular groove 106, and when the valve body 80 is moved leftwards to assume the second switching position,the oil passage 41' is communicated with the oil passage 85 through the annular groove 107.In the position halfwaywherein the valve body 80 is moved between the first switching position and the second switching position, the output oil passage 85 is temporarily shut offfrom the input oil passage 411' and is communicated with the oil tank R. Other constructions are the same asthoseshown in the previous embodiment. In Fig. 6, parts having the same function as that ofthe previous embodiment are given the same reference characters.

In this embodiment, when the vehicle speed increases and the shift valve V1 is switched due to the difference between the governor pressure Pg and the throttle pressure Pt and the operating oil pressure is supplied from the operating oil passage 412 in orderto establish the middle-speed stage geartrain G2so that the middle-speed stage clutch C2 is actuated, said oil pressure is simultaneously introduced into the second pilot oil pressure chamber 81' ofthetiming valveTv through the oil passage412', by which introduced oil pressure, the valve body 80 is shifted to the left second switching position. The operating conditions ofthe timing valveTv during that period are shown in Figs. 7 A-D.

First, Fig. 7A shows the state similarto Fig. 6 in which the oil pressure is not applied to the second pilot oil pressure chamber 81'. In this case, the oil passage 411' is communicated with the oit passage 85 through the annular groove 106. When the vehicle speed increases and the pressure of the oil passage 412 is increased by the switching operation of the shift valve Vt orV2, the pressure within the second pilot oil pressure chamber81 is increased through the oil passage 412'. When this pressure becomes greater than the set load of a spring 108, thevalve body 80 begins to be moved leftwards and the oil passage 41, is closed as shown in Fig.7B. The oil passage 85 also remains closed, and the modulator pressure Pm is maintained constant. When the pressure within the second pilot oil pressure chamber 81 'further increases, the valve body 80 is further moved leftwa rds and the oil passage 85 is communicated with the oil passage 104 as shown in Fig. 7C whereby the pressure oil within the oil passage 85 is circulated to the oil tank R. Thus, the modulator pressure Pm lowers and the piston 13 ofthe direct coupling clutch Cd is moved leftwards to releast the lock-up.When the pressure within the second pilot oil pressure chamber ' further increases and the valve body 80 is further moved leftwards, the output oil passage 85 is shut off from the oil passage 104 as shown in Fig. 7D and connected to the input oil passage 411' through the annular groove 1 07.Thus, the oil pressure ofthe input oil passage 411' passes through the output oil passage 85, thence passes th rough the input and output ports 89,90 of the modulatorvalve Mv in the open position, and is again introduced into the oil pressure cylinder 14ofthe direct coupling clutch Cd.

Fig. 8 represents the variation ofthe modulator pressure Pm, that is, the engaging force ofthe direct coupling clutch Cd, with the time given by the abscissa. As will be apparentfrom Fig. 8, during the variation of the oil pressuretransmittedthrough the oil passage 412,,that is, during the change gear operation, the modulator pressure Pm is lowerthan the internal pressure Pc of the torque converter T and the operation ofthe direct coupling clutch Cd is temporarily released.

When the vehicle speed increases and the middlehigh speed shift valve V2 is actuated and the highspeed stage clutch C3 receives the operating oil from the operating oil passage 413 for operation, that is, when the shift-up is effected, the operating oil pressure of the middle-speed stage clutch C2 is simultaneously released to the oil tank Rand therefore, the oil pressure within the second pilot oil pressure chamber 81 ' ofthetiming valve Tv is also released to the oil tank R through the oil passage 412'.

Thus, the valve body 80 is moved rightwards by the biasing force of the spring 108. Atthis time, the timing valve Tv is operated in orderofthe mode of Figs. 7C, 7B and 7Afrom the mode of Fig. 7D. Thus, even at the change geartime, the modulator pressure Pm is temporarily lowered to release the operation ofthe direct coupling clutch Cd.

The above-described operation is likewise carried out atthetime of shift-down, wherein the high-speed stage geartrain G3 isshifted to the middle-speed stage geartrain G2 and the middle-speed stage geartrain G2 is shifted to the low-speed stage gear train G1. In either case, connection and interruption of the middle-speed stage clutch C2 are detected wherebythetiming valve Tv is operated and the direct coupling clutch Cd is temporarily released.

According to this embodiment, in the timing valve Tv, only the modulator pressure Pm is lowered without connecting the operating oil pressure ofthe low-speed stage clutch C1 with the oil passage 104 in communication with the oil tank R, to release the engagementofthe direct coupling clutch Cd. Therefore, it is not feared that the operating oil pressure of the low-speed stage clutch C1 is excessively lowered with the result that the clutch C, slips to shorten the service life.

Fig. 9 shows a fourth embodiment of the present invention. This embodiment is differentfrom that of Fig. 6 in the control device Dc and in a source ofthe operating oil pressure of the direct coupling clutch Cd, the source being the discharge side of the oil pressure pump P, that is, the line pressure PI. However, the operation therefor is almostthe same and therefore, parts in Fig. 9 corresponding to those of Fig. 6 are given the same reference characters.

The control device Dc has a modulator valve Mvfor generating a variable modulator pressure Pm by the governor pressure Pg guided through the oil passage 47i', similar to the embodiment of Fig. 6, and the timing valveTv is connected at the downstream side of the modulatorvalve Mv. An oil passage 104 branched from an output oil passage 91 of the modulator valve Mv and connected to the oil tank R is opened and closed by the timing valve Tv. The valve body 80 ofthe timing valve Tv is moved from the first switching position to the lower second switching position as shown by the operating oil pressure of the middle-speed stage clutch C2. The valve body 80 closes the oil passage 104 atthefirst switching position and second switching position.That is, when the operating oil pressure ofthe middle-speed stage clutch C2 is the maximum and zero, namely, atmospheric pressure, the oil passage 104 is closed to transmitthe output oil pressure of the modulator valve My to the direct coupling clutch Cd. However, in the halfway ortransit stage, the oil passage 104 is opened to connectthe oil pressurecylinderl4ofthe direct coupling clutch Cd with the oil tank R to release the operation thereof. Ath rottle 108 is provided at an upstream from the branched point of the oil passage 104 in order to sufficiently reduce the pressure within the oil pressure cylinder 14.

In this embodiment, even when the manual valve Vm is shifted to the middle-speed stage retaining position lI,the oil passage 46 (see Fig. 6) is pressurized to generate the governor pressure Pg, and therefore, thedirectcouplingclutch Cd can be actuated.

Fig. 10 shows a fourth embodimentofthe present invention. Also in this embodiment, the line pressure PI is used as an oil pressure source similarly to the embodiment of Fig. 9.

A spool valve body 111 of the modulator valve Mv is biased towards the open side as shown by means of a spring 112 and biased toward the right open side by the oil pressure ofthe output oil passage 113. A part of the output oil pressure is guided also to the oil pressure chamber 114. This oil pressure chamber 114 is connected to the oil tank R through the oil passage 115which is in turn opened and closed by a pilot valve 107 driven buy a solenoid 116. The pilot valve 117 is always biased by a spring 118 and normally closes the oil passage 115. However, when the solenoid 116 is excited, the oil passage 115 is opened to release the oil pressure chamber 11 4to the oil tank R. Thus, when the solenoid 116 is deenergized, the oil pressure applied to the valve body 111 ofthemodulatorvalveMvis equal to each other on both sides thereof and the valve body 111 remains positioned as shown by the force of the spring 112. Therefore, the line pressure Pl is released to the oil passage 113 but when the solenoid 116 is excited, the valve body 111 is moved rightwards and a fixed pressure lower than the line pressure Pl determined by the strength of the spring 112 is released to the oil passage 113.

A lock-up release valve Rv is connected to the output oil passage 113Ofthe modulatorvalve Mv.Aspool valve body 119 ofthe lock-up release valve Rv is biased rightwards by a spring 1 20.The oil pressure of the oil passage 113 is guided through a throttle 122 to an oil pressure chamber 121 on the right side of the lick-up release valve Rv. This oil pressure chamber 121 is connected to the oil tank R through an oil passage 123 which is in turn opened and closed by a pilot valve 124. The pilot valve 124 is driven by a solenoid 125, and when the solenoid 125 is deenergized, the oil passage 123 is closed by a spring 126 but when the solenoid 125 is excited, the oil passage 123 is opened.

Thus, when the solenoid 125 is deenergized, the valve body 119 assumes a position shown leftwardly by the pressure oil supplied to the oil pressure chamber 121 throughthethrottle 122 to connectthe oil passage 113 to the output passage 127 to guide the oil pressure of the oil passage 123 to the oil pressure cylinder 14 of the direct coupling clutch Cd. When the solenoid 125 is excited, the oil pressure chamber 121 is open to the oil tank R, and the valve body 119 is moved rightwards by the force ofthe spring 120 to place the oil passage 127 in communication with the oil tank R to releasethe operation ofthe direct coupling clutch Cd.

These two solenoids 116 and 125 are excited or deenergized by an electronic circuit 128. This electro nic circuit 128 control the solenoids 116,125 in response to signals from a vehicle speed detector 129 and an engine load detector 130. For example, the solenoid 116 isturned On when the vehicle speed is for example below 60 Km/h and turned ON when it is above 60 Km/h. The solenoid 125 is turned ON when the engine is in the idle condition and turned OFF when the engine is in the other conditions, or said solenoid is turned ON when the vehicle speed is for example below 20 Km/h and turned OFF when the vehicle speed is above 20 Km/h. In this manner, until the vehicle speed reaches 20 Km/h afterthevehicle started, the direct coupling clutch Cd is released bythe function of the solenoid 125 and the function of the torque converterT can be utilized.Atthe vehicle speed lower than 60 Km/h, even if the direct coupling clutch Cd is actuated, the engaging force thereof is weak.

Whenthethrottle pedal istrod,a relative motion occurs between the pump vane wheel 2 ofthetorque converterT and the turbine vane wheel 3 even during the operation of the direct coupling clutch Cd. There assumes the power divisional operation wherein a part of power is transmitted even through the torque converterT.

The pressure oil within the pilot oil pressure chamber 121 of the release valve Rv is discharged to the oil tank R by the excitement ofthe solenoid 125 as described above and at the same time, a part of the oil pressure is discharged at a certain time during the change gear operation even bythetiming valve Tv provided parallel to the release valve Rv. The con struction and operation ofthetiming valve Tv are the same as those shown in Fig. 9 and therefore the explanation thereof will be omitted. Ifthe pressure oil within the pilot oil pressure chamber 121 is discharged, the operation of the direct coupling clutch Cd is released and therefore the intended object can be achieved.

In accordance with this embodiment, sincethe direct coupling clutch Cd ofthe torque converterT can be actuated irrespective of the shift position of the manual valve Vm,thetorque converterT can be locked up in three ranges, namely, the drive position D, middle-speed retaining position II and backwardmovement position Re.

Furthermore, in accordance with this embodiment, the timing valve Tv is used asthe pilot valve, and the operating oil is circulated bythe release valve Rv from the oil pressure cylinder 14 ofthe direct coupling clutch Cd to the oil tank R. Therefore, despite the fact thatthetiming valve Tv itselfis simple as in the embodiment shown in Fig. 9, the engagement and release of the direct coupling clutch Cd can be carried out more accurately.

As described above, in the present invention, the direct coupling clutch is actuated bythe signal pressure increased or reduced by the selection of either geartrain and the oil pressure source for generating oil pressure in common even ifeithergear train is selected, and when the signal pressure varies, the operation ofthe direct coupling clutch is released.

For example, if an arrangement is made so asto detect and control the operating oil pressure ofthe middlespeed stage clutch, the release of coupling and re-coupling ofthe direct coupling clutch can be effected efficiently atthe time of two change gear modes, that is, the low-speed stage to middle-speed stage and the middle-speed stage to high-speed stage. Asingletiming valve orthe like used will suffice, and therefore, the construction of the device is simple and the reliance is high. In addition, sincethe locking-up ofthetorque converteroverthree adjacent speed ratios may be achieved, fuel cost can be materially improved.Even in the automatic transmissionwith fourstages offorward, if the locking-up is made with three stages, the second, third and top, the fuel cost equal to that ofthe geartransmission can be expected.

Fig. 12 shows a sixth embodiment of the present invention.This embodiment is different from the previous embodiment in the control device Dc. This control device Dc comprises a timing valve Tv, a modulator valve Mv and an ON/OFF valve Vo which are hydraulically connected in series. Here, the order of connection of these valves is not limited to the illustrated order but other orders may be employed.

The timing valve Tv is provided to temporarily release the lock-up condition of the direct coupling clutch Cd atthe time of change gear and comprises a spool valve body 285 which is moved between a right firstswitching position and a left second switching position,a pilotoil pressure chamber 286to which a left end surface of the valve body 285 faces, a second pilot oil pressure chamber 287 to which a right end surface of the valve body 285 faces, and a spring 288 for biasing the valve body 285 rightwards, wherein an oil passage412' branched from the operating oil passage 412 ofthe middle-speed stage clutch C2 is connected to the second pilot oil pressure chamber 287, and the first pilot oil pressure chamber 286 is communicated with the oil tank R through an oil passage 290. The valve body 285 is provided in the outer circumference thereof with two symmetrical left and rightannular grooves 292,293 with a iand 291 sandwiched therebetween.When the valve body 285 is in the first switching position as shown, the oil passage 411' branched from the operating oil passage 411 to the low-speed stage clutch C1 is communicated with an output oil passage 294 to the modulatorvalve Mv.Thiscondition remains unchanged even when the valve body 285 is in the left second switching position but in the position halfway wherein the valve body 285 is moved between the first switching position and the second switching position, the output oil passage 294 is temporarily shut off from the oil passage 411' and is communicated with onlythe oil passage 283 branched from the lubricating oil passage 38.

For example, in the event that the valve body 285 is movedfromthe first switching position to the second switching position as shown, the oil passage 284 is firstctosed by the land 291, the oil passage 283 is then communicated with the output oil passage 294 and the output oil passage 294 is closed passing through the land 291. Then, the output oil passage 294 is again communicated with the oil passage 411'. Conversely, in the eventthatthe valve body 285 is moved rightwards from the second switching position to the first switching position, the land 291 first closes the output oil passage 294, the output oil passage 294 is then communicated with the oil passage 283, the oil passage 283 is closed and finally the output oil passage 294 is communicated with the oil passage 411'.

Wherrthe valve body 285 is in the position as shown, the oil passage 285 is communicated with the oil tank Rthrnughthefirstpilotoil presssure chamber 286 but the valve body 285 is moved leftwards during the engagementofthe middle-speed stage clutch C2 and communicatedwith the oil passage 283 but shut off fromtheoittankR.

The modulator valve Mv is provided to form the lock-up engaging force with the governor pressure Pg serving as a base and comprises a spool valve body 296which is moved between a right closed position anda leftopen position, a spring 297 for biasing the valve body296towards the open position, a first pilot oil pressure chamber 298 to which a left end surface of thevalve body 296 faces, a second pilot oil pressure chamber 299 to which a right end surface ofthe valve body 296 faces, an input port 300 and an output port 301. The input 300 is connected to the output oil passage 294 of the timing valve Tv, and the output port 301 is connected to the oil passage 302. The first pilot oil pressure chamber 298 is always communicated with the output port 301 through a throttle 103 provided on the valve body 296.

The second pilot oil pressure chamber 299 is connected through a high-select valve Vs to the oil passage 295 and to the oil passage 471 ' branched from the first signal oil passage 471 which guides the governor pressure Pg. The high-select valve Vs is constructed such that a spherical valve body 326 is housed within a casing 325 which concentrically connects the oil passage 295 and oil passage471'.The high-select valve Vs comparesthe oil pressure of the oil passage 295, namely, the lubricating oil pressure Puorzero (atmospheric pressure)with the oil pressure of the oil passag e 471', na namely, the governor pressure Pg, and the higher pressure among them is introduced into the second pilot oil pressure chamber 299 ofthe modulator valve Mv.

The ON/OFF valve Vo is provided to release the lock-up of the direct coupling clutch Cd when the opening degree ofthrottle is in the idle position and comprises a spool valve body 305 which is moved between a right closed position, that is, a lock-up release position and a left open position, a spring 306 for biasing the valve body 305 towards the closed side, a first pilot oil pressure chamber 307 to which a left end surface of the valve body 305 faces, and a second pilot oil pressure chamber 308 to which a right end surface ofthe valve body 305 faces. The input port is communicated with the oil passage 302from the modulator valve Mv, and the output port is communicated with the interior of the oil pressure cylinder of the direct coupling clutch Cd th rough an output oil passage 309.The second pilot oil pressure chamber 308 is connected to an oil passage 310 branched from the oil passage 282 which guides oil pressure prop ortional to the opening degreeofthethrottle ofthe engine E to back-pressure chambers of the accumulators72 and 73 from the valve Vt', and the first pilot oil pressure chamber307 is connected to the oil tank R.

The ON/OFF valve Vo is opened when the output of the valve Vt',that is, the oil pressure proportional to the opening degree of the throttle ofthe engine E overcomes the spring force of the spring 306 to guide the output ofthe modulatorvalve Mvto the oil pressure cylinder 14 of the direct coupling clutch Cd.

When the output of the valve Vt' is smallerthan the springforceofthespring 306,thevalveopensto bring the oil passage 309 into communication with a release port 311, and the oil pressure within the oil pressure cylinder 14 is released to the oil tank R.

While the oil pressure from the valve Vt' provided to alleviate the shock at the time of change gear is exerted on the second pilot oil pressure chamber 308, it is noted that in principle, the throttle pressure Pt from the throttle valve Vtcan be exerted thereon.

Next, the operation of thins embodimentwill be explained. The lock-up control of the direct coupling clutch Cd is effected only when the manual valve Vm is in the drive position D and therefore, only this case will be explained.

First, when the vehicle is started with the manual valve Vm shifted to the drive position D, the oil pressure is not exerted on the oil passage 289 because the change gear ratio is initially in the low-speed stage, and thus the timing valve Tv is inthefirst switching position shown in Fig. 12. The oil pressure ofthe oil passage 295 is zero, and the governor pressure Pg from the oil passage 47,'is exerted on the second pilot oil pressure chamber 299 of the modula torvalve Mv from the high-select valve Vs.

At that time, in the modulator valve Mv, the oil pressure ofthe output port 301 is exerted on the first pilot oil pressure chamber 298 through the throttle 303, and said oil pressure imparts the rightwardly moving force to the valve body 296. When this rightwardlymoving force overcomesthe leftwardly moving force for the valve body 296 resulting from the spring 297 and the governor pressure Pg introduced into the second pilot oil pressure chamber 299, the valve body 296 is moved rightwards so as to close the inputport300.Whentherelation oftheforces therebetween is reversed, the valve body 296 is operated so asto open the input port 300.As a consequence, the output oil pressure of the output port 301, that is, the operating oil pressure ofthe direct coupling clutch Cd is increased to a fixed level from the governor pressure Pg proportional to the vehicle and is as shown by the curve a in Fig. 13. When the operating oil pressure reaches the vehicle speed A above the internal pressure Pcofthetorque converter T, the piston 13 ofthe direct coupling clutch Cd is moved rightwards at a speed above said vehicle speed, the direct coupling clutch Cd is engaged and the torque converter T is locked up.

When the vehicle speed further increasesto establish the change gear ratio ofthe middle-speed stage, the timing valve Tv is moved leftwardstoassumethe second switching position and the oil passage 295 is communicated with the oil passage 283. Therefore, the oil pressure guided from the high-selectvalve Vs to the second pilot oil pressure chamber 299 ofthe modulatorvalve Mv is a higher one among the governor pressure Pg or lubricating oil pressure Pu, and the oil pressure resulting from the increase in such higher oil pressure is the output oil pressure of the modulatorvalve Mv, that is,the operating oil pressure of the direct coupling clutch Cd.The magnitude of the lubricating oil pressure Pu can be selected as shown in Fig. 13 to thereby make the aforesaid operating oil pressure higherthan the internal pressure Pe of the torque converterT as shown in the curve (3,and the direct coupling clutch Cd can be locked up at a speed lowerthan the vehicle speed A. In Fig. 13, a slightly right and upward indication ofthe lubricating oil pressue Pu results from the phenomen wherein the quantity of surplus oil increases with the increase in vehicle speed, that is, with the increase in the number of revolutions of the engine E, but it can be considered to be approximately horizontal.

In case ofthe change gear ratio ofthe high-speed stage, it is limited thatthe lock-up operation ofthe direct coupling clutch Cd is effected at a speed above the vehicle speed A, butthere practically poses no problem as shown in Fig. 14. That is, in Fig. 14 showing the typical characteristic map of the hyd raulicautomatictransmission,threezones 1, II and Ill defined by the dotted lines designate the low-speed zone, middle-speed zone and high-speed zone, respectively. Since the zone Ill ofthe high-speed zone is limited to the speed above the vehicle speed, there is no actual harm.On the other hand, in the middle speed zone 11, the lock-up operation can be made in its whole zone, and the actual fuel cost is improved.

While it is obvious if one assumes the time the vehicle is stopped, when the shift-down is made to the low-speed stage, the lock-up condition is released at a speed below the vehicle speed A. Thus, the possibility ofthe engine stop can be avoided without using a special switching valve which performs the switching operation in response to the vehicle speed. The horizontal line indicated bythesolid lines in Fig. 14 designates the lock-up release line bythe action ofthe ON/OFF valve Vo.

While in this embodiment, the switching ofthe action ofthe lubricating oil pressure Pu to the oil passage 295 has been performed by the timing valve Tv, an exclusive-use switching valve forthe purpose of such switching can be provided separately from the timing valve Tv. In addition, while the governor pressure Pg and lubricating oil pressure Pu have been introduced into the high-select valve Vs, oil pressure from another oil pressure generating means for generating a substantially fixed oil pressure in responseto the operation ofthe engine E, in place ofthe lubricating oil pressure Pu, can be introduced into the high-selectvalve Vs.

Fig. 15 shows another structure ofthetiming valve.

In this timing valve Tv, between a port 283a to which is connected the oil passage 283 and a port 294a to which is connected the oil passage 294 is provided a further port 328 which is in turn communicated with the oil tank R. According to this embodiment, when the valve body 285 is moved rightwardsto assume the firstswitching position, the oil passage295 iscom- municated with the oil tank R through the port 328, and the oil pressure of the oil passage 295 is zero.

While the function similarto the timing valve Tv in Fig.

12 can be performed even by the timing valve Tv, the timing valve Tv in Fig. 12 can be constructed to be more compactthanthe other. In the timing valve Tv in Fig. the description has been made such that when the valve body 285 is moved between the first switching position and the second switching position, the oil passage 283 is temporarily com municated with the output oil passage 294 to releasethe lock-up, but this is limited to the case where the lubricating oil pressure Pu is lower than the internal pressure Pcof the torque converterT. Otherwise, a port 328 in communication with the oil tank R need be provided asinthetimingvalveTvin Fig. 15.

The oil passage 411' branched from the oil passage 411 for supplying the operating oil to the low-speed stage clutch C1 is connected to the timing valve Tv in Figs. 12 and 15 because the lock-up ofthetorque converter T is effected only at the drive position D, and in orderthatsaid lock-up is effected atthe middlespeed retaining position II, the oil passage branched from the oil passage 43 can be connected thereto.

While the aforesaid timing valve Tv is madeto have the switching function ofthe lubricating oil pressure Pu, it will be noted that an exclusive-use switching valve for switching the lubricating oil pressure can be provided separately from these timing valves Tv.

Fig. 16 shows an embodiment in which the lock-up ofthetorque converterT is effected cnly atthe time of change gear ratios of the middle-speed stage and high-speed stage. Atiming valveTv is interposed between the oil passage 412' branched from the oil passage 412 (see Fig. 12) for supplying the operating oil to the manual valve Mv and middle-speed stage clutch C2 and the oil passage 413' branched from the oil passage 4l3for supplying the operating oil to the high-speed stage clutch C3.This timing valveTv comprises a spool valve body 331 which is moved between a leftfirstswitching position and a right second switching position, a first pilot oil pressure chamber 332 to which a left end surface of the valve body 331 faces, and a second pilot oil pressure chamber to which a right end surface ofthe valve body 331 faces, wherein the first pilot oil pressure chamber 332 is communicated with the oil passage 413' through a throttle 334, andthe second pilot oil pressure chamber 333 is communicated with the oil passage 412' through a throttle 335.Thus, when the change gear ratio ofthe middle-speed stage is established, the valve body 331 is in the leftfirst switching position and the oil passage 412' is communicated with the output oil passage 294. When the change gear ratio of the high-speed stage is established, the valve body 331 is in the right second switching position, and the oil passage 413' is communicated with the output oil passage 294. Since the lock-up is not effected at the low-speed stage, the oil passage 283for guiding the lubricating oil pressure Pu is directly connected to the high-select valve Sv.

According to this embodiment, when the change gear ratios ofthe middle-speed stage and high-speed stage are established, torque coverterT is locked up, and therefore, this mode is distinguisded from the embodiment in connection with Fig. 14 in which the torque converterT is not locked up at a speed below the vehicle speed A.

Fig. shows an embodiment in which the lubricating oil pressure Pu is so high that the lock-up may be effected only by itself. In this embodiment, it is not necessary to increase the lubricating oil pressure Pu bythe modulatorvalve Mv. Therefore, the high-select valve Vs is arranged so that the oil pressure of the output oil passage 302 from the inodulatorvalve My is compared with the oil pressure of the oil passage 283 for guiding the lubricating oil pressure Pu, and the higher oil pressure resulting therefrom is guided to the ON/OFF valve Vo.

Fig. 18 shows an embodiment in which the operation release ofthetorque converterT are controlled in response to the vehicle speed. A second pilotoil pressure chamber308 ofthe ON/OFFvalveVo is connected to the oil tank R through the switching valve Vc. This switching valve Vc comprises a spool valve body 340 which is moved between a left closed position and a right open position, a spring 341 for biasing the valve body 340 towards the open side, a first pilot oil pressure chamber 342 to which a left end surface of the valve body 340 faces, and a second pilot oil pressure chamber 343 to which a right end surface of the valve body 340 faces.An oil passage 344 branched from an oil passage 310 for guiding the oil pressure proportional to the opening degree of the throttle of the engine E to the second pilot oil pressure chamber 308 ofthe ON/OFF valve Vo is connected to the first pilot oil pressure chamber 342, and an oil passage 345 branched from the oil passage 471 ' for guiding the governor pressure Pg is connected to the second pilot oil pressure chamber 343. The second pilot oil pressure chamber 308 of the ON/OFF valveVo is connected to an input port 346 through an oil passage 347, and an output port 348 is connected to the oil tank R.

In accordance with this embodiment,when the vehicle speed lowers, the valve body 340 is moved rightwardsto bring the input port346 into com munication with the output port 348, the oil pressure within the second pilot oil pressure chamber 308 is released to the oil tank R to close the ON/OFF valve Vo, and the oil pressure within the cylinder 14 in the direct coupling clutch Cd is released to the oil tank.

Accordingly, the lock-up condition of the torque converter T is forcibly released at a speed below the vehicle speed, and therefore, the lock-up zone in the low-speed stage can be enlarged towards the lower speed side.

While in any ofthe above-described embodiments, the description has been made ofthe automatic transmission of three stages of forward, it will be noted that in the automatic transmission of four stages of forward, the torque converterTcan be locked up at each of change gear stages, namely, the second, third and top. In that case, it is necessary to use an oil pressure source which can be increased at each of change gear stages, namely, the second, third and top but cannot be increased at the change gear stage of low gear. Such an oil pressure source used is the oil pressure of the output oil passage 70 of the low-middle speed shift valve V1.

While in the foregoing, the clutches C1, C2 and C3 are increased in pressure to establish the gear trains G1, G2and G3, respectively, it will be noted that in case of using brake bands, the clutches are reduced in pressure to establish the gear trains G1,G2 and G3, respectively. It will be apparentthat even in such a case adjust mentioned, movement of the aforesaid timing valveTv is merely reversed and the similar operation is obtained.

Moreover, while in the above-described embodiments, the direct coupling clutch Cd used was of the roller type, it is noted that othertypes of the direct coupling clutch can be used. For example, the direct coupling clutch includes one which is the disktype with a facing material adhered thereto, which receives the internal pressure ofthetorque converterTto couplethe input and output members. This can be easily applied by an arrangement wherein for example, a timing valve is used as a pilot valve and an orginal control valve is shifted to an inoperative position.

As described above, in the present invention, there are provided an oil pressure generating means for generating oil pressure of a fixed level in response to the operation of the engine and a selection means for comparing the governor pressurefrom the governor valve with the oil pressure generated by said oil pressure generating means to select and release a higher oil pressure among them, and the output ofthe selection means is used as an index for controlling the engaging force ofthe direct coupling clutch. Therefore, even during the running at the change gear ratio ofthe low-speed stage, the engaging oil pressure necessaryfor locking up the torque converter can be secured and the problem of vibrations in the middlespeed zone can be solved to considerably improve the practical fuel cost. Furthermore, if a switching valve is provided to switch a supply of the operating oil pressure to the direct coupling clutch, the zone that may lock up the torque converter is extended to a lower speed zone. Yet, since the direct coupling clutch is ofthe power divisional type, even ifthetorque converter is locked up in the low-speed zone, it is not feared that the performance of power is deteriorated and the vibration ofthe vehicle body is increased. As a result, the governor pressu re can be set so as to have the characteristic most suitable forthe change gear to increase the freedom of design.

Moreover, a control means for interrupting between a selecting means and an oil pressure generating means when the gear change ratio ofthe low-speed state is established is interposed between the selecting means and the oil pressure generating means.

Therefore, the characteristic wherein the governor pressure is rapidly lowered in response to the lowering of the vehicle speed can be utilized to release the lock-up condition ofthetorque converter in the change gear ratio of the low-speed stage. Accordingly, it is possible to extend the lock-up zone to the lower speed zone without occurence of the engine stop in the low-speed zone, without provision of an exclusiveuse switching valve of which switching mode varies with the vehicle speed, and possible to improve the practical fuel cost.

Claims

1. In an automatic transmission comprising a fluid type torque converter having an input member including a pump vane wheel and an output member including a turbine vane wheel, and an auxiliary transmission having one or plural stages of gear trains through which the torque of said output member is transmitted to driving wheels, a lock-up control device for a torque converter in an automatictransmission for vehicle comprising a hydraulic direct coupling clutch having a slip characteristic provided between the input and output members of the torque converter and capable of mechanically coupling said both members and a modulator valve disposed in an oil passage for connecting an oil pressure cylinder of said direct coupling clutch with an oil pressure source, said modulatorvalve being composed of a valve body for opening and closing said oil passage, a spring for biasing said valve body in a valve-opening direction, a first oil pressure chamberfor introducing pilot oil pressure for biasing said valve body in a valve-closing direction from an input port side of said modulator valve, and a second pilot oil pressure chamber for introducing pilot oil pressure for biasing said valve body in the valve-opening direction, wherein an output side of a device for generating oil pressure proportional to vehicle speed for releasing oil pressure which is changed proportional to the vehicle speed is connected through a throttleto said second pilotoil pressure chamber and a valve device for detecting the idle state of an engine throttle valve to release said second pilot oil pressure chamberto atmosphere is connected to said pilot oil pressure chamber.

2. In an automatic transmission comprising a fluid type torque converter having an input member and an output member; a hydraulic direct coupling clutch provided between the input and output members and capable of being actuated to mechanically coupling said both members; an auxiliary transmission connected to said torque converter and having plural stages of geartrains, said auxiliarytransmission capable of being changed in speed to a plurality of speed ratios by selection of said geartrains; and a control mechanism for automatically effecting the selection of geartrains of said auxiliarytransmission in accordance with the running condition of the vehicle, a lockup control device for a torque converter in an automatictransmission forvehicle comprising signal pressure which is increased or reducedwhen one of & id gear trains is selected so as to assume a certain speed ratio and which is conversely reduced or increasedwhen the otherofgeartrains is selected so as to assume a speed ratio adjacent to the ?iist- mentioned speed--ratio,a lock-up actuating means-for actuating saiddirntt coupfing clutch by common oil: pressure even when-eithergeartrain is selecd, and a release means for detecting a variation in saio' signal pressure to release The lock-u-p said direct coupling clutch during a periodiof said variation.

3. A control device as defined in claim 2 wherein there are more than-three stages ofsaid geartrains, and even when eithergeartrain among three stages thereofisselected,thecommon oil pressu re compris- es said oil pressure source.

4. A control device asdefinedinclaim 2 or 3 wherein said release means can release the lock-up of the direct coupling clutch when said signal pressure is between two already set values different from each other and can stop the release ofthe lock-up when said signal pressure is nottherebetween.

5. A control device as defined in claim 2 or 3 wherein said direct coupling clutch has an oil pressure cylinder adapted to effectthe lock-up function by the introduction of pressure of said oil pressure source, and said release means has a control valve provided in an oil passage connecting these oil pressure source and oil pressure cylinderto selectively switch said oil pressure cylinderto said oil pressure source or an oil tank in accordance with said signal pressure.

6. In an automatic transmission for a vehicle comprising a fluid type torque converter having an input member and an output memberto which the output ofthe engine is transmitted; a hydraulic direct coupling clutch provided between said input and output members and capable of being actuated to mechanically engage said both members; an auxiliary transmission connected to the output member of said torque converter and having plural stages of gear trains, said auxiliary transmission capable of being changed in speed to a plurality of speed ratios by selection of said geartrains; and a control mechanism having a governorvaiveforreleasing governor pressure proportional to the vehicle speed and automatically selecting the geartrain of said auxiliary transmission in accordance with the running condition of the vehicle, a lock-up control device for a torque converter in an automatictransmission forvehicle comprising an oil pressure generating means for generating oil pressure at a substantially given level at all times during the operation ofthe engine; and a selection means for comparing the governor pressure from said governorvalve with the generated oil pressure of said oil pressure generating means to select higher one of oil pressure, output pressure of said selection means being used as an index for controlling the engaging force of said direct coupling clutch.

7. A control device as defined in claim 6 wherein said oil pressure generating means comprises a pressure regulator valve which makes a water head for lubricating various parts ofthe automatictrans- mission.

8. In an automatic transmission for vehicle comprising a fluid type torque converter having an input member and an output memberto which the output of the engine is transmitted; a hydraulic direct coupling clutch provided between said input and output members and capable of being actuated to mechanically engage said both members; an auxiliary transmission connected to the output member of said torque converter and having plural stages of gear trains, said auxiliary transmission capable of being changed in speed to a plurality of speed ratios by selection of said gear trains; and a control mechanism having a governor valve for releasing goverpressure proportional tothevehicle speed and automatically selecting the geartrain of said auxiliary transmission in accordancewith the running condition ofthe vehicle, a lock-up control device for a torque converter in an automatic transrrlission forveh icle comprising an oil pressure generating means for generating oil pressure at a substantially given level at all times during the operation of the engine; a selecting means for comparingthe governor pressure from said governorvalve with the generated oil pressure of said oil pressure generating means to select higher one of oil pressure; and an interruption means interposed between said selection means and said oil pressure generating means to cut-offaconnection between said selection means and said oil pressure generating means when the speed ratio ofthe low speed stage is establised, output pressure of said selection means being usedasan index forcontrolling the engaging force of said direct coupling clutch.

9. A control device as defined in claim 8 wherein said interruption means comprises a switching mechanism which is interlocked with the establish mentofthespeed ratio ofthe middle-speed stage to releasethecut-offcondition between the selection means and the ail pressure generating means and whichreleasestheengaging condition of said direct coupling clutch at the time of shifting the mode from said cut-off condition to the associated condition between the selection means and the oil pressure generating means and atthetime of shifting the mode from the associated condition to the cut-off condition.

10. An automatic transmission substantially as hereinbefore described with reference to Figures 1 to 4, or Figure 5, or Figures 6to 8, or Figure9, or Figure 10, or Figures 12 and 13, or Figures 12 and 13with the modification of Figure 15, or Figure 16, or Figure 17, or Figure 18, and Figures 11 and 1 4 of the accompanying drawings.