Hydraulic control device for automatic transmission for vehicle having two parallel input clutches

Abstract: For an automatic transmission for a vehicle such as an automobile having a speed stage shifting mechanism including parallelly arranged first and second input clutches and adapted to selectively engage the first and second input clutches in three ways of engaging the first input clutch with the second input clutch being disengaged to provide a first speed stage, engaging the second input clutch with the first clutch being disengaged to provide a second speed stage and engaging both the first and second clutches to provide a third speed stage, a hydraulic control device has a first valve for switching over connection of the first input clutch with a hydraulic pressure supply and a drain, a second valve for exchanging connection of the second input clutch and a fail safe port with a hydraulic pressure supply and a drain, and a passage for connecting the drain for the first valve with the fail safe port of the second valve so that at least one of the first and second input clutch is supplied with hydraulic pressure regardless of sticking of the first and/or the second valve.

Description: Background of the Invention Field of the Invention The present invention relates to a hydraulic control device for an automatic transmission for a vehicle such as an automobile, and more particularly, to a hydraulic control device for such an automatic transmission having two parallelly arranged input clutches which are selectively engaged or disengaged in providing a plurality of speed stages. Description of the Prior Art The hydraulically operated automatic transmission for a vehicle such as an automobile generally includes a hydraulically operated input clutch which is sometimes called a forward clutch and which, when engaged, connects the speed stage shifting gear mechanism of the transmission to a rotational power input member therefor which is generally a rotational output member of the fluid torque converter forming a power inlet portion of the automatic transmission. Such a forward clutch is engaged to provide all forward speed stages available by the transmission by a hydraulic pressure supplied thereto under the control of the manual shift valve when it is shifted to any one of forward drive ranges such as the so-called D range, S or 2 range, and L range. The manually operated shift valve generally never fails to provide a hydraulic pressure to the forward clutch when it is shifted to either one of the forward drive ranges. Therefore, it is generally improbable that the vehicle equipped with such a hydraulically operated automatic transmission is disabled to drive forward due to non engagement of the forward clutch. Such a construction is shown, for example, in US-A-4 667 541. In Japanese Patent Application 62-195471 filed on August 5, 1987 and laid open to public on February 13, 1989, which represents the preamble of Claim 1, and EP-A-0 302 723, published 8.2.89, two of the inventors of the present invention have proposed an automatic transmission for a vehicle such as an automobile in which a speed stage shifting mechanism includes two parallelly arranged input clutches and is adapted so that a first one of the two input clutches is engaged when it provides a first speed stage, a second speed stage and a third speed stage, whereas a second one of the two input clutches is engaged when it provides the third speed stage and a fourth speed stage. Therefore, with regard to the two input clutches there exist three conditions for forward driving of the vehicle that the first clutch only is engaged, the first and the second clutch are both engaged, and the second clutch only is engaged. In other words, the switching over of the two clutches is not an alternative selection. In order to operate such a transmission mechanism automatically, provided that the clutches are of a hydraulically operable type, normally at least two automatically operable hydraulic pressure switching over valves would be required. When two hydraulic pressure switching over valves are employed for the control of such two clutches, there is a probability that according to a sticking of either or both of the valves at one switching over position thereof none of the two clutches is supplied with hydraulic pressure. If it happens, no forward driving of the vehicle is available. Summary of the Invention In view of the above-mentioned problem it is the primary object of the present invention to provide a hydraulic control device for an automatic transmission for a vehicle such as an automobile having a speed stage shifting mechanism including two parallelly arranged input clutches, wherein the hydraulic control device provides three conditions of selectively engaging only a first one of the two input clutches, only a second one of the two input clutches, and both said first and second input clutches with a fail safe mechanism which eliminates the probability of neither said first and second input clutches being engaged due to sticking of hydraulic pressure switching over valves. In the hydraulically operated automatic transmissions for a vehicle such as an automobile a certain forward speed stage, mostly the lowest forward speed stage, is often set up by only one input clutch being engaged with or without assistance of automatic engagement of a one way clutch or a one way brake. This is true with the transmission proposed in the aforementioned Japanese patent application. However, as is mostly true with other conventional automatic transmissions for a vehicle such as an automobile, it is also required in the speed stage shifting gear mechanism proposed in the aforementioned Japanese patent application that, in order to set up a second forward speed stage other than said certain forward speed stage, a third hydraulically operated friction engaging means such as a clutch or a brake (clutch in this case) is engaged by particular supply of a hydraulic pressure thereto in addition to the engagement of a certain one of the two input clutches. Since such a third hydraulically operated friction engaging means must of course be controlled separately from said certain one input clutch by a separate hydraulic pressure switching over valve so as to provide still other speed stage or stages, this third hydraulically operated friction engaging means is also affected by a sticking of said separate hydraulic pressure switching over valve. In view of the above-mentioned requirements and the first mentioned problems, it is a secondary object of the present invention to provide a hydraulic control device for an automatic transmission for a vehicle such as an automobile having a speed stage shifting mechanism including two parallelly arranged input clutches, wherein the hydraulic control device provides three conditions of selectively engaging only a first one of the two input clutches, only a second one of the two input clutches, and both said first and second input clutches with a fail safe mechanism which eliminates the probability of neither said first and second input clutches being engaged due to sticking of hydraulic pressure switching over valves and which also eliminates by said fail safe mechanism the probability of said third hydraulically operated friction engaging means being not engaged when said certain one input clutch is engaged. According to the present invention, for an automatic transmission for a vehicle such as an automobile having a speed stage shifting mechanism including parallelly arranged first and second input clutches and adapted to selectively engage said first and second input clutches in three ways of engaging said first input clutch with said second input clutch being disengaged to provide a first speed stage, engaging said second input clutch with said first clutch being disengaged to provide a second speed stage and engaging both said first and second clutches to provide a third speed stage, the above-mentioned primary object is accomplished by a hydraulic control device comprising: a first hydraulic pressure switching over valve having an input port to be supplied with an input hydraulic pressure, an output port connected with said first input clutch and a drain port and adapted to be switched over between a first shift position of connecting said output port thereof with said input port thereof while isolating said output port thereof from said drain port thereof and a second shift position of connecting said output port thereof with said drain port thereof while isolating said output port thereof from said input port thereof; a second hydraulic pressure switching over valve having an input port to be supplied with an input hydraulic pressure, an output port connected with said second input clutch, a drain port and a fail safe port and adapted to be switched over between a first shift position of connecting said output port thereof with said input port thereof on the one hand while connecting said fail safe port thereof with said drain port thereof on the other hand and a second shift position of connecting said output port thereof with said drain port thereof on the one hand while connecting said fail safe port thereof with said input port thereof on the other hand; and a first passage means for connecting said said fail safe port of said second hydraulic pressure switching over valve with said first clutch when said first hydraulic pressure switching over valve is in said second shift position thereof and said second hydraulic pressure switching over valve is in said second shift position thereof. By the hydraulic control device of the above-mentioned construction, at least one of said first and second input clutches is supplied with the input hydraulic pressure regardless of a sticking of said first hydraulic pressure switching over valve and/or said second hydraulic pressure switching over valve at any of said first and second shift positions thereof. Said first passage means may comprise a passage means for connecting said fail safe port of said second hydraulic pressure switching over valve with said drain port of said first hydraulic pressure switching over valve. Alternatively, said first passage means may comprise a first one way switching over valve having a first and a second input port, an output port and a valve element provided between said first and second input ports thereof so as to allow only either one of said first and second input ports thereof to connect with said output port thereof at a time, a passage means for connecting said output port of said first hydraulic pressure switching over valve with said first input port of said first one way switching over valve, a passage means for connecting said fail safe port of said second hydraulic pressure switching over valve with said second input port of said first one way switching over valve and a passage means for connecting said output port of said first one way switching over valve with said first input clutch. Further, for an automatic transmission for a vehicle such as an automobile in which said speed stage shifting mechanism further comprises a third hydraulically operated friction engaging means to be engaged together with said second input clutch to provide said second speed stage, the above-mentioned secondary object of the present invention is accomplished by a hydraulic control device such as summarized above further comprising a third hydraulic pressure switching over valve having an input port to be supplied with an input hydraulic pressure, an output port connected with said third hydraulically operated friction engaging means and a drain port and adapted to be switched over between a first shift position of connecting said output port thereof with said input port thereof while isolating said output port thereof from said drain port thereof and a second shift position of connecting said output port thereof with said drain port thereof while isolating said output port thereof from said input port thereof, and a second passage means for connecting said fail safe port of said second hydraulic pressure switching over valve with said third hydraulically operated friction engaging means when said third hydraulic pressure switching over valve is in said second shift position thereof and said second hydraulic pressure switching over valve is in said second shift position thereof. By the hydraulic control device of the above-mentioned construction having further said third hydraulic pressure switching over valve with said fail safe means further compensating for sticking of said third hydraulic pressure switching over valve, said third hydraulically operated friction engaging means is infallibly supplied with the input hydraulic pressure when said second input clutch is supplied with the input hydraulic pressure. Said second passage means may comprise a passage means for connecting said fail safe port of said second hydraulic pressure switching over valve with said drain port of said third hydraulic pressure switching over valve. Alternatively, said second passage means may comprise a second one way switching over valve having a first and a second input port, an output port and a valve element provided between said first and second input ports thereof so as to allow only either one of said first and second input ports thereof to connect with said output port thereof at a time, a passage means for connecting said output port of said third hydraulic pressure switching over valve with said first input port of said second one way switching over valve, a passage means for connecting said fail safe port of said second hydraulic pressure switching over valve with said second input port of said second one way switching over valve and a passage means for connecting said output port of said second one way switching over valve with said third hydraulically operated friction engaging means. Brief Description of the Drawings In the accompanying drawings; Fig. 1 is a schematic illustration of a planetary gear type speed change device for an automatic transmission having substantially the same speed shift gear mechanism as that disclosed in the above-mentioned Japanese patent application to which the hydraulic control device according to the present invention is applicable; Fig. 2 is a table showing combinations of energization of the solenoid valves and engagement of the clutches and brakes for setting up the respective speed stages; Fig. 3 is a diagram showing an embodiment of a hydraulic control device for an automatic transmission for a vehicle according to the present invention; Figs. 4 through 7 are diagrams showing the essential portion of the hydraulic control device shown in Fig. 3 in the conditions operating at respective speed stages; and Figs. 8-10 are diagrams showing other embodiments of the hydraulic control device according to the present invention showing only the essential portions thereof in the same manner as in Figs. 4-7. Description of the Preferred Embodiments In the following the invention will be described in detail with respect to some preferred embodiments thereof with reference to the accompanying drawings. Referring to Fig. 1, the speed stage shifting mechanism herein shown comprises a first planetary gear mechanism having a first sun gear 10, a first ring gear 12 coaxial with said first sun gear 10, a first planetary pinion 14 meshing with said first sun gear 10 and said first ring gear 12, and a first carrier 16 rotatably supporting said first planetary pinion 14, and a second planetary gear mechanism having a second sun gear 20, a second ring gear 22 coaxial with said second sun gear 20, a second planetary pinion 24 meshing with said second sun gear 20 and said second ring gear 22, and a second carrier 26 rotatably supporting said second planetary pinion 24. The first ring gear 12 is connected with the second carrier 26 by a connecting member 30. The first carrier 16 is connected with the second ring gear 22 by a connecting member 32. A first one way clutch 34 and a second one way clutch 36 are provided in series between a housing 50 and the first carrier 16 which is also connected with the second ring gear 22 by the connecting member 32. The first one way clutch 34 is closer to the first carrier 16 and the second one way clutch 36 is closer to the housing 50. In more detail, the first one way clutch 34 has an inner race 34a connected with the first carrier 16 and an outer race 34b connected via a connecting member 31 with an inner race 36a of the second one way clutch which also has an outer race 36b connected with the housing 50. The first one way clutch 34 is engaged when the outer race 34b would rotate relative to the inner race 34a in in a first rotational direction and slips when the inner race 34a rotates relative to the outer race 34b in a second direction opposite to said first direction. Similarly, the second one way clutch 36 is engaged when the inner race 36a would rotate relative to the outer race 36b in said first direction and slips when the inner race 36a rotates relative to the outer race 36a in said second direction. The second carrier 26 is connected with an annular gear member 54 which operates as an output rotational member of this speed stage shifting mechanism. A first clutch 38 is provided between the second sun gear 20 and an input shaft 52 for selectively connecting these two members with one another. A second clutch 40 is provided between the first carrier 16 and the input shaft 52 for selectively connecting these two members with one another. A third clutch 42 is provided between the first sun gear 10 and the input shaft 52 for selectively connecting these two members with one another. A fourth clutch 44 is provided between the first sun gear 10 and the connecting member 31 for selectively connecting the sun gear 10 with the outer race 34b of the one way clutch 34 and the inner race 36b of the one way clutch 36. A first brake 46 is provided between the connecting member 31 and the housing 50 for selectively fixing the connecting member 31 relative to the housing 50. A second brake 48 is provided between the combination of the second ring gear 22 and the first carrier 16 and the housing 50 for selectively fixing the second ring gear 22 and the first carrier 16 with respect to the housing 50. The manner of providing a first speed stage, a second speed stage, a third speed stage (direct connection stage), a fourth speed stage (overdrive stage) and a reverse stage is shown in Table 1 and Fig. 2. In Table 1 and Fig. 2 a circle (O) indicates that the corresponding clutch, brake or one way clutch is engaged in engine drive state, and in Table 1 a circle in parentheses ((O)) indicates that the corresponding clutch or brake is engaged to provide the corresponding speed stage with the effect of engine braking. When the ratio of the number of gear teeth of the first ring gear 12 to that of the first sun gear 10 is r₁, and the ratio of the number of gear teeth of the second ring gear 22 to that of the second sun gear 20 is r₂, speed change gear ratios at the respective speed stages are as shown in Table 2. The first clutch 38, the second clutch 40, the third clutch 42, the fourth clutch 44, the first brake 46 and the second brake 48 are all of a hydraulically operating type having, as shown in Fig. 3, hydraulic pressure chambers 38a, 40a, 42a, 44a, 46a and 48a plus 48b, respectively, and are adapted to be engaged when a hydraulic pressure is supplied to the hydraulic pressure chambers and are disengaged when the hydraulic pressure has been exhausted from the hydraulic pressure chambers. The supply and the exhaust of the hydraulic pressure to and from these hydraulic pressure chambers are carried out by a hydraulic control device such as shown in Fig. 3. The input shaft 52 of the above-mentioned planetary gear type speed change device is drivingly connected with a motor such as an internal combustion engine not shown in the figure via a fluid torque converter 60 such as shown in Fig. 3. The fluid torque converter 60 is of a three elements two phases type comprising a pump impeller 62 drivingly connected with an output member of the motor, a turbine rotor 64 drivingly connected with the input shaft 52 of the planetary gear type speed stage shifting mechanism, and a stator 66 rotatable only in one direction. The fluid torque converter 60 further comprises a lock-up clutch 68 which is engaged to connect the pump impeller 62 directly with the turbine rotor 64 when a hydraulic pressure is supplied to its port 60a and is disengaged when a hydraulic pressure is supplied to its port 60b. The supply of hydraulic pressure to the ports 60a and 60b is carried out by the hydraulic control device shown in Fig. 3. The outline of the oil hydraulic control device shown in Fig. 3 will now be described with further reference to Figs. 4-7. The oil hydraulic control device comprises a pump 70 which takes in an operating hydraulic fluid such as an oil from a reservoir not shown in the figure and supplies the hydraulic fluid to a primary regulator valve 80 generally called a line pressure control valve and also to a throttle valve 120. The maximum value of the hydraulic pressure supplied by the pump 70 to the primary regulator valve 80 is restricted by a pressure relief valve 72. The throttle valve 120 provides in a passage 138 a hydraulic pressure which varies in accordance with the load on the engine and is generally called a throttle pressure. The primary regulator valve 80 is supplied with the throttle pressure and a reverse boost pressure and provides in a passage 98 the line pressure which generally increases along with increase of the throttle opening and a hydraulic pressure for a secondary regulator valve 100 generally called a converter pressure control valve. The secondary regulator valve 100 is supplied with the throttle pressure and provides a converter pressure (lubricating oil pressure) in a passage 118. The line pressure in the passage 98 is supplied to a port 194 of a manual valve 190. The manual valve 190 has a spool 192 adapted to be operated by a hand of a driver and selectively provides the line pressure supplied to the port 194 at a D port 196 in the so-called D range, also at an S port 198 in the so-called S or 2 range, further at an L port 200 in the so-called L range, and at an R port 202 in the so-called R range. The line pressure supplied to the D port 196 is conducted through a passage 204 to a D port 214 of a 1-2 shift valve 210, a D port 246 of a 2-3 shift valve 240, and a D port 274 of a 3-4 shift valve 270. The line pressure supplied to the S port 198 is conducted through a passage 206 to an S port 248 of the 2-3 shift valve 240. The line pressure supplied to the L port 200 is conducted through a passage 208 to an L port 250 of the 2-3 shift valve 240. The line pressure supplied to the R port 202 is conducted through a passage 203 to a reverse inhibit valve 360. As shown in more detail in Fig. 4 the 2-3 shift valve 240 comprises a spool element 242 and a plug element 244, and in addition to the above-mentioned ports further comprises drain ports 251, 252 and 253, a clutch port 254, brake ports 256 and 258 and a fail safe port 260. When a hydraulic pressure is supplied to a control port 261, the plug element 244 and the spool element 242 are shifted downward in the figure to a "1,2" shift position as shown in the right half portion thereof by overcoming the spring force of a compression coil spring 262 so as to connect the clutch port 254 with the drain port 252, the brake port 256 with the S port 248, the brake port 258 with the L port 250, and the fail safe port 260 with the D port 246, respectively. In contrast, when no hydraulic pressure is supplied to the control port 261, the plug element 244 and the spool element 242 are shifted upward in the figure to a "3,4" shift position as shown in the left half portion thereof by the spring force of the compressing coil spring 262 so as to connect the clutch port 254 with the D port 246, and the brake ports 256 and 258 and the fail safe port 260 with the drain ports 251, 252 and 252, respectively. The supply of the hydraulic pressure to the control port 261 is controlled by a first solenoid valve 400. The clutch port 254 is connected through a passage 263 with the hydraulic pressure chamber 40a of the second clutch 40 and an accumulator chamber 472 of an accumulator 470 for the clutch C₂. The clutch port 254 is also connected through a passage 264 with a hold port 220 of the 1-2 shift valve 210, and also through a passage 265 with a fail safe port 222 of the 1-2 shift valve 210. The fail safe port 222 also has a concept of drain port because it is connectable to drain through ports 252 and 254 of the 2-3 shift valve. The brake port 256 is connected through a passage 266 with the S port 216 of the 1-2 shift valve 210. The brake port 258 is connected through a passage 267 with the L port 218 of the 1-2 shift valve 210. The fail safe port 260 is connected through a passage 268 with a hold port 278 of the 3-4 shift valve 270 and also connected through a passage 269 with a drain port 280 of the 3-4 shift valve 270. As also shown in Fig. 4, the 1-2 shift valve 210 comprises a spool element 212, and in addition to the above-mentioned ports further comprises a clutch port 224, brake ports 226 and 228, an R port 230, a port 232 and a clutch port 234. When a hydraulic pressure is supplied to a control port 238 the spool element 212 is shifted downward in the figure as shown in the left half portion thereof to a "1" shift position by overcoming the spring force of a compression coil spring 236 so as to connect the clutch port 224 with the fail safe port 222, the brake port 226 with the R port 230, and the brake port 228 with the L port 218, while isolating the port 232 from the clutch port 234. In contrast, when no hydraulic pressure is supplied to the control port 238, the spool element 212 is shifted upward in the figure as shown in the right half portion thereof to a "2,3,4" shift position by the spring force of the compression coil spring 236 so as to connect the clutch port 224 with the D port 214, the brake port 226 with the S port 216, the brake port 228 with the R port 230, and the port 232 with the clutch port 234. The supply of the hydraulic pressure to the control port 238 is controlled by a second solenoid valve 410. The control port 238 is connected through a passage 239 with a control port 288 of the 3-4 shift valve 270. The clutch port 224 is connected through a passage 225 with the hydraulic pressure chamber 44a of the fourth clutch 44 and an accumulator chamber 492 of an accumulator 490 for the clutch C₄. The brake port 226 is connected through a passage 227 with an S port 276 of the 3-4 shift valve 270. The brake port 228 is connected through a passage 229 with an accumulator chamber 532 of an accumulator 530 for the brake B₂, and is further connected through a passage 231 with the inside hydraulic pressure chamber 48a of the second brake 48. The port 232 is connected through a passage 233 with a port of a C₁ control valve 300. The clutch port 234 is connected through a passage 235 with the hydraulic chamber 38a of the first clutch 38. Also referring to Fig. 4, the 3-4 shift valve 270 comprises a spool element 272, and in addition to the above-mentioned ports further comprises a clutch port 282 and a brake port 284. When no hydraulic pressure is supplied to the hold port 278 while a hydraulic pressure is supplied to the control port 288, the spool element 272 is shifted downward in the figure to a "4" shift position as shown in the right half portion thereof by overcoming the spring force of a compression coil spring 286 so as to connect the clutch port 282 with the drain port 280, and the brake port 284 with the D port 274. In contrast, when a hydraulic pressure is supplied to the hold port 278, or when no control pressure is supplied to the control port 288, the spool element 272 is shifted upward in the figure to a "1,2,3" shift position as shown in the left half portion thereof by the oil pressure supplied to the port 278 and/or the spring force of the compression coil spring 286 so as to connect the clutch port 282 with the D port 274, and the brake port 284 with the S port 276. The clutch port 282 is connected through a passage 290 with the C₁ control valve 300. The brake port 284 is connected through a passage 292 with the oil hydraulic pressure chamber 46a of the first brake 46 and an accumulator chamber 512 of an accumulator 510 for the brake B₁. The first solenoid valve 400 and the second solenoid valve 410 are normally open type valves which open their ports when not energized and close their ports when energized. The manner of energization of these solenoid valves is shown in Fig. 2 in relation with the speed stages to be set up. In Fig. 2 a circle (O) indicates energization of the corresponding solenoid valve. The first solenoid valve 400 is connected through a passage 408 with the control port 261 of the 2-3 shift valve 240 and is also connected through a passage 406 with a port of the C1 control valve 300. The second solenoid valve 410 is connected through a passage 418 with the control port 238 of the 1-2 shift valve 210, and is also connected through a passage 239 with the control port 288 of the 3-4 shift valve 270. Therefore, when the solenoid valve 400 is energized the control port 261 of the 2-3 shift valve 240 is supplied with a hydraulic pressure, and when the solenoid valve 410 is energized the control port 238 of the 1-2 shift valve 210 and also the control port 288 of the 3-4 shift valve 270 are supplied with a hydraulic pressure. The C₁ control valve 300 controls switching over of the first clutch 38 by switching over the connection of the passage 290 with passages 233, 326 and 328 according to whether the speed stage to be set up requires engagement of the first clutch 38 or not. The passage 328 is connected through a passage 329, an accumulator chamber 452 of an accumulator 450 for the clutch C₁, a passage 468 and a one way valve 469 with the hydraulic pressure chamber 38a of the first clutch 38. The passage 326 is connected with a port of a 4-3 control valve 330. The 4-3 control valve 330 controls the timing of the engagement of the first clutch 38 in speed stage shifting between the third speed stage and the fourth speed stage by connecting the passage 326 with either a passage 352 or a passage 356 incorporating an orifice 350 or 354 having each particular throttling ratio so as to switch over the rate of supply of hydraulic pressure to the hydraulic pressure chamber 38a. The passages 352 and 356 are both connected with a passage 329 which is connected through the accumulator chamber 452, the passage 468 and the one way valve 469 with the hydraulic pressure chamber 38a of the first clutch 38. The reverse inhibit valve 360 is supplied with the line pressure from the R port 202 of the manual valve 190 through a passage 203, and is switched over according to opening or closing of the third solenoid valve 420 so as to be at an inhibit position where a spool 362 is shifted up as shown in a left half portion thereof when the vehicle is running forward at a speed greater than a predetermined value and to be in a non inhibit position where the spool element 362 is shifted down as shown in the right half portion thereof during other operating conditions while allowing the line pressure from the passage 203 to flow to the passage 398 toward the hydraulic pressure chamber 42a of the third clutch 42, to the passages 396 and 394 toward the R port 230 of the 1-2 shift valve 210, and also to the passage 396, a B₂ sequence valve 610 and a passage 392 toward the outside hydraulic pressure chamber 48b of the second brake 48. The B₂ sequence valve 610 operates in response to the hydraulic pressure in the inside hydraulic pressure chamber 48a of the second brake 48 so as to connect the passage 396 with the passage 392 so that the outside hydraulic pressure chamber 48b is supplied with the hydraulic pressure when the oil pressure in the inside hydraulic pressure chamber 48a is greater than a predetermined value. Accumulators 450, 470, 490, 510 and 530 are back pressure control type accumulators having back pressure chambers 454, 474, 494, 514 and 534, respectively. The hydraulic pressure supplied to these back pressure chambers is controlled by a second accumulator control valve 560. The second accumulator control valve 560 is supplied with a duty hydraulic pressure controlled by a duty solenoid valve 590 and the hydraulic pressure from the first accumulator control valve 550 to change its output control pressure. The duty solenoid valve 590 is supplied with a pulse signal having a determinate duty ratio and cyclically opens and closes according to the duty ratio so as to control a modulate hydraulic pressure from a duty control valve 580 according to the duty ratio. The duty hydraulic pressure controlled by the duty solenoid valve 590 for the second accumulator control valve 560 is rectified of its pulses by a duty pressure accumulator 600. The first accumulator control valve 550 is supplied with the throttle pressure from the throttle valve 138 so as to control the oil pressure supplied to the second accumulator control valve 560 and the 4-3 control valve 330 in accordance with the throttle pressure. The supply of the converter pressure to the ports 60a and 60b of the fluid torque converter 60 is controlled by a lock up relay valve 140. The lock up relay valve 140 is switched over according to a selective supply of an oil pressure from a lock up signal valve 160. The lock up relay valve 140 supplies hydraulic fluid, i.e., oil, toward an oil cooler 170. The hydraulic pressure in the passage including the oil cooler 170 is limited by a cooler by-pass valve 172 and a relief valve 174. The lock up signal valve 160 is supplied with an oil pressure from the clutch port 224 of the 1-2 shift valve 210 and is switched over in accordance with on and off of the third solenoid valve 420 so as to supply the hydraulic pressure supplied from the clutch port 224 to the lock up relay valve 140 and to engage the lock up clutch 68 when the third solenoid valve 420 is energized. The third solenoid valve 420 is selectively energized as shown in Fig. 2 for inhibiting engagement of the lock up clutch 68 in the reverse stage where the manual shift valve is shifted to the R range and when the manual shift valve is sifted to the D range. The operation of the hydraulic control device according to the present invention will now be described principally with respect to the speed stage shifting operation in the D range with reference to Figs. 4-7. In Figs. 4-7 the bold lines indicate that a hydraulic pressure is supplied in those lines in the respective speed stages. First referring to Fig. 4, the operation in the first speed stage will be described. In the first speed stage the first solenoid valve 400 and the second solenoid valve 410 are both energized, and therefore the control port 261 of the 2-3 shift valve 240, the control port 238 of the 1-2 shift valve 210 and the control port 288 of the 3-4 shift valve 270 are supplied with the hydraulic pressure. Therefore, the plug element 244 and the spool element 242 of the 2-3 shift valve 240 are shifted to the "1,2" shift position shown in the right half portion thereof, and the spool element 212 of the 1-2 shift valve 210 is shifted to the "1" shift position shown in the left half portion thereof. Therefore, the line pressure from the D port 196 of the manual shift valve 190 is supplied through the passage 204, the D port 246 of the 2-3 shift valve 240, the fail safe port 260, and the passage 268 to the hold port 278 of the 3-4 shift valve 270. The 3-4 shift valve 270 is supplied with the hydraulic pressure at the control port 288. However, since the hold port 278 is also supplied with the hydraulic pressure, the spool element 272 is shifted to the "1,2,3" shift position shown in the left half portion thereof by the spring force of the compression coil spring 286. Therefore, the D port 274 is connected with the clutch port 282, and the line pressure from the D port 196 of the manual shift valve 190 is supplied the passage 290, the C₁ control valve 300, through the passages 328 and 329, the accumulator chamber 452 of the accumulator 450 for the clutch C1, and the one way valve 469 to the hydraulic pressure chamber 38a of the first clutch C₁ which is then engaged. Thus the first speed stage of the D range is set up. Next, referring to Fig. 5, the second speed stage will be described. In this speed stage the first solenoid valve 400 is only energized, so that the control port 261 of the 2-3 shift valve 240 only is still supplied with the oil pressure. Therefore, the plug element 244 and the spool element 242 of the 2-3 shift valve 240 remain in the "3,4" shift position, whereas the spool element 212 of the 1-2 shift valve 210 is shifted to the "2,3,4" shift position shown in the right half portion thereof by the spring force of the compression coil spring 236. In the 3-4 shift valve 270 the hydraulic pressure in the control port 288 disappears and the spool element 272 still remains at the "1,2,3" shift portion shown in the left half portion thereof by the hydraulic pressure supplied to the hold port 278 and the spring force of the compression coil spring 286. By the shifting over of the 1-2 shift valve 210 the D port 214 is now connected with the clutch port 224 so that the line pressure from the D port 196 of the manual shift valve 190 is supplied to the passage 225 to the hydraulic pressure chamber 44a of the fourth clutch 44 which is then engaged. Thus the first clutch 38 and the fourth clutch 44 are engaged, thereby setting up the second speed stage of the D range. Next, referring to Fig. 6, the third speed stage will be described. In this speed stage the first solenoid valve 400 and the second solenoid valve 410 are both not energized, so that the control port 238 of the 1-2 shift valve 210 and the control port 261 of the 2-3 shift valve 240 are both not supplied with hydraulic pressure. Therefore, the plug element 244 and the spool element 242 of the 2-3 shift valve 240 are lifted to the "3,4" shift position as shown in the left half portion in the figure by the spring force of the compression coil spring 262, whereby the D port 246 of the 2-3 shift valve 240 is isolated from the fail safe port 260 thereof and is connected with the clutch port 254. Thus the line pressure from the D port 196 of the manual shift valve 190 is conducted through the passage 263 to the hydraulic pressure chamber 40a of the second clutch 40 which is then engaged. In the 3-4 shift valve 270, although the hold port 278 is no longer supplied with the hydraulic pressure, the spool element 272 still remains in the lifted "1,2,3" shift position by the spring force of the compression coil spring 286. In the 1-2 shift valve 210, the spool element 212 remains in the lifted "2,3,4" shift position as in the second speed stage. Therefore, in addition to the first clutch 38 and the fourth clutch 44 the second clutch 40 is now engaged thereby setting up the third speed stage of the D range. Next, referring to Fig. 7, the fourth speed stage will be described. In this speed stage the second solenoid valve 410 only is energized. Therefore, the control port 238 of the 1-2 shift valve 210 and the control port 288 of the 3-4 shift valve 270 are supplied with the hydraulic pressure. In the 1-2 shift valve 210 the hold port 220 is supplied with the hydraulic pressure from the clutch port 254 of the 2-3 shift valve 240 through the passage 264. Therefore, in spite of the supply of the hydraulic pressure to the control port 238 the spool element 212 remains in the lifted "2,3,4" shift position shown in the right half portion thereof by the spring force of the compression coil spring 236. However, in the 3-4 shift valve 270, since the hold port 278 is connected through the passage 268 and the fail safe port 260 of the 2-3 shift valve 240 to the drain port 253, the spool element 272 is shifted downward in the "4" shift position by the oil pressure supplied to the control port 288 by overcoming the spring force of the compression coil spring 286. Therefore, the D port 274 is connected with the brake port 284 instead of the clutch port 282 which is now connected to the drain port through the port 280. Thus the hydraulic pressure chamber 38a of the first clutch 38 is now exhausted of the oil pressure, and the first clutch 38 is disengaged. Instead the line pressure is supplied to the hydraulic pressure chamber 46a of the first brake 46 which is now engaged. Therefore, the second clutch 40, the fourth clutch 44 and the first brake 46 are engaged, thereby setting up the overdrive fourth speed stage of the D range. If for some reasons the spool element 272 of the 3-4 shift valve 270 has stuck to the "4" shift position shown in the right half portion in the figure, the clutch port 282 is continually connected with the drain port 280, while isolating the supply of the line pressure from the D port 274. Let us suppose that in such a condition the manual shift valve 190 was shifted from the N range position to the D range position. At this time, in the 2-3 shift valve 240 the plug element 244 and the spool element 242 are positioned at the "1,2" shift position shown in the right half portion in the figure with the D port 246 being connected with the fail safe port 260. Therefore, the line pressure supplied to the D port 246 is conducted through the fail safe port 260, the passages 268 and 269, and the drain port 280 of the 3-4 shift valve 270 to the clutch port 282. Therefore, even when the spool element 272 of the 3-4 shift valve 270 has stuck to the "4" shift position for setting up the fourth speed stage, the supply of the hydraulic pressure to the hydraulic pressure chamber 38a of the first clutch 38 is supported so that the first clutch 38 is engaged. At this time, if the 1-2 shift valve 210 is normally operating with the spool element 212 being shifted to the "1" shift position shown in the left half portion in the figure, the first speed stage is set up by the engagement of only the first clutch 38. On the other hand, if the spool element 212 of the 1-2 shift valve 210 has been sticking to the "2,3,4" shift position for setting up the second speed stage, the third speed stage and the fourth speed stage, the hydraulic pressure chamber 44a of the fourth clutch 44 is also supplied with the hydraulic pressure, thereby setting up the second speed stage. If at this time the spool element 272 of the 3-4 shift valve 270 remains as sticking to the "4" shift position, the hydraulic pressure is also supplied to the hydraulic pressure chamber 46a of the first brake 46. However, the engagement of the first brake 46 does not obstruct the setting up of the first speed stage and the second speed stage. If the spool element 242 of the 2-3 shift valve 240 has stuck to the "3,4" shift position shown in the left half portion thereof in the figure for setting up the third speed stage and the fourth speed stage, the line pressure is not supplied from the fail safe port 260 to the drain port 280 of the 3-4 shift valve 270, thereby obstructing the engagement of the first clutch 38. However, since the D port 246 is connected with the clutch port 254, the second clutch 40 is engaged. If at this time the spool element 212 of the 1-2 shift valve 210 is shifted to the "1" shift position shown in the left half portion thereof in the figure, the line pressure at the clutch port 254 of the 2-3 shift valve 240 is supplied to the hydraulic pressure chamber 40a of the second clutch 40 and also through the passage 265 to the fail safe port 222 of the 1-2 shift valve 210 and further through the clutch port 224 to the hydraulic pressure chamber 44a to the fourth clutch 44. If at this time the spool element 272 of the 3-4 shift valve 270 is shifted to the "1,2,3" shift position as shown in the left half portion thereof in the figure, the hydraulic pressure is supplied to the hydraulic pressure chamber 40a of the first clutch 40 which is then engaged, thereby setting up the third speed stage. On the other hand, if the spool element 272 of the 3-4 shift valve 170 is shifted to the "4" shift position as shown in the right half portion thereof in the figure, the hydraulic pressure is supplied to the hydraulic pressure chamber 46a of the first brake 46 which is then engaged, thus setting up the fourth speed stage. Further, if the spool element 242 of the 2-3 shift valve 240 has stuck to the "3,4" shift position shown in the left half portion thereof in the figure, while the spool element 212 of the 1-2 shift valve 210 is shifted to the "2,3,4" shift position as shown in the right half portion thereof in the figure, the clutch port 224 is supplied with the line pressure from the D port 214, and therefore the third speed stage or the fourth speed stage are set up in the same manner as described above. Therefore, even if any of the spool elements of the 1-2 shift valve 210, the 2-3 shift valve 240 and the 3-4 shift valve 270 have stuck to any shift position thereof, either one of the first through the fourth speed stages is set up with shifting of the manual shift valve to the D range, avoiding that the vehicle is completely disabled in forward driving. Fig. 8 shows a second embodiment of the hydraulic control device according to the present invention in the essential portions thereof. In Fig. 8 the portions corresponding to those shown in Figs. 4-7 are designated by the same reference numerals as in Figs. 4-7. In this second embodiment the clutch port 282 of the 3-4 shift valve 270 is connected with the C₁ control valve 300 through a passage 290, a one way switching over valve 298 and a passage 294 while the drain port 280 is modified to be a simple drain port as separated from the passage 268. The passage 268 connected with the fail safe port 260 of the 2-3 shift valve 240 is connected to a side of the one way switching over valve 298 opposite to the other side thereof where the passage 290 is connected through the passage 296, instead of the drain port 280 in the first embodiment. The one way switching over valve 298 is of a check ball type, and closes the passage 296 when the passage 290 is supplied with the hydraulic pressure so as to connect the passage 290 with the passage 294, while on the other hand when the passage 296 only is supplied with the hydraulic pressure, the valve closes the passage 290 and connects the passage 296 with the passage 294. By this arrangement the passage 294 is supplied with the hydraulic pressure when the hydraulic pressure is supplied in at least one of the passages 290 and 296. Therefore, also in this second embodiment, if the spool element 272 of the 3-4 shift valve 270 has stuck to the "4" shift position as shown in the right half portion thereof in the figure, thus failing to supply the hydraulic pressure to the clutch port 282, the hydraulic pressure is supplied from the fail safe port 260 of the 2-3 shift valve 240 through the passages 268 and 296, the one way switching over valve 298 and the passage 294 to the C₁ control valve 300 so that the first clutch 38 is engaged. Therefore, this second embodiment also provides the same functions and effects as the aforementioned first embodiment. Fig. 9 shows a third embodiment of the hydraulic control device according to the present invention in the essential portion thereof in the same manner as in Figs. 4-8. In Fig. 9 the portions corresponding to those shown in Figs. 4-8 are designated by the same reference numerals as in Figs. 4-8. In this third embodiment, the clutch port 224 of the 1-2 shift valve 210 is connected with the fourth clutch C₄ through the passage 225, a one way switching over valve 299 and a passage 297, while the fail safe port 222 is modified to be a simple drain port as separated from the clutch port 254 of the 2-3 shift valve 240. On the other hand, the clutch port 254 of the 2-3 shift valve 240 connected with the second clutch C₂ by the passage 263 is also connectable with the fourth clutch C₄ through a passage 295 and the one way switching over valve 299 when the supply of hydraulic pressure from the clutch port 224 of the 1-2 shift valve 210 fails. Therefore, this third embodiment also provides the same functions and effects as the aforementioned first and second embodiments. Fig. 10 shows a fourth embodiment of the hydraulic control device according to the present invention also in the essential portions thereof in the same manner as in Figs. 4-9. In Fig. 10 the portions corresponding to those shown in Figs. 4-9 are designated by the same reference numerals. In this fourth embodiment the modifications according to the second and the third embodiment are both incorporated. Since the modification in this fourth embodiment is an addition of those in the second and the third embodiments, further redundant descriptions will be omitted for the brevity of the specification.

Claims: A hydraulic control device comprising of an automatic transmission for a vehicle such as an automobile having a speed stage shifting mechanism including parallelly arranged first and second hydraulically operated input clutches (C1, C2) adapted to be selectively engaged such that said first input clutch (C1) only is engaged while said second input clutch (C2) and other input clutch, if any, are disengaged to provide a first forward speed stage (1st speed stage), and said first input clutch (C1) is disengaged while said second clutch (C2) is engaged to provide a second speed stage (4th speed stage), comprising: a first hydraulic pressure switching over valve (270) having an input port (274) to be supplied with an input hydraulic pressure, an output port (282) connected with said first input clutch (C1) and a drain port (280) and adapted to be switched over between a first shift position (up) for connecting said output port thereof with said input port thereof while isolating said output port thereof from said drain port thereof and a second shift position (down) for connecting said output port thereof with said drain port thereof while isolating said output port thereof from said input port thereof; and a second hydraulic pressure switching over valve (240) having an input port (246) to be supplied with an input hydraulic pressure, an output port (254) connected with said second input clutch (C2) and a drain port (252) and adapted to be switched over between a first shift position (up) for connecting said output port thereof with said input port thereof while isolating said output port thereof from said drain port thereof and a second shift position (down) for connecting said output port thereof with said drain port thereof while isolating said output port thereof from said input port thereof; characterized in that said second hydraulic pressure switching over valve (240) further has a fail safe port (260) adapted to be connected with a drain port (253) when switched over to said first shift position (up) and to be connected with said input port thereof (246) when switched over to said second shift position (down), and a passage means (268, 269, 280 in Figs. 4-7; 268, 296, 298 in Figs 8 and 10) for conducting the hydraulic pressure supplied to said fail safe port (260) of said second hydraulic pressure switching over valve (240) to said first clutch (C1) when said first hydraulic pressure switching over valve is in said second shift position (down). A hydraulic control device according to claim 1, wherein said passage means comprises a passage means (268) for connecting said fail safe port (260) of said second hydraulic pressure switching over valve (240) with said drain port (280) of said first hydraulic pressure switching over valve (270). A hydraulic control device according to claim 1, wherein said passage means comprises a one way switching over valve (298) having a first and a second input port, an output port and a valve element provided between said first and second input ports thereof so as to allow only either one of said first and second input ports thereof to connect with said output port thereof at a time, a passage means (290) for connecting said output port (282) of said first hydraulic pressure switching over valve (270) with said first input port of said first one way switching over valve (298), a passage means (268, 296) for connecting said fail safe port (260) of said second hydraulic pressure switching over valve (240) with said second input port of said first one way switching over valve (298) and a passage means (294) for connecting said output port of said first one way switching over valve (298) with said first input clutch C1). A hydraulic control device according to claim 1, 2 or 3, wherein said speed stage shifting mechanism further comprises a third hydraulically operated input clutch (C4) to be engaged to provide said second speed stage (4th speed stage), further comprising a third hydraulic pressure switching over valve (210) having an input port (214) to be supplied with an input hydraulic pressure, an output port (224) connected with said third input clutch (C4) and a drain/fail safe port (222) and adapted to be switched over between a first shift position (up) for connecting said output port thereof with said input port thereof while isolating said output port thereof from said drain/fail safe port thereof and a second shift position (down) for connecting said output port thereof with said drain/fail safe port thereof while isolating said output port thereof from said input port thereof, and a passage means (265) for connecting said drain/fail safe port (222) of said third hydraulic pressure switching over valve (210) with said output port (254) of said second hydraulic pressure switching over valve (240). A hydraulic control device according to claim 1, 2 or 3, wherein said speed stage shifting mechanism further comprises a third hydraulically operated input clutch (C4) to be engaged to provide said second speed stage (4th speed stage), further comprising a third hydraulic pressure switching over valve (210) having an input port (214) to be supplied with an input hydraulic pressure, an output port (224) connected with said third input clutch (C4) and a drain port (222) and adapted to be switched over between a first shift position (up) for connecting said output port thereof with said input port thereof while isolating said output port thereof from said drain port thereof and a second shift position (down) for connecting said output port thereof with said drain port thereof while isolating said output port thereof from said input port thereof, and a passage means having a one way switching over valve (299) having a first and a second input port, an output port and a valve element provided between said first and second input ports thereof so as to allow only either one of said first and second input ports thereof to connect with said output port thereof at a time, a passage means (263, 295) for connecting said output port (254) of said second hydraulic pressure switching over valve (240) with said first input port of said last mentioned one way switching over valve (299), a passage means (225) for connecting said output port (224) of said third hydraulic pressure switching over valve (210) with said second input port of said last mentioned one way switching over valve (299).

Inventors: FUNAHASHI MAKOTO, ITOH HIROSHI, TAKADA MITSURU, TAKAHASHI TOKUYUKI, FUNAHASHI, MAKOTO, ITOH, HIROSHI, TAKADA, MITSURU, TAKAHASHI, TOKUYUKI
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1989
Main classification: F16H61
IPC codes: F16H59, F16H61