Automatic transmission

An automatic transmission includes a planetary gear mechanism, an engagement element group including a particular engagement element having first and second pressure chambers, a pressure control valve to regulate the fluid pressure for the particular engagement element, and a selector valve arranged to connect the second pressure chamber with the pressure control valve at a first valve position, and to disconnect the second pressure chamber from the pressure control valve at a second valve position. A shift control section is configured to command a shift operation from a first gear position, to a second gear position, by controlling the selector valve to the second valve position and to supply the fluid pressure to the first pressure chamber, and to judge the selector valve to be in an abnormal state, in accordance with a parameter in the shift operation.

BACKGROUND OF THE INVENTION

The present invention relates to technique of detecting a failure of an engaging element in a step automatic transmission, and technique of a fail-safe control in case of such a failure.

A step automatic transmission includes a planetary gear mechanism and a plurality of friction engaging elements or devices to select a desired gearing or gear position to provide a desired speed or gear ratio by changing over between an engaged state and a disengaged or released state. Among various friction engaging elements, there is such a friction engaging element that a required engagement capacity varies widely in dependence on the gearing position. If a hydraulic circuit is to change a hydraulic fluid pressure supplied to such a friction engaging element, to meet required engagement capacities differing largely in dependence on the gear speed, then the hydraulic pressure control becomes very complicated.

Therefore, a Japanese patent document JP 05-288264A discloses technique of preventing deterioration of a shift shock by employing a friction engaging element formed with two pressure chambers having different pressure receiving surfaces, and a hydraulic circuit to supply an oil pressure to one or both of the pressure chambers in accordance with the required engagement capacity.

SUMMARY OF THE INVENTION

For such a friction engaging element, it is possible to employ a hydraulic system including a pressure control valve for controlling the supply of a hydraulic pressure to the friction engaging element by regulating a line pressure, and a selector valve for selectively supplying the outlet pressure of the pressure control valve to the larger pressure chamber having the larger pressure receiving area.

However, the supply of the fluid pressure to the larger pressure chamber continues invariably in case of double failure in which the selector valve is stuck by a foreign object such a burr at the valve position to supply the fluid pressure to the larger pressure chamber, and thereafter the pressure control valve is stuck at the valve position to supply the fluid pressure.

By such a double failure, the friction engaging element is held engaged. Therefore, if a further shift is commanded in accordance with a vehicle operating condition, and another friction engagement element is engaged, the simultaneous engagement of the two engaging elements could cause interlock resulting in hard deceleration of the vehicle.

It is therefore an object of the present invention to provide technique of detecting abnormality in a selector valve accurately. It is another object of the present invention to provide technique of detecting abnormality in a selector valve accurately and to performs a fail-safe control to prevent interlock.

According to one aspect of the present invention, an automatic transmission comprises: a planetary gear mechanism, an engagement element group, a pressure control valve, a selector valve and a shift control section. The engagement element group includes a plurality of friction engagement elements to achieve a plurality of gear positions in the planetary gear mechanism. At least one of the friction engagement elements is a particular engagement element (or variable engagement element, or multi-chamber engagement element) including first and second hydraulic pressure chambers to which a hydraulic fluid pressure is to be supplied to actuate the friction engagement element. The pressure control valve is a valve to regulate the hydraulic fluid pressure to be supplied to the particular engagement element. The selector valve is arranged to connect the second pressure chamber of the particular engagement element with the pressure control valve when the selector valve is at a first valve position, and to disconnect the second pressure chamber from the pressure control valve when the selector valve is at a second valve position. The shift control section is configured to command a shift operation from a first gear position in which the particular engagement element is disengaged, to a second gear position in which the particular engagement element is engaged, by controlling the selector valve to the second valve position to disconnect the second pressure chamber from the pressure control valve and to supply the hydraulic fluid pressure from the pressure control valve to the first pressure chamber of the particular engagement element, and to judge the selector valve to be in an abnormal state in which the selector valve is unable to disconnect the second pressure chamber from the pressure control valve, in accordance with a parameter in the shift operation from the first gear position to the second gear position.

According to another aspect of the invention, an automatic transmission comprises: a planetary gear mechanism; an engagement element group including a plurality of friction engagement elements to achieve a plurality of gear ratios in the planetary gear mechanism, at least one of the friction engagement elements being a first (or variable) engagement element including a first hydraulic pressure chamber and a second hydraulic pressure chamber; a hydraulic circuit including a pressure control valve to produce a hydraulic fluid pressure to be supplied to at least one of the first and second pressure chambers of the particular engagement element, and a selector valve including a first valve position to connect the second pressure chamber of the particular engagement element with the pressure control valve, and a second valve position to disconnect the second pressure chamber from the pressure control valve; and a shift control section configured to command a shift operation from a first gear ratio to a second gear ratio by producing a command signal to control the selector valve to the second valve position to disconnect the second pressure chamber from the pressure control valve and to supply the hydraulic fluid pressure from the pressure control valve to the first pressure chamber to engage the particular engagement element, and to determine whether the selector valve is in an abnormal state or not, by monitoring a parameter representing speed of engagement of the particular engagement element in the shift operation from the first gear ratio to the second gear ratio.

According to still another aspect of the present invention, for an automatic transmission including at least a planetary gear mechanism; an engagement element group including at least one first (or variable) engagement element including a first pressure chamber and a second pressure chamber; a pressure control valve to produce a hydraulic fluid pressure to be supplied to the variable engagement element; and a selector valve having a first valve position to connect the second pressure chamber with the pressure control valve and a second valve position to disconnect the second pressure chamber from the pressure control valve: abnormality detecting technique (apparatus and/or process) or controlling technique includes at least a shifting element for commanding a shift operation from a first gear ratio, to a second gear ratio, by producing a command signal to control the selector valve to the second valve position to disconnect the second pressure chamber from the pressure control valve and to engage the particular engagement element by supplying the hydraulic fluid pressure from the pressure control valve to the first pressure chamber of the particular engagement element; a monitoring element for monitoring behavior of engagement of the particular engagement element responsive to the command signal, and a judging element for determining whether the selector valve is in an abnormal state or not, in accordance with the behavior of the engagement of the particular engagement element.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows, in a skeleton diagram, an automatic transmission according to a first embodiment of the present invention. The automatic transmission shown inFIG. 1is a step automatic transmission having seven forward speeds and one reverse speed. The automatic transmission includes a shift gear mechanism including a planetary gear mechanism and an engagement device group. In the example shown inFIG. 1, the planetary gear mechanism includes four planetary gear sets G1˜G4, and the engagement element group includes seven friction engagement elements C1˜C3and B1˜B4. A driving force of an engine91is inputted, through a torque converter TC, to an input shaft92of the automatic transmission. Rotation is transmitted from input shaft92through the planetary gear mechanism to an output shaft93to drive a vehicle. A gear ratio is determined by the planetary gear mechanism and the engagement element group. An oil pump OP is provided coaxially with a pump impeller of torque converter TC, and arranged to pressurize an operating oil by being driven by the driving force of engine91.

There are further provided an engine controller (ECU)10to control engine91, an automatic transmission controller (ATCU)20to control the automatic transmission, and a control valve unit (CVU)30(serving as shift controlling means) to control fluid (oil) pressures for the friction engagement elements under the control of automatic transmission controller20. Engine controller10and transmission controller20are connected by communicating means such as a CAN communication line, and arranged to share information such as sensor information and control information.

ECU10is connected with an accelerator position sensor (APO sensor)1for sensing a driver's accelerator input by sensing an accelerator pedal operation quantity, and an engine speed sensor2for sensing an engine speed (rpm) of engine91. In accordance with the sensed accelerator pedal operation quantity and sensed engine speed, ECU10controls the engine output speed and engine torque by controlling the fuel injection quantity and throttle opening.

ATCU20is connected with a first (turbine) speed sensor3for sensing the rotational speed of a first planet carrier PC1, a second (turbine) speed sensor4for sensing the rotational speed of a first ring gear R1, an output shaft speed sensor5for sensing the rotational speed of the output shaft93, and an inhibitor switch6for sensing a driver's shift lever operating condition. In a D range, ATCU20selects an optimum command speed (or gear ratio) in accordance with a vehicle speed Vsp and the accelerator pedal operation quantity APO, and sends a control command to achieve the command speed, to CVU30.

The planetary gear mechanism is connected between the input and output shafts92and93. The planetary gear mechanism of this example includes a first planetary gear system GS1(G1, G2) and a second planetary gear system GS2(G3, G4). First planetary gear system GS1is disposed axially between the torque converter TC and the second planetary gear system GS2. The engagement element group includes a plurality of clutches C1, C2and C3, and a plurality of brakes B1, B2, B3and B4. Furthermore, there are provided a plurality of one way clutches F1and F2.

First planetary gear set G1is a single pinion planetary gear set including first sun gear S1, first ring gear R1and first planet carrier PC1carrying first pinions P1each engaging with both the first sun gear S1and first ring gear R1. Second planetary gear set G2is a single pinion planetary gear set including second sun gear S2, second ring gear R2and second planet carrier PC2carrying second pinions P2engaging with both the second sun gear S2and second ring gear R2. Third planetary gear set G3is a single pinion planetary gear set including third sun gear S3, third ring gear R3and third planet carrier PC3carrying third pinions P3engaging with both the third sun gear S3and third ring gear R3. Fourth planetary gear set G4is a single pinion planetary gear set including fourth sun gear S4, fourth ring gear R4and fourth planet carrier PC4carrying fourth pinions P4engaging with both the fourth sun gear S4and fourth ring gear R4.

Input shaft92is connected to second ring gear R2. The rotational driving force of engine91transmitted through torque converter TC is inputted to second ring gear R2. Output shaft93is connected with third planet carrier PC3. The output rotational driving force is transmitted from output shaft93, through a final gear unit to drive wheels of the vehicle.

A first connecting member M1connects first ring gear R1, second planet carrier PC2and fourth ring gear R4so that they rotate as a unit. A second connecting member M2connects third ring gear R3and fourth planet carrier PC4so that they rotate as a unit. A third connecting member M3connects first sun gear S1and second sun gear S2so that they rotate as a unit.

The above-mentioned first planetary gear system GS1is formed by connecting first and second planetary gear sets G1and G2with first and third connecting members M1and M3. Thus, first planetary gear system GS1is composed of four rotating members. Second planetary gear system GS2is formed by connecting third and fourth planetary gear sets G3and G4with second connecting member M2. Therefore, second planetary gear system GS2is composed of five rotating members.

In the first planetary gear system GS1, torque is inputted from input shaft92to second ring gear R2, and the torque is transmitted through first connecting member M1to the second planetary gear system GS2. In the second planetary gear system GS2, torque can be inputted from input shaft92directly to second connecting member M2, and, moreover, torque is transmitted through first connecting member M1to fourth ring gear R4. Then, the torque is transmitted from third planet carrier PC3to output shaft93.

First clutch C1is an input clutch for selectively making and breaking connection between input shaft92and second connecting member M2. Second clutch C2is a direct clutch for selectively making and breaking connection between fourth sun gear S4and fourth planet carrier PC4.

Third clutch C3is an H&LR clutch for selectively making and breaking connection between third sun gear S3and fourth sun gear S4. Second one way clutch F2is disposed between third sun gear S3and fourth sun gear S4. When H&LR clutch C3is disengaged, and the rotational speed of fourth sun gear S4is higher than that of third sun gear S3, then the third and fourth sun gears S3and S4rotate at different speeds independently. Therefore, third and fourth planetary gear sets G3and G4connected by second connecting member M2can achieve independent gear ratios, respectively.

First brake B1is a front brake disposed between a transmission case95and the first planet carrier PC1, for selectively holding the first planet carrier PC1. First one way clutch F1is connected in parallel with this front brake B1. Second brake B2is a low brake for selectively holding the third sun gear S3. Third brake B3is a 2346 brake for selectively holding the third connecting member M3connecting first sun gear S1and second sun gear S2. Fourth brake B4is a reverse brake for selectively holding the fourth planet carrier PC4.

The thus-constructed shift gear mechanism can achieve a desired speed by changing the engagement states of these friction engagement elements or devices as shown in an engagement table ofFIG. 2. InFIG. 2, each of small circles denotes engagement of a corresponding friction engagement element. Each of small circles in parentheses indicates that a corresponding friction engagement element is engaged at a range position at which engine braking is applied.

FIG. 3shows a hydraulic circuit section for low brake B2which is to be engaged only at first, second and third speeds, and which can serve as a particular engagement element (or variable engagement element or multi-chamber engagement element) having at least two hydraulic pressure chambers. The circuit section shown inFIG. 3is a part of the hydraulic circuit of CVU30.

CVU30includes a pressure regulator valve31and a manual valve32. Pressure regulator valve31produces a line pressure by regulating a pressure discharged from oil pump OP in accordance with an opening of pressure regulator valve31. Manual valve32selects a supply passage to supply the line pressure from pressure regulator valve31, to a selected one or more of the engaging elements.

Low brake B2(corresponding to a particular engagement element or multi or dual-chamber engagement element having at least two hydraulic pressure chambers) includes an alternating friction plate pack of first friction plates33and second friction plates44, and a piston for compressing the friction plate pack to engage the brake. The piston of low brake B2includes a first piston portion35and a second piston portion36. The first piston portion35has a first pressure receiving area, and the second piston portion36has a second pressure receiving area which is greater than the first pressure receiving area of first piston portion35. The first and second piston portions35and36are integral parts of the piston. A first pressure chamber37is arranged to apply a first hydraulic fluid pressure to the first piston portion35to force the piston toward the clutch plate pack. A second pressure chamber38is arranged to apply a second hydraulic fluid pressure to the second piston portion36to force the piston toward the clutch plate pack. The hydraulic circuit section is arranged to supply fluid pressures to the first and second pressure chamber37and38independently. The piston pushes the friction plate pack (33,34) with a pressure force which is equal to a sum of a first product of the first pressure in the first pressure chamber37and the first pressure receiving area of first piston portion35and a second product of the second pressure in the second pressure chamber38and the second pressure receiving area of the second piston portion36, and thereby produces the engagement capacity of low brake B2. In this example, the second pressure chamber38is an outer chamber surrounding the first pressure chamber37, as shown inFIG. 3, and the second piston portion36is an outer portion surrounding the first piston portion35which is an inner portion closer to the axis of low brake B2.

The hydraulic circuit section for low brake B2includes a pressure control valve39for regulating a hydraulic fluid pressure to be supplied to low brake B2, a first selector valve40for opening and closing a first pressure supply passage to supply the fluid pressure to the first pressure chamber37, and a second selector valve41(serving as a selector valve or changeover valve) for opening and closing a second pressure supply passage to supply the fluid pressure to the second pressure chamber38.

The opening of pressure control valve39is controlled in accordance with an operation quantity of a linear solenoid50. By the action of an on/off solenoid51, the first selector valve40moves between a first valve position (or connecting position) connecting the first pressure chamber37with the pressure control valve39, and a second valve position (or disconnecting position) disconnecting the first pressure chamber37from the pressure control valve39. The second selector valve41receives, as pilot pressure, the supply pressure to input clutch C1and the supply pressure to direct clutch C2, and moves between a first valve position (or connecting position) connecting the second pressure chamber38with the pressure control valve39, and a second valve position (or disconnecting position) disconnecting the second pressure chamber38from the pressure control valve39. The second selector valve41is shifted to the first valve position (or connecting position) when no fluid pressures are supplied to input clutch C1and direct clutch C2. When the oil pressure is supplied to either of the input clutch C1and direct clutch C2, the second selector valve41is shifted to the second valve position (disconnecting position).

The pressure control valve39receives the line pressure PLsupplied from manual valve32to the hydraulic circuit section for low brake B2, and produces a low brake operating fluid pressure by regulating the line pressure PL. The hydraulic circuit section for low brake B2does not supply the low brake operating fluid pressure to either of the first and second pressure chambers37and38when the first and second selector valves40and41are at the respective second (disconnecting) valve positions. When either of the first and second selector valves40and41is at its first (connecting) valve position, then the low brake operating fluid pressure is supplied through the selector valve40or41at the first (connecting) valve position, to the corresponding one of the first and second pressure chambers37and38. When the first and second selector valves40and41are both at the respective first (connecting) valve positions, then the low brake operating fluid pressure is supplied to both of the first and second pressure chambers37and38.

As shown in the engagement table ofFIG. 2, the low brake B2is engaged only at first, second and third speeds. In the case of first and second speeds, the torque ratio (share torque) is great and the low brake B2requires a greater engagement capacity between the first friction plates33and second friction plates44. Therefore, the first and second selector valves40and41are both put in the respective first (connecting) valve positions. In the case of third speed, the torque ratio is smaller and the required engagement capacity is not so great. Therefore, the first selector valve40is controlled to the first (connecting) valve position and the second selector valve41is controlled to the second (disconnecting) valve position.

In the shift from third speed to second speed in this automatic transmission, for example, the second selector valve41is changed over from the second (disconnecting) valve position to the first (connecting) valve position. If, in this changeover, the second selector valve41sticks and becomes immovable because of involvement of a removed burr, and thereafter the pressure control valve39sticks at the valve position to supply the oil pressure, then the oil pressure is supplied invariably to the second pressure chamber38. If, in this state, another clutch or brake is engaged, simultaneously with low brake B2, in a subsequent shift operation, the vehicle might be decelerated abruptly by interlock in the automatic transmission.

FIG. 4shows, in the form of a flowchart, a control process performed by ATCU20according to the first embodiment, to prevent such a problem.

In the control process ofFIG. 4, ATCU first clears a first counter C1at a step S1, and then clears a timer T at a step S2. Counter C1and timer T are incremented at later steps as explained later.

At a next step S3, ATCU examines whether a coast 4-3 shift operation is in progress. From S3, ATCU proceeds to a step S4when the coast 4-3 shift operation is in progress, and returns to S2when the coast 4-3 shift operation is not in progress. ATCU judges that the coast 4-3 shift operation is in progress when the vehicle is a coast operation and the automatic transmission is in a shift operation from fourth speed (a first gearing state) to third speed (a second gearing state). ATCU can ascertain the coast operation by checking whether an idle switch (not shown) is ON or not. Alternatively, it is optional to ascertain the coast operation by examining whether the accelerator operation quantity sensed by APO sensor1is smaller than or equal to a predetermined value, or by examining whether the throttle opening is smaller than or equal to a predetermined value.

At step S4, ATCU examines whether a detection permitting condition is satisfied or not. FROM S4, ATCU proceeds to a step S5when the detection permitting condition is satisfied, and returns to S2when the detection permitting condition is not satisfied. The detection permitting condition is a condition which is satisfied when all the following first, second, third and fourth conditions are satisfied. The first condition is satisfied when the inhibitor switch6is normal. The second condition is satisfied when a drive wheel spin is not detected. The third condition is satisfied when there is no hard vehicle deceleration. The fourth condition is satisfied when the shift position of the automatic transmission is in the D range.

At step S5, ATCU increments the before-mentioned timer T (or add a predetermined number to timer T). The timer T is used to measure time (an inertia phase time) required from a start of a coast 4-3 shift operation to an end of the coast 4-3 shift operation.

At a step S6. ATCU examines whether the 4-3 shift operation is finished or not. From S6, ATCU proceeds to a step S7when the judgment is that the 4-3 shift operation is finished, and returns to step S3when the judgment is that the 4-3 shift operation is not yet finished. ATCU examines whether the 4-3 shift operation is finished, by examining whether the inertia phase is finished or not.

FIG. 5(FIGS. 5A˜5D) is a time chart of a 4-3 shift operation for illustrating the examination to detect an end of the 4-3 shift operation in terms of an acceleration of the output shaft (FIG. 5A), a rotational speed of the input shaft (FIG. 5B), a command pressure of the H&LR clutch (FIG. 5C), and a command pressure of the low brake (FIG. 5D).

When a 4-3 shift command is outputted at an instant t1, the command pressure of H&LR clutch C3is decreased like a step and the command pressure of low brake B2is increased gradually. At an instant t2, H&LR clutch C3is disengaged completely, and low brake B2starts engaging. Therefore, at t2, the gear ratio starts varying toward the speed ratio of the third speed from the speed ratio of the fourth speed. As a result, the input speed of input shaft92starts increasing, and the deceleration of output shaft93starts increasing. Thereafter, when low brake B2is engaged completely at an instant t3, the deceleration of output shaft93becomes approximately equal to zero, and the input speed of input shaft92becomes approximately constant. Accordingly, at an instant t4, ATCU increases the opening of pressure control valve39to the maximum level, and increases the command pressure of low brake B2like a step.

In this example, the inertia phase is a period from t2to t3during which the speed ratio is varying. Thus, ATCU decides that the 4-3 shift operation is finished, at the end t3of the inertia phase.

At step S7, ATCU examines whether the timer T is shorter than or equal to a predetermined time length. From S7, ATCU proceeds to a step S8when the timer T is equal to or shorter than the predetermined time length, and returns to S1when the timer T is longer than the predetermined time length.

In the form of a time chart similar toFIG. 5(FIGS. 5A˜5D),FIG. 6(FIGS. 6A˜6D) shows a 4-3 shift operation in an abnormal state to clarify the meaning of the predetermined time length of step S7.FIG. 6Ashows the acceleration of output shaft93,FIG. 6Bshows the rotational speed of input shaft92,FIG. 6Cshows the command pressure of H&LR clutch C3, andFIG. 6Dshows the command pressure of low brake B2.

In the state in which, because of a failure in the second selector valve41, the fluid pressure is supplied invariably to the second pressure chamber38of low brake B2, the second selector valve41is held in the first valve position without regard to the command pressure for low brake B2in the 4-3 shift, and the second pressure chamber38is held in fluid communication with pressure control valve39. Therefore, the engagement capacity for the fluid pressure actually supplied to low brake B2becomes excessive beyond a proper value. As a result, after a start t2of the inertia phase, the shift of low brake B2proceeds faster, the rate of increase of the input speed of input shaft92is higher, the deceleration (or the rate of decrease of the rotational speed) of output shaft93is higher as compared to normal, and the inertia phase time becomes significantly shorter than normal. In order to detect such an inertia phase time accurately, the predetermined time length of step S7is determined in accordance with an inertia phase time obtained when the fluid pressure for the 4-3 shift operation is supplied simultaneously to both the first and second pressure chambers37and38.

At step S8, ATCU increments the first counter C1(or add a predetermined number to first counter C1). First counter C1is for counting the number of judgments that the timer T is equal to shorter than the predetermined time length.

At a step S9, ATCU examines whether the first counter C1is greater than or equal to a predetermined first number or not. From S9, ATCU proceeds to a step S10when the first counter C1is greater than or equal to the predetermined first number, and returns to step S2when the first counter C1is smaller than the predetermined first number. The predetermined first number is a number so determined experimentally in advance as to represent the number of times of consecutive judgments of abnormality that the time of the coast 4-3 shift is too short, in one driving cycle, required to discriminate an actual failure securely from a temporary irregularity. The driving cycle is a period from a turn-on of an ignition key switch to a turn-off of the ignition key switch.

At step S10, ATCU examines whether a flag F is equal to one or not. From S10, ATCU proceeds to a step S11when F=1, and proceeds to a step S13when F=0. Flag F is a condition code to indicate the execution of at least one incrementing operation of incrementing a second counter C2.

At step S11, ATCU examines whether addition has been performed to the second counter C2in the previous driving cycle. From S11, ATCU proceeds to a step S13when the addition to second counter C2has been performed in the previous driving cycle, and proceeds to a step S12when the second counter C2is not increased in the previous driving cycle. The second counter C2is a counter for measuring the number of driving cycles in which the first counter C1becomes greater than or equal to the predetermined first number.

At step S12, ATCU clears the second counter C2. At step S13, ATCU increases the second counter C2by addition of a predetermined number. At a step S14, ATCU sets flag F to one.

At a step S15(abnormality detecting or judging means), ATCU examines whether the second counter C2is greater than or equal to a second predetermined number. From S15, ATCU proceeds to a step S17when second counter C2is greater than or equal to the second predetermined number, and proceeds to a step S16when second counter C2is smaller than the second predetermined number.

At step S16, ATCU examines whether the current driving cycle is finished or not. From S16, ATCU returns to step S1when the current driving cycle is finished, and repeats step S16when the current driving cycle is not yet finished. ATCU checks whether the key switch of the vehicle is turned off, to determine whether the current driving cycle is finished.

At step S17, ATCU performs a fail-safe control operation in response to the affirmative answer of S15warning the detection of an abnormal condition. In this example, ATCU limits the selectable speed to the first speed, second speed and third speed after the vehicle is stopped. Thus, ATCU prevents occurrence of interlock by preventing a shifting operation requiring disengagement of low brake B2. Thus, as a control in an abnormal state, the control system of this example limits the selectable speed to the first, second and third speeds after a stop of the vehicle.

In the first embodiment shown inFIG. 4, ATCU20monitors the inertia phase time as a parameter in a shift from 4th speed to 3rd speed, and determines whether the second selector valve41is in the abnormal state or not, in accordance with the inertia phase time. Therefore, the control system can detect a failure in the second selector valve41accurately, and prevent abrupt deceleration of the vehicle due to an interlock in the automatic transmission, despite of a subsequent failure in the pressure control valve39.

The control system including ATCU20as a main component can detect a failure in the second selector valve41accurately by monitoring, as the parameter in the 4-3 shift, the inertia phase time which does not change during the shift, and which does not depend on the sensitivity of the vehicle.

The control system performs the abnormality check of second selector valve41by using frequent 4-3 shifts during the coasting operation of the vehicle. Therefore, the control system have many opportunities for the abnormality check. Moreover, the control system can judge the abnormality in the second selector valve41stably and accurately by using the coasting operation in which the input torque is stable.

The fail-safe control operation is performed when the second counter C2representing the number of consecutive abnormality judgments in consecutive driving cycles is greater than or equal to the second predetermined number. Therefore, the control system can prevent superfluous fail-safe control responsive to temporary sticking in the second selector valve41and thereby prevent deterioration of the driving performance. Furthermore, even in case of a failure in the second selector valve41, the automatic transmission is still be able to achieve all the shift speeds, and a fail-safe control operation responsive to the failure of the second selector valve41is not necessarily urgent. Therefore, by performing the fail-safe control operation when the counter C2becomes equal to or greater than the predetermined second number, the control system can detect a failure of the second selector valve41accurately, and prevent interlock or undesired simultaneous engagement of two friction engagement elements in preparation of a failure in the pressure control valve39.

In the fail-safe control, the control system prevents shifting operations to the 4th through 7th speeds requiring engagement of one or more friction engagement element which would cause interlock if engaged simultaneously with the engagement of the low brake B2. Therefore, the control system can prevent interlock due to a failure of the pressure control valve39subsequent to a failure of the second selector valve41, and thereby prevent abrupt deceleration of the vehicle.

FIG. 7shows a control process performed by ATCU20in an automatic transmission according to a second embodiment of the present invention. The construction of the automatic transmission according to the second embodiment is the same as that of the first embodiment as shown inFIGS. 1˜3.

Steps S21˜S24are substantially identical to steps S1˜S4ofFIG. 4.

At a step S25, ATCU ascertains an acceleration of output shaft93, and stores the acceleration in a memory. A step S26is substantially identical to step S6ofFIG. 4.

At a step S27reached when the answer of S26is YES, ATCU checks a minimum value among stored values of the acceleration of output shaft93stored at step S25, and determines whether the minimum value of the acceleration of output shaft93is lower than or equal to a predetermined acceleration value or not. From S27, ATCU proceeds to a step S28when the minimum acceleration value of output shaft93is equal to or lower than the predetermined acceleration value, and returns to step S21when the minimum output shaft acceleration value is higher than the predetermined acceleration value. So as to make it possible to detect an abnormality accurately, the predetermined acceleration value is determined in accordance with the acceleration of output shaft93obtained when the hydraulic fluid pressure is supplied simultaneously to the first and second pressure chambers37and38.

Steps S28˜S37are substantially identical to steps S8˜S17ofFIG. 4.

Thus, ATCU20according to the second embodiment utilizes the output acceleration of output shaft93as the parameter to determine whether a condition to increase the first counter C1is satisfied or not, in place of the time required until an end of the coast 4-3 shift.

The acceleration (or the time rate of change of the rotational speed) of output shaft93becomes negative during the coast 4-3 shift as shown inFIG. 5A. In the abnormal condition in which the time for the 4-3 shift is short, the acceleration of output shaft93further decreases (that is, the deceleration increases) beyond normal, as shown inFIG. 6A. Therefore, the control system can ascertain the occurrence of an abnormal condition by checking whether the minimum value of the acceleration of output shaft93is smaller than or equal to the predetermined acceleration value.

In the second embodiment shown inFIG. 7, ATCU20monitors the output shaft acceleration as the parameter in the shift from 4th speed to 3rd speed, and determines whether the second selector valve41is in the abnormal state or not, in accordance with the output shaft acceleration. Therefore, the control system can detect a failure in the second selector valve41accurately, and prevent abrupt deceleration of the vehicle due to an interlock in the automatic transmission, despite of a subsequent failure in the pressure control valve.

The control system according to the second embodiment can detect a failure in the second selector valve41accurately, as in the first embodiment, by monitoring, as the parameter in the 4-3 shift, the output shaft acceleration (or the rate of decrease of the output rotational speed of output shaft93).

The control system according to the second embodiment performs the abnormality check of second selector valve41by using the chances of frequently occurring 4-3 shifts during the coasting operation of the vehicle. Therefore, the control system can have many opportunities for the abnormality check. Moreover, the control system can judge the abnormality in second selector valve41stably and accurately by utilizing the coasting operation during which the input torque is stable.

The fail-safe control operation is performed when the second counter C2representing the number of consecutive abnormality judgments in consecutive driving cycles is greater than or equal to the second predetermined number. Therefore, the control system according to the second embodiment can prevent superfluous fail-safe control operation responsive to temporary sticking in the second selector valve41and thereby prevent deterioration of the driving performance. Furthermore, even in case of a failure in the second selector valve41, the automatic transmission is still be able to achieve all the speeds, and a fail-safe control operation responsive to the failure of the second selector valve41is not strictly urgent. Therefore, by performing the fail-safe control operation when the counter C2becomes equal to or greater than the predetermined second number, the control system can detect a failure of the second selector valve41accurately, and prevent interlock or undesired simultaneous engagement of two friction engagement elements in preparation for a failure in the pressure control valve39.

In the fail-safe control, the control system according to the second embodiment prevents shifting operations to the 4th through 7th speeds which are the speeds requiring engagement of one or more friction engagement element which would cause interlock if engaged simultaneously with the engagement of low brake B2. Therefore, the control system can prevent interlock due to a failure of the pressure control valve39subsequent to a failure of the second selector valve41, and thereby prevent abrupt deceleration of the vehicle.

FIG. 8shows a control process performed by ATCU20in an automatic transmission according to a third embodiment of the present invention. The construction of the automatic transmission according to the third embodiment is the same as that of the first embodiment as shown inFIGS. 1˜3.

Steps S41˜S44are substantially identical to steps S1˜S4ofFIG. 4.

At a step S45, ATCU ascertains the rate of change of the rotational speed of input shaft92with respect to time, and stores the rate of change of the input shaft speed in a memory. A step S46is substantially identical to step S6ofFIG. 4.

At a step S47, ATCU checks an average of the rate of change of the input shaft speed stored at step S45in the inertia phase, and determines whether the average of the rate of change of the input shaft speed is greater than or equal to a predetermined rate value or not. From S47, ATCU proceeds to a step S48when the average rate of change of the input speed of input shaft92is equal to or higher than the predetermined rate value, and returns to step S41when the average rate of change of the input speed is lower than the predetermined rate value. So as to make it possible to detect an abnormality accurately, the predetermined rate value is determined in accordance with the average rate of change of input speed of input shaft92obtained when the fluid pressure is supplied simultaneously to the first and second pressure chambers37and38.

Steps S48˜S57are substantially identical to steps S8˜S17ofFIG. 4.

Thus, ATCU20according to the third embodiment utilizes the average of the rate of change of the rotational speed of input shaft92in the inertia phase, as the parameter to determine whether the condition to increase the first counter C1is satisfied or not, in place of the time required to accomplish the coast 4-3 shift.

The time rate of change of the rotational speed of input shaft92during the coast 4-3 shift becomes greater in the abnormal state as shown inFIG. 6Bwhere the time for the 4-3 shift is short, than in the normal state shown inFIG. 5B. Therefore, the control system can ascertain the occurrence of an abnormal condition by comparing the average of the rate of change of the input speed of input shaft92in the inertia phase of the 4-3 shift with the predetermined rate value.

In place of the average of the rate of change of the input speed of input shaft92, it is optional to employ a maximum value of the rate of change of the input speed of input shaft92.

In the third embodiment shown inFIG. 8, ATCU20monitors the rate of change (or the rate of increase) of the input shaft speed as the parameter in the shift from 4th speed to 3rd speed, and determines whether the second selector valve41is in the abnormal state or not, in accordance with the rate of change of the input shaft speed. Therefore, the control system can detect a failure in the second selector valve41accurately, and prevent abrupt deceleration of the vehicle due to an interlock in the automatic transmission, despite of a subsequent failure in the pressure control valve.

The control system according to the third embodiment can detect a failure in the second selector valve41accurately, as in the first embodiment, by monitoring, as the parameter in the 4-3 shift, the variation or behavior of the input shaft speed such as the rate of change of the input shaft speed.

The control system according to the third embodiment performs the abnormality check of the second selector valve41by using the chances of frequently occurring 4-3 shifts during the coasting operation of the vehicle. Therefore, the control system can have many opportunities for the abnormality check. Moreover, the control system can judge the abnormality in the second selector valve41stably and accurately by utilizing the coasting operation during which the input torque is stable.

The fail-safe control operation is performed when the second counter C2representing the number of consecutive abnormality judgments in consecutive driving cycles is greater than or equal to the second predetermined number. Therefore, the control system according to the third embodiment can prevent superfluous fail-safe control responsive to temporary sticking in the second selector valve41and thereby prevent deterioration of the driving performance. Furthermore, even in case of a failure in the second selector valve41, the automatic transmission is still be able to achieve all the shift speeds, and a fail-safe control operation responsive to the failure of the second selector valve41is not necessarily urgent. Therefore, by performing the fail-safe control operation when the counter C2becomes equal to or greater than the predetermined second number, the control system can detect a failure of the second selector valve41accurately, and prevent interlock or undesired simultaneous engagement of two friction engagement elements in preparation for a failure in the pressure control valve39.

In the fail-safe control, the control system according to the third embodiment prevents shifting operations to the 4th through 7th speeds requiring engagement of one or more friction engagement element which would cause interlock if engaged simultaneously with the engagement of the low brake B2. Therefore, the control system can prevent interlock due to a failure of the pressure control valve39subsequent to a failure of the second selector valve41, and thereby prevent abrupt deceleration of the vehicle.

FIG. 9shows a control process performed by ATCU20in an automatic transmission according to a fourth embodiment of the present invention. The construction of the automatic transmission according to the fourth embodiment is the same as that of the first embodiment as shown inFIGS. 1˜3.

Steps S61˜S64are substantially identical to steps S1˜S4ofFIG. 4.

At a step S65, ATCU ascertains a rate of change of the gear ratio, and stores the rate of change of the gear ratio. A step S66is substantially identical to step S6ofFIG. 4.

At a step S67, ATCU checks the rate of change of the gear ratio stored at step S65, and determines whether the rate of change of the gear ratio is greater than or equal to a predetermined gear ratio rate value or not. From S67, ATCU proceeds to a step S68when the rate of change of the gear ratio is equal to or higher than the predetermined gear ratio rate value, and returns to step S61when the rate of the gear ratio is lower than the predetermined gear ratio rate value. So as to make it possible to detect an abnormality accurately, the predetermined gear ratio rate value is determined in accordance with the rate of change of the gear ratio obtained when the oil pressure is supplied simultaneously to the first and second pressure chambers37and38.

Steps S68˜S77are substantially identical to steps S8˜S17ofFIG. 4.

Thus, ATCU20according to the fourth embodiment utilizes the rate of change of the gear ratio, as the parameter to determine whether the condition to increase the first counter C1is satisfied or not, in place of the time required to accomplish the coast 4-3 shift.

The rate of change of the gear ratio during the coast 4-3 shift becomes greater in the abnormal state where the time for the 4-3 shift is short, than in the normal state. Therefore, the control system can ascertain the occurrence of an abnormal condition by comparing the rate of change of the gear ratio with the predetermined gear ratio rate value.

In the fourth embodiment shown inFIG. 9, ATCU20monitors the rate of change of the gear ratio as the parameter in the shift from 4th speed to 3rd speed, and determines whether the second selector valve41is in the abnormal state or not, in accordance with the rate of change of the gear ratio. Therefore, the control system can detect a failure in the second selector valve41accurately, and prevent abrupt deceleration of the vehicle due to an interlock in the automatic transmission, despite of a subsequent failure in the pressure control valve.

The control system according to the fourth embodiment can detect a failure in the second selector valve41accurately, as in the first embodiment, by monitoring, as the parameter in the 4-3 shift, the variation of the gear ratio such as the rate of change of the gear ratio.

The control system according to the fourth embodiment performs the abnormality check of the second selector valve41by using the chances of frequently occurring 4-3 shifts during the coasting operation of the vehicle. Therefore, the control system can have many opportunities for the abnormality check. Moreover, the control system can judge the abnormality in the second selector valve41stably and accurately by utilizing the coasting operation during which the input torque is stable.

The fail-safe control operation is performed when the second counter C2representing the number of consecutive abnormality judgments in consecutive driving cycles is greater than or equal to the second predetermined number. Therefore, the control system according to the fourth embodiment can prevent superfluous fail-safe control responsive to temporary sticking in the second selector valve41and thereby prevent deterioration of the driving performance. Furthermore, even in case of a failure in the second selector valve41, the automatic transmission is still be able to achieve all the shift speeds, and a fail-safe control operation responsive to the failure of the second selector valve41is not necessarily urgent. Therefore, by performing the fail-safe control operation when the counter C2becomes equal to or greater than the predetermined second number, the control system can detect a failure of the second selector valve41accurately, and prevent interlock or undesired simultaneous engagement of two friction engagement elements in preparation for a failure in the pressure control valve39.

In the fail-safe control, the control system according to the fourth embodiment prevents shifting operations to the 4th through 7th speeds requiring engagement of one or more friction engagement element which would cause interlock if engaged simultaneously with the engagement of the low brake B2. Therefore, the control system can prevent interlock due to a failure of the pressure control valve39subsequent to a failure of the second selector valve41, and thereby prevent abrupt deceleration of the vehicle.

In the example ofFIG. 1, the speed sensors3and4can serve as an input speed sensor for sensing the rotational speed of input shaft92. The rotational speed (N(R2) of input shaft92(and second ring gear R2) can be calculated from the rotational speed (N(PC1)) of first planet carrier PC1sensed by first speed sensor3, and the rotational speed (N(PC2)) of second planet carrier PC2sensed by second speed sensor4according to the following equation.
N(R2)=(1+β2/β1)N(PC2)−(β2/β1)N(PC1)
where β1 is a ratio (Zs1/ZR1) of the number (Zs1) of teeth of first sun gear S1to the number (ZR1) of teeth of first ring gear R1, and β2 is a ratio (Zs2/ZR2) of the number (Zs2) of teeth of second sun gear S2to the number (ZR2) of teeth of second ring gear R2. Although the input speed is calculated in this way from the signals from the first and second speed sensors3and4in the example ofFIG. 1, it is possible to sense the rotational speed of input shaft92with an input shaft speed sensor arranged to sense the rotational speed of input shaft92directly. Thus, the system according to the third embodiment shown inFIG. 8can ascertain the actual rotational speed of input shaft92by using the output signals from the sensors3and4, or by using the output signal from the input shaft speed sensor directly sensing the rotation of input shaft92, and calculates the rate of change of the input shaft speed with respect to time, from the actual rotational speed of input shaft92, at step S45.

According to the fourth embodiment, the system can determine the actual gear ratio from the actual input shaft speed determined by using the sensors3and4or the above-mentioned input shaft speed sensor, and the actual output shaft speed sensed by the output shaft speed sensor5. Thus, the system determines the actual gear ratio (the actual input shaft speed/the actual output shaft speed) from the actual input and output shaft speeds, and calculate the rate of change of the actual gear ratio at step S65.

In the example ofFIG. 4according to the first embodiment, the system determines the inertia phase time (T) by monitoring variation of the actual gear ratio (the actual input shaft speed/the actual output shaft speed). More specifically, the system judges that the shift (the inertia phase) from the before-shift gear position (fourth speed) to the after-shift gear position (third speed) is started when the actual gear ratio is varied by a predetermined amount from the gear ratio of the before-shift gear position (fourth speed); and the system judges that the shift (the inertia phase) from the before-shift gear position (fourth speed) to the after-shift gear position (third speed) is finished when the actual gear ratio enters a predetermined range near the gear ratio of the after-shift gear position (third speed). Thus, ATCU20can start the measurement of the inertia phase time (T) (at step S3) when the actual gear ratio is varied from the gear ratio of the before-shift gear position (fourth speed) toward the gear ratio of the after-shift gear position (third speed) and the difference between the actual gear ratio and the gear ratio of the before-shift gear position becomes greater than the predetermined amount (in the coasting operation); an ends the measurement of the inertial phase time (T) (at step S6) when the actual gear ratio approaches the gear ratio of the after-shift gear position (third speed), and the difference between the actual gear ratio and the gear ratio of the after-shift gear position becomes smaller than a predetermined value. However, the measurement of the inertia phase time is not limited to this method based on the actual gear ratio. For example, it is possible to detect the start and end of an inertia phase by monitoring variation of the input shaft speed (as shown inFIG. 5B).

According to the illustrated embodiments, an automatic transmission includes at least: a planetary gear mechanism; an engagement element group (or device group) including a plurality of friction engagement elements (or devices) to achieve a plurality of gear ratios in the planetary gear mechanism, at least one of the friction engagement elements being a first (or variable) engagement element including a first pressure chamber and a second pressure chamber; a pressure control valve to produce a hydraulic fluid pressure to be supplied to the particular engagement element; and a selector valve arranged to connect the second pressure chamber of the particular engagement element with the pressure control valve when the selector valve is at a first valve position, and to disconnect the second pressure chamber from the pressure control valve when the selector valve is at a second valve position. For this automatic transmission, a controlling or abnormality detecting apparatus (such as ATCU20) includes at least a shifting means for commanding a shift operation from a first gear ratio, to a second gear ratio, by producing a command signal to control the selector valve to the second valve position to disconnect the second pressure chamber from the pressure control valve and to engage the particular engagement element by supplying the hydraulic fluid pressure from the pressure control valve to the first pressure chamber of the particular engagement element; and monitoring means for monitoring behavior of engagement of the particular engagement element responsive to the command signal, and for determining whether the selector valve is in an abnormal state or not, in accordance with the behavior of the engagement of the particular engagement element. At least one of steps S5, S7, S25, S27, S45, S47, S65and S67may correspond to at least part of the monitoring means. For the automatic transmission, a process (such as a control or abnormality detecting process performed by ATCU20) includes at least a step of commanding a shift operation from a first gear ratio, to a second gear ratio, by producing a command signal to control the selector valve to the second valve position to disconnect the second pressure chamber from the pressure control valve and to engage the particular engagement element by supplying the hydraulic fluid pressure from the pressure control valve to the first pressure chamber of the particular engagement element; a step of monitoring behavior of engagement of the particular engagement element responsive to the command signal, and a step of determining whether the selector valve is in an abnormal state or not, in accordance with the behavior of the engagement of the particular engagement element. The process may further includes a step of performing a fail-safe control operation (corresponding to S17, S37, S57and S77) when the selector valve is judged to be in the abnormal state.

This application is based on a prior Japanese Patent Application No. 2007-001500 filed on Jan. 9, 2007 in Japan. The entire contents of this Japanese Patent Application No. 2007-001500 are hereby incorporated by reference.