Automatic transmission

An automatic transmission includes a first frictional engagement element (a low clutch 40), a second frictional engagement element (an L/R brake 60), two hydraulic chambers (a gap adjustment chamber 64 and a pressure chamber 65) provided in the second frictional engagement element, a first hydraulic pressure generator 101 (an electric pump 101) generating a hydraulic pressure during an automatic stop of the engine, and a control unit (a control unit 200) controlling the hydraulic pressure in the first and second frictional engagement elements. The control unit supplies the hydraulic pressure generated by the first hydraulic pressure generator to the first frictional engagement element and one of the two hydraulic chambers of the second frictional engagement element when the automatic transmission is in the non-traveling range and the engine has been automatically stopped.

TECHNICAL FIELD

The technique disclosed herein relates to an automatic transmission for a vehicle to which an idle stop control is applied to stop an engine automatically when the vehicle is stopped, and relates to a technical field of such an automatic transmission for vehicles.

BACKGROUND ART

In conventional automatic transmissions, one frictional engagement element and a one-way clutch are generally engaged to establish a starting gear position. However, such a one-way clutch is heavy, and may cause drag in gear positions except for the starting gear position. Accordingly, an attempt has been made to eliminate such a one-way clutch for, e.g., improving engine fuel consumption performance, and to engage two frictional engagement elements to establish the starting gear position.

Vehicles equipped with an idle stop control system have been commercially practical, in which an engine is automatically stopped when a predetermined stop condition is satisfied. Automatic transmissions mounted in such vehicles are provided with an electrically driven oil pump (hereinafter referred to as “electric pump”) in addition to a mechanically driven oil pump (hereinafter referred to as “mechanical pump”) driven by an engine to enable quick start of the vehicle in the next start. Supplying a hydraulic pressure generated by this electric pump allows for, even during an engine stop, advance engagement of start frictional engagement elements which transmit a motive force in starting the vehicle.

However, there may be a situation where a vehicle's operator allows an automatic transmission to switch from a traveling range such as D-range to a non-traveling range such as N-range before or after the engine is automatically stopped when the vehicle is stopped. In such a situation, an engagement hydraulic pressure is released from each of the frictional engagement elements in this automatic transmission. Thus, the start frictional engagement elements are not engaged even if the electric pump is driven while the engine is being automatically stopped. The start frictional engagement elements will be engaged again when a switch is made to the traveling range in starting the vehicle. At that time, however, the vehicle may possibly fail to start smoothly after a restart of the engine due to engagement delay of the frictional engagement elements.

In order to handle such a problem, Patent Document 1 discloses an automatic transmission including an electric pump which is operated when the engine has been automatically stopped. This automatic transmission is allowed to control supply of a hydraulic pressure generated by the electric pump to start frictional engagement elements even when a switch is made to a non-traveling range in the automatic transmission before or after an automatic stop of the engine, thereby allowing for engaging the start frictional engagement elements in advance in this non-traveling range just like in a traveling range. According to this configuration, when a switch is made to the traveling range in the automatic transmission in starting the vehicle, the vehicle can be started immediately after a restart of the engine. This configuration allows for a smooth start-up of the vehicle.

CITATION LIST

Patent Document

SUMMARY OF THE INVENTION

Technical Problem

In the idle stop control applied to stop an engine automatically during a vehicle stop, what is called “system restart” is performed to restart the engine automatically if, e.g., a battery charge level falls to be equal to or lower than a predetermined value, or a high power consumption device such as an air conditioner is activated. At that time, if the automatic transmission controls start frictional engagement elements to be engaged in the non-traveling range, the vehicle is erroneously started due to a restart of the engine against the will of the vehicle's operator.

If the engine is restarted when the automatic transmission is in the non-traveling range and the start frictional engagement elements are engaged, the electric pump is stopped, and the start frictional engagement elements are disengaged by releasing a hydraulic pressure supplied to the start frictional engagement elements by a hydraulic control valve, such as a solenoid valve, provided in a hydraulic passage where the hydraulic pressure is supplied to the start frictional engagement elements from the electric pump. However, if an open failure occurs in the hydraulic control valve (a failure where the valve is not operated while the hydraulic passage is in a communicating state), the hydraulic pressure is not immediately released from the electric pump. As a result, the engine is restarted with the start frictional engagement elements kept engaged. This results in the above-described erroneous start of the vehicle in the non-traveling range.

To address such a problem, Patent Document 1 discloses providing a pressure release circuit in a position upstream of the solenoid valve in the hydraulic passage which begins at the electric pump and ends at the start frictional engagement elements through the solenoid valve, the circuit being configured to partially release a hydraulic fluid from the hydraulic passage. This circuit is configured to release the hydraulic pressure supplied to the start frictional engagement elements by stopping the electric pump even if an open failure occurs in the solenoid valve. This configuration prevents, at the time of open failure of the solenoid valve, an erroneous start of the vehicle in the non-traveling range due to a restart of the engine with the start frictional engagement elements kept engaged.

However, if the above pressure release circuit is provided in the hydraulic passage which begins at the electric pump and ends at the start frictional engagement elements, the hydraulic fluid discharged from the pump is partially released from the pressure release circuit whenever the electric pump is operated. Therefore, the electric pump needs to increase its capacity in order to ensure the quantity of the operating hydraulic fluid or a hydraulic pressure necessary to engage the start frictional engagement elements during an engine stop.

In particular, in the above automatic transmission where a one-way clutch is eliminated and two frictional engagement elements are engaged for establishing a starting gear position, the size of the electric pump increases to allow for engaging the start frictional engagement elements during an engine stop. This results in an increase in weight of the vehicle, an increase in electric power consumption for driving the electric pump, or other unwanted events.

In view of the foregoing, the technique disclosed herein relates to an automatic transmission mounted in a vehicle to which idle stop control for an engine is applied, and allows this automatic transmission to ensure a smooth start of the vehicle after a switch is made from a non-traveling range to a traveling range in a situation where this automatic transmission allows a hydraulic pressure generated by an electric pump to engage start frictional engagement elements in the traveling range and the non-traveling range during an automatic stop of the engine. The technique disclosed herein also allows this automatic transmission to prevent an erroneous start of the vehicle in the non-traveling range at the time of open failure of a hydraulic control valve such as the solenoid valve without causing an increase in size of the electric pump and an increase in electric power consumption thereof.

Solution to the Problem

In order to solve the above problems, the technique disclosed herein relates to an automatic transmission mounted in a vehicle to which idle stop control for an engine is applied such that the engine is automatically stopped when a predetermined stop condition is satisfied, and the engine is automatically restarted when a predetermined restart condition is satisfied during the automatic stop of the engine, the automatic transmission switching between a traveling range and a non-traveling range in response to an operation of a vehicle's operator, the automatic transmission comprising: a first frictional engagement element and a second frictional engagement element engaged when the vehicle is started in the traveling range; two hydraulic chambers provided in the second frictional engagement element, and engaging the second frictional engagement element when a hydraulic pressure is supplied to the two hydraulic chambers; a first hydraulic pressure generator generating the hydraulic pressure when the engine has been automatically stopped; and a control unit controlling the hydraulic pressure in the first and second frictional engagement elements, wherein the control unit supplies the hydraulic pressure generated by the first hydraulic pressure generator to the first frictional engagement element and one of the two hydraulic chambers of the second frictional engagement element when the automatic transmission is in the non-traveling range and the engine has been automatically stopped.

The control unit supplies the hydraulic pressure generated by the first hydraulic pressure generator to the first frictional engagement element when the automatic transmission is in the non-traveling range and the engine has been automatically stopped. This allows for engagement of the first frictional engagement element. The control unit also supplies the hydraulic pressure generated by the first hydraulic pressure generator to one of the two hydraulic chambers of the second frictional engagement element. At that time, the second frictional engagement element is not engaged, but in, what is called, a prepared-for-engagement state. Accordingly, when a switch is made from the non-traveling range to the traveling range in this prepared-for-engagement state, supplying the hydraulic pressure to the other hydraulic chamber of the second frictional engagement element allows for engagement of the second frictional engagement element. The second frictional engagement element is engaged more quickly as compared with a case where this element turns to the engaged state from its completely disengaged state. This allows for a quick start of the vehicle after a restart of the engine.

On the other hand, when the automatic transmission is in the non-traveling range and the system of the engine is restarted due to, e.g., reduced battery charge level, the hydraulic pressure supplied to the first frictional engagement element is released, thereby disengaging the frictional engagement element. At that time, even if the first frictional engagement element cannot be disengaged, the automatic transmission is not in a starting gear position. That is because only one of the two hydraulic chambers of the second frictional engagement element is supplied with the hydraulic pressure, and the second frictional engagement element is not in the engagement state that allows transmission of a motive force. As a result, the vehicle is not erroneously started even if the engine is restarted.

This eliminates a conventional need for providing a pressure release circuit which partially releases an operating hydraulic fluid at any time to a hydraulic passage that allows the first frictional engagement element to communicate with the first hydraulic pressure generator (configured as an electric pump, for example) which is operated during an automatic stop of the engine. As a result, this reduces an increase in size of the electric pump and in electric power consumption, for example.

The second frictional engagement element may be engaged when the engine is operated in a reverse gear of the traveling range or in the non-traveling range, the control unit may release the hydraulic pressure from the first frictional engagement element and supplies the hydraulic pressure to the two hydraulic chambers of the second frictional engagement element when the transmission is in the non-traveling range and the engine automatically stopped is restarted, and the control unit may continuously supply the hydraulic pressure to one of the two hydraulic chambers of the second frictional engagement element in a situation where the control unit is unable to release the hydraulic pressure from the first frictional engagement element when the transmission is in the non-traveling range and the engine automatically stopped is restarted.

Suppose a situation where the vehicle that has traveled forward in the D-range is once stopped, and then travels backward. At that time, the range of the automatic transmission switches from the D-range to the N-range, and then switches to the R-range. That is, the range of the automatic transmission once switches from the traveling range to the non-traveling range, and then switches to the traveling range again. Since the second frictional engagement element is configured to be engaged at the time of both forward and backward travel of the vehicle in the traveling range, engaging the second frictional engagement element by the supply of the hydraulic pressure to both of the two hydraulic chambers thereof when the transmission is in the non-traveling range and the engine is operated allows for continuously engaging the second frictional engagement element when the range of the automatic transmission switches from the D-range to the N-range, and then, switches to the R-range in the above situation. This establishes the reverse gear position immediately after a switch is made to the R-range.

In the above configuration, when the transmission is in the non-traveling range and the engine automatically stopped is restarted, the hydraulic pressure is supplied to both of the two hydraulic chambers of the second frictional engagement element, whereas the hydraulic pressure in the first frictional engagement element is released to prevent an erroneous start of the vehicle. However, if the hydraulic pressure in the first frictional engagement element cannot be released, the hydraulic pressure is supplied to only one of the two hydraulic chambers of the second frictional engagement element. That is, of the hydraulic pressure to be supplied to both of the two hydraulic chambers, the hydraulic pressure is released from either one of the chambers. This does not allow for engaging the second frictional engagement element, thereby preventing an erroneous start of the vehicle in the non-traveling range.

The control unit may supply the hydraulic pressure generated by first hydraulic pressure generator to the first frictional engagement element and one of the two hydraulic chambers of the second frictional engagement element when the transmission is in the traveling range and the engine has been automatically stopped.

During an automatic stop of the engine, the hydraulic pressure is supplied to the first frictional engagement element and one of the two of the hydraulic chambers of the second frictional engagement element irrespective of whether the automatic transmission is in the traveling range or the non-traveling range. Therefore, even when a switch is made from the traveling range to the non-traveling range during the automatic stop of the engine, the second frictional engagement element is still in the prepared-for-engagement state.

The automatic transmission may further includes: a first hydraulic control valve having an input port, an output port, and a drain port; a first hydraulic passage provided so as to allow the first hydraulic pressure generator to communicate with the hydraulic chamber of the first frictional engagement element through the input port and the output port of the first hydraulic control valve, and capable of releasing the hydraulic pressure supplied to the hydraulic chamber from only the drain port of the first hydraulic control valve; and a second hydraulic passage allowing the first hydraulic pressure generator to communicate with one of the two hydraulic chambers of the second frictional engagement element.

When the automatic transmission is in the non-traveling range and the engine has been automatically stopped, supplying the first frictional engagement element with the hydraulic pressure generated by the first hydraulic pressure generator through the first hydraulic passage via the first hydraulic control valve allows for engaging the first frictional engagement element. Besides, the hydraulic pressure generated by the first hydraulic pressure generator is supplied to one of the two hydraulic chambers of the second frictional engagement element through the second hydraulic passage. As a result, the second frictional engagement element enters the prepared-for-engagement state.

On the other hand, when the automatic transmission is in the non-traveling range and the system of the engine is restarted due to, e.g., reduced battery charge level, communication between the output port and the drain port of the first hydraulic control valve allows for releasing the hydraulic pressure that has been supplied to the first frictional engagement element, thereby disengaging the first frictional engagement element. At that time, if an open failure occurs in the first hydraulic control valve, the first frictional engagement element may not be disengaged. However, even in such a case, the automatic transmission is not in the starting gear position and the vehicle is not erroneously started after a restart of the engine because the second frictional engagement element is in the prepared-for-engagement state.

This eliminates the conventional need for, in preparation for the open failure of hydraulic control valve, providing a pressure release circuit which partially releases an operating hydraulic fluid at any time into a hydraulic passage that allows the first frictional engagement element to communicate with the hydraulic pressure generator such as an electric pump which is operated during an automatic stop of the engine. As a result, this reduces an increase in size of the electric pump and in electric power consumption, for example.

The two hydraulic chambers of the second frictional engagement element may serve as a pressing hydraulic chamber pressing friction plates of the second frictional engagement element through a pressure piston when the two hydraulic chambers are supplied with the hydraulic pressure, and a gap adjustment hydraulic chamber reducing a gap between the pressure piston and the friction plates when the two hydraulic chambers are supplied with the hydraulic pressure, and the second hydraulic passage may allow the first hydraulic pressure generator to communicate with the gap adjustment hydraulic chamber.

The two hydraulic chambers in the second frictional engagement element serve as a pressing hydraulic chamber pressing friction plates of the second frictional engagement element through a pressure piston when the two hydraulic chambers are supplied with the hydraulic pressure, and a gap adjustment hydraulic chamber reducing a gap between the pressure piston and the friction plates when the two hydraulic chambers are supplied with the hydraulic pressure. The hydraulic pressure generated by the first hydraulic pressure generator is supplied to the gap adjustment hydraulic chamber through the second hydraulic passage. This allows the second frictional engagement element to enter the prepared-for-engagement state, i.e., the state where the second frictional engagement element is disengaged and there is a smaller gap between the pressure piston and the friction plates during an automatic stop of the engine in the non-traveling range.

Accordingly, at the time of occurrence of an open failure in the first hydraulic control valve, an erroneous start of the vehicle due to a restart of the engine in the non-traveling range is reliably prevented, whereas the second frictional engagement element is able to be engaged immediately after a switch is made to the traveling range.

The automatic transmission may further includes: a second hydraulic pressure generator driven by the engine and generating a hydraulic pressure; a third hydraulic passage allowing the second hydraulic pressure generator to communicate with the pressing hydraulic chamber of the second frictional engagement element; and a second hydraulic control valve provided in the third hydraulic passage, and capable of releasing the hydraulic pressure supplied to the pressing hydraulic chamber of the second frictional engagement element in a situation where the first hydraulic control valve becomes unable to release the hydraulic pressure supplied to the first frictional engagement element when the transmission is in the non-traveling range and the engine is restarted automatically.

When the automatic transmission is in the non-traveling range and the engine is restarted, the hydraulic pressure generated by the second hydraulic pressure generator is supplied to the pressure hydraulic chamber of the second frictional engagement element through the third hydraulic passage. This allows for engaging the second frictional engagement element. At that time, if the first frictional engagement element is not disengaged due to the open failure of the first hydraulic control valve, the vehicle would be erroneously started in the non-traveling range. However, the third hydraulic passage is provided with the second hydraulic control valve capable of releasing the hydraulic pressure supplied to the pressing hydraulic chamber of the second frictional engagement element if the first hydraulic control valve becomes unable to disengage the first frictional engagement element. The second hydraulic control valve thus allows for preventing engagement of the second frictional engagement element at the time of a restart of the engine. This thus prevents an erroneous start of the vehicle in the non-traveling range if an open failure occurs in the first hydraulic control valve.

The automatic transmission may further includes a third hydraulic control valve provided between the second hydraulic control valve in the third hydraulic passage and the pressing hydraulic chamber of the second frictional engagement element, and is able to switch between a first state where the second hydraulic control valve communicates with the pressure hydraulic chamber and a second state where there is no communication between the second hydraulic control valve and the pressure hydraulic chamber. The third hydraulic control valve may be configured to switch to the first state if the hydraulic pressure is supplied to the gap adjustment hydraulic chamber through the second hydraulic passage.

The third hydraulic control valve is provided between the second hydraulic control valve in the third hydraulic passage and the pressure hydraulic chamber of the second frictional engagement element. The third hydraulic control valve switches to the first state where the second hydraulic control valve communicates with the pressing hydraulic chamber if the hydraulic pressure is supplied to the gap adjustment hydraulic chamber through the second hydraulic passage. Thus, the hydraulic pressure is supplied to, and released from, the pressing hydraulic chamber by the second hydraulic control valve, in other words, the second frictional engagement element is engaged and disengaged with a smaller gap between the pressure piston and the friction plates.

This configuration, in which the third hydraulic control valve is provided, also allows for preventing an erroneous start of the vehicle in the non-traveling range reliably. That is because, if the first hydraulic control valve becomes unable to disengage the first frictional engagement element, the second hydraulic control valve is provided to allow for releasing the hydraulic pressure supplied to the pressure hydraulic chamber of the second frictional engagement element.

Advantages of the Invention

As can be seen from the foregoing description, the above automatic transmission allows for preventing an erroneous start of a vehicle in a non-traveling range.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment will be described.FIG. 1is a schematic diagram of the configuration of an automatic transmission according to the embodiment. This automatic transmission1includes: an input shaft2receiving an engine output through a torque converter (not shown); first, second, and third planetary gear sets (hereinafter referred to as simply “first, second, and third gear sets”)10,20, and30disposed on the input shaft2in this order from a side adjacent to the engine (the right side of the figure); a low clutch40and a high clutch50, as a hydraulic frictional engagement element for switching power transmission paths configured to, as the gear sets10,20, and30, selectively transmitting a motive force from the input shaft2toward the gear sets10,20, and30; a low reverse brake (hereinafter referred to as “L/R brake”)60; a second gear/sixth gear/brake (hereinafter referred to as “2/6 brake”)70; and a reverse gear/third gear/fifth gear/brake (hereinafter referred to as “R/3/5 brake”)80. The L/R brake60, the 2/6 brake70, and the R/3/5 brake80is configured to fix predetermined rotation elements, namely, the respective gear sets10,20, and30.

The gear sets10,20, and30are respectively comprised of sun gears11,21, and31, pinions12,22, and32respectively engaged with the sun gears11,21, and31, carriers13,23, and33respectively supporting the pinions12,22, and32, and ring gears14,24, and34respectively engaged with the pinions12,22, and32.

The sun gear11of the first gear set10and the sun gear21of the second gear set20are connected together to be coupled to an output member41of the low clutch40. The carrier23of the second gear set20is connected to an output member51of the high clutch50, and the sun gear31of the third gear set30is directly connected to the input shaft2.

The ring gear14of the first gear set10and the carrier23of the second gear set20are connected together, and the L/R brake60is disposed between these elements and a transmission case3. The ring gear24of the second gear set20and the carrier33of the third gear set30are connected together, and the 2/6 brake70is disposed between these elements and the transmission case3. Furthermore, the R/3/5 brake80is disposed between the ring gear34of the third gear set30and the transmission case3. An output gear4is connected to the carrier13of the first gear set10, the output gear4outputting an output of the automatic transmission1to driving wheels (not shown).

According to the above configuration, through engagement combinations of the low clutch40, the high clutch50, the L/R brake60, the 2/6 brake70, and the R/3/5 brake80, the automatic transmission1establishes the six gears in forward traveling ranges such as the D-range and the reverse gear of the reverse range, as shown inFIG. 2. As is clear inFIG. 2, in this embodiment, the low clutch40and the L/R brake60are implementation of first and second frictional engagement elements which will be engaged at the time of vehicle start.

The L/R brake60of the automatic transmission1according to this embodiment includes a double-acting hydraulic actuator having a gap adjustment function for improving response performance at the time of its engagement.

Specifically, as illustrated inFIGS. 3A-3C, the hydraulic actuator61of the L/R brake60includes a gap adjustment piston62fitted in a cylinder3aprovided in the transmission case3and movable in the shaft direction, and a pressure piston63fitted in the gap adjustment piston62in a cylinder62aprovided inside the gap adjustment piston62and relatively movable in the shaft direction. A region behind the gap adjustment piston62in the cylinder3aof the transmission case3is a hydraulic chamber64for gap adjustment (hereinafter referred to as a “gap adjustment chamber”), and a region behind the pressure piston63in the cylinder62aof the gap adjustment piston62is a pressure chamber65for engagement of the L/R brake (hereinafter referred to as a “pressure chamber”).

As illustrated inFIG. 3A, supplying the gap adjustment chamber64and the pressure chamber65with a hydraulic pressure allows the gap adjustment piston62to move toward the left side of the figure against the biasing force of a spring66to come into contact with a stopper67. This supply also allows the pressure piston63to move toward the left side of the figure in the cylinder62aof the gap adjustment piston62to press a plurality of friction plates68alternately engaged with the transmission case3and a rotation braked member (not shown). This allows for engaging the L/R brake60.

As illustrated inFIG. 3B, releasing the hydraulic pressure from the pressure chamber65in this state allows releasing the pressing force of the pressure piston63to disengage the L/R brake60with the gap adjustment piston62and the pressure piston63remaining in the positions shown inFIG. 3A, i.e., the end of the pressure piston63kept in contact with the friction plates68. In addition, releasing the hydraulic pressure also from the gap adjustment chamber64in this state allows the gap adjustment piston62to move toward the right side by the biasing force of the spring66, as illustrated inFIG. 3C. At that time, the pressure piston63moves toward the right side together with the gap adjustment piston62by, e.g., friction of a sealing member, while maintaining the positional relationship with the gap adjustment piston62.

In the next engagement of the L/R brake60, the gap adjustment chamber64is first supplied with the hydraulic pressure, thereby allowing the gap adjustment piston62and the pressure piston63to move toward the left side while their positional relationship is maintained. Then, the movement of the pressure piston63for engagement is finished, and the end of the pressure piston63is in contact with, or substantially in contact with, the friction plates68without pressing the friction plates68. As a result, the L/R brake60enters the prepared-for-engagement state.

Upon supply of the pressure chamber65with the hydraulic pressure in this state, the friction plates68are pressed substantially simultaneously with the supply, thereby establishing the engagement of the L/R brake60with improved response. This is because the movement of the pressure piston63for the engagement has already been finished.

The hydraulic pressure is supplied to the gap adjustment chamber64prior to the supply to the pressure chamber65whenever the L/R brake60is engaged in the state illustrated inFIG. 3C, whereas the hydraulic pressure is released from the pressure chamber65prior to the release from the gap adjustment chamber64whenever the L/R brake60is disengaged in the state illustrated inFIG. 3A. In other words, the hydraulic pressure is supplied to, and released from, the pressure chamber65in a state where the hydraulic pressure is supplied to the gap adjustment chamber64illustrated inFIG. 3Band the gap adjustment piston62moves toward the engagement side. In order to implement such a configuration, an L/R shift valve107(seeFIG. 4) is included in a hydraulic circuit that will be described later.

The automatic transmission1includes this hydraulic circuit for establishing the various speed change gears by selectively supplying the respective frictional engagement elements40-80with the hydraulic pressure. Next, with reference toFIG. 4, a configuration of a part of this hydraulic circuit100will be described which relates to hydraulic pressurecontrol during an idle stop of the engine, specifically, which controls the supply of the hydraulic pressure to the low clutch40and the L/R brake60that are engaged at the time of vehicle start.

As illustrated inFIG. 4, the hydraulic circuit100is configured to receive the hydraulic pressure generated by the electric pump (i.e., a “first hydraulic pressure generator”)101driven by a motor101aduring the engine stop, and the hydraulic pressure generated by the mechanical pump (i.e., a “second hydraulic pressure generator”)102driven by the engine.

The hydraulic circuit100includes, as valves for supplying the low clutch40and the L/R brake60with the hydraulic pressures supplied from the pumps101and102, a pump switching valve103, a manual valve104, a first linear solenoid valve (i.e., a “first hydraulic control valve,” hereinafter referred to as a “first LSV”)105, a second linear solenoid valve (i.e., a “second hydraulic control valve,” hereinafter referred to as a “second LSV”)106, and the L/R shift valve107. The pump switching valve103switches supply destinations of the hydraulic pressure generated by the electric pump101or the mechanical pump102between the low clutch40and the L/R brake60. The manual valve104links with the range operation by the vehicle's operator. The first LSV105controls the hydraulic pressure supplied to the low clutch40, and the second LSV106controls the hydraulic pressure supplied to the L/R brake60. The L/R shift valve107regulates the order of the supply and release of the hydraulic pressure to and from the gap adjustment chamber64and the pressure chamber65in the L/R brake60as stated above.

The pump switching valve103includes, at both ends, a first switching port a and a second switch port b each switching positions of a spool103a. When the electric pump101is operated, the hydraulic pressure is introduced from the electric pump101into the first switch port a in the left side of the figure, thereby allowing the spool103ato be in a first position, i.e., the right side (the position illustrated in the figure). When the mechanical pump102is operated, the hydraulic pressure is introduced from the mechanical pump102into the second switch port b in the right side of the figure, thereby allowing the spool103ato be in a second position, i.e., the left side.

The pump switching valve103also includes first and second input ports c and d, and an output port e which are provided for the low clutch, and first and second input ports f and g, and an output port h which are provided for the L/R brake. When the spool103ais in the first position, the first input port c for the low clutch communicates with the output port e for the low clutch, and the first input port f for the L/R brake communicates with the output port h for the L/R brake, as illustrated in the figure. Although not shown, when the spool103ais in the second position, the second input port d for the low clutch communicates with the output port e for the low clutch, and the second input port g for the L/R brake communicates with the output port h for the L/R brake.

The first input port c for the low clutch is connected to a first input line (i.e., an upstream portion of a “first hydraulic passage”)111introduced from the electric pump101, and the first input port f for the L/R brake is connected to a second input line (i.e., an upstream portion of a “second hydraulic passage”)112introduced from the electric pump101. The second input port d for the low clutch is connected to a third input line113introduced from the mechanical pump102through the manual valve104, and the second input port g for the L/R brake is connected to a fourth input line114introduced directly from the mechanical pump102.

The output port e for the low clutch of the pump switching valve103is introduced into a hydraulic chamber of the low clutch40by a low clutch line (i.e., a downstream portion of the “first hydraulic passage”)115through the first LSV105. The output port h for the L/R brake is introduced into the gap adjustment chamber64of the L/R brake60by a gap adjustment line (i.e., a downstream portion of the “second hydraulic passage”)116.

Furthermore, a pressure line (i.e., a “third hydraulic passage”)117branching from the third input line113in a position downstream of the manual valve104is introduced into the pressure chamber65of the L/R brake60through the second LSV106and the L/R shift valve107.

This L/R shift valve107is configured to be supplied with a hydraulic pressure from the gap adjustment line116as a switching pressure. When this hydraulic pressure is supplied, i.e., a hydraulic pressure is supplied to the gap adjustment chamber64of the L/R brake60, the second LSV106of the pressure line117communicates with the pressure chamber65.

The manual valve104is configured to allow the mechanical pump102to communicate with the third input line113and the pressure line117, which are located downstream of the manual valve104at the time of the D-range operation, and to allow these lines113and117to be drained at the time of the N-range operation.

Each of the first and second LSVs105and106has an upstream input port i, a downstream output port j, and a downstream drain port k. These ports are configured such that the input port i communicates with the output port j when the valve is opened, whereas the port i does not communicate with the port j and the downstream output port j communicates with the drain port k when the valve is closed.

Such a configuration of the automatic transmission1according to this embodiment allows for controlling engagement of the low clutch40and the L/R brake60in association with the idle stop control of the engine. The automatic transmission1includes a control unit200for such control.

As illustrated inFIG. 5, the control unit200is configured to receive, for example, a signal from a range sensor201detecting the range of the automatic transmission1selected by the operation of the vehicle's operator, a signal from a vehicle speed sensor202detecting the vehicle speed of the vehicle, a signal from an accelerator operation amount sensor203detecting an operation amount of the accelerator pedal of the vehicle's operator, a signal from a brake switch204detecting stepping on the brake pedal, a signal from an engine rotation speed sensor205detecting the rotation speed of the engine, a signal from an electric pump rotation speed sensor206detecting the rotation speed of the electric pump101, and a signal from a battery charge level sensor207detecting the battery charge level.

Based on these signals, the control unit200is configured to output signals for an automatic stop or an automatic restart to a fuel supply device211, an ignition device212, an engine start device213of the engine to perform idle stop control of the engine. The control unit200is also configured to output control signals for engagement control of the low clutch40and the L/R brake60of the automatic transmission to the first and second LSVs105and106, and to output a signal for instruction of the operation of a motor101aof the electric pump101.

Next, a first operation example in this embodiment including a control operation by the control unit200will be described in accordance with flowcharts ofFIGS. 6A and 6B, and timing charts ofFIGS. 7A and 7B.

The flowcharts ofFIGS. 6A and 6Bshow an operation when the vehicle transitions from the traveling state to the stopping state. In Step S1, various signals are first input from the switch and the sensors201-207. In Step S2, a determination is made whether or not the current range of the automatic transmission1is the N-range.

When the vehicle is being stopped, the automatic transmission1is in the D-range. When the engine is not automatically stopped yet, the spool103aof the pump switching valve103in the hydraulic circuit100ofFIG. 4is in the second position (the left side), and the hydraulic pressure generated by the mechanical pump102driven by the engine is supplied to the hydraulic chamber of the low clutch40through the manual valve104, the third input line113, the pump switching valve103, the low clutch line115, and the first LSV105. This allows for engaging the clutch40(see the reference character α1ofFIG. 7A).

The hydraulic pressure generated by the mechanical pump102is supplied to the gap adjustment chamber64of the L/R brake60through the fourth input line114, the pump switching valve103, and the gap adjustment line116, and is also supplied to the pressure chamber65of the L/R brake60through the pressure line117branching from the third input line113, the second LSV106, and the L/R shift valve107. This allows for engaging the L/R brake60(reference characters α2and α3).

If the automatic transmission1is still in the D-range in this state, the process jumps from Step S2inFIG. 6Ato Step S50. The control in Step S50will be described later. On the other hand, if the range of automatic transmission1switches to the N-range, the process proceeds from Step S2to Step S3. Specifically, the spool of the manual valve104moves to the N position, and the third input line113and the pressure line117are drained. This allows for releasing the hydraulic pressure from the hydraulic chamber of the low clutch40and the pressure chamber65of the L/R brake60, thereby disengaging the low clutch40and the L/R brake60(reference characters α4and α5).

At that time, the second LSV106also releases the hydraulic pressure from the pressure chamber65of the L/R brake60. On the other hand, the hydraulic pressure is continuously supplied to the gap adjustment chamber64of the L/R brake60because the gap adjustment chamber64communicates directly with the mechanical pump102.

Furthermore, in Step S4, a determination is made whether or not a condition for an automatic stop of the engine is satisfied based on, e.g., the vehicle speed, and conditions of the brake and the accelerator. If a predetermined automatic stop condition is satisfied, the control unit200outputs a signal for stopping the engine to, e.g., the fuel supply device211and the ignition device212of the engine. Then, in Step S5, the engine is automatically stopped, i.e., in the idle stop state.

At that time, the mechanical pump102is stopped. In Step S6, the motor101aof the electric pump101receives an operation signal and the electric pump101starts its operation. In Step S7, switching the operating pumps allows the spool103aof the pump switching valve103to move to the first position (right side), thereby making a transition to a state shown in Step S8. Specifically, in this state, the hydraulic pressure generated by the electric pump101is supplied to the hydraulic chamber of the low clutch40through the first input line111, the pump switching valve103, the low clutch line115, and the first LSV105, and is also supplied to the gap adjustment chamber64of the L/R brake60through the second input line112, the pump switching valve103, and the gap adjustment line116.

This allows for engaging the low clutch40again, and causes an increase in the hydraulic pressure in the gap adjustment chamber64that once reduced at the time of stop of the mechanical pump102(reference characters α6and α7). At that time, in the L/R brake60, the hydraulic pressure is supplied to the gap adjustment chamber64whereas the hydraulic pressure is released from the pressure chamber65by the second LSV106. Therefore, the L/R brake60is in the prepared-for-engagement state illustrated inFIG. 3Bwhere the gap adjustment piston62and the pressure piston63move toward the left side of the figure with their positional relationship maintained, and the end of the pressure piston63is in contact with, or substantially in contact with, the friction plates68without pressing the friction plates68.

Next, in Step S9, a determination is made whether or not the automatic transmission1has switched from the N-range to the D-range. If this switch has been made, the engine is automatically restarted according to Steps S10-S12. Besides, the spool103aof the pump switching valve103moves to the second position again, and the hydraulic pressure generated by the mechanical pump102that has started its operation is supplied to the hydraulic chamber of the low clutch40, and the gap adjustment chamber64and the pressure chamber65of the L/R brake60. At this time, in Step S13, the electric pump101is stopped.

In this manner, the hydraulic pressure generated by the mechanical pump102allows for engaging the low clutch40and the L/R brake60, and thus the vehicle is ready to start in the first gear position. Since the L/R brake60has been in the prepared-for-engagement state in advance as stated above, they are engaged simultaneously with the supply of the hydraulic pressure to the pressure chamber65. Accordingly, when a switch is made to the D-range, a smooth start-up of the vehicle can be obtained.

On the other hand, before the automatic transmission1is switched to the D-range, a determination is made whether or not the battery charge level is reduced to the predetermined value or less in Step S14. If it is reduced to the predetermined value or less, i.e., the system of the engine is restarted, the first LSV105releases the hydraulic pressure supplied to the hydraulic chamber of the low clutch40through the low clutch line115in Step S15. Then, the engine is automatically restarted in Step S16. Accordingly, the engine is restarted with the low clutch40disengaged. The vehicle is not erroneously started with the automatic transmission1in the N-range.

Thereafter, the spool103aof the pump switching valve103again moves to the second position in Steps S17and S18in association with the restart of the engine, and the pump supplying the hydraulic pressure to the gap adjustment chamber64of the L/R brake60is switched from the electric pump101to the mechanical pump102. Then, the electric pump101is stopped in Step S13.

If the first LSV105releases the hydraulic pressure supplied to the hydraulic chamber of the low clutch40in Step S15, the first LSV105may become inoperable with the input port i and the output port j communicating with each other due to the open failure of the first LSV105. In such a situation, the hydraulic pressure supplied to the hydraulic chamber of the low clutch40cannot be released from the drain port k of the first LSV105, and the low clutch40cannot be disengaged (the reference character α8).

Accordingly, if the L/R brake60were also engaged, the vehicle would be erroneously started in the N-range at the time of restart of the system of the engine in Step S16. However, the L/R brake60is maintained in the above-described prepared-for-engagement state, i.e., the state where the pressure piston63is in contact with the friction plates68without pressing the friction plates68. This does not allow the power transmission path of the automatic transmission1to be in the first gear position even if the low clutch40is not disengaged due to the open failure of the first LSV105. Thus, the vehicle is not started even if the engine is started.

In this case, the prepared-for-engagement state of the L/R brake60prevents an erroneous start of the vehicle. This eliminates the conventional need for providing the hydraulic circuit with a pressure release circuit for preventing the erroneous start, thereby avoiding problems caused by the pressure release circuit, such as an increase in the size of the electric pump and an increase in power consumption.

Step S50inFIG. 6Ais shown in the flow ofFIG. 6B. If the automatic transmission1is in the D-range in Step S51, the process proceeds to Step S52. If the automatic transmission1is not in the D-range, the process ofFIG. 6Bends, and the process returns from Step S50in the flow ofFIG. 6A. Step S52is repeatedly performed until the vehicle is stopped. If the vehicle is stopped, the process proceeds Step S53. In Step S53, the spool103aof the manual valve104is in the D position. This maintains the hydraulic pressure in the hydraulic chamber of the low clutch40, and the gap adjustment chamber64and the pressure chamber65of the L/R brake60, thereby continuously engaging the low clutch40and the L/R brake60(reference characters α9, α10, and all ofFIG. 7B).

Furthermore, in Step S54, a determination is made whether or not a condition for an automatic stop of the engine is satisfied based on, e.g., the vehicle speed, conditions of the brake and the accelerator. If such a predetermined automatic stop condition is satisfied, the control unit200outputs a signal for stopping the engine to, e.g., the fuel supply device211and the ignition device212of the engine. In Step S55, the engine is automatically stopped, i.e., the engine enters the idle stop state.

At that time, the mechanical pump102is stopped. In Step S56, the motor101aof the electric pump101receives an operation signal, and the electric pump101starts its operation. In Step S57, switching the operating pumps allows the spool103aof the pump switching valve103to move to the first position (right side), thereby making a transition to a state shown in Step S58. Specifically, in this state, the hydraulic pressure generated by the electric pump101is supplied to the hydraulic chamber of the low clutch40through the first input line111, the pump switching valve103, the low clutch line115, and the first LSV105, and is also supplied to the gap adjustment chamber64of the L/R brake60through the second input line112, the pump switching valve103, and the gap adjustment line116. On the other hand, the stop of the engine stops supplying the hydraulic pressure through the pressure line117, and the second LSV106releases the hydraulic pressure from the pressure chamber65of the L/R brake60, thereby disengaging the L/R brake60(reference character α12).

The low clutch40is continuously engaged. In this L/R brake60, the hydraulic pressure is supplied to the gap adjustment chamber64with the hydraulic pressure released from the pressure chamber65. As a result, the L/R brake60enters the prepared-for-engagement state illustrated inFIG. 3B.

Next, in Step S59, a determination is made whether or not the automatic transmission1has switched from the D-range to the N-range. If this switch has not been made, a determination is made whether or not a condition for a restart is satisfied in Step S516. If the condition for the restart is not satisfied in Step S516, the process returns to Step S59. On the other hand, if the condition for the restart is satisfied in Step S516, the engine is automatically restarted according to Steps S517-S519. Besides, the spool103aof the pump switching valve103moves to the second position again, and the hydraulic pressure generated by the mechanical pump102that has started operating is supplied to the hydraulic chamber of the low clutch40, and to the gap adjustment chamber64and the pressure chamber65of the L/R brake60. In Step S515, the electric pump101is stopped.

In this manner, the hydraulic pressure generated by the mechanical pump102allows for engaging the low clutch40and the L/R brake60, and the vehicle is ready to start in the first gear position. Since the L/R brake60has been in the prepared-for-engagement state in advance as stated above, the L/R brake60is engaged simultaneously with the supply of the hydraulic pressure to the pressure chamber65.

If a switch is made to the N-range in Step S59, the process proceeds to Step S510, and a determination is made whether or not the battery charge level is reduced to the predetermined value or less. If it is reduced to the predetermined value or less, i.e., the system of the engine is restarted, the first LSV105releases the hydraulic pressure supplied to the hydraulic chamber of the low clutch40through the low clutch line115in Step S511. Then, the engine is automatically restarted in Step S512. Accordingly, the engine is restarted with the low clutch40disengaged, and the vehicle is not erroneously started when the automatic transmission1is in the N-range.

Thereafter, the spool103aof the pump switching valve103again moves to the second position in Steps S513and S514in association with the restart of the engine, and the pump supplying the hydraulic pressure to the gap adjustment chamber64of the L/R brake60switches from the electric pump101to the mechanical pump102. Then, the electric pump101is stopped in Step S515.

If the first LSV105releases the hydraulic pressure supplied to the hydraulic chamber of the low clutch40in Step S511, the first LSV105may become inoperable with the input port i and the output port j communicating with each other due to the open failure of the first LSV105. In such a situation, the hydraulic pressure supplied to the hydraulic chamber of the low clutch40cannot be released from the drain port k of the first LSV105, and the low clutch40cannot be disengaged (the reference character α13).

Accordingly, if the L/R brake60were also engaged, the vehicle would be erroneously started in the N-range at the time of restart of the system of the engine in Step S16. However, the L/R brake60is maintained in the above-described prepared-for-engagement state, i.e., the state where the pressure piston63is in contact with the friction plates68without pressing the friction plates68. This does not allow the power transmission path of the automatic transmission1to be in the state of the first gear position even if the low clutch40is not disengaged due to the open failure of the first LSV105. Thus, the vehicle is not started even if the engine is started.

Accordingly, as illustrated inFIG. 10, the hydraulic pressure is supplied to all the pressure chamber of the low clutch40, the pressure chamber65and the gap adjustment chamber64of the L/R brake60during the engine operation in the D-range (Steps S12, S53, and S519). On the other hand, during the automatic stop of the engine, the hydraulic pressure is supplied to the pressure chamber of the low clutch40, and the gap adjustment chamber64of L/R brake60, whereas the hydraulic pressure is not supplied to the pressure chamber65of L/R brake60(Step S58). In the N-range, during an engine operation, the hydraulic pressure is supplied to the gap adjustment chamber64of the L/R brake60, and the hydraulic pressure is not supplied to the pressure chamber of the low clutch40and the pressure chamber65of the L/R brake60(Steps S3, S18, and S514). On the other hand, during the automatic stop of the engine, the hydraulic pressure is supplied to the pressure chamber of the low clutch40and the gap adjustment chamber64of the L/R brake60, whereas the hydraulic pressure is not supplied to the pressure chamber65of the L/R brake60(Step S8).

Next, a second operation example in this embodiment will be described in accordance with flowcharts ofFIGS. 8A and 8B, and timing charts ofFIGS. 9A and 9B.

In Step S21of the flowchart ofFIG. 8A, various signals are first input from the switch and the sensors201-207illustrated inFIG. 5. In Step S22, a determination is made whether or not the current range of the automatic transmission1is the N-range.

When the vehicle is being stopped, the automatic transmission1is in the D-range. When the engine is not automatically stopped yet, the spool103aof the pump switching valve103in the hydraulic circuit100ofFIG. 4is in the second position as well as in the first operation example, and the hydraulic pressure generated by the mechanical pump102driven by the engine is supplied to the hydraulic chamber of the low clutch40through the manual valve104, the third input line113, the pump switching valve103, the low clutch line115, and the first LSV105. This allows for engaging the clutch40(see the reference character (31ofFIG. 9A).

The hydraulic pressure generated by the mechanical pump102is supplied to the gap adjustment chamber64of the L/R brake60through the fourth input line114, the pump switching valve103, and the gap adjustment line116, and is also supplied to the pressure chamber65of the L/R brake60through the pressure line117branching from the third input line113, the second LSV106, and the L/R shift valve107. This allows for engaging the L/R brake60(reference characters β2and β3).

If the automatic transmission1is still in the D-range in this state, the process proceeds jumps from Step S22inFIG. 8Ato Step S60. The control in Step S60will be described later. On the other hand, if the range of automatic transmission1switches to the N-range, the process proceeds from Step S22to Step S23inFIG. 8A. Specifically, the spool103aof the manual valve104moves to the N position, and the low clutch line115is drained. This allows for releasing the hydraulic pressure from the hydraulic chamber of the low clutch40, thereby disengaging the low clutch40(reference character (34).

At that time, in this operation example, the pressure line117is not drained by the manual valve104. The hydraulic pressure generated by the mechanical pump102is supplied to the gap adjustment chamber64and the pressure chamber65of the L/R brake60, and the L/R brake60is continuously engaged. This is performed to allow an immediate start of the vehicle when a switch is made from the N-range to the R-range to start the vehicle in the reverse gear position.

Next, in Step S24, a determination is made whether or not a condition for an automatic stop of the engine is satisfied based on, e.g., the vehicle speed, conditions of the brake and the accelerator. If a predetermined automatic stop condition is satisfied, the control unit200outputs a signal for stopping the engine to, e.g., the fuel supply device211and the ignition device212of the engine. In Step S25, the engine is automatically stopped, i.e., the engine enters the idle stop state. At that time, the mechanical pump102is stopped. In Step S26, the hydraulic pressure supplied to the pressure chamber65of the L/R brake60is released or reduced, thereby disengaging the L/R brake60(reference character β5).

On the other hand, in Step S27, the motor101aof the electric pump101receives an operation signal and the electric pump101starts its operation. In Step S57, switching operating pumps allows the spool103aof the pump switching valve103to move to the first position, thereby making a transition to a state shown in Step S29. Specifically, in this state, the hydraulic pressure generated by the electric pump101is supplied to the hydraulic chamber of the low clutch40through the first input line111, the pump switching valve103, the low clutch line115, and the first LSV105, and is also supplied to the gap adjustment chamber64of the L/R brake60through the second input line112, the pump switching valve103, and the gap adjustment line116.

This allows for engaging the low clutch40again, and causes an increase in the hydraulic pressure that once reduced at the time of stop of the mechanical pump102(reference characters β6and β7). At that time, in the L/R brake60, the hydraulic pressure is supplied to the gap adjustment chamber64whereas the hydraulic pressure is continuously released from the pressure chamber65. Therefore, the L/R brake60is in the prepared-for-engagement state illustrated inFIG. 3B.

Next, in Step S30, a determination is made whether or not the automatic transmission1has switched from the N-range to the D-range. If this switch has been made, the engine is automatically restarted according to Steps S31-S33. Besides, the spool103aof the pump switching valve103moves to the second position, again, and the hydraulic pressure generated by the mechanical pump102that has started its operation is supplied to the hydraulic chamber of the low clutch40, and the gap adjustment chamber64and the pressure chamber65of the L/R brake60. In Step S34, the electric pump101is stopped.

In this manner, the hydraulic pressure generated by the mechanical pump102allows for engaging the low clutch40and the L/R brake60, and the vehicle is ready to start. Since the L/R brake60has been in the prepared-for-engagement state in advance as stated above, this engagement is performed simultaneously with the supply of the hydraulic pressure to the pressure chamber65. Accordingly, when a switch is made to the D-range, a smooth start-up of the vehicle can be obtained.

On the other hand, before the automatic transmission1is switched to the D-range, a determination is made whether or not the battery charge level is reduced to the predetermined value or less in Step S35. If it is reduced to the predetermined value or less, i.e., the system of the engine is restarted, the first LSV105releases the hydraulic pressure supplied to the hydraulic chamber of the low clutch40through the low clutch line115in Step S36, thereby disengaging the low clutch40.

In this situation, in Step S37, a determination is made whether or not an open failure has occurred in the first LSV105. If the open failure has not occurred, i.e., the hydraulic pressure supplied to the hydraulic chamber of the low clutch40is released and the low clutch40is disengaged, the engine is automatically restarted in Step S38. Accordingly, in this case, the engine is restarted with the low clutch40disengaged. This prevents an erroneous start of the vehicle in the N-range.

On the other hand, if a determination is made that an open failure has occurred in the first LSV105in Step S37, and the hydraulic pressure supplied to the hydraulic chamber of the low clutch40is not released (reference character β8), the second LSV106stops supplying the hydraulic pressure to the pressure chamber65of the L/R brake60from the mechanical pump102in the subsequent Step S39. Then, the engine is automatically restarted in Step S38.

Thus, in this situation, even if the restart of the engine allows the mechanical pump102to generate the hydraulic pressure, this pressure is not supplied to the pressure chamber65of the L/R brake60, and the L/R brake60is continuously disengaged (reference character β9). This prevents an erroneous start of the vehicle at the time of engine restart in the N-range even if the low clutch40is not disengaged due to the open failure of the first LSV105.

Thereafter, in either situation, the spool103aof the pump switching valve103again moves to the second position in Steps S40and S41, and the pump supplying the gap adjustment chamber64of the L/R brake60with the hydraulic pressure switches from the electric pump101to the mechanical pump102. Then, the electric pump101is stopped in Step S34.

Step S60inFIG. 8Ais shown in the flow ofFIG. 8B. If the automatic transmission1is in the D-range in Step S61, the process proceeds to Step S62. If the automatic transmission1is not in the D-range, the process ofFIG. 8Bends, and the process returns from Step S60in the flow ofFIG. 8A. Step S62is repeatedly performed until the vehicle is stopped. If the vehicle is stopped, the process proceeds Step S63. In Step S63, the spool of the manual valve104is in the D position. This maintains the hydraulic pressure in the hydraulic chamber of the low clutch40, and the gap adjustment chamber64and the pressure chamber65of the L/R brake60, thereby continuously engaging the low clutch40and the L/R brake60(reference characters β10, β11, and β12ofFIG. 9B).

Furthermore, in Step S64, a determination is made whether or not a condition for an automatic stop of the engine is satisfied based on, e.g., the vehicle speed, conditions of the brake and the accelerator. If such a predetermined automatic stop condition is satisfied, the control unit200outputs a signal for stopping the engine to, e.g., the fuel supply device211and the ignition device212of the engine. In Step S65, the engine is automatically stopped, i.e., the engine enters the idle stop state.

At that time, the mechanical pump102is stopped. In Step S66, the motor101aof the electric pump101receives an operation signal, and the electric pump101starts its operation. In Step S67, switching the operating pumps allows the spool103aof the pump switching valve103to move to the first position (right side), thereby making a transition to a state shown in Step S68. Specifically, in this state, the hydraulic pressure generated by the electric pump101is supplied to the hydraulic chamber of the low clutch40through the first input line111, the pump switching valve103, the low clutch line115, and the first LSV105, and is also supplied to the gap adjustment chamber64of the L/R brake60through the second input line112, the pump switching valve103, and the gap adjustment line116. On the other hand, the operation of the mechanical pump102is stopped, and the hydraulic pressure supplied to the pressure chamber65of the L/R brake60is released or reduced, thereby disengaging the L/R brake60(reference character β13).

The low clutch40is continuously engaged. In this L/R brake60, the hydraulic pressure is supplied to the gap adjustment chamber64with the hydraulic pressure released from the pressure chamber65. As a result, the L/R brake60enters the prepared-for-engagement state illustrated inFIG. 3B.

Next, in Step S69, a determination is made whether or not the automatic transmission1has switched from the D-range to the N-range. If this switch has not been made, a determination is made whether or not a condition for a restart is satisfied in Step S618. If the condition for the restart is not satisfied in Step S618, the process returns to Step S69. On the other hand, if the condition for the restart is satisfied in Step S618, the engine is automatically restarted according to Steps S619-S621. Besides, the spool103aof the pump switching valve103moves to the second position again, and the hydraulic pressure generated by the mechanical pump102that has started its operation is supplied to the hydraulic chamber of the low clutch40, and to the gap adjustment chamber64and the pressure chamber65of the L/R brake60. In Step S617, the electric pump101is stopped.

In this manner, the hydraulic pressure generated by the mechanical pump102allows for engaging the low clutch40and the L/R brake60, and the vehicle is ready to start in the first gear position. Since the L/R brake60has been in the prepared-for-engagement state in advance as stated above, the L/R brake60is engaged simultaneously with the supply of the hydraulic pressure to the pressure chamber65.

If a switch is made to the N-range in Step S69, the process proceeds to Step S610, and a determination is made whether or not the battery charge level is reduced to the predetermined value or less. If it is reduced to the predetermined value or less, i.e., the system of the engine is restarted, the first LSV105releases the hydraulic pressure supplied to the hydraulic chamber of the low clutch40through the low clutch line115in Step S611.

In this case, in Step S612, a determination is made whether or not an open failure has occurred in the first LSV105. If the open failure has not occurred, i.e., the hydraulic pressure supplied to the hydraulic chamber of the low clutch40is released and the low clutch40is disengaged, the engine is automatically restarted in Step S614.

The restart of the engine allows the mechanical pump102to generate hydraulic pressure. Thereafter, the spool103aof the pump switching valve103again moves to the second position in Steps S615and S616in association with the restart of the engine, and the pump supplying the hydraulic pressure to the gap adjustment chamber64of the L/R brake60switches from the electric pump101to the mechanical pump102. Although the hydraulic pressure is also supplied to the pressure chamber65of the L/R brake60(reference character β14), the low clutch40is disengaged, thereby preventing an erroneous start of the vehicle in the N-range, as described above. Then, in Step S617, the electric pump101is stopped.

On the other hand, if a determination is made that the open failure has occurred in the first LSV105in Step S612, and the hydraulic pressure supplied to the hydraulic chamber of the low clutch40is not released (reference character β15), the second LSV106is controlled to stop supplying the hydraulic pressure to the pressure chamber65of the L/R brake60from the mechanical pump102in the subsequent Step S613. Then, the engine is automatically restarted in Step S614.

Thus, in this case, even if the restart of the engine allows the mechanical pump102to generate the hydraulic pressure, this pressure is not supplied to the pressure chamber65of the L/R brake60, and the L/R brake60is continuously disengaged (reference character β16). This prevents an erroneous start of the vehicle at the time of the engine restart in the N-range even if the low clutch40is not disengaged due to the open failure of the first LSV105.

Accordingly, as shown inFIG. 10, the second operation example is the same as the first one in the supply and release of the hydraulic pressure to and from the pressure chamber of the low clutch40and the pressure chamber65and the gap adjustment chamber64of the L/R brake60in the D-range. However, the second operation example is different from the first one in that, in the second operation example, the hydraulic pressure is supplied to the pressure chamber65of the L/R brake60during the engine operation in the N-range.

As can be seen in the foregoing, the operation according to the second operation example also avoids the problems, such as an increase in size of the electric pump and an increase in power consumption, caused by the pressure release circuit provided in the hydraulic passage between the electric pump and the hydraulic control valve for preventing the above-described erroneous start of the vehicle.

INDUSTRIAL APPLICABILITY

As can be seen from the foregoing description, the technique disclosed herein allows an automatic transmission, mounted in a vehicle to which idle stop control is applied to stop the engine, to ensure a smooth start of the vehicle when a switch is made from a non-traveling range to a traveling range. The technique disclosed herein also allows this automatic transmission to prevent an erroneous start of the vehicle in the non-traveling range at the time of restart of the system of the engine without increasing the size of the electric pump and electric power consumption. This technique thus may be appropriately used in industrial fields of manufacturing automatic transmissions of this type and vehicles mounting such transmissions.

DESCRIPTION OF REFERENCE CHARACTERS