System and method for controlling power transmission mechanism, and utility vehicle

A system includes a power transmission mechanism having a rotation shaft, a power transmission gear, a dog ring, a dog clutch, a switching mechanism to move the dog ring in an axial direction to switch a power transmission state, and a switching controller to control an operation of the switching mechanism. The switching controller determines whether the dog clutch is in an engaged state when giving a switching command to cause the dog ring to be moved to a side of the power transmission gear in the axial direction. After the dog clutch is determined not to be in the engaged state, the switching controller causes the dog ring to be moved to the side opposite to the power transmission gear, and then retries movement of the dog ring to the side of the power transmission gear.

BACKGROUND OF THE INVENTION

The present invention relates to a system and a method for controlling a power transmission mechanism, and a utility vehicle equipped with such a system.

U.S. Pat. No. 8,082,817 B2 discloses a power transmission mechanism having a plurality of dog clutches. When a certain dog clutch is switched from a non-engaged state to an engaged state, a dog claw may not be fitted into an engagement hole, and the non-engaged state of the dog clutch may be continued.

SUMMARY OF THE INVENTION

An object of the present invention is to prevent continuation of a non-engaged state of a dog clutch.

A first aspect of the present invention provides a system for controlling a power transmission mechanism. The system includes: a power transmission mechanism including a rotation shaft; a power transmission gear rotatably fitted to the rotation shaft and locked to the rotation shaft in an axial direction; a dog ring fitted to the rotation shaft so as to be slidable in the axial direction and locked to the rotation shaft in a circumferential direction; and a dog clutch provided in the dog ring and the power transmission gear, a switching mechanism that moves the dog ring in the axial direction to switch a power transmission state, and a switching controller that controls operation of the switching mechanism. The switching controller determines whether the dog clutch becomes in an engaged state in a case of giving a switching command for switching the power transmission state by moving the dog ring to the power transmission gear side in the axial direction, and causes the dog ring to be moved to a side opposite to the power transmission gear side in the axial direction in a case where the dog clutch is determined not to be in the engaged state, and then retries movement of the dog ring to the power transmission gear side.

A second aspect of the present invention provides a method for controlling a power transmission mechanism including a rotation shaft, a power transmission gear rotatably fitted to the rotation shaft and locked to the rotation shaft in an axial direction, a dog ring fitted to the rotation shaft so as to be slidable in the axial direction and locked to the rotation shaft in a circumferential direction, and a dog clutch provided in the dog ring and the power transmission gear. The method includes the steps of determining whether the dog clutch becomes in an engaged state in a case where a switching command for switching a power transmission state by moving the dog ring to the power transmission gear side in the axial direction is given, and causing the dog ring to be moved to a side opposite to the power transmission gear side in the axial direction in a case where the dog clutch is determined not to be in the engaged state, and then retrying movement of the dog ring to the power transmission gear side.

A third aspect of the present invention provides a utility vehicle including a rotation shaft, a power transmission gear rotatably fitted to the rotation shaft and locked to the rotation shaft in an axial direction, a dog ring fitted to the rotation shaft so as to be slidable in the axial direction and locked to the rotation shaft in a circumferential direction, a dog clutch provided in the dog ring and the power transmission gear, a shift member that is engaged with the dog ring and moves the dog ring in the axial direction, and a controller that controls movement of the shift member. The controller determines whether the dog clutch becomes in an engaged state in a case of giving a switching command for switching a power transmission state by moving the dog ring to the power transmission gear side in the axial direction, and causes the dog ring to be moved to a side opposite to the power transmission gear side in the axial direction in a case where the dog clutch is determined not to be in the engaged state, and then retries movement of the dog ring to the power transmission gear side.

According to the above configuration, when the dog clutch is determined not to be in the engaged state at the time of switching of the power transmission state, the dog ring temporarily moves to the side opposite to the power transmission gear side, and then moves again to the power transmission gear side. By allowing this retry to be automatically performed, it is possible to prevent continuation of a non-engaged state of the dog clutch even in a case where the dog clutch is not engaged at the time of switching of the power transmission state.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An embodiment will be described with reference to the drawings. Note that the same or corresponding elements are denoted by the same reference numerals throughout the drawings, and overlapping of detailed description will be omitted.

FIG.1illustrates a utility vehicle1as an example of a vehicle equipped with a control system100(seeFIG.4) of a power transmission mechanism10(seeFIG.2). The utility vehicle1includes four wheels2including left and right front wheels2F and left and right rear wheels2R, and a power unit3that drives the wheels2. The power unit3is arranged between the front wheel2F and the rear wheel2R in a vehicle length direction.

Referring toFIG.2, the power unit3includes a drive source9and the power transmission mechanism10. The drive source9generates power for rotating the wheel2. The drive source9is, for example, an engine. The drive source9may include an electric motor instead of or in addition to an engine. The engine has, as a drive source output shaft9a, a crankshaft that is rotationally driven in accordance with combustion of an air-fuel mixture containing fuel.

The power transmission mechanism10transmits power generated by the drive source9to the wheel2. The power transmission mechanism10includes a primary reduction mechanism11, clutches12A and12B, a transmission13, a final reduction mechanism14, a rear differential mechanism15, and a power distribution unit16. In the present embodiment, the two clutches12A and12B are interposed between the drive source9and the transmission13, and the transmission13is a dual clutch transmission (DCT).

The primary reduction mechanism11transmits rotation of the drive source output shaft9ato each input element12aof the clutches12A and12B, and decelerates the rotation in the process. In the primary reduction mechanism11, an intermediate gear11bis meshed with the driving gear11afixed on the drive source output shaft9a. The intermediate gear11bis also meshed with a first driven gear11c1fixed to the input element12aof the first clutch12A and a second driven gear11c2fixed to the input element12aof the second clutch12B.

A state of each of the clutches12A and12B is switched between an engaged state in which rotation of the input element12ais transmitted to an output element12band a released state in which the input element12aand the output element12bare disconnected from each other. A type of the clutches12A and12B is not particularly limited, and is, for example, a multiple plate friction clutch of a hydraulic drive system.

The transmission13includes, as an example of a rotation shaft, a first input shaft21, a second input shaft22, a low shaft23, a counter shaft24, and an output shaft25. The output elements12bof the first and second clutches12A and12B are fixed onto the first and second input shafts21and22, respectively. Each of the first and second input shafts21and22rotates integrally with a corresponding one of the output elements12bunless the corresponding clutches12A and12B are in the released state. The transmission13outputs rotation of the first or second input shaft21or22to the output shaft25.

The transmission13selectively sets one gear position from a plurality of (for example, seven) forward positions and one or more (for example, one) reverse positions. A power transmission path in the transmission13from the input shafts21and22to the output shaft25is switched according to a gear position, and thereby, rotation of the first or second input shaft21or22is changed in speed at a gear ratio according to a gear position before being output to the output shaft25. Note that the transmission13may also be capable of selecting, as one of gear positions, a neutral position at which a power transmission path between the input shafts21and22and the output shaft25is disconnected.

The final reduction mechanism14decelerates rotation of the output shaft25. The rear differential mechanism15distributes the rotation decelerated by the final reduction mechanism14to the left and right rear wheels2R. The power distribution unit16distributes the rotation decelerated by the final reduction mechanism14to the left and right front wheels2F (seeFIG.1). Note thatFIG.2illustrates only a gear provided on the final shaft14aconstituting the final reduction mechanism14in the power distribution unit16. In the present embodiment, all the four wheels2are drive wheels to which power from the drive source9is transmitted by the power transmission mechanism10.

Switching of a power transmission state (at least switching of a state of each of the clutches12A and12B and switching of a gear position set to the transmission13) in the power transmission mechanism10is automatically performed without manual operation by the driver. A switching timing is determined by electronic control. The switching operation is performed by using hydraulic pressure, and the hydraulic pressure is adjusted by electronic control.

In addition to the rotation shafts21to25described above, the transmission13includes a plurality of power transmission gears31to37and41to44, a plurality of dog rings51to54, a plurality of dog clutches56to59, a one-way clutch60, a bypass gear61, a forward and reverse selector62, and an output gear63. The rotation shafts21to25are parallel to each other and extend, for example, in a vehicle width direction. A plurality of the power transmission gears31to37and41to44, the bypass gear61, and the output gear63are parallel shaft gears that are constantly meshed, and transmit power between two shafts of the rotation shaft21to25.

The bypass gear61includes an upstream gear61afixed on the first input shaft21, and first and second downstream gears61D and61R provided on the low shaft23so as to be relatively rotatable and arranged in an axial direction. The idle gear61bis interposed between the first downstream gear61D and the upstream gear61a, while the second downstream gear61R directly meshes with the upstream gear61a. The first downstream gear61D rotates in the same forward direction as the first and second input shafts21and22, and the second downstream gear61R rotates in a reverse direction opposite to the forward direction. The forward and reverse selector62includes a sleeve arranged between the downstream gears61D and61R in the axial direction. The sleeve is displaceable in the axial direction between a forward position where the sleeve is engaged with the first downstream gear61D and a reverse position where the sleeve is engaged with the second downstream gear61R, and rotates integrally with the low shaft23. Hereinafter, unless otherwise specified, the sleeve is at the forward position, rotation of the first input shaft21is transmitted to the low shaft23via the first downstream gear61D, and the low shaft23rotates in the forward direction. The output gear63includes an upstream gear63afixed on the counter shaft24and a downstream gear63bfixed on the output shaft25and meshing with the upstream gear63a, and decelerates rotation of the counter shaft24and transmits the rotation to the output shaft25.

The power transmission gear includes a first to seventh gear driving gears31to37and low gear, second gear, middle gear, and high gear driven gears41to44. The first gear driving gear31is provided on the low shaft23, the third, fifth, and seventh gear driving gears33,35, and37are provided on the first input shaft21, and the second, fourth, and sixth gear driving gears32,34, and36are provided on the second input shaft22. The driven gears41to44are provided on the counter shaft24. Each of the driving gears31to37constantly meshes with any of the driven gears41to44. The first and third gear driving gears31and33mesh with the low gear driven gear41, the second gear driving gear32meshes with the second gear driven gear42, the fourth and fifth gear driving gears34and35mesh with the middle gear driven gear43, and the sixth and seventh gear driving gears36and37mesh with the high gear driven gear44.

The second gear driving gear32is fixed on the second rotation shaft22and rotates integrally with the second rotation shaft22. The other ones, the driving gears31and33to37, are rotatably fitted to a corresponding rotation shaft (for example, the first input shaft21, the second input shaft22, or the low shaft23) in the axial direction, and are locked to the rotation shaft in the axial direction. For example, each of the driving gears31and33to37is supported on an outer peripheral surface of the corresponding rotation shaft via a bearing such as a needle bearing so as to be relatively rotatable with respect to the corresponding rotation shaft. Each of the driving gears31and33to37is held on an outer peripheral surface of the corresponding rotation shaft by a holder such as a snap ring so as not to be displaced in the axial direction. Note that the downstream gears61D and61R may be configured in the same manner. The second gear driven gear42is supported on the counter shaft24via the one-way clutch60. The other driven gears41,43, and44are fixed on the counter shaft24and rotate integrally with the counter shaft24.

Each of the dog rings51to54is slidably fitted to a corresponding rotation shaft (for example, the first input shaft21, the second input shaft22, or the low shaft23) in the axial direction, and is locked to the rotation shaft in a circumferential direction. For example, each of the dog rings51to54is spline-fitted to a corresponding rotation shaft, and, in this manner, displaceable in the axial direction along a spline groove, and engages with the rotation shaft in the circumferential direction at the spline groove to rotate integrally with the rotation shaft. Note that the sleeve of the forward and reverse selector62may be configured in the same manner.

Each of the dog clutches56to59is provided on one of the dog rings51to54and one or two power transmission gears (in particular, the driving gears31and33to37) adjacent to one of the dog rings51to54in the axial direction.

The first dog clutch56is provided on the first dog ring51provided on the low shaft23and the first gear driving gear31adjacent to the first dog ring51in the axial direction. The second dog clutch57is provided on the second dog ring52provided on the first input shaft21and the third gear driving gear33adjacent to the second dog ring52in the axial direction. The position in the axial direction of the first dog ring51is switched between two positions, that is, an engaged position at which the first dog ring51is engaged with the first gear driving gear31and a neutral position away from the first gear driving gear31. The second dog ring52is also of this two-position type.FIG.2illustrates a state in which the first and second dog rings51and52are at the neutral positions.

The third dog clutch58is provided on the third dog ring53provided on the second input shaft22and the fourth and sixth gear driving gears34and36sandwiching the third dog ring53in the axial direction. The fourth dog clutch59is provided on the fourth dog ring54provided on the first input shaft21and the fifth and seventh gear driving gears35and37sandwiching the fourth dog ring54in the axial direction. The position in the axial direction of the third dog ring53is switched between three positions, that is, a first engaged position at which the third dog ring53engages with the fourth gear driving gear34on the relatively low gear side, a second engaged position at which the third dog ring53engages with the sixth gear driving gear36on the relatively high gear side, and a neutral position between the two engaged positions and away from any of the driving gears34and36. The fourth dog ring54is also of this three-position type.FIG.2illustrates a state in which the third and fourth dog rings53and54are at the neutral positions.

In the dog clutches56and57of the two-position type, two elements form a set for engagement between the dog rings51and52and the power transmission gears31and33, and are provided separately on opposing surfaces of the dog rings51and52and opposing surfaces of the power transmission gears31and33. This engagement set may be composed of two elements of a dog tooth and a dog tooth. In this case, the dog teeth are provided on both the opposing surfaces of the dog rings51and52and the opposing surfaces of the power transmission gears31and33. The engagement set may be composed of two elements of a dog tooth and an engagement hole. In this case, the dog tooth is provided on one of the opposing surfaces of the dog rings51and52and the opposing surfaces of the power transmission gears31and33, and the engagement hole is provided on the other. When the dog rings51and52are in the engaged position, the two elements are engaged with each other, and the dog clutches56and57are in an engaged state in which rotation of the dog rings51and52is transmitted to the power transmission gears31and33. When the two elements are a dog tooth and a dog tooth, the dog teeth mesh with each other in the engaged state. When the two elements are a dog tooth and an engagement hole, in the engaged state, the dog tooth fits into the engagement hole. When the dog rings51and52are in the neutral positions, the two elements are released from each other in the axial direction, and the dog clutches56and57are brought into a non-engaged state in which rotation of the dog rings51and52cannot be transmitted to the power transmission gears31and33. The dog clutches58and59of the three-position type are also configured similarly to the dog clutches of the two-position type except that a constituent of the engagement set is provided on both side surfaces of the dog rings53and54.

In the transmission13, all the dog clutches56to59are brought into the non-engaged state, or one of the dog clutches56to59is brought into the engaged state. By the above, rotation decelerated by the primary reduction mechanism11is transmitted to the counter shaft24via any one of the first to seventh gear driving gears31to37.

At a first gear position, the first dog clutch56is in the engaged state, the other dog clutches57to59are in the non-engaged state, the first clutch12A is in the engaged state, and the second clutch12B is in the released state. Rotation of the first input shaft21is transmitted to the counter shaft24via the bypass gear61, the sleeve at the forward position, the low shaft23, the first dog ring51, the first dog clutch56, the first gear driving gear31, and the low gear driven gear41.

At a second gear position, all the dog clutches56to59are in the non-engaged state, the second clutch12B is in the engaged state, and the first clutch12A is in the released state. Rotation of the second input shaft22is transmitted to the counter shaft24via the second gear driving gear32, the second gear driven gear42, and the one-way clutch60. Note that, at even-numbered gear positions (fourth gear position and sixth gear position) other than the second gear position, the second gear driven gear42idles due to an action of the one-way clutch60.

At a third gear position, the second dog clutch57is in the engaged state, the other dog clutches56,58, and59are in the non-engaged state, the first clutch12A is in the engaged state, and the second clutch12B is in the released state. Rotation of the first input shaft21is transmitted to the counter shaft24via the second dog ring52, the second dog clutch57, the third gear driving gear33, and the low gear driven gear41.

At a fourth gear position, the third dog clutch58is in the engaged state at the first engaged position, the other dog clutches56,57, and59are in the non-engaged state, the second clutch12B is in the engaged state, and the first clutch12A is in the released state. Rotation of the second input shaft22is transmitted to the counter shaft24via the third dog ring53, the third dog clutch58, the fourth gear driving gear34, and the middle gear driven gear43.

At a fifth gear position, the fourth dog clutch59is in the engaged state at the first engaged position, the other dog clutches56to58are in the non-engaged state, the first clutch12A is in the engaged state, and the second clutch12B is in the released state. Rotation of the first input shaft21is transmitted to the counter shaft24via the fourth dog ring54, the fourth dog clutch59, the fifth gear driving gear35, and the middle gear driven gear43.

At a sixth gear position, the third dog clutch58is in the engaged state at the second engaged position, the other dog clutches56,57, and59are in the non-engaged state, the second clutch12B is in the engaged state, and the first clutch12A is in the released state. Rotation of the second input shaft22is transmitted to the counter shaft24via the third dog ring53, the third dog clutch58, the sixth gear driving gear36, and the high gear driven gear44.

At a seventh gear position, the fourth dog clutch59is in the engaged state at the second engaged position, the other dog clutches56to58are in the non-engaged state, the first clutch12A is in the engaged state, and the second clutch12B is in the released state. Rotation of the first input shaft21is transmitted to the counter shaft24via the fourth dog ring54, the fourth dog clutch59, the seventh gear driving gear37, and the high gear driven gear44.

At odd-numbered gear positions of the first gear position, the third gear position, the fifth gear position, and the seventh gear position, the first clutch12A is in the engaged state, and rotation of the first input shaft21is transmitted to the counter shaft24. At even-numbered gear positions of the second gear position, the fourth gear position, and the sixth gear position, the second clutch12B is in the engaged state, and rotation of the second input shaft22is transmitted to the counter shaft24.

The first input shaft21is an odd-numbered shaft forming a power transmission path of an odd-numbered gear position. The second input shaft22is an even-numbered shaft forming a power transmission path of an even-numbered gear position. Switching of the power transmission state (that is, gear position) includes shift-up for increasing the ordinal number of a gear position to decrease a reduction ratio and shift-down for decreasing the ordinal number of a gear position to increase a reduction ratio. In both shift-up and shift-down, in principle, the ordinal number changes by one. In other words, the switching of the power transmission state (that is, gear position) is, in principle, switching between a state in which rotation of an odd-numbered shaft (the first input shaft21) is transmitted to the counter shaft24and a state in which rotation of an even-numbered shaft (the second input shaft22) is transmitted to the counter shaft24. In this switching, a state of the dog clutches56to59(that is, the position in the axial direction of the dog rings51to54) is switched.

Hereinafter, under a situation where a power transmission state is about to be switched from one gear position to another gear position, the gear position set before the switching is referred to as a “pre-switching gear position”, and the gear position to be set after the switching is referred to as a “target gear position”. Unless otherwise specified, the target gear position is a gear position on the higher gear side by one gear (for example, fourth gear position) or a gear position on the lower gear side by one gear (for example, second gear position) from the pre-switching gear position (for example, third gear position).

Hereinafter, a dog clutch corresponding to the “pre-switching gear position” is referred to as a “pre-switching dog clutch”, a dog ring constituting the pre-switching dog clutch is referred to as a “pre-switching dog ring”, and a power transmission gear constituting the pre-switching dog clutch is referred to as a “pre-switching gear”. For example, in a case where the pre-switching gear position is the third gear position, the second dog clutch57, the second dog ring52, and the third gear driving gear33are the pre-switching dog clutch, the pre-switching dog ring, and the pre-switching gear, respectively.

Hereinafter, a dog clutch corresponding to the “target gear position” is referred to as a “target dog clutch”, a dog ring constituting the target dog clutch is referred to as a “target dog ring”, and a power transmission gear constituting the target dog clutch is referred to as a “target gear”. For example, as illustrated inFIGS.6A to6D, in a case where the target gear position is the fourth gear position, the third dog clutch58, the third dog ring53, and the fourth gear driving gear34are a target dog clutch55, a target dog ring50, and a target gear30, respectively.

In a transition period from unsetting of the pre-switching gear position to completion of setting of the target gear position, the position in the axial direction of the target dog ring50is in a process of being displaced from the neutral position to the engaged position, and the target dog clutch55is in the non-engaged state. The control system100determines whether or not transition to the target gear position has been appropriately completed, and if the transition is not completed (that is, in a case where the target dog clutch55is not brought into the engaged state), the operation for transition to the target gear position is retried. The continuation of the non-engaged state of the target dog clutch55can be prevented as a result by retrying rather than by leaving the target dog clutch55in the state of not being in the engaged state, and by the above, prolongation of the transition period can be prevented.

Note that, as an example of a situation in which the target dog clutch55is not brought into the engaged state, a situation in which tips of dog teeth collide with each other in the axial direction in a case where the two elements of the engagement set are a dog tooth and a dog tooth, and a situation in which a rotational speed difference between the target dog ring50and the target gear30is small can be exemplified. Under this situation, the dog teeth hardly overlap each other in the axial direction, and hardly mesh with each other in the circumferential direction. In the present embodiment, a synchromesh mechanism is omitted from the transmission13, so that simplification of a configuration of the transmission13is achieved. Even without a synchromesh mechanism, continuation of the non-engaged state of the target dog clutch55is prevented.

As illustrated inFIGS.3A,3B, and4, the control system100includes a switching mechanism70and a controller80in addition to the power transmission mechanism10described above. The switching mechanism70moves the dog rings51to54in the axial direction to switch a power transmission state. A processor of the controller80functions as a switching controller82that controls operation of the switching mechanism70.

Referring toFIGS.3A and3B, the switching mechanism70includes a pump71that supplies hydraulic pressure, cylinders72A to72D that operate according to hydraulic pressure supplied by the pump71, valves73A to73C that control supply and discharge of pressure oil to and from the cylinders72A to72D, and shift members75A to75D driven by the cylinders72A to72D. The pump71is single. The cylinders72A to72D and the shift members75A to75D are provided as many as the dog rings51to54(for example, four), and correspond to the dog rings51to54on a one-to-one basis. A plurality (for example, three) of the valves73A to73C are provided.

A gear17(seeFIG.2) for driving an auxiliary machine is provided on the drive source output shaft9aor any shaft constituting the power transmission mechanism10. The pump71is driven by power extracted from the gear17. Each of the valves73A to73C is connected to a discharge port of the pump71via a pump line74a, and is connected to a port72bof the cylinders72A to72D via a control line74b. The valves73A to73C are electromagnetic valves that operate in accordance with a switching command given from the controller80. The “switching command” is a control command output from the controller80to the switching mechanism70to displace the position in the axial direction of the target dog ring50from the neutral position to the engaged position, and more specifically, is an electric signal that excites or demagnetizes a solenoid of the valves73A to73C as electromagnetic valves. The valves73A to73C may be linear solenoid valves, and a current value of the electric signal may be variably set.

Each of the cylinders72A to72D includes a cylinder body72a, a port72b, a piston72c, and an operation rod72d1. The piston72cpartitions the inside of the cylinder body72ainto two oil chambers. Each of the cylinders72A to72D is of a double-acting type, and two of the ports72bcommunicate with two oil chambers. The operation rod72d1extends in a cylinder axial direction. A proximal end of the operation rod72d1is fixed to a first end surface of the piston72c, and a distal end of the operation rod72d1protrudes to the outside of the cylinder body72a. The shift members75A to75D are fixed to the distal end of the operation rod72d1and engage with an outer peripheral surface of the corresponding dog rings51to54. The cylinder axial direction is parallel to the axial direction of the rotation shafts21to25. As supply and discharge of pressure oil to and from two oil chambers are controlled, the operation rod72d1moves in the axial direction together with the piston72cand the corresponding shift members75A to75D, and the corresponding dog rings51to54are displaced in the axial direction.

The first and second cylinders72A and72B correspond to the first and second dog rings51and52of the two-position type, respectively, and are of a single-rod type. When the piston72cof the cylinders72A and72B is positioned at a predetermined initial position in the cylinder body72a, the dog rings51and52are positioned at the neutral positions. The piston72cis biased to the initial position by a biasing force of a return spring. A second end surface of the piston72creceives pressure of pressure oil, and the piston72cmoves against the biasing force, so that the dog rings51and52are displaced from the neutral position to the engaged position.

The third and fourth cylinders72C and72D correspond to the third and fourth dog rings53and54of the three-position type, respectively, and are of a both-rod type. The cylinders72C and72D have a counter rod72d2extending from the second end surface of the piston72cto the side opposite to the operation rod72d1, and a pressure receiving area of the piston72cis equal between the first end surface and the second end surface. A biasing force in the axial direction is applied to both of the end surfaces of the piston72c, and the piston72cis biased to the initial position set at the center in the axial direction inside the cylinder body72a. When the piston72cis positioned at the initial position, the dog rings53and54are positioned at the neutral position. The second end surface of the piston72creceives pressure of the pressure oil, and the piston72cmoves from the initial position to a first side in the axial direction, so that the dog rings53and54are displaced from the neutral position to the first engaged position. The first end surface of the piston72creceives pressure of the pressure oil, and the piston72cmoves from the neutral position to a second side in the axial direction, so that the dog rings53and54are displaced from the neutral position to the second engaged position.

Referring also toFIG.4, the controller80is connected to an operation sensor91that detects operation of the dog rings51to54and a rotation speed sensor94that detects a rotation speed difference between the dog rings51to54and a power transmission gear (in particular, the driving gears31and33to37).

The operation sensor91includes position sensors92A to92D of a contact-type that are in contact with an operation portion that moves in conjunction with the dog rings51to54and detect the position of the dog rings51to54. The “operation portion” constitutes a part of the switching mechanism70, and includes, for example, the piston72c, the operation rod72d1, and the shift members75A to75D. The dog rings51to54operate independently of one another. For this reason, the position sensors92A to92D are provided as many as the dog rings51to54(for example, four), and correspond to the dog rings51to54on a one-to-one basis.

In the present embodiment, each of the position sensors92A to92D is provided in a corresponding one of the cylinders72A to72D, and detects whether or not the corresponding piston72cis positioned at the initial position. When the piston72cis positioned at the initial position, each of the position sensors92A to92D comes into contact with an outer peripheral surface of the piston72cand outputs an ON signal. When the piston72cis displaced from the initial position, each of the position sensors92A to92D is separated from the piston72cand outputs an OFF signal.

Regarding the third and fourth cylinders72C and72D corresponding to the third and fourth dog rings53and54of the three-position type, respectively, each of the position sensors92A to92D outputs the same OFF signal in a case where the piston72cis displaced from the initial position to the first engaged position or to the second engaged position.

The operation sensor91includes pressure sensors93C and93D that detect pressure of the pressure oil supplied to at least one of the two ports72bof each of the third and fourth cylinders72C and72D. In the present embodiment, one of the pressure sensors93C and93D is provided for each of these two cylinders72C and72D. For example, the pressure sensors93C and93D detect pressure in an oil passage connected to the port72bcommunicating with an oil chamber that the second end surface of the piston72cfaces. Under a situation where the position sensors92A to92D output the OFF signal, if the pressure shows a high value exceeding a first predetermined value, this shows that the piston72cmoves to the first side in the axial direction, and the corresponding dog rings53and54are displaced from the neutral position to the first engaged position of the two engaged positions. If the pressure shows a low value below a second predetermined value, this shows that the piston72cmoves to the second side in the axial direction, and the corresponding dog rings53and54are displaced from the neutral position to the second engaged position of the two engaged positions.

The rotation speed sensor94may include, for example, a set of an upstream rotation speed sensor95that detects a rotation speed of the drive source output shaft9a(seeFIG.2) and a downstream rotation speed sensor96that detects a rotation speed of the final shaft14a(seeFIG.2). The dog rings51to54are rotating bodies on the drive source9side, and the power transmission gear (driving gears31and33to37) are rotating bodies on the wheel2side. A rotation speed of the dog rings51to54can be acquired by multiplying a detection result of the upstream rotation speed sensor95by a speed ratio from a detection target (here, the drive source output shaft9a) of the upstream rotation speed sensor95to the dog rings51to54. A rotation speed of the power transmission gear (driving gears31and33to37) can be acquired by multiplying a detection result of the downstream rotation speed sensor96by a speed ratio from a detection target (here, the final shaft14a) of the downstream rotation speed sensor96to each gear. Since the clutches12A and12B are interposed between the drive source9and the dog rings51to54, a state of the clutches12A and12B may be considered when a rotation speed of the dog rings51to54is estimated.

A sensor that detects a rotation speed of the drive source output shaft9ais originally mounted on a vehicle for controlling the drive source9. A sensor that detects a rotation speed of the final shaft14ais originally mounted on a vehicle for detecting or estimating a vehicle speed. Since such an existing sensor is used as the rotation speed sensor94, simplification of the configuration of the control system100is achieved. Note that, in order to accurately detect a rotation speed of the dog rings51to54regardless of a state of the clutches12A and12B, the upstream rotation speed sensor95may include a sensor that detects a rotation speed of the first input shaft21and a sensor that detects a rotation speed of the second input shaft22. The downstream rotation speed sensor96may be a sensor that detects a rotation speed of a rotation shaft other than the final shaft14a, for example, the counter shaft24or the output shaft25.

Referring toFIG.4, the controller80includes a receiving unit81, a switching controller82, and a storage unit83. A function implemented by a constituent described in the present description may be implemented in circuitry or processing circuitry, including a general purpose processor, an application specific processor, an integrated circuit, application specific integrated circuits (ASICs), a central processing unit (CPU), a conventional circuit, and/or a combination of these programmed to implement the described function. A processor includes a transistor and other circuits, and is regarded as circuitry or processing circuitry. The processor may be a programmed processor that executes a program stored in a memory. In the present description, circuitry, a means, or a unit is hardware programmed to implement a described function or hardware executing the function. The hardware may be any hardware disclosed in the present description, or any hardware programmed to implement or known to execute the described function. In a case where the hardware is a processor regarded as a type of circuitry, the circuitry, means, or unit is a combination of hardware and software used to configure the hardware and/or the processor.

The receiving unit81receives a detection result output from various sensors. The various sensors include the operation sensor91and the rotation speed sensor94described above. Other than the above, the various sensors include a sensor that detects information indicating an acceleration or deceleration request of a driver, such as an acceleration operation amount sensor97that detects an operation amount of an acceleration operation element (for example, an accelerator pedal) by the driver. The storage unit83temporarily or permanently stores information necessary for processing performed by the switching controller82.

The switching controller82determines a switching timing of a power transmission state, in other words, whether or not switching of a power transmission state is necessary based on a detection result received by the receiving unit81. When determining that the switching timing has come, the switching controller82determines the target gear position. The switching controller82gives a switching command to the switching mechanism70in order to switch a power transmission state from the pre-switching gear position to the target gear position according to the determined target gear position. In other words, in order to switch the pre-switching dog clutch from the engaged state to the neutral state and switch the target dog clutch55from the neutral state to the engaged state, a fluid pressure adjustment command for adjusting fluid pressure is provided to at least one of the valves73A to73C. Specifically, both the switching command and the fluid pressure adjustment command are electric signals supplied to a solenoid of the valves73A to73C. Furthermore, in the present embodiment, since the transmission13is a DCT, a state of the first and second clutches12A and12B is switched in the switching of a power transmission state.

Next, the switching controller82determines whether the target dog clutch55has been brought into (is in) the engaged state. In this determination, the switching controller82refers to a detection result of the operation sensor91and the rotation speed sensor94received by the receiving unit81. In a case where the target dog clutch55is determined not to be in the engaged state, the switching controller82moves the target dog ring50in the axial direction to the side opposite to the target gear30side. That is, the switching controller82once returns the target dog ring50to the neutral position. After the above, the switching controller82retries the movement in the axial direction of the target dog ring50toward the target gear30side. That is, the switching controller82again displaces the target dog ring50from the neutral position to the engaged position. The return to the neutral position and the re-movement to the engaged position of the target dog ring50are also realized by giving a switching command to the switching mechanism70or a fluid pressure adjustment command to the valves73A to73C. Note that the switching controller82may change a phase of the target dog ring50with respect to the target gear30in a case where the target dog clutch55is determined not to be in the engaged state. This change in phase is performed after the target dog clutch55is determined not to be in the engaged state and before movement in the axial direction of the target dog ring50toward the target gear30side is retried.

A method for controlling the power transmission mechanism10according to the present embodiment executed by the control system100will be described with reference to flowcharts ofFIGS.5A and5Band operation diagrams ofFIGS.6A to6Dalthough partially overlapping with the above description regarding the configuration of the control system100.

First, the switching controller82determines whether or not a switching timing of a power transmission state has arrived (Step S1). While the switching timing does not arrive (S1: NO), a current power transmission state is maintained (Step S2). When the switching time arrives (S1: YES), the target gear position is set (Step S3).

As also illustrated inFIG.6A, the switching controller82gives a switching command to the switching mechanism70so that the pre-switching dog clutch becomes in the non-engaged state and the target dog clutch55becomes in the engaged state (that is, the previous dog ring is displaced from the engaged position to the neutral position and the target dog ring50is displaced from the neutral position to the engaged position) (Step S4). In other words, a fluid pressure adjustment command is given to the valves73A to73C of the switching mechanism70. In still other words, an electric signal is supplied to a solenoid of the valves73A to73C so that a power transmission state is switched from the pre-switching gear position to the target gear position.

The receiving unit81receives a detection result output from the operation sensor91and the rotation speed sensor94(Step S5). Based on a detection result received by the receiving unit81, the switching controller82determines whether the target dog clutch55is brought into the engaged state (Step S6). When the target dog clutch55is determined to be brought into the engaged state until a predetermined period (see Step S7) elapses after the switching command is given (S6: YES), the processing of switching the power transmission state ends. At this time, the setting of the pre-switching gear position is released, and the setting of the target gear position is completed (Step S8). In a case where the transmission13is a DCT, at this time, preparation for transition to the target gear position may be completed. Note that the “predetermined period” in the determination processing of Step S7is, for example, 0.2 to 0.5 seconds.

The switching controller82determines whether or not the position sensors92A to92D corresponding to the target dog ring50output an OFF signal. In a case of an ON signal, the target dog ring50is not displaced from the neutral position in the first place. When the target dog ring50is of the three-position type, the switching controller82determines whether a detection result of the pressure sensors93C and93D corresponding to the target dog ring50is a high value or a low value, and determines whether or not the detection result matches the target gear position. In a case where the target dog ring50is recognized to be displaced from the neutral position to an appropriate engaged position corresponding to the target gear position from a detection result of the operation sensors91, the switching controller82determines whether or not a rotation speed difference is equal to or less than a predetermined value based on a detection result of the rotation speed sensor94. In a case where the predetermined value is exceeded, the switching controller82determines that the engaged state is not established.

In a case where a non-engaged state of the target dog clutch55continues for a predetermined period after the switching command is provided (S6: NO AND S7: YES), the switching controller82provides a switching command to the switching mechanism70to return the dog clutch to the original state (Step S9). The dog clutch to be returned to the original state includes at least the target dog clutch55. For this reason, as also illustrated inFIG.6B, the target dog ring50once returns from the engaged position to the neutral position. The dog clutch to be returned to the original state may include the pre-switching dog clutch. In this case, the pre-switching dog ring returns from the neutral position to the engaged position, and the pre-switching gear position is reset once.

Next, the switching controller82performs phase change processing for changing a phase of the target dog ring50with respect to the target gear30(Step S10). Referring also toFIG.6C, in the phase change processing, the phase may be changed passively or actively. The phase change processing may start while the dog ring is being returned (that is, from before completion of the returning).

Regarding the passive control, due to a difference in moments of inertia between the target dog ring50and the target gear30, and the like, the phase should be naturally changed as time elapses without further operation. Therefore, in the phase change processing (Step S9), when the target dog ring50returns to the neutral position, passive control in which this state (that is, a state in which the corresponding position sensors92A to92D output an ON signal) is maintained for a predetermined period may be simply performed.

Regarding the active control, the switching controller82may change a rotation speed of a rotating body on the drive source9side among the target dog rings50and the target gears30. In the present embodiment, in any of four of the dog clutches56to59, the dog rings51to54are rotating bodies on the drive source9side, and the power transmission gears (driving gears31and33to37) are rotating bodies on the wheel2side. A change in a rotation speed N1of the dog rings51to54(rotating bodies on the drive source9side) may be either increasing or decreasing. Increasing and decreasing may be switched between at the time of shift-up and at the time of shift-down. In a case where the drive source9includes an engine, the opening degree of an electronic throttle valve, a fuel injection amount, or an ignition timing may be changed in order to change the rotation speed N1. The degree of slippage of the clutches12A and12B connected to the rotation shafts21and22to which the target dog ring50is fixed may be changed. By the above, the rotation speed N1of the rotating body on the drive source9side can be easily made different from a rotation speed N2of the rotating body on the wheel2side, and the phase is easily shifted.

Next, as also illustrated inFIG.6D, the switching controller82gives a switching command to the switching mechanism70to displace the target dog ring50from the neutral position to the engaged position again (Step S11). The switching controller82counts up the number of retries stored in the storage unit83by one (Step S12).

The switching controller82again determines whether or not the target dog clutch55is in the engaged state (Step S6). When the target dog clutch55is determined to be in the engaged state (S6: YES), the processing of switching the power transmission state is ended. In a case where the non-engaged state of the target dog clutch55continues for a predetermined period after the switching command is given (S6: NO AND S7: YES), the switching controller82proceeds to Step S9and returns the target dog ring50to the original state so as to retry transition to the target gear position again. Here, the switching controller82determines whether or not the number of retries is less than a predetermined number (for example, two) (Step S13). When the predetermined number is not reached (S13: YES), the processing proceeds to Step S10. The switching controller82performs the phase change processing (Step S10), displaces the target dog clutch55to the engaged position again (Step S11), and increments the number of retries (Step S12).

When the number of retries reaches the predetermined number (S13: NO), transition to the target gear position is abandoned. At the time of the abandonment, resetting of the pre-switching gear position may be attempted, or a gear position that can be set as long as the second clutch12B can operate even when all the dog clutches56to59are in the non-engaged state, that is, a second gear position may be temporarily set. Further, display indicating that a failure occurs in the power unit3may be displayed on an instrument panel.

The control system100according to the present embodiment includes the power transmission mechanism10having the rotation shafts21to25, the power transmission gears31and33to37rotatably fitted to the rotation shafts21to25and locked in the axial direction, the dog rings51to54slidably fitted in the axial direction and locked in the circumferential direction to the rotation shafts21to25, and the dog clutches56to59provided in the dog rings51to54and the power transmission gears31and33to37, the switching mechanism70that moves the dog rings51to54in the axial direction to switch a power transmission state, and the switching controller82that controls operation of the switching mechanism70. In a case of giving a switching command for switching a power transmission state by moving the dog rings51to54(in particular, the target dog ring55) to the power transmission gears31and33to37side (in particular, the target gear30side) in the axial direction, the switching controller82determines whether the dog clutches56to59(in particular, the target dog clutch50) are brought into the engaged state. In a case where the dog clutches56to59(in particular, the target dog clutch55) is determined not to be in the engaged state, the dog rings51to54(in particular, the target dog ring50) is moved to the side opposite to the power transmission gears31and33to37side (in particular, the target gear30side) in the axial direction. After the above, the switching controller82retries movement of the dog rings51to54(in particular, the target dog ring50) to the power transmission gears31and33to37side (in particular, the target gear30side).

When the target dog clutch55is determined not to be in the engaged state, the target dog ring50is moved to the side opposite to the target gear30side, and then moved again to the target gear30side. By the above, it is possible to prevent the non-engaged state from being continued when two elements of the engagement set of the target dog clutch55collide with each other in the axial direction.

The switching mechanism70includes the shift members75A to75D that are engaged with the dog rings51to54and move the dog rings51to54in the axial direction of the rotation shaft, the pump71that supplies fluid pressure, the cylinders72A to72D that move the shift members75A to75D in the axial direction of the rotation shafts21to25according to liquid pressure supplied by the pump71, and the valves73A to73D that adjust fluid pressure supplied to the cylinders72A to72D. By giving a fluid pressure adjustment command to the valves73A to73C, the switching controller82moves the shift members75A to75D and moves the dog rings51to54in the axial direction of the rotation shafts21to25.

When the fluid pressure adjustment command is given to the valves73A to73C, the dog rings51to54are moved in the axial direction of the rotation shafts21to25. In a case where the shift members75A to75D are moved using fluid pressure, it is difficult to grasp movement of the shift members75A to75D as compared with a case where the shift members75A to75D are mechanically moved by a cam mechanism using a shift drum. However, since the engaged state of the dog clutches56to59is determined, continuation of the non-engaged state can be prevented.

The control system100includes the operation sensor91that detects operation of the dog rings51to54. The switching controller82determines whether the dog clutches56to59(in particular, the target dog clutch55) is in the engaged state based on operation of the dog rings51to54detected by the operation sensor91.

The engaged state of the dog clutches56to59is determined based on operation of the dog rings51to54which is a premise of engagement of the dog clutches56to59. It is possible to prevent an erroneous determination that the dog clutches56to59are in the engaged state when movement of the dog rings51to54is not sufficient.

The switching mechanism70includes an operation portion that operates in conjunction with the dog rings51to54. The operation sensor91is the position sensors92A to92D of a contact-type that detect the position of the dog rings51to54by contacting the operation portion. Note that an operating position includes, for example, the piston72c, the operation rod72d1, and the shift members75A to75D.

The position of the dog rings51to54can be easily and inexpensively detected by the position sensors92A to92D of a contact-type, and the engaged state of the dog clutches56to59can be easily determined.

The control system100includes the rotation speed sensor94that detects a rotation speed difference between the dog rings51to54(in particular, the target dog ring50) and the power transmission gears31and33to37(in particular, the target gear30). The switching controller82determines whether the dog clutches56to59(in particular, the target dog clutch55) is in the engaged state based on a rotation speed difference detected by the rotation speed sensor94.

Here, when the target dog clutch55is in the engaged state, since the target dog ring50and the target gear30rotate in synchronization, a rotation speed difference should be zero or a value close to zero. In the present embodiment, the engaged state of the target dog clutch55is determined based on a rotation speed difference between the target dog ring50and the target gear30. It is possible to prevent an erroneous determination that the target dog clutch55is in the engaged state when the target dog ring50moves from the neutral position and the target dog clutch55is in the non-engaged state.

The switching controller82determines whether the dog clutches56to59(in particular, the target dog clutch55) is in the engaged state based on operation of the dog rings51to54(in particular, the target dog ring50) detected by the operation sensor91and a rotation speed difference detected by the rotation speed sensor94.

The engaged state of the target dog clutch55is determined based not only on operation of the target dog ring50but also on a rotation speed difference between the target dog ring50and the target gear30. As compared with a case where the engaged state of the target dog clutch55is determined based only on operation of the target dog ring50, the engaged state of the dog clutches56to59can be determined with high accuracy.

In a case where the dog clutches56to59(in particular, the target dog clutch55) are determined not to be in the engaged state after giving a switching command to move the dog rings51to54(in particular, the target dog ring50) to the power transmission gears31and33to37side (in particular, the target gear30side), the switching controller82changes a phase of the dog rings51to54(in particular, the target dog ring50) and the power transmission gears31and33to37(in particular, the target gear30).

When the target dog clutch55is not engaged, a phase of the target dog ring50with respect to the target gear30is changed. Therefore, when the target dog ring50is moved again to the target gear30side, two elements of an engagement set provided in the target dog ring50and the target gear30can be easily engaged.

The control system100includes the drive source9and the drive wheels2F and2R to which power from the drive source9is transmitted through the dog rings51to54and the power transmission gears31and33to37. When changing a phase between the dog rings51to54(in particular, the target dog ring50) and the power transmission gears31and33to37(in particular, the target gear30), the switching controller82changes a rotation speed of one of the dog rings51to54(in particular, the target dog ring50) and the power transmission gears31and33to37(in particular, the target gear30) provided on the drive source9side.

A rotation speed of the rotating body on the drive source9side among the target dog rings50and the target gears30is changed. It is easier to change a phase between the target dog ring50and the target gear30than in the opposite case.

Although an embodiment is described above, the above configuration can be appropriately added, deleted, and/or changed within the scope of the gist of the present invention.

The exemplified type of the transmission13is merely one example. The number of clutches may be one. However, it is advantageous if the control system according to the present embodiment is applied to a transmission not including a synchromesh mechanism.

The control system100and the control method executed by the control system100are also applicable to a vehicle other than the utility vehicle1, for example, a motorcycle.