BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a four-wheel-drive vehicle in which a changeover between a two-wheel-drive state and a four-wheel-drive state can be made.

2. Description of Related Art

[0002] There is known a four-wheel-drive vehicle that is equipped with an engine and a motor-generator that output a driving force for running, and a transfer for distributing the driving force for running to front wheels and rear wheels (e.g., see Japanese Patent Application Publication No. 2011-218871 (JP-2011-218871 A)).

[0003] In the four-wheel-drive vehicle of Japanese Patent Application Publication No. 2011-218871 (JP-2011-218871 A), the transfer is provided with a control coupling, and the driving force from the engine and the motor-generator is input to an input shaft of the transfer. In addition, in this four-wheel-drive vehicle, the control coupling is released when the vehicle is in a two-wheel-drive state, and the driving force input to the input shaft is directly transmitted only to a rear propeller shaft. On the other hand, the control coupling is engaged when the vehicle is in a four-wheel-drive state, and the driving force input to the input shaft is transmitted to the rear propeller shaft and also distributed to a front propeller shaft.

SUMMARY OF THE INVENTION

[0004] In the case where the driving force is distributed to the front wheels and the rear wheels by the transfer as is the case with the four-wheel-drive vehicle disclosed in Japanese Patent Application Publication No. 2011-218871 (JP-2011-218871 A), the rotational direction of a motive power transmission path to the front wheels is determined by the rotational direction of the input shaft of the transfer. Thus, the direction in which the front propeller shaft extends (the position of the front propeller shaft with respect to the rear propeller shaft in a vehicle width direction), the position of a ring gear of a front differential gear in the vehicle width direction, and the like are limited. It is therefore difficult to enhance the degree of freedom in design.

[0005] The invention provides a four-wheel-drive vehicle that makes it possible to enhance a degree of freedom in design.

[0006] A four-wheel-drive vehicle according to an aspect of the invention is equipped with a motor, an engine, a transmission, a case, a front-wheel propeller shaft, and a front-wheel differential unit. The motor is configured to drive front wheels. The engine is configured to drive rear wheels. The transmission is configured to shift a speed of an output of the engine. The case is arranged on an output side of the transmission. The motor is provided in the case. The front- wheel differential unit has a ring gear. The motor is connected to the ring gear via the front-wheel propeller shaft. The ring gear is arranged on the engine side in a vehicle width direction.

[0007] Owing to this configuration, as opposed to the case where the driving force is distributed to the front wheels and the rear wheels by the transfer, the rotational direction of the motor that drives the front wheels can be set irrespective of the rotational direction of the engine that drives the rear wheels. Thus, the direction in which the front-wheel propeller shaft extends, the position of the ring gear of the front-wheel differential unit in the vehicle width direction, and the like can be freely set. Therefore, the degree of freedom in design can be enhanced.

[0008] The four-wheel-drive vehicle according to the invention makes it possible to enhance a degree of freedom in design.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic block diagram showing a four-wheel-drive vehicle according to the first embodiment of the invention;

FIG. 2 is a schematic block diagram showing a four-wheel-drive vehicle according to the second embodiment of the invention;

FIG. 3 is a schematic block diagram showing a four-wheel-drive vehicle according to the third embodiment of the invention; and

FIG. 4 is a schematic block diagram showing a four-wheel-drive vehicle according to the fourth embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0010] The embodiments of the invention will be described hereinafter on the basis of the drawings.

(First Embodiment)

[0011] First of all, a four-wheel-drive vehicle 100 according to the first embodiment of the invention will be described with reference to FIG. 1.

[0012] The four-wheel-drive vehicle 100 is a hybrid vehicle that adopts a standby four-wheel-drive system based on a front-engine rear-drive (FR) system. This four-wheel-drive vehicle 100 is configured such that a ^" changeover between a two-wheel-drive state in which only rear wheels 7 are driven and a four-wheel-drive state in which both the rear wheels 7 and front wheels 11 are driven can be made.

[0013] Specifically, as shown in FIG. 1 , the four-wheel-drive vehicle 100 is equipped with an engine 1 that drives the rear wheels 7, a primary transmission 2 that shifts a speed of an output of the engine 1, and a motor 33 that is accommodated in a case 3 to drive the front wheels 11.

[0014] The engine (an internal combustion engine) 1 is a known motive power unit that outputs a motive power by burning fuel for a gasoline engine, a diesel engine or the like. _; The engine 1 is configured such that an operation state, for example, a throttle opening degree (an intake air amount) of a throttle valve that is provided in an intake passage, a fuel injection amount, an ignition timing and the like can be controlled. An output shaft (a crankshaft) of this engine 1 is coupled to the primary transmission 2.

[0015] The primary transmission 2 includes, for example, a torque converter and an automatic transmission. The torque converter has an input-side pump impeller, an output-side turbine runner, and the like, and is configured such that a motive power is transmitted between the pump impeller and the turbine runner via a fluid (a hydraulic fluid). The pump impeller is coupled to the output shaft of the engine 1, and the turbine runner is coupled to an input shaft of the automatic transmission via a turbine shaft. The automatic transmission has frictional engagement elements, a planetary gear train and the like, and is configured such that a plurality of shift speeds are established by selectively engaging the frictional engagement elements. An output shaft of the automatic transmission is coupled to a secondary transmission 31. Incidentally, the primary transmission 2 is an example of "the transmission" of the invention.

[0016] The case 3 is attached to an output side of the primary transmission 2 (the other side of the engine 1). That is, the case 3 is arranged closer to the rear wheel 7 sides than the primary transmission 2 and a front-wheel differential unit 9.

[0017] In this case 3, the secondary transmission 31 to which the output shaft of the primary transmission 2 is coupled, a rear-wheel output shaft 32 as an output shaft of the secondary transmission 31, a motor 33 that drives the front wheels 11, a motive power transmission mechanism 34, and a front- wheel output shaft 35 are accommodated.

[0018] The secondary transmission 31 has a planetary gear train and the like, and is configured such that a high range or a low range can be selected. For example, the secondary transmission 31 directly transmits rotation of the output shaft of the primary transmission 2 to the rear-wheel output shaft 32 if the high range is selected, and reduces the speed of rotation of the output shaft of the primary transmission 2 and transmits the rotation to the rear-wheel output shaft 32 if the low range is selected.

[0019] The rear-wheel output shaft 32 is rotatably supported by the case 3, and is arranged concentrically with the output shaft of the primary transmission 2 (an input shaft of the case 3) and a rotary shaft of the motor 33. A rear-wheel propeller shaft 4 is coupled to the rear-wheel output shaft 32 via a constant-speed universal joint 4a. The rear wheels 7 are connected to this rear-wheel propeller shaft 4 via a constant-speed universal joint 4b, a rear- wheel differential unit 5, and rear- wheel drive shafts 6.

[0020] The motor 33 mainly functions as ari electric motor, and also functions as an electric generator depending on the situation. The motor 33 is, for example, an alternating-current synchronous electric motor, and has a rotor 33a made from a permanent magnet, and a stator 33b around which a three-phase winding is wound. A tubularly formed motor output shaft 33c is integrally coupled to the rotor 33a. Incidentally, the rear-wheel output shaft 32 is arranged inside the motor output shaft 33c. The stator 33b is fixed to the case 3.

[0021] Besides, the motor 33 is connected to a battery via an inverter. The inverter can convert a direct current supplied from the battery into an alternating current to drive the motor 33 (power running control), and convert an alternating current generated by the motor 33 into a direct current to output the direct current to the battery (regeneration control).

[0022] The motive power transmission mechanism 34 has sprockets 34a and 34b and a chain 34c. The sprocket 34a is coupled to the motor output shaft 33c, and the sprocket 34b is coupled to the front-wheel output shaft 35. The chain 34c is wound and hung between the sprockets 34a and 34b. That is, the motive power transmission mechanism 34 has a function of transmitting a motive power of the motor output shaft 33c to the front-wheel output shaft 35, which is arranged parallel to the motor output shaft 33c in a vehicle width direction (an X-direction).

[0023] The front-wheel output shaft 35 is rotatably supported by the case 3, and is arranged parallel to the rear-wheel output shaft 32 and the motor output shaft 33c. A front- wheel propeller shaft 8 is coupled to the front- wheel output shaft 35 via a constant-speed universal joint 8a. The front wheels 11 are connected to this front-wheel propeller shaft 8 via a constant-speed universal joint 8b, the front- wheel differential unit 9, and front- wheel drive shafts 10. Incidentally, the front- wheel propeller shaft 8 is arranged on the left side, as viewed in a direction toward a vehicle front, with respect to the engine 1, the primary transmission 2 and the rear- wheel propeller shaft 4.

[0024] Besides, the front-wheel differential unit 9 is provided to absorb a turning radius difference. This front- wheel differential unit 9 includes a drive pinion gear 91, a ring gear 92, a pair of differential pinion gears 93, and a pair of side gears 94. The drive pinion gear 91 is formed in such a manner as to rotate integrally with the front- wheel propeller shaft 8.

[0025] The ring gear 92 meshes with the drive pinion gear 91, and is coupled to a differential case 95. This ring gear 92 is arranged on the engine 1 side with respect to the differential case 95 in the vehicle width direction. That is, the ring gear 92 is arranged inside in the four-wheel-drive vehicle 100 in the vehicle width direction (on the right side in the front-wheel differential unit 9 as viewed in a direction toward a vehicle front).

[0026] The differential pinion gears 93 are rotatably supported by a differential pinion shaft 96 that is coupled to the differential case 95. The side gears 94 mesh with the differential pinion gears 93 respectively, and are coupled to the front- wheel drive shafts 10 respectively.

[0027] It should be noted herein that the secondary transmission 31 , the motor 33, and the motive power transmission mechanism 34 are arranged in this order from the front side toward the rear side in the case 3. That is, the motor 33 is arranged on the primary transmission 2 side front side) with respect to the motive power transmission mechanism 34.

[0028] In addition, as shown in FIG. 1, in the four-wheel-drive vehicle 100, a motive power from the engine 1 is transmitted to the rear wheels 7 via the primary transmission 2, the secondary transmission 31 , the rear-wheel output shaft 32, the rear- wheel propeller shaft 4, the rear- wheel differential unit 5, and the rear- wheel drive shafts 6, and a motive power from the motor 33 is transmitted to the front wheels 11 via the motive power transmission mechanism 34, the front- wheel output shaft 35, the front- wheel propeller shaft 8, the front-wheel differential unit 9, and the front-wheel drive shafts 10. Incidentally, in the four-wheel-drive vehicle 100, the motive power of the engine 1 is not transmitted to the front wheels _. 11, and the motive power of the motor 33 is not transmitted to the rear wheels 7.

[0029] Thus, in the four-wheel-drive vehicle 100 according to the first embodiment of the invention, the rotational direction of the motor 33 that drives the front wheels 11 can be set irrespective of the rotational direction of the engine 1. For example, the front-wheel propeller shaft 8 is rotated in an Rpl direction by rotating the motor 33 in an Rml direction. Therefore, the front- wheel drive shafts 10 can be rotated in an Rdl direction (in a forward direction).

[0030] Besides, in the four-wheel-drive vehicle 100, a changeover between the two-wheel-drive state in which the engine 1 drives the rear wheels 7 and the four-wheel-drive state in which the engine 1 drives the rear wheels 7 and the motor 33 drives the front wheels 11 is appropriately made in accordance with the running state or the like. For example, the four-wheel-drive vehicle 100 is rendered in the two-wheel-drive state during steady running or the like, and in the four-wheel-drive state during takeoff, low μ road running or the like.

[0031] - Effects -

In the first embodiment of the invention, as described above, the engine 1 that drives the rear wheels 7 and the motor 33 that drives the front wheels 11 are provided, and the respective drive systems are made independent of each other. Thus, as opposed to the case where a driving force- is distributed to the front wheels and the rear wheels- by the transfer, the rotational direction of the motor 33 that drives the front wheels 11 can be set irrespective of the rotational direction of the engine 1 that drives the rear wheels 7. Thus, the direction in which the front-wheel propeller shaft 8 extends (the position of the front-wheel propeller shaft 8 with respect to the rear-wheel propeller shaft 4 in the vehicle width direction), the position of the ring gear 92 of the front-wheel differential unit 9 in the vehicle width direction, and the like can be freely set. Therefore, the degree of freedom in design can be enhanced. Thus, components can be used in common, and hence a reduction in cost can be achieved.

[0032] Besides, in the first embodiment of the invention, the ring gear 92 is arranged on the engine 1 side with respect to the differential case 95 in the vehicle width direction, whereby the mountability of the front-wheel differential unit 9 can be improved.

[0033] Besides, in the first embodiment of the invention, the case 3 in which the motor 33 is accommodated is attached to the output side of the primary transmission 2. Thus, the mounting space of the motor 33 can be made wider than in the case where the motor is arranged in the vicinity of the front-wheel differential unit. Therefore, the output of the motor 33 can be enhanced.

(Second Embodiment)

[0034] FIG. 2 is a schematic block diagram showing a four-wheel-drive vehicle according to the second embodiment of the invention. Next, a four-wheel-drive vehicle 200 according to the second embodiment of the invention will be described with reference to FIG. 2. Incidentally, hereinafter, components identical to those of the first embodiment of the invention will be denoted by the same reference symbols respectively, and redundant description will be omitted.

[0035] In the four-wheel-drive vehicle 200 according to the second embodiment of the invention, as opposed to the first embodiment of the invention, the front-wheel propeller shaft 8 is arranged on the right side, as viewed in a direction toward a vehicle front, with respect to the rear-wheel propeller shaft 4. In addition, the ring gear 92 is arranged inside in the four-wheel-drive vehicle 200 in the vehicle width direction (on the left side in the front- wheel differential unit 9 as viewed in a direction toward a vehicle front).

[0036] Thus, in the four-wheel-drive vehicle 200 according to the second embodiment of the invention, the front-wheel propeller shaft 8 is rotated in an Rp2 direction by, for example, rotating the motor 33 in an Rm2 direction irrespective of the rotational direction of the engine 1. Therefore, the front-wheel drive shafts 10 can be rotated in an Rd2 direction (in the forward direction).

[0037] Incidentally, the second embodiment of the invention is identical in other configurational details and effects to the first embodiment of the invention.

(Third Embodiment)

[0038] FIG. 3 is a schematic block diagram showing a four-wheel-drive vehicle according to the third embodiment of the invention. Next, a four-wheel-drive vehicle 300 according to the third embodiment of the invention will be described with reference to FIG. 3. Incidentally, hereinafter, components identical to those of the first embodiment of the invention will be denoted by the same reference symbols respectively, and redundant description will be omitted.

[0039] In the four-wheel-drive vehicle 300 according to the third embodiment of the invention, a motive power transmission mechanism 301 is provided instead of the motive power transmission mechanism 34 (see FIG. 1) according to the first embodiment of the invention. This motive power transmission mechanism 301 has a counter drive gear 301a that is coupled to the motor output shaft 33c, a counter driven gear 301b that is coupled to the front- wheel output shaft 35, and an intermediate gear 301c that meshes with the counter drive gear 301a and the counter driven gear 301b.

[0040] Thus, in the four-wheel-drive vehicle 300 according to the third embodiment of the invention, the front-wheel propeller shaft 8 is rotated in an Rp3 direction by, for example, rotating the motor 33 in an Rm3 direction irrespective of the rotational direction of the engine 1. Therefore, the front- wheel drive shafts 10 can be rotated in an Rd3 direction (in the forward direction).

[0041] Incidentally, the third embodiment of the invention is similar in other configurational details and effects to the first embodiment of the invention.

(Fourth Embodiment)

[0042] FIG. 4 is a schematic block diagram showing a four-wheel-drive vehicle according to the fourth embodiment of the invention. Next, a four-wheel-drive vehicle 400 according to the fourth embodiment of the invention will be described with reference to FIG. 4. Incidentally, hereinafter, components identical to those of the third embodiment of the invention will be denoted by the same reference symbols respectively, and redundant description will be omitted.

[0043] As opposed to the third embodiment of the invention, a motive power transmission mechanism 401 of the four-wheel-drive vehicle 400 according to the fourth embodiment of the invention is not provided with an intermediate gear 301c (see FIG. 3), and is configured such that a counter drive gear 401a that is coupled to the motor output shaft 33c directly meshes with a counter driven gear 401b that is coupled to the front- wheel output shaft 35.

[0044] Thus, in the four-wheel-drive vehicle 400 according to the fourth embodiment of the invention, the front-wheel propeller shaft 8 is rotated in an Rp4 direction by, for example, rotating the motor 33 in an Rm4 direction irrespective of the rotational direction of the engine 1. Therefore, the front- wheel drive shafts 10 can be rotated in an Rd4 direction (in the forward direction).

[0045] Incidentally, the fourth embodiment of the invention is similar in other configurational details and effects to the first embodiment of the invention.

(Other Embodiments)

[0046] Incidentally, the embodiments of the invention disclosed herein are . exemplary in all respects, and do not constitute a basis of limitative construal. Accordingly, the technical scope of the invention should not be construed only by the foregoing embodiments thereof, but is defined on the basis of the description of the claim.

Besides, the technical scope of the invention encompasses all the modifications that are equivalent in significance and scope to the claim.

[0047] For example, each of the first to fourth embodiments of the invention· - shows an example in which the motor is arranged closer to the primary transmission side than the motive power transmission mechanism in the case. However, the invention is not limited to this example. The motor may be arranged closer to the rear side than the motive power transmission mechanism in the case.

[0048] Besides, each of the first to fourth embodiments of the invention shows the primary transmission 2 including the multi-staged automatic transmission that has the frictional engagement elements, the planetary gear train and the like. However, the invention is not limited to this primary transmission. The primary transmission may include a continuously variable transmission (a CVT) that adjusts the speed ratio steplessly.

Besides, the primary transmission may be a manual transmission (a hand-operated transmission).

[0049] Besides, each of the third and fourth embodiments of the invention shows an example in which the front- wheel propeller shaft 8 is arranged on the left side as to the forward direction of the vehicle with respect to the rear-wheel propeller shaft 4. However, the invention is not limited to this example. The front-wheel propeller shaft may be arranged on the right side, as viewed in a direction toward a vehicle front, with respect to the rear-wheel propeller shaft.

[0050] The invention is available to a four-wheel-drive vehicle in which a changeover between a two-wheel-drive state and a four-wheel-drive state can be made.