JP2000127789A - Four wheel drive vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a four wheel drive vehicle having low fuel consumption without incurring lowering of the comfortability of a passenger compartment and an increase in the weight of the vehicle. SOLUTION: A drive power is mechanically transmitted from one end part (rear end part) of a crankshaft 16 of an engine 14 to rear wheels 18 through the intermediary of a rear wheel drive power transmission device 20, and a drive power is mechanically transmitted from the other end part (front end part) of the crankshaft 16 to front wheels 22 through the intermediary of a front wheel drive power transmission device 24. Accordingly, in comparison with a four wheel drive condition of such a type that a mechanical drive power delivered from the engine 14 is converted into a hydraulic power by means of the hydraulic pump, and accordingly, hydraulic oil discharged from the hydraulic pump is fed into a hydraulic motor provided to an auxiliary drive wheel, it is possible to eliminate power loss caused by such a problem that the hydraulic oil is fed from the hydraulic pump into the hydraulic motor through a pipe line or a hose. Thus, it is possible to eliminate such a disadvantage that power transmission loss becomes larger so as to increase fuel consumption. Further, it is possible to eliminate the necessity of a transfer and a propeller shaft extending from the transfer to the auxiliary drive wheel. Thereby it is possible to prevent lowering of the comfortability of the passenger compartment and increasing of the weight of the vehicle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive vehicle capable of transmitting a driving force output from an engine to front and rear wheels, and more particularly to a technique for obtaining high transmission efficiency.

[0002]

2. Description of the Related Art It has been proposed to use a four-wheel drive mechanism to improve the running performance, running stability and traction of a vehicle when traveling on a road surface having a low coefficient of friction, such as a frozen road or a snow-covered road. In a conventional four-wheel drive vehicle, a clutch, a propeller shaft, a differential gear device, a transfer,
A four-wheel drive mechanism including an axle shaft is used, and each wheel is mechanically connected to the engine.

In general, the conventional four-wheel drive mechanism as described above requires additional components such as a transfer, a propeller shaft, and a differential gear device as compared with the two-wheel drive mechanism, so that the mounting of the components is required. As a result, the cabin becomes narrow or high, so that the livability is impaired, or the fuel consumption rate increases due to an increase in the weight of the vehicle.

On the other hand, a driving force output from an engine is transmitted to a main driving wheel, one of a front wheel and a rear wheel, using a mechanical power transmission mechanism, and a part of the driving force generated by the engine is transmitted. The hydraulic pump is used to output a hydraulic pressure, and the hydraulic pressure is used to drive the pair of sub-drive wheels by hydraulic motors provided on a pair of sub-drive wheels, which are the other of the front wheels and the rear wheels. Such a four-wheel drive vehicle has been proposed. For example, Japanese Patent Laid-Open No. 5-1
This is the vehicle drive device described in Japanese Patent No. 04971.

[0005] According to the above-described vehicle drive device, the hydraulic pump provided on the engine and the hydraulic motor provided on the auxiliary drive wheel are connected by pipes or hoses having flexibility which are easy to bend. Therefore, the disadvantages that the cabin becomes narrow or high and the livability is impaired, and that the fuel consumption rate increases due to an increase in the weight of the vehicle are suitably solved.

[0006]

However, according to the above vehicle drive device, in the four-wheel drive state, the mechanical driving force output from the engine is converted to hydraulic pressure by using the hydraulic pump and flows out from the hydraulic pump. Since the hydraulic oil is circulated at a predetermined flow rate in the pipe or hose and the hydraulic motor, the transmission loss of the driving force is large compared to a four-wheel drive vehicle that drives the sub-drive wheels via a mechanical transmission mechanism. As a result, the fuel consumption rate becomes high.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a four-wheel vehicle having a low fuel consumption rate without lowering the livability of the passenger compartment and increasing the weight of the vehicle. It is to provide a driving car.

[0008]

The gist of the present invention to achieve the above object is to provide a four-wheel drive vehicle capable of transmitting a driving force output from an engine to front wheels and rear wheels. a) a rear wheel driving force transmission device for mechanically transmitting driving force from one end of the output shaft of the engine to the rear wheel; and (b) the front wheel from the other end of the output shaft of the engine. And a front wheel driving force transmission device for mechanically transmitting the driving force toward the front wheel.

[0009]

In this manner, the driving force from one end of the output shaft of the engine is mechanically transmitted to the rear wheels by the rear wheel driving force transmission device, and the driving force from the other end of the output shaft is transmitted. Is mechanically transmitted to the front wheels by the front wheel driving force transmission device, so that the mechanical driving force output from the engine is converted into hydraulic pressure using a hydraulic pump, and the hydraulic oil flowing out of the hydraulic pump is transmitted to the auxiliary driving wheels. As compared with the four-wheel drive state of the type supplied to the provided hydraulic motor, the power loss caused by the hydraulic oil being circulated from the hydraulic pump via the pipe or the hose and the hydraulic motor is eliminated, The disadvantage that the transmission loss of the driving force is increased and the fuel consumption rate is increased is eliminated. In addition, since the driving force to the rear wheel and the front wheel is extracted from both ends of the output shaft, a transfer shaft and a propeller shaft from the transfer to the auxiliary drive wheel are not required, which reduces the comfort in the vehicle interior and increases the weight of the vehicle. Is not accompanied.

[0010]

In another preferred embodiment of the present invention, a control clutch provided in series in a power transmission path from the other end of the output shaft to the front wheel, and a connection state in which the power transmission path is connected, There is further provided a switching mechanism interposed in the power transmission path for selectively switching to a cutoff state in which the power transmission path is shut off. If you do this,
Even if the control clutch is dragged, by being switched to the disconnected state by the switching mechanism,
Power loss during two-wheel drive traveling due to the drag is prevented.

Preferably, a power transmission path is provided in the housing of the engine from the other end of the output shaft to a differential gear device provided on the axle of the front wheel.
In this power transmission path, the control clutch and the switching mechanism are provided in series. With this configuration, the front wheel driving force transmission device that transmits driving force from the other end of the output shaft to the front wheels is housed in the engine housing, thereby eliminating the need for a propeller shaft, a joint, and the like. Therefore, it is possible to more suitably suppress the deterioration of the livability in the vehicle compartment and the increase in the vehicle weight.

Preferably, in a power transmission path from the other end of the output shaft to a differential gear device provided on the axle of the front wheel, the switching mechanism transmits power without reversing the rotation direction. And a first coupling that couples a power transmission path that transmits power without reversing the rotation direction by using the forward / reverse gear device that can be switched between a rotating state and a state of transmitting power by reversing the rotation direction. A state, and a second coupling state in which a power transmission path for transmitting power by reversing the rotation direction by the forward-reverse gear device;
This selectively switches to a cutoff state in which the power transmission path is cut off. With this configuration, four-wheel drive traveling can be performed in each of the forward traveling and the reverse traveling of the vehicle.

Preferably, the rear wheel driving force transmission device constantly transmits the driving force output from the engine to the rear wheels via a stepped transmission, and the front wheel driving force transmission device includes: The driving force is transmitted to the front wheels at the same gear ratio as that of the second or third gear of the stepped transmission. In this way, by directly engaging the control clutch, the same running performance, running stability, and traction as in the direct-coupled four-wheel drive vehicle can be obtained at the second speed or the third speed.

[0014] Preferably, the electronic control unit of the four-wheel drive vehicle includes a slip determination means for determining occurrence of slip of a rear wheel which is a main drive wheel during acceleration operation of the vehicle, and the slip determination means. Control clutch control means for increasing the engagement torque of the control clutch so that the actual engine speed is substantially maintained at the engine speed at the time of occurrence of the slip, when occurrence of slip of the rear wheel is determined. Is included. In this way, when the driver operates the acceleration operation member for an acceleration operation such as when the vehicle starts, if the rear wheels slip due to a low μ road or the like, the actual Since the driving force from the engine is supplied to the front wheels so that the engine rotation speed of the vehicle is substantially maintained at the engine rotation speed at the time of occurrence of the slip, the increase in the engine output after the occurrence of the slip is exclusively supplied to the front wheels Therefore, when a slip occurs on the rear wheels, the four-wheel drive state is automatically set, the engine stall due to the start of engagement of the control clutch is prevented, and the vehicle can be started and accelerated properly.

[0015] Preferably, the vehicle further comprises turning traveling determining means for judging turning of the vehicle, and when the turning traveling of the vehicle is judged by the turning traveling determining means, the control clutch control means controls the control clutch. The clutch is operated to the release side more than before. If you do this,
If the vehicle turns while the control clutch is engaged for four-wheel drive traveling, the engagement torque of the control clutch is suppressed, so that tight corner braking occurs during four-wheel drive traveling. Automatically prevented.

Preferably, the stepped transmission is an automatic transmission, and the electronic control unit of the four-wheel drive vehicle starts the vehicle on a road surface having a low road surface friction coefficient, such as a snow-covered road or a frozen road. Selecting means for selecting a low-μ road starting mode for driving the vehicle, and when the low-μ road starting mode is selected by the mode selecting means, the automatic transmission is set to the second gear or the third gear when starting the vehicle. When the low μ road starting mode is selected by the mode selection means and the second or third speed gear of the automatic transmission is selected by the speed control means. Includes control clutch control means for engaging the control clutch to drive the front wheels. With this configuration, when the vehicle is started on a road surface having a low coefficient of road surface friction, the automatic transmission is automatically set to the second speed or the third speed and the rear wheels are driven. Since the control clutch is engaged and the front wheels are also driven, the startability of the vehicle on a low μ road is enhanced.

[0017]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a four-wheel drive vehicle 1 according to one embodiment of the present invention.
FIG. 3 is a diagram showing a power transmission mechanism of No. 0 and an electronic control unit 12 configured by a so-called computer for controlling the power transmission mechanism. A four-wheel drive vehicle 10 shown in FIG. 1 transmits a driving force from a rear end of a crankshaft 16 which is an output shaft provided in a housing of an engine 14 to a pair of rear wheels 18 which are main driving wheels. A driving force transmitting device 20 for transmitting driving force from a front end portion of the crankshaft 14 to a pair of front wheels 22 serving as auxiliary driving wheels; This is a vehicle based on FR drive, in which the vehicle 22 is driven by an assist as needed.

The rear wheel driving force transmission device 20 includes a power opening / closing joint 26 such as a clutch or a torque converter provided outside the engine 14 from the rear end of the crankshaft 16, and a manual or automatic transmission. 28, a driving force is transmitted to the rear wheel 18 via the differential gear device 30, and a pair of axles 32 in order. When the transmission 28 is a well-known manual transmission that can be shifted according to a manual operation, the power opening / closing joint 26 includes a clutch such as a dry single-plate clutch that opens and closes a power transmission path according to a clutch pedal operation. In the case where the transmission 28 is a well-known automatic transmission in which a gear stage is automatically switched based on an actual vehicle speed V and an accelerator opening Acc from a previously stored shift diagram, the power opening / closing joint Reference numeral 26 denotes a torque converter or a fluid coupling.

The front wheel driving force transmission device 24 is provided with a control clutch for opening and closing a front wheel power transmission path, which is provided from a front end of the crankshaft 16 to a transmission device 34 and an inside of a housing of the engine 14, for example, an oil pan. 36, a switching mechanism 38 that is switched to couple or cut off the power transmission path, a differential gear device 39, and a driving force to the front wheels 22 via a pair of axles 40 in sequence to transmit the driving force to the second gear of the transmission 28. Alternatively, the transmission is performed by the same gear ratio of the rear wheel driving force transmission device 20 as in the case of the third gear.

The control clutch 36 comprises an engagement clutch such as a dog clutch, a fluid coupling to which power is transmitted via a fluid, a torque converter, and the like. The input shaft 42 and the output shaft 44 are connected to each other to transmit power. And a state in which the input shaft 42 and the output shaft 44 are released to interrupt power transmission. The input shaft 42 is provided in parallel with the crankshaft 16,
The transmission 34 is provided between the front end of the crankshaft 16 and the input shaft 42. The transmission 34 is composed of, for example, a pair of pulleys 48 around which a transmission band 46 such as a chain or a timing belt is wound. In FIG. 1, the transmission 34 is provided outside the engine 10, but may be provided inside the housing of the engine 10.

The switching mechanism 38 includes an input side gear 50 connected to the output shaft 44, a first output side gear 52 and a second output side gear 54 provided concentrically with the input side gear 50, and a first output side gear 52 and a forward / reverse gear 58 provided between the second output gear 54 and the output shaft 56, and meshed with the input gear 50 and the first output gear 52 or the second output gear 54. 2 for transmitting the driving force from the front end portion of the crankshaft 16 in the same rotational direction as shown in FIG. FIG. 3 shows a forward connection state, in which the driving force from the front end of the crankshaft 16 is transmitted in the opposite rotation direction, and FIG. 3 shows a state in which a power transmission path from the front end of the crankshaft 16 to the front wheel 22 is cut off. It is adapted to be selectively switched to a disconnected state.

That is, the forward-reverse gear device 58 is a so-called planetary gear device, and includes a ring gear 66 connected to the first output gear 52 and the output shaft 56, and a second gear
A sun gear 68 connected to the output side gear 54 and a pinion 72 rotatably supported by a carrier 70 fixed to a non-rotating member and meshing with the ring gear 66 and the sun gear 68 are provided. The sleeve 60 is formed on the outer peripheral surface with the first inner peripheral teeth 74 meshing with the outer peripheral teeth of the input gear 50, the second inner peripheral teeth 76 for meshing with the first output gear 52 or the second output gear 54. And a cylindrical member provided with an annular engagement groove 78. The switching actuator 62 includes a hydraulic cylinder, a pneumatic cylinder, an electric motor, and the like. The shift fork 80 slidably engaged in the annular engagement groove 78.
It has.

When the shift fork 80 and the sleeve 60 which is rotatably engaged with the shift fork 80 are driven to the most advanced position of the control clutch 36 as shown in FIG. Since the gear 50 and the first output gear 52 are connected via the sleeve 60, the input gear 50 and the output shaft 56 are mutually connected so as to rotate integrally, so that the crankshaft 16 A power transmission path from the front end to the front wheel 22 is achieved, and a driving force in the same rotational direction as the crankshaft 16 is transmitted to the front wheel 22. The switching actuator 62
When the shift fork 80 and the sleeve 60 rotatably engaged with the shift fork 80 are driven to the reverse position adjacent to the differential gear device 39 with respect to the forward position as shown in FIG. Since the input-side gear 50 and the second output-side gear 54 are connected via the sleeve 60, the input-side gear 50 and the output shaft 56 are operatively connected to be inverted with each other. A power transmission path from the front end to the front wheel 22 is achieved, and a driving force in a rotational direction opposite to the crankshaft 16 is transmitted to the front wheel 22. At this time, the total gear ratio of the front wheels 22 and the rear wheels 18
Differential gear device 3 so that the total gear ratio of the
If a gear ratio of 9 is set, the same running performance as that of a direct-coupled four-wheel drive vehicle can be obtained even in reverse. Also,
The shift fork 80 is operated by the switching actuator 62.
When the sleeve 60 rotatably engaged with the sleeve 60 is driven to the neutral position adjacent to the differential gear device 39 with respect to the reverse position as shown in FIG. And the first output side gear 52 or the second
Since the engagement between the output side gear 54 and the sleeve 60 is released, the connection between the input side gear 50 and the output shaft 56 is released, and the mutual connection state is canceled.
The power transmission path from the front end of the front wheel 6 to the front wheel 22 is shut off.

The electronic control unit 12 includes, for example, an accelerator operation amount Acc, which is represented by an operation amount of an accelerator pedal and an opening amount of a throttle valve, a fuel injection amount, or a required load or required output amount of the engine 14 which is an intake air amount. Output amount sensor 82 for detecting the rotational speed N of the engine 14
An engine speed sensor 84 for detecting _E , a steering angle sensor 86 for detecting the steering amount of the steering wheel or the steering angle of the front wheels 22, a shift sensor 88 for detecting the actual gear position of the transmission 28, and a manual operation for assist drive selection Alternatively, a signal is supplied from a mode setting unit 90 for setting the four-wheel drive mode in response to the automatic determination. The mode setting device 90 is provided when a snow mode setting switch operated to start the vehicle at the second speed or the third speed is provided on a low μ road such as a frozen road or a snow-covered road. Is set to the four-wheel drive mode in response to the operation of the snow mode setting switch.

The electronic control unit 12 includes a CPU, a RAM, an R
A so-called microcomputer including an OM, an interface, etc., processes input signals in accordance with a program stored in advance in a ROM while utilizing a temporary storage function of a RAM, and controls the control clutch 36 and the switching actuator 62.
Control. When the transmission 28 is an automatic transmission, the gear position of the transmission 28 is determined based on the actual vehicle speed V and the required load amount (for example, the accelerator opening Acc) from a shift diagram stored in advance. Automatic shift control for outputting a shift command for realizing the determined gear position is also executed. In the automatic gear shift control, when the snow mode or the four-wheel drive mode is selected, the gear at the time of starting the transmission 28 is automatically selected as the second gear or the third gear. .

FIG. 5 is a functional block diagram for explaining main control functions of the electronic control unit 12. As shown in FIG. In FIG. 5, the mode determining means 100 determines whether or not the four-wheel drive mode has been set by the mode setting device 90. The shift position determining means 102 determines whether the vehicle is in the forward or reverse state based on whether the actual gear of the transmission 28 is the forward gear or the reverse gear when the four-wheel drive mode is set. judge. The switching control means 104
The mode determination means 100 determines that the four-wheel drive mode has been set, and the shift position determination means 1
02, it is determined that the vehicle is in the forward state by using the switching mechanism 62 by the switching actuator 62 in FIG.
In the forward drive state. However, the mode determining means 1
00, it is determined that the four-wheel drive mode has been set, and when the shift position determination means 102 determines that the vehicle is in the reverse state, the switching control means 10
4 sets the switching mechanism 38 by the switching actuator 62 to the reverse drive state in FIG.

The slip determining means 106 is a four-wheel drive
When the motion mode is set,
The rear wheel 18, which is the main drive wheel, slips due to the work
Whether the rear wheel rotation speed has changed or
The determination is made based on the difference between the wheel rotation speed and the front wheel rotation speed. D
The engine rotation speed storage means 108 stores the slip determination information.
It is determined by the step 106 that the rear wheel 18 has slipped.
Is detected by the engine speed sensor 84 when
Rotational speed N of the crankshaft 16 of the engine 14 _E1Remember
I do.

The acceleration operation during the determination unit 110, the rise in the engine rotational speed N _E, the increase in the accelerator pedal operation amount Acc, or during acceleration operation of the vehicle based the like on the signal of the accelerator switch for detecting the return of the accelerator pedal Is determined. The turning traveling determination means 112 determines that, for example, the actual steering angle θ _ST of the vehicle is smaller than a predetermined determination reference value θ ₀ , or that the lateral G of the vehicle is equal to or less than a predetermined determination reference value G _1. Based on the above, it is determined whether or not the vehicle is turning.

The control clutch control means 114 determines whether the vehicle is being accelerated by the acceleration operation determining means 110 and determines that the vehicle is not turning by the turning travel determining means 112. in fact when the engine rotational speed N _E is slip of the rear wheels 18 occurs, or as the slip of the rear wheels 18 within a range in which the engine stall does not occur coincident with the rotational speed N _E1 immediately before the engine 14 for generating Then, the transmission torque of the control clutch 36 is controlled in a range where the transmission torque is zero to 1/2 of the engine output torque. However, during the acceleration operation determination means 1
Even if it is determined that the vehicle is in the accelerating operation by 10, if the turning traveling determination means 112 determines that the vehicle is in the turning operation, the control clutch control means 114 determines whether the vehicle is in the acceleration operation. While the means 110 determines that the vehicle is accelerating, the transmission torque of the control clutch 36 is reduced to such an extent that the tight corner braking phenomenon does not occur.

The four-wheel drive mode end determination means 116 determines that the accelerator pedal has been depressed and the required output of the engine 14 has become zero, the brake pedal has been operated, or the shift lever has been shifted from the travel range by N Or P
The end of the four-wheel drive mode is determined based on, for example, operation to the range. The switching control means 104 determines that
When the end of the four-wheel drive mode is determined by the wheel drive mode end determination means 116, the switching mechanism 38 is set to the neutral state shown in FIG. 4, that is, the power transmission path from the engine 14 to the front wheels 22 is cut off, and the control clutch 36 This prevents power loss that occurs in two-wheel drive even when a drag exists.

FIG. 6 is a flowchart for explaining a main part of the control operation of the electronic control unit 12, and shows a sub-drive wheel assist control routine. In FIG. 6, in a step SA1 corresponding to the mode determining means 100 (hereinafter, the step is omitted), it is determined whether or not the four-wheel drive mode is set. If the determination in SA1 is affirmative, the process proceeds to S corresponding to the shift position determination means 102.
At A2, it is determined whether the transmission 28 is in the reverse gear. If the determination at SA2 is affirmative, S
In A3, the switching mechanism 62 is switched by the switching actuator 62.
8 is set to the reverse coupling state shown in FIG. 3, and the control clutch 36 is released. However, if the determination in SA2 is negative, the vehicle is in the forward traveling state, so in SA4, the switching mechanism 38 is brought into the forward coupling state shown in FIG. 2 by the switching actuator 62 and the control clutch 36 is released. In the present embodiment, SA3 and SA4 correspond to the switching control means 104.

Next, at SA5 corresponding to the slip judging means 106, it is judged whether or not the rear wheel 18, which is the main driving wheel, has slipped. If the determination in SA5 is denied, the vehicle can be started or accelerated without performing the four-wheel drive, so that the control clutch 36 is released by executing SA12 and below, which will be described later. However, if the determination in SA5 is affirmative, in SA6 corresponding to the engine rotational speed storage means 108, the rear wheels 18
The engine speed N _E1 at the time of occurrence of a slip is, for example, R
It is stored in a storage area provided in a part of the AM.

Then, at SA7 corresponding to the acceleration operation determination means 110, it is determined whether the vehicle is being accelerated. If the determination in SA7 is denied, it is not the start acceleration of the vehicle, so that the control clutch 36 is released by executing SA12 and below, which will be described later. However, the above S
If the determination in A7 is affirmative, in SA8 corresponding to the turning traveling determination means 112, it is determined whether the steering angle θ _ST is smaller than a predetermined determination reference value θ ₀ .

If the vehicle is running straight, the judgment at SA8 is affirmative, so that the control clutch control means 11
In SA9 corresponding to No. 4, the engine 1 when the actual engine rotational speed N _E
The transmission torque of the control clutch 36 is controlled so as to match the rotation speed N _{E1 of the} fourth wheel 4, that is, to supply an increase in the driving force for accelerating the vehicle to the front wheels 22. In SA11 corresponding to the four-wheel drive mode end determination means 116, the accelerator pedal is depressed and the required output of the engine 14 becomes zero, the brake pedal is operated, or the shift lever is operated. The end of the four-wheel drive mode is determined based on, for example, operation from the travel range to the N or P range. Initially the above SA
Since the determination at 11 is denied, the above SA5 and subsequent steps are repeatedly executed to control the transmission torque of the control clutch 36.

In this state, if the vehicle is turned from straight running to turning, the judgment at SA8 is negative, so that
In SA10 corresponding to the control clutch control means 114, the transmission torque of the control clutch 36 is reduced while turning is determined so that the tight corner braking phenomenon due to four-wheel drive does not occur.

While the above control is repeatedly executed, 4
If the wheel drive mode is canceled and the determination in SA11 is affirmative, the control clutch 36 is released in SA12, and then the above SA1 and subsequent steps are repeatedly executed. For this reason,
Since the determination of SA1 in the next control cycle is denied, in SA13 corresponding to the switching control means 104, the switching mechanism 38 is set to the power transmission path cutoff state, and the control clutch 36 is released.

As described above, according to the present embodiment, the driving force from one end (rear end) of the crankshaft 16 of the engine 14 is mechanically transmitted to the rear wheel 18 by the rear wheel driving force transmission device 20. Since the driving force from the other end (front end) of the crankshaft 16 is mechanically transmitted to the front wheels 22 by the front wheel driving force transmission device 24, the mechanical driving force output from the engine 14 is It is converted to hydraulic pressure using a pump,
Hydraulic oil is circulated from the hydraulic pump through a pipe or a hose and a hydraulic motor as compared with a four-wheel drive state in which hydraulic oil flowing out of the hydraulic pump is supplied to a hydraulic motor provided on a sub-drive wheel. As a result, the power loss due to the driving force is eliminated, and the disadvantage that the transmission loss of the driving force is increased and the fuel consumption rate is increased is eliminated. Further, since the driving force to the rear wheel 18 and the front wheel 22 is taken out from both ends of the crankshaft 16, respectively, the transfer and the propeller shaft from the transfer to the auxiliary drive wheel are not required, and the comfort in the vehicle interior is lowered and the vehicle There is no accompanying weight increase.

Further, according to the present embodiment, the crankshaft 16
And a control clutch 36 provided in series in a power transmission path from the front end to the front wheel 22 to selectively switch between a coupled state in which the power transmission path is coupled and a disconnected state in which the power transmission path is disconnected. Since the switching mechanism 38 interposed in the power transmission path is further provided, even if the control clutch 36 is dragged, the control clutch 36 is switched to the disconnected state by the switching mechanism 38, thereby causing the drag. Power loss during two-wheel drive traveling is prevented.

Further, according to the present embodiment, the front wheel 2 is inserted into the housing of the engine 14 from the front end of the crankshaft 16.
A power transmission path leading to a differential gear device 39 provided on the second axle 40 is provided. In this power transmission path, the control clutch 36 and the switching mechanism 38 are provided in series. Since the front wheel driving force transmission device 24 for transmitting the driving force from the section to the front wheel 22 is housed in the housing of the engine 14, a propeller shaft and a joint are not required, and the size is reduced. Impairment of livability and increase in vehicle weight are more suitably suppressed.

According to this embodiment, the crankshaft 16
In the power transmission path from the front end of the vehicle to the differential gear device 36 provided on the axle 40 of the front wheel 22, the switching mechanism 38
Includes a forward-reverse gear device 58 that can be switched between a state where power is transmitted without reversing the rotation direction and a state where power is transmitted while reversing the rotation direction.
2, the power transmission path for transmitting power without reversing the rotation direction is coupled to the first coupling state shown in FIG. 2, and the power transmission path for reversing the rotation direction and transmitting power by the forward / reverse gear unit 58 is coupled. Since the vehicle is selectively switched between the second coupled state in FIG. 3 and the disconnected state in FIG. 4 in which the power transmission path is interrupted, four-wheel drive traveling can be performed in each of forward traveling and reverse traveling of the vehicle. .

Further, according to the present embodiment, the rear wheel driving force transmission device 20 constantly transmits the driving force output from the engine 14 to the rear wheels via the stepped transmission 28. The force transmitting device 24 operates the front wheels 22 at the same speed ratio as that of the second or third gear of the stepped transmission 28.
Since the driving force is transmitted to the
Are directly driven, the same running performance, running stability, and traction as those of the direct-coupled four-wheel drive vehicle can be obtained at the second speed or the third speed.

According to the present embodiment, the four-wheel drive vehicle 10
The electronic control unit 12 determines whether or not the rear wheel 18, which is the main driving wheel, is slipped during the acceleration operation of the vehicle. The slip determination means 106 (SA5) and the slip determination means 106 generates the slip of the rear wheel 18. There when it is determined, the actual engine rotational speed N _E is controlled clutch control means for increasing the transmission (engagement) torque control clutch 36 so as to be substantially maintained in the engine rotational speed N _E1 at the time of slip occurrence 114 (SA9), when the driver operates the acceleration operation member for an acceleration operation such as when starting the vehicle, a slip occurs on the rear wheel 18 due to a low μ road or the like. when the actual driving force from the engine 14 to the front wheels 22 so that the engine rotational speed N _E is substantially maintained in the engine rotational speed N _E1 at the time of slip occurrence When the slip is generated, the increase in the engine output after the occurrence of the slip is exclusively supplied to the front wheels 22 and when the rear wheels 18 slip, the four-wheel drive state is automatically established. Is prevented, and the vehicle can be suitably started and accelerated.

Further, according to the present embodiment, the vehicle further comprises a turning traveling determining means 112 (SA8) for determining the turning traveling of the vehicle 10, and the turning traveling determining means 112
Is determined, the control clutch control means 114 (SA10) operates the transmission torque of the control clutch 36 to the release side more than before. In this way, the control clutch 36 for four-wheel drive traveling can be used.
When the vehicle is turning while the vehicle is engaged, the engagement torque of the control clutch 36 is suppressed, so that the occurrence of the tight corner braking phenomenon during four-wheel drive traveling is automatically prevented.

According to this embodiment, the transmission 28
Is an automatic transmission, the electronic control unit 12 includes a mode determination unit 100 (SA1) that selects a low μ road start mode for starting the vehicle on a road surface having a low road surface friction coefficient such as a snow-covered road or a frozen road; When the low-μ road starting mode is selected by the mode determining means 100, a shift control means for switching the automatic transmission to a second speed or a third speed when the vehicle starts, and the mode determining means When the low-μ road starting mode is selected by 100 and the second speed or the third speed of the automatic transmission is selected by the shift control means, the control clutch 36 is driven to drive the front wheels 22. Control clutch control means 1 to be engaged
14 (SA9), when the vehicle is started on a road surface having a low coefficient of road surface friction, the automatic transmission is automatically set to the second or third gear and the rear wheels are driven. At the same time, the control clutch 36 is engaged and the front wheels are also driven at the same speed ratio as the second or third gear, so that the vehicle can be more easily started on a low μ road.

Next, another embodiment of the present invention will be described. In the following embodiments, the same reference numerals are given to portions common to the above description, and the description will be omitted.

FIGS. 7 and 8 show the construction of another embodiment of the switching mechanism 38. FIG. 7 shows a forward coupling state, and FIG. 8 shows a power transmission for transmitting a driving force to the front wheels 22. It shows a blocking state in which a route is blocked. The switching mechanism 38 of the present embodiment is different from the switching mechanism 38 shown in FIGS. 1 to 4 in that the second output gear 54 and the forward / reverse gear 58 are eliminated. According to this embodiment, the same effects as those of the above-described embodiment can be obtained during forward running.

FIG. 9 is a diagram showing the configuration of another embodiment of the four-wheel drive vehicle 10. As shown in FIG. In the four-wheel drive vehicle 10 of the present embodiment, the switching mechanism 38 is removed in the power transmission path from the front end of the crankshaft 16 to the front wheels 22 as compared with the embodiment shown in FIGS. Are different. Also in this embodiment, the same effects as those of the above-described embodiment can be obtained except for those derived from the switching mechanism 38.

Although the embodiment of the present invention has been described with reference to the drawings, the present invention can be applied to other embodiments.

For example, in the above embodiment, the front wheel 2
The differential gear device 39 provided on the second axle 40 may be provided with a differential limiting device. In such a case, there is an advantage that the startability of the four-wheel drive vehicle 10 can be enhanced even when there is a difference between the rotational speeds of the left and right front wheels 22.

The above-described front wheel driving force transmission device 24
Although the transmission 28 is set to the same gear ratio as that of the rear wheel driving force transmission device 20 when the transmission 28 is in the second or third gear, the transmission 28 is in the first gear. For example, the gear ratio may be set to be the same as the gear ratio of the rear wheel driving force transmission device 20 at the time of a low gear.

The four-wheel drive vehicle 10 of the above embodiment is
Although the FR-based 4WD is of a type that constantly drives the rear wheel 18 and appropriately assists with the front wheel 22, the F-type of the type that constantly drives the front wheel 22 and appropriately assists with the rear wheel 18 is used.
An F-based 4WD may be used.

In the above-described embodiment, the front wheel driving force transmission device 24 is housed in the housing of the engine 10. However, as in the transaxle housing,
It may be in a housing integrally connected to the engine 10.

Although the transmission 28 in the above-described embodiment is a stepped manual transmission or an automatic transmission, it may be a continuously variable transmission such as a CVT.

The shift position determining means 102 in the above-described embodiment determines forward or reverse based on the actual gear position of the transmission 28. However, when the shift lever is in the R (reverse) range or the D (drive) ) Forward or backward may be determined based on the operation to the range.

The above is merely an example of the present invention, and the present invention can be variously modified without departing from the gist thereof.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a power transmission device for a four-wheel drive vehicle according to an embodiment of the present invention.

FIG. 2 is a view for explaining a configuration of a switching mechanism provided in the front wheel driving force transmission device of FIG. 1, and is a view showing a forward coupling state.

FIG. 3 is a diagram for explaining a configuration of a switching mechanism provided in the front wheel driving force transmission device of FIG. 1, and is a diagram showing a reverse coupling state.

FIG. 4 is a diagram illustrating a configuration of a switching mechanism provided in the front wheel driving force transmission device of FIG. 1, and is a diagram illustrating a power transmission path interrupted state.

FIG. 5 is a functional block diagram illustrating a main part of a control function of the electronic control device of FIG. 1;

6 is a flowchart illustrating a main part of a control operation of the electronic control device of FIG. 1 and is a diagram illustrating a sub-drive wheel assist routine.

FIG. 7 is a diagram for explaining a configuration of a switching mechanism in another embodiment of the present invention, and is a diagram corresponding to FIG. 2 showing a forward coupling state.

8 is a diagram for explaining the configuration of the switching mechanism in the embodiment of FIG. 7, and is a diagram corresponding to FIG. 4 showing a power transmission path cut-off state.

FIG. 9 is a diagram showing a configuration of a four-wheel drive vehicle according to another embodiment of the present invention, and is a diagram corresponding to FIG.

[Explanation of symbols]

 10: four-wheel drive vehicle 14: engine 16: crankshaft (output shaft) 20: rear wheel drive force transmission device 24: front wheel drive force transmission device 36: control clutch 38: switching mechanism

Claims (2)

[Claims] 1. A four-wheel drive vehicle capable of transmitting a driving force output from an engine to a front wheel and a rear wheel, wherein the driving force is mechanically transmitted from one end of an output shaft of the engine to the rear wheel. A rear wheel driving force transmitting device for transmitting, and a front wheel driving force transmitting device for mechanically transmitting a driving force from the other end of the output shaft of the engine to the front wheel. Four-wheel drive vehicle. A control clutch provided in series in a power transmission path from the other end of the output shaft to the front wheel; a coupled state for coupling the power transmission path; and a disconnected state for disconnecting the power transmission path. 2. A four-wheel drive vehicle according to claim 1, further comprising: a switching mechanism interposed in said power transmission path for selectively switching the vehicle.