JP7639647B2 - Four-wheel drive vehicles - Google Patents

Description

The present invention relates to a four-wheel drive vehicle.

Conventionally, there is known a front/rear wheel drive force distribution control device that controls the drive force between the front and rear wheels of a four-wheel drive vehicle (see, for example, Patent Document 1). In Patent Document 1, for example, in a gear change period in which the drive force is intermittent, if the main drive wheels slip significantly, the drive force that should be applied to the main drive wheels is also distributed to the secondary drive wheels, thereby suppressing the occurrence of energy loss related to slip loss.

Japanese Patent Application Publication No. 7-186758

However, in a four-wheel drive vehicle that can control the distribution of drive force between the main drive shaft and the slave drive shaft (between the front and rear wheels), the vibration intensity of the drive system increases during a gear change period that involves the intermittent supply of drive force, and this increase in vibration intensity can cause discomfort to the vehicle occupants as a gear change shock. Patent Document 1 does not take any measures against this phenomenon of increased vibration intensity during gear changes.

The invention disclosed in this specification aims to suppress the increase in vibration intensity during a gear change period that involves interruption of the driving force in a four-wheel drive vehicle that can control the distribution of driving force between the main drive shaft and the slave drive shaft.

The four-wheel drive vehicle disclosed in this specification includes a driving force source, a transmission that can change the gear used to transmit the driving force while interrupting the driving force output from the driving force source, and outputs the driving force to a driving force transmission shaft, a driving force distribution device that distributes the driving force output to the driving force transmission shaft to a main drive shaft that drives a main drive wheel and a slave drive shaft that drives a slave drive wheel according to a distribution ratio, and a driving force distribution control unit that controls the distribution ratio of the driving force between the main drive shaft and the slave drive shaft in the driving force distribution device, and the driving force distribution control unit controls the distribution ratio so that the driving force distributed to the slave drive shaft during a gear change period in the transmission is smaller than the driving force distributed to the main drive shaft.

In a four-wheel drive vehicle having the above configuration, the driving force distribution control unit can be configured to reduce the driving force distributed to the slave drive shaft during the shift period in accordance with the driving force output to the driving force transmission shaft determined by the driving force output from the driving force source and the gear ratio of the gears provided in the transmission.

The four-wheel drive vehicle disclosed in this specification is capable of controlling the distribution of driving force between the main drive shaft and the slave drive shaft, and is therefore capable of suppressing an increase in vibration intensity during a gear change period that involves interruption of the driving force.

FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle according to a first embodiment. FIG. 2 is a flowchart showing an example of driving force distribution control during a gear shift in the vehicle of the first embodiment. FIG. 3 is an example of a time chart showing changes in various values during a shift period in the vehicle of the first embodiment. FIG. 4 is a graph showing changes in torque of the main drive shaft and the slave drive shaft during a gear shift in the vehicle of the first embodiment. FIG. 5 is an example of a time chart showing changes in various values during a shift period in a vehicle of a comparative example. FIG. 6 is a graph showing changes in torque of the main drive shaft and the slave drive shaft during a gear shift in a comparative vehicle. FIG. 7 is a graph showing vibration strength during a gear shift in the comparative example and vibration strength during a gear shift in the first embodiment.

Embodiments of the present invention will be described below with reference to the attached drawings. However, the dimensions and ratios of each part in the drawings may not be illustrated to be exactly the same as the actual ones. Also, some details may be omitted in the drawings.

First Embodiment
<Four-wheel drive vehicle>
First, a schematic configuration of a four-wheel drive vehicle (hereinafter simply referred to as "vehicle") 1 according to a first embodiment will be described with reference to Fig. 1. The vehicle 1 employs a four-wheel drive system based on a front engine, front drive system (FF drive system).

The vehicle 1 includes an engine 10, a transmission 11, a transaxle 13 including a front differential device (hereinafter simply referred to as "front diff") 12, and a transfer device 14. The vehicle 1 further includes left and right main drive wheels 15L, 15R, left and right main drive shafts 16L, 16R, a propeller shaft 17, an electronically controlled coupling 18, and a rear differential device (hereinafter simply referred to as "rear diff") 19. The vehicle 1 further includes left and right slave drive wheels 20L, 20R, left and right slave drive shafts 21L, 21R, and an ECU (Electronic Control Unit) 23.

The engine 10 corresponds to a driving force source. The engine 10 in this embodiment is an in-line 4-cylinder engine that uses gasoline as fuel, but the number of cylinders and the cylinder arrangement method are not limited to this. For example, the number of cylinders can be appropriately selected from 3 cylinders, 6 cylinders, 8 cylinders, etc. In addition, the cylinder arrangement method can be appropriately selected from conventionally known cylinder arrangement methods such as V-type. In addition, instead of gasoline, fuels such as hydrocarbon fuels such as diesel, alcohol fuels that are a mixture of alcohol such as ethanol and gasoline, and other fuels that have traditionally been used as fuel for internal combustion engines can be appropriately selected. Furthermore, instead of the internal combustion engine alone, a motor generator may be combined with the internal combustion engine to serve as a driving force source. The driving force (torque) of the engine 10 is output and taken out via the crankshaft 10a. Note that the vehicle is not limited to one that uses the engine 10 as a driving force source. It can also be applied to so-called hybrid vehicles (HEVs: Hybrid Electric Vehicles), plug-in hybrid vehicles (PHEVs: Plug-in Hybrid Electric Vehicles), fuel cell electric vehicles (FCEVs: Fuel Cell Electric Vehicles), and even electric vehicles (BEVs: Battery Electric Vehicles). In short, it can be applied to any vehicle that can be equipped with a driving force source that can be used in combination with the transmission 11, which will be described in detail later.

The transmission 11 is provided between the engine 10 and the front differential 12. The transmission 11 includes a torque converter 30, a gear unit 31 with multiple forward gears and a reverse gear, and an output shaft 32. The transmission 11 converts the rotation of the crankshaft 10a input via the torque converter 30 into a rotation speed and torque according to the gear ratio of the selected gear, and outputs it to the output shaft 32. The output shaft 32 corresponds to a drive force transmission shaft.

The transmission 11 in this embodiment is an automatic transmission whose shifting operation is controlled by a shift control unit 23a, which will be described later. The transmission 11 in this embodiment changes the gear combination built into the gear unit 31 using a planetary gear type shifting mechanism, but it may also be a transmission equipped with a clutch operated by an actuator. Any transmission having a shifting mechanism that exhibits a transition period during which the state in which the gear stage before the shift is engaged and the state in which the gear stage after the shift is engaged gradually switch during the shifting period can be applied to the vehicle 1 in this embodiment.

An output gear 33 is attached to one end of the output shaft 32 so that it can rotate integrally with the output shaft 32, and the rotation of the output shaft 32 is transmitted to the front differential 12 via the output gear 33.

The front differential 12 includes a differential case 40. The differential case 40 is rotatably supported on the housing 13a of the transaxle 13 via bearings (not shown). A ring gear 41 that meshes with the output gear 33 is provided on the outer periphery of the differential case 40, and a pair of differential pinion gears 42 arranged opposite each other are provided inside the differential case 40.

The pair of differential pinion gears 42 are capable of revolving together with the differential case 40 and are rotatable relative to the differential case 40. A pair of side gears 43 arranged opposite each other mesh with the pair of differential pinion gears 42. The pair of side gears 43 are connected to the main drive wheels 15L and 15R via the main drive shafts 16L and 16R, respectively. The front differential 12 distributes and transmits a portion of the driving force output from the engine 10 via the transmission 11 to the main drive wheels 15L and 15R. The front differential 12 allows a difference in rotational speed between the main drive wheels 15L and 15R. The main drive wheels 15L and 15R are steered wheels.

The transfer device 14 is positioned in the direction in which the rotation shaft of the front differential 12 extends. The direction in which the rotation shaft of the front differential 12 extends is the same as the direction in which the rotation shafts of the differential case 40 and the main drive shafts 16L and 16R extend.

The end of the differential case 40 is provided with a cylindrical boss 40a that protrudes into the transfer device 14. The transfer device 14 is equipped with a bevel gear 50 provided at the end of the boss 40a and an output pinion 51 that meshes with the bevel gear 50.

The propeller shaft 17 is provided between the transfer device 14 and the electronically controlled coupling 18. An output pinion 51 included in the transfer device 14 is provided at the end of the propeller shaft 17 on the transfer device 14 side. The front end of the electronically controlled coupling 18 is connected to the propeller shaft 17, and the rear end is connected to the rear differential 19.

The electronically controlled coupling 18 corresponds to a driving force distribution device. The electronically controlled coupling 18 is operated by a control signal output from a driving force distribution control unit 23b, which will be described later. The electronically controlled coupling 18 distributes the driving force output to the output shaft 32 extending from the transmission 11 to the main driving shafts 16L, 16R that drive the main driving wheels 15L, 15R and the slave driving shafts 21L, 21R that drive the slave driving wheels 20L, 20R.

The rear differential 19 has a differential case 60. The rear differential 19 has a ring gear 61 on the outer periphery of the differential case 60 that meshes with the drive pinion gear 18a of the electronically controlled coupling 18. Inside the differential case 60, a pair of differential pinion gears 62 are provided, arranged opposite each other.

The pair of differential pinion gears 62 are capable of revolving together with the differential case 60 and are rotatable relative to the differential case 60. The pair of differential pinion gears 62 are meshed with a pair of side gears 63 arranged opposite each other. The pair of side gears 63 are connected to the driven wheels 20L and 20R via the driven shafts 21L and 21R, respectively. The rear differential 19 distributes and transmits the driving force transmitted via the electronically controlled coupling 18 to the driven wheels 20L and 20R. The rear differential 19 allows for a difference in rotational speed between the driven wheels 20L and 20R.

The ECU 23 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), backup RAM, and other storage devices. The ECU 23 executes calculations and various controls based on programs and maps stored in the CPU, ROM, and other storage devices. The RAM is a memory that temporarily stores the results of calculations performed by the CPU and data input from various sensors, and the backup RAM is a non-volatile memory that stores data that should be saved when the engine 10 is stopped, etc.

The ECU 23 functions as a shift control unit 23a and a driving force distribution control unit 23b by performing calculations based on programs and maps stored inside. An accelerator opening sensor 71, a vehicle speed sensor 72, and an engine speed sensor 73 are electrically connected to the ECU 23, and the shift control unit 23a controls the shifting of the transmission 11 based on values acquired from these sensors. The accelerator opening sensor 71 detects the amount of accelerator depression, and the vehicle speed sensor 72 detects the vehicle speed. The engine speed sensor 73 detects the engine speed. The driving force distribution control unit 23b controls the driving force distributed to the slave drive shafts 21L, 21R by the electronically controlled coupling 18 based on the state of the engine 10 and the transmission 11 during the shifting period when the shift control unit 23a is causing the transmission 11 to perform a shifting operation.

The ECU 23 executes various controls related to the operation of the engine 10, such as controlling the opening of a throttle valve (not shown) that adjusts the amount of intake air to the engine 10, and controlling the opening and closing of intake and exhaust valves (neither shown). For this reason, the ECU 23 is connected to sensors for performing various controls other than those for the transmission 11 and electronically controlled coupling 18, and various programs and maps are stored therein, but a description of these will be omitted here.

The above is a schematic configuration of the vehicle 1 of this embodiment. As described above, the vehicle 1 of this embodiment employs a four-wheel drive system based on the FF drive system, but may employ a four-wheel drive system based on other drive systems such as a front engine, rear drive system (FR drive system). When the vehicle employs a four-wheel drive system based on the FR drive system, the axles and wheels located at the front of the vehicle are the slave drive axles and slave drive wheels, respectively, and the wheels and axles located at the rear of the vehicle are the main drive axles and main drive wheels, respectively.

<Drive force distribution control during gear shift>
Next, the driving force distribution control between the main drive shafts 16L, 16R and the slave drive shafts 21L, 21R during a gear shift in this embodiment will be described with reference to Figures 2 to 7. In the following description, the control in this embodiment will be described first with reference to Figures 2 to 4, and then the driving force distribution control in a comparative example will be described with reference to Figures 5 and 6. Then, the effect of this embodiment will be described in comparison with the comparative example with reference to Figure 7.

First, in step S1, the gear shift control unit 23a determines whether or not there is a gear shift request based on the running state of the vehicle 1, more specifically, whether or not there is a request to shift up from a lower gear to a higher gear. The gear shift control unit 23a performs gear shift control of the transmission 11 based on values acquired from the vehicle speed sensor 72 and the engine speed sensor 73.

Now, with reference to Figure 3, various numerical values related to the drive force distribution control of the vehicle 1 during the gear shift period will be explained. Note that the basic control policy is the same in all cases, such as when shifting up from 1st gear to 2nd gear, when shifting up from 2nd gear to 3rd gear, and when shifting up from 3rd gear to 4th gear, so here, the case of shifting up from 1st gear to 2nd gear will be explained.

Referring to FIG. 3, the shift period is from time t1 to time t4, and the change from first gear to second gear begins at time t1. Time t1 is the timing at which the shift program provided in the shift control unit 23a determines whether the requested gear has changed from first gear to second gear based on a map with accelerator depression amount, vehicle speed, and engine speed as parameters. If the shift control unit 23a determines that the requested gear has changed from first gear to second gear, it proceeds to step S2 (FIG. 2).

The release oil pressure shown in FIG. 3 indicates the change in oil pressure for engaging the gear selected before the shift. When the shift is performed, the release oil pressure is lowered to gradually release the engagement state of the gear selected before the shift, i.e., the first gear. On the other hand, the engagement oil pressure indicates the change in oil pressure for engaging the gear selected after the shift. When the shift is performed, the engagement oil pressure is increased to gradually engage the gear selected after the shift, i.e., the second gear. These oil pressures are controlled by the shift control unit 23a, which controls the hydraulic control unit (not shown). The second gear starts to engage from time t3, and the engagement of the second gear is completed at time t4. The engagement transition flag in FIG. 3 indicates whether the second gear starts to engage, and is set to the ON state at time t3.

The engine speed shown in FIG. 3 indicates the rotation speed of the engine 10, and the torque converter turbine rotation speed indicates the rotation speed of the turbine provided in the torque converter 30 (see FIG. 1). The engine speed and the torque converter turbine rotation speed decrease slightly before time t3. This is because the gear shift control unit 23a slightly decreases the engine speed in preparation for engaging the second gear. The engine torque shown in FIG. 3 indicates the driving force of the crankshaft 10a. As the gear shift control unit 23a reduces the engine speed, the engine torque decreases momentarily after time t3.

The gear ratio shown in FIG. 3 shows that the release oil pressure starts to decrease after time t1 and the engagement oil pressure starts to increase, so that the gear ratio gradually transitions from the first gear ratio to the second gear ratio from approximately time t2. The gear ratio of vehicle 1 is the first gear ratio at time t1, and completely switches to the second gear ratio at time t4.

The total torque shown in FIG. 3 is a value determined by the engine torque and the gear ratio, and is the driving force output to the output shaft 32 (see FIG. 1). This total torque is distributed to the main drive shafts 16L, 16R and the slave drive shafts 21L, 21R by the electronically controlled coupling 18. The total torque is affected by the engine torque and the gear ratio, so it changes and decreases during the shift period.

3 indicates the ratio of the total torque distributed to the main drive shafts 16L, 16R and the slave drive shafts 21L, 21R by the electronically controlled coupling 18. In this embodiment, the main-slave torque distribution ratio is changed in accordance with the drop in the total torque. Specifically, the ratio distributed to the slave drive shaft is reduced, thereby reducing the slave drive shaft torque command value. If the main-slave torque distribution ratio is constant, the slave drive shaft torque command value shows a change similar to the curve showing the change in total torque as shown by the dotted line in FIG. 3. The slave drive shaft torque command value of this embodiment is set to be lower than the value shown by the curve similar to the curve showing the change in total torque as shown by the dashed line in FIG. 3. At this time, it is desirable to set the lower limit value of the slave drive shaft torque command value within a range that can avoid slipping of the vehicle 1. Note that the main-slave torque distribution ratio before entering the shift period is controlled by the running state of the vehicle 1 before time t1, but detailed description thereof will be omitted here.

The wheel speeds shown in Figure 3 indicate the rotational speeds of the front and rear wheels of vehicle 1. In Figure 3, 4WD vehicle front wheels are shown as the average speed of the primary drive wheels 15L, 15R, and 4WD vehicle rear wheels are shown as the average speed of the secondary drive wheels 20L, 20R. Figure 3 also shows the wheel speeds of the front and rear wheels of a FF vehicle under the same conditions in order to evaluate changes in vehicle behavior during gear changes in vehicle 1, which is a four-wheel drive vehicle.

In an FF vehicle, the wheel speed of the front wheels is slightly faster than that of the rear wheels, and this relationship is maintained throughout the shifting period. On the other hand, in the vehicle 1 of this embodiment, as in an FF vehicle, the main drive wheels 15L, 15R are slightly faster than the secondary drive wheels 20L, 20R, and this relationship is maintained throughout the shifting period. Here, the wheel speeds of the front and rear wheels are shown because it is believed that the relationship between the wheel speeds of the front and rear wheels affects the vibration intensity G. If a state occurs in which the wheel speeds of the front and rear wheels are reversed, it is believed that the vibration intensity G will increase accordingly. This point will be explained later while showing a comparative example.

Figure 3 shows the vibration intensity G in vehicle 1 (a 4WD vehicle) and the vibration intensity G in an FF vehicle. At the timing X1 shown in Figure 3, the amplitude of the vibration intensity G fluctuates in both vehicles, but there is no significant difference in the amount of amplitude between the two.

Now, we return to the explanation based on the flowchart shown in FIG. 2. If the gear shift control unit 23a makes a positive determination (Yes determination) in step S1, the process proceeds to step S2. On the other hand, if the gear shift control unit 23a makes a negative determination (No determination) in step S1, the process of step S1 is repeated.

In step S2, the driving force distribution control unit 23b acquires the slave drive shaft torque command value shown in FIG. 3. The driving force distribution control unit 23b then proceeds to step S3. In step S3, the driving force distribution control unit 23b operates the electronically controlled coupling 18 so that the driving force distributed to the slave drive shafts 21L, 21R becomes the slave drive shaft torque command value acquired in step S2. The slave drive shaft torque command value is determined in advance by a simulation-based adaptation operation and is stored as a map in the driving force distribution control unit 23b, and the driving force distribution control unit 23b reads out this map to control the electronically controlled coupling 18. This completes the control for one upshift, and the process returns. The ECU 23 performs this type of control each time an upshift is performed.

Figure 4 shows the torque transition of the main drive shafts 16L, 16R and the slave drive shafts 21L, 21R during the shifting period in this embodiment. Although both of them drop slightly at first, they do not reverse. If a reverse phenomenon occurs between the two, it is thought that this will cause an increase in vibration intensity G, but in this embodiment, such a reverse phenomenon does not occur and the increase in vibration intensity G is also suppressed.

Here, the phenomenon of torque reversal between the main drive shafts 16L, 16R and the slave drive shafts 21L, 21R will be explained together with the details of the driving force distribution control in the comparative example vehicle 1'. The hardware configuration of the comparative example vehicle 1' is common to the hardware configuration of the vehicle 1 of the first embodiment, but the ECU 23' of the vehicle 1' executes a program different from the program executed by the ECU 23 provided in the vehicle 1 of the first embodiment.

Referring to FIG. 5, the gear ratio in vehicle 1' is constant from time t1 to time t4 as shown by the solid line. In other words, although the actual gear ratio gradually transitions from the gear ratio of 1st gear to the gear ratio of 2nd gear during the shifting period as shown by the dotted line, in the comparative example, this point is not taken into consideration and the gear ratio is switched for the first time at time t4. In addition, in the comparative example, the total torque is also changed at time t4 when the shifting is completed. In other words, in the comparative example, the total torque is estimated without considering the change in engine torque or the change in gear ratio during the shifting period. Furthermore, in the comparative example, the master/slave torque distribution ratio does not change during the shifting period and is set to a constant value.

As a result, the main drive shaft torque command value in the comparative example is constant during the gear shift period, as shown by the solid line, unlike the main drive shaft torque command value in the first embodiment shown by the dashed line in Figure 5. In this way, if the main drive shaft torque command value is left constant, the front and rear wheel speeds are reversed at timing X2 shown in Figure 5, resulting in increased vibration intensity G. As in Figure 3, Figure 5 also shows the wheel speeds and vibration intensity G for the FF vehicle, but the vibration intensity G in the comparative example has a larger amplitude than the vibration intensity G for the FF vehicle.

Figure 6 shows the torque transitions of the main drive shafts 16L, 16R and the slave drive shafts 21L, 21R during the shift period in the comparative example. In both comparative examples, the torque on the rear wheel side momentarily exceeds the torque on the front wheel side, and this phenomenon is thought to lead to the reversal of the front and rear wheel speeds at timing X2 in Figure 5. It is thought that such a reversal of the front and rear wheel speeds increases the amplitude of the vibration intensity G.

As shown in FIG. 6, the torque of the slave drive shafts 21L and 21R exceeds that of the main drive shafts 16L and 16R because the slave drive shaft torque command value is calculated while ignoring the changes in engine torque and gear ratio that actually occur during the shift period.

In this embodiment, the driving force distributed to the slave drive shafts 21L, 21R during the shifting period in the transmission 11 is controlled to be smaller than the driving force distributed to the main drive shafts 16L, 16R.

As a result, as shown in FIG. 7, the maximum amplitude Acom of the vibration intensity G during the shift period can be made smaller than the maximum amplitude Aemb of the vibration intensity G during the shift period in the comparative example. This prevents the occupants of the vehicle 1 from feeling any unpleasant shift shock during the shift period.

In the vehicle 1 of this embodiment, the driving force distribution control unit 23b distributes the driving force distributed to the slave drive shafts 21L, 21R during the shifting period in the transmission 11 so that it is smaller than the driving force distributed to the main drive shafts 16L, 16R. This makes it possible to suppress an increase in vibration intensity G during the shifting period.

In addition, at this time, the driving force distributed to the slave drive shafts 21L, 21R during the shift period is reduced according to the driving force (total torque) transmitted to the output shaft 32. Therefore, the driving force distributed to the slave drive shafts 21L, 21R can be appropriately controlled according to the torque actually exerted by the output shaft 32. As a result, the increase in vibration intensity G can be more effectively suppressed.

In addition, by lowering the distribution ratio allocated to the slave drive shafts, the driving force allocated to the slave drive shafts 21L, 21R can be reduced with a margin relative to the driving force allocated to the main drive shafts 16L, 16R.

The above embodiments are merely examples for implementing the present invention, and the present invention is not limited to these. Various modifications of these embodiments are within the scope of the present invention. Furthermore, it is self-evident from the above description that various other embodiments are possible within the scope of the present invention.

REFERENCE SIGNS LIST 1 vehicle 10 engine 10a crankshaft 11 transmission 12 front differential device 13 transaxle 13a housing 14 transfer device 15L, 15R main drive wheels 16R, 16L main drive shaft 17 propeller shaft 18 electronically controlled coupling 19 rear differential device 20L, 20R driven wheels 21L, 21R driven shaft 23a gear shift control unit 23b driving force distribution control unit 30 torque converter 31 gear unit 32 output shaft 33 output gear 40 differential case 42 differential pinion gear 43 side gear

Claims (1)

A driving force source;
a transmission that is capable of changing a gear used for transmitting the driving force while interrupting the driving force output from the driving force source, and outputs the driving force to a driving force transmission shaft;
a driving force distribution device that distributes a total torque of the driving force output to the driving force transmission shaft via the transmission to a main drive shaft that drives a main drive wheel and a slave drive shaft that drives a slave drive wheel in accordance with a main-slave torque distribution ratio ;
a driving force distribution control unit that controls the main/sub torque distribution ratio ,
The driving force distribution control unit sets the master /slave torque distribution ratio during the shift period so that the driving force distributed to the slave drive shaft is smaller than the driving force distributed to the main drive shaft compared to the master/slave torque distribution ratio at the start of the shift by the transmission, and obtains the total torque using engine torque and a gear ratio value that gradually changes from the gear ratio of the gear stage before the shift to the gear ratio of the gear stage after the shift, and operates the driving force distribution device so that the total torque becomes a slave drive shaft torque command value obtained using the master/slave torque distribution ratio.
Four-wheel drive vehicle.

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