JP6776822B2 - Control device for driving force transmission device - Google Patents

Description

The present invention relates to a control device for a driving force transmitting device that transmits driving force to auxiliary driving wheels of a four-wheel drive vehicle.

Conventionally, the main drive wheels that constantly transmit the driving force of the drive source, the auxiliary drive wheels that transmit the drive force of the drive source according to the driving conditions, and the drive that can adjust the drive force transmitted to the auxiliary drive wheels. A four-wheel drive vehicle including a force transmission device and a control device for controlling the driving force transmission device is known (see, for example, Patent Document 1).

The control device (ECU as a load drive device) described in Patent Document 1 PWM-controls the drive current supplied to the drive force transmission device as a load by switching the FET. Further, in order to suppress the loss during switching of the FET and suppress the heat generation due to the loss, this control device increases the gate current flowing through the gate of the FET during the switching operation as the rotation speed of the engine as a drive source increases. It is configured to be.

In the first embodiment of Patent Document 1, the increase / decrease of the gate current is realized by a control current change circuit having a multiplexer having a multiplexer that selectively connects any of a plurality of resistors between the power supply for the control signal and the gate of the FET. Has been done. Further, in the second embodiment of Patent Document 1, the increase / decrease in the gate current is realized by the D / A converter.

Japanese Unexamined Patent Publication No. 2004-235939

In the control device described in Patent Document 1, the above-mentioned control current changing circuit and D / A converter are required to increase or decrease the gate current, which increases the cost. Further, if the gate current is increased, noise may affect equipment such as a radio (see paragraph [0026] of Patent Document 1).

Therefore, an object of the present invention is to provide a control device for a driving force transmission device capable of suppressing heat generation of a switching element without increasing the current for operating the switching element.

In order to achieve the above object, the present invention uses a drive source that generates a driving force according to the operation amount of the accelerator pedal, a main drive wheel that constantly transmits the driving force of the drive source, and a supplied current. It is mounted on a four-wheel drive vehicle provided with an auxiliary drive wheel in which the drive force of the drive source is transmitted via a drive force transmission device that transmits the corresponding drive force, and supplies the current to the drive force transmission device. A control device for a driving force transmission device that has a switching element and switches a DC voltage based on a PWM signal in which an on state or an off state of the switching element is determined for each PWM cycle to generate the current. The PWM signal generation unit has a switching power supply unit for generating the PWM signal, and the PWM signal generation unit reduces the operation amount of the accelerator pedal when the deceleration is smaller than a predetermined value. Provided is a control device for a driving force transmission device that prolongs the PWM cycle as compared with the case where the predetermined value is larger than the predetermined value.

According to the control device of the driving force transmission device according to the present invention, it is possible to suppress heat generation of the switching element without increasing the current for operating the switching element.

It is a schematic block diagram which shows the schematic block block example of the four-wheel drive vehicle equipped with the control device of the driving force transmission device which concerns on embodiment of this invention. It is sectional drawing which shows the structural example of the driving force transmission device. It is the schematic which shows the schematic functional configuration example of the control device. It is a graph which shows an example of the temporal change of the drain-source voltage and drain current at the time of switching to the on / off state of FET. It is a graph which shows an example of the temporal change of the gate-source voltage and drain current of FET when the PWM cycle is short. It is a graph which shows an example of the temporal change of the gate-source voltage and drain current of FET when the PWM cycle is long. It is a flowchart which shows an example of the process which CPU of a control device executes as a PWM signal generation part.

[Embodiment]
Embodiments of the present invention will be described with reference to FIGS. 1 to 7. It should be noted that the embodiments described below are shown as suitable specific examples for carrying out the present invention, and there are some parts that specifically exemplify various technically preferable technical matters. , The technical scope of the present invention is not limited to this specific aspect.

FIG. 1 is a schematic configuration diagram showing a schematic configuration example of a four-wheel drive vehicle equipped with a control device for a driving force transmission device according to an embodiment of the present invention.

As shown in FIG. 1, the four-wheel drive vehicle 1 has an engine 11 as a drive source that generates a driving force (torque) for traveling according to an operation amount (depression amount) of the accelerator pedal 110, and an output of the engine 11. The transmission 12 that shifts the speed, the left and right front wheels 181, 182 as the main drive wheels that constantly transmit the driving force of the engine 11 that has been changed by the transmission 12, and the drive of the engine 11 according to the running state of the four-wheel drive vehicle 1. It is equipped with left and right rear wheels 191 and 192 as auxiliary drive wheels to which force is transmitted. The four-wheel drive vehicle 1 has a four-wheel drive state in which the driving force of the engine 11 is transmitted to the left and right front wheels 181, 182 and the left and right rear wheels 191, 192, and a two-wheel drive state in which the driving force is transmitted only to the left and right front wheels 181, 182. And can be switched.

Further, the four-wheel drive vehicle 1 includes a front differential 13, a propeller shaft 14, a rear differential 15, left and right front wheel side drive shafts 161, 162, and left and right rear wheel side drive shafts 171 and 172. A driving force transmission device 2 arranged between the propeller shaft 14 and the rear differential 15 and a control device 7 for controlling the driving force transmission device 2 are mounted.

The driving force transmission device 2 transmits a driving force corresponding to the current supplied from the control device 7 from the propeller shaft 14 side to the rear differential 15 side. The control device 7 controls the driving force transmission device 2 by supplying an electric current to the driving force transmission device 2. Hereinafter, the current output by the control device 7 to control the driving force transmission device 2 is referred to as a control current.

The drive source of the four-wheel drive vehicle 1 is not limited to an engine that is an internal combustion engine, and a high-power motor such as an IPM (Interior Permanent Magnet) motor may be used. Further, the drive source of the four-wheel drive vehicle 1 may be configured by combining the engine and the high output motor.

The driving force of the engine 11 is transmitted to the left and right front wheels 181, 182 via the transmission 12, the front differential 13, and the drive shafts 161 and 162 on the left and right front wheels. The front differential 13 is a pair of side gears 131 and 131 connected to the drive shafts 161 and 162 on the left and right front wheels so as not to rotate relative to each other, and a pair of pinion gears that mesh with the pair of side gears 131 and 131 with their gear axes orthogonal to each other. It has 132, 132, a pinion gear shaft 133 that supports a pair of pinion gears 132, 132, and a front differential case 134 that accommodates them.

A ring gear 135 is fixed to the front differential case 134, and the ring gear 135 meshes with a pinion gear 141 provided at an end portion of the propeller shaft 14 on the front side of the vehicle. The rear end of the propeller shaft 14 on the vehicle rear side is connected to the housing 20 of the driving force transmission device 2. The driving force transmission device 2 has an inner shaft 23 that is rotatably arranged relative to the housing 20, so that the driving force corresponding to the control current supplied from the control device 7 cannot rotate relative to the inner shaft 23. It is transmitted to the rear differential 15 via the connected pinion gear shaft 150. The details of the driving force transmission device 2 will be described later.

The rear differential 15 is a pair of side gears 151 and 151 connected to the drive shafts 171 and 172 on the left and right rear wheel sides so as not to rotate relative to each other, and a pair of side gears 151 and 151 that mesh with each other with their gear axes orthogonal to each other. It has a pinion gear 152, 152, a pinion gear shaft 153 that supports a pair of pinion gears 152, 152, a rear differential case 154 that accommodates the pinion gears 152, 152, and a ring gear 155 that is fixed to the rear differential case 154 and meshes with the pinion gear shaft 150.

(Configuration of driving force transmission device)
FIG. 2 is a cross-sectional view showing a configuration example of the driving force transmission device 2. In FIG. 2, the upper side of the rotation axis O shows the operating state (torque transmission state) of the driving force transmission device 2, and the lower side shows the non-operating state (torque non-transmission state) of the driving force transmission device 2. Hereinafter, the direction parallel to the rotation axis O is referred to as an axial direction.

The driving force transmission device 2 is formed between a housing 20 composed of a front housing 21 and a rear housing 22, a tubular inner shaft 23 supported so as to be rotatable relative to the housing 20, and the housing 20 and the inner shaft 23. The main clutch 3 is arranged in, a cam mechanism 4 for generating a pressing force for pressing the main clutch 3, and an electromagnetic clutch mechanism 5 for operating the cam mechanism 4 by receiving the rotational force of the front housing 21. Has been done. Lubricating oil (not shown) is sealed in the internal space of the housing 20.

The front housing 21 has a bottomed cylindrical shape having a cylindrical cylindrical portion 21a and a bottom portion 21b integrally. A female screw portion 21c is formed on the inner surface of the opening end portion of the tubular portion 21a. A propeller shaft 14 (see FIG. 1) is connected to the bottom portion 21b of the front housing 21 via, for example, a cross joint. Further, the front housing 21 has a plurality of outer spline protrusions 211 extending in the axial direction on the inner peripheral surface of the tubular portion 21a. The outer spline protrusion 211 protrudes inward in the radial direction toward the rotation axis O of the housing 20 and the inner shaft 23.

The rear housing 22 is a second annular member made of a non-magnetic material such as austenitic stainless steel, which is integrally bonded to the inner peripheral side of the first annular member 221 made of a magnetic material such as iron and the first annular member 221 by welding or the like. It is composed of 222 and a third annular member 223 made of a magnetic material such as iron integrally bonded to the inner peripheral side of the second annular member 222 by welding or the like. An annular accommodation space 22a for accommodating the electromagnetic coil 53 is formed between the first annular member 221 and the third annular member 223. Further, a male threaded portion 221a screwed into the female threaded portion 21c of the front housing 21 is formed on the outer peripheral surface of the first annular member 221.

The inner shaft 23 is supported on the inner peripheral side of the housing 20 by a ball bearing 24 and a needle roller bearing 25. The inner shaft 23 has a plurality of inner spline protrusions 231 extending in the axial direction on the outer peripheral surface. Further, a spline fitting portion 232 in which one end portion of the pinion gear shaft 150 (see FIG. 1) is fitted so as not to rotate relative to each other is formed on the inner surface of one end portion of the inner shaft 23.

The main clutch 3 is a friction clutch having a plurality of main outer clutch plates 31 and a plurality of main inner clutch plates 32 arranged alternately along the axial direction. The frictional sliding between the main outer clutch plate 31 and the main inner clutch plate 32 is lubricated by the lubricating oil (not shown) sealed between the housing 20 and the inner shaft 23, and wear and seizure are suppressed.

The main outer clutch plate 31 has a plurality of engaging protrusions 311 that engage with the outer spline protrusions 211 of the front housing 21 at the outer peripheral end portion. The main outer clutch plate 31 is movable in the axial direction with respect to the front housing 21 while the relative rotation with the front housing 21 is restricted by engaging the engaging protrusion 311 with the outer spline protrusion 211.

The main inner clutch plate 32 has a plurality of engaging protrusions 321 at the outer peripheral end that engage with the inner spline protrusions 231 of the inner shaft 23. The main inner clutch plate 32 is movable in the axial direction with respect to the inner shaft 23 while the relative rotation with the inner shaft 23 is restricted by engaging the engaging protrusion 321 with the inner spline protrusion 231. Further, in the main inner clutch plate 32, a plurality of oil holes 322 through which lubricating oil flows are formed inside the main outer clutch plate 31.

The cam mechanism 4 is between the pilot cam 41 that receives the rotational force of the housing 20 via the electromagnetic clutch mechanism 5, the main cam 42 as a pressing member that presses the main clutch 3 in the axial direction, and the pilot cam 41 and the main cam 42. It is configured to have a plurality of spherical cam balls 43 arranged in.

The main cam 42 has a ring plate-shaped pressing portion 421 that contacts the main inner clutch plate 32 at one end of the main clutch 3 and presses the main clutch 3, and a cam provided on the inner peripheral side of the main cam 42 with respect to the pressing portion 421. It has a portion 422 integrally. In the main cam 42, the spline engaging portion 421a formed at the inner peripheral end portion of the pressing portion 421 engages with the inner spline protrusion 231 of the inner shaft 23, and the relative rotation with the inner shaft 23 is restricted. Further, the main cam 42 is urged so as to be axially separated from the main clutch 3 by a disc spring 44 arranged between the main cam 42 and the stepped surface 23a formed on the inner shaft 23.

The pilot cam 41 has a spline engaging portion 411 at the outer peripheral end portion that receives a rotational force that rotates relative to the main cam 42 from the electromagnetic clutch mechanism 5. A thrust needle roller bearing 45 is arranged between the pilot cam 41 and the third annular member 223 of the rear housing 22.

A plurality of cam grooves 41a and 422a whose axial depths change along the circumferential direction are formed on the facing surfaces of the pilot cam 41 and the cam portion 422 of the main cam 42. The cam ball 43 is arranged between the cam groove 41a of the pilot cam 41 and the cam groove 422a of the main cam 42. Then, the cam mechanism 4 generates an axial pressing force for pressing the main clutch 3 by rotating the pilot cam 41 relative to the main cam 42. The main clutch 3 receives a pressing force from the cam mechanism 4, and the main outer clutch plate 31 and the main inner clutch plate 32 are in frictional contact with each other, and the driving force is transmitted by this frictional force.

The electromagnetic clutch mechanism 5 includes an armature 50, a plurality of pilot outer clutch plates 51, a plurality of pilot inner clutch plates 52, and an electromagnetic coil 53.

The electromagnetic coil 53 is held by an annular yoke 530 made of a magnetic material, and is housed in a storage space 22a of the rear housing 22. The yoke 530 is supported by a third annular member 223 of the rear housing 22 by a ball bearing 26, and its outer peripheral surface faces the inner peripheral surface of the first annular member 221. Further, the inner peripheral surface of the yoke 530 faces the outer peripheral surface of the third annular member 223. The control current of the control device 7 is supplied to the electromagnetic coil 53 as an exciting current via the electric wire 531.

The plurality of pilot outer clutch plates 51 and the plurality of pilot inner clutch plates 52 are alternately arranged along the axial direction between the armature 50 and the rear housing 22. A plurality of arc-shaped slits are formed in the radial center portion of the pilot outer clutch plate 51 and the pilot inner clutch plate 52 in order to prevent a short circuit of magnetic flux generated by energization of the electromagnetic coil 53.

The pilot outer clutch plate 51 has a plurality of engaging protrusions 511 that engage with the outer spline protrusions 211 of the front housing 21 at the outer peripheral end portion. The pilot inner clutch plate 52 has a plurality of engaging protrusions 521 that engage with the spline engaging portion 411 of the pilot cam 41 at the inner peripheral end portion.

The armature 50 is an annular member made of a magnetic material such as iron, and a plurality of engaging protrusions 501 that engage with the outer spline protrusions 211 of the front housing 21 are formed on the outer peripheral portion thereof. As a result, the armature 50 can move in the axial direction with respect to the front housing 21, and the relative rotation with respect to the front housing 21 is restricted.

In the driving force transmission device 2 configured as described above, the armature 50 is attracted to the rear housing 22 side by the magnetic force generated by supplying the control current to the electromagnetic coil 53, and the pilot outer clutch plate 51 and the pilot inner clutch Friction contact with the plate 52. As a result, the rotational force of the housing 20 is transmitted to the pilot cam 41, the pilot cam 41 rotates relative to the main cam 42, and the cam ball 43 rolls in the cam grooves 41a and 422a. Due to the rolling of the cam ball 43, a cam thrust force for pressing the main clutch 3 is generated on the main cam 42, and a frictional force is generated between the plurality of main outer clutch plates 31 and the plurality of main inner clutch plates 32. Then, due to this frictional force, torque is transmitted between the housing 20 and the inner shaft 23. The torque transmitted by the main clutch 3 increases or decreases according to the control current supplied to the electromagnetic coil 53.

(Configuration of control device 7)
As shown in FIG. 1, the control device 7 includes a CPU 71, which is an arithmetic processing device, a storage unit 72 composed of semiconductor storage elements such as ROM and RAM, and a switching power supply unit 73 that generates a control current. ..

FIG. 3 is a schematic view showing a schematic functional configuration example of the control device 7. The control device 7 has a PWM signal generation unit 70 that generates a PWM (Pulse Width Modulation) signal, and a switching power supply unit 73 that generates a control current based on the PWM signal. In the present embodiment, the CPU 71 functions as the PWM signal generation unit 70 by executing the program stored in the storage unit 72. That is, the function of the PWM signal generation unit 70 is realized by the CPU 71.

The PWM signal generation unit 70 includes rotation speed sensors 61 to 64 for detecting the rotation speeds of the left and right front wheels 181, 182 and left and right rear wheels 191, 192, respectively, and an accelerator pedal sensor 65 for detecting the operation amount of the accelerator pedal 110. The detection results can be acquired, and the driving force transmission device 2 is controlled based on these detection results. More specifically, for example, the greater the difference between the average rotational speed of the left and right front wheels 181, 182 and the average rotational speed of the left and right rear wheels 191, 192, and the greater the amount of depression of the accelerator pedal 110, the greater the driving force left and right. The driving force transmission device 2 is controlled so as to be transmitted to the rear wheels 191 and 192.

The PWM signal generation unit 70 calculates the command torque to be transmitted by the driving force transmission device 2 based on the detection results of the rotation speed sensors 61 to 64 and the accelerator pedal sensor 65, and the driving force transmission device according to the command torque. The command current value, which is the target value of the control current to be supplied to 2, is calculated. Then, the switching power supply unit 73 is PWM-controlled so that the control current of the command current value is output to the driving force transmission device 2.

The switching power supply unit 73 includes a FET (field effect transistor) 74 which is a switching element, a freewheeling diode 75, a temperature sensor 76 for detecting the temperature of the FET 74, a shunt resistor 77 for detecting a control current, and a shunt resistor 77. It has an operational amplifier 78 as an amplifier that amplifies the potential difference between both ends of the above. Specifically, the FET 74 is a MOSFET, and its on state or off state is determined by a rectangular wave-shaped PWM signal.

The PWM signal is input to the gate of the FET 74 to generate a gate-source voltage. When a gate-source voltage is generated by the PWM signal, the FET 74 is turned on in the saturation region. When the FET 74 is turned on, a current (drain current) flows from the drain to the source, and when the FET 74 is turned off, this current flow is cut off. A DC voltage of, for example, 12 V is supplied to the switching power supply unit 73 from the battery B mounted on the four-wheel drive vehicle 1 via the power connector 7a. The switching power supply unit 73 switches this DC voltage based on the PWM signal to generate a control current.

The control device 7 outputs a control current from the pair of terminals 7b and 7c to the electromagnetic coil 53 of the driving force transmission device 2. In the off state of the FET 74, a current flows through the freewheeling diode 75 due to the inductance of the electromagnetic coil 53. In the freewheeling diode 75, the anode is connected to the terminal 7c and the drain of the FET 74, and the cathode is connected to one end of the power connector 7a and the shunt resistor 77. The other end of the shunt resistor 77 is connected to the terminal 7b.

The PWM signal generation unit 70 detects the control signal output to the electromagnetic coil 53 by the output signal of the operational amplifier 78, and generates the PWM signal so that the detected value approaches the command current value. Specifically, if the detected value of the control signal is lower than the command current value, the duty ratio of the PWM signal is increased, and if the detected value of the control signal is lower than the command current value, the duty ratio of the PWM signal is decreased. Here, the duty ratio of the PWM signal means the ratio of the time during which the voltage of the PWM signal is the voltage at which the FET 74 is turned on in the unit time. The PWM signal generation unit 70 determines whether to turn the FET 74 on or off at each predetermined PWM cycle, and generates a PWM signal according to the result.

By the way, when a switching element such as a FET is switched from an off state to an on state (turn on) and when a switching element such as an FET is switched from an on state to an off state (turn off), a power loss called a switching loss occurs. This switching loss will be described with reference to FIG.

FIG. 4 is a graph showing an example of temporal changes in the drain-source voltage (Vds) and drain current (Id) when the FET switches from the off state to the on state and further switches from the on state to the off state. .. The horizontal axis of this graph is the time axis, and the vertical axis shows the magnitude of the drain-source voltage and the drain current.

The power consumed by the FET is roughly determined by the product of the drain-source voltage and the drain current. Therefore, if the drain-source voltage or drain current is substantially zero, the FET does not consume power. However, in the switching time (Tsw), which is the time zone of the transient state in turn-on and turn-off, both the drain-source voltage and the drain current are in a non-zero state, so that power is consumed by the FET. That is, power loss occurs in the FET. Then, the FET generates heat due to this power loss.

The PWM signal generation unit 70 can detect the temperature of the FET 74 from the output signal of the temperature sensor 76. As the temperature sensor 76, for example, a thermistor can be used. The temperature sensor 76 is arranged in contact with, for example, the FET 74 or the heat radiation fins that dissipate the heat thereof. Alternatively, the temperature sensor 76 may be arranged in the vicinity of the FET 74 and the heat radiation fins.

5 and 6 show an example of temporal changes in the gate-source voltage (Vgs) and drain current (Id) of the FET 74 when the duty ratios of the PWM signals are both 50% and the PWM cycles are different. It is a graph. The gate-source voltage corresponds to a PWM signal. The horizontal axes of FIGS. 5 (a) and 5 (b) and 6 (a) and 6 (b) are time axes, and their time scales are common. The vertical axis of FIGS. 5 (a) and 6 (a) indicates the magnitude of the gate-source voltage, and the vertical axis of FIGS. 5 (b) and 6 (b) indicates the magnitude of the drain current. ..

5 and 6 show a case where the gate-source voltage is switched between a state higher and a state lower than the gate threshold voltage (voltage at which the drain current starts to flow) for each PWM cycle. The PWM period (T ₁ ) of the graph shown in FIG. 5 is one-fourth of the PWM period (T ₂ ) of the graph shown in FIG. The PWM cycle (T ₁ ) is, for example, 1 ms, and the PWM cycle (T ₂ ) is, for example, 4 ms.

The drain current gradually increases when the gate-source voltage is higher than the gate threshold voltage, and gradually decreases when the gate-source voltage is lower than the gate threshold voltage. Further, as is clear from the comparison of FIGS. 5 and 6, the change width of the drain current becomes smaller as the PWM cycle is shorter, and the change width becomes larger as the PWM cycle is longer. From this, it can be seen that the shorter the PWM cycle, the more accurately the drain current can be adjusted.

On the other hand, as described above, switching loss occurs when the FET 74 is switched between the off state and the on state. Therefore, it can be said that a long PWM cycle is desirable in order to suppress heat generation of the FET 74.

In the present embodiment, paying attention to these points, if the PWM cycle is lengthened when the drain current (control current) is not adjusted with high accuracy, the running of the four-wheel drive vehicle 1 becomes unstable. Based on the finding that the heat generation of the FET 74 can be suppressed, the PWM cycle is lengthened during deceleration by the engine brake. Next, with reference to FIG. 7, a specific example of the process executed by the CPU 71 operating as the PWM signal generation unit 70 will be described.

FIG. 7 is a flowchart showing an example of the processing executed by the CPU 71. The CPU 71 repeatedly executes the process shown in this flowchart at predetermined control cycles.

The CPU 71 determines whether or not the temperature of the FET 74 is equal to or higher than a predetermined value based on the output signal of the temperature sensor 76 (step S1), and if it is equal to or higher than the predetermined value (step S1: Yes), the protection control is performed. (Step S2). The predetermined value of the temperature in step 1 is, for example, the upper limit temperature of the temperature range in which the FET 74 operates stably. This protection control is for protecting the FET 74 from damage due to overheating and the like, and specifically, it is a control for reducing the control current to substantially zero. In the present embodiment, the CPU 71 performs the following processing in order to avoid a situation in which the protection control is executed.

When the temperature of the FET 74 is less than a predetermined value as a result of the determination in step S1 (step S1: No), the CPU 71 reads the detection values of the rotation speed sensors 61 to 64 and the accelerator pedal sensor 65 (step S3). The difference in rotational speed between the front and rear wheels and the amount of operation of the accelerator pedal are calculated based on the detected values (step S4). The difference in rotational speed between the front and rear wheels can be obtained from the difference between the average rotational speeds of the left and right front wheels 181, 182 and the average rotational speeds of the left and right rear wheels 191, 192.

Next, the CPU 71 determines whether or not the vehicle speed is in the medium-high speed range equal to or higher than the predetermined speed (step S5). This predetermined speed is, for example, 40 km / h. The vehicle speed can be obtained, for example, based on the rotation speed of the wheel having the slowest rotation speed among the left and right front wheels 181, 182 and the left and right rear wheels 191, 192. Further, the vehicle speed information may be acquired from the host controller.

As a result of the determination in step S5, when the vehicle speed is equal to or higher than the predetermined speed (step S5: Yes), the CPU 71 determines whether or not the operation amount of the accelerator pedal 110 is less than the predetermined value (step S6). The predetermined value in step S6 is, for example, a value corresponding to an upper limit value of the operating amount of the accelerator pedal 110 on which the engine brake acts.

As a result of the determination in step S6, when the operation amount of the accelerator pedal 110 is less than a predetermined value (step S6: Yes), the CPU 71 increments the engine brake corresponding control counter (step S7). The engine brake compatible control counter is cleared to zero when the engine 11 is started (when the ignition is turned on), for example.

Next, the CPU 71 determines whether or not the value (counter value) of the engine brake compatible control counter is less than a predetermined value (step S8), and if this counter value is less than a predetermined value (step S8: Yes). , The engine brake corresponding control is executed (step S9). In this engine brake compatible control, the PWM cycle is lengthened and the duty ratio of the PWM signal is set to a constant value. In this way, the CPU 71 that functions as the PWM signal generation unit 70 has a case where the operation amount of the accelerator pedal 110 is a predetermined value in step S6 or a step when the operation amount of the accelerator pedal 110 is smaller than the predetermined value in step S6. The PWM cycle is lengthened as compared with the case where it is larger than the predetermined value of S6.

The PWM cycle in the engine brake compatible control is set to, for example, twice or more the length as compared with the case where the engine brake compatible control is not performed. As a result, as described above, switching loss can be suppressed and overheating of the FET 74 can be prevented. Further, if the PWM cycle during engine braking compatible control is set to a length of 4 times or more, the effect of suppressing switching loss becomes more remarkable.

Further, when the counter value of the engine brake compatible control counter is equal to or higher than a predetermined value (step S8: No), the CPU 71 does not perform engine brake compatible control. That is, when the operation amount of the accelerator pedal 110 is smaller than the predetermined value (step S6: Yes) and the vehicle speed is equal to or higher than the predetermined speed (step S5: Yes), the CPU 71 continues the PWM cycle for a predetermined time. Continue to execute engine brake compatible control. The predetermined value in step S8 is set to a value such that the time for continuously performing the engine brake corresponding control is, for example, 3 to 5 seconds. In this way, the engine brake compatible control counter serves as a timer that measures the elapsed time from the start of the engine brake compatible control mode.

When the counter value of the engine brake compatible control counter is equal to or greater than a predetermined value (step S8: No), the CPU 71 executes the first return process (step S10). In this first return process, the PWM cycle is restored, and the duty ratio of the PWM signal is changed from a constant value in the engine brake compatible control to a value according to the vehicle running state, that is, the difference in rotational speed between the front and rear wheels and the accelerator pedal. This is a process of diversion to a value according to the amount of operation. That is, in the first recovery process, the duty ratio of the PWM signal is gradually changed by a predetermined time constant. The first return process is a predetermined time after the counter value of the engine brake compatible control counter becomes equal to or higher than the predetermined value when the operation amount of the accelerator pedal 110 is smaller than the predetermined value and the vehicle speed is equal to or higher than the predetermined speed. This is a process that is executed over a period of time, and is for suppressing disturbance of vehicle behavior due to a sudden change in driving force transmitted to the left and right rear wheels 191, 192.

On the other hand, when the vehicle speed is less than the predetermined speed (step S5: No) or when the operation amount of the accelerator pedal 110 is equal to or more than the predetermined value (step S6: No), the CPU 71 clears the counter value of the engine brake compatible control counter to zero. (Step S11). Then, the CPU 71 determines whether or not the engine brake correspondence control is being performed or the first return process is in progress (step S12), and if the result of this determination is Yes, the second return process is executed (step). S13).

Similar to the first return process in step 10, this second return process restores the PWM cycle and sets the duty ratio of the PWM signal according to the difference in rotational speed between the front and rear wheels and the operation amount of the accelerator pedal. However, the rate of change is different from that of the first restoration process. In the present embodiment, the rate of change of the duty ratio in the second return process is faster than the rate of change of the duty ratio in the first return process. That is, during the second return process, the duty ratio of the PWM signal approaches a value corresponding to the difference in rotational speed between the front and rear wheels and the operation amount of the accelerator pedal more quickly than during the first return process.

Further, the CPU 71 sets the duty ratio of the PWM signal to a value according to the difference in rotational speed between the front and rear wheels and the operation amount of the accelerator pedal unless the engine brake corresponding control is being performed or the first recovery process is being performed (step S12: No). (Step S14).

The PWM signal for which the duty ratio is set as described above is input to the FET 74 as a gate signal. As a result, the control current according to the duty ratio is supplied to the electromagnetic coil 53 of the driving force transmission device 2. Then, the driving force is transmitted by the main clutch 3 according to the control current supplied to the electromagnetic coil 53.

(Actions and effects of embodiments)
According to the embodiment described above, since the PWM cycle is long in the engine brake corresponding control, the frequency of switching the on / off state of the FET 74 is reduced, and the switching loss is suppressed. As a result, the heat generation of the FET 74 is suppressed, and it becomes easy to avoid the protection control (step S2) being executed due to the overheating of the FET 74.

(Additional note)
Although the present invention has been described above based on the first and second embodiments, these embodiments do not limit the invention according to the claims. It should also be noted that not all combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

Further, the present invention can be appropriately modified and implemented without departing from the spirit of the present invention. For example, the configurations of the four-wheel drive vehicle 1 and the driving force transmission device 2 are not limited to those illustrated in FIGS. 1 and 2, and various configurations can be used.

1 ... Four-wheel drive vehicle 2 ... Driving force transmission device 7 ... Control device 11 ... Engine (drive source)
70 ... PWM signal generation unit 73 ... Switching power supply unit 181, 182 ... Left and right front wheels (main drive wheels) 191, 192 ... Left and right rear wheels (auxiliary drive wheels)

Claims (4)

A drive source that generates a drive force according to the amount of operation of the accelerator pedal, a main drive wheel that constantly transmits the drive force of the drive source, and a drive force transmission device that transmits the drive force according to the supplied current. It is a control device of a driving force transmitting device mounted on a four-wheel drive vehicle provided with an auxiliary driving wheel to which the driving force of the driving source is transmitted via the driving force transmitting device and supplying the current to the driving force transmitting device.
A switching power supply unit having a switching element and generating the current by switching a DC voltage based on a PWM signal in which the on state or the off state of the switching element is determined for each PWM cycle, and the PWM signal are generated. It has a PWM signal generator and
The PWM signal generation unit lengthens the PWM cycle when the accelerator pedal operation amount is smaller than a predetermined value and decelerates, as compared with the case where the accelerator pedal operation amount is larger than the predetermined value or the predetermined value. ,
Control device for driving force transmission device. The PWM signal generation unit lengthens the PWM cycle when the operation amount of the accelerator pedal is smaller than the predetermined value and the vehicle speed is equal to or higher than the predetermined speed.
The control device for the driving force transmission device according to claim 1. The PWM signal generation unit sets the duty ratio of the PWM signal to a constant value in a state where the PWM cycle is lengthened.
The control device for the driving force transmission device according to claim 1 or 2. When the operation amount of the accelerator pedal is smaller than the predetermined value and the vehicle speed continues to be equal to or higher than the predetermined speed , the PWM signal generation unit continues the state in which the PWM cycle is lengthened for a predetermined time, and then continues. , The duty ratio of the PWM signal is changed to a value according to the vehicle running state.
The control device for the driving force transmission device according to claim 1 .

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