JP3974129B2 - Control device for friction engagement element for electric motor in hybrid vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve fuel consumption by controlling a frictional engagement element to hold down a loss (a motor loss) due to drag of a motor caused by the engagement of the frictional engagement element when the motor is inoperative and a frictional engagement element loss due to friction generated by releasing the frictional engagement element as much as possible in a control device of the frictional engagement element for the motor provided in a hybrid vehicle to be freely switched between the power transmission enable state and the disabled state between the motor and wheels. <P>SOLUTION: In a change characteristic (a line) of a motor loss to the vehicle speed and change characteristics (b1, b2, b3 lines) of frictional engagement element loss to the vehicle speed varied depending on the temperature of the frictional engagement element, the vehicle speed at which a motor loss obtained from the change characteristic of the frictional engagement element loss corresponding to the temperature at this point of time is substantially equal to the frictional engagement element loss is taken as a threshold, in the case of a vehicle speed lower than the threshold, the frictional engagement element is engaged, and in the case of a vehicle speed higher than the threshold, the frictional engagement element is released. <P>COPYRIGHT: (C)2006,JPO&amp;NCIPI

Description

  The present invention is provided in a hybrid vehicle including a prime mover and an electric motor as drive sources so that the power transmission between the electric motor and wheels to be driven by the electric motor can be switched between a state where power transmission is possible and an impossible state. The present invention relates to a control device for a frictional engagement element.

  Conventionally, a hybrid vehicle is known in which one of the front and rear wheels is driven by an engine as a prime mover and the other is driven by an electric motor. In such a hybrid vehicle, when a speed reducer with a large reduction ratio is interposed between the motor and a wheel to be driven by the motor so that a large driving torque can be obtained with a small motor, the rotational speed of the motor is When the rotational speed of the wheel becomes considerably faster than the vehicle speed and exceeds a certain limit, the rotational speed of the electric motor exceeds the allowable upper limit speed (rated speed). Therefore, a friction engagement element composed of a hydraulic clutch and a hydraulic brake for switching between a state where power transmission between the electric motor and the wheel is possible and a state where the power transmission is impossible is provided, and if the vehicle speed is lower than a predetermined threshold, The friction engagement element is engaged so that power transmission is possible, but if the vehicle speed is higher than the threshold value, the friction engagement element is released so that power transmission is disabled, and the motor is driven in reverse from the wheel side. There are known ones that prevent excessive rotation exceeding the rated speed (see, for example, Patent Documents 1 and 2).

  Even if the friction engagement element is released, the frictional torque of the friction engagement element generated due to the viscosity of the oil is transmitted from the wheel side, and the rotational speed of the motor temporarily overshoots. The amount of overshoot increases as the temperature of the oil increases. Therefore, in the one described in Patent Document 1, the threshold value is corrected so that the threshold value is changed to the lower vehicle speed side as the temperature of the friction engagement element decreases, and the friction engagement element is moved at a relatively low vehicle speed at low temperatures. It is made to release, and it can prevent that the rotational speed of an electric motor exceeds a rated speed by the overshoot.

By the way, if the motor is made large to a certain extent, the reduction ratio of the reduction gear interposed between the motor and the wheels is reduced, or if a motor with a high rated speed is used, the motor will be used unless it runs at an extremely high vehicle speed. No over-rotation occurs. However, if the friction engagement element is maintained in the engaged state when the motor is not operating (the state where neither driving by the motor nor regenerative power generation is performed) and the motor is reversely driven from the wheel side, the drag of the motor A loss (a loss due to the generation of the counter electromotive force) occurs, and this loss increases at an accelerated speed as the vehicle speed increases as shown by line a in FIG. Further, when the friction engagement element is released when the electric motor is not operated, a loss due to friction of the friction engagement element due to the viscosity of the oil occurs. This loss is greater than the loss due to dragging of the motor in the low to medium vehicle speed range as shown by the lines b1, b2 and b3 in FIG. Further, the loss due to friction of the friction engagement element is highly temperature dependent. If the temperature of the friction engagement element is normal temperature, the loss is relatively small as shown by line b1, but the temperature of the friction engagement element is low. As shown by lines b2 and b3, the loss increases. In order to improve fuel efficiency, it is necessary to appropriately control the friction engagement element in consideration of a loss due to dragging of the motor and a loss due to friction of the friction engagement element.
Japanese Patent No. 3551178 JP 2004-208445 A

  In view of the above, the present invention controls the friction engagement element so that the loss caused by dragging of the motor and the loss caused by friction of the friction engagement element can be kept as low as possible to improve fuel efficiency. An object of the present invention is to provide a control device for a frictional engagement element for an electric motor in a hybrid vehicle that can be improved as much as possible.

  In order to solve the above-described problems, the present invention provides a hybrid vehicle having a prime mover and an electric motor as drive sources, a state in which power transmission between the electric motor and wheels to be driven by the electric motor is possible, and a state in which power cannot be transmitted. A control device for a frictional engagement element provided so as to be switchable to a vehicle speed detecting means for detecting a vehicle speed, and when the detected vehicle speed of the vehicle speed detecting means is lower than a predetermined threshold when the electric motor is not operated. Friction that engages the friction engagement element to enable the power transmission, and releases the friction engagement element to disable the power transmission if the vehicle speed detected by the vehicle speed detection means is higher than the threshold. And an engagement element control means, and a temperature detection means for detecting the temperature of the friction engagement element, and the threshold value is changed to a higher vehicle speed side as the temperature detected by the temperature detection means becomes lower. Characterized in that it comprises a first threshold value correcting means for correcting the threshold value as.

  In particular, in the present invention, the loss due to dragging of the motor caused by the engagement of the friction engagement element when the motor is not operated is referred to as motor loss, and the friction engagement element caused by the release of the friction engagement element when the motor is not operated. With the loss due to friction as the friction engagement element loss, the first threshold value correction means determines the change characteristic of the motor loss with respect to the vehicle speed (a line in FIG. 7) and the temperature of the friction engagement element is the detected temperature of the temperature detection means. The threshold value is corrected to a vehicle speed at which the motor loss and the friction engagement element loss obtained from the change characteristics of the friction engagement element loss with respect to the vehicle speed (b1, b2, and b3 lines in FIG. 7) are substantially equal. It is desirable to be configured.

  Here, in a vehicle speed range lower than the vehicle speed at which the motor loss and the friction engagement element loss are equal, the friction engagement element loss is larger than the motor loss. However, according to the above configuration, the friction engagement factor is lost in this vehicle speed range. Since the combined element is maintained in the engaged state, no friction engagement element loss occurs, and the generated loss is a relatively small motor loss. On the other hand, in the vehicle speed range higher than the vehicle speed at which the motor loss and the friction engagement element loss are equal, the motor loss is larger than the friction engagement element loss. As the element is released, there is no motor loss and the resulting loss is a relatively small frictional engagement element loss. That is, the friction engagement element is switched between engagement and disengagement so that the larger one of the motor loss and the friction engagement element loss does not occur, so the fuel efficiency is improved as much as possible by reducing the loss. To do.

  Further, since the friction engagement element loss increases as the temperature of the friction engagement element decreases, the vehicle speed at which the motor loss and friction engagement element loss are equal changes to the higher vehicle speed side as the friction engagement element temperature decreases. To do. Therefore, if the threshold value is changed to the higher vehicle speed side as the temperature of the friction engagement element becomes lower as described above, loss can be reduced and fuel efficiency can be improved. In this specification, the “temperature of the friction engagement element” that is the detection target of the temperature detection means is limited to the temperature of the constituent member of the friction engagement element such as the friction plate (the temperature of the friction engagement element itself). It is not a thing, but includes the temperature of the location which can estimate the temperature of friction engagement elements, such as the temperature of oil, and the temperature of the arrangement part of a friction engagement element.

  By the way, when the outside air temperature is low, there is a high possibility that the vehicle travels on a frozen road surface, and the frequency of driving assistance by the electric motor is increased to stabilize the vehicle when slipping. Here, when a slip occurs during traveling in a vehicle speed range higher than the threshold corrected by the first threshold correcting means, that is, when traveling with the friction engagement element released, friction engagement occurs. Until the elements are engaged, drive assist by the electric motor cannot be performed, and drive assist response is deteriorated.

  Therefore, when the detected temperature of the outside air temperature detecting means for detecting the outside air temperature and the outside air temperature detecting means is equal to or lower than the predetermined temperature, the threshold value is set to a higher vehicle speed side than the threshold value corrected by the first threshold value correcting means. It is desirable to provide a second threshold value correcting means for correcting to the second threshold value. According to this, when the vehicle is cold, the vehicle speed range in which the friction engagement element is maintained in the engaged state is widened, and it becomes possible to perform drive assist with the electric motor with good responsiveness at the time of slip. In addition, the frictional engagement element is engaged each time it slips from the released state, and is released after stabilization by drive assist, preventing frequent engagement / release of the frictional engagement element and improving durability. It is advantageous in aiming at.

  Since the possibility of road surface freezing increases as the outside air temperature decreases, it is desirable to expand the vehicle speed range in which the friction engagement element is maintained in the engaged state to the higher vehicle speed side as the outside air temperature decreases. For this purpose, the second threshold value correcting means may be configured to change the second threshold value to the higher vehicle speed side as the detected temperature of the outside air temperature detecting means becomes lower.

  When the road surface friction coefficient estimated by the road surface friction coefficient estimation unit and the road surface friction coefficient estimation unit are less than a predetermined value, the threshold value is corrected by the first threshold value correction unit. It is desirable to include a third threshold value correction unit that corrects the vehicle speed to be higher than the threshold value. According to this, even when a slip occurs due to a decrease in a road surface friction coefficient that cannot be predicted at an outside air temperature on a dirt road or the like, the drive assist by the electric motor can be performed with high responsiveness.

  Here, when the present invention is applied to a control device for a frictional engagement element for an electric motor provided in a four-wheel drive hybrid vehicle in which one of the front and rear wheels of the vehicle is driven by a prime mover and the other is driven by an electric motor, This can advantageously improve stability. However, the present invention can also be applied to a control device for a frictional engagement element for an electric motor provided in a two-wheel drive hybrid vehicle in which one of the front and rear wheels is driven by a prime mover and an electric motor.

  In the embodiment described later, the friction engagement element control means corresponds to the brake control process shown in FIG. 3, and the first threshold value correction means corresponds to S3-4 in FIG. The process in steps up to S3-8, which corresponds to the second threshold value correction means, is a process from S3-14 to S3-15 in FIG. The processing corresponding to the correcting means is processing from S3-12 to S3-17 in FIG.

  Referring to FIG. 1, reference numeral 1 designates four wheels in which left and right front wheels 2 and 2 are driven by a prime mover 3 and left and right rear wheels 4 and 4 are driven by an electric motor (hereinafter referred to as a first motor) 5. A drive-type hybrid vehicle is shown.

  The prime mover 3 is composed of a hybrid power unit including an engine (internal combustion engine) 3a and an electric motor (hereinafter referred to as a second motor) 3b on its output shaft (crankshaft). The prime mover 3 is connected to a front axle 2b connected to a front wheel 2 via a constant velocity joint 2a via a transmission 6 and a front differential gear 7. The second motor 3b is connected to the storage battery 10 via a first PDU (power drive unit) 9-1 controlled by a controller 8 composed of an in-vehicle computer, and the front wheels by the second motor 3b according to the traveling state of the vehicle 1. 2 driving and regenerative power generation are performed.

  The first motor 5 is connected via a power transmission mechanism 11 to a rear axle 4b connected to the rear wheel 4 via a constant velocity joint 4a. The first motor 5 is connected to the storage battery 10 via the second PDU 9-2 controlled by the controller 8, and driving and regeneration of the rear wheels 4 by the first motor 5 according to the traveling state of the vehicle 1. Power generation is performed.

  The power transmission mechanism 11 includes a planetary gear mechanism 12 and a rear differential gear 13. The planetary gear mechanism 12 meshes with both the sun gear 12a, the ring gear 12b, the sun gear 12a, and the ring gear 12b that are directly connected to the rotor 5a of the first motor 5 that is rotatably supported about the same axis as the rear axle 4b. The planetary pinion 12c and the carrier 12d that pivotally supports the planetary pinion 12c are configured. The carrier 12d is integrated with the input case 13a of the rear differential gear 13. Here, the ring gear 12b is connected to the casing 11a of the power transmission mechanism 11 via a hydraulic brake 14 which is a friction engagement element. Thus, when the hydraulic brake 14 is engaged to restrict the rotation of the ring gear 12b, the ring gear 12b functions as a reaction force receiver, and the planetary pinion 12c revolves while rotating with the rotation of the sun gear 12a. As a result, the input case 13a of the rear differential gear 13 is rotated via this, and power transmission between the first motor 5 and the rear differential gear 13 becomes possible. On the other hand, when the hydraulic brake 14 is released and the restraint of the ring gear 12b is released, the ring gear 12b does not function as a reaction force receiver, and power transmission between the first motor 5 and the rear differential gear 13 becomes impossible. The hydraulic brake 14 is switched between an engaged state and a released state by supplying and discharging oil through a control valve 14a controlled by the controller 8 provided in a hydraulic circuit (not shown).

  The controller 8 includes a wheel speed sensor 15 as vehicle speed detecting means for detecting the rotational speed of each wheel 2, 4, an accelerator opening sensor 17 for detecting an opening including on / off of the accelerator pedal 16, and a pedaling force of the brake pedal 18. A brake pedal force sensor 19 that detects the steering angle, a steering angle sensor 21 that detects the steering angle of the steering wheel 20, a yaw rate sensor 22 that detects the yaw rate of the vehicle 1, a gradient sensor 23 that detects the gradient of the travel path, and the temperature of the hydraulic brake 14 Detection signals of various sensors such as a brake temperature sensor 24 serving as a temperature detecting means and an outside temperature sensor (outside air temperature detecting means) 25 detecting an outside air temperature are input. Then, the controller 8 executes the control process shown in FIG. 2 at a predetermined time interval (for example, 10 msec) based on the detection signals of these sensors. Note that the temperature detected by the brake temperature sensor 24 is not limited to the temperature of the components of the hydraulic brake 14 such as the friction plate, but the temperature of the hydraulic brake 14 such as the temperature of the oil or the casing 11a of the power transmission mechanism 11 is estimated. It may be the temperature at the location where the

  In the control process, first, a target driving force setting process is performed in step S1-1. In this process, the target driving force is searched for a map using the vehicle speed calculated based on the detection signal of the wheel speed sensor 15 and the accelerator opening detected by the accelerator opening sensor 17 as parameters. Next, a driving mode selection process is performed in step S1-2. In this process, the optimum travel mode is determined from the vehicle speed, accelerator opening, accelerator opening change speed, target driving force, acceleration / deceleration determination, remaining power of the storage battery 10, motor output, and the like. The travel modes include a rear wheel drive mode using only the first motor 5, a front wheel drive mode using only the engine 3a, a front wheel drive mode using the engine 3a and the second motor 3b, and a four wheel drive mode using the engine 3a and the first motor 5. There are a four-wheel drive mode by the engine 3a, the second motor 3b and the first motor 5, a regeneration mode by the first motor 5, a regeneration mode by the first motor 5 and the second motor 3b, and the like. In step S1-2, the distribution of the front wheel driving force between the engine 3a and the second motor 3b is also determined.

  Next, the control process of the hydraulic brake 14 is performed at step S1-3. This process will be described in detail later. Next, in step S1-4, the setting process of the driving force distribution for the front wheels 2 and the rear wheels 4 is performed. In this process, according to the travel mode selected in step S1-2, based on the vehicle front / rear weight distribution, the motor 5 and 3b drive / regeneration, road gradient, vehicle speed, steering angle, yaw rate, etc. are taken into account. The driving force distribution between the front wheels 2 and the rear wheels 4 is determined. Next, in step S1-5, a drive / regeneration control process for the first motor 5 is performed. In this process, the driving force or regenerative force of the first motor 5 is determined according to the target driving force determined in step S1-1 and the rear wheel driving force distribution determined in step S1-4, and the first driving force is determined accordingly. 2 PDU 9-2 is controlled to perform rear wheel drive or regenerative power generation by the first motor 5. Next, in step S1-6, drive / regeneration control processing of the second motor 3b is performed. In this process, according to the target driving force determined in step S1-1, the front wheel driving force distribution determined in step S1-4, and the driving force distribution of the engine 3a and the second motor 3b determined in step S1-2. The driving force or regenerative force of the second motor 3b is determined, and the first PDU 9-1 is controlled in accordance with this to perform front wheel driving or regenerative power generation by the second motor 3b. Next, drive control processing of the engine 3a is performed at step S1-7. In this process, according to the target driving force determined in step S1-1, the front wheel driving force distribution determined in step S1-4, and the driving force distribution of the engine 3a and the second motor 3b determined in step S1-2. The driving force of the engine 3a is determined, and the throttle, fuel injection valve, etc. (not shown) of the engine 3a are controlled accordingly.

  Details of the brake control process in step S1-3 are as shown in FIG. 3. First, in step S2-1, the vehicle speed V calculated based on the detection signal of the wheel speed sensor 15 is read, and then in step S2-2. It is determined whether or not the vehicle speed V is zero. If V ≠ 0, the process proceeds to step S2-3, and it is determined whether or not the first motor 5 is inactive based on the travel mode selected in step S1-2. Specifically, when the traveling mode selected in step S1-2 is a mode in which neither driving of the first motor 5 nor regenerative power generation is performed, it is determined that the first motor 5 is inoperative. And when the 1st motor 5 is non-operation, it progresses to step S2-6 after performing the brake engagement release determination process mentioned later at step S2-4. On the other hand, when V = 0 or when the first motor 5 is operating, the brake engagement flag F-Bon is set to “1” in step S2-5, and then the process proceeds to step S2-6. In step S2-6, it is determined whether the brake engagement flag F-Bon is set to “1”. If F-Bon = 1, the engagement process of the hydraulic brake 14 is performed in step S2-7. If F-Bon = 0, release processing of the hydraulic brake 14 is performed in step S2-8.

  Here, when the hydraulic brake 14 is maintained in the engaged state when the first motor 5 is not operated and the first motor 5 is reversely driven from the rear wheel 4 side, a loss (back electromotive force) due to the drag of the first motor 5 occurs. Loss due to the generation of electric power). The work amount of the loss due to dragging of the first motor 5 (hereinafter referred to as motor loss) increases at an increasing speed as the vehicle speed increases as shown by the a line in FIG. Further, if the hydraulic brake 14 is released when the first motor 5 is not in operation, a loss due to the friction of the hydraulic brake 14 due to the viscosity of the oil occurs. The work amount of loss due to friction of the hydraulic brake 14 (hereinafter referred to as brake loss) is larger than the motor loss in the low and medium vehicle speed regions as shown by lines b1, b2, and b3 in FIG. Furthermore, the brake loss is highly temperature dependent. When the temperature Tb of the hydraulic brake 14 is normal temperature T1, the loss is small as shown by the line b1, but the temperature Tb of the hydraulic brake 14 is T2 (<T1), T3 (< As T2) decreases, the loss increases as shown by lines b2 and b3. In order to improve fuel efficiency, it is necessary to appropriately control the hydraulic brake 14 in consideration of a loss due to dragging of the first motor 5 and a loss due to friction of the hydraulic brake 14.

  Therefore, the controller 8 stores the change characteristic of the motor loss with respect to the vehicle speed as indicated by a line in FIG. 7 as a data table, and the change characteristic of the brake loss with respect to the temperature and the vehicle speed as indicated by lines b1, b2, and b3 in FIG. Is stored as a data map. In the brake engagement release determination process in step S2-4, the motor loss and the brake loss are compared, and the vehicle speed at which the motor loss and the brake loss are equal (for example, V1-1, Tb when Tb = T1). V1-2 when T = T2, and V1-3 when Tb = T3), and the hydraulic brake 14 is engaged in a vehicle speed range lower than the threshold (a region where the motor loss is smaller than the brake loss). The brake engagement permission flag F-preBon is set to “1” and the hydraulic brake 14 should be released in a vehicle speed range higher than the threshold (a region where the brake loss is smaller than the motor loss). Judging, the brake engagement permission flag F-preBon is reset to “0”.

  The details of the brake engagement release determination process are as shown in FIG. 4. First, in step S3-1, the previous value F-Boold of the brake engagement flag is updated to the current value F-Bon. Next, in step S3-2, the map is searched for and read the brake loss WB corresponding to the current temperature and the vehicle speed of the hydraulic brake 14 detected by the brake temperature sensor 24, and in step S3-3, the current time The motor loss WM corresponding to the vehicle speed is retrieved from the table and read.

  Next, in step S3-4, the previous value WBold of the brake loss is compared with the previous value WMold of the motor loss. If WBold ≧ WMold, the difference between the current motor loss WM and the brake loss WB in step S3-5. Is greater than or equal to a predetermined value YW, and if WBold <WMold, whether or not the difference between the current brake loss WB and the motor loss WM is greater than or equal to the predetermined value YW in step S3-6. Is determined. When it is determined in step S3-5 that WB-WM ≧ YW, or when it is determined in step S3-6 that WM-WB <YW, the routine proceeds to step S3-7, where the brake engagement permission flag F− When preBon is reset to “0” and WB−WM <YW is determined in step S3-5, or when WM−WB ≧ YW is determined in step S3-6, step S3-8 is performed. Then, the brake engagement permission flag F-preBon is set to “1”.

  According to the above processing, if WB ≧ WM (basically, the hydraulic brake 14 is engaged) in the previous time, even if this time WB <WM, that is, from the threshold value at which the vehicle speed becomes WB = WM. Even if the hydraulic brake 14 is basically released and released, the brake engagement permission flag F-preBon is not reset to “0” unless WM ≧ WB + YW. Further, if WB <WM (basically, the hydraulic brake 14 is released) last time, even if WB ≧ WM this time, that is, the vehicle speed is basically lower than the threshold value at which WB = WM. Even when the hydraulic brake 14 is engaged, the brake engagement permission flag F-preBon is not set to “1” unless WB ≧ WM + YW. Thus, YW becomes a hysteresis, and the occurrence of hunting of engagement / release of the hydraulic brake 14 is prevented. Note that when the temperature of the hydraulic brake 14 decreases, the brake loss WB increases, so that the vehicle speed at which engagement / release of the hydraulic brake 14 is switched increases.

  In order to cancel the counter electromotive force generated by the reverse drive from the rear wheel 4 side when the first motor 5 is not operated, a control system is adopted in which the drive power for the counter electromotive force is input to the first motor 5. In this case, this driving power becomes a parameter representing the motor loss WM. Therefore, it is also possible to read the driving power of the first motor 5 in step S3-2 and perform the discrimination processing in steps S3-4 to S3-6 using this driving power instead of the motor loss.

  The vehicle speed at which the brake loss WB and the motor loss WM are equal is set as the first threshold value V1, and the change characteristic of the first threshold value V1 with respect to the temperature change of the hydraulic brake 14 is stored in the controller as a data table. The table is searched for the first threshold value V1 corresponding to the current temperature of the hydraulic brake 14 detected by the sensor 24, and the brake engagement permission flag F-preBon is set and reset by comparing the threshold value V1 with the vehicle speed V. It is also possible to do this. In this case, in order to prevent hunting of engagement / release of the hydraulic brake 14, a predetermined hysteresis ΔV is added, and when V ≦ V1, the brake engagement permission flag F-preBon is set to “1”, but V> After the brake engagement permission flag F-preBon is reset to “0” at V1, the brake engagement permission flag F-preBon is not set to “1” until V ≦ V1−ΔV.

  As described above, when the brake engagement permission flag F-preBon is set and reset in steps S3-7 and S3-8, the previous values WBold and WMold of the brake loss and the motor loss are next obtained in step S3-9. After updating to the values WB and WM, it is determined in step S3-10 whether or not the brake engagement permission flag F-preBon is set to “1”. If F-preBon = 1, the process proceeds to step S3-17, and the brake engagement flag F-Bon is set to “1”.

  On the other hand, if F-preBon = 0, the estimated value of the road surface friction coefficient μ is read in step S3-11. The road surface friction coefficient μ is estimated by the controller 8 by calculation based on the driving force of the front wheels 2, the rotational speed difference between the front wheels 2 and the rear wheels 4, and the like. Therefore, the controller 8 constitutes a road surface friction coefficient estimating means. Next, in step S3-12, it is determined whether or not the road surface friction coefficient μ is equal to or less than a predetermined value Yμ. If μ ≦ Yμ, the process proceeds to step S3-17. Therefore, when the vehicle speed threshold value (hereinafter referred to as the first threshold value V1) for switching between engagement and disengagement of the hydraulic brake 14 determined by comparing the brake loss WB and the motor loss WM is substantially infinite. As a result, the hydraulic brake 14 is always engaged.

  Here, when the front wheel 2 slips during traveling in the two-wheel drive mode with only the front wheel 2, the first motor 5 shifts to the four-wheel drive mode in which the rear wheel 4 is driven, but the hydraulic brake 14 is released. In this case, it takes some time until the hydraulic brake 14 is engaged, and the response of the rear wheel drive by the first motor 5 is deteriorated. On the road surface with a low friction coefficient μ such as a dirt road, there is a high possibility of slipping. Therefore, in this embodiment, the hydraulic brake 14 is always engaged when μ ≦ Yμ, and the first motor has good responsiveness when the front wheel slips. The rear wheel drive by 5 can be performed. Note that when μ ≦ Yμ, the hydraulic brake 14 may be released when the vehicle speed becomes equal to or higher than a predetermined speed set higher than the first threshold value V1.

  When μ> Yμ, after reading the outside air temperature Tatm detected by the outside air temperature sensor 25 in step S3-13, the outside air temperature Tatm is equal to or lower than a predetermined temperature YT (for example, 5 ° C.) in step S3-14. It is determined whether or not. If Tatm ≦ YT, it is determined in step S3-15 whether or not the vehicle speed V is equal to or lower than a second threshold value V2 (see FIG. 7) set higher than the first threshold value V1. If V> V2, the brake engagement flag F-Bon is reset to “0” in step S3-18. If V ≦ V2, the process proceeds to step S3-17. Therefore, during cold weather where Tatm ≦ YT, the vehicle speed range in which the hydraulic brake 14 is maintained in the engaged state is expanded to the high speed side. Here, when the vehicle is cold, the road surface is likely to freeze, and the front wheel 2 may suddenly slip when the vehicle 1 enters the freezing place. As a result, the frequency of performing the rear wheel drive by the first motor 5 during cold weather increases, but in the present embodiment, the rear wheel drive by the first motor 5 can be performed with good responsiveness over a wide vehicle speed range. Since the possibility of road surface freezing increases as the outside air temperature decreases, it is desirable to expand the vehicle speed range in which the hydraulic brake 14 is maintained in the engaged state to the higher vehicle speed side as the outside air temperature decreases. Therefore, in the present embodiment, as shown in FIG. 8, the second threshold value V2 is changed to the higher vehicle speed side as the outside air temperature becomes lower.

  When Tatm> YT, it is determined in step S13-16 whether or not the vehicle speed V is equal to or lower than a third threshold value V3 (for example, 50 km / h) set to be relatively low. If V> V3, the process proceeds to step S3-18. If V ≦ V3, the process proceeds to step S3-17. Therefore, the hydraulic brake 14 is always maintained in the engaged state in the low vehicle speed range where V ≦ V3. This is because in the low vehicle speed range, the frequency of performing the rear wheel drive by the first motor 5 is high, and it is required to improve the response of the rear wheel drive. In the low vehicle speed range, the difference between the brake loss WB and the motor loss WM is small, and the brake loss WB is also small. Therefore, even if the hydraulic brake 14 is always kept in an engaged state, there is a particular problem in terms of loss. Absent.

  The details of the brake engagement processing in step S2-7 are as shown in FIG. 5. First, in step S4-1, whether or not the previous value F-Boold of the brake engagement flag is “0”, that is, It is determined whether or not the hydraulic brake 14 is being released. When F-Bold = 1, that is, when the hydraulic brake 14 is engaged, the process proceeds to step S4-6 to maintain the hydraulic pressure command value PB of the hydraulic brake 14 at the previous value PBold. On the other hand, when F-Bold = 0, the slip amount (rotation speed of the ring gear 12b) ΔNB of the hydraulic brake 14 is read in step S4-2, and then the hydraulic command value change amount ΔPB is calculated in step S4-3. To do. This change amount ΔPB is retrieved from the data table shown in FIG. 9A using the basic amount ΔPBb retrieved from the brake slip amount ΔPB as a parameter, and from the data table shown in FIG. 9B using the temperature TB of the hydraulic brake 14 as a parameter. It is calculated by multiplying the temperature correction coefficient Kt (ΔPB = ΔPBb × Kt). Next, in step S4-4, it is determined whether or not the brake slip amount ΔNB is greater than a predetermined value YΔN. Update to the added value. Thereby, the hydraulic pressure of the hydraulic brake 14 is increased via the control valve 14a, and the hydraulic brake 14 is engaged. If ΔNB ≦ YΔN, the process proceeds to step S4-6, and the hydraulic pressure command value PB is not increased any more.

  The details of the brake release process in step S2-8 are as shown in FIG. 6. First, in step S5-1, whether or not the previous value F-Bond of the brake engagement flag is “1”, that is, hydraulic pressure It is determined whether or not the brake 14 is engaged. When F-Bond = 0, that is, when the hydraulic brake 14 is released, the routine proceeds to step S5-6, where the hydraulic pressure command value PB of the hydraulic brake 14 is made zero. On the other hand, if F-Boold = 1, the slip amount ΔNB of the hydraulic brake 14 is read in step S5-2, and then the hydraulic command value change amount ΔPB is calculated in step S5-3. Similar to the brake engagement process, the change amount ΔPB is changed from the data table shown in FIG. 9A to the basic amount ΔPBb searched using the brake slip amount ΔPB as a parameter, and from the data table shown in FIG. 9B to the hydraulic brake 14. The temperature is calculated by multiplying the temperature correction coefficient Kt searched using the temperature TB as a parameter. Next, in step S5-4, it is determined whether or not the previous value PBold of the hydraulic pressure command value is larger than the predetermined pressure YPB. If PBold> YPB, the hydraulic pressure command value PB is changed from the previous value PBold in step S5-5. The value ΔPB is updated to the value obtained by subtraction. Thereby, the hydraulic pressure of the hydraulic brake 14 is reduced via the control valve 14a, and the hydraulic brake 14 is released. If PBold ≦ YPB, the process proceeds to step S5-6, and the hydraulic pressure command value PB is set to zero.

  As described above, the hydraulic brake 14 is used as the friction engagement element that switches between the state where the power transmission between the first motor 5 and the rear wheel 4 can be performed and the state where the power transmission is impossible, and the present invention is applied as a control device for the hydraulic brake 14. However, it is also possible to use a hydraulic clutch that is interposed in series in the power transmission path between the first motor 5 and the rear differential gear 13 as the friction engagement element. The present invention can be similarly applied as a control device.

  In the above embodiment, the front wheel 2 is driven by the prime mover 3 and the rear wheel 4 is driven by the first motor 5. However, the rear wheel 4 is driven by the prime mover 3 and the front wheel 2 is driven by the first motor 5. It is also possible to drive. Further, as in the second embodiment shown in FIG. 10, the first motor 5 is connected to the front differential gear 7 via a hydraulic clutch 14 ′ as a friction engagement element, and the front wheel 2 is connected by the prime mover 3 and the first motor 5. Can also be driven. In this case as well, the present invention can be applied as a control device for the hydraulic clutch 14 'as in the above embodiment. In FIG. 10, the same reference numerals as those described above are attached to the same members as those in the above embodiment. Moreover, in the said embodiment, although the hybrid type power unit which consists of the engine 3a and the 2nd motor 3b is used as the motor | power_engine 3, you may comprise the motor | power_engine 3 only with an engine.

Explanatory drawing which shows the hybrid vehicle which comprises the control apparatus of embodiment of this invention. FIG. 2 is a flowchart showing overall control of the vehicle in FIG. 1. The flowchart which shows control of a hydraulic brake. The flowchart which shows the content of the brake engagement release determination process included in the control of FIG. The flowchart which shows the content of the brake engagement process included in the control of FIG. The flowchart which shows the content of the brake release process included in the control of FIG. The graph which shows the change characteristic with respect to the vehicle speed of a motor loss and a brake loss. The figure which shows the data table of the 2nd threshold value V2 used by the process of FIG. (a) The figure which shows the data table of basic quantity (DELTA) PBb used for calculation of (DELTA) PB in the process of FIG. 5, FIG. 6, (b) The figure which shows the data table of the temperature correction coefficient Kt used for calculation of (DELTA) PB. Explanatory drawing which shows the hybrid vehicle of 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Hybrid vehicle, 2 ... Front wheel, 3 ... Motor | power_engine, 4 ... Rear-wheel, 5 ... 1st motor (electric motor), 8 ... Controller (Control means for friction engagement elements, 1st thru | or 3rd threshold value correction means, road surface Friction coefficient estimating means), 14 ... hydraulic brake (friction engaging element), 14 '... hydraulic clutch (friction engaging element), 15 ... wheel speed sensor (vehicle speed detecting means), 24 ... brake temperature sensor (friction engaging element) Temperature detecting means), 25... Outside air temperature sensor (outside air temperature detecting means).

Claims (6)

Friction engagement provided in a hybrid vehicle having a prime mover and an electric motor as a drive source so that the power transmission between the electric motor and a wheel to be driven by the electric motor can be switched between a state where power transmission is possible and a state where it is impossible. An element control device,
A vehicle speed detecting means for detecting a vehicle speed; and when the electric motor is not operated, the friction engagement element is engaged so that the power can be transmitted if the detected vehicle speed of the vehicle speed detecting means is lower than a predetermined threshold, And a friction engagement element control means for releasing the friction engagement element so that the power transmission is disabled when the detected vehicle speed of the vehicle speed detection means is higher than the threshold.
Temperature detecting means for detecting the temperature of the friction engagement element;
And a first threshold value correcting means for correcting the threshold value so that the threshold value is changed to a higher vehicle speed side as the temperature detected by the temperature detecting means becomes lower. Control device. Loss due to dragging of the motor caused by engagement of the friction engagement element when the motor is not operated is motor loss, and friction of the friction engagement element caused by release of the friction engagement element when the motor is not operated Loss due to friction engagement element loss,
The first threshold value correction means is obtained from a change characteristic of the motor loss with respect to the vehicle speed and a change characteristic of the friction engagement element loss with respect to the vehicle speed when the temperature of the friction engagement element is equal to the detected temperature of the temperature detection means. 2. The control apparatus for a friction engagement element for an electric motor in a hybrid vehicle according to claim 1, wherein the threshold value is corrected to a vehicle speed at which the generated motor loss and friction engagement element loss are substantially equal. Outside temperature detecting means for detecting outside temperature;
When the detected temperature of the outside air temperature detecting means is equal to or lower than a predetermined temperature, the second threshold value is corrected to a second threshold value set at a higher vehicle speed side than the threshold value corrected by the first threshold value correcting means. The control device for a frictional engagement element for an electric motor in a hybrid vehicle according to claim 1, further comprising a threshold correction unit.   4. The hybrid vehicle according to claim 3, wherein the second threshold value correcting means is configured to change the second threshold value to a higher vehicle speed side as the detected temperature of the outside air temperature detecting means becomes lower. The control apparatus of the friction engagement element for electric motors in FIG. Road surface friction coefficient estimating means for estimating the friction coefficient of the road surface;
Third threshold correction means for correcting the threshold to a higher vehicle speed side than the threshold corrected by the first threshold correction means when the road friction coefficient estimated by the road friction coefficient estimation means is less than or equal to a predetermined value. The control device for a frictional engagement element for an electric motor in a hybrid vehicle according to any one of claims 1 to 4, wherein   6. The control device for a friction engagement element for an electric motor in a hybrid vehicle according to claim 1, wherein one of the front and rear wheels of the vehicle is driven by the prime mover and the other is driven by the electric motor. .

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