JP5951956B2 - Vehicle drive device - Google Patents

Description

  The present invention relates to a vehicle drive device, and more particularly to a vehicle drive device that can start reliably even when a traveling load is large on an uphill road or the like.

  2. Description of the Related Art A vehicle drive device that has an engine, a clutch, and a transmission and is controlled by an electronic control device that incorporates a microcomputer has become common. In this vehicle drive device, the accelerator pedal functions not as a means for operating the throttle valve of the engine but as a means for inputting the driver's intention to start and accelerate to the electronic control device. The electronic control unit detects the operation amount of the accelerator pedal, sets a target value (rotation speed and torque) of the engine output power by internal calculation, and controls the throttle valve to adjust the intake air amount and the fuel supply amount. In addition, the electronic control unit controls not only the engine but also the clutch and the transmission in a coordinated manner so as to perform smooth start, stop, and acceleration / deceleration. In general, a plurality of electronic control devices share functions and perform drive control.

  An example of technology for controlling this type of vehicle drive device is disclosed in Patent Document 1. The vehicle control apparatus disclosed in Patent Document 1 includes means for calculating a target rotational speed and target torque of the engine based on an accelerator operation amount, and means for controlling the engagement force of the lockup clutch so as to obtain the target rotational speed. And a means for controlling the engine torque so as to obtain the target torque. Thereby, it is supposed that the fuel consumption at the time of vehicle start can be improved without depending on the operation of the driver.

JP 2010-255660 A

  By the way, in Patent Document 1, the target rotational speed and target torque of the engine are calculated based on the accelerator operation amount, and the lockup clutch and the engine are controlled. However, the vehicle start requiring a large torque cannot be performed satisfactorily. There is a fear. In particular, when the traveling load is large on an uphill road or an uneven road with unevenness, the vehicle driving force is insufficient at the target rotational speed and target torque based on the accelerator operation amount, and the output rotational speed increases as the clutch engagement progresses. It tends to decrease. When the output rotational speed falls to a low rotational speed range of the engine output torque characteristic, the output torque decreases as the output rotational speed decreases.

  Such a phenomenon can be avoided if the driver depresses the accelerator pedal strongly and starts the vehicle with a large output torque when the traveling load is large. However, it is desirable that the vehicle can start reliably regardless of the travel load or the amount of operation of the accelerator pedal. In other words, it is desirable to set an output rotation speed and output torque that can sufficiently cope with the traveling load without being restricted by the amount of operation of the accelerator pedal when starting when the traveling load is large.

  The present invention has been made in view of the above-mentioned problems of the background art, and always and reliably and quickly by variably controlling the output speed and output torque of the engine in response to the magnitude of the running load at the start of the vehicle. It is an object to be solved to provide a vehicle drive device that can perform a smooth start.

The vehicle drive device of the present invention includes an engine that can variably adjust the output rotational speed and output torque of an output shaft by controlling output power, a clutch that is rotatably connected to the output shaft of the engine, and A transmission connected to the output side of the clutch, a power train for transmitting the output power to the drive wheels, and the output rotational speed of the engine based on a state of the vehicle including an operation amount of an accelerator pedal; A control unit configured to set at least one target value of the output torque and control the engine so that at least one of the output rotation speed and the output torque matches the target value, wherein the control The load estimating means for estimating the traveling load at the time of starting the vehicle, and the engine required to obtain the vehicle propulsion force corresponding to the estimated traveling load Lower limit value setting means for variably setting a lower limit value of the output speed, and propulsive force holding means for largely controlling the output power of the engine when the output speed of the engine decreases and reaches the lower limit value And the lower limit value is set to be smaller than the rotational speed at which the output torque is maximum in the mountain-shaped characteristic curve of the output torque characteristic of the engine and larger than the rotational speed at which there is a risk of engine stall. ing.

  Further, the engine has a throttle valve that can variably adjust the output rotational speed and output torque of the output shaft by adjusting the intake air amount, and the propulsive force holding means largely controls the opening degree of the throttle valve. The output power of the engine may be largely controlled by increasing the intake air amount.

Further, the propulsive force holding means controls the output power of the engine to be greater than or equal to a predetermined lower limit value when the output speed decreases and reaches the lower limit value of the output speed. It is preferable to adjust to.

  Furthermore, it is preferable that the load estimating means estimates that the traveling load is larger as the inclination of the time increase of the output rotational speed of the engine or the input rotational speed of the transmission when the vehicle starts is smaller.

  Further, the lower limit value setting means holds a lower limit value map for setting at least one of the lower limit value of the output rotation speed and the lower limit value of the output torque using the operation amount of the accelerator pedal and the traveling load as parameters. Also good.

According to the vehicle drive device of the present invention, the control unit estimates the traveling load at the time of starting the vehicle, and variably sets the lower limit value of the output rotational speed necessary for obtaining the vehicle driving force corresponding to the traveling load. When the actual output speed decreases and reaches the set lower limit value, the output power of the engine is largely controlled. Therefore, even when the driving load is high on an uphill road, the vehicle driving force can be secured by obtaining an output speed and output torque sufficient to handle the driving load without being restricted by the amount of operation of the accelerator pedal . Always start reliably and quickly while avoiding fear .

  Further, in an aspect in which the engine has a throttle valve, the output power of the engine can be largely controlled by increasing the intake amount by largely controlling the opening of the throttle valve, and the same effect as in claim 1 is produced.

  Furthermore, when the output speed decreases and reaches the lower limit value, the output torque is adjusted to the lower limit value or more, and even when the output speed falls to the low speed range of the engine torque characteristics, the lower limit value is reached. The above output rotation speed and output torque can be secured. As a result, the required vehicle propulsion force can be ensured and the vehicle can always start reliably and quickly.

  Further, in an aspect in which it is estimated that the traveling load increases as the inclination of the time increase of the engine output rotational speed or the transmission input rotational speed when the vehicle starts is small, the index is highly correlated with the acceleration applied to the vehicle. To estimate the running load. Accordingly, the estimation accuracy of the running load is high, and the lower limit value of at least one of the output rotation speed and the output torque can be set appropriately. If the accuracy of the running load is low and the lower limit value is set too small, the timing for greatly controlling the engine output power is delayed and time is required for starting. If the lower limit value is set too large, the output power of the engine becomes extremely larger than the power corresponding to the amount of operation of the accelerator pedal, and acceleration more than expected occurs, resulting in a decrease in drivability.

  Moreover, in the aspect in which the lower limit setting means holds the lower limit map, the lower limit of at least one of the output rotation speed and the output torque can be set appropriately and easily.

It is a lineblock diagram showing typically the vehicle drive device of the embodiment of the present invention. It is a figure of the output torque characteristic of an engine which explains typically a function of a lower limit value setting means and propulsion power maintenance means in case there is running load at the time of vehicle starting. It is a time chart explaining operation | movement when there exists driving | running | working load at the time of vehicle start with the vehicle drive device of embodiment. It is a time chart explaining operation | movement when there exists driving | running | working load at the time of vehicle start with the vehicle drive device of a prior art.

  An embodiment for carrying out the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram schematically showing a vehicle drive device 1 according to an embodiment of the present invention. The thick lines in the figure indicate the power train path, and the broken arrows indicate the flow of information and control. The vehicle drive device 1 according to the embodiment includes an engine 2, a clutch 3 and a transmission 4 that constitute a power train, a control unit 7, and the like.

  As the engine 2, an engine having a known general method / structure, for example, a gasoline engine using gasoline as a fuel, a diesel engine using light oil as a fuel, or the like can be used. The engine 2 has an output shaft 21, a throttle valve 22, and an output rotation speed sensor 23. The output shaft 21 rotates integrally with a crankshaft that is driven to rotate by a piston and outputs power. The throttle valve 22 is disposed in the middle of a path for taking air in the engine room into the engine, and the opening degree S is variably controlled by the control unit 7. When the opening degree S of the throttle valve 22 is largely controlled and the intake air amount increases, the supply amount of the air-fuel mixture containing fuel increases, the output power from the output shaft 21 increases, and the output rotational speed NE and the output torque TE. Has come to increase. The output rotation speed sensor 23 is disposed in the vicinity of the output shaft 21, detects the output rotation speed NE of the output shaft 21, and sends a detection signal to the control unit 7.

  The clutch 3 is rotationally coupled to the output shaft 21 of the engine 2 so as to be able to be connected and disconnected, and a dry friction clutch is used in this embodiment. The clutch 3 includes a drive side member 31 that is rotationally connected to the output shaft 21 of the engine 2, and a driven side member 32 that is adjusted to a connected state and a disconnected state with respect to the drive side member 31. Operated. When the clutch actuator 33 performs a joint operation based on a command from the control unit 7, the torque that can be transmitted by frictional sliding between the driving side member 31 and the driven side member 32 is adjusted, and the driving side member 31 and the driven side are adjusted. The member 32 is synchronously rotated by frictional coupling. The clutch actuator 33 can be configured using a servo motor, a hydraulic operation mechanism, or the like. The transmission 4 is rotationally connected to the output side of the clutch 3, and for example, a stepped automatic transmission can be used. The transmission 4 includes an unillustrated transmission gear set that constitutes a plurality of shift stages, and an unillustrated synchronization device for synchronously coupling the respective transmission gear sets. In the transmission 4, the transmission actuator 43 drives the synchronizer in response to a command from the control unit 7 so that one transmission gear set is selectively meshed. The input shaft 41 of the transmission 4 is rotationally connected to the driven member 32 of the clutch 3, and the output shaft 42 is rotationally connected to the differential device 5. An input rotation speed sensor 44 is disposed in the vicinity of the input shaft 41, detects the input rotation speed Ni of the input shaft 41, and sends a detection signal to the control unit 7.

  The output side of the differential device 5 is rotationally connected to a pair of left and right drive wheels 6. A path from the clutch 3 to the drive wheel 6 via the transmission 4 and the differential device 5 is a power train that transmits the output power of the engine 2.

  The control unit 7 is configured by an electronic control unit (ECU) that incorporates a microcomputer and operates by software. The control unit 7 acquires information on the accelerator opening degree Ac representing the operation amount as a relative value from an accelerator sensor 82 that detects the operation amount of the accelerator pedal 81. Then, the control unit 7 sets a target value of at least one of the output speed and output torque of the engine 2 based on the state of the vehicle including the accelerator opening degree Ac, and sets the output speed NE and output torque TE to the target values. The opening S of the throttle valve 22 of the engine 2 is variably controlled so that at least one of the two coincides. In addition to the accelerator opening degree Ac, the vehicle speed, the output rotational speed NE of the engine 2, the input rotational speed Ni of the transmission 4, the shift speed selected by the transmission 4, the brake not shown The pedal operation amount, the steering operation amount of the steering wheel (not shown), etc. are referred to as appropriate.

  Further, the control unit 7 controls the clutch actuator 33 of the clutch 3 to control the joining operation and the disconnecting operation, and controls the transmission actuator 43 of the transmission 4 to control the shift speed switching operation. Furthermore, the control unit 7 has three functional means mainly realized by software, that is, a load estimation means 71, a lower limit value setting means 72, and a propulsion force holding means 73, which will be described in detail below.

  The load estimation means 71 is a means for estimating a traveling load when the driver D depresses the accelerator pedal 81 to start the vehicle. The load estimating means 71 estimates that the traveling load is larger as the inclination of the time increase of the output rotational speed NE of the engine 2 or the input rotational speed Ni of the transmission 4 at the time of starting the vehicle is smaller, and uses this traveling load map. Make an estimate.

  For example, the load estimation means 71 acquires the input rotational speed Ni of the transmission 4 at a constant time interval, and calculates the increment every time. This calculation means obtaining the increase rate of the input rotational speed Ni, and corresponds to obtaining an index having a very high correlation with the acceleration of the vehicle. As is well known, when the constant output torque TE is generated, the traveling load is larger as the acceleration applied to the vehicle is smaller. Therefore, a travel load map for estimating the travel load is created in advance using the opening degree S of the throttle valve 22 of the engine 2 and the gradient of the increase in the input rotational speed Ni as parameters, and is stored in the control unit 7. The opening degree S of the throttle valve 22 is a parameter that governs the output torque TE of the engine 2, and indirectly uses the output torque TE as a parameter. And the load estimation means 71 estimates a driving | running load using a driving | running | working load map.

  Note that the load estimating means 71 can be similarly configured by using the output rotational speed NE of the engine 2 instead of the input rotational speed Ni of the transmission 4, but it is necessary to consider the state of the clutch 3. Furthermore, the load estimating means 71 is not limited to the above-described configuration. As an alternative means, even if the acceleration is estimated from the detection information of a wheel speed sensor (not shown) or the acceleration is directly measured to measure the acceleration, The load can be estimated.

  The lower limit setting unit 72 is a unit that variably sets the lower limit values Nmin and Tmin of at least one of the output rotation speed and the output torque necessary for obtaining the vehicle driving force corresponding to the estimated traveling load. Here, the running load acts to reduce the acceleration applied to the vehicle against the output torque TE of the engine 2, so qualitatively, the lower limit value Tmin of the output torque is set larger as the running load is larger. Quantitatively, a torque lower limit value map for variably setting the lower limit value Tmin of the output torque with the travel load as a parameter is created in advance and held in the control unit 7, and the lower limit value setting means 72 uses this map. The lower limit value Tmin is set.

  Further, the lower limit value setting means 72 sets the lower limit value Nmin of the output speed with reference to the output torque characteristics of the engine 2. More specifically, the output torque characteristic of the engine 2 is a basic characteristic that is referred to when the engine 2 is controlled, and the control unit 7 holds the output torque characteristic in the form of a map in a list form, for example. In general, the output torque characteristic is represented by a graph showing the relationship between the output rotational speed NE on the horizontal axis and the output torque TE on the vertical axis, with the opening degree S of the throttle valve 22 as a parameter. The output torque characteristic of the engine 2 has a mountain-shaped characteristic curve in which the output torque TE is the largest in the middle and middle speed range NM of the output speed NE, and the output torque TE gradually decreases in the low speed range NL and the high speed range NH. Yes.

  Here, in the high rotational speed range NH of the output torque characteristic, the output torque TE increases as the output rotational speed NE decreases. Therefore, there is a possibility that the output torque TE can be maintained and stable start can be performed even if the acceleration is temporarily reduced due to a traveling load when the vehicle starts. However, in the low rotational speed range NL of the output torque characteristic, the output torque TE decreases as the output rotational speed NE decreases. Therefore, when the vehicle starts and there is a running load and the acceleration temporarily decreases, the output torque TE also decreases and the vehicle speed decreases, and a stable start cannot be expected and the engine stalls. In order to avoid such a situation, the lower limit value Nmin of the output rotation speed is set before the peak characteristic curve of the output torque characteristic falls to the low rotation range NL or at an initial stage of the low rotation range NL.

  By the way, the shape and position of the mountain-shaped curve of the output torque characteristic of the engine 2 change depending on the opening degree S of the throttle valve 22, and the above-described range of the low rotation region NL also changes. Further, the opening degree S of the throttle valve 22 is controlled in association with the accelerator opening degree Ac of the accelerator pedal 81 before the thrust holding means 73 described later functions. Accordingly, a rotation speed lower limit value map for variably setting the lower limit value Nmin of the output rotation speed with the accelerator opening Ac of the accelerator pedal 81 as a parameter is created in advance and held in the control unit 7. Uses this map to set the lower limit Nmin.

  The propulsion force holding means 73 is means for largely controlling the output power of the engine 2 when at least one of the output rotational speed NE and the output torque TE of the engine 2 decreases and reaches the lower limit values Nmin and Tmin. Specifically, it is means for largely controlling the opening degree S of the throttle valve 22. Further, when the output rotational speed NE decreases and reaches the lower limit value Nmin, the propulsive force holding means 73 controls the opening degree S of the throttle valve 22 to adjust the output torque TE to be equal to or higher than the lower limit value Tmin. . Supplementally, the propulsive force holding means 73 largely controls the opening S of the throttle valve 22 as necessary in order to secure the vehicle propulsive force even if the accelerator opening Ac of the accelerator pedal 81 is constant.

  FIG. 2 is a diagram of output torque characteristics of the engine 2 for schematically explaining the functions of the lower limit value setting means 72 and the propulsion force holding means 73 when there is a traveling load when the vehicle starts. Specifically, (1) in FIG. 2 shows the setting of the lower limit value Tmin of the output torque by the lower limit setting means 72, (2) shows the transition of the operating point of the engine 2 when there is a traveling load, (3 ) Shows the setting of the lower limit value Nmin of the output speed by the lower limit value setting means 72, the control of the opening degree S of the throttle valve 22 by the propulsive force holding means 73, and the transition of the operating point of the engine 2.

  In FIG. 2 (1), when the load estimating means 71 estimates the running load at the start of the vehicle, the lower limit value setting means 72 sets the lower limit value Tmin of the output torque corresponding to the running load using the torque lower limit value map. . Further, as shown in FIG. 2 (2), when the engine 2 is operated at the opening S1 of the throttle valve 22 associated with the accelerator opening Ac of the accelerator pedal 81 at the time of starting the vehicle, the output torque TE becomes the lower limit. It is smaller than the value Tmin. For this reason, the vehicle propulsive force is insufficient, and the operating point of the engine 2 is changed from the operating point P1 in the high rotation region NH of the mountain-shaped curve characteristic of the opening degree S1, to the operating point P2 and the operating point P3 in the intermediate rotation region NM. Then, it moves to the operating point P4 in front of the low rotation range NL. As a result, the vehicle speed decreases and the output torque TE also decreases. If left as it is, the operating point may move further to the low rotation side as indicated by the arrow P5, leading to an engine stall.

  On the other hand, as shown in (3) of FIG. 2, the lower limit value setting means 72 uses the rotation speed lower limit value map to set the lower limit value Nmin of the output rotation speed near the operating point P4 before the low rotation speed range NL. Set to. Then, when the output rotational speed NE of the engine 2 decreases and reaches the operating point P4, the propulsive force holding means 73 largely controls the opening degree S1 of the throttle valve 22. Further, the propulsive force holding means 73 controls the opening degree S2 of the throttle valve 22 so that the actual output torque TE becomes the lower limit value Tmin of the output torque. Thereby, the operating point of the engine 2 moves from the operating point P4 on the opening degree S1 to the operating point P6 on the opening degree S2, and the lower limit value Tmin of the output torque is satisfied, and the vehicle driving force is ensured. Thereafter, acceleration is applied to the vehicle to increase the vehicle speed, and the operating point of the engine 2 moves to the high rotation side on the opening S2 as indicated by an arrow P7.

  Next, operation | movement of the vehicle drive device 1 of embodiment is demonstrated compared with a prior art. FIG. 3 is a time chart for explaining the operation when there is a traveling load when the vehicle starts in the vehicle drive device 1 according to the embodiment. FIG. 4 is a time chart for explaining the operation when there is a traveling load when the vehicle starts with the vehicle drive device of the prior art. 3 and 4, the upper row shows the rotational speed N, the middle row shows the torque T, the lower row shows the accelerator opening degree Ac, and the horizontal axis is the common time t.

  In FIG. 3 showing the embodiment, when the depression operation of the accelerator pedal 81 is started at time t1, the vehicle start control is started, and the accelerator opening Ac is gradually increased as shown in the lower stage. Then, at the time t2 delayed by the response time of the engine 2 and the clutch 3, a substantial increase in the output power of the engine 2 and the clutch engagement operation are started. That is, the output rotational speed NE (shown by a solid line) of the engine 2 shown in the upper stage suddenly increases from the idle rotational speed NEi, and the output torque TE (shown by a solid line) in the middle stage gradually increases. In addition, the torque Tc (indicated by the alternate long and short dash line) that can be transmitted as shown in the middle stage is gradually increased as the engagement operation of the clutch 3 gradually proceeds, and the input shaft 41 of the transmission 4 is rotationally driven by the transmission of the torque Tc, The input rotational speed Ni (indicated by the alternate long and short dash line) shown in the upper stage also increases gradually.

  During the time period when the accelerator opening degree Ac is gradually increasing, the load estimating means 71 and the lower limit value setting means 72 variably set the lower limit value Tmin (shown by the broken line) of the output torque and the lower limit value Nmin of the output speed. . In this example, since there is a traveling load, the output torque TE of the engine 2 is insufficient with respect to the lower limit value Tmin. At time t3, the accelerator opening Ac stops increasing, the torque Tc that can be transmitted by the clutch 3 is increased, and the joining operation is almost finished.

  At this time t3, the output rotational speed NE of the engine 2 decreases to the lower limit value Nmin, and the propulsive force retaining means 73 operates. That is, corresponding to the movement from the operating point P4 to the operating point P6 in (3) of FIG. 2, the opening degree S of the throttle valve 22 is greatly adjusted, and the output torque TE increases sharply to the lower limit value Tmin. Will be equal. Thereafter, the output torque TE of the engine 2 and the torque Tc that can be transmitted by the clutch 3 change substantially coincident with each other. Further, at time t4, the output rotational speed NE of the engine 2 and the input rotational speed Ni of the transmission 4 coincide with each other and rotate synchronously. Thereby, the required vehicle propulsion force can be ensured and a reliable and quick start can be performed. Thereafter, when the accelerator pedal 81 is further depressed at time t5, the rotational speeds NE, Ni and torques TE, Tc increase stably, and stable acceleration performance is obtained.

  On the other hand, when the same vehicle start control is performed in FIG. 4 showing the prior art, the same control is performed before time t3 except for the lower limit values Tmin and Nmin. Then, at time t3, the accelerator opening Ac stops increasing, and the opening S of the throttle valve 22 is not adjusted even if the engagement operation of the clutch 3 is almost completed. For this reason, the state where the output torque TE is insufficient with respect to the lower limit value Tmin of the output torque is not resolved after the time t3. As a result, the rotational speeds NE and Ni do not increase, the required vehicle propulsion force cannot be secured, and reliable and quick start cannot be performed. Further, even when the accelerator pedal 81 is further depressed at time t5, the increase in the rotational speed NE, Ni, and the torque TE, Tc is slow, and stable acceleration performance cannot be obtained.

  According to the vehicle drive device 1 of the embodiment, the lower limit value Tmin of the output torque of the engine 2 is set according to the traveling load at the start of the vehicle, and the output rotational speed of the engine 2 according to the accelerator opening degree Ac of the accelerator pedal 81. The lower limit value Nmin is set. Then, when the output rotational speed NE decreases and reaches the lower limit value Nmin, the opening degree S of the throttle valve 22 of the engine 2 is largely controlled so that the output torque TE is adjusted to the lower limit value Tmin. Therefore, even when the traveling load is large on an uphill road or the like, the vehicle driving force can be secured by obtaining the output rotational speed NE and the output torque TE that can sufficiently cope with the traveling load without being restricted by the operation amount of the accelerator pedal 81. Always start reliably and quickly.

  Further, the traveling load is estimated from an index that has a very high correlation with the gradient of the temporal increase in the input rotational speed Ni of the transmission 4 when the vehicle starts, that is, the acceleration applied to the vehicle. Therefore, the estimation accuracy of the running load is high, the output rotation speed NE and the lower limit values Tmin and Nmin of the output torque NT can be set appropriately, and it does not take time to start or reduce drivability.

  Further, since the lower limit value setting means 72 holds the torque lower limit value map and the rotation speed lower limit value map, the lower limit values Tmin and Nmin can be set appropriately and easily.

  The traveling load estimation method by the load estimation means 71 and the lower limit values Tmin and Nmin setting methods by the lower limit value setting means 72 are not limited to the above-described embodiment. In addition, the present invention can be variously applied and modified.

1: Vehicle drive device 2: Engine 21: Output shaft 22: Throttle valve 23: Output rotation speed sensor 3: Clutch
31: Drive side member 32: Driven side member 33: Clutch actuator 4: Transmission
41: input shaft 42: output shaft 43: transmission actuator
44: Input speed sensor 5: Differential device 6: Drive wheel 7: Control unit 71: Load estimation means 72: Lower limit value setting means 73: Propulsion force holding means 81: Accelerator pedal 82: Accelerator sensor Ac: Accelerator opening degree S, S1, S2: Throttle valve opening NE: Engine output speed Ni: Transmission input speed TE: Engine output torque Tc: Torque that can be transmitted by clutch Nmin: Lower limit of output speed Tmin: Output torque lower limit

Claims (5)

An engine that can variably adjust the output speed and output torque of the output shaft by controlling the output power;
A power train that includes a clutch that is rotatably connected to the output shaft of the engine and a transmission that is rotationally connected to an output side of the clutch, and that transmits the output power to driving wheels;
A target value of at least one of the output rotational speed and the output torque of the engine is set based on a state of the vehicle including an operation amount of an accelerator pedal, and at least one of the output rotational speed and the output torque matches the target value. And a control unit for controlling the engine as described above,
The controller is
Load estimating means for estimating a running load at the time of vehicle start;
Lower limit value setting means for variably setting a lower limit value of the output speed of the engine required for obtaining a vehicle propulsion force corresponding to the estimated traveling load;
Propulsive force holding means for largely controlling the output power of the engine when the output speed of the engine decreases and reaches the lower limit value,
The lower limit value is a vehicle drive apparatus in which the lower limit value is set to be smaller than the rotational speed at which the output torque is maximum in the mountain-shaped characteristic curve of the engine output torque characteristic and larger than the rotational speed at which there is a risk of engine stall . The engine has a throttle valve that can variably adjust the output rotational speed and output torque of the output shaft by adjusting the intake air amount,
2. The vehicle drive device according to claim 1, wherein the propulsion force holding means largely controls the output power of the engine by largely controlling an opening degree of the throttle valve and increasing the intake air amount. The propulsive force holding means controls the output torque of the engine to be larger than a predetermined lower limit value by largely controlling the output power of the engine when the output speed decreases and reaches the lower limit value of the output speed. The vehicle drive device according to claim 1 or 2.   The load estimation means estimates that the traveling load is larger as the inclination of the time increase of the output rotation speed of the engine or the input rotation speed of the transmission is smaller when the vehicle starts. The vehicle drive device according to item.   The lower limit value setting means holds a lower limit value map for setting at least one of a lower limit value of the output rotation speed and a lower limit value of the output torque using the operation amount of the accelerator pedal and the travel load as parameters. The vehicle drive device as described in any one of 1-4.

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