Vehicle running gear

Abstract

To provide a vehicle travelling device which causes an internal combustion engine to start and or to stop in accordance with required power, and which can output power enabling a vehicle to travel at high energy efficiency.SOLUTION: A vehicle travelling device 10 performs travelling control which controls power output from an internal combustion engine and from a motor to cause a vehicle 100 to travel autonomously. The travelling control enables the vehicle to coast in order to decelerate the vehicle. The vehicle travelling device causes the internal combustion engine to start when required power reaches a first start determination value, in accelerating the vehicle when not performing the travelling control, and causes the internal combustion engine to start when the required power reaches a second start determination value, in acceleration of the vehicle when performing the travelling control. The second start determination value is set to be a value smaller than the first start determination value.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a vehicle travel apparatus.

Background Art

[0002] A hybrid vehicle that travels using engine power and motor power is known. The engine power is power output from an internal combustion engine of a drive device, and the motor power is power output from a motor of the drive device. When the required power is relatively high, the hybrid vehicle travels using both engine power and motor power, and when the required power is relatively low, the hybrid vehicle travels using only motor power. Accordingly, the internal combustion engine of the hybrid vehicle is started when the required power increases and reaches a predetermined value (engine start determination value), and is stopped when the required power decreases and reaches a predetermined value (engine stop determination value). A hybrid vehicle configured to operate the internal combustion engine at an optimal operating point or an operating point near the optimal operating point is also known. The optimal operating point is an operating point at which the fuel consumption rate of the internal combustion engine is minimized. The operating point is a point defined by the rotational speed of the internal combustion engine and the load on the internal combustion engine.

[0003] There is also known a vehicle travel apparatus that sets the engine stop determination value to a value lower than the engine start determination value in order to prevent frequent starting and stopping of the internal combustion engine of a hybrid vehicle. Furthermore, there is also known a vehicle travel apparatus that executes automatic driving for causing a hybrid vehicle to travel autonomously by autonomously controlling acceleration and deceleration of the hybrid vehicle.

[0004] Furthermore, in a hybrid vehicle, fluctuations in required power are smaller during automatic driving than during manual driving. Therefore, during automatic driving, even if the difference (hysteresis) between the engine start determination value and the engine stop determination value is smaller than that during manual driving, there is a possibility that the frequency of starting and stopping the internal combustion engine can fall within an allowable range. Accordingly, there is also known a vehicle travel apparatus configured to reduce hysteresis by setting the engine stop determination value to a larger value during automatic driving than during manual driving (see, for example, Patent Document 1).

Prior Art Literature

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-54111 [Overview of the project]

[0006] Incidentally, in hybrid vehicles, setting a high engine start threshold is effective in preventing frequent starting and stopping of the internal combustion engine. On the other hand, if the engine start threshold is set high, even though the internal combustion engine could be operated at its optimal operating point to output power to drive the vehicle with high energy efficiency, the engine will not be started, and the motor alone will have to output the power equivalent to the required power. As a result, the drive system will be operated in an energy-inefficient state.

[0007] The object of the present invention is to provide a vehicle running gear that starts and stops an internal combustion engine according to the required power, and that can output power to drive a vehicle with high energy efficiency.

[0008] The vehicle running gear according to the present invention is a device that performs driving control to autonomously drive a vehicle by controlling the power output from an internal combustion engine and a motor. The driving control is a control that controls the power so that an index value representing the driving state of the vehicle is maintained within a predetermined range, and when decelerating the vehicle, it is a control that decelerates the vehicle by coasting. When the vehicle running gear according to the present invention accelerates the vehicle when the driving control is not being performed, it operates only the motor with the internal combustion engine stopped while the required power is less than a first start determination value to accelerate the vehicle, and starts the internal combustion engine to accelerate the vehicle when the required power reaches the first start determination value. When the vehicle is being accelerated while the driving control is being performed, it operates only the motor with the internal combustion engine stopped while the required power is less than a second start determination value to accelerate the vehicle, and starts the internal combustion engine to accelerate the vehicle when the required power reaches the second start determination value. The second start determination value is set to a value smaller than the first start determination value.

[0009] According to the present invention, when driving control, which utilizes coasting to decelerate the vehicle, is being performed, the internal combustion engine is started when the required power is lower compared to when driving control is not being performed. Therefore, it is prevented from driving the vehicle solely on the power output from the motor until the required power becomes relatively high, so that power can be output to drive the vehicle with high energy efficiency.

[0010] Furthermore, the vehicle running device according to the present invention is front record run During row control, the system may be configured to limit the power output from the internal combustion engine to a predetermined upper limit value from the time the internal combustion engine is started until exhaust recirculation control is initiated to recirculate the exhaust gas back into the internal combustion engine.

[0011] When exhaust recirculation control is not in operation, if the power output from the internal combustion engine is large, the energy efficiency for outputting power to drive the vehicle decreases. According to the present invention, until exhaust recirculation control is initiated, the power output from the internal combustion engine is limited to a predetermined upper limit. Therefore, it is possible to avoid a decrease in energy efficiency when outputting power to drive the vehicle.

[0012] Furthermore, in the vehicle running device according to the present invention, the predetermined upper limit may be set based on the running state of the vehicle.

[0013] The predetermined upper limit limits the power output from the internal combustion engine, and the power required from the internal combustion engine varies depending on the vehicle's driving conditions. Therefore, it is preferable to set the predetermined upper limit according to the vehicle's driving conditions. According to the present invention, the predetermined upper limit is set based on the vehicle's driving conditions. Therefore, a suitable predetermined upper limit can be set.

[0014] Furthermore, in the vehicle running device according to the present invention, the running state includes, for example, information on the inter-vehicle distance, which is the distance between the vehicle and the preceding vehicle. In this case, the predetermined upper limit may be set to a smaller value when the inter-vehicle distance is less than the predetermined inter-vehicle distance compared to when the inter-vehicle distance is equal to or greater than the predetermined inter-vehicle distance.

[0015] When the distance between vehicles is small, the likelihood of accelerating the vehicles for an extended period is low, and therefore, the power output from the internal combustion engine can be small to accelerate the vehicles. Furthermore, reducing the power output from the internal combustion engine can improve the energy efficiency of the internal combustion engine. According to the present invention, when the distance between vehicles is small and therefore the likelihood of accelerating the vehicles for an extended period is low, the predetermined upper limit is set to a small value. As a result, the power output from the internal combustion engine is kept low, and the energy efficiency of the internal combustion engine can be improved.

[0016] Furthermore, in the vehicle running device according to the present invention, the running state includes, for example, information on whether or not the vehicle is running on a downhill road. In this case, the predetermined upper limit may be set to a smaller value when the vehicle is running on the downhill road than when the vehicle is not running on the downhill road.

[0017] When a vehicle is traveling downhill, the likelihood of accelerating the vehicle for an extended period is low, and therefore, the power output from the internal combustion engine may be small to accelerate the vehicle. Reducing the power output from the internal combustion engine improves the energy efficiency of the engine. According to the present invention, when a vehicle is traveling downhill and therefore, the likelihood of accelerating the vehicle for an extended period is low, the predetermined upper limit is set to a small value. As a result, the power output from the internal combustion engine is kept low, improving the energy efficiency of the engine.

[0018] The components of the present invention are not limited to the embodiments described below with reference to the drawings. Other objects, features, and incidental advantages of the present invention will be readily apparent from the description of the embodiments. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a diagram showing a vehicle running gear according to an embodiment of the present invention. [Figure 2] Figure 2(A) shows a scene where driving speed control is being performed, and Figure 2(B) shows a scene where inter-vehicle distance control is being performed. [Figure 3] Figure 3 is a flowchart showing the routine executed by a vehicle running device according to an embodiment of the present invention. [Figure 4] Figure 4(A) shows a scene where driving speed control is being performed, and Figure 4(B) shows a scene where inter-vehicle distance control is being performed. [Figure 5] Figure 5 is a flowchart showing the routine executed by a vehicle running device according to an embodiment of the present invention. [Figure 6] Fig. 6 is a flowchart showing a routine executed by the vehicle travel device according to the embodiment of the present invention. Mode for Carrying Out the Invention

[0020] Hereinafter, a vehicle travel device according to an embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, the vehicle travel device 10 according to the embodiment of the present invention is mounted on a vehicle 100 or a host vehicle 100. The vehicle travel device 10 includes an ECU (electronic control unit) 90.

[0021] The vehicle travel device 10 is configured to execute travel control or automatic driving control. Travel control is control for causing the vehicle 100 to travel by autonomously controlling the drive device 20 and the braking device 30 to accelerate and decelerate the vehicle 100, and in this example, the travel control is travel speed control and inter-vehicle distance control. Further, in this example, the drive device 20 includes an internal combustion engine 21 and a motor 22, and the braking device 30 includes a hydraulic brake device 31.

[0022] Travel speed control, as shown in (A) of Fig. 2, is control executed when there is no preceding vehicle ahead of the vehicle 100, and is control that autonomously controls the drive device 20 and the braking device 30 based on a difference between the travel speed V of the vehicle 100 and a set speed Vset. The set speed Vset is the travel speed V of the vehicle 100 set by a user (particularly, a driver) of the vehicle 100. Note that the vehicle travel device 10 acquires the travel speed V of the vehicle 100 by means of a vehicle speed detection device 45. Further, the travel speed V of the vehicle 100 is an index value representing the travel state of the vehicle 100.

[0023] Furthermore, the inter-vehicle distance control, as shown in Figure 2(B), is a control that is executed when a preceding vehicle 200 is present in front of vehicle 100, and autonomously controls the drive unit 20 and the braking unit 30 based on the difference between the inter-vehicle distance D and the target inter-vehicle distance Dtgt. The inter-vehicle distance D is the distance between vehicle 100 and the preceding vehicle 200. The target inter-vehicle distance Dtgt is the inter-vehicle distance D set by the user of vehicle 100 (especially the driver). Note that the inter-vehicle distance D is an index value representing the driving state of vehicle 100.

[0024] The operation of the vehicle running gear 10 will be explained in more detail below. The vehicle running gear 10 executes the routine shown in Figure 3 at a predetermined calculation cycle. When the vehicle running gear 10 starts processing from step S300 of the routine shown in Figure 3, it proceeds to step S305 and determines whether the driving control execution condition C0 is met. The driving control execution condition C0 is the condition that the execution of driving control is requested. The user of the vehicle 100 (especially the driver) can request the execution of driving control from the vehicle running gear 10 by operating the driving control request operator 51 (driving support button).

[0025] If the vehicle running gear 10 determines "Yes" in step S305, it proceeds to step S310 to determine whether the first condition C1 is met. The first condition C1 is that the execution of the second running control or economy running control is not requested. The user of the vehicle 100 (especially the driver) can request the vehicle running gear 10 to execute the second running control by operating the second running control request operator 52 (economy running button). In this example, the second running control is the second running speed control and the second inter-vehicle distance control, which will be described later.

[0026] If the vehicle running gear 10 determines "Yes" in step S310, it executes the first running control. In this example, the first running control is the first running speed control and the first inter-vehicle distance control, which will be described later.

[0027] More specifically, if the vehicle running gear 10 determines "Yes" in step S310, it proceeds to step S315 to determine whether or not a preceding vehicle 200 exists. The vehicle running gear 10 can determine whether or not a preceding vehicle 200 exists based on the surrounding detection information IS. The surrounding detection information IS is information provided by the surrounding information detection device 60. In this example, the surrounding information detection device 60 includes a radar sensor 61 and a camera sensor 62. The surrounding information detection device 60 provides the vehicle running gear 10 with surrounding detection information IS, which is information about the area around the vehicle 100 acquired by the radar sensor 61 (radar detection information). The surrounding information detection device 60 also provides the vehicle running gear 10 with surrounding detection information IS, which is image data (image information) about the area around the vehicle 100 acquired by the camera sensor 62.

[0028] If the vehicle driving system 10 determines "Yes" in step S320, it proceeds to step S320 and executes the first inter-vehicle distance control. The first inter-vehicle distance control is a control that maintains the inter-vehicle distance D at a target inter-vehicle distance Dtgt. More specifically, the first inter-vehicle distance control is a control that autonomously controls the drive unit 20 and the braking unit 30 to accelerate and decelerate the vehicle 100 so that the inter-vehicle distance D is maintained at a target inter-vehicle distance Dtgt. Therefore, the first inter-vehicle distance control is a so-called follow-me driving control or adaptive cruise control. The vehicle driving system 10 obtains the inter-vehicle distance D from surrounding detection information IS (particularly radar detection information).

[0029] Subsequently, the vehicle running gear 10 proceeds to step S395 and terminates the processing of this routine.

[0030] On the other hand, if the vehicle running gear 10 determines "No" in step S315, it proceeds to step S325 and executes the first running speed control. The first running speed control is a control that maintains the running speed V of the vehicle 100 at a set speed Vset. More specifically, the first running speed control is a control that autonomously controls the drive unit 20 and the braking unit 30 to accelerate and decelerate the vehicle 100 so that the running speed V of the vehicle 100 is maintained at the set speed Vset. Therefore, the first running speed control is a so-called constant speed driving control or cruise control.

[0031] Subsequently, the vehicle running gear 10 proceeds to step S395 and terminates the processing of this routine.

[0032] Furthermore, if the vehicle running gear 10 determines "No" in step S310, it proceeds to step S330 to determine whether or not a preceding vehicle 200 exists. That is, if the first condition C1 is not met in step S310, and therefore the second condition C2, which states that execution of the second running control or economy running control is required, is met, the vehicle running gear 10 proceeds to step S330 to determine whether or not a preceding vehicle 200 exists.

[0033] If the vehicle running gear 10 determines "Yes" in step S330, it proceeds to step S335 and executes the second inter-vehicle distance control. The second inter-vehicle distance control is a control that maintains the inter-vehicle distance D within a predetermined distance range Rd that includes the target inter-vehicle distance Dtgt. More specifically, the second inter-vehicle distance control is a control that accelerates the vehicle 100 by controlling the drive unit 20 when the inter-vehicle distance D increases and reaches the upper limit of the predetermined distance range Rd, and decelerates the vehicle 100 by controlling the drive unit 20 when the inter-vehicle distance D decreases and reaches the lower limit of the predetermined distance range Rd. When the vehicle running gear 10 is accelerating the vehicle 100 during the execution of the second inter-vehicle distance control, and the internal combustion engine 21 is operating, it operates the drive unit 20 so that power is output from the drive unit 20 with the highest energy efficiency. In particular, when the vehicle running gear 10 is accelerating the vehicle 100 during the execution of the second inter-vehicle distance control, if the internal combustion engine 21 is operating, it operates the internal combustion engine 21 at the optimal operating point. The optimal operating point is the operating point at which the energy efficiency of the internal combustion engine 21 is highest when outputting power. The operating point is determined by the rotational speed of the internal combustion engine 21 and the load on the internal combustion engine 21. Furthermore, when the vehicle running gear 10 is accelerating the vehicle 100 during the execution of the second inter-vehicle distance control, it may be configured to operate the internal combustion engine 21 at an operating point near the optimal operating point. On the other hand, when the vehicle running gear 10 is decelerating the vehicle 100 during the execution of the second inter-vehicle distance control, it controls the drive unit 20 so that the vehicle 100 coasts.

[0034] Subsequently, the vehicle running gear 10 proceeds to step S395 and terminates the processing of this routine.

[0035] On the other hand, if the vehicle running gear 10 determines "No" in step S330, it proceeds to step S340 and executes the second running speed control. The second running speed control is a control that maintains the running speed V of the vehicle 100 within a predetermined speed range Rv, which includes the set speed Vset. More specifically, the second running speed control is a control that accelerates the vehicle 100 by controlling the drive unit 20 when the running speed V of the vehicle 100 decreases and reaches the lower limit of the predetermined speed range Rv, and decelerates the vehicle 100 by controlling the drive unit 20 when the running speed V of the vehicle 100 increases and reaches the upper limit of the predetermined speed range Rv. When the vehicle running gear 10 is accelerating the vehicle 100 during the execution of the second running speed control, and the internal combustion engine 21 is operating, it operates the drive unit 20 so that power is output from the drive unit 20 with the highest energy efficiency. In particular, when the vehicle running gear 10 is accelerating the vehicle 100 while the second inter-vehicle distance control is being performed, if the internal combustion engine 21 is operating, the internal combustion engine 21 is operated at the optimal operating point. Alternatively, when the vehicle running gear 10 is accelerating the vehicle 100 while the second driving speed control is being performed, if the internal combustion engine 21 is operating, it may be configured to operate the internal combustion engine 21 at an operating point near the optimal operating point. On the other hand, when the vehicle running gear 10 is decelerating the vehicle 100 while the second driving speed control is being performed, the drive unit 20 is controlled so that the vehicle 100 coasts.

[0036] Subsequently, the vehicle running gear 10 proceeds to step S395 and terminates the processing of this routine.

[0037] Furthermore, if the vehicle running device 10 determines "No" in step S305, it proceeds directly to step S395 and terminates the processing of this routine.

[0038] Furthermore, as shown in Figure 4(A), the vehicle running device 10 may be configured to set a predetermined speed range Rv so that the vehicle's running speed V becomes an appropriate speed based on the running speed of the following vehicle 300 and / or the distance between the following vehicle 300 and the vehicle 100, when the second running speed control is being performed and a following vehicle 300 is present.

[0039] Similarly, the vehicle running device 10 may be configured, as shown in Figure 4(B), to set a predetermined distance range Rd such that the inter-vehicle distance D is an appropriate distance based on the speed of the following vehicle 300 and / or the distance between the following vehicle 300 and the vehicle 100 when the second inter-vehicle distance control is being performed and a following vehicle 300 is present.

[0040] Incidentally, the vehicle running gear 10 starts and stops the internal combustion engine 21 according to the requested power Preq. Next, the control of the internal combustion engine 21 by this vehicle running gear 10 will be explained in more detail. In this example, the requested power Preq is the power that is required to be output from the drive unit 20.

[0041] The vehicle running gear 10 executes the routine shown in Figure 5 at a predetermined calculation cycle. When the vehicle running gear 10 starts processing from step S500 of the routine shown in Figure 5, it proceeds to step S505 and determines whether or not the internal combustion engine 21 is stopped.

[0042] If the vehicle running gear 10 determines "Yes" in step S505, it proceeds to step S510 to determine whether the engine start condition Cstart is met. The engine start condition Cstart is that the required power Preq is equal to or greater than a predetermined value (engine start determination value Pstart). In this example, the engine start determination value Pstart is set to a value greater than zero.

[0043] If the vehicle running gear 10 determines "Yes" in step S510, it proceeds to step S515 and starts the internal combustion engine 21. In this case, the vehicle running gear 10 operates the internal combustion engine 21 and the motor 22 so that the sum of the power output from the internal combustion engine 21 (engine power) and the power output from the motor 22 (motor power) matches the required power Preq. That is, in this case, power is output from both the internal combustion engine 21 and the motor 22, or power is output from only the internal combustion engine 21, depending on the magnitude of the required power Preq.

[0044] Subsequently, the vehicle running gear 10 proceeds to step S595 and terminates the processing of this routine.

[0045] On the other hand, if the vehicle running gear 10 determines "No" in step S510, it proceeds to step S520, where it determines in step S515 whether a predetermined time Tth has elapsed since the internal combustion engine 21 was started. The vehicle running gear 10 may also be configured to determine in step S520 whether the exhaust gas recirculation rate is equal to or greater than a predetermined recirculation rate. The exhaust gas recirculation rate is the ratio of the amount of recirculated exhaust gas to the total amount of gas drawn into the combustion chamber of the internal combustion engine 21. The amount of recirculated exhaust gas is the amount of exhaust gas introduced into the combustion chamber of the internal combustion engine 21 by exhaust gas recirculation control.

[0046] If the vehicle running gear 10 determines "Yes" in step S520, it proceeds to step S525 and executes exhaust gas recirculation control. Next, the vehicle running gear 10 proceeds to step S530. Exhaust gas recirculation control is a control that introduces exhaust gas discharged from the internal combustion engine 21 into the combustion chamber of the internal combustion engine 21 by introducing it into the intake passage of the internal combustion engine 21. While the vehicle running gear 10 is executing exhaust gas recirculation control, it controls the amount of exhaust gas introduced into the combustion chamber of the internal combustion engine 21 by controlling the opening degree of the exhaust gas recirculation valve 71 of the exhaust gas recirculation device 70.

[0047] On the other hand, if the vehicle running gear 10 determines "No" in step S520, it proceeds directly to step S530.

[0048] When the vehicle running gear 10 proceeds to step S530, it determines whether the engine stop condition Cstop is met. The engine stop condition Cstop is the condition that the required power Preq is less than or equal to a predetermined value (engine stop determination value Pstop). In this example, the engine stop determination value Pstop is set to a value greater than zero. Also, the engine stop determination value Pstop is set to a value less than the engine start determination value Pstart.

[0049] If the vehicle running gear 10 determines "Yes" in step S530, it proceeds to step S535 and stops the internal combustion engine 21. In this case, the motor 22 is operated so that the power output from the motor 22 (motor power) matches the required power Preq. That is, in this case, power is output only from the motor 22.

[0050] Subsequently, the vehicle running gear 10 proceeds to step S595 and terminates the processing of this routine.

[0051] On the other hand, if the vehicle running gear 10 determines "No" in step S530, it proceeds directly to step S595 and terminates the processing of this routine.

[0052] Furthermore, when accelerating the vehicle 100 during the execution of the first driving control, the vehicle running gear 10 calculates the required power Preq based on the vehicle's running speed V and controls the drive unit 20 so that power equivalent to the required power Preq is output from the drive unit 20. At this time, the required power Preq increases as the vehicle's running speed V increases.

[0053] Furthermore, when the vehicle running gear 10 accelerates the vehicle 100 during the execution of the second running control, it calculates the required power Preq based on the vehicle's running speed V and controls the drive unit 20 so that power equivalent to the required power Preq is output from the drive unit 20. At this time, the required power Preq increases as the vehicle's running speed V increases.

[0054] Furthermore, if neither the first nor the second driving control is being performed, the vehicle running gear 10 determines the required power Preq based on the amount of operation of the accelerator pedal 41 and the driving speed V of the vehicle 100, and controls the drive unit 20 so that power corresponding to the required power Preq is output from the drive unit 20. The vehicle running gear 10 acquires the amount of operation of the accelerator pedal 41 using the accelerator pedal operation amount sensor 42. Furthermore, if neither the first nor the second driving control is being performed, the vehicle running gear 10 determines the required braking force based on the amount of operation of the brake pedal 43, and controls the braking unit 30 so that braking force corresponding to the required braking force is applied to the vehicle 100 from the hydraulic brake unit 31. The vehicle running gear 10 acquires the amount of operation of the brake pedal 43 using the brake pedal operation amount sensor 44.

[0055] Furthermore, the vehicle running gear 10 sets the engine start determination value Pstart and the engine stop determination value Pstop by executing the routine shown in Figure 6 at a predetermined calculation cycle. When the vehicle running gear 10 starts processing from step S600 of the routine shown in Figure 6, it proceeds to step S605 and determines whether or not the second driving control is being executed.

[0056] If the vehicle running device 10 determines "No" in step S605, it proceeds to step S630 to determine whether or not the first running control is currently being executed.

[0057] If the vehicle running gear 10 determines "No" in step S630, that is, if neither the first running control nor the second running control is executed, it proceeds to step S640, sets the engine start determination value Pstart as the standard start determination value Pstart_0, and sets the engine stop determination value Pstop as the standard stop determination value Pstop_0. After that, the vehicle running gear 10 proceeds to step S695, and the processing of this routine is temporarily terminated.

[0058] On the other hand, if the vehicle running gear 10 determines "Yes" in step S630, that is, if it is executing the first running control, it proceeds to step S635, sets the first start determination value Pstart_1 as the engine start determination value Pstart, and sets the first stop determination value Pstop_1 as the engine stop determination value Pstop. In this example, the first start determination value Pstart_1 is a smaller value than the reference start determination value Pstart_0. After that, the vehicle running gear 10 proceeds to step S695, and the processing of this routine is temporarily terminated.

[0059] Furthermore, if the vehicle running gear 10 determines "Yes" in step S605, that is, if it is executing the second running control, it proceeds to step S610, sets the second start determination value Pstart_2 as the engine start determination value Pstart, and sets the second stop determination value Pstop_2 as the engine stop determination value Pstop. In this example, the second start determination value Pstart_2 is a smaller value than the first start determination value Pstart_1.

[0060] Next, the vehicle running gear 10 proceeds to step S615 to determine whether or not exhaust gas recirculation control is being performed.

[0061] If the vehicle running gear 10 determines "No" in step S615, it proceeds to step S625 and executes the engine power limiting process. The engine power limiting process is a process that limits the engine power to a predetermined value (predetermined upper limit) or less.

[0062] Furthermore, the above predetermined upper limit may be a constant value, but may also be set based on driving conditions such as the distance between vehicles D. In this case, the predetermined upper limit is set to a smaller value when the distance between vehicles D is less than a predetermined value (predetermined distance between vehicles) compared to when the distance between vehicles D is equal to or greater than the predetermined distance between vehicles. Alternatively, the predetermined upper limit may be set based on driving conditions such as whether or not vehicle 100 is traveling downhill. In this case, the predetermined upper limit is set to a smaller value when vehicle 100 is traveling downhill compared to when vehicle 100 is not traveling downhill. Alternatively, the predetermined upper limit may be set based on driving conditions such as the relative speed of the preceding vehicle 200 to vehicle 100 or the acceleration of the preceding vehicle 200. In this case, the predetermined upper limit is set to a smaller value when the relative speed of the preceding vehicle 200 with respect to vehicle 100 is less than a predetermined value (predetermined relative speed) compared to when the relative speed of the preceding vehicle 200 with respect to vehicle 100 is equal to or greater than the predetermined relative speed. Also, when the acceleration of the preceding vehicle 200 is less than a predetermined value (predetermined acceleration), the predetermined upper limit is set to a smaller value compared to when the acceleration of the preceding vehicle 200 is equal to or greater than the predetermined acceleration.

[0063] When the distance D between vehicles is small, or when vehicle 100 is traveling downhill, or when the relative speed of the preceding vehicle 200 to vehicle 100 is small, or when the acceleration of the preceding vehicle 200 is small, the possibility of accelerating vehicle 100 for a long time by optimal acceleration control is low, and therefore, the engine power may be small in order to accelerate vehicle 100. Furthermore, by reducing the engine power, the energy efficiency of the internal combustion engine 21 can be improved.

[0064] Therefore, as described above, by setting a predetermined upper limit based on the driving state of the vehicle 100, the engine power can be kept low when there is little possibility of accelerating the vehicle 100 for a long period of time by optimal acceleration control, thereby improving the energy efficiency of the internal combustion engine 21.

[0065] Then, after executing step S625, the vehicle running device 10 proceeds to step S695 and terminates the processing of this routine.

[0066] On the other hand, if the vehicle running gear 10 determines "Yes" in step S615, it proceeds to step S620 and stops the engine power limiting process. After that, the vehicle running gear 10 proceeds to step S695 and terminates the processing of this routine.

[0067] The vehicle running gear 10 provides the following effects. Specifically, the internal combustion engine 21 is started when the required power Preq increases and reaches the engine start determination value Pstart, and is stopped when the required power Preq decreases and reaches the engine stop determination value Pstop. If the engine start determination value Pstart and the engine stop determination value Pstop are set to the same value, there is a high possibility that the internal combustion engine 21 will be started and stopped frequently, which is undesirable. Therefore, the vehicle running gear 10 sets the engine start determination value Pstart to a value greater than the engine stop determination value Pstop. In other words, hysteresis is provided between the engine start determination value Pstart and the engine stop determination value Pstop. This reduces the frequency with which the internal combustion engine 21 is started and stopped.

[0068] To reduce the frequency of starting and stopping the internal combustion engine 21, it is effective to increase the hysteresis. Therefore, if the engine stop judgment value Pstop is set to a constant value, the hysteresis can be increased by setting the engine start judgment value Pstart to a larger value.

[0069] However, if the engine start determination value Pstart is set to a large value, the internal combustion engine 21 will remain stopped until the required power Preq reaches the engine start determination value Pstart. This is because, even though the internal combustion engine 21 could be operated at its optimal operating point to output power to drive the vehicle with high energy efficiency, the internal combustion engine 21 will remain stopped, and power equivalent to the required power Preq will be output only from the motor 22. In this case, the energy efficiency of the drive unit 20 will be lower compared to when the internal combustion engine 21 is operating.

[0070] On the other hand, when the vehicle 100 is accelerated or decelerated by the second driving control, the fluctuation of the required power Preq is small, so even if the hysteresis is small, the frequency of starting and stopping the internal combustion engine 21 can be kept within an acceptable range.

[0071] According to the vehicle running gear 10, when the second running control is being executed, the engine start determination value Pstart is set to a smaller value compared to when the second running control is not being executed. As a result, the internal combustion engine 21 is started while the required power Preq is small. Therefore, it is prevented from running the vehicle 100 using only motor power until the required power Preq becomes relatively high, and thus power can be output to run the vehicle 100 with high energy efficiency.

[0072] Furthermore, the present invention is not limited to the embodiments described above, and various modifications can be adopted within the scope of the present invention. [Explanation of symbols]

[0073] 10...Vehicle running gear, 20...Drive system, 21...Internal combustion engine, 22...Motor, 90...ECU, 100...Vehicle

Claims

1. A vehicle running gear that performs driving control to autonomously drive a vehicle by controlling the power output from an internal combustion engine and a motor, The aforementioned driving control is a control that controls the power so that an index value representing the driving state of the vehicle is maintained within a predetermined range, and when the vehicle is to be decelerated, the control is to decelerate the vehicle by allowing it to coast. In vehicle running gear, When accelerating the vehicle while the aforementioned driving control is not being performed, the vehicle is accelerated by operating only the motor with the internal combustion engine stopped while the requested power is less than the first start determination value, and when the requested power reaches the first start determination value, the internal combustion engine is started and the vehicle is accelerated. When accelerating the vehicle while the aforementioned driving control is being performed, the vehicle is accelerated by operating only the motor with the internal combustion engine stopped while the requested power is less than the second start determination value, and when the requested power reaches the second start determination value, the internal combustion engine is started and the vehicle is accelerated. The second start determination value is set to a value smaller than the first start determination value. Vehicle running gear.

2. In the vehicle running device according to claim 1, During the aforementioned driving control, from the time the internal combustion engine is started until exhaust recirculation control is initiated to recirculate the exhaust gas back into the internal combustion engine, the power output from the internal combustion engine is limited to a predetermined upper limit. Vehicle running gear.

3. In the vehicle running device according to claim 2, The predetermined upper limit is set based on the driving state of the vehicle. Vehicle running gear.

4. In the vehicle running device according to claim 3, The aforementioned driving conditions include information on the distance between vehicles, which is the distance between the vehicle and the preceding vehicle. The predetermined upper limit is set to a smaller value when the following distance is less than the predetermined following distance compared to when the following distance is equal to or greater than the predetermined following distance. Vehicle running gear.

5. In the vehicle running device according to claim 3, The aforementioned driving conditions include information on whether or not the vehicle is traveling on a downhill slope. The predetermined upper limit is set to a smaller value when the vehicle is traveling on the downhill road compared to when the vehicle is not traveling on the downhill road. Vehicle running gear.

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