Electric vehicle control device

Abstract

To provide an electric vehicle control device appropriately exerting a torque amplification function while reducing energy loss due to a torque converter.SOLUTION: An electric vehicle control device is provided with: an engine; a motor; a torque converter connected to the motor; a lock-up clutch integrally rotating the torque converter by being in an engaged state; and an output shaft which is connected to the engine so as to enable a differential rotation and in which torque is transmitted from the motor via the torque converter. The lock-up clutch is released (step S3 or S7) when the torque required by the motor is larger than a released threshold value (Yes in Step S2 or S6), and the lock-up clutch is engaged (step S5 or S9) when the torque required by the motor is an engagement threshold value or less (Yes in Step S4 or S8).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a control device for an electric vehicle that is equipped with at least two driving power sources, that is, a motor as a driving power source and another driving power source. [Background technology]

[0002] Patent Document 1 describes a control device for a vehicle including an engine as a driving force source, a torque converter connected to the output shaft of the engine, a lock-up clutch that selectively connects a pump impeller and a turbine runner in the torque converter, a power transmission device connected to the output shaft of the torque converter, and drive wheels connected to the power transmission device. This control device is configured to suppress deterioration of fuel economy by engaging the lock-up clutch when the vehicle is traveling at low vehicle speeds and the engine is rotating at low revolutions per minute. On the other hand, when three conditions are met: multiple engine misfires, the vehicle is traveling uphill with the engine operating at low revolutions per minute and high load, and the accelerator is operated, in order to suppress engine stall. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-71662 Summary of the Invention [Problem to be solved by the invention]

[0004] The control device described in Patent Document 1 is configured to engage the lock-up clutch when the differential rotational speed between the pump impeller and the turbine runner reaches a predetermined differential rotational speed. Meanwhile, when the vehicle is stopped, the turbine runner, which is the output member of the torque converter, stops, and the pump impeller rotates at a rotational speed approximately equal to the engine's idle speed. In this case, all of the power output from the engine is absorbed by the oil in the torque converter and converted into heat, resulting in energy loss. Furthermore, when the vehicle starts moving, the torque converter amplifies the engine's output torque, but the lock-up clutch cannot be engaged until the turbine runner's rotational speed increases to approximately equal the engine's idle speed. Similarly, energy loss inevitably occurs during this time.

[0005] The present invention has been made in light of the above technical problems, and aims to provide a control device for an electric vehicle that can appropriately perform torque amplification function while reducing energy loss caused by a torque converter. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the present invention provides a control device for an electric vehicle comprising a motor as a driving force source, another driving force source different from the motor, a torque converter connected to the motor, a lock-up clutch that rotates the torque converter integrally when engaged, and an output shaft that is connected to the other driving force source so as to be capable of differential rotation and to which torque is transmitted from the motor via the torque converter, the control device comprising a controller that controls the lock-up clutch, the controller disengaging the lock-up clutch when the torque required of the motor or the driving force required of the electric vehicle is greater than a predetermined release threshold, and engaging the lock-up clutch when the torque required of the motor or the driving force required of the electric vehicle is equal to or less than a predetermined engagement threshold. [Effects of the Invention]

[0007] According to the present invention, a lockup clutch connected to the motor is disengaged when the torque required for the motor or the driving force required for the electric vehicle is greater than a disengagement threshold, and is engaged when the torque required for the motor or the driving force required for the electric vehicle is equal to or less than an engagement threshold. Therefore, the lockup clutch is disengaged when the torque required for the motor or the driving force required for the electric vehicle is greater than a disengagement threshold. In other words, the lockup clutch is disengaged when the torque required for the motor or the driving force required for the electric vehicle is large. This allows for increased driving force during start-up or acceleration at low vehicle speeds. Furthermore, the lockup clutch is engaged when the torque required for the motor or the driving force required for the electric vehicle is equal to or less than an engagement threshold. In other words, the lockup clutch is engaged when the torque required for the motor or the driving force required for the electric vehicle is small. Therefore, when the required driving force can be satisfied by outputting torque from the motor or another driving force source, the torque converter is not operated, thereby reducing energy loss caused by operating the torque converter. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a skeleton diagram illustrating an example of an electric vehicle according to an embodiment of the present invention. [Figure 2] (a) is a nomographic diagram showing the operating states of the engine, first motor, and second motor when traveling forward, and (b) is a nomographic diagram showing the operating states of the engine, first motor, and second motor when traveling backward. [Figure 3] 4 is a flowchart illustrating an example of control executed by a control device according to an embodiment of the present invention. [Figure 4] FIG. 10(a) is a diagram showing a first release threshold and a first engagement threshold on a flat road, and FIG. 10(b) is a diagram showing a second release threshold and a second engagement threshold on an uphill road. [Figure 5]FIG. 1(a) is a diagram showing a schematic diagram of the regions in which the lock-up clutch is released and engaged on a flat road, and FIG. 1(b) is a diagram showing a schematic diagram of the regions in which the lock-up clutch is released and engaged on an uphill road. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described based on the embodiments shown in the drawings. Note that the embodiments described below are merely examples of specific embodiments of the present invention and are not intended to limit the present invention.

[0010] FIG. 1 shows a schematic diagram of an example of an electric vehicle according to an embodiment of the present invention. The electric vehicle (hereinafter simply referred to as vehicle) Ve shown in FIG. 1 is a hybrid vehicle equipped with an engine (ENG) 1 and two motors 2 and 3 as a driving force source. The engine 1 can be configured similarly to engines provided in conventional vehicles, and is configured to generate power by burning a mixture of air and fuel, and is configured to be able to autonomously rotate at a speed equal to or higher than a predetermined speed. The engine 1 corresponds to the "other driving force source" in the embodiment of the present invention.

[0011] The motors 2 and 3 are configured as motor generators that function not only as motors that output drive torque when supplied with power from a power storage device (not shown), but also as generators that convert at least a portion of the power into electric power when the output shaft is rotated, similar to motors provided as drive power sources for conventional electric vehicles and hybrid vehicles. Specifically, they are configured as synchronous motors or induction motors.

[0012] A power split mechanism 5 is connected to the output shaft 4 of the engine 1, and splits the torque of the engine 1 and connects the engine 1 to an output shaft 6 (described later) so that they can rotate differentially. The power split mechanism 5 is a single-pinion planetary gear mechanism, and is configured as a differential mechanism having a sun gear S1, a ring gear R1 provided concentrically with the sun gear S1, a pinion gear P1 meshing with the sun gear S1 and the ring gear R1, and a carrier C1 that holds the pinion gear P1 rotatably and revolves around the central axis of rotation of the sun gear S1.

[0013] A first motor (MG1) 2 disposed between the engine 1 and the power split mechanism 5 is connected to the sun gear S1, an output shaft 4 of the engine 1 is connected to the carrier C1, and an output shaft 6 of the power split mechanism 5 is connected to the ring gear R1. That is, the carrier C1 functions as an input element, the sun gear S1 functions as a reaction element, and the ring gear R1 functions as an output element. Torque input from the engine 1 is divided and transmitted to the sun gear S1 and the ring gear R1 according to the gear ratio of the power split mechanism 5. The output shaft 6 corresponds to the "output shaft" in the embodiment of the present invention.

[0014] In the example shown in FIG. 1 , a second motor (MG2) 3 is provided alongside the power split device 5, and a torque converter 7 is connected to the second motor 3. Similar to torque converters provided in conventional vehicles that use an engine as a driving force source, the torque converter 7 is composed of a pump impeller 8, a turbine runner 9 arranged opposite the pump impeller 8, and a stator 10 provided between the pump impeller 8 and the turbine runner 9 and directing the flow of oil from the pump impeller 8 to the turbine runner 9 in a predetermined direction. The pump impeller 8 is connected to the second motor 3, an output shaft 11 is connected to the turbine runner 9, and a housing 13 is connected to the stator 10 via a one-way clutch 12. The second motor 3 corresponds to the "motor" in the embodiments of the present invention.

[0015] In other words, when the rotation speed of the second motor 3 is higher than the rotation speed of the output shaft 11, the torque converter 7 is configured to amplify the torque of the second motor 3 and transmit it to the output shaft 11 according to the speed ratio, which is the rotation speed of the output shaft 11 relative to the rotation speed of the second motor 3.

[0016] A forward / reverse switching mechanism 14, which is disposed between the second motor 3 and the torque converter 7, is connected to the output shaft 11 of the torque converter 7. The forward / reverse switching mechanism 14 is configured by a single-pinion planetary gear mechanism, with the output shaft 11 of the torque converter 7 connected to the sun gear S2 and an intermediate shaft 15 connected to the ring gear R2. A forward clutch (Fed CL) 16, which is selectively connected to the sun gear S2, and a reverse brake (Rev BK) 17, which is selectively connected to the housing 13, are provided on the carrier C2.

[0017] Therefore, by engaging the forward clutch 16, the forward / reverse switching mechanism 14 rotates integrally and transmits the torque output from the torque converter 7 directly to the intermediate shaft 15, and by engaging the reverse brake 17, the direction of the torque output from the torque converter 7 is reversed, amplified, and transmitted to the intermediate shaft 15. The forward clutch 16 and the reverse brake 17 are arranged side by side on the opposite side of the forward / reverse switching mechanism 14 in the axial direction of the output shaft 6, with the torque converter 7 in between.

[0018] A lock-up clutch (L / U CL) 18 is provided on the outer periphery of the forward / reverse switching mechanism 14, and when engaged, rotates the pump impeller 8 and the turbine runner 9 together. This lock-up clutch 18 may be a hydraulic clutch mechanism in which the engagement pressure is determined according to hydraulic pressure, as with conventional lock-up clutches, or an electromagnetic clutch in which the engagement pressure is determined according to electromagnetic force. It may also be a friction clutch mechanism in which an input side rotating member and an output side rotating member are frictionally engaged, or a meshing clutch mechanism in which the members rotate together by meshing dog teeth. Furthermore, it may be a normally closed clutch mechanism that is engaged when no hydraulic pressure or electromagnetic force is applied, or a normally open clutch mechanism that is engaged when hydraulic pressure or electromagnetic force is applied.

[0019] A reduction mechanism 19 formed by a single-pinion planetary gear mechanism is connected to the intermediate shaft 15. Specifically, the intermediate shaft 15 is connected to the sun gear S3 of the reduction mechanism 19, the housing 13 is connected to the ring gear R3, and the output shaft 6 is connected to the carrier C3. In other words, the torque output from the second motor 3 is combined with the torque transmitted from the engine 1 to the output shaft 6 via the torque converter 7 or lock-up clutch 18, the forward / reverse switching mechanism 14, and the reduction mechanism 19. In the example shown in FIG. 1, a rotation speed sensor 20 is provided to detect the rotation speed of the sun gear S3.

[0020] 1 is also provided with an electronic control device (hereinafter referred to as a controller) 21 for controlling the engine 1, the motors 2 and 3, the lock-up clutch 18, etc. Like controllers provided in conventional vehicles, this controller 21 is mainly composed of a microcomputer, and is configured to receive signals from various sensors provided in the vehicle Ve and output command signals to the engine 1, the motors 2 and 3, the lock-up clutch 18, etc. based on the received signals and pre-stored maps, arithmetic expressions, etc.

[0021] Figure 2(a) shows an example of the operating states of the engine 1, the first motor 2, and the second motor 3 when the vehicle Ve configured as described above is traveling forward, and Figure 2(b) shows an example of the operating states of the engine 1, the first motor 2, and the second motor 3 when the vehicle Ve is traveling backward.

[0022] "Output" shown in Figures 2(a) and 2(b) indicates the rotation speed of the output shaft 6, which varies depending on the vehicle speed. Meanwhile, because the power split mechanism 5 is configured as a differential mechanism, it is possible to control the rotation speed of the engine 1 by controlling the rotation speed of the first motor 2. In other words, even when the vehicle is stopped or traveling at an extremely low speed, it is possible to maintain the engine rotation speed at a predetermined rotation speed, such as an idle speed, by increasing the rotation speed of the first motor 2.

[0023] Furthermore, as described above, the ring gear R3 of the reduction mechanism 19 is connected to the housing 13 and is stopped, so the rotation speed of the sun gear S3 (i.e., the rotation speed of the intermediate shaft 15) is based on the vehicle speed (the rotation speed of the output shaft 6) and the gear ratio of the reduction mechanism 19.

[0024] Furthermore, in the forward / reverse switching mechanism 14, when the forward clutch 16 is engaged, the ring gear R2 (intermediate shaft 15) and the sun gear S2 rotate at the same rotation speed, and when the lock-up clutch 18 is engaged, the second motor 3 also rotates at the same rotation speed. On the other hand, when the reverse brake 17 is engaged, the carrier C2 is fixed to the housing 13 and is stopped, so the sun gear S2 rotates in the opposite direction to the ring gear R2, and the rotation speed of the sun gear S2 corresponds to the rotation speed of the ring gear R2 and the gear ratio of the forward / reverse switching mechanism 14. When the lock-up clutch 18 is engaged, the sun gear S2 and the second motor 3 rotate together.

[0025] That is, even when the vehicle is stopped or traveling at an extremely low speed, the lock-up clutch 18 can be kept engaged while the engine 1 is stopped or maintained at a predetermined rotation speed such as idle rotation speed. In other words, even when starting or accelerating from an extremely low vehicle speed, the lock-up clutch 18 can remain engaged and torque can be transmitted from the engine 1 to the drive wheels while torque can be transmitted from the second motor 3 to the drive wheels. As a result, when the vehicle is stopped or accelerating from an extremely low vehicle speed, the lock-up clutch 18 does not need to be released, and power loss can be reduced by the amount that the torque converter 7 does not operate.

[0026] Conversely, by disengaging the lockup clutch 18, the torque of the second motor 3 can be amplified and output in accordance with the speed ratio between the pump impeller 8 and the turbine runner 9, thereby increasing the maximum driving force of the vehicle Ve compared to when the lockup clutch 18 is not provided. In other words, the driving force can be increased when starting or accelerating from an extremely low vehicle speed. Therefore, when the required driving force is high and it is necessary to operate the torque converter 7, the lockup clutch 18 can be disengaged, thereby reducing energy loss caused by the torque converter 7 and enabling the torque amplification function to be performed at an appropriate timing.

[0027] On the other hand, as described above, the torque converter 7 amplifies and outputs the torque of the second motor 3 in accordance with the speed ratio between the pump impeller 8 and the turbine runner 9. Therefore, if the lock-up clutch 18 is released after the output torque of the second motor 3 reaches its upper limit torque, the maximum driving force of the vehicle Ve cannot be generated until the rotational speed of the second motor 3 increases to the upper limit rotational speed. In other words, the responsiveness of the driving force of the vehicle Ve deteriorates. Note that the torque of the second motor can be increased more quickly than by increasing the rotational speed of the second motor 3.

[0028] Therefore, when starting on an uphill road where torque responsiveness is required, the lock-up clutch 18 is configured to be released earlier than when starting on a flat road where torque responsiveness is acceptable.

[0029] Fig. 3 shows a flowchart for explaining an example of control for switching between engagement and release of lock-up clutch 18. In the control example shown in Fig. 3, first, it is determined whether or not vehicle Ve is on an uphill road (step S1). This step S1 can be determined based on a signal from an acceleration sensor provided in vehicle Ve, based on an estimated driving force based on the command torque of engine 1 and second motor 3 and the longitudinal acceleration of vehicle Ve (or a derivative value of vehicle speed), or based on position information such as GPS and map information such as a navigation system.

[0030] If the answer to step S1 is negative because the vehicle Ve is not on an uphill slope, the next step is to determine whether the torque required of the second motor 3 is greater than a first release threshold (step S2). Step S2 is a step for determining whether the required driving force can be satisfied without disengaging the lock-up clutch 18. Therefore, in step S2, the driving force required of the vehicle Ve is first calculated based on the amount of operation of the accelerator device, etc., and the required torque of the engine 1 and the required torque of the second motor 3 to satisfy the required driving force are calculated. Then, it is determined whether the required torque of the second motor 3 is greater than the maximum torque that can be continuously output (continuous rated torque) taking into account heat generation from coils, etc. That is, the first release threshold in step S1 is set to a value equal to or less than the continuous rated torque (dashed line) of the second motor 3, as shown by the solid line (thick line) in FIG. 4(a). The first release threshold may be set to a larger value as the rotation speed of the second motor 3 increases (i.e., as the vehicle speed increases), as indicated by the solid line (thin line) in FIG. 4(a).

[0031] If the requested torque of the second motor 3 is greater than the first release threshold and therefore the answer to step S2 is affirmative, a command to release the lock-up clutch 18 is output (step S3). Note that if the lock-up clutch 18 has already been released when this routine is executed, the lock-up clutch 18 remains released in step S3.

[0032] Following step S3, or if the determination in step S2 is negative because the required torque of the second motor 3 is equal to or less than the first release threshold, it is determined whether the required torque of the second motor 3 is less than the first engagement threshold (step S4). This step S4 is a step for determining whether the released lock-up clutch 18 can be engaged, and the first engagement threshold is set to a value smaller than the first release threshold. Note that, like the first release threshold, the first engagement threshold may also be set to a larger value as the rotational speed of the second motor 3 increases (i.e., as the vehicle speed increases), as indicated by the dashed line (thin line) in FIG. 4(a).

[0033] If the required torque of the second motor 3 is less than the first engagement threshold and therefore the answer in step S4 is YES, an instruction to engage the lockup clutch 18 is output (step S5), and this routine is temporarily terminated. If the lockup clutch 18 is already engaged when this routine is executed, the lockup clutch 18 remains engaged in step S5. Conversely, if the required torque of the second motor 3 is equal to or greater than the first engagement threshold and therefore the answer in step S4 is NO, this routine is temporarily terminated.

[0034] On the other hand, if the vehicle Ve is located on an uphill road and a positive determination is made in step S1, torque responsiveness is required. Therefore, it is preferable to disengage the lock-up clutch 18 and allow the torque converter 7 to perform the torque amplification function when the required driving force is relatively small. In other words, it is preferable to make the rotational speed of the pump impeller 8 higher than the rotational speed of the turbine runner 9 before the second motor 3 outputs the continuous rated torque. Therefore, if a positive determination is made in step S1, it is determined whether the torque required of the second motor 3 is greater than a second release threshold (step S6). The second release threshold in step S6 is a value determined taking into account the time required to increase the rotational speed of the second motor 3 in order to allow the torque converter 7 to perform the torque amplification function, and is set to a value smaller than the first release threshold, as shown by the solid line (thin line) in FIG. 4(b). Note that, like the first release threshold, the second release threshold may be set to a larger value as the rotational speed of the second motor 3 increases (i.e., as the vehicle speed increases).

[0035] If the requested torque of the second motor 3 is greater than the second release threshold and therefore the answer to step S6 is affirmative, a command to release the lock-up clutch 18 is output (step S7). If the lock-up clutch 18 has already been released when this routine is executed, the lock-up clutch 18 is maintained in the released state in step S7.

[0036] Following step S7, or if the determination in step S6 is negative because the required torque of the second motor 3 is equal to or less than the second release threshold, it is determined whether the required torque of the second motor 3 is less than the second engagement threshold (step S8). Step S8 is a step for determining whether the disengaged lock-up clutch 18 can be engaged, and the second engagement threshold is set to a value smaller than the second release threshold, as indicated by the dashed line (thin line) in FIG. 4(b). Note that, like the second release threshold, the second engagement threshold may also be set to a larger value as the rotational speed of the second motor 3 increases (i.e., as the vehicle speed increases).

[0037] If the required torque of the second motor 3 is less than the second engagement threshold and therefore the answer in step S8 is YES, an instruction to engage the lockup clutch 18 is output (step S9), and this routine is temporarily terminated. If the lockup clutch 18 is already engaged at the time this routine is executed, the lockup clutch 18 remains engaged in step S9. Conversely, if the required torque of the second motor 3 is equal to or greater than the second engagement threshold and therefore the answer in step S8 is NO, this routine is temporarily terminated.

[0038] 5(a) and 5(b) schematically show regions A and C in which lock-up clutch 18 is disengaged and regions B and D in which lock-up clutch 18 is engaged when vehicle Ve is on a flat road and when it is on an uphill road. The outlines in Figures 5(a) and 5(b) represent the maximum driving force that can be output when maximum torque is output from engine 1, continuous rated torque is output from second motor 3, and lock-up clutch 18 is disengaged and engaged based on the control example shown in Figure 3 above.

[0039] By disengaging the lock-up clutch 18 as shown in region A in Figure 5(a) and region C in Figure 5(b), a greater driving force can be obtained at low vehicle speeds than when the continuous rated torque is output from the second motor 3 without disengaging the lock-up clutch 18 (dashed line) or when maximum torque is output from the second motor 3 (dotted line). The torque converter 7 amplifies torque according to the speed ratio, which is the rotation speed of the turbine runner 9 relative to the rotation speed of the pump impeller 8, and the second motor 3 has a set upper rotation speed limit due to its configuration. Therefore, as shown in Figures 5(a) and 5(b), as the vehicle speed (i.e., the rotation speed of the turbine runner 9) increases, the settable speed ratio increases, and the maximum driving force decreases.

[0040] As described above, when the required torque of the second motor 3 is higher than the first disengagement threshold, which is lower than the continuous rated torque, the lock-up clutch 18 is disengaged, thereby increasing the driving force when starting or accelerating at low vehicle speeds. Furthermore, in region B in FIG. 5(a) or region D in FIG. 5(b), where the required driving force is small, the lock-up clutch 18 is engaged, thereby reducing energy loss by the torque converter 7 while satisfying the required driving force. As a result, the fuel economy and electricity efficiency (travel distance relative to power consumption) of the vehicle Ve as a whole can be improved.

[0041] Furthermore, as shown in FIG. 5B, by setting the second disengagement threshold lower than the first disengagement threshold, the torque converter 7 can function effectively on uphill roads when the required driving force is relatively low. In other words, the rotation speed of the second motor 3 can be increased independently of the vehicle speed. Therefore, the rotation speed of the second motor 3 can be increased before the required driving force increases to a level that cannot be met when the second motor 3 outputs the continuous rated torque. As a result, when a driving force greater than that required when the second motor outputs the continuous rated torque or maximum torque while the lock-up clutch 18 is engaged is required, the torque of the second motor 3 can be increased. This allows the driving force to increase in response to the increase in the required driving force, thereby improving acceleration response.

[0042] Note that the electric vehicle in the embodiment of the present invention is not limited to a hybrid vehicle as long as it includes a motor as a driving force source and another driving force source. That is, for example, it may be an electric vehicle provided with two motors and a torque converter with a lock-up clutch in the path that transmits torque from one of the motors to the drive wheels. Furthermore, in the above example, lock-up clutch 18 is configured to be disengaged in accordance with the required torque of the second motor, but lock-up clutch 18 may also be configured to be disengaged when the required driving force (i.e., the required torque of output shaft 6) is equal to or greater than a predetermined driving force (predetermined torque). [Explanation of symbols]

[0043] 1 engine 2,3 Motor 4,6,11 Output shaft 5 Power split mechanism 7. Torque converter 8 Pump Impeller 9 Turbine Runner 10 Stator 14 Forward / reverse switching mechanism 15 Intermediate shaft 16 Forward clutch 17 Reverse brake 18 Lock-up clutch 19 Reduction mechanism 21 Electronic control device (controller) Vehicle

Claims

[Claim 1] A control device for an electric vehicle including a motor as a driving force source, another driving force source different from the motor, a torque converter connected to the motor, a lock-up clutch that rotates the torque converter integrally by being engaged, and an output shaft that is connected to the other driving force source so as to be capable of differential rotation and to which torque is transmitted from the motor via the torque converter, a controller for controlling the lock-up clutch, The controller disengaging the lock-up clutch when a torque required for the motor or a driving force required for the electric vehicle is greater than a predetermined disengagement threshold; The lock-up clutch is engaged when the torque required for the motor or the driving force required for the electric vehicle is equal to or less than a predetermined engagement threshold. A control device for an electric vehicle.

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