Hybrid vehicle

Abstract

A hybrid vehicle (10) in which a control section (112) determines whether the sum of the required output P ENG‑RQ of the engine and the maximum output P GEN‑DRV of the power running of the generator is less than a prescribed determination threshold P TH , and controls the required torque of the engine in accordance with the torque feedback correction amount of the engine calculated from the deviation of the target speed of the engine in the case where the sum is less than the prescribed determination threshold.

Description

Technical Field

[0001] This invention relates to a control technology for a hybrid vehicle equipped with a motor (electric motor) and an engine (internal combustion engine). Background Technology

[0002] It is known that the output performance of rechargeable secondary batteries (batteries) decreases at low temperatures, especially in plug-in and series hybrid vehicles, where insufficient driving force due to reduced battery output is considered a significant issue. To address this insufficient driving force, for example, Patent Document 1 proposes a control method that temporarily increases engine torque and thus increases generator output when the driver requests a higher-than-prescribed output through throttle operation at low temperatures where battery output performance is reduced.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-162930

[0006] The technical problem that the invention aims to solve

[0007] In the control method disclosed in Patent Document 1, when the driver requests an increase in output above a specified value at low temperatures, the engine torque is increased to suppress the reduction in power performance. Therefore, the control action depends on the driver's throttle operation and only works while driving.

[0008] However, when driving in EV mode or when parked, the engine may start to generate electricity regardless of the driver's throttle input. In this situation, with reduced battery output, the engine speed cannot be maintained at the target value, potentially leading to engine stall (stalling). As will be described in detail later, the inventors of this application discovered that this decrease in engine speed is caused by a torque error between the engine and generator due to the difference in the rate of rise of the engine's coolant and oil temperatures (see [link to relevant documentation]). Figure 3 Without throttle operation, the engine requires its output to be maintained at a specified value. Therefore, as long as the generator's power output is sufficient, normal control can be maintained by using the generator's power output to exceed the torque error.

[0009] However, the generator's power output is derived from the battery to drive the generator motor, thus increasing the engine speed. Therefore, as the battery output decreases, the generator's power output also decreases, reaching zero at extremely low temperatures or when the battery deteriorates. In this way, when the generator's power output decreases, the combined output of the engine and the generator decreases due to torque error, causing the engine speed to drop and eventually stall. See below for further details. Figure 1 Please provide an explanation.

[0010] exist Figure 1 In the EV driving mode, the engine starts at time t1 and transitions to series driving at time t2. When the engine starts, the generator drives the motor, causing the engine speed to rise and reach the target speed. However, when the driver does not operate the throttle, the engine requires a constant output. As the generator's power output decreases with the battery output, the generator's auxiliary power decreases, and the combined output of the engine and the generator begins to fall below the torque error. Consequently, the engine speed cannot maintain the target and begins to gradually decrease, stopping and stalling at time tx. Such stalling cannot be prevented in control methods that rely on driver throttle operation, as described in Patent Document 1. Summary of the Invention

[0011] The present invention was made in view of the above circumstances, and the object of the present invention is to provide a hybrid vehicle that can maintain engine speed and prevent engine stalling even when the battery output is reduced.

[0012] Technical means for solving technical problems

[0013] According to one embodiment of the present invention for achieving the above-mentioned objective, a hybrid vehicle includes: an engine; a generator mechanically connected to the output shaft of the engine and capable of performing regenerative braking or power operation; a battery that stores electricity generated during the regenerative braking of the generator and supplies electricity during the power operation of the generator; a motor that converts the electricity supplied from the battery into driving force for drive wheels; and a control unit that controls the engine, the generator, and the motor, wherein, when the engine is started, the control unit determines whether the sum of the required output of the engine and the maximum power operation output of the generator is less than a predetermined determination threshold; if the sum is less than the predetermined determination threshold, the control unit calculates a torque feedback correction amount for the engine based on the deviation from the target speed of the engine and controls the required torque of the engine.

[0014] Alternatively, according to one embodiment of the present invention, for each target speed of the engine, the predetermined determination threshold may be preset based on the engine's cooling water temperature.

[0015] In addition, according to one embodiment of the present invention, the control unit may further determine whether the total value is less than the value obtained by adding a hysteresis setting value to the predetermined determination threshold. If the total value is less than the value obtained by adding a hysteresis setting value to the predetermined determination threshold, the control unit calculates the torque feedback correction amount of the engine based on the deviation from the target speed of the engine and controls the required torque of the engine.

[0016] Furthermore, according to one embodiment of the present invention, the control unit may reduce the torque feedback correction amount of the engine by a predetermined ratio at least at the end of the required torque control of the engine.

[0017] In addition, according to one embodiment of the present invention, the predetermined determination threshold can be an output value corresponding to the maximum torque error, which includes the friction torque error of the output shaft of the engine.

[0018] The effects of the invention

[0019] According to one embodiment of the present invention, when the sum of the required output of the engine and the maximum power output of the generator is less than a predetermined judgment threshold, the required torque of the engine is controlled by the torque feedback correction amount of the engine. Therefore, it is advantageous to maintain the engine speed and prevent stalling without relying on the driver's operation, for example, when the battery is in a state of reduced output at low temperatures.

[0020] Furthermore, according to one embodiment of the present invention, by pre-setting a predetermined judgment threshold for the target speed of each engine depending on the engine coolant temperature, it is possible to perform correct judgment processing at high speed, which is advantageous in reliably preventing engine stalling.

[0021] Furthermore, according to one embodiment of the present invention, the engine's required torque is controlled by determining whether the sum of the engine's required output and the generator's maximum power output is less than a value obtained by adding a hysteresis setting to a predetermined determination threshold. Therefore, control oscillations caused by the increase or decrease in power consumption due to the switching on and off of auxiliary equipment such as those in hybrid vehicles can be prevented.

[0022] Furthermore, according to one embodiment of the invention, the torque feedback correction amount is gradually reduced at least at the end of the time when the engine requires torque control, which is advantageous in mitigating vehicle vibration and driver discomfort.

[0023] Furthermore, according to one embodiment of the present invention, by setting a predetermined determination threshold to an output value corresponding to the maximum torque error including the friction torque error of the engine's output shaft, the torque feedback correction amount is calculated taking into account the maximum torque error, which is advantageous in preventing engine stalling. Attached Figure Description

[0024] Figure 1 This is a timing diagram showing the changes in engine required torque, speed, and generator torque when the battery output decreases in a hybrid vehicle in the background technology.

[0025] Figure 2 This is a block diagram illustrating the schematic structure of a control system in a hybrid vehicle according to an embodiment of the present invention.

[0026] Figure 3 It is a graph that shows the changes in engine coolant temperature, oil temperature, and their temperature difference over time.

[0027] Figure 4A It is a schematic block diagram representing the flow of energy between the engine, generator, and battery in a hybrid vehicle.

[0028] Figure 4B This is a schematic diagram illustrating the determination threshold used in the control of this embodiment.

[0029] Figure 5 This is a flowchart illustrating the control method of this embodiment.

[0030] Figure 6 This is a timing diagram illustrating an example of the operation of the control device in this embodiment. Detailed Implementation

[0031] 1. Vehicle structure

[0032] like Figure 2 As illustrated, in a hybrid vehicle 10 according to one embodiment of the present invention, a battery 100 is connected to inverters 101, 102, and 103, each inverter being connected to a front motor 104, a rear motor 105, and a generator 106. Inverters 101 and 102 convert the DC power supplied from the battery 100 into three-phase AC power, which is then supplied to the front motor 104 and the rear motor 105, respectively.

[0033] Inverter 103 converts the three-phase AC power generated by generator 106 into DC power, which is used to charge battery 100 and power auxiliary equipment (not shown). Furthermore, during regenerative braking of the hybrid vehicle 10, front motor 104 and rear motor 105 function as generators, and the three-phase AC power generated by each motor is converted into DC power by inverters 101 and 102 for charging battery 100.

[0034] The rotating sub-shaft of generator 106 is mechanically connected to the output shaft of engine 107, and electricity is generated by the rotation of engine 107. Here, the rotational speeds of engine 107 and generator 106 are the same. In addition, generator 106 also functions as a motor. Specifically, it can also function as a starter for starting engine 107, or rotate engine 107 as a load to generate waste electricity.

[0035] Furthermore, if the hybrid vehicle 10 is a plug-in hybrid, the battery 100 can also be charged via a charging device (not shown) using power supplied from a commercial power source for home use or a fast-charging power source for a charging station.

[0036] The clutch CL mechanically disconnects or connects the transmission of rotational torque from engine 107 to gear mechanism 108. When clutch CL is disconnected, the output shaft of engine 107 is mechanically connected only to generator 106, and the hybrid vehicle 10 enters EV driving mode or series driving mode. When clutch CL is engaged, the output shaft of engine 107 is connected to gear mechanism 108 in addition to generator 106. Gear mechanism 108 transmits the drive torque of front motor 104 to front wheel 109, and if clutch CL is engaged, the drive torque of engine 107 can also be transmitted to front wheel 109. Additionally, rear motor 105 transmits drive torque to rear wheel 111 via gear mechanism 110.

[0037] The electronic control unit (ECU) 112 constitutes the control unit of the hybrid vehicle 10. Specifically, it calculates the vehicle output required for the operation of the hybrid vehicle 10 based on various detection quantities and various operating information, switches the driving mode (EV mode, series mode) by controlling the clutch CL and inverters 101, 102, and 103, and performs output control of the engine 107, the front motor 104 and the rear motor 105, and the generator 106, etc.

[0038] Furthermore, the driving modes of the hybrid vehicle 10 are described below.

[0039] In EV mode, the clutch CL is disengaged and the engine 107 is stopped. The vehicle is driven by the power supplied from the battery 100 to power the front motor 104 and the rear motor 105. Alternatively, if the power supplied from the battery 100 is insufficient to meet the required output, the engine 107 is started by switching to the series mode described below, and the power generated by the generator 106 is also used to drive the front motor 104 and the rear motor 105.

[0040] In series mode, the clutch CL is disengaged, and all driving force from the engine 107 is applied to the generator 106. The front motor 104 and rear motor 105 are then driven by the electricity generated by the generator 106 for propulsion. If the power generated by the generator 106 is insufficient to meet the required output, the power stored in the battery 100 is also used to drive the front motor 104 and rear motor 105. Conversely, if the power generated by the generator 106 exceeds the required output, the remaining power is used to charge the battery 100.

[0041] Furthermore, the ECU 112 uses the judgment threshold stored in the judgment threshold table 113 described later and the following sensor signals as inputs to perform engine torque control in this embodiment: throttle opening signal from a throttle position sensor (not shown) that detects the amount and speed of the throttle pedal operated by the driver; engine speed signal from a speed sensor (not shown) that detects the rotational speed "rpm" of the output shaft of the engine 107; engine coolant temperature signal from a coolant temperature sensor (not shown) that detects the temperature of the coolant in the engine 107; and SOC signal from a SOC (State of Charge) sensor (not shown) that detects the battery balance and state of charge of the battery 100.

[0042] Furthermore, the ECU112 is configured to include a processor such as a CPU (Central Processing Unit), a ROM (Read-only memory) storing the control program executed by the processor, a RAM (Random Access Memory) serving as the working area for the control program, and an interface section for peripheral circuits. The aforementioned determination threshold table 113 can also be stored in a ROM that can be deleted and rewritten. The control method of this embodiment can be implemented by executing a program on the processor of the ECU112. Hereinafter, after explaining the torque error between the engine and the generator, the control method of this embodiment will be described in detail.

[0043] 2. Calculation of torque error

[0044] As mentioned above, when the battery output decreases due to low temperatures or battery degradation and cannot assist the generator's power operation, a torque error will occur, preventing the engine speed from being maintained at the target value unless the driver increases the engine's required output. This torque error occurs due to the deviation between the engine's coolant and oil temperatures, as described below.

[0045] like Figure 3As shown, the engine coolant temperature (ENG coolant temperature) and oil temperature (ENG oil temperature) have different rates of temperature rise, resulting in a temperature difference that changes over time. In particular, the deviation between coolant and oil temperatures tends to increase when the engine is repeatedly started and stopped in short intervals. The frictional torque caused by friction acting on the engine's output shaft is determined by both oil temperature and engine speed; the lower the oil temperature, the greater the frictional torque. When the oil temperature is estimated based on the coolant temperature, a large deviation between the coolant and oil temperatures leads to an error between the actual frictional torque value and the value calculated from the coolant temperature. The maximum torque error is calculated by adding the error relative to the engine command and the frictional torque of the reducer connected to the engine. Therefore, it is necessary to control the engine to increase the required output to prevent a decrease in engine speed due to this maximum torque error.

[0046] 3. Engine torque control

[0047] like Figure 4A As shown, during regeneration, the rotational torque of the engine 107 is transmitted to the generator 106, which generates electricity to charge the battery 100. Conversely, during power operation, power is supplied from the battery 100 to the generator 106, which acts as a motor to rotate the engine 107. For example, when the engine speed of the engine 107 decreases below a target value, the ECU 112 controls the generator 106 to operate as a motor, thereby maintaining the engine speed of the engine 107 near the target value. However, if the battery 100 is in a reduced output state, the power output of the generator 106 cannot be sufficiently increased. In other words, the possible value of the power output of the generator 106 corresponds to the possible value of the battery 100's output.

[0048] like Figure 4B As shown, in order to prevent the engine speed of 107 from decreasing due to torque error, the required output P of engine 107 needs to be achieved. ENG-RQ The maximum power output P of generator 106 during operation GEN-DRV The total value is above the torque error. Therefore, when the maximum torque error occurs, the engine requires an output P that will not reduce the speed of engine 107. ENG-RQ With the generator's maximum output P GEN-DRV The total value is set as the judgment threshold P. TH .

[0049] Judgment threshold P TH For each target speed of engine 107, which is preset based on engine coolant temperature, the decision threshold table 113 within ECU 112 or a separate storage device can be stored. Multiple assumed decision thresholds P are stored in decision threshold table 113. THThe ECU112 can quickly obtain the correct judgment threshold P based on sensor data of the engine's target speed and coolant temperature. TH In addition, the engine requires an output P ENG-RQ Maximum output P of generator power operation GEN-DRV and the judgment threshold P TH The unit is power "kW", and the engine is required to output P. ENG-RQ The engine requires power output.

[0050] Preferably, the decision threshold P is... TH The determination is made by adding a hysteresis setpoint ΔH. Adding the hysteresis setpoint ΔH can absorb fluctuations caused by the power consumption of auxiliary equipment (such as air conditioning) within the vehicle 10. That is, the normal engine output value also includes the power consumption of auxiliary equipment, and therefore the power consumption varies depending on whether the auxiliary equipment is turned on or off. Therefore, the engine requires an output P whenever the auxiliary equipment is turned on or off. ENG-RQ With the generator's maximum output P GEN-DRV The total value exceeds or falls below the judgment threshold P TH This can lead to control oscillations. Adding a hysteresis setpoint ΔH is to prevent these oscillations.

[0051] As described below, when the engine requires an output P ENG-RQ With the generator's maximum output P GEN-DRV The total value is lower than the judgment threshold P TH In this case, ECU112 feeds back (F / B) the engine torque correction amount based on the deviation from the target engine speed, thereby controlling the engine torque in a way that follows the target engine speed.

[0052] like Figure 5 As shown, ECU112 determines whether the current driving mode is a series mode (step 201). If it is a series mode ("Yes" in step 201), it inputs the target engine speed and engine coolant temperature and obtains the judgment threshold P from the judgment threshold table 113. TH And determine the current engine output requirement P. ENG-RQ With the generator's maximum output P GEN-DRV Is the total value less than the judgment threshold P? TH (Step 202).

[0053] The current engine requires an output of P ENG-RQ With the generator's maximum output P GEN-DRV The total value is less than the judgment threshold P THIn the case of "Yes" in step 202, as described above, the engine speed of engine 107 decreases due to torque error, which may cause stalling. Therefore, ECU 112 calculates an engine torque F / B correction amount based on the difference between the current engine speed and the target speed, and controls the engine torque of engine 107 according to the calculated engine torque F / B correction amount to avoid stalling (step 203). At this time, it is preferable to make the change in engine torque based on the engine torque F / B correction amount gradual. For example, instead of a sharp increase at the beginning of the engine torque F / B correction, a predetermined increase rate is set to reduce vehicle vibration and driver discomfort.

[0054] Furthermore, the engine torque F / B correction is calculated using PI (Proportional-Integral) control, which consists of an integral term and a proportional term, as described later. Integral correction alone would cause speed oscillations, therefore a proportional correction is added to stabilize the control. The unit for the engine torque F / B correction is "Nm".

[0055] Next, ECU112 determines that the controlled engine requires P output. ENG-RQ With the generator's maximum output P GEN-DRV Is the total value less than the judgment threshold P? TH The sum of P and the hysteresis setting term ΔH (step 204). If P ENG-RQ +P GEN-DRV <P TH If +ΔH ("Yes" in step 204), then ECU112 repeats the above engine torque F / B correction control (step 203).

[0056] If P ENG-RQ +P GEN-DRV For P TH If +ΔH or higher (No in step 204), ECU 211 ends engine torque correction control, but at this time performs a smoothing process (step 205) to gradually reduce the variation in engine torque based on the engine torque F / B correction amount. Instead of abruptly reducing the engine torque at the end of the F / B correction, a predetermined reduction rate is set, thereby reducing vehicle 10 vibration and driver discomfort. At this moment, since the possibility of engine 107 stalling is considered low, the reduction rate can be made less than the increase rate of the engine torque F / B correction amount in step 203, further reducing vehicle 10 vibration and driver discomfort.

[0057] When P in step 202 ENG-RQ +P GEN-DRV For P THIf the above situation (No in step 202) or the smoothing process (step 205) ends, ECU 112 performs normal control during series driving (step 206). If the driving mode is other than series mode (No in step 201), the control of this embodiment ends and normal control continues.

[0058] 4. Actions

[0059] Next, refer to Figure 6 The operation of the hybrid vehicle 10 according to this embodiment will be described in detail.

[0060] First, such as Figure 6 As shown in (B) and (C), ECU112 is set to input the engine's required output P. ENG-RQ Maximum output P of generator power operation GEN-DRV The threshold P is determined by the engine speed and engine coolant temperature. TH And judged to be in P ENG-RQ +P GEN-DRV <P TH The +ΔH state indicates that the generator 106 is in a state of insufficient power output.

[0061] like Figure 6 As shown in (A), when the power output of generator 106 is insufficient, at time t1 during EV driving, engine 107 starts, and at time t2, it transitions to series driving. During engine startup, as... Figure 6 As shown in (F) and (G), the engine starts to rotate under the power of the generator 106 and reaches the target speed.

[0062] When the transition to series driving occurs at time t2, ECU112 as follows: Figure 6 As shown in (F), the deviation between the engine speed 107 and the target speed is referenced, and the following calculations are performed: Figure 6 The proportional correction amount (engine torque F / B correction amount (P item) "Nm") shown in (d1) and Figure 6 The integral correction (engine torque F / B correction (I term) "Nm") shown in (d2) is calculated by multiplying the sum of the proportional correction and the integral correction by a switching factor that uses an increasing rate of increase. Figure 6 (d3)), and calculated Figure 6 The required engine torque F / B correction amount is shown in (D).

[0063] Because after time t2, the engine speed slightly exceeds the target speed ( Figure 6 Therefore, the engine torque F / B correction is required to display a negative value, but then increases and remains at a positive value as shown in curve 301. The result is, as... Figure 6 As shown in (E), the engine requires an increase in torque and maintains that increase, and the actual torque 302 follows the engine's required torque.

[0064] Because the engine requires increased torque, such as Figure 6 As shown in (F), the engine speed 303 remains almost at the target value and continues to move after time t2, preventing the speed reduction and engine stall 402 that occurred in the previous curve 401.

[0065] When the above series driving continues, and if Figure 6 As shown in (B) and (C), at time t3, P ENG-RQ +P GEN-DRV Become P TH When the value is above +ΔH, ECU112 determines that the power output of generator 106 has been restored, and if... Figure 6 As shown in (d3), the switching coefficient 304 gradually decreases from time t3 to time t4. Accompanying this, as... Figure 6 As shown in (D), the engine torque F / B correction is required to decrease from time t3 and become zero at time t4.

[0066] Because the engine torque F / B correction is required to be zero, therefore... Figure 6 As shown in (E), the engine torque value required at this point is maintained thereafter, thus... Figure 6 As shown in (F), the engine speed is also maintained. Additionally, as... Figure 6 As shown in (G), after time t3, the power output of generator 106 is restored, so it can operate as a generator or motor as needed.

[0067] also, Figure 6 The illustrated timing diagram shows a scenario where the driver does not increase the output through throttle operation, resulting in series driving. When the driver increases the engine's output demand, the control based on this embodiment does not operate. That is, the control based on this embodiment applies when the hybrid vehicle 10 is parked or driving at low output.

[0068] Various embodiments have been described above with reference to the accompanying drawings, but the present invention is certainly not limited to these examples. Those skilled in the art will obviously be able to conceive of various modifications or alterations within the scope of the claims, and these are naturally understood to fall within the technical scope of the present invention. Furthermore, the constituent elements of the above embodiments can be combined arbitrarily without departing from the spirit of the invention.

[0069] Furthermore, this application is based on Japanese Patent Application No. 2021-123380, filed on July 28, 2021, the contents of which are incorporated herein by reference.

[0070] Symbol Explanation

[0071] 10 Hybrid vehicles

[0072] 100 batteries

[0073] Inverters 101, 102, and 103

[0074] 104 front motor

[0075] 105 rear motor

[0076] 106 Generator

[0077] 107 engine

[0078] 108 Gear Mechanism

[0079] 109 front wheel

[0080] 110 Gear Mechanism

[0081] 111 Rear Wheel

[0082] 112 Electronic Control Unit (ECU)

Claims

1. A hybrid vehicle comprising: an engine; a generator mechanically connected to the output shaft of the engine and capable of performing regenerative braking or power operation; a battery storing electricity generated during the regenerative braking of the generator and supplying electricity during the power operation of the generator; a motor converting the electricity supplied from the battery into driving force for drive wheels; and a control unit controlling the engine, the generator, and the motor, characterized in that... When starting the engine, the control unit determines whether the sum of the engine's required output and the generator's maximum power output is less than a predetermined threshold. If the total value is less than the predetermined judgment threshold, the control unit calculates the torque feedback correction amount of the engine based on the deviation from the target speed of the engine and controls the required torque of the engine.

2. The hybrid vehicle according to claim 1, characterized in that, For each target speed of the engine, the predetermined judgment threshold is preset based on the engine's coolant temperature.

3. The hybrid vehicle according to claim 1, characterized in that, The control unit also determines whether the total value is less than the value obtained by adding a hysteresis setting value to the predetermined judgment threshold. If the total value is less than the value obtained by adding a hysteresis setting to the predetermined judgment threshold, the control unit calculates the torque feedback correction amount of the engine based on the deviation from the target speed of the engine and controls the required torque of the engine.

4. The hybrid vehicle according to claim 2, characterized in that, The control unit also determines whether the total value is less than the value obtained by adding a hysteresis setting value to the predetermined judgment threshold. If the total value is less than the value obtained by adding a hysteresis setting to the predetermined judgment threshold, the control unit calculates the torque feedback correction amount of the engine based on the deviation from the target speed of the engine and controls the required torque of the engine.

5. The hybrid vehicle according to claim 1, characterized in that, The control unit reduces the torque feedback correction amount of the engine by a predetermined ratio at least at the end of the required torque control of the engine.

6. The hybrid vehicle according to claim 2, characterized in that, The control unit reduces the torque feedback correction amount of the engine by a predetermined ratio at least at the end of the required torque control of the engine.

7. The hybrid vehicle according to claim 3, characterized in that, The control unit reduces the torque feedback correction amount of the engine by a predetermined ratio at least at the end of the required torque control of the engine.

8. The hybrid vehicle according to claim 4, characterized in that, The control unit reduces the torque feedback correction amount of the engine by a predetermined ratio at least at the end of the required torque control of the engine.

9. The hybrid vehicle according to any one of claims 1 to 8, characterized in that, The specified threshold value is the output value corresponding to the maximum torque error, which includes the friction torque error of the engine's output shaft.

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