Method for controlling a powertrain unit for a motor vehicle having a hybrid electric transmission

Abstract

A method for controlling a powertrain unit of a motor vehicle, the powertrain unit comprising an internal combustion engine (2), a main electric machine (3) and an auxiliary electric machine (4) connected to the internal combustion engine, the method comprising the following steps, in a series hybrid powertrain mode in which the main electric machine alone generates mechanical power to the wheels and the internal combustion engine drives the auxiliary electric machine as a generator so as to generate charging power: - controlling the engine speed at a set value, wherein the torque of the engine is controlled on the basis of a torque value to be applied to the auxiliary machine; - checking for a condition of saturation of the torque control of the auxiliary electric machine; and - in the event of saturation, correcting the torque demanded to the internal combustion engine so that the engine speed returns to its set value.

Description

Technical Field

[0001] This invention relates to the field of hybrid powertrains for motor vehicles. More particularly, this invention relates to a method for controlling a hybrid powertrain for a motor vehicle, the hybrid powertrain comprising an internal combustion engine, a main electric motor, and an auxiliary electric motor mechanically connected to the internal combustion engine. Background Technology

[0002] Hybrid powertrain architecture (where the powertrain includes a main motor and an auxiliary motor called a "high-voltage starter generator" (HSG), which is mechanically rotatably connected to the internal combustion engine) is well known, especially through Figure 1 An example of a hybrid powertrain architecture is given. The presence of this auxiliary unit can add a great deal of functionality to the powertrain, especially in terms of the starting speed of the internal combustion engine.

[0003] according to Figure 1 For example, the hybrid powertrain 1 includes an internal combustion engine 2 (ICE), a main motor 3 (ME), and an auxiliary motor 4 (HSG). These two motors are electrically connected to the vehicle's battery (BAT). The powertrain 1 includes: a solid main shaft 5 connected to the engine 2; a hollow main shaft 6 coaxial with the solid main shaft and connected to the main motor 3; a secondary shaft 7; and a solid auxiliary shaft 8 connected to the auxiliary motor 4 via a fixed input pinion 9 of the auxiliary motor engaging a fixed auxiliary coupling pinion 10 carried on the auxiliary shaft 8. The solid main shaft 5 also carries a fixed main coupling pinion 11, which engages with the fixed auxiliary coupling pinion 10 of the auxiliary shaft 8, thereby ensuring continuous motion transmission to the auxiliary shaft 8. The internal combustion engine 2, connected to the solid main shaft 5, is therefore permanently connected to the auxiliary motor 4. In other words, the two power units (the internal combustion engine 2 and the auxiliary motor 4, respectively) rotate systematically at proportional speeds according to the ratios formed by the gear transmissions 9, 10, and 11.

[0004] The engagement and disengagement of the gear ratio are ensured by a coupling system with dog-tooth or flat teeth (also known as "pawls") that can move axially on the shaft, independent of the synchronizing device. The dog-tooth teeth are controlled in a direction toward the axially fixed pinions, which idle on their shafts. The engagement of the movable dog-tooth teeth with the pinions engages the shaft and pinions, thereby transmitting torque to the wheels at the engaged gear ratio.

[0005] Here, the transmission uses three engagement systems C1, C2, and C3 with dog-tooth gears. This is a semi-automatic type of gearbox, meaning it operates the same as a manual gearbox, but gear shifting is done automatically by means of an actuation system for engaging and disengaging the dog-tooth gears.

[0006] The gearbox combines torque from engine 2, main motor 3, and auxiliary motor 4 on the countershaft 7, directed towards the vehicle's wheels. Gear shifting is controlled by three dog-tooth coupling systems C1, C2, and C3, respectively arranged on the solid main shaft 5, countershaft 7, and intermediate shaft 8. The first coupling system (referred to as the main coupling C1) on the solid main shaft 5 engages the short-combustion engine gear ratio (on the left) corresponding to the second reduction ratio of the transmission and the long-combustion engine gear ratio (on the right) corresponding to the fourth reduction ratio of the transmission. The second coupling system (referred to as the auxiliary coupling C2) on the countershaft 7 engages the two electric gear ratios EV1 and EV2 of the main motor. The third coupling system (referred to as the transmission coupling C3) on the auxiliary shaft 8 transmits torque from the auxiliary motor 4 to the countershaft 7 (right side) or the hollow main shaft 6 (left side).

[0007] This architecture allows for the combination of pure combustion engine gear ratios (where only the first main shaft is mechanically connected to the secondary shaft), pure electric gear ratios (where only the second main shaft is mechanically connected to the secondary shaft), and hybrid power gear ratios (where both the first and second main shafts are mechanically connected to the secondary shaft).

[0008] One specific operating mode of this transmission is the so-called series hybrid mode. In this mode, the main motor 3 is connected to the wheels via an electric gear ratio EV1 or EV2. The internal combustion engine 2, connected to the auxiliary motor 4, remains in neutral, meaning it does not transmit torque to the wheels but is rotating. This provides the possibility of providing torque to the internal combustion engine via the auxiliary motor 4 connected to it and thus charging the battery (or directly powering the main motor 3). Therefore, in series hybrid mode, the internal combustion engine drives the auxiliary motor, which operates as a generator, and provides electrical energy to the battery and, possibly, the main motor. The main motor itself provides mechanical power to the wheels. Energy is thus transferred in series from the internal combustion engine through the auxiliary motor to the battery or the main motor.

[0009] In this series hybrid mode, the main motor 3 is therefore the only power unit connected to the vehicle wheels via an electric gear ratio EV1 or EV2. One advantage of this mode is that the main motor 3 can be used to drive the vehicle, while the auxiliary motor 4, driven by the internal combustion engine, operates as a generator. This allows the transmission to be positioned at an efficiency point beneficial to the internal combustion engine, enabling the generation of charging power while simultaneously adjusting the target speed to suit noise constraints (thus primarily avoiding excessive speeds), and keeping the wheels rotating at low speeds, as the main motor is responsible for their rotation. Therefore, this mode is particularly advantageous at low speeds, where no gear ratio can engage the internal combustion engine (as the speed would be too low). In this mode, the internal combustion engine speed is adjusted to allow it to operate even when the vehicle is stationary, charging the battery to power the vehicle's appliances or the main motor, ensuring the vehicle can be driven.

[0010] However, the internal combustion engine and the auxiliary motor do not have the same torque-generating dynamics. Therefore, the response of the electrically controlled auxiliary motor will be much faster than that of the internal combustion engine. Thus, in this mode, the speed regulation calculation for the auxiliary motor must be applied to its torque. This requires the internal combustion engine to generate power in parallel. Considering that to ensure speed balance, the auxiliary motor must be able to absorb all the power generated by the internal combustion engine, it can be inferred that the electrical power supplied to the vehicle's HT grid (which has a higher voltage compared to the 12V low voltage of the onboard grid) (to provide power to the battery and, possibly, to the main motor) will be equivalent to the power supplied by the internal combustion engine, with comparable efficiency.

[0011] The resulting problem is how to manage and precisely control the power supplied by the internal combustion engine, especially since the latter is quite imprecise in producing the required torque. Therefore, there is often an error of tens of Nm between the set torque demanded by the engine and the actual torque produced. For example, if the engine overproduces the required torque, two scenarios may occur. If the auxiliary motor / battery unit can absorb the excess power supplied by the internal combustion engine, the adjustment will be designed to increase the charging power of the auxiliary motor to maintain the engine speed at its set value. The impact in this case is not significant, as the charging power will only be slightly higher than expected.

[0012] In contrast, if the auxiliary motor / battery unit cannot absorb the excess power provided by the internal combustion engine, speed regulation will limit the auxiliary motor to its capacity. However, since the internal combustion engine provides more power, speed regulation will begin at saturation and the speed of the internal combustion engine / auxiliary motor unit will increase, possibly until the peak speed limit (maximum permissible speed) of the internal combustion engine is reached. This will significantly reduce its torque, which is therefore very undesirable in terms of noise. Moreover, as mentioned above, the series hybrid mode is used especially at low speeds, so if this occurs, no external noise will be able to mask the surge in speed.

[0013] One solution to this problem is to significantly increase the size of the auxiliary motor, ensuring it can always absorb excess power from the internal combustion engine. However, this solution is impractical due to cost and size considerations. A simpler solution is to allow for a margin in the potential capacity of the auxiliary motor / battery unit when calculating the power required from the internal combustion engine. For example, if the auxiliary motor / battery unit can only charge 20kW, then by taking a 20% margin, the power required from the internal combustion engine will not exceed 16kW.

[0014] However, this margin system fails to operate when the battery no longer allows for sufficient charging power (e.g., less than 5 kW). This can occur in cold conditions, especially below -15°C, where the battery can only support a few kW of charging power. It can also happen after prolonged charging, as the battery adjusts its charging power. Furthermore, when the foot is released from the brake pedal and the brake pedal is depressed, the main motor charges the battery, thus utilizing all of its potential charging capacity, leaving no usable charging power for the auxiliary motor. In all these cases, very low potential charging power is observed, and the margin provided in terms of potential capacity becomes inefficient.

[0015] Specifically, even with a 20% margin when the potential charging power is, for example, 2kW, this is equivalent to demanding 1600W from the internal combustion engine. When the engine speed is adjusted to the target value of approximately 1500rpm, the torque demanded from the engine for 1600W would be 10Nm. However, as noted above, the engine may have an error of tens of Nm relative to the required set torque. Therefore, in this case, sufficient margin cannot be taken, as this is equivalent to demanding zero torque from the engine to prevent it from excessively producing the required 10Nm of torque. Summary of the Invention

[0016] In view of the above, the object of the present invention is to provide a method for controlling a hybrid powertrain in a motor vehicle, which overcomes the aforementioned deficiencies in the extreme states of a series hybrid mode. More specifically, the present invention aims to enable compensation for errors in the excessive torque generation of the internal combustion engine in the series hybrid mode of the powertrain.

[0017] Therefore, the present invention relates to a method for controlling a powertrain for a motor vehicle having a hybrid electric drive system, the powertrain including an internal combustion engine, a main motor, and an auxiliary motor mechanically rotatably connected to the internal combustion engine, the two motors being connected to a vehicle's battery, the method comprising the step of adjusting the engine speed to a set value in a series hybrid drive mode where the main motor alone generates mechanical power toward the vehicle's wheels and the internal combustion engine drives the auxiliary motor, which operates as a generator, to generate charging power, wherein the torque of the engine is controlled based on a torque setpoint to be applied to the auxiliary motor, the method being characterized in that the method includes the step of checking for torque control saturation of the auxiliary motor; and, if saturation is found, correcting the torque demanded on the internal combustion engine to return the engine speed to its set value.

[0018] Advantageously, the step of correcting the torque required by the internal combustion engine is performed by adjusting the torque margin maintained between the torque setpoint of the auxiliary motor and the maximum potential torque that the auxiliary motor can produce relative to a given minimum torque margin value to be maintained. This adjustment can ensure the minimum torque margin value of the auxiliary motor, thereby ensuring speed stability.

[0019] Advantageously, starting from the minimum torque margin value, the adjustment calculation is used to correct the torque of the internal combustion engine related to the saturation of the auxiliary motor, which is intended to correct the target torque required by the internal combustion engine.

[0020] Advantageously, the maximum potential torque that the auxiliary motor can generate corresponds to the maximum potential charging power that the auxiliary motor / battery cell can generate.

[0021] Advantageously, when the torque of the auxiliary motor approaches its saturation value, a step is triggered to correct the torque required by the internal combustion engine.

[0022] Advantageously, the saturation value corresponds to the maximum torque value that the auxiliary motor can produce.

[0023] Advantageously, when the internal combustion engine excessively generates the required torque, a step to correct the torque required by the internal combustion engine is triggered. Attached Figure Description

[0024] Other features and advantages of the invention will become more apparent from the following description, given in a non-limiting manner with reference to the accompanying drawings, in which:

[0025] [ Figure 1 [This is an example of a powertrain architecture for a hybrid electric vehicle, on which the control method of the present invention can be implemented;]

[0026] [ Figure 2 [This is a block diagram of the second adjustment performed in the method of the present invention;]

[0027] [ Figures 3A to 3E [ ] is a graph showing the changes in torque of the internal combustion engine and auxiliary motor, as well as engine speed, during the method of the present invention. Detailed Implementation

[0028] For reference Figure 1 As can be seen, in the series hybrid mode of the transmission, speed regulation regarding the setpoint, especially the setpoint adapted to noise constraints (usually a setpoint that avoids excessively high speeds), is performed by the auxiliary motor 4, and is achieved through the different dynamic characteristics of the torque generated between the auxiliary motor 4 and the internal combustion engine 2. For this purpose, such as... Figure 2 As shown, the speed regulation in the series hybrid mode is designed to calculate the torque setpoint C_req_HSG to be applied to the auxiliary motor operating in generator mode to generate a given charging power, while regulating the speed to the set value, and in parallel requesting the internal combustion engine 2 to generate power according to the torque target Target_ICE_basic representing the charging target.

[0029] When entering a series hybrid drive system, the speed regulation of the internal combustion engine / auxiliary motor unit therefore includes determining the torque setpoint to be applied to the auxiliary motor, and includes controlling the internal combustion engine in parallel based on this torque setpoint to produce the corresponding power.

[0030] The present invention aims to optimize the saturation of the auxiliary motor in a series hybrid power mode.

[0031] There is a risk of auxiliary motor saturation when its torque approaches its saturation value (the maximum torque the auxiliary motor can produce). This maximum torque saturation occurs when the internal combustion engine produces excessive torque as required by the engine, and the auxiliary motor / battery unit cannot absorb the excess power. In this situation, the speed regulation control auxiliary motor reaches its capacity limit. Auxiliary motor saturation prevents it from following the torque trajectory of the engine, which is providing more power, meaning there is a risk of overspeeding.

[0032] To address this issue and to optimally manage auxiliary motor saturation in series hybrid mode, the principle of this invention lies in adding a second regulation in addition to speed regulation. This second regulation is designed to adjust the torque margin (Margin_HSG) maintained between the torque setpoint sent to the auxiliary motor (calculated by speed regulation) and the maximum potential torque that the auxiliary motor can produce. This maximum potential torque is obtained from the maximum potential charging power that the auxiliary motor / battery unit can produce.

[0033] Therefore, the second regulation only intervenes when the torque of the auxiliary motor is detected to be too close to its saturation limit. Only under these circumstances can the torque setpoint of the internal combustion engine be lowered, bringing the speed back under control, that is, back to its set value. Thus, the second regulation comes into play when the first regulation (i.e., the speed regulation performed by the auxiliary motor) is saturated.

[0034] Returning to the example given above (where the engine speed is adjusted to a setpoint of approximately 1500 rpm, and where a torque of 10 Nm is required from the internal combustion engine for a target power of 1600 W), the open-loop control of the internal combustion engine is therefore based on the torque target Target_ICE_basic corresponding to the required torque of 10 Nm. If the internal combustion engine does not excessively produce the required torque, the auxiliary motor is fully capable of absorbing the power provided by the internal combustion engine, and therefore the second regulation will not intervene.

[0035] On the other hand, if the internal combustion engine excessively generates the torque target Target_ICE_basic, the auxiliary motor will reach saturation to absorb the undesirable additional power provided by the internal combustion engine, thus triggering a second adjustment. This second adjustment takes the maintained torque margin Margin_HSG of the auxiliary motor as input, considering the torque setpoint C_req_HSG calculated by the speed regulation, and adjusts the maintained torque margin to ensure that the auxiliary motor always maintains a predetermined minimum torque margin value Cmin_HSG, thereby ensuring speed stability. In other words, the minimum torque margin value Cmin_HSG can define the target torque margin for adjusting the auxiliary motor in relation to its saturation. The torque margin adjustment of the auxiliary motor is then designed to calculate a torque correction value C_cor_ICE of the internal combustion engine related to the saturation of the auxiliary motor, which is intended to correct the torque target Target_ICE_basic required by the internal combustion engine. Applying the correction value C_cor_ICE to the torque target Target_ICE_basic provides the final torque setpoint C_req_ICE of the internal combustion engine, making it possible to manage the saturation of the auxiliary motor. This second adjustment uses, for example, an integral regulator, which takes as input the difference between the saturation torque obtained from the speed regulation and the maximum permissible charging torque (from which the target margin of the regulation is subtracted). If higher power is required, a proportional component can also be added.

[0036] Figures 3A to 3E This is a graph showing the torque changes of the internal combustion engine and the auxiliary motor, as well as the engine speed changes, during the method of the present invention, under test conditions simulating a sudden loss of potential charging capability on the battery side of the auxiliary motor (i.e., in these cases, the battery does not leave any available charging power for the auxiliary motor). This is typically a case where the driver lifts their foot off the accelerator, in which case the charging power is provided by the main motor to, for example, meet the driver's expectations. Figure 3E This phenomenon is illustrated in the graph, which shows the curve of the battery-side potential charging capacity P_BAT, which rapidly rises from a possible potential charging capacity of approximately 35kW to 0kW. Figure 3D As shown, this sudden drop in the battery's potential charging capacity manifests as the auxiliary motor's available potential torque P_HSG (negative, due to charging mode) rising to the torque C_req_HSG actually required by the speed regulation, leading to auxiliary motor saturation. Figure 3CAs shown, due to the slow response of the internal combustion engine, its torque cannot decrease dynamically in the same way as the auxiliary motor, therefore the engine speed R will briefly increase relative to the speed setpoint R_req_ICE. In this saturation state of the auxiliary motor, the second adjustment performed by the method of the present invention will, as described above, reduce the torque demanded by the internal combustion engine until the speed recovers to its setpoint R_req_ICE. Therefore, according to this example, it is possible to... Figure 3C It can be seen that the engine speed R increased by 500 rpm, and then gradually returned to its set value R_req_ICE. If the second adjustment is not performed, the speed will reach the peak speed limit of over 6000 rpm.

Claims

1. A method for controlling a powertrain for a motor vehicle having a hybrid electric transmission, the powertrain comprising an internal combustion engine (2), a main electric machine (3) and an auxiliary electric machine (4) mechanically connected in rotation to the internal combustion engine, said main and auxiliary electric machines being connected to a storage battery (BAT) of the vehicle, said method comprising, in a series hybrid transmission mode in which the main electric machine (3) alone generates mechanical power towards the wheels of the vehicle and the internal combustion engine (2) drives the auxiliary electric machine (4) operating as a generator to generate charging power, a step of regulating the engine speed to a set value (R_req_ICE) in which the torque of the engine is controlled on the basis of a torque setpoint (C_req_HSG) to be applied to said auxiliary electric machine, said method being characterized in that it comprises: a step of checking a condition of torque control saturation of said auxiliary electric machine; and in case of saturation, a step of correcting the torque requested to the internal combustion engine so that the engine speed returns to its set value, wherein the step of correcting the torque requested to the internal combustion engine is performed according to an adjustment of the torque margin maintained between the torque setpoint of said auxiliary electric machine and the maximum potential torque that the auxiliary electric machine is able to generate, with respect to a given minimum torque margin value to be maintained, said adjustment being able to ensure said minimum torque margin value of said auxiliary electric machine, thus ensuring the stability of the speed.

2. The method of claim 1, wherein, From this minimum torque margin value, the adjustment calculates a torque correction value (C_cor_ICE) of the internal combustion engine related to the saturation of the auxiliary electric machine, this torque correction value being intended to correct the torque target (Target_ICE_basic) requested to the internal combustion engine.

3. The method of claim 1 or 2, wherein, The maximum potential torque that the auxiliary electric machine is able to generate corresponds to the maximum potential charging power that the auxiliary electric machine / battery unit is able to generate.

4. The method of any of the preceding claims, wherein, The step of correcting the torque requested to the internal combustion engine is triggered when the torque of the auxiliary electric machine approaches a saturation value.

5. The method of claim 4, wherein, Said saturation value corresponds to the maximum torque value that said auxiliary electric machine is able to generate.

6. The method of any of the preceding claims, wherein, The step of correcting the torque requested to the internal combustion engine is triggered when the internal combustion engine excessively generates the requested torque.

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