Patent Description:
The invention relates to the technical field of vehicle control, and in particular to a method for controlling a driving mode switching of a hybrid electric vehicle, a vehicle, and a storage medium.

With the advent of the global energy revolution, oil resources are increasingly scarce over time. Reduction in fuel consumption of conventional pure internal combustion engine-driven vehicles becomes increasingly costly and difficult while regulations on fuel consumption grow increasingly stringent. Reduction in fuel consumption of hybrid electric vehicles is expectable with the assistance of a driving motor. A P2 configuration and a dual-motor planetary gear power split configuration represented by European manufacturers have been mass-produced and exhibited remarkable performance on fuel consumption, and thus have won the favor of mass consumers. However, a three-clutch module with a C0 motor in the P2 configuration has a complex structure and high requirements for clutch control. The dual-motor planetary gear power split configuration involves complex three-motor control.

Since a dual-motor series-parallel configuration can facilitate switching between a hybrid electric vehicle (HEV) and a plug-in hybrid electric vehicle (PHEV), it has been identified as a hybrid power configuration easy to implement in recent years. In response to a vehicle being at a medium-low speed, a clutch is disengaged, the vehicle works in a series driving mode and is driven by a driving motor, and an engine stops or works in an economic electric generation area. In response to the vehicle being at a medium-high speed, the clutch is engaged, the vehicle works in a parallel driving mode and is directly driven by the engine at a fixed speed ratio, and a load on the engine can be adjusted through the driving motor, so that the engine still works in a low-oil-consumption economic area. With the above solution implemented, fuel consumption can be less than <NUM> per <NUM> kilometers under the new European driving cycle (NEDC) test conditions.

Owing to variability of vehicle operating conditions and frequent series-parallel switching control of a vehicle driving mode, it is of vital importance to provide an efficient and reasonable series-parallel switching control method.

<CIT> discloses a hybrid vehicle wherein a power transmission engaging/disengaging portion is applied or released to switch a form of drive sources for driving and a method for controlling same.

<CIT> discloses methods and a system for changing between series and parallel hybrid driveline operating modes.

<CIT> discloses a controller for hybrid vehicle to prevent fluctuation of rotation or torque when switching is made between series running mode and parallel running mode.

<CIT>, <CIT> and <CIT> provide related technical solutions; however, the above mentioned problem still remains unsolved.

The invention provides a method for controlling a driving mode switching of a hybrid electric vehicle, a vehicle, and a storage medium. Accordingly, frequent series-parallel switching demand of the vehicle can be met, a clear control strategy can be realized while timely and effective switching between series driving and parallel driving is ensured, and therefore calibration and application are facilitated.

The invention employs the technical solutions as follows:
A method for controlling a driving mode switching of a hybrid electric vehicle includes:.

The invention further provides a vehicle. The vehicle is configured for executing the method for controlling a driving mode switching of a hybrid electric vehicle.

The invention further provides a storage medium. The storage medium stores a computer program, where the computer program implements the method for controlling a driving mode switching of a hybrid electric vehicle, when the program is executed by at least one processor.

In the figures:
<NUM>. Engine; <NUM>. Electric generator; <NUM>. Clutch; <NUM>. Driving motor; <NUM>. Main decelerator and differential; <NUM>.

The technical solutions in the embodiments of the invention are described below with reference to the accompanying drawings, and the described examples are merely some examples rather than all examples of the invention.

In the description of the invention, unless otherwise explicitly specified and limited, the terms "connected", "connection", and "fixed" should be understood in a broad sense. For example, a connection can be a fixed connection, a detachable connection, an integrated connection, a mechanical connection, an electric connection, a direct connection, an indirect connection via an intermediate medium, communication inside two elements, or an interaction relation of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

In the invention, unless otherwise explicitly specified and limited, a first feature is "on" or "underneath" a second feature can include that the first feature and the second feature are in direct contact, or in indirect contact through another feature there between. Moreover, the first feature is "on", "above", and "over" the second feature includes that the first feature is exactly above the second feature or not, or indicates that the first feature has a higher level than the second feature. The first feature is "underneath", "below", and "under" the second feature includes that the first feature is exactly below the second feature or not, or indicates that the first feature has a lower level than the second feature.

A vehicle is provided in the embodiment. As shown in <FIG>, the vehicle includes an engine <NUM>, an electric generator <NUM>, a clutch <NUM>, a driving motor <NUM>, a main decelerator and differential <NUM>, and a gear pair <NUM>. The engine <NUM> is connected to the electric generator <NUM> through the gear pair <NUM>, the clutch <NUM> is connected between the engine <NUM> and the driving motor <NUM>, and the main decelerator and differential <NUM> is connected between the driving motor <NUM> and an axle.

In response to the vehicle being in a series driving mode, the clutch <NUM> is engaged, the vehicle is driven by the driving motor <NUM>, and the engine <NUM> outputs negative torque and maintains at a desired rotation speed to ensure that a certain electric generation power is output. The "peak load shifting and valley filling" of an engine power is realized through charging and discharging of a battery to maintain that the engine <NUM> works in an economic fuel area.

In response to the vehicle being in a parallel driving mode, the clutch <NUM> is engaged, and a speed ratio of a rotation speed of the engine <NUM> to a vehicle speed is fixed. The engine <NUM> works in a zero-torque following mode, and the engine <NUM> and the driving motor <NUM> jointly drive the vehicle. In the parallel driving mode, a working state of the engine <NUM> has a driving and charging sub-mode, a driving and assisting sub-mode, and an engine <NUM> fuel cut-off sub-mode. The distribution relations among torque demanded by a driver, torque of the engine, and torque of the driving motor in different sub-modes vary. Accordingly, target torque of the engine also depends on different sub-modes.

As shown in <FIG>, a method for controlling a driving mode switching of a hybrid electric vehicle is provided in the embodiment. The control method is configured to the above-mentioned vehicle and includes:
At step <NUM>: a switching state of the driving mode of the hybrid electric vehicle is determined.

The switching state of the driving mode of the hybrid electric vehicle includes a state to switch the driving mode of the hybrid electric vehicle from a series driving mode to a parallel driving mode, and a state to switch the driving mode of the hybrid electric vehicle from the parallel driving mode to the series driving mode.

A vehicle controller determines whether the vehicle (the hybrid electric vehicle) is required to be switched between the series driving mode and the parallel driving mode in real time, and in response to the vehicle being required to be switched between the series driving mode and the parallel driving mode in real time, determines whether the driving mode of the hybrid electric vehicle is switched from the series driving mode to the parallel driving mode or from the parallel driving mode to the series driving mode.

At step <NUM>, in response to the switching state being to switch the driving mode of the hybrid electric vehicle from the series driving mode to the parallel driving mode, the method includes:
At step S21, the torque of an engine <NUM> is adjusted to target torque of the engine <NUM> in the parallel driving mode, and a rotation speed of the engine <NUM> is adjusted to be the same as a current rotation speed of a driving motor <NUM> in the series driving mode.

The target torque of the engine <NUM> is determined as TEng_Tgt, target torque of the driving motor <NUM> is determined as TTm_Tgt, the target rotation speed of the engine <NUM> is determined as nEng_Tgt, and request torque of the electric generator <NUM> is determined as TGm_Tgt; and in the parallel driving mode, a working state of the engine <NUM> has a driving and charging sub-mode, a driving and assisting sub-mode, and an engine <NUM> fuel cut-off sub-mode,.

Since the engine <NUM> has a slower torque response than the driving motor <NUM>, the torque of the engine <NUM> is not adjusted as far as possible while vehicle torque is adjusted through the driving motor <NUM>. Accordingly, in the step, the torque of the engine <NUM> is required to be adjusted to the target torque of the engine <NUM> in the parallel driving mode. Moreover, in order to reduce the impact caused by a rotation speed difference of the clutch <NUM> in response tothe clutch <NUM> beingengaged, it is required to adjust the rotation speed of the engine <NUM> to be the same as the current rotation speed of the driving motor <NUM> in the series driving mode.

In the step, the clutch <NUM> is not engaged. Although the torque and the rotation speed of the engine <NUM> are adjusted to parameters required in the parallel driving mode, the vehicle is still in the series driving mode and is driven by the driving motor <NUM>.

In response to the torque and the rotation speed of the engine <NUM> being adjusted, whether a difference between the torque of the engine <NUM> and the target torque of the engine <NUM> is less than a preset torque difference and whether a difference of the rotation speed of the engine <NUM> and the target rotation speed of the engine <NUM> is less than a preset rotation speed difference are determined in real time. The clutch <NUM> is engaged only if the difference between the torque of the engine <NUM> and the target torque of the engine <NUM> is less than the preset torque difference and the difference between the rotation speed of the engine <NUM> and the target rotation speed of the engine <NUM> is less than the preset rotation speed difference. The preset torque difference and the preset rotation speed difference are obtained through a test, in which a vehicle impact degree in an engagement stage of the clutch <NUM> and power continuity in a power source alternation stage are primarily considered.

At step S22, the clutch <NUM> is engaged.

In the engagement stage of the clutch <NUM>, an engagement request is sent to the clutch <NUM>. In response to the clutch <NUM> executing an engagement process, the electric generator <NUM> still maintains the rotation speed of the engine <NUM> as that of the driving motor <NUM>. Therefore, no impact is generated in the engagement process of the clutch <NUM>. The vehicle is still driven by the driving motor <NUM>. Therefore, control targets of all components in the engagement stage of the clutch <NUM> are consistent with working data of the engine <NUM> in step S21.

Although a difference between the rotation speed of the engine <NUM> and the rotation speed of the driving motor <NUM> has been controlled to be slight through the electric generator <NUM> in step S21, in order to further reduce an impact degree of the clutch <NUM> during engagement, an oil pressure of the clutch <NUM> is also gradually increased in the engagement process of the clutch <NUM>. An oil pressure loading speed is obtained in combination with vehicle performance calibration.

Compared with the step S21, control of the clutch <NUM> is added to the step, and the engagement stage of the clutch <NUM> is listed individually. Accordingly, step S21 involves a dynamic adjustment of the torque and the rotation speed of the engine <NUM>, which is conducive to reuse of a module function.

At step S23, the torque of the electric generator <NUM> is reduced to zero, and the torque of the driving motor <NUM> is reduced.

In order to switch an output power of the engine <NUM> from electric transmission to mechanical transmission, electric generation torque of the electric generator <NUM> is gradually reduced. Therefore, the torque of the engine <NUM> is released to the clutch <NUM>. The torque of the driving motor <NUM> is synchronously reduced, and a torque reduction of the driving motor <NUM> equals a torque reduction of the electric generator <NUM>. Since the torque of the electric generator <NUM> and the torque of the driving motor <NUM> have the same synchronous adjustment amount, it can be ensured that total torque output by the engine <NUM>, the electric generator <NUM>, and the driving motor <NUM> to the outside is unchanged to ensure continuity of driving force.

After the torque of the electric generator <NUM> has been reduced to zero, and the torque of the driving motor <NUM> has been reduced to the target torque of the driving motor <NUM> in the parallel driving mode, the vehicle enters the parallel driving mode.

In the example, the target torque of the driving motor <NUM> is determined as TTm_Tgt, and request torque of the electric generator <NUM> is determined as TGmTgt, <MAT>.

Wherein TDrv is the driver demand torque, TEng_Act denotes the actual torque of the engine <NUM>, ΔTstp denotes the synchronous torque adjustment step size of the electric generator <NUM> and the driving motor <NUM>, and T*Gm_Tgt and T*Tm_Tgt denote the output request torque of the electric generator <NUM> and the output target torque of the driving motor <NUM> in a last calculation cycle respectively.

In response to a first stage of a switching process is ended, the torque of the engine <NUM> has already equaled the target torque of the engine in the parallel driving mode. That is, in this case, the engine <NUM> and the driving motor <NUM> can meet respective vehicle driving torque demands. Therefore, in the power source switching stage, the influence from a torque response difference between the engine <NUM> and the driving motor <NUM> on the vehicle power performance is not considered. Moreover, since no power interruption is generated in the switching process, the requirement for a total switching duration is low, and the influence from a dynamic response time of the driving motor <NUM> on the switching process can be neglected.

At step <NUM>, if the switching state is to switch the driving mode of the hybrid electric vehicle from the parallel driving mode to the series driving mode, the method includes:
At step S31, the negative electric generation torque of the electric generator <NUM> is increased to absorb torque of the engine <NUM>, and the torque absorbed by the electric generator <NUM> is transferred to the driving motor <NUM> with the same amplitude.

In the example, since the electric transmission is realized after the clutch <NUM> is disengaged, the mechanical transmission is required to be switched to the electric transmission before the clutch <NUM> is disengaged. The negative electric generation torque of the electric generator <NUM> is increased to absorb the torque of the engine <NUM>. Moreover, the torque absorbed by the electric generator <NUM> is transferred to the driving motor <NUM> with the same amplitude. Accordingly, driving by the engine <NUM> is switched to driving by the driving motor <NUM> without changing total driving torque. Thereafter, all powers of the engine <NUM> are absorbed by the electric generator <NUM>, and no torque is transmitted between two ends of the clutch <NUM>. After the torque of the engine <NUM> is completely absorbed by the electric generator <NUM>, that is, in response to the torque of the electric generator <NUM> being equal tothe torque of the engine <NUM>, power source switching is completed.

The target torque of the engine <NUM> is determined as TEng_Tgt, the target torque of the driving motor <NUM> is determined as TTm_Tgt, and request torque of the electric generator <NUM> is determined as TGm_Tgt; where in the parallel driving mode, a working state of the engine <NUM> has a driving and charging sub-mode, a driving and assisting sub-mode, and an engine <NUM> fuel cut-off sub-mode,.

At stepS32, under the condition of determining that the torque of the electric generator <NUM> equals the torque of the engine <NUM>, the torque of the driving motor <NUM> is adjusted to the target torque of the driving motor <NUM> in the series driving mode, and the rotation speed of the engine <NUM> equals the rotation speed of the driving motor <NUM>, the clutch <NUM> is disengaged.

In the embodiment, in the disengagement process of the clutch <NUM>, since the disengagement process requires a certain time, in order to avoid the impact caused by inconsistent rotation speeds at two ends of the clutch <NUM> in such a period, the electric generator <NUM> adjusts the rotation speed of the engine <NUM> to be the same as that of the driving motor <NUM> through rotation speed control. In this process, all vehicle driving torque is executed by the driving motor <NUM>.

The target torque of the driving motor <NUM> is determined as TTm_Tgt, the target rotation speed of the engine <NUM> is determined as nEng_Tgt, and the request torque of the electric generator <NUM> is determined as TGm_Tgt, <MAT>.

TDrv denotes the driver demand torque, nTm denotes a current rotation speed of the driving motor <NUM>, TEng_Act denotes the actual torque of the engine <NUM>, JEng denotes the moment of inertia of the engine <NUM>, JGm denotes the moment of inertia of the electric generator <NUM>, JGear denotes the moment of inertia of a gear set between the engine <NUM> and the electric generator <NUM>, and TCL denotes speed adjustment PI torque.

At stepS33, the torque and the rotation speed of the engine <NUM> are adjusted to target torque of the engine <NUM> and a target rotation speed of the engine <NUM> in the series driving mode respectively.

In the embodiment, after the clutch <NUM> is disengaged, the engine <NUM> has been disconnected from the driving motor <NUM>. In this case, the engine is already in an "electric transmission" state, the torque and the rotation speed of the engine <NUM> are adjusted to the target torque of the engine <NUM> and the target rotation speed of the engine <NUM> in the series driving mode. The driving motor <NUM> independently drives the vehicle. In such a stage, the torque of the engine <NUM>, the torque of the driving motor <NUM>, and the rotation speed of the engine <NUM> match corresponding data in the series driving mode. After the torque and the rotation speed of the engine <NUM> are adjusted to be close to the target torque of the engine <NUM> and the target rotation speed of the engine <NUM> in the series driving mode, a torque and rotation speed adjustment stage of the engine <NUM> is ended, and the vehicle enters the series driving mode.

The target torque of the engine <NUM> is determined as TEng_Tgt, and the target rotation speed of the engine <NUM> is determined as nEng_Tgt, where <MAT> where
TEng_Se and nEng_Se denote torque and a rotation speed, calculated through a vehicle energy management module, of the engine at an electric generation power target point.

In the embodiment, by analyzing the vehicle series-parallel driving mode, the process from the series driving mode to the parallel driving mode is divided into three stages, and the process from the parallel driving mode to the series driving mode is also divided into three stages. Finally, such control is completed through four software modules. Therefore, frequent series-parallel switching demand of the vehicle can be met, a software structure is simplified while timely and effective switching between series driving and parallel driving is ensured, and therefore calibration and application of a software model are facilitated.

In response to being at a medium-low speed, the vehicle works in the series driving mode, and the rotation speed of the engine <NUM> is decoupled from a vehicle speed. The electric generator <NUM> works in a high-efficiency area for electric generation, and a loss of an electric energy conversion efficiency is compensated after the fuel economy of the engine <NUM> is improved to realize a high efficiency of a system. When the vehicle speed is high and a vehicle driving power is moderate, the vehicle works in the parallel driving mode, and the clutch <NUM> is engaged, which is equivalent to a high gear of a conventional vehicle. The high fuel economy can still be obtained by reasonably setting the speed ratio. The electric generator <NUM> works in a zero-torque following mode, and the engine <NUM> and the driving motor <NUM> jointly drive the vehicle. The essence of switching from series driving to parallel driving is to switch from the electric transmission to the mechanical transmission from the engine <NUM> to a wheel end in terms of power. In terms of torque, it is to switch from independent driving by the driving motor <NUM> to joint driving by the engine <NUM> and the driving motor <NUM> while the consistency of the vehicle driving torque and the rotation speed in the switching process is ensured, avoiding the switching impact.

In addition, since speed ratios of different components vary, in order to ensure that the torque and the rotation speed of each component can be directly compared and calculated, in the embodiment, the rotation speeds and the torque of a plurality of components are converted to one fixed component, that is, the engine, according to a speed ratio relation. Therefore, the consistency of reference points is realized, and the control accuracy is improved.

A storage medium is further provided in the example. The storage medium stores a computer program, where the computer program implements the above control method for switching a driving mode of a hybrid electric vehicle, when the program is executed by a processor.

Claim 1:
A method for controlling a driving mode switching of a hybrid electric vehicle, comprising:
determining a switching state of the driving mode of the hybrid electric vehicle, wherein the switching state comprises a state to switch the driving mode of the hybrid electric vehicle from a series driving mode to a parallel driving mode, and a state to switch the driving mode of the hybrid electric vehicle from the parallel driving mode to the series driving mode;
in response to the switching state being to switch the driving mode of the hybrid electric vehicle from the series driving mode to the parallel driving mode, adjusting a torque of an engine (<NUM>) to a target torque of the engine (<NUM>) in the parallel driving mode, adjusting a rotation speed of the engine (<NUM>) to be the same as a current rotation speed of a driving motor (<NUM>) in the series driving mode, engaging a clutch (<NUM>), reducing the torque of an electric generator (<NUM>) to zero, and reducing the torque of the driving motor (<NUM>); wherein a torque reduction of the driving motor (<NUM>) equals a torque reduction of the electric generator (<NUM>);
in response to the switching state being to switch the driving mode of the hybrid electric vehicle from the parallel driving mode to the series driving mode, increasing the torque of the electric generator (<NUM>) to absorb the torque of the engine (<NUM>), and transferring the torque absorbed by the electric generator (<NUM>) to the driving motor (<NUM>) with the same amplitude, and in response to determining that the torque of the electric generator (<NUM>) equals the torque of the engine (<NUM>), adjusting the torque of the driving motor (<NUM>) to the target torque of the driving motor (<NUM>) in the series driving mode, and in response to the rotation speed of the engine (<NUM>) being equal to the rotation speed of the driving motor (<NUM>), disengaging the clutch (<NUM>), and adjusting the torque of the engine (<NUM>)and the rotation speed of the engine (<NUM>) to the target torque of the engine (<NUM>) and a target rotation speed of the engine (<NUM>) in the series driving mode respectively.