Control method and control system for hybrid vehicles

Abstract

To provide a control method and a control system of a hybrid vehicle which appropriately control a friction fastening element provided between an engine and a motor, when starting an engine of the hybrid vehicle, so as to suppress shock from occurring in the vehicle, while securing responsiveness to the engine starting.SOLUTION: In a hybrid vehicle 10, a controller 20 increases a rotating speed of an engine 2 by cranking a motor 4, while transferring a first clutch CL1 (friction fastening element) in a released state to a fastened state, when starting the engine in order to switch a travelling mode; temporality decreases fastening torque of the first clutch CL1 before the rotating speed of the engine matches a rotating speed of the motor, after increasing the rotating speed of the engine by cranking the motor 4, so as to temporarily decrease the fastening torque of the first clutch CL1; and then increases the fastening torque so that the first clutch CL1 is set in a complete fastened state, after the rotating speed of the engine matches the rotating speed of the motor.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a control method and a control system for a hybrid vehicle having an engine and a motor as power sources, and a friction fastening element (clutch) that switches between torque transmission and interruption between the engine and the motor.

Background Art

[0002] Conventionally, a hybrid vehicle having an engine (internal combustion engine), a motor (electric motor) provided on the downstream side of the engine on the power transmission path to the wheels, and a clutch (friction fastening element) provided intermittently between the engine and the motor is known. This hybrid vehicle is configured to be able to switch between a first driving mode (EV driving mode) in which the hybrid vehicle is driven using the torque of the motor without using the torque of the engine, and a second driving mode (engine driving mode or hybrid driving mode) in which the hybrid vehicle is driven using at least the torque of the engine. In particular, when switching from the first driving mode to the second driving mode, this hybrid vehicle performs control to transfer the torque of the motor to the engine via the clutch (in other words, to crank the engine by the motor) while shifting the clutch in the released state to the engaged state in order to start the stopped engine, that is, engine start control.

[0003] Techniques related to such hybrid vehicles are described in, for example, Patent Document 1. Specifically, Patent Document 1 describes a technique for suppressing the occurrence of a torque shock in the vehicle due to the connection of the clutch by gradually increasing the transmission torque of the clutch until the rotational speed difference between the input shaft and the output shaft of the clutch becomes less than a threshold value when shifting from the first driving mode (EV mode) to the second driving mode (HV mode).

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-30507 [Overview of the project] [Problems that the invention aims to solve]

[0005] In hybrid vehicles like the one described above, when switching from the first driving mode to the second driving mode, that is, when the engine is started by engine start control, the motor speed basically changes according to the driver's request because the motor is being used for propulsion, while the engine speed increases from zero due to the motor's cranking and eventually synchronizes with the motor speed. When the engine speed and motor speed are synchronized in this way, there may be a difference in torque between the engine and the motor. In this case, if the torque of the engine and motor is fully transmitted to each other, that is, if the clutch is fully engaged and transmits all torque, a relatively large vibration (hereinafter referred to as "vehicle shock") may occur due to the difference in torque between the engine and the motor, which may cause discomfort to the occupants. On the other hand, if the control of the clutch and motor is performed in a way that prioritizes suppressing such vehicle shock, the responsiveness of engine starting will deteriorate.

[0006] The present invention was made to solve the problems of the prior art described above, and aims to provide a control method and control system for a hybrid vehicle that can suppress vehicle shock while ensuring responsiveness of engine starting by accurately controlling the friction fastening element provided between the engine and the motor when the engine of the hybrid vehicle is started. [Means for solving the problem]

[0007] To achieve the above objective, the present invention is applicable to a hybrid vehicle having an engine, a motor, and a friction fastening element intermittently provided between the engine and the motor, and is a control method for a hybrid vehicle that performs engine start control to start a stopped engine in order to switch from a driving mode in which the hybrid vehicle is driven using the torque of the motor without using the torque of the engine to a driving mode in which the hybrid vehicle is driven using at least the torque of the engine, and comprises: a first step of increasing the engine speed by cranking the motor while moving the friction fastening element from the released state to the fastened state when the engine start control is started; a second step of temporarily decreasing the fastening torque of the friction fastening element after the engine speed has increased by cranking the motor in the first step, but before this engine speed matches the motor speed; and a third step of increasing the fastening torque to set the friction fastening element to a fully fastened state after the engine speed and motor speed have matched, after the fastening torque has been temporarily decreased in the second step. death , The friction fastening element is configured to operate in response to the applied hydraulic pressure, and the first step includes the step of applying a first hydraulic pressure to the friction fastening element so as to fill the hydraulic chamber of the friction fastening element with oil, and the step of continuously applying a second hydraulic pressure lower than the first hydraulic pressure to the friction fastening element between the application of the first hydraulic pressure and the application of the second hydraulic pressure, and the first step includes the step of temporarily reducing the hydraulic pressure applied to the friction fastening element to a third hydraulic pressure lower than the second hydraulic pressure between the application of the first hydraulic pressure and the application of the second hydraulic pressure if there is no predetermined acceleration request from the driver during engine start control, and the step of continuing to apply the second hydraulic pressure to the friction fastening element without temporarily reducing the hydraulic pressure applied to the friction fastening element to the third hydraulic pressure between the application of the first hydraulic pressure and the application of the second hydraulic pressure, and the hydraulic pressure applied to the friction fastening element in the second step is less than the second hydraulic pressure and greater than or equal to the third hydraulic pressure. It is characterized by the following:

[0008] In the present invention configured as described above, when the engine is started to switch driving modes, after the engine speed increases due to motor cranking, the fastening torque of the friction fastening element is temporarily reduced before the engine speed matches the motor speed. This allows the transmitted torque of the friction fastening element to be reduced when the engine speed and motor speed synchronize. As a result, the torque difference between the engine and motor can be released in the friction fastening element, which is in a slip state with reduced transmitted torque, that is, released as sliding torque of the friction fastening element, making it possible to suppress vehicle shock caused by torque differences. Furthermore, since this reduction in the fastening torque of the friction fastening element is temporary, the responsiveness of engine starting can be ensured. Therefore, according to the present invention, when the engine is started to switch driving modes, vehicle shock can be suppressed while ensuring the responsiveness of engine starting. The fastening torque of a friction fastening element is the torque applied to the friction fastening element and corresponds to the degree of fastening. Furthermore, the transmitted torque of a friction fastening element corresponds to the torque transmitted between the motor and the engine via the friction fastening element. Furthermore, according to the present invention, by transitioning a friction fastening element from a released state to a fastened state and transmitting the torque of the motor to the engine via this friction fastening element, the engine speed can be accurately increased. Furthermore, according to the present invention, when there is no predetermined acceleration requirement, the shock generated when the friction fastening element, which is in a released state, begins to fasten can be reduced, and when there is a predetermined acceleration requirement, a quick start of the engine can be ensured. Furthermore, according to the present invention, it is possible to effectively achieve both responsiveness in engine starting and suppression of vehicle shock.

[0009] In the present invention, preferably, in the second step, a temporary decrease in the fastening torque is initiated when the difference between the engine speed and the motor speed falls below a predetermined value. According to the present invention configured in this manner, vehicle shock caused by the difference in torque between the engine and the motor during rotational synchronization can be effectively suppressed.

[0010] In the present invention, preferably, in the third step, when the difference between the engine speed and the motor speed remains below a predetermined value for a predetermined period of time, the temporary decrease in fastening torque ends and the increase in fastening torque to set the friction fastening element to a fully fastened state is started. With the present invention configured in this way, the temporary decrease in fastening torque can be precisely terminated at the moment when the torque difference between the engine and the motor has almost disappeared, thereby effectively achieving both responsiveness in engine starting and suppression of vehicle shock.

[0014] In other words, in order to achieve the above objectives, the present invention provides a control system for a hybrid vehicle comprising: an engine and a motor; a friction fastening element intermittently provided between the engine and the motor; and a control device configured to control the engine, motor and friction fastening element in order to perform engine start control to start a stopped engine in order to switch from a driving mode in which the hybrid vehicle is driven using the torque of the motor without using the torque of the engine to a driving mode in which the hybrid vehicle is driven using at least the torque of the engine, wherein when engine start control is initiated, the control device moves the friction fastening element from the released state to the fastened state, while increasing the engine speed by cranking the motor. The first control and After the engine speed increases due to motor cranking, and before this engine speed matches the motor speed, the fastening torque of the friction fastening element is temporarily reduced. The second control and After temporarily reducing the fastening torque, and once the engine speed and motor speed match, the fastening torque is increased to set the friction fastening elements to a fully fastened state. Third control and , Perform It is configured in such a way, The friction fastening element is configured to operate in response to the applied hydraulic pressure. The first control includes a control that applies a first hydraulic pressure to the friction fastening element to fill the hydraulic chamber of the friction fastening element with oil, and a control that continues to apply a second hydraulic pressure lower than the first hydraulic pressure to the friction fastening element between the application of the first hydraulic pressure and the application of the second hydraulic pressure. The first control also includes a control that, if there is no predetermined acceleration request from the driver during engine start control, temporarily reduces the hydraulic pressure applied to the friction fastening element to a third hydraulic pressure lower than the second hydraulic pressure between the application of the first hydraulic pressure and the application of the second hydraulic pressure, and a control that, if there is a predetermined acceleration request from the driver during engine start control, continues to apply the second hydraulic pressure to the friction fastening element without temporarily reducing the hydraulic pressure to the third hydraulic pressure between the application of the first hydraulic pressure and the application of the second hydraulic pressure. The hydraulic pressure applied to the friction fastening element in the second control is less than the second hydraulic pressure and greater than or equal to the third hydraulic pressure. It is characterized by the following: With the present invention configured in this way, it is possible to suppress vehicle shock while ensuring responsiveness of engine starting when starting the engine to switch driving modes. [Effects of the Invention]

[0015] According to the hybrid vehicle control method and control system of the present invention, by accurately controlling the friction fastening element provided between the engine and the motor when the engine of the hybrid vehicle is started, it is possible to suppress vehicle shock while ensuring the responsiveness of engine starting. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram of a hybrid vehicle according to an embodiment of the present invention. [Figure 2]It is a schematic configuration diagram of a first clutch according to an embodiment of the present invention. [Figure 3] It is a block diagram showing an electrical configuration of a hybrid vehicle according to an embodiment of the present invention. [Figure 4] It is a time chart showing an example of conventional engine start control. [Figure 5] It is a time chart showing an example of engine start control according to an embodiment of the present invention. [Figure 6] It is a flowchart showing engine start control according to an embodiment of the present invention.

Mode for Carrying Out the Invention

[0017] Hereinafter, a control method and a control system for a hybrid vehicle according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0018] [Device Configuration] FIG. 1 is a schematic configuration diagram of a hybrid vehicle to which a control method and a control system for a hybrid vehicle according to an embodiment of the present invention are applied.

[0019] As shown in FIG. 1, the hybrid vehicle 1 mainly includes an engine 2 (for example, a gasoline engine) that generates torque for driving the hybrid vehicle 1, a motor 4 that is provided downstream of the engine 2 in the power transmission path of the hybrid vehicle 1 and generates torque for driving the hybrid vehicle 1, a battery 5 that exchanges electric power with the motor 4 via an inverter (not shown), a transmission 6 that is provided downstream of the motor 4 in the power transmission path of the hybrid vehicle 1 and changes the rotational speed of the engine 2 and / or the motor 4, a power transmission system 8 that transmits the torque from the transmission 6 to the downstream side, a drive shaft 10 that drives the wheels 12 by the torque from the power transmission system 8, and the wheels (drive wheels) 12.

[0020] The output shaft of engine 2 and the rotation shaft of motor 4 are coaxially connected by shaft AX1 via a first clutch CL1 that can be connected and disconnected. This first clutch CL1 allows switching between torque transmission and interruption between engine 2 and motor 4. For example, the first clutch CL1 is composed of a dry multi-plate clutch or a wet multi-plate clutch, which can change the transmitted torque capacity by continuously or stepwise controlling the clutch hydraulic fluid flow rate and / or clutch hydraulic pressure using a motor or solenoid (not shown).

[0021] Here, with reference to Figure 2, the specific configuration of the first clutch CL1 will be described. Figure 2 is a schematic diagram showing an example of the first clutch CL1. As shown in Figure 2, the first clutch CL1 includes a hydraulic chamber 15a into which oil is introduced, an oil passage 15b that supplies oil to the hydraulic chamber 15a (see arrow A1), a clutch piston 15c that operates in accordance with the oil (i.e., hydraulic pressure) supplied to the hydraulic chamber 15a (see arrow A2), a first clutch plate 15d that the clutch piston 15c contacts, a second clutch plate 15e that transmits torque between the clutch piston 15c and the first clutch plate 15d when the clutch piston 15c contacts the first clutch plate 15d, and a solenoid 15f provided on the oil passage 15b that can adjust the hydraulic pressure supplied to the hydraulic chamber 15a.

[0022] The first clutch CL1 can switch between a released state, where the clutch piston 15c is separated from the first clutch plate 15d, and a engaged state, where the clutch piston 15c is in contact with the first clutch plate 15d, by controlling the applied hydraulic pressure. In the released state of the first clutch CL1, torque transmission between the engine 2 and the motor 4 is interrupted, and in the engaged state of the first clutch CL1, torque is transmitted between the engine 2 and the motor 4. This engagement state is a state in which the clutch piston 15c is in contact with the first clutch plate 15d, as described above. This state includes a slip state in which the first clutch plate 15d and the second clutch plate 15e slip (typically a state in which the first clutch plate 15d and the second clutch plate 15e are separated and torque is transmitted through the oil between them) and a fully engaged state in which torque is completely transmitted between the first clutch plate 15d and the second clutch plate 15e (basically a state in which the first clutch plate 15d and the second clutch plate 15e are firmly in contact). Such a first clutch CL1 is an example of a "friction engagement element" in the present invention.

[0023] Returning to Figure 1, the rotating shaft of the motor 4 and the rotating shaft of the transmission 6 are coaxially connected by shaft AX2. The transmission 6 is typically an automatic transmission that includes one or more planetary gear sets, including a sun gear S1, a ring gear R1, a pinion gear P1 (planetary gear), and a carrier C1, as well as friction fastening elements such as a clutch and brake, and has the function of automatically switching gear stages (gear ratios) according to the vehicle speed, engine speed, etc. The ring gear R1 is arranged concentrically with the sun gear S1, and the pinion gear P1 is positioned between the sun gear S1 and the ring gear R1 so as to mesh with the sun gear S1 and the ring gear R1. The carrier C1 holds the pinion gear P1 so that it can rotate on its own axis and revolve around the sun gear S1.

[0024] Furthermore, the transmission 6 is equipped with an intermittent (disconnected) second clutch CL2, which allows for switching between the transmission and interruption of torque between the upstream side of the transmission 6 (engine 2 and motor 4) and the downstream side of the transmission 6 (wheels 12, etc.). For example, the second clutch CL2 is composed of a dry multi-plate clutch or a wet multi-plate clutch, which can change the transmitted torque capacity by continuously or stepwise controlling the clutch hydraulic fluid flow rate and / or clutch operating hydraulic pressure using a motor or solenoid (not shown). The second clutch CL2 can also be switched between an open state and an engaged state (slip state or fully engaged state) by controlling the applied hydraulic pressure. The second clutch CL2 is actually composed of numerous clutches used to switch between various gear stages in the transmission 6. Also, although Figure 1 shows only one planetary gear set for simplification, the transmission 6 actually has multiple planetary gear sets. By selectively engaging multiple friction fastening elements, such as the clutch represented by the second clutch CL2 and multiple brakes (not shown), and switching the power transmission path through each planetary gear set, it is possible to achieve, for example, multiple forward gear stages and one reverse gear stage.

[0025] Torque is input to the power transmission system 8 via the output shaft AX3 of the transmission 6. The power transmission system 8 includes a differential gear that distributes the driving force to a pair of left and right wheels 12, as well as a final gear.

[0026] The hybrid vehicle 1 described above can switch driving modes by switching the engagement and disengagement of the first clutch CL1. Specifically, the hybrid vehicle 1 has a first driving mode in which the first clutch CL1 is set to the disengaged state and the hybrid vehicle 1 is driven using the torque of the motor 4 without using the torque of the engine 2, and a second driving mode in which the first clutch CL1 is set to the engaged state and the hybrid vehicle 1 is driven using at least the torque of the engine 2. The first driving mode is a so-called EV driving mode, and the second driving mode includes an engine driving mode in which the hybrid vehicle 1 is driven using only the torque of the engine 2, and a hybrid driving mode in which the hybrid vehicle 1 is driven using the torque of both the engine 2 and the motor 4.

[0027] Next, Figure 3 is a block diagram showing the electrical configuration of a hybrid vehicle according to an embodiment of the present invention.

[0028] As shown in Figure 3, the controller 20 receives signals from the engine speed sensor SN1, which detects the rotational speed of the engine 2; the motor speed sensor SN2, which detects the rotational speed of the motor 4; the accelerator opening sensor SN3, which detects the accelerator opening corresponding to the amount the driver presses the accelerator pedal; and the gradient sensor SN4, which detects the gradient angle of the road surface on which the hybrid vehicle 1 is traveling (or the longitudinal inclination angle of the hybrid vehicle 1 on the road surface).

[0029] The controller 20 is comprised of a computer comprising one or more processors 20a (typically CPUs) and memory 20b such as ROM or RAM for storing various programs (including basic control programs such as an OS and application programs launched on the OS to realize specific functions) and various data interpreted and executed on the processors. The controller 20 corresponds to the "control device" in the present invention and also executes the "control method for hybrid vehicles" in the present invention.

[0030] Specifically, the controller 20 outputs control signals to the engine 2, motor 4, first clutch CL1, and second clutch CL2 based on the detection signals from the sensors SN1 to SN4 described above, and controls them accordingly. For example, the controller 20 controls the ignition timing, fuel injection timing, and fuel injection amount of the engine 2, the rotational speed and torque of the motor 4, and switches the state of the first and second clutches CL1 and CL2 (released state, slipped state, fully engaged state). In practice, the controller 20 controls the spark plugs, fuel injectors, and throttle valves of the engine 2, controls the motor 4 via an inverter, and controls the first and second clutches CL1 and CL2 via a hydraulic control circuit (motor, solenoid 15f, etc.).

[0031] [Hybrid Vehicle Control] Next, the control performed by the controller 20 in this embodiment will be described. In this embodiment, the controller 20 mainly controls the hydraulic pressure applied to the first clutch CL1 (hereinafter referred to as "CL1 hydraulic pressure") to start the stopped engine 2, thereby transitioning the first clutch CL1 from the released state to the engaged state, and simultaneously controlling the motor 4 and engine 2 to start the engine 2 by cranking the motor 4. The CL1 hydraulic pressure corresponds to the command value (instructed hydraulic pressure) of the hydraulic pressure applied to the first clutch CL1. To realize this CL1 hydraulic pressure, the controller 20 controls the hydraulic control circuit of the first clutch CL1 (for example, a solenoid 15f).

[0032] First, the basic concepts of engine starting control will be explained with reference to Figure 4. Figure 4 is a time chart showing an example of conventional engine starting control. In Figure 4, graph G1 shows the time change of CL1 hydraulic pressure, and graphs G21 and G22 show the time changes of engine speed and motor speed, respectively.

[0033] At time t1, the controller 20 initiates engine start control to start the stopped engine 2 in order to switch from the first driving mode to the second driving mode. Specifically, from time t1, the controller 20 sets the CL1 hydraulic pressure to a relatively high first hydraulic pressure P1 in order to fill the hydraulic chamber 15a of the first clutch CL1 with oil (pre-charge) (period T1). Then, from time t2 onward, the controller 20 brings the clutch piston 15c, which is separated in the first clutch CL1, into contact with the first clutch plate 15d, and then, with the first clutch plate 15d and the second clutch plate 15e slipping, gradually increases the engine speed by cranking the motor 4. Specifically, the controller 20 first maintains the CL1 hydraulic pressure at a third hydraulic pressure P3, which is significantly lower than the first hydraulic pressure P1, in order to reduce the shock when the clutch piston 15c contacts the first clutch plate 15d (period T2). Then, from time t3, the controller 20 maintains the CL1 hydraulic pressure at the second hydraulic pressure P2, which is greater than the third hydraulic pressure P3, and waits for the engine speed to increase due to the cranking of the motor 4 (period T3).

[0034] Next, at time t4, the increased engine speed reaches the motor speed, and thereafter, the controller 20 slightly increases the CL1 hydraulic pressure to synchronize the engine speed and motor speed (specifically, to achieve a stable rotational synchronization state) (period T4). Next, at time t5, the engine speed and motor speed are synchronized, and thereafter, the controller 20 further increases the CL1 hydraulic pressure to set the first clutch CL1 to a fully engaged state, and once the first clutch CL1 is set to a fully engaged state, the increase in CL1 hydraulic pressure is stopped and the CL1 hydraulic pressure is maintained at a constant level (period T5).

[0035] Here, as described above, when the engine speed and motor speed are synchronized, there may be a torque difference between engine 2 and motor 4. In this case, if the first clutch CL1 is in a state where it transmits the torque of engine 2 and motor 4 almost completely (fully engaged or in a slip state close to fully engaged), the torque difference between engine 2 and motor 4 may cause relatively large vibrations (vehicle shocks), potentially causing discomfort to the occupants. On the other hand, if the first clutch CL1 and motor 4 are controlled gently to prioritize the suppression of such vehicle shocks, the responsiveness of engine starting will deteriorate.

[0036] Therefore, in this embodiment, when starting the engine 2 to switch from the first driving mode to the second driving mode, the first clutch CL1 is controlled to ensure both responsiveness of engine starting and suppression of vehicle shock. Specifically, the controller 20 temporarily reduces the CL1 hydraulic pressure to reduce the engagement torque of the first clutch CL1 (the torque applied to the first clutch plate 15d and the second clutch plate 15e in the first clutch CL1, which corresponds to the degree of engagement of the first clutch CL1) just before the engine speed, which has increased due to the cranking of the motor 4, matches the motor speed. This makes it possible to temporarily reduce the transmission torque of the first clutch CL1 (corresponding to the torque transmitted from the motor 4 to the engine 2 via the first clutch CL1) when the engine speed and motor speed are synchronized. As a result, the torque difference between the engine 2 and the motor 4 can be released in the first clutch CL1, which is in a slip state with reduced transmission torque, that is, it can be released as the slip torque of the first clutch CL1, making it possible to suppress vehicle shock. Furthermore, since this decrease in the engagement torque of the first clutch CL1 is temporary, it is possible to ensure responsiveness for engine starting.

[0037] Next, with reference to Figure 5, the engine start control according to this embodiment will be described in detail. Figure 5 is a time chart showing an example of engine start control according to this embodiment. In Figure 5, graphs G11 and G12 show the time change of CL1 hydraulic pressure (indicated hydraulic pressure), and graphs G21 and G22 show the time change of engine speed and motor speed, respectively. In particular, graph G12 shows the CL1 hydraulic pressure applied when the driver makes a predetermined acceleration request during engine start control, more specifically a request to quickly start the engine 2 and accelerate the hybrid vehicle 1 at a relatively high acceleration (hereinafter referred to as a "fast start request"), and graph G11 shows the CL1 hydraulic pressure applied when there is no such fast start request. A fast start request occurs when the accelerator opening detected by the accelerator opening sensor SN3 is greater than or equal to a predetermined value, or when the road surface gradient angle detected by the gradient sensor SN4 is greater than or equal to a predetermined value. In Figure 5, elements with the same reference numerals as in Figure 4 have the same meaning as in Figure 4, and their explanations will be omitted as appropriate.

[0038] First, let's explain the case where there is no fast start request (see graph G11). From time t1 to just before time t4 (periods T1, T2, T3), the controller 20 performs the same control as in Figure 4. In this embodiment, just before time t4, when the engine speed, which has increased due to the cranking of the motor 4, reaches the motor speed, the controller 20 temporarily reduces the CL1 hydraulic pressure to the fourth hydraulic pressure P4 (period T4) in order to reduce the engagement torque of the first clutch CL1. Specifically, from time t4a, when the difference between the engine speed and the motor speed falls below a predetermined value. This fourth hydraulic pressure P4 is less than the second hydraulic pressure P2 applied in period T3 and greater than or equal to the third hydraulic pressure P3 applied in period T2 (P3 ≤ P4). <P2)。

[0039] Next, the controller 20 terminates the temporary decrease in CL1 hydraulic pressure at time t5a, a predetermined time after time t5 when the engine speed and motor speed match; in other words, at time t5a, when the difference between the engine speed and motor speed has remained below a predetermined value (close to 0) for a predetermined period of time. This time t5a corresponds to the timing when the torque difference between the engine 2 and the motor 4 has almost disappeared. Then, from time t5a onward, the controller 20 increases the CL1 hydraulic pressure to set the first clutch CL1 to a fully engaged state, and once the first clutch CL1 is set to a fully engaged state, it terminates the increase in CL1 hydraulic pressure and maintains the CL1 hydraulic pressure at a constant level (period T5).

[0040] Next, we will explain the case where a fast start request is made (see Graph G12). Here, we will only explain the differences from the case where there is no fast start request (see Graph G11). When there is a fast start request, in period T2 immediately following period T1, in which the CL1 hydraulic pressure is set to the first hydraulic pressure P1 in order to fill the hydraulic chamber 15a with oil, the controller 20 does not temporarily lower the CL1 hydraulic pressure to the third hydraulic pressure P3 to reduce the shock when the clutch piston 15c contacts the first clutch plate 15d, as it does when there is no fast start request. Specifically, when there is a fast start request, the controller 20 sets the CL1 hydraulic pressure to the second hydraulic pressure P2, which is applied in period T3, when waiting for the engine speed to increase, in period T2, that is, it maintains the CL1 hydraulic pressure at the second hydraulic pressure P2 throughout periods T2 and T3. In this way, it allows for a certain degree of shock when the clutch piston 15c contacts the first clutch plate 15d, prioritizing the quick start of the engine 2.

[0041] Next, with reference to Figure 6, the overall flow of engine start control according to this embodiment will be described. Figure 6 is a flowchart showing the engine start control performed by the controller 20 in this embodiment. The engine start control related to this flowchart is initiated when a start request is issued for the currently stopped engine 2. For example, this start request is issued when the driver requests relatively large acceleration in EV mode (i.e., when the driver requests acceleration that would necessitate switching the driving mode from EV mode to HV mode). In addition to such driver requests, start requests are also issued by the control system, including the powertrain (hereinafter, this start request will be referred to as a "system request" as appropriate). This system request is issued when the driving mode of the hybrid vehicle 1 should be switched from EV mode to HV mode depending on the vehicle speed, load, battery status, engine temperature, etc. For example, a system request is issued when the driving force of motor 4 alone is insufficient to achieve the target driving force, when the battery 5 should be charged (when the State of Charge of battery 5 is below a predetermined value), or when engine braking by engine 2 should be applied during deceleration.

[0042] When engine start control is initiated, first, in step S101, the controller 20 acquires various information. Specifically, the controller 20 acquires detection signals from at least the sensors SN1 to SN4 described above.

[0043] Next, in step S102, the controller 20 controls the first clutch CL1 to set the CL1 hydraulic pressure to a relatively large first hydraulic pressure P1 in order to fill the hydraulic chamber 15a of the first clutch CL1 with oil (pre-charge). Then, the controller 20 proceeds to step S103 and determines whether a predetermined time has elapsed since the CL1 hydraulic pressure was set to the first hydraulic pressure P1. This predetermined time is determined in advance based on the time required to fill the hydraulic chamber 15a of the first clutch CL1 with oil (determined by experiment, simulation, or a predetermined calculation formula).

[0044] If the predetermined time has elapsed (Step S103: Yes), the controller 20 proceeds to Step S104. Conversely, if the predetermined time has not elapsed (Step S103: No), the controller 20 returns to Step S102. In this case, the controller 20 maintains the CL1 hydraulic pressure at the first hydraulic pressure P1 by repeating Steps S102 and S103 until the predetermined time has elapsed.

[0045] Next, in step S104, the controller 20 determines whether or not there is a request for a fast start of the engine 2. The controller 20 determines that there is a request for a fast start if the accelerator opening detected by the accelerator opening sensor SN3 is greater than or equal to a predetermined value, or if the gradient angle of the road surface detected by the gradient sensor SN4 is greater than or equal to a predetermined value (step S104: Yes), and proceeds to step S105. On the other hand, if there is no such request for a fast start (step S104: No), the controller 20 proceeds to step S106.

[0046] If there is no request for a fast start (step S104: No), the controller 20 controls the first clutch CL1 in step S106 to set the CL1 hydraulic pressure to a third hydraulic pressure P3, which is significantly lower than the first hydraulic pressure P1, in order to reduce the shock when the clutch piston 15c contacts the first clutch plate 15d. Then, the controller 20 proceeds to step S107 and determines whether a predetermined time has elapsed since the CL1 hydraulic pressure was set to the third hydraulic pressure P3. This predetermined time is determined in advance based on the time (determined by experiment, simulation, or a predetermined calculation formula) from when oil is filled into the hydraulic chamber 15a of the first clutch CL1 until the clutch piston 15c contacts the first clutch plate 15d.

[0047] If the predetermined time has elapsed (Step S107: Yes), the controller 20 proceeds to Step S105. Conversely, if the predetermined time has not elapsed (Step S107: No), the controller 20 returns to Step S106. In this case, the controller 20 maintains the CL1 hydraulic pressure at the third hydraulic pressure P3 by repeating Steps S106 and S107 until the predetermined time has elapsed.

[0048] On the other hand, if there is a request for a fast start (step S104: Yes), the controller 20 controls the first clutch CL1 in step S105 to set the CL1 hydraulic pressure to the second hydraulic pressure P2, which is greater than the third hydraulic pressure P3, instead of setting the CL1 hydraulic pressure to the third hydraulic pressure P3, in order to prioritize the quick start of the engine 2. Also, if there is no request for a fast start, the controller 20 controls the first clutch CL1 to set the CL1 hydraulic pressure from the third hydraulic pressure P3 to the second hydraulic pressure P2 after maintaining the CL1 hydraulic pressure at the third hydraulic pressure P3 for a predetermined time (step S107: Yes → step S105).

[0049] When the CL1 hydraulic pressure is set to the second hydraulic pressure P2, the first clutch CL1 becomes capable of transmitting the torque of the motor 4 to the engine 2 (specifically, it enters a slipping state). At this time, the controller 20 controls the engine 2 and the motor 4 to increase the engine speed by cranking the motor 4. In this way, the controller 20 maintains the CL1 hydraulic pressure at the second hydraulic pressure P2 while waiting for the engine speed to increase.

[0050] Next, after step S105, the controller 20 proceeds to step S108 to determine whether the difference between the engine speed and the motor speed (speed difference) has fallen below a predetermined value. Here, the controller 20 determines that the engine speed, which has increased due to the cranking of the motor 4, is about to reach the motor speed. If the speed difference falls below a predetermined value (step S108: Yes), the controller 20 determines that the engine speed is about to reach the motor speed and proceeds to step S109 to control the first clutch CL1 to temporarily reduce the CL1 hydraulic pressure to the fourth hydraulic pressure P4. This suppresses vehicle shock caused by the difference in torque during rotational synchronization between the engine 2 and the motor 4. From this perspective, the predetermined value for determining the rotational speed difference in step S108 is set in advance based on the timing before the engine speed reaches the motor speed, when a temporary decrease in CL1 hydraulic pressure should be initiated to effectively suppress such vehicle shocks. Furthermore, the fourth hydraulic pressure P4, which temporarily reduces the CL1 hydraulic pressure, is set to a CL1 hydraulic pressure that suppresses such vehicle shocks without worsening the responsiveness of engine starting. Basically, the fourth hydraulic pressure P4 is set to be at least less than the second hydraulic pressure P2 and at least greater than the third hydraulic pressure P3. These predetermined values ​​and the fourth hydraulic pressure P4 are determined based on experiments, simulations, and predetermined calculation formulas.

[0051] On the other hand, if the rotational speed difference is not below a predetermined value (step S108: No), the controller 20 returns to step S105. In this case, the controller 20 maintains the CL1 hydraulic pressure at the second hydraulic pressure P2 by repeating steps S105 and S108 until the rotational speed difference falls below a predetermined value.

[0052] Next, after step S109, the controller 20 proceeds to step S110, where it determines whether the difference between the engine speed and the motor speed (speed difference) has remained below a predetermined value (a value close to 0) for a predetermined period of time. Here, the controller 20 determines that the torque difference between the engine 2 and the motor 4 has almost disappeared. Therefore, the predetermined time used in step S110 is predetermined based on the time required from when the engine speed and the motor speed are nearly the same until the torque difference between the engine 2 and the motor 4 almost disappears (determined by experiment, simulation, or a predetermined calculation formula).

[0053] If, as a result of step S110, the controller 20 determines that the rotational speed difference remains below a predetermined value for a predetermined period of time (step S110: Yes), it proceeds to step S111. Conversely, if the rotational speed difference does not remain below a predetermined value for a predetermined period of time (step S110: No), the controller 20 returns to step S109. In this case, the controller 20 maintains the CL1 hydraulic pressure at the fourth hydraulic pressure P4 by repeating steps S109 and S110 until the rotational speed difference remains below a predetermined value for a predetermined period of time.

[0054] Next, in step S111, the controller 20 controls the first clutch CL1 to gradually increase the CL1 hydraulic pressure, ending the temporary decrease in CL1 hydraulic pressure to the fourth hydraulic pressure P4, in order to set the first clutch CL1 to a fully engaged state. Then, when the CL1 hydraulic pressure reaches the final target hydraulic pressure corresponding to the fully engaged state of the first clutch CL1, the controller 20 proceeds to step S112, ending the gradual increase in CL1 hydraulic pressure and maintaining the CL1 hydraulic pressure at a constant level. After this, the controller 20 terminates the engine start control.

[0055] [Mechanism of Action and Effects] Next, the operation and effects of the control method and control system for a hybrid vehicle according to an embodiment of the present invention will be described.

[0056] According to this embodiment, when the controller 20 starts the engine 2 to switch from the first driving mode to the second driving mode, after the engine speed increases due to the cranking of the motor 4, but before the engine speed matches the motor speed, the controller 20 temporarily reduces the hydraulic pressure applied to the first clutch CL1 to reduce the engagement torque of the first clutch CL1. This allows the transmission torque of the first clutch CL1 to be reduced when the engine speed and motor speed synchronize. As a result, the torque difference between the engine 2 and the motor 4 can be released in the first clutch CL1, which is in a slip state with reduced transmission torque, that is, released as the slip torque of the first clutch CL1, making it possible to suppress vehicle shock caused by the torque difference. Furthermore, since this reduction in the engagement torque of the first clutch CL1 is temporary, the responsiveness of engine starting can be ensured. Therefore, according to this embodiment, when starting the engine 2 to switch from the first driving mode to the second driving mode, it is possible to suppress vehicle shock while ensuring the responsiveness of engine starting.

[0057] Furthermore, according to this embodiment, when the difference between the engine speed and the motor speed falls below a predetermined value, the controller 20 starts a temporary decrease in the engagement torque of the first clutch CL1, thereby effectively suppressing vehicle shock caused by the torque difference during rotational synchronization between the engine 2 and the motor 4.

[0058] Furthermore, according to this embodiment, when the difference between the engine speed and the motor speed remains below a predetermined value for a predetermined period of time, the controller 20 terminates the temporary decrease in the engagement torque of the first clutch CL1 and begins to increase the engagement torque to set the first clutch CL1 to a fully engaged state. This allows the temporary decrease in engagement torque to be terminated precisely at the moment when the torque difference between the engine 2 and the motor 4 disappears, making it possible to effectively achieve both responsive engine starting and suppression of vehicle shock.

[0059] Furthermore, according to this embodiment, when controlling engine start, the controller 20 applies a first hydraulic pressure P1 to the first clutch CL1 to fill the hydraulic chamber 15a of the first clutch CL1 with oil, and then continues to apply a second hydraulic pressure P2, which is lower than the first hydraulic pressure P1, to the first clutch CL1. This causes the first clutch CL1, which is in the disengaged state, to be engaged, and the engine speed can be accurately increased by the cranking of the motor 4.

[0060] Furthermore, according to this embodiment, if there is no request for a fast start of the engine 2, the controller 20 temporarily reduces the hydraulic pressure applied to the first clutch CL1 to a third hydraulic pressure P3, which is lower than the second hydraulic pressure P2, between applying the first hydraulic pressure P1 and applying the second hydraulic pressure P2. This reduces the shock that occurs when the first clutch CL1, which is in the released state, begins to engage. On the other hand, if there is a request for a fast start of the engine 2, the controller 20 continues to apply the second hydraulic pressure P2 to the first clutch CL1 after applying the first hydraulic pressure P1, without temporarily reducing the hydraulic pressure applied to the first clutch CL1 to the third hydraulic pressure P3. This prioritizes the rapid start of the engine 2.

[0061] Furthermore, according to this embodiment, the controller 20 sets the hydraulic pressure (fourth hydraulic pressure P4) applied to the first clutch CL1 in order to temporarily reduce the engagement torque of the first clutch CL1 to less than the second hydraulic pressure P2 and greater than or equal to the third hydraulic pressure P3. This makes it possible to effectively achieve both the responsiveness of engine starting and the suppression of vehicle shock. [Explanation of Symbols]

[0062] 1. Hybrid vehicle 2 engines 4 motors 5 batteries 6-speed transmission 8 Power transmission system 12 wheels 15a Hydraulic chamber 15c Clutch Piston 15d First clutch plate 15e Second clutch plate 15f solenoid 20 Controller (control device) CL1 First clutch (friction engagement element) CL2 Second Clutch

Claims

1. A control method for a hybrid vehicle having an engine, a motor, and a friction fastening element intermittently provided between the engine and the motor, which performs engine start control to start the stopped engine in order to switch from a driving mode in which the hybrid vehicle is driven using the torque of the motor without using the torque of the engine, to a driving mode in which the hybrid vehicle is driven using at least the torque of the engine, When the engine start control is initiated, the first step is to increase the engine speed by cranking the motor while shifting the friction fastening element from the released state to the fastened state, A second step involves temporarily reducing the fastening torque of the friction fastening element after the engine speed has increased due to the cranking of the motor in the first step, but before this engine speed matches the motor speed. After temporarily reducing the fastening torque in the second step, and after the engine speed and motor speed match, the third step involves increasing the fastening torque to set the friction fastening element to a fully fastened state. It has, The friction fastening element is configured to operate in response to the applied hydraulic pressure. The first step is, A step of applying a first hydraulic pressure to the friction fastening element so as to fill the hydraulic chamber of the friction fastening element with oil, Between the application of the first hydraulic pressure and the second step, a step is taken to continuously apply a second hydraulic pressure lower than the first hydraulic pressure to the friction fastening element, It has, The first step is, If there is no predetermined acceleration request from the driver during the engine start control, the process of temporarily reducing the hydraulic pressure applied to the friction fastening element to a third hydraulic pressure lower than the second hydraulic pressure between applying the first hydraulic pressure and applying the second hydraulic pressure, When the driver requests the predetermined acceleration during the engine start control, the process of applying the first hydraulic pressure and continuing to apply the second hydraulic pressure to the friction fastening element without temporarily reducing the hydraulic pressure applied to the friction fastening element to the third hydraulic pressure, It has, The hydraulic pressure applied to the friction fastening element in the second step is less than the second hydraulic pressure and greater than or equal to the third hydraulic pressure. A control method for a hybrid vehicle characterized by the following features.

2. The control method for a hybrid vehicle according to claim 1, wherein in the second step, when the difference between the engine speed and the motor speed falls below a predetermined value, a temporary decrease in the fastening torque is initiated.

3. The control method for a hybrid vehicle according to claim 1, wherein in the third step, when the difference between the engine speed and the motor speed remains below a predetermined value for a predetermined period of time, the temporary decrease in the fastening torque ends and the increase in the fastening torque to set the friction fastening element to a fully fastened state begins.

4. A control system for hybrid vehicles, Engine and motor, A friction fastening element intermittently provided between the engine and the motor, The system includes a control device configured to control the engine, the motor, and the friction fastening element in order to perform engine start control to start the stopped engine in order to switch from a driving mode in which the hybrid vehicle is driven using the torque of the motor without using the torque of the engine, to a driving mode in which the hybrid vehicle is driven using at least the torque of the engine. The control device is When the engine start control is initiated, a first control is performed which moves the friction fastening element from the released state to the fastened state, while simultaneously increasing the engine speed by cranking the motor. A second control is performed to temporarily reduce the fastening torque of the friction fastening element after the engine speed increases due to the cranking of the motor, but before this engine speed matches the motor speed. A third control that temporarily reduces the fastening torque, and then increases the fastening torque after the engine speed and motor speed match, in order to set the friction fastening element to a fully fastened state, It is configured to do the following: The friction fastening element is configured to operate in response to the applied hydraulic pressure. The first control is, Control to apply a first hydraulic pressure to the friction fastening element so as to fill the hydraulic chamber of the friction fastening element with oil, Between the application of the first hydraulic pressure and the second control, the control continues to apply a second hydraulic pressure lower than the first hydraulic pressure to the friction fastening element. It has, The first control is, If there is no predetermined acceleration request from the driver during the engine start control, the control temporarily reduces the hydraulic pressure applied to the friction fastening element to a third hydraulic pressure lower than the second hydraulic pressure between the application of the first hydraulic pressure and the application of the second hydraulic pressure. When the driver requests the predetermined acceleration during the engine start control, the control continues to apply the second hydraulic pressure to the friction fastening element without temporarily reducing the hydraulic pressure applied to the friction fastening element to the third hydraulic pressure between the application of the first hydraulic pressure and the second control, It has, The hydraulic pressure applied to the friction fastening element in the second control is less than the second hydraulic pressure and greater than or equal to the third hydraulic pressure. A control system for hybrid vehicles characterized by the following features.

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