System and method for controlling engine torque of a hybrid vehicle

Abstract

A vehicle includes an engine and a motor selectively coupled via a clutch. A controller of the vehicle is programmed to limit the rate of increase of the output torque of the engine to a limit having a first value in response to a driver-requested torque exceeding a maximum torque of the motor and the clutch being locked, and to reduce the limit to a second value in response to the driver-requested torque being met.

Description

Technical Field

[0001] The present disclosure relates to controlling engine torque of a hybrid vehicle, and more particularly to systems and methods for rate limiting increases in engine torque. Background Art

[0002] A hybrid electric powertrain includes an engine and an electric motor. The torque (or power) generated by the engine and / or the electric motor can be transferred to the drive wheels via a transmission to propel the vehicle. A traction battery provides energy to the electric motor. The hybrid powertrain is also capable of performing regenerative braking, in which the electric motor charges the battery by converting mechanical power into electricity to brake the vehicle. Summary of the invention

[0003] According to one embodiment, a vehicle includes an engine and a motor, the engine and the motor being selectively coupled via a clutch. A controller of the vehicle is programmed to limit the rate of increase of the output torque of the engine to a limit having a first value in response to a driver-requested torque exceeding a maximum torque of the motor and the clutch being locked, and to reduce the limit to a second value in response to the driver-requested torque being met.

[0004] According to another embodiment, a vehicle includes a traction battery, an engine, a step ratio gearbox including a plurality of discrete gear ratios, and a motor coupled to the gearbox with a torque converter. The motor is electrically connected to the traction battery. A disconnect clutch selectively couples the engine and the motor when locked. A controller is programmed to start the engine and command the disconnect clutch to engage in response to a driver-requested torque exceeding a maximum torque of the motor. The controller is also programmed to command the engine torque such that an increase in the torque is rate limited according to a first rate of change until the driver-requested torque is reached, and then rate limited according to a second rate of change less than the first rate of change in response to the disconnect clutch being locked.

[0005] According to yet another embodiment, a method of rate limiting engine torque is presented. The method is executed by a vehicle controller and includes, in response to a clutch being locked to ground an engine to a motor and a driver-requested torque exceeding a maximum torque of the motor, limiting the rate of increase of the output torque of the engine to a limit having a first value, and in response to satisfying the driver-requested torque, reducing the limit to a second value. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a schematic diagram of a hybrid electric vehicle according to one embodiment.

[0007] Figure 2is a graph showing engine torque, motor torque, and driver requested torque for an example engine starting situation.

[0008] Figure 3 is a graph showing engine torque, motor torque, and driver requested torque and engine and motor speeds for another example engine starting scenario in which the increase in engine torque is rate limited according to a single rate.

[0009] Figure 4 is a graph showing engine torque, motor torque, and driver requested torque and engine and motor speeds for another example engine starting scenario in which the increase in engine torque is rate limited according to a pair of rates.

[0010] Figure 5 is a flow chart showing an algorithm for applying a rate limit to increases in engine torque. DETAILED DESCRIPTION

[0011] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples and that other embodiments may take various forms and alternative forms. The drawings are not necessarily drawn to scale; some features may be enlarged or minimized in order to show the details of a particular component. Therefore, the specific structural details and functional details disclosed herein should not be interpreted as being restrictive, but merely as a representative basis for teaching those skilled in the art to adopt the embodiments in different ways. As will be understood by those of ordinary skill in the art, the various features shown and described with reference to any one of the accompanying drawings may be combined with the features shown in one or more other drawings to produce embodiments that are not explicitly shown or described. The combination of features shown provides representative embodiments for typical applications. However, various combinations and modifications of features consistent with the teachings of the present disclosure may be desired for specific applications or implementations.

[0012] refer to Figure 1 , a schematic diagram of a hybrid electric vehicle (HEV) 10 is shown according to an embodiment of the present disclosure. Figure 1 Representative relationships between components are shown. The physical placement and orientation of the components within the vehicle may vary. The HEV 10 includes a powertrain 12. The powertrain 12 includes an engine 14 that drives a transmission 16, which may be referred to as a modular hybrid transmission (MHT). As will be described in further detail below, the transmission 16 includes an electric machine, such as an electric motor / generator (M / G) 18, an associated traction battery 20, a torque converter 22, and a multi-ratio transmission or gearbox 24. The engine 14, M / G 18, torque converter 22, and automatic transmission 16 are connected in series, as shown in FIG. Figure 1 For simplicity, the M / G 18 may be referred to as a motor.

[0013] The engine 14 and the M / G 18 are both drive sources for the HEV 10 and can be referred to as actuators. The engine 14 generally represents a power source, which may include an internal combustion engine, such as a gasoline, diesel, or natural gas powered engine. When the separation clutch 26 between the engine 14 and the M / G 18 is at least partially engaged, the engine 14 generates engine power and corresponding engine torque, which is provided to the M / G 18. The M / G 18 can be implemented by any of a variety of types of motors. For example, the M / G 18 can be a permanent magnet synchronous motor. The power electronics regulate the direct current (DC) power provided by the battery 20 according to the requirements of the M / G 18, as will be described below. For example, the power electronics can provide three-phase alternating current (AC) to the M / G 18.

[0014] When the disconnect clutch 26 is at least partially engaged, power flow from the engine 14 to the M / G 18 or from the M / G 18 to the engine 14 is possible. For example, the disconnect clutch 26 can be engaged, and the M / G 18 can be operated as a generator to convert rotational energy provided by the crankshaft 28 and the M / G shaft 30 into electrical energy for storage in the battery 20. The disconnect clutch 26 can also be disengaged to isolate the engine 14 from the rest of the powertrain 12 so that the M / G 18 can be used as the sole drive source for the HEV 10. The shaft 30 extends through the M / G 18. The M / G 18 is continuously drivingly connected to the shaft 30, while the engine 14 is drivingly connected to the shaft 30 only when the disconnect clutch 26 is at least partially engaged. When the disconnect clutch 26 is locked (fully engaged), the crankshaft 28 is fixed to the shaft 30.

[0015] A separate starter motor 31 can selectively engage the engine 14 to spin the engine to allow combustion to begin. Once the engine is started, the starter motor 31 can be disengaged from the engine via, for example, a clutch (not shown) between the starter motor 31 and the engine 14. In one embodiment, the starter motor 31 is a belt-driven starter generator (BISG). In one embodiment, the engine 14 is started by the starter motor 31 while the disconnect clutch 26 is open, thereby keeping the engine disconnected from the M / G 18. Once the engine has been started and accelerated with the M / G 18, the disconnect clutch 26 can couple the engine 14 to the M / G 18 to allow the engine to provide drive torque.

[0016] In another embodiment, a starter motor 31 is not provided, and the engine 14 is instead started by the M / G 18. To do this, the disconnect clutch 26 is partially engaged to transfer torque from the M / G 18 to the engine 14. The M / G 18 may need to increase torque to meet the driver demand while also starting the engine 14. Once the engine speed reaches the speed of the M / G, the disconnect clutch 26 can be fully engaged.

[0017] The M / G 18 is connected to the torque converter 22 via the shaft 30. Thus, when the disconnect clutch 26 is at least partially engaged, the torque converter 22 is connected to the engine 14. The torque converter 22 includes a pump wheel 23 fixed to the M / G shaft 30 and a turbine 23 fixed to the transmission input shaft 32. The torque converter 22 provides a hydraulic coupling between the shaft 30 and the transmission input shaft 32. When the pump wheel rotates faster than the turbine, the torque converter 22 transfers power from the pump wheel 23 to the turbine 25. The magnitude of the turbine torque and the pump wheel torque generally depends on the relative speed. When the ratio of the pump wheel speed to the turbine speed is high enough, the turbine torque is a multiple of the pump wheel torque. A torque converter bypass clutch 34 may also be provided, which frictionally or mechanically couples the pump wheel and turbine of the torque converter 22 when engaged, thereby allowing more efficient power transmission. The torque converter bypass clutch 34 may be operated as a starting clutch to provide a smooth vehicle start. Alternatively or in combination, a launch clutch similar to disconnect clutch 26 may be provided between M / G 18 and gearbox 24 for applications that do not include torque converter 22 or torque converter bypass clutch 34. In some applications, disconnect clutch 26 is generally referred to as the upstream clutch, and launch clutch 34 (which may be a torque converter bypass clutch) is generally referred to as the downstream clutch.

[0018] The gearbox 24 may include a gear set, such as a planetary gear set, which is selectively placed in different gear ratios through the selective engagement of friction elements such as clutches and brakes to establish a desired plurality of discrete or stepped transmission ratios. For simplicity, the gear ratios may be referred to as gears, i.e., first gear, second gear, etc. The friction elements are controllable via a shifting schedule that connects and disconnects certain elements of the gear set to control the speed and torque ratio between the transmission output shaft 36 and the transmission input shaft 32. The gearbox 24 may have six speeds, including first gear to sixth gear. In this example, the sixth gear may be referred to as the highest gear. The first gear has the lowest gear ratio and the highest torque ratio between the input shaft 32 and the output shaft 36, and the highest gear has the highest gear ratio and the lowest torque ratio. Based on various vehicle and environmental conditions, the gearbox 24 automatically shifts from one ratio to another through an associated controller such as a powertrain control unit (PCU). The gearbox 24 then provides the powertrain output torque to the output shaft 36.

[0019] It should be understood that the hydraulically controlled gearbox 24 used with the torque converter 22 is only one example of a gearbox or transmission device; any multiple ratio gearbox that accepts input torque from an engine and / or motor and then provides torque to an output shaft in different ratios is acceptable for use with embodiments of the present disclosure. For example, the gearbox 24 can be implemented by an automatic mechanical (or manual) transmission (AMT) that includes one or more servomotors to translate / rotate a shift fork along a shift rail to select a desired gear ratio. As is generally understood by those of ordinary skill in the art, an AMT can be used, for example, in applications with higher torque requirements.

[0020] like Figure 1 As shown in the representative embodiment of FIG. 4 , the output shaft 36 is connected to a differential 40. The differential 40 drives a pair of wheels 42 via respective axles 44 connected to the differential 40. The differential delivers approximately equal torque to each wheel 42 while allowing for slight speed differences, such as when the vehicle is turning. Different types of differentials or similar devices may be used to distribute torque from the drivetrain to one or more wheels. In some applications, the torque distribution may vary depending on, for example, a particular operating mode or condition.

[0021] The powertrain 12 also includes one or more controllers 50, such as a powertrain control unit (PCU), an engine control module (ECM), and a motor control unit (MCU). Although shown as one controller, the controller 50 may be part of a larger control system and may be controlled by various other controllers throughout the vehicle 10, such as a vehicle system controller (VSC). It should therefore be understood that the controller 50 and one or more other controllers may be collectively referred to as a "controller," which controls various actuators in response to signals from various sensors to control functions such as start / stop, operate the M / G 18 to provide wheel torque or charge the battery 20, select or plan transmission shifts, and the like. The controller 50 may include a microprocessor or central processing unit (CPU) that communicates with various types of computer-readable storage devices or media. The computer-readable storage devices or media may include, for example, volatile and non-volatile memory in a read-only memory (ROM), a random access memory (RAM), and a keep-alive memory (KAM). KAM is a persistent or non-volatile memory that can be used to store various operating variables when the CPU is powered off. The computer readable storage device or medium may be implemented using any of a number of known memory devices, such as a PROM (programmable read-only memory), EPROM (electronic PROM), EEPROM (electrically erasable PROM), flash memory, or any other electronic, magnetic, optical, or combination memory device capable of storing data, some of which represent executable instructions used by the controller to control the vehicle.

[0022] The controller communicates with various vehicle sensors and actuators via an input / output (I / O) interface, which may be implemented as a single integrated interface that provides various raw data or signal conditioning, processing and / or conversion, short circuit protection, etc. Alternatively, one or more dedicated hardware or firmware chips may be used to condition and process specific signals before providing them to the CPU. Figure 1 As generally shown in the representative embodiment of FIG. 1 , the controller 50 can communicate signals to and / or from the engine 14, the disconnect clutch 26, the M / G 18, the launch clutch 34, the transmission gearbox 24, and the power electronics 56. Although not explicitly shown, one of ordinary skill in the art will recognize the various functions or components that can be controlled by the controller 50 within each of the subsystems identified above. Representative examples of parameters, systems, and / or components that can be directly or indirectly actuated using control logic executed by the controller include fuel injection timing, rate and duration, throttle position, spark plug firing timing (for spark ignition engines), intake / exhaust valve timing and duration, front end accessory drive (FEAD) components such as an alternator, air conditioning compressor, battery charging, regenerative braking, M / G operation, clutch pressure for the disconnect clutch 26, the launch clutch 34, and the transmission gearbox 24, etc. Sensors communicating input via the I / O interface may be used to indicate, for example, turbocharger boost pressure, crankshaft position (PIP), engine speed (RPM), wheel speed (WS1, WS2), vehicle speed (VSS), coolant temperature (ECT), intake manifold pressure (MAP), accelerator pedal position (PPS), ignition switch position (IGN), throttle position (TP), air temperature (TMP), exhaust oxygen (EGO) or other exhaust constituent concentration or presence, intake air flow (MAF), transmission gear, ratio or mode, transmission oil temperature (TOT), transmission-turbine speed (TS), torque converter bypass clutch 34 state (TCC), deceleration or shift mode (MDE).

[0023] The control logic or functions performed by the controller 50 may be represented by a flowchart or similar diagram in one or more of the accompanying drawings. These diagrams provide representative control strategies and / or logic that may be implemented using one or more processing strategies (such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc.). Therefore, the various steps or functions shown may be performed in the order shown, in parallel, or omitted in some cases. Although not always explicitly shown, one of ordinary skill in the art will recognize that one or more of the steps or functions shown may be repeatedly performed depending on the specific processing strategy used. Similarly, the processing sequence is not necessarily required to achieve the features and advantages described herein, but is provided for ease of illustration and description. The control logic may be implemented primarily with software executed by a microprocessor-based vehicle, engine and / or powertrain controller (such as controller 50). Of course, depending on the specific application, the control logic may be implemented in one or more controllers with software, hardware, or a combination of software and hardware. When implemented with software, the control logic may be provided in one or more computer-readable storage devices or media storing data representing codes or instructions, which are executed by a computer to control a vehicle or its subsystems. The computer-readable storage device or medium may include one or more of a number of known physical devices that utilize electronic, magnetic, and / or optical storage devices to store executable instructions and associated calibration information, operating variables, and the like.

[0024] The vehicle driver uses the accelerator pedal 52 to provide the required torque, power or drive command to propel the vehicle. Typically, depressing and releasing the pedal 52 generates an accelerator pedal position signal, which can be interpreted by the controller 50 as requiring an increase in power or a decrease in power, respectively. Based at least on the input from the pedal, the controller 50 commands the torque from the engine 14 and / or the M / G 18. The controller 50 also controls the timing of the shift in the gearbox 24, as well as the engagement or disengagement of the disconnect clutch 26 and the torque converter bypass clutch 34. Like the disconnect clutch 26, the torque converter bypass clutch 34 can be adjusted within a range between an engaged position and a disengaged position. In addition to the variable slip generated by the hydraulic coupling between the impeller and the turbine, this also generates a variable slip in the torque converter 22. Alternatively, depending on the specific application, the torque converter bypass clutch 34 can be operated to be locked or opened without using the modulation operating mode.

[0025] To drive the vehicle with the engine 14, the disconnect clutch 26 is at least partially engaged to transfer at least a portion of the engine torque through the disconnect clutch 26 to the M / G 18 and then from the M / G 18 through the torque converter 22 and the gearbox 24. When the engine 14 alone provides the torque required to propel the vehicle, this operating mode may be referred to as an "engine mode," "engine-only mode," or "mechanical mode."

[0026] The M / G 18 may assist the engine 14 by providing additional power to rotate the shaft 30. This operating mode may be referred to as a "hybrid mode," an "engine-motor mode," or an "electric assist mode."

[0027] To drive the vehicle using the M / G 18 as the sole power source, the power flow remains the same except that the disconnect clutch 26 isolates the engine 14 from the rest of the powertrain 12. During this time, combustion in the engine 14 may be disabled or otherwise shut down to save fuel. The traction battery 20 transmits the stored electrical energy via line 54 to the power electronics 56, which may include, for example, an inverter. The power electronics 56 converts the DC voltage from the battery 20 to an AC voltage to be used by the M / G 18. The controller 50 commands the power electronics 56 to convert the voltage from the battery 20 to an AC voltage provided to the M / G 18 to provide positive torque (drive torque) or negative torque (regenerative braking) to the shaft 30. This operating mode may be referred to as an "electric only mode," "EV (electric vehicle) mode," or "motor mode."

[0028] In any operating mode, the M / G 18 can function as a motor and provide drive to the powertrain 12. Alternatively, the M / G 18 can function as a generator and convert kinetic energy from the powertrain 12 into electrical energy for storage in the battery 20. For example, the M / G 18 can function as a generator when the engine 14 provides propulsion power to the vehicle 10. The M / G 18 can also additionally function as a generator during regenerative braking, in which rotational energy from the rotating wheels 42 is transferred back through the gearbox 24 and converted into electrical energy for storage in the battery 20. The M / G 18 can be referred to as providing negative torque when functioning as a generator.

[0029] It should be understood that Figure 1 The schematic diagrams shown in are merely exemplary and are not intended to be limiting. Other configurations are contemplated that utilize selective engagement of the engine and motor to transmit through the transmission. For example, the M / G 18 may be offset from the crankshaft 28, and / or the M / G 18 may be disposed between the torque converter 22 and the gearbox 24. Other configurations are contemplated without departing from the scope of the present disclosure.

[0030] The hybrid powertrain 12 of the vehicle 10 has multiple actuators, such as engines and motors that can be used to generate a given driver-required torque. These actuators can be controlled by different control modules, each of which communicates with the VSC via a data bus (e.g., CAN). In one embodiment, the engine is controlled by the ECM and the motor is controlled by the MCU. The VSC can reside inside the ECM and communicate with the MCU via the CAN. The communication between the ECM and the MCU via the CAN may introduce a phase delay between the information at the MCU and the ECM. The phase delay may cause one or more of the actuators to generate a torque different from the command torque in a short duration. This may cause the final output torque at the drive wheel 42 to be greater or less than the torque required by the driver.

[0031] refer to Figure 2 , at time t1 when the engine torque increases and the motor torque decreases, a torque exchange between the engine and the motor is commanded. Torque exchange refers to a situation where the torque change rates of the motor and the engine are in opposite directions, for example, the engine increases and the motor decreases, or vice versa. At time t1, the controller begins to command the engine to increase torque production and begins to command the motor to reduce torque production. Ideally, the actuator will respond immediately, but in reality, phase delays and other inefficiencies can cause the actuator to produce an actual torque that is different from the commanded torque. The phase delay between the motor and the engine causes the motor to produce an actual torque that is greater than the commanded torque. Therefore, the combined torque actually produced by the actuator has a torque error (i.e., the difference between the torque requested by the driver and the actual torque) caused by the phase error. This torque error causes a torque peak 60 at the input shaft of the gearbox. The torque peak 60 propagates through the drive train and enters the drive wheels to generate interference, which can be perceived by the driver if the torque peak 60 has a sufficiently large magnitude. Torque peaks caused by phase delays (such as torque peak 60) are particularly noticeable during torque exchange when the torque requested by the driver remains constant because the driver does not expect acceleration or deceleration of the vehicle.

[0032] When the motor torque changes rapidly, the torque error is more significant. Error Δτ in the powertrain torque estimate err Defined by Equation 1, where Δτ mtr is the change in motor torque during instantaneous changes, is the rate of change of the motor torque, and t 延迟 is the communication time delay between control modules.

[0033]

[0034] As demonstrated in Equation 1, the effect of the phase error between the motor and the engine can be reduced by limiting the rate of change of torque of the motor and / or the engine. Return to Reference Figure 2 , if the rate of change of the engine torque between times t1 and t2 had been limited to a rate less than that shown, the peak torque 60 would be smaller. In general, the rate of change of torque and the peak torque are directly proportional, i.e., reducing the rate will reduce the peak torque. However, limiting the rate will increase the amount of time required to complete the torque exchange because the engine will approach the desired torque more slowly. In some cases, such as Figure 2 , the time at which the torque exchange is completed is not as critical because the driver-requested torque is constant. However, in other situations - such as in hard acceleration situations where the driver-requested torque exceeds the maximum motor torque - timing is more critical because the driveline output torque delivered by the vehicle will be insufficient until the engine reaches the required torque, which can produce slow acceleration. The maximum motor torque may be the physical limit of the electric machine, or it may be an artificial limit imposed by the designer.

[0035] Figure 3 A situation is shown where rate limiting (limiting) the engine torque reduces the torque peak, but also produces a delayed acceleration of the vehicle. Prior to time t1, the vehicle is traveling in EV mode. At time t1, the driver depresses the accelerator pedal, thereby substantially increasing the driver-requested torque above the maximum motor torque. This triggers the engine to start because the engine will need to provide a torque shortfall between the driver-requested torque and the maximum motor torque. To prevent a torque peak at the gearbox input shaft, the rate of change of the engine torque is limited to rate A between times t3 and t4. Limiting the rate of change of the engine torque to rate A increases the amount of time required to meet the driver-requested torque, which occurs at time t4. The vehicle substantially produces insufficient powertrain output torque between times t2 and t4, which may be perceived as slow acceleration.

[0036] As explained above, phase-delay-induced torque spikes may occur during torque exchanges between the engine and the motor. If no torque exchange occurs, the phase delay does not present a torque spike problem, and there is no need to limit the engine torque rate to a rate calculated to prevent the torque spike. Therefore, the vehicle can be programmed to limit the engine torque increase according to a first rate limit during torque exchange conditions and according to a second rate limit during other conditions (such as an engine start in response to a driver-requested torque exceeding the maximum motor torque).

[0037] By using a larger rate limit, during an engine start in response to the driver requested torque exceeding the maximum motor torque and the disconnect clutch closed, the driver requested torque can be met more quickly, which enhances vehicle acceleration. Figure 4, before time t1, the vehicle is traveling in EV mode. At time t1, the driver depresses the accelerator pedal, thereby substantially increasing the torque required by the driver to above the maximum motor torque. This triggers the engine to start, because the engine will need to provide the torque shortfall between the torque required by the driver and the maximum motor torque. The engine starts at time t1 and is connected to the transmission at time t3 when the separation clutch is locked. At time t3, the engine torque rises to meet the torque required by the driver. Between time t3 and t4, the rate at which the engine torque increases is limited to a limit so that the rate of change of the engine torque during this period is limited to rate B. Rate B is set independently of the torque peak because no actuator exchange occurs between time t3 and t4. Since the torque peak is not a problem, rate B can be greater than rate A, which allows the torque required by the driver to be met more quickly. Rate B can be constrained by the resonant frequency of the driveline to prevent hardware damage to the driveline.

[0038] In comparison Figure 3 and Figure 4 , it can be seen that Figure 3 The vehicle acceleration delay between time t2 and t4 is much greater than Figure 4 The vehicle acceleration delay between time t2 and t4 in FIG. Once the driver's requested torque is met, actuator exchange may occur and the torque peak must be controlled. To this end, the rate limit of the engine torque is switched from rate limit B to rate limit C at time t4. Rate C is less than rate B and is calibrated to maintain the torque peak within the allowable tolerance.

[0039] The rate of change of the engine torque increase can be limited to different rates depending on the driver's requested torque and the maximum motor torque. In one embodiment, a pair of rate limits (e.g., rate limits B and C) are used during engine starting when the driver's requested torque exceeds the maximum motor torque limit, and a single rate limit (e.g., rate limit C) is used during engine starting when the driver's requested torque is less than the maximum motor torque limit. Rate limit C can also be used for conditions other than engine starting.

[0040] The rate limit C can vary based on the gear ratio of the gearbox, that is, the magnitude of the rate C depends on the current gear ratio of the gearbox. This is because the torque peak appears on the gearbox input shaft and is amplified by the gearbox and the final reducer of the differential before propagating to the drive wheel. The amount of amplification varies with the gear ratio of the gearbox. For example, in a six-speed transmission, the torque peak is amplified to the greatest extent when the transmission is the lowest gear (first gear), and the torque peak is amplified to the least extent when the transmission is the highest gear (sixth gear). Therefore, the rate of change of the engine must be limited to a rate of change lower than that in the sixth gear in the first gear. The magnitude of the rate C of each gear can be calibrated by determining the acceptable torque peak amount at the drive wheel (which can be 200 to 600 Newton meters). Once this is determined, the magnitude of the torque peak at the input shaft can be calculated for each gear ratio of the gearbox. The individual magnitudes of the rate C of each gear can then be calibrated to ensure that the torque peak at the input shaft is within the permissible envelope. Alternatively, the rate limit C can be static and have a magnitude that prevents excessive torque peaks for all gear ratios of the transmission. Rate Limit B may also be based on the gear ratio of the gearbox. Rate Limit B is set to prevent excitation of the driveline. Since the engine torque is multiplied in the gearbox, different values ​​may be used for Rate Limit B. Typically, Rate Limit B is lowest in first gear and highest in highest gear. The specific values ​​of Rate Limits C and B are driveline specific and vary depending on the gear, but an example rate limit for first gear may be 250 Nm / s for Rate C and 1000 Nm / s for Rate B.

[0041] refer to Figure 5 , a flowchart 100 is shown, which shows an algorithm for selecting between engine-torque rate limits for various engine starting situations. At operation 102, the controller determines whether an engine start is occurring. If not, control is passed to other control logic. If yes, control passes to operation 104, and the controller calculates the desired torque distribution between actuators (such as motors and engines) to produce the torque requested by the driver. At operation 106, the controller determines whether the torque requested by the driver exceeds the maximum motor torque. If not, control passes to operation 108 and limits the requested engine torque rate to a rate calibrated to prevent excessive torque peaks at the transmission input shaft - such as rate C. At operation 110, the controller calculates the desired motor torque based on the torque requested by the driver and the actual engine torque produced.

[0042] If the driver requested torque is greater than the maximum motor torque during engine starting, control is transferred to operation 112. In operation 112, the requested engine torque rate is limited to a rate that is calibrated not to excite the resonant frequency and cause other problems within the powertrain system - such as rate B. The rate used in operation 112 is greater than the rate used in 108 to prevent delayed acceleration of the vehicle. At operation 114, the controller calculates the desired motor torque based on the driver requested torque and the actual engine torque. In operation 116, the controller determines whether the sum of the actual engine and motor torques is less than the torque requested by the driver. If not, the driver requested torque is met and control is transferred to operation 108, where the rate limit of the engine is reduced from rate limit B to rate limit C, for example. If it is yes at operation 116, the powertrain is still producing insufficient torque and the rate limit is maintained at the higher limit of operation 112 until the driver requested torque is met, at which time control is transferred to operation 108 and the rate limit is reduced.

[0043] The process, method or algorithm disclosed herein can be provided to / implemented by a processing device, a controller or a computer, which can include any existing programmable electronic control unit or a dedicated electronic control unit. Similarly, the process, method or algorithm can be stored as data and instructions that can be executed by a controller or a computer in many forms, including but not limited to information permanently stored on a non-writable storage medium such as a ROM device and information that can be modified and stored on a writable storage medium such as a floppy disk, a tape, a CD, a RAM device and other magnetic and optical media. The process, method or algorithm can also be implemented with a software executable object. Alternatively, the process, method or algorithm can be implemented in whole or in part using suitable hardware components, such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a state machine, a controller or other hardware component or device, or a combination of hardware, software and firmware components.

[0044] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms covered by the claims. The words used in the specification are descriptive rather than limiting, and it should be understood that various changes can be made without departing from the spirit and scope of the present disclosure. As previously mentioned, the features of the various embodiments can be combined to form other embodiments of the present invention that may not be explicitly described or illustrated. Although various embodiments may have been described as providing advantages or superiority over other embodiments or prior art implementations with respect to one or more desired characteristics, it is recognized by those of ordinary skill in the art that one or more features or characteristics may be compromised to achieve the desired overall system properties, depending on the specific application and implementation. These properties may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, applicability, weight, manufacturability, ease of assembly, etc. Therefore, to the extent that any embodiment is described as not as good as other embodiments or prior art implementations with respect to one or more characteristics, these embodiments are not outside the scope of the present disclosure and may be desirable for specific applications.

[0045] According to the present invention, a vehicle is provided, the vehicle having: an engine and a motor, the engine and the motor being selectively coupled via a clutch; and a controller, the controller being programmed to limit the rate of increase of the output torque of the engine to a limit having a first value in response to a driver-required torque exceeding a maximum torque of the motor and the clutch being locked, and to reduce the limit to a second value in response to the torque required by the driver being met.

[0046] According to one embodiment, the controller is further programmed to limit the rate of increase of the output torque of the engine to the second value in response to (i) the torque of the motor decreases and the torque of the engine increases and (ii) the torque requested by the driver is less than the maximum torque of the motor.

[0047] According to one embodiment, the second value is greater than zero.

[0048] According to one embodiment, the second value is based on a phase delay associated with a command between the motor and the controller.

[0049] According to one embodiment, the invention also features a gearbox that includes a plurality of discrete gear ratios, and wherein the limiting is based on the gear ratios of the gearbox.

[0050] According to one embodiment, the gear ratios include a first gear ratio having a lowest gear ratio and a second gear ratio having a higher gear ratio than the first gear ratio, wherein the controller is further programmed to set a first magnitude of the first value in response to the gearbox being in the first gear ratio, and to set a second magnitude of the first value in response to the gearbox being in the second gear ratio, and wherein the second magnitude is greater than the first magnitude.

[0051] According to one embodiment, the controller is further programmed to set a first magnitude of the second value in response to the gearbox being in the first gear ratio, and to set a second magnitude of the second value in response to the gearbox being in the second gear ratio.

[0052] According to one embodiment, the invention also features a gearbox and a torque converter having a pump impeller fixed to an output shaft of the motor and a turbine fixed to an input shaft of the gearbox.

[0053] According to one embodiment, the engine and the motor are arranged in series.

[0054] According to the present invention, a vehicle is provided, the vehicle having: a traction battery; an engine; a step ratio gearbox including a plurality of discrete gear ratios; a motor coupled to the gearbox with a torque converter and electrically connected to the traction battery; a disconnect clutch selectively coupling the engine and the motor when locked; and a controller programmed to: in response to a driver-requested torque exceeding a maximum torque of the motor, start the engine and command the disconnect clutch to engage, and in response to the disconnect clutch being locked, command the torque of the engine such that an increase in the torque is rate limited according to a first rate of change until the driver-requested torque is reached, and then rate limited according to a second rate of change that is less than the first rate of change.

[0055] According to one embodiment, the controller is also programmed to command the engine torque such that the increase in the engine torque is rate limited according to the second rate of change in response to (i) a decrease in the torque of the motor and an increase in the torque of the engine and (ii) a driver-requested torque that is less than the maximum torque of the motor.

[0056] According to one embodiment, the first rate of change and the second rate of change depend on an engaged gear ratio of the gearbox.

[0057] According to one embodiment, the gear ratios include a first gear ratio having a lowest gear ratio and a second gear ratio having a higher gear ratio than the first gear ratio, wherein the controller is further programmed to set a first magnitude of the second change rate in response to the gearbox being in the first gear ratio, and to set a second magnitude of the second change rate in response to the gearbox being in the second gear ratio, and wherein the second magnitude is greater than the first magnitude.

[0058] According to one embodiment, the second rate of change is based on a phase delay associated with a command between the motor and the controller.

[0059] According to one embodiment, the disconnect clutch is arranged in series with the engine and the motor.

[0060] According to the present invention, a method for rate limiting engine torque is provided, the method causing a controller to limit the rate of increase of the output torque of the engine to a limit having a first value in response to a clutch being locked to fix the engine to a motor and a torque required by a driver exceeding the maximum torque of the motor, and to reduce the limit to a second value in response to the torque required by the driver being met.

[0061] According to one embodiment, the present invention is further characterized by limiting the rate of increase of the output torque of the engine to the second value in response to (i) the torque of the motor decreases and the torque of the engine increases and (ii) the torque required by the driver is less than the maximum torque of the motor.

[0062] According to one embodiment, the limitation is based on a gear ratio of the gearbox.

[0063] According to one embodiment, the first value is minimum when the gearbox is in a first gear ratio having a lowest transmission ratio, and the first value is maximum when the gearbox is in a second gear ratio having a highest transmission ratio.

[0064] According to one embodiment, the second value is based on a phase delay associated with a command between the motor and a controller.

Claims

1. A vehicle, comprising: an engine and a motor, the engine and the motor being selectively coupled via a clutch; as well as A controller programmed to: In response to a driver demanded torque exceeding a maximum torque of the motor and the clutch being locked, limiting a rate of increase in output torque of the engine to a limit having a first value, and In response to a sum of the motor torque and the engine torque satisfying the driver requested torque, the limit is reduced from a first value to a second value.

2. The vehicle of claim 1 wherein the controller is further programmed to limit the rate of increase of the engine's output torque to the second value in response to (i) a decrease in the motor's torque and an increase in the engine's torque and (ii) a driver-requested torque that is less than the maximum torque of the motor. The vehicle of claim 1 , wherein the second value is greater than zero.

4. The vehicle of claim 1 wherein the second value is based on a phase delay associated with a command between the motor and the controller.

5. The vehicle of claim 1, further comprising a gearbox including a plurality of discrete gear ratios, and wherein the limit is based on the gear ratios of the gearbox.

6. The vehicle of claim 5, wherein the gear ratios include a first gear ratio having a lowest gear ratio and a second gear ratio having a higher gear ratio than the first gear ratio, wherein the controller is further programmed to set a first magnitude of the first value in response to the gearbox being in the first gear ratio, and to set a second magnitude of the first value in response to the gearbox being in the second gear ratio, and wherein the second magnitude is greater than the first magnitude.

7. The vehicle of claim 6, wherein the controller is further programmed to set a first magnitude of the second value in response to the gearbox being in the first gear ratio, and to set a second magnitude of the second value in response to the gearbox being in the second gear ratio.

8. The vehicle of claim 1, further comprising a gearbox and a torque converter having a pump impeller fixed to an output shaft of the motor and a turbine fixed to an input shaft of the gearbox.

9. The vehicle of claim 1, wherein the engine and the motor are arranged in series.

10. A vehicle, comprising: Traction batteries; engine; a step ratio gearbox, the step ratio gearbox comprising a plurality of discrete gear ratios; a motor coupled to the gearbox with a torque converter and electrically connected to the traction battery; a disconnect clutch that selectively couples the engine and the motor when locked; as well as A controller programmed to: In response to a driver requested torque exceeding the maximum torque of the motor, starting the engine and commanding engagement of the disconnect clutch, and In response to the disconnect clutch being locked, commanding the torque of the engine such that the increase in the torque is rate limited according to a first rate of change until the sum of the torque of the motor and the torque of the engine reaches the torque requested by the driver, and then rate limited according to a second rate of change that is less than the first rate of change.

11. A vehicle as described in claim 10, wherein the controller is further programmed to command engine torque such that the increase in engine torque is rate limited according to the second rate of change in response to (i) a decrease in torque of the motor and an increase in torque of the engine and (ii) a driver-requested torque less than the maximum torque of the motor.

12. The vehicle of claim 10, wherein the first rate of change and the second rate of change are dependent upon an engaged gear ratio of the gearbox.

13. The vehicle of claim 10, wherein the gear ratios include a first gear ratio having a lowest gear ratio and a second gear ratio having a higher gear ratio than the first gear ratio, wherein the controller is further programmed to set a first magnitude of the second rate of change in response to the gearbox being in the first gear ratio, and to set a second magnitude of the second rate of change in response to the gearbox being in the second gear ratio, and wherein the second magnitude is greater than the first magnitude.

14. The vehicle of claim 10, wherein the second rate of change is based on a phase delay associated with a command between the motor and the controller.

15. The vehicle of claim 10, wherein the disconnect clutch is arranged in series with the engine and the motor.

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