Generator gap crossing management in hybrid power split vehicles

Abstract

The invention provides generator gap crossing management in a hybrid power split vehicle. Methods and systems are provided for managing lash crossing in a hybrid power split vehicle. In one aspect, the method includes limiting an increase in engine speed in response to generator torque approaching zero generator torque during a selected condition. In one example, the selected conditions include a driver pedal operation less than a threshold, a non-engine start condition, emission control, and a battery state of charge greater than a threshold.

Description

Technical Field

[0001] The present subject matter relates to a system and method for generator lash crossing management in a vehicle, particularly a hybrid power-split vehicle. Background Art

[0002] A hybrid power-split powertrain is a hybrid propulsion system used in a vehicle that integrates an internal combustion engine, an electric motor, and a generator with a transmission to deliver wheel torque to a drive axle. The engine, motor, and generator can work together to propel the vehicle. For example, the generator can control the engine speed, and the motor can provide tractive force.

[0003] When the engine is running, the generator can control the engine speed target by applying positive or negative torque. The amount of generator torque requested to maintain the engine speed can depend on the engine's torque output. Additionally, if the engine is operating at low torque, such as during a full high-voltage battery condition, the generator torque can be negative and close to zero. If the driver then depresses the driver pedal with sufficient demand, the powertrain control system will aim to increase the engine speed to meet the torque request, which, due to the low engine torque, will result in a positive generator torque command to meet the requested increase in engine speed. This causes the generator to transition from negative torque to positive torque, which can be referred to as crossing the lash or lash crossing. During lash crossing, the backlash or lash can be caused by the void or clearance between mating parts. However, in some examples, the mechanical clearance in the mating parts can produce a metallic sound (e.g., also referred to as a shunt), which refers to the sensation of the teeth of a gear upon contact after crossing the zero-torque point (also referred to as the lash zone), and this metallic sound can be heard and felt in the vehicle.

[0004] Other attempts to address the metallic sound caused by backlash include torque shaping through the lash zone. In U.S. Patent No. 6,754,573, Russell and Kotwicki teach a system and method for transitioning through the lash zone based on an estimate of the transmission ratio across a torque converter. When near the lash zone, the engine torque can be adjusted at a predetermined rate until the system passes through the lash zone. Decelerating the engine torque through the lash zone in this manner minimizes the metallic sound by causing the gear teeth to gently contact. Summary of the Invention

[0005] However, the inventors have recognized potential problems with such systems. As an example, due to the multiple power inputs to the transmission and the resulting complex power flow, torque shaping for minimizing metallic sounds in a hybrid power-split powertrain is particularly challenging. For example, it may be difficult to identify the specific source of metallic sounds, such as between which components of the transmission gear train and under what conditions. Therefore, applying torque shaping methods to a power-split powertrain may be impractical.

[0006] In one example, the above problems can be addressed by a method for managing gap crossings in a hybrid power-split vehicle, the method including restricting an increase in engine speed in response to generator torque approaching zero torque during selected conditions. In this way, gap crossings are reduced during the selected conditions, and as more engine torque becomes available, engine speed is allowed to increase.

[0007] It should be understood that the above Summary is provided to introduce in a simplified form a series of concepts that are further described in the Detailed Description. This is not meant to identify key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims that follow the Detailed Description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a schematic view of a hybrid power-split vehicle.

[0009] Figure 2A is a first flowchart showing an exemplary method for gap crossing management.

[0010] Figure 2B is a second flowchart showing an exemplary method for gap crossing management.

[0011] Figure 3 is a timing diagram showing exemplary predictive operations of a method for gap crossing management.

[0012] Figure 4 is a timing diagram showing a second exemplary predictive operation of a method for gap crossing management. DETAILED DESCRIPTION

[0013] The following description relates to methods for Figure 1Systems and methods for generator lash crossing management in a split power delivery hybrid vehicle of the type shown. Such a vehicle can include an engine, a planetary gear unit, an electric motor, and a generator. To manage potential metallic noises during generator torque reversals, a lash crossing management strategy can be implemented by the vehicle's power split powertrain control system, as shown in Figure 1 which is shown in Figure 2A is a flowchart of a first method 200 for generator lash crossing management in the vehicle system described in Figure 1 which is shown in Figure 2B is a flowchart of a second method 250 for generator lash crossing management in the vehicle system described in Figure 1 which is shown in Figures 3 to 4 In some examples, the method reduces the incidence of metallic noises generated by generator lash crossing by applying an inertia-based rate limit to engine speed increases during selected conditions. Figure 3 is a timing diagram of a predictive example of operating one or more of the lash crossing management methods described herein. For example, Figure 4 shows a first predictive example of the method, where a selected condition is met and an inertia-based rate limit is applied to engine speed increases.

[0014] Figure 1 includes a schematic block diagram representation of a vehicle system 100 to illustrate an embodiment of a system or method for controlling a vehicle powertrain according to the present disclosure. The vehicle system 100 generally represents any vehicle having a hybrid electric powertrain with an internal combustion engine (ICE) 102. In the depicted embodiment, the vehicle system 100 is a hybrid electric vehicle (HEV) system, where the powertrain 104 includes an ICE 102, a battery 112, a planetary gear unit, a motor 106, and a generator 108. The vehicle system 100 includes a drive axle 114 that includes axle shafts 116 coupled to a pair of wheels 118 and the powertrain 104. The vehicle system 100 includes a control system 14 having a controller 12 that receives signals from various sensors 16 and employs actuators 18 to adjust powertrain operation based on the received signals and instructions stored in the memory of the controller 12. However, it should be understood that in alternative embodiments, the powertrain control methods discussed herein may be applied to other hybrid vehicle configurations.

[0015] The powertrain 104 includes an ICE 102 and a motor 106 and a generator 108 coupled to the ICE 102 via a planetary gear unit 110. In other examples, other types of power transfer units (including other gear sets and transmissions) may be used to connect the ICE 102 to the motor 106 and the generator 108. The planetary gear unit 110 may be a conventional planetary gear unit including a ring gear, a gear carrier, planetary gears, and a sun gear. In one example, the generator 108 is connected to the sun gear, the ICE 102 is connected to the gear carrier via a damper, and the motor 106 is connected to the ring gear. However, other arrangements are possible.

[0016] The generator 108 can be used to control the rotational speed of the ICE 102 via the planetary gear unit 110. For example, the generator 108 controls the engine speed by applying a generator torque 144 via a shaft coupled to the planetary gear unit 110. The generator 108 can also assist the ICE 102 in meeting driver demands. The generator torque 144 applied to the planetary gear unit 110 can be positive or negative, as indicated by the double-headed arrow. The motor 106 can be used to control the traction force supplied to the drive axle 114 via the planetary gear unit 110. For example, the motor 106 controls the traction force by applying a motor torque 148 via a shaft coupled to the planetary gear unit 110. The motor 106 can also assist the ICE 102 in meeting driver demands. The motor torque 148 applied to the planetary gear unit 110 can be positive or negative, as indicated by the double-headed arrow. The operation of the ICE 102 supplies an engine torque 150 to a shaft coupled to the planetary gear unit 110. The engine torque 150 applied to the planetary gear unit 110 can be a positive engine torque, as indicated by the single-headed arrow. The operation of the powertrain 104 supplies a wheel torque 152 to a shaft coupled to the planetary gear unit 110 and the drive axle 114. The wheel torque 152 applied to the drive axle 114 can be positive or negative, as indicated by the double-headed arrow.

[0017] In Figure 1 the illustrated embodiment, both the generator 108 and the motor 106 can operate as motors using current 146 from the battery 112 or another current source to provide a desired output torque. Alternatively, the generator 108 and the motor 106 can operate as generators supplying current 146 to a high voltage bus and / or to an energy storage device such as the battery 112. Other types of energy storage devices and / or output devices that can be used include, for example, capacitor banks, fuel cells, flywheels, etc. Other vehicles within the scope of the present disclosure may have different motor arrangements, such as more or fewer than the two motors (generator 108 and motor 106) depicted herein.

[0018] The controller 12 may form part of a control system 14. One or more controllers 12 implemented in hardware and / or software are provided to control components of the powertrain 104. In Figure 1 an embodiment, the controller 12 is a vehicle system controller (VSC). The controller 12 is shown as a conventional microcomputer and includes: a microprocessor unit 2, input / output ports 4, a read-only memory 6 for executable programs (e.g., executable instructions) and calibration values (e.g., non-transitory memory for storing instructions), shown in this particular example as a non-transitory read-only memory chip, a random access memory 8, a keep-alive memory 9, and a conventional data bus. The controller 12 may include an interface 10. The interface 10 may include various interfaces, such as one or more interfaces for the user. The interface 10 may include a data output device.

[0019] Although the controller 12 is shown as a single controller, it may include multiple hardware and / or software controllers. For example, the controller 12 may include a separate powertrain control module (PCM), which may be software embedded within the controller 12 or the PCM may be implemented by a separate hardware device with corresponding software. A controller area network (CAN) may be used to transfer control data and / or commands between the controller 12, the powertrain 104, and one or more other controllers such as a battery control module (BCM). For example, the BCM may transfer data such as battery temperature, state of charge (SOC), discharge power limit, and / or other operating conditions or parameters of the battery 112. Devices other than the battery 112 may also have dedicated controllers or control modules that communicate with the controller 12 to implement control of the vehicle and the powertrain. For example, an engine control unit (ECU) may communicate with the controller 12 to control the operation of the ICE 102. Similarly, the controller 12 may include a separate generator control unit (GCU) and a separate motor control unit (MCU) to implement control of the electric machine.

[0020] The control system 14 including the controller 12 can communicate with one or more of the ICE 102, the motor 106, the generator 108, the battery 112, the drive axle 114, and the driver pedal 30. The control system 14 can receive sensed feedback information from one or more of the ICE 102, the motor 106, the generator 108, the battery 112, the drive axle 114, and the driver pedal 30. Examples of the sensors 16 can detect driver demand, engine speed, engine torque, motor torque, motor speed, generator torque, generator speed, wheel speed, battery charge, and other powertrain operating parameters. Additionally, in response to the sensed feedback, the control system 14 can send control signals to one or more of the ICE 102, the motor 106, the generator 108, and the battery 112, etc. via one or more of the actuators 18. The control system 14 can receive an indication of an operator request for an output (torque increase, decrease) of the powertrain from a human operator or an autonomous controller.

[0021] For example, in response to the driver 32 (human or autonomous) depressing the driver pedal 30 (e.g., an accelerator pedal condition), the controller 12 can generate a wheel torque request 126 to provide a desired vehicle speed and rate of increase based on the position of the driver pedal 30 indicated by the pedal position sensor 34 and feedback of the wheel torque 142 delivered as indicated by the wheel speed sensor 121. The wheel torque request 126 can generate a plurality of commands to the ICE 102, the generator 108, and the motor 106 to adjust the wheel torque 152 to achieve the target of the delivered wheel torque 142. Based on the wheel torque request 126, the controller 12 can generate an ICE power command 128 and an ICE torque command 130 to adjust the engine torque 150 output by the ICE 102. The generator 108 applies a counter torque to the positive engine torque, thus resisting the ICE 102. The generator torque 144 output by the generator 108 can be a negative mechanical torque that corresponds to the generated power or discharge power depending on the speed of the generator 108. The ICE speed command 132 and the ICE speed 120 can be input to the generator speed control 134 to generate a generator torque command 136. The generator torque command 136 controls the output of the generator torque 144 between the generator 108 and the planetary gear unit 110 based on feedback from the ICE speed 120 to maintain the ICE speed command 132. Based on the wheel torque request 126 and the generator speed control 134, the motor torque determination 138 is performed and a motor torque command 140 is obtained therefrom. The motor torque command 140 controls the output of the motor torque 148 between the motor 106 and the planetary gear unit 110 to provide traction to the wheels 118.

[0022] When the ICE 102 produces positive torque, the generator torque 144 constrains the ICE speed 120. The amount of generator torque 144 commanded to maintain the ICE speed command 132 depends on the engine torque 150 output by the ICE 102. If an increase in speed is requested, the generator torque command 136 can be adjusted to less constrain the ICE 102 and allow the engine torque to increase the ICE speed 120. In some examples, the generator 108 can assist the ICE 102 to increase the ICE speed 120. In this case, the generator 108 drives the ICE 102 rather than constraining the ICE 102. The driver pedal 30 can affect (e.g., full pedal, less than full pedal) whether generator assistance is desired or whether the generator torque 144 can remain negative and resist the ICE 102 to some extent.

[0023] For example, under conditions where the ICE 102 is operating and operating at low torque, such as when the battery 112 is full, the generator torque 144 can be slightly negative and close to zero. In an example of an existing control strategy, if the driver presses the pedal, the control system aims to increase the ICE speed to meet the wheel torque request. In such examples, due to the low engine torque, the control system generates a positive generator torque command to assist the engine to meet the increased engine speed request. As a result, the generator crosses the gap, and then driveline metallic sounds can be heard and felt in the vehicle.

[0024] The systems and methods disclosed herein reduce the incidence of metallic sounds caused by the generator 108 transitioning from a low negative torque to a positive torque. As an example, a controller (such as controller 12) can be configured to limit the increase in engine speed in response to the generator torque approaching zero generator torque during selected conditions. When the feedback control based on the target engine speed adjusts the generator torque command 136 by slowing the rate of increase of the ICE speed command 132, the generator torque command 136 can remain negative, continue to constrain the ICE 102, and thereby prevent generator gap crossing. As several non-limiting examples, the selected conditions can include driver pedal operation less than a threshold, standard engine operating conditions, and a battery state of charge greater than a threshold. In one example, driver pedal operation less than a threshold can include an accelerator pedal depression condition less than a full pedal request. Standard engine operating conditions can include non-engine start conditions and engine operation, e.g., the engine is being supplied fuel and burning a fuel mixture, and can also include conditions where the emissions control strategy meets expectations. A battery state of charge greater than a threshold can include a threshold calibrated to provide the battery demand for predicted / estimated vehicle operation. In one example, the selected conditions can include those conditions where it is acceptable to limit to some extent the rate at which the wheel torque request is met, and conditions where the disclosed strategy does not interfere with other (e.g., higher priority) control strategies (such as emissions control, battery power control, and engine start). During the selected conditions, the generator torque can remain negative during the duration of the driver depressing the accelerator pedal, and the limitation can be reduced as more engine torque becomes available during the accelerator pedal depression. In one example, the limitation can include an inertia-based rate limit on the engine speed command, and the inertia-based rate limit can be determined based on an estimate of the amount of allowable engine speed increase while maintaining negative generator torque. In this way, by limiting the engine speed request and allowing a higher engine speed change rate as more engine torque becomes available, the incidence of generator gap crossing and the resulting metallic sounds can be reduced under selected conditions.

[0025] Figure 2A and Figure 2B An exemplary method for managing gap crossing in a hybrid power-split vehicle in accordance with at least some of the embodiments of the present disclosure is shown. The exemplary method manages generator gap crossing by applying an inertia-based rate limit to the engine speed increase in response to the generator torque approaching zero generator torque during selected conditions. Figure 2A A first method 200 for determining whether the selected conditions are met to apply the inertia-based rate limit is described. Figure 2B A second method 250 for determining the inertia-based rate limit is described. In some examples, reference Figure 2BThe described method 250 may be a sub-method of the method 200 described with reference to Figure 2A The instructions for performing method 200 and the remaining methods included herein may be executed by the controller based on instructions stored in the controller's memory and in combination with signals received from sensors of the powertrain, such as the control system 14, controller 12, and sensor 16 described above with reference to Figure 1 The controller may adjust the actuators of the powertrain according to the methods described below to adjust the operation of the powertrain.

[0026] At 202, method 200 may include determining an operating condition. The operating condition may include the position of the driver's pedal (e.g., pressing the accelerator pedal, releasing the accelerator pedal), engine speed, generator speed, motor speed, battery state of charge (SOC), wheel speed, etc. In one example, the driver's pedal may control vehicle speed rather than the vehicle wheel brake calipers.

[0027] At 204, method 200 may include determining whether engine operation is indicated. In one example, method 200 may determine that the engine is operating based on a sensor signal from one of sensors 16 indicating an engine speed greater than a threshold. In one example, the engine speed greater than the threshold may be a non-zero positive value threshold. As a non-limiting example, the threshold engine speed may be greater than 600 RPM. In one example, engine operation may indicate a standard engine condition, e.g., a non-engine starting condition and an emissions control condition. If engine operation is indicated, the method may proceed to 206. If engine operation is not indicated, the method proceeds to 214.

[0028] At 214, method 200 includes determining whether an engine start timer is greater than a threshold. In one example, the engine start timer threshold may be a non-zero positive value threshold. As a non-limiting example, the engine start time threshold may be 5 seconds. In one example, the engine start timer being greater than the threshold may indicate a standard engine condition. For example, completion of the cold start emissions control mode is a prerequisite for the engine start timer. If the engine start timer being greater than the threshold is indicated, method 200 may proceed to 206. If the engine start timer being greater than the threshold is not indicated, method 200 may monitor the engine start time threshold at 214.

[0029] At 206, method 200 may include determining whether an accelerator pedal depressed condition is indicated. In other words, method 200 may include determining whether a wheel torque request is received based on a pedal position sensor signal indicating the accelerator pedal being depressed or the depression applied to the driver's pedal. In some examples, the accelerator pedal may be applied by the driver, such as driver 32 to Figure 1Apply pressure to the driver pedal 30 therein. If there is no indication to step on the accelerator pedal, the method can proceed to 204. If stepping on the accelerator pedal does not occur, the method can include continuously monitoring for an indication of the accelerator pedal depression condition.

[0030] If stepping on the accelerator pedal is indicated, then at 208, method 200 can include determining selected conditions. For example, the selected conditions can include standard engine operating conditions (as determined above), a driver pedal position less than a threshold, and a battery charge state greater than a threshold. In one example, the threshold driver pedal position can be a non-zero positive value threshold. As a non-limiting example, the threshold driver pedal position can be a pedal position indicating less than 70% depressed. In one example, the battery charge state greater than the threshold can be a non-zero positive value threshold. In one example, the method can include comparing the calibrated buffered battery power charge state minus a value with the threshold battery charge state. As a non-limiting example, the threshold battery charge state can be greater than 25% charged.

[0031] At 210, method 200 can include determining whether the selected conditions are met. For example, the method can include determining whether one or more of the selected conditions are met. In other examples, the method can include determining whether multiple conditions are met. In yet another example, the method can include determining whether each condition is met. Determining whether each condition is met can ensure that the strategy does not interfere with higher priority control strategies (such as emissions control, battery power control, and engine start), nor overly constrain vehicle operation. For example, during a high pedal position, reducing the wheel torque request satisfaction rate may have a negative impact on the overall driving experience.

[0032] If the selected conditions are met, then at 212, the method can include determining an inertia-based rate limit for engine speed increase. In one example, the inertia-based rate limit is determined based on an estimate of the amount of allowable engine speed increase while maintaining negative generator torque. An exemplary method for determining the inertia-based rate limit is described below with reference to Figure 2B Describe an exemplary method for determining the inertia-based rate limit.

[0033] At 216, the method may include applying an inertia-based rate limit to the engine speed command. For example, the controller may determine a control signal to send to the generator control unit, such as a pulse width modulation signal, the pulse width of which corresponds to the inertia-based rate limit. In some examples, method 200 may include reducing the inertia-based rate limit as more engine torque becomes available. For example, the method may include monitoring the engine torque output, and in response to the engine torque output exceeding a threshold, the method may include reducing the inertia-based rate limit at a calibrated rate based on the engine torque output. In some examples, in response to applying the inertia-based rate limit to the engine speed command, the method may further include commanding an increase in motor torque to assist the powertrain in delivering the wheel torque request indicated by the driver depressing the accelerator pedal. In one example, in response to one or more selected conditions no longer being met during the rate limit, the method may include removing the inertia-based rate limit. For example, the rate may increase discontinuously (e.g., creating an inflection point in the speed command).

[0034] In this way, methods for generator clearance management can be selectively applied and interference with other control strategies, such as engine starting, emission control, battery power management, and high pedal demand, can be reduced.

[0035] Figure 2B A second method 250 for managing generator clearance crossings is described, which includes an exemplary method for determining an inertia-based rate limit such as described above with reference to Figure 2A as described.

[0036] At 252, method 250 may include receiving an engine torque estimate. In one example, the controller and / or ECU may estimate the engine torque based on one or more sensor signals. For example, controller 12 may receive signals from one or more of sensors 16 indicating one or more of crankshaft position, throttle position, mass air flow reading, manifold pressure reading, and air-fuel ratio, and controller 12 may estimate the amount of engine torque generated based on the signals.

[0037] At 254, method 250 may include receiving a generator torque estimate. In one example, the controller and / or GCU may estimate the generator torque based on one or more sensor signals. For example, controller 12 may receive signals from one or more of sensors 16 indicating the current and / or voltage through the generator, and the controller may estimate the amount of generator torque generated based on the signals.

[0038] At 256, method 250 may include receiving a vehicle speed. In one example, the controller and / or GCU may estimate generator torque based on one or more sensor signals. For example, controller 12 may receive a signal indicative of the rotational speed of the wheels from wheel speed sensor 121, and the controller may estimate the vehicle speed based on the signal.

[0039] At 258, method 250 may include calibrating an offset based on the vehicle speed. For example, the method may include obtaining a calibrated offset based on a two-dimensional function with the vehicle speed as an input. In one example, the calibrated offset output by the two-dimensional function may increase as the vehicle speed decreases and decrease as the vehicle speed increases. In other words, the method may include a larger offset at lower vehicle speeds, thereby implementing a more conservative intervention to reduce gap crossing. At higher vehicle speeds, where road noise, wind, and vibration are present to mask gap crossing, the offset may be smaller. In some examples, the method may include calibrating a negative offset at higher speeds to allow generator torque assistance (e.g., and gap crossing) of engine speed.

[0040] At 260, method 250 may include determining an inertia torque. In one example, the inertia torque may be determined based on the engine torque estimate minus the calibrated offset. Additionally, if the offset is calibrated in terms of generator torque, the method may include using the gear ratio to convert the offset to the engine torque domain.

[0041] At 262, method 250 may include determining an inertia-based rate limit. In one example, the inertia-based rate limit may be determined based on the inertia torque divided by the lumped engine and generator inertia. In some examples, the lumped engine and generator torque may be determined experimentally. In other examples, if the individual engine and generator inertias are known, the relationship of the generator and engine relative to the planetary gear unit may be used to derive the lumped inertia. For example, the lumped inertia may be determined based on the sum of the engine inertia and the generator inertia divided by the square of the engine-to-generator gear ratio.

[0042] In this way, a method for generator gap management may consider the amount of engine torque being generated (including the calibrated offset) to predict the amount of engine speed increase allowed while maintaining negative generator torque during acceleration pedal depression.

[0043] Figure 3 and Figure 4 are timing diagrams showing a series of actions performed within a method for generator gap crossing management in an exemplary hybrid power split vehicle system. The method for generator gap crossing management may be associated with the above reference respectively at Figures 2A to 2BThe series of actions described by the methods 200 and 250 shown are the same or similar. The hybrid power split vehicle system can be the same as or similar to the Figure 1 vehicle 100 shown. The instructions for performing the methods described in the timing diagrams 300, 400 can be executed by a controller (e.g., controller 12) based on instructions stored in the controller's memory and in combination with sensing feedback received from components of the vehicle powertrain system, the components including sensors (e.g., sensor 16) for detecting driver wheel requests, engine speed, engine torque, motor torque, motor speed, generator torque, generator speed, wheel speed, battery charge, and other powertrain operating parameters as described above with reference to Figure 1 In a predictive example, the controller determines whether an acceleration pedal depression is indicated. If an acceleration pedal depression is indicated, the controller determines whether a selected condition is met. In response to the selected condition being met, the controller determines an inertia-based rate limit and applies the inertia-based rate limit to the engine speed command, which is determined based on the driver wheel torque request indicated by the acceleration pedal depression. By applying the inertia-based rate limit, the generator can be controlled not to cross a gap, or in other words, not to exceed zero torque. Figure 3 depicts a scenario showing a generator gap crossing management strategy where the selected condition is met. Figure 4 depicts a scenario showing a generator gap crossing management strategy where the selected condition is not met. The horizontal line (x-axis) represents time, and the vertical markers t0 - t4 and t0 - t6 respectively identify the relevant times for generator gap crossing management in the timing diagrams 300, 400.

[0044] Figure 3The timing diagram 300 shows curves 302, 304, 306, 308, 310, 312, 314, 316, and 324 that show the component states and / or control settings of a vehicle system over time. Curve 302 indicates the wheel torque request. Curve 304 indicates the engine speed. Curve 306 indicates the engine torque estimate. Curve 308 indicates the driver pedal including the accelerator pedal threshold 320. Increasing the driver pedal indicates depressing the accelerator pedal, or in other words, increasing the wheel torque request. The accelerator pedal threshold can represent a positive non-zero threshold, for example, depressed more than 90%, which can indicate a relatively high pedal position or an emergency wheel torque request. Curves 310 and 312 indicate the generator torque estimate and the motor torque estimate, respectively, which can be positive or negative. Curve 314 indicates the generator perturbation, which can be a measurement of the generator angular rate of change of the rotational speed. Curve 316 indicates the state of charge (SOC) of the battery including the battery charge threshold 322. The magnitude of the inertia-based rate limiting is indicated in curve 324, and the normal engine speed rate of change limit is indicated in curve 318. In one example, the normal engine speed rate of change limit can be selected to balance the fast engine power output response for optimal performance with NVH (noise, vibration, and harshness) and the engine speed busyness constraint on the maximum rate of change of the engine speed. When the magnitude of the inertia-based rate limiting is greater than the normal engine speed rate of change limit, the inertia-based rate limiting has no effect. Additionally, when the entry condition is not met (e.g., see Figure 4 ), the normal engine speed rate of change limit is used regardless of whether the clearance reduction rate limit is smaller. The battery charge threshold can represent a positive non-zero threshold that can be calibrated to a sufficient battery charge level to limit the engine speed increase by the inertia-based rate limiting, for example, charged more than 30%. Curves 310, 312 show a positive increase upward along the y-axis, and the values become more and more negative downward along the y-axis. Curves 302, 304, 306, 308, 314, 316, 324 show an increase upward along the y-axis.

[0045] At t0, in curve 302, the wheel torque request is approximately zero. In curve 304, the engine speed is low. In curve 306, the engine torque is close to zero. In curve 308, the driver pedal is not depressed. The generator torque is slightly negative in curve 310. In curve 312, the motor torque is approximately zero. In curve 314, the generator perturbation is close to zero. The battery SOC is relatively high. In curve 324, the inertia-based rate limiting is not applied. The normal engine speed rate of change limit in curve 318 is applied. From t0 to t1, the curves remain relatively constant.

[0046] At t1, detection of an accelerator pedal depression is detected in graph 308. In response to the accelerator pedal depression, from t1 to t2, the controller determines selected conditions for managing the generator gap. In this example, the selected conditions include a driver pedal operation less than a threshold in curve 308, a state of charge of the battery greater than a threshold in curve 316, and an engine speed indicating a non-engine start condition in curve 304. Not shown in timing diagram 300, emissions control is also a selected condition determined by the controller.

[0047] At t2, the controller determines that the selected conditions are met. Thus, at t2, the controller determines an inertia-based rate limit to be applied to the engine speed command. The inertia-based rate limit is determined based on the inertia torque divided by the lumped engine and generator inertia. The inertia torque is determined based on the difference between the estimated engine torque (in graph 306) and a calibrated offset related to the vehicle speed (e.g., received via Figure 1 the wheel speed sensor 121 in). In other words, the inertia-based rate limit can estimate the threshold rate at which the engine speed increases while maintaining a negative generator torque, or how quickly the engine speed in graph 304 can change with the generator torque remaining positive (crossing the gap) to assist.

[0048] From t2 to t3, the controller applies the inertia-based rate limit to the engine speed command. The magnitude of the inertia-based rate limit in graph 324 is relatively low near t2 and increases with the engine torque. Applying the inertia-based rate limit to the engine speed command constrains the engine speed rise rate, which is indicated by the very gradual increase in the engine speed in graph 304. It can be seen that the engine speed is almost horizontal for most of the time from t2 to t3 and increases as the engine torque in graph 306 increases as time approaches t3. As the engine torque increases as time approaches t3, the magnitude of the inertia-based rate limit increases. By restricting the engine speed rise rate, no generator torque is commanded to produce positive torque to assist the engine speed increase. Instead, the generator continues to provide a drag torque to the positive engine torque, which is indicated by the decreasing generator torque from t2 to t3 in graph 310. The controller commands the motor to increase the motor torque to assist in wheel torque delivery to meet the wheel torque request in graph 302, which is indicated by the increase in the motor torque in graph 312. Thus, the state of charge of the battery in graph 316 slightly decreases from t2 to t3. From t2 to t3, the generator torque remains negative, thereby reducing gap crossing, which is indicated by the very low generator perturbation in graph 314.

[0049] At t3, the calculation of the inertia-based rate limit in graph 324 is greater than the normal engine speed change rate limit in graph 318. As can be understood, the engine torque when the engine speed is no longer modified by the inertia-based rate limit depends on the normal engine speed change rate limit, which varies based on other conditions. From t3 to t4, the inertia-based rate limit has no effect on the engine speed in graph 304, and the normal engine speed limit in graph 318 is applied to the engine speed to achieve the target of the engine speed command. At t4, a release of the accelerator pedal is detected.

[0050] Figure 4 The timing diagram 400 shows graphs 402, 404, 406, 408, 410, 412, 414, and 416 that show the component states and / or control settings of the vehicle system changing over time. Graph 402 indicates the wheel torque request. Graph 404 indicates the engine speed. Graph 406 indicates the engine torque estimate. Graph 408 indicates the driver pedal including the accelerator pedal threshold 418. An increase in the driver pedal indicates depressing the accelerator pedal, or in other words, an increase in the wheel torque request. The accelerator pedal threshold can represent a positive non-zero threshold, for example, depressed more than 90%, which can indicate a relatively high pedal position or an emergency wheel torque request. Graphs 410 and 412 indicate the generator torque estimate and the motor torque estimate, respectively, which can be positive or negative. Graph 414 indicates the generator disturbance, which can be a measurement of the generator angular change rate of the rotational speed. Graph 416 indicates the state of charge (SOC) of the battery including the battery charge threshold 422. The battery charge threshold 422 can represent a positive non-zero threshold, which can be calibrated to a sufficient battery charge level to limit the engine speed increase by the inertia-based rate limit, for example, charged more than 40%. The magnitude of the normal engine speed change rate limit is indicated in graph 424. When the entry condition is not met, the normal engine speed change rate limit in graph 424 is used regardless of whether the inertia-based rate limit curve is smaller. Graphs 410, 412 show a positive increase upward along the y-axis, and the values become more and more negative downward along the y-axis. Graphs 402, 404, 406, 408, 414, 416, and 424 show an increase upward along the y-axis.

[0051] At t0, in graph 402, the wheel torque request is approximately zero. In graph 404, the engine speed is low. In graph 406, the engine torque is low (close to zero). In graph 408, the driver's pedal is not depressed. In graph 410, the generator torque is negative. In graph 412, the motor torque is slightly positive. In graph 414, the generator disturbance is close to zero. The battery SOC is medium high. From t0 to t1, the graphs remain relatively constant. The normal engine speed change rate limit is applied in graph 424.

[0052] At t1, the depression of the accelerator pedal is detected in graph 408. In response to the depression of the accelerator pedal, from t1 to t2, the controller determines the selected conditions for managing the generator clearance. In this example, the selected conditions include a driver pedal operation less than a threshold in curve 408, a battery state of charge greater than a threshold in curve 416, and an engine speed indicating a non-engine start condition in curve 404. Emission control, not shown in timing diagram 400, is also a selected condition determined by the controller.

[0053] At t2, the driver's pedal is increased above the threshold driver pedal operation in graph 408, indicating that the selected conditions are not met. Thus, at t2, the controller generates a command to increase the engine speed in graph 404 by applying the normal engine speed change rate limit in graph 424 based on the wheel torque request in graph 402. From t2 to t3, the controller commands the engine speed to increase by applying the normal engine speed change rate limit, or in other words, there is no inertia-based rate limiting. The controller commands the generator to assist the engine to ramp up the engine speed to meet the wheel torque request, which is indicated by the increase in generator torque from t2 to t3 in graph 410.

[0054] At t3, the generator torque crosses the zero torque point, such as crossing the clearance. From t3 to t4, the clearance crossing is shown as an increasing generator disturbance in graph 414. The generator torque is positive and assists the engine speed to ramp up to the engine speed command. The engine torque increases from t3 to t4. Since the engine is ramping up in speed with the assistance of the generator, the engine speed in graph 404 increases from t3 to t4. In this case, and indicated by the high driver pedal position, reducing generator disturbances (such as jolts, clearances, and / or metallic noises) may be a lower priority for the driver compared to meeting the wheel torque request.

[0055] At t4, feedback control indications from the engine speed estimate in graph 404 and the engine speed command based on the wheel torque request in graph 402 can reduce the positive generator torque assist that ramps up the engine speed. Thus, at t4, the controller commands the generator to reduce the generator torque, which is indicated by the reduction in generator torque from t4 to t5 in graph 410.

[0056] At t5, the generator torque crosses the zero torque point, such as crossing a gap. From t5 to t6, the gap crossing is sensed as an increased generator perturbation in graph 414. At t6, the release of the accelerator pedal is detected.

[0057] In this way, the systems and methods described herein manage generator gap crossings in a hybrid power-split powertrain vehicle. The disclosed method mitigates engine start-up and driver-actuated accelerator pedal generator gap crossings by applying inertia-based rate limiting to engine speed increases under selected conditions. The inertia-based rate limiting can include a control strategy that takes into account the amount of engine torque being generated, including a calibrated offset, and that predicts the amount of allowable engine speed increase without causing the generator to cross the gap. As a result, the generator is less likely to cross the gap, thereby maintaining negative generator torque during the duration of the driver-actuated accelerator pedal. By applying inertia-based rate limiting under selected conditions and not applying the limiting when the conditions are not met, the method attempts to reduce the gap during conditions where it is acceptable to limit to some extent the rate at which the wheel torque request is satisfied, and during conditions where the disclosed strategy does not interfere with other (e.g., higher priority) control strategies such as high pedal demand, emissions control, battery power control, and engine start-up. The technical effect of generator gap management in a hybrid power-split powertrain is improved drivability.

[0058] The present disclosure provides support for a method for managing gap traversal in a hybrid power-split vehicle, the method including limiting an increase in engine speed in response to generator torque approaching zero generator torque during selected conditions. In a first example of the method, the selected conditions include driver pedal operation less than a threshold, a non-engine-start condition, emission control, and a battery state of charge greater than a threshold. In a second example of the method (optionally including the first example), the generator torque is maintained negative during a duration of the driver depressing the accelerator pedal. In a third example of the method (optionally including one or both of the first example and the second example), the method further includes: reducing the limitation as engine torque increases during depression of the accelerator pedal. In a fourth example of the method (optionally including one or more or each of the first example to the third example), the limitation includes applying an inertia-based rate limit to an engine speed request. In a fifth example of the method (optionally including one or more or each of the first example to the fourth example), the inertia-based rate limit is determined based on a threshold rate of engine speed increase while maintaining negative generator torque. In a sixth example of the method (optionally including one or more or each of the first example to the fifth example), the inertia-based rate limit is determined based on an amount of generated engine torque and a calibrated offset. In a seventh example of the method (optionally including one or more or each of the first example to the sixth example), the calibrated offset is determined based on a two-dimensional function having an input of vehicle speed. In an eighth example of the method (optionally including one or more or each of the first example to the seventh example), the inertia-based rate limit is determined based on inertial torque divided by a lumped engine and generator inertia, wherein the inertial torque is determined based on a difference between an engine torque estimate and the calibrated offset. In a ninth example of the method (optionally including one or more or each of the first example to the eighth example), the method further includes: commanding an increase in motor torque in response to limiting the engine speed.

[0059] The present disclosure also provides support for a system including: a powertrain having an engine, an electric motor, a generator, a battery, and a planetary gear unit; and a controller that stores instructions in a non-transitory memory, the instructions when executed causing the controller to limit an increase in engine speed in response to generator torque approaching zero generator torque during selected conditions. In a first example of the system, the selected conditions include a driver pedal operation less than a threshold, a non-engine start condition, emission control, and a battery state of charge greater than a threshold. In a second example of the system (optionally including the first example), the generator torque is maintained negative during a duration in which the driver presses the accelerator pedal. In a third example of the system (optionally including one or both of the first example and the second example), the controller is further configured to decrease the limit as engine torque increases during pressing of the accelerator pedal. In a fourth example of the system (optionally including one or more or each of the first example to the third example), the limit includes an inertia-based rate limit on an engine speed request.

[0060] The present disclosure also provides support for a method for a hybrid power-split vehicle, the method including: during an accelerator pedal press condition and in response to selected conditions, receiving an estimated engine torque, an estimated generator torque, and a vehicle speed; calibrating an offset based on the vehicle speed; determining an inertia torque based on the engine torque, the offset, and a ratio of the engine torque to the generator torque; determining an inertia-based rate limit based on the inertia torque and an aggregated engine and generator inertia; and applying the inertia-based rate limit to an engine speed command. In a first example of the method, the selected conditions include a driver pedal operation less than a threshold, a non-engine start condition, emission control, and a battery state of charge greater than a threshold. In a second example of the method (optionally including the first example), the generator torque is maintained negative during a duration of the accelerator pedal press condition. In a third example of the method (optionally including one or both of the first example and the second example), the method further includes: commanding an increase in motor torque in response to applying the inertia-based rate limit. In a fourth example of the method (optionally including one or more or each of the first example to the third example), the method further includes: decreasing the inertia-based rate limit as more engine torque becomes available during pressing of the accelerator pedal.

[0061] Note that the example control and estimation routines included herein can be used with a variety of engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in a non-transitory memory and can be executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies (such as event-driven, interrupt-driven, multitasking, multithreaded, etc.). Accordingly, the various acts, operations, and / or functions shown can be executed in the sequence shown, executed in parallel, or omitted in some cases. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the acts, operations, and / or functions shown can be repeatedly executed according to the particular strategy used. Additionally, the acts, operations, and / or functions described can graphically represent code to be programmed into the non-transitory memory of a computer-readable storage medium of an engine control system, where the described acts are implemented by executing instructions in a system including various engine hardware components in conjunction with an electronic controller.

[0062] The appended claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to "a" element or "a first" element or the equivalent thereof. Such claims are to be understood to include the combination of one or more such elements, neither requiring nor precluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the claims or by filing new claims in this or a related application. Such claims, whether broader, narrower, equivalent, or different in scope from the original claims, are also regarded as included within the subject matter of this disclosure.

[0063] According to the present invention, a method for managing gap crossing in a hybrid power-split vehicle includes: restricting an increase in engine speed in response to generator torque approaching zero generator torque during a selected condition.

[0064] In one aspect of the present invention, the selected condition includes a driver pedal operation less than a threshold, a non-engine start condition, emission control, and a battery state of charge greater than a threshold.

[0065] In one aspect of the present invention, the generator torque is maintained negative during a duration in which the driver depresses the accelerator pedal.

[0066] In one aspect of the present invention, the method includes decreasing the restriction as engine torque increases during depression of the accelerator pedal.

[0067] In one aspect of the present invention, the limitation includes applying an inertia-based rate limit to the engine speed request.

[0068] In one aspect of the present invention, the inertia-based rate limit is determined based on a threshold rate at which the engine speed increases while maintaining negative generator torque.

[0069] In one aspect of the present invention, the inertia-based rate limit is determined based on the amount of engine torque generated and a calibrated offset.

[0070] In one aspect of the present invention, the calibrated offset is determined based on a two-dimensional function with an input of vehicle speed.

[0071] In one aspect of the present invention, the inertia-based rate limit is determined based on inertial torque divided by the combined engine and generator inertia, where the inertial torque is determined based on the difference between an engine torque estimate and a calibrated offset.

[0072] In one aspect of the present invention, the method includes commanding an increase in motor torque in response to limiting the engine speed.

[0073] According to the present invention, there is provided a system having: a powertrain having an engine, an electric motor, a generator, a battery, and a planetary gear unit; and a controller that stores instructions in a non-transitory memory, the instructions when executed causing the controller to limit an increase in engine speed in response to generator torque approaching zero generator torque during a selected condition.

[0074] According to an embodiment, the selected condition includes a driver pedal operation less than a threshold, a non-engine start condition, emission control, and a battery state of charge greater than a threshold.

[0075] According to an embodiment, the generator torque is maintained negative during a duration in which the driver presses the accelerator pedal.

[0076] According to an embodiment, the controller is further configured to decrease the limitation as the engine torque increases during pressing of the accelerator pedal.

[0077] According to an embodiment, the limitation includes an inertia-based rate limit on the engine speed request.

[0078] According to the present invention, a method for a hybrid power-split vehicle includes: during an accelerator pedal depression condition; and in response to a selected condition, receiving an estimated engine torque, an estimated generator torque, and a vehicle speed; calibrating an offset based on the vehicle speed; determining an inertia torque based on the engine torque, the offset, and a ratio of the engine torque to the generator torque; determining an inertia-based rate limit based on the inertia torque and an aggregated engine and generator inertia; and applying the inertia-based rate limit to an engine speed command.

[0079] In one aspect of the present invention, the selected condition includes a driver pedal operation less than a threshold, a non-engine start condition, an emissions control, and a battery state of charge greater than a threshold.

[0080] In one aspect of the present invention, the generator torque is maintained negative during the duration of the accelerator pedal depression condition.

[0081] In one aspect of the present invention, the method includes commanding an increase in motor torque in response to applying the inertia-based rate limit.

[0082] In one aspect of the present invention, the method includes decreasing the inertia-based rate limit as more engine torque becomes available during an accelerator pedal depression.

Claims

1. A method for managing gap ride-through in a hybrid power-split vehicle, the method comprising: An increase in engine speed is limited in response to the generator torque approaching zero generator torque during selected conditions. 2 . The method of claim 1 , wherein the selected conditions include driver pedal operation less than a threshold, a non-engine start condition, emission control, and a battery state of charge greater than a threshold. 3 . The method of claim 1 , wherein the generator torque is maintained negative during a driver tip-in duration. 4 . The method of claim 1 , further comprising decreasing the limit as engine torque increases during a tip-in. The method of claim 1 , wherein said limiting comprises applying an inertia-based rate limiter to the engine speed request. 6 . The method of claim 5 , wherein the inertia-based rate limiting is determined based on a threshold rate at which engine speed can increase while maintaining negative generator torque. 7 . The method of claim 5 , wherein the inertia-based rate limiting is determined based on an amount of generated engine torque and a calibrated offset.

8. The method of claim 7, wherein the calibrated offset is determined based on a two-dimensional function having as input vehicle speed. 9 . The method of claim 5 , wherein the inertia-based rate limiter is determined based on an inertia torque divided by a lumped engine and generator inertia, wherein the inertia torque is determined based on a difference between an engine torque estimate and a calibrated offset. 10 . The method of claim 1 , further comprising commanding a motor torque increase in response to limiting the engine speed.

11. A system comprising: a powertrain having an engine, an electric motor, a generator, a battery, and a planetary gear unit; as well as A controller stores instructions in non-transitory memory that, when executed, cause the controller to limit an increase in engine speed in response to the generator torque approaching zero generator torque during selected conditions.

12. The system of claim 11, wherein the selected conditions include driver pedal operation less than a threshold, a non-engine start condition, emission control, and a battery state of charge greater than a threshold.

13. The system of claim 11 wherein the generator torque is maintained negative during the duration of a driver tip-in.

14. The system of claim 11, the controller further configured to decrease the limit as engine torque increases during a tip-in.

15. The system of claim 11 wherein said limitation comprises an inertia-based rate limiter of an engine speed request.

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