Method for controlling a hybrid powertrain and a vehicle

Abstract

Method for controlling a hybrid powertrain, comprising: Issuing a command to a power machine to generate a torque input into a clutch; Issuing a command to an electric machine to output a rotational speed based on an estimated torque supplied via the clutch; Providing a feedback loop that indicates a discrepancy between the commanded speed and the actual speed of the electric machine; and Modifying the command for the electric machine to minimize the discrepancy, further comprising, in response to the fact that the speed of the electric machine is less than a threshold, ignoring the discrepancy between the commanded speed and the actual speed of the electric machine for a predetermined period of time.

Description

TECHNICAL AREA

[0001] The present disclosure relates to a method for controlling a hybrid powertrain and a vehicle. BACKGROUND

[0002] Vehicles with automatic transmissions change gear ratios based on vehicle speed and driver acceleration requirements. During deceleration, automatic transmissions shift through gradually lower gear ratios. The smooth shift from one gear to the next affects noise, vibration, and roughness perceived by the driver.

[0003] Hybrid vehicles can use one or more electric machines with a motor-generator in combination with an internal combustion engine. Depending on vehicle operating conditions, the electric machine can selectively switch between serving as a drive source and a deceleration load on the drivetrain.

[0004] Such vehicle powertrains are known from WO 2014 / 158 888 A1, DE 10 2014 225 300 A1 and DE 10 2007 008 086 A1. SUMMARY

[0005] In at least one embodiment, a method for controlling a hybrid powertrain output comprises issuing a command to a power machine to generate a torque input to a clutch. The method further comprises issuing a command to an electric machine to output a rotational speed based on an estimated torque supplied via the clutch. The method also includes modifying the command to the electric machine based on a discrepancy between the commanded rotational speed and the actual rotational speed of the electric machine.

[0006] In at least one embodiment, a vehicle includes a power machine for providing output torque to a clutch and an electric machine for modulating torque received by the clutch and transmitted to an output shaft. The vehicle further includes a controller programmed to command an output speed of the electric machine based on a predicted torque supplied via the clutch. The controller is also programmed to modify the command based on the commanded output speed and the actual speed of the output shaft, and to disregard any discrepancy between the commanded output speed and the actual speed of the output shaft in response to the output shaft speed being lower than a predetermined speed threshold. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation of a hybrid electric vehicle. Fig. Figure 2 is a system block diagram of a powertrain speed control algorithm. Fig. 3 and Fig. 3A is a flowchart of a powertrain control procedure. DETAILED DESCRIPTION

[0007] As required, detailed embodiments of the present invention are disclosed herein; however, it is understood that the disclosed embodiments are purely exemplary of the invention, which can be implemented in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching a person skilled in the art how to use the present invention in various ways.

[0008] Fig. Figure 1 schematically shows a hybrid electric vehicle (HEV) 10 and illustrates representative relationships between the vehicle components. The physical placement and orientation of the components in the vehicle may vary. The vehicle 10 includes a powertrain 12 comprising a motor 14 that drives a transmission 16. As will be described in more detail below, the transmission 16 includes an electric machine, such as an electric motor / generator (M / G) 18, a torque converter 22, and a multi-stage automatic transmission or gearbox 24. Furthermore, a high-voltage traction battery 20 is provided in conjunction with the M / G 18 for supplying energy to and receiving energy from the M / G 18.

[0009] The power unit 14 and the M / G 18 are both capable of providing motive power for the HEV 10. The power unit 14 is generally a drive unit that can include an internal combustion engine, such as a gasoline, diesel, or natural gas engine, or a fuel cell. The power unit 14 generates power and a corresponding output torque, which is supplied to the M / G 18 when a disconnect clutch 26 between the power unit 14 and the M / G 18 is at least partially engaged. The M / G 18 can be implemented by any of several types of electric machines. For example, the M / G 18 can be a permanent magnet synchronous electric motor. The power electronics 28 prepares the direct current (DC) power supplied by the battery 20 for the requirements of the M / G 18, as described below. The power electronics can, for example, provide three-phase alternating current (AC) for the M / G 18.Furthermore, a DC / DC converter 56 is provided, which reduces the voltage from the high-voltage battery 20 to power other, smaller vehicle loads. In at least one embodiment, the DC / DC converter prepares power to drive an auxiliary transmission pump and a low-voltage starter motor.

[0010] The transmission 16 can be operated to provide a variable gear ratio. The gear unit 24 can contain internal gear sets (not shown) which, by selectively engaging friction elements such as clutches and brakes (not shown), are placed into different gear ratios to produce the desired multiple discrete or stage speed ratios. The friction elements are controlled by a shift pattern that connects or disconnects certain elements of the gear sets to control the speed ratio between a transmission input shaft 34 and the transmission output shaft 38. The gear unit 24 ultimately provides the drivetrain output torque through the output shaft 38. For example, two rows of clutches can be provided, corresponding to odd-numbered and even-numbered gear sets, respectively.During the shift from the current gear ratio to a requested adjacent gear ratio, a clutch from the first row is simultaneously disengaged while a clutch from the second row is engaged. After completion of the transition from the first to the second clutch as part of a gear change, both the speed ratio and the torque ratio between the transmission output shaft 38 and the transmission input shaft 34 change according to the gear selection.

[0011] As in the embodiment of Fig. As further shown in Figure 1, the output shaft 38 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 transmits torque assigned to each wheel 42 while allowing slight differences in rotational speed, for example, when the vehicle is driving around a curve. Various types of differentials or similar devices can be used to distribute torque from the drivetrain to one or more wheels. In some applications, the torque distribution can vary depending on, for example, the specific operating mode or operating condition.

[0012] Furthermore, the vehicle 10 includes a parking brake system 54. The brake system may include friction brakes capable of selectively applying pressure by means of stationary shoes attached to a rotor mounted on each wheel. The applied pressure between the shoes and rotors generates friction to resist rotation of the vehicle wheels 42 and is therefore able to slow the speed of the vehicle 10.

[0013] When the disconnect clutch 26 is at least partially engaged, power can flow from the power unit 14 to the M / G 18 or from the M / G 18 to the power unit 14. When the disconnect clutch 26 is engaged, the M / G 18 can, for example, operate as a generator to convert rotational energy supplied by a crankshaft 30 via the M / G shaft 32 into electrical energy to be stored in the battery 20. As discussed in more detail below, the rotational resistance exerted on the shaft by energy recovery can be used as a brake to decelerate the vehicle. The disconnect clutch 26 can also be disengaged to decouple the power unit 14 from the rest of the drivetrain 12, so that the M / G 18 can be operated as the sole power source for the vehicle 10.

[0014] A main transmission pump 46 is used to operate the transmission 16 when the engine 14 is running. The main transmission pump 46 is driven by the vehicle's engine 14. The main pump 46 draws fluid from a reservoir in the lower part of the transmission 16 and generates pressure in the hydraulic system. The main transmission pump 46 is generally driven by the engine 18. Pressure is supplied to the transmission and the disconnect clutch as long as the engine is rotating at a sufficiently high speed. When the engine is stopped, an auxiliary electric pump 52 provides certain functions of the main transmission pump 46 and supports limited transmission operation. Therefore, the disconnect clutch 26 and other transmission mechanisms can be engaged by the auxiliary pump 52 to maintain functionality under certain operating conditions.

[0015] Operating states of the powertrain 12 can be specified by at least one controller. In at least one embodiment, a larger control system containing multiple controllers is provided. The individual controllers or the control system can be influenced by various other controllers throughout the vehicle 10, with a vehicle system controller (VSC) 48 operating at a higher hierarchy with respect to other subordinate controllers. The output of the VSC 48 can directly or indirectly specify or influence several vehicle functions, such as starting / stopping the engine 14, operating the motor / gear unit 18 to provide wheel torque or recharging the traction battery 20, selecting or initiating gear changes, etc.For example, the VSC 48 can receive data from other subordinate controllers that may operate lower in a control hierarchy compared to the VSC 48 and issue commands to them. Other controllers that communicate with the VSC include, for example, a transmission control module (TCM) 56, a brake system control module (BSCM), a high-voltage battery energy control module (BECM), an inverter system controller (ISC), and other communicating controllers responsible for various vehicle functions. In at least one embodiment, the BECM and the ISC are contained within the power electronics 28.

[0016] Any of the controllers mentioned above may also include a microprocessor or central processing unit (CPU) that communicates with various types of computer-readable storage devices or media. Computer-readable storage devices or media may include volatile and non-volatile storage, such as read-only memory (ROM), random-access memory (RAM), and keep-alive memory (KAM). KAM is a persistent or non-volatile memory that can be used to store various operating variables while the CPU is powered off.Computer-readable storage devices or media can be implemented using any of several known storage devices, such as PROMs (Programmable Read-Only Memory), EPROMs (electrical PROMs), EEPROMs (Electrically Erasable PROMs), flash memory, or any other electrical, magnetic, optical, or combined storage devices capable of storing data, some of which may be executable instructions used by the controller to control the power machine or vehicle.

[0017] The VSC 48 and other controllers communicate with various power machine / vehicle sensors and actuators via an input / output (I / O) interface, which can be implemented as a single integrated interface providing various raw data or signal conditioning, processing, and / or conversion, short-circuit protection, and the like. Alternatively, one or more dedicated hardware or firmware chips can be used to condition and process specific signals before they are fed to the CPU. As in the embodiment of Fig. In general terms, the VSC 48 can communicate signals to and / or from the electronics in the high-voltage battery 20 and the power electronics 28. The power electronics 28 may include both the ISC and the BECM, which manage energy flow to and from the battery 20. Furthermore, the VSC 48 can communicate with other vehicle controls, as discussed above, or directly with vehicle sensors and / or components, including the power unit 14, the braking system 54, the DC / DC converter 56, the low-voltage battery 58, and the starter 60. Although not explicitly shown, the average person will recognize various functions or components controllable by the VSC 48 in each of the subsystems identified above.

[0018] Representative examples of parameters, systems and / or components that can be actuated directly or indirectly by control logic executed by the control unit include fuel injection timing, rate and duration, throttle position, spark plug ignition timing (in spark-ignition engines), intake / exhaust valve timing and duration, front-end accessory drive (FEAD) components such as an alternator, an air conditioning compressor, battery charging, regenerative braking, M / G operation, clutch pressures for the disconnect clutch 26, the torque converter lock-up clutch 36 and the gearbox 24, and the like.Sensors that communicate an input through an I / O interface can be used to indicate, for example, crankshaft position, engine speed (RPM), M / G shaft speed, powertrain output shaft speed, wheel speeds, engine coolant temperature, intake manifold pressure, accelerator pedal position, ignition switch position, throttle valve position, air temperature, exhaust oxygen content or any other exhaust component concentration or presence, intake airflow, transmission gear, ratio or mode, transmission oil temperature, transmission turbine speed, torque converter lock-up clutch status, deceleration or shift mode.

[0019] The VSC 48 also incorporates a torque control logic feature. The VSC 48 can interpret driver requests based on multiple vehicle inputs. These inputs can include, for example, gear selection (PRNDL), accelerator pedal input, brake pedal input, battery temperature, voltage, current, and battery state of charge (SOC). The VSC 48 can, in turn, send command signals to the power electronics 28 to influence the operation of the M / G 18.

[0020] The M / G 18 is also connected to the torque converter 22 via shaft 32. The torque converter 22 is therefore connected to the power machine 14 when the disconnect clutch 26 is at least partially engaged. The torque converter 22 includes an impeller attached to the M / G shaft 32 and a turbine attached to a transmission input shaft 34. The torque converter establishes a fluidic coupling between the electric machine and the output shaft. In particular, the torque converter 22 provides a hydraulic coupling between shaft 32 and the transmission input shaft 34. Furthermore, an internal torque converter lock-up clutch 36 may be provided, so that when the clutch 36 is engaged, it frictionally or mechanically couples the impeller and the turbine of the torque converter 22, thereby enabling more efficient power transmission.The torque converter 22 and its lock-up clutch 36 can be replaced by a launch clutch to provide vehicle starting assistance. Conversely, when the lock-up clutch 36 is disengaged, the M / G 18 can be mechanically decoupled from the differential 40 and the vehicle axles 44. For example, the lock-up clutch 36 can disengage during deceleration at low vehicle speeds, thus decoupling the engine from the transmission and drivetrain to allow the engine to idle and run at low vehicle speeds or when stopped. The timing and degree of alternating operation of the M / G can be used to optimize fuel economy and should coincide with the transmission's gear-shift operations.

[0021] A driver of the vehicle 10 can provide an input at the accelerator pedal 50, generating a torque request, a power request, or a driving command to propel the vehicle 10. Generally, pressing and releasing the pedal 50 generates an accelerator pedal input signal, which the VSC 48 can interpret as a request for higher or lower power. Based on at least one input from the accelerator pedal, the controller 48 can assign torque commands between the power unit 14 and / or the M / G 18 to fulfill the vehicle torque output requested by the driver. The controller 48 can also control the timing of gear changes in the gear transmission 24, as well as the engagement or disengagement of the disconnect clutch 26 and the torque converter lock-up clutch 36. The torque converter lock-up clutch 36 can be modulated over a range between the engaged and disengaged positions.This can generate variable slip in the torque converter 22 in addition to the variable slip generated by the hydrodynamic coupling between the pump impeller and the turbine. Alternatively, the torque converter lock-up clutch 36 can be operated as locked or open, depending on the specific application, without using a modulated operating mode.

[0022] The driver of vehicle 10 can also provide input at the brake pedal to generate a vehicle braking request. Depressing the brake pedal generates a brake input signal, which is interpreted by the controller 48 as a command to decelerate the vehicle. The VSC 48 can, in turn, issue commands to apply negative torque to the drivetrain output shaft 38. In addition to or concurrently with this, the controller can issue commands to activate the braking system 54 to apply frictional braking resistance and thus prevent rotation of the vehicle wheels 42. The negative torque values ​​provided by both the drivetrain and the friction brakes can be assigned to modify the amount by which they each fulfill the driver's braking request.

[0023] The M / G 18 can operate as a generator to convert kinetic energy from the drivetrain 12 into electrical energy to be stored in the battery 20. For example, the M / G 18 can function as a generator while the power unit 14 provides the sole driving force for the vehicle 10. Furthermore, the M / G 18 can operate as a generator during regenerative braking, whereby rotational energy from the rotation of the output shaft 38 is transferred back through the gear train 24 and converted into electrical energy for storage in the high-voltage battery 20 or low-voltage battery 58.

[0024] It should be obvious that the in Fig. The schematic representation shown in Figure 1 is purely exemplary and not intended to be limiting. Other configurations are considered that utilize the selective use of both a power unit and a motor for transmission via a gearbox. Other configurations are also considered without deviating from the scope of protection of this disclosure.

[0025] In general, the electric machine has a wider torque range compared to the power machine. Therefore, the power machine generally operates under torque control, and the electric machine can be operated using speed control to precisely control the overall drivetrain output speed, if necessary. According to a drivetrain of the present disclosure, the power machine dictates the power output to the system, and the electric machine controls the system speed. In this case, the electric machine is used to modulate the overall speed output of the drivetrain system.

[0026] The effectiveness of using the electric machine to modulate system speed can be monitored by measuring the torque and rotational speed at the impeller input of the torque converter 22. In general, the torque of the torque converter impeller can be described by the following equation (1). τimp=τe+τm

[0027] In equation (1) τ imp the pump impeller torque, τ e the engine output torque and τ m The output torque of the electric machine. τ m It is positive when the electric motor assists the combustion engine in propelling the vehicle. τ m is negative if the electric machine operates as a generator and absorbs some of the power machine's output torque.

[0028] The dynamics determining the output of the electrical machine can be approximated by the following equation (2). Jm⋅ω˙m=τclt+τm+τtc where J m the inertia of the electric machine is, ω̇ m The rotational acceleration output from the electric machine is τ clt the clutch torque is and τ tc The torque loss at the torque converter is the clutch torque τ. clt is the torque applied to the electric machine and depends on whether the clutch is open or closed or in a slip mode.

[0029] In the simplest case, when the clutch is open, zero torque is transmitted through the clutch. When the clutch is locked, the clutch torque capacity is high enough that the torque transmitted through the clutch equals the engine braking torque minus the engine inertia. Equation (3) below is a representative estimate of the clutch torque in a locked state. τclt=τe−Je⋅ω˙e

[0030] When the clutch is in a slip mode, the clutch torque is equal to the torque capacity and is a function of the surface condition of the clutch plates λ and the hydraulic pressure p applied across the clutch. Equation (4) below represents a typical relationship. τclt=f(λ,p)

[0031] As discussed above, the power machine torque output can exceed and / or fall below an ideal value depending on the clutch state. The inertia of the powertrain system varies significantly between pure electric mode and hybrid vehicle modes. It is advantageous to use both feed-forward information from the disconnect clutch and feedback of any speed error in the electric machine to manage the powertrain speed output. According to aspects of the present disclosure, the engine control unit can make a preliminary estimate of τ cltFeedforward information can be used to counteract changes in clutch torque associated with state changes. Furthermore, feedback from the actual output speed can be used to reject disturbances and limit errors in the speed output. Equation (5) below presents a speed range transfer function. τm(s)=−τcltest(s)+Gm(s)⋅(ωmr(s)−ωm(s)) τcltest(s) is the estimated torque across the clutch, which is continuously adjusted by feedback terms based on the actual drivetrain output. ωmr(s) is the commanded speed of the electric machine and ω m(s) is the measured actual speed output of the electric machine. The difference between the commanded speed of the electric machine and the actual speed of the electric machine is used in a setting part of algorithm G. m(s)The modified term is then used to improve the estimated clutch torque.

[0032] The torque estimation algorithm is shown in the control system diagram of Fig. Figure 2 shows System 200. System 200 represents the flow of information between controllers in a system that uses a combination of both feed-forward and feedback information to control the drivetrain system speed.

[0033] A feed-forward part of the algorithm is illustrated at the clutch control unit 202. Based on information from the power machine 204 (i.e., output torque and speed) and information from the clutch (i.e., locking state, surface condition, and hydraulic pressure), an estimated clutch torque 208 is provided. The motor control unit 210 uses the clutch torque estimate to generate a command for controlling the speed of the electric machine. In practice, the clutch torque estimate 208 is often inaccurate due to changes in system dynamics.

[0034] In particular, the motor dynamics 212 strongly influence the actual speed output 214 of the electric machine. The actual output torque 216 of the electric machine and the actual clutch torque 218 are influenced by the inertia 220 of the electric machine and the vehicle speed and acceleration profiles 222. The actual speed output 214 of the electric machine is measured and fed back to the motor speed control 210. Any error between the commanded speed 224 of the electric machine and the actual speed output 214 of the electric machine is used to modify the speed command. The measured error, including noise 226 of the electric machine, is fed back to the motor speed control 210 to influence the control system gain 228 and to act as an error correction.This in turn improves the clutch torque estimation 208, thereby minimizing the error between the speed command and the actual speed. Overall, the feedback control works to improve the stability and transient response of the powertrain system.

[0035] In general, the feedback portion of the control algorithm includes error correction to compensate for and reduce speed discrepancies, thereby improving stability. However, the feedback portion is reactive, and there is some inherent time delay in the correction. The feed-forward portion of the control algorithm predicts power output and avoids some of the output speed error. By changing the inputs, the downstream speed output is predicted before it occurs. Feed-forward control can compensate for known engine dynamics to some extent before the error occurs, thus reducing system delays. However, feed-forward control is most effective when the system's response is highly predictable. Clutch torque prediction can be subject to errors for various reasons.For example, the loss of a clutch pressure indicator signal, loss of communication between controllers in the control system, poor general signal conditions, and significant communication delay can all contribute to errors in clutch torque estimation. When both types of control are used together, the feed-forward component supports the provision of fast system response, and the feedback component supports the compensation of unavoidable errors in the powertrain system model. The present control method provides a stable way of controlling hybrid powertrain output.

[0036] The speed control mode can be applied to the drive train of the present disclosure to improve operation in several special operating conditions. Fig. Figure 3 is a flowchart of procedure 300, which provides an example of the mode determination of the speed control in the various powertrain operating states.

[0037] In step 302, the control of the speed of the electric machine, even if the drive train is not in a formal speed control mode, can be used to protect against certain potential drive train fault conditions in order to protect the power machine and / or the transmission.

[0038] At step 304, if the speed of the electric machine is below a first threshold, such as when the vehicle comes to a stop, the controller can command the electric machine to stop in order to conserve energy. If the torque of the electric machine is negative at step 306, the controller can command the electric machine to ramp down smoothly to zero speed at step 308. In at least one embodiment, in response to an imminent vehicle stop, the controller causes an immediate ramp-down by generating a smooth reduction in the target speed command for the electric machine. The controller can use the torque of the electric machine to regulate the speed until it is close enough to zero.A dead zone in the speed control is implemented at very low speeds to completely reduce the torque of the electric machine to zero and allow the speed of the electric machine to decrease to a steady state on its own using the resistance of the cooling oil.

[0039] If the electric machine's torque is positive at step 306, the deadband at step 310 can be one-sided and also have a target speed of zero. The advantage of deadband control at low speeds is that it ensures the electric machine's torque is zero when the electric machine is completely stopped. For example, electric machine speeds below 20 RPM can be subject to deadband to allow the speed to remain at zero if desired. At such low speeds, more precise control may be necessary because noise during speed measurement significantly affects system correction. Using deadband avoids small torque fluctuations at zero speed due to measurement or calculation with accumulated errors.If error correction is otherwise used at very low speeds, errors in the speed of the electric machine can lead to persistent low torque settings, which is both unnecessary and inefficient.

[0040] If the motor speed at step 304 is greater than the first threshold, the controller can still provide protection regarding minimum oil pressure in the transmission. For example, if the torque converter is closed, the impeller speed can be regulated to protect high-priority transmission operation. The transmission requires the impeller speed to be higher than a value that ensures sufficient oil pressure. This is typically between 300 and 400 RPM. When the system is in torque control mode, an inaccuracy in the torque output can cause a drop in impeller speed. If the impeller speed at step 312 falls below a pressure threshold speed, the controller can activate transmission speed protection at step 314 to increase the output of the electric motor and thus ensure that the impeller speed is higher than a predetermined minimum impeller speed.In a second example, a similar speed protection can be applied to control the pump impeller speed when it is at zero, in order to prevent the pump impeller speed from becoming negative in the event of multiple control / system failures.

[0041] If the pump impeller speed at step 312 is greater than the pressure threshold speed, the controller can still provide protection regarding a minimum idle speed for both the power unit and the electric motor, even if the drivetrain is in torque control mode. Normal operation in speed control mode sends a torque command to both the power unit and the motor. However, if the calculation is incorrect, or the actuator output is too low or too high, the combined torque could be in the wrong direction, resulting in a sharp drop in idle speed, especially if the torque converter lock-up clutch is disengaged. While the power unit is running and the lock-up clutch is engaged, the controller can command an engine speed to maintain the power unit speed above an idle speed threshold.If the power machine speed is less than an idle speed threshold at step 316, the controller can activate an idle speed protection at step 318 to increase the output of the electric machine and thus keep the power machine speed above the threshold.

[0042] According to aspects of the procedures described herein, the control system can protect the drive train speed from falling below a target idle speed when the engine is switched on, from falling below the minimum speed for transmission pressure in EV mode, and from falling below zero in all application cases.

[0043] If speed control is enabled at step 302, the controller can adjust the output speed of the electric machine to reduce powertrain roughness under various operating conditions. If the vehicle powertrain is idling at step 320, the controller can enable idle speed control for both EV and HEV modes.

[0044] If no power machine start is imminent at step 322, the feed-forward term of the idle speed control can be zero when the power machine is switched off. Therefore, the torque of the electric machine is used at step 324 to directly control the pump impeller speed, for example by using the feedback calculation in equation (5) discussed above, where the estimated clutch torque is zero.

[0045] Although the powertrain is operating in EV mode, several conditions can trigger a power machine start to supplement power. For example, if the vehicle is idling in EV mode, a low state of charge (SOC) may require the power machine to start to prevent the SOC from dropping below a predetermined charge threshold. Similarly, a power machine start may be required when the powertrain is idling in EV mode to provide power for high electrical loads, such as an air conditioning compressor. In another example, a steep increase in driver acceleration demand or accelerator pedal tap-in may exceed the electric machine's output torque capabilities. A power machine start may be required to supplement the drive torque.However, once the power machine has started, it can cause a high load on the motor and disturb the system speed. If a power machine start is imminent at step 322, the motor speed can be ramped up in preparation for repelling the disturbance. For example, the disconnect clutch torque calculated by equation (4) can be used as the feed-forward term. In at least one embodiment, at step 326, the controller can command a ramp-up of the electric machine speed in response to an imminent power machine start event. The ramp-up can be characterized by a speed profile exhibiting a rate of change lower than a predetermined roughness threshold. This speed ramp-up can serve to minimize discrepancies in the powertrain output torque during the power machine start event.

[0046] If the vehicle is in speed control mode at low engine speeds above idle (step 320), a target speed output from the electric machine used at step 328 may be present in response to an imminent gear change by the transmission. Target speed control, referred to as "Target-N," is a special speed control mode used when the transmission initiates a downshift before the torque converter is fully open. The control is programmed to maintain the pump impeller speed at a predetermined speed, or Target-N (step 330), to provide a smooth torque transition during a gear change event. In such a case, the speed control gains are not the same as those used in the idle speed control discussed above.Target-N requires a set of much less aggressive enhancements to achieve the goal of maintaining the pump impeller speed to minimize torque effects on the drivetrain. In at least one embodiment, Target-N is a fixed value used during the shift event to predetermine the engine speed and thus stabilize the pump impeller speed. One exemplary application is during transmission downshifting at very low vehicle speeds above idle. In another example, Target-N may include a speed profile that varies during the shift event to smooth out torque surges. Similar to other aspects of the present disclosure, the speed profile may include a rate of change below a roughness threshold to promote smooth transitions.

[0047] If no target-N control is used at step 328, the controller can employ special conditions when speed control resumes from zero. If speed control resumes at step 332, both speed resumption profiling and one-sided deadband control can be used. Both aspects are discussed in more detail below.

[0048] In step 334, the control unit can command a ramp-up of the initial speed according to a predetermined profile to mitigate potential chatter due to backlash in the transmission system and fluctuations due to drivetrain resonance. A control mechanism referred to as input shaping can be applied to the target engine speed. The speed ramp-up rate must be designed to be able to change with respect to the actual characteristics of the drivetrain system. Calibration or control parameters can be used to both set and filter the speed ramp-up rate to achieve a smooth torque response.

[0049] Applying a speed profile to the electric motor's output can also be used to coordinate transmission engagement when the gearshift lever is moved from a non-moving gear, such as "Park" or "Neutral," to a moving gear, such as "Forward" or "Reverse." Transmission oil pressure is generally proportional to the torque converter pump wheel speed. A target speed profile can result in a rapid recovery of oil pressure while still allowing sufficient time for the transmission control unit to engage all clutches. The pump wheel speed should not increase again before the transmission has fully engaged; otherwise, a driver may experience a rattling noise.

[0050] In step 334, the controller can also activate deadband control at a specific speed in response to the resumption of speed control from zero. At lower impeller speeds, the following can occur: Fig.The overall control architecture shown in Figure 2 can be modified to disable the feed-forward term. Feed-forward clutch torque estimation is inaccurate at speeds lower than the engine's idle speed, which can also result in inaccurate reported engine torque. Engine start can also be blocked at pump impeller speeds lower than the minimum engine combustion speed. In this case, the feed-forward clutch torque estimation term can lead to unexpected conditions, such as an undesirable drop in speed from zero to negative, where a speed recovery has been commanded. To provide smooth ramp-up without the risk of a negative pump impeller speed when the engine speed is low, the speed control is designed to be one-sided.In this way, only the engine torque is used to accomplish an increase in engine speed from zero to idle, or at least to a value at which the speed has increased to such an extent that it is close to idle speed.

[0051] If speed control is not resumed, the controller can activate a dead zone control at step 332, as discussed above for low speeds.

[0052] This disclosure provides representative control strategies and / or logic that can be implemented using one or more processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Thus, various steps or functions shown can be performed in the sequence shown, in parallel, or, in some cases, omitted. Although not explicitly shown, it is obvious to a person skilled in the art that one or more of the steps or functions shown may be performed repeatedly, depending on the specific processing strategy used. Similarly, the processing sequence is not strictly necessary to achieve the features and benefits described herein but is given for clarity and description.

[0053] The control logic can primarily be implemented in software, which is used to control a vehicle, engine, and / or powertrain on a microprocessor basis. Of course, the control logic can be implemented in software, hardware, or a combination of both in one or more controllers, depending on the specific application. When implemented in software, the control logic can be stored in one or more computer-readable storage devices or media containing data that represents code or instructions executed by a computer to control the vehicle or its subsystems.The computer-readable storage devices or media may include one or more of a number of known physical devices that use electrical, magnetic, and / or optical memory to hold executable instructions and associated calibration information, operating variables, and the like. Alternatively, the processes, methods, or algorithms may be implemented wholly or partially using suitable hardware components, such as ASICs (application-specific integrated circuits), FPGAs (field-programmable gate arrays), state machines, controllers, or other hardware components or devices, or a combination of hardware, software, and firmware components.

[0054] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The terms used in the description serve for illustrative purposes and not for limitation, and it is understood that various modifications can be made without departing from the intent and scope of protection of the disclosure. As previously described, the features of different embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated.While various embodiments may have been described as offering advantages or being preferable to other embodiments or implementations of the prior art with respect to one or more desired properties, it is, as is obvious to the person skilled in the art, that compromises may be made between one or more features or properties in order to achieve the desired overall system characteristics, depending on the specific application and implementation. These features may include, but are not limited to, cost, strength, durability, life-cycle costs, marketability, appearance, packaging, size, ease of maintenance, weight, manufacturability, ease of assembly, etc.Embodiments that are described as less desirable than other embodiments or implementations of the prior art with respect to one or more properties are therefore not outside the scope of protection of the disclosure and may be desirable for certain applications.

Claims

[1] Method for controlling a hybrid powertrain, comprising: Issuing a command to a power machine to generate a torque input into a clutch; Issuing a command to an electric machine to output a rotational speed based on an estimated torque supplied via the clutch; Providing a feedback loop that indicates a discrepancy between the commanded speed and the actual speed of the electric machine; and Modifying the command for the electric machine to minimize the discrepancy, further comprising, in response to the fact that the speed of the electric machine is less than a threshold, ignoring the discrepancy between the commanded speed and the actual speed of the electric machine for a predetermined period of time. [2] Method according to claim 1, further comprising, in response to an imminent vehicle stop, issuing a command to the electric machine to ramp down the rotational speed to zero and to cease modifying the command to the electric machine during deceleration at a vehicle speed below a threshold. [3] Method according to claim 1 or 2, further comprising, at vehicle speeds below a speed threshold, issuing a command to the electric machine to deliver a rotational speed greater than a predetermined minimum rotational speed, irrespective of the discrepancy. [4] Method according to any one of claims 1 to 3, further comprising, in response to an imminent engine start event, issuing a command to the electric machine to ramp up a torque output in order to minimize the speed discrepancy between the commanded speed and the actual speed during the engine start event. [5] Method according to any one of claims 1 to 4, wherein the hybrid powertrain includes a transmission with variable ratio and the method further comprises issuing a command to the electric machine to ramp up the rotational speed in response to the transmission being switched from a non-moving gear to a moving gear. [6] Method according to any one of claims 1 to 5, wherein the hybrid powertrain includes a torque converter configured to fluidically couple the electric machine to a powertrain output shaft, and in response to a downshift of a transmission gear ratio at a vehicle speed below a speed threshold, the command for the electric machine causes a predetermined speed during a disengagement of the torque converter. [7] Method according to claim 6, wherein the predetermined speed of the electric machine comprises a constant speed or a speed profile with a rate of change of less than a roughness threshold. [8] Method according to any one of claims 1 to 7, wherein the hybrid powertrain includes a torque converter configured to fluidically couple the electric machine to a powertrain output shaft, and during a powertrain idle condition a combination of commands for both the engine and the electric machine causes a pump impeller speed of the torque converter to be greater than a predetermined minimum pump impeller speed. [9] Vehicle, comprising: a power unit for providing output torque to a clutch; an electric machine for modulating the power received from the coupling and torque transmitted to an output shaft; and a control programmed to (i) command an output speed of the electric machine based on a predicted torque supplied via the clutch, (ii) modify the command based on the commanded output speed and an actual speed of the output shaft, and (iii) ignore any discrepancy between the commanded output speed and the actual speed of the output shaft in response to the output shaft speed being less than a predetermined speed threshold. [10] Vehicle according to claim 9, further comprising a transmission with variable ratio, wherein the control is further programmed to command a ramp-up of the output speed of the electric machine in response to the transmission being switched from a non-moving gear to a moving gear.

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