Method for damping vibrations in the powertrain of a hybrid electric vehicle and vehicle system control for the procedural control of a hybrid vehicle powertrain

Abstract

A method for damping vibration in a primary rotary drive source (26) in an electric hybrid vehicle powertrain, wherein the powertrain comprises a secondary rotary drive source and a transmission (10), defining partially separate torque flow paths from the primary and secondary drive sources to the vehicle traction wheels, wherein the secondary drive source comprises an electric motor (16) electrically coupled to an electric generator (14), the generator being mechanically coupled to the primary drive source (26), comprising the following steps: measuring the current rotational speed of the primary drive source (26); commanding a desired rotational speed of the primary drive source (26); measuring the rotational speed of the electric motor (16); determining a rotational speed command of the primary drive source (26);Determining a generator torque command based on a closed-loop control of the primary drive source speed using the current speed of the primary drive source (26) as a feedback variable, wherein the generator torque corresponds to a torque transmitted to an element of the transmission (10); coordinating a torque of the transmission element and a motor torque requested by a vehicle driver to form a matched electric motor torque command; deriving an active damping torque for the electric motor (16) as a function of an actual rotational speed of the electric motor (16);and combining the active damping electric motor torque with the coordinated electric motor torque command to form an effective electric motor torque command, thereby damping fluctuations in internal combustion engine speed and dynamic acceleration fluctuations during internal combustion engine start and stop events.

Description

The invention relates to a method for managing the power flow in the drive train of a hybrid electric vehicle with a primary drive source and an electric motor drive source, with which vibrations of the primary drive source are reduced during starting and stopping, as well as a vehicle system control for the methodical control of a hybrid vehicle drive train. In an electric hybrid vehicle powertrain, as described, for example, in US 2005 / 0061564A1, an electric motor and an internal combustion engine are used to distribute power to the vehicle's traction wheels via a gearbox. The gearbox creates multiple power transmission paths from the internal combustion engine to the vehicle's traction wheels, with a reaction element of the gearbox being driven by a generator in an electric drive source configuration comprising a battery, an electric motor, and the generator. In this configuration, the generator and the internal combustion engine are mechanically coupled via the gearbox. The battery acts as an energy storage medium for the generator and the electric motor. In a first operating mode, the internal combustion engine, which acts as the primary drive source, will generate a drive torque in a forward direction, provided the generator produces a reaction torque. Alternatively, in the case of a purely mechanical internal combustion engine drive, the reaction torque can be generated by a generator brake. Since, in such a powertrain configuration, the combustion engine speed can be considered decoupled from the vehicle speed due to the properties of the planetary gear system, the combustion engine speed is determined by controlling the generator speed. This results in split power transmission paths: a first power transmission path is a mechanical path from a combustion engine torque output element, and a second power transmission path is an electrical path in which electrical energy is supplied to the electric motor to which the generator is electrically coupled.Because of the decoupling of the functions of the electrical power flow path and the mechanical power flow path, a drive train consisting of the electric motor, the generator and the gearbox can be attributed power transmission properties that are similar to the power transmission properties of a conventional continuously variable transmission (CVT) system. In such a powertrain configuration, where the electric motor acts as a secondary drive source, it draws energy from the battery and provides propulsion independently of the combustion engine, thus driving the vehicle either forwards or backwards. Furthermore, the electric motor can provide electric braking torque and recover the vehicle's kinetic energy during braking. In a conventional powertrain without hybrid capabilities, this kinetic energy would otherwise be lost as heat. The recovered kinetic energy of an electric hybrid powertrain can be used to recharge the battery.Furthermore, the generator can act as an electric motor using battery energy, while a one-way clutch serves as a reaction element for the transmission, allowing the vehicle to move forward. The primary and secondary drive sources can simultaneously propel the vehicle forward to meet driver torque requirements and achieve better acceleration performance. Conventional CVT powertrains for vehicles enable improved fuel economy and a reduction in unwanted combustion engine emissions by operating the engine—as far as possible—within its most efficient speed and torque range. Hybrid powertrains of the type discussed above exhibit a far more effective potential for improving fuel economy and reducing unwanted emissions compared to conventional vehicles equipped with CVT powertrains. This is because the combustion engine size can be reduced for the same vehicle performance, resulting from the use of two power sources.This is further based on the fact that combustion engine operation can be better optimized, as the combustion engine can be stopped when the required operating conditions for high fuel economy are not favorable, thus reducing unwanted exhaust emissions. Furthermore, as mentioned above, the regenerative kinetic energy generated during braking of the vehicle's combustion engine can be recovered and stored in the battery. To integrate the dual drive sources so that they work together seamlessly, and to achieve improved performance, fuel economy, and a reduction in unwanted combustion engine exhaust emissions, coordination of the drive source control is necessary. This control, as explained in the aforementioned patent application, is achieved using a hierarchical vehicle system control to manage the drive distribution of each of the two drive sources. Under normal powertrain operating conditions, with the powertrain subsystems and components functioning, the vehicle system control will interpret a driver request to accelerate or decelerate and then determine the traction wheel torque command based on the driver request within certain powertrain drive limits, including battery power limits.Furthermore, the vehicle control system determines when and how much energy is to be supplied from each drive source to meet the driver's demands and achieve the specified vehicle performance, i.e., in terms of fuel economy, reduction of unwanted combustion engine exhaust emissions, drivability, etc. Thus, the vehicle control system determines when the combustion engine must be switched off and when it must be switched on. It also determines the combustion engine speed and operating torque point for each given power demand when the combustion engine is running. One of the measures that can be taken to achieve better fuel economy and reduce unwanted combustion engine exhaust emissions in an electric hybrid vehicle powertrain, as explained above, is to switch off the combustion engine when it cannot operate within its desired efficient operating range, for example, when the vehicle is stopped at a traffic light during city driving. Consequently, unlike a conventional powertrain where the combustion engine must be started during the initial start-up phase of the vehicle and is only switched off by an ignition key, the combustion engine in an electric hybrid vehicle powertrain is started and stopped relatively frequently during normal city driving.These start-stop events of the combustion engine in an electric hybrid vehicle can occur unexpectedly for a driver. Therefore, they are required to be imperceptible. For an internal combustion engine to start smoothly, it is desirable that no oscillating seat-rail acceleration occurs. In practical operation, there is a tendency for undesirable vibrations, referred to as "harshness," to occur during an internal combustion engine start. Such vibrations and harsh powertrain operating events can occur in two separate phases in which they are perceptible to a driver: The first phase is the engine speed ramp-up or starting phase. The second is the initial combustion phase of the internal combustion engine. These two separate phases are caused by two sources of vibration: The first source is the compression forces in the internal combustion engine cylinders during the engine speed ramp-up, and the second source is the sudden initial combustion forces during an internal combustion engine start. During the combustion engine start-up phase, the generator in a drivetrain of the type disclosed in the aforementioned application provides starter torque to start the combustion engine, resulting in cylinder compression forces. These compression forces and inertial forces, caused by the reciprocating motion of the combustion engine pistons, can excite the natural torsional vibration modes of the combustion engine. If the combustion engine speed is not precisely controlled, the natural torsional vibration frequencies become noticeable to the driver when the vibrations pass through a torsional resonance region of the combustion engine. This can also cause a "shaking" of the combustion engine block.Furthermore, the generator starting torque, at which the internal combustion engine is started by the generator acting as an electric motor, is transmitted through the drivetrain due to the mechanical connection between the generator and the vehicle's traction wheels. This starting torque can excite the drivetrain's natural torsional vibration modes. Similarly, during the initial combustion phase of an internal combustion engine start event, the sudden initial engine torque can excite the internal combustion engine's torsional vibration modes in the same way as the drivetrain's torsional vibration modes. Cylinder compression forces can also be felt during engine shutdown, when the engine is switched off by the vehicle's control system. The resonance vibrations of the combustion engine and the drivetrain, and the "shaking" of the combustion engine, result in vehicle body vibrations and the occurrence of a hardness that is transmitted from the drivetrain mounting to the vehicle chassis. US Patent 6,247,437 B1 discloses an electric hybrid vehicle powertrain comprising an internal combustion engine and two electric motors working in conjunction with a planetary torque splitter transmission unit. The control system, used to manage the power flow from the internal combustion engine and the electric motors, features a generator torque command profile for starting the internal combustion engine. As in the case of the powertrain of the aforementioned patent application, the powertrain generator according to patent 437 is used to provide an internal combustion engine starting torque. The torque profile varies depending on whether the internal combustion engine is cold. The control is an open-loop control for guiding the internal combustion engine speed when a driver torque command is given to start the internal combustion engine. It does not include a closed-loop feedback feature to compensate for unsafe operating conditions that could lead to undesirable internal combustion engine starting vibrations. Furthermore, a subsequent switch to a closed-loop control with speed feedback is provided after the internal combustion engine has started.This change from an open-loop control to a closed-loop control with feedback can cause unwanted internal combustion engine vibrations and harshness during the initial combustion period. Another example of an electric hybrid vehicle powertrain using an internal combustion engine, two electric motors, and a planetary gear unit to create multiple torque flow paths from the electric motors and the internal combustion engine to the vehicle's traction wheels is known from US 6,278,195 B1. This document describes a generator torque command profile to reduce the internal combustion engine speed while the engine is shut down in a manner similar to the open-loop control of the '437 patent. The '195 patent does not address the possibility that the internal combustion engine could be subjected to an immediate reversing drive torque while the engine is stopped. No compensation is provided for torque reversal that may occur due to internal combustion engine vibrations.Furthermore, neither the '195 patent nor the '437 patent provides for active damping to suppress drivetrain oscillations during stopping or starting of the internal combustion engine. From EP 1 300 587 A1, a method for controlling a powertrain in a hybrid vehicle with an internal combustion engine and an electric motor, both of which are mechanically connected to the rest of the powertrain, is known, in which switching on or off of the internal combustion engine is carried out via a closed control loop with a specified target speed. One object of the invention is to minimize vibrations and harshness in an electric hybrid vehicle powertrain during the starting and stopping of the internal combustion engine, and to minimize vibrations at the vibration source during engine start-up, during the initial combustion process, and during engine shutdown or shutdown. This can be achieved by suppressing any powertrain oscillations initiated by the vibration source, by control when the internal combustion engine speed is increased, and by suppressing powertrain oscillations using active electric motor damping. The aforementioned problem is solved according to the invention by means of a method with the features of claims 1 and 6, and by a vehicle system control unit designed to carry out these methods with the features of claim 7. Advantageous embodiments of the invention are explained in the dependent patent claims. The generator, in the same manner as in the subject matter of the aforementioned pending patent application, is required to provide starter torque to bring the internal combustion engine up to speed during a start-up. This starter torque determines the level of internal combustion engine vibration. Due to the acceleration or deceleration of the generator mass, the generator's moment of inertia will be reflected onto the transmission's torque output element in the shared power flow path defined by the transmission, as a result of the transmission's mechanical properties. This reflected torque will tend to impart an immediate reversing torque to the vehicle's traction wheels. The electric motor will then provide an equal amount of torque at the drive wheels to compensate for this reflected torque, thus reducing drive torque fluctuations.This can be achieved by coordinating the torque control between the electric motor and the generator. During engine shutdown, the generator provides a torque load to the engine to reduce its speed. The manner in which this shutdown occurs affects engine vibrations and the harshness of the shutdown. The electric motor is required to counteract the torque reflected from the engine shutdown by applying immediate reverse vehicle drive torque to the vehicle's traction wheels. The generator torque required to start and stop the internal combustion engine is determined by a closed-loop control system using the actual engine speed as a feedback variable. Thus, the generator can control the engine speed using this closed-loop control. A closed-loop control can still be used to control the generator speed, since a generator speed command can be derived from an internal combustion engine speed command, with the actual electric motor speed based on the kinematics of the gearbox. For closed-loop control, suitable internal combustion engine speed commands are required. During engine start and stop, an internal combustion engine torsional resonance can be excited if the engine speed slowly passes through an internal combustion engine resonance frequency range (i.e., between 200 and 400 RPM). The internal combustion engine speed command issued by the vehicle control system generates an internal combustion engine reference speed for the loop control, ensuring that the engine speed quickly passes through the internal combustion engine resonance frequency range, thereby minimizing the magnitude of the torsional vibrations. Furthermore, the internal combustion engine speed is not reduced when the ambient temperature is low and the vehicle battery capacity is weak. The method according to the invention also creates an actively damping torque when determining a torque command, since the electric motor torque suppresses drive train oscillations. The invention is described below by way of example with reference to the accompanying drawings, in which: Fig. 1 shows a schematic overall view of an electric hybrid vehicle powertrain in which the invention is implemented; Fig. 2a is a time diagram of an internal combustion engine speed during a start-up phase of the internal combustion engine speed and during an initial combustion phase during an internal combustion engine start event; Fig. 2b is a time diagram of a vehicle seat rail acceleration during the start-up phase of the internal combustion engine speed shown in Fig. 2a, and during the initial combustion phase shown in Fig. 2a; Fig. 3a is a time diagram of the vehicle internal combustion engine speed during an internal combustion engine stop event; Fig. 3b is a time diagram of a seat rail acceleration during an internal combustion engine stop event; Fig.Figure 4 is a diagram illustrating the relationship between a generator torque command and an electric motor torque command from a driver when the electric motor torque and generator torque are coordinated to produce an effective electric motor torque command; Figure 5 is a schematic diagram illustrating the closed-loop control of the internal combustion engine speed for developing a generator torque used for electric motor torque and generator torque coordination purposes; Figure 6 is a flowchart illustrating the control strategy for determining generator torque during an internal combustion engine ramp-up phase during an internal combustion engine start event; Figure 7 is a flowchart illustrating the strategy for generator torque determination for the internal combustion engine ramp-down phase during an internal combustion engine shutdown event; and Figure 8 is a diagram illustrating the relationship between generator torque determination and generator torque determination for the internal combustion engine ramp-down phase during an internal combustion engine shutdown event.Figure 8 is a flowchart showing the strategy for determining electric motor torque during the start-up and stop-down phases of the internal combustion engine. Fig. 1 shows a schematic diagram of a hybrid powertrain for a vehicle. This includes a transmission 10 with a planetary gear unit 12, an electric generator 14, and an electric motor 16, which can be a high-voltage induction motor. The planetary gear unit 12 comprises a ring gear 18, a planet carrier 20 which rotatably supports the planet pinions, and a sun gear 22. The planet pinions engage with the sun gear 22 and the ring gear 18. The carrier 20 is connected to an internal combustion engine drive shaft 24 for an internal combustion engine 26. A freewheel clutch 28 can be used to prevent reverse rotation of the shaft 24 while forward drive motion is being received by the shaft 24. The ring gear 18 is connected to the torque drive pinion 32 of a torque transmission intermediate shaft gearbox 34 via a torque transmission element 30. The electric motor 16 is mechanically coupled to the drive torque pinion 36 for the intermediate shaft gearbox 34, which is driven by the electric motor. A gear 38, driven by the intermediate gear 34, is connected to vehicle traction wheels 40 via a differential and axle assembly 42. The electric motor 16, the generator 14 and a battery control module 44 are electrically coupled via a high-voltage bus, which is shown schematically at 46. The sun gear and the generator are mechanically coupled via a shaft 48. The shaft 48 can be braked by a mechanical brake 52, which locks the sun gear 22 and the generator 14 in an operating mode in which the combustion engine output force is to be distributed only via the mechanical power transmission path. The transmission is controlled by a transmission control module 54, which outputs command signals to the transmission. These signals are shown separately in Fig. 1 as an electric motor control signal in a signal flow path 56, as a generator control signal in a signal control path 58, and as a generator brake control signal in a signal flow path 60. The internal combustion engine, the transmission control module, and the battery control module are monitored and controlled by a vehicle system control unit 62. The control unit 62 responds to a driver signal 64 indicating the driver's selection of the PRND mode (Park, Reverse, Neutral, Forward). The control unit also responds to an accelerator pedal position sensor (APPS) signal 66 and a regenerative braking command signal 68, which is generated by the regenerative braking control module 70 based on a brake pedal position sensor (BPPS) signal 72. The vehicle system control unit 62 responds to the input signals to issue a desired wheel torque command, a desired electric motor speed command, and a generator brake command to the transmission control module 54, as shown in 74. It also responds to the control signals to issue a battery control module contact switch signal 76, which activates or deactivates the module 44. As mentioned above, when the generator acts as an electric motor, it can drive the sun gear. The combustion engine starting torque, which acts with the ring gear 18 as the reaction element, is generated during the combustion engine speed ramp-up phase of a combustion engine start event and during the initial combustion phase of a combustion engine start event. These two phases are illustrated in Fig. 2a, which shows a time diagram of a combustion engine speed. At time 80 shown in Fig. 2a, the combustion engine speed ramp-up phase ends and the initial combustion phase begins. The combustion engine ramp-up phase begins, as shown at 82, at zero speed. The diagram according to Fig. 2a shows the engine speed ramp-up profile for an internal combustion engine that does not incorporate the improvements according to the invention. The ramp-up phase is characterized by irregular speed change steps, as shown at 84, as the engine speed increases from 0 to approximately 1000 rpm. During the engine speed ramp-up phase, a seat-rail acceleration occurs, as graphically illustrated in Fig. 2b. At the beginning of the engine start event, the seat-rail acceleration is zero, as shown at 86. During the engine speed ramp-up phase of a typical start event without the features of the invention, seat-rail acceleration peaks occur, as indicated at 88, until the ramp-up phase is complete. During the initial combustion phase, which occurs later than the start-up phase of the combustion engine start event, the combustion engine speed can be irregular, as shown by the speed irregularity at 90 in Fig. 2a. During this phase, seat-rail acceleration pulses occur, as shown by the peak values ​​at 92. The seat-rail acceleration pulses continue until the end of the initial combustion phase. To obtain the data for the diagram in Fig. 2b, an accelerometer can be mounted on the vehicle chassis at a fixed position, such as on the seat rail. In this way, the ordinate for the diagram in Fig. 2b is determined as a seat-rail acceleration diagram. The seat-rail acceleration forces would be perceptible to the driver. Fig. 3a is a time diagram of the internal combustion engine speed during an internal combustion engine shutdown event, when the speed is reduced from 1000 rpm to zero. Typically, in a control system not encompassed by the present invention, the internal combustion engine speed is irregular, as shown by the internal combustion engine speed steps at 94. As the internal combustion engine speed is reduced from a time point of 10 seconds to a time point of 10.8 or 2.8 seconds, the corresponding seat-rail acceleration shown in Fig. 3b occurs during an internal combustion engine shutdown event. As the internal combustion engine speed is reduced, as shown at 94 in Fig. 3a, seat-rail acceleration pulses occur as described above. These are represented by acceleration diagram peaks 96, as shown in Fig. 3b. The larger peaks, as shown in Fig.Figure 3b represents acceleration and deceleration values ​​at the resonant frequencies of the powertrain. The resonant frequencies in the combustion engine and in the powertrain as a whole, in the same way as the so-called "shaking" of the powertrain, lead to vehicle body vibrations and to harshness transmitted to the vehicle chassis via the powertrain mountings, which is perceptible to the driver. The invention minimizes the vibrations shown in Figures 2b and 3b by suppressing drivetrain oscillations caused by vibration sources during engine start-up, initial combustion, and engine shutdown. This suppression of oscillations is achieved through active electric motor damping. Fig. 4 shows an electric motor and generator torque coordinating control system used according to the invention. A driver command for an electric motor torque 98 is generated by the vehicle system control, which forms an electric motor torque command 100 in Fig. 4. A generator torque command 102 issued to the generator and the battery control module develops a generator torque 104 in Fig. 4. The inertia of the generator rotor and the inertia of the sun gear, both of which have substantial mass, result in a generator moment of inertia at 106, which is subtracted from the generator torque at 104 to generate an effective sun gear torque at 108. After taking the transmission ratio into account, the sun gear torque at 110 is combined with the driver command for an electric motor torque to generate an effective electric motor torque command at 100. Fig. 5 shows how the electric motor torque command is influenced by the closed-loop control according to the invention. A generator torque command at 102' is generated by a feedback control section of the vehicle system control for the internal combustion engine speed, as shown at 112 in Fig. 5. The feedback control receives an internal combustion engine speed command from the vehicle system control, as shown at 114. This value is output to a low-pass filter 116, the output signal of which is fed to the feedback control 112. The filtered output signal is combined with the actually measured internal combustion engine speed – the feedback variable of the closed-loop control – as shown at 118. The combustion engine speed is thus controlled in a closed loop mode at 120 to generate the effective generator torque command 102'. This results in a generator torque 104', which is combined at 122 with the generator and sun gear moment of inertia 106'. This results in an effective sun gear torque at 108'. After the sun gear torque is modified by the gear ratio and combined with the driver torque command to the electric motor, as shown at 98', an electric motor torque command 100' is generated. This electric motor torque command is further modified by the active damping torque feature shown in Fig. 5. This feature is characterized by open-loop speed control for the electric motor, in which the actual electric motor speed is measured, as shown at 124, and filtered at 126 to generate an active damping value for the electric motor torque at 128. This value is combined with the electric motor torque command at 100' to generate an actual electric motor torque output command at 100". This electric motor torque command 100" reduces or dampens the torque shown in Fig.Figure 3b shows the peak values ​​of the seat-rail acceleration during the deceleration of the combustion engine speed. This further dampens, as shown in Figure 2b, the seat-rail acceleration values ​​during the acceleration phase of the combustion engine speed. If desired, the feature shown in Fig. 5, where the combustion engine speed is the feedback variable for the closed-loop control, can be modified to use a generator speed feedback variable instead. This is possible because a generator speed command can be derived from a combustion engine speed command, and the actual electric motor speed is based on the kinematics of the transmission. The closed-loop combustion engine speed command reduces noise, vibration, and harshness (NVH) during combustion engine start and stop by avoiding or reducing combustion engine torsional resonance due to the engine speed quickly passing through its resonant frequency range. A low-pass filter is used with a stepwise combustion engine command to establish a combustion engine speed reference for the closed-loop control. This ensures that the engine speed quickly passes through its resonant range to minimize torsional vibrations (which would result in unsatisfactory NVH during engine start / stop) and that the engine speed is not reduced when the ambient temperature is cold and the available battery capacity is low.This is because the magnitude of the stepped combustion engine speed command is low under these operating conditions; and the lower the magnitude, the lower the rise of the low-pass filter's output signal. The low-pass filter's time constant can vary depending on the operating conditions. At extremely cold temperatures or with very low battery energy limits, slower filtering (a larger time constant) is desired to ensure proper combustion engine start-up without exceeding battery limits. The method according to the invention takes into account an actively damping torque when determining the electric motor torque command in order to suppress any drive train oscillation movements. This actively damping torque is determined by appropriate filtering of the electric motor speed. Examples of this are a derivation with a gain or a lead-lag filter near the origin of the coordinate system; i.e. The strategy used by the vehicle control unit when executing the functions described in the previous paragraphs is illustrated in Figures 6, 7 to 8. Figure 6 shows the strategy for determining generator torque during the combustion engine speed ramp-up phase of a combustion engine start event. At action block 130, the control unit reads the inputs and stores them in the RAM portion of the vehicle control unit's memory. These inputs include a determination of the operating mode and the combustion engine speed. If the operating mode is a combustion engine start mode, as determined at decision block 132, the routine will proceed to action block 134, where the combustion engine speed command is set to a specific value, such as 1075 rpm. If the combustion engine is not in a combustion engine start mode, the routine terminates, as shown in Figure 136. Following the setting of the internal combustion engine speed command at 134, the routine will proceed to action block 138, where the internal combustion engine speed reference value is set by the low-pass filter 116 shown in Fig. 5. This value is used by the closed-loop control 112 of the internal combustion engine speed shown in Fig. 5. After the internal combustion engine speed reference value has been determined, a speed error is calculated in action block 140 by subtracting the actual speed from the reference internal combustion engine speed. The next step in the routine is a calculation of a generator torque command, as shown at 102' in Fig. 5. This is executed at action block 142 in Fig. 6. Decision block 144 determines whether the internal combustion engine has been started. If the engine has started, the routine is completed. If it has not started, the routine is repeated, as shown in 146. The flowchart in Fig. 7 illustrates a strategy for determining generator torque during the combustion engine shutdown phase from a combustion engine shutdown mode. The control inputs are read at 148. These include reading the combustion engine start operating mode and the actual combustion engine speed. Using this data, step 150 determines whether the combustion engine operating mode is a combustion engine shutdown mode. If not, the routine completes, as shown at 152. If the combustion engine shutdown mode is in effect, the routine continues to set the combustion engine speed command to zero RPM, as shown at action block 154. This step is followed by the determination of the combustion engine reference speed at 112 in Fig. 5. This is performed at action block 155 in Fig. 7. In action block 156 in Fig. 7, the speed error for the controller 120 is determined. The routine then proceeds to action block 157, where the generator torque command is calculated from the controller 120. This can be a proportional-integral, closed-loop control step, using the internal combustion engine speed as the feedback variable, as shown in Fig. 5, and using the proportional constant Kp and the integral constant Ki, as shown in Fig. 7. The next step in the routine takes place at decision block 158, which determines whether the internal combustion engine has stopped. If the engine has stopped, the routine is completed. If it has not stopped, the routine is repeated, as shown in 160. Fig. 8 shows a control strategy for determining the electric motor torque command using the active damping feature shown in Fig. 5. At the beginning of the routine shown in Fig. 8, the control system reads the necessary inputs to determine the electric motor torque for an internal combustion engine start and stop. The driver torque command shown at 98' in Fig. 5 is read in action block 162 according to Fig. 8, along with the electric motor speed and the generator speed. The generator speed is required for calculating the generator inertia torque, as shown at 106' in Fig. 5. The next step in the routine involves calculating the active damping torque, as shown in action block 164. The active damping torque is equal to a damping constant K, which is multiplied by a time derivative of the electric motor torque or by a lead lag-filtered electric motor speed, as explained above. This step is followed by the step in action block 166, where the electric motor torque command is calculated, as shown in Fig. 5 at 100". The electric motor torque command is determined as follows: The particular embodiment of the powertrain system shown in Fig. 1 is representative of an electric hybrid vehicle powertrain configuration; however, the invention is not limited in its application to an electric hybrid vehicle powertrain of the type shown in Fig. 1. It can be used in any of the many electric hybrid vehicle powertrain configurations in which drive sources, such as an internal combustion engine and an electric motor, are used in separate power flow paths for driving the vehicle traction wheels.

Claims

A method for damping vibration in a primary rotary drive source (26) in an electric hybrid vehicle powertrain, wherein the powertrain comprises a secondary rotary drive source and a transmission (10), defining partially separate torque flow paths from the primary and secondary drive sources to the vehicle traction wheels, wherein the secondary drive source comprises an electric motor (16) electrically coupled to an electric generator (14), the generator being mechanically coupled to the primary drive source (26), comprising the following steps: measuring the current rotational speed of the primary drive source (26); issuing commands to a desired rotational speed of the primary drive source (26); measuring the rotational speed of the electric motor (16); determining a rotational speed command of the primary drive source (26);Determining a generator torque command based on a closed-loop control of the primary drive source speed using the current speed of the primary drive source (26) as a feedback variable, wherein the generator torque corresponds to a torque transmitted to an element of the transmission (10); coordinating a torque of the transmission element and a motor torque requested by a vehicle driver to form a matched electric motor torque command; deriving an active damping torque for the electric motor (16) as a function of an actual rotational speed of the electric motor (16);and combining the active damping electric motor torque with the coordinated electric motor torque command to form an effective electric motor torque command, thereby damping fluctuations in internal combustion engine speed and dynamic acceleration fluctuations during internal combustion engine start and stop events. Method according to claim 1, characterized in that the primary drive source is an internal combustion engine (26) which is mechanically coupled to the vehicle traction wheels (40), and the electric motor (16) is mechanically coupled to the vehicle traction wheels (40) independently of the internal combustion engine (26). Method according to claim 1 or 2, characterized in that the active damping torque is calculated using an electric motor speed filter. Method according to claim 3, characterized in that the electric motor speed filter is characterized by the differential of the measured electric motor speed. Method according to one of claims 1 to 4, characterized in that the generator torque transmitted to the element of the transmission (10) is determined by forming a generator inertia torque value and by combining the generator inertia torque value with the generator torque. Method for controlling an internal combustion engine (26) in an electric hybrid vehicle powertrain, wherein the powertrain comprises a subsystem having an electric motor (16), a battery (44) and a generator (14), wherein the powertrain has a transmission (10) that defines partially separate torque flow paths from the internal combustion engine (26) and the electric motor (16) to the vehicle traction wheels (40), wherein the generator (14) is mechanically coupled to the internal combustion engine (26) via the transmission (10), and the method comprises the steps: measuring the current speed of the internal combustion engine (26); measuring the current speed of the electric motor (16); determining an internal combustion engine speed command;Determining a generator torque as a function of the internal combustion engine speed command, wherein the generator torque corresponds to a torque transmitted to an element of the transmission (10), and wherein, to form a coordinated torque value, the transmission (10) coordinates the torque of the transmission element and an engine torque requested by a vehicle driver; and calculating an effective electric motor torque command based on the coordinated torque value, wherein the internal combustion engine speed and the dynamic acceleration fluctuations during internal combustion engine start events and internal combustion engine stop events are damped, wherein the effective electric motor torque command is calculated by filtering an electric motor speed to form an actively damping electric motor torque, and by combining the actively damping electric motor torque with the coordinated torque value. Vehicle system control (62) for a hybrid vehicle powertrain, wherein the hybrid vehicle powertrain comprises an internal combustion engine (26) and a subsystem comprising an electric motor (16), a battery (44) and a generator (14), wherein the hybrid vehicle powertrain comprises a transmission (10) which defines partially separate torque flow paths from the internal combustion engine (26) and the electric motor (16) to the vehicle traction wheels (40), wherein the generator (14) is mechanically coupled to the internal combustion engine (26) via the transmission (10), characterized in that the vehicle system control (62) is configured to carry out a method according to one of the preceding claims.

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