DE102011111025B4 - Managing output torque in a vehicle having an electric powertrain - Google Patents

Abstract

A method (100) for managing a threshold for an increase in an output torque limit in a vehicle (10), the method (100) comprising: detecting the threshold for an increase in the output torque limit using a controller (24); Position of an accelerator pedal (15) of the vehicle (10) is measured using a pedal sensor (26); an interval of elapsed time is measured in which the accelerator pedal (15) has been held in a substantially constant position; using the controller (24) a rate of change of an actual output torque (28) from a transmission (14) of the vehicle (10) is automatically limited when the amount of the elapsed time exceeds a calibrated time threshold; the actual output torque (28) with the aid of a drive motor (12 ) is only provided using battery power from an energy storage system (22); wherein the detecting of the threshold value for an increase comprises evaluating a difference between a current value of the actual output torque (28) and an average value of a calibrated number of previous values of the actual output torque (28).

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority and benefit of U.S. Provisional Patent Application No. 61 / 380,354, filed Sep. 7, 2010, which is incorporated herein by reference in its entirety.

TECHNICAL AREA

The present invention relates to managing output torque in a vehicle having an electric powertrain.

BACKGROUND

Battery electric vehicles (BEV), electric vehicles with increased range (EREV) and hybrid electric vehicles (HEV) can be operated in at least one purely electric drive mode, i.e. an electric vehicle mode (EV mode). One or more high voltage drive motors provide sufficient motor torque to operate the vehicle in such a mode. Each drive motor is powered by a battery that is supplied by a high-voltage energy storage system (ESS). While the vehicle is in operation, the ESS can be recharged as required, for example during regenerative braking. The ESS can also be recharged when the vehicle is not running by connecting the ESS to a non-vehicle power supply. If a charge state of the ESS has largely been exhausted during an EREV, a small internal combustion engine can be started automatically and used to supply an electrical generator with power. The power output from the generator provides the electrical energy needed to maintain EV mode.

Vehicle drivetrains include a transmission that transfers engine torque from a driven element of the drive motor to an output element of the transmission. The actual output torque acting on the output member ultimately provides power to a set of drive wheels to propel the vehicle. Shift times in such transmissions can be relatively long. Additionally, in a vehicle having an EV powertrain, the output torque limit or capability may increase suddenly and noticeably, such as when the available battery power suddenly increases.

DE 10 2004 046 194 A1 discloses a hybrid vehicle control device that controls an electric machine in such a way that torque fluctuations that occur when a multi-step transmission are shifted are minimized by the output power provided by the electric machine.

In the pamphlet U.S. 5,629,593 A A method for matching an output torque after a shift with an output torque before the shift in an automatic transmission is disclosed in which disturbances in the drive train after the shift are eliminated by adjusting a motor current so that the output torque after the shift is equivalent to the output torque before the switching process is.

The object of the invention is to treat a suddenly occurring increase in an output torque limit in a hybrid vehicle in such a way that an output torque of the drive motor is as imperceptible as possible to a driver of the hybrid vehicle.

This object is achieved by the subjects of the independent claims.

SUMMARY

A method is disclosed herein for managing a sudden increase in output torque capacity in a vehicle having an electric vehicle (EV) powertrain. Implementation of the present method helps ensure that the sudden increase in torque capacity is imperceptible to a driver of the vehicle. The method includes where a rate of change of an actual output torque transmitted to the output element of the transmission is slowed once an increased torque capacity is realized. This occurs during a predetermined vehicle condition, e.g., a period of time with a substantially constant requested output torque, as determined by processing position signals from an accelerator pedal. Torque sag is effectively eliminated while the shift time is reduced. The increased battery power can be used to accomplish faster shifts with minimal disruption to the output torque.

The present method can be implemented as an algorithm or code, recorded on a computer-readable / non-transistor medium and automatically by associated hardware components of an in-vehicle controller are executed. The controller detects a threshold for a sudden increase in output torque capacity. This may result in automatically comparing the current output torque capacity with an average of a number of previous samples. The controller may set a flag indicating a threshold value for a sudden increase in output torque capacity if the current value exceeds the mean value by a calibrated amount. The controller automatically limits the rate of change in actual output torque when the increase is detected, and in one embodiment does so as a function of accelerator pedal position.

For example, a slower rate limit can be applied if the accelerator pedal position is held fairly constant over a calibrated interval. The rate limit may increase in conjunction with an increasing difference between the output torque capacity and the actual output torque. In one embodiment, shift durations can be reduced by automatically lowering an engine speed target value with the aid of the controller during the shift event, while at the same time increasing the short term rate limit.

In particular, a method is provided to manage a sudden increase in output torque capacity in a vehicle that includes a controller, transmission, and drive motor powered by battery power from an energy storage system (ESS). The method includes using the controller to detect a threshold value for an increase in the output torque capacity and automatically limit the rate of change of an actual output torque from the transmission in response to the threshold value for an increase. The actual output torque is provided with the aid of the drive motor alone using the battery power from the ESS.

The method may include calculating a difference between the threshold for increase and the actual output torque and limiting the rate of change using a rate proportional to the difference. Detecting the threshold for an increase in output torque capacity may include evaluating a difference between a current derivative of the actual output torque and an average of a calibrated number of previous output torque derivative values.

In one embodiment, the controller measures a position of an accelerator pedal of the vehicle using a pedal sensor and the method includes limiting the rate of change in the actual output torque as a function of the position of the accelerator pedal. The method may also include measuring an interval of elapsed time that the accelerator pedal has been held in a substantially constant position and automatically limiting the rate of change in actual output torque when the amount of elapsed time exceeds a calibrated time threshold .

A vehicle includes an ESS for supplying battery power, a drive motor that is driven by the battery power from the ESS, a transmission having an output member, and a controller. The output element is driven by the ESS with the aid of the drive motor using battery power. The controller is configured to detect a threshold for an increase in output torque capacity and to automatically limit the rate of change of actual output torque from the transmission in response to the threshold for an increase.

The foregoing features and advantages and other features and advantages of the present invention will be readily apparent from the following detailed description of the best modes for carrying out the invention when read in conjunction with the accompanying drawings.

Figure list

• 1 Fig. 13 is a schematic representation of a vehicle having an electric vehicle (EV) powertrain and a controller that manages a threshold for a sudden increase in output torque capacity;
• 2 is a time record of various torque readings for the in 1 shown vehicle; and
• 3 FIG. 13 is a flow chart illustrating a method of managing a threshold value for a sudden increase in output torque capacity in the in FIG 1 describes the vehicle shown.

DESCRIPTION

Referring to the drawings, there is a vehicle 10 in 1 shown schematically. The vehicle 10 contains a controller 24 that is designed to be a process 100 to perform, one embodiment of which is shown in 3 shown and is described in detail below. The vehicle 10 is any vehicle that has an electric vehicle powertrain (EV powertrain), e.g. a battery electric vehicle (BEV), an extended range electric vehicle (EREV), a hybrid electric vehicle (HEV), or any other vehicle that is in an EV propulsion mode can be driven, that is, in which only one electric motor torque is used. The controller 24 automatically manages a sudden increase in output torque capacity on board the vehicle 10 by controlling a rate of change of an actual output torque when an increased output torque capacity is realized.

A high voltage electric drive motor 12th provides engine torque to a transmission 14th and thereby operates the vehicle 10 in the EV drive mode. It can be an internal combustion engine 18th be included that can be used to power the gearbox 14th to provide power in an HEV construction. In the embodiment shown, an engine 18th of reduced size used to make an electric generator 20th in the in 1 to operate the EREV embodiment shown. For example, a crankshaft 16 the prime mover 18th be turned if additional electrical power is required beyond a level that can only be supplied by an energy storage system (ESS) 22nd is delivered. The additional electrical power is in 1 by arrow 27 displayed. If a charge status of the ESS 22nd exceeds a calibrated threshold, the engine may 18th switched off to save fuel. The vehicle 10 can then be operated in EV mode, which can contain several EV modes depending on the transmission design.

The controller 24 may be programmed with the code or instructions necessary to carry out the present method 100 are needed. Such instructions can be stored on a computer readable non-transitory storage medium and from associated hardware components of the controller 24 selectively executed, for example, one or more host machines configured as disclosed below. The controller 24 precisely and automatically determines when and how to manage an increase in output torque capacity. From the controller 24 Considered operating conditions can, in one possible embodiment, be a measured or detected position of an accelerator pedal 15th include. The position of the accelerator pedal 15th can for example from a pedal sensor 26th automatically recorded, with the measured pedal position to the controller 24 as a pedal position signal (arrow 25th ) is transmitted to determine an output torque request intended by a driver.

The controller 24 selectively controls a rate of change of an actual output torque, a value included in 1 by arrow 28 is shown. Usually this means a decrease in the rate of change to the change for a driver of the vehicle 10 to make it as imperceptible as possible. Such rate limiting functionality is provided by the controller 24 automatically applied when a threshold for a change in output torque capacity is detected. Operation of the controller 24 thus eliminates a drop in torque during a shift period of the transmission 14th is shortened. In addition, the reduction in shift time can improve overall fuel economy and ride quality of the vehicle.

Still referring to 1 instructs the transmission 14th an input element 30th and an output element 32 on. The gear 14th can be designed as an electrically adjustable transmission (EVT) or as any other suitable transmission that is able to generate torque with the aid of the output element 32 to a set of drive wheels 34 transferred to. The output element 32 supplies the actual output torque (arrow 28 ) in response to a speed request from a driver of the vehicle 10 which ultimately from the controller 24 is determined by any suitable means, e.g. by processing the pedal position signals (arrow 25th ) using the pedal position sensor 26th as mentioned above.

The drive motor 12th can be configured as a multi-phase electrical machine with about 60 VAC to about 300 VAC or more, depending on the construction required. A drive motor for simplicity 12th additional drive motors may be used depending on the vehicle design. Every drive motor 12th can using a high voltage AC bus 33 , a drive rectifier / inverter module (TPIM) 36 and a high voltage DC bus 31 with the ESS 22nd be electrically connected. During regenerative braking or other regenerative event, the ESS 22nd can be selectively recharged. An auxiliary power module (APM) 38 , e.g. a DC / DC power converter or other suitable device can be made using the DC bus 31 with the ESS 22nd be electrically connected. The APM 38 turn can with an auxiliary battery 40 e.g. a 12 volt DC battery using a low voltage DC bus 35 be electrically connected, the APM being one or more auxiliary systems 42 , about a Radio, headlights, windshield wipers, etc. supplied with energy.

The controller 24 may be a single controller or a distributed and networked controller that is associated with the engine 18th , the drive motor 12th , the ESS 22nd , the APM 40 , the TPIM 36 and the auxiliary battery 40 is electrically connected by means of suitable control channels or is in electrical communication with this in some other way. Such control channels may include any required transmission lines that provide a hardwired or wireless control coupling that is used to transmit and receive the necessary electrical control signals for proper power flow control and coordination on board the vehicle 10 are suitable. The controller 24 may contain additional control modules and capacities to the extent necessary to provide the required power flow control functionality on board the vehicle 10 in the way you want.

The in 1 shown controller 24 may be configured as a digital computer hardware device related to the various powertrain components of the vehicle 10 is connected to provide proportional-integral-derivative control functionality (PID control functionality). The controller 24 has a microprocessor or a central processing unit, read-only memory (ROM), random access memory (RAM), electrically erasable programmable read-only memory (EEPROM), a high-speed clock, analog / digital and / or digital / analog converter circuits (A / D and / or D / A converter circuits) and input / output circuits and devices (I / O) as well as suitable signal conditioning and buffer circuits. Any algorithms and reference tables that are in the controller 24 present or available to the same, including any algorithms necessary to carry out the present method 100 are needed and a rate limit table 80 referred to below with reference to 3 may be stored in computer readable non-transitory media and, as mentioned above, by the hardware components of the controller 24 , for example a host machine, can be executed automatically in order to provide the respective functionality.

Regarding 2 contains a chronological record 50 Gradients 52 , 54 and 56 , where time is shown with the help of the horizontal axis. The history 52 represents an example of a sudden change in the threshold value in the output torque capacity. The curves 54 and 56 represent an actual output torque. The curve represents 54 represents the actual output torque as reported by the controller 24 is managed. The history 54 rises from the origin at point 51 off and cuts the gradient 52 at point 55 . The history 56 represents the increase in actual output torque when performing the present method 100 absent, with the course 56 increases rapidly to the course 52 at point 53 to cut. By automatically rate limiting the actual output torque, as disclosed herein, to the course 54 the controller avoids 24 of 1 a sudden increase in type caused by the course 56 is shown. Such a pronounced increase can be perceived by a driver under some circumstances, which can worsen the overall driving feeling and the fuel economy.

An increase in the available battery power from the ESS 22nd can reduce the amount of time it takes for a switching event to occur on board the in 1 shown vehicle 10 complete. However, it has been recognized here that the additional torque capacity provided by the increased battery power should not be realized in the actual output torque range. Therefore the controller determines 24 when to apply a specific rate limit to control the rate of change in actual output torque, e.g., during a shift event or period with a relatively steady output torque request. This is an initial phase of torque management that is carried out by the controller 24 provided.

A second phase of torque management also recognizes that reduced shift time may be used during periods of relatively low battery power provided that an engine speed target is reduced and the ESS battery power limits 22nd in a vehicle equipped in this way, for example a hybrid electric vehicle, can be temporarily increased. A set of calibration tables, e.g. the one in 1 rate limit table shown 80 or another suitable look-up table or tables may be used to modify the engine speed target during a shift event, with table 80 indexed by battery performance. That is, the lower the battery power, the lower the engine speed temporal target becomes, a relationship that results in a faster shift period. This is how the controller manages 24 not only shift durations as discussed above, but it also manages a sudden increase in output torque capacity regardless of the reason for the increase. For those powertrains that are configured without an engine, temporarily increasing the battery power limits during a shift is sufficient to prevent the Reduce shift time without allowing output torque to increase.

Regarding 3 in connection with the structure of the in 1 shown vehicle 10 begins a trial 100 with step 102 . At step 102 the controller filters 24 an output torque request from the driver using the accelerator pedal 15th and the pedal position signals (arrow 25th ) is entered. A maximum torque limit is the maximum amount of output torque that can be delivered by the powertrain given battery power limits, clutch torque limits, and engine limits. This value is calculated first and then it is filtered. For example can step 102 include passing these values through a low pass and / or high pass filter to remove any initial external noise.

The controller 24 can then process the filtered results through a first order derivation operation. As understood in the art, the derivative control term determines any three term PID controller, ie the controller 24 , a correct corrective action to apply based on the rate of change of error determined using the proportional (P) and integral (I) terms. The controller 24 then re-filters the output to remove noise from the derivative operation. The filtered output torque derivative value can be recorded in a ring matrix or a ring buffer with a calibrated number of data positions. This enables the calibrated number of previous output torque derivative values to be retained for use, as indicated below.

At step 104 the controller determines 24 whether there is a sudden increase threshold in output torque capacity by processing a set of predetermined vehicle operating values. For example, a sudden increase in output torque capacity can be determined by evaluating a difference between the current output torque derivative and an average of the calibrated number of previous output torque derivative values. If this difference exceeds a threshold calibration, for example four or more previous values in one possible embodiment, then it can be determined that there is a sudden increase.

step 104 may further include that a duration is recorded in which the accelerator pedal 15th with respect to a specific position is held. This can help ensure that any transient response that causes a large derivative value affects the rate limiting logic of the process 100 does not trigger and thereby inadvertently applies a rate cap when it is not necessary.

When the controller 24 determines that there is a threshold for the sudden increase in torque capacity, the method continues 100 to step 108 further and alternatively it goes to step 106 continue if the sudden surge is absent. At step 108 can the controller 24 set a Boolean flag or a value to true. A true flag or equivalent indicates that a rate limitation of the actual output torque should be applied, and the method 100 goes to step 110 further. In contrast to this, a false flag indicates that at step 106 it is set that the rate limit should not be applied, whereby the procedure 100 step 102 repeated whenever the flag is wrong.

At step 110 the rate limit is applied and remains applied until the Boolean flag described above becomes false. That is, once the flag becomes true, it will remain true until the output torque capacity is again within a calibrated range around the actual output torque, e.g. point 55 of 2 . A simple finite state machine or other suitable means can be used to accomplish this result. The controller 24 may limit the rate of increase in actual output torque by an amount inversely proportional to the amount of time that has passed since a driver increased the output torque request, such as by using the accelerator pedal 15th is signaled.

In the 1 rate limit look-up table shown and applied as discussed above 80 is therefore a function of two different inputs: the difference between the rate limited output torque and the actual output torque and the length of time that the accelerator pedal is depressed 15th remains in a substantially constant position. Taking into account the difference between the rate limited output torque and the actual output torque request allows the rate limit to be set at a relatively fast rate when the difference is greater than a threshold difference. In the same way, the rate limit can be set to a relatively slow rate if the difference is less than the threshold difference.

Factoring the length of time that the accelerator pedal 15th of 1 has been held in a substantially constant position, ensures that when a driver of the vehicle 10 , this in 1 has held a fairly constant pedal position for a sufficient length of time, the controller 24 can ensure that the output torque rate limit will not change even if output torque constraints change. This in turn ensures the ride quality of the vehicle 10 is not worsened.

To determine how long the accelerator pedal 15th has been held in a constant position, the mean of a previous set of pedal positions can be compared to the current pedal position, for example the previous twenty or more positions in one possible embodiment. If these two values differ by less than a calibrated amount, the position of the accelerator pedal may 15th can be regarded as essentially constant and the aforementioned timer can be started. The timer can be controlled by the controller 24 be reset when the pedal position of the accelerator pedal 15th is no longer constant.

In one embodiment, an additional calibration can be included, which takes into account the severity of the change in the pedal position. For example, consider a scenario where a threshold calibration is set to 10% of a maximum torque capacity, ie a pedal position change greater than the 10% level will reset the timer and cause the rate limit to be relatively fast. When the driver presses the accelerator 15th held at a fairly constant position prior to a tap with an additional 9% torque request, the rate limit will still be slow without additional logic and will not change. If the driver releases the accelerator pedal by the same torque request of 9% and then depresses it by 11%, the driver has the accelerator pedal 15th not deflected by noticeably more than was the case in the previous maneuver, ie seen from the perspective of the driver. However, the timer is reset and causes the rate limit to speed up significantly.

Therefore, the timer calibration reduces the amount of time spent on the rate limit table 80 of the controller 24 is sent based on the change in the position of the accelerator pedal 15th . If the driver performs the same maneuver when this calibration is in place, tapping 9% of the torque capacity will not force the timer to reset, but instead the calibration time table will subtract a period of time from the value sent to the rate limit table which speeds up rate capping a little. If the same driver releases the accelerator and then depresses it with the 11% level, the increase in the rate limit will be proportional to the previous maneuver. Finally, the amount of time entered into the rate limit table is saturated by calibration to ensure that the amount of time does not continuously increase beyond the table.

Claims (6)

A method (100) for managing a threshold for an increase in an output torque limit in a vehicle (10), the method (100) comprising: detecting the threshold for an increase in the output torque limit using a controller (24); a position of an accelerator pedal (15) of the vehicle (10) is measured using a pedal sensor (26); measuring an elapsed time interval during which the accelerator pedal (15) has been held in a substantially constant position; with the aid of the controller (24) a rate of change of an actual output torque (28) from a transmission (14) of the vehicle (10) is automatically limited when the amount of the elapsed time exceeds a calibrated time threshold value; wherein the actual output torque (28) is provided with the aid of a drive motor (12) using only battery power from an energy storage system (22); wherein detecting the threshold value for an increase comprises evaluating a difference between a current value of the actual output torque (28) and an average of a calibrated number of previous values of the actual output torque (28). Method (100) according to Claim 1 further comprising: calculating a difference between the threshold for an increase and the actual output torque (28); and limiting the rate of change using a rate proportional to the difference. Method (100) according to Claim 1 further comprising: limiting the rate of change as a function of the position of the accelerator pedal (15). A vehicle (10) comprising: an electrical storage system (ESS) (22); a drive motor (12) operated using battery power from the ESS (22); a transmission (14) with an output element (32), the output element (32) being driven with the aid of the drive motor (12); an accelerator pedal (15) and a pedal sensor (26); and a controller (24) configured to: detect a threshold for an increase in the output torque limit of the transmission (14); measure a position of the accelerator pedal (15) using the pedal sensor (26); measuring an interval of elapsed time in which the accelerator pedal (15) has been held in a substantially constant position; and automatically limit the rate of change of actual output torque (28) from the transmission (14) in response to the threshold for increase when the amount of elapsed time exceeds a calibrated time threshold; wherein the controller (24) is further configured to: detect the threshold value for an increase, which comprises determining a difference between a current value of the actual output torque (28) and an average of a calibrated number of previous values of the actual output torque (28 ) Is evaluated. Vehicle (10) after Claim 4 wherein the controller (24) is further configured to: calculate a difference between the threshold for an increase and the actual output torque (28); and limit the rate of change using a rate proportional to the difference. Vehicle (10) after Claim 4 wherein the controller (24) is further configured to: limit the rate of change in the actual output torque (28) as a function of the position of the accelerator pedal (15).

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