System and method for controlling an output voltage of an alternator or an integrated starter-generator

Abstract

Motor vehicle (10) comprising: a battery (16), an engine (12); an ambient light sensor (24), an alternator or an integrated starter generator (14) and at least one controller (20) with a ramp algorithm configured to reduce a voltage output of the alternator or the integrated starter generator (14) to a target voltage at a first voltage ramp rate before initiating an automatic stop of the engine (12), wherein the target voltage is greater than the voltage output of the battery (16), and wherein the first voltage ramp rate depends on an ambient light intensity detected by the ambient light sensor, and wherein the controller (20) is configured with the ramp algorithm to reduce the voltage output of the alternator or the integrated starter generator (14) from the target voltage to another target voltage at a second voltage ramp rate and subsequently initiate a stop of the engine (12) if a vehicle speed of the vehicle (10) reaches zero, and wherein the second voltage ramp rate differs from the first voltage ramp rate.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to strategies for controlling an output voltage of an alternator or an integrated starter generator before automatically stopping an engine. BACKGROUND

[0002] A micro-hybrid vehicle can automatically stop its internal combustion engine for a period of time during intervals of a drive cycle when the vehicle speed approaches or is equal to 0. These automatic engine stops improve fuel economy by reducing engine idle time (and thus fuel consumption) for the drive cycle.

[0003] EP 1 405 768 A1, US 4 689 545 A, US 6 566 816 B2, JP 2006- 183 546 A and US 6 049 171 A disclose generic motor vehicles and methods for controlling vehicles. SUMMARY

[0004] The objective technical problem to be solved can be seen as eliminating the disadvantages of the prior art. This problem is solved by the subject matter of patent claim 1. A motor vehicle can include an engine, an alternator, or an integrated starter-generator and at least one controller. The at least one controller can receive information about ambient light intensity and information about the vehicle's speed and, before initiating an automatic engine stop, reduce the voltage output of the alternator or the integrated starter-generator based on the received information.A method for controlling the output voltage of an alternator or an integrated starter-generator of a vehicle may include determining a threshold vehicle speed greater than 0, comparing the vehicle speed to the threshold vehicle speed, and reducing the output voltage of the alternator or the integrated starter-generator before initiating an automatic engine stop if the vehicle speed is less than or equal to the threshold vehicle speed. A motor vehicle may include an engine, an alternator, or an integrated starter-generator, and at least one controller. The at least one controller may reduce the voltage output of the alternator or the integrated starter-generator before initiating an automatic engine stop. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a micro hybrid vehicle. Fig. Figure 2 is a flowchart illustrating an algorithm for controlling the output voltage of the alternator or integrated starter generator. Fig. Figure 3 is a graph of an alternator or integrated starter generator output voltage as a function of time. Fig. Figure 4 is a graph of vehicle speed as a function of time. Fig. Figure 5 is a graph of vehicle speed as a function of time. DETAILED DESCRIPTION

[0005] As required, detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied 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. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as an illustrative basis for teaching one skilled in the art the various uses of the present invention. Vehicles equipped with assisted direct start or stop / start systems may shut off the engine when the vehicle coasts to a stop or after the vehicle has come to a stop.During engine shutdown, the maximum vehicle bus voltage decreases from the output voltage of the alternator or integrated starter-generator (typically 14.5 volts at idle) to the battery voltage (typically 12.5 volts) unless supported by other means. When this 2-volt reduction in system voltage at engine shutdown is applied to the headlights or other vehicle lamps, a noticeable reduction in light output (measured in lumens) may be observed, particularly when background or ambient light levels are low. When background or ambient light levels are high, reductions in vehicle light output may go undetected.A DC / DC converter connected between the battery and certain high-priority (or base) electrical loads (e.g., the radio) can be switched on during an automatic engine stop to maintain or minimize the voltage drop experienced by the selected base electrical loads. However, vehicle lamps cannot be designated as base electrical loads. Thus, an additional battery or capacitive device can be used to minimize or eliminate fluctuations in light output during a stop / start shutdown and restart. Alternatively, a higher-power DC / DC converter can be used to support both the vehicle lights and the base electrical loads during a stop / start shutdown and restart.However, these arrangements can increase the packaging volume and cost of a stop / start system. As mentioned above, vehicle lighting systems can be prone to perceived functional performance issues due to voltage fluctuation / degradation during an automatic stop event. Thus, alternator or integrated starter-generator controllers can be used to ramp the system voltage down to a target voltage prior to engine shutdown to minimize perceived lighting changes. Parameters such as the ramp rate, ramp duration, and target voltage can be calibrated to balance functionality, fuel economy, and consistency with engine shutdown events. Darkroom tests have shown that if the rate of change of the voltage applied to the lamps can be reduced, the observed light output fluctuations are less disruptive.However, it has also been found that under certain conditions (e.g., long ramp times before shutdown), such voltage ramping can compromise the fuel economy gains associated with a stop / start vehicle. Stop / start voltage ramping before shutdown can thus be minimized or eliminated when ambient light levels are high (e.g., when the headlights are off), as light output fluctuations may go undetected.The output from an ambient light sensor is used as input to a ramping algorithm to either change the voltage ramp rate (for example, the target volts / second rate used in controlling the voltage ramp-down of the alternator or integrated starter-generator) as a function of ambient light levels, or to override the voltage ramp when the ambient light levels exceed a predetermined threshold. The output from ambient light sensors can already be used to automatically turn on the headlights of certain vehicles. This output can also be used as input to a voltage ramp-down control of an alternator or integrated starter-generator. On . Fig. 1, a motor vehicle 10 may include an engine 12, an alternator or integrated starter-generator 14, a battery 16, a plurality of electrical loads 18 (e.g., the lighting system, etc.), and one or more controllers 20. The engine 12 generates motive power to move the vehicle 10 and mechanically drives the alternator or integrated starter-generator 14. The alternator or integrated starter-generator 14 and the battery 16 are electrically connected to each other and to the electrical loads 18. The engine 12, the alternator or integrated starter-generator 14, and the battery 16 are in communication with and / or controlled by the controllers 20. Other arrangements are, of course, possible. For example, the vehicle 10 may further include a traction battery and an electric machine (not shown) to selectively generate motive power to move the vehicle 10, etc.The alternator or integrated starter-generator 14 generates electrical power to charge the battery 16 and for consumption by the electrical loads 18 when the engine 12 is running. The battery 16 may provide electrical power for consumption by the electrical loads 18 when the engine 12 is not running. As explained above, the output voltage of the alternator or integrated starter-generator 14 may be greater than the output voltage of the battery 16.To minimize instances of perceived changes in the brightness of the lighting system 18, the controllers 20 may ramp down the output voltage of the alternator or integrated starter-generator 14 prior to an automatic stop of the engine 12, such that when the alternator or integrated starter-generator 14 switches to the battery 16 as the source of electrical power for consumption by the electrical loads 18, a change in the system voltage is minimized. Various parameters may be used to anticipate when the engine 12 may be automatically stopped. In one example, the vehicle 10 further includes a speed sensor 22 and / or a headlight and / or ambient light sensor 24.Information from these and / or other sensors / data sources may be used as input to a lookup table stored in memory associated with the controllers 20 to determine a threshold vehicle speed below which the controllers 20 begin ramping down the output voltage of the alternator or integrated starter-generator 14 to a desired output voltage in anticipation of an impending automatic engine stop (assuming that when a speed of the vehicle 10 becomes less than the predetermined threshold speed, an automatic engine stop is imminent). Such a lookup table may be generated through testing, simulation, or any other suitable / known technique. Alternatively, the threshold speed may be computationally determined based on the input, etc.Information from one / both of sensors 22, 24 and / or other sensors / data sources may also be used to determine a ramp rate for output voltage reduction, the desired output voltage, and / or to determine whether to prevent the alternator or integrated starter-generator 14 output voltage from ramping down (due to the potential adverse impact of such ramping on vehicle fuel economy). A lookup table or calculation tool, etc., may be employed for these purposes. [Refer to . Fig. 2, an algorithm for controlling the output voltage of an alternator or integrated starter-generator begins in step 26. It is determined whether the ambient light level is less than a predetermined threshold. The controllers 20 may, for example, determine whether ambient light levels are less than a threshold (determined, for example, via testing) based on information from sensor 24. If not, the algorithm returns to step 26. If yes, then in step 28 it is determined whether the headlights are on. If no, then the algorithm returns to step 28. If yes, then in step 30 the threshold rate for starting the ramp of the output voltage of the alternator or integrated starter-generator is determined.For example, the controllers 20 may use the vehicle speed and the vehicle deceleration rate as input and use a lookup table or suitable computational technique to determine the threshold vehicle speed. Other such inputs may include, for example, traffic conditions (as determined via a navigation system) and road wetness (as determined via a wetness sensor or based on feedback from a traction control system), etc. In this example, the threshold vehicle speed increases with increasing deceleration rate. Likewise, the threshold vehicle speed increases with increasing vehicle speed. However, other relationships are also contemplated. In step 32, it is determined whether the vehicle speed is less than the threshold vehicle speed. The controllers 20 may, for example, compare information from sensor 22 to the threshold speed determined in step 30.If no, the algorithm returns to step 32. If yes, step 34 initiates the ramping down of the alternator or integrated starter-generator output voltage to a target voltage. For example, controllers 20 may cause the alternator 14 output voltage to decrease by issuing a reduced set voltage command to alternator 14. A voltage regulator on alternator 14 may then act to reduce the field current associated with alternator 14 accordingly. Step 36 determines whether the alternator or integrated starter-generator output voltage is equal to the target voltage. For example, controllers 20 may compare the alternator or integrated starter-generator output voltage to the target voltage. If no, the algorithm returns to step 36.If so, a determination is made in step 38 as to whether the engine is in the pre-stop phase. For example, the controllers 20 may determine whether the speed of the vehicle 10 is equal to 0. If so, the engine 12 is in the pre-stop phase. If not, the algorithm returns to step 38. If so, an automatic engine stop is initiated in step 40. As is known in the art, the controllers 20 may issue commands to prepare vehicle systems for the impending engine stop, to halt fuel flow to the engine 12, etc. In the example of FIG. Fig. 2, it is assumed that the ambient light level and headlight status are used to determine whether to prevent / delay the alternator or integrated starter-generator output voltage from ramping down. However, in other examples, these parameters may not be used in this way. This means that certain algorithms may not provide a measure to prevent / delay the alternator or integrated starter-generator output voltage from ramping down. Likewise, the alternator or integrated starter-generator output voltage does not need to be ramped to a setpoint. Instead, the alternator or integrated starter-generator output voltage can simply be reduced until the alternator or integrated starter-generator is no longer the power source for electrical loads.However, this scenario can lead to periods of unnecessary battery discharge after the alternator or integrated starter-generator voltage becomes less than or equal to the battery output voltage. Other scenarios are also possible. It should be clear that the example algorithm from [the original text] is not suitable for the battery. Fig. 2 does not preclude automatic engine stops. Instead, the algorithm addresses whether a ramp of the output voltage should be performed. If the algorithm remains at step 28 because, for example, the headlights are off, the controllers 20 may nevertheless initiate an automatic engine stop if the conditions for an automatic stop are met (for example, the engine speed is approximately 0, etc.). Likewise, the controllers 20 may initiate an automatic engine stop even if the algorithm remains at step 26 because the ambient light intensity is greater than the predetermined threshold. Fig. 3, Fig. 4 and Fig.5, the output voltage of the alternator or integrated starter-generator (for example, 14.3 V), the vehicle speed, and the engine speed are relatively constant initially at time t0. At time t1, the vehicle speed begins to decrease because, for example, a driver may remove their foot from the accelerator pedal and place it on the brake pedal. At time t2, the engine speed begins to decrease in response to the decrease in vehicle speed to its desired idle speed. At time t3, the output voltage of the alternator or integrated starter-generator begins to decrease because the vehicle speed drops below the threshold vehicle speed, as discussed above. At time t4, the output voltage of the alternator or integrated starter-generator reaches its first desired voltage (for example, 13 V).At time t5, the output voltage of the alternator or integrated starter-generator begins to decrease from the first target voltage to a second target voltage (e.g., 12.5 V), which is approximately equal to the battery output voltage, because the vehicle speed has reached 0. At time t6, the engine is stopped. The time between t3 and t4 (e.g., 2 s) and the corresponding first ramp rate are fixed in this example. Thus, the time period between t4 and t5 can vary depending on the vehicle threshold speed. This means that the time period between t4 and t5 can increase as the vehicle threshold speed increases, and vice versa. The first ramp rate in this example is set to a value that minimizes perceived changes in light output.The first target voltage is chosen to be greater than the battery output voltage to avoid battery discharge during the time period between t4 and t5. In scenarios without a target voltage, the output voltage of the alternator or integrated starter-generator can continue to decrease until it is less than the battery output voltage, leading to battery discharge. The time between t5 and t6 is shown at its minimum in this example (for example, 1 / 2 s). Thus, the corresponding second ramp rate is set to a value to allow the output voltage of the alternator or integrated starter-generator to change from the first target value to the second target value within this minimum time period.The algorithms disclosed herein may be provided to or implemented by a processing device, such as the controllers 20, which may include, for example, any existing electronic control units or a dedicated electronic control unit in many forms, including, but not limited to, information permanently stored on non-writable storage media, such as ROM devices, and information modifiably stored on writable storage media, such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The algorithms may also be implemented in an executable software object.Alternatively, the algorithms may be implemented in whole or in part using suitable hardware components, such as ASICs (Application-Specific Integrated Circuits), FPGAs (Field-Programmable Gate Arrays), state machines, or other hardware components or devices, or a combination of hardware, software, and firmware components. Although example embodiments are described above, these embodiments are not intended to describe all possible forms of the invention. Instead, the terms used in the description are terms of description and not of limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Furthermore, the features of different implementation embodiments may be combined to form further embodiments of the invention.

Claims

[1] Motor vehicle (10) comprising: a battery (16), an engine (12); an ambient light sensor (24), an alternator or an integrated starter generator (14) and at least one controller (20) with a ramp algorithm configured to reduce a voltage output of the alternator or the integrated starter generator (14) to a target voltage at a first voltage ramp rate before initiating an automatic stop of the engine (12), wherein the target voltage is greater than the voltage output of the battery (16), and wherein the first voltage ramp rate depends on an ambient light intensity detected by the ambient light sensor, and wherein the controller (20) is configured with the ramp algorithm to reduce the voltage output of the alternator or the integrated starter generator (14) from the target voltage to another target voltage at a second voltage ramp rate and subsequently initiate a stop of the engine (12) if a vehicle speed of the vehicle (10) reaches zero, and wherein the second voltage ramp rate differs from the first voltage ramp rate. [2] The vehicle (10) of claim 1, wherein the at least one controller (20) is further configured to reduce the voltage output from the target voltage to another target voltage approximately equal to the voltage output of the battery (16). [3] The vehicle (10) of claim 1, wherein the at least one controller (20) is further configured to determine a threshold vehicle speed at which to begin reducing the voltage output of the alternator or the integrated starter generator (14). [4] The vehicle (10) of claim 3, wherein the at least one controller (20) is further configured to receive vehicle speed information and determine the threshold vehicle speed based on the vehicle speed information.

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