METHOD FOR COMPENSATING FOR ACCESSORY LOADING
An internal combustion engine includes an advanced vehicle system controller (VSC) that calculates a total power demand to meet a driver wheel power demand plus any accessory loads and independently schedules an engine speed and load operating point to meet the total power demand. A reduction in available engine brake power that is not associated with a driver input, and would ordinarily cause the VSC to respond by raising engine speed, is detected. The driver wheel power demand is reduced to compensate for the reduction in available engine brake power such that the VSC does not need to raise engine speed to meet the driver wheel power demand. A magnitude of the reduction may be determined according to a calibration map to allow a trade off to be made between driveability and noise, vibration, and harshness.
Latest Ford Patents:
1. Field of the Invention
The invention relates to an internal combustion engine which includes an advanced vehicle system controller (VSC) that calculates the total engine power needed to meet the driver demand plus all accessory loads and independently schedules the engine speed and load operating point, with or without feedback of actual engine performance, to meet the total power demand.
2. Background Art
In an existing internal combustion engine including an advanced vehicle system controller (VSC), the VSC calculates the total engine power needed to meet the driver wheel power demand plus all accessory loads, and independently schedules the engine speed and load operating point, with or without feedback of actual engine performance, to meet the total power demand. By scheduling the most efficient engine speed and load operating point, the VSC may attempt to maximize fuel economy. Examples of powertrain systems which may involve VSCs include continuously variable transmission (CVT) and power split hybrid applications.
In an existing hybrid electric vehicle including such a VSC, the engine speed can flare up by 1,000 rpm when the air conditioner (A/C) compressor clutch engages. When the A/C compressor clutch disengages, the engine speed falls by 1,000 rpm. This engine speed cycling would typically occur at higher altitudes where the engine is running at wide open throttle (WOT). If the hybrid electric vehicle runs the engine at WOT at lower altitudes, then engine speed cycling at lower altitudes can also occur. The compressor clutch engaging and disengaging is driven by low and high pressure cut-out switches in the A/C system. Accordingly, the A/C compressor clutch cycles independently of the climate control panel's mode selector switch and the driver's accelerator pedal position. As such, the changes in engine speed are not associated with a driver input. Therefore, this engine speed behavior may be intrusive and disturbing to the operator of the vehicle.
In the existing hybrid electric vehicle, the engine speed flare up is a result of the VSC's response to a reduction in available engine brake power caused by the A/C compressor clutch engagement. Put another way, the VSC calculates the total engine power needed to meet the driver demand plus all accessory loads and independently schedules the engine speed and load operating point to meet the total power demand. The engaging of the A/C compressor clutch increases the accessory load, thus increasing the total power demand. When the engine is operating at WOT, in order to maintain the driver's requested wheel power output and the high voltage battery charge balance, the VSC must compensate for the power lost to the A/C system by raising the engine speed.
When the engine is not running at WOT, the VSC may respond to A/C cycling by adjusting the throttle position to increase or decrease the brake engine power as necessary. These throttle position adjustments are sufficient to make up the power consumed by the A/C system and the VSC does not need to increase the engine speed. However, at higher elevations, the VSC runs the engine at wide open throttle (WOT) frequently so that the VSC responds to A/C compressor clutch engagements by increasing the engine speed.
In general, any change to engine brake power not associated with a driver input can cause the VSC to respond with an intrusive engine speed change.
For the foregoing reasons, there is a need for a method for controlling an internal combustion engine including an advanced vehicle system controller that addresses these engine speed flare ups.
SUMMARY OF THE INVENTIONIn accordance with the invention, in an internal combustion engine including an advanced VSC that calculates the total engine power needed to meet the driver demand plus all accessory loads and independently schedules the engine speed and load operating point, the driver demanded wheel power is reduced (for example, by reducing driver demanded wheel torque) to compensate for the power consumed by the A/C compressor so that the VSC no longer needs to raise the engine speed to maintain the high voltage battery charge balance. It is appreciated that reducing the driver demanded wheel power in accordance with the invention may be used to compensate for any change to engine brake power not associated with a driver input that ordinarily would cause the VSC to respond with an intrusive engine speed change. Such changes may include electrical loads (for example, an electric A/C system or any other electric load) because in order to maintain battery charge neutrality it would ordinarily be necessary to increase engine speed to make up for the electric load. Further, it is appreciated that the invention is applicable to any advanced VSC; examples of powertrain systems that may have such VSCs include continuously variable transmission (CVT) and power split hybrid applications.
This reduction in driver demanded wheel power is preferably only allowed when the engine is at wide open throttle, minimum vehicle speed and maximum driver demand power thresholds are satisfied, and the wheel power reduction is transparent to the driver. Hysteresis should be applied to these conditions to prevent dithering. Further, it is preferred that the wheel power reduction be applied and removed smoothly through a software filter.
In more detail, an electronic throttle control feature may determine whether or not the engine is at wide open throttle. Specifically, the electronic throttle control feature examines the ambient barometric pressure, throttle opening, mass airflow sensor output and engine speed to infer whether or not additional throttle opening would result in more engine torque. If more torque is not possible, a flag is set to notify the VSC that the engine is operating at wide open throttle. The VSC should use this flag as a necessary condition to reduce the driver demanded wheel power. Further, other methods of determining wide open throttle may be used, including direct measurement of barometric pressure and manifold pressure.
In a preferred implementation, the magnitude of the wheel power adjustment is determined by a calibration mapping. In this A/C example, the mapping tabulates compressor power usage at various engine speeds and refrigerant pressures. Additional tables can be used to map other adjustments to prevent unwanted engine speed changes.
BRIEF DESCRIPTION OF THE DRAWINGS
A hybrid electric vehicle powertrain is shown in
The transmission 14 includes a planetary gear unit 20, which comprises a ring gear 22, a sun gear 24, and a planetary carrier assembly 26. The ring gear 22 distributes torque to step ratio gears comprising meshing gear elements 28, 30, 32, 34, and 36. A torque output shaft 38 for the transmission is drivably connected to vehicle traction wheels 40 through a differential and axle mechanism 42.
Gears 30, 32, and 34 are mounted on a countershaft, with gear 32 engaging a motor-driven gear 44. Electric motor 46 drives gear 44, which acts as a torque input for the countershaft gearing.
The battery delivers electric power to the motor through power flow path 48, 54. Generator 50 is connected electrically to the battery and to the motor in a known fashion as shown at 52.
The power split powertrain system of
In general, VSC 10 calculates the total engine power needed to meet the driver wheel power demand plus all accessory loads (for example, A/C compressor 17), and independently schedules the engine speed and load operating point, with or without feedback of actual engine performance, to meet the total power demand. This type of approach is typically used to maximize fuel economy and may be used in other types of powertrain systems that have such VSCs including CVT and other hybrid applications.
The power flow paths between the various elements of the power split powertrain diagram shown in
Generator 50, when acting as a motor, can deliver power to the planetary gearing. When acting as a generator, generator 50 is driven by the planetary gearing. Similarly, power distribution between the motor 46 and the countershaft gears 30, 32, 34 can be distributed in either direction.
As shown in
In accordance with the invention, which is applicable to any advanced VSC, to avoid engine speed flare up at wide open throttle when the A/C compressor clutch engages or when any other change to available engine brake power not associated with a driver input occurs, driver demanded wheel power is reduced subject to certain exceptions.
The wheel power reduction should only be allowed when the engine is at wide open throttle, minimum vehicle speed and maximum driver demand power thresholds are satisfied, and the wheel speed reductions are transparent to the driver. Further, hysteresis is applied to these conditions to prevent dithering. Still further, the wheel power reduction should be applied and removed smoothly through a software filter.
As further illustrated in
As mentioned previously, the wheel power reduction should only occur when the engine is at wide open throttle.
Whether or not the engine is at wide open throttle (WOT) may be determined by existing logic in the electronic throttle control feature that examines ambient barometric pressure, throttle opening, mass airflow sensor output and engine speed to infer whether or not additional throttle opening will result in more engine torque. In the event that the engine is not operating at WOT, the throttle may be opened further to provide more engine torque instead of reducing driver demanded wheel power. However, when operating at WOT, driver demanded wheel power should be reduced in response to the change in available engine brake power.
Preferably, the test conditions at decision blocks 84, 86 and 88 use hysteresis to prevent rapid toggling. As well, when wheel power is reduced at block 90, the reduction should be applied through a software filter so that the torque reduction is not overly abrupt.
With regard to the minimum vehicle speed threshold, the power needed to run the compressor is a larger percentage of the driver demanded wheel power at lower vehicle speeds. This could make wheel power adjustments more intrusive and introduce drivability problems. Accordingly, driver demanded wheel power is not reduced when the minimum vehicle speed threshold is not met. In addition, when the driver is requesting the maximum powertrain output, the VSC should not reduce the wheel torque for any reason.
The magnitude of the wheel power adjustment is determined by calibration mapping. In this A/C example, the mapping tabulates compressor power usage at various engine speeds and refrigerant pressures. Additional tables can be used to map other adjustments to prevent unwanted engine speed changes. Reducing the delivered wheel power independently of the driver's request is preferably performed in a way that is transparent to the driver. In the A/C compressor example, when the power needed to run the A/C compressor is a small percentage of the power being generated to drive the vehicle (5%-10%), the wheel power reduction has little impact on driveability. In other applications where the A/C power usage is a larger percentage of the driver demanded wheel power, the tables used to schedule the wheel power reduction could be calibrated smaller to minimize the drivability issue. This aspect of the invention allows a tradeoff to be made between driveability and noise, vibration, and harshness (NVH) concerns.
While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.
Claims
1. A method of controlling an internal combustion engine which includes an advanced vehicle system controller (VSC) that calculates a total power demand to meet a driver wheel power demand plus any accessory loads and independently schedules an engine speed and load operating point to meet the total power demand, the method comprising:
- detecting a reduction in available engine brake power for meeting the driver wheel power demand that is not associated with a driver input and would ordinarily cause the VSC to respond by raising engine speed; and
- reducing the driver wheel power demand to compensate for the reduction in available engine brake power such that the VSC does not need to raise engine speed to meet the driver wheel power demand.
2. The method of claim 1 wherein the reduction in available engine brake power is due to engagement of an accessory load.
3. The method of claim 2 wherein the accessory load comprises an air conditioning compressor.
4. The method of claim 1 wherein the engine includes a power split hybrid powertrain.
5. The method of claim 1 further comprising:
- determining an existence of a wide open throttle condition; and
- only reducing the driver wheel power demand when the wide open throttle condition exists and the reduction in available engine brake power is detected.
6. The method of claim 5 wherein determining the existence of the wide open throttle condition comprises:
- determining whether or not additional throttle opening would increase available engine brake power.
7. The method of claim 1 further comprising:
- only reducing the driver wheel power demand when a minimum vehicle speed threshold is met and the reduction in available engine brake power is detected.
8. The method of claim 1 further comprising:
- only reducing the driver wheel power demand when a maximum driver demand power threshold is met and the reduction in available engine brake power is detected.
9. The method of claim 1 further comprising:
- applying the driver wheel power demand reduction as a filtered driver wheel power demand reduction to prevent abrupt driver wheel power demand changes.
10. The method of claim 1 wherein a magnitude of the reduction is determined according to a calibration map.
11. An internal combustion engine which includes an advanced vehicle system controller (VSC) that calculates a total power demand to meet a driver wheel power demand plus any accessory loads and independently schedules an engine speed and load operating point to meet the total power demand, the VSC being programmed to:
- detect a reduction in available engine brake power for meeting the driver wheel power demand that is not associated with a driver input and would ordinarily cause the VSC to respond by raising engine speed; and
- reduce the driver wheel power demand to compensate for the reduction in available engine brake power such that the VSC does not need to raise engine speed to meet the driver wheel power demand.
12. The engine of claim 11 wherein the reduction in available engine brake power is due to engagement of an accessory load.
13. The engine of claim 12 wherein the accessory load comprises an air conditioning compressor.
14. The engine of claim 11 wherein the engine includes a power split hybrid powertrain.
15. The engine of claim 11 wherein the VSC is further programmed to:
- determine an existence of a wide open throttle condition; and
- only reduce the driver wheel power demand when the wide open throttle condition exists and the reduction in available engine brake power is detected.
16. The engine of claim 15 wherein determining the existence of the wide open throttle condition comprises:
- determining whether or not additional throttle opening would increase available engine brake power.
17. The engine of claim 11 wherein the VSC is further programmed to:
- only reduce the driver wheel power demand when a minimum vehicle speed threshold is met and the reduction in available engine brake power is detected.
18. The engine of claim 11 wherein the VSC is further programmed to:
- only reduce the driver wheel power demand when a maximum driver demand power threshold is met and the reduction in available engine brake power is detected.
19. The engine of claim 11 wherein the VSC is further programmed to:
- apply the driver wheel power demand reduction as a filtered driver wheel power demand reduction to prevent abrupt driver wheel power demand changes.
20. The engine of claim 11 wherein a magnitude of the reduction is determined according to a calibration map.
Type: Application
Filed: May 1, 2006
Publication Date: Nov 1, 2007
Applicant: Ford Global Technologies, LLC (Dearborn, MI)
Inventors: Shunsuke Okubo (Belleville, MI), Fazal Syed (Canton, MI)
Application Number: 11/381,008
International Classification: B60K 6/00 (20060101); G06F 19/00 (20060101); F02N 17/00 (20060101);