The present disclosure relates generally to the control of internal combustion gas engines and, more particularly, to a method and system for controlling the engine during a return to idle when the engine's oil is highly aerated.
With the development of advanced valve train technologies (e.g., MultiAir®), it is now possible to control the amount of air used for combustion in each individual engine cylinder. A vehicle equipped with such technology (often referred to as variable valve actuation technology) manages the torque and power delivered by the engine by varying the lift profile of intake valves without direct use of a throttle. Instead, air intake is controlled using electro-hydraulic components that include a valve tappet, moved by a mechanical intake cam, connected to the intake valve through a hydraulic chamber that is controlled by a solenoid valve. The vehicle's engine control unit provides optimum intake valve opening schedules throughout the operation of the engine.
Standard engine oil is used as the valve operating fluid in the variable valve actuated engines described above. At high engine speeds, the oil is pressurized and typically free from air or air bubbles, which is desirable. However, when the oil pressure drops, air can effervesce from the oil (via e.g., the oil gallery), causing the oil to become aerated, which is not desirable.
One known situation where oil aeration can occur is when the engine speed is returned to idle. During a return to idle maneuver, oil pressure drops and air can effervesce from the oil. It has been discovered that valve lift can be lost due to a return to idle, especially in conditions of high oil aeration.
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In one form, the present disclosure provides a method of controlling an engine of a vehicle to set a speed of the engine to a predetermined idle speed. The method comprises determining, at a processor, if the engine's oil is highly aerated; and if the engine's oil is highly aerated, setting, via the processer, the engine speed to an intermediate idle speed for a predetermined time period before setting the engine speed to the predetermined idle speed.
The present disclosure also provides an engine system of a vehicle. The system comprises a solenoid valve connected to a cylinder head connected to the engine; and a controller connected to the solenoid valve and the engine. The controller adapted to set a speed of the engine to a predetermined idle speed by determining if the engine's oil is highly aerated; and if the engine's oil is highly aerated, setting the engine speed to an intermediate idle speed for a predetermined time period before setting the engine speed to the predetermined idle speed.
Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description, including disclosed embodiments and drawings, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the invention, its application or use. Thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention.
The disclosed system and method will implement a stepped return to idle maneuver when engine oil has a predetermined amount of aeration. The predetermined amount of aeration is an amount that could cause an engine to stall due to valve lift loss if the engine speed were reduced to the idle speed in the conventional manner. It is believed that the air bubbles within the oil gallery grow and coalesce when oil pressure drops at low engine speeds. If the engine speed is allowed to first dwell at an intermediate calibratable engine speed for a calibratable amount of time before returning to the typical idle speed (e.g., 700 RPM), then valve lift loss is substantially eliminated. The system and method disclosed herein are suitable for use with MultiAir® and other variable valve actuation systems/vehicles.
The engine 14 is also connected to an engine control unit (ECU) 30 or similar type controller. The ECU 30 could be a processor programmed to perform the method 100 discussed below and/or other necessary controller functions. The ECU 30 includes a valve control module (VCM) 32 that controls the timing of the solenoid valve 16, which is used to control the opening/closing of the intake valves. The ECU 30 can receive an engine speed or other input from the engine 14 or a sensor attached to the engine that indicates what the engine speed is.
The ECU 30 is adapted to set, clear, and read an oil aeration indicator. The indicator could be a software variable that is stored in a memory within the ECU 30 or external to the ECU 30. Alternatively, or in addition to, the oil aeration indicator could be a hardware register that is part of the ECU 30 or external to the ECU 30, as desired. The oil aeration indicator will have a first value indicating that the engine's 14 oil is aerated (in accordance with the disclosed principles) and a second value indicating that the engine's 14 oil is not aerated.
In one embodiment, the aeration indicator will be set when the engine speed and amount of time the engine was at the speed indicates that aeration is probable. Known aeration percentages based on engine speed and the time at speed will be stored in a table or hardware registers accessible by the ECU 30. In an example embodiment, the aeration indicator will be set when the engine speed and time the engine was at the speed indicate that there is at least an 18% aeration of the engine oil. It should be appreciated that the subject matter disclosed herein is not limited to an 18% aeration of the oil and that any amount of aeration can be used to set the aeration indicator.
Moreover, other factors can be used to determine whether the oil is aerated enough to cause potential valve lift loss. That is, oil aeration can be effected by the dynamic operation of the vehicle. For example, when a vehicle makes sharp turns, the engine oil can enter the timing chain's case and touch the timing chain, which can cause additional aeration. Thus, having inputs from accelerometers can help determine whether the manner in which the vehicle is being driven is causing additional aeration of the engine oil. In addition, the oil's temperature could be an indication of aeration.
Thus, the disclosed system 10 can optionally include inputs from one or more accelerometers 20, and oil temperature sensor 22 or other sensors that can be used to determine oil aeration. The ECU 30 could use one or more of these inputs to determine the amount of aeration and set the aeration indicator. In another embodiment, the system 10 can input oil pressure from e.g., an oil pressure sensor and then perform an analysis (e.g., a Fourier analysis) on the oil pressure to determine if the oil is aerated, as the inventors have determined that air bubbles tend to damp high frequency content. It should be appreciated that the subject matter disclosed herein is not limited to how the aeration of the oil is determined. For example, aeration could be determined based on the existing VCM aeration algorithm, if desired. Moreover, the subject matter disclosed herein is not limited to when the ECU 30 makes the oil aeration computation/determination. That is, the oil aeration computation/determination can be performed periodically as a background or other process performed by the ECU 30.
The method 100 should be run when the ECU 30 or other vehicle sensor/module detects that a return to idle maneuver is being performed. For example, the ECU 30 can detect that an accelerator pedal “tip-out” was performed. An accelerator pedal “tip-out” is the action of a driver releasing the accelerator pedal from a depressed position to a completely released or mostly released position. Regardless of how return to idle maneuver is detected, or how/when the method 100 is executed, the method 100 begins when the ECU 30 determines whether the aeration indicator is set to the first value indicating that the engine's 14 oil is “highly” aerated (step 102). As mentioned above, in one example embodiment, the aeration indicator will be set to the first value if there is at least an 18% aeration of the engine oil. If at step 102, it is determined that the aeration indicator is not set to the first value (i.e., the engine's 14 oil is not “highly” aerated), the method 100 terminates.
However, if at step 102, it is determined that the aeration indicator is set to the first value indicating that the engine's 14 oil is “highly” aerated, the method continues at step 104 to initiate a stepped return to idle maneuver. That is, instead of immediately returning the engine to its normal idle speed (e.g., 700 RPM), step 104 will set the idle speed to an intermediate value “N” for predetermined a period of time “X”. The ECU 30 and the VCM 32 will control the solenoid valve 16 and engine 14 to set the engine 14 to the intermediate idle speed N. The exact value of the intermediate value N will be determined by a calibration process. Likewise, the predetermined time period X will be determined by the calibration process. During the calibration process, the engine 14 can be tested in a manner described below with reference to
After time X has elapsed, the method 100 continues at step 106 where the idle speed is set to the engine's normal idle speed. The ECU 30 and the VCM 32 will control the solenoid valve 16 and engine 14 to set the engine 14 to the normal idle speed. The engine 14 will idle at the normal speed and because valve lift loss has been substantially eliminated, the engine will not stall. Thus, the method 100 implements a calibratable controlled return to idle after sustained high RPM driving or other driving conditions. The controlled, stepped return to idle will substantially prevent valve lift loss and ensure that the engine will not stall.