Methods and apparatus for measuring atmospheric pressure and exhaust back pressure

An engine including, in one embodiment, a pressure sensor utilized for determining both barometric pressure and engine exhaust back pressure is described. More specifically, and in the one embodiment, the engine includes an electronic control unit (ECU) including a processor. The pressure sensor is a component of the ECU, and the pressure sensor is in communication, e.g., via a conduit, with the engine exhaust duct. The processor is programmed to obtain signals from the pressure sensor that are representative of both barometric pressure and engine exhaust back pressure. More particularly, the processor is programmed to sample a pressure representative signal generated by the sensor during a first time period to obtain a signal representative of barometric pressure, and to sample a pressure representative signal generated by the sensor during a second time period to obtain a signal representative of engine exhaust back pressure. The first time period initiates when the engine ignition switch is turned on, and terminates prior to when the engine generates exhaust. The second time period initiates upon termination of the first time period, and terminates when the engine ignition switch is turned off.

BACKGROUND OF THE INVENTION
 This invention relates generally to marine propulsion engines, and more
 specifically, to determining atmospheric pressure and exhaust back
 pressure.
 Fuel flow to cylinders in engines including electronic fuel injection
 systems typically is adjusted based on a number of engine operating
 parameters, including air flow. For example, as air flow to the cylinders
 increases, fuel flow to the cylinders also must increase in order to
 maintain good combustion. As air flow to the cylinders decreases, fuel
 flow also must decrease.
 Fuel flow to the cylinders also is adjusted based on operating parameters
 such as atmospheric pressure and intake air temperature. An absolute
 pressure sensor typically is utilized for generating a signal
 representative of atmospheric pressure, and a temperature sensor typically
 is located at the engine air intake to generate a signal representative of
 intake air temperature. The sensors are coupled to, or part of, an
 electronic control unit (ECU), which samples the signals generated by the
 sensors and adjusts fuel flow according to the sampled signals.
 Another parameter that has a significant impact on air flow through the
 engine is exhaust back pressure. Specifically, outboard motors vent
 exhaust gases downwardly through an exhaust housing to a through-the-hub
 propeller. Hydrodynamic effects due, for example, to propeller rotation,
 impact the exhaust back pressure. Increased back pressure can restrict or
 prevent the venting of exhaust gases.
 To determine exhaust back pressure, a pressure sensor can be added in the
 exhaust flow path. Adding a pressure sensor, however, increases the engine
 cost and complexity. Further, by adding another sensor, engine reliability
 may be adversely impacted since an extra sensor increases the possibility
 for a sensor failure.
 It would be desirable to enable determination of both atmospheric pressure
 as well as engine exhaust back pressure, yet avoid the extra cost and
 complexity, and reliability concerns associated with adding an additional
 sensor to the engine.
 BRIEF SUMMARY OF THE INVENTION
 These and other objects may be attained by an engine including, in one
 embodiment, a pressure sensor utilized for determining both atmospheric,
 or barometric, pressure and engine exhaust back pressure. More
 specifically, and in the one embodiment, the engine includes an electronic
 control unit (ECU) including a processor. The pressure sensor is a
 component of the ECU, and the pressure sensor is in communication, e.g.,
 via a conduit, with the engine exhaust duct.
 The processor is programmed to obtain signals from the pressure sensor that
 are representative of both barometric pressure and engine exhaust back
 pressure. More particularly, the processor is programmed to sample a
 pressure representative signal generated by the sensor during a first time
 period to obtain a signal representative of barometric pressure, and to
 sample a pressure representative signal generated by the sensor during a
 second time period to obtain a signal representative of engine exhaust
 back pressure. The first time period initiates when the engine ignition
 switch is turned on, and terminates prior to when the engine generates
 exhaust. The second time period initiates upon termination of the first
 time period, and terminates when the engine ignition switch is turned off.
 Using the pressure sensor and processor described above, both atmospheric
 pressure as well as engine exhaust back pressure are determined, yet the
 extra cost and complexity associated with adding an extra sensor are
 avoided. In addition, by using only one sensor to determine both
 barometric and engine exhaust back pressure, reliability concerns
 associated with adding an additional sensor to the engine are avoided.

DETAILED DESCRIPTION OF THE INVENTION
 The present invention is described herein in the context of an outboard
 engine. The present invention could, however, be utilized in connection
 with a stern drive engine as well as with an outboard engine. Further, the
 present invention is not limited to practice with any one particular
 engine, and therefore, the following description of an exemplary engine
 relates to only one exemplary implementation of the present invention.
 Referring more particularly to the drawings, FIG. 1 is a perspective view
 of an outboard engine 10, such as an outboard engine commercially
 available from Outboard Marine Corporation, Waukegan, Ill. Engine 10
 includes a cover 12 which houses a power head 14, an exhaust housing 16,
 and a lower unit 18. A drive shaft 20 extends from power head 14, through
 exhaust housing 16, and into lower unit 18.
 Lower unit 18 includes a gear case 22 which supports a propeller shaft 24.
 One end of propeller shaft 24 is engaged to drive shaft 20, and a
 propeller 26 is engaged to an opposing end of shaft 24. Propeller 26
 includes an outer hub 28 through which exhaust gas is discharged. Gear
 case 22 includes a bullet, or torpedo, 30 and a skeg 32 which depends
 vertically downwardly from torpedo 30.
 Power head 14 includes an internal combustion engine having an exhaust
 system with an exhaust outlet. Power head 14 also includes an adapter 30.
 A port 34 is located in adapter and typically is used for emission testing
 of engine 10. A main exhaust gas duct extends through adapter 30 and
 exhaust housing 16 and into lower unit 18 so that exhaust flows from power
 head 14 through the gas duct and out hub 28.
 As explained above, a parameter that has a significant impact on air flow
 through engine 10 is exhaust back pressure. At high speeds or when engine
 10 is raised up in the water so that hub 28 is near the surface of the
 water, exhaust gases can easily pass through exhaust housing 16 and out
 through hub 28. At idle or slow speed conditions, however, propeller 26 is
 lower in the water, which results in an increased back pressure at hub 28.
 The increased back pressure can restrict or prevent the venting of exhaust
 gases. The speed of the boat, and the particular boat configuration (e.g.,
 the depth at which the exhaust exits through propeller 26) impact exhaust
 back pressure.
 Referring to FIG. 2, and to determine exhaust back pressure, a differential
 pressure sensor 50 can be added in the exhaust flow path. A temperature
 sensor 52 and an absolute pressure sensor 54 also are provided for
 measuring inlet air temperature and atmospheric pressure, respectively.
 Sensors 50, 52, and 54 are coupled to an electronic control unit (ECU) 56,
 which is well known in the art. ECU 56 includes a processor, and the ECU
 processor samples the respective signals generated by sensors 50, 52, and
 54 to adjust fuel flow during engine operation. As used herein, the term
 processor is not limited to a microprocessor, but includes circuits,
 controllers and all other known electronic controls and apparatus capable
 of controlling at least some aspects of engine operations.
 Temperature sensor 52 and absolute pressure sensor 54 typically are used in
 connection with engines having fuel injection. Adding differential
 pressure sensor 50 increases the engine cost and complexity. Further, by
 adding sensor 50, engine reliability may be adversely impacted since an
 extra sensor increases the possibility for a sensor failure.
 FIG. 3 is a block diagram of a system 100 for sensing temperature,
 atmospheric pressure, and exhaust back pressure in accordance with one
 embodiment of the present invention. As shown in FIG. 3, a temperature
 sensor 102 and an absolute pressure sensor 104 are coupled to an ECU 106.
 ECU 106 samples the respective signals generated by sensors 102 and 104 to
 adjust fuel flow during engine operation. Temperature sensor 102, as is
 known in the art, is utilized for measuring inlet air temperature.
 Absolute pressure sensor 104 is utilized for measuring both atmospheric, or
 barometric, pressure and exhaust back pressure. Particularly, and in one
 embodiment, sensor 104 is mounted on the same circuit board along with the
 ECU processor and other components. Sensor 104, in this embodiment, is a
 component of ECU 106. A flexible tube or conduit extends from sensor 104,
 to the engine main exhaust duct, e.g., to port 34, and sensor 104 is
 exposed to the pressure at port 34. In one embodiment, a diaphragm is
 positioned at an intermediate location between first and second conduit
 sections so that the pressure is effectively communicated, but exhaust
 gases as well as any dirt or other debris are blocked from direct contact
 with sensor 104. Sensor 104 generates a signal representative of such
 pressure, and the ECU processor samples the signal generated by sensor
 104.
 Sensor 104 may be any pressure sensor capable of sensing pressure in a
 range of about 60 to 115 k.p.a. One such commercially available and known
 sensor is the Motorola MPX 4115 sensor. Many other commercially available
 sensors could be utilized.
 In an alternative embodiment, sensor 104 is located at port 34, and is
 electrically connected to the ECU processor via a communications bus. Such
 an arrangement provides the benefit of eliminating the conduit and
 diaphragm arrangement described above. However, sensor 104 may be more
 exposed to exhaust, heat, and water. Many other embodiments and variations
 are possible.
 FIG. 4 is a flow chart 120 of process steps executed by the electronic
 control unit in accordance with one embodiment of the present invention.
 As explained above, ECU 106 includes a processor, or controller, as is
 known in the art. The ECU processor is coupled to sensor 104, and in one
 embodiment, is programmed to determine both barometric pressure and
 exhaust back pressure from sensor 104.
 More specifically, and once the ignition key is turned on, ECU 106 is
 energized 122 and processor begins operations, even before the engine
 crankshaft begins to turn. Upon power-up, the ECU processor samples 124
 absolute pressure sensor 104 during first time period to obtain a pressure
 representative signal. The first time period initiates when the engine
 ignition switch is turned on and ends before engine 10 generates exhaust.
 In this condition, the sample from pressure sensor is representative of
 barometric pressure and not exhaust back pressure since the engine
 crankshaft has not even yet begun to rotate. Since the crankshaft is not
 rotating, no air is moving due to engine operation. Therefore, the
 pressure in exhaust housing 16 is equal to the atmospheric pressure. The
 value obtained from pressure sensor 104 is then stored 126 in a
 predesignated memory location of ECU memory for use during engine
 operations, and is utilized whenever a barometric pressure value is needed
 during engine operations.
 Since barometric pressure will not normally change significantly during one
 cycle of engine operations, i.e, one cycle refers to the duration of
 engine operations from turning the ignition key on to turning the ignition
 key off, the barometric pressure can be determined just once and stored in
 memory for use during the entire cycle. Particularly, since there is no
 significant change in altitude on a body of water, there should be no
 change in barometric pressure during the cycle of operation.
 During normal engine operations, e.g., the second time period, the ECU
 processor samples pressure sensor in accordance with its pre-programmed
 instructions to determine engine exhaust back pressure, as needed, 128.
 The second time period initiates upon termination of the first time period
 and ends when the ignition key is turned off. The fuel flow can then be
 adjusted based on the stored value representative of barometric pressure
 and the most recently determined value of engine exhaust back pressure.
 The above described system for sensing both atmospheric pressure as well as
 engine exhaust back pressure avoids the extra cost and complexity, and
 reliability concerns associated with adding an additional sensor to the
 engine. In addition, the pressure values obtained using such system are
 reliable and can be used to control fuel flow to the engine cylinders.
 From the preceding description of various embodiments of the present
 invention, it is evident that the objects of the invention are attained.
 Although the invention has been described and illustrated in detail, it is
 to be clearly understood that the same is intended by way of illustration
 and example only and is not to be taken by way of limitation. Accordingly,
 the spirit and scope of the invention are to be limited only by the terms
 of the appended claims.