Significant improvements in both fuel efficiency and performance of an internal combustion engine may be realized by selective switching of a cam profile. However, cam profile switching technologies have been difficult to implement in various valvetrain settings, such as roller finger follower valvetrains.
One method of implementing cam profile switching in a roller finger follower valvetrain has been to utilize a “drop finger” follower, wherein the roller finger is movably coupled to the follower body in such a manner that the finger can be operated in either a coupled mode, in which the roller finger is locked in position relative to the follower body, or in a decoupled mode, in which the roller finger is decoupled from and allowed to move relative to the follower body. This allows the cam and valve to have different lifts, depending upon whether the roller finger is coupled to or decoupled from the follower body.
One difficulty that has been encountered in implementing roller finger follower valve systems involves actuation of the roller finger decoupling mechanism. Both hydraulic and electromechanical actuation systems have been proposed. However, hydraulic systems may cause a power demand on the engine, as these systems require the oil pump to do additional work. Likewise, solenoids used in electromechanical systems may be relatively large and bulky.
The inventors herein have realized that the above-described problems may be addressed through the use of a mode-switching cam follower having a body, a cam contact movably coupled to the body, a latch member movably coupled to the body, wherein the latch member is movable between a coupled position in which the cam contact is held in a fixed relation to the body by the latch member and a decoupled position in which the cam contact is decoupled from the latch member and movable relative to the body, and an actuator in communication with the latch member, wherein the actuator comprises a shape memory alloy member. In some embodiments, the cam contact includes a roller finger, while in other embodiments includes a sliding contact. Such a mode-switching cam follower may allow actuation of the latch member while avoiding problems with the size and power demands found in other actuation systems.
Engine 10 typically includes a plurality of cylinders, one of which is shown in
Intake manifold 22 communicates with a throttle body 42 via a throttle plate 44. Intake manifold 22 is also shown having a fuel injector 46 coupled thereto for delivering fuel in proportion to the pulse width of signal (fpw) from controller 12. Fuel is delivered to fuel injector 46 by a conventional fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). Engine 10 further includes a conventional distributorless ignition system 48 to provide an ignition spark to combustion chamber 14 via a spark plug 50 in response to controller 12. In the embodiment described herein, controller 12 is a conventional microcomputer including: a microprocessor unit 52, input/output ports 54, an electronic memory chip 56, which may be electronically programmable memory, a random access memory 58, and a conventional data bus.
Controller 12 receives various signals from sensors coupled to engine 10, in addition to those signals previously discussed, including: measurements of inducted mass air flow (MAF) from a mass air flow sensor 60 coupled to throttle body 42; engine coolant temperature (ECT) from a temperature sensor 62 coupled to cooling jacket 64; a measurement of manifold pressure (MAP) from a manifold absolute pressure sensor 66 coupled to intake manifold 22; a measurement of throttle position (TP) from a throttle position sensor 68 coupled to throttle plate 44; and a profile ignition pickup signal (PIP) from a Hall effect sensor 70 coupled to crankshaft 40 indicating an engine speed (N).
Exhaust gas is delivered to intake manifold 22 by a conventional EGR tube 72 communicating with exhaust manifold 24, EGR valve assembly 74, and EGR orifice 76. Alternatively, tube 72 could be an internally routed passage in the engine that communicates between exhaust manifold 24 and intake manifold 22.
As described above, valves 26 and 28 may be operated by the combination of one or more camshafts and a mode-switching follower, such as a drop finger follower. One type of drop finger follower, which may be referred to as a roller finger follower, includes one or more rollers mounted to a follower body (such as a rocker arm), wherein a cam lobe on the camshaft contacts the roller. The roller may be configured to be selectively coupled to or decoupled from the follower body. In the coupled operating mode, the roller is locked in position relative to the follower body, whereas in the decoupled operating mode, the roller is allowed to float in position relative to the follower body. This allows the valve operating to be varied without adjusting the camshaft. Furthermore, multiple rollers may be mounted to the follower body, thereby allowing different profile cams to be used to operate a valve by selectively coupling and decoupling rollers to/from the follower body. This allows valve lift and timing to be controlled.
As mentioned above, problems have been encountered with hydraulic and electromechanical actuation systems for operating the drop finger decoupling mechanism. For example, hydraulic systems may cause a power demand on the engine due to the work performed by the oil pump in providing hydraulic power. Likewise, solenoids used in electromechanical systems may be large and bulky, and therefore difficult to use with many engines.
Roller finger follower 202 further comprises a latch member 212 which is selectively engageable with roller frame 210. Engaging latch member 212 with roller frame 210 places roller finger follower 200 in the coupled mode, as shown in
Roller finger follower 202 further includes an actuator 214 formed from a shape memory alloy wire. Shape memory alloys are materials that undergo a dimension-changing phase transition upon a temperature change, and that return to the “original” geometry upon a reverse temperature change. The length of the shape memory alloy wire may be changed simply by controlling an electrical current through the wire to control a resistive heating of the wire. In this manner, the use of actuator 214 may allow the operating mode of roller finger follower 202 to be effectively controlled without the disadvantages encountered with hydraulic and electromechanical actuators.
Any suitable shape memory alloy material may be used as actuator 214. Examples of suitable materials may include, but are not limited to, shape memory alloys with the following elemental combinations: Ag—Cd, Cu—Al—Ni, Cu—Sn, Cu—Zn, Cu—Zn—X (X═Si, Sn, Al), In—Ti, Ni—Al, Ni—Ti, Fe—Pt, Mn—Cu, Fe—Mn—Si, Ti—Ni—V, Ni—Ti—Cr, Ni—Ti—Fe, Ni—Ti—Cu various Pt alloys, Co—Ni—Al, and Co—Ni—Ga.
Shape memory alloy actuator 214 may be coupled to latch member 212 and rocker arm 202 in any suitable manner. In the depicted embodiment, shape memory wire actuator 214 extends substantially around an outer circumference of latch member 212 and ball socket 204, and along an underside of rocker arm 202. Therefore, with materials that undergo a contracting phase change when heated, application of a current through shape memory alloy wire actuator 214 may cause the length of the wire to contract, pulling latch member 212 from a decoupled configuration into a coupled configuration. Likewise, the cessation of current through the actuator may cause shape memory alloy actuator 214 to cool and expand, thereby allowing latch member 212 to move from a coupled configuration to a decoupled configuration. One or more springs 216 may be provided biasing latch member 212 toward the decoupled position. Furthermore, additional cooling may be provided via forced air, engine oil, or other engine coolant. When latch member 212 is in a decoupled mode, roller 208 may be displaced relative to rocker arm 202 by the corresponding cam lobe such that motion of the cam lobe is not transferred to the valve. In this mode, alternate rollers 218 may interact with corresponding alternate cam lobes on the camshaft (not shown) to allowing the use of an alternate valve lift and/or timing. Furthermore, a spring 220 may be provided to bias roller 208 toward a default position while in the decoupled mode.
While the depicted actuator 214 takes the form of a wire extending substantially around a lengthwise perimeter of roller finger follower 202, it will be appreciated that actuator 214 may be coupled to rocker arm 202 in any other suitable manner. Furthermore, while the depicted actuator 214 includes a single length of wire, it will be appreciated that a shape memory alloy actuator may also include more than one wire. For example, such an actuator may include two or more wires arranged in a parallel bundle, in series, or in any other suitable geometric relation.
It will be appreciated that the physical properties of the alloy and the structure of roller finger follower 200 may be factors to be considered in the specific design of actuator 214. For example, different alloys may have different electrical, mechanical and thermal properties, including but not limited to phase transition temperatures, coefficients of expansion, electrical conductivities, etc. These and other properties may affect the design of a specific embodiment of actuator 214, including but not limited to the length, diameter, and other geometrical aspects of actuator 214, as well as where and how the actuator is coupled to the follower.
Another consideration in the design of shape memory alloy actuator 214 may be the desired actuator response time between controller 12 directing actuation and actuator 214 undergoing a phase change. For example, the current and/or voltage applied to shape memory actuator may effect the response time.
In some embodiments, a pulse having multiple voltage levels may be used. For example, a higher voltage portion of the pulse may be used initially to cause the shape memory alloy actuator to heat quickly, and then a lower voltage may be used to maintain the shape memory alloy actuator in the higher temperature phase. Removal of the lower voltage pulse may then allow the shape memory alloy wire to cool more quickly than if a voltage pulse of a single, higher voltage is used. In other embodiments, three or even more voltage levels may be used. In yet other embodiments, a duty cycle of the signal applied to shape memory alloy actuator 214 may be adjusted to control the temperature of actuator 214.
Shape memory alloy actuator 214 may include any suitable configuration of electrical connections for connecting the actuator to a power supply. Two possible examples are shown in
Electrical leads may be provided at each end of actuator 214. In the embodiment depicted in
Continuing, a latch member 810 is pivotally coupled to drop member 803, and a shape memory alloy actuator 812 is coupled to latch member 808. Actuator 812 extends around latch member 808, and is coupled to drop member 803 at a location intermediate the length of roller drop member 803 and rocker arm 802.
Referring next to
Any suitable engine operating condition or change in engine operating condition may trigger actuation of a change in valve operating mode. For example, engine operating conditions that may trigger a change in valve operating mode to a decoupled mode (wherein valve lift is reduced, or even shut off) include, but are not limited to, detecting a decrease in engine torque.
Likewise, engine operating conditions that may trigger a change in valve operating mode to a coupled mode (wherein valve lift is increased or restored) include, but are not limited to, detecting an increase in engine torque.
Referring next to step 1104, the temperature of the shaped memory alloy actuator may be changed in any suitable manner. For example, the temperature of the shaped memory alloy may be increased by applying a voltage pulse across the alloy, thereby causing an electric current to flow through the alloy. The voltage pulse may have any suitable magnitude, and may have either a constant value, or a value that changes over time. For example, a higher initial voltage may be used to heat the alloy rapidly, and then a lower voltage may follow the higher initial voltage to maintain the alloy in the high-temperature phase for the desired duration and yet to permit more rapid cooling of the alloy upon cessation of the voltage pulse. Furthermore, the temperature of the alloy may also be increased by increasing a duty cycle of a signal applied across the alloy.
Likewise, the temperature of the shape memory alloy actuator may be decreased by lowering the voltage applied across the alloy, including lowering the voltage to approximately zero, or by decreasing a duty cycle of the signal applied across the alloy. Furthermore, cooling of the alloy may be assisted by exposing the alloy to a coolant such as forced air, engine oil or other engine coolant.
While the concepts disclosed herein are depicted and described in the context of roller finger followers, it will be appreciated that a mode-switching follower incorporating any of the features disclosed herein may have any other suitable cam contact than a roller, including but limited to sliding contacts. Furthermore, while the embodiments depicted herein show exemplary embodiments of roller finger followers each configured to be switched from a decoupled mode to a coupled mode when the shape memory alloy actuator decreases in dimension, it will be appreciated that an actuator may also be configured to be switched from a coupled mode to a decoupled mode by a decrease in actuator dimension.
Furthermore, it will be appreciated that the various embodiments of mode-switching roller finger followers disclosed herein are exemplary in nature, and these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. The subject matter of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various features, functions, and/or properties disclosed herein. The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the various features, functions, elements, and/or properties disclosed herein may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.
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Number | Date | Country |
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2001173550 | Jun 2001 | JP |
Number | Date | Country | |
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20080127917 A1 | Jun 2008 | US |