Camshaft assembly for an internal combustion engine

A camshaft assembly for an internal combustion engine includes a camshaft, a first lobe set, and a second lobe set, extending along, and rotatable about, a cam axis. The first lobe set includes a first, second, and third lobe. The second lobe set includes a first and second lobe. The first lobe set is movable along the cam axis between a first, second, and third position. The second lobe set is movable along the cam axis between a first and second position. The first and second position of each of the first and second lobe sets corresponds to lift of a respective valve stem in the engine. The third position of the first lobe set corresponds to zero lift of the respective valve stem to provide cylinder deactivation of a corresponding cylinder within the engine.

TECHNICAL FIELD

The disclosure generally relates to a camshaft assembly for an internal combustion engine.

BACKGROUND

Internal combustion engines (ICE) are often called upon to generate considerable levels of power for prolonged periods of time on a dependable basis. Many such ICE assemblies employ a supercharging device, such as an exhaust gas turbine driven turbocharger, to compress the airflow before it enters the intake manifold of the engine in order to increase power and efficiency.

Specifically, a turbocharger is a centrifugal gas compressor that forces more air and, thus, more oxygen into the combustion chambers of the ICE than is otherwise achievable with ambient atmospheric pressure. The additional mass of oxygen-containing air that is forced into the ICE improves the engine's volumetric efficiency, allowing it to burn more fuel in a given cycle, and thereby produce more power.

Additionally, ICE's are being methodically developed to consume smaller amounts of fuel. Various technologies are frequently incorporated into ICE's to generate on-demand power, while permitting the subject engine to operate in a more fuel-efficient mode. Such fuel saving technologies may shut off operation of some of the engine's cylinders when engine power requirement is reduced and even completely stop the engine when no engine power is required.

SUMMARY

A vehicle includes an internal combustion engine. The internal combustion engine includes an engine block, a plurality of valve stems, a first camshaft assembly, and a second camshaft assembly. The engine block defines a first set of cylinders and a second set of cylinders. The valve stems are configured to provide selective fluid communication with the first and second set of cylinders.

The first camshaft assembly and a second camshaft assembly each extend along, and are each rotatable about, a respective cam axis. The first and second camshaft assembly are each disposed in operative communication with at least one of the valve stems.

The first camshaft assembly is configured to provide lift to at least one of the respective valve stems to selectively allow air to enter at least one of the first and second set of cylinders in response to rotation of the first camshaft assembly about the respective cam axis. Likewise, the second camshaft assembly is configured to provide lift to the respective valve stems to selectively allow air to exit at least one of the first and second set of cylinders in response to rotation of the second camshaft about the respective cam axis.

Each camshaft assembly is configured to provide lift to at least one of a plurality of valve stems to selectively allow air to respectively enter and exit at least one of the first and second set of cylinders.

Each camshaft assembly includes a camshaft, a first lobe set, and a second lobe set. The camshaft extends along, and is rotatable about, a cam axis. The first lobe set is operatively attached to the camshaft such that the first lobe set surrounds the cam axis. The first lobe set includes a first lobe, a second lobe, and a third lobe. The first lobe, the second lobe, and the third lobe of the first type of first lobe set each have a different profile from one another. The first lobe set is movable along the cam axis between a first position, a second position, and a third position. The first position of the first lobe set corresponds to selection of the first lobe so that lift is provided to the respective valve stem as a function of the profile of the first lobe of the first lobe set as the camshaft rotates about the cam axis. The second position corresponds to selection of the second lobe so that lift is provided to the respective valve stem as a function of the profile of the second lobe of the first lobe set as the camshaft rotates about the cam axis. The third position corresponds to selection of the third lobe so that lift is provided to the selective valve stem of the first lobe set as the camshaft rotates about the cam axis.

The second lobe set is operatively attached to the camshaft such that the second lobe set surrounds the cam axis. The second lobe set includes a first lobe and a second lobe such that the second lobe set includes a fewer number of lobes than the first lobe set. The first lobe and the second lobe of the second lobe set each have a different profile from one another. The second lobe set is movable along the cam axis between a first position and a second position. The first position corresponds to selection of the first lobe so that lift is provided to the respective valve stem corresponding to the profile of the first lobe of the second lobe set as the camshaft rotates about the cam axis. The second position corresponds to selection of the second lobe so that lift is provided to the respective valve stem of the second lobe of the second lobe set as the camshaft rotates about the cam axis.

DETAILED DESCRIPTION

Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” “top,” “bottom,” etc., are used descriptively for the figures, and do not represent limitations on the scope of the disclosure, as defined by the appended claims.

Referring to the Figures, wherein like numerals indicate like parts throughout the several views,FIG. 1illustrates a vehicle20employing a powertrain22for propulsion thereof via driven wheels24. As shown, the powertrain22includes an internal combustion engine26, such as a spark- or compression-ignition type, and a transmission assembly28operatively connected thereto. The powertrain22may also include one or more electric motor/generators, none of which are shown, but the existence of which may be envisioned by those skilled in the art.

With continued reference toFIG. 1, the engine26includes a cylinder block30with a plurality of cylinders32arranged therein and a cylinder head31that is coupled to the cylinder block30. The cylinder head31may be integrated into or cast together with the cylinder block30. The cylinder head31receives air and fuel from an intake system36to be used inside the cylinders32for subsequent combustion. The air and fuel or air alone is admitted into the cylinder head31for each individual cylinder32via appropriately configured valve(s) that are not shown, but known to those skilled in the art.

The cylinders32are separated into a first cylinder or set of cylinders32A and a second cylinder or set of cylinders32B. The engine26also includes a mechanism38configured to selectively activate and deactivate the first set of cylinders32A during operation of the engine26.

Each cylinder32includes a piston, which is not specifically shown, but known to those skilled in the art to reciprocate therein. Combustion chambers, which are not specifically shown, but known to those skilled in the art, are formed within the cylinders32between the bottom surface of the cylinder head31and the tops of the pistons. As known by those skilled in the art, each of the combustion chambers receive fuel and air from the cylinder head31that form a fuel-air mixture for subsequent combustion inside the subject combustion chamber. Each cylinder32includes an intake valve and an exhaust valve, which are not specifically shown, but known to those skilled in the art to respectively provide air to, and exhaust gasses from, the respective combustion chamber. Although an in-line four-cylinder engine is shown, nothing precludes the present disclosure from being applied to an engine having a different number and/or arrangement of cylinders.

In the case of the in-line four-cylinder engine26depicted in the figures, the first set of cylinders32A may include two individual cylinders, while the second set of cylinders32B may include the remaining two individual cylinders. The deactivation of the first set of cylinders32A via the mechanism38is intended to permit the engine26to operate on only the second set of cylinders32B when a load on the engine26is sufficiently low so that power from both the first and second sets of cylinders32A,32B is not required drive the vehicle20. For example, such low load operation may take place when the vehicle26is cruising at a steady state highway speed and the engine26is mostly used to overcome air drag and rolling resistance of the vehicle20. Accordingly, operation of the engine26on solely the second set of cylinders32B permits reduced consumption of fuel when engine power from the first set of cylinders32A is not required to drive the vehicle20.

The engine26also includes a crankshaft (not shown) configured to rotate within the cylinder block. As known to those skilled in the art, the crankshaft is rotated by the pistons, as a result of an appropriately proportioned fuel-air mixture being burned in each combustion chamber. After the air-fuel mixture is burned inside a specific combustion chamber, the reciprocating motion of a particular piston serves to exhaust post-combustion gasses from the respective cylinder32. The cylinder head31is also configured to exhaust post-combustion gasses from the combustion chambers to an exhaust system42via an exhaust manifold44. As shown inFIG. 1, the exhaust manifold44may be internally cast, i.e., integrated, into the cylinder head31. The exhaust manifold44defines at least part of a passage46that is in fluid communication with the cylinder head31. The first set of cylinders32A and the second set of cylinders32B discharge the post-combustion gasses into the passage46. The passage46includes an outlet48defined by the exhaust manifold44. Accordingly, the post-combustion gasses from each of the first and second sets of cylinders32A,32B may exit the exhaust manifold44via the outlet48.

The engine26also includes a turbocharging system50configured to develop boost pressure, i.e., pressurize an airflow that is received from the ambient, for delivery to the cylinders32. The turbocharging system50is configured as a single-stage forced induction arrangement for the engine26. The turbocharging system50includes a turbocharger52that is in fluid communication with the passage46and configured to be driven by the post-combustion gasses from the outlet48. The turbocharger52pressurizes and discharges the airflow to the cylinder head31, via passage34. When the first set of cylinders32A are deactivated via the mechanism38, the turbocharger52can be driven by the post-combustion gasses from only the second set of cylinders32B and supply the pressurized airflow to feed the second set of cylinders32B for combustion with an appropriate amount of fuel therein.

The turbocharger52includes a rotating assembly54. The rotating assembly54includes a turbine wheel56mounted on a shaft58. The turbine wheel56is rotated along with the shaft58by the post-combustion gasses. The turbine wheel56is disposed inside a turbine housing60. The turbine housing60includes an appropriately configured, i.e., designed and sized, turbine volute or scroll62, a relatively high-pressure inlet64, and a relatively low-pressure outlet (not shown in detail, but known to those skilled in the art), that, along with the turbine wheel56, provides a turbine subassembly, a.k.a., a turbine. The turbine scroll62of the turbine housing60receives the post-combustion gasses and directs the gasses to the turbine wheel56. The turbine scroll62is configured to achieve specific performance characteristics, such as efficiency and response, of the turbocharger52.

The rotating assembly54also includes a compressor wheel68mounted on the shaft58. The compressor wheel68is configured to pressurize the airflow being received from the ambient for eventual delivery to the cylinders32. The compressor wheel68is disposed inside a compressor cover70. The compressor cover70includes a compressor volute or scroll72, a relatively low-pressure inlet (not shown in detail, but known to those skilled in the art), and a relatively high-pressure outlet78, that, along with the compressor wheel68, generates a compressor subassembly, a.k.a., a compressor. As understood by those skilled in the art, the variable flow and force of the post-combustion gasses influences the amount of boost pressure that may be generated by the compressor wheel68of the turbocharger52throughout the operating range of the engine26.

Additionally, referring again toFIG. 1, the vehicle includes a programmable controller82configured to regulate operation of the engine26, such as by controlling an amount of fuel being injected into the cylinders32for mixing and subsequent combustion with the pressurized airflow. The physical hardware embodying the controller may include one or more digital computers having a processor33and a memory35, e.g., a read only memory (ROM), random access memory (RAM), electrically-programmable read only memory (EPROM), high speed clock, analog to digital (A/D) and digital to analog (D/A) circuitry, and input/output circuitry and devices (I/O) including one or more transceivers37for receiving and transmitting any required signals in the executing of a method, as well as appropriate signal conditioning and buffer circuitry. Any computer-code resident in the controller or accessible thereby, including the algorithm, can be stored in the memory and executed via the processor(s) to provide the functionality set forth below.

The controller82ofFIG. 1may be configured as a single or a distributed control device. The controller82is electrically connected to, or otherwise in hard-wired or wireless communication with, the engine26via suitable control channels, e.g., a controller area network (CAN) or serial bus, including for instance any required transfer conductors, whether hard-wired or wireless, sufficient for transmitting and receiving the necessary electrical control signals for proper power flow control and coordination aboard the vehicle20.

With reference toFIGS. 1 and 2, the engine26includes a first camshaft assembly84A and a second camshaft assembly84B. Each camshaft assembly84A,84B includes a camshaft86and a plurality of lobe sets88operatively attached to the camshaft86. Each camshaft86is rotatable about a respective cam axis90. The lobe sets88may be slidably attached to the camshaft86for axial movement along the camshaft86, and for rotation with the camshaft86about the cam axis90.

For a four-cylinder engine26, each camshaft assembly84A,84B includes two types of lobe sets88, i.e., a first lobe set88A and a second lobe set88B. The first lobe set88A corresponds to the first set of cylinders32A and the second lobe set88B corresponds to the second set of cylinders32B. A pair of the first lobe sets88A corresponds to the pair of the first set of cylinders32A and a pair of the second lobe sets88B corresponds to the pair of the second set of cylinders32B. As such, for each camshaft assembly84A,84B, each one of the first and second type lobe sets88A,88B corresponds to a respective one of the four cylinders32. It should be appreciated, however, there may be more or less lobe sets88A,88B, so as to correspond to a respective number of cylinders32in the engine26.

Referring specifically toFIG. 2, each lobe set88A,88B includes a plurality of lobes. The plurality of lobes of the first lobe set88A includes a first lobe88A-1, a second lobe88A-2, and a third lobe88A-3. Likewise, the plurality of lobes of the second lobe set88B includes only a first lobe88B-1and a second lobe88B-2. Each of the first, second, and third lobes88A-1,88A-2,88A-3defines a different profile from one another, which is perpendicular to the cam axis90. Similarly, each of the first and second lobes88B-1,88B-2defines a different profile from one another. The respective lobes88A-1,88A-2,88A-3of the first lobe set88A and the respective lobes88B-1,88B-2of the second lobe set88B are arranged in series along the cam axis90. Referring toFIGS. 1 and 2, the first lobe sets88A may be arranged adjacent one another on the cam axis90such that the first lobe sets88A are sandwiched between the second lobe sets88B. Alternatively, the second lobe sets88B are arranged adjacent one another on the cam axis90such that the second lobe sets88B are sandwiched between the first lobe sets88A. Further, it should be appreciated that the profile of the first lobes88A-1,88B-1of the types of the lobe sets88A,88B may be identical to one another and the profile of the second lobes88A-2,88B-2of the types of lobe sets88A,88B may be identical to one another.

The intake valves are configured to selectively move to an open position, in response to actuation by one of the lobes88A-1,88A-2,88B-1,88B-2of a respective lobe set88A,88B, and thereby allow air into the respective cylinder32. Likewise, the exhaust valve stem is configured to selectively move to an open position, in response to actuation by one of the lobes88A-1,88A-2,88B-1,88B-2of a respective lobe set88A,88B, and thereby exhaust gasses from the cylinder32.

For the first lobe set88A and the second lobe set88B, the profile of each of each first lobe88A-1,88B-1is configured to provide a maximum lift and the profile of each second lobe88A-2,88B-2is configured to provide a minimum lift. For the first lobe set88A, the profile of each third lobe88A-3is configured to provide zero lift.

Each lobe set88A,88B is movable along the respective cam axis90, relative to the camshaft86, between a number of positions corresponding to the number of lobes in the respective lobe set88A,88B. Therefore, the first lobe set88A is configured to move along the cam axis90between a first position92A, a second position92B, and a third position92C. The first position92A corresponds to the selection of the first lobe88A-1, the second position92B corresponds to the selection of the second lobe88A-2, and the third position92C corresponds to the selection of the third lobe88A-3. Likewise, the second lobe set88B is configured to move along the cam axis90between only the first position92A and the second position92B. Similarly, the first position92A corresponds to the selection of the first lobe88B-1and the second position92B corresponds to the selection of the second lobe88B-2.

The engine26includes a cam mechanism112, in operative communication with the controller82. The cam mechanism112is configured to selectively move one or more lobe sets88A,88B along the cam axis90, into a required position92A,92B,92C. The lobe sets88A,88B are configured to be axially slid relative to the camshaft86between the three positions92A,92B,92C and two positions92A,92B, respectively. Movement of the lobe sets88A,88B, relative to the camshaft86, allows each lobe set88A,88B to be positioned relative to the respective valve stem. By changing the axial positions of one or more of the sets of lobes, relative to the camshaft, a lift for each valve stem may be altered, as a function of the selected lobes88A-1,88.

Each lobe88A-1,88A-2,88A-3,88B-1,88B-2for the first and second lobe sets88A,88B is configured to provide valve timing by opening the respective valve at the proper time, while giving the valve proper lift, by keeping the valve open for a sufficient amount of time, and by allowing the valve to close at the proper time. Referring toFIGS. 3 and 4, the profile for each lobe88A-1,88A-2,88A-3,88B-1,88B-2dictates the valve timing. The profile for each lobe88A-1,88A-2,88A-3,88B-1,88B-2has a base circle96having a base radius R1. With reference toFIG. 3, the center C1of the base circle96is operatively disposed on the cam axis90. In order to create the required lift during rotation of the first lobe88A-1,88A-2or second lobe88B-1,88B-2about the cam axis90, a ramp100extends from the base circle96, to a peak104. Since the third lobe88A-3(shown inFIG. 4) does not provide any lift, the third lobe88A-3only includes the base circle96.

Referring again to the first lobe88A-1,88A-2and second lobe88B-1,88B-2(shown inFIG. 3), a peak distance D1is defined between the peak104and the center C1of the base circle96. Referring toFIGS. 5 and 6, a follower or poppet106is operatively disposed between the respective first and second lobe set88A,88B and a valve stem108, as known to those in the art. As each first lobe88A-1,88A-2or second lobe88B-1,88B-2rotates about the cam axis90, the respective lobe88A-1,88A-2,88B-1,88B-2converts rotation into a linear or vertical motion by using the follower106to lift an associated valve stem. The lift is a function of a lift distance D2, as illustrated inFIG. 3, which is defined as the distance beyond the base radius R1of the circle, i.e., a difference between the peak distance D1and the base radius R1. The lift of the respective valve stem eventually rises to its peak, i.e., a highest point beyond the base radius R1for the circle. Therefore, the difference between the peak distance D1and the base radius R1of each first lobe88A-1,88A-2and second lobe88B-1,88B-2is the lift component of the first and second lobes88A-1,88A-2,88B-1,88B-2. The lift is created as the follower106, which is in contact with the circumference of the lobe88A-1,88A-2,88B-1,88B-2, gradually moves from the base circle96, i.e., base radius R1, to the peak104, i.e., the peak distance D1.

With reference toFIGS. 5 and 6, for each lobe set88A,88B, the peak distance D1of the first lobes88A-1,88B-1is greater than the peak distance D1of the second lobes88A-2,88B-2. As such, the first lobes88A-1,88B-1are configured to generate more lift than the second lobes88A-2,88B-2. Further, since the third lobe88A-3has only the base circle96with the base radius R1, zero lift is generated.

Referring toFIG. 1, in combination withFIGS. 5 and 6, the controller82is configured to receive input (arrow S110) from a plurality of sensors110and then determine a required position of one or more of the lobe sets, i.e., the first position92A, the second position92B, and/or the third position92C, along the cam axis90. The required position(s)92A,92B,92C of each of the lobe sets88A,88B is output as a signal (arrow S112) to the respective cam mechanism112. The cam mechanisms112may be a slide cam mechanism and the like. Each cam mechanism112is operatively attached to the respective lobe set88A,88B to individually slide the desired lobe set(s)88A,88B along the camshaft86, to a required position.

During engine26operation, the controller82determines vehicle20and engine26parameters including, but not limited to, a vehicle speed, an engine load, a throttle position, exhaust temperature, and the like. The controller82may determine the required position(s) of each lobe set88A,88B, as a function of the vehicle20and engine26parameters. In one embodiment, the controller82may determine that the vehicle speed and engine load are such that only the second set of cylinders32B are required for operation of the engine26. As a result, the controller82may send a signal (arrow S112) to the cam mechanisms112to move the first lobe sets88A to the third position92C, as illustrated inFIG. 5. When the first lobe set88A is in the third position92C, zero lift is provided to the associated poppet valve106, resulting in the first set of cylinders32A being deactivated. As a result of the deactivation of the first set of cylinders32A, fuel may be saved and fuel economy of the vehicle20may be improved.

The controller82may further determine that when the first lobe set88A is required to be in the third position92C, the second lobe sets88B are required to be in either the first position92A or the second position92B, as illustrated inFIG. 6. More specifically, the controller82may determine that each of the second lobe sets88B are required to be in the second position92B, to provide minimum lift, when the vehicle speed and engine load are no greater than a minimum load threshold. Therefore, the controller82may send a signal (arrow S112) to the cam mechanisms112to move the second lobe sets88B to the second position92B. This configuration of the lobe sets88A,88B thus provides a maximum fuel economy for the vehicle.

However, the controller82may determine that when the first lobe set88A is required to be in the third position92C, the second lobe sets88B are required to be in the first position92A, to provide maximum lift, when the vehicle speed and engine load are greater than the minimum load threshold and less than a maximum load threshold. As such, the controller82may also send a signal (arrow S112) to the cam mechanisms112to move the second lobe sets88B to the first position92A.

Additionally, the controller82may determine that, based on the vehicle20and engine26parameters, the required position of each of the first and second lobe sets88A,88B is the first position92A. This configuration is required when the controller82determines a wide-open throttle (WOT) position is required to maximize engine torque. As a result, the controller82may send a signal (arrow S112) to the cam mechanisms112to move the first lobe sets88A and second lobe sets88B to the first position92A.

Further, the use of lobe sets88A having three lobes88A-1,88A-2,88A-3allow the use of a high-lift configuration (i.e., the first lobes88A-1are in the first position92A) and low-lift configuration (i.e., the second lobes88A-2are in the second position92B) for an improved torque and transient response, and also providing a zero lift option to deactivate the first set of cylinders32A for improved fuel economy, all while using only a single scroll turbocharger52. It should be appreciated that the engine26is not limited to having only two cylinders32A deactivated, as more cylinders may be deactivated, as desired. Further, this configuration provides for an optimized peak torque for the single scroll turbo, i.e., the configuration reduces a low-end compromise of a single valve event. Further, by providing the three lobes88A-1,88A-2,88A-3on both camshaft assemblies84A,84B, inlet and exhaust valvetrain designs may be commonized.