Engine cast component having witness marks and method of machining same

A component (100) for an internal combustion engine includes a plurality of as-cast features (e.g. 116) formed thereon, and a plurality of machined features (e.g. 120). The component (100) also includes at least one witness mark (128), the witness mark (128) including a cavity (202) surrounded by a first lateral surface (204), a first inclined surface (208), a second inclined surface (210), and a valley surface (212). The at least one witness mark (128) is formed during a casting operation, and is used to locate the component (100) on a fixture (300). The plurality of machined features (120) do not encroach onto an area of the at least one witness mark (128). The first inclined surface (208) and the second inclined surface (210) are at an angle (α) with respect to each other.

FIELD OF THE INVENTION

This invention relates to internal combustion engines, including but not limited to crankcase machining and datum features therefor.

BACKGROUND OF THE INVENTION

Internal combustion engines include crankcases having a plurality of cylinders. The cylinders contain pistons whose reciprocating motion due to combustion events may be transferred through a crankshaft to yield a torque output of the engine. Often, engine crankcases are made of cast metal, and include features that are either formed or machined therein subsequent to the casting thereof.

Known methods for machining crankcases include the casting of machining datums, or, cast features that are used to locate the casting onto a machining device. By proper placement and location of a casting onto a machining device, positional and tolerance dimensions may be accomplished in the creation of various machined features in a crankcase.

Typical machining datums are “nubs”, or protrusions, that are cast into the metal of the crankcase and that fit into openings in a “table” of a machining device. These nubs typically serve no purpose other than to locate the crankcase, and are usually placed onto surfaces that will eventually be machined themselves thus obliterating the nubs. The reason for deletion of the nubs is primarily to reduce the weight of the finished and machined crankcase, and to also improve the shape, appearance, and fit of same in an engine.

One disadvantage of the existing machining datum configuration, or nubs, for cast metal crankcases is that their shape, typically a rectangular shape, does not allow for alignment of a casting for more than two degrees of freedom of motion. Moreover, existing datum configurations that are obliterated in the finished product do not allow for a dimensional check for the quality of each machining operation in the finished product.

Accordingly, there is a need for an improved machining datum design configuration that allows for location for more than two degrees of freedom of the casting for machining, and that allow for a dimensional check for the quality of each machining operation in the finished product.

SUMMARY OF THE INVENTION

A component for an internal combustion engine includes a plurality of as-cast features formed thereon, and a plurality of machined features. The component also includes at least one witness mark, the witness mark including a cavity surrounded by a first lateral surface, a first inclined surface, a second inclined surface, and a valley surface. The at least one witness mark is formed during a casting operation, and is used to locate the component on a fixture. The plurality of machined features do not encroach onto an area of the at least one witness mark. The first inclined surface and the second inclined surface are at an angle with respect to each other.

DESCRIPTION OF A PREFERRED EMBODIMENT

The following describes an apparatus for and method of creating datums, or machining marks, that allow for location for more than two degrees of freedom of the casting for machining, and that allow for a dimensional check for the quality of each machining operation in the finished product, in accordance with the invention. The datums described herein may also be referred to as “witness” marks, because they are not obliterated after the machining process on the crankcase is completed, and may serve as “witnesses” for early machining operations.

An outline view of a crankcase100for an engine is shown inFIG. 1. The crankcase100shown is a crankcase for an eight (8) cylinder engine having a “V” configuration. Two banks102each having four (4) cylinders104are oppositely located on either side of the crankcase100along its entire length. The cylinder banks102are connected to a valley structure106occupying a central portion of the crankcase100. A cylinder head108is shown attached to the crankcase100on one of the cylinder banks102. The cylinder head108may include additional engine components (not shown) such as fuel injectors, intake and exhaust valves, over-head camshafts, and so forth. The crankcase100may also include a number of different integrated passages and/or cavities. For example, a coolant passage110, a turbocharger oil supply passage112, a timing chain cavity116, and others, may be formed in the crankcase100.

A central oil supply passage118may be drilled through an entire length of the valley structure106of the crankcase100. An operation commonly referred to as “gun drilling” may be used to form the passage188by drilling a long opening through a metal body of the crankcase100. The passage118may be used to transfer oil or another fluid from one end of the crankcase100to another. The oil in the passage118may be used for various purposes during operation of an engine, for example, for lubrication of various engine components, for actuation of fuel injectors, for lubrication and/or actuation of an overhead cam structure, and others. Typically, oil from the passage118may be distributed to other passages.

The crankcase100includes various other machined features. For example, a surface120on each of the top of the cylinder banks102, commonly referred to as the “flame deck’ may be the interface between the crankcase100and the cylinder head108. A valley surface122disposed in the valley of the crankcase100may serve as an interface to other engine components, and a rear face124may serve as an interface for attachment on a rear housing (not shown) that may be used to mount a transmission (not shown). The cylinder bores104have lateral cylindrical surfaces126that are machined and are used to house pistons (not shown). All these surfaces, and others, that are formed on the crankcase100require precise positional and tolerance dimensions to be accomplished during various machining operations of the crankcase.

The crankcase100may advantageously include a plurality of witness marks128formed therein. Each of the witness marks128may be located in different areas of the crankcase100and serve as machining datums for machining operations that are performed after the crankcase100has been cast to create many of the features that are required in the crankcase100for interfaces to various components. Machining datums, as is known, are features that help locate reference points to guide machining cutters, drills, and so forth, that form various features on a casting.

A machining operation may use the witness marks128to establish a coordinate system of the crankcase100, that may subsequently be used by a computer controlled machine or machines that will apply cutters, drills, end-mills, and so forth, to remove metal from a casting and form various features therein. This coordinate system that is created is advantageously based on locations of the crankcase100that are more important to the fit, form, and function of a the finished and machined crankcase.

A close-up view of a witness mark128, in cross section, is shown inFIG. 2. The witness mark128may be formed during a casting operation and may include a localized cavity or depression202. The depression202may be surrounded by a first lateral surface204, a first inclined surface208, a second inclined surface210, and a valley surface212. The first inclined surface208may be oriented at an angle, α, with respect to the second inclined surface210to facilitate multi-axial positioning, as described below. The witness mark128is disposed close to an edge214and, thus, does not have a second lateral surface (not shown) surrounding the cavity202, but would have a second lateral surface had the witness mark had been disposed away from the edge214. The second lateral surface would be across from the first lateral surface204around the cavity202.

A detail view during a positioning operation of the crankcase100into a machine300is shown inFIG. 3. The machine300, partially shown, may include a plurality of locators302(only one shown) that are arranged to correspond to one or more witness marks128. Each locator302is arranged to fit within each witness mark128, as shown, to help locate the crankcase100onto the machine300. Each locator302includes a shank portion304, a first beveled surface306, a second beveled surface308, and a tip portion310disposed at a distal end thereof. The crankcase100may move during this operation along a direction312until the witness mark128engages the locator302.

A detail view of the locator302engaged with the witness mark128is shown inFIG. 4. While the locator302is engaged with the witness mark128, the first beveled surface306is planarly aligned and touching the first inclined surface208, the second beveled surface308is planarly aligned with and touching the second inclined surface210, and the tip310advantageously may not touch the valley surface212, thus forming a gap402therebetween.

Each connection between a witness mark128and a locator302is advantageously capable of locating the crankcase100to the machine300with respect to three degrees of freedom. A coordinate system404may be defined having an axis, X, defined to measure the distance between the crankcase100and the machine300, a second axis, Y, to measure the relative positional alignment between the crankcase100and the machine300, and a “moment,” M(z), to measure the relative rotation of the crankcase100to the machine300about an axis, Z, that is perpendicular to each of the axes X and Y. Engagement of the locator302with the witness mark128is capable of restricting and defining the position of the crankcase100on the machine300with respect to axial motion along X and Y, and rotation along M(z).

Restriction of motion along the X and Y axes, and rotation about M(z), is advantageously accomplished by a resistance to motion and rotation between the beveled surfaces306and310and the inclined surfaces208and210that are at the angle α with respect to each other and touching. The angle α may be selected to be any acute angle, and may advantageously be selected to be an included angle of about 90 degrees when constrain according to a perpendicular coordinate system is desired. By use of at least three (3) witness marks that may be oriented at 90 degrees to each other, one can advantageously fully constrain and locate the crankcase100to the machine300.

A flowchart for a method of machining a cast component is shown inFIG. 5. The component may have been formed in a previous casting operation to include witness mark features or openings formed therein. The component may be positioned in the proximity of a machine or fixture at step502. Some or all of the witness marks on the component may be arranged to be adjacent to some or more locators disposed on the machine at step504. The component may be put onto the machine at step506such that each witness mark engages each corresponding locator. Each witness mark may advantageously constrain the component with respect to the machine with respect to three degrees of freedom at step508. The machine may perform various machining operations onto the component, for example, planning, grinding, drilling, polishing, and so forth, at step510. When the machining operations are complete, the component may be optionally repositioned onto the machine using different or the same witness marks that engage different or the same locators at step512.

One embodiment of a complete datum configuration for a crankcase600that is capable of locating an orientation and location of a crank core opening602is shown in the cross-section view ofFIG. 6. The crankcase600has a surface604on the top of a cylinder bank606. A plurality of cylinder bore openings608that make up the cylinder bank606are typically created during a casting operation that forms the crankcase600. The openings or bores608may generally be created when metal flows around a crank core (not shown). It is advantageous to the structure of the crankcase600to ensure proper alignment and centering between the surface604and each of the bores608.

A location of the surface604with respect to the crankcase600may be established through use of a plurality of witness marks610(only one of three shown) as described above. More advantageously, a relationship may be established between a plane that is defined by the surface604and the crank core, or indirectly, each of the bores608, by use of a second plurality of core witness marks612that are formed into the crankcase600by the crank core during the casting operation that forms the crankcase600. Each of the core witness marks612is advantageously located in a valley portion614of the crankcase600, and may be used for positional reference for both banks (only the one bank606shown here).

Each of the core witness marks612may advantageously have a rectangular shape that includes a bottom surface616that should be parallel to a valley surface618of the valley portion614of the crankcase600, and that is at a predetermined distance and angle to the surface604, when the bores608are properly aligned. By locating the surface604on the left bank606, a corresponding surface on the right bank (not shown), and a distance to a line defined by the core witness marks612when taken together, or a point when considered separately, all cast and machined features of the crankcase600, along with core location during casting, may advantageously be accomplished.

A block diagram for a dimensioning scheme for a crankcase700is shown inFIG. 7. The crankcase700may have a set of planes or surfaces A and B defined to coincide with each of the cylinder head interface surfaces. The surfaces A and B may be defined with witness marks as described above. As is known, a distance, D, of the surfaces A and B from a crankshaft centerline, and an angle, θ, between the surfaces A and B, are important for the fit, form, and function of the crankcase700. To facilitate inspection and set-up for machining the crankcase700, a height, d, may be determined based on a height, C, that is established by the core witness marks between the two banks, as described above. Therefore, the witness marks that establish the surfaces A and B, as well as the core witness marks that establish the height C, may advantageously adequately define important dimensional parameters of the crankcase700.