Patent Description:
Gear manufacturers utilize various machining processes and corresponding tools to produce gears. Exemplary processes can include hobbing, shaping, milling, shear cutting and grinding. The process selected by the gear manufacturer can depend on the type of gear being machined and the tolerances within which the gear is produced. Other considerations in selecting the method can include the size of the gear, the configuration of internal sections or flanges, the quantity of gears to be produced, and gear-to-pinion ratio and costs.

Gear teeth adjacent to other part features are currently limited to production methods such as shaping or rack rolling. For internal gear teeth, shaping or broaching are the traditional manufacturing methods, but each process is limited to the part type. In other words, broaching must have a completely un-obstructed part layout so the tool can pass completely through the part. Gear shaping allows teeth to be cut against an interfering surface, but is inherently slow in terms of machine cycle and flexibility.

Gear skiving is a recent development in gear manufacturing that reduces traditional gear shaping cycle times by up to <NUM>%. While extremely fast, traditional skiving is limited to cutter clearances and part configurations.

In <CIT> there is dsclosed a coolant delivery assembly as it is defined in the preamble of claim <NUM>. <CIT> further dscloses a method of forming a gear using a gear cutter tool and a coolant delivery assembly having a a retaining cooling nut that retains the gear cutter tool relative to a tool holder, which method comprises coupling the gear cutter tool relative to the tool holder with the retaining cooling nut, the gear cutter tool having a cutting face; advancing the gear cutter tool into engagement with the gear while rotating the gear cutter tool around an axis of rotation; and delivering coolant through at least one coolant passage defined in the retaining cooling nut wherein the coolant flows through the at least one coolant passage and out a coolant outlet in a direction toward the cutting face such that coolant is sprayed directly onto the cutting face.

The present invention is a coolant delivery assembly as it is defined in claim <NUM> and a method of forming a gear as it is defined in claim <NUM>. The coolant delivery assembly is configured for use with a gear cutter tool that cuts gear teeth into a workpiece to form a gear and includes a retaining cooling nut that will retain the gear cutter tool relative to a tool holder, a tool holder and a coupling member. The retaining cooling nut has a nut body that defines a plurality of coolant flow passages therein. The tool holder will support the gear cutter tool. The coupling member couples the retaining cooling nut to the mount. The retaining cooling nut is configured to receive coolant and deliver the coolant through the plurality of coolant flow passages and direct the coolant toward the gear cutter tool.

The nut body further comprises an engaging end that is configured to engage the gear cutter tool and an opposite end. The plurality of coolant flow passages each define a linear portion and an arcuate portion. The linear portions communicate coolant from the engaging end toward the opposite end.

An exemplary involute gear cutter system (hereinafter "system") includes a computer numerically controlled (CNC) lathe and modified tooth proportion gear cutter (hereinafter "cutter") configured to cut a gear in a blank orientation to remove shavings from the gear in multiple passes so as to produce a precision gear in its final orientation. The CNC lathe includes a chuck and an active sub-spindle, i.e. controlled rotating motion through CNC controls. The cutter can be mounted on the spindle, and the gear in the blank configuration may be attached to the chuck. More specifically, the cutter can have a plurality of cutting teeth, and each one of the cutting teeth can have a pair of cutting edges configured to cut the gear in the blank orientation to provide the gear in the final orientation.

In the final orientation, the gear has an involute tooth profile including a plurality of cut teeth and a plurality of valleys therebetween. The cutting edges may be configured to cut the gear in the blank orientation, such that the gear in the final orientation includes an active profile section and an operating pitch diameter that are spaced apart from one another. Thus, the cutter can apply a generally constant force in a single or unilateral direction along the surface of the gear to increase the accuracy of machining the gear within, for example, a <NUM> inch tolerance, without requiring special cutting tools or cutting systems.

Referring to <FIG>, an exemplary prior art system <NUM> includes a computer numerically controlled (CNC) lathe <NUM> having in part a chuck <NUM> and a spindle <NUM>. The system <NUM> further includes a cutter <NUM> that is attached to the spindle <NUM>, which is in turn configured to rotate the cutter <NUM> about a cutting axis <NUM> so as to cut a gear <NUM> in a blank orientation (<FIG>) and produce the gear <NUM> in the final orientation (<FIG>). The cutter <NUM> in this form is an external gear configured to cut an internal gear <NUM> in a blank orientation to produce the internal gear <NUM> in the final orientation. The internal gear <NUM> in the final orientation has a plurality of cut teeth <NUM>. The teeth <NUM> have an involute tooth profile <NUM> including an active profile section <NUM>, which is a portion of each tooth surface configured to contact the opposing teeth of a meshed gear.

The gear <NUM> in the blank orientation is mounted to the chuck <NUM>, which is configured to rotate the gear <NUM> about a cut axis <NUM> (<FIG>), such that the cut axis <NUM> and the cutting axis <NUM> are spaced apart from one another by a center distance CDw. In addition, the cut axis <NUM> and the cutting axis <NUM> are disposed at a cross-axis angle α with respect to one another when the gear <NUM> is in the final orientation. As used herein, the term "cross-axis" is an angle that defines the difference between the two rotational axes of the gear workpiece and the cutting tool.

The system <NUM> can further include a flushing device <NUM> configured to deliver a fluid to the gear <NUM> to remove shavings, chips or dust from the gear <NUM> when the spindle <NUM> rotates the cutter <NUM> to cut the gear <NUM> in multiple passes. The fluid can also remove heat from the system <NUM>. In one example, the flushing device <NUM> is a fluid line <NUM> communicating with a reservoir <NUM> to supply water, nitrogen gas or another fluid to the external gear <NUM>. In the final orientation, the gear <NUM> has an involute tooth profile including a plurality of cut teeth <NUM> and a plurality of valleys therebetween. The involute tooth profile <NUM> includes the active profile section <NUM>, and the operating pitch diameter is spaced apart from the same when the gear <NUM> is in its final orientation. Additional description of a prior art skiving tool may be found in commonly owned <CIT> the contents of which are expressly incorporated herein by reference.

The present disclosure allows the skiving of gear teeth previously not possible with current methods due to its ability to cut against interfering part geometries and can eliminate certain cutter/workpiece interferences. For particular gear components such as Heavy Duty Transmission mainshaft gears, the internal clutch teeth design in combination with the integral thrust washer provides a compact product design. In order to manufacture the clutch teeth, gear shaping is the only current method of production possible. As machine technology advances, the gear shaping machine has now become the constraint machine within production cells and manufacturing output is limited by the shaping process. Gear skiving can remove this constraint machine within the cell layout and reduce gear machining cycle times by approximately <NUM>% for mainshaft gears. The present disclosure facilitates improvements in part geometry and cutter tool life which can allow gear skiving in a production environment feasible.

During the gear skiving, the evacuation of chips is critical for the skiving process to be successful. Without successful chip evacuation, excessive tool wear, and even tool failure can occur very rapidly. For example, in one prior art skiving method, chips can be generated at a rate of <NUM> chips per second. Any stray chips that get reintroduced into the cutting zone can cause cutting edge damage on the tool or if severe enough can cause a catastrophic tool failure. The present disclosure provides an assembly and chip evacuation method that provides improved chip evacuation during the skiving process.

With reference now to <FIG>, <FIG>, <FIG> and <FIG>, a gear cutter constructed in accordance to one prior art example is shown and generally identified at reference <NUM>. The gear cutter <NUM> includes a plurality of teeth <NUM>. Each tooth <NUM> defines a helix angle <NUM>. The helix angle <NUM> is defined as an angle formed between a centerline or cut axis <NUM> of the gear cutter <NUM> and a line <NUM> transverse to a tooth face <NUM>. The tooth face <NUM> has a tooth face angle <NUM> relative to the workpiece <NUM> (<FIG> and <FIG>). The tooth face angle <NUM> is perpendicular to the helix angle <NUM>. The tooth face angle <NUM> slopes downward and to the right as viewed from the cut axis <NUM> of the gear cutter <NUM>. In some examples, the configuration of the gear cutter <NUM> can experience localized or accelerated tool wear indicated generally at reference <NUM>, <FIG>. As shown in <FIG>, the tooth face angle <NUM> is parallel to a workpiece <NUM>. The workpiece <NUM> is cut at the location shown by the arrow by the teeth <NUM>. During cutting, both the gear cutter <NUM> and the workpiece <NUM> are rotating, but at different revolutions per minute (RPM).

With reference to <FIG> and <FIG>, a gear cutter constructed in accordance to one example of the present disclosure is shown and generally identified at reference <NUM>. The gear cutter <NUM> includes a plurality of teeth <NUM>. Each tooth <NUM> defines a tooth face <NUM> and a tooth face angle <NUM> relative to the workpiece <NUM> (<FIG>). The tooth face angle <NUM> is an angle defined between the tooth face <NUM> and a face of the workpiece <NUM>. The tooth face angle <NUM> is sloped downward and to the left relative to a rotational axis <NUM> of the cutting tool <NUM>. Explained further, the tooth face angle <NUM> is sloped in an opposite direction as compared to the tooth face angle <NUM>. In this regard, the tooth face angle <NUM> defines a cut angle <NUM> that is not parallel to the workpiece <NUM> during cutting. The grind of the gear cutter <NUM> is angled differently as compared to the gear cutter <NUM>. More cutting occurs by providing a cut angle <NUM> as compared to the parallel relationship of the face angle <NUM> and workpiece <NUM> shown in <FIG>.

The workpiece <NUM> is cut at arrow called <NUM> (internal spline of workpiece <FIG>) by the teeth <NUM>. During cutting, both the gear cutter <NUM> and the workpiece <NUM> are rotating, but at different RPM. In one example, the workpiece <NUM> can be tilted while the cutting tool <NUM> is advanced linearly along the tool feed direction <NUM> toward the workpiece <NUM>. In the example shown twenty-two teeth <NUM> are provided on the gear cutter <NUM>. In this regard, with each full rotation of the gear cutter <NUM>, twenty-two slivers of workpiece material are sequentially cut away from the workpiece <NUM>. As shown in <FIG>, a cutter cross-axis <NUM> is defined between a first rotational axis <NUM> of the workpiece <NUM> and a second rotational axis <NUM> of the cutting tool <NUM>.

Additional advantages of the instant gear cutter <NUM> and related system for cutting the internal gear teeth or splines of a gear are realized by the instant disclosure. For example, the cutting action can be at a more aggressive angle without requiring the workpiece to be tilted more. The amount of time necessary for the gear cutter to operate in a negative rake angle condition is reduced. As a result, tool life is improved and costs are reduced. The geometry of the gear cutter <NUM> balances the active lengths of both gear flanks. This creates a more useable tooth length for more compact product designs. The gear cutter <NUM> is able to generate gear teeth closer to blind shoulders. This shortens the overall width of gear teeth which yields an increase in power-density for a geartrain system, or more power transferred per volume of the system.

Turning now to <FIG>, <FIG> and <FIG>, a coolant delivery assembly constructed in accordance to one example of the present disclosure is shown and generally identified at reference numeral <NUM>. The coolant delivery assembly <NUM> generally includes a retaining cooling nut <NUM>, a tool holder or mount <NUM>, a plenum <NUM>, and a coupling member <NUM> that couples the retaining cooling nut <NUM> to the mount <NUM>. In the example shown in <FIG>, the retaining cooling nut <NUM> secures a cutting tool <NUM> generally to the mount <NUM> during cutting of a workpiece <NUM>. The coupling member <NUM> can be a threaded shaft that threadably mates with a threaded bore <NUM> defined through the retaining cooling nut <NUM>. The cutting tool <NUM> can be any cutting tool such as the gear cutters <NUM>, <NUM>, <NUM> disclosed herein, or other cutting tool.

With particular reference to <FIG>, additional features of the coolant delivery assembly <NUM> will now be described. The retaining cooling nut <NUM> has a nut body <NUM> that defines a plurality of coolant flow passages <NUM> defined therein. Each of the coolant flow passages <NUM> define a coolant inlet and a coolant outlet <NUM> and <NUM>, respectively. As will become appreciated herein, coolant <NUM> is directed from a coolant source <NUM>, through the tool holder <NUM>, through the plenum <NUM>, and into the coolant inlets <NUM>, through the coolant flow passages <NUM> and directed out of the retaining cooling nut <NUM> from the coolant outlets <NUM>.

The plenum <NUM> can provide circumferential coolant communication between the tool holder <NUM> and an engaging end <NUM> of the retaining cooling nut <NUM>. The plenum <NUM> can provide a chamber that facilitates full <NUM> degree coolant supply to the retaining cooling nut <NUM>. In some examples, the coolant <NUM> can be configured to flow through the mount <NUM> from the coolant source <NUM> to the retaining cooling nut <NUM>. Other configurations are contemplated for providing coolant to the cooling retaining nut <NUM>.

With particular reference to <FIG>, each of the coolant flow passages <NUM> define a linear portion <NUM> and an arcuate portion <NUM>. The linear portions <NUM> communicate the coolant <NUM> from the engaging end <NUM> of the retaining cooling nut <NUM> toward an opposite end <NUM> of the retaining cooling nut <NUM>. The arcuate portions <NUM> generally route the coolant <NUM> from the linear portions <NUM> in a direction toward the cutting tool <NUM>. The coolant flow passages <NUM> are configured to direct streams of coolant <NUM> onto a face <NUM> of the cutting tool <NUM>. <FIG> show the retaining cooling nut <NUM> and cutting tool <NUM> together.

The delivery of coolant directly to the cutting edge or face <NUM> yields a profound improvement of chip evacuation over conventional arrangements. The coolant delivery assembly <NUM> virtually eliminated a significant issue of chip re-cutting during the machining process. Chip re-cutting occurs when a fragment of metal (cutting chip) does not exit the cutting zone and gets pulled into the cutting zone a second time. This creates extreme tool pressure and can fracture the edge of the tooth resulting in a catastrophic failure of the tool. The coolant delivery assembly <NUM> that utilizes the retaining cooling nut <NUM> to both deliver coolant and secure the cutting tool creates a more compact design. This facilitates machining into tight workpiece clearances which leads to a more compact component design.

With reference to <FIG>, a coolant delivery assembly <NUM> constructed in accordance to one prior art example is shown. The coolant delivery assembly <NUM> generally includes a deflector <NUM> that is configured to deflect coolant sprayed generally upward back toward the cutting tool <NUM>. The coolant delivery assembly <NUM> can be inefficient at directing the coolant flow. Cycle time and tool life of the coolant deliver assembly <NUM> are not cost effective. In particular, the re-cutting of chips slows down the machining process to make sure all the chips were evacuated. Cycle time using the coolant delivery assembly <NUM> is reduced by around <NUM>% and tool wear is stabilized at around <NUM>% of a typical wear value compared to conventional systems such as shown in <FIG>.

Claim 1:
A coolant delivery assembly (<NUM>) configured for use with a gear cutter tool (<NUM>, <NUM>, <NUM>, <NUM>) that cuts gear teeth into a workpiece (<NUM>) to form a gear, the coolant deliver assembly comprising:
a retaining cooling nut (<NUM>) that can retain the gear cutter tool relative to a tool holder, wherein the retaining cooling nut is configured to receive coolant (<NUM>) and deliver the coolant through the plurality of coolant flow passages and direct the coolant toward the gear cutter tool;
a tool holder (<NUM>) that can support the gear cutter tool; and
a coupling member (<NUM>) that couples the retaining cooling nut to the tool holder (<NUM>);
characterized in that the retaining cooling nut (<NUM>) has a nut body (<NUM>) that defines a plurality of coolant flow passages (<NUM>) therein, wherein the nut body further comprises an engaging end (<NUM>) that is configured to engage the gear cutter tool and an opposite end (<NUM>), wherein the plurality of coolant flow passages each define a linear portion (<NUM>) and an arcuate portion (<NUM>), wherein the linear portions communicate coolant from the engaging end toward the opposite end.