Patent Description:
Traditional cylinder barrels, e.g., for piston pumps, are made of tungsten carbide, which provides excellent wear resistance in a fuel pump application. However, tungsten carbide cylinder barrels are also very dense and heavy, which can be a draw back in certain applications where the weight of the components must be carefully considered. A prior art barrel is shown in <CIT>.

There remains a need for a highly wear resistant material which is lighter and/or less dense than traditional materials. This disclosure provides a solution for this need.

In accordance with at least one aspect of this disclosure, a system comprises, a cylinder barrel configured to rotate within a pump housing. In embodiments, the cylinder barrel includes a main cylindrical body, a center recess defined within the main cylindrical body configured to seat a drive shaft therein, and a plurality of bores defined in the main cylindrical body, extending in an axial direction, wherein the plurality of bores are spaced apart circumferentially relative to one another about the main cylindrical body radially outward of the center recess. Each of the plurality of bores are configured to seat a respective piston therein and allow fluid flow therethrough. In embodiments, the main cylindrical body is of silicon nitride.

In embodiments, the system can further include the pump, including each respective piston seated within the respective bore of the plurality of bores. In embodiments, each respective piston further includes a ring disposed at an end thereof configured to form a hydrodynamic seal with an inner surface of the respective bore. In certain embodiments, the ring can be of tool steel. In certain embodiments, a friction coefficient between the ring and the inner surface of the respective bore can be about <NUM>.

In embodiments, the pump can be or can include a piston pump. In certain embodiments, the piston pump can be or can include a bent axis variable displacement piston pump. In certain embodiments, the plurality of bores can include at least <NUM> bores. In certain embodiments, the plurality of bores can include up to <NUM> bores.

In accordance with at least one aspect of this disclosure, a method includes forming a silicon nitride cylinder barrel of a piston pump, and installing the cylinder barrel into the piston pump. In embodiments, forming the silicon nitride cylinder barrel can further include, forming a main cylindrical body, forming a center recess configured to seat a drive shaft therein, forming a plurality of bores each extending in an axial direction through the main cylindrical body, the plurality of bores forming a pattern disposed circumferentially about the main cylindrical body radially outward of the center recess, configured to seat a respective piston therein and allow fluid flow therethrough.

The method can further include, operating the piston pump. In embodiments, during operation of the piston pump, the plurality of bores can be configured to remain substantially the same diameter throughout the life of the cylinder barrel.

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, an illustrative view of an embodiment of a system in accordance with the disclosure is shown in <FIG> and is designated generally by reference character <NUM>. Other embodiments and/or aspects of this disclosure are shown in <FIG>.

In accordance with at least one aspect of this disclosure, e.g., as shown in <FIG>, a system <NUM> can include a pump <NUM>. In embodiments, the pump <NUM> can be or include a piston pump, and in certain embodiments, the pump can be or include a bent axis variable displacement piston pump (e.g., shown in <FIG>). The pump <NUM> can include, at least, a pump housing <NUM>, a drive shaft <NUM>, a cylinder barrel <NUM>, and a plurality of pistons <NUM>. The cylinder barrel <NUM> can be operatively connected to the drive shaft <NUM> to rotate within the pump housing <NUM>.

With reference now to <FIG>, in embodiments, the cylinder barrel <NUM> can include a main cylindrical body <NUM> defining a barrel axis. In certain embodiments, the main cylindrical body can be formed monolithically. A center recess <NUM> can be defined within the main cylindrical body <NUM> configured to seat the drive shaft <NUM> therein, along the barrel axis A. A plurality of bores <NUM> can be defined in the main cylindrical body <NUM>, extending in an axial direction through the main cylindrical body <NUM> (e.g., in a direction parallel to the barrel axis A). As shown, the plurality of bores <NUM> can be spaced apart circumferentially relative to one another about the main cylindrical body <NUM>, and radially outward of the center recess <NUM>. Each of the plurality of bores <NUM> can be configured to seat a respective piston therein (e.g., piston <NUM>) and allow fluid flow therethrough. During operation of the pump <NUM>, the respective pistons <NUM> translate axially along the barrel axis A within the respective bores <NUM> to selectively change an amount of flow through the respective bore <NUM>, and ultimately the total displacement through the pump <NUM>. In certain embodiments, the plurality of bores <NUM> can include at least <NUM> bores, for example, and up to <NUM> bores. An embodiment of the cylinder barrel <NUM> having <NUM> bores <NUM> is shown. Any suitable number of bores <NUM> is contemplated herein.

In embodiments, each respective piston <NUM> further includes a piston ring <NUM> disposed at an end <NUM> thereof (or integrally formed thereon at an end <NUM> thereof) configured to form a hydrodynamic seal with an inner surface <NUM> of the respective bore <NUM>. In certain embodiments, the piston <NUM> can be of tool steel and the piston ring <NUM> can be of tool steel. In certain embodiments, only the piston ring <NUM> is of tool steel. According to the invention, the main cylindrical body <NUM> is entirely of silicon nitride. A friction coefficient between the piston ring <NUM> and the inner surface <NUM> of the respective bore <NUM> can be about <NUM> when hydrodynamically lubricated. The selection of materials for the main cylindrical body <NUM> and the piston rings <NUM> (e.g., lubricated silicon nitride and tool steel, respectively) can allow for about <NUM>% reduction in friction coefficient, as compared to a lubricated tool steel piston ring and a tungsten carbide cylindrical body (friction coefficient of <NUM>), for example. As tungsten carbide parts wear, tool steel piston ring and tungsten carbide cylindrical body interfaces can become poorly lubricated and increase in friction coefficient towards unlubricated values of <NUM>. Although the wear life of silicon nitride on tool steel has been shown to be an order of magnitude higher than tungsten carbide-tool steel interfaces, as wear occurs between silicon nitride cylindrical barrels and tool steel piston rings, the friction coefficient will tend towards an unlubricated value of about <NUM> (about a <NUM>% decrease compared to the unlubricated tungsten carbide-tool steel value of about <NUM>).

In accordance with at least one aspect of this disclosure, a method can include forming a silicon nitride cylinder barrel (e.g., cylinder barrel <NUM>) of a piston pump (e.g., pump <NUM>), and installing the cylinder barrel into the piston pump. In embodiments, forming the silicon nitride cylinder barrel can further include, forming a main cylindrical body (e.g., body <NUM>), forming a center recess (e.g., recess <NUM>) configured to seat a drive shaft therein, forming a plurality of bores (e.g., bores <NUM>) each extending in an axial direction through the main cylindrical body, the plurality of bores forming a pattern disposed circumferentially about the main cylindrical body radially outward of the center recess, configured to seat a respective piston (e.g., piston <NUM>) therein and allow fluid flow therethrough.

The method can further include, operating the piston pump. In embodiments, during operation of the piston pump, the plurality of bores can be configured to remain substantially the same diameter throughout the life of the cylinder barrel, i.e. the bore should remain substantially the same size due to the silicon nitrides natural resistance to wear in high friction applications.

Embodiments provide for a lower density main cylindrical body, which can reduce the overall weight of the pump. The silicon nitride cylindrical body is configured to withstand the load demands of the pump. Embodiments having a silicon nitride cylinder barrel are naturally more lubricious based on material and wear properties silicon nitride derives from its crystal structure. In combination with its lubricity, engineered versions of silicon nitride can have high strength and high toughness to survive service conditions and also reduce part degradation which provides slower wearing cylinder barrels which are rotated or rubbed against mated surfaces. This can increase the total number service hours of the cylinder barrel and even the pump as a whole.

Claim 1:
A system, comprising:
a cylinder barrel (<NUM>) configured to rotate within a pump housing (<NUM>), the cylinder barrel (<NUM>) including:
a main cylindrical body (<NUM>);
a center recess (<NUM>) defined within the main cylindrical body (<NUM>) configured to seat a drive shaft (<NUM>) therein; and
a plurality of bores (<NUM>) defined in the main cylindrical body (<NUM>), extending in an axial direction, wherein the plurality of bores (<NUM>) are spaced apart circumferentially relative to one another about the main cylindrical body (<NUM>) radially outward of the center recess (<NUM>), and wherein the plurality of bores (<NUM>) are each configured to seat a respective piston (<NUM>) therein and allow fluid flow therethrough,
characterized in that
the main cylindrical body (<NUM>) is of silicon nitride.