Patent Description:
Fuel systems for modern internal combustion engines typically employ either <NUM>) port fuel injection (PFI) where fuel is injected into an air intake manifold of the internal combustion engine at relatively low pressure (typically below about <NUM> kPa) and subsequently passed to the combustion chamber of the internal combustion engine or <NUM>) gasoline direct injection (GDi) where fuel is injected directly into the combustion chamber of the internal combustion engine at relatively high pressure (typically above about <NUM> MPa). In PFI systems, the fuel is typically pumped from a fuel tank to the internal combustion engine by an electric fuel pump which is located with the fuel tank of the fuel system. However, GDi systems require an additional fuel pump to boost the pressure of the fuel compared to the pressure which can be achieved by the electric fuel pump. In order to elevate the fuel pressure to the magnitude needed for direct injection, it is typical to employ a piston-type high-pressure fuel pump which is driven by a camshaft of the internal combustion engine.

In a typical high-pressure fuel pump, a pump housing defines an inlet, an outlet, a pumping chamber, and a plunger bore which opens into the pumping chamber. A pumping plunger is reciprocated within the plunger bore by a camshaft of the internal combustion engine such that each cycle of the pumping plunger increases and decreases the volume of the pumping chamber. An inlet valve selectively opens when the pumping plunger is moving in a direction which increases the volume of the pumping chamber, i.e. the inlet stroke, thereby allowing low-pressure fuel to enter the pumping chamber. When the pumping plunger is moving in a direction which decreases the volume of the pumping chamber, i.e. the pressure stroke, fuel within the pumping chamber is elevated in pressure as a result of the decreased volume. When the pressure of the fuel within the pumping chamber reaches a predetermined threshold, an outlet valve opens, thereby allowing high-pressure fuel to be discharged from the outlet. An example of such a high-pressure fuel pump is disclosed in <CIT> which is hereinafter referred to as <CIT>shows a high-pressure fuel pump for gasoline direct injection comprising plungers with sealing rings.

In order to allow for efficient operation of a high-pressure fuel pump as described above, it is necessary to minimize leakage between the pumping plunger and the plunger bore. Minimization of leakage between the pumping plunger and the plunger bore is typically dealt with by providing a close clearance between the pumping plunger and the plunger bore. In order to keep leakage at an acceptable level, the clearance is less than <NUM> microns. However, it is important that the clearance between the pumping plunger and the plunger bore not be too small because there is a risk that the pumping plunger could seize within the plunger bore during operation due to heat generated by operation of the high-pressure pump causing the pumping plunger to expand radially outward to a greater extent than the plunger bore expands, due to poor lubrication as a result of insufficient clearance for fuel between the pumping plunger and the plunger bore, and due to side load effects on the pumping plunger. As a result, a clearance of <NUM> microns plus or minus <NUM> micron may be a typical acceptable tolerance in the manufacture of the pumping plunger and the plunger bore. Such a tolerance is costly to implement and may require match honing between the pumping plunger and the plunger bore, thereby adding time and complexity to the manufacturing process. Furthermore, such a tolerance may require that the pump be increased in fuel pumping capacity to accommodate the low efficiency that is experienced, particularly at low-speed operation of the internal combustion engine.

What is needed is a high-pressure fuel pump which minimizes or eliminates one or more of the shortcomings as set forth above.

Briefly described, a high-pressure fuel pump includes a pump housing which defines a pumping chamber, a fuel inlet which allows low-pressure fuel into the pumping chamber, a fuel outlet which allows high-pressure fuel out of the pumping chamber, and a plunger bore which extends along an axis and opens into the pumping chamber. The high-pressure fuel pump also includes a pumping plunger which reciprocates within the plunger bore along the axis such that reciprocation of the pumping plunger within the plunger bore increases and decreases a volume of the pumping chamber. Low-pressure fuel flows from the fuel inlet to the pumping chamber when the volume increases and high-pressure fuel is discharged from the pumping chamber through the fuel outlet when the volume decreases. The pumping plunger is attached to a cam follower which contacts a cam shaft, in use, to drive reciprocating movement of the pumping plunger, and wherein a return spring is compressed axially between the pump housing and the cam follower to maintain the cam follower in contact with the camshaft, in use. The pumping plunger includes a sealing ring groove, therein, for preventing fuel from escaping the pumping chamber between the interface of the pumping plunger and plunger bore, wherein the sealing ring engages said plunger bore in an interference fit, such that said sealing ring is held in radial compression by said pumping plunger and said plunger bore and wherein said sealing ring is held in axial compression within said sealing ring groove. A diametric clearance in the range of <NUM> to <NUM> microns is provided between the pumping plunger and the plunger bore.

In the high-pressure fuel pump the pumping plunger may also include: a second sealing ring groove which may be concentric with plunger bore, the second sealing ring groove including a second sealing ring, which may engage the plunger bore in an interference fit.

In the high-pressure fuel pump the sealing ring groove may be annular.

In the high-pressure fuel pump the sealing ring may be annular.

Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.

This invention will be further described with reference to the accompanying drawings in which:.

In accordance with a preferred embodiment of this invention and referring to <FIG>, a fuel system <NUM> for an internal combustion engine <NUM> is shown. Fuel system <NUM> generally includes a fuel tank <NUM> which holds a volume of fuel to be supplied to internal combustion engine <NUM> for operation thereof; a plurality of high-pressure fuel injectors <NUM> which inject fuel directly into respective combustion chambers (not shown) of internal combustion engine <NUM>; a low-pressure fuel pump <NUM>; and a high-pressure fuel pump <NUM> where the low-pressure fuel pump <NUM> draws fuel from fuel tank <NUM> and elevates the pressure of the fuel for delivery to high-pressure fuel pump <NUM> where the high-pressure fuel pump <NUM> further elevates the pressure of the fuel for delivery to high-pressure fuel injectors <NUM>. By way of non-limiting example only, low-pressure fuel pump <NUM> may elevate the pressure of the fuel to about <NUM> kPa or less and high-pressure fuel pump <NUM> may elevate the pressure of the fuel to above about <NUM> MPa where pressures on the order of <NUM> MPa and above are anticipated. While four high-pressure fuel injectors <NUM> have been illustrated, it should be understood that a lesser or greater number of high-pressure fuel injectors <NUM> may be provided. As shown, low-pressure fuel pump <NUM> may be provided within fuel tank <NUM>, however low-pressure fuel pump <NUM> may alternatively be provided outside of fuel tank <NUM>. Low-pressure fuel pump <NUM> may be an electric fuel pump. A low-pressure fuel supply passage <NUM> provides fluid communication from low-pressure fuel pump <NUM> to high-pressure fuel pump <NUM>. High-pressure fuel pump <NUM> will be described in greater detail in the paragraphs that follow.

High-pressure fuel pump <NUM> includes a pump housing <NUM> which defines a pumping chamber <NUM> and a plunger bore <NUM> which opens into pumping chamber <NUM> such that plunger bore <NUM> extends along an axis <NUM>. Pump housing <NUM> also includes a fuel inlet <NUM> in fluid communication with low-pressure fuel supply passage <NUM> such that fuel inlet <NUM> selectively allows low-pressure fuel from low-pressure fuel pump <NUM> to enter pumping chamber <NUM> as will be described in greater detail later. Pump housing <NUM> also defines a fuel outlet <NUM> which selectively allows high-pressure fuel to exit pumping chamber <NUM> as will be described in greater detail later. While pump housing <NUM> has been illustrated schematically as single-piece construction, it should be understood that pump housing <NUM> may comprise two or more pieces which are joined together to provide the features described herein.

High-pressure fuel pump <NUM> also includes a pumping plunger <NUM> located within plunger bore <NUM> such that pumping plunger <NUM> reciprocates within plunger bore <NUM> along axis <NUM>. Pumping plunger <NUM> is reciprocated within plunger bore <NUM>, by way of non-limiting example only, by a camshaft <NUM> of internal combustion engine <NUM>. Pumping plunger <NUM> is attached to (in contact with) a cam follower <NUM> which follows the profile of camshaft <NUM>. Cam follower <NUM> is axially guided within a cam follower bore <NUM> of pump housing <NUM> such that a return spring <NUM> is compressed axially between pump housing <NUM> and cam follower <NUM> to maintain cam follower <NUM> in contact with camshaft <NUM> as camshaft <NUM> rotates. While cam follower <NUM> has been embodied as being guided within cam follower bore <NUM> of pump housing <NUM>, it should now be understood that cam follower <NUM> may alternatively be guided within a bore of internal combustion engine <NUM> that is not within pump housing <NUM>. When camshaft <NUM>, cam follower <NUM>, and return spring <NUM> cause pumping plunger <NUM> to move downward as viewed in the figures, the volume of pumping chamber <NUM> is increased, thereby resulting in an inlet stroke. Conversely, when camshaft <NUM> and cam follower <NUM> cause pumping plunger <NUM> to move upward as viewed in the figures, the volume of pumping chamber <NUM> is decreased, thereby resulting in a pressure stroke. While not shown, it should be understood that a low-pressure seal may be provided to prevent fuel, that has leaked past the clearance between pumping plunger <NUM> and plunger bore <NUM>, from mixing with oil that lubricates internal combustion engine <NUM>. One arrangement of such a low-pressure seal is illustrated by Nakayama et al. which was previously referenced above.

High-pressure fuel pump <NUM> also includes an inlet valve <NUM> which selectively opens to permit fuel to enter pumping chamber <NUM> from low-pressure fuel supply passage <NUM>. Inlet valve <NUM> may be, by way of non-limiting example only, a solenoid operated valve which is controlled by a controller <NUM>. Controller <NUM> may receive input from a pressure sensor <NUM> which supplies a signal indicative of the pressure of the fuel being supplied to high-pressure fuel injectors <NUM>. As illustrated, a pressure sensor <NUM> may arranged to read the fuel pressure within a high-pressure fuel rail <NUM> which receives high-pressure fuel from fuel outlet <NUM> through a high-pressure fuel supply passage <NUM> such that high-pressure fuel rail <NUM> distributes high-pressure fuel to each of high-pressure fuel injectors <NUM>. However, it should be understood that pressure sensor <NUM> may be positioned at other locations that are indicative of the pressure of the fuel being supplied to high-pressure fuel injectors <NUM>. Controller <NUM> sends signals to inlet valve <NUM> to open and close inlet valve <NUM> as necessary to achieve a desired fuel pressure at pressure sensor <NUM> as may be determined by current and anticipated engine operating demands. When inlet valve <NUM> is opened while pumping plunger <NUM> is moving to increase the volume of pumping chamber <NUM>, i.e. when inlet valve <NUM> is moving downward as viewed in the figures, fuel from low-pressure fuel supply passage <NUM> is allowed to flow into pumping chamber <NUM> through fuel inlet <NUM>.

High-pressure fuel pump <NUM> also includes an outlet valve <NUM> which selectively opens to permit fuel to exit pumping chamber <NUM> to high-pressure fuel supply passage <NUM>. Outlet valve <NUM> may be a spring-biased valve which opens when the pressure differential between pumping chamber <NUM> and high-pressure fuel supply passage <NUM> is greater than a predetermined threshold. Consequently, when camshaft <NUM> and cam follower <NUM> cause pumping plunger <NUM> to decrease the volume of pumping chamber <NUM>, the fuel within pumping chamber <NUM> is pressurized. Furthermore, when the pressure within pumping chamber <NUM> is sufficiently high, outlet valve <NUM> is urged open by the fuel pressure, thereby causing pressurized fuel to be supplied to high-pressure fuel injectors <NUM> through fuel outlet <NUM>, high-pressure fuel supply passage <NUM>, and high-pressure fuel rail <NUM>.

Reference will now be made to <FIG> which shows an enlarged portion of <FIG>, more particularly, an enlarged portion showing portions of pump housing <NUM> and pumping plunger <NUM>. In order to improve efficiency, particularly at low rotational speeds of camshaft <NUM> caused by low operating speeds of internal combustion engine <NUM>, and to permit greater annular clearance between pumping plunger <NUM> and plunger bore <NUM>, pumping plunger <NUM>, which is cylindrical, is provided with a sealing ring groove <NUM> within which is located a sealing ring <NUM>. Sealing ring groove <NUM> is annular in shape and concentric with pumping plunger <NUM> and plunger bore <NUM> such that sealing ring groove <NUM> extends radially inward from the outer periphery of pumping plunger <NUM>. Sealing ring <NUM> is preferably made of PTFE (polytetrafluoroethylene) due to low friction and fuel resistant properties, however, other materials may be substituted. During installation, sealing ring <NUM> is elastically stretched over pumping plunger <NUM> and slid on the outer periphery of pumping plunger <NUM> until sealing ring <NUM> is aligned with sealing ring groove <NUM>. After sealing ring <NUM> is aligned with sealing ring groove <NUM>, sealing ring <NUM> retracts into sealing ring groove <NUM>. Sealing ring <NUM> is sized to engage plunger bore <NUM> in an interference fit. Since sealing ring <NUM> engages plunger bore <NUM> in an interference fit, the diametric clearance between pumping plunger <NUM> and plunger bore <NUM> can be greater than <NUM> microns, thereby eliminating the need to match hone pumping plunger <NUM> and plunger bore <NUM>. The diametric clearance between pumping plunger <NUM> and plunger bore <NUM> is in the range of <NUM> microns to <NUM> microns. Furthermore, sealing ring <NUM> engaging plunger bore <NUM> in an interference fit increases the efficiency of high-pressure fuel pump <NUM>, particularly at low rotational rates of camshaft <NUM>, by minimizing fuel leakage between pumping plunger <NUM> and plunger bore <NUM>. Sealing ring <NUM> is also sized such that when pumping plunger <NUM> with sealing ring <NUM> is installed within plunger bore <NUM>, sealing ring <NUM> is held in radial compression between plunger bore <NUM> and pumping plunger <NUM>. Furthermore, the radial compression of sealing ring <NUM> by plunger bore <NUM> and pumping plunger <NUM> causes sealing ring <NUM> to expand axially such that sealing ring <NUM> is held in axial compression between the upper and lower walls (as oriented in the figures) of sealing ring groove <NUM>. Another added benefit of pumping plunger <NUM> including sealing ring <NUM> is that the risk of pumping plunger <NUM> seizing within plunger bore <NUM> is minimized because the clearance between pumping plunger <NUM> and plunger bore <NUM> can be increased to an extent such that thermal expansion of pumping plunger <NUM> in use will not be sufficient to bind pumping plunger <NUM> within plunger bore <NUM>.

It is important to note that Nakayama et al. , which was introduced above in the Background of Invention section, discloses a seal system, identified by reference number <NUM> in Nakayama et al. , which maintains separation between gasoline and engine oil. However, the seal system of Nakayama et al. , unlike sealing ring <NUM> of the present invention, does nothing to improve the efficiency of the fuel pump because the seal system of Nakayama et al. is on the low-pressure side of the interface of the pumping plunger and the plunger bore. Consequently, the efficiency of the fuel pump of Nakayama et al. is dependent upon the clearance between the pumping plunger and the plunger bore.

In operation, during the inlet stroke, inlet valve <NUM> is opened to allow fuel to flow into pumping chamber <NUM> from fuel inlet <NUM> as pumping plunger <NUM> is increasing the volume of pumping chamber <NUM> as a result of camshaft <NUM> and return spring <NUM>. Inlet valve <NUM> may remain open during the inlet stroke for a period of time, determined by controller <NUM>, which is sufficient to allow a volume of fuel into pumping chamber <NUM> that will satisfy the fueling needs of internal combustion engine <NUM>. During the pressure stroke, when inlet valve <NUM> is closed, pumping plunger <NUM> decreases the volume of pumping chamber <NUM> as a result of camshaft <NUM>. Decreasing the volume of pumping chamber <NUM> results in increasing the pressure of the fuel within pumping chamber <NUM> where the high-pressure fuel is contained within pumping chamber <NUM>, in part, by the interference fit between sealing ring <NUM> and plunger bore <NUM>. When the pressure within pumping chamber <NUM> is sufficiently high, outlet valve <NUM> is opened, thereby allowing high-pressure fuel to exit pumping chamber <NUM> through fuel outlet <NUM> and to be communicated to high-pressure fuel rail <NUM>.

In a variation of <FIG> and <FIG>, <FIG> shows that pumping plunger <NUM> may include two sealing ring grooves <NUM> such that each sealing ring groove contains a respective sealing ring <NUM> which engages plunger bore <NUM> and pumping plunger <NUM> in the same manner described earlier with respect to <FIG>. It should now be understood that additional sealing ring grooves <NUM> and sealing rings <NUM> may also be included.

As should now be readily apparent, the inclusion of sealing ring groove <NUM> and sealing ring <NUM> provides for greater efficiency of high-pressure fuel pump <NUM>. In one test that was conducted on high-pressure fuel pumps that were otherwise the same, inclusion of sealing ring groove <NUM> and sealing ring <NUM> provided increased efficiency at all operational speeds of the high-pressure fuel pumps, with a particularly significant increase in efficiency at lower operating speeds. This increase in efficiency may allow for high-pressure fuel pump <NUM> to be downsized in fuel pumping capacity, thereby reducing the cost of high-pressure fuel pump <NUM>, since high-pressure fuel pump <NUM> does not need to accommodate a loss in efficiency, particularly at low operational speeds of internal combustion engine <NUM>. Downsizing the fuel pumping capacity of high-pressure fuel pump <NUM>, for example by decreasing the diameter of pumping plunger <NUM>, is important because emission regulation are continually being made more stringent and the desire to provide fuel at higher pressure is more desirable to better atomize the fuel which is beneficial for reducing emissions of internal combustion engine <NUM>. Decreasing the diameter of pumping plunger <NUM> is a way to limit excessive loads on the valve train of internal combustion engine <NUM>, but this can only be done if the efficiency of high-pressure fuel pump <NUM> is improved at higher pressures. A further benefit of sealing ring groove <NUM> and sealing ring <NUM> is that the clearance between pumping plunger <NUM> and plunger bore <NUM> is able to be increased, thereby eliminating the need for time consuming and costly manufacturing techniques such as match honing of pumping plunger <NUM> and plunger bore <NUM>.

Claim 1:
A high-pressure fuel pump (<NUM>) for gasoline direct injection and comprising:
a pump housing (<NUM>) which defines a pumping chamber (<NUM>), a fuel inlet (<NUM>) which allows low-pressure fuel into said pumping chamber (<NUM>), a fuel outlet (<NUM>) which allows high-pressure fuel out of said pumping chamber (<NUM>), and a plunger bore (<NUM>) which extends along an axis (<NUM>) and opens into said pumping chamber (<NUM>); and
a pumping plunger (<NUM>) which reciprocates within said plunger bore (<NUM>) along said axis (<NUM>) such that reciprocation of said pumping plunger (<NUM>) within said plunger bore (<NUM>) increases and decreases a volume of said pumping chamber (<NUM>), such that low-pressure fuel flows from said fuel inlet (<NUM>) to said pumping chamber (<NUM>) when said volume increases, and high-pressure fuel is discharged from said pumping chamber (<NUM>) through said fuel outlet (<NUM>) when said volume decreases;
wherein the pumping plunger (<NUM>) is attached to a cam follower (<NUM>) which is contactable with a camshaft (<NUM>), configured to drive reciprocating movement of the pumping plunger (<NUM>), and wherein a return spring (<NUM>) is compressed axially between the pump housing (<NUM>) and the cam follower (<NUM>) to maintain the cam follower (<NUM>) in contact with the camshaft (<NUM>), in use,
wherein said pumping plunger (<NUM>) includes a sealing ring groove (<NUM>) which is concentric with said plunger bore (<NUM>), said sealing ring groove (<NUM>) including a sealing ring (<NUM>) therein, for preventing fuel from escaping the pumping chamber (<NUM>) between the interface of the pumping plunger (<NUM>) and plunger bore (<NUM>), wherein the sealing ring (<NUM>) engages said plunger bore (<NUM>) in an interference fit, such that said sealing ring (<NUM>) is held in radial compression by said pumping plunger (<NUM>) and said plunger bore (<NUM>) ;
and wherein said sealing ring (<NUM>) is held in axial compression within said sealing ring groove (<NUM>); and
wherein a diametric clearance in the range of <NUM> to <NUM> microns is provided between said pumping plunger (<NUM>) and said plunger bore (<NUM>).