Patent Application
20120177505
This invention relates to high pressure fuel systems and, more particularly, to control structure for controlling an engine-driven fuel pump in a manner such that noise and fuel pressure pulsations are reduced in the fuel system.
In conventional high-pressure fuel systems, an engine-driven fuel pump is a key source of unwanted audible noise as well as a source of fuel pressure pulsations, which complicate the fuel metering task. Management of these pulsations requires 1) extra volume in the fuel rail, which increases the time required to achieve target fuel pressure at engine start, 2) orifices, which increase the pump power consumption, and 3) an increased relief valve set-point, which increases the pressure at which the injectors must open and thus compromises the configuration of the injectors for other targets.
The present state-of-the-art high-pressure fuel pump includes a solenoid and an inlet check valve. To control the volume of fuel pumped, the solenoid holds the electrically-operated inlet check valve open during the beginning of the pumping stroke, then allows the inlet check valve to close at a time during the pumping phase calculated to cause precisely the desired quantity of fuel to be pumped into the fuel rail. This occurs at any fuel demand less than 100% of the pump capability, which is the case nearly 100% of the time during engine operation. Given the practical requirement for an approximately sinusoidal movement of the pump piston, the piston velocity, and therefore the velocity of fuel flowing backward through the inlet check valve before it is allowed to close, is at a maximum just before the valve closes. This high velocity results in slamming of the inlet check valve, a key source of audible noise, and further results in a significant pump-internal fuel pressure spike of hundreds of psi due to reversal of the fuel motion. These fuel pressure spikes result in adverse design requirements for the opening pressure of a required pressure relief valve, the volume of the fuel rail, and the opening pressure of the fuel injectors.
The rapid movement of the solenoid armature between its end stops, one cycle per pumping stroke, is also a significant source of audible noise.
Thus, there is a need to provide control structure for an engine-driven fuel pump that that reduces the audible noise and pressure pulsations, enabling a design choice of reducing the fuel rail volume, enlarging the orifices, and/or reducing the relief valve set-point.
An object of the invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is achieved by control structure for controlling movement of a high pressure fuel pump piston of a fuel system, preferably for a vehicle. The piston is constructed and arranged to be inserted into or withdrawn from a pumping chamber to control a flow of fuel from the pumping chamber. The control structure includes a rocker arm with an associated roller follower. The roller follower is constructed and arranged to engage a camshaft of an engine. The rocker arm is operatively associated with the piston such that movement of the camshaft causes movement of the rocker arm and thus movement of the piston. The control structure also includes actuator structure associated with the rocker arm and constructed and arranged to vary a percentage of camshaft motion imparted to the piston via the rocker arm.
In accordance with another aspect of an embodiment, a method is provided for controlling movement of a high pressure fuel pump piston of a fuel system. The piston is constructed and arranged to be inserted into or withdrawn from a pumping chamber to control a flow of fuel from the pumping chamber. The method provides a rocker arm with an associated roller follower so that the roller follower engages a camshaft of an engine with the rocker arm being operatively associated with the piston such that movement of the camshaft causes movement of the rocker arm and thus movement of the piston. The rocker arm is controlled to vary a percentage of camshaft motion that is imparted to the piston.
Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.
The invention will be better understood from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which:
The system 10 includes a stroke control actuator structure 36, which can be electric only, electro-hydraulically, or hydraulically operated. For example, the actuator structure 36 can be a stepper motor, DC motor, similar to those used for throttle control, reduction gears, worm gears, a direct solenoid, hydraulically controlled with oil control solenoid valves similar to those used for camshaft phase control, hydraulically controlled by the fuel pressure in the fuel rail, or other control structure. The actuator structure 36 controls the position of a moveable control element 38 along a required path, between two endpoints, in response to control inputs (e.g., shown as electrical inputs V+ and V−), as explained more fully below. The control element 38 can be considered to be part of the actuator structure 36.
If actuation is purely electrical, the control element 38 may default to a specified “limp home” position when electrical current is zero. If actuation is electro-hydraulic, the control element 38 may default to two different specified “limp home” positions when electrical current is zero, depending upon whether or not normal oil supply pressure is available.
The control structure 11 preferably includes a rocker arm 42 with associated roller follower 44 that provides a low-friction interface with a camshaft 40 of an engine. For a typical high-pressure direct injection engine, the number of lobes of the camshaft 40 is such that one pump stroke will occur for each cylinder combustion event. As the camshaft 40 turns, the rocker arm 42 with follower 44 moves according to the profile of the camshaft 40. The rocker arm 42 directly or indirectly imparts its motion to the piston 18 of the pump 12, preferably via roller follower 45 due to the arc motion of the rocker arm 42. The percentage of camshaft 40 motion that is imparted to the piston 18 via the rocker arm 42 varies depending solely upon the position of the support pivot 46 coupling the rocker arm 42 to the moveable control element 38. The support pivot 46 follows an arc-shaped path between two endpoints to provide the desired pump piston stroke, with a variable withdrawing piston position and preferably a constant inserting piston position, with respect to the pump housing 14. The rocker arm 42 will experience some amount of “lost motion” which is not imparted to the piston 18 of the pump 12 when controlled for less than 100% pump stroke.
A spring 48 biases the rocker arm 42 to ensure the roller follower 44 will always be in contact with the camshaft 40, even at the zero stroke control position when the spring 22 associated with the pump 12 is not contributing force. Though a coil spring is shown, leaf, helical, or other spring configurations may be used.
The system 10 is shown in
With reference to
In addition to the parts common to
In the embodiment of
It is noted that in the Figures, the rocker arm 42, 42′, 42″, camshaft 40, and other affected parts are shown solid at the position corresponding to maximum camshaft lift, and are shown dashed at the position corresponding to minimum camshaft lift.
Thus, the embodiments use control structure 11, 11′ 11″ provided between the engine camshaft 40 and the pump 12 that varies the amount of displacement transferred from the camshaft 40 to the pump piston 18, according to the fuel demand. The control structure 11, including the variable rocker arm 42, modulates the pump stroke, so that no other device is required to modulate the fuel quantity pumped. For example, at a fuel demand equal to 50% of the pump capacity, the piston stroke will be controlled to approximately 50% of maximum, modulated to achieve the target fuel pressure in the fuel rail. For optimum pumping efficiency, the stroke control structure should leave the unswept volume of the pumping chamber relatively unchanged regardless of stroke (e.g., only the distance the piston is withdrawn from the pump body should be affected). During periods of zero fuel injection demand, and when a failure eliminates the fuel supply to the pump 12, the piston stroke will be controlled to zero, completely eliminating concerns regarding piston overheating and pump failure during these modes.
The moving parts of the control structure 11, 11′ 11″ can be completely contained within the engine cylinder head, be lubricated with engine oil, and be configured to operate with continuous, linear loads. Thus, no impacts occur that could result in objectionable noise. The control structure can be chosen from among a large variety of available configurations for achieving variable engine valve lift, but can be cost-reduced due to the much less severe loading conditions and less strict tolerances required for driving the fuel pump.
The embodiments can completely eliminate the conventional fuel pump solenoid and, thus, eliminates the solenoid noise from the pump 12. The inlet check valve 27 is allowed to always act purely hydraulically, and therefore always closes at a similar low fuel velocity early in the pumping stroke, with low noise and less or no pressure pulsations resulting. Thus, audible noise and the pulsations are reduced or eliminated, thereby allowing elimination of noise mitigation parts, reduction of fuel rail volume, and reduction of the time required to achieve target fuel pressure at engine start. By reducing or eliminating the pressure pulsations, the embodiments also allow for the reduction of the required opening pressure for the pressure relief valve 34, which in turn allows reduction of the maximum pressure at which the fuel injectors are required to open, which in turn may allow improvement of the injector working flow range. In the same manner, the embodiments can also increase the diameter of the flow restriction orifice typically provided between the fuel pump and the fuel rail, such that the amplitude of pressure pulsations at the injectors is unchanged, but the required pump mechanical power consumption is reduced.
The use of lost-motion rocker arms as the control structure 11, 11′, 11″ is compatible with existing pump and multi-lobe camshaft designs, and preserves the capability for one pump stroke per fuel injection event, with synchronized timing. The embodiments improve the durability of the pump 12 due to the reduced average piston speed, reduced average pressure on the piston during the pumping phase, and reduced internal pressure pulsations. The present state-of-the art fuel pump relies on fuel flow to keep its piston from overheating and failing, which could occur during long periods of zero fuel injection demand, or even during very short periods of zero fuel supply due to a failure. The embodiments eliminate this reliance on fuel flow and therefore completely eliminate these durability concerns.
Further features of the embodiments are:
Thus, the embodiments provide a variable stroke system compatible with engine driven piston pumps and existing multi-lobe camshaft configurations, to obtain all of the functional benefits described above.
The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the scope of the following claims.
