Patent Application
20120199101
The present disclosure relates generally to fuel systems and fuel system operating methods, for internal combustion engines, and relates more particularly to a pressure recovery method for use when operating a common rail fuel system having a cam actuated pressure intensifier in a low leakage mode.
Many types of fuel injection systems for internal combustion engines have been developed over the years. Common rail fuel injection systems are well known and widely used in connection with multi-cylinder internal combustion engines. A typical common rail fuel system includes a low-pressure fuel source, a high-pressure pump and a common rail connecting the high pressure pump with a plurality of fuel injectors. Injection of fuel at rail pressure can occur relatively precisely by electronically controlling each of the fuel injectors coupled with the common rail. Common rail systems have seen widespread success in part because they provide a relatively simple and straightforward means for providing fuel to a plurality of fuel injectors, and enable injection of fuel at relatively precise times and injection amounts. Common rail systems have also proven to be a relatively efficient and effective way to handle relatively high fuel pressures. While known common rail systems have long served as an industry standard for high pressure fuel injection practices, there is room for improvement.
On the one hand, containing a volume of highly pressurized fuel can be relatively difficult, requiring specialized hardware such as seals and plumbing. Parts subjected to extremely high pressures may also have a tendency to wear relatively more quickly than parts used in lower pressure environments. It can also require significant engine output energy to maintain a relatively large volume of fuel at high pressure. Relying solely upon a common rail as a pressure source for fuel can ultimately impact engine efficiency.
Systems have been proposed where a common rail is used to supply fuel at a first pressure to a plurality of fuel injectors of an engine system. A hydraulically actuated or cam actuated pressure intensifier may also be used in such systems to enable fuel injection at selective times at a higher pressure. United States Patent Application Publication No. 2006/0243253 to Knight proposes incorporating a cam actuated piston to a common rail system to enable injection of fuel at rail pressure from the common rail, or at a higher pressure from the pressure intensifier. In Knight's system, the cam actuated pressure intensifier is also used to assist in maintaining the pressure of the common rail when it is not being used to directly elevate fuel pressure for an injection. As a result, the piston in Knight will apparently pump at high pressure continuously. Continuously subjecting components of the fuel system to high pressure from the piston in Knight may result in excessive leakage between and among certain components. Leakage of high pressure fuel as in Knight would tend to waste energy, as the engine output energy used to pressurize the leaked fuel cannot readily be recovered.
In one aspect, a method of operating a fuel system for an internal combustion engine including a step of injecting fuel into an engine cylinder at a medium pressure at least in part by fluidly connecting a nozzle outlet of a fuel injector with a common rail. Also included is a step of increasing a pressure of fuel in a plunger cavity of the fuel injector from a low pressure to the medium pressure by fluidly connecting the plunger cavity with the common rail. The method also includes a step of increasing a pressure of fuel in the plunger cavity from the medium pressure to a high pressure by moving a tappet of a pressure intensifier. Also included is a step of injecting fuel at the high pressure into the engine cylinder at least in part by fluidly connecting the nozzle outlet with the plunger cavity. The method also includes a step of operating the fuel system in a pressure recovery mode subsequent to injecting fuel at the high pressure at least in part via a step of returning a pressure of fuel in the plunger cavity from the high pressure to the medium pressure.
In another aspect, a fuel injector including an injector body defining a nozzle supply passage, a nozzle outlet connecting with the nozzle supply passage, a control passage, a low pressure space, at least one fuel inlet connecting with the nozzle supply passage, a plunger cavity, a pressure intensification passage connecting the plunger cavity with the nozzle supply passage within the injector body, a pressure recovery conduit, and at least one drain. The fuel injector also includes a direct control needle check positioned within the injector body and movable between a closed position blocking the nozzle outlet from the nozzle supply passage and an open position, the direct control needle check having an opening hydraulic surface exposed to a fluid pressure in the nozzle supply passage and a closing hydraulic surface exposed to a fluid pressure in the control passage. Also included in the fuel injector is a check control valve movable between a first injection control position at which the control passage is blocked from the low pressure space and a second injection control position at which the control passage is open to the low pressure space. The fuel injector further includes a pressure intensifier positioned partially within the injector body, the pressure intensifier including a tappet and a plunger configured to move between a first plunger position and an advanced plunger position within the plunger cavity. Also included in the fuel injector is a one-way valve positioned fluidly between the pressure intensification passage and the nozzle supply passage and permitting fluid flow from the plunger cavity to the nozzle supply passage. The fuel injector further includes an injection pressure control mechanism having a first pressure control configuration and a second pressure control configuration, the injection pressure control mechanism blocking the plunger cavity from the at least one fuel inlet and fluidly connecting the plunger cavity with the low pressure space in the first pressure control configuration, and the injection pressure control mechanism fluidly connecting the plunger cavity with the at least one fuel inlet and blocking the plunger cavity from the low pressure space in the second pressure control configuration. The fuel injector also includes a pressure recovery mechanism having a first pressure recovery configuration and a second pressure recovery configuration, the pressure recovery mechanism blocking the low pressure space from the pressure recovery conduit and fluidly connecting the low pressure space with the drain conduit in the first pressure recovery configuration, and the pressure recovery mechanism fluidly connecting the low pressure space with the pressure recovery conduit and blocking the low pressure space from the drain conduit in the second pressure recovery configuration.
In yet another aspect, a fuel system for an internal combustion engine including a plurality of fuel injectors, each of the fuel injectors including an injector body defining a nozzle supply passage, a nozzle outlet connecting with the nozzle supply passage, a low pressure space, and a drain. The fuel system further includes a plurality of mechanically actuated pressure intensifiers each including a tappet and being positioned partially within one of the injector bodies. Also included in the fuel system is a common rail fluidly connecting with each of the fuel injectors. Each of the fuel injectors further include an injection pressure control mechanism which includes an injection pressure control valve movable between a first pressure control position and a second pressure control position, and wherein each of the injection pressure control valves blocks the corresponding pressure intensifier from the common rail and fluidly connects the pressure intensifier with the low pressure space at the first pressure control position, and wherein each of the injection pressure control valves fluidly connects the pressure intensifier with the common rail and blocks the pressure intensifier from the low pressure space at the second pressure control position. Each fuel injector also includes a pressure recovery mechanism, which includes a pressure recovery valve movable between a first pressure recovery position and a second pressure recovery position, and wherein each of the pressure recovery valves blocks the corresponding pressure intensifier from the common rail and fluid connects the pressure intensifier with the drain at the first pressure recovery position, and wherein each of the pressure recovery valves fluidly connects the pressure intensifier with the common rail and blocks the pressure intensifier from the drain at the second pressure recovery position.
Referring to
Internal combustion engine 10 may further include a camshaft 22 rotatable via operating internal combustion engine 10, and having a plurality of cams 21 each having at least one cam lobe 24 positioned thereon. Each of cam lobes 24 may rotate in contact with a tappet 32 of each one of fuel injectors 30, the significance of which is further described herein. Each of fuel injectors 30 may further include an injection pressure control mechanism 80 positioned therein which enables selection of a fuel injection pressure corresponding to a fuel pressure from medium pressure common rail 44, or an intensified pressure from a pressure intensifier actuated via the corresponding tappet 32, and further described herein. Each fuel injector 30 may further include an outlet check (not shown in
Referring now to
Fuel injector 30 may further include a check control mechanism 68 including a needle control valve 69 movable between a first injection control position at which control passage 52 is blocked from a drain conduit 53 and a second injection control position at which control passage 52 is open to drain conduit 53. A low pressure outlet or drain 55 is shown connecting between needle control valve 69 and low pressure fuel return conduit 41/drain conduit 53.
Fuel injector 30 may further include a mechanically actuated pressure intensifier 70 positioned partially within injector body 46. Mechanically actuated pressure intensifier 70 includes tappet 32 and also includes a plunger 72. Plunger 72 is configured to move between a first plunger position and an advanced plunger position within plunger cavity 58, in response to rotation of cam lobe 24, which is rotatably coupled with cam 21. Fuel injector 30 may also include a first one way valve 74 positioned fluidly between pressure intensification passage 60 and nozzle supply passage 48 and permitting fluid flow from plunger cavity 58 to nozzle supply passage 48. A one way valve 102 may be positioned fluidly between medium pressure inlet 56 and a bidirectional passage 100, and permits fluid flow from medium pressure inlet 56 to bidirectional passage 100. Bidirectional passage 100 can fluidly connect pressure intensification passage 60, and hence plunger cavity 58, with either of medium pressure inlet 56 or low pressure space 54, in a manner and for reasons further described herein.
Fuel injector 30 may further include an injection pressure control mechanism 80 having a first pressure control configuration and a second pressure control configuration. Injection pressure control mechanism 80 blocks plunger cavity 58 from medium pressure inlet 56 and fluidly connects plunger cavity 58 with low pressure space 54 by way of bidirectional passage 100 in the first pressure control configuration. Injection pressure control mechanism 80 fluidly connects plunger cavity 58 with medium pressure inlet 56 by way of bidirectional passage 100, and blocks plunger cavity 58 from low pressure space 54 in the second pressure control configuration. In one embodiment, injection pressure control mechanism 80 may include a poppet valve 82 movable within fuel injector 30. Injector body 46 may define a first seat 84 and a second seat 86. The first pressure control configuration may include a first poppet valve position at which poppet valve 82 contacts first seat 84, and the second pressure control configuration may include a second poppet valve position at which poppet valve 82 contacts second seat 86. Injection pressure control mechanism 80 may further include a first electrical actuator 88 coupled with poppet valve 82 and configured to move poppet valve 82 between the first poppet valve position and the second poppet valve position, alternately contacting first seat 84 or second seat 86.
In the embodiment shown, a single poppet valve 82 is depicted as part of injection pressure control mechanism 80. Poppet valve 82 may be biased toward its first position with a biasing spring 81. Poppet valve 82 may be coupled with a first electrical actuator 88 to facilitate movement of the poppet valve 82 from its first position to its second position. A medium pressure supply passage 98 is shown connecting medium pressure inlet 56 with nozzle supply passage 48, however, an alternative strategy might be used such as connecting nozzle supply passage 48 with medium pressure inlet 56 through another portion of injector body 46. It should be appreciated that other embodiments are contemplated where, for example, a plurality of valves are used in place of a single poppet valve. In still other embodiments, one or more slide-type valves such as spool valves might be used. It should thus be appreciated that a single poppet valve movable between a first seat and a second seat is but one illustrative embodiment, and the present disclosure is not thereby limited.
As mentioned above, fuel injector 30 may also include needle control valve 69 therein. Needle control valve 69 may be biased toward its first position with a biasing spring 71. A second electrical actuator 90 may be coupled with needle control valve 69 and configured to move needle control valve 69 between the first and second injection control positions. Injector body 46 may further define a third seat 92 and a fourth seat 94. As shown in
Fuel injector 30 may further include a pressure recovery control mechanism 130. The pressure recovery control mechanism may include a pressure recovery valve 132 movable between a first valve position and a second valve position. In the first position, the pressure recovery valve 132 is biased upward by a biasing spring 134 to a fifth seat 133. In this first position, pressure recovery valve allows fluid communication between the low pressure space 54 and fuel return conduit via drain conduit 136 and drain 57. Those skilled in the art will recognize that alternate embodiments may combine drain 55 and drain 57 into a single drain. Pressure recovery valve 132 includes a hydraulic surface 140 that is exposed to pressurized fluid from plunger cavity 58 via a pressure recovery actuating conduit 142. When hydraulic opening surface received sufficient opening pressure to cause pressure recovery valve 132 to overcome the upward force of biasing spring 134, pressure recovery valve moves to its second position wherein it engages a sixth seat 135. In the second position, pressure recovery valve 132 allows fluid communication between the low pressure space 54, and medium pressure common rail 44 via a pressure recovery conduit 138 formed in injector body 46.
The foregoing description of an example fuel injector 30 described in connection with
Poppet valve 82 is shown in the first pressure control position at which poppet valve 82 contacts first seat 84. As described herein, with poppet valve 82 at the first pressure control position, plunger cavity 58 is connected with low pressure space 54 by way of pressure intensification passage 60, and bidirectional passage 100. Fuel at medium pressure in nozzle supply passage 48 urges one way valve 74 toward a closed position at which nozzle supply passage 48 is blocked from pressure intensification passage 60. One way valve 102 permits fuel at the medium pressure to flow from medium pressure inlet 56 to nozzle supply passage 48, at least until such time as fuel pressure in nozzle supply passage 48 becomes equal to the medium pressure.
In
When it is desirable to inject fuel into an associated engine cylinder 20 at a medium pressure, second electrical actuator 90 may be energized to move poppet valve 69 away from third seat 92 and towards fourth seat 94. Upon poppet valve 69 contacting fourth seat 94, control passage 52 will be blocked from nozzle supply passage 48, and open to drain 55. As a result, fuel pressure in nozzle supply passage 48 can act on opening hydraulic surface 64 to move needle check 62 towards an open position and thereby allow fuel to be injected via nozzle outlet 50. To end fuel injection, second electrical actuator 90 may be de-energized, allowing poppet valve 69 to move back towards its first injection control position contacting third seat 92. The aforementioned fuel injection process may take place with poppet valve 82 maintained at its first pressure control position contacting first seat 84. It should be appreciated that injection of fuel at the medium pressure may take place irrespective of cam angle, and thus independently of a position or state of pressure intensifier 70. Thus, injection at the medium pressure may take place while plunger 72 is advancing, retracting or stationary. One way valve 74 may block plunger cavity 58 from nozzle supply passage 48 during injecting fuel at the medium pressure, as well as any other time where fuel pressure is greater in nozzle supply passage 48 than in pressure intensification passage 60 and plunger cavity 58.
When it is desirable to inject fuel at a high pressure, first electrical actuator 88 may be energized to move poppet valve 82 to its second pressure control position, fluidly connecting plunger cavity 58 with medium pressure common rail 44 by way of bidirectional passage 100, and blocking plunger cavity 58 from low pressure space 54. Moving poppet valve 82 to the second pressure control position may, but need not, take place just prior to or while plunger 72 is retracting. When poppet valve 82 is moved to its second pressure control position, fuel at the medium pressure may flow by way of one way valve 102, bidirectional passage 100 and pressure intensification passage 60 into plunger cavity 58. It will be recalled that plunger 72 is displacing fuel at low pressure to and from low pressure space 54 in response to rotation of cam lobe 24 so long as poppet valve 82 is in its first pressure control position. Fluidly connecting plunger cavity 58 with medium pressure common rail 44, however, will increase a pressure of fuel in plunger cavity 58 from the low pressure to the medium pressure. Increasing the pressure of fuel from the low pressure may take place while plunger 72 is stationary or retracting. Rotation of cam lobe 24 may be causing plunger 72 to move in a retracting direction, or causing no movement of plunger 72 during increasing the pressure in plunger cavity 58 from the low pressure to the medium pressure, depending upon the profile of cam lobe 24. One way valve 74 may block plunger cavity 58 from nozzle supply passage 48 during increasing a pressure of fuel in plunger cavity 58 from the low pressure to the medium pressure.
In response to further rotation of cam lobe 24 tappet 32 and plunger 72 may move in an advancing direction, and a pressure of fuel in plunger cavity 58 may be increased from the medium pressure to a high pressure. In other words, cam lobe 24 will tend to drive plunger 72 downwardly in the
Following injecting fuel at the high pressure, fuel system 12 may be operated in a pressure recovery mode. Operating fuel system 12 in a pressure recovery mode may be understood as returning high pressure fuel back to the medium pressure common rail 44 as opposed to allowing it to be drained back to the fuel source 34. As stated above, injection of fuel at high pressure may be ended when first electrical actuator 88 and second electrical actuator 90 are de-energized and poppet valves 69 and 82 are returned to their respective first positions on valve seats 92 and 84. When this happens, high pressure fuel may still remain in pressure intensification passage 60. Taking the path of least resistance, this high pressure fuel may enter the pressure recovery actuating conduit 142, and apply a force to hydraulic surface 140 of pressure recovery valve 132. The pressure exerted on hydraulic surface 140 causes pressure recovery valve 132 to overcome the force of biasing spring 134. Pressure recovery valve 132 is thus moved to its second position, wherein it engages the sixth seat 135. When pressure recovery valve 132 is in its second position, fluid communication between low pressure space 54 and pressure recovery conduit 138 is established. Thus, so long as poppet valve 82 is in its first position, the high pressure of the fluid in the pressure intensification passage 60 may flow across poppet valve 82, through low pressure space 54, and to pressure recovery conduit 138. Ultimately, this high pressure fuel may be returned to the medium pressure of the medium pressure common rail 44. As pressure within the pressure intensification passage 60 dissipates, there may no longer enough pressure in the pressure recovery actuating conduit 142 to keep pressure recovery valve 132 in its second position. As the force of the biasing spring 134 overcomes the downward pressure of fluid acting on the hydraulic surface 140 of pressure recovery valve 132, the pressure recovery valve 132 is moved back to its first position where it engages the fifth seat 133. When the pressure recovery valve 132 is in its first position, fluid communication is established between low pressure space 54 and drain conduit 136. Fuel within pressure intensification passage 60, whose pressure has now dissipated to the point where it is below rail pressure, is now allowed to drain out of fuel injector 30 via drain conduit 136 and drain 57. This drained fuel is then returned to fuel source 34 via low pressure fuel return conduit 41.
Following injection of fuel at high pressure and operation of fuel system 12 in pressure recovery mode, fuel system 12 may be operated in a low leakage mode. Operating fuel system 12 in a low leakage mode may be understood as returning fuel system 12 to a state at which pressure intensifier 70 is displacing fuel to and from low pressure space 54, and thus returning pressure in plunger cavity 58 to low pressure. To commence operation in the low leakage mode, poppet valve 82 may be returned to the first pressure control position, contacting seat 84. Operation in the low leakage mode may be essentially continuous, except where a high pressure injection is desired, improving over designs where a pressure intensifier continuously pumps at high pressure or a single stage pump attempts to achieve and maintain a high pressure continuously.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims.
