Pumps with variable cam profiles

Abstract

The present invention discloses a fuel injection system 100. The fuel injection system includes a pump (102), the pump including a housing, a plunger reciprocating in the housing, and a cam 108 driving the plunger, the cam having a profile on a cam surface, the profile including: a first portion 200 to help the plunger to be lifted at a first slope 206 of plunger lift relative to cam angle rotation; a second portion 202 to help the plunger to be lifted at a second slope 208 of plunger lift relative to cam angle rotation. The fuel injection system includes an injector (104) to receive pressurized fuel from the pump (102), and the injector injects the pressurized fuel into an engine.

Description

[0001] The following description describes and defines the nature of the invention and the manner in which it will be performed. Technical Field

[0002] The present invention relates generally to the field of fuel injection systems. The present invention relates to a fuel pump having a variable cam surface to effectively control fuel injection into an engine. Background Art

[0003] Typical diesel fuel injection systems in the prior art use a common rail and electronically controlled injectors to inject fuel into the engine. The common rail is maintained at a required pressure, and depending on the engine operating conditions, the injectors are operated to inject the required amount of fuel into the engine.

[0004] The pump that supplies fuel to the common rail is driven by a cam. US Patent Application 20020096145 discloses a fuel injection system including a high-pressure fuel pump. The high-pressure fuel pump is driven by a cam having a varying surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Different forms of the present invention are disclosed in detail in the specification and shown in the accompanying drawings:

[0006] Figure 1 A schematic diagram of a fuel injection system is shown.

[0007] Figure 2A and 2B A schematic diagram of a cam having a varying cam surface according to an embodiment of the present invention is shown.

[0008] Figure 3A and 3B A schematic diagram showing a cam with a varying cam surface according to another embodiment of the present invention is shown. DETAILED DESCRIPTION

[0009] exist Figure 1 1 is a fuel injection system 100. The main components of the fuel injection system are a fuel pump 102, a fuel injector 104 and an electronic control unit ECU 106. The fuel pump 102 is a high pressure pump. The fuel pump is simply referred to as a pump. A low pressure pump may precede this pump 102. The pump 102 receives fuel from a fuel tank 110 and pressurizes the fuel. The pressurized fuel is delivered to the injector 104 for injection into the engine. Figure 1 Also shown are a pressure sensor 110 that reads fuel pressure, a temperature sensor 112 that reads coolant temperature, an engine speed sensor 114 , an accelerator load sensor 116 , and a fuel filter 118 .

[0010] Here, the pump 102 is a mechanical pump driven by a cam 108, which is driven by the engine. The injector is an electronic injector and is controlled by an electronic control unit ECU. The ECU controls the injector by opening or closing the injector for fuel injection. The ECU determines the amount of fuel to be injected into the engine based on various engine operating parameters (such as engine speed, engine load, fuel pressure, coolant temperature, etc.). Based on the amount of fuel to be injected into the engine, the ECU determines an activation time for the injector. During the calculated activation time, the ECU provides the required power to the injector in terms of pulse width modulation. The injector valve opens and fuel injection occurs. After the activation time ends, the ECU provides power to the injector and the injector valve returns to the closed position, thereby stopping fuel injection.

[0011] In a typical prior art system for diesel fuel injection, the fuel injection system comprises a common rail in which the fuel is stored. A pump supplies fuel to the common rail, where the fuel is stored at a more or less constant pressure. The common rail supplies fuel to the injectors. Since the pressure in the common rail is at a much higher level than the operating pressure of the injectors, it is possible to inject without any fluctuations.

[0012] In the present invention, a fuel injection system is used for low-cost vehicles and therefore eliminates the common rail. The pump supplies pressurized fuel directly to the injector. A pump operating with a typical cam profile (as in the prior art) will have a lift cycle for the plunger, followed by a dwell cycle in which the plunger is held at a constant position, and then a descending cycle of the plunger. During the lift cycle, the cam pushes the plunger, thereby increasing the pressure. During the dwell cycle, the cam rotates, but the plunger is held at a constant position due to the cam profile. This is to maintain the fuel pressure at a constant level in the fuel supply path. During the descending cycle, the cam rotates further and the plunger retards. The retardation of the plunger refers to the movement of the plunger toward the cam. The pressure in the fuel supply path is reduced.

[0013] In the prior art, this type of pump operation has the disadvantage that during the dwell period in which the pressure in the fuel supply path should be constant, the pressure actually drops. This is due to leaks in the injector. This leads to fluctuations in the injector operation.

[0014] To overcome this, the present invention proposes a cam profile that eliminates the drop in pressure during the dwell period.

[0015] Figure 2A A cam profile according to one embodiment of the invention is shown. Figure 2BA diagram of plunger lift relative to cam angular rotation is shown. The X-axis represents cam angular rotation, and the Y-axis represents plunger lift. The cam profile has a first portion 200 to lift the plunger at a first lift rate 206, a second portion 202 to lift the plunger at a second lift rate 208, and a portion to then retract the plunger. The first lift rate is also referred to as a first slope 206 of plunger lift relative to cam angular rotation. The second lift rate is also referred to as a second slope 208 of plunger lift relative to cam angular rotation.

[0016] When the cam 108 rotates, it pushes the plunger, or allows the plunger to retreat. When the cam pushes the plunger, the fuel pressure in the fuel supply path increases. When the plunger retreats, the fuel pressure in the fuel supply path decreases. The fuel supply path is the path that connects the pump to the injector.

[0017] When the first portion 200 of the cam profile contacts the plunger, the cam causes the plunger to lift at a first lift rate 206, thereby pressurizing the fuel. During this cycle, the plunger lift has a first slope 206 corresponding to the first angle. When the plunger contacts the first portion 200 of the cam profile, it is referred to as the first lift cycle. When the second portion 202 of the cam profile contacts the plunger, the cam causes the plunger to lift at a second lift rate 208, thereby further pressurizing the fuel. During this cycle, the plunger lift has a second slope 208 corresponding to the second angle. The first angle is steeper than the second angle. When the plunger contacts the second portion 202 of the cam profile, it is referred to as the second lift cycle.

[0018] When the plunger reaches the end of the first lifting cycle, the injector can start to spray. As the plunger lift continues further until the end of the second lifting cycle, the pressure continues to increase. This compensates for any leakage in the injector, and the fuel injection continues smoothly.

[0019] Figure 3A A cam profile according to another embodiment of the invention is shown. Figure 3B A graph of plunger lift relative to cam angle rotation is shown. The X-axis represents cam angle rotation, and the Y-axis represents plunger lift. Figure 3AThe cam profile shown in has a first portion 200, a first dwell portion D1, a second portion 202, a second dwell portion D2, and a descending portion. This type of cam profile is useful for multiple fuel injections in one cycle. They can be a pilot injection, a main injection, and a post injection. The pilot injection can occur just before the main injection, and the post injection can occur just after the main injection. The descending portion refers to the period when the pressure begins to decrease. This is caused when the plunger begins to retract. In this embodiment, the cam pressurizes the fuel, keeps it constant during the D1 period, and then pressurizes the fuel again, keeps it constant during the D2 period, and then retracts. This Figure 3B Displayed in.

[0020] The present invention has the advantage that the common rail is eliminated from the fuel injection system, thereby significantly reducing the cost of the fuel injection system.Variations in pressure during injection are eliminated by having a second boost period in which the pressure in the fuel supply path is increased.

Claims

1. A cam (108) driving a plunger, the cam having a profile on a cam surface, the profile comprising: - a first portion (200) to assist in lifting the plunger at a first slope (206) of lift relative to the angular rotation of the cam (108); - a second portion (202) to assist in raising the plunger at a second slope (208) of lift relative to the angular rotation of the cam (108), wherein the second slope begins immediately at the end of the first slope, Wherein, when the plunger reaches the end of a first lifting period defined by the first portion (200), the injector (104) starts to inject.

2. A fuel pump (102), comprising: -case; - a plunger reciprocating in said housing; a cam (108) for driving the plunger, the cam (108) having a profile on a cam surface, the profile comprising: a first portion (200) to assist in lifting the plunger at a first slope (206) of plunger lift relative to cam angular rotation; a second portion (202) to assist in lifting the plunger at a second slope (208) of plunger lift relative to cam angular rotation, wherein the second slope begins immediately at the end of the first slope, Wherein, when the plunger reaches the end of a first lifting period defined by the first portion (200), the injector (104) starts to inject.

3. A fuel injection system (100), comprising: - A pump (102) comprising: a housing, a plunger reciprocating in the housing, a cam (108) driving the plunger, the cam having a profile on a cam surface, the profile comprising: a first portion (200) to assist in lifting the plunger at a first slope (206) of plunger lift relative to cam angle rotation; a second portion (202) to assist in lifting the plunger at a second slope (208) of plunger lift relative to cam angle rotation, wherein the second slope begins immediately after the first slope ends; - an injector (104) to receive the pressurized fuel from the pump (102), the injector causing the pressurized fuel to be injected into the engine, Wherein, when the plunger reaches the end of a first lifting period defined by the first portion (200), the injector (104) starts to inject.

4. The fuel injection system (100) according to claim 3, wherein: The pump (102) is a mechanical pump.

5. The fuel injection system according to claim 3, wherein: The injector (104) is an electronic injector controlled by an electronic control unit (106).

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