CAMSHAFT AND FOLLOWER GEOMETRY
An internal combustion engine includes a camshaft with a lobe rotatable about a camshaft axis and a follower and which follows the lobe and is reciprocated along a follower axis by the lobe. A contact force is generated between the lobe and the follower such that the contact force is cyclic between a minimum contact force and a maximum contact force. The follower axis is offset from the camshaft axis such that the lobe contacts the follower at a contact point that is substantially aligned with the follower axis when the maximum contact force is generated between the lobe and the follower. In this way, the side load on the follower is minimized.
The present invention relates to an internal combustion engine with a camshaft having a lobe and a follower which follows the lobe; more particularly to such an internal combustion engine in which the follower imparts a pumping stroke on a pumping plunger of a fuel pump; and more particularly to such an internal combustion engine which minimizes tipping forces imparted on the follower.
BACKGROUND OF INVENTIONIt is known in art of internal combustion engines to provide a fuel pump which is driven by a camshaft which rotates about a camshaft axis. U.S. Pat. No. 7,568,469 to Tokuo et al. shows an example of such an arrangement. The camshaft includes a lobe which is followed by a follower of the fuel pump and which reciprocates about a follower axis which is typically perpendicular to and aligned with the camshaft axis. The lobe reciprocates the follower through one or more pumping strokes for each rotation of the camshaft, thereby reciprocating a pumping plunger of the fuel pump to pressurize the fuel. Due to geometry of the lobe, the point of contact between the lobe and the follower varies in a cyclic patter from being aligned with the follower axis to being eccentric to the follower axis. A contact force between the follower and the lobe is generated which also varies in a cyclic pattern as a function of the rotational position of the lobe such that the highest contact force occurs when the contact point is not aligned with the follower axis which results in a side load being applied to the follower. This side load may result in reduced durability and may require followers which are manufactured with increased strength to be capable of accommodating the side load, thereby increasing manufacturing costs.
What is needed is an internal combustion engine which minimizes or eliminates one or more of the shortcomings as set forth above.
SUMMARY OF THE INVENTIONBriefly described, an internal combustion engine includes a camshaft with a lobe rotatable about a camshaft axis and a follower which follows the lobe and which is reciprocated along a follower axis by the lobe. A contact force is generated between the lobe and the follower such that the contact force is cyclic between a minimum contact force and a maximum contact force. The follower axis is offset from the camshaft axis such that the lobe contacts the follower at a contact point that is substantially aligned with the follower axis when the maximum contact force is generated between the lobe and the follower. In this way, the side load on the follower is minimized.
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
Fuel pump 12 generally includes a fuel inlet 18, an inlet valve 20, a pressure chamber 22, a pumping plunger 24, a return spring 25, an outlet valve 26, and a fuel outlet 28 which may be in fluid communication with a fuel rail 30 to which fuel injectors 16 are connected and receive pressurized fuel from. Fuel inlet 18 receives fuel from a fuel source, for example a fuel tank (not shown) with a lift pump (not shown) at a relatively low pressure. Inlet valve 20 may be, for example, a solenoid operated valve which is controlled by a controller 32. Controller 32 may receive input from a pressure sensor 34 which supplies a signal indicative of the pressure of the fuel being supplied to fuel injectors 16. While pressure sensor 34 is shown arranged to read the fuel pressure within fuel rail 30, it should be understood that pressure sensor 34 may be positioned at other locations that are indicative of the pressure of the fuel being supplied to fuel injectors 16. Controller 32 sends signals to inlet valve 20 to open and close inlet valve 20 as necessary to achieve a desired fuel pressure at pressure sensor 34 as may be determined by current and anticipated engine operating demands. When inlet valve 20 is opened, fuel from fuel inlet 18 is allowed to flow into pressure chamber 22.
Pumping plunger 24 is slidably received within a plunger bore 36 that is in fluid communication with pressure chamber 22. Pumping plunger 24 is reciprocated within plunger bore 36 along a plunger axis 38 by camshaft 14 and return spring 25 as will be described later. Pumping plunger 24 includes a follower 40 at an axial end thereof that is distal from pressure chamber 22 for following camshaft 14 as will also be described later. Follower 40 reciprocates within a follower bore 41 which may be, for example only, a bore in the engine block, intake manifold, or cylinder head of internal combustion engine 10 or may alternatively be a bore in a separate housing of fuel pump 12. Follower 40 is guided by follower bore 41 which is substantially coaxial with plunger bore 36. After inlet valve 20 has been closed, reciprocation of pumping plunger 24 toward pressure chamber 22 causes the fuel within pressure chamber 22 to be compressed. The pressurized fuel causes outlet valve 26 to open, thereby allowing pressurized fuel to be expelled from fuel outlet 28 to fuel rail 30 and fuel injectors 16.
Camshaft 14 rotates about a camshaft axis 42 and includes a lobe 44 which is followed by follower 40 of pumping plunger 24. As shown in
A description of the rotation of camshaft 14 will now be given. For this description, rotation positions will be assigned as follows: 0° is the center of base portion 52a, 63° is nose 50a, 120° is the center of base portion 52b, 183° is nose 50b, 240° is the center of base portion 52c, and 303° is nose 50c; however, it should be understood that these values are exemplary only. A contact force is generated between lobe 44 and follower 40 as a result of return spring 25 urging follower 40 into contact with lobe 44 and also as a result of the pressure being elevated within pressure chamber 22 during the pumping stroke. This contact force is cyclic between a minimum contact force and a maximum contact force and varies as a function of the rotational position of camshaft 14. As shown by contact force trace 54 in
While an exemplary lobe 44 has been described herein, it should be understood that other lobe geometries are contemplated. For example only, the location, duration, lift properties, and quantities of compression flanks 46a, 46b, 46c; refill flanks 48a, 48b, 48c; noses 50a, 50b, 50c; and base portions 52a, 52b, 52c may be altered in order to obtain desired operating performance of fuel pump 12.
While this invention has been described in terms of preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.
Claims
1. An internal combustion engine comprising:
- a camshaft having a lobe rotatable about a camshaft axis; and
- a follower which follows said lobe and is reciprocated along a follower axis by said lobe whereby a contact force is generated between said lobe and said follower such that said contact force is cyclic between a minimum contact force and a maximum contact force;
- wherein said follower axis is offset from said camshaft axis such that said lobe contacts said follower at a contact point that is substantially aligned with said follower axis when said maximum contact force is generated between said lobe and said follower, thereby minimizing side load on said follower.
2. An internal combustion engine as in claim 1 wherein said follower reciprocates within and is guided by a follower bore.
3. An internal combustion engine as in claim 1 wherein reciprocating motion of said follower is translated to a pumping plunger which reciprocates within a plunger bore.
4. An internal combustion engine as in claim 3 wherein said plunger bore is in fluid communication with a pumping chamber and reciprocation of said pumping plunger pressurizes fuel within said pumping chamber.
5. An internal combustion engine as in claim 4 wherein said follower reciprocates within and is guided by a follower bore.
6. An internal combustion engine as in claim 5 wherein said follower bore is coaxial with said plunger bore.
Type: Application
Filed: Nov 15, 2013
Publication Date: May 21, 2015
Inventor: TIMOTHY W. KUNZ (ROCHESTER, NY)
Application Number: 14/081,041
International Classification: F01L 1/04 (20060101);