TECHNICAL FIELD

The subject matter described herein, in general, relates to a fuel pump and in particular, relates to a system for driving a fuel pump.

BACKGROUND

Generally, internal combustion (IC) engines can be classified into two categories, namely, two-stroke engines and four-stroke engines, based on the number of strokes per combustion cycle. In the two-stroke engines, a combustion cycle is completed in every rotation of a crankshaft and on the other hand, in the four-stroke engines, a combustion cycle is completed in every two rotations of a crankshaft. The IC engines can be further classified based on the type of fuel used for combustion, for example, diesel engines and petrol engines. Further, a two-stroke engine can be the diesel engine or the petrol engine.

A two-stroke diesel engine includes a fuel supply system that may have a fuel pump to provide fuel at an elevated pressure from a fuel tank to a fuel injector. The fuel pump is driven by a camshaft through a cam, whereas the camshaft is driven by the crankshaft through power transfer drives using intermediate components, for example, a belt, a chain or a gear. In the two-stroke diesel engine, since the combustion cycle is completed every rotation of the crankshaft, the fuel needs to be pumped by the fuel pump to the fuel injector every combustion cycle. For this purpose, the camshaft needs to be driven at the same speed of the crankshaft. However, these intermediate components result in transmission losses between the crankshaft and the fuel pump and adversely affect the efficiency of the engine.

Under extreme operating conditions of the two-stroke diesel engine, such as high load and high speed, the engine, especially the intermediate components are subjected to considerably large mechanical stresses. The stresses are caused by high contact fatigue at elevated temperatures on the cam, and the other fuel pump intermediate drive components. Additionally, the high pressures demanded from the fuel supply system at these high operating speeds results in large combined stresses. Additionally, a need for compactness of the intermediate components is compounded with targets of high durability, competitive cost, and reliable operation of system with least parasitic losses.

SUMMARY

The subject matter described herein is directed towards a system for driving a fuel pump included in an internal combustion (IC) engine. In one embodiment, the system includes a crankshaft, a cam, and the fuel pump having a plunger. The plunger is driven by the cam through a roller follower, which is operably coupled to the plunger. In said embodiment, the cam is mounted on the crankshaft so that the cam is driven at the speed of the crankshaft. In other embodiments, the cam may be mounted on a balancer shaft, which is in turn driven by a primary gear mounted on the crankshaft. In yet another embodiment, the cam may be mounted on a gear shaft, which is also driven by the primary gear mounted on the crankshaft. Such a direct transmission mechanism eliminates additional intermediate components, such as gears, shafts, etc., between the crankshaft and the drive to the fuel pump, especially components required to drive an independent camshaft. As a result, mechanical stress on components of the engine is significantly minimized, with a perceivable improvement in their reliability, thereby ensuring smooth operation of the engine.

In an implementation, the cam and the roller follower are coated with material such as tungsten carbide, diamond-like carbon (DLC), etc., having high strength and surface properties to withstand high contact fatigue loads at elevated temperatures, to reduce friction and to prevent wear and tear of the cam and the roller follower. The proposed embodiments have the additional advantage of utilizing already existing components in the engine such as the crankshaft, the balancer shaft, the gear shaft, and the cam, to drive the fuel pump, thereby enhancing the performance of the fuel pump without introducing any new components.

These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used for limiting the scope of the claimed subject matter.

BRIEF DESCRIPTION OF DRAWING

The above and other features, aspects of the subject matter will be better understood with reference to the following description, where:

Fig. 1 illustrates a front view of an internal combustion (IC) engine, in accordance with one embodiment of the present subject matter.

Fig. 2 illustrates a sectional view of the IC engine of Fig. 1 having an exemplary system for driving a fuel pump according to an embodiment of the present subject matter.

Fig. 3 illustrates a magnified view of a sleeve of the fuel pump according to an embodiment of the present subject matter.

Fig. 4 illustrates an exemplary location of a cam driving the fuel pump according to an embodiment of the present subject matter.

DETAILED DESCRIPTION

The subject matter described herein relates to a system for driving a fuel pump of an internal combustion (IC) engine, for example a two-stroke diesel engine. In one embodiment, the system includes a crankshaft, a fuel pump, and a cam. The fuel pump includes a plunger, which pressurizes fuel to high pressure. In an implementation, the plunger can be driven by a cam through a roller follower, operably coupled to the plunger. The cam is mounted on the crankshaft of the engine such that the cam rotates at the speed of the crankshaft of the engine, for example, a two-stroke diesel engine. Therefore, upon rotation of the crankshaft, the cam rotates to impart reciprocating motion to the plunger, which compresses the fuel inside the fuel pump to attain a sufficiently high pressurized state of the fuel. The pressurized fuel is then transferred to an injection component, for example, a fuel injector. In another embodiment, the cam can be mounted on a balancer shaft operably connected to die crankshaft of the IC engine, such that the cam rotates at the speed of the balancer shaft. In yet another embodiment, the cam can be mounted on a gear shaft of the IC engine, such that the cam rotates at speed of the gear shaft.

The subject matter in the detailed description has been explained with respect to a cam mounted on a crankshaft. However, it will be understood by a person ordinarily skilled in the art that the system for driving a fuel pump can also be implemented by mounting the cam on a balancer shaft or a gear shaft, providing the same advantages as that by the system with the cam mounted on the crankshaft. As would be clear to a person skilled in the art, the fuel pump can be mounted on the crankcase assembly such that the cam is in contact with the roller follower.

Fig. 1 illustrates a front view of an internal combustion (IC) engine 100, such as a two-stroke diesel engine, interchangeably referred to as the engine 100, in accordance with one embodiment of the present subject matter. In said embodiment, the engine 100 includes a crankcase assembly that houses a crankshaft (not shown in the figure). For discussion purposes, the crankcase assembly can be divided into a first crankcase sub assembly 102, and a second crankcase sub assembly 104. In one implementation, the first crankcase sub assembly 102 is the left hand side of the engine 100 and the second crankcase sub assembly 104 the right hand side of the engine 100, with the crankshaft extending in both the assemblies 102 and 104. The crankshaft is connected to a piston (not shown in the figure) of the engine 100 through a connecting rod 106. The crankcase assembly also includes an intake manifold 108 for the intake of charge into a cylinder (not shown in the figure) of the engine 100.

The crankshaft provides drive to a driveline of the engine 100 through a primary drive gear (not shown in this figure) mounted on the crankshaft and housed in the second crankcase sub assembly 104. The second crankcase sub assembly 104 also houses a primary driven gear (not shown in the figure) for driving a gear shaft (not shown in the figure). Further, the second crankcase sub assembly 104 houses a balancer gear (not shown in the figure), which is also driven by the primary drive gear.

The second crankcase sub assembly 104 includes a sleeve 110 for guiding a roller follower (not shown in this figure), and mounting a fuel supply means, such as a fuel pump 112, in the proximity of the crankshaft and the primary drive gear. In one embodiment, the fuel pump 112 is mounted on the sleeve 110 and is fitted in the second crankcase sub assembly 104 through a flange and fixed by means of fasteners, such as bolts, screws, rivets etc. The sleeve 110 serves as a guide to the roller follower and also acts as an adaptor or spacer to position the fuel pump 112 at a desired height from the crankshaft axis. In another embodiment, the fuel pump 112 is provided with an integral cast sleeve for guiding the roller follower. In such an embodiment, the fuel pump 112 with the integral cast sleeve can be mounted on the crankcase assembly. The fuel pump 112 has an outlet port 114 for attaching a pipe (not shown in the figure) to transfer fuel from the fuel pump 112 to a fuel rail (not shown in the figure). The fuel rail is connected to a fuel injector (not shown in the figure). In operation, the fuel pump 112 is driven by the crankshaft through a cam (not shown in the figure), due to which the fuel pump 112 pressurizes the fuel for injection and provides the fuel to the fuel injector through the fuel rail.

Fig. 2 illustrates a sectional view 200 of the IC engine 100 of Fig. 1 having an exemplary system for driving a fuel pump 112 according to an embodiment of the present subject matter. The system includes a crankshaft 202, a cam 204, the sleeve 110, and having a roller follower 206. The fuel pump 112 includes a plunger 208 placed inside a compression spring and operably coupled to the roller follower 206. The engine 100 further includes a cylinder 210, a cylinder head 212, a fuel rail 214, a fuel injector 216 mounted on the cylinder head 212, a piston 218, a combustion chamber 220, a primary drive gear 222, and the connecting rod 106. The piston 218 is slidably disposed inside the cylinder 210 and is connected to the crankshaft 202 through the connecting rod 106. The crankshaft 202 is rotatably mounted inside both the crankcase assemblies 102 and 104.

The primary drive gear 222 is mounted on the crankshaft 202 and is rotated at the speed of the crankshaft 202. In this embodiment, the cam 204 is mounted on the crankshaft 202 such that the cam 204 rotates at the speed of the crankshaft 202. The cam 204 is in contact with the roller follower 206 operably coupled to the plunger 208, and freely rotatable along its axis. The fuel pump 112 receives the fuel from a fuel tank (not shown in the figure) and provides the fuel at high pressure through the outlet port 114 of the fuel pump 112. The outlet port 114 is connected to the fuel rail 214 through a pipe (not shown in the figure), which transfers the pressurized fuel to the fuel injector 216. The fuel injector 216 injects the fuel at high pressure into the combustion chamber 220.

During operation, the piston 218 compresses the air inside the combustion chamber 220 to achieve an extremely high temperature of the air. At such high temperature, when the fuel injector 216 injects the fuel in the combustion chamber 220, the fuel mixes with compressed hot air and undergoes combustion. As a result, the piston 218 is pushed downwards to drive the crankshaft 202. Subsequently, the piston 218 again moves up towards the combustion chamber 220 to compress a fresh volume of air and the process of driving or rotating the crankshaft 202 continues.

On rotation, the cam 204, which is mounted on crankshaft 202, drives the roller follower 206, which is in contact with the cam 204 by the action of the compression spring mounted on the plunger 208. In an implementation, the cam 204 is an eccentric cam, which imparts a reciprocating motion to the roller follower 206. In another implementation, the cam 204 is a lobed cam.

The roller follower 206 reciprocates inside the sleeve 110 and pushes the plunger 208 to reciprocate in the fuel pump 112. In essence, the cam 204 converts the rotary motion of the crankshaft 202 into the reciprocating motion of the plunger 208 through the roller follower 206. The reciprocating movement of the plunger 208 compresses the fuel inside the fuel pump 112 thus raising pressure of the fuel inside the fuel pump 112. Thus, the motion of the crankshaft 202 can be directly used to drive the fuel pump 112 without any intermediate components such as chains and gears.

The present system, in addition to providing pressurized fuel, substantially reduces space constraint inside the engine 100, by eliminating the intermediate components conventionally used for transmission of motion from the crankshaft 202 to the plunger 208 in the fuel pump 112. The system also effectively minimizes mechanical stress on the engine 100 and transmission losses caused due to the intermediate components. Further, the system ensures that the crankshaft 202 can smoothly operate the primary drive gear 222 to reliably drive a clutch assembly (not shown in the figure) and a balancer system (not shown in the figure), when implemented in a vehicle.

However, at different load and speed conditions in which a vehicle operates, especially at extreme conditions such as at fuel pressures greater than 500 bar for systems at high engine speeds of about 5000 rpm, the fuel supply system operates at an elevated temperature and the mechanical stresses due to contact fatigue is large at such elevated temperatures. This stress at elevated temperatures may cause wear and tear of different components, such as the cam 204 and the roller follower 206 thereby disrupting smooth operation of the engine 100. Therefore, in one embodiment, the cam 204 and the roller follower 206 are coated with materials for example, tungsten carbide, diamond-like carbon (DLC), and so on, having good surface properties, which can provide high contact fatigue strength even at elevated temperatures, with improved friction behavior. Such a coating provides high surface fatigue strength and low friction for the surfaces of the cam 204 and the roller follower 206 and lends strength against wear and tear.

The engine 100 is also provided with a mechanism for lubricating the cam 204 and the roller follower 206. The lubrication mechanism can be either a splash lubrication mechanism or a forced lubrication mechanism using a mechanical or an electrical pump. In one embodiment, a $ splash lubrication mechanism is used for lubricating the cam 204 and the roller follower 206. For the purpose, a clutch housing (not shown in the figure) that is riveted with the primary driven gear (not shown in figure) is used to splash lubricating oil on the cam 204 and the sleeve 110. During the operation of the engine 100, clutch plates (not shown in the figure) rotate inside the clutch housing splashing the lubricating oil in an upward direction, such that it reaches the primary drive gear 222, the cam 204, and the roller follower 206 through the sleeve 110.

Fig. 3 illustrates a magnified view of the sleeve 110 according to an embodiment of the present subject matter. The sleeve 110 is provided with openings 302-1 and 302-2 through which the lubricating oil splashed through the clutch housing can enter the sleeve 110 and lubricate the roller follower 206. For the purpose of lubrication, the sleeve 110 is further provided with grooves, such as an annular groove 304 on its inner surface. During operation, when the clutch housing splashes the lubricating oil upwards towards the cam 204 and the sleeve 110, the oil enters the sleeve 110 through the openings 302-1 and 302-2 and starts flowing inside the groove 304 as depicted by the arrows 306, 308, 310, and 312. The flow of the lubricating oil in the grooves helps in lubricating the roller follower 206 as well as a guide surface provided for guiding the roller follower 206 inside the sleeve 110.

Fig. 4 illustrates an exemplary location of the cam 204 inside the engine 100, according to an embodiment of the present subject matter. As shown, the engine 100 includes the crankshaft 202, the cam 204, a pair of bearings, 402-1 and 402-2, and the primary drive gear 222. The crankshaft 202 is rotatably mounted inside the crankcase assembly with the help of bearings for example, 402-1 and 402-2. In an embodiment, the primary drive gear 222 and the cam 204 can be integrated to form a single component and can be mounted and locked axially on the crankshaft 202 by a locking nut 404. This configuration of the cam 204 integrated with the primary drive gear 222 to form a single component provides a robust and compact assembly for driving the fuel pump 112 in the engine 100. In another embodiment, the cam 204 can be mounted on the crankshaft 202 as a separate component from the primary drive gear 222. The cam 204 can be arranged on the crankshaft 202 in many other ways as would be clear to a person skilled in the art.

Though the above description has been provided with reference to the cam 204 being mounted on the crankshaft 202, it will be understood that the cam 202 may be mounted on other existing shafts without using intermediate components. For example, in one embodiment, the cam 204 can be mounted on a balancer shaft (not shown in the figure) of a balancer assembly (not shown in the figure), such that the cam 204 is driven at the speed of the balancer shaft. The balancer shaft is coupled to the crankcase assembly and oriented in parallel to the crankshaft 202. The balancer shaft may be operably coupled with the primary drive gear 222 through balancer gears (not shown in the figure), such that the primary drive gear 222 drives the balancer shaft at the same speed of the crankshaft 202. As would be clear to a person skilled in the art, the fuel pump 112 and the sleeve 110 in said embodiment can be mounted on the crankcase assembly such that the cam 204 is in contact with the roller follower 206. Therefore, upon rotation of the balancer shaft, the cam 204 rotates to impart reciprocating motion to the plunger 208, which compresses the fuel inside the fuel pump 112 to attain a sufficiently high pressurized state of the fuel. Such a placement of the cam 204 allows for an engine assembly that is compact. Further, the transmission losses during operation of the fuel pump 112 are substantially minimized due to elimination of additional intermediate components between the crankshaft 202 and the cam 204, and an appropriate pressure of the fuel supplied to the fuel rail 214 can be ensured.

In another embodiment, the cam 204 can be mounted on a gear shaft (not shown in the figure) of a driveline (not shown in the figure) of a four-stroke engine, such that the cam 204 is driven at the speed of the gear shaft. The gear shaft may be operably coupled with the primary drive gear 222 such that the primary drive gear 222 drives the gear shaft at a 1:1 ratio i.e. at the same speed of the crankshaft 202 or at a 1:2 ratio i.e. at half the speed of the crankshaft 202. Such a placement of the cam 204 allows for an engine assembly that is compact. Further, the transmission losses during operation of the fuel pump 112 are substantially minimized due to elimination of intermediate components between the crankshaft 202 and the cam 204. As a result an appropriate pressure of the fuel supplied to the fuel rail 214 can be ensured. As would be clear to a person skilled in the art, the fuel pump 112 and the sleeve 110 in said embodiment can be suitably mounted on the crankcase assembly such that the cam 204 is in contact with the roller follower 206.

The previously described versions of the subject matter and variants thereof have many advantages, including those which are described below. The subject matter described herein provides a compact and light weight IC engine 100 with the cam 204 being mounted on the crankshaft 202. Owing to the fact that the cam 204 for driving the fuel pump 112 is mounted on the crankshaft 202, the cam 204 is driven at the speed of the crankshaft 202. Such a placement of the cam 204 allows for an engine assembly that is compact. Since, the transmission losses during operation of the fuel pump 112 are substantially minimized due to elimination of additional intermediate components between the crankshaft 202 and the cam 204, the transmission losses are rninimized and an appropriate pressure of the fuel supplied to the fuel rail 214 can be ensured. As a consequence, the performance of the fuel pump 112 is enhanced substantially, i.e., the fuel pump 112 pumps the fuel at elevated pressure to the fuel rail 214 even at extreme operating conditions of the vehicle. The present embodiments have the additional advantage of utilizing components existing in the engine such as the crankshaft 202, the balancer shaft, the gear shaft, and the cam 204, thereby enhancing the performance of the fuel pump 112 without introducing any new components.

The subject matter in the detailed description has been explained with respect to a two-stroke engine, however, it will understood by a person ordinarily skilled in the art that the system for driving a fuel pump can be implemented in any type of both two-stroke engines and four-stroke engines.

Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained therein.

I/We claim:

1. An internal combustion (IC) engine (100) comprising:

a fuel pump (112) comprising a plunger (208); and

a crankshaft (202) housed inside a crankcase;

characterized in that

a roller follower (206) is operably coupled to the plunger (208); and

a cam (204) is mounted on the crankshaft (202), wherein the cam (204) drives the
plunger (208) through the roller follower (206).

2. The IC engine (100) as claimed in claim 1, wherein the cam (204) is mounted on the crankshaft (202) by a locking nut (404).

3. The IC engine (100) as claimed in claim 1, wherein the cam (204) is integral to a primary drive gear (222) to form a single component.

4. The IC engine (100) as claimed in claim 1 or 3, wherein the cam (204) and the primary drive gear (222) are separate components.

5. An internal combustion (IC) engine (100) comprising:

a fuel pump (112) comprising a plunger (208); and

a balancer shaft;

characterized in that

a roller follower (206) is operably coupled to the plunger (208); and

a cam (204) is mounted on the balancer shaft, wherein the cam (204) drives the
plunger (208) through the roller follower (206).

6. An internal combustion (IC) engine (100) comprising:

a fuel pump (112) comprising a plunger (208); and

a gear shaft;

characterized in that

a roller follower (206) is operably coupled to the plunger (208); and

a cam (204) is mounted on the gear shaft, wherein the cam (204) drives the plunger (208) through the roller follower (206).

7. The IC engine (100) as claimed in any of the claims 1, 5 or 6, wherein the fuel pump (112) is mounted on a sleeve (110), and wherein the sleeve (110) houses the roller follower (206).

8. The IC engine (100) as claimed in claim 7, wherein the sleeve (110) is provided with openings (302-1,302-2) for lubrication of the roller follower (206).

9. The IC engine (100) as claimed in claim 7, wherein the roller follower (206) and the sleeve (110) are lubricated using splash lubrication.

10. The IC engine (100) as claimed in any of the claims 1, 5 or 6, wherein the fuel pump (112) is mounted on a crankcase assembly, and wherein the fuel pump (112) is provided with an integrated cast sleeve for guiding the roller follower (206).

11. The IC engine (100) as claimed in any of the claims 1, 5 or 6, wherein the cam (204) is selected from a group of an eccentric cam and a lobed cam.

12. The IC engine (100) as claimed in any of the claims 1, 5 or 6, wherein the cam (204) and the roller follower (206) are coated with a material selected from a group of diamond-like carbon (DLC) and tungsten carbide.