GB2290835A

GB2290835A - Fuel injection pump

Info

Publication number: GB2290835A
Application number: GB9512627A
Authority: GB
Inventors: Masato Tsuzuki; Toshio Fujimura; Toshikazu Watanabe; Shigeyuki Kondo
Original assignee: Toyota Motor Corp; NipponDenso Co Ltd
Current assignee: Denso Corp; Toyota Motor Corp
Priority date: 1994-06-30
Filing date: 1995-06-21
Publication date: 1996-01-10
Anticipated expiration: 2015-06-21
Also published as: JPH0814133A; GB2290835B; DE19523781C2; DE19523781A1; GB9512627D0

Description

2290835 FUEL INJECTION PUMP 1 BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention generally relates to a fuel injection pump, and more particularly to a fuel injection pump which supplies pressurized fuel to an internal combustion engine in accordance with radial movements of plungers of a rotor relative to a housing during a rotation of the rotor.

(2) Description of the Related Art

Japanese Laid-Open Patent Application No.62- 288362 discloses an inner-cam type fuel injection pump. This pump supplies pressurized fuel to cylinders of a diesel engine by radial movements of plungers on a rotor relative to a housing during a rotation of the rotor.

In the fuel injection pump disclosed in the above-mentioned publication, a can ring having a plurality of teeth on its inner peripheral surface is slidably held. This fuel injection pump includes a rotor which is rotated in synchronism with the rotation of the engine. A plurality of plungers are inserted in the rotor, and the plungers are moved in radial directions of the rotor when they are engaged with the teeth of the cam ring during the rotation of the rotor. A timing lever which moves a position of the cam ring to a housing in a circumferential direction of the rotor in accordance with operating conditions of the engine is provided. The timing of the fuel injection by the above conventional pump can be adjusted by moving the position of the cam ring to the housing in the circumferential direction 30 by using the timing lever. In order to allow the timing of the fuel injection to be adjusted independently of the rotation of the rotor, it is necessary that the cam ring is rotatably 1 held by the housing on the above fuel injection pump. For this reason, a clearance between the outer peripheral surface of the cam ring and the inner peripheral surface of the housing is provided. This clearance is filled with fuel contained in the pump, and this fuel in the clearance serves as a lubricant which reduces a sliding friction between the housing and the cam ring.

However, in the above fuel injection pump, there is a problem that the inner peripheral surface of the housing and the outer peripheral surface of the cam ring are worn or burned during the rotation of the rotor in a certain condition. The provision of only the clearance on the above conventional pump is not sufficient to avoid this problem.

More specifically, reactions are exerted on the cam ring in the circumferential direction when the plungers of the rotor are respectively engaged with the teeth of the cam ring during the rotation of the rotor. The cam ring is merely rotatably held by the housing on the above conventional pump. The cam ring vibrates in the radial direction and in the circumferential direction because of the reactions during the rotation of the rotor.

If the clearance between the housing and the cam ring is constantly an appropriate distance, no problem will arise from the vibrations of the cam ring. However, as the housing is thermally expanded due to heat generated during operation of the pump, the clearance between the housing and the cam ring is increased. If the clearance is too great to maintain the lubricant with a proper film thickness in the clearance between the housing and the cam ring, a cavitation occurs due to the above vibrations of the cam ring, which produces bubbles in the clearance and results in a lack of the lubricant with a proper film thickness in the clearance. Therefore, the inner peripheral 1 surface of the housing and the outer peripheral surface of the cam ring are worn or burned. An increase of the vibration energy on the cam ring will more severely cause the wearing or burning of the housing and the cam ring because of the lack of the lubricant with a proper film thickness.

Further, reactions are exerted on the cam ring in the radial directions when the plungers of the rotor are engaged with the teeth of the cam ring during the rotation of the rotor. The tooth portions of the cam ring are deformed in the radial directions due to the above reactions. The outer peripheral surfaces of the tooth portions of the cam ring and the inner peripheral surface of the housing are brought into contact due to the deformation.

is Accordingly, in the above conventional pump, the inner peripheral surface of the housing and the outer peripheral surface of the can ring are worn or burned during the rotation of the rotor, which significantly lowers the performance of the fuel injection of the pump. 20 SUMMARY OF THE INVENTION Accordingly, it is a general object of the present invention to provide an improved fuel injection pump in which the above-described problem is eliminated. 25 Another object of the present invention is to provide a fuel injection pump which realizes a safe and stable fuel injection operation without arising the problem of the wearing or burning of the outer peripheral surface of the cam ring and the inner peripheral surface of the housing during the rotation of the rotor.

Still another object of the present invention is to provide a fuel injection pump which realizes a safe and stable fuel injection operation wherein the occurrence 1 of a cavitation due to vibrations of the cam ring to the housing and the lack of the lubricant with a proper film thickness in the clearance between the housing and the cam ring are prevented.

The above-mentioned objects of the present invention are achieved by a fuel injection pump which includes: a housing; a cam ring having a plurality of teeth on an inner peripheral surface of the cam ring, the cam ring being rotatably held by the housing; a rotor which is rotated in synchronism with a rotation of an internal combustion engine; a plurality of plungers which are arranged in the rotor and moved in radial directions of the rotor by engagement with the teeth of the cam ring during the rotation of the rotor; and a timing control unit which moves the cam ring relative to the housing in a circumferential direction of the rotor in accordance with operating conditions of the engine, wherein pressurized fuel is supplied to cylinders of the engine in accordance with the radial movements of the plungers during the rotation of the rotor, characterized by a mechanism for preventing wearing of an inner peripheral surfa.a of the housing and an outer peripheral surface of the cam ring during the rotation of the rotor.

According to the present invention, the clearance between the housing and the cam ring is maintained to an appropriate distance even when the fuel injection pump is heated. The occurrence of the cavitation and the lack of the lubricant due to the vibrations of the cam ring to the housing during the rotation of the rotor can be prevented.

Therefore, the wearing of the outer peripheral surface of the cam ring and the inner peripheral surface of the housing during the rotation of the rotor can be prevented.

1 BRIEF DESCRIPTION OF THE DRAWINGS other objects, features and advantages of the present invention will be more apparent from the following detailed description when read in conjunction with the accompanying drawings in which:

FIG.1 is a view of a fuel injection pump to which a first embodiment of the present invention is applied; FIG.2 is an enlarged cross-sectional view of the fuel injection pump taken along a line II-II in FIG.1; FIG.3 is an enlarged cross-sectional view of a fuel injection pump in a second embodiment of the present invention; FIG.4 is an enlarged cross-sectional view of is a sliding member of the fuel injection pump in the second embodiment; FIG.5 is an enlarged cross-sectional view of another sliding member of the fuel injection pump in the second embodiment; 20 FIG.6 is an enlarged cross-sectional view of a fuel injection pump in a third embodiment of the present invention; and FIG.7 is an enlarged crosssectional view of a fuel injection pump in a fourth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A description will now be given of a fuel injection pump to which a first embodiment of the present invention is applied.

FIG.1 shows a fuel injection pump 10 to which the first embodiment of the present invention is applied. In FIG.1, the fuel injection pump 10 includes a housing 11, 1 and a cam chamber 12 provided inside the housing 11.

Various component parts of the pump are arranged within the housing 11, and fuel from a fuel tank (not shown) is stored in the cam chamber 12.

In the housing 11 of the fuel injection pump in FIG.1, an overflow valve 20, a spill valve 30, a fuel return valve 40, an accumulator 50, and a constant-pressure valve 60 are arranged. The space inside the housing 11 is divided into three major portions: a main portion including a can ring 110 and a drive shaft 70; a distribution head portion including a cylinder 100; and a cover portion including a rotation angle sensor 122.

The overflow valve 20 communicates with the cam chamber 12, and this overflow valve 20 serves to avoid an excessive pressure of the fuel stored in the cam chamber 12. The overflow valve 20 is a non-return valve which is comprised of a ball valve 22 and a spring 24. When the pressure of the fuel stored in the cam chamber 12 is greater than a biasing force of the spring 24, the ball valve 22 is raised against the force of the spring 24 and the overflow valve 20 is opened to return the fuel back to the fuel tank.

The spill valve 30 is an electromagnetic valve which is opened and closed by an electromagnetic force produced at an electromagnetic coil 31. A valve element 32 of the spill valve 30 is biased upward by a spring 33. When the spill valve 30 is closed, the valve element 32 rests on a valve seat 37, and when the spill valve 30 is opened, the valve element 32 is raised from the valve seat 37.

An armature 34 which transmits the electromagnetic force from the electromagnetic coil 31 and a stopper 36 which is biased downward by a spring 35 are connected to the top of the valve element 32. The movement of the valve element 32 to the valve seat 37 is restricted 1 by the armature 34 and the stopper 36. The spill valve 30 is opened and closed to control a flow of fuel between the spill valve 30 and a fuel inlet gallery 17, and a flow of fuel between the fuel return valve 40 and the cylinder 100 through a fuel spill passage 103.

When the spill valve 30 is closed, the pressure of the fuel is applied to only the side surface of the valve element 32. At this time, the spilling of the pressurized fuel from the spill valve 30 is stopped, and the pressurized fuel is supplied from the fuel injection pump 10 to the diesel engine. On the other hand, when the spill valve 30 is opened, the pressure of the fuel is applied to not only the side surface of the valve element 32 but also the top of the valve element 32. At this time, the pressurized fuel is spilled into the cam chamber 12 or the fuel inlet gallery 17, and the supply of the pressurized fuel to the diesel engine is stopped.

The operation of the spill valve 30 will be explained in more detail. An electromagnetic force is generated at the electromagnetic coil 31 when current flows through the electromagnetic coil 31. The valve element 32 is pressed downward by the armature 34 due to this electromagnetic force. At the same time, the valve element 32 is biased downward by the spring 35. As a sum of the downward force of the armature 34 by the electromagnetic coil 31 and the downward biasing force of the spring 35, which is exerted on the valve element 32 downward, is greater than the upward biasing force of the spring 33, the valve element 32 rests on the valve seat 37 so that the spill valve 30 is closed.

On the other hand, when the supply of current to the electromagnetic coil 31 is turned off, the downward force of the armature 34 on the valve element 32 is 1 eliminated. As the downward biasing force of the spring 35 is smaller than the upward biasing force of the spring 33, the valve element 32 is raised from the valve seat 37, so that the spill valve 30 is opened. The opening and closing of the spill valve 30 is sensitive to the ONIOFF of the electromagnetic coil 31 because the pressure of the fuel is applied to the valve element 32. Therefore, accurate timing of the fuel injection or fuel spilling of the fuel injection pump 10 can be determined by controlling the operation of the spill valve 30.

The fuel return valve 40 is a non-return valve which is comprised of a ball valve 42 and a spring 44. This structure of the fuel return valve 40 is similar to that of the overflow valve 20. When the spill valve 30 is opened, the pressurized fuel is spilled to the fuel inlet gallery 17. The pressurized fuel is contained in the cylinder 100. The fuel return valve 40 serves to reduce the pressure of the fuel, supplied from the cylinder 100 via the fuel spill passage 103, to a certain low pressure. Also.

the fuel return valve 40 returns the fuel back to the fuel tank (not shown). The accumulator 50 absorbs a fluctuation of the pressure of the fuel contained in the fuel inlet gallery 17 and in the cylinder 100. The accumulator 50 includes a 25 piston 52, a spring 54, and a fuel chamber 57. The fuel chamber 57 communicates with the inside of the cylinder 100 and the fuel inlet gallery 17 via a passage 56. The piston 52 is biased in one direction by the spring 54, and it is moved against the biasing force of the spring 54 in accordance with the pressure of the fuel contained in the fuel chamber 57. This movement of the piston 52 within the accumulator 50 produces a negative pressure in the fuel chamber 57. This makes it possible to absorb a fluctuation _; 9 - 1 of the pressure of the fuel in the fuel inlet gallery 17 and in the cylinder 100.

In the actual fuel injection pump, a plurality of constant-pressure valves 60 which correspond to the respective cylinders of the diesel engine are provided. However, for the sake of simplicity of explanation, only one constant-pressure valve 60 is shown in FIG.1.

The constant-pressure valve 60 maintains the pressure of the fuel contained in fuel lines from fuel outlet ports 102 to fuel injectors (not shown) of the diesel engine to be constant. The fuel outlet ports 102 are provided within the housing 11 of the pump. When the internal pressure of the fuel outlet ports 102 is higher than a reference pressure, the constant-pressure valve 60 serves to supply the pressurized fuel to the fuel injectors of the engine. When the internal pressure of the fuel outlet ports 102 is lower than the reference pressure, the constant-pressure valve 60 serves to keep the pressure of the fuel in the fuel lines between the valve 60 and the fuel injectors of the engine constant. At this time, no fuel is supplied from the constant-pressure valve 60 to the fuel injectors of the engine. In the cam chamber 12 of the housing 11, the drive shaft 70, a fuel feed pump 80, the rotor 90, the 25 cylinder 100, and the cam ring 110 are arranged. The drive shaft 70 is rotated at a rotation speed which is half a rotation speed of a crankshaft of the diesel engine. The fuel feed pump 80 is actuated by a rotating force of the drive shaft 70 to supply fuel. The rotor 90 is rotated in synchronism with the rotation of the diesel engine. The rotor 90 has a small-diameter portion and a large-diameter portion. The cylinder 100 is fitted into the small-diameter portion of the rotor 90. The cam 1 ring 110 is arranged so that it encompasses the outer peripheral surface of the large-diameter portion of the rotor 90.

The drive shaft 70 is rotatably supported by a bushing 13 and a bearing 14. The bushing 13 is arranged at one end portion of the housing 11, and the bearing 14 is arranged at an intermediate portion of the housing 11. A certain amount of fuel is supplied to a portion where the drive shaft 70 and the bushing 13 join, and this fuel serves to reduce a sliding friction between the drive shaft 70 and the bushing 13. An oil passage 16 is arranged so that a fuel inlet 15 communicates with the bushing 13 via the oil passage 16. This oil passage 16 serves to deliver the fuel from the fuel inlet 15 to the bushing 13. In addition, an oil seal 18 is arranged at the end of the drive shaft 70 which is connected to the diesel engine.

A pulse unit 120 is arranged on the drive shaft 70 in the vicinity of the bearing 14. A plurality of teeth 121 are formed at equal intervals on an outer peripheral surface of the pulse unit 120. The rotation angle sensor 122 is fixed to the cam ring 110, and this sensor 122 generates a pulse signal in accordance with the rotation of the teeth 121 of the pulse unit 120 around the drive shaft 70. The pulse signal, generated by the rotation angle sensor 122, indicates a rotation angle of the rotor 90 around the drive shaft 70. The timing of each of radial movements of plungers on the rotor 90 during the rotation of the rotor 90 can be detected by using the pulse signal from the rotation angle sensor 122.

The fuel feed pump 80 is a vane pump which is comprised of an outer wall 81 and a rotor 83 having a plurality of vanes 82. The outer wall 81 is secured to the housing 11. The fuel feed pump 80 includes an inlet opening 1 84 and an outlet opening 85 which are formed in the housing 11. The inlet opening 84 of the fuel feed pump 80 communicates with the fuel inlet 15. The pressure of fuel supplied from the inlet opening 84 is increased by the vanes 82 of the fuel feed pump 80 during the rotation of the rotor 83 around the drive shaft 70, and the fuel is discharged from the outlet opening 85.

The rotor 90 is connected to the drive shaft 70, and the rotor 90 is rotatably supported on an inner peripheral surface 100a of the cylinder 100. The rotor 90 is rotated by the drive shaft 70 in a liquid-proof manner. The large- diameter portion of the rotor 90 contains a pressure chamber 91, and the small-diameter portion of the rotor 90 contains a fuel inlet 92, a fuel outlet 93, first fuel passages 94, and second fuel passages 95. The fuel inlet 92 of the rotor 90 is open to fuel supply ports 101 of the cylinder 100, and the fuel outlet 93 of the rotor 90 is open to fuel outlet ports 102 of the cylinder 100. The fuel inlet 92 and the fuel outlet 93 communicate with each other via the first fuel passages 94. The fuel outlet 93 and the pressure chamber 91 communicate with each other via the second fuel passages 95.

In the pressure chamber 91 of the rotor 90, a plurality of plungers 96a through 96d are inserted. The plungers 96a through 96d are respectively movable on the rotor 90 in radial directions of the rotor 90 in a liquid proof manner. In addition, an annular groove 97 which is open to the fuel outlet 93 is formed throughout the outer periphery of the rotor 90.

In the cylinder 100, there are provided the fuel supply ports 101 and the fuel outlet ports 102. As described above, the fuel inlet gallery 17 and the inside of the rotor 90 communicate with each other via the fuel supply 1 ports 101, and the inside of the rotor 90 and the constantpressure valve 60 communicate with each other via the fuel outlet ports 102.

The fuel inlet gallery 17 communicates with the outlet opening 85 of the fuel feed pump 80 via an external fuel line (not shown).

The fuel supply ports 101 and the fuel outlet ports 102 which correspond to the respective cylinders of the diesel engine are provided in the cylinder 100. When the rotor 90 is rotated in synchronism with the rotation of the diesel engine, one of the fuel supply ports 101 is opened to the fuel inlet gallery 17, and one of the fuel outlet ports 102 is opened to one specific constant-pressure valve 60 (which is connected to the related cylinder of the engine), in accordance with the rotation angle of the diesel engine. In addition, the cylinder 100 further includes the fuel spill passage 103 which communicates with the spill valve 30. The annular groove 97 is open to the 20 fuel spill passage 103, and the annular groove 97 always communicates with the spill valve 30 during the rotation of the rotor. Referring next to FIG.2, a description will be given of the fuel injection pump 10 in the first embodiment of the present invention. The fuel injection pump 10 in this embodiment is applicable to a six-cylinder internal combustion engine.

In the fuel injection pump 10, as shown in FIG.2, the rotor 90 which is rotated in synchronism with the rotation of the engine (not shown) is provided. The cam ring 110 having a plurality of teeth 110a through 11Of at equal intervals on the inner peripheral surface of the cam ring is rotatably held by the housing 11. The plungers 96a 1 through 96d are inserted in the rotor 90.

During the rotation of the rotor 90, all the plungers 96a through 96d are moved in the inward radial directions of the rotor 90 when they are engaged with the teeth of the cam ring. on the other hand, when the plungers 96a through 96d are disengaged from the teeth of the cam ring, all the plungers are moved in the outward radial directions of the rotor 90. Such reciprocating movements of the plungers are repeated.

When all the plungers 96a through 96d are moved in the inward radial directions of the rotor, the fuel included in the pressure chamber 91 is pressurized, and the pressurized fuel is supplied to corresponding one of the cylinders of the diesel engine. On the other hand, when all the plungers 96a through 96d are moved in the outward radial directions of the rotor, fuel from the fuel tank is supplied to the pressure chamber 91.

When the rotor 90 is rotated by one revolution, the crankshaft of the diesel engine is rotated two revolutions. In this embodiment, the pressure of the fuel in the pressure chamber 91 is increased six times during one revolution of the rotor 90.

On the rotor 90 of the fuel injection pump 10, rollers 99a through 99d, which serve to smoothly transmit the reacting forces from the teeth of the cam ring to the plungers 96a through 96d, are respectively arranged at the outside ends of the plungers 96a through 96d. The rollers 99a through 99d are respectively held by roller shoes 98a through 98d.

During the rotation of the rotor 90, the fuel inlet 92 is opened to one of the fuel supply ports 101 subsequently to the outward radial movements of the plungers. The fuel is sucked from that fuel supply port 101 1 into the pressure chamber 91 due to the negative pressure produced there by the outward radial movements of the plungers. After this, the passage of the fuel inlet 92 and the fuel supply port 101 is closed.

Further, the fuel outlet 93 is opened to one of the fuel outlet ports 102, and subsequently the inward radial movements of the plungers 96a through 96d take place to pressurize the fuel in the pressure chamber 91. If the spill valve 30 is closed at this time, the pressurized fuel in the pressure chamber 91 is supplied to the diesel engine via the constant-pressure valve 60. If the spill valve 30 is opened at this time, the pressurized fuel in the pressure chamber 91 is partially returned to the fuel tank and partially returned to the fuel inlet gallery 19 through the spill valve 30. The supplying of the pressurized fuel to the diesel engine is stopped.

When the pressurized fuel is spilled by the spill valve 30, the internal pressure of the first and second fuel passages 94 and 95 of the rotor 90 may be changed to a negative pressure due to the inertia of the spilled fuel. If these passages 94 and 95 are subjected to such a negative pressure, the relationship of the quantity of the pressurized fuel being injected versus the radial movement of the plungers may be significantly changed, which will lower the accuracy of the quantity of the pressurized fuel being injected by the fuel injection pump 10.

In the above fuel injection pump 10, the pressurized fuel spilled from the spill pump 30 is partially returned to the fuel inlet gallery 17, and the accumulator 50 is provided to communicate with the fuel inlet gallery 17, in order to avoid the above-mentioned problem. Even when the internal pressure of the first and second fuel passages 94 and 95 is changed to a negative pressure due to 1 the inertia of the spilled fuel, the part of the spilled fuel is returned to the fuel inlet gallery 17 to raise the internal pressure of the fuel inlet gallery 17. The accumulator 50 absorbs the fluctuation of the pressure of the fuel in the fuel inlet gallery 17 and in the cylinder due to the returning of the spilled fuel, and stabilizes the pressure of the fuel therein.

Further, in the above fuel injection pump 10, the spilled fuel is partially returned to the fuel inlet gallery 17. That is, this spilled fuel as well as the fuel from the fuel feed pump 80 is supplied to the pressure chamber 91. Therefore, a safe and reliable supplying of the fuel to the pressure chamber 91 is realized by the above fuel injection pump 10 even at the time of high-speed rotation of the diesel engine.

Next, in the above fuel injection pump 10, a timing control unit 130 is provided, as shown in FIG.2. In FIG.2, the timing control unit 130 includes two opposing pistons 131 and 132, and a rod 133 held by the two pistons 131 and 132. The rod 133 is secured to the cam ring 110.

Therefore, the cam ring 110 is rotatably held by the housing 11 but it is fixed to the rod 133 of the timing control unit 130.

This timing control unit 130 moves the cam ring 110 relative to the housing 11 in a circumferential direction of the rotor 90 in accordance with operating conditions of the diesel engine.

The two pistons 131 and 132 are slidably arranged in a timing control unit housing 130a. In the timing control unit 130, a high-pressure chamber 134 is constituted by an internal portion of the housing 130a to the right of the piston 131, and a low-pressure chamber 135 is constituted by an internal portion of the housing 130a to 1 the left of the piston 132. The high-pressure chamber 134 communicates with the fuel outlet port 85 of the fuel feed pump 80, and the low-pressure chamber 135 communicates with the fuel inlet port 84 of the fuel feed pump 80.

In the low-pressure chamber 135 of the housing 130a, a spring 136 is arranged to bias the piston 132 to the right in FIG.2. The high-pressure chamber 134 and the low-pressure chamber 135 communicate with each other via an external pipe line (not shown). This external pipe line is opened or closed by switching ONIOFF of an electromagnetic valve 140 shown in FIG.1. If the switching of the electromagnetic valve 140 is controlled by using an appropriate method, the cam ring 110 can be set to a desired angular location to the housing 11.

The pistons 131 and 132 are moved to the left or the right in accordance with the difference in the fuel pressure between the high-pressure chamber 134 and the low pressure chamber 135. The rod 133 is moved to the left or the right in accordance with the movement of the pistons 131 and 132. Accordingly, the timing control unit 130 moves the cam ring 110 relative to the housing 11 in the circumferential direction of the rod 110.

In the above fuel injection pump 10, the timing of the radial movements of the plungers 96a through 96d can be adjusted by moving the cam ring 110 relative to the housing 11 in the circumferential direction of the rotor by using the timing control unit 130. Therefore, the timing of the fuel injection by the fuel injection pump 10 can be controlled by using the timing control unit 130.

In the above fuel injection pump 10, there is provided a clearance between the outer peripheral surface of the cam ring 110 and the inner peripheral surface of the housing 11. This clearance is filled with the fuel from the 1 cam chamber 12, and this fuel serves as the lubricant which reduces the sliding friction between the cam ring and the housing.

However, as previously described, in the conventional fuel injection pump, there is a problem in that the above- mentioned clearance may deviate from an appropriate distance due to heat generated during the operation of the fuel injection pump and due to reactions exerted on the cam ring by the plungers when they are engaged with the teeth of the cam ring. If theclearance is increased to an excessively large distance, it is difficult that the fuel in the clearance has a proper film thickness of the lubricant. The cavitation in the fuel included in the clearance will take place, and the fuel included in the is clearance will lack the lubricant with a proper film thickness. Therefore, the wearing or burning of the peripheral surfaces of the housing and the cam ring may occur.

In the first embodiment of the present invention, a plurality of struts 150 are arranged in the housing 11 at portions adjacent to the cam ring 110. The struts 150 are made of a material with a small coefficient of thermal expansion. The material of the struts 150 has at least mechanical characteristics greater than those of a material of the housing 11. An example of the material of the struts 150 is 11SPC2011 according to Japanese Industrial Standards (JIS). The struts 150 are arranged in the housing 11 at the portions which are opposite to the outer peripheral 30 surface of the cam ring 110. Therefore, the struts 150 which are formed in the housing 11 encompass the cam ring 110. In order to arrange the above struts 150 in 1 the housing 11, openings are formed in the housing 11 at respective locations of the struts 150 in the housing 11, and the struts 150 within the housing 11 are subsequently formed through casting by putting the material of the struts 150 into the openings of the housing 11. Even though a wall thickness of the housing 11 is relatively small, the struts 150 can easily be arranged in the housing 11 by using this method.

In the above first embodiment, the struts 150 having a small coefficient of thermal expansion are arranged in the housing 11 at portions adjacent to the cam ring 110. Even when the housing 11 is heated to a high temperature due to heat generated during operation of the fuel injection pump 10, the thermal expansion of the housing 11 is prevented by the inclusion of the struts 150, and an appropriate distance between the inner peripheral surface of the housing 11 and the outer peripheral surface of the cam ring 110 is maintained.

Therefore, the first embodiment can prevent the wear or burning of the inner peripheral surface of the housing 11 and the outer peripheral surface of the cam ring 110. As the clearance between the housing 11 and the cam ring 110 is maintained to an appropriate distance, it is possible to prevent the vibration of the cam ring 110 to the housing 11 during the rotation of the rotor. Also, the prevention of the vibration of the cam ring 110 to the housing 11 makes it possible to prevent the occurrences of the cavitation and the lack of the lubricant between the housing 11 and the cam ring 110 even when the viscosity of the fuel in the clearance is lowered due to the heat of the fuel injection pump 10.

Accordingly, in the fuel injection pump 10 in the above first embodiment, the cam ring 110 can smoothly be 1 rotated within the housing 11 even when the fuel injection pump 10 is heated to a high temperature during operation.

Therefore, the fuel injection pump 10 in this embodiment can control the timing of the fuel injection to the diesel engine in an appropriate manner.

In the above first embodiment, a plurality of struts 150 are arranged in the housing 11 at the portions adjacent to the cam ring 110. However, the scope of the present invention is not limited to this embodiment. It is possible to use a continuous strut which is arranged throughout the periphery of the housing 11 to fully encompass the outer peripheral surface of the cam ring 110, instead of the plurality of struts 150.

Next, a description will be given of a second embodiment of the present invention.

FIG.3 shows a fuel injection pump in the second embodiment of the present invention. In FIG.3, the parts which are the same as corresponding parts in FIGS.1 and 2 are dasignated by the same reference numerals, and a description thereof will be omitted.

In the fuel injection pump in the second embodiment, a sliding member is arranged between the inner peripheral surface of the housing 11 and the outer peripheral surface of the cam ring 110 to prevent the wearing of the respective surfaces of the housing 11 and the cam ring 110. In FIG.3, the sliding member is a radial ball bearing 160.

FIG.4 shows the sliding member in the second embodiment. In FIG.4, the radial ball bearing 160 includes an outer ring 161, an inner ring 162, and a plurality of balls 163 between the outer ring 161 and the inner ring 162.

The outer ring 161 is secured to the inner peripheral surface of the housing 11, and the inner ring 162 is secured 1 to the outer peripheral surface of the cam ring 110.

In the above second embodiment, the radial ball bearing 160 is arranged between the inner peripheral surface of the housing 11 and the outer peripheral surface of the cam ring 110. The cam ring 110 can smoothly be rotated within the housing 11 without causing the wear of the peripheral surfaces of the two elements, because of the radial ball bearing 160.

Accordingly, even though the cam ring 110 and the housing 11 are deformed due to heat generated during operation of the fuel injection pump 10 or due to reactions exerted on the cam ring 110 by the plungers 96a-96d when they are engaged with the teeth 110a-110f of the cam ring, the cam ring 110 and the housing 11 do not contact each other because of the radial ball bearing 160. Therefore, in the above second embodiment, it is possible to prevent the wear or burning of the inner peripheral surface of the housing 11 and the outer peripheral surface of the cam shaft 110. The radial ball bearing 160 in this embodiment reduces the sliding friction of the cam ring 110 when it is rotated within the housing 11.

FIG.5 shows another sliding member of the fuel injection pump in the second embodiment. In FIG.5, a sliding member is arranged between the inner peripheral surface of the housing 11 and the outer peripheral surface of the cam ring 110, and this sliding member comprises a radial tapered roller bearing 170, a washer 174, and an elastic material 175.

In the embodiment shown in FIG.5, the radial tapered roller bearing 170 is resistant to both a radial load exerted on the cam ring 110 in a radial direction of the rotor 90 and a thrust load exerted on the cam ring 110 in an axial direction of the rotor 90. The bearing 170 1 comprises an outer ring 171, an inner ring 172, and a plurality of tapered rollers 173 between the outer ring 171 and the inner ring 172. The outer ring 171 is secured to the inner peripheral surface of the housing 11, and the inner ring 172 is secured to the outer peripheral surface of the cam ring 110. The tapered rollers 173 are inserted between two opposing surfaces of the outer and inner rings 171 and 172. The opposing surfaces of the rings 171 and 171 are formed into tapered slanting surfaces. Therefore, the radial tapered roller bearing 170 is capable of resisting to both the radial load and the thrust load.

To allow the radial tapered roller bearing to resist to the thrust load, the washer 174 is arranged on one side of the bearing 170, and the elastic material 175 which is secured to the housing 11 is arranged on the washer 174. The washer 174 is made of a material with a small coefficient of friction.

In the above embodiment in FIG.5, the rotation of the cam ring 110 to the housing 11 is stably maintained by the radial tapered roller bearing 170 even when the cam ring 110 and the housing 11 are deformed due to the heat generated during the operation of the pump 10 or due to the radial load exerted on the cam ring 110. As the housing 11 and the cam ring 110 are not brought into contact, the wearing of the inner peripheral surface of the housing 11 and the outer peripheral surface of the cam ring is prevented. Also, even when the thrust load is exerted on the cam ring 110, the fuel injection pump 10 in this embodiment is capable of resisting to the thrust load by the elastic material 175. A smooth rotation of the cam ring 110 to the housing 11 is maintained.

FIG.6 shows a fuel injection pump in a third embodiment of the present invention. In FIG.6, the parts 1 which are the same as corresponding parts in FIGS.1 and 2 are designated by the same reference numerals, and a description thereof will be omitted.

In the third embodiment in FIG.6, a sliding member is arranged between the inner peripheral surface of the housing 11 and the outer peripheral surface of the cam ring 110, and this sliding member is an elastic material 180 with a small coefficient of friction. Examples of the elastic material 180 which are applicable to this embodiment are an engineering plastic having a small coefficient of friction and a certain modulus of elasticity, and a porous metal having a certain modulus of elasticity and containing lubricating oil.

In the above third embodiment, the elastic is material 180 is arranged between the housing 11 and the cam ring 110, and the cam ring 110 is rotatable to the housing 11 as the elastic material 180 has an appropriate sliding characteristic. Even when the housing 11 and the cam ring 110 are deformed due to the heat generated during the operation of the fuel injection pump 10 or due to the reactions exerted on the cam ring 110, the cam ring 110 is rotatable to the housing 11 because the elastic material 180 has a small coefficient of friction. Also, vibrations transmitted from the cam ring 110 to the housing 11 are absorbed by the elastic material 180, and the occurrence of noises due to the vibrations of the cam ring 110 is avoided.

Further, the above third embodiment can prevent the wearing of the inner peripheral surface of the housing 11 and the outer peripheral surface of the housing 11.

FIG.7 shows a fuel injection pump in a fourth embodiment of the present invention. In FIG.7, the parts which are the same as corresponding parts in FIGS.1 and 2 are designated by the same reference numerals, and a 1 description thereof will be omitted.

In the fuel injection pump in the fourth embodiment, recesses 190a through 190f are formed in the inner peripheral surface of the housing 11 at respective portions which are opposite to outer peripheral surface portions of the cam ring 110 corresponding to the teeth 110a through 110f. The recesses 190a-190f in this embodiment are formed into a cylindrical shape as shown in FIG.7. The distance between the housing 11 and the cam ring 110 is greater at the recesses 190a-190f than at the other peripheral surface portions.

When the fuel injection pump in the fourth embodiment is operated, the plungers 96a-96d of the rotor 90 are engaged with the teeth 110a-110f of the cam ring 110 during the rotation of the rotor 90. The reactions are exerted on the cam ring 110 in the radial direction at the related outer surface portions corresponding to the teeth 110a-110f by the engagements between the plungers 96a-96d and the teeth 110a-110f. At this time, the related outer surface portions of the cam ring 110 are respectively deformed toward the inner peripheral surface of the housing 11 due to the radial-direction reactions on the cam ring 110.

In the above fourth embodiment, the recesses 190a-190f are formed in the inner peripheral surface of the housing 11 at the respective portions which are opposite to the outer peripheral surface portion of the cam ring 110 corresponding to the teeth 110a-110f, and the distance between the housing 11 and the cam ring 110 is greater at the recesses 190a-190f than at the other peripheral surface portions. Therefore, even when the cam ring 110 is deformed, the cam ring 110 and the housing 11 are not brought into contact because of the recesses 190a-190f. The - 24 1 above fourth embodiment can prevent the wearing of the inner peripheral surface of the housing 11 and the outer peripheral surface of the cam ring 110.

In addition, the clearance between the housing 11 and the cam ring 110 at the peripheral surface portions, other than the recesses 190a-190f, is maintained to an appropriate distance. The cam ring 110 and the housing 11 do not rattle during the rotation of the rotor 90, and the occurrence of the cavitation and the lack of the lubricant can be avoided in the fourth embodiment.

Further, the present invention is not limited to the above-described embodiments, and variations and modifications may be made without departing from the scope of the present invention.

Claims

1 CLAIMS:

1. A fuel injection pump which includes:

housing (11); cam ring (110) having a plurality of teeth (110a) through (110f) on an inner peripheral surface of the cam ring, said cam ring being rotatably held by said housing; a rotor (90) which is rotated in synchronism with a rotation of an internal combustion engine; a plurality of plungers (96a) through (96d) which are arranged in said rotor and moved in radial directions of said rotor by engagement with said teeth of said cam ring during the rotation of the rotor; and a timing control unit (130) which moves said cam ring relative to said housing in a circumferential direction of the rotor in accordance with operating conditions of the engine, wherein pressurized fuel is supplied to cylinders of the engine in accordance with the radial movements of the plungers during the rotation of the rotor, 25 characterized in that said fuel injection pump comprises means for preventing wearing of an inner peripheral surface of the housing (11) and an outer peripheral surface of the can ring (110) during the rotation of the rotor. 30 26 - 1

2. The fuel injection pump according to claim 1, characterized in that said means comprises struts (150) which are arranged in the housing at portions adjacent to the cam ring, said struts being made of a material with a small coefficient of thermal expansion.

3. The fuel injection pump according to claim 1, characterized in that said means comprises a sliding member which is arranged between the inner peripheral surface of the housing and the outer peripheral surface of the cam ring. 15

4. The fuel injection pump according to claim 3, characterized in that said sliding member comprises a bearing (160).

5. The fuel injection pump according to claim 3, characterized in that said sliding member comprises an elastic material (180) with a small coefficient of friction.

1

6. The fuel injection pump according to claim 3, characterized in that said sliding member comprises a bearing (170), a washer (174) with a small coefficient of friction, and an elastic material (175). 5

7. The fuel injection pump according to claim 1, characterized in that said means comprises recesses (190a) through (190f) which are formed in the inner peripheral surface of the housing at respective portions which are opposite to outer peripheral surface portions of the cam ring corresponding to the teeth, wherein a distance between the housing and the cam ring is greater at said recesses than at other peripheral surface portions.

8. The fuel injection pump substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.