Plunger type high pressure fuel pump (high pressure fuel pump), driven by the camshaft through the fuel pump drive gear

The pump has eight pumping sections combined in a common aluminum housing 10 driven by a common camshaft 16.

Together with the high-pressure pump, this unit combines an automatic injection advance clutch, which is fixed at the front end of the camshaft, a speed controller located in housing 12, and a fuel priming pump 13.

The main working element of each pump section is a plunger pair that supplies fuel to the nozzle and consists of a plunger 46 and a bushing 52.

MAZ injection pump

The plunger and sleeve are machined with high precision and paired with each other not by joint grinding, but by the method of selective (selective in size) assembly.

A plunger pair selected at the factory cannot be dismantled in the future: parts are replaced only as a complete set.

Each fuel pump is equipped with plunger pairs of the same size group.

The lower part of the plunger has two guides that fit into the grooves of the rotary sleeve 45 mounted on the plunger sleeve.

A ring gear 43 is fixed on the rotary sleeve with a coupling screw, which is engaged with the rack 8 of the fuel pump.

This rail is moved by a regulator; at the same time, all rotary bushings are rotated simultaneously, and, consequently, the plungers in the bushings of all eight pump sections. This changes the amount of fuel supplied.

The required position of the rack in relation to the ring gear is determined by the locking screw included in the longitudinal groove of the rack.

The angular displacement of the rotary sleeve 45 relative to the ring gear 43, with the screw 44 loosened, regulates the fuel supply by each section of the pump.

Under the action of spring 47, the plunger with its lower head through the upper plate 26 of the pusher spring is tightly pressed against the head of the adjusting bolt 49 screwed into the pusher 51 of the plunger, the other end of the spring 47 rests on the lower plate 48 installed in the annular recess of the pump housing.

The pusher roller 54 is pressed against the cam of the roller 16 and is fixed from rotation by the axis 52 of the roller, the protrusions of which enter the grooves on the bores of the pump housing. The pusher roller has a floating bushing.

Under the action of the cam of the roller 16 of the pump and the spring 47, the plunger reciprocates in the sleeve.

Adjusting bolt 49, screwed into the pusher, is locked with locknut 50 and serves to adjust the start of fuel supply.

A discharge valve 39 is installed on the upper end of the sleeve 42 of the plunger. It is pressed against the seat 41 by the spring 38.

The discharge valve serves to separate the discharge and suction pipelines when the plunger moves down.

Injection valves, like plunger pairs, are divided into two groups according to hydraulic density.

Fuel pumps are equipped with delivery valves of only one group.

Disassembly of the valve-seat pair during operation is unacceptable in the same way as the plunger pair.

Axial movement of the camshaft 16 in bearings is allowed within 0.01-0.07 mm.

To eliminate excessive movement of the roller, a set of shims 21 is used.

Rail 8 of the fuel pump moves in guide bushings pressed into the pump housing.

The end of the rack protruding from the pump is protected by a bushing 5, into which a screw 6 is screwed, which limits the engine power during running-in. This screw is wired and sealed.

In the upper part of the pump housing there are channels for supplying and discharging fuel, through which it enters the plunger pairs.

Excess fuel is discharged through bypass valve 9.

The fuel supplied by the booster pump enters the space above the plunger through the inlet in the plunger sleeve.

When the plunger moves up, the fuel first flows back into the fuel supply channel until the upper edge of the plunger end closes the inlet.

The fuel begins to compress, and at a pressure of 10 - 18 kgf / cm2 the discharge valve, overcoming the resistance of the spring, rises, and the fuel enters the high-pressure fuel line to the injector.

With the further movement of the plunger 46 upwards, the pressure in the fuel line increases and when the value of 200 kgf/cm2 is reached, fuel is injected into the combustion chamber by the nozzle.

Continuing to move up, the plunger with its helical edge opens the outlet in the sleeve, connected to the outlet channel.

As the outlet opening opens, the fuel pressure above the plunger decreases sharply, and the pressure valve begins to close under the action of the spring.

When the plunger moves down under the action of the plunger spring, the space above the plunger is filled with fuel and the process is repeated.

The amount of fuel supplied by each section per plunger stroke is determined by the length of the injection stroke.

The length of the injection stroke is changed by turning the plunger relative to its sleeve, i.e., by changing the position of the helical cut-off edge of the plunger relative to the outlet of the sleeve.

Thus, the dosing of the amount of fuel supplied is carried out by changing not the beginning, but the end of the fuel supply.

Injection pump repair

Before proceeding with the test, the pump must be thoroughly flushed, observing the following sequence:

  • -wash all exterior surfaces until dirt is completely removed;
  • - after unscrewing the screws, remove the side and bottom covers of the pump, as well as the regulator cover with all the parts in it;
  • - thoroughly wash the opened internal cavities.

Washing is recommended to be carried out in an installation designed for this purpose using special washing solutions (heated to a temperature of 70 - 90 ° C) of the following composition:

- for pump body

  • soda ash 0.1 - 0.2%
  • Sodium bichromate 0.05 - 0.1%

- for other parts made of non-ferrous metals (brass, bronze, aluminum)

  • emulsol - 3.5%
  • liquid glass - 0.15%

- for steel and cast iron parts

  • trisodium phosphate - 1.0 - 1.5%
  • Sodium nitrate - 0.5 - 1.0%
  • triethanolamine - 1.0 - 2.0%

Through the opened cavities, carefully examine the condition of the parts.

Details that have breakages, chipping and local wear must be replaced or restored.

Particular attention is paid to the condition of the pusher springs.

On the regulator spring there should be no wear in the places of its engagement with the levers, and on the end of the regulator coupling there should be no wear (in the form of radial grooves) from the load rollers.

Check the condition of the bearings and the camshaft support, as well as the bearings of the speed controller.

In addition, you should check the smoothness of the movement of the rack while turning the camshaft of the pump, as well as the ease of moving the weights, the regulator lever and the rocker bracket.

It is necessary to check and, if necessary, adjust the play of the camshaft by removing the appropriate number of shims from under the front cover, as described below.

Check the gap in the engagement "pump rack - ring gear"; with a fixed ring gear, the travel of the rack should not exceed 0.25 mm.

After a control inspection and elimination of the noticed shortcomings, the camshaft cavity, pusher springs and regulator are washed with clean kerosene and the unit is assembled.

After filling in the cavity of the camshaft, regulator a and the injection advance clutch of the required amount of oil, they begin to determine the technical condition of the unit, for which the high-pressure fuel pump is installed on the adjustment stand.

The main criterion that determines the technical condition of the fuel pump is the amount of wear of the plunger pairs.

Assessment of the suitability of plunger pairs for further operation should be carried out in terms of ensuring the maximum possible starting fuel supply.

The value of the maximum starting fuel supply, which can be obtained by turning the plunger (gear ring) relative to the sleeve, must be at least 180 mm3/cycle at 80 min-1pump camshaft.

If the specified requirement is not met, the plunger pairs should be replaced with subsequent adjustment of the pump.

The tightness of the discharge valves is checked by pressing them with filtered diesel fuel through the pump inlet at a pressure of 1.7 - 2.0 kgf / cm2 with the rail position corresponding to the off supply.

The check is carried out within 2 minutes, fuel leakage from the connecting nipples is not allowed.

If malfunctions are detected, the pump is disassembled to the extent required by the repair conditions, with a more thorough examination of the condition of parts and assemblies.

For a quality repair, the correct determination of the scope of work for disassembling the pump is of great importance. It is not recommended to disassemble components such as the plunger pusher.

It is recommended to disassemble and assemble the pump (see Fig. 1) on a device that prevents deformation of the housing and protects it from damage.

Injection pump repair Injection pump repair

The disassembly sequence is as follows:

  • - use a special wrench to unscrew the nut 2 fastening the automatic clutch and remove the coupling 1 with a puller shown in fig. 2;
  • - unscrew the three bolts securing the fuel priming pump and remove the pump and side cover 24;
  • - unscrew the cap nuts 36, remove the connecting nipples 37 and locking crackers 33;
  • - turn out the fitting 31 and remove the valve stops with springs 38 of the discharge valves;
  • - using the puller shown in fig. 3, remove the seats with pressure valves from the pump body;
  • - with the help of a special device shown in fig. 4, compress the pusher springs and remove the lower plates of the pusher springs with tweezers;
  • - unscrew the set screws 28 of the plunger bushings and remove the plunger pairs from the pump housing;
  • - slightly compress the springs 47 and remove them from the housing together with the upper plates 26, bushings 45 of the gear rims and gear rims 43;
  • - remove the pushers 51 from the guides in the pump housing.

In order to preserve the factory assembly, it is recommended to disassemble the pump sections, observing the fastening of the components to the sections.

It is not allowed to disassemble the plunger pairs, parts of the delivery valves, as well as the upper and lower halves of the intermediate support of the camshaft.

To remove the pump camshaft, you need additionally:

  • - disassemble regulator body
  • - unscrew the locking screw of the camshaft support, press out the keys from both ends of the camshaft;
  • - unscrew the screws securing the front bearing cover, remove the cover 4 and remove the camshaft 16 complete with inner bearing races and cages;
  • - check the condition of the seals and bearings of the camshaft, if necessary, press out the seals to replace them and press the bearings with a puller.

Checking the technical condition of pump parts

Through a magnifying glass, inspect the condition of the parts of the discharge valve.

Risks and scratches on conical ground surfaces, as well as ring workings are not allowed.

Risks and traces of corrosion on the end surface of the seat can be eliminated by lapping the seat on the lapping plates.

If there are dull spots or scratches of small depth on the shutoff cone of the valve or on the chamfer of the seat, it is allowed to grind them together using a fine-grained paste.

If deep longitudinal scratches are found on the working surface of the valve relief band or cone, the valve and seat are replaced as a set.

After inspecting and eliminating the detected defects, the valve parts are thoroughly washed with kerosene.

The valve, lubricated with clean diesel fuel, must freely sit on the sealing cone under the action of its own weight from any position in height and angle of rotation relative to the seat.

Resistance when moving the valve in the seat and sticking are not allowed. The discharge valve assembly is checked for tightness along the cone and discharge belt.

The tightness of the valve along the cone is checked by air pressing the valve to the seat under a pressure of 5 - 6 kgf / cm2.

Check by turning the valve approximately 120˚ at three positions relative to the seat.

In each position, the discharge valve is kept under pressure for at least 15 s.

Air passage, which is determined by the release of air bubbles when the valve is immersed in diesel fuel, is not allowed.

If there is insufficient tightness, the valve cone must be rubbed over the seat cone with fine GOI lapping paste.

The condition of the edges and the cylindrical part of the plunger is checked with a magnifying glass.

If deep scratches, dull spots or chips are found on these areas of the surface, then the plunger pair is replaced.

When examining the plunger sleeve, pay attention to its end.

Scratches and corrosion on the bushing face can be removed by lapping the face on the lapping plates.

After inspection and elimination of the detected defects, a preliminary check of the plunger pair is carried out; for this, the parts of the pair are thoroughly washed with kerosene and lubricated with clean diesel fuel.

The plunger, extended from the sleeve by 20 - 25 mm, in a vertical position should smoothly lower in the sleeve under the action of its own weight along the entire stroke length at various angles of rotation of the plunger in the sleeve.

Local resistance and sticking when moving the plunger in the sleeve are not allowed.

Then, the plunger pair is tested for its performance, i.e., to ensure that it provides the above value of the maximum possible starting fuel supply.

If there are cracks and breaks in the main threads (for example, under the pump fitting), the housing is replaced.

The pusher is installed in the hole of the pump housing with an initial clearance of 0.020 - 0.063 mm.

When parts are worn, the gap should not exceed 0.2 mm.

The nominal total clearance of the connection roller - bushing - pusher axis should not exceed 0.3 mm. The measurement must be carried out as an assembly.

The camshaft is not should have thread breakage and there should be no chipping, pitting wear, cracks and scuff marks on the surface of the cam profile, the shaft should not have thread breakage.

The maximum allowable clearance in the connection shaft (cam) - support (middle) should not exceed 0.18 mm, with a nominal 0.04 - 0.93 mm.

The gap between the rail and the rail bushing must not exceed 0.24 mm. Bushing replacement is allowed. New bushings must be pressed in to a depth of 11.8 - 12.2 mm from the end of the pump housing.

After that, the inner diameters of the bushings must be machined up to 14.0 + 0.019 mm with a surface roughness of at least 1.24 microns.

The alignment of the holes is checked with a gauge with a diameter of 13.980 - 13.985 mm, which must pass freely through both holes.

Parts that act as a seal (gaskets, o-rings, washers, seals, etc.). replace.

The assembly sequence is as follows:

  • - install an intermediate support on the shaft and press on the front and rear roller bearings without outer races;
  • - each bearing must rest against the shoulder of the shaft with a thickened part of the inner race;
  • - press the seals into the front cover and the regulator housing flush with the end surfaces;
  • - screw the regulator housing to the fuel pump housing, having previously lubricated the mating surfaces with sealant paste, and using a mandrel that protects the oil seal from damage, install the camshaft assembly;
  • - screw in the locking screw of the support;
  • - caulk the screws for fastening the regulator body and the support screw;

install the front cover, protecting the working edge of the stuffing box from damage by the keyway;

  • - with the screws of the bearing cap tightly tightened, the cam shaft must turn by hand without noticeable jamming and shocks, while the axial play of the shaft under a force of 5 - 6 kgf must be within 0.01 - 0.07 mm, if necessary, it can be regulated by placing gaskets 21 (see Fig. 1) under the flange of the front cover;
  • - caulk the screws for fastening the case and the front cover;
  • - install the pushers, the height of the pusher assembly with the screw should be 37.3 - 37.5 mm;
  • - install the crown with the ring gear bushing, the upper plate and the spring into the body;
  • - the middle tooth of the crown must be in the middle cavity of the rail, and the slot of the crown and the hole for the set screw in the pump housing must lie in the same plane;
  • - install the plunger pair and tighten the plunger bushing set screw;
  • - when installing a pair, the protrusion of the plunger, marked with a risk, must face the groove of the plunger bushing for the set screw.

After tightening the set screw, the rail should have a stroke of at least 25 mm and move easily, without tangible difficulty;

Injection pump repair

  • - using a tool (see Fig. 4), compress the spring and insert the lower spring plate, check the plunger travel reserve, which, at the extreme upper position of the pusher, should be at least 0.6 mm;
  • - install the discharge valve, fitting and use a torque wrench to tighten it with a torque of 10 - 12 kgf-m;
  • - after tightening each fitting, check the ease of movement of the rack and the amount of free play of the rack, which should not exceed 0.25 mm with a fixed ring gear;
  • - install booster pump, bottom and side covers, connecting nipples, cap nuts. Install and tighten the locking nut.

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