DE2824639A1 - IC engine low pressure fuel injection system - has fuel distributor rotor displaced hydraulically, to meter fuel corresponding to engine requirements - Google Patents

Abstract

The fuel injector pump consists of a housing provided with a low pressure fuel inlet union and a number or outlet unions corresponding to the number of injectors to be fed. The housing contains a fuel distributor rotor turned in synchrony by the engine. The rotor can be displaced axially by hydraulic pressure to meter the fuel via triangular slots. The hydraulic displacement of the rotor is controlled by an electronic regulator receiving impulses from an oxygen sensor located in the exhaust system, an air intake volume transducer located upstream to the throttle flap and an engine temp. sensor. The rotor displacement medium is fuel whose flow and return is regulated by two electro magnetic valves opening and closing in response to signals transmitted by an electronic regulator.

Description

TlEDTKE - BüHLING - KlNNE -

Dipl.-Ohem. G. Buehling Dipl.-Ing. R. Kinne 3 Dipl.-Ing. P. Grupe

Bavariaring 4, P.O. Box 20 24

9P9 / RQQ 8000 Munich 2

/ O 4 4 QO y Tel .: (0 89) 53 96 53

Telex: 5-24845 tipat

cable: Germaniapatent Munich

June 5th 1978

B 8959 / case A2940-02 Toyota &

Soken

Nippon Soken, Inc.
Nishio-shi / Japan

Toyota Jidosha Kogyo Kabushiki Kaisha Toyota-shi / Japan

Fuel injection system for an internal combustion engine

The invention relates to a fuel injection system for an internal combustion engine.

Fuel injection systems of the type discussed here are known for example from JA-OS 19 817/77. In this known fuel injection system, a measuring flap is in the suction line of an internal combustion engine arranged so that it corresponds to the air flow to the internal combustion engine is deflected, the deflection of the measuring flap being transmitted to a control piston via a mechanical linkage and this is adjusted in the axial direction. The control piston is also rotated by the crankshaft of the internal combustion engine. This causes the fuel to be distributed and metered.

A disadvantage of this conventional fuel injection system is that the air flow sensor, to which the measuring flap belongs, with the fuel control unit, which the

603849/1031

Dresdner Bank (Munich) KIo. 3939 844 Postschock (Munich) Km 670-Ί3-804

- 4 - B 8959

Fuel metered and distributed, assembled into a unit, so that the dimensions of the system are proportionate are great. Another disadvantage of the conventional fuel injection system is that it is functional must be properly coupled to the air flow sensor and the crankshaft of the internal combustion engine, so that the installation and connection of the conventional fuel injection system in the limited engine compartment of motor vehicles and the like is difficult.

Because the air flow sensor and the fuel control unit are mechanically coupled with each other, another disadvantage of the conventional fuel injection system is that that this can not be controlled by means of electrical control signals, which are present, for example, when an oxygen sensor should be used to measure the air-fuel ratio of the mixture approximately to the stoichiometric view To regulate value, or if a temperature sensor for the cooling water temperature of the internal combustion engine are used should, according to the cooling water temperature, the fuel amount to correct.

The invention is based on the object of a fuel injection system to create, which is designed so that the air flow sensor and the fuel control unit on can be installed in various locations to make it easier to install the fuel injection system in the engine compartment is and so it is also possible in a simple manner, the amount of fuel in accordance with electrical detector signals to correct by different feeling devices.

The fuel injection system according to the invention, which this Problem solves is characterized in the claims.

809849/1031

In the fuel injection system according to the invention the amount of axial displacement of the control piston of the fuel control unit by means of a hydraulic servomechanism controlled, and the target value of the amount of fuel is by means of an electronic control device from electrical detector signals from various sensing devices, including an air flow sensor, calculated and according to the output signal of the electronic Control device, the hydraulic servomechanism is operated.

Further features and advantages of the invention emerge from the following description of an exemplary embodiment with reference to the drawings. Show it:

Figure 1 is a schematic representation of a

Fuel injection system, its fuel control unit is shown in longitudinal section;

Figure 2 shows a longitudinal section through an injection

valve of the fuel injection system according to Figure 1;

Figure 3 is a section through a pressure regulator

the fuel injection system according to Figure 1;

FIG. 4 shows a sectional view according to IV-IV

in Figure 1;

Figure 5 is a schematic diagram showing the

Intersection of slots of the force

609849/1031

B 8959

shows fuel injection system according to Figure 1;

Figure 6

Figure 7 Figure 8 is a graph showing the relationship between the piston travel L and the amount of fuel Q represents;

a diagram showing the course of the detector signal of an oxygen sensor shows the fuel injection system according to Figure 1; and

a circuit diagram of an electronic control device of the fuel injection system according to Figure 1.

608649/1031

In the following the invention is explained in more detail using an example shown in the figures, wherein FIG. 1 will first be discussed. There is an internal combustion engine in it 10, which is a conventional four-stroke internal combustion engine with reciprocating pistons and spark ignition acts. By suction line branches 11a, 11b, 11c and 11d, air is drawn into the internal combustion engine, and fuel is made by injectors 12a, 12b, 12c and 12d injected, with an injection valve being attached to each of the suction line branches.

As Figure 2 shows, each injection valve is 12a, 12b, 12c and 12d designed as an automatic injection valve which has a housing 13 in which a fuel filter 14 is arranged and a fuel passage 15 are formed. At the front end of the housing 13 is a nozzle body 17 is arranged in which a nozzle is formed by a conical valve element 16 is opened and closed. The valve element 16 is in the closing direction of a Compression spring 20 pressed, which engages via a plate-shaped valve seat 19 and a shaft 18 on the valve element. When the fuel pressure exceeds a certain fourth, the valve element 16 is thus turned to the right (in Figure 2) pressed so that fuel is injected through the nozzle.

Reference is again made to FIG. 1 below. The air is passed through an air filter 21, past a throttle valve 23 and sucked through a distribution chamber 24a and passed into the suction line branches 11a to 11d. The sucked in The amount of air is controlled by the throttle valve 23, which can be operated at will.

608649/1031

This results from the combustion of the air-fuel mixture in the internal combustion engine 10 resulting exhaust gas is in a Abgaskrüiraner 24b issued, from which the exhaust gas through a Exhaust pipe 25, a catalytic triple converter 26 and a muffler, not shown, to the surrounding Atmosphere is derived. The triple catalytic converter 26 can exhaust the exhaust gas simultaneously both in terms of Nitrogen oxides, carbon monoxide and unburned hydrocarbons clean and work with the highest degree of efficiency, when the air-fuel ratio is at least approximately the stoichiometric air-fuel ratio.

The fuel system comprises a fuel tank 30 from which the fuel is under pressure from an electrically driven Fuel pump 31 is supplied. The intake vacuum serves as the reference pressure for the delivery pressure of the fuel. which is fed on a line 34. The pressure of the fuel is controlled by a pressure regulator 32, as he is shown in Figure 3, regulated to a certain overpressure (2 to 10 atmospheres) above the reference pressure. Of the Pressure regulator 32 directs excess fuel to the fuel tank 30 back so that fuel is delivered at regulated pressure on a line 33. The line 33 leads to a fuel control unit 40.

The fuel control unit 40 meters the fuel and distributes it to the injection valves 12a to 12d assigned to the individual cylinders. Thereby the control unit

40 in turn controlled by a hydraulic signal. The control unit 40 is close to the crankshaft of the internal combustion engine 10 arranged. In a cylindrical case

41 of the control unit 40 a single, radially extending inlet 42 for fuel is formed: in the inner wall

- 9 -

608849/1031

In the housing 41, an annular channel 43 is formed which is in communication with the inlet 42. As Figure 4 shows, has the housing 41 has four outlets 44a, 44b, 44c and 44d for fuel, the number of which corresponds to the number of cylinders of the Internal combustion engine corresponds and which extend radially each with a distance of 90 ° in the circumferential direction from one another are arranged. Furthermore, a return outlet 45 is formed in the housing 41, through which fuel has seeped through is returned to the fuel tank 30.

The inlet 42 is connected to the line 33, the outlets 44a to 44d are connected to lines 46a, 46b, 46c, respectively and 46d, which lead to the individual injection valves 12a to 12d, and the return outlet 45 is on a line 47 connected to the fuel tank 30 leads.

Inside the housing 41 there are two ball bearings 48 and 49, in which a shaft designated as rotor 50 is rotatably mounted. At the right end of the rotor 50 is non-rotatable with the rotor a gear 51 connected so that the rotor 50 synchronously with the crankshaft of the internal combustion engine 10 over the gear 51 and a toothed belt 52 can be rotated. The speed ratio between the crankshaft of the internal combustion engine 10 and rotor 50 is set to 2: 1. This value applies to a four-stroke internal combustion engine, at which come to two revolutions of the crankshaft of the internal combustion engine for each work cycle. Hence this is Speed ratio preferably set to 1: 1 for the Case of a two-stroke internal combustion engine in which there is one revolution of the crankshaft for every work cycle.

A fuel control piston 55 is arranged in the housing 41.

- 10 -

609849/1031

- 10 - B 3959 2824633

arranges that it can be rotated as well as displaced in the axial direction. The control piston 55 is fitted into the housing 41 in a fluid-tight manner. As Figure 4 shows, a fuel channel 56 is formed in the interior of the control piston 55,
and the control piston 55 also has an inlet opening 57 which leads through the wall of the control piston to the fuel channel and is formed approximately in a region of the control piston corresponding to the inlet 42 of the housing 41. Fuel is introduced into the fuel channel 56 through the inlet opening 57.

One end of the fuel passage 56 in the control piston 55 is
by means of a closure element 58 and an O-ring
sealed fluid-tight. Furthermore, the control piston 55 has a single, triangular slot 59 through which the
Fuel is distributed from the fuel passage 56 to the outlets 44a to 44d.

At its right-hand end in FIG. 1, there is 55 on the control piston
a slot 60 is formed into which a projection 61 of the rotor 50 is fitted. As a result, the control piston 55 is rotated by the rotor 50, the control piston 55 also being able to be pushed back and forth in the axial direction independently of the rotor 50 by hydraulic pressure prevailing in a working chamber 62.

The metering and distribution of the fuel is controlled by the Extent of connection between the slot 59 in the control piston 55 and slots 63a, 63b, 63c and 63d causes, respectively are formed at the inner end of the outlets 44a to 44d.

The fuel is distributed through rotation

- 11 -

008849/1031

of the control piston 55, and the metering of the fuel takes place in accordance with the length or duration of the overlap between the slot 59 of the control piston 55 and the slots 63a to 63d. This is for the slot 63a in FIG shown. The free cross section of the slots 63a to 63d is small compared to the slot 59, so that the ever Unit of time fuel flowing through the slots 63a to 63d amount is practically constant. When the relative position between the slot 59 and the slot 63a is as it is is shown with solid lines in Figure 5, the overlap length or duration L- | these slits big, so that a relatively large amount of fuel is fed will. However, if the relative position is as shown by the dashed lines in FIG is, the intersection length L "is relatively small, so that accordingly the amount of fuel fed is small.

If the speed of the control piston 55 or the speed of the internal combustion engine 10 is constant, it depends on the outlets 44a to 44c delivered fuel quantity Q exclusively from the axial displacement or the piston travel L des Control piston 55 from. When the slot is triangular, there is a linear relationship between the amount of fuel Q and the piston travel L, as shown in Figure 6, so that the metering of the fuel by the axial adjustment of the control piston 55 can be done.

The piston travel L of the control piston 55 is determined by means of a position sensor 68 for the control piston. Of the Position sensor 68 comprises a toroidal core 65 which is attached to the control piston 55, and a primary winding 66 and a secondary winding 67 attached to the housing 41.

- 12 -

808849/1031

The position sensor 68 is a known, working on the principle of the differential transformer Position sensor that generates an electromotive force proportional to the piston travel.

A helical spring 70, which tries to push the control piston to the left in FIG. 1, acts on the control piston 55. The hydraulic pressure in the working chamber 62, which moves the control piston 55 to the right, also acts on the control piston tried to push in Figure 1. The working chamber 62 is limited in part by a cap 71 which is at one end of the Housing 41 is attached and in which a fuel inlet 72 and a fuel outlet 73 are formed over which the hydraulic pressure in the working chamber 62 is controlled.

The fuel injection system also includes solenoid valves 75 and 76, which form a hydraulic servomechanism, by means of which the axial position of the control piston 55 is determined will. The solenoid valves 75 and 76 only open when a switch-on signal is applied. The solenoid valve 75 is in a line 77 connecting the line 33 to the inlet 72, and the solenoid valve 76 is in one Line 78, which connects the outlet 73 with the line 47. When the solenoid valve 75 is open and the solenoid valve 76 is closed, the hydraulic pressure in the working chamber 62 increases so that the control piston 55 counteracts the force of the helical spring 70 is shifted to the right in FIG. On the other hand, when the solenoid valve 75 is closed and the solenoid valve 76 is open, the hydraulic pressure in the working chamber 62 drops, so that the The control piston 55 is displaced to the left in FIG. 1 by the force of the helical spring 70. The position or the

- 13 -

609849/1031

- 13 - B 8959

The piston travel of the control piston 55 is thus corresponding to the duration of the opening and closing phases of the solenoid valves

75 and 16 controlled.

The solenoid valves 75 and 76 are electrically connected to an electronic control device 80, the duration the opening and closing phases of the solenoid valves 75 and

76 controls depending on the output signals of various sensors. These sensors are an air flow sensor 22 which is arranged in the suction line of the internal combustion engine 10, an oxygen sensor 27 which is arranged in the exhaust pipe of the internal combustion engine 10, a temperature sensor 28 for the cooling water temperature which is arranged in a cooling water line of the internal combustion engine 10 , and the position sensor 68 arranged in the control unit 40 for the position of the control piston. The air flow sensor 22 is designed as a measuring flap sensor known per se and comprises a measuring flap 22b, which is arranged upstream of the throttle flap 23 and can be pivoted about a shaft 22a in accordance with the air flow, as well as a potentiometer 22c which converts the rotary position of the measuring flap 22b into a voltage. The oxygen sensor 27 works with a coating of catalytic material, for example platinum, on a surface made of zirconium dioxide (ZrO ₂ ) or titanium dioxide (TiO ₂ ) The stoichiometric air-fuel ratio changes rapidly as shown in FIG. The output voltage of the oxygen sensor 27 is relatively high when the exhaust gas does not contain oxygen and it is relatively low when the exhaust gas contains oxygen. The temperature sensor 28 for the cooling water comprises a temperature sensitive

- 14 -

608849/1031

borrowed device, for example a thermistor, and generates a voltage proportional to the cooling water temperature. The voltages generated by the sensors 22, 27 and 28 are a measure of the operating conditions of the internal combustion engine 10.

The structure of the electronic control device 80 is shown in FIG. The temperature sensor 28 is connected to the junction of two series-connected resistors 801 and 802, and the oxygen sensor is connected to an integrator 807. The potentiometer of the air flow sensor 22 is connected to resistors 812 and 813 connected in series and is supplied with a constant negative voltage (-V). In parallel with the resistors 801 and 802, series-connected resistors 803 and 804 are connected, which share a fixed positive voltage V, so that a fixed voltage V _{1 is} generated, which is applied to a function amplifier 810 via a resistor 805. The voltage V ~ present at the junction of the resistors 801 and 802 changes with the resistance value of the temperature sensor 28 for the cooling water temperature, namely it increases with a decrease in the cooling water temperature. The voltage V _? is applied to the functional amplifier 810 via a resistor 806. When the output voltage of the oxygen sensor 27 is high, the integrator 807 produces a voltage increasing with time, whereas when the output voltage of the oxygen sensor 27 is low, the integrator 807 produces a voltage decreasing with time. The integrator voltage V, which changes as a function of the output voltage of the oxygen sensor 27, is divided by resistors 808 and 809 and is applied to the function amplifier 810. The operational amplifier 810 includes negative feedback via

- 15 -

609849/1031

a resistor 811 so that it operates as a differential amplifier and consequently supplies an output voltage V. which varies as a function of the applied voltages V-, V _? and V., changes. The voltage V. is proportional to (-V ₁ -V ^ V-.) And is applied to an input X of an analog multiplier circuit 814, for example a circuit "Intersil IC 8013". At an input X of the analog multiplier device 814, a voltage V, - is applied, which increases in the negative direction proportional to the air flow to the internal combustion engine. The output of the analog multiplier circuit 814 is fed back and connected to an input Z, which defines the constant of proportionality of the product. The voltages V, and V ₁ . are multiplied together and a voltage Vg is generated which is proportional to the product of the multiplication (V.xVj.). This voltage V, indicates the setpoint value for the amount of fuel to be supplied to internal combustion engine 10. This amount of fuel should be increased when the air flow increases, during the time during which the exhaust gas contains oxygen, and when the cooling water temperature decreases.

The electronic control device 80 further comprises an oscillator 815 which supplies a periodic signal by means of which the primary winding 66 of the position sensor 68 is periodically excited, and a rectifier 816 which rectifies the output alternating voltage of the secondary winding 67 and converts it into a direct voltage. The output voltage V _{7 of} the rectifier 816 changes as a function of the position of the ring core 65, in such a way that the voltage V ₇ increases proportionally to the piston travel of the control piston 55 to the left or proportionally to the actual value of the amount of fuel fed in.

- 16 -

809849/1031

The setpoint V, the amount of fuel to be supplied to the internal combustion engine 10, and the actual value V_ of the amount of fuel actually supplied to the internal combustion engine 10 are compared by means of a comparator 817 to which the voltages V _fi and V _{7 are} applied. The comparator 817 has positive feedback through a resistor 818 so that the comparator 817 has hysteresis properties. Resistors 819 and 820 connected in series are connected to the output of the comparator 817. The comparator 817 generates a low voltage signal when the voltage V \ - is greater than the voltage V_, ie when the setpoint value is greater than the actual value of the fuel quantity. In contrast, the comparator 817 generates a high voltage signal when the voltage V 1 - is lower than the voltage V ₇ , ie when the setpoint value is less than the actual value of the fuel quantity. The output voltage of the comparator 817 is applied to the solenoid valve 75 through an amplifier 821, and also the output voltage of the comparator is applied to the solenoid valve 76 through an inverter 822 and an amplifier 823. Since the solenoid valves 75 and 76 only open when a high voltage signal is applied, the solenoid valve 76 is only opened when the setpoint is greater than the actual value of the fuel quantity, whereas when the setpoint is smaller than the actual value of the fuel quantity, only the solenoid valve 75 is opened.

The fuel injection system described above operates in the following way. The fuel supplied under pressure by the fuel pump 31, its pressure from the pressure regulator 32 is regulated to a certain value, the fuel control unit 40 is fed to the line 33. The fuel flows into the inlet 42 of the housing 41, from where it flows through the annular channel 43 and the inlet opening 57 in the

- 17 -

8Q9849 / 1031

Control piston 55 enters fuel duct 56. If the slot 59 due to the rotational position of the control piston 55 intersects with one of the slots 63a to 63d, flows the fuel through the slot 59 into that one of the slots 63a to 63d which just intersects with the slot 59. Through one of the assigned outlets 44a to 44d and one of the assigned lines 46a to 46d then the fuel is supplied to one of the injection valves 12a to 12d. Each of the injection valves 12a to 12d injects when fuel is supplied to it, this fuel into the associated suction line branch 11a or 11b or 11c or 11d, which leads to an assigned cylinder of the internal combustion engine 10.

Since the rotor 50 turns the control piston 55 once every two revolutions of the crankshaft of the internal combustion engine 10 rotates and since the housing 41 has the four slots 63a to 63d and the four outlets 44a to 44d, is due to the above-described mode of operation of the fuel every two revolutions of the crankshaft of the internal combustion engine 10 each of the outlets 44a to 44d of the housing 41 is supplied once, so that the fuel to each of the Injection valves 12a to 12d of the cylinders of the internal combustion engine 10 is fed to the internal combustion engine 10 once every two revolutions of the crankshaft. Two turns the crankshaft of the internal combustion engine correspond to a work cycle, with the fuel in the respective Cylinder of the internal combustion engine 10 is introduced during the correct cycle. The Fuel is thus injected intermittently.

The amount of fuel injected is metered through the axial position or the piston travel of the control piston 55. These

- 13 -

609849/1031

- 1ί

The axial position of the control piston 55 is controlled by the hydraulic pressure in the working chamber 62. This hydraulic one In turn, pressure is provided by the hydraulic servomechanism comprising solenoid valves 75 and 76, as well as the electronic control device 80, which controls the solenoid valves 75 and 76 as a function of the signals the sensor 22, 27 and 28 controls so that the position of the control piston 55 according to the operating conditions of the Internal combustion engine 10 is properly controlled.

As a result, the amount of fuel injected by the injection valves 12a to 12d is also constantly corresponding to the Operating states of the internal combustion engine 10 correctly metered. In other words, if the electronic Control device 80 on the basis of the signal from position sensor 68 determines that the amount of fuel injected is smaller than the setpoint value of the fuel quantity determined from the signals from sensors 22, 27 and 28, the solenoid valve 75 feeds with a switch-off signal and the solenoid valve 76 with a switch-on signal, so that part of the Fuel in the working chamber 62 is returned to the fuel tank 30 and the hydraulic pressure in the Working chamber 62 drops, whereby the control piston 55 is shifted to the left and thereby the amount of the injected Fuel is increased. On the other hand, if the electronic control device 80 determines that the The amount of fuel is greater than the setpoint value of the amount of fuel, it feeds the solenoid valve 75 with a Switch-on signal and the solenoid valve 76 with a switch-off signal ·, so that the hydraulic pressure in the working chamber 62 is increased and the control piston 55 is shifted to the right, whereby the amount of injected fuel is reduced will.

- 19 -

809849/1031

In the embodiment described above, the electronic control device 80 is only with the output signals the air flow sensor 22, the oxygen sensor 27 and the temperature sensor 28 are fed. It can but also the output signals of other sensors, such as a temperature sensor for the temperature of the Intake air, a pressure sensor for the atmospheric pressure, a speed sensor for the speed of the internal combustion engine, a speed sensor for vehicle speed, etc., to the electronic control device 80 are given in order to thereby improve the accuracy in calculating the setpoint value of the internal combustion engine 10 to increase the amount of fuel required.

In the exemplary embodiment shown, the control piston 55 is pressed to the left by the helical spring 70. It however, it is also possible to provide a working chamber at the right end of the control piston 55 in which a suitable Throttle bore a certain hydraulic pressure is generated, thereby applying the desired preload force to the Apply control piston.

In the fuel injection system according to the invention Thus, through the rotation of the control piston, the fuel is distributed to the cylinders of an internal combustion engine and The amount of fuel supplied is metered through the axial displacement of the control piston. The works with the control piston Working chamber together, the extent of the axial displacement of the control piston by the pressure in the working chamber is determined. The servomechanism is used to control the pressure in the working chamber, which in turn is used accordingly the result of a comparison is controlled in which the setpoint of the engine to be supplied to the engine

- 20 -

809849/1031

amount of substance derived from the operating state of the internal combustion engine is determined, is compared with the actual value of the amount of fuel suppliedj that from the axial position of the control piston is determined.

808849/1031

Claims (3)

Claims Fuel injection system for an internal combustion engine, characterized by a housing (41) with a fuel inlet (42), the fuel from a fuel tank (30) is supplied, and a plurality of fuel outlets (44a, 44b, 44c, 44d) through which the cylinders of the Internal combustion engine (10) to be supplied fuel is delivered, a control piston (55) inserted into the housing, by means of which that from the fuel inlet to the fuel outlets Conducted fuel is distributed to the cylinders by turning the control piston and by axial displacement of the control piston is metered, a working chamber (62) into which a hydraulic medium is introduced, the pressure of which the amount of axial displacement of the control piston determines a hydraulic servo mechanism (75, 76) for controlling of the pressure in the working chamber as a function of applied electrical control signals, delivering detector signals Sensing devices (22, 27, 28) for determining the operating state of the internal combustion engine, a position sensor (68), which determines the axial position of the control piston and delivers a position signal, and an electronic control device (80), which is connected to the sensing devices and the position sensor, the electronic control device a setpoint value of the cylinders of the internal combustion 309849/1031 Dresdner Bank (Munich) Account 3939 844 Posischeck (Munich) toilet 670-43-804 - 2 - B 8959 The amount of fuel to be supplied to the machine is calculated from the detector signals from the operating state sensing devices and also an actual value of the fuel quantity supplied to the cylinders of the internal combustion engine from the position signal calculated by the position sensor and the setpoint and the actual value are compared and the electrical control signals generated according to the result of the comparison. 2. Fuel injection system according to claim 1, characterized in that the operating state sensing devices an air flow sensor (22) which is arranged upstream of a throttle valve (23) in the internal combustion engine (10) is and determined the air flow to the internal combustion engine, as well as an oxygen sensor (27) include the Determined oxygen content in the exhaust gas of the internal combustion engine. 3. Fuel injection system according to claim 1 or 2, characterized characterized in that the hydraulic medium is fuel and that the hydraulic servomechanism is a first Solenoid valve (75) that controls the amount of fuel introduced into the working chamber (62) from the fuel tank (30) controls, as well as a second solenoid valve (76), which is returned from the working chamber to the fuel tank Fuel amount controls, the first and second solenoid valves being controlled by the electronic control device (80) generated electrical control signals for controlling the pressure in the working chamber opened and closed will. 803849/1031