US3728993A

US3728993A - Fuel injection apparatus including an air sensor and means for the direction-dependent damping of its movement

Info

Publication number: US3728993A
Application number: US00208699A
Authority: US
Inventors: K Eckert; H Knapp; W Sautter; V Stein
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1970-12-17
Filing date: 1971-12-16
Publication date: 1973-04-24
Anticipated expiration: 1990-04-24
Also published as: AU3695471A; BE776833R; FR2131294A6; DE2062078C3; SE365023B; DE2062078A1; PL83049B3; DE2062078B2; NL7117284A; GB1363740A; JPS5421891B1; AU449161B2; CS157133B4; SU512721A4; ES398040A2; IT972069B

Abstract

In a fuel injection apparatus - in which the air-fuel ratio is maintained constant by an air sensor displaceable in the suction tube by the intake air drawn into the internal combustion engine with which the fuel injection apparatus is associated - in order to prevent undesired shifts in the metered fuel quantities in the low rpm range, the pressurized liquid used as a return force for the air sensor passes through a throttle assembly which throttles the liquid flow to an extent dependent upon the direction of flow therethrough.

Description

United States Patent [4 1 Apr. 24,1973

Eckert et al.

[541 FUEL INJECTION APPARATUS [56] References Cited INCLUDING AN AllR SENSOR AND UNITED STATE PATENTS MEANS FOR THE DIRECTION- S DEPENDENT DAMPING OF ITS 3,015,548 1/1962 McClain ..261/50 A X I 3,628,515 12/1971 Knapp et a1 MOVEMENT 3,680,535 8/1972 Eckert et a1. ..123/119 R [75] lnventors: Konrad Eckert, '7 Stuttgart-bad Cannstadt; Heinrich Knapp, Primary E.raminer-Wendell E. Burns Leonberg-Silberberg; Wilfried AIl0rney-Edwin E. Greigg Sautter, Stetten 1.R.; Volkhard Stein, Stuttgart, all of Germany 1 1 ABSTRACT [73] AssigneeZ Robert Bosch GmbH, Stuttgart, Gen In a fuel injection apparatus in which the air-fuel many 7 ratio is maintained constant by an air sensor displaceable in the suction tube by the intake air drawn into the Filed: 9 1971 internal combustion engine with'which the fuel injec- 21 A l N 208,699 tion apparatus is associated in order to prevent un- 1 pp 0 desired shifts in the metered fuel quantities in the low [30] Foreign Application Priority Data rpm range, the pressurized liquid used as a return force for the air sensor passes through a throttle as- Dec. 17, 1970 Germany ..P 20 62 078.4 sembly which thromes the liquid flow to an extent pendent upon the direction of flow therethrough. [52] U.S.Cl ,.l23/ll9 R, 123/139 AW, 26l/50A [51 Int. Cl ..F02m 69/00 [58] Field of Search ..123/139 AW, 119R; 1

261/50 A, 44, 50 AA 7 Claims, 6 Drawing Figures 2s 30 /7 5E 75 I6 3 4 27 lg 34 58 38 L 77 c II I 6 1. dkq

F UEL INJECTION APPARATUS INCLUDING AN AIR SENSOR AND MEANS FOR THE DIRECTION- DEPENDENT DAMPING OF ITS MOVEMENT BACKGROUND OF THE INVENTION bitrarily operable butterfly valve are serially disposed.

The air sensor is deflected by the flow of the intake air to an extent proportionate to the throughgoing air quantities against a constant return or resetting force.

The air sensor displaces the movable part (for example, a control plunger) of a quantity distributor valve disposed in the fuel line for metering the fuel in a manner proportionate to the intake air quantities. The return force is derived from a pressurized liquid which is delivered continuously and under constant pressure in a pressure conduit and which affects a piston that reciprocates in a cylinder. The latter communicates with the said pressure conduit by a connecting conduit containing a throttle, as shown in German Published Application 1,960,144.

In the aforeoutlined fuel injection apparatus the pressurized liquid that serves as a return force for the air sensor is forced through a throttle for the purpose of damping the oscillation of the air sensor. If a conventional throttle is used, air or sensor vibrations cause, in the lower rpm range, a mean value increase of the position of the control plunger in the metering valve; thus, an undesired increase in the metered fuel quantities occurs.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention to provide an improved fuel injection apparatus in which the enriching of the fuel mixture is avoided in the low rpm range and the metering of the fuel is effected according to the operational requirements of the internal combustion engine.

Briefly stated, according to the invention, the aforenoted throttle is so designed that its throttling effect on the flow of the liquid supplying the resetting force is smaller in the direction of the pressure chamber (where the piston is located) than in the opposite, discharging direction.

The invention will be better understood as well as further objects and advantages become more apparent from the ensuing detailed specification of four exemplary embodiments taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal sectional view ofa fuel injection apparatus incorporating a first embodiment of the invention;

FIG. 2 is a longitudinal sectional view of a second embodiment of the invention;

FIG. 2a is an end view of one component forming part of the second embodiment;

FIG. 3 is a longitudinal sectional view ofa third embodiment of the invention;

FIG. 3a is an end view of one component forming part of the third embodiment and FIG. 4 is a longitudinal sectional view of a fourth embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS In the fuel injection apparatus illustrated in FIG. 1, the intake air flows through an air filter (not shown) in the direction of the arrow A in an intake tube portion 1 having a flaring, conical portion 6 in which there is disposed an air sensor 2. After having passed the air sensor 2, the intake air flows through a connecting hose portion 3 and an intake tube portion 4 in which there is disposed an arbitrarily operable butterfly valve 5. Therefrom the intake air is admitted to the cylinders 5 (not shown) of an internal combustion engine (also not shown). The air sensor 2 is formed as a disc oriented normal to the direction of air flow and displaceable in the conical portion 6 linearly proportionately to the air quantities passing through the intake tube. In case of a constant return force applied to the air sensor 2 in a direction opposite to the air flow and a constant air pressure applied to the air sensor 2, the pressure prevailing between the air sensor 2 and the butterfly valve 5 also remains constant.

The air sensor 2 directly controls a fuel metering and distributor valve 7. For transmitting the setting motion of the air sensor 2 to the valve 7, there is provided a lever 8 which is pivotal and with low friction supported at 9 and which, upon its pivotal motion, displaces a movable valve component 11 (formed as a control plunger) of the metering valve 7 by means of a nose It) integral with the lever 8. The frontal face 12 of the control plunger 1 1 disposed remote from the nose 10, is exposed to pressurized liquid which serves as the return force for the air sensor 2.

The fuel supply is effected by a fuel pump 15 which is driven by an electromotor l4 and which draws fuel from a tank 16 and forces the same through a conduit 17 to the metering valve 7. From the conduit 17 there extends, back into the tank 16, a conduit 18 in which there is disposed a pressure limiting valve 19.

From the conduit 17 the fuel is introduced into a channel 22 in the housing of the metering valve 7. The channel 22 leads to an annular groove 23 of the control plunger 11 and also to a plurality of chambers 24 in which the fuel under pressure exerts a force to one side of a diaphragm 25 Dependent upon the position of the control plunger 11, the land 1121 forming part of the plunger and bounding the annular groove 23, covers to a greater or a lesser extent the control slots 26. Each control slot 26, through an associated port 27, communicates with a chamber 28 separated from an adjacent chamber 24 by means of the diaphragm 25. From each chamber 28 the fuel is admitted through a channel 29 to the associated individual fuel injection valve (not shown) which is disposed in the air intake tube in the vicinity of an engine cylinder. The diaphragm 25 serves as the movable part of a flat seat valve which is maintained in an open position by means of a spring 30 when the fuel injection apparatus is not operating. It is noted that the number of the flat seat valve assemblies formed of

components

24, 25, 28, 30 is identical to the number of the control or metering slots 26 and thus the number of cylinders in the internal combustion engine. Each flat

seat valve assembly

24, 25, 28, 30 ensures that independently from the extent of overlap between the annular groove 23 and the control slots 26, thus independently from the fuel quantities flowing to the fuel injection valves, the pressure drop across the

fuel metering valve

23, 26 is maintained substantially at a constant value. In this manner it is ensured that the extent of displacement of the control plunger 11 is proportionate to the metered fuel quantity.

The conical portion dot the air intake tube is so designed that the. annular flow passage section defined by the periphery of the disc 2 and the cone wall is proportionate to the displacement of the disc 2 which causes, through the pivotal motion of lever 8, a shift in the metering plunger 1 1. Consequently, there is a linear dependence between the motion of the air sensor 2 and the displacement of the control plunger 11, so that the fuel metered at 23, 26 will at any time be proportionate to the air quantities flowing through the intake tube.

The pressurized liquid serving as a constant return force and affecting the control plunger 11 is fuel. For this purpose there is provided a conduit 33 extending from the conduit 17 to the pressure chamber 34 into which extends that terminus of the control plunger 11 which is remote from the pivotal lever 8. In the conduit 33 there is disposed an advance throttle 35 which separates the supply circuit 17 of the fuel metering valve 7 from the

control pressure circuit

33, 36 of the regulator assembly 37. From the conduit 33 downstream of the advance throttle 35 there extends a conduit 36 to the regulator assembly 37 which, in turn, is connected with the fuel tank 16 with a return conduit 38. The regulator assembly 37 is formed as a flat seat valve 40 which has a diaphragm 41 serving as its movable valving member. A very slight motion of the diaphragm 41 in a direction away from its seat is sufficient to fully open the valve 40. The fuel flowing through the valve 40 from the conduit 36 returns depressurized to the fuel tank 16 through the return conduit 38. The diaphragm 41 is loaded by a spring 42, the bias of which is changeable by magnitudes dependent upon operational engine variables. For this purpose there is provided a three-dimensional cam 43 which is rotatable as a unit with the butterfly valve I and is axially displaceable as a function of the vacuum prevailing in the air intake tube downstream of the butterfly valve 5. For permitting the aforenoted axial shift, the three-dimensional cam 43 is held axially slidably on a shaft 44 of the butterfly valve 5 which is arbitrarily turnable by a lever 45. The three-dimensional cam 43 is rotatably coupled to the shaft 44 by a pin 46. One end of the three-dimensional cam 43 is rotatably secured to a diaphragm 47 bounding a vacuum chamber 48 which is connected by means of a conduit 49 with the air intake tube at a location downstream of the butterfly valve .5. In case of a sufficient vacuum, the threedimensional cam 43 is axially displaced by the diaphragm 47 against the force of a return spring 50 disposed in the vacuum chamber 48. The three-dimensional cam 43 is scanned by a follower pin 53, the motion of which is transmitted through a spring seat disc 54 to the spring 42, the bias of which determines the return force for the air sensor 2.

The fuel that pressurizes the chamber 34 passes through a throttle assembly 57 disposed in the inlet of the pressure chamber 34 and comprising a throttle plate 58 axially movable in a bore portion 62 of the housing of the valve 7 and a closure plate 60 held in said housing parallel and adjacent to the throttle plate 58. The closure plate 60 has an aperture 59 coupled to the terminus of the pressure conduit 33. The throttle plate 58 has a small throttle opening 63 aligned with the aperture 59 and a large throttle opening 64 facing a wall portion of the closure plate 60. The operation of the throttle assembly 57 will be described in detail as the specification progresses. The throttle assembly 57 effects a substantially temperature-independent damping of the motion of the air sensor 2 since fuel is used as the damping liquid.

The aforedescribed fuel injection apparatus operates as follows.

When the internal combustion engine is running, the

pump 15 driven by the electromotor 14 draws fuel from the tank 16 and forces it through conduit 17 to the fuel metering valve 7. Simultaneously, the internal combustion engine draws air through the suction tube 1, 6, 3, 4 which causes the air sensor 2 to be deflected to a certain extent from its position of rest. In proportion to the deflection of the air sensor 2, the control plunger 1 1 is shifted by means of the lever 8 and as a result, the flow passage section at the control slots 26 is enlarged. The direct connection between the air sensor 2 and the control plunger 11 results in a constant ratio between the air quantities and the metered fuel quantities.

In order to maintain the fuel-air ratio at a richer or leaner value as a function of the operational range of the internal combustion engine, the constant resetting force affecting the air sensor 2 has to be changed. The parameters for the load and rpm are the angular position of the butterfly valve 5 and the magnitude of the vacuum in the air intake tube. Thus, the return force is expediently changed by these two variables. For this purpose the force of the spring 42 of the regulator assembly 37 is varied by axially and/or angularly displacing the three-dimensional cam 43 as a function, respectively, of said vacuum in the suction tube downstream of the butterfly valve 5 and of the position of the butterfly valve. The follower pin 53, in engagement with the three-dimensional cam 43, determines the position of the spring seat disc 54 which, in turn determines the extent of compression (bias) of the spring 42. If, for example, during full load, the butterfly valve 5 is in a position in which the air intake tube is fully open, then a highest output, that is, a relatively rich air-fuel mixture is desired. Since the bias of the spring 42 of the regulator assembly 37 determines the pressure of the fuel which affects in the pressure chamber 34 the redial face 12 of the control plunger 11, the return force affecting the air sensor 2 has to be slightly decreased to cause the control plunger 11 to be shifted into a position in which the control slots 26 are opened to a greater extent. Such occurrence results in an-increase of the fuel quantity metered for injection. In the range of partial loads, a relatively higher pressure affecting the radial face 12 of the control plunger 11 allows a relatively smaller deflection of the air sensor 2 and thus the result will be a leaner air-fuel mixture.

The pressure of the fuel which affects the radial face 12 of the control plunger 11 and which acts as the return force for the air sensor 2, is thus maintained at a constant value and is varied only as a function of engine variables.

The

control pressure circuit

33, 36 separated from the supply conduit 17 by means of the advance throttle 35 affects the radial face 12 of the control plunger 11 and thus acts as a return force on the air sensor 2 through the throttle assembly 57 as a function of the load and the rpm-dependent position of the regulator assembly 37. The throttle assembly 57 is necessary as a damping means for preventing overshoots of the air sensor 2 during acceleration and to limit the effect of the suction thrusts of the engine. Such unrestrained oscillations of the air sensor 2 (and the lever 8) would cause a corresponding reciprocation of the control plunger 11 which, in turn, would lead to an undesired fluctuation in the fuel metering and to a jerky engine run.

In case the aforenoted throttle is of conventional structure, in the range of low rmps there occurs a shift of the mean position of the control plunger 11 in the direction of increasing fuel quantities and thus an undesired enriching of the air-fuelmixture would result. This is so, since during acceleration and the suction strokes of the internal combustion engine the control plunger 11 is, because of a greater air speed, accelerated by the air sensor 2 to a greater extent than in the opposite direction when it is driven by the pressure in the pressure chamber 34. Thus, in the first instance (i.e., upon deflection of the air sensor 2 in response to the air flow), the pressure in the chamber 34 builds up to a substantially larger value than the magnitude of the pressure affecting the control plunger 11 in the return direction.

According to the invention, for the aforeoutlined reasons the throttle assembly 57 is so designed that its throttling effect for damping the oscillations is dependent upon the flow direction. If the control plunger 11 moves in a direction out of the pressure chamber 34 (to the left, when viewed in FIG, 1) because of a drop in the force on the air sensor plate 2, the pressure in the chamber 34 decreases andfalls below the. control pressure of the liquid in the conduit 33. This pressure difference causes the movable throttle plate 58 to assume its position as shown in FIG. 1, in which the large throttle bore 64 of the throttle plate 58 is open. This is so because the throttle plate 58 is now positioned at a distance from the closure plate 60, defining therewith a space 61. As a result, the pressurized liquid may flow rapidly from conduit 33 into the pressure chamber 34 because it may flow through both the small throttle opening 63 and the large throttle opening 64 provided in the throttle plate 58. If, on the other hand, the air sensor 2, because of the pressure difference at the sensor, moves in the direction of air flow, the lever 8 seeks to push the control plunger 11 into the pressure chamber 34 (i.e. towards the right, as viewed in FIG. 1). Such displacement of the control plunger 11 increases the pressure in the pressure chamber 34with respect to the pressure in the conduit 33, so that the throttle plate 58 is moved to the right and pressed against the closure plate 60 in a face-to-face engagement. In this position of the throttle plate 58 the large throttle opening 64 of the throttle plate 58 is entirely blocked by the contacting wall of the closure plate 60. Consequently, from the chamber 34 to the conduit 33 the fuel can flow only through the small throttle opening 63. Thus, the throttling effect of the throttle assembly 57 depends upon the direction of liquid flow therethrough. By utilizing such a direction-dependent throttle assembly for dampening the flow of the pressurized liquid used as a return force, an exact matching of the metered fuel quantities with the performance curve of the internal combustion engine in the range of lower rpms can be obtained.

FIGS. 2, 2a, 3, 3a, and 4 show three other embodiments of the aforedescribed direction-dependent throttle assembly.

In the throttle assembly 57a according to FIG. 2, there is provided a closure plate 68 against which there is pressed, in its position of rest, a triangular throttle plate 69 by means of a spring 70. If the control plunger 1 l, responding to a force applied to the sensor 2, moves into the pressure chamber 34, then the throttle plate 69 lies flat against the closure plate 68 and the pressurized liquid can return to the regulator assembly 37 solely through the small throttle opening 71 aligned with the aperture 59 provided in the closure plate 68. If the pressure of the pressurized liquid in the pressure chamber 34 falls below the control pressure in the conduit 33, then by virtue of this pressure difference, the throttle plate 69 is displaced against the force of the spring axially in the cylindrical bore 72. As a result, the pressurized liquid may additionally flow through the now open large throttle openings 73 into the pressure chamber 34. FIG. 2a illustrates an end view of the throttle plate 69 taken in the direction of arrow B.

Turning now to the throttle assembly 57b illustrated in FIG. 3, a throttle plate, or, more accurately, a tongue-shaped plate valve 76 having a small throttle opening 77, is clamped between a closure plate 78 and the housing of the valve 7. The aperture 59a in the closure plate 78 merges into a counterbore 79 oriented towards the valve 76. Normally, the plate valve 76 is in a faceto-face engagement with the closure plate 78. Thus, from the pressure chamber 34 to the conduit 33 the liquid is constrained to flow solely through the small throttle opening 77 in registry with the counterbore 79. On the other hand, if the direction of flow is opposite, the valve plate 76 resiliently yields to the greater force applied to it from the side of the conduit 33, thus increasing the flow passage section of the throttle assembly 57b. FIG. 3a is an end view of the plate valve 76 taken in the direction of arrow C.

Turning now to FIG. 4, the throttle assembly 570 shown therein has a closure plate 82 which presses a throttle plate firmly against an annular shoulder 93 with the interposition of a spacer ring 92. The closure plate 82 has an aperture 83 through which the pressurized liquid is admitted from the conduit 33 into an accumulator chamber 84 bounded by the closure plate 82 and the throttle plate 85. The accumulator chamber 84 is in continuous communication with the pressure chamber 34 through a smaller throttle opening 86 of the throttle plate 85. A second, larger throttle opening 87 provided in the throttle plate 85 is normally maintained in a closed position by means of a spherical valve formed of a ball 88, a spring seat disc 89 and a spring 90 bearing against an annular shoulder 91. When the control plunger 11 moves outwardly (ie to the left),

the pressure difference between the pressure in the acthe spring 90, whereupon the ball 88 is unseated and the liquid can flow from the conduit 33 to the pressure chamber 34 through both

throttle openings

86 and 87.

What is claimed is:

1. In a fuel injection apparatus for introducing metered fuel in the air intake tube of an internal combustion engine, the improvement comprising A. a butterfly valve disposed in said air intake tube for controlling the flow of intake air therein,

B. means for arbitrarily varying the position of said butterfly valve,

C. an air sensor disposed in said air intake tube spaced from said butterfly valve, said air sensor being displaced to an extent proportionate to the throughgoing air quantities,

D. a fuel metering valve having a movable valving member the position of which determining the fuel quantities to be injected,

E. means for transmitting the motion of said air sensor to said movable valving member of said fuel metering valve for effecting a metering of fuel quantities proportionate to said air quantities,

F. a pressure chamber,

G. a pressure conduit connected with said pressure chamber for carrying liquid under pressure thereto and therefrom,

l-l. means for pressurizing said liquid carried by said pressure conduit to said pressure chamber,

I. a movable plunger having a work face disposed in said pressure chamber and exposed to the pressure therein, said pressure urging said plunger out of said pressure chamber, said plunger being connected to said means defined in (E) for exerting a return force on said air sensor by virtue of the pressurized liquid in said pressure chamber, said means defined in (E) urging said plunger into said pressure chamber in response to the deflecting forces exerted on said air sensor and J. a throttle assembly arranged betweensaid pressure conduit and said pressure chamber to restrict the flow of said liquid to and from said pressure chamber, said throttle assembly including direction-dependent means for throttling the flow of said liquid to a smaller extent in a direction from said pressure conduit to said pressure chamber and to a greater extent in a direction from said pressure chamber to said pressure conduit.

2. An improvement as defined in claim 1, said throt tle assembly including A. a movable throttle plate exposed to said liquid to assume a first position in response to the liquid flowin a direction from said pressure conduit to said pressure chamber and to assume a second position in response to the liquid flow in a opening and B. stationary wall means blocking said relatively large throttle opening in said second position of said movable throttle plate. 3. An improvement as defined in claim 1, said throttle assembly including A. a chamber of circular cross section, B. a triangular throttle plate movable in said chamber and having a continuously open, relatively small throttle opening, the contour of said triangular throttle plate and said last-named chamber defining relatively large throttle openings,

C. stationary wall means bounding the last-named chamber and D. spring means disposed in the last-named chamber in engagement with said triangular throttle plate, said triangular throttle plate being urged by said spring means into engagement with said stationary wall means for blocking said relatively large throttle openings, said triangular throttle plate being adapted to be moved out of engagement with said stationary wall means by said liquid flowing from said pressure conduit to said pressure chamber.

4. An improvement as defined in claim 1, said throttle assembly including A. a stationary component having 1. an aperture coupled to said pressure conduit, 2. a counterbore communicating with said aperture and Ba tongue valve plate having a throttle opening in registry with said counterbore, said tongue valve plate being resiliently urged against said stationary component over said counterbore, said tongue valve plate being adapted to move away from said counterbore by said liquid flowing from said pressure conduit to said pressure chamber.

5. An improvement as defined in claim 1, said throttle assembly including A. means defining a continuously open, relatively small throttle opening,

B. means defining a relatively large throttle opening,

C. a valve ball cooperating with said relatively large throttle opening,

D. means urging said valve ball into engagement with said means defining said relatively large throttle opening for closing the same, said valve ball being adapted to move away from the last-named means for opening said relatively large throttle opening by means of said liquid flowing from said pressur conduit to said pressure chamber.

6. An improvement as defined in claim 1, including a regulator assembly means communicating with said pressure conduit for affecting the pressure therein as a function of at least one engine variable.

7. An improvement as defined in claim 1, said movable valving member of said fuel metering valve and said plunger being one and the same component.

Claims

1. In a fuel injection apparatus for introducing metered fuel in the air intake tube of an internal combustion engine, the improvement comprising A. a butterfly valve disposed in said air intake tube for controlling the flow of intake air therein, B. means for arbitrarily varying the position of said butterfly valve, C. an air sensor disposed in said air intake tube spaced from said butterfly valve, said air sensor being displaced to an extent proportionate to the throughgoing air quantities, D. a fuel metering valve having a movable valving member the position of which determining the fuel quantities to be injected, E. means for transmitting the motion of said air sensor to said movable valving member of said fuel metering valve for effecting a metering of fuel quantities proportionate to said air quantities, F. a pressure chamber, G. a pressure conduit connected with said pressure chamber for carrying liquid under pressure thereto and therefrom, H. means for pressurizing said liquid carried by said pressure conduit to said pressure chamber, I. a movable plunger having a work face disposed in said pressure chamber and exposed to the pressure therein, said pressure urging said plunger out of said pressure chamber, said plunger being connected to said means defined in (E) for exerting a return force on said air sensor by virtue of the pressurized liquid in said pressure chamber, said means defined in (E) urging said plunger into said pressure chamber in response to the deflecting forces exerted on said air sensor and J. a throttle assembly arranged between said pressure conduit and said pressure chamber to restrict the flow of said liquid to and from said pressure chamber, said throttle assembly including direction-dependent means for throttling the flow of said liquid to a smaller extent in a direction from said pressure conduit to said pressure chamber and to a greater extent in a direction from said pressure chamber to said pressure conduit.

2. An improvement as defined in claim 1, said throttle assembly including A. a movable throttle plate exposed to said liquid to assume a first position in response to the liquid flow in a direction from said pressure conduit to said pressure chamber and to assume a second position in response to the liquid flow iN a direction from said pressure chamber to said pressure conduit, said throttle plate having

2. a continuously open relatively small throttle opening and B. stationary wall means blocking said relatively large throttle opening in said second position of said movable throttle plate.

2. a counterbore communicating with said aperture and B. a tongue valve plate having a throttle opening in registry with said counterbore, said tongue valve plate being resiliently urged against said stationary component over said counterbore, said tongue valve plate being adapted to move away from said counterbore by said liquid flowing from said pressure conduit to said pressure chamber.

3. An improvement as defined in claim 1, said throttle assembly including A. a chamber of circular cross section, B. a triangular throttle plate movable in said chamber and having a continuously open, relatively small throttle opening, the contour of said triangular throttle plate and said last-named chamber defining relatively large throttle openings, C. stationary wall means bounding the last-named chamber and D. spring means disposed in the last-named chamber in engagement with said triangular throttle plate, said triangular throttle plate being urged by said spring means into engagement with said stationary wall means for blocking said relatively large throttle openings, said triangular throttle plate being adapted to be moved out of engagement with said stationary wall means by said liquid flowing from said pressure conduit to said pressure chamber.

4. An improvement as defined in claim 1, said throttle assembly including A. a stationary component having

5. An improvement as defined in claim 1, said throttle assembly including A. means defining a continuously open, relatively small throttle opening, B. means defining a relatively large throttle opening, C. a valve ball cooperating with said relatively large throttle opening, D. means urging said valve ball into engagement with said means defining said relatively large throttle opening for closing the same, said valve ball being adapted to move away from the last-named means for opening said relatively large throttle opening by means of said liquid flowing from said pressure conduit to said pressure chamber.