Control device for a filling-ratio adjusting pump

A control device for a filling-ratio adjusting pump with at least one displacement space works on the suction-throttle principle with a positive variation in volume of the displacement space or displacement spaces and is intended inter alia particularly for common-rail diesel injection systems. It allows an exact, precise and highly dynamic control of the filling-ratio adjusting pump at low outlay, without the system being impaired by undesirable cavitation. Located on the suction side of the pump is at least one throttling 2/2-way valve (21, 21a, 21b; 134; 51, 52, 53, 54; 81; 103) actuated by pressure difference. Either such a 2/2-way valve can be used for a group of displacement spaces or for the entire pump or a respective valve of this type can be inserted in front of each individual displacement space. The pressure-difference control of the or each 2/2-way valve takes place via an adjusting device (27; 150) which is arranged on the inflow side of the 2/2-way valve and which is designed either as a throttling valve or as a flow-regulating valve.

TECHNICAL FIELD 
The invention relates to a control device for a filling-ratio adjusting 
pump with at least one displacement space which works on the 
suction-throttle principle with a positive variation in volume of the 
displacement space or of the displacement spaces, which obtains the liquid 
to be conveyed from a liquid reservoir, having a free surface loaded with 
a gas pressure, usually atmospheric pressure, by means of a conduit or, if 
appropriate, via a hydraulic system, but without a supply of gas. 
BACKGROUND ART 
Filling-ratio adjusting pumps are hydrostatic pumps with a displacement 
effect by means of lifting pistons (for example, radial piston pump, axial 
piston pump, in-line pump) or rotary or pivoting piston pumps (for 
example, vane-cell pump, blocking-vane pump, roller-cell pump). The 
invention relates only to those filling-ratio adjusting pumps which work 
on the principle of suction throttling with a positive displacement 
movement. In these, a partial filling of the displacement space occurs as 
a result of a controlled cavitation in the compressed liquid. Both pistons 
with an oscillating movement and rotary displacers (vane-cell pump, 
blocking-vane pump, etc.) can be considered as positively moved 
displacers. 
To increase the energy efficiency in hydrostatic systems, there has already 
long been the desire for an increased use of adjusting pumps. However, the 
currently obtainable designs of such adjusting pumps, which are mostly 
produced on the principle of stroke adjustment, are still too expensive 
for many uses or have too low an efficiency during part conveyance, that 
is to say at a low filling ratio. 
At the same time, on account of the gain/cost ratio of the electronics 
which rises undiminished, there is a continuing trend towards the 
interlinking of electronics and fluid technology, so that there is a 
growing demand for a direct, but nevertheless cost-effective electrical 
control of adjusting pumps. 
To be incorporated into regulating systems (in the form of actuating 
members), future adjusting pumps must have specific conveyed-stream 
characteristics and must reproduce these accurately, with low hysteresis 
and sufficient rapidity (that is to say, for example, without a long idle 
time). As is known, for actuating members in control loops, such 
properties are in part indispensable and in part at least of considerable 
advantage. 
Furthermore, a high conveying uniformity of the individual displacers 
relative to one another is important, on the one hand on account of the 
noise generation and on account of any consumers relying on uniformity 
and, on the other hand, so that no additional disturbances of different 
frequency which could irritate a controller are carried into the 
high-pressure system. 
Hydrostatic filling-ratio adjusting pumps of this type can be employed in 
many areas of use in vehicle, industrial, aeronautical and water 
hydraulics and, in particular, for general motor-vehicle hydraulics and 
the so-called common-rail diesel injection systems. By the use of the 
phase-control principle in such filling-ratio adjusting pumps (see the 
list of literature references at the end of the description), very high 
efficiencies can be achieved even during part conveyance and, in 
particular, even in the case of low-viscosity media, very high pressures 
and the lowest possible rotational speed. Particularly in contrast to this 
stroke-adjusting pump, in the phase-controlled pump, with a decreasing 
conveyed quantity per work cycle, there is also a reduction in the 
duration of pressure loading of the displacer bodies and the lost work 
associated with it (such as, for example, piston-gap leakage). This 
property of leakage insensitivity results, in addition to other reasons 
(see 2 and 4 of the list of literature references at the end of the 
description), in the particular suitability of such pumps for the 
common-rail diesel injection technique. 
Such a reason is also the low consumption of energy or of force for the 
adjustment, since this frequently takes place via the adjustment of a 
throttle in the low-pressure part (U.S. Pat. No. 4,907,949). This also 
inter alia makes manual adjustment possible. 
In principle, the low consumption of force also allows very high adjustment 
dynamics, so that the necessary adjustments can not only be rapidly 
calculated electronically, but the adjustments can be implemented by the 
use of high-speed components for electric direct drive. In view of the low 
forces, the size and production costs of the electric drives are likewise 
low. In general, low forces make it possible to regulate 
hydraulic/mechanical systems with a substantial absence of interaction 
between the correcting variable and the measurement signal. 
An example of high adjustment dynamics required is, once again, the 
common-rail diesel injection system; the distributor tube (=common rail) 
and the other volumes carrying high pressure must be capable, in response 
to a signal from the engine electronics, of being pumped up very rapidly 
(an order of magnitude of 0.2 seconds when it is used in automobiles) to a 
considerably higher pressure. For this purpose, the conveyed quantity of 
the pump must be capable of being adjusted a further order of magnitude 
more rapidly--one pump work cycle is the minimum which can be achieved. 
This can be read up again in 4) of the list of literature references. 
Also, even when the pressure is constant, such a pump must be capable of 
providing other conveyed quantities within the order of magnitude of 
approximately two injections. 
Other previous solutions, for example with individually controlled inlet 
valves, are too complicated particularly for pumps with a relatively large 
number of displacement spaces. It is a great advantage to make do with 
only one adjusting element for a large number of cylinders. 
An example of a generic control device for filling-ratio adjusting pumps, 
which makes do with only one transducer element for a multiplicity of 
displacement spaces and has slit control on the inlet side and which is 
sufficient for many uses, is known from PCT/EP89/01057. A special flow 
guidance in the eccentric housing is intended to bring about a uniform 
filling of all the displacement spaces and therefore a high constant 
conveyance even during part conveyance sufficiently low for many uses. 
However, the dynamics are not adequate for various instances of use, since 
all the cylinders are filled from the central eccentric housing, and, 
during immediate transition to full conveyance, the latter first has to be 
filled by the throttle element and, in the reverse operation, has to be 
emptied, before a stationary state is reestablished in the filling and in 
the conveyed stream. However, surface and gravity effects can even then 
still generate sporadic local bubble accumulations with subsequent 
breakaway in groups, for example from walls, and this can lead to 
statistical conveyed-quantity dispersions and hysteresis effects during 
the operation of the pump. For example, states may be established, in 
which some displacement spaces receive more liquid and the other 
displacement spaces a higher cavity fraction during filling, conveyance 
thereby likewise becoming non-uniform. 
The dynamics of a pump designed in a similar way to that in the 
abovementioned patent was measured by Fa.beta.bender (see 6 in the list of 
literature references). In this particular case, the conveyed stream lags 
behind the movement of the actuating member by an idle time of 
approximately 7 work cycles. A high-speed actuator alone is therefore 
insufficient. In the common-rail diesel injection technique already 
adopted as an example above, in this timespan the pressure in the 
distributor tube, because of its small volume, would already rise 
unacceptably and would be capable of being regulated only with difficulty. 
A further example of a generic control device for a pump with inlet valves 
produced as non-return valves is known from CH 674,243=EP-A-299,337 which 
corresponds with U.S. Pat. No. 4,884,545. This published state of the art 
does not indicate any particulars regarding the pressures used. In tested 
pumps of this type, however, it was found that they suffer from cavitation 
during suction throttling, thereby generating considerable gas volumes 
which appreciably impair the desired accurate, precise and simple control. 
In view of the cavitation during suction throttling with a positive 
displacement movement, the throttle-adjusting element was placed close to 
the displacement space in order to achieve the desired high dynamics. 
Consequently, at least in the radial-piston design, one transducer from 
each displacement space or a complicated mechanical linkage becomes 
necessary once again. The single-cylinder design was preferred, and either 
a multiple cam or a gear was proposed in order to achieve a higher 
volumetric flow and a higher pumping frequency. Apart from the 
construction and, if appropriate, load-related restrictions associated 
with this, such a solution having n cams or n drive transmission ratio 
relative to a pump having n cylinders results, it is true, in a high 
periodicity, that is to say a high similarity of the individual conveying 
trends, but also in a higher degree of interruption, considerably (n 
times) higher torque peaks in the drive, greater noise emissions as a 
result of (n times) deeper pressure rises in the cylinders and the risk 
that the process of the reentry of gas molecules from the cavities back 
into the liquid can no longer keep pace with the speed of the pressure 
rises (see 1 in the list of literature references) and cavitation damage 
can then occur under this condition. 
The company Cooper Bessemer Corporation, Mt. Vernon, Ohio, USA, has for 
many years built a two-cylinder piston pump of the generic type for 
common-rail diesel injection systems. This pump possessed two cylinders, 
the adjusting throttle element being arranged between the two cylinders, 
so that the harmful spaces capable of being filled with cavities were 
minimal. Here too, the expansion to more than two cylinders is difficult 
and complicated. The position of the adjusting throttle element between 
the two cylinders restricts freedom in the displacer arrangement (radial, 
axial, in-line). This pump was, in turn, equipped with inlet slits, a 
satisfactory tightness of the displacement spaces obviously being achieved 
by a long-stroke design (that is to say, correspondingly large sealing 
lengths and smaller gap lengths), but this necessitated a correct 
crankshaft with cup tappets absorbing transverse forces and considerably 
increased the overall volume. 
In conclusion, it may be said (in the first place) that a disadvantage is 
that there is even today the problem that, for optimum dynamics, exactness 
of the conveying characteristic and absence of hysteresis, these being 
properties particularly desirable when the pump is used in regulating 
systems, each displacement space has to be equipped with its own actuating 
element with drive or the actuating elements have to be connected to a 
central drive element by means of a complicated mechanism, along with the 
corresponding problems of quantity balancing. This conflict of aim between 
simplicity (as few actuating elements as possible or only one actuating 
element) and high dynamics, exactness of the conveying characteristic and 
absence of hysteresis comes to light all the more clearly when the 
individual displacement spaces are located far apart from one another, as, 
for example, in radial or in-line arrangements, or when there is a large 
number of displacement spaces. If the displacement spaces were located 
close to one another, as in axial-piston pumps, a central arrangement of 
an adjusting element would be fundamentally possible, but the 
constructional space is often too confined or is provided for other 
components. 
The cause of these various restrictions in the use of the filling control 
by suction throttling with a positive displacement movement is founded in 
the cavitation which has hitherto been necessary for adjusting the 
conveyed quantity and which, on account of the ever-present turbulence 
sometimes desirable for the purpose of independence from viscosity, 
usually already commences in the throttling device and not only in the 
displacement spaces. 
DISCLOSURE OF THE INVENTION 
The object of the invention is, therefore, to provide a control device 
according to the preamble which can be produced cost-effectively and 
which, at a low outlay, can at least considerably contain the effect of 
this obstacle of premature cavitation and consequently, with general 
validity for different pump types of the displacement type, help to 
provide different greater degrees of freedom in the implementation of this 
actually extremely interesting and forward-looking conveyed-stream 
control. By the provision of degrees of freedom is meant that, from the 
point of view of production costs, of the abovementioned generally valid 
applicability to different pump types, overall size and the design of the 
pump as a whole, it is to be possible to combine actuating elements and, 
for example, actuate them directly from an electromechanical transducer as 
well as have the capability of arranging the adjustable elements at any 
location of the pump, without a significant impairment of the properties, 
or have the capability of placing them even at some distance from the 
pump, thus affording a remote-control possibility. 
Cavitation in liquids in the case of stationary flows and the associated 
cavitation damage have often been investigated in the past. However, the 
non-stationary and virtually non-flowing case of cavitation in pump 
cylinders has hitherto been investigated to only a lesser extent. It is 
obvious, however, that, with materials customary in pump construction, 
damage caused by cavity breakdown is not to be expected. One of several 
reasons is possibly that the time is too short to dissolve out truly large 
gas or vapor quantities. Schweitzer (please see reference no. 5) in the 
list of literature references appearing hereinbelow) investigated the 
escape of dissolved gases out of liquids and found diffusion time 
constants which are well above typical work-cycle periods of hydrostatic 
pumps. Fassbender (reference no. 6) in the list of literature references) 
measured gas-outlet pressures, and these are actually very low for many 
relevant liquids. 
The present invention makes use of these physical phenomena and of the 
further fact, better known per se, that liquid, which has been given time 
to become saturated in a gas atmosphere above pressure p1, for example at 
rest in a tank ventilated to the atmosphere, has a pronounced tendency, in 
the event of a shortfall of this pressure, above all when there is 
additionally also turbulence during the flow through or round an obstacle, 
to rid itself of the excess gas. This may be little in terms of mass, but 
nevertheless, in terms of volume, can fill a large part of a conduit or 
volume, thus necessitating, with respect to dynamics, the abovementioned 
filling-up or emptying operations, until a new stationary state is 
established. 
To achieve the objects set above, according to the invention a control 
device is provided. The main characteristic of the invention is a 
preconnection of passive throttling valves, pressurized according to the 
rules of the claims, upstream of the individual displacement spaces, 
upstream of groups of displacers or the entire pump, thus ensuring that 
the pressure downstream of a throttle-actuating element to a point 
upstream of these valves does not at least essentially fall short of the 
pressure p1 of the liquid reservoir and preferably p1 plus an amount 
.increment..sub.pTemp explained later, and consequently restricts an 
appreciable disruptive cavitation to the comparatively small volume 
downstream of these valves as far as the displacement spaces. This 
procedure is unusual, since throttlings with a loss of pressure in pumps 
are otherwise avoided as far as possible, for example by not pressurizing 
inlet valves at all or pressurizing them only slightly, in order to 
acquire some self-priming capability of the pump or to reduce the risk of 
cavitation in the intake conduit, for example at kinks. For this purpose, 
the pressure p3 upstream of the throttling valves must, as a rule, be 
raised slightly by means of a pressure source of a known type, for which a 
height difference between the liquid reservoir and the valve inlet would 
also be possible. Most hydraulic systems, but particularly hydraulic and 
fuel-supply systems in vehicles, for these reasons operate in any case 
with pumps which generate low to very low admission pressures, so that in 
practice, as a result of this condition, there is no appreciable 
restriction in the use or incorporation of the invention. 
An important discovery on which the invention is based is that, at 
atmospheric pressure, one liter of fuel or of hydraulic fluid is capable 
of absorbing approximately 10% by volume of air in dissolved form, and 
this also goes for a fuel tank of a vehicle. At atmospheric pressure, 
therefore, a gas volume of approximately 100 cc is contained in one liter 
of fuel. When the pressure is reduced, this dissolved air escapes in gas 
form from the solution and, in terms of volume, the gas volume expands to 
1000 cc according to the prevailing negative pressure, for example, at 0.1 
bar, by ten times. Such gas volumes can very quickly fill the volume 
present downstream of the valves as far as the displacement spaces and 
thereby greatly impair the delivery and control of a fuel pump. The same 
consideration also applies to other liquids. As a result of the 
restriction according to the invention of .increment..sub.Pomin to no less 
than 0.9 bar and preferably in the range of between 1.0 and 1.5 bar, the 
formation of gas volume is kept to a minimum or prevented completely, so 
that the delivery and control of the pump system do not suffer from this. 
The rules in claims 5 and 6 take into account the specific properties of 
liquids and gases. The formula according to claims 5 and 6 makes it 
possible, both for pumps with inlet slits and for pumps with automatic 
spring-loaded inlet valves controlled by the displacer travel, to 
determine the minimum opening-pressure difference .increment..sub.Pomin at 
which the or each throttling 2/2-way valve actuated by pressure difference 
opens. If gas-outlet pressures pgasout and vapor-outlet pressures 
pvaporout are not known, then 0 bar for these pressures in the formula is 
on the safe side. 
The so-called solubility coefficient describes specifically for a liquid 
and specifically for a gas the solution behavior according to Henry's 
equation: 
EQU cs=k*p 
wherein 
cs=saturation concentration of the dissolved gas or gas mixture in the 
liquid 
p=pressure at saturation equilibrium (p1) 
k=k(T)=solubility coefficient of the gas or gas mixture in the liquid. 
In many systems, particularly, for example, in vehicle use, for example on 
the way from a still cold tank to an already hot engine, a liquid to be 
conveyed can experience a rapid temperature change. 
If the solubility coefficent is lower in the direction of the temperature 
change, there can occur a sudden supersaturated state of the liquid which 
can lead to a disturbing gas release as early as upstream of the 
throttling spring-loaded valve. 
In order reliably to prevent this, that is to say at least maintain the 
saturation concentration, the maximum temperature-related decrease in the 
solubility coefficient k occurring during operation can be precluded by 
increasing the minimum opening difference by an amount .increment.ptemp. 
If cs.sub.x =cs.sub.1, then, with Henry, the following is true 
k(T.sub.x)p.sub.x =k(T.sub.1)p.sub.1 and p.sub.x /p.sub.1 
=K(T.sub.1)/K(T.sub.x) or .increment..sub.ptemp =p.sub.x -p.sub.1 
=(p.sub.x /p.sub.1 -1) p.sub.1 =(k(T.sub.1)/k(T.sub.x)-1)p.sub.1 when 
k(T.sub.x)&lt;k(T.sub.1) in which T.sub.x and T.sub.1 define the maximum 
temperature difference of the liquid occurring during operation at a time 
interval of a few hours between the liquid reservoir and the throttling 
spring-loaded valve. 
The main advantage of the control device selected according to the 
invention is the desired rapid, reproducible, low-hysteresis and low-idle 
time reaction of the conveyed quantity to adjustments of the correcting 
members. This exact calculable assignment of the collecting-member 
position and pump throughflow is, again, a precondition for the 
incorporation of this pump into control loops of hydraulic systems, 
particularly into those with stringent requirements demanded of the 
control dynamics, such as there are inter alia also for common-rail diesel 
injection systems. In view of a theoretically infinitely rapid setting 
operation of the actuator, the associated full response of the conveyed 
quantity already occurs with the first subsequent complete suction 
operation (it cannot, in principle, take place any more rapidly at all). 
In the hydraulic system, therefore, with knowledge of an expected sudden 
change in consumption, the conveyed flow of the pump can already also be 
varied simultaneously. 
The pronounced lack of cavities as far as the throttling valve near the 
displacement space (and, in the special case, when the latter is designed 
as an inlet valve, as far as the limit of the displacement space) allows 
the use of various adjusting devices for filling control and many 
advantageous specializations, since degrees of freedom are obtained in the 
most diverse pumps of the displacement type. 
Particularly preferred embodiments of the control device according to the 
invention for a filling-ratio adjusting pump can be taken from the further 
subclaims.

BEST MODES FOR CARRYING OUT THE INVENTION 
FIG. 1 shows a first possible version of a control device for a pump having 
automatically working inlet valves. 
The pump according to the diagrammatic representation of FIG. 1 has three 
individual displacement pistons 9, only one of which can be seen in FIG. 
1. The three displacers are driven by a rotary shaft 12 via respective 
eccentrics 11, each eccentric 11 being arranged in a lifting member 10 
which is located at the lower end of the associated piston 9. 
In this case, the rotational movement A of the eccentric 11 initiates an 
oscillating movement B, the piston 9 moving as a displacer in the 
displacement space 15 to and fro between the two dead-center positions C 
(bottom dead center) and D (top dead center) and triggering the periodic 
suction movement. As a result of the lifting member 10, the piston does 
not lift off in any phase of its movement from the eccentric 11 (positive 
displacement movement). An inlet valve 28 and an outlet valve 17 are 
provided in a way known per se for each displacement space, and both the 
inlet valve 28 and the outlet valve 17 can be pressurized in each case 
into the closed positions by respective springs (for example, 29 for the 
inlet valve 28). This means that the valve 28 is designed as an inlet 
non-return valve. As a result of the movement of the displacer 9, by 
virtue of the rotational movement of the eccentric 11 the inlet non-return 
valve is opened in a known way via the pressure difference p4-p5 occurring 
and the suction operation is triggered. During the upwardly directed 
stroke of the displacer 9, the liquid quantity hitherto collected is 
displaced out of the displacement space 15 through the outlet valve 17, 
that is to say the latter lifts off from its seat counter to the effect of 
the pressurizing spring and the liquid, which is now under high pressure, 
is conveyed via the conduit 18, together with corresponding liquid 
quantities via the conduits 18a and 18b, into a common conduit 19, where a 
pressure p6 prevails and which constitutes, for example, the so-called 
"common rail" (the distributor pipe) of a "common-rail" injection system. 
As is customary in such multi-piston arrangements, the individual pistons 
or displacers 9 are moved with a phase shift, in order to achieve an 
equalization of the outlet pressure p6 into the common conduit and in 
order to ensure that the pump operates with as little vibration as 
possible. That is to say, if there are three displacers, as shown in the 
example according to FIG. 1, the individual displacement pistons execute 
their lifting movement in each case with a phase shift of 120.degree. 
relative to the adjacent displacer. 
The throughflow quantity through each displacer is determined by a 
respective throttling spring-loaded 2/2-way valve 21 located upstream of 
this and by an adjusting device 27 which, in this example, is designed as 
an adjusting throttle 30. 
The adjusting device 27, like the identically designed adjusting device 27a 
and 27b, is fed from a common conduit 32 which supplies the liquid to be 
conveyed, here diesel oil, at a pressure p2. The diesel fuel 2 comes from 
a liquid reservoir 1, where it is in contact with a gas 3 at a pressure 
p.sub.1, here air at atmospheric pressure 1, at a contact face 4. The 
liquid can be saturated with gas. The liquid first flows through a system 
7, in which preferably no further gas is to be introduced into the liquid. 
Since the pressure is to be increased from p1 to p2, a pressure-increasing 
device, that is to say a pressure source 8 in this example, is integrated 
into the system 7. 
The diesel liquid in the conduit 32 then flows through the three adjusting 
throttles 30, 30a, 30b and the throttling 2/2-way valves 21, 21a and 21b 
assigned to these and actuated by pressure difference. By virtue of the 
continuity equation for incompressible media (which can be assumed only on 
the basis of the absence of cavities), the throughflow quantity through 
each adjusting throttle and through the 2/2-way valve 21, 21a and 21b 
assigned to it is identical. From this is established a state of 
equilibrium arising from the pressure p3 at the effective face 24 of the 
2/2-way valve 21 on one side and a reservoir-like pressure p12, close to 
p1, of the effective face 23 on the other side of the 2/2-way valve and 
from the force of the spring 22 dependent on the opening travel. The 
adjusting throttles 30, 30a, 30b can theoretically be adjusted 
individually for being coordinated with one another. 
FIG. 1 discloses a further important advantage of the invention. The system 
possesses, with the valve effective faces 24, 24a, 24b and the associated 
throttles 30, 30a, 30b, an inherent damping effect which increases with 
sharper throttling and which is important for the maintenance and 
reproducibility of the conveying characteristics (see FIGS. 10 and 11). 
Damping functions in that, even when there is only a slight overshooting 
of the throttling 2/2-way valves 21, 21a, 21b in the suddenly commencing 
opening phase, the increase in volume generated by the product of the face 
24, 24a, 24b and the stroke difference in the connection 31, 31a, 31b 
causes a lowering of the pressure p.sub.3 by considerable amount 
.increment.p.sub.3 which counteracts the overshooting, this being on 
account of the lack of cavities according to the invention| 
The lower the throttle is set, the longer the time until medium can flow on 
and the more sustained is the damping effect. 
In this exemplary embodiment, the throttling 2/2-way valves 21, 21a and 21b 
actuated by pressure difference are each connected at their effective face 
23 to the return 6, with the result that the reservoir-like pressure p12, 
close to p1, prevails at the effective face 23. 
The advantage of this arrangement is that, depending on the size of the 
face 23, the spring 22 can be selected so as to be very weak and serves 
less for pressurizing than, instead, for the regulating resetting of the 
valve (21) counter to the opening pressure p3 on the other effective face 
24, since, with the pressure p12 at the effective face 23, there is 
already a considerable part of the necessary pressurizing and perhaps even 
more. 
FIG. 2 illustrates a similar control device to that of FIG. 1, with the 
difference that the pump has inlet slits 35 and only one central adjusting 
device 27 possessing an adjusting throttle 30 is provided. Pumps with 
inlet slits can as a rule be produced more cost-effectively in contrast to 
those with inlet valves, whereas they are used to a lesser extent at very 
high pressures and with low-viscosity pressure media. 
In this exemplary embodiment, the aim of low cost is achieved by the 
central adjusting device 27 which basically allows simple manual 
adjustment or electrical adjustment. The individual adjusting throttle 30 
in the adjusting device 27 can likewise be produced cost-effectively in a 
way known per se. In the suction phases, the pressure difference p2-p3 
across the adjusting throttle is kept approximately constant, irrespective 
of the throughflow quantity, by means of a pressure-differential valve 40 
connected in parallel, with the result that the combination of the 
adjusting throttle 30 and the pressure-difference valve 40 gives the 
effect of a flow-regulating valve. The simple act of using the same 
adjusting throttle 30 for all the displacement elements 16, 16a, 16b 
affords further advantages in this configuration having the inlet-side 
slit control of the pump. 
A first advantage is that, for a specific rotational speed and a specific 
relative filling of the displacement spaces, in terms of the number of 
displacement spaces served, and the shortness of the respective suction 
phases, the control cross section of the throttle 30 is substantially 
larger than, for example, in the individual throttles in the configuration 
according to FIG. 1. (The same rotational speed and the same relative 
filling are assumed. 
This has a favorable effect on the price and on the production tolerances. 
Moreover, special contouring of the control cross section over the 
throttle opening travel is more easily possible, as is an application of 
the control principle to extremely small pumps. 
A second advantage is that, because the short suction phases and uniform 
phase shift of the displacement movement (=displacement control by the 
rotary shaft with eccentrics), an overlap of the suction phases is 
relatively slight or even absent. (An overlap of the suction phases is 
even absent if the height of the orifice 35 is kept so small that the 
region covered, that is to say the angular range of the eccentric 11 or of 
the rotary shaft 12, during the opening of the orifice 35 by the piston 9 
is a maximum of 360.degree./number of displacement elements. 
This is equivalent to a locking of one and the same throttle on to the 
various displacement elements in succession. This signifies the equality 
of the throttle cross section for each displacement element as an ideal 
precondition for equal filling or equal conveyance of all the displacement 
elements. 
A third advantage is obtained when the opening angle described is somewhat 
smaller than the 360.degree. number of displacement elements. More or less 
short intermediate phases, in which none of the displacement spaces sucks, 
are then obtained. 
The filling of the channel portions 36, 36a, 36b between the respective 
2/2-way valve 21, 21a, 21b and the respective inlet cross sections 35 
(35a, 35b concealed, cannot be seen in the drawing) can basically continue 
between the suction phases. This also helps to achieve at least a lack of 
cavities in the channel portions 36, 36a, 36b, that is to say as far as 
the displacement-space limit in the form of the inlet cross section 35. 
In the intermediate phases, the pressure p.sub.3 in the connecting channels 
can rise even to a maximum of p.sub.2, since no displacement element 
extracts fluid from the channel portions 36, 36a, 36b by means of a 
suction operation. This leads to a temporarily larger opening of the 
2/2-way valves and to an acceleration in the filling-up of the channel 
portions. 
FIG. 3 illustrates a particularly favorable embodiment of the control 
device of FIG. 1. 
This shows the possibility, achieved as a result of the absence of 
cavities, of arranging the adjusting device for the throttling 2/2-way 
valves 21, here integrated in the pump, at a greater distance from these 
or the individual displacement spaces. This makes it possible to combine a 
plurality of or all the actuating elements into one actuator 60 in the 
form of a continuous directional valve with only one drive, which then 
again makes, for example, simple manual actuation possible. In the event 
of an electrical pump adjustment, the need for only one transducer for a 
plurality of or all displacement spaces is a great advantage in terms of 
cost and of constructional space. 
Simply combining the individual throttles belonging to the displacement 
elements into the continuous directional valve 60 also allows an optimum 
equal control of the individual throttles. As is known, the control 
orifices of control slides and housings of such valves are usually 
produced in a fixture, which means a low-fault immovable positioning of 
these orifices relative to one another. 
An important property of the invention is the liquid volumes enclosed 
between the one adjusting device 27 and the individual throttling 2/2-way 
valves 21 in a channel are scarcely elastic on account of the absence of 
cavities, so that also scarcely any additional liquid quantities have to 
flow in or flow out in order to achieve the particular stationary states 
of a filling operation or of the time period located between two filling 
operations. Consequently, the geometrical channel volumes are permitted to 
deviate sharply from one another, which is why the invention is suitable 
for all geometrical displacer arrangements (for example, axial, radial, 
in-line in the case of piston pumps). A location for the adjusting device 
27 which is favorable in terms of the constructional space and of the 
appearance can be found for all these displacer arrangements. 
In this example, the adjusting device 27 is even linked to the pump by 
means of hose conduits 41, 41a, 41b, thus allowing a possibility for the 
remote control of the pump over a length which is a multiple of the 
characteristic pump dimension (for example, the diameter in the case of a 
radial piston pump). 
FIG. 3 also shows a further possible and advantageous version of the 
invention, in so far as an additional damper supplements the inherent 
damping described further above under FIG. 1. The damper shown is only one 
example of possible designs. In this example, the respective throttling 
2/2-way valves 21 actuated by pressure difference are connected to 
respective damping pistons 73 which are movable to and fro in respective 
cylinders 70 according to the movement of the slides of the 2/2-way valves 
21. In view of the lack of cavities, the effect of the damping is good and 
constant. At the same time, damping chambers 71 and 72 are formed in the 
respective cylinder 70 on opposite sides of the respective damping pistons 
73. During the displacement of the damping pistons 73 according to the 
opening or closing of the respective slide of the associated 2/2-way valve 
21, liquid flows past the piston from the chamber 71 into the chamber 72 
or from the chamber 72 into the chamber 71 and through the guide gap of 
the rod 74 and damps the movement of the piston and therefore of the 
corresponding slide of the 2/2-way valve 21. This contributes to avoiding 
an uncontrolled overshooting of the valve movement, since this would have 
an influence on the conveyed-flow characteristics. 
FIG. 3 also shows a favorable version of the invention, in so far as the 
2/2-way valves 21 actuated by pressure difference are designed at the same 
time as inlet valves, thereby making a saving in outlay. 
FIGS. 4 and 5 show, in cross-section and in longitudinal section 
respectively, a particularly favorable design of a pump with a control 
device according to the invention. The pump according to FIGS. 4 and 5 is 
equipped with four displacement spaces 129a-d which are arranged in pairs 
above and below the drive shaft 110. The displacement space 129b cannot be 
seen in the drawing, since, in FIG. 5, it is located behind the sectional 
plane (V--V in FIG. 4) in the upper part of the drawing. 
A respective piston or displacer 117 is provided for each displacement 
space. The displacers 117 are kept in contact by means of respective 
springs 135 with two drive rings 114 mounted eccentrically on the drive 
shaft 110. The drive rings 114 are mounted rotatably by means of needle 
bearings 115 on eccentrics 113 which are connected fixedly in terms of 
rotation to the drive shaft 110 in a manner offset relative to one 
another. 
The springs 135 for the respective displacement pistons 117 are supported 
on a plate-like abutment 116 at the end of each individual displacement 
piston, and the drive ring 114 presses on to the respective sides of the 
spring abutments 116 located opposite the displacement pistons 117. The 
rotation of the drive shaft 110 therefore causes, via the eccentrics 113 
connected fixedly in terms of rotation to it and via the rings 114, a 
to-and-fro movement of the displacement pistons 117, the stroke movement 
of the upper displacement pistons 117 taking place in a manner offset at 
180.degree. to the stroke movement of the respective opposite lower 
displacement pistons 117. This means, for example, that the displacement 
space 129a has its smallest volume while the displacement space 129b has 
its largest volume, and vice versa. Two eccentrics 113 are connected to 
the rotary shaft 110 in a manner offset at 90.degree. relative to one 
another, so that the stroke-phase difference of two displacement pistons 
117 arranged next to one another, that is to say of the lower displacement 
pistons 117 in FIG. 5 and the upper displacement pistons, likewise amounts 
to 90.degree.. This contributes, on the one hand, to a quiet running of 
the pump and, on the other hand, to a uniform delivery of liquid. 
The rotary shaft 110 is mounted rotatably in the main housing 138 of the 
pump via the ballbearing 136 and the roller bearing 137. 
The respective inlet valve 134 and the respective outlet valve 118 are 
provided for each displacement space 129a-d (of which the displacement 
space 129c is not shown). The respective pairs of inlet and outlet valves 
134, 118 belonging to respective displacement spaces 129a-d are 
accommodated in respective housing parts 133a-133d, in which the cylinders 
forming the displacement spaces 129a-d and serving for receiving the 
displacement pistons 117 are also arranged. These housing parts 133a-d 
each have a cylindrical extension which is arranged coaxially to the 
respective cylinder, that is to say to the respective displacement piston 
117, and which is inserted in a corresponding cylinder bore of the main 
housing part 138. A respective annular gasket is located between the 
cylindrical extension of each housing part 133a-d and the housing 138, so 
that the main housing 138 is sealed off against leakage. Moreover, the 
cylindrical extension of each housing part 133a-d has an annular shoulder, 
on which the end of the respective spring 135 facing away from the 
plate-like abutment 116 is supported. That is to say, the annular shoulder 
forms a further abutment for the spring 135. 
Each housing part 133a-133d is also provided with a respective valve cover 
119a-d, the individual valve covers 119a-d each having a cylindrical 
recess 121 which is arranged coaxially to the cylindrical extension of the 
respectively assigned housing part 133a-d and which receives a shank part 
of the inlet valve 134 and the components which cooperate with this and 
which are shown on an enlarged scale in FIGS. 6A and 6B. The valve covers 
119a-d and the housing parts 133a-d are screwed to the crankcase 138 by 
means of continuous screws which are shown in FIG. 5. 
On the left-hand side of FIG. 4 a hollow rotary slide valve 150 can be 
seen, which is integrated into the construction and which can be designed, 
for example, according to German Patent Specification 3,714,691. To this 
embodiment, the valve 150 constitutes the adjustable element which serves 
for controlling the throttling 2/2-way valves actuated by pressure 
difference, which, in this embodiment, are formed by the respective inlet 
valves 134 together with the associated parts, as described in more detail 
a little later. 
Starting from the rotary slide valve 150, there are provided four 
distributor bores or distribution paths 130a-d (130c not shown) which lead 
to the respective inlet valves 134, specifically, in each case, into a 
chamber 134a-d on the shank side of the valve, immediately adjacent to the 
respective valve seat, the chamber 134c not being shown. Starting from 
each distribution path 130a-d, there are located in the respective 
cylinder heads 119a-d respective oblique bores 127a-d which open into the 
cylindrical spaces 121, the oblique bores 127c and 127d being shown. 
On the inlet side, the hollow rotary slide valve 150, which, in this 
example, is designed as a plug-in cartridge exchangeable in a simple way, 
receives liquid in the direction of the arrow E via a housing bore 132 
from a reservoir 1 of the pressure p2, as shown, for example in FIG. 3. 
The fluid passes further, without any significant pressure loss, into the 
interior of the hollow rotary slide via a constantly opened sufficiently 
large inlet cross section 156. As a result of the rotation of the hollow 
rotary slide, which can take place by means of an electrical drive 158 
(FIG. 5) or a gas linkage which is not itself shown, but which engages on 
the part 159, an adjustable throttle effect is achieved by the cooperation 
of elongate linear control slits 155a-155d in the hollow rotary slide 150 
with the mouth edges of the distributor bores 130a-d (130c not shown), so 
that the pressures p3 prevailing in the distribution conduits 130a-d can 
be set exactly and rapidly by means of the actuating element 159. 
In particular, the valve cartridge, on the rearside (not shown), can have 
in each chamber symmetrically opposed identical orifices 115a-115d and 156 
and the movable slide can be made very thin-walled, so that the valve has 
the advantages of a valve according to German Patent Specification 
3,714,691. 
As can be gleaned from German Patent Specification 3,714,691, the advantage 
of rotary slides or axial slides of this type is that, as a result of low 
friction, low inertia and low flow forces, they can be actuated very 
quickly and accurately by means of low actuating forces, so that the 
electrical actuating drive (actuating-drive motor) 158 can be made small 
and cost-effective. On the outlet side, as provided in the previous 
embodiments, there extend away from the respective outlet valves 118 
flow-off bores 112a-d, of which the flow bores 112c and d are not shown 
and which merge into a common flow-off conduit 111 which leads, for 
example, to the "common rail" of a common-rail diesel injection system. 
The pressure p3 in the distribution conduits 130a to 130d is communicated 
via the oblique bores 127a-d in the respective cylinder spaces 121 and 
here acts in the opening direction on the valve 134 via the 
cross-sectional surface of the shank of the valve 134. In the closed state 
of the valve 134, the same pressure p3 also acts in the opening direction 
of the valve on the side of the valve head facing the chamber 134 sic!. 
At this stage, the two springs 125 and 126 exert a closing force on the 
valve 124. The relatively strong spring 125, which engages on the abutment 
124 at the end of the valve shank, permanently exerts a closing force on 
the valve 124, whilst the relatively weak spring 126 is supported on a 
spring plate 126T which is arranged displaceably opposite the valve 124 in 
the chamber 121. In the closed state of the valve and when the spring 
plate 126T bears on the abutment 124, the spring 126 also exerts a closing 
force on the valve 134. However, the spring plate 126T with spring 126 
primarily serves for damping purposes. When the respective displacement 
space 129a-d is enlarged as a result of the movement of the respective 
displacement piston away from the top dead center (TDC), a lower pressure 
prevails on the displacement-space side of the valve than in the 
cylindrical space 121, so that, altogether, a force acts on the valve 
member 134a which leads to an opening of this member. At the same time, 
both the strong spring 125 and the weak spring 126 are compressed. The 
liquid located underneath the spring plate 126T escapes through the 
damping orifices in the spring plate 126T and therefore slows the opening 
of the valve member 134. 
The amount of the opening stroke of the valve member 134 and the quantity 
of liquid flowing past the head of the valve member 134 into the 
displacement space 129 depend on the pressure p3 in the distribution 
conduit 130. 
During the displacement movement of the displacement piston 117, the volume 
of the displacement space 129 decreases and the pressure in this space 
rises, albeit initially only slightly on account of the small quantity of 
gas or liquid molecules which have escaped. The result of this is, on the 
one hand, that a closing force which is higher than the opening forces is 
exerted on the valve member 134, so that the valve 134 closes. By this 
stage, the damping orifices in the spring plate 126T work in order to damp 
the closing movement of the spring plate, so that the valve 134 closes 
against the valve seat relatively gently and the spring plate 126T at a 
somewhat later time likewise comes to bear gently against the abutment 
124. This means that the damper is designed so that it is effective only 
during the opening stroke of the throttling valve, that is to say in the 
phase in which vibrations would most easily be introduced and would be 
effective the longest. According to FIG. 6, in the closing phase, the 
damping piston can lag behind the valve movement. Fluid flows through the 
orifice which is becoming exposed into the damper space under the damping 
piston and prevents negative pressure and cavities from forming. The 
rising pressure in the displacement spaces 129a-d also causes the 
respective outlet valve 118 to lift off, so that diesel passes at the 
desired initial pressure into the conduits 112a-d or 111. 
This arrangement has various advantages. The valve 150 can be integrated 
into the pump construction in a space-saving manner, since it is not 
important to have distribution paths 130a-d of differing length. The 
design of the valve 150 with elongate linear slits 155a-d allows 
particularly good regulatability of the pump down to the very smallest 
conveyed quantities. 
The use of seat valves 134a-d as inlet valves, which serve here at the same 
time as the throttling 2/2-way valves actuated by pressure difference 
according to the invention, is, as a rule, the version which is more 
cost-effective than the use of slide valves, and above all the 
displacement space has one leakage path less, which is particularly 
important in pumps for very high pressures, low rotational speeds and very 
low viscosities (such as occur in conjunction with common-rail diesel 
injection), if very high efficiencies are to be achieved. The tightness of 
the inlet seat valves 134 also has a positive effect on the equal 
conveyance from displacement space 129a-d to displacement space 129a-d, 
since leakage is usually closely associated with component tolerance. The 
general conveying characteristics of the pump, too, can be maintained more 
effectively in mass production in constructions with a seat valve. 
Vibrations of the throttling valves, like vibrations in general, can lead 
to spring fractures or, in the case of seat valves, to increased wear or 
shank fracture, and here these vibrations are, above all, also harmful 
with regard to the conveying characteristic which is varied thereby. 
Vibrations often occur by chance as a result of stochastically fluctuating 
damping effects or excitations. In such a case, there would arise on the 
pump stochastic fluctuations in the conveyed quantity or hysteresis 
effects which would both make it difficult to use the pumps for regulating 
purposes. For the purpose of specific valve damping, therefore, the use of 
a damper on the throttling valve is proposed. In the simple piston dampers 
of known type, the damping forces also generate negative pressures which 
can in turn generate cavities harmful for the damping function. This can 
be eliminated by a higher valve pressurization when such a damper is used. 
If the damping-piston diameter is kept large, for example at the size of a 
valve diameter, the negative pressures and necessary additional valve 
pressurization are reduced. This is desirable since the admission pressure 
of pumps is, as always, to be kept as low as possible. 
The possibility of arranging the adjusting elements at a greater distance 
from the throttling valves or individual displacement spaces makes it 
possible to combine a plurality of or all the actuating elements into one 
actuator with only one drive, which in turn then makes, for example, 
simple manual actuation possible. In the event of electrical pump 
adjustment, the need for only one transducer for a plurality of or all the 
displacement spaces is a great advantage in terms of cost and of 
constructional space. In addition, the liquid volumes enclosed between an 
adjusting element and a throttling valve in a channel are scarcely elastic 
on account of the absence of cavities, so that also scarcely any 
additional liquid quantity has to flow in or out in order to achieve, in 
each case, the stationary states of a filling operation or of the period 
of time located between two filling operations. Consequently, the 
geometrical channel volumes are permitted to deviate sharply from one 
another, which is why the invention is suitable for all geometrical 
displacer arrangements (for example, axial, radial, in-line in the case of 
piston pumps) and a location for the adjusting device 27 which is 
favorable in terms of the construction space and the appearance can be 
found for all of these. 
FIG. 7 shows, for throttle-actuating elements, some particular features of 
the design of the throttling valves, for example of the valves 30 in FIG. 
1 or 150 in the version according to FIGS. 4 to 6. 
However, for the exemplary embodiments of FIGS. 1, 3, 4 and 5, each with a 
throttle point for each displacement space, this involves a high outlay. 
With the arrangement according to the invention, the pressure difference at 
the adjusting element influences the metered liquid quantity with the root 
of the pressure difference. At a fixed feed pressure, however, this 
pressure difference decreases with increasing throttle-valve opening. The 
use of a differential-pressure valve 40 in FIG. 2 shows how this pressure 
difference can be kept basically constant, in that, by the use of the 
differential-pressure valve, the admission pressure can be co-varied in 
parallel with the pressure upstream of the throttling valve. 
However, the same objective can be at least essentially achieved in that 
the spring-loaded throttling 2/2-way valves have a steep opening 
characteristic, this being achieved by means of a soft spring or a large 
pressure-loaded valve face or a combination of both, and in that the feed 
pressure p2 is not sufficiently high, so that even for a maximum 
volumetric flow of the pump, that is to say a large valve opening, the 
pressure difference is not appreciably reduced via the adjusting device. 
These measures thus basically ensure that the throughflows at the throttle 
elements are influenced only slightly by dispersions of the spring 
rigidity or spring pretension of the inlet-valve springs or by differences 
in the effective valve face. This design therefore also does away with the 
need for accurate spring sorting or the setting of the spring pretension 
on each individual inlet valve. 
FIGS. 8, 9 and 10 show diagrammatically, for the versions according to FIG. 
3 and 4, 5 respectively, different displacement-space fillings at the same 
rotational speed and how the dynamic process of a work cycle takes place 
with the spring design, as explained above. FIG. 8 shows the state for the 
full filling or conveyance of the displacement spaces 15, FIG. 9 the state 
for the half filling or conveyance of the displacement spaces 15 and FIG. 
10 the state of not quite zero conveyance of the displacement spaces 15, 
specifically as a function of the rotary angle of the drive shaft, in 
relation to the top dead center TDC and bottom dead center BDC of the 
respective displacement pistons 9. In FIGS. 8 and 9, the valve 
cross-section trends A.sub.valve and the pressure p5 in the cylinder 
during the suction stroke are almost rectangular for full 
displacement-space filling V=V.sub.max and for half displacement-space 
filling V=0.5 V.sub.max, and, despite the dynamics, the pressure 
differences P.sub.feed -P.sub.channel suction =p2-p3 during filling are 
stable and almost equal for all conveyed quantities. 
The reason why the stroke of the throttling 2/2-way valve 21 and the 
pressure p.sub.4 can be established virtually immediately and in a stable 
manner is the cavitation avoided, according to the invention, in the 
channels 31a, b, c or 31 a, b, c or 130a, b, c, d or adjusting element 27 
or 150. 
As already stated further above, for the pressure p.sub.5 in the 
displacement space 15, in each case a constantly low value, in the example 
close to zero, is established beyond BDC up to the valve closing. 
In this way, during the entire suction operation (valve opening to 
closing), virtually constant boundary conditions in the form of virtually 
constant values of the feed pressure p.sub.2 and of the displacement-space 
pressure p.sub.5 prevail. 
In view of the absence or lack of cavities achieved according to the 
invention in the connections 41a, b, c or 130a, b, c, d, incompressibility 
may be assumed between the inflow at pressure p.sub.2 and displacement 
space p.sub.5. Consequently, the pressure p.sub.3 upstream of the 
throttling valve 21 is established without appreciable delay as a result 
of the continuity condition that the throughflow at the individual 
throttle cross section 30, V.sub.30, must be equal to the throughflow of 
the throttling valve 21, V.sub.21 : 
##EQU1## 
with .alpha..sub.21, .alpha..sub.30 c.sub.1, c.sub.2 constants which 
define A.sub.21 (p.sub.3), and 
p is the liquid density. 
In the suction phase, therefore, a specific A.sub.21 (p.sub.3) and, via the 
constants c.sub.1 and c.sub.2, also a specific p.sub.3 are fixedly 
assigned to a specific A.sub.30. 
Compliance with the fixed assignment, for example as safety against the 
overshooting of the valve 21 during opening, is ensured by the inherent 
damping, already described further above, of the arrangement according to 
the invention and the additional damping 70 or the valve damping described 
in FIG. 6A. 
The pressures p.sub.3 for the various filling situations are close to one 
another in comparison with p.sub.2 and p.sub.5 as a result of the special 
valve design (see FIG. 7). The above equation is thereby simplified to 
##EQU2## 
In the complete filling of the displacement space 15 according to FIG. 8, 
the free flow cross section A.sub.valve through the inlet valves 28 
assumes the maximum value. In the half filling of the displacement space 
15 according to FIG. 9, the valves 28 are only partially opened. The 
conveyed volumes V correspond to the areas under the volumetric-flow 
functions. FIG. 10 shows the situation in which conveyance is exactly 0 
and filling therefore likewise goes towards 0. In FIG. 10, as a limit 
situation, the liquid is still at p.sub.5 =p.sub.6 at top dead center, 
that is to say is compressed to the high pressure of the system and 
decompressed again, but nothing is expelled in the meantime. Despite 0 
conveyance, a slight filling of the displacers can occur, in order to 
cover any piston leakage as a result of compression/decompression. A 
minimal opening A.sub.suction (V.fwdarw.0) is therefore marked in FIG. 10. 
The duration of this opening extends approximately over the entire 
revolution, interrupted only by the relatively short 
compression/decompression phase. Similar trends occur for the further 
embodiments according to FIGS. 2, 3 and 4 to 6 as well as 13, 14, 15, 16 
and 17. 
FIG. 11 shows the conveyed-flow characteristics volumetric flow V=dV/dt as 
a function of the throttle cross section A.sub.throttle1 to 
A.sub.throttle4 of the adjusting throttle 30 of this control device. The 
characteristics increase asymptotically from the respective limiting 
rotational speed C.sub.m limit1 to C.sub.m limit4 towards a volumetric 
flow double the limiting rotational speed, since, in addition to the 
suction cross section, the suction time is also influential and, as is 
also evident from FIGS. 8, 9 and 10, this increases, with a conveyed 
quantity per stroke towards zero, from a half revolution originally to 
almost one complete revolution, that is to say double. 
FIG. 12 shows the corresponding conveyed-flow characteristics for 
slit-controlled pumps, as in the version according to FIG. 2. 
FIG. 13 shows an embodiment similar to that of FIG. 3, but with a different 
design of the throttling 2/2-way valves actuated by pressure difference 
and with a different type of actuation of the adjusting throttle. The 
2/2-way valves of the embodiment according to FIG. 13 each comprise a ball 
54 which is pressed on to a valve seat by means of a spring 53. The 
movement of the ball 54 in relation to the valve seat in the opened state 
of the valve depends on the pressure p3 prevailing in the respective 
conduit 31, 31a and 31b, with the result that the filling of the 
displacement spaces is controlled in dependence on p3. Whilst a transducer 
27 for actuating the adjusting throttle according to FIG. 1 is 
particularly suitable for incorporating into analog control loops, a 
switching valve 50 has a transducer according to FIG. 13 has advantages in 
conjunction with digital electronics. 
The illustration of FIG. 13 shows such an arrangement, and, as in FIG. 2, 
with slit-controlled pumps and with an opening angle adapted to the number 
of cylinders, a switching valve 50 is sufficient for a plurality of 
displacement elements 9. 
FIG. 14 shows an embodiment in which only one 2/2-way valve 81 is used for, 
in this example, three displacement spaces, the 2/2-way valve 81 being 
arranged outside the pump and feeding the individual displacement spaces 
15 via conduits 36, 36a and 36b. 
In this example, the adjusting device comprises an adjustable displacement 
machine 84 acting with a throughflow-limiting function. Preferably, 
however, the displacement machine 84 is driven by an electric machine of 
variable rotational speed. The displacement machine is designed as a 
constant displacement machine and obtains the liquid to be conveyed 
directly out of the conduit 33 or indirectly out of the liquid reservoir 
via the system 7. In this case, the pressure-relief valve has the function 
of a safety valve or blow-off valve. This prevents an inadmissible 
increase in the pressure difference at the conveying fore-pump, if the 
latter is adjusted into a position in which it conveys more than the 
maximum absorption quantity of the main pump. 
If, in this example, the throttling 2/2-way valve were not represented as a 
spring-loaded non-return valve 81, but similarly to the valve 21 in FIG. 
2, that is to say as a slide valve without an intended reaction of the 
pressure p.sub.4 on the valve opening, even then specific valve opening 
would remain if interruptions occurred between the suction phases of the 
individual displacement elements. In such interruption phases, the 
pressure p.sub.4 rises quickly to the pressure P.sub.3, with the result 
that the proportion of cavities in the channels 7, 7a, 7b is reduced in 
each case. Such interruption phases are achieved by selecting the height 
of the orifice 35 in such a way that the latter is opened by the piston 9 
in each case for only less than 360.degree./number of displacement spaces. 
FIG. 15 is very similar to the embodiment of FIG. 14 and likewise makes use 
of the presence of a regulatable conveying fore-pump, here in the form of 
the adjustable displacement machine 86, which is driven at the pump 
rotational speed or at a rotational speed proportional to this. In 
principle, for example, the drive of the displacement machine 84 can be 
effected via the drive shaft 12 of the pump. 
FIG. 16 shows an embodiment similar to the embodiment of FIG. 3, in which 
the conveying fore-pump 34 runs at a constant speed, but in which the 
control of the inlet pressure takes place by controlling the spring 
pretension of the pressure-relief valve 90, that is to say the variable 
pressure-relief valve constitutes the adjusting device. 
FIG. 17 shows a solution which allows a separation of the conveyed liquid 
from the reservoir and of the actuating medium (but the same fluid is also 
possible). 
This configuration has advantages when the fluid to be conveyed is of very 
high viscosity or contains impurities which could impair the functioning 
(Example: common-rail injection system for heavy-oil engines), or when the 
adjusting pump is to be self-priming or is to be operated only at a very 
low admission pressure. It is then merely necessary to have a pressure 
source 100 of substantially lower power for the actuating fluid, such a 
pressure source frequently being available already (for example, 
compressed-air network). 
The actuating fluid is conducted at the controllable pressure p10 to the 
individual 2/2-way valves 103 via the conduits 101. In this case, the 
pressure p10 acts on the effective face 102 on one side of the slide of 
the 2/2-way valve 103, whilst a spring 104 and the outlet pressure of the 
2/2-way valve act via the conduit 106 on the effective face 105 on the 
other side of the slide 102. 
FIG. 18 shows a diagrammatic representation of a pump of the radial type 
with three displacement pistons 9, only the central part of the pump 
housing around the drive shaft 12 being shown and only the upper 
displacement piston 9 being drawn in completely. 
As is clear, all three displacement pistons 9 operate with a common 
eccentric cam 11, which rotates together with the shaft 12. 
As is evident from the representation of the upper displacement piston, the 
latter, like the two further displacement pistons as well, is always held 
in contact with the eccentric cam 11 via a spring 200. Although in the 
present drawing all three displacement pistons are driven by the common 
eccentric cam 11, it would also be possible to offset the displacement 
pistons in the axial direction of the drive shaft and drive them via 
separate eccentric cams. Any other number of displacement pistons can also 
be selected. 
An essential feature of the filling-ratio adjusting pump of FIG. 18 is that 
the liquid to be displaced passes to the individual displacement pistons 9 
via the interior and sic! 202 of the pump housing. 
As hitherto indicated, the connecting conduit to the liquid reservoir bears 
the reference symbol 33. The reference symbol 30 denotes an adjustable 
throttle element which leads via the conduit 31 into the interior 202. The 
pump of FIG. 18 is slit-controlled and, for this purpose, has inlet slits 
35 (shown only for the upper displacement piston), the inlet slits 35 
communicating with the interior 202 in each case via a throttling 2/2-way 
valve 51 actuated by pressure difference (as shown in FIG. 13) and 
corresponding conduit portions 204 and 206 in the pump housing. As 
hitherto, the reference symbol 17 denotes the outlet valve which is 
combined via a conduit 18 with corresponding conduits of the further 
displacement pistons 9 (not shown) and which finally leads to the "common 
rail" of the internal combustion engine connected thereto. 
In order to ensure slit control over a corresponding rotary-angle range of 
the eccentric cam 11, an orifice 208 communicating with the inlet slit 35 
and cooperating with the latter in the desired angular range is provided 
in the displacement piston 9. 
When the pump is in operation, the individual displacement pistons 9 are 
moved to and fro in the respective cylinders 210 by the eccentric cam 11 
with the cooperation of the corresponding spring 200. The fuel is thereby 
sucked through the conduit 33, the throttle 30, the conduit 31, the 
interior 202, the conduit 206, the 2/2-way valve 51, the conduit 204, the 
inlet slit 35 the orifice 208 of the displacement piston 9 into the 
displacement space and subsequently flows out through the outlet valve 17 
under the effect of the displacement piston 9. 
Due to the relatively large volume of the interior 202, it becomes 
possible, by means of the invention, to limit the escape of gases in this 
interior to such an extent that the pump functions perfectly. It should 
also be pointed out that it is also possible, in this embodiment, to 
insert (not shown) the 2/2-way valves into the respective displacement 
piston 9. 
LITERATURE 
(1) Welschof, B. 
Analytische Untersuchungen uber die Einsatzmoglichkeit einer 
sauggedrosselten Hydraulik-pumpe zur Leistungssteuerung am Beispiel eines 
hydrostatischen Nebenaggregateantriebs im Kraftfahrzeug Analytical 
investigations on the possibility of using a suction-throttled hydraulic 
pump for power control by the example of a hydrostatic secondary drive in 
the motor vehicle! Dissertation RWTH Aachen, 1992 
(2) Schneider, W. 
Pumpen fur zukunftige Dieseleinspritzsysteme O+P (Oelhydraulik und 
Pneumatik) Pumps for future diesel injection systems O+P (Oil hydraulics 
and Pneumatics)! 36 (1992) 5, pages 304-310 
(3) Cooper Bessemer Fuel Injection Manual 
(4) Schneider, W., Stockli, M., Lutz T., Eberle, M. 
Hochdruckeinspritzung und Abgasrezirkulation High pressure injection and 
exhaust gas recirculation! MTZ 54 (1993) 11 
(5) Schweitzer, P. H., Szebehely, V. G. 
Gas Evolution in Liquids and Cavitation Journal of Applied Physics 21 
(1950) December, pages 1218-1224 
(6) Fassbender, A. 
Saugdrosselung--der Einfluf yon Druckmedium und Temperatur Suction 
throttling--the influence of pressure medium and temperature! O+P 
(Oelhydraulikund Pneumatik) Oil hydraulics and Pneumatics! 37 (1993) 9 
(7) Schmitt, Th. 
Untersuchungen zur stationaren und instationaren Stromung durch 
Drosselquerschnitte in Kraftstoffein-spritzsystemen von Dieselmotoren 
Investigations on stationary and non-stationary flow through throttle 
cross sections in fuel injection systems of diesel engines! Dissertation 
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