DE2339124A1 - Hydraulic pressure electrically controlled choke - has two measuring chokes between which is flow obstruction coupled to heater wire - Google Patents

Abstract

Electrically controlled precontrol choke for generating a hydraulic pressure which is directly or reciprocally analogous to the electrical current, with a pair of opposite measuring chokes connected via a fixed choke to a pressure supply and whose feed is connected to a pressure reducing or raising pressure chamber of a hydraulically controlled pressure regulating mechanism for a working medium and with a flow obstruction between the measuring chokes to vary the effective choke cross sections where the obstruction can be moved out of the mid position between the chokes in one direction or the other by an electrical device according to the size of a current. The flow obstruction is mechanically coupled with an electrically insulated, spring loaded heater wire joined to electrical terminals at its ends.

Description

Daimler-Benz Aktiengesellschaft Daitn 9927 / (t

Stuttgart-Untertiirkheim

Hot wire controlled pilot throttle

The invention relates to a pilot throttle, which can be influenced by an electric current, for generating a current direct or reciprocal analog hydraulic pressure with at least one measuring throttle, preferably with a pair of each other opposite measuring throttles, each via a pressure reaction preventing member, preferably via each a fixed throttle is or are connected to a pressure source and their inlet preferably each with a related of a working pressure pressure-increasing or pressure-decreasing pressure chamber of a hydraulically controllable pressure regulating member is connected for a working medium and arranged in front of the measuring throttle or between the measuring throttles and in front or movable back and forth between them, preferably pivotable and thereby the effective cross-section of the throttle or a throttle to the disadvantage of the other changing flow obstacle, which is caused by an electrical device depending on a current more or less from the central position between the measuring throttles to one or the other Direction can be moved out.

In previously known devices of this type (see, for example, US Pat. No. 3,023,782), the flow obstacle is pivotable between the two opposing measuring throttles attached baffle plate, which with the beam-like armature of a complicated Magnet system consisting of permanent magnets and electromagnets

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connected is. Because of the required precise reproducibility of hydraulic pressures by an electrical quantity it is necessary to use this magnet system with the highest possible precision and the lowest possible mechanical and magnetic hysteresis produce, especially since deviations from the target assignment of a pair of hydraulic pressure / electrical current in the first stage of an amplifier device at whose Auegang itself accordingly make them more noticeable. The use of high-quality magnetic materials and the high manufacturing accuracy make the device very expensive.

The object of the invention is to make the pilot throttle simpler and thus cheaper without sacrificing accuracy. These The object is achieved in that the flow obstacle is mechanically isolated with an electrically isolated in the Direction of movement of the flow obstacle stretched out, held under spring tension, electrically at its ends is conductively coupled to the hot wire connected to power connections as an electrical device.

In contrast to the forces that can be sensitively dosed with a magnet system, the forces that can be achieved with a Hot wire can be wielded a lot larger. Mechanical frictional resistance in a hot wire instrument can therefore usually not come to an order of magnitude where it can influence the measurement or reproduction accuracy, since the stretching forces of the hot wire are many orders of magnitude higher. The requirements for precision and The moving mechanical parts of the pilot control throttle need to run smoothly in order to achieve the same good results as with previously known pilot control throttles, not so high, see below will. It is true that the hot wire must be responsible for converting an electrical into a mechanical one (elongation) Part can be manufactured precisely in terms of its electrical and mechanical properties. However, that is a requirement

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The precision of a simple piece of wire can be fulfilled much more easily than with a complicated one out of many Share existing magnet system.

In order to be able to precisely set the center position of the flow obstacle SU, it is advisable that one end of the hot wire is in Unclamping direction is adjustable.

Deviations of the hot wire from its nominal properties can be partially compensated for by the fact that the extended position and / or that the electrical tap length of the hot wire can be set independently of one another.

The invention is explained in more detail below with reference to an exemplary embodiment shown in the drawing; The figure shows a longitudinal section through a hot wire pilot throttle according to the invention with the working pressure regulating element influenced by it.

The device shown comprises an electrical / mechanical control variable converter 1 and a hydraulic amplifier 2. In the control variable converter 1 there is provided a lever 4 which is mounted so as to be pivotable with little friction about the fixed pivot point 3 (knife-edge joint) and to which a further knife-edge joint 5 and a cup-like insulator with blade handle 6 and seal holder 7, the hot wire 8 is attached. At the a spring plate 9 is arranged at one end of the lever 4, in which a spring 10 which relaxes the hot wire 8 is placed, which, on the other hand, is supported on the stationary but adjustable spring abutment 11. The hot wire is on the other end in a screwable in the unclamping direction electrically not conductive, heat-resistant seal holder 12 fixed to the frame by means of a at different longitudinal points of the wire 8 as desired Clampable Verstellplombe 13 held, which also serves to supply power and with a slightly flexible cable l4

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large wire cross-section is soldered. Means «of the adjustable seal holder 12 can on the one hand with unchanged clamping position of the seal 13 set the desired position of the lever k corresponding to a fixed mean value or a zero value of the heating current or on the other hand it can be used to change the clamping position of the adjustment seal at the same time, the stretched and the current-applied length of the hot wire can be changed. On the hot wire 8, a power connection terminal 15 is arranged so that it can be clamped in different longitudinal positions and is also soldered to a flexible cable l6 with a large area in the line cross section. The cables l4 and l6 are connected to the connector plugs 17 and 17 fastened in an isolated manner. With the adjustable power connection terminal 15, the length of the hot wire to which the current is applied can be changed independently of its extended length.

In the hydraulic booster 2 are on one of the converter facing point two measuring throttles opposite one another 19 and 20 arranged, the end faces of which are a defined distance from each other and their exaggerated size shown Throttle bores have a defined diameter. On the lever 4 is a bottom protruding from the converter 1 Flapper plate 21 attached of a certain thickness, namely the baffle plate is about half the throttle bore diameter thinner than the opening distance of the two measuring throttles. By this close proximity of the baffle surface to the measuring throttle orifice it represents a flow obstacle influencing the outflow resistance, its resistance with further Approach can still be increased.

The measuring throttles are constantly supplied from the pressure source 22 via the filter 23 and the two fixed throttles 2k and 25 as well as the pressure chambers 26 and 27 with working oil in a small quantity flow, which is caused by the oil return, which has a large cross-section

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can run off again without a jam in the oil sump 29. If necessary, the interior of the converter 1 can be closed off by an easily movable and oil-resistant membrane penetrated by the lever h and the baffle plate 21. The fixed throttles 24 and 25 prevent a rapid pressure equalization between the two pressure chambers 26 and 271, ie during the response time of the pressure booster.

Inside the amplifier there is also a control slide 30 which, together with the bore and the housing, forms four control edge pairs 3l / 32, 33 / 3Ί, 35/36 and 37/3 $ and which acts on the end faces with two adjustable spring force Springs 39 and kO is adjustable in such a spring equilibrium position that the control edges just coincide with one another. Due to a more or less large pressure difference in the pressure chambers 26 and 27, the slide 30 can be moved more or less to one side according to this pressure difference and thereby two of the four control edge pairs are opened and the other two are over- docked , with the oil inlet 43 coming from the pressure source 22 and connected differently to the oil return 28. The hydraulic booster 2 with its individual parts is constructed symmetrically with regard to their hydraulic action, and in the undisturbed symmetrical equilibrium position, both working connections 4i and h2 are pressureless. Depending on the adjustment of the baffle plate 21 sw: See the two measuring throttles 19 and 20 from the Mittallagö - this happens through a more or less strong electrical heating and corresponding temperature expansion of the hot wire 8 - the functional symmetry of the amplifier is disturbed and before that throttle, which the baffle plate has approached a little closer and in dsm ssugehörigea. Dsruckx'aum a greater pressure is built up and accordingly the slide against the force of one of the springs 39 or kO from the source

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weight position shifted so that one of the working connections via a more or less open control edge pair is connected to the pressure source and the other working connection via another pair of Steuerlcantenpaar with the oil drain. Ever after electrically triggered displacement of the baffle plate in terms of amount and direction, one of the two working connections is available more or less pressurized. In this way an electrical / hydraulic size conversion is achieved with the interposition of a hydraulic booster stage.

In the illustrated and above-described double-sided, symmetrically structured and operating embodiment of the control variable converter, a certain mean current value indicates the hydraulic zero point at which the functional symmetry exists and both working connections kl and hZ are disconnected from the pressure supply. Deviations from the current mean value upwards or downwards cause a pressure increase corresponding to the mean value deviation at one or the other work port. To Aufreehterhaltxmg the zero point so the constant flow sines current from the height of St.rooiinittölwörtes is required "That disser power consumption is possible goring _t but also so that the Wärnicspeicherkapasität dos Prahtss is as small as possible and Teaiperatu.randerungisii and deriienfcsp.rsciiesid Langexxanderungen the hot wire os the imprinted esa Stsroriianderungon mö glichet v & vzö gcrtisigsfrsx follow, can ,. : Csrner so accuracy * jehan part of the device is as high as possible reasons is the Innenv / Ide.rstand dos © ioktri will Dei act constructively practically predetermined length of Hitadsrahto "its diameter as small as possible to be. J0 greater the resistance of the wire is greater for a given current change are also dia tsmperaturbsdingten length changes χχηά the greater the deraentsprecheBid Reproduzierganaui.glco.it of Ura-formere · On the other hand dor must i'iit & drafot in Q'aeraclmitt sufficiently large

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be measured to be safe even in red-hot State to be able to absorb the tension force of the spring 10. The shrinkage force of the heat turned must be apart from the spring force also exceed the frictional forces of the system by several orders of magnitude. From these diverse The optimal hot wire cross-section must be determined from partially contradicting aspects. The low heat capacity of the hot wire makes it sensitive to external temperature fluctuations. He must therefore in a small one if necessary artificially kept at the same temperature chamber be arranged and good against thermal external interference be encapsulated and insulated.

In the above-described version of a hot wire pilot control throttle it is merely one of a large number of conceivable exemplary embodiments according to the invention. In particular a unilateral version is conceivable for according to a measuring or control current measured from zero, a pressure is applied to only one working connection.

For various reasons it is desirable to have feedback in the system, as was the case with those previously known magnetic variable controllers is common. This refers to measures, features or precautions that ensure that a change in the throttle cross-sections initiated by the hot wire on the part of the hydraulic part of the Facility is weakened again. Such feedback makes the system less sensitive to occurrence of control variable fluctuations} it can also make the springs 39 and 40 unnecessary. In the illustrated embodiment a return could be achieved in that the console 45 carrying the cutting edge 44 of the cutting edge joint 3, but at least the cutting joint 3 itself is moved along with the slide. Another way of getting a regression

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The real thing could be that the two measuring throttles 19 and 20 are arranged inside the slide 30 and the lever k with the baffle plate extends into the inside of the slide. In such a variant, however, the measuring throttles would have to be reversed in relation to the example shown in the slide, i.e. the measuring throttle (20) connected to the right pressure chamber 26 would have to be to the left of the baffle plate and the measuring throttle (19) connected to the left pressure chamber 27 be arranged to the right of the baffle plate. Such a return would also be applicable with the same effect with corresponding modification and adaptation in the case of a unilateral control variable converter mentioned above.

Feedback is required for pressure control, for a cross-sectional regulation may, under certain circumstances, be dispensable.

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Claims (1)

- 9 - Daim 9927/4 Claims I. Influenced by an electric current for generating a pilot throttle the flow directly or inversely analog hydraulic pressure, with at least one metering orifice, preferably with a pair of oppositely s Overlying measuring throttles, each of which is or are connected to a pressure source, preferably via a fixed throttle, and the inlet of which is or are each connected to a pressure chamber of a hydraulically controllable pressure regulating element for a working medium which acts to increase or decrease the working pressure and to a in front of the measuring throttle or between the measuring throttles and in front of her or between them reciprocating, preferably pivotable and thereby the effective cross section of the throttle or a throttle to the detriment of the other changing Stromungshxndernxs, which by an electrical device according to a current more or less can be moved out of the central position between the measuring throttles in one direction or the other, characterized in that the flow obstacle (21) is mechanically isolated with an electrically isolated in the direction of movement of the flow obstacle The hot wire (8), which is stretched out under spring tension (spring 10) and electrically connected at its ends to power connections (l7 | lß), is coupled as an electrical device. 2. pilot throttle according to claim 1, characterized in that one end of the hot wire adjustable in position in the unclamping direction is hung. - 10 - S09808 / 0078 - IC - Palm 9927 / fr 3 * pilot throttle according to claim 1 or 2, characterized in that the extended length of the hot wire (8) is changeable and adjustable. 4. pilot throttle according to claim 1, 2 or 3 · characterized in that the electrical tap length of the stretched hot wire (ö) is variable and adjustable. 509808/0078