Patent Application
20170254317
The invention is based on a piston pump.
Electromagnetic piston pumps of the kind known today, as described in GB 2484855A for example, operate in accordance with the following principle: current is supplied to a magnet coil and said magnet coil generates a magnetic field in the process. A magnetic circuit is formed in the metallic and magnetizable components of the piston pump. The components of the magnetic circuit include, for example, the piston, the cylinder, the housing, the armature plate and the stop of the piston pump.
The magnetic field pulls the piston, which is arranged in the cylinder and also called the magnet armature, in the direction of the stop of the armature plate. During this process, a fluid is drawn through an inlet valve into a compression chamber which is arranged in the cylinder between the inlet valve in the cylinder base and the piston. If the magnetic field is switched off, a spring which is arranged between the piston and the stop pushes the piston (magnet armature) in the direction of the cylinder base and in the process firstly compresses the fluid and secondly pushes the fluid out of the compression chamber via the outlet valve.
Efforts are currently being made to increase the degree of efficiency of piston pumps and their functional reliability and also to improve the dynamics and the robustness of piston pumps.
The invention is based on the knowledge that, after the magnetic field is switched off, so-called magnetic adhesion of the piston (magnet armature) to the stop is possible. This magnetic adhesion is the result of the residual magnetization of the magnetic circuit and its components, such as the piston, the cylinder, the housing, the armature plate and the stop for example, after the magnetic field is switched off. Consequently, the return force of the spring is insufficient to overcome the magnetic adhesion and to release the piston from the stop under certain circumstances.
However, the piston pump according to the invention has the effect that the magnetic adhesion is minimized or eliminated. This results in an increase in the functional reliability and an improvement in the dynamics of the piston pump.
To this end, it is provided that the magnetic circuit has at least one region which comprises a non-magnetic material at the stop-side reversal point of the piston, in particular when the piston stops against the stop. The expression “at the stop-side reversal point” means that the magnetic circuit and its components are taken into consideration at the point in time at which the piston is at its stop-side reversal point.
Within the meaning of the invention, particularly those components of the piston pump through which the eddy of the magnetic field extends with the maximum magnetic flux density belong to the magnetic circuit. Therefore, in particular, no components, regions or the like which are located outside the piston pump in the magnetic stray field are taken into consideration.
The region comprising the non-magnetic material has, in particular, a higher magnetic resistance (reluctance) Rm (DIN EN 80000-6) than the other components, such as the piston, the cylinder, the housing, the armature plate and the stop for example, in the magnetic circuit. As a result, the total magnetic resistance of the magnetic circuit is increased, so that the residual magnetization of the magnetic circuit dies away as quickly as possible and there is no magnetic adhesion of the piston to the stop. In particular, the region itself does not exhibit any residual magnetization or only negligible residual magnetization.
The magnetic resistance Rm of a component i in the magnetic circuit is given by:
R
m,i
=L
i/(μ0μrAi),
with the length L and the cross-sectional area A of the component i in the magnetic circuit and the vacuum permeability μ0 and the relative permeability μr of the material. The total magnetic resistance for the magnetic circuit is calculated analogously to the node and network rules of electrical resistance in an electrical circuit.
In addition to the metallic components of the electromagnetic piston pump, gaps between individual components can also contribute to the total magnetic resistance. The gaps can be filled with different materials, such as a gas for example, e.g. air or a liquid. By way of example, there is an air gap of variable length between the piston and the stop of the armature plate. The length of the air gap changes depending on the phase of the pumping cycle. After the magnetic field is switched off, the piston spring pushes the piston from the stop in the opposite direction and the air gap and its magnetic resistance increase. When the magnetic field is switched on, the piston is moved toward the armature plate and the air gap decreases. When the piston is fully drawn, that is to say the piston stops against the stop of the armature plate, the air gap and its magnetic resistance are minimal. The contribution of the air gap to the total magnetic resistance of the magnetic circuit is typically negligibly small in this phase of the pump cycle. The magnetic resistance of the air gap is then possibly too small to prevent the magnetic adhesion of the piston to the armature plate.
Therefore, according to the invention, a region comprising a non-magnetic material and, in particular, having a relatively high magnetic resistance in the magnetic circuit of the piston pump is provided, said region increasing the total magnetic resistance above a minimum value. The lower limit for the total magnetic resistance of the magnetic circuit of a piston pump depends on the dimensions of the piston pump. The total magnetic resistance of the magnetic circuit depends on the total volume and on the remanence properties of the materials of which the components which are situated in the magnetic circuit consist. The greater the total volume and the remanence of the materials used, the higher the minimum total magnetic resistance of the magnetic circuit has to be.
The region according to the invention has, in particular, a constant magnetic resistance within one pump cycle and/or over several pump cycles in comparison to the air gap between the piston and the stop. The region according to the invention is, in particular, not the variable air gap between the piston and the stop of the armature plate or the air gap between other components of the magnetic circuit.
One advantageous development of the piston pump according to the invention provides that the region comprises not only non-magnetic material but rather that the material is also a non-magnetizable or only weakly magnetizable material. In a preferred development, the region consists of the material. The material can have, for example, a relative permeability μr of not greater than 1.1. In particular, μr of the material is less than 1.
It has been found to be advantageous that the region comprises a material which has a solid aggregate state. By way of example, the region can be formed by a film/foil. The film/foil is preferably non-magnetic and/or non-magnetizable. Examples include plastic films, such as films comprising polyethylene (PE), polyamide (PA), polyoxymethylene (POM) or polystyrene (PS) for example.
As an alternative or in addition, the region can also be a coating on a component surface. The coating is preferably non-magnetic and/or non-magnetizable. By way of example, the coating can consist of chromium, a chromium alloy or a nitrided layer.
As an alternative or in addition, the region can also be formed by a treated surface. The treated surface can be, for example, nitrided (DIN 17022-4).
As an alternative or in addition, the region can also be a separating plate. The separating plate is preferably composed of a non-magnetic and/or non-magnetizable material, for example of a non-magnetic steel based on a cobalt/nickel alloy or a copper/beryllium alloy or a chromium/nickel alloy, available from Sandvik Materials Technology as Sandvik 13Rm19 for example.
The region typically has a thickness in the region of less than 5 mm. The thickness preferably lies in a range of from 1 μm to 500 μm, in particular in a range of from 10 μm to 100 μm. The thickness of the region depends on the dimensions of the piston pump, the selected material and/or the selected embodiment (separating plate, film/foil, coating, treated surface) of the region.
In principle, the region can be arranged at any point within the magnetic circuit. However, the region is preferably arranged on that side of the piston which faces the stop, also called the piston rear side. This has the advantage that the region with the low or negligible residual magnetization prevents direct contact between the piston and the stop of the armature plate and therefore reduces the mutual attraction between the piston and the stop on account of the residual magnetization. The probability of magnetic adhesion of the piston and of the stop is minimized in this way.
In addition or as an alternative, the region can be arranged on the surface of the stop. This has the same advantages as those described in the paragraph above.
If a region is formed both on the piston rear side and also on the surface of the stop, the regions on the piston rear side and the surface of the stop can consist of the same or different materials.
In addition or as an alternative to the region with a relatively high magnetic resistance, the probability of magnetic adhesion can also be reduced by the proportion of magnetic or ferromagnetic material, in particular iron-containing material, in the magnetic circuit being reduced.
This can be realized, for example, by a profile which is formed on that end side of the piston which faces the armature plate (piston rear side) and/or on the stop of the armature plate. The profile does not mean the hollow space which is formed within the piston and the associated opening at that end side of the piston which faces the armature plate, in which piston, for example, a spring is arranged.
The profile typically has a depth T of not less than 2% of a total length L of the piston and/or of not greater than 10% of the total length L of the piston, wherein the total length L of the piston is the distance from the end side which faces the armature plate to an end side of the piston which is situated opposite said end side.
The profile is advantageously formed by at least one, in particular annular or straight, groove. In this case, that end side of the piston which faces the armature plate has two regions which consist of different materials. There is, for example, a first region which consists of the same material as the piston. The second region is created by the groove/grooves being formed on the piston rear side or on the stop. This region is filled, for example, with air or fuel.
The groove can be annular or straight. The straight groove extends from the piston edge to the center of the piston rear side.
When providing a profile comprising a plurality of grooves, said grooves can be arranged parallel or at an angle β in relation to one another. The angle β between two grooves lies in the range of from 0°-180°, in particular in the range of from 22°-90°.
A plurality of grooves, which are arranged at an angle in relation to one another, typically have the same or a similar angle in relation to one another. The plurality of grooves advantageously each have an angle of approximately 360°/n between adjacent grooves, wherein n is the number of grooves.
The grooves can have a width of from 5% to 50% of the piston diameter. The greater the number of grooves, the narrower the individual groove. By way of example, a profile with a low number of grooves, in which the grooves are very wide, that is to say the groove width lies in the range of from 40%-50% of the piston diameter, or a profile with a large number of grooves, in which the individual grooves are narrower, that is to say the groove width lies in the range of from 5%-15% of the piston diameter, can be selected. The regions which are situated between the grooves and are composed of the piston material then assume the form of webs.
As an alternative, the profile can also be formed by at least one, in particular annular, step or by at least one bevel, in particular formed along the circumference. The bevel can be formed either from the piston rear side in the direction of the outer edge of the piston or from the piston rear side in the direction of the center of the piston rear side.
In addition to reducing the proportion of the magnetic material in the magnetic circuit, the provision of profiles on the piston rear side or on the stop has the further technical effect that the profile can be formed such that the profile experiences defined wear during operation of the pump. Owing to wear of the profile, the stroke of the piston increases and the piston pump can deliver more fluid in this respect. Secondly, wear also occurs between the piston and the cylinder wall, so that the gap between the piston and the cylinder wall increases over the service life of the piston pump. This leads to a reduction in the delivery quantity. The profile is ideally selected with its defined wear such that the increase in the stroke directly compensates for the losses in delivery quantity owing to the increasing gap between the piston and the cylinder wall, and therefore the degree of efficiency of the piston pump remains constant over the service life of the piston pump.
a) shows a cross section through the piston with the piston rear side having a shoulder.
b) shows a cross section through the piston with the piston rear side being beveled.
a) shows a rear side of the piston with an alternative profile.
b) shows a rear side of the piston with another alternative profile.
A piston spring 7 is arranged between the piston 6 and the armature plate 3. On that side of the piston spring 7 which faces the armature plate 3, said piston spring is fixed by a spring holder 8. The piston spring 7 can be arranged partially or completely within the piston 6. The piston rear side 10 then has an opening in which the piston spring 7 is arranged. The piston spring 7 is compressed owing to the piston movement in the direction of the armature plate 3. After the magnetic field is switched off, the piston spring 7 pushes the piston 6 back in the opposite direction.
Furthermore, an inlet valve 11 and an outlet valve 12 are arranged in the cylinder 4, in particular in the cylinder base. The cylinder 4 is delimited on one side by the armature plate 3 and on the opposite side by the cylinder base. The inlet valve 11 and/or the outlet valve 12 can be in the form of diaphragm valves. In this exemplary embodiment of a piston pump 1, the inlet valve 11 and the outlet valve 12 and therefore also the inlet and the outlet are arranged on the same side of the cylinder 4. In particular, the inlet and the outlet can be coaxial, for example the line for the outlet is arranged within the line for the inlet. A valve body 13 is arranged between the inlet valve 11 and the outlet valve 12.
Fuel lines via which a fuel is drawn from a tank, through the inlet valve 11, into the compression chamber within the cylinder 4 on account of the negative pressure are not shown. The negative pressure in the cylinder or in the compression chamber is created by the movement of the piston 6 in the direction of the armature plate 3. The fuel is pushed from the piston 6 to an injection valve via further fuel lines and the outlet valve 12.
In this exemplary embodiment, the surface of the stop 9 has a region 15. This region 15 is distinguished in that it consists of a non-magnetic and/or non-magnetizable or only weakly magnetizable material. The material of the region has, for example, a relative permeability μr of less than 1.1, in particular of less than 1. The region preferably has a higher magnetic resistance than the other components, such as piston 6, cylinder 4, housing 2 and/or armature plate 3 for example, in the magnetic circuit.
The region 15 can be applied in the form of a film/foil or as a coating, for example as a chromium layer, to the surface of the stop 9 or can be a surface treatment, such as nitriding for example, or a separating plate. The thickness of the region 15 depends on the material used and/or the dimensions of the piston pump 1. The thickness of the region typically lies in the range of from 0.01 mm to 10 mm.
The exemplary embodiment according to
The exemplary embodiment according to
The items and/or embodiments mentioned in the exemplary embodiments (separating plate, film/foil, coating, treated surface) for the region 15 can also be combined with one another. When combining the various exemplary embodiments, the region can consist of the same or different materials at the different points.
In addition or as an alternative, the piston rear side 10 can have a profile, so that the contact area between the piston rear side 10 and the stop 9 is reduced. This has the advantage that, owing to the relatively small contact area, the magnetic resistance increases and the proportion of ferromagnetic materials in the magnetic circuit reduces. Both effects counteract the residual magnetization of the magnetic circuit and its components. In addition to preventing magnetic adhesion of the piston 6 to the stop 9, wear of the piston 6 is also reduced and, respectively, the delivery quantity loss of the piston pump is compensated for, as already explained above.
When the width of the grooves 17 increases, the remaining contact area reduces in size, as shown in
The piston rear side 10 and its contact areas are worn over the service life of the piston pump 1, as a result of which the stroke of the piston 6 and therefore the stroke of the piston pump 1 increase. This increased stroke corresponds to an increase in the delivery quantity. Therefore, the wear which occurs between the piston 6 and the cylinder 4 and the associated loss of delivery quantity over the service life are compensated for.
The region 15 according to the invention, when combined with a profiled piston rear side 10, is preferably formed on the remaining contact area.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2014 218 594.7 | Sep 2014 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/068699 | 8/13/2015 | WO | 00 |
