GAS SPRING WITH EXPANSION WAX, DRIVE SYSTEM WITH THE GAS SPRING

Description

Technical area

[0001] The invention relates to a gas pressure spring with an expansion wax as a compensating medium for reducing a temperature dependence of a spring force of the gas pressure spring in a working temperature range of the gas pressure spring extending from a minimum temperature to a maximum temperature.

[0002] The invention further relates to a drive system for a flap with a gas pressure spring for supporting the flap and an electromechanical drive for driving the flap. State of the art

[0003] In gas springs, the fact that the pressure of the working gas used increases with temperature (linearly in the case of an ideal working gas) results in a gas spring characteristic with a temperature-dependent spring force. However, in many applications, such as drive systems for flaps, especially vehicle flaps, a temperature-independent spring force is desired. Therefore, gas springs designed to compensate for the temperature dependence of the gas spring characteristics with the aid of a compensating medium are known from the prior art.

[0004] For this purpose, the gas spring comprises, for example, as described in EP 1 795 777 A2, a working cylinder which, together with a compensating piston arrangement, defines a working chamber filled with a working medium, and a working rod which projects displaceably into the working chamber through an opening in the working cylinder. The compensating piston arrangement is subjected to the pressure of the working medium and the pressure of the compensating medium provided in a compensating chamber, which expands when the temperature increases, in a direction that increases the volume of the working chamber. To ensure that the compensating piston reversibly returns to its initial position when the temperature decreases, it can also be subjected to the pressure of a return medium provided in a return chamber, in a direction that reduces the volume of the working chamber.

[0005] Regarding the substances that can be used as a compensating medium, DE 31 41 295 A1 refers quite generally to a "special fluid." In contrast, DE 25 11 289 A1, which covers the same subject matter, explicitly mentions hydraulic oil as a compensating medium. Finally, according to US Pat. No. 4,613,115, two-phase systems of certain substances are used as compensating media, more specifically, systems in which the liquid and gaseous phases of the substance in question coexist under the respective pressure-temperature conditions.

[0006] US3782121 discloses a compensating medium for gas springs in which the liquid and solid phases coexist, but in a temperature range between 80°C and 105°C and without monohydric alcohols.

[0007] However, all of these compensating media have proven unsatisfactory in practice. In particular, the conventionally used mineral oil has insufficient usable volume expansion in the typically considered operating range of gas springs. In two-phase systems, the high volume expansion, which primarily results from the gas phase, is negated by the high compressibility of the gas phase.

[0008] According to EP 1 795 777 A2, the compensating medium is preferably a liquid just below its boiling point or in a supercritical state, since such a liquid, on the one hand, has a relatively large volume expansion, but on the other hand, due to its property of still being a liquid, is essentially incompressible. Examples of preferred compensating media are carbon dioxide (CO 2 ), ethane (C 2 H 6 ), propane (C 3 H 8 ), hydrogen sulfide (H 2 S), ammonia (NH 3 ), methylene chloride (CH 3 Cl), sulfur dioxide (SO 2 ) and sulfur hexafluoride (SF 6 ). A disadvantage of these compensating media, however, is that they can only be introduced into a gas spring and kept there permanently with great effort, particularly because they are highly volatile and sometimes also corrosive and / or toxic.In addition, many of these compensation media are highly flammable, which is particularly problematic for use in vehicles for safety reasons and transport regulations. Technical task

[0009] The object of the invention is to create a particularly easy-to-manufacture and durable gas pressure spring and a drive system for a flap therewith, wherein the temperature dependence of the gas spring characteristics is reliably compensated. Technical solution

[0010] The subject matter of the present invention provides a gas spring according to claim 1, which solves the technical problem. The problem is also solved by a drive system according to claim 9. Advantageous embodiments emerge from the dependent claims. Description of the execution types

[0011] The invention relates to a gas pressure spring with an expansion wax as a compensating medium for reducing a temperature dependence of a spring force of the gas pressure spring in a working temperature range of the gas pressure spring extending from a minimum temperature between -40 °C and + 10 °C to a maximum temperature between +50 °C and +100 °C.

[0012] The gas spring can, for example, be constructed essentially like the gas springs described in DE 31 41 295 A1 or EP 1 795 777 A2. The gas spring preferably comprises a working cylinder, which, together with a compensating piston arrangement, defines a working chamber filled with a working medium, in particular a gaseous one, and a working rod that projects displaceably into the working chamber through an opening in the working cylinder. The compensating piston arrangement is subjected to the pressure of the working medium and the pressure of the compensating medium provided in a compensating chamber, which expands with temperature increase, in a manner that increases the volume of the working chamber.

[0013] In order for the compensating piston to return reversibly to its initial position when the temperature decreases, it can also be acted upon by a return medium provided in a return chamber in a manner that reduces the volume of the working chamber.

[0014] When the temperature increases within the operating temperature range, the expansion wax undergoes at least one phase transition, in particular from a waxy solid to a liquid phase, with a significant relative increase in volume, for example, by 5% to 20%, in particular by 10% to 15%. This allows the increase in volume of the expansion wax to be used to enlarge the working space of the gas spring, preventing an increase in pressure of the working medium and the associated increase in the spring force of the gas spring due to the temperature increase.

[0015] The relative volume increase δV is defined as the quotient of the absolute volume increase ΔVby the volume V Tmin at the minimum temperature. The absolute volume increase ΔV is the difference in volume V Tmax at the maximum temperature Tmax the working temperature range minus the volume V Tmin at the minimum temperature Tmin of the working temperature range: δV = ΔV / V Tmin = V Tmax − V Tmin / V Tmin

[0016] For a working temperature range from a minimum temperature of Tmin = -30 °C up to a maximum temperature of Tmax = +80 °C advantageously results in a relative increase in volume δV from 14% to 18%.

[0017] In this application, temperature-dependent effects are generally described using the example of an increase in temperature. It is generally assumed that the temperature-dependent effects are reversible, i.e., they occur essentially in the opposite way when the temperature decreases than when the temperature increases.

[0018] Compared to other working media, expansion wax has the advantage that it can be easily incorporated into the gas spring due to its waxy consistency and low chemical reactivity. Furthermore, because it is solid or liquid within the operating temperature range and chemically reactive, it can be easily and permanently sealed within the gas spring, ensuring long-term, reliable operation.

[0019] The expansion wax comprises at least one liquid phase and at least one solid phase throughout the entire operating temperature range. Due to the coexistence of at least one solid and at least one liquid phase, an at least approximately linear increase in volume of the expansion wax occurs with a temperature increase, which can almost completely compensate for the generally also approximately linear increase in pressure of the working medium across the entire operating temperature range.

[0020] Because at least one liquid phase and at least one solid phase are present over the entire working temperature range, the expansion wax differs from expansion waxes commonly used in thermostatic valves, where a liquid and a solid phase are only intended to coexist in the narrowest possible temperature range in order to achieve a well-defined switching temperature of the thermostatic valve.

[0021] The at least one liquid phase and the at least one solid phase are preferably mixed with each other or form a gel to effect a homogeneous temperature-dependent volume change of the compensation medium and to avoid possible interface effects that could impair the linearity of the volume change. However, the at least one liquid phase and the at least one solid phase can also be spatially separated from each other by at least one phase boundary.

[0022] Properties of substances and mixtures of substances stated in this application refer to standard pressure (100 kPa), unless otherwise stated.

[0023] The expansion wax contains a number of primary alcohols. Primary alcohols offer a number of advantages as a leveling medium, in particular, they are immiscible with water and thus provide corrosion protection for the gas spring. Furthermore, primary alcohols are neutral and harmless to health. Primary alcohols with a defined chain length and thus a defined melting point are also readily available.

[0024] The minimum temperature is preferably -30 °C to 0 °C, in particular -20 °C to -10 °C. The maximum temperature is preferably +50 °C to +80 °C, in particular +60 °C to +70 °C. The specified minimum and maximum temperatures result in a working temperature range that covers a wide range of typical applications for gas springs, particularly in vehicle construction, thus avoiding undesirable effects due to a temperature dependence of the spring force of the gas spring in typical applications.

[0025] The expansion wax comprises a number of alkanes, preferably a plurality of alkanes with mutually different chain lengths, wherein the alkanes preferably have a minimum chain length in the range of 5 to 20, particularly preferably 10 to 15, and a maximum chain length in the range of 20 to 35, particularly preferably 25 to 30.

[0026] The expansion wax can, for example, comprise 10 to 25, in particular 15 to 20, alkanes with different chain lengths.

[0027] Alkanes offer a number of advantages as a balancing medium. In particular, they are inert due to their stable carbon chains without functional groups. They are flame-resistant above a certain chain length and can only be split in the presence of catalysts. Furthermore, alkanes are miscible, harmless to health, inexpensive, and, due to their hydrophobic properties, provide corrosion protection for gas springs starting at a chain length of approximately 16.

[0028] Furthermore, the melting temperatures of alkanes with adjacent chain lengths are very close to each other. Adding an additional carbon atom in the chain typically increases the melting temperature by about 3 K. The narrow range of melting temperatures allows for a particularly uniform expansion of the expansion material across the entire operating temperature range.

[0029] Alkanes with the chain lengths mentioned exhibit melting temperatures distributed across the operating temperature range of the gas spring, thus ensuring that at least one liquid and at least one solid phase coexist in the compensation medium across the entire operating temperature range. Tests have shown that the melting temperatures of the alkanes in the compensation medium do not differ significantly from the corresponding melting temperatures of the alkanes as pure substances.

[0030] The disadvantage of alkanes is that complex separation processes are necessary to obtain alkanes with a precisely defined chain length or a precisely defined mixture of chain lengths.

[0031] The expansion wax preferably comprises a plurality of primary alcohols with mutually different chain lengths, wherein the primary alcohols preferably have a minimum chain length in the range of 3 to 15, particularly preferably 5 to 10, and a maximum chain length in the range of 10 to 25, particularly preferably 15 to 20.

[0032] The expansion wax can, for example, comprise 2 to 15, in particular 5 to 10, primary alcohols with different chain lengths.

[0033] Primary alcohols with the chain lengths mentioned exhibit melting temperatures distributed across the operating temperature range of the gas spring, thus ensuring that at least one liquid and at least one solid phase coexist in the compensation medium across the entire operating temperature range. Tests have shown that the melting temperatures of the primary alcohols in the compensation medium do not differ significantly from the corresponding melting temperatures of the primary alcohols as pure substances.

[0034] The wax consists of several alkanes and several primary alcohols with different chain lengths. Primary alcohols are generally miscible with alkanes, so a homogeneous wax can be advantageously produced from primary alcohols and alkanes.

[0035] Primary alcohols, with very short chain lengths of, for example, eight to ten carbon atoms, are characterized by a low melting point of -16 °C to 7 °C, while simultaneously having a relatively high flash point compared to alkanes with the same melting temperature. Therefore, primary alcohols can achieve a low minimum temperature without causing the wax to become highly flammable.

[0036] In addition, primary alcohols exhibit a high melting temperature of 49 °C to 59 °C even with relatively short chain lengths of, for example, 16 to 18 carbon atoms. The melting temperature of an alkane with 18 carbon atoms, in contrast, is only 28 °C. Therefore, a high maximum temperature can be achieved with relatively short-chain primary alcohols. To achieve the same maximum temperature, alkanes with significantly longer chain lengths would be necessary, which would be chemically less stable and more expensive than the shorter-chain primary alcohols.

[0037] Mixtures of primary alcohols are generally more expensive than mixtures of alkanes. Furthermore, the melting points of primary alcohols with adjacent chain lengths are further apart than those of alkanes. Therefore, it is more difficult to achieve uniform expansion of the wax across the entire operating temperature range with primary alcohols than with alkanes.

[0038] In order to create the most cost-effective and safe expansion wax with uniform expansion over the entire working temperature range, it is therefore particularly advantageous if the expansion wax comprises a number of primary alcohols and a number of alkanes.

[0039] The chain lengths of the primary alcohols and / or alkanes are preferably within the aforementioned ranges. The expansion wax can, for example, comprise or consist of primary alcohols with chain lengths of 8 to 18 carbon atoms and alkanes with chain lengths of 14 to 25 carbon atoms.

[0040] The primary alcohols contained in the expansion wax include a number of primary alcohols that have a lower melting temperature than all alkanes contained in the expansion wax and / or a number of primary alcohols that have a higher melting temperature than all alkanes contained in the expansion wax.

[0041] At the upper and / or lower end of the working temperature range, primary alcohols are used instead of alkanes to ensure uniform expansion of the wax without increasing its flammability and cost or reducing its chemical stability. In the middle of the working temperature range, however, alkanes are used to ensure low costs and, due to the close melting points of the alkanes, uniform expansion of the wax. This combination of primary alcohols and alkanes optimally utilizes the respective advantages of both groups of substances.

[0042] The primary alcohols constitute a molar fraction of 1% to 30%, preferably 10% to 25%, of the expansion wax. With such a molar fraction, the inventive melting behavior of the expansion wax and high application reliability of the gas spring can be achieved at low cost. For example, the inventive melting behavior is achieved for an expansion wax consisting of 25% octanol and 75% of the commercially available alkane expansion wax RubiTherm RT35.

[0043] The invention relates to a drive system for a flap with a gas pressure spring according to the invention for supporting the flap and an electromechanical drive, for example a linear drive, in particular a spindle drive, for driving the flap. The flap can be, for example, a vehicle flap, in particular a hood, a trunk lid, a luggage compartment lid, or a wing door.

[0044] Drive systems for a flap with a gas spring to support the flap and an electromechanical drive to drive the flap are known in the prior art. Except for the use of a gas spring according to the invention instead of a generic gas spring, the drive system according to the invention can be constructed like a corresponding drive system from the prior art, for example, from DE 103 13 440 A1 or DE 10 2008 045 903 A1.

[0045] The gas spring of the drive system serves to hold the flap in any position against gravity, while the electromechanical drive is used to open and close the flap. Additionally, manual operation of the flap can be provided, as described in DE 103 13 440 A1 and DE 10 2008 045 903 A1.

[0046] The gas spring must have such a high spring force that it can hold the flap closed even at low ambient temperatures. Since the spring force of conventional gas springs increases with temperature, this means that at high temperatures, a very high force must be applied by the electromechanical drive or an operator to close the flap. Therefore, the drive system must include a very powerful electromechanical drive, which is expensive, requires a lot of space, and consumes a lot of energy during operation. Furthermore, this leads to significant wear on the electromechanical drive and other parts mechanically connected to the flap, such as hinges.

[0047] In the prior art, these problems are circumvented by using a spring strut instead of a gas spring (e.g., DE10 2008 045 903 A1, paragraph

[0021] ). Although a spring strut has a spring force that is virtually independent of temperature, it is larger, heavier, and more expensive than a gas spring with comparable spring force.

[0048] By using a temperature-compensated gas spring according to the invention instead of a conventional gas spring, a particularly cost-effective, easy-to-manufacture, durable, compact, energy-saving and easy-to-operate drive system for a flap is created. Short description of the drawings

[0049] Further advantages, objects, and features of the invention will be explained with reference to the following description and the accompanying drawings, which illustrate exemplary objects according to the invention. Features that are at least substantially identical in function in the figures may be identified by the same reference numerals, although these features need not be numbered and explained in all figures. Figure 1 shows the relative volume change of an expansion wax of a gas spring according to the invention depending on the temperature. Figure 2 shows the relative volume change of another expansion wax of a gas pressure spring according to the invention depending on the temperature. Fig.1

[0050] Figure 1 shows the relative volume change δV in % of an expansion wax of a gas spring according to the invention depending on the temperature T in °C.

[0051] The for Figure 1 The expansion wax tested was prepared by mixing the commercially available waxes RubiTherm RT35, Mahle-Beer, and Paramelt Dilavest 0-30 in equal proportions and contains the alkanes listed in Table 1 below. The molar fractions were determined by gas chromatography. Table 1: name Chain length Melting point / °C Molar fraction / % n-Dodecan 12 -10 0,0 n-Tridecan 13 -5 0,1 n-Tetradecan 14 6 9,5 n-pentadecane 15 9 6,2 n-Hexadecan 16 18 3,9 n-Heptadecan 17 21 6,5 n-Octadecan 18 28 15,8 n-Nonadecan 19 32 9,1 n-Eicosane 20 37 10,4 n-Heneicosane 21 40 11,2 n-Docosane 22 44 9,1 n-Tricosane 23 48 6,1 n-Tetracosane 24 50 4,4 n-pentacosane 25 54 3,1 n-Hexacosane 26 56 1,8 n-Heptacosane 27 59 0,8 n-Octacosane 28 61 0,3 n-Nonacosane 29 64 0,3 n-Triacontan 30 65 0,0 sum 98,5

[0052] To measure the temperature dependence of the volume of the expansion wax, an initial volume of 3198.4 mm 3< of the expansion wax was filled into a cylindrical measuring cartridge (6 mm inner diameter, 114 mm inner length) with a cylindrical plunger (3.98 mm diameter, 12.4 mm 2< cross-sectional area) at an initial temperature of -10 °C.

[0053] The measuring cartridge was subjected to a temperature ramp in a tempering furnace. At each temperature tested, after a waiting time of approximately 20 minutes, the distance by which the plunger was expelled from the cartridge relative to the initial temperature due to the expansion of the wax against a counterforce of 3 N was recorded using a displacement sensor.

[0054] The relative volume change of the expansion wax was calculated as the product of the absorbed displacement with the cross-sectional area of ​​the plunger divided by the initial volume. Figure 1shows the values ​​obtained for heating (circles) and cooling (squares) of the expansion wax.

[0055] The essential components (mole fraction > 5%) of the Figure 1 The waxes tested exhibit melting temperatures ranging from 6 °C to 48 °C (Table 1). Accordingly, the wax comprises at least one solid and at least one liquid phase over a total operating temperature range of approximately 10 °C to approximately 50 °C.

[0056] This results in, as in Figure 1 As can be seen, an approximately linear relative volume increase with increasing temperature in the operating temperature range. A linear regression (dotted line) of the measured data in this range shows a correlation coefficient of R 2 < = 0.96.

[0057] Overall, a relative volume increase of 15% is achieved across the tested temperature range of -10 °C to +60 °C, which is sufficient to compensate for the temperature dependence of the gas spring. With a relative volume increase of 15%, with suitable transmission ratios in the design, it is possible to achieve a compensating stroke that is sufficient to fully compensate or even overcompensate for the temperature dependence of the gas spring.

[0058] Overcompensation offers the possibility to work very flexibly and to adjust the exact desired expansion for each gas spring type by mixing with appropriate oils with a lower volume increase. Fig.2

[0059] Figure 2 shows the relative volume change δV in % of another expansion wax of a gas spring according to the invention depending on the temperature T in °C.

[0060] The for Figure 2 The wax tested was prepared by mixing three commercially available waxes from Orbesen with melting ranges of 6 °C to 12 °C, 15 °C to 40 °C, and 56 °C to 62 °C in equal proportions and contains the primary alcohols listed in Table 2 below. The molar fractions were determined by gas chromatography. Table 2: name Chain length Melting point / °C Molar fraction / % n-octanol 8 -16 0,0 n-Decanol 10 7 43,8 n-Dodecanol 12 24 0,0 n-Tetradecanol 14 38 24,0 n-Hexadecanol 16 49 31,4 n-octadecanol 18 59 0,0 sum 99,3

[0061] The relative volume change of the wax was determined as well as Figure 1 described. In contrast to Figure 1 an initial temperature of -20 °C was chosen.

[0062] The essential components (mole fraction > 5%) of the Figure 1The waxes tested exhibit melting temperatures ranging from 7 °C to 59 °C (Table 2). Accordingly, the wax comprises at least one solid and at least one liquid phase over a total operating temperature range of approximately 10 °C to approximately 50 °C.

[0063] This results in Figure 2 An approximately linear relative volume increase with increasing temperature is evident in the operating temperature range. A linear regression (dotted line) of the measured data in this range shows a correlation coefficient of R 2 < = 0.98.

[0064] Overall, a relative volume increase of 12% is achieved over the investigated temperature range from -20 °C to +75 °C, which is sufficient to compensate or even overcompensate for the temperature dependence of the gas spring.

Claims

1. A gas pressure spring comprising an expanding wax as a compensating medium for reducing a temperature dependency of a spring force of the gas pressure spring in an operating temperature range of the gas pressure spring spanning a minimum temperature of -40 °C to +10 °C up to a maximum temperature of +50 °C to +100° C characterised in that a. the expanding wax comprises at least one liquid phase and at least one solid phase in the entire operating temperature range; b. wherein the expanding wax is composed of a number of alkanes and a number of primary alcohols having chain lengths which differ from each other, c. wherein the primary alcohols constitute a percentage of 10 % to 30 % of the substance amount of the expanding wax; and d. wherein the primary alcohols contained in the expanding wax i. comprise a number of primary alcohols having a lower melting temperature than all alkanes contained in the expanding wax, and / or ii. comprise a number of primary alcohols having a higher melting temperature than all alkanes contained in the expanding wax.

2. The gas pressure spring according to claim 1, characterised in that the minimum temperature is -30 °C to 0 °C, preferably or -20 °C to -10 °C.

3. The gas pressure spring according to claim 1 or 2, characterised in that the maximum temperature is +50 °C to +80 °C, preferably +60 °C to +70 °C.

4. The gas pressure spring according to any of claims 1 to 3, characterised in that the expanding wax comprises a plurality of alkanes having chain lengths which differ from each other.

5. The gas pressure spring according any of claims 1 to 4, characterised in that the alkanes have a minimum chain length within the range of 5 to 20, preferably of 10 to 15; and a maximum chain length within the range of 20 to 35, preferably of 25 to 30.

6. The gas pressure spring according to any of claims 1 to 5, characterised in that the primary alcohols constitute a percentage of 10 % to 25 % of the substance amount of the expanding wax.

7. The gas pressure spring according to any of claims 1 to 6, characterised in that the expanding wax comprises a plurality of primary alcohols having chain lengths which differ from each other.

8. The gas pressure spring according to any of claims 1 to 7, characterised in that the primary alcohols have a minimum chain length within the range of 3 to 15, preferably of 5 to 10; and a maximum chain length within the range of 10 to 25, preferably from 15 to 20.

9. A drive system for a flap comprising: a. a gas pressure spring according to one of the claims 1 to 8 for supporting the flap; and b. an electromechanical drive, preferably a spindle drive, for driving the flap.