DE102016211924B4 - Method for controlling the ride height of a vehicle with air springs - Google Patents

Abstract

Method for regulating the height level (sist) of a vehicle, the structure of which is supported at least on one axle with air springs relative to the wheels of this axle, with different adaptation speeds of the actual height level (sist) to a target height level (ssetpoint) depending on the situation using target-actual -Comparison and minimization of the target-actual deviation (Δs) with respect to a parameter are represented, characterized in that a travel speed (v, vist) of the vehicle body relative to the wheels is used as said parameter, for which purpose depending on a measurable target value Actual deviation (Δs) of the height different target traversing speeds (vsoll) are stored and the control is carried out in such a way that the difference (Δv) between the target traversing speed (vsoll) and a currently determined actual traversing speed (vist) is minimized.

Description

The invention relates to a method for regulating the height of a vehicle, the structure of which is supported at least on one axle with air springs relative to the wheels of this axle, with different adaptation speeds of the actual height to a target height depending on the situation by comparing the target/actual value and minimizing the Target/actual deviation regarding a parameter can be displayed. In addition to the state of the art, EP 1 744 914 B1 and the DE 10 2008 052 779 A1 in particular to that used to form the preamble of claim 1 DE 103 30 432 A1 referred to which in their 3 and 4 shows a vehicle air suspension system that is also possible for the present invention.

In order to vary the so-called height of a motor vehicle with air suspension, the pressure in the bellows of the air springs is increased, as a result of which the vehicle body rises relative to the road or the wheels and is moved in the vertical direction away from the road, or it becomes Pressure in the air springs is reduced, causing the vehicle body to lower and move towards the road. The resulting travel speed of the vehicle body (relative to the road or the wheels of the vehicle) is subject to various influencing factors such as the pre-pressure in the air bellows, a counter-pressure in a compressed air reservoir provided in particular in the case of a closed air supply, the ambient pressure and the ambient temperature and at least In the case of an electric motor-driven compressor to pump air into the air suspension bellows, this also includes the vehicle's current electrical system voltage. One consequence of these many dependencies or changing influencing variables is large fluctuations in the traversing speed over a longer period of time, which is undesirable at least if it cannot be specifically influenced. However, it may also be desirable to specifically represent a specific travel speed, which depends on a given boundary condition. For example, a change in the height of the vehicle body above the road, which is caused, for example, by the current driving condition such as the driving speed or the condition of the road surface, should take place relatively quickly, while a load compensation is to be carried out with a view to ensuring that the height remains as constant as possible despite different loads on the vehicle is, should be done slowly and imperceptibly.

In the one mentioned at the beginning DE 103 30 432 A1 a method for height control of an air-suspended vehicle is described, in which an adjustment of the actual height to the target height with a view to minimizing the target-actual deviation of the height is carried out in a controlled manner with a control speed dependent on current driving parameters. For this purpose, valves which release or block the air supply into the air springs or the air removal from the air springs or their bellows(s) are suitably controlled. These valves can be continuously controllable or can be controlled as discontinuously controllable so-called clock valves with a suitable switching sequence.
The controlled variable in this known prior art is the vehicle height, with the valves in question being controlled differently with regard to a different opening cross section depending on the current boundary conditions in order to achieve either a higher or a lower control speed.

In this known state of the art, however, with different influencing factors mentioned at the beginning and in particular with different vehicle weights, different so-called traversing speeds arise with which the vehicle body is raised or lowered relative to the vehicle wheels (or the road), which - how has already been carried out - is undesirable.

This is therefore intended to show a method according to the preamble of claim 1, with which specifically specified travel speeds of the vehicle body relative to the wheels can actually be maintained in the event of the body being raised or lowered (= object of the present invention). The solution to this problem results from the features of claim 1; Advantageous further developments are the content of the subclaims.

According to the invention, the travel speed of the vehicle body serves as a controlled variable, ie as the parameter whose target-actual deviation is to be minimized in the control process. A regulation is therefore carried out in such a way that a desired travel speed of the vehicle body relative to the road or, more precisely, relative to the wheels of the vehicle results. This height change with a predetermined travel speed (= target travel speed) is carried out according to the invention by detecting the actual travel speed and the deviation between “actual” and “target”, for example as is known, by suitable control of valves which control the supply and/or controlling the removal of air into and/or out of the air springs is minimized. Alternatively, the delivery rate of a compressor that provides the compressed air for the air springs or that conveys air into the air springs can also be adjusted pressors can be set in a controlled manner in order to minimize the target-actual deviation of the travel speed of the vehicle body.

It is true that when the delivery capacity offered by a compressor for air or generally a fluid, which can be supplied to the air springs of the vehicle wheel suspension (or wheel suspensions), is regulated and when, as usual, for the four air springs, for example In a passenger car, only a single compressor is provided, all air springs only represent the same travel speed (initially, i.e. with the features specified so far only in the sense of raising the vehicle body), but this is usually also desirable, since the vehicle body In the course of a change in height, it should not be tilted or tilted, but should change its height (above the road) as parallel to the road as possible.

If the said compressor can also extract air from the air springs or from their air spring bellows by appropriately laying lines of the air supply system of the air springs and by appropriately switching valves provided in these lines, then the removal of air from the air spring can also be regulated analogously and so that the travel speed of the vehicle body towards the road, ie when lowering, can be specifically regulated by adjusting the suction power of the compressor that extracts air from the air spring. This is particularly useful in the case of a closed air supply system for the air springs. An example of such a closed air supply system, in which the compressor takes the air to be supplied to the air springs in particular from a compressed air reservoir and alternatively removes air from the air springs and supplies it in compressed form to this compressed air reservoir, is also in the one mentioned at the beginning EP 1 744 914 B1 shown. As an alternative to the controlled suction of air from the air springs by the compressor, air can of course also be removed from the air springs driven solely by the pressure present therein, for which valves assigned to the air springs must then be suitably controlled in order to achieve the desired control of the body travel speed; Alternatively, the air flowing out of the air springs can then be counteracted by the compressor with a lower counterpressure (than that prevailing in the air springs).

If the compressor in question is driven by an electric motor, the electric motor can be controlled in a suitable and preferably pulse width modulated manner (with regard to supplied electrical current and/or applied electrical voltage) for the desired control of the compressor performance. Basically, a pulse width modulated control of a compressor electric motor in a vehicle air suspension system is, for example, from the one mentioned above DE 10 2008 052 779 A1 known, but this is only suggested in the document mentioned for a soft start of the electric motor. In the present case, however, a desired travel speed of the vehicle body relative to the road is regulated.

If, as further suggested, in an electronic control circuit provided according to the invention for regulating, for example, the compressor power (and/or the temporal flow rate through the valves mentioned), a measurement signal, preferably filtered depending on the vehicle speed, of the actual height of the vehicle body with the respective and, for example, also driving situation-dependent target value. If the height level is compared, which can be stored, for example, in an electronic control unit in which the above-mentioned control loop is implemented, it can be done easily and (due to the vehicle speed-dependent filtering) free of interference depending on this actual/target difference in the height level also stored suitable target traversing speed can be called up. This target travel speed is, firstly, direction-dependent (i.e. directional) and therefore contains information about whether the vehicle body needs to be raised or lowered and, secondly, its amount can depend on the size of the specified target-actual difference in height. If this target-actual difference has the value "zero", the value of the target traversing speed is (at least theoretically) also "zero", while it makes sense to specify a higher target traversing speed in a certain range of values for larger target-actual differences than with a smaller target-actual difference. This means that the travel speed can, firstly with a view to maximum efficiency and secondly with a view to favorable controller behavior and a quick minimization of the target-actual difference (the height) also depend on the size of the target-actual deviation (= target-actual difference = Actual-target difference) of the vehicle height can be dependent and such travel speeds are selected with which the target-actual difference is minimized, i.e. the actual height is brought closer to the target height. In this context, different target travel speeds can also be stored for different boundary conditions or situations, for example for different driving states, but also for load compensation or other special cases.

As far as the actual controller in a control circuit according to the invention is concerned, it receives as input variables information about the target traversing speed and the actual traversing speed, which should be as close as possible to the target traversing speed. In order to avoid jumps in the specification of the target traversing speed, it is proposed to connect a suitable filter to the target traversing speeds selected, for example, in accordance with the previous paragraph and specified in succession, and only to supply a correspondingly filtered signal to the controller. This prevents an (undesirable) abrupt increase or decrease, so that the electrical inrush current of the electric compressor drive can also be reduced.

So that the actual actuator controller can adapt the actual traversing speed to the target traversing speed, the actual traversing speed must be known and it is proposed to derive this using a differentiating element from the actual height measured using a suitable sensor system. This derived signal is again suitably filtered in order to eliminate speed components that come from road excitations. The filtered actual speed, as well as the current values for the controlled variable, i.e. for example the drive power currently supplied to the drive unit of the compressor and/or the valve control, are then supplied to the actuator controller. In the event that the compressor drive power is the controlled variable, the actuator controller ideally also controls the valves, which control the supply and removal of air into and out of the air springs, in such a way that when the vehicle body is to be raised, air is supplied to the air springs, while when the vehicle body is to be lowered, air can be removed from the air springs. Typically, the valve is controlled using a current regulator that is suitable for electrically switched valves.

Further in particular (but not obligatory) referring to the case in which the compressor delivery capacity (or suction capacity) is the controlled variable, the size or intensity of the air flow or air mass flow supplied to or removed from the air springs can be controlled with an independent controller be regulated, which adjusts the compressor performance (ie the delivery performance and/or suction performance) appropriately. The absolute control deviation of the target and actual travel speeds as well as, for example, the electric compressor drive current serve as input variables. Here too, the inrush current of the compressor drive can be influenced in order to avoid high electrical current peaks. The compressor drive current to be adjusted or the pulse width modulated signal determined in the controller can still be limited with a saturation element. A lower limit, ie activating the compressor only in cases in which a minimum amount of air is required, has the advantage that it can prevent the compressor from wobbling or not starting. Furthermore, this offers an energetic advantage in that, in the event of small control deviations, the compressor drive is not activated at all, but rather a small amount of air required (which remains below the minimum air quantity mentioned above), for example, is only taken from a pressure accumulator (already mentioned). If necessary, a small amount of air can also flow from one of the vehicle's several air springs into another air spring without the compressor having to be put into operation. And in particular, a slight lowering of the vehicle body can easily be achieved by a slight outflow of air from the air springs, without the compressor being put into operation for this purpose.
However, the compressor output can also be limited upwards, ie practically to a maximum air delivery rate, which advantageously not only improves the acoustics, but in particular limits the energy requirement, for example by limiting it to a maximum continuous electrical current. This upper limit value can be or will be variably tailored to different situations or operating states of the vehicle, for example to its electrical system stability and/or to the vehicle driving speed.

The enclosed 1 shows an exemplary control circuit for carrying out the method according to the invention, controlled by an electronic control unit, which also includes an actuator controller 1 , which is exemplified in 2 is shown is implemented. The 3a - 3c show how different target travel speeds can be specified depending on the target-actual deviation of the height or stored in the electronic control unit mentioned.

First up 1 Referring to this, the reference number 1 denotes a comparator element or subtractor element in the control loop, which determines the target-actual deviation Δs of the height of the vehicle body, namely as a difference between the situation-dependent predetermined or by the control unit based on current boundary conditions, which is not the case here The target height S determined in the manner explained and provided with the reference number 7a as well as the actual height measured _by means of suitable sensors and provided with the reference number 7c Altitude S _is , which, however, was subjected to suitable filtering in a filter 15, as explained before the description of the figures, before the difference was formed, which results in the filtered actual altitude S _is ', marked with reference number 7b.

A target trajectory v(Δs) suitable for the target-actual altitude deviation Δs is determined from a lookup table 2a of the control loop, from which a target traversing speed V _set marked with reference number 2b results directly. (Examples of Look Table 2a show those explained later 3a - 3c ). The target traversing speed v _shall is then subjected to filtering in a filter 3a, which was explained before the description of the figures, and reaches an actuator controller 5a as a filtered target traversing speed v _shall ', marked with the reference number 3b. Its possible structure will be explained later using the example of 2 explained.
Still in the control circuit of 1 remaining, the actuator controller 5a is also supplied with the suitably filtered (and marked with reference number 3c) actual travel speed v _ist ' (of the vehicle body), which is derived from the filtered actual height s _ist ' marked with reference number 7b through time derivation is obtained in a differentiating element 4, the result of which in the form of the actual traversing speed v _ist marked with reference number 3d is subjected to filtering in a filter 16, which was explained before the description of the figures.

Furthermore, for a successful control process, the actuator controller 5a is informed in particular of the current electrical drive power made available to the drive of a compressor, with which air can be controllably supplied to the vehicle air springs via the compressor power and can be removed from the air springs by controlled suction (here as compressor current 6b) as well as the electrical power supplied to the valves of the vehicle air suspension system (together with the compressor power, referred to here as “valve & compressor current” 6b). With these listed input variables, the actuator controller 5a creates the output signals or control signals marked with the reference number 5b both for the electric drive of the compressor and for the suitable control of the said valves, which are either closed or opened so that an air flow conveyed or extracted by the compressor such as is desired to be conveyed into or out of the air springs. These output signals, referred to here as “PWM valves/compressor” 5b, then go to what is known in technical jargon as the controller path 6a, which is formed by the vehicle air suspension system with the air springs, their valves and the compressor with drive. PWM stands for pulse width modulation.

Now up 2 For reference, a possible actuator controller 5a is shown here. On the left side you can see the previously explained input variables v _should ' and v _is ' and on the right side those from the control system 6a (from 1 ) coming input variables 6b 1 , namely “valve & compressor flow”. Output variables of the actuator controller 5a are as just in connection with 1 explains the control signals 5b (from 1 ) for the valves and the compressor, namely “PWM valves/compressor.

In the actual actuator controller 5a, the drive power to be supplied to the compressor and the appropriate control of the valves of the air suspension system are determined separately, with a target-actual deviation between the input variables v _shall for what is known here and marked with the reference number 10 “valve sequencer including current controller”. and v _is 'insignificant, since the required switching positions of the individual valves can be derived solely from the directional target traversing speed v _should '. The current regulator under reference number 10 is only needed to bring the valves safely into their desired switching position and to keep them in this position; For this purpose, the valve currents are also communicated to it, from which the output signal “PWM valves” is derived.

A so-called “controller including saturation” marked with the reference number 12, on the other hand, which determines the amount of compressor power required in each case in the sense of a control process according to the invention, must take into account the target-actual deviation with regard to the variable to be regulated, namely the travel speed (of the vehicle body compared to the wheels or the road), which is why the target-actual difference Δv of the traversing speed marked with reference number 9 is initially formed as the difference between the target traversing speed v _should ' and the actual traversing speed v _is '. Of this, only the absolute amount is required to determine the compressor power, which is why the target-actual difference Δv is fed to an amount generator 11a, the output of which is the desired traversing speed v to be produced for the next step in the control process (marked with the reference number 11b), which should be generated with the compressor power to be provided. Taking into account the current compressor power (referred to as “compressor current”), the controller 12, including saturation, can then suitably control the drive of the compressor - and as described in detail before the description of the figures - with the output signal “PWM compressor”.

Now onto that 3a - 3c Various dependencies of the target traversing speed V _target on the target-actual deviation Δs of the height of the vehicle body are detailed here as so-called lookup tables (see reference number 2a in 1 ) shown. These lookup tables (2a) are shown here in the form of a graph 8a, 8b, 8c in a Cartesian coordinate system with the altitude target-actual deviation Δs as the abscissa and the target travel speed V _shall as the ordinate. It makes sense that the target traversing speed V _should also has the value “zero” in all tables if the target/actual height deviation Δs from the value “zero”.

3a shows a first lookup table with a relatively quick adjustment of the actual height to the target height, since a height deviation Δs of an amount of 15 _results in a high target traversing speed V target with an amount of "5". In contrast, the lookup table from 3b a slower adaptation for a different situation or driving condition than in 3a , since at 3b With a height deviation of “15”, a target travel speed V _should is of the order of “2”. In these 3a , 3b It can also be seen, in particular from the two branches 8a and 8c of the graph, that the target traversing speed V _target is directional, after a positive target traversing speed v target _results for a negative height level target-actual deviation Δs and for a positive height level - Target-actual deviation Δs results in a negative target traversing speed V _target . Furthermore, it can be seen that in the area of smaller height-target-actual deviations Δs (between -12 and +12) there _is a proportional dependence on the target traversing speed V target, while in the case of larger height-target-actual deviations Δs there is a constant positive one or negative target traversing speed V _shall is specified.
However, in the area of very small height-target-actual deviations Δs, no change at all can be initiated, ie a target traversing speed V of the value “zero” _should be provided, as 3c shows.

Claims (7)

Method for regulating the height level (s _ist ) of a vehicle, the structure of which is supported at least on one axle with air springs relative to the wheels of this axle, with different adaptation speeds of the actual height level (s _ist ) to a target height level (s _shall) depending on the situation Target-actual comparison and minimization of the target-actual deviation (Δs) are represented with respect to a parameter, characterized in that a travel speed (v, v _is ) of the vehicle body relative to the wheels is used as said parameter, for which purpose a measurable target-actual deviation (Δs) of the height, different target traversing speeds (v _target ) are stored and the control is carried out in such a way that the difference (Δv) between the target traversing speed (v _target ) and a currently determined actual traversing speed (v _is ) is minimized. Procedure according to Claim 1 , whereby valves, which control the supply and/or the removal of air into the air springs and/or out of the air springs, are controlled in a controlled manner in the sense of minimizing the target-actual deviation (Δv) of the body travel speed. Procedure according to Claim 1 or 2 , whereby the delivery capacity of a compressor providing compressed air for the air springs is adjusted in a controlled manner in order to minimize the target-actual deviation (Δv) of the travel speed of the vehicle body. Procedure according to Claim 3 with a compressor driven by an electric motor, the electric motor being controlled in a pulse width modulated manner to regulate the compressor performance. Method according to one of the preceding claims, wherein in the control loop a time-filtered measurement signal (s _is ') of the actual altitude (s _is ) is compared with the target altitude (s _should ) and depending on this difference value (Δs) one of several target traversing speeds (v _target ) stored for different situations are selected. Method according to one of the preceding claims, wherein a suitably time-filtered signal (v _target ') of the target traversing speed (v _target ) as well as a suitably filtered signal (v _is ') of the time derivative (ds/dt) of the possibly filtered measurement signal (s _is ') of the actual height (s _is ) is fed to an actuator controller (5), which controls the valves that control the supply and / or removal of air into the air springs and / or from the air springs and / or a drive of the compressor is controlled appropriately. Procedure according to Claim 6 , whereby a certain minimum air quantity requirement and/or a maximum compressor performance that is variable depending on the situation is taken into account for the control of the compressor drive.

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