Method for the weight-dependent control of the internal pressure of a supporting body loaded by a weight load or a payload

Abstract

A method for the weight-dependent control of the internal pressure of a supporting body loaded by a weight load or payload, wherein the internal pressure is produced by means of an electric-motor-driven compressor, and the weight load or payload which is present and which acts on a supporting body in the form of a mass m.sub.Load under the effect of acceleration due to gravity g is determined in that a reduction and a subsequent increase in the internal pressure take place, wherein the increase in the internal pressure causes the position of an application point of the weight load or payload to change by a position difference Z, wherein: during the increasing of the internal pressure by means of the compressor, the motor current I.sub.Load of the drive motor of the compressor is measured with a constant motor voltage U and integrated over the time of the increase in pressure, and the electrical work W.sub.Load which is necessary for the change in position is determined therefrom, wherein the electrical work W.sub.Load the electrical work W.sub.Load is compared with a characteristic value of the electrical work W.sub.0 from a characteristic diagram, wherein the change in position Z, the difference in mass m and the difference in payload F.sub.Z are determined from the difference W between W.sub.Load and W.sub.0 and the mass m.sub.Load and the weight load or payload which is actually present as a result is determined therefrom.

Claims

1. A method for the weight-dependent control of the internal pressure of a supporting body loaded by a weight load or payload, wherein the internal pressure is produced by means of an electric-motor-driven compressor, characterized in that the weight load or payload which is present and which acts on a supporting body in the form of a mass m.sub.Load under the effect of acceleration due to gravity g is determined in that a reduction and a subsequent increase in the internal pressure take place, wherein the increase in the internal pressure causes the position of an application point of the weight load or payload to change by a position difference Z, wherein the following further method steps are carried out: during the increasing of the internal pressure by means of the compressor, the motor current I.sub.Load of the drive motor of the compressor is measured with a constant motor voltage U and integrated over the time of the increase in pressure, wherein the electrical work W.sub.Load which is necessary for the change in position is determined as a product of the motor voltage and integrated motor current, the electrical W.sub.Load is compared with a characteristic value of the electrical work W.sub.0 from a characteristic diagram in which the values for the electrical work for achieving a normal position or standard position of the application point under normal load are stored in accordance with a normal load acting in the form of a normal mass m.sub.0 under the effect of acceleration due to gravity g, and further parameters of the supporting body, the change in position Z, the difference in mass Am and the difference in payload F.sub.Z are determined from the difference AW between W.sub.Load and W.sub.0 by means of the relationships
W=F.sub.Z.Math.Z and
m.sub.LOADm.sub.0=m and
F.sub.Z=g.Math.m and in turn the weight load or payload which is present after the pressure increase is determined therefrom, from the mass $m_{\mathrm{LOAD}}=\frac{U}{g.Math.Z}\left[I_{\mathrm{LOAD}}\left(t\right)\mathrm{dt}-W_0\right]+m_0$ taking into account the acceleration due to gravity g, after which the compressor is switched off in accordance with the weight load or payload which is determined in this way, when an internal pressure which is predefined for the determined weight load or payload on the basis of the parameters of the supporting body is reached.

2. The method as claimed in claim 1, in which the electric-motor-driven compressor is controlled by means of an electronic motor control unit, the motor voltage and motor current are acquired and processed in such a way that the product of the motor voltage and integrated motor current is determined and compared with values of a characteristic diagram stored in an electronic memory of the motor control unit, wherein an electronic motor driver apparatus for the drive motor of the compressor is actuated in accordance with the weight load or payload which is also determined by the motor control unit, and after comparison with values of a characteristic diagram, stored in a further electronic memory of the motor control unit, for the internal pressure which is predefined for the respective weight load or payload.

3. The method as claimed in claim 1, in which the electric-motor-driven compressor is provided with a pressure sensor which detects the internal pressure of the supporting body, or with a corresponding pressure-sensitive evaluation of the motor characteristic variables, as result of which a signal which is proportional to the internal pressure is transmitted to the electronic motor control unit and/or to the electronic motor driver apparatus.

4. The method as claimed in claim 1, which at least the determined weight load or payload and the determined internal pressure in the supporting body are transmitted as signals to further control or monitoring apparatuses of surrounding systems.

5. The method as claims in claim 1, wherein the supporting body is an air spring bellows of a vehicle pneumatic suspension system.

Description

(1) The method according to the invention is to be explained in more detail below on the basis of an exemplary embodiment, specifically on the basis of a tire repair kit for motor vehicle tires. In the drawings:

(2) FIG. 1 shows a basic view of the design of an air compressor unit for a device which is embodied as a tire repair kit and has the purpose of carrying out the method according to the invention, and

(3) FIG. 2 shows a schematic view of the inflation process of a vehicle tire.

(4) FIG. 1 shows a basic view of the design of an air compressor unit 1 for a device which is embodied as a tire repair kit and has the purpose of carrying out the method according to the invention, that is to say an electronically assisted tire repair kit. A control unit 2 (MCU) controls the connected air compressor 4 by means of a motor driver 3 (MD) via the user interface 5 (UI) depending on the user's requirements.

(5) Therefore, the term air compressor unit denotes here the assembly of the tire repair kit which comprises the control unit, the motor driver, the air compressor as such with piston compressor, motor and transmission and the user interface.

(6) During operation, the control unit (MCU) acquires all the relevant system parameters such as the temperature, motor voltage, motor current or counterpressure. In this context, the pressure measurement can be carried out by means of an electronic pressure sensor or else by means of the evaluation of the data of the average motor current, as stated above.

(7) FIG. 2 is a schematic illustration of the process of inflating a vehicle tire 6 with air. From the state A (deficiency of air or excessively low internal pressure) to the state B (prescribed air pressure) the air pressure in the tire 6 is increased from the pressure P.sub.START to the pressure P.sub.END by the air compressor 4. Here, the center of gravity of the tire is raised by the magnitude difference Z. Here, the air compressor 4 carries out the electrical work W.sub.LOAD at the motor voltage U and the instantaneous current I.sub.LOAD.

(8) $W_{\mathrm{LOAD}}=U.Math.\underset{t_0\left(P=P_{\mathrm{START}}\right)}{\overset{t_1\left(P=P_{\mathrm{END}}\right)}{}}{I}_{\mathrm{LOAD}}\left(t\right)\mathrm{dt}$

(9) Here, the work which is carried out is composed of the part W.sub.0 of the increase in pressure of the tire which is normally loaded with the mass m.sub.0 and the part W of the movement of the center of gravity of the tire which is additionally loaded by the mass
m.sub.LOAD=m.sub.0+m.
W.sub.LOAD=W.sub.0+W

(10) The portion W.sub.0 has been determined in advance in a calibration measurement for the corresponding system configuration (vehicle type, tire size, tire position, operating voltage, operating temperature, starting pressure and end pressure) and stored as a value table or as a characteristic diagram in the control unit (MCU). By measuring and integrating the instantaneous motor current I.sub.LOAD it is possible to measure the work W.sub.LOAD in the control unit (MCU) and therefore calculate the portion of the movement of the center of gravity.
W=U[I.sub.LOAD(t)dtW.sub.0]

(11) With the relationship W=F.sub.Z.Math.Z it is possible to calculate from this value the weight force F.sub.Z=g.Math.m acting in addition to the normally loaded case, and therefore also to calculate the wheel load m.sub.LOAD.

(12) $m_{\mathrm{LOAD}}=\frac{U}{g.Math.Z}\left[I_{\mathrm{LOAD}}\left(t\right)\mathrm{dt}-W_0\right]+m_0$

(13) In order to estimate the measuring accuracy, the average motor current .sub.LOAD and .sub.0 are also finally considered here.

(14) $m=\frac{U}{g.Math.Z}\left[{\stackrel{\_}{I}}_{\mathrm{LOAD}}.Math.t-{\stackrel{\_}{I}}_0.Math.t\right]=\frac{U.Math.\stackrel{\_}{I}.Math.t}{g.Math.Z}$

(15) Where =.sub.LOAD.sub.0 the following is obtained

(16) $\stackrel{\_}{I}=\frac{g.Math.m.Math.Z}{U.Math.t}.Math.\frac{m}{\stackrel{\_}{I}}=\frac{U.Math.t}{g.Math.Z}$

(17) For the typical parameters U=12V, t=300 s and Z=5 cm, an accuracy factor of 7.3 kg/mA is obtained. Given a measuring accuracy of the motor current measurement of 5 mA it is therefore possible to determine a wheel load with an accuracy of approximately 40 kg. This is completely sufficient for setting the optimum tire pressure.

LIST OF REFERENCE NUMBERS

(18) (Part of the Description)

(19) 1 Air compressor unit 2 Control unit (MCU) 3 Motor driver (MD) 4 Air compressor 5 User interface (UI) 6 Vehicle tire