Method for controlling a gear pump

Abstract

A method for controlling a gear pump by a control device to compensate a tooth engagement-induced volume flow pulsation to reduce noise emissions. The method includes acquiring a gear angle and an actual speed of the gear pump; keeping a relationship between a respective modulation angle and an amplitude of a pilot control torque of the gear pump to compensate the volume flow pulsation to an actual speed; modulating the pilot control torque on the basis of the acquired gear angle, a predetermined correction angle, the modulation angle, a number of teeth of the gear pump and the amplitude; and driving the gear pump with a drive torque overlaid with the modulated pilot control torque. The modulation angle is calculated using a PT element with the actual speed as the input variable.

Claims

1. A method for controlling a gear pump by way of a control device to compensate a tooth engagement-induced volume flow pulsation, wherein the control device includes an acquisition unit, a computing device, and a memory device, wherein the method comprises at least the following steps: a. by way of the acquisition unit, acquiring a gear angle and an actual speed of the gear pump; b. by way of the memory device, maintaining a relationship between a respective modulation angle and an amplitude of a pilot control torque of the gear pump to compensate the volume flow pulsation to an actual speed of the gear pump; c. by way of the computing device, modulating the pilot control torque on a basis of the acquired gear angle, a predetermined correction angle, the modulation angle, a number of teeth of the gear pump and the amplitude, wherein the modulation angle is calculated using a PT element with the actual speed as an input variable; and d. by way of a drive unit, driving the gear pump with a drive torque overlaid with the modulated pilot control torque.

2. The method according to claim 1, wherein the predetermined correction angle is determined in a step e. by way of a one-time and preliminary calibration measurement.

3. The method according to claim 1, wherein, in a step c2., the amplitude of the pilot control torque is modulated using an actual amplitude which is dependent on the actual speed and a correction factor which is dependent on the actual speed.

4. The method according to claim 3, wherein, in step c2., the actual amplitude is further determined as a function of a leakage factor, wherein the leakage factor is dependent on the actual speed and a differential pressure at the gear pump.

5. The method according to claim 3, wherein the correction factor of the amplitude and/or the modulation angle are determined continuously.

6. The method according to claim 1, wherein, in a step f. a maximum value limitation of the pilot control torque is carried out.

7. The method according to claim 1, wherein, in a step g. the pilot control torque modulated in step c. is regulated by way of a regulation factor, wherein the regulation factor is determined as a function of the vehicle speed, the differential pressure, and/or the actual speed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-described invention is discussed in detail in the following in the context of the relevant technical background with reference to the accompanying drawings which show preferred embodiments. The invention is not limited in any way by the purely schematic drawings, whereby it should be noted that the drawings are not true to scale and are not suitable for defining dimensional relationships. The figures show:

(2) FIG. 1 is a diagram of a pilot control torque, an actual speed and a fluid flow over a gear angle;

(3) FIG. 2 is a schematic block diagram of the control system of the gear pump;

(4) FIG. 3 is a regulation block according to FIG. 2;

(5) FIG. 4 is a pilot control torque block according to FIG. 2;

(6) FIG. 5 is a flow chart of a method for controlling a gear pump;

(7) FIG. 6 is a schematic illustration of a gear pump;

(8) FIG. 7 depicts a chassis hydraulics with a gear pump; and

(9) FIG. 8 depicts a motor vehicle comprising a chassis hydraulics according to FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

(10) FIG. 1 shows a diagram of a pilot control torque 9, an actual speed 6 and a fluid flow 26 over a gear angle 5. The gear angle 5 is plotted on the abscissa and the speed (for example in revolutions per minute), the fluid flow 26 (for example in cubic meters per second) and the gear angle 5 (in degrees) are plotted on the ordinate.

(11) The design of a gear pump 1 causes fluctuations in the fluid flow 26, i.e., the volume flow of a fluid conveyed by means of the gear pump 1. The fluctuations lead to the sinusoidal shape of the fluid flow 26 in relation to the gear angle 5 shown here, for instance. The fluctuations are in a range of, for example, one to three percent around a fluid flow average value 27. Such fluctuations lead to undesirable noise emission, for example.

(12) A tooth engagement of the gear pump 1 therefore causes a full phase cycle, i.e., extends over a phase angle of 360. The diagram shown here is for a gear pump 1 comprising 15 teeth 11 on the smaller driven internal gear 39. A tooth engagement, i.e., a phase angle range of 360, thus corresponds to a gear angle range of 24. The diagram shows a first tooth engagement 28 and a second tooth engagement 29.

(13) To compensate these fluctuations, the actual speed 6 of the gear pump 1 is controlled such that it oscillates in the opposite direction. In other words, a base speed 30, which is the average value of the actual speed 6, is overlaid with a sinusoidal modulated speed oscillation. The course of the actual speed 6 is 180 out of phase with the fluid flow 26, i.e., a maximum of the actual speed 6 occurs at the same gear angle 5 as a minimum in the fluid flow 26 and vice versa. The fluid flow fluctuations can thus be at least partly compensated.

(14) The actual speed 6 is modulated via a torque control. For this purpose, a drive torque 14, which forms a mean value here, is overlaid with a sinusoidal pilot control torque 9. To generate a desired actual torque 31 with the pilot control torque 9, the pilot control torque 9 is amplified in amplitude 8 in relation to the desired actual torque 31 and shifted by a phase angle to correct the transmission behavior of a torque controller and the electrical path (to generate phase currents and electrical fields in the drive unit of the gear pump).

(15) The phase progression of an actual torque 31 for generating the desired actual speed 6 is shifted forward (to the left in the illustration) compared to the course of the actual speed 6 by a 90 phase angle and has the same frequency as the actual speed 6 and the fluid flow 26. The amplitude 8 of the actual torque 31 is calculated on the basis of an inertia factor, a leakage factor and a pulsation factor according to the formula:

(16) $3.3:{\stackrel{\_}{M}}_{n_{\mathrm{ist}}}=.Math.\frac{{}^2}{60}.Math..Math.{\tilde{n}}_{\mathrm{ist}}.Math..Math.n_{\mathrm{ist}}.Math.f_p$

(17) is the inertia factor, f.sub.p is the pulsation factor, .Math.n.sub.ist is the actual speed and .sub.ist is the leakage factor.

(18) To generate this actual torque 31, the pilot control torque 9 is determined by means of a control device 2, which comprises a computing device 3 and a memory device 4. The pilot control torque 9 is determined according to the formula, for example:
M.sub.n=M.sub.n.Math.sin[15.Math.(.sub.w.sub.k.sub.M)]3.5:

(19) M.sub.n is the amplitude 8 of the pilot control torque 9, Pw is the gear angle 5, .sub.M is the modulation angle 7 and 15 is the number of teeth.

(20) The phase angle of the pilot control torque 9 is corrected by two offset values. One offset value is the predetermined correction angle 10, which specifies the angular offset between a zero crossing of gear angle 5 and a zero crossing of the phase angle of the torque. The correction angle 10 reflects the angular offset between the zero position of the drive shaft of the gear pump 1 and the tooth engagement in degrees of gear angle 5, for instance. The correction angle 10 is preferably determined at the factory, once in a preliminary calibration measurement.

(21) The modulation angle 7 is determined as the second angular offset. The modulation angle 7 is determined as a function of the actual speed 6 according to the formula:

(22) 0$1.1:{}_{\stackrel{\_}{M}}=\frac{1}{a}.Math.\left[-\arctan \left(\frac{}{2}.Math..Math.n_{\mathrm{ist}}.Math..Math.{}_M\right)-\frac{}{2}.Math.T_{\mathrm{tot}}.Math..Math.n_{\mathrm{ist}}.Math.\right]$

(23) Here, .sub.M is the modulation angle, a is the number of teeth (15), n.sub.ist is the actual speed, .sub.M is a time constant and T.sub.tot is a dead time of the torque controller. The modulation angle 7 corresponds to a phase correction of the transmission behavior of the torque controller in degrees relative to the gear angle 5, i.e., one shaft revolution of the drive shaft of the gear pump 1, for example.

(24) The actual amplitude 15 of the actual torque 31 is corrected by a correction factor. The correction factor is preferably calculated using the following formula:

(25) $3.1:f_{\mathrm{korr}}=\sqrt{1+{\left(\frac{}{2}.Math..Math.n_{\mathrm{ist}}.Math..Math.{}_M\right)}^2}$

(26) The actual amplitude 15 is calculated using the formula 3.3.

(27) FIG. 2 shows a schematic block diagram of the control system of the gear pump 1. A decision parameter 32 can be used to select between a test mode and an operating mode. The test mode is illustrated by a correction angle block 33, which is the determination of the correction angle 10, for example in a preliminary calibration measurement. The operating mode is illustrated by a pilot control torque block 34, by means of which the modulation of the pilot control torque 9 is carried out, and a regulation block 35, by means of which the modulated pilot control torque 9 is regulated.

(28) The regulation block 35 provides a regulation factor 17, which preferably has a value between 0 and 1, as the output variable. This value is multiplied by the pilot control torque 9 modulated in pilot control torque block 34 to regulate the pilot control torque 9.

(29) FIG. 3 shows the regulation block 35 according to FIG. 2 in detail. The regulation block 35 receives the measured actual speed 6, the differential pressure 16 at the gear pump 1 and the vehicle speed 18 as input variables. A characteristic diagram, which assigns a regulation factor 17 to the respective input variable, is preferably kept for each of the input variables by means of the memory device 4. Alternatively, a calculation formula for the regulation factor 17 is stored as a function of the input variable, for example.

(30) The regulation factor 17 for a medium speed range of the actual speed 6 has the value 1, for instance, and decreases for lower or higher speeds. In a range between 750 revolutions per minute and 1500 revolutions per minute, for example, the regulation factor 17 has the value 1. At less than 250 revolutions per minute or more than 2000 revolutions per minute, for example, the regulation factor 17 has the value 0.

(31) For a low differential pressure 16, for example, the regulation factor 17 has the value 0 and for a high differential pressure 16 it has the value 1. Between the high and the low differential pressure 16, the regulation factor 17 is described by a straight line, for instance. The low differential pressure 16 is 10 bar and the high differential pressure 16 is 25 bar, for example.

(32) The regulation factor 17 for a medium speed range of the vehicle speed 18 has the value 1, for instance, and decreases for lower or higher speeds. In a range between 10 kilometers per hour and 100 kilometers per hour, for example, the regulation factor 17 has the value 1. At 0 kilometers per hour or more than 150 kilometers per hour, for example, the regulation factor 17 has the value 0.

(33) The lowest of the three thus determined regulation factors 17 is selected by means of a decision function, and used to regulate the pilot control torque 9 as discussed with reference to FIG. 2.

(34) FIG. 4 shows a pilot control torque block 34 according to FIG. 2 in detail. The pilot control torque block 34 receives the actual speed 6, the differential pressure 16 and the gear angle 5 as input variables. In an amplitude block 36, the amplitude 8 of the pilot control torque 9 is determined using the formula:

(35) $3.4:{\stackrel{\_}{M}}_n=\sqrt{1+{\left(\frac{}{2}.Math..Math.n_{\mathrm{ist}}.Math..Math.{}_n\right)}^2}.Math.\underset{{\stackrel{\_}{M}}_{n_{\mathrm{ist}}}}{\underset{}{.Math.\frac{{}^2}{60}.Math..Math.{\tilde{n}}_{\mathrm{ist}}.Math..Math.n_{\mathrm{ist}}.Math.f_p}}$

(36) and/or a characteristic diagram as a function of the input variables actual speed 6 and differential pressure 16. The correction factor, which is multiplied by the actual amplitude 15 of the actual torque 31, is stored in a characteristic diagram as discussed above, for example.

(37) In a PT element 12, also referred to here as a modulation angle block, the modulation angle 7 of the pilot control torque 9 is modulated as a function of the actual speed 6. For this purpose, for example a characteristic diagram, which depicts the modulation angle 7 as a function of the actual speed 6, is stored in the memory device 4. The modulation angle 7 can alternatively or additionally be calculated using Formula 1.1, for example.

(38) In a sum block 37, the modulation angle 7 determined in the modulation angle block or the PT element 12 and the correction angle 10 determined in the correction angle block 33 (see FIG. 2) are subtracted from the measured gear angle 5. For this purpose, the correction angle 10 determined in the preliminary calibration measurement according to the correction angle block 33 is kept by the memory device 4. In a direction block 38, a suitable sign for the correction angle 10 is determined as a function of the direction of rotation of the gear 39 or the drive shaft of the gear pump 1, for example.

(39) The pilot angle summed up in the sum block 37 is multiplied by the number of teeth 11 of the driven gear 39 or the number of pairs of teeth of the gear pump 1 over a 360 gear angle 5 and the sine is calculated. The function of the pilot control torque 9 then corresponds to a multiplication of the amplitude 8 by the thus determined phase response. Before the pilot control torque 9 is output as the output variable, a maximum value limitation or a minimum value limitation takes place in a filter block 40, for example.

(40) FIG. 5 shows a flow chart of a method for controlling a gear pump 1, for example according to the diagram and block diagram of FIG. 1 to FIG. 4.

(41) In a step e. the preliminary calibration measurement is carried out and the predetermined correction angle 10 determined. The preliminary calibration measurement is preferably carried out once at the factory.

(42) In the preliminary calibration measurement, a specific test speed, a specific test torque and a specific test differential pressure, for example, are set on the gear pump 1. A preferably sinusoidal test oscillation is iteratively applied to the test torque and the differential pressure level is measured. The test phase angle of the test torque is shifted to iteratively determine the test phase angle having the lowest differential pressure level.

(43) For each iterative measurement of the differential pressure level, the test phase angle of the test torque is shifted by no more than 2 (two degrees), no more than 1 (one degree) or no more than 0.5 (half a degree) of the gear angle 5, for example. The differential pressure level is calculated using a fast Fourier transform or a bandpass filter, for instance.

(44) This results in a test angle of

(45) $2.1:{}_{\mathrm{Test}}^{}=i^{*}.Math.\frac{}{180}$

(46) wherein i* is the distance of the test phase angle, with which the differential pressure level is the lowest, relative to a zero crossing of the gear angle 5 in (degrees).

(47) The predetermined correction angle 10 is determined on the basis of the test angle, for example using the following formula:

(48) $2.2:{}_k=i^{*}.Math.\frac{}{180}-\frac{1}{a}.Math.\left[-\arctan \left(\frac{}{2}.Math..Math.n_{\mathrm{Test}}.Math..Math.{}_M\right)-\frac{}{2}.Math.T_{\mathrm{tot}}.Math..Math.n_{\mathrm{Test}}.Math.\right]$

(49) The predetermined correction angle 10 is therefore an offset value for defining the tooth engagement behavior, and with it the volume flow pulsation, in relation to the gear angle 5.

(50) In a step a., the gear angle 5 is acquired by means of the angle encoder. The gear angle 5 is an angle of a drive shaft of the gear pump 1, for example. The angle is measured by means of an angle encoder using a reference point on the drive shaft, for example. The actual speed 6 is acquired as well. The actual speed 6 is a speed of the gear 39, preferably an internal gear 39, of the gear pump 1 or the drive shaft, for example. The actual speed 6 is preferably also determined by means of the angle encoder or with a separate measuring device.

(51) In step b. now, a relationship between the modulation angle 7 for determining the phase of the pilot control torque 9 and the actual speed 6 of the gear pump 1 is kept on the memory device 4. The relationship between the modulation angle 7 and the actual speed 6 includes a characteristic diagram, an analytical description, for instance a model, or another algorithm, for example. A relationship between the amplitude 8 of the pilot control torque 9 and the actual speed 6 of the gear pump 1 is kept on the memory device 4 as well. The relationship between the amplitude 8 and the actual speed 6 includes a characteristic diagram, an analytical description, for instance a model, or another algorithm, for example.

(52) In a step c., the pilot control torque 9 is modulated by means of the computing device 3 on the basis of the acquired gear angle 5, the predetermined correction angle 10, the modulation angle 7, the number of teeth 11 of the gear pump 1 and the amplitude 8.

(53) In a step d., the gear pump 1 is then driven by means of the drive torque 14 overlaid with the pilot control torque 9. The drive torque 14 is provided by means of a drive unit 13 controlled by the control device 2, preferably an electric motor. A torque controller is used.

(54) The modulation angle 7 is determined in a PT element 12 and is carried out in a step c1. The amplitude 8 is determined, preferably in parallel, in a step c2. Steps c1. and c2. are preferably continuous.

(55) A maximum value limitation or a minimum value limitation of the pilot control torque 9 is then carried out in an optional step f. It is thus possible to prevent an overreaction or negative values, for instance.

(56) The pilot control torque 9 is moreover regulated in an optional step g., as described above. The pilot control torque 9 can be dimmed as a function of the vehicle speed 18, the differential pressure 16 of the gear pump 1 and/or the actual speed 6, for example, for instance to avoid inappropriately high amplitudes 8 of the pilot control torque 9 at low speeds or vehicle speeds 18.

(57) In a step d., the pilot control torque 9 overlaid with the drive torque 14 is used to control the gear pump 1 by way of the drive unit 13.

(58) FIG. 6 shows a gear pump in a schematic illustration. According to the illustration, the gear pump 1 is a crescent pump. The internal gear 39 can be driven by a drive unit 13. As can be seen, the internal gear 39 comprises 15 teeth 11. The number of teeth 11 of the driven gear 39 determines the frequency at which the fluid flow 26 oscillates in relation to the rotation of the drive shaft, because this determines the number of tooth engagements per revolution of the drive shaft or per 360 gear angle 5. The teeth 11 of the internal gear 39 engage the teeth 11 of the gear ring 19, so that said gear ring is caused to rotate as well.

(59) As can be seen, a crescent is disposed in a lower portion of the gear pump 1. According to the illustration, the gears 39 rotate counterclockwise, i.e., in a left hand rotation. The gear pump accordingly comprises an inlet area in a portion on the left in the illustration, into which the fluid is drawn with low pressure. The rotation of the gears 39, 19 causes the fluid to be conveyed along the crescent and thereby compressed. An outlet region, out of which the fluid is pushed with higher pressure, is accordingly disposed on the right side in the illustration.

(60) FIG. 7 shows a chassis hydraulics 20 comprising a gear pump 1. The gear pump 1 is preferably controlled by a control device 2 according to FIG. 1 to FIG. 4. This is a gear pump 1 according to FIG. 6, for instance.

(61) The gear pump 1 is disposed in a hydraulic circuit for conveying a hydraulic fluid. For this purpose, the gear pump 1 is fluidically connected to two chambers 41 of a damper device 21 on both sides of a working piston 42 in a cylinder 43.

(62) An equalizing container 44 for the hydraulic fluid and a circuit which, as can be seen, consists of two restrictors 45 and two check valves 46, are provided as well for regulating the damper device 21.

(63) One end of the damper device 21 is connected to a vehicle body 24 of a motor vehicle 22 and one end is connected to a wheel 23 of the motor vehicle 22 in order to damp said body and said wheel when they move relative to one another.

(64) FIG. 8 shows a motor vehicle 22 comprising a chassis hydraulics 20 according to FIG. 7. The motor vehicle 22 comprises four wheels 23, which, according to the illustration, are all configured as drive wheels and are connected to the vehicle body 24 by means of a damper device 21 (as can be seen, this is provided with reference signs once pars pro toto). Relative movements and accelerations between the vehicle body 24 and the wheels 23 can be damped by means of the chassis hydraulics 20 or the damper device 21. Pitching movements, yaw movements and rolling movements due to vehicle accelerations, uneven roads, cornering or other reasons, for instance, can be damped.

(65) As can be seen, the motor vehicle 22 further comprises two drive motors 25, one for the front axle and one for the rear axle, which are both connected to the respective wheels 23 in a torque-transmitting manner.

(66) The invention relates to a method for controlling a gear pump to compensate a tooth engagement-induced volume flow pulsation and thus reduce noise emissions.

(67) The features of the following claims can be combined in any technically meaningful manner, for which purpose it is also possible to consult the explanations from the following description and features from the figures, which comprise additional configurations of the invention.