GB2393519A

GB2393519A - A method and device for measuring the number of revolutions of a pump motor

Info

Publication number: GB2393519A
Application number: GB0318695A
Authority: GB
Inventors: Juergen Hachtel
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2002-09-12
Filing date: 2003-08-08
Publication date: 2004-03-31
Anticipated expiration: 2023-08-08
Also published as: JP2004101527A; GB2393519B; DE10242305A1; GB0318695D0; DE10242305B4

Abstract

According to the method it is provided that the pressure signal (P) is measured on a pump outlet valve and the distance proportional to the number of revolutions between successive pressure pulses which exceed a predeterminable threshold value is determined, wherein high-frequency pressure fluctuations occurring between the pressure pulses are suppressed and the threshold value is reset depending on the temperature (T) of the pump medium. The device according to the invention provides that on a pump outlet valve a pressure sensor is arranged, the signal of which is led via a high-pass filter (1) to a comparator (2), the threshold value of which is adjustable depending on the temperature (T) of the pump medium, the output of which is fed back to its input via a delay circuit (3) and the output of which is led to a timer (4) counting the period of the comparator output signal.

Description

Method for measuring the number of revolutions of a pump motor The

invention relates to a method and a device for 5 measuring the number of revolutions of a pump motor with the features named in the preambles of claims 1 and 3.

Prior art

10 Normally the number of revolutions of a pulp drive is determined by a measurement on the electric drive machine of the pump. The measurement of the number of revolutions helps in controlling the pump, as, among other things, the pump noise can be influenced by the number of revolutions.

15 To determine the number of revolutions of an electric motor, magnetic or optical transmitters are known, which are attached to the shaft of the machine and are scanned via corresponding magnetic or optical sensors on the stator housing. Devices of this kind are, however, associated with 20 a relatively high cost outlay.

For electric machines operated by a voltage controlled by pulse-width (PWM), in other words clocked, as a simpler and more economical method it is known in the non-activated 25 phases to measure the generator-produced voltage, the level of which is proportional to the number of revolutions of the motor. The level of voltage is, however, not a very accurate measurement for the number of revolutions, so the method is unsuitable for precise control.

From US-PS 5,664,047 a solution is known in which the ripple in the current (current ripple) of a PWM-controlled electric motor is intended to be involved in determining the number of revolutions. However, the measurement is made

difficult by the constant changing between activated and non-activated phase of the motor. The shorter the current pulses are, which depends on the chosen clock frequency, the desired number of revolutions and the loading of the 5 motor, the more uncertain is the measuring signal, which can lead to faulty control operations and therefore to fluctuations in the number of revolutions.

From DE 41 33 269 Al a method is known in which the current 10 ripple is likewise utilised for measuring the number of revolutions. The current ripple the frequency of which is directly proportional to the number of revolutions is subjected twice to a Fourier transformation. After the second Fourier transformation the number of revolutions 15 occurs as a maximum and can thus be evaluated. The solution presupposes analog to digital conversion and corresponding computer capacity and is therefore quite cost-intensive.

Advantages of the invention The method according to the invention and the device according to the invention with the features named in claims 1 and 3, on the other hand, offer the advantage that in a simple manner the number of revolutions of a pump 25 motor can be detected economically but accurately.

According to the invention the object is achieved by the features of claims 1 and 3. Advantageous configurations are the subject of the subordinate claims.

According to this the pressure signal on the pump outlet valve is measured and the distance between successive

pressure pulses which exceed a predeterminable threshold value is determined, wherein high-frequency pressure fluctuations occurring between the pressure pulses are suppressed and the threshold value is reset depending on 5 the temperature of the pump medium.

The knowledge is herein utilised that the pressure output signal of a hydraulic conveying device, in particular a piston pump, has a very characteristic course. However, the 10 pressure fluctuations proportional to the number of revolutions, which go with the current ripple of the pump motor, are of such high-frequency that they can be detected by a low- cost microcontroller only to a limited extent. The invention therefore uses the high pressure amplitudes 15 rising appreciably in the pressure signal at the beginning of a pump lift. This lift changes with the temperature, however. The threshold value for the amplitude is therefore orientated to the temperature of the pump medium.

20 The method has the advantage that it usually supplies a reliable value for the number of revolutions of a pump motor without an additional sensor, as the pressure signal on the pump outlet valve is usually measured in any case.

The number of revolutions signal gained can, moreover, be 25 even further analyzed. For instance, from differentiation of the number of revolutions signal (first derivation) it can be seen, for example, whether air is just taken in with a pump which otherwise pumps a fluid. This is possible, as, if a hydraulic conveying device sucks air, the load moment 30 of the pump motor changes drastically and thus produces fluctuations in the number of revolutions.

Advantageous configurations of the invention emerge from the features named in the subordinate claims.

Drawings The invention is explained in greater detail below in an embodiment example using the associated drawings.

Fig. 1 shows a course of the pressure signal on the outlet 10 valve of a piston pump.

Fig. 2 shows a basic circuit of the device according to the invention. 15 Description of the embodiment example

Fig. 1 shows the pressure signal P of a piston pump on its pump outlet valve.

20 The pressure signal P on the pump outlet valve contains a direct component and a higher frequency component in a corresponding electrical signal, in other words a DC and an AC component. The direct component (DC) rises with the increase in pressure in the following pressure store, 25 identifiable from the rising initial amplitudes of the pump lifts. With each pump lift a high-frequency component (AC) occurs. The amplitude of the high-frequency component is temperature dependent.

30 Fig. 2 shows a basic circuit diagram of a measuring arrangement for gaining a number of revolutions signal.

By building in a high-pass filter 1 the AC component is separated from the DC component in the pressure signal P. Subsequently this AC component is converted into rectangular signals via a comparator 2, the threshold of 5 which changes with the temperature T. In order to avoid the highfrequency AC component exceeding the comparator threshold multiply during the same pump lift, by means of a delay circuit 3 (monoflop) the input of the comparator 2 is applied to a defined voltage. In this way there arises at 10 the output of the comparator 2 a rectangular signal the period of which can be counted out in a hardware timer 4 (for example a controller). This period is a measurement for the number of revolutions n of the pump motor.

Claims

Patent claims

1. Method for measuring the number of revolutions of a pump motor, characterized in that the pressure signal (P) is measured on a pump outlet valve and the distance proportional to the number of revolutions between successive pressure pulses which exceed a predeterminable threshold value is determined, wherein high-frequency pressure fluctuations occurring between the pressure pulses are suppressed and the threshold value is reset depending on the temperature (T) of the pump medium.

2. Method according to claim 1, characterized in that the first derivation, for identifying air taken in by a hydraulic conveying device, is formed from the gained value of the number of revolutions.

3. Device for measuring the number of revolutions of a pump motor, characterized in that on a pump outlet valve a pressure sensor is arranged, the signal of which is led via a high-pass filter (1) to a comparator (2), the threshold value of which is adjustable depending on the temperature (T) of the pump medium, the output of which is fed back to its input via a delay circuit (3) and the output of which is led to a timer (4) counting the period of the comparator output signal.

4. Method substantially as hereinbefore described with reference to the . accompanying drawings.

5. Device substantially as hereinbefore described with reference to the . accompanying drawings.