The invention relates to a method for ascertaining an rpm as generically defined by the preamble to claim 1, and to an apparatus for ascertaining an rpm as generically defined by the preamble to claim 5.
In many fields in technology, it is necessary to know a precise rpm or a precise rotary position of a motor. With direct current motors, for instance, it is known to detect the rpm. Various methods are used for this. One inexpensive variant is to calculate the rpm with the aid of Hall sensors; a Hall sensor detects the position of a rotor and sends that onward to a control unit. The Hall sensors react to the magnetic field of the rotating rotor, which is made of a magnetic material. For calculating the rpm, the time between two edges of a Hall signal is measured, and the rpm is calculated from that.
The object of the invention is to furnish a fast method for ascertaining an rpm and an apparatus for performing the method.
The object of the invention is attained by the method as defined by the characteristics of claim 1 and by the apparatus as defined by the characteristics of claim 5.
One advantage of the method of the invention is that an rpm estimate is made if a signal to be received from a position sensor is delayed. The arrival of a new position signal is delayed whenever the rpm has decreased. To that end, preferably the time that has elapsed since the last position signal and the arrival of the next position signal is measured and compared with the most recently measured rpm. If the time that has elapsed since the last position signal is greater than expected on the basis of the rpm, then the rpm is ascertained from the time that has elapsed since the last position signal.
In this way, it becomes possible to ascertain the rpm precisely and quickly.
In a preferred embodiment, as the elapsed time after which an rpm estimate is made, the difference between two preceding position signals is used. By using the position signals, complicated recalculation is made unnecessary. Thus the method can be performed quickly and requires only little computation power.
In a preferred embodiment, the rpm is calculated at fixed time intervals. Current rpm information is thus furnished on an ongoing basis.
For calculating the elapsed time, a counter is preferably used that at fixed time intervals increases a counter value by a fixed value. Thus the counter state is proportional to the time that has elapsed since the last position signal. Using a counter makes a simple, economical execution of the method of the invention possible.
In a preferred embodiment, an intervention is made into the rpm regulation of the electric motor if the time since the last position signal is longer than it should be on the basis of the most recently measured rpm. The rpm is then estimated on the basis of the time elapsed since the last position signal. In this way, fast and precise regulation of the electric motor is obtained. In particular, this procedure offers a reliable method for obtaining constant rpm regulation in direct current motors with low rotary speeds. Particularly in direct current motors that run at low rotary speeds, torque fluctuations can lead to uneven running of the motor, and the motor can be induced to vibrate. Increasing motor vibration may for instance even cause the motor to stop. The method of the invention reliably avoids these disadvantageous effects.
The invention will be described in further detail below in conjunction with the drawings.
The invention will be described below in terms of a direct current motor 1 but can be used for any type of motor. Preferably, the direct-current motor is used in the form of a pump motor for an electrohydraulic power steering system in a motor vehicle. With the aid of the motor 1, however, any other type of device, in particular in a motor vehicle, can be triggered.
As a function of the position of the rotor 10, the control unit 5 controls the supply of current to the magnet coils 13, 14, 15 of the stator 11. As a result of the interaction among the magnetic fields that are generated by the magnet coils and the magnetic fields of the rotor 10, the rotor 10 is excited to perform a rotation at a desired rpm.
In the graph in
Typically, the control unit 5, with the aid of the Hall signals HS1, HS2, HS3, calculates the rpm of the rotor. In the process, the control unit 5 uses the leading or trailing edges, for instance, of a Hall signal HS1, HS2, HS3. The control unit knows that three of the Hall sensors 2, 3, 4 are disposed around the motor 1. Moreover, per revolution of the rotor 10, three Hall signals are generated in each Hall sensor 2, 3, 4. Thus the leading edges of one Hall signal of one Hall sensor have a chronological spacing of 120°, and 360° represents one revolution of the rotor 10.
If the rotor 10 now rotates as a result of appropriate current supplied to the magnet coils 13, 14, 15, then at time t1 a magnet pole of the rotor moves past the first Hall sensor 2. In the first Hall sensor 2, a leading edge of a Hall signal is generated at time t1. This signal is reported to the control unit 5. At time t2, the control unit 5 receives a leading edge of the second Hall sensor 3. At time t3, the control unit 5 receives a report of a leading edge from the third Hall sensor 4. At time t7, a leading edge is again generated in the first Hall sensor 2, and at time t8, a leading edge is again generated in the second Hall sensor 3.
If the counter state of the internal timer 3 shows a differential value of 8000, for instance, between two leading edges of the same Hall signal, and the internal counter 33 increases its counter state every 2 μs, then between two leading edges of the first Hall signal HS1, a time of 16000 μs has elapsed. During one rotation of the rotor 10, three leading edges are generated in one Hall sensor. The measured time represents one-third of one rotation. The control unit calculates the rpm U by the following formula:
U=1/(3·0.016s)=20.833=1/s=1250 U/min.
Instead of calculating the rpm using the leading edges, the trailing edges of the Hall signals HS1, HS2, HS3 can be used. In the exemplary embodiment shown, the control unit 5 receives a trailing edge of the first Hall signal HS1 at time t4, a trailing edge of the second Hall signal HS2 at time t5, and a trailing edge of the third Hall signal HS3 at time t6. Correspondingly, the control unit 5 calculates the rpm of the motor 1, using the method described above for the leading edges.
The timer 6 runs parallel to this and is always reset when a Hall signal arrives. Upon receiving the leading edge of the first Hall signal HS1 at time t1, the control unit 5 starts the timer 6. The timer 6 increments an internal counter upward at fixed chronological increments. If the control unit 5 at time t2 receives the leading edge of the second Hall sensor HS2, then the control unit 5 stops the timer 6, reads out the counter state, sets the counter state to zero, and starts the timer 6 again. With the timer, independently of the capture function and of the internal timer 33, the elapsed time since the most recent edge of a Hall signal is detected. Since the Hall signals occur with chronological staggering, the counter state of the timer 6 is less, by a factor of six, then the time between two leading or trailing edges of one Hall signal.
If no trailing or leading edge of a Hall signal has arrived, then the most recently calculated rpm is compared by the control unit 5 with the elapsed time since the arrival of the most recent leading or trailing edge. If the elapsed time is greater than it should be on the basis of the most recently calculated rpm, then an rpm calculation is made on the basis of the counter state of the counter 6. This estimation operation is repeated until a leading or trailing edge of a Hall signal is detected, or a time-out signal for likely blocking of the motor arrives.
If the comparison shows that the counter state is greater than the chronological spacing, then the rpm is calculated from the counter state of the timer 6. The timer 6 preferably has a greater chronological pulse rate than the internal counter 33. Preferably, this chronological pulse rate is in the range of 1 ms, after which the timer 6 increases its counter state.
If the comparison shows that the counter state is greater than the chronological spacing of the most recent two leading or trailing edges of the Hall signals, then the following method is performed.
If the counter state of the counter 6 exceeds a predetermined counting time, which time corresponds to the chronological spacing of the last two leading or trailing edges of a Hall signal, then the rpm is estimated on the basis of the counter state of the timer 6, by the following formula:
U=1/(3·counter state·n), where n stands for the number of Hall sensors, and the factor of 3 is due to the fact that the rotor has three magnet coils 30, 31, 32.
If the counter state is for instance (0.017/n) s, then the result is an rpm of
1/(3·0.017 s)=19.608
1/s=1176 1/min.
Thus an estimated rpm is obtained even though no edge signal of the same Hall signal has been detected.
Preferably, the estimation of the rpm is done at fixed chronological spacings, for instance every millisecond. In the instance described, at a counter state of (0.018/n) s, the new rpm U is thus calculated:
U=1/(3·0.018 s)=18.519
1/s=1111 1/min.
In a corresponding way, an rpm estimate is made every millisecond, until a new capture value for an edge of a Hall signal has been detected, or until a time-out signal appears. Preferably, the control unit 5 compares the time since the last position signal with the most recently measured rpm. If the comparison shows that the time since the last position signal is greater than the time on the basis of which the most recently ascertained rpm was derived, then the rpm is estimated on the basis of the time since the last position signal. In this way, rpm fluctuations or an rpm drop can be reacted to more quickly.
Instead of the Hall sensors 2, 3, 4, other types of position transducers may also be used.
Number | Date | Country | Kind |
---|---|---|---|
10223140.0 | May 2002 | DE | national |
10227523.8 | Jun 2002 | DE | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/DE03/01439 | 5/6/2003 | WO |