JPS6136910Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a torque detection method for a DC electric dynamometer.

Conventional DC electric dynamometers allow the stator of a DC motor or DC generator (hereinafter simply referred to as a DC machine) to swing around a rotation axis, and measure the torque acting between the stator and rotor. A common method is to measure with a weighing device connected to the stator or a strain detection gauge attached to the load shaft.

On the other hand, the torque T of a DC machine is generally expressed as T=A・I・Φ−T _M (1). However, A is a proportional constant I is armature current Φ is field magnetic flux T _M is mechanical loss torque Therefore, torque T can be calculated from armature current I, field magnetic flux Φ, mechanical loss torque T _M , etc. I can do it.

By the way, since it is generally difficult to directly detect the magnetic flux Φ, the magnetic flux Φ is usually derived based on the following relational expression.

Φ=B・B/N …(2) However, B is a proportionality constant E is a back electromotive force N is the rotational speed Here, since accurate measurement of the rotational speed N is relatively easy, based on equation (2) In order to accurately derive the magnetic flux Φ, it is necessary to accurately measure the back electromotive force E.

Conventionally, as a method for easily obtaining the back electromotive force E, there is a method of measuring the terminal voltage V of the armature 1 and using it as the back electromotive force E, as shown in FIG. 1a. That is, E
This is a method that considers ≒V.

However, this method cannot accurately measure the back electromotive force. This is because the equivalent circuit of the armature winding is as shown in FIG. 1b, and has a DC resistance Ra. In other words, if the back electromotive force is E, the DC resistance of the armature winding is Ra, the terminal voltage of the armature winding is V, and the current flowing through the armature winding is I, then E=V-1・Ra... (3).

Therefore, in this method, an error corresponding to I.Ra always exists, and it cannot be said to be an accurate measurement method. Therefore, if you want to obtain a more accurate back electromotive force, you have no choice but to rely on other appropriate means.

There is a method shown in FIGS. 2a and 2b that is a relatively popular method for obtaining a back electromotive force with relative accuracy.

Figure 2a is a circuit diagram for deriving the back electromotive force, and Figure 2b is its equivalent circuit, where 2 is a resistor with a resistance value of _R2 , and 3 and 4 are resistors with a resistance value of _R3 and _R4, respectively. ,
5 and 6 are terminals between the armature 1 and the resistor 2 and between the resistors 3 and 4, respectively, and 7 and 8 are terminals to which an external power source is connected.

The principle of this system will be explained with reference to FIG.

Assuming that a voltage V is now applied to the terminals 7 and 8, the voltage V _R4 across the resistor 4 and the voltage _VR2 across the resistor 2 can be determined by the following equations.

V _R4 = V・R ₄ /R ₃ +R ₄ …(4) V _R2 =(V−E)・R ₂ /Ra+R ₂ …(5) Therefore, the voltage between terminals 5 and 6 is Here, if each resistance value is selected so that R ₃ /R ₄ =Ra/R ₂ In other words, if the ratio Ra/R ₂ remains constant, the voltage between terminals 5 and 6 will be a value proportional to the back electromotive force E, so the back electromotive force will increase without being affected by the armature current or armature voltage. E can be detected.

However, in reality, the value of the DC resistance Ra of the armature winding fluctuates in response to changes in temperature during operation, resulting in errors and cannot be said to be an accurate detection method. In other words, the armature winding resistance Ra
is caused by outside air or temperature changes associated with driving.
It changes as shown in equation (8).

Ra = Rao (1 + αt) ...(8) where Rao is the resistance of the armature winding at the reference temperature α is the temperature coefficient of resistance t is the temperature difference between the reference temperature and the temperature of the armature winding Therefore, the ratio Ra/R The method shown in Fig. ₂ , which can accurately measure the back electromotive force under the condition that 2 remains constant, cannot be expected to always provide accurate measurements.

This invention was made in view of the above-mentioned drawbacks of the conventional art, and aims to always obtain an accurate back electromotive force and thereby derive an accurate torque.

3 and 4 are circuit diagrams showing an embodiment of this invention, in which FIG. 3 is a circuit for deriving a back electromotive voltage, and FIG. 4 is an equivalent circuit of FIG. 3. In the figure, 9 is an armature winding, 10 is a commutator winding, 1
1 and 12 are resistors with resistance values R ₅ and R ₆ respectively, V _B is a brush drop voltage, and Ri is a commutator winding resistance. Note that there is a relationship R ₅ /R ₆ =Ra/Ri between the resistance values R ₅ and R ₆ of the resistors 11 and 12.

This method is almost the same as the conventional example shown in Fig. 2, but in the conventional example shown in Fig. 2, an external resistor 2 is connected in series with the armature winding. The proposed method is different in that it uses a commutator winding resistance inside the DC machine, and this difference makes the measured value of the back electromotive force an extremely accurate value, as described below.

Now, in the circuits shown in FIGS. 3 and 4, if the potential difference V between the terminals 5 and 6 is derived, it is expressed by the following equation in the same way as it was derived by equation (7).

Transforming equation (8), E=V・(Ra/Ri+1)−V _B …(9) In other words, if the ratio Ra/Ri remains constant, the back electromotive force will not be affected by the armature current or armature voltage. Voltage can be derived accurately. Furthermore, the commutator winding 10 is present inside the DC machine like the armature winding 9, and the temperature changes due to outside air or operation in substantially the same way. Therefore, the ratio Ra/Ri is considered to be always constant even when the temperature changes. Therefore, by obtaining an accurate back electromotive force, accurate torque can be derived.

As described above, according to this invention, the armature winding resistance and the commutating pole winding resistance have the same ratio.
R ₅ and R ₆ are connected in series and inserted in parallel to the armature, and the connection point and resistance between the armature winding and the commutator winding that exists inside the DC machine as well as this armature winding
Based on the potential difference V between the connection point of R ₅ and R ₆ , the back electromotive force E=V・Ra+Ri/Ri−V _B is obtained, and the torque is further derived based on this back electromotive force. , without being affected by armature current or armature voltage.
Further, even if the armature winding temperature fluctuates, an accurate back electromotive voltage can be obtained without being affected, and therefore an accurate torque can be derived.

[Brief explanation of the drawing]

Figures 1 and 2 are circuit diagrams showing circuits for obtaining back electromotive force of a DC machine, Figures 3 and 4 respectively.
The figure is a circuit diagram showing an embodiment of this invention. In the figure, 1 is the armature, 2 to 4 and 11,1
2 is a resistor, 9 is an armature winding, and 10 is a commutator winding. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of claim for utility model registration] Armature winding resistance Ra and commutator winding resistance Ri of a DC machine
Resistors R ₅ and R ₆ with the same resistance ratio Ra/Ri are connected in series and inserted in parallel to the armature, and the connection point between the armature winding and the commutator winding, and the resistance Equipment R ₅
The back electromotive force of the above DC machine is calculated from the potential difference _V between the connection point between R6 and _{R6 .} An electric dynamometer characterized by deriving torque.