Motor temperature sensor system and method to determine motor performance

• US 6,903,525 B2
• Filed: 08/05/2003
• Issued: 06/07/2005
• Est. Priority Date: 08/05/2003
• Status: Expired due to Fees

• Current Assignee: Kendro Laboratory Products LP (Thermo Fisher Scientific Incorporated)
• Original Assignee: Kendro Laboratory Products LP (Thermo Fisher Scientific Incorporated)
• Inventors: Hall, Richard, Carson, David M.
• Primary Examiner(s): Martin, David
• Assistant Examiner(s): MILLER, PATRICK L
• Application Number:
  US10/633,533
• Publication Number:
  US 20050029975A1
• Time in Patent Office: 672 Days
• Field of Search: 318/431, 318/434, 318/708, 318/930, 318/432, 318/634, 318/641, 318/783, 318/47, 318 1- 73, 388/934, 310/315, 310/16, 310/68.C, 361/24, 361/25
• US Class Current: 318/432
• CPC Class Codes: G01K 13/08 in rotary movement
• CPC Class Codes: G01K 7/42 Circuits effecting compensation of thermal inertia; Circuits for predicting the stationary value of a temperature
• CPC Class Codes: H02K 11/25 Devices for sensing temperature, or actuated thereby
• CPC Class Codes: Y10S 388/934 Thermal condition

Abstract

A method and apparatus is herein disclosed for determining the motor performance of an electric motor through monitoring the temperature of rotor magnets. The temperature is determined by initially heating the rotor magnets to two known temperatures and subsequently recording the temperature at each known temperature. From the known and recorded temperatures, an offset, if any, is calculated. An actual temperature is then determined from the subsequent temperatures of the magnets and the offset. The actual temperature is then used as a basis to determine the motor performance.

Claims

1. A method for determining the output mechanical torque generated by an electric motor comprising:

sensing a local temperature inside the motor;

determining a temperature of at least one rotor magnet of the motor;

determining an offset between the local temperature at the location inside the motor and the temperature of the rotor magnet;

receiving a temperature signal;

using the determined offset between the local temperature at the location inside the motor and the temperature of the rotor magnets and the received temperature signal to calculate an actual temperature of the rotor magnets; and

calculating the output mechanical torque generated by the motor based upon the actual temperature.

2. The method of claim 1, wherein the receiving the temperature signal comprises receiving an analog signal.

3. The method of claim 1, wherein the receiving the temperature signal comprises receiving a digital signal.

4. The method of claim 1, wherein the step of determining the offset between the local temperature at the location inside the motor and the temperature of the rotor magnets comprises:

heating the rotor magnets to at least two different known temperatures;

sensing the corresponding local temperatures at the location inside the motor; and

using an interpolation algorithm to determine the offset between the local temperature at the location inside the motor and the temperature of the rotor magnets.

5. The method of claim 4, wherein the interpolation algorithm is based on a linear relationship.

6. The method of claim 5, wherein the step of calculating the output mechanical torque generated by the motor comprises:

calculating the percent decrease in the output mechanical torque generated by the motor Δ

τ

for the actual temperature of the rotor magnets, T_M according to

Δ

τ

=(T_M−

T_M1)·

(Δ

B_r),

and

wherein T_M is a current temperature of the rotor magnets and Δ

B_r is a decrease in a magnetic flux of a rotor magnet material; and

calculating an output mechanical torque generated by the motor for τ

for a calculated percent of motor torque remaining according to

τ

=[k<sub>t(T°

C.)</sub>I_S]·

τ

_remaining,

τ

_{r remaining} is the percent of motor torque remaining

k<sub>t(T°

C.)</sub> is a maximum torque constant of the motor, in/lbs-amp

T°

C. is a temperature in celsius degrees, and

I_S is a known input stator current.

7. The method of claim 6, wherein T°

C. is 20°

C.

8. The method of claim 1, wherein the step of determining the offset between the local temperature at the location inside the motor and the temperature of the rotor magnets comprises:

heating the rotor magnets to two known temperatures T_M1 and T_M2;

recording corresponding local temperatures at the T_S1 and T_S2 location inside the motor in response to the T_M1 and T_M2 temperatures, wherein T_S1 is the recorded temperature at the known temperature T_M1 and T_M2 is the recorded temperature at the known temperature T_M2; and

determining the actual temperature (T_M) of the rotor magnets according to

T_M=[(T_M2−

T_M1)/(T_S2−

T_S1)]·

T_S+T_M2−

[(T_M2−

T_M1)/(T_S2−

T_S1)]·

T_S2,

where T_S is a subsequently sensed local temperature inside the motor.