Power assist device, and vehicle equipped with said power assist device

Patent metadata

Field	Value
Publication number	US-10625818-B2
Application number	US-201615760355-A
Country	US
Kind code	B2
Filing date	Aug 23, 2016
Priority date	Sep 17, 2015
Publication date	Apr 21, 2020
Grant date	Apr 21, 2020

Abstract

A power assist device may include a motor, a motor driving circuit, sensors to output signals in accordance with a rotational speed of the wheel, a memory, and a signal processor. The memory stores information of a parameter defining a transfer function that interrelates a total torque to be input to the vehicle and a rotational speed of the wheel, and an inverse transfer function thereof. Based on the inverse transfer function, the signal processor determines an estimated value of total torque from a detected value of rotational speed of the wheel. Moreover, based on the transfer function, the signal processor updates at least a portion of the information of the parameter so that, for example, an error between a detected value of rotational speed of the wheel and an estimated value of rotational speed of the wheel as determined from the estimated value of total torque is reduced.

First claim

The invention claimed is:

1. A power assist device for a vehicle which includes a wheel and which is driven by a first force, the power assist device comprising:
a motor to generate a motor torque;
a motor driving circuit to supply an electric power to the motor;
a sensor to output a signal which is in accordance with a rotational speed of the wheel;
a memory storing information of a parameter defining a transfer function that interrelates a total torque to be input to the vehicle and a rotational speed of the wheel, and an inverse transfer function thereof; and
a signal processor connected to the memory and the motor driving circuit, wherein,
the signal processor is configured to:
(0) receive the signal which is output from the sensor, and determines a detected value of rotational speed of the wheel,
(1) read information of the parameter from the memory, and, based on the inverse transfer function defined by the parameter, determines an estimated value of total torque from the detected value of rotational speed of the wheel,
(2) acquire information representing an operating state of the motor, and, based on the information, determines an estimated value of a motor torque that is being generated by the motor,
(3) determine, as an estimated value of the first force, a value which is obtained by subtracting the estimated value of motor torque from the estimated value of total torque,
(4) determine a command value for the motor torque based on the estimated value of the first force, and inputs the command value for the motor torque to the motor driving circuit, and
(5) update at least a portion of the information of the parameter stored in the memory so that an error between the detected value of rotational speed of the wheel and an estimated value of rotational speed of the wheel that is determined from a given torque value based on the transfer function defined by the parameter is reduced.

2. The power assist device of claim 1 , wherein the given torque value is the estimated value of the total torque.

3. The power assist device of claim 1 , wherein the signal processor is configured to perform the process of (5) by using a sequential least squares algorithm.

4. The power assist device of claim 1 , wherein the transfer function defined by the parameter is a transfer function of a linear first order lag system.

5. The power assist device of claim 4 , wherein a time constant of the transfer function of the linear first order lag system is determined based on a moment of inertia and a viscous drag coefficient.

6. The power assist device of claim 1 , wherein the signal processor is configured to perform the process of (5) while substantially absent of the first torque.

7. The power assist device of claim 6 , wherein,
the vehicle comprises pedals, and is driven by the first torque which is input via the pedals;
the power assist device further comprises a pedal angle sensor to output an angle signal which is in accordance with angles of the pedals; and
the signal processor is configured to:
perform the process of (5) when the angle signal which is output from the pedal angle sensor indicates a top dead center angle or a bottom dead center angle of the pedals, or when the first force is not being generated on the basis of the angle signal which is output from the pedal angle sensor.

8. The power assist device of claim 6 , wherein,
the vehicle comprises a grip, and is driven by a second force which is input via the grip;
the power assist device further comprises a detector to detect whether the second force is being applied to the grip or not; and
the signal processor performs the process of (5) when the detector detects an absent of the second force.

9. The power assist device of claim 1 , further comprising an inclination angle sensor to output a signal which is in accordance with an acceleration or an angle of inclination of a road surface, wherein,
before the process of (3), the signal processor is configured to:
(6) determine an estimated value of angle of inclination of the road surface based on the signal which is output from the inclination angle sensor, and estimates a slope resistance torque from the estimated value of angle of inclination, and
(7) estimate an aerodynamic resistance torque which is proportional to a square of the detected value of rotational speed of the wheel, and,
in the process of (3), determines an estimated value of the first force based on a value which is obtained by subtracting the estimated value of the motor torque from the estimated value of the total torque and adding up the slope resistance torque and the aerodynamic resistance torque.

10. The power assist device of claim 9 , wherein,
the inclination angle sensor is an acceleration sensor; and
the signal processor is configured to perform the process of (6) by integrating a signal which is output from the acceleration sensor over a predetermined time slot.

11. The power assist device of claim 1 , further comprising a torque sensor to output a torque detection signal which is in accordance with the first force, wherein,
the signal processor is configured to
perform one of: a process of determining the command value for the motor torque based on the torque detection signal and inputting the command value for the motor torque to the motor driving circuit; and the processes from (0) to (4).

12. The power assist device of claim 11 , wherein the signal processor is configured to perform the processes from (0) to (4) when the torque detection signal is not available.

13. The power assist device of claim 12 , wherein the signal processor is configured to perform the processes from (0) to (4) in accordance with a previously determined time constraint.

14. The power assist device of claim 1 , wherein,
the motor driving circuit outputs a signal representing a magnitude of an electric current flowing through the motor; and
in the process of (2), the signal processor acquires a signal representing the magnitude of the electric current flowing through the motor as information representing the operating state of the motor.

15. The power assist device of claim 14 , wherein,
the sensor is a Hall sensor that outputs a signal representing a rotational speed of the motor which is in accordance with the rotational speed of the wheel; and
a plurality of said Hall sensors are provided.

16. The power assist device of claim 15 , wherein, in the process of (4), the signal processor inputs the command value for motor torque to the motor driving circuit as a PWM signal.

17. An electrically assisted vehicle comprising:
a wheel; and
the power assist device of claim 1 , wherein,
the motor of the power assist device is mechanically connected to the wheel; and
the wheel rotates with the first torque and the motor torque of the motor.

18. A signal processing module comprising:
a memory storing information of a parameter defining a transfer function that interrelates a total torque to be input to an electrically assisted vehicle which includes a motor and a wheel and a rotational speed of the wheel, and an inverse transfer function thereof; and
a signal processor connected to the memory, wherein,
when incorporated in the electrically assisted vehicle, the signal processor is connected to a sensor to output a signal which is in accordance with the rotational speed of the wheel and to a driving circuit for the motor, and is configured to:
(0) receive the signal which is output from the sensor, and determines a detected value of rotational speed of the whe

Assignees

• Nidec Corp

Inventors

• Kikkawa Jun

Classifications

• B60W2510/083

  Torque · CPC title

• B60W2520/28

  Wheel speed · CPC title

• B60W2530/16

  Driving resistance · CPC title

• B60W2050/0019

  Control system elements or transfer functions · CPC title

• B60W2300/36

  Cycles; Motorcycles; Scooters · CPC title