Dual data rate traction control system for a four wheel drive electric vehicle

Patent metadata

Field	Value
Publication number	US-9469199-B1
Application number	US-201514723679-A
Country	US
Kind code	B1
Filing date	May 28, 2015
Priority date	May 28, 2015
Publication date	Oct 18, 2016
Grant date	Oct 18, 2016

Abstract

A traction control system is provided that is applicable to both two wheel drive and four wheel drive electric vehicles, and which is capable of handling both low frequency and high frequency control duties. The system uses proportional gains in order to minimize controller delays and insure a natural feeling traction control system.

First claim

What is claimed is:

1. A method of providing traction control in an electric vehicle, wherein the electric vehicle is comprised of a first motor coupled to a first axle via a first locking differential and a second motor coupled to a second axle via a second locking differential, the method comprising:
monitoring a plurality of wheel speed sensors corresponding to a plurality of vehicle wheels;
determining a maximum wheel speed corresponding to said plurality of vehicle wheels;
determining a minimum wheel speed corresponding to said plurality of vehicle wheels;
determining a first maximum motor speed and a first minimum motor speed corresponding to said first motor, wherein said first maximum motor speed and said first minimum motor speed are based on said maximum wheel speed and said minimum wheel speed and a first slip speed map;
determining a second maximum motor speed and a second minimum motor speed corresponding to said second motor, wherein said second maximum motor speed and said second minimum motor speed are based on said maximum wheel speed and said minimum wheel speed and a second slip speed map;
determining a torque distribution between said first axle and said second axle;
determining a modified first motor torque demand corresponding to said first motor, wherein said modified first motor torque demand is based on said first maximum motor speed, said first minimum motor speed, a first motor speed and said torque distribution; and
determining a modified second motor torque demand corresponding to said second motor, wherein said modified second motor torque demand is based on said second maximum motor speed, said second minimum motor speed, a second motor speed and said torque distribution.

2. The method of claim 1 , said step of determining said first maximum motor speed and said first minimum motor speed further comprising:
monitoring a first torque value corresponding to said first motor;
selecting a first synchronized wheel speed from said maximum and minimum wheel speeds, wherein said minimum wheel speed is selected as said first synchronized wheel speed if said first torque value for said first motor is positive, and wherein said maximum wheel speed is selected as said first synchronized wheel speed if said first torque value for said first motor is negative;
multiplying said first synchronized wheel speed by a first transmission ratio to yield a first synchronized motor speed, wherein said first transmission ratio corresponds to said first locking differential, and wherein said first synchronized motor speed is at a first sample frequency;
translating said first synchronized motor speed to a second synchronized motor speed, wherein said second synchronized motor speed is at a second sample frequency, and wherein said second sample frequency is higher than said first sample frequency; and
defining said first maximum motor speed and said first minimum motor speed from said second synchronized motor speed and said first slip speed map.

3. The method of claim 2 , further comprising defining said first transmission ratio when said first locking differential is locked.

4. The method of claim 2 , wherein said first sample frequency is approximately 100 Hz.

5. The method of claim 2 , wherein said second sample frequency is approximately 1000 Hz.

6. The method of claim 2 , said translating step further comprising interpolating said first synchronized motor speed to generate said second synchronized motor speed.

7. The method of claim 2 , further comprising defining said first slip speed map, wherein said first slip speed map defines a first maximum acceptable wheel slip.

8. The method of claim 2 , said step of determining said second maximum motor speed and said second minimum motor speed further comprising:
monitoring a second torque value corresponding to said second motor;
selecting a second synchronized wheel speed from second maximum and second minimum wheel speeds, wherein said second minimum wheel speed is selected as said second synchronized wheel speed if said second torque value for said second motor is positive, and wherein said second maximum wheel speed is selected as said second synchronized wheel speed if said second torque value for said second motor is negative;
multiplying said second synchronized wheel speed by a second transmission ratio to yield a third synchronized motor speed, wherein said second transmission ratio corresponds to said second locking differential, and wherein said third synchronized motor speed is at a third sample frequency;
translating said third synchronized motor speed to a fourth synchronized motor speed, wherein said fourth synchronized motor speed is at a fourth sample frequency, and wherein said fourth sample frequency is higher than said third sample frequency; and
defining said second maximum motor speed and said second minimum motor speed from said fourth synchronized motor speed and said second slip speed map.

9. The method of claim 8 , further comprising defining said second transmission ratio when said second locking differential is locked.

10. The method of claim 8 , wherein said third sample frequency is approximately 100 Hz.

11. The method of claim 8 , wherein said fourth sample frequency is approximately 1000 Hz.

12. The method of claim 8 , said translating step further comprising interpolating said third synchronized motor speed to generate said fourth synchronized motor speed.

13. The method of claim 8 , further comprising defining said second slip speed map, wherein said second slip speed map defines a second maximum acceptable wheel slip.

14. The method of claim 8 , wherein said first transmission ratio is equivalent to said second transmission ratio.

15. The method of claim 8 , wherein said first slip speed map is equivalent to said second slip speed map.

16. The method of claim 1 , said step of determining said torque distribution between said first axle and said second axle further comprising:
determining a torque request;
determining an initial first motor torque demand and an initial second motor torque demand based on said torque request and a predefined torque split map;
determining a slip ratio between said first axle and said second axle;
determining an optimized torque split from said slip ratio and a predefined torque split offset map; and
determining a current first motor torque demand and a current second motor torque demand based on said torque request and said optimized torque split.

17. The method of claim 1 , said step of determining said modified first motor torque demand further comprising:
inputting said first maximum motor speed, said first minimum motor speed, and said first motor speed corresponding to said first motor into a traction controller;
determining a first motor speed error from said first maximum motor speed and said first motor speed;
determining a second motor speed error from said first minimum motor speed and said first motor speed;
saturating said first motor speed error to obtain a first motor speed error correction value;
saturating said second motor speed error to obtain a second motor speed error correction value;
selecting a first particular motor speed error correction value from said first and second motor speed error correction values;
feeding said first particular motor speed error correction value to said traction controller;
creating a first torque correction command that brings said first particular motor speed error correction value to zero, wherein said step of creating said first torque correction command is performed

Assignees

• Atieva Inc

Inventors

• Gauthier Jean-Philippe

Classifications

• B60W30/18172

  Preventing, or responsive to skidding of wheels · CPC title

• Y02T10/644

  Cross-Sectional Technologies · mapped topic

• B60L3/104 Primary

  by indirect measurement of vehicle speed · CPC title

• B60L11/1803

  Operations & Transport · mapped topic

• Y02T10/7275

  Cross-Sectional Technologies · mapped topic