Engine speed governor having improved low idle speed stability

• US 6,202,629 B1
• Filed: 06/01/1999
• Issued: 03/20/2001
• Est. Priority Date: 06/01/1999
• Status: Expired due to Term

• Current Assignee: Cummins Incorporated
• Original Assignee: Cummins Incorporated
• Inventors: Sisson, Albert E., Zhu, G. George
• Primary Examiner(s): Argenbright, Terry M.
• Application Number:
  US09/323,462
• Time in Patent Office: 658 Days
• Field of Search: 123/339.19, 123/339.21, 123/352-358, 701/104
• US Class Current: 123/339.21
• CPC Class Codes: F02D 2041/1409 using at least a proportional, integral or derivative controller
• CPC Class Codes: F02D 2041/143 the control loop including a non-linear model or compensator
• CPC Class Codes: F02D 2041/1432 the system including a filter, e.g. a low pass or high pass filter
• CPC Class Codes: F02D 31/007 controlling fuel supply
• CPC Class Codes: F02D 41/0097 using means for generating speed signals

Abstract

A system and method for controlling the speed of an engine, or a speed governor, receives an error signal indicative of the difference between the actual engine speed and a commanded engine speed. This error signal is passed through a linear controller that determines a fuel flow rate in units of volume per unit time. The fuel flow rate is a substantially linear function of engine speed, and more specifically engine speed error. The output of the linear controller is fed to a non-linear compensator that determines a fueling command signal as a non-linear function of actual engine speed and fuel flow rate. The speed governor can accurately control engine speeds at low idle conditions. In one embodiment, the non-linear compensator utilizes a three-dimensional table of fueling command values as a function of fuel flow rate and engine speed. In another embodiment, the compensator applies a transfer function utilizing low and high calibration speed values enveloping a low engine speed. In another feature of the invention, a speed sensing system applies a zero order sample and hold to a sensor pulse train to generate a preliminary speed signal. This preliminary speed signal is fed to a software-based first order sample and hold component that calculates an integrated error value, leading to a speed signal value that is substantially free from frequency aliasing.

Claims

1. A method for controlling the speed of an internal combustion engine having an engine speed sensor for generating an engine speed signal indicative of the actual engine speed and a fuel system responsive to a fuel control signal to fuel the engine, the method comprising the steps of:

generating a reference signal indicative of a reference engine speed;

comparing the engine speed signal to the reference signal to yield an error signal;

obtaining a fueling flow rate signal as a function of the error signal, the magnitude of the flow rate signal being indicative of a volume of fuel per unit time; and

generating a fuel control signal as a function of the fueling flow rate signal and the engine speed signal.

2. The method for controlling engine speed according to claim 1, wherein said step of obtaining a fueling flow rate signal includes passing the error signal through a linear controller to apply a transfer function to the error signal.

3. The method for controlling engine speed according to claim 2, wherein the linear controller is a PID controller.

4. The method for controlling engine speed according to claim 1, wherein said step of generating a fuel control signal includes providing the flow rate signal and the engine speed signal to a non-linear compensator.

5. The method for controlling engine speed according to claim 4, wherein the non-linear compensator is operable to divide the flow rate signal by the engine speed signal.

6. The method for controlling engine speed according to claim 5, wherein the non-linear compensator is operable to apply a predetermined gain to the flow rate signal.

7. The method for controlling engine speed according to claim 5;

wherein said step of generating a fuel control signal includes replacing the engine speed signal with a first threshold speed signal if the engine speed signal is less than the first threshold speed signal.

8. The method for controlling engine speed according to claim 7, wherein said step of generating a fuel control signal includes replacing the engine speed signal with a second threshold speed signal if the engine speed signal is greater than the second threshold speed signal.

9. The method for controlling engine speed according to claim 8, wherein said step of generating a fuel control signal includes replacing the engine speed signal with a first threshold speed signal if the engine speed signal is less than the threshold speed signal.

10. The method for controlling engine speed according to claim 9, wherein the first threshold speed signal and the second threshold speed signal are calibrated to envelope a low idle speed for the engine.

11. A system for controlling the speed of an internal combustion engine having an engine speed sensor for sensing actual engine speed and a fuel system having a flow control valve responsive to a fuel control signal to supply a quantity of fuel to the engine;

the system comprising;

means for generating an error signal as a function of the difference between the actual engine speed and a reference speed;

a linear controller operable to generate a fuel flow signal in response to the error signal, said fuel flow signal indicative of a fuel volume per unit time; and

means for converting said fuel flow signal to a fuel control signal as a function of the actual engine speed, wherein said fuel control signal is indicative of a volume of fuel per actuation of the flow control valve of the fuel system.

12. The system for controlling the speed of an engine according to claim 11, wherein said linear controller is a PID controller.

13. The system for controlling the speed of an engine according to claim 11, wherein said means for converting includes a non-linear compensator receiving said fuel flow signal and the engine speed as inputs.

14. The system for controlling the speed of an engine according to claim 13, wherein said linear controller includes software operable to apply a transfer function C_n(N) to said fuel control signal, said transfer function being of the form;

$C_n<br><br>\left(N\right)=\frac{1000·<br><br>G}{3·<br><br>\min <br><br>〈<br><br>\max <br><br>\left(N_{\mathrm{MIN}},N\right),N_{\mathrm{MAX}}〉<br><br>},$

where G is a predetermined gain value, N is the actual engine speed, and N_MIN and N_MAX are calibration speed values.

15. The system for controlling the speed of an engine according to claim 14, wherein said calibration speed values envelope a low idle speed for the engine.

16. The system for controlling the speed of an engine according to claim 11, wherein said means for converting includes:

a three-dimensional table maintained in a memory, said table consisting of values for said fuel control signal as a function of said fuel control signal and the engine speed; and

a table look-up processor for extracting a fuel control signal value based on said inputs to said means for converting.

17. A system for controlling the speed of an internal combustion engine having an engine speed sensor for generating a signal indicative of the actual engine speed and a fuel system with a flow control valve responsive to a fuel control signal to supply a quantity of fuel to the engine, the system comprising:

means for generating an error signal as a function of the difference between the actual engine speed and a reference speed;

a linear controller receiving said error signal as an input and operable to generate a fuel flow signal as a substantially linear function of said error signal, said fuel flow signal indicative of a fuel volume per unit time; and

a non-linear compensator receiving said fuel flow signal and said actual engine speed signal as inputs and operable to generate a fuel control signal as a function of said fuel flow signal and the actual engine speed.