System and method for estimating vehicle mass

• US 20030040861A1
• Filed: 08/23/2001
• Published: 02/27/2003
• Est. Priority Date: 08/23/2001
• Status: Active Grant

• Current Assignee: Cummins Incorporated
• Original Assignee: Cummins Incorporated
• Inventors: Tyler, Brian C., Kalill, John F., Bellinger, Steven M.
• Granted Patent: US 6,567,734 B2
• Time in Patent Office: Days
• US Class Current: 701/51
• CPC Class Codes: B60T 2250/02 Vehicle mass
• CPC Class Codes: F16H 59/52 dependent on the weight of the machine, e.g. change in weight resulting from passengers boarding a bus
• CPC Class Codes: G01G 19/086 wherein the vehicle mass is dynamically estimated

Abstract

A system for estimating vehicle mass includes a control circuit determining an instantaneous vehicle acceleration signal (VA) and an instantaneous vehicle drive force (F_DW). As long as a number of preconditions are met, such as vehicle speed within speed range, fueling command above a fueling threshold, gear ratio within a predefined range and VA above an acceleration threshold, the control circuit computes a number of instantaneous vehicle mass estimates (VM) as a function of the VA and F_DW values. When any one of the preconditions is no longer met, the control circuit computes a vehicle speed change during the next gear shift and disregards the number of vehicle mass estimates if this vehicle speed change is outside predefined boundaries. Otherwise, the control computer processes the number of vehicle mass estimates to form an updated vehicle mass estimate.

Claims

1. A system for estimating vehicle mass comprising:

a speed sensor producing a vehicle speed signal indicative of road speed of a vehicle carrying an internal combustion engine having a transmission coupled thereto;

means for determining a gear ratio of said transmission; and

a control circuit determining a vehicle driving force, computing a vehicle acceleration as a function of said vehicle speed signal and estimating a mass of said vehicle as a function of said vehicle driving force and said vehicle acceleration only if said gear ratio is between predefined high and low gear ratio values.

2. The system of claim 1 wherein said transmission includes a number of selectable gear ratios, said predefined high gear ratio corresponding to a numerically low transmission gear and said predefined low gear ratio corresponding to a numerically higher transmission gear.

3. The system of claim 1 wherein said control circuit is operable to determine said vehicle driving force, compute said vehicle acceleration value and estimate said mass of said vehicle further conditioned upon said vehicle speed signal being between a first low road speed and a second higher road speed.

4. The system of claim 1 further including a fuel system responsive to a fueling signal to supply fuel to said engine;

wherein said control circuit is operable to produce said fueling signal based on a fuel command value;

and wherein said control circuit is operable to determine said vehicle driving force, compute said vehicle acceleration value and estimate said mass of said vehicle further conditioned upon said fueling command value being above a fueling command threshold.

5. The system of claim 1 wherein said control circuit is operable to determine said vehicle driving force and estimate said mass of said vehicle further conditioned upon said vehicle acceleration value being above a vehicle acceleration threshold.

6. The system of claim 1 wherein said control circuit is a control computer operable to control and manage overall operation of said engine.

7. The system of claim 1 wherein said control circuit is a control computer associated with said transmission and operable to control and manage overall operation of said transmission.

8. The system of claim 1 wherein said control circuit is an auxiliary computer operable to control a vehicular feature other than overall operation of said engine and overall operation of said transmission.

9. The system of claim 1 wherein said control circuit is a first control computer operable to control a first apparatus carried by said vehicle;

and wherein said system further includes;

a second control computer operable to control a second apparatus carried by said vehicle, said second apparatus different that said first apparatus; and

a communications path disposed between said first and second apparatuses, said first and second apparatuses configured to communicate information therebetween via said communications path, said information including information relating to said mass of said vehicle.

10. A method of estimating vehicle mass comprising:

determining a road speed of a vehicle carrying an internal combustion engine coupled to a transmission;

determining a gear ratio of said transmission;

determining a vehicle driving force;

computing a vehicle acceleration value as a function of said road speed; and

estimating a mass of said vehicle as a function of said vehicle driving force and said vehicle acceleration value only if said gear ratio is between first and second predefined gear ratio values.

11. The method of claim 10 wherein the estimating step is further conditioned upon said road speed being between first and second predefined road speed values.

12. The method of claim 11 wherein the estimating step is further conditioned upon an engine fueling command being above a fueling command threshold.

13. The method of claim 10 wherein the estimating step is further conditioned upon said vehicle acceleration value being above a vehicle acceleration threshold.

14. A system for estimating vehicle mass comprising:

a first sensor producing a vehicle speed signal indicative of road speed of a vehicle carrying an internal combustion engine;

a second sensor producing an engine speed signal indicative of rotational speed of said engine;

a fuel system responsive to a fueling signal to supply fuel to said engine; and

a control circuit producing said fueling signal and computing an engine driving force as a function thereof, said control circuit responsive to said engine speed signal to determine a first resistance force associated with at least one accessory driven by said engine and to compute a net driving force as a function of said engine driving force and said first resistance force, said control circuit determining a vehicle acceleration value as a function of said vehicle speed signal and estimating a mass of said vehicle as a function of said vehicle acceleration value and said net driving force.

15. The system of claim 14 wherein said control circuit is responsive to said vehicle speed signal and an established vehicle mass value to determine a second resistance force corresponding to a force required to overcome a rolling resistance of at least one wheel driven by said engine, said control circuit computing said net driving force further as a function of said second resistance force.

16. The system of claim 15 wherein said control circuit is responsive to said vehicle speed signal to determine a third resistance force corresponding to a force required to overcome a rotational resistance of a drivetrain driven by said engine, said control circuit computing said net driving force further as a function of said third resistance force.

17. The system of claim 16 wherein said control circuit is responsive to said vehicle speed signal to determine a fourth resistance force corresponding to a force required to overcome an aerodynamic resistance acting upon said vehicle, said control circuit computing said net driving force further as a function of said fourth resistance force.

18. The system of claim 17 wherein said control circuit is operable to compute said net driving force as a difference between said engine driving force and a sum of said first, second, third and fourth resistance forces.

19. The system of claim 14 wherein said control circuit is a control computer operable to control and manage overall operation of said engine.

20. The system of claim 14 further including a transmission coupled to said engine;

and wherein said control circuit is a control computer associated with said transmission and operable to control and manage overall operation of said transmission.

21. The system of claim 14 wherein said control circuit is an auxiliary computer operable to control a vehicular feature other than overall operation of said engine.

22. The system of claim 14 wherein said control circuit is a first control computer operable to control a first apparatus carried by said vehicle;

and wherein said system further includes;

a second control computer operable to control a second apparatus carried by said vehicle, said second apparatus different that said first apparatus; and

a communications path disposed between said first and second apparatuses, said first and second apparatuses configured to communicate information therebetween via said communications path, said information including information relating to said mass of said vehicle.

23. A method of estimating vehicle mass comprising:

determining a road speed of a vehicle carrying an internal combustion engine;

determining a rotational speed of said engine;

computing a vehicle acceleration value as a function of said road speed;

determining an engine driving force;

determining a first resistance force as a function of said rotational speed, said first resistance force corresponding to a force required to overcome a load resistance of at least one accessory driven by said engine;

computing a net driving force as a function of said engine driving force and said first resistance force; and

estimating a mass of said vehicle as a function of said vehicle acceleration value and said net driving force.

24. The method of claim 23 further including the step of determining a second resistance force as a function of said road speed and of an established vehicle mass value, said second resistance force corresponding to a force required to overcome a rolling resistance of at least one wheel driven by said engine;

wherein the step of computing said net driving force includes computing said net driving force as a function of said second resistance force.

25. The method of claim 24 further including the step of determining a third resistance force as a function of said road speed, said third resistance force corresponding to a force required to overcome a rotational resistance of a drivetrain driven by said engine;

wherein the step of computing said net driving force includes computing said net driving force as a function of said third resistance force.

26. The method of claim 25 further including the step of determining a fourth resistance force as a function of said road speed, said fourth resistance force corresponding to a force required to overcome an aerodynamic force acting upon said vehicle;

wherein the step of computing said net driving force includes computing said net driving force as a function of said fourth resistance force.

27. The method of claim 26 wherein the step of computing said net driving force includes computing said net driving force as a difference between said engine driving force and a sum of said first, second, third and fourth resistance forces.

28. A system for estimating vehicle mass comprising:

a speed sensor producing a vehicle speed signal indicative of road speed of a vehicle carrying an internal combustion engine; and

a control circuit responsive to said vehicle speed signal to compute a vehicle acceleration value, said control circuit responsive to said vehicle acceleration value exceeding an acceleration threshold to execute a data collection sequence by periodically computing instantaneous vehicle mass values as functions of instantaneous vehicle driving force and vehicle acceleration value pairs, and to said vehicle acceleration value dropping below said acceleration threshold to terminate said data collection sequence, said control circuit estimating a vehicle mass value as a function of only instantaneous vehicle mass values computed near termination of said data collection sequence.

29. The system of claim 28 wherein said control circuit is configured such that execution of said data collection sequence is further conditioned upon said vehicle speed signal being between a first road speed value and a second higher road speed value.

30. The system of claim 29 wherein said control circuit is configured to terminate said data collection sequence if said vehicle speed signal drops below said first road speed value or exceeds said second higher road speed value.

31. The system of claim 28 further including means for determining a current gear ratio of a transmission coupled to said engine;

wherein said control circuit is configured such that execution of said data collection sequence is further conditioned upon said current gear ratio being between a first gear ratio value and a second higher gear ratio value.

32. The system of claim 31 wherein said control circuit is configured to terminate said data collection sequence if said current gear ratio indicates an out-of-gear condition.

33. The system of claim 28 further including a fuel system responsive to a fueling signal to supply fuel to said engine;

wherein said control circuit is configured such that execution of said data collection sequence is further conditioned upon a fueling command corresponding to said fueling signal being greater than a fueling command threshold.

34. The system of claim 33 wherein said control circuit is configured to terminate said data collection sequence if said fueling command drops below said fueling command threshold.

35. The system of claim 28 wherein said control circuit is a control computer operable to control and manage overall operation of said engine.

36. The system of claim 28 further including a transmission coupled to said engine;

and wherein said control circuit is a control computer associated with said transmission and operable to control and manage overall operation of said transmission.

37. The system of claim 28 wherein said control circuit is an auxiliary computer operable to control a vehicular feature other than overall operation of said engine.

38. The system of claim 28 wherein said control circuit is a first control computer operable to control a first apparatus carried by said vehicle;

and wherein said system further includes;

a second control computer operable to control a second apparatus carried by said vehicle, said second apparatus different that said first apparatus; and

a communications path disposed between said first and second apparatuses, said first and second apparatuses configured to communicate information therebetween via said communications path, said information including information relating to said mass of said vehicle.

39. A method of estimating vehicle mass comprising:

determining a road speed of a vehicle carrying an internal combustion engine;

computing a vehicle acceleration value as a function of said road speed;

executing a data collection sequence by periodically computing instantaneous vehicle mass values as functions of instantaneous vehicle driving force and vehicle acceleration pairs if said vehicle acceleration value exceeds a vehicle acceleration threshold;

terminating said data collection sequence if said vehicle acceleration value drops below said vehicle acceleration threshold; and

estimating a vehicle mass value as a function of only a subset of said instantaneous vehicle mass values computed near termination of said data collection sequence.

40. The method of claim 39 wherein the executing step is further conditioned upon said road speed being between a first road speed value and a second greater road speed value.

41. The method of claim 40 wherein the terminating step includes terminating said data collection sequence if said road speed value drops below said first road speed value or exceeds said second greater road speed value.

42. The method of claim 39 further including the step of determining a current gear ratio of a transmission coupled to said engine;

wherein the executing step is further conditioned upon said current gear ratio being between a first gear ratio value and a second greater gear ratio value.

43. The method of claim 42 wherein the terminating step includes terminating said data collection sequence if said current gear ratio indicates an out-of-gear condition.

44. The method of claim 39 further including the step of producing a fueling command for supplying a corresponding amount of fuel to said engine;

wherein the executing step is further conditioned upon said fueling command exceeding a fueling command threshold.

45. The method of claim 44 wherein the terminating step further includes terminating said data collection sequence if said fueling command falls below said fueling command threshold.

46. A system for estimating vehicle mass comprising:

a sensor producing a vehicle speed signal indicative of road speed of a vehicle carrying an internal combustion engine having a transmission coupled thereto; and

a control circuit determining a vehicle driving force, computing a vehicle acceleration as a function of said vehicle speed signal and computing an instantaneous vehicle mass value as a function of said vehicle drive force and said vehicle acceleration, said control circuit monitoring said vehicle speed signal and said transmission and estimating a vehicle mass value as a function of said instantaneous vehicle mass value only if said road speed changes less than a road speed change amount during a subsequent transmission gear shift.

47. The system of claim 46 wherein said control circuit is operable to determine whether said road speed changes less than said road speed change amount by computing a difference in said road speed during said gear shift and comparing said difference to upper and lower difference limits, said road speed changing less than said road speed change amount if said difference is between said upper and lower difference limits.

48. The system of claim 47 wherein said control circuit is configured to disregard said instantaneous vehicle mass value if said difference exceeds said upper difference value or falls below said lower difference value.

49. The system of claim 48 further including means for determining a currently engaged gear ratio of said transmission;

and wherein said control circuit is operable to monitor said currently engaged gear ratio and compute said difference in road speed when said currently engaged gear ratio indicates an out-of-gear condition pursuant to said gear shift.

50. The system of claim 49 wherein said control circuit is configured to determine a first road speed value upon detection of said out-of-gear condition, and to determine a second road speed value upon detection of a first to occur of a confirmation of engagement of a next transmission gear and an expiration of a predefined time interval since determining said first road speed value, said control circuit computing said difference in road speed as a difference between said first and second road speed values.

51. The system of claim 46 further including a memory having said road speed change amount stored therein.

52. The system of claim 46 wherein said control circuit is configured to determine said road speed change amount as a function of said vehicle acceleration prior to said gear shift.

53. The system of claim 46 wherein said control circuit is a control computer operable to control and manage overall operation of said engine.

54. The system of claim 46 further including a transmission coupled to said engine;

and wherein said control circuit is a control computer associated with said transmission and operable to control and manage overall operation of said transmission.

55. The system of claim 46 wherein said control circuit is an auxiliary computer operable to control a vehicular feature other than overall operation of said engine.

56. The system of claim 46 wherein said control circuit is a first control computer operable to control a first apparatus carried by said vehicle;

and wherein said system further includes;

a second control computer operable to control a second apparatus carried by said vehicle, said second apparatus different that said first apparatus; and

a communications path disposed between said first and second apparatuses, said first and second apparatuses configured to communicate information therebetween via said communications path, said information including information relating to said mass of said vehicle.

57. A system for estimating vehicle mass comprising:

a sensor producing a vehicle speed signal indicative of road speed of a vehicle carrying an internal combustion engine having a transmission coupled thereto; and

a control circuit determining a vehicle driving force, computing a vehicle acceleration as a function of said vehicle speed signal and estimating a vehicle mass value as a function of said vehicle driving force and said vehicle acceleration, said control circuit monitoring said vehicle speed signal and said transmission and disregarding said vehicle mass value if said road speed changes more than a road speed change amount during a subsequent transmission gear shift.

58. The system of claim 57 wherein said control circuit is operable to determine whether said road speed changes less than said road speed change amount by computing a difference in said road speed during said gear shift and comparing said difference to upper and lower difference limits, said road speed changing more than said road speed change amount if said difference is above said upper difference limit or below said lower difference limit.

59. The system of claim 58 further including means for determining a currently engaged gear ratio of said transmission;

and wherein said control circuit is operable to monitor said currently engaged gear ratio and compute said difference in road speed when said currently engaged gear ratio indicates an out-of-gear condition pursuant to said gear shift.

60. The system of claim 59 wherein said control circuit is configured to determine a first road speed value upon detection of said out-of-gear condition, and to determine a second road speed value upon detection of a first to occur of a confirmation of engagement of a next transmission gear and an expiration of a predefined time interval since determining said first road speed value, said control circuit computing said difference in road speed as a difference between said first and second road speed values.

61. The system of claim 57 further including a memory having said road speed change amount stored therein.

62. The system of claim 57 wherein said control circuit is configured to determine said road speed change amount as a function of said vehicle acceleration prior to said gear shift.

63. The system of claim 57 wherein said control circuit is a control computer operable to control and manage overall operation of said engine.

64. The system of claim 57 further including a transmission coupled to said engine;

and wherein said control circuit is a control computer associated with said transmission and operable to control and manage overall operation of said transmission.

65. The system of claim 57 wherein said control circuit is an auxiliary computer operable to control a vehicular feature other than overall operation of said engine.

66. The system of claim 57 wherein said control circuit is a first control computer operable to control a first apparatus carried by said vehicle;

and wherein said system further includes;

a second control computer operable to control a second apparatus carried by said vehicle, said second apparatus different that said first apparatus; and

a communications path disposed between said first and second apparatuses, said first and second apparatuses configured to communicate information therebetween via said communications path, said information including information relating to said mass of said vehicle.

67. A method of estimating vehicle mass comprising:

sensing road speed of a vehicle carrying an internal combustion engine having a transmission coupled thereto;

determining a vehicle driving force;

computing a vehicle acceleration value as a function of said road speed;

computing an instantaneous vehicle mass value as a function of said vehicle driving force and said vehicle acceleration value;

monitoring said road speed during a gear shift of said transmission subsequent to computing said instantaneous vehicle mass value; and

estimating a vehicle mass value as a function of said instantaneous vehicle mass value if said road speed changes less than a road speed change amount during said gear shift.

68. The method of claim 67 wherein the step of estimating a vehicle mass value includes:

determining a first road speed value upon detection of an out-of-gear condition pursuant to said gear shift;

determining a second road speed value upon detection of a first to occur of a confirmation of engagement of a next gear of said transmission and expiration of a predefined time interval since determining said first road speed value;

computing a difference between said first and second road speed values; and

determining that said road speed changes less than said road speed change amount if said difference is above a first difference limit or below a second higher difference limit.

69. The method of claim 67 wherein the estimating step includes recalling said road speed change amount from a memory unit.

70. The method of claim 67 further including the step of determining said road speed change amount as a function of said vehicle acceleration prior to said gear shift.

71. A method of estimating vehicle mass comprising:

sensing road speed of a vehicle carrying an internal combustion engine having a transmission coupled thereto;

determining a vehicle driving force;

computing a vehicle acceleration value as a function of said road speed;

estimating a vehicle mass value as a function of said vehicle driving force and said vehicle acceleration value;

monitoring said road speed during a gear shift of said transmission subsequent to estimating said vehicle mass value; and

disregarding said vehicle mass value if said road speed changes more than a road speed change amount during said gear shift.

72. The method of claim 71 wherein the disregarding step includes:

determining a first road speed value upon detection of an out-of-gear condition pursuant to said gear shift;

determining a second road speed value upon detection of a first to occur of a confirmation of engagement of a next gear of said transmission and expiration of a predefined time interval since determining said first road speed value;

computing a difference between said first and second road speed values; and

determining that said road speed changes more than said road speed change amount if said difference is below a first difference limit or above a second higher difference limit.

73. The method of claim 71 wherein the estimating step includes recalling said road speed change amount from a memory unit.

74. The method of claim 71 further including the step of determining said road speed change amount as a function of said vehicle acceleration prior to said gear shift.

75. A system for estimating vehicle mass comprising:

a speed sensor producing a vehicle speed signal indicative of a road speed of a vehicle carrying an internal combustion engine; and

a control circuit determining a vehicle driving force, computing a vehicle acceleration as a function of said vehicle speed signal and estimating a vehicle mass value as a function of said vehicle driving force and said vehicle acceleration, said control circuit combining said vehicle mass value with an existing vehicle mass estimate if a difference therebetween is less than a difference value.

76. The system of claim 75 wherein said control circuit includes a memory having said existing vehicle mass estimate stored therein, said control circuit configured to combine said vehicle mass value with said existing vehicle mass estimate by incorporating said vehicle mass value into said existing vehicle mass estimate.

77. The system of claim 75 wherein said control circuit is configured to estimate a plurality of vehicle mass values as functions of corresponding vehicle driving force and vehicle acceleration values, said control computer replacing said existing vehicle mass estimate with an updated vehicle mass estimate if differences between a number of consecutive ones of said plurality of vehicle mass values and said existing vehicle mass estimate are greater than said difference value.

78. The system of claim 77 further including a memory unit, said updated vehicle mass estimate stored in said memory unit.

79. The system of claim 78 wherein said updated mass estimate corresponds to a first vehicle mass value if said number of consecutive ones of said plurality of vehicle mass values are less than said existing vehicle mass estimate.

80. The system of claim 79 wherein said updated mass estimate corresponds to a second vehicle mass value greater than said first vehicle mass value if said number of consecutive ones of said plurality of vehicle mass values are greater than said existing vehicle mass estimate.

81. The system of claim 77 wherein said control computer is operable to determine said updated vehicle mass estimate as a function of at least some of said number of consecutive ones of said plurality of vehicle mass values.

82. The system of claim 75 wherein said control circuit is a control computer operable to control and manage overall operation of said engine.

83. The system of claim 75 further including a transmission coupled to said engine;

and wherein said control circuit is a control computer associated with said transmission and operable to control and manage overall operation of said transmission.

84. The system of claim 75 wherein said control circuit is an auxiliary computer operable to control a vehicular feature other than overall operation of said engine.

85. The system of claim 75 wherein said control circuit is a first control computer operable to control a first apparatus carried by said vehicle;

and wherein said system further includes;

a second control computer operable to control a second apparatus carried by said vehicle, said second apparatus different that said first apparatus; and

a communications path disposed between said first and second apparatuses, said first and second apparatuses configured to communicate information therebetween via said communications path, said information including information relating to said mass of said vehicle.

86. A system for estimating vehicle mass comprising:

a speed sensor producing a vehicle speed signal indicative of a road speed of a vehicle carrying an internal combustion engine; and

a control circuit determining a plurality of vehicle driving force values, computing a corresponding plurality of vehicle acceleration values as a function of said vehicle speed signal and estimating a corresponding plurality of vehicle mass values as functions of said plurality of vehicle driving force and vehicle acceleration values, said control circuit establishing an updated vehicle mass estimate if differences between a consecutive number of said plurality of vehicle mass values and an existing vehicle mass estimate exceed a difference value.

87. The system of claim 86 further including a memory unit, said updated vehicle mass estimate stored in said memory unit.

88. The system of claim 87 wherein said updated mass estimate corresponds to a first vehicle mass value if said number of consecutive ones of said plurality of vehicle mass values are less than said existing vehicle mass estimate.

89. The system of claim 88 wherein said updated mass estimate corresponds to a second vehicle mass value greater than said first vehicle mass value if said number of consecutive ones of said plurality of vehicle mass values are greater than said existing vehicle mass estimate.

90. The system of claim 86 wherein said control computer is operable to determine said updated vehicle mass estimate as a function of at least some of said number of consecutive ones of said plurality of vehicle mass values.

91. The system of claim 86 wherein said control circuit is a control computer operable to control and manage overall operation of said engine.

92. The system of claim 86 further including a transmission coupled to said engine;

and wherein said control circuit is a control computer associated with said transmission and operable to control and manage overall operation of said transmission.

93. The system of claim 86 wherein said control circuit is an auxiliary computer operable to control a vehicular feature other than overall operation of said engine.

94. The system of claim 86 wherein said control circuit is a first control computer operable to control a first apparatus carried by said vehicle;

and wherein said system further includes;

a second control computer operable to control a second apparatus carried by said vehicle, said second apparatus different that said first apparatus; and

a communications path disposed between said first and second apparatuses, said first and second apparatuses configured to communicate information therebetween via said communications path, said information including information relating to said mass of said vehicle.

95. A method of estimating vehicle mass comprising:

sensing a plurality of road speed values of a vehicle carrying an internal combustion engine;

computing a corresponding plurality of vehicle acceleration values as functions of said plurality of road speed values;

determining a corresponding plurality of vehicle drive force values;

estimating a corresponding plurality of vehicle mass values each as a function of corresponding ones of said plurality of vehicle acceleration and vehicle drive force values;

comparing said plurality of vehicle mass values with an existing vehicle mass estimate; and

combining said plurality of vehicle mass values with said existing vehicle mass estimate if differences between said plurality of vehicle mass values and said existing vehicle mass estimate are less than a difference value.

96. A method of estimating vehicle mass comprising:

sensing a plurality of road speed values of a vehicle carrying an internal combustion engine;

computing a corresponding plurality of vehicle acceleration values as functions of said plurality of road speed values;

determining a corresponding plurality of vehicle drive force values;

estimating a corresponding plurality of vehicle mass values each as a function of corresponding ones of said plurality of vehicle acceleration and vehicle drive force values;

comparing said plurality of vehicle mass values with an existing vehicle mass estimate; and

replacing said existing vehicle mass estimate with an updated vehicle mass estimate if differences between a number of said plurality of vehicle mass values and said existing vehicle mass estimate are greater than a difference value.