Method of adjusting an estimated value of the height of the gravity center of a vehicle

Abstract

A method for adjusting an estimated height of the center of gravity (HCOG) value of a vehicle includes concomitant calculations, based on parameters dependent on the HCOG value and parameters independent from the HCOG value. The method further comprises the adjustment of a parameter related to the HCOG value.

Claims

1. A method for adjusting an estimated HCOG value of a vehicle V, comprising a front axle and a rear axle, said method comprising the steps of: a) determining the slippage rate (RF) for the wheels of the front axle and the slippage rate (RR) for the wheels of the rear axle during a braking period according to the general formulae: $\begin{array}{cc}RF=\frac{\mathrm{VS}-\mathrm{WSF}}{\mathrm{VS}}*100& \left(i\right)\\ RR=\frac{\mathrm{VS}-\mathrm{WSR}}{\mathrm{VS}}*100& \left(\mathrm{ii}\right)\end{array}$ wherein (VS) denotes the linear speed of the vehicle (V), (WSF) denotes the linear speed of the front wheel, (WSR) denotes the linear speed of the rear wheel, b) deducing from the slippage rate (RF) and (RR) determined in step a), the reference value (Nref) corresponding to the difference between the normal force (NF) applied to the wheels of said front axle and the normal force (NR) applied to the wheels of said rear axle, using parameters independent from the HCOG value, by: b1) determining the adherence (AF) for the wheels of said front axle, and the adherence (AR) for the wheels of said rear axle, according to at least one pre-established curve linking the slippage rate of a wheel to its adherence, b2) determining the tangential forces (TF) for the wheels of said front axle and the tangential forces (TR) for the wheels of said rear axle according to the formulae: $\begin{array}{cc}\mathrm{TF}=\frac{Q*\mathrm{KF}}{\mathrm{Wrad}}& \left(\mathrm{iii}\right)\\ \mathrm{TR}=\frac{Q*\mathrm{KR}}{\mathrm{Wrad}}& \left(\mathrm{iv}\right)\end{array}$ wherein (Q) denotes the brake factor, (KF), and (KR) respectively denote the brake pressure at the front wheels and at the rear wheels, (Wrad) denotes the radius of the considered wheels (W), b3) deducing from the steps b1) and b2) the normal force (NF) for the wheels of said front axle, and the normal force (NR) for the wheels of said rear axle according to the formulae: $\begin{array}{cc}\mathrm{AF}=\frac{\mathrm{TF}}{\mathrm{NF}}& \left(v\right)\\ \mathrm{AR}=\frac{\mathrm{TR}}{\mathrm{NR}}& \left(\mathrm{vi}\right)\end{array}$ wherein (AF), (AR), denote the adherence determined in step b1), (TF), (TR) denote the tangential forces determined in step b2), and (NF), (NR), respectively denote the normal forces at the front wheels and at the rear wheels, c) determining the difference (N) between the normal forces applied to the wheels of the front axle and the normal forces applied to the wheels of the rear axle, according to formula: $\begin{array}{cc}N=\frac{B*\mathrm{YG}}{D}& \left(\mathrm{vii}\right)\end{array}$ wherein (YG) is a variable parameter related to the height of the gravity center of the vehicle, (D) is the distance separating the front axle and the rear axle, and wherein (B) denotes the global braking torque applied to the wheels of the vehicle and is defined by formula (5): $\begin{array}{cc}B=Q\left(\mathrm{KF}+\mathrm{KR}\right)& \left(\mathrm{viii}\right)\end{array}$ d) comparing (N) determined in step c) with (Nref) determined in step b), e) adjusting the variable parameter (YG), when necessary, in such a way the difference between (N) and (Nref) is below 10%, and f) adjusting the HCOG value according to (YG) determined in step e), wherein a computing unit provides instructions to a dynamic control system to increase or decrease the HCOG value by a certain amount.

2. The method according to claim 1, wherein the slippage rates (RF) and (RR) are determined by the means of sensors.

3. A system for adjusting the height of the gravity center of a vehicle comprising a front axle and a rear axle, said system comprising a computing unit (CE), wherein that said computing unit (CE) receives data from one or more sensors (SE) of the vehicle, and a Read Only Memory (ME), wherein said computing unit (CE) is configured to: a) determine the slippage rate (RF) for the wheels of the front axle and the slippage rate (RR) for the wheels of the rear axle during a braking period according to the general formulae: $\begin{array}{cc}\mathrm{RF}=\frac{VS-\mathrm{WSF}}{\mathrm{VS}}*100& \left(i\right)\\ \mathrm{RR}=\frac{VS-WSR}{VS}*100& \left(\mathrm{ii}\right)\end{array}$ wherein (VS) denotes the linear speed of the vehicle (V), (WSF) denotes the linear speed of the front wheel, (WSR) denotes the linear speed of the rear wheel, b) deduce from the slippage rate (RF) and (RR) determined in step a), the reference value (Nref) corresponding to the difference between the normal force (NF) applied to the wheels of said front axle and the normal force (NR) applied to the wheels of said rear axle, using parameters independent from the HCOG value, by: b1) determining the adherence (AF) for the wheels of said front axle, and the adherence (AR) for the wheels of said rear axle, according to at least one pre-established curve linking the slippage rate of a wheel to its adherence, b2) determining the tangential forces (TF) for the wheels of said front axle and the tangential forces (TR) for the wheels of said rear axle according to the formulae: $\begin{array}{cc}\mathrm{TF}=\frac{Q*\mathrm{KF}}{Wrad}& \left(\mathrm{iii}\right)\\ \mathrm{TR}=\frac{Q*KR}{Wrad}& \left(\mathrm{iv}\right)\end{array}$ wherein (Q) denotes the brake factor, (KF), and (KR) respectively denote the brake pressure at the front wheels and at the rear wheels, (Wrad) denotes the radius of the considered wheels (W), b3) deducing from the steps b1) and b2) the normal force (NF) for the wheels of said front axle, and the normal force (NR) for the wheels of said rear axle according to the formulae: $\begin{array}{cc}\mathrm{AF}=\frac{\mathrm{TF}}{\mathrm{NF}}& \left(v\right)\\ \mathrm{AR}=\frac{TR}{NR}& \left(\mathrm{vi}\right)\end{array}$ wherein (AF), (AR), denote the adherence determined in step b1), (TF), (TR) denote the tangential forces determined in step b2), and (NF), (NR), respectively denote the normal forces at the front wheels and at the rear wheels, c) determine the difference (AN) between the normal forces applied to the wheels of the front axle and the normal forces applied to the wheels of the rear axle, according to formula: $\begin{array}{cc}N=\frac{B*YG}{D}& \left(\mathrm{vii}\right)\end{array}$ wherein (YG) is a variable parameter related to the height of the gravity center of the vehicle, (D) is the distance separating the front axle and the rear axle, and wherein (B) denotes the global braking torque applied to the wheels of the vehicle and is defined by formula: $\begin{array}{cc}B=Q\left(\mathrm{KF}+\mathrm{KR}\right)& \left(\mathrm{vii}\right)\end{array}$ d) compare (N) determined in step c) with (Nref) determined in step b), e) adjusting the variable parameter (YG), when necessary, in such a way the difference between (N) and (Nref) is below 10%, and f) adjust the HCOG value according to (YG) determined in step e), and wherein said computing unit (CE) provides instructions to a dynamic control system to increase or decrease the HCOG value by a certain amount.

4. A vehicle comprising a front axle and a rear axle and equipped with a system for adjusting the height of the gravity center of the vehicle, said system comprising a computing unit (CE), wherein that said computing unit (CE) receives data from one or more sensors (SE) of the vehicle, and a Read Only Memory (ME), wherein said computing unit (CE) is configured to: a) determine the slippage rate (RF) for the wheels of the front axle and the slippage rate (RR) for the wheels of the rear axle during a braking period according to the general formulae: $\begin{array}{cc}\mathrm{RF}=\frac{VS-\mathrm{WSF}}{VS}*100& \left(i\right)\\ \mathrm{RR}=\frac{VS-WSR}{VS}*100& \left(\mathrm{ii}\right)\end{array}$ wherein (VS) denotes the linear speed of the vehicle (V), (WSF) denotes the linear speed of the front wheel, (WSR) denotes the linear speed of the rear wheel, b) deduce from the slippage rate (RF) and (RR) determined in step a), the reference value (Nref) corresponding to the difference between the normal force (NF) applied to the wheels of said front axle and the normal force (NR) applied to the wheels of said rear axle, using parameters independent from the HCOG value, by: b1) determining the adherence (AF) for the wheels of said front axle, and the adherence (AR) for the wheels of said rear axle, according to at least one pre-established curve linking the slippage rate of a wheel to its adherence, b2) determining the tangential forces (TF) for the wheels of said front axle and the tangential forces (TR) for the wheels of said rear axle according to the formulae: $\begin{array}{cc}\mathrm{TF}=\frac{Q*\mathrm{KF}}{Wrad}& \left(\mathrm{iii}\right)\\ \mathrm{TR}=\frac{Q*KR}{Wrad}& \left(\mathrm{iv}\right)\end{array}$ wherein (Q) denotes the brake factor, (KF), and (KR) respectively denote the brake pressure at the front wheels and at the rear wheels, (Wrad) denotes the radius of the considered wheels (W), b3) deducing from the steps b1) and b2) the normal force (NF) for the wheels of said front axle, and the normal force (NR) for the wheels of said rear axle according to the formulae: $\begin{array}{cc}\mathrm{AF}=\frac{\mathrm{TF}}{\mathrm{NF}}& \left(v\right)\\ \mathrm{AR}=\frac{TR}{NR}& \left(\mathrm{vi}\right)\end{array}$ wherein (AF), (AR), denote the adherence determined in step b1), (TF), (TR) denote the tangential forces determined in step b2), and (NF), (NR), respectively denote the normal forces at the front wheels and at the rear wheels, c) determine the difference (N) between the normal forces applied to the wheels of the front axle and the normal forces applied to the wheels of the rear axle, according to formula: $N=\frac{B*YG}{D}$ wherein (YG) is a variable parameter related to the height of the gravity center of the vehicle, (D) is the distance separating the front axle and the rear axle, and wherein (B) denotes the global braking torque applied to the wheels of the vehicle and is defined by formula: $\begin{array}{cc}B=Q\left(\mathrm{KF}+\mathrm{KR}\right)& \left(\mathrm{viii}\right)\end{array}$ d) compare (N) determined in step c) with (Nref) determined in step b), e) adjust the variable parameter (YG), when necessary, in such a way the difference between (N) and (Nref) is below 10%, and f) adjust the HCOG value according to (YG) determined in step e), and wherein said computing unit (CE) provides instructions to a dynamic control system to increase or decrease the HCOG value by a certain amount.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 Distribution of the normal forces and tangential forces during the braking of a vehicle.

(2) FIG. 2 graphical representation of the method

(3) FIG. 3 Schematic representation of the system used to adjust the estimated HCOG value Detailed description

(4) In one step of the present method, during a braking period, the slippage rate R of a wheel W is determined according to the general Formula (1) below:

(5) $\begin{array}{cc}R=\frac{\mathrm{VS}-\mathrm{WS}}{\mathrm{VS}}*100& \left(1\right)\end{array}$
Wherein

(6) R denotes the slippage rate of a given wheel W, provided as a percentage,

(7) VS denotes the linear speed of the vehicle V, provided in meters per second,

(8) WS denotes the linear speed of the wheel W, also provided in meter per second,

(9) The linear speed WS of a wheel W is easily deduced from the rotational speed of the wheel W, knowing its radius. Thus, le linear speed WS of a wheel corresponds to the linear speed VS of the vehicle if no slippage occurs.

(10) Although the slippage of each wheel W is independently determined, an average slippage rate RF is determined for the front wheels, and an average slippage rate RR is determined for the rear wheels of the vehicle. In other words, the slippage rate RF may be determined from the formula (1a),

(11) $\begin{array}{cc}\mathrm{RF}=\frac{\mathrm{VS}-\mathrm{WSF}}{\mathrm{VS}}*100& \left(1a\right)\end{array}$

(12) Wherein VS has the same meaning as above, and wherein the linear speed WSF for the front wheels is considered, while the slippage rate RR for the rear wheels is determined according to formula (1b):

(13) $\begin{array}{cc}\mathrm{RR}=\frac{\mathrm{VS}-\mathrm{WSR}}{\mathrm{VS}}*100& \left(1b\right)\end{array}$

(14) Wherein VS has the same meaning as above, and wherein the linear speed WSR for the rear wheels is considered.

(15) The front wheels preferably denote the wheels of one front axle, and the rear wheels preferably denote the wheels of one rear axle, either twined or single. In case the vehicle comprises more than one front axle and/or more than one rear axle, an average slippage rate may be determined for each of the front axles, and each of the rear axles. Alternatively, the average slippage rate may be determined for all the front axles, and an average slippage rate may be determined for all the rear axles of the vehicle.

(16) A vehicle is usually characterized by a pre-established experimental curve which links the slippage R of the wheels to the adherence A. Thus, based on the characteristics of the vehicle, the adherence AF of the wheels of the front axle can be deduced from the slippage rate RF of the front wheels determined as above described. Similarly, the adherence AR of the wheels of the rear axle may be deduced from the slippage rate RR of the rear wheels.

(17) The adherence is commonly defined by the ratio of the tangential forces T to the normal forces N. Thus, the adherence of the wheels of a front axle AF is defined by the formula (2a), and the adherence AR of the wheels of a rear axle is defined by the formula (2b):

(18) $\begin{array}{cc}\mathrm{AF}=\frac{\mathrm{TF}}{\mathrm{NF}}& \left(2a\right)\\ \mathrm{AR}=\frac{\mathrm{TR}}{\mathrm{NR}}& \left(2b\right)\end{array}$
Wherein

(19) AF, AR, respectively denote the adherence of the wheels of a front axle and a rear axle,

(20) TF, TR respectively denote the tangential forces at the front wheels and at the rear wheels,

(21) NF, NR, respectively denote the normal forces at the front wheels and at the rear wheels.

(22) The tangential forces TF and TR are easily determined according to the formulae (3a) and (3b):

(23) $\begin{array}{cc}\mathrm{TF}=\frac{Q*\mathrm{KF}}{\mathrm{Wrad}}& \left(3a\right)\\ \mathrm{TR}=\frac{Q*\mathrm{KR}}{\mathrm{Wrad}}& \left(3b\right)\end{array}$
Wherein

(24) TF and TR have the same meaning as above,

(25) Q denotes the brake factor,

(26) KF, and KR respectively denote the brake pressure at the front wheels and at the rear wheels,

(27) Wrad denotes the radius of the wheel W.

(28) Wrad is usually the same for the front and the rear wheels. However, a specific radius may be considered for each wheel. The same applies for the brake factor Q.

(29) It appears that the tangential forces TF. TR, as determined in formulae (3a) and (3b), only relate to the vehicle characteristics. The brake factor is inherent to the braking system of the vehicle, and the wheel radius Wrad is determined by construction. The brake pressure (KF, KR) is measured by the corresponding brake sensors already present on the vehicle. Knowing the tangential forces (TF, TR) and the corresponding adherence (AF, AR) of the front and the rear wheels, the corresponding normal forces (NF, NR) are easily deduced from the formulae (2a) and (2b).

(30) The difference between the normal forces of the front wheels NF and the rear wheels NR, determined as above, during a braking period, provides a reference value Nref. More particularly:
Nref=NRNF
Wherein NR and NF are determined as above-described.

(31) Alternatively, the absolute value of the difference between NR and NF may be considered as a reference value.

(32) Simultaneously, the difference N between the normal forces at a front axle and the normal forces at a rear axle is determined according to the geometry of the vehicle according to the formula (4):

(33) $\begin{array}{cc}N=\frac{B*\mathrm{YG}}{D}& \left(4\right)\end{array}$
Wherein

(34) B denotes the global braking torque applied to the wheels of the vehicle during the braking period,

(35) YG is a variable parameter related to the height of the gravity center of the vehicle,

(36) D is the distance separating the front axle and the rear axle.

(37) The global braking torque B is determined by the brake sensors of the vehicle. The global braking torque B is defined by formula (5):
B=Q(KF+KR)(5)
Wherein B, Q, KF and KR have the same meaning as above.
The distance D is known from the vehicle characteristics.

(38) In such a way, the difference of the normal forces N only depends on the variable parameter YG.

(39) Since N and Nref are simultaneously determined during the same braking period, they can be compared to each other. The variable parameter YG is adjusted in such a way that N and Nref become identical or almost identical. In other words, the difference between N and Nref may be considered acceptable if it is below 10%, or below 5% or below 1%. More particularly, an updated variable parameter YG will be considered for adjusting the estimated HCOG value in the dynamic control system if NNref, or if N=Nref

(40) The optimization of the variable parameter YG may request several iterations, wherein N is compared to Nref at each iteration, until the values of N and Nref are sufficiently close to each other. The variable parameter YG may thus be increased or decreased by a predetermined value, like 1%, or 5% or 10%, at each iteration.

(41) Each iteration may correspond to separate activation of the brake pedal. However, the present method preferably allows fast iterations during a single braking action. It is thus possible to adapt the estimated HCOG value of the vehicle within a limited number of brake activations. Ideally, the estimated HCOG value can be adjusted as soon as the first braking action.

(42) The present invention further comprises a system E for estimating and adapting the estimated HCOG value of a vehicle according to its payload. Said system E collects data from one or more sensors SE of the vehicle, and in particular wheel rotation sensors and brake pressure sensors. The system E further collects data stored in a Read Only Memory ME and related to the geometry of the vehicle. In particular such data comprise the distance D separating a front and a rear axle, the weight of the vehicle or elements of the vehicle, and other dimensions related to the vehicle.

(43) The System E comprises a computing unit CE, able to compute the data received from sensors and from the Read Only Memory ME according to the method above described. The system E provides instructions to the dynamic control system to increase or decrease the HCOG value by a certain amount.

(44) The present invention is also directed to a vehicle equipped with a system E, or an equivalent system designed for computing the data according to the method above described.