Method and system for boosting engine braking

Abstract

A method for boosting the engine brake of an engine for a vehicle, the method comprising: Determining the change in the kinetic energy of the vehicle over a period of time; Determining the energy output from a powertrain of the vehicle over the time period; Comparing the change in kinetic energy with the energy output; and increasing the vehicle's engine braking if the change in kinetic energy is greater than the energy output over the time period; and Determining the energy input to a braking system of the vehicle; and increasing the engine braking of the vehicle when the temperature of the braking system is greater than a predetermined temperature.

Description

[0001] This disclosure relates to a method and system for increasing engine braking of an engine for a vehicle, and more particularly, but not exclusively, to a method and system for increasing engine braking of an engine for a vehicle when the vehicle is determined to be traveling downhill. introduction

[0002] US 2014 / 0114553 A1 already discloses a method for operating a motor vehicle in different operating modes. US 2011 / 0125376 A1 relates to an automatic hill descent system. DE 10 2007 044 434 A1 discloses a method for controlling an automated multi-step transmission. DE 698 12 469 T2 discloses a lock-up clutch control for a hydrodynamic torque converter of an automatic transmission. DE 197 52 345 A1 relates to a method for limiting the operating temperature of motor vehicle brakes.

[0003] It is common for a vehicle driver to select a higher gear to optimize fuel economy. If the vehicle has an automatic transmission, a vehicle's control unit can be configured to select an appropriate gear based on vehicle speed and the driver's torque demand. The control unit typically uses an algorithm to optimize fuel economy, vehicle performance, or a combination of both.

[0004] During extended downhill driving, for example, on a mountain road, the driver's torque demand is typically very low. As a result, the automatic transmission control unit selects a high gear to optimize the vehicle's fuel consumption. However, the high gear selected by the control unit results in a low level of engine braking. The driver must therefore rely on the vehicle's brakes to slow the vehicle during the extended downhill drive.

[0005] Such use of the brakes can cause the brake pads to wear out more quickly, resulting in more frequent brake pad replacement. Furthermore, heavy use of the brakes during extended downhill riding can lead to a deterioration in braking performance. Brief description of the invention

[0006] According to one aspect of the present disclosure, a method is provided for boosting engine braking of an engine for a vehicle, the method comprising: determining the change in kinetic energy of the vehicle over a period of time; determining the energy output from a powertrain of the vehicle over the period of time; comparing the change in kinetic energy to the energy output; and boosting engine braking of the vehicle if the change in kinetic energy is greater than the energy output over the period of time.

[0007] In the context of the present disclosure, the term "engine braking" refers to when the deceleration forces in an engine are used to slow a vehicle, as opposed to using an additional external braking system, such as friction brakes. However, in the context of modern vehicles, the term "engine braking" may apply to any suitable braking action applied to the vehicle's powertrain, such as braking applied by an electric machine of a hybrid vehicle.

[0008] The method may include initiating, e.g., performing, a downshift of a transmission of the vehicle to augment engine braking, e.g., when the change in kinetic energy is greater than the energy dissipation over the time period. The transmission may be a manual transmission. The transmission may be an automatic transmission. The method may include causing the automatic transmission of the vehicle to downshift. The method may include providing an indication to the driver of the vehicle to initiate a transmission downshift. The method may include activating an electric machine coupled to a powertrain of the vehicle to augment engine braking.

[0009] The method may include determining the energy required to overcome the rolling resistance of the vehicle over the time period. The energy required to overcome the rolling resistance of the vehicle over the time period may be determined by integrating the power required to overcome the rolling resistance of the vehicle over the time period. The method may include comparing the energy output to the energy required to overcome the rolling resistance of the vehicle. The method may include boosting the engine brake of the vehicle when the change in kinetic energy plus the energy required to overcome the rolling resistance of the vehicle over the time period is greater than the energy output by a powertrain of the vehicle over the time period.

[0010] The method may include determining the energy required to overcome the vehicle's aerodynamic drag over the time period. The energy required to overcome the vehicle's aerodynamic drag over the time period may be determined by integrating the power required to overcome the vehicle's aerodynamic drag over the time period. The method may include comparing the energy output to the energy required to overcome the vehicle's aerodynamic drag over the time period. The method may include boosting the vehicle's engine braking if the change in kinetic energy over the time period is greater than the energy output from a powertrain of the vehicle less the energy required to overcome the vehicle's aerodynamic drag over the time period.

[0011] The method may include estimating the change in potential energy of the vehicle using at least one of the following steps: the determined change in kinetic energy of the vehicle over the time period; the determined energy output from a powertrain of the vehicle over the time period; the determined energy required to overcome rolling resistance of the vehicle over the time period; and the determined energy required to overcome aerodynamic drag of the vehicle over the time period.

[0012] The method may include determining the inclination of the vehicle using one or more sensors. The method may include determining the elevation of the vehicle using one or more sensors. The method may include determining the potential energy of the vehicle, for example, determining the change in potential energy of the vehicle over the time period. The method may include confirming that the vehicle is traveling downhill by comparing the estimated change in potential energy and the change in potential energy of the vehicle determined by the one or more sensors. The method may include preventing the transmission from downshifting in response to a lack of confirmation that the vehicle is traveling downhill.

[0013] The method may include determining the energy input to a braking system of the vehicle. The method may include increasing the level of engine braking, for example, only when the temperature of the braking system is greater than a predetermined temperature. The method may include preventing the increase of engine braking in response to one or more engine protection parameters.

[0014] The time period may be any suitable time period over which the above determinations / calculations can be performed by a controller of the vehicle. The time period may range from approximately 0.5 seconds to 10 seconds. The time period may be greater than approximately 60 seconds. For example, the method according to the present disclosure may be implemented when the vehicle is engaged in extended downhill operation, for example, when the vehicle is traveling down a mountain road.

[0015] The method may include determining an average kinetic energy of the vehicle over the time period. The method may include determining an average energy supplied to the vehicle's powertrain during the time period. The method may include comparing the average kinetic energy to the average energy supplied to the powertrain. The method may include boosting the vehicle's engine braking if the average kinetic energy of the vehicle is greater than the average energy supplied to the powertrain over the time period.

[0016] According to another aspect of the present invention, there is provided a system for augmenting engine braking of an engine for a vehicle, the system comprising a controller configured to: determine the change in kinetic energy of the vehicle over a period of time; determine the energy output from a powertrain of the vehicle over the period of time; compare the change in kinetic energy to the energy output; and cause an increase in the amount of engine braking when the change in kinetic energy is greater than the energy output over the period of time.

[0017] The disclosure also provides software, such as a computer program or computer program product, for performing any of the methods described herein, and a computer-readable medium having stored thereon a program for performing any of the methods described herein. A computer program embodying the disclosure may be stored on a computer-readable medium, or it could be in the form of a signal, such as a downloadable data signal provided from an Internet website, or it could be in some other form. Short description of the drawings

[0018] For a better understanding of the present disclosure and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Fig. 1 shows a graphical representation of the power output of a vehicle over time and a graphical representation of the kinetic energy of the vehicle over time; and Fig. 2 shows a method for boosting the engine brake. Detailed description

[0019] When a vehicle, such as a car, van, truck, or motorcycle, travels downhill, the power output from the vehicle's drivetrain is low because the vehicle's motion is assisted by gravity. As a result, there is a low torque demand on the engine, and a higher gear of the vehicle's transmission may be selected to improve fuel economy.

[0020] Fig. Figure 1 shows the power output of the vehicle's drivetrain over time. The power output may increase, decrease, or remain constant depending on the driving conditions and / or the torque requested by the driver. For example, when the vehicle is climbing an incline and / or when the vehicle is accelerating, the level of power output may increase if requested by the driver. When the vehicle begins to descend, the driver may decrease the level of requested torque, and as a result, the power output from the engine decreases. If the vehicle is equipped with an automatic transmission, control of the transmission may cause the transmission to upshift in an attempt to improve fuel economy.Under such circumstances, the level of engine braking is reduced due to the longer gear ratio, and the driver may use the vehicle's braking system more frequently to slow the vehicle while descending a hill. Increased use of the braking system during downhill driving can lead to brake overheating and deterioration of braking performance.

[0021] The present disclosure provides a method 100 for increasing the engine braking of the vehicle's engine, for example, during an extended period of downhill driving. Increasing the level of engine braking allows for a reduction in the use of the vehicle's braking system, which may help maintain the efficiency of the braking system, for example, by reducing the amount of heat generated by the braking system during downhill driving. Further, the present disclosure provides a method 100 for determining whether the vehicle is traveling downhill without using a system configured to determine the position, elevation, and / or inclination of the vehicle. Instead, the method 100 may determine whether the vehicle is traveling downhill based solely on the vehicle's operating parameters.

[0022] The term "extended downhill descent" as used in the present disclosure refers to a period of downhill driving of sufficient length and / or inclination angle that the performance of the braking system may be adversely affected due to the extent of braking system use. For example, extended downhill driving conditions may be experienced while driving downhill on a mountain road. During a downhill descent, a transmission upshift may be performed upon detecting a reduction in engine power output. The downhill driving period may range from approximately 0.5 to 10 seconds or may be substantially longer, depending on the length of the downhill portion of the road. However, the method may be performed in any suitable downhill driving condition and / or over any suitable period of time.For example, the time period may be limited only by the time required for a vehicle controller to process data relating to the operating parameters of the engine and / or the vehicle.

[0023] The method 100 includes determining the kinetic energy KE of the vehicle. In particular, the method includes a step 110 for determining the change in the kinetic energy ΔKE of the vehicle over a time period T, for example, a time period in the range of approximately 0.5 to 10 seconds. The kinetic energy of the vehicle can be determined using Equation 1 below, where m denotes the mass of the vehicle and v denotes the speed of the vehicle. The change in the kinetic energy of the vehicle can be determined by calculating the kinetic energy of the vehicle over the time period T, for example, using Equation 2, which shows that the change in the kinetic energy of the vehicle is the difference between the kinetic energy KE t1 of the vehicle at a first time t1 and the kinetic energy KE t2 of the vehicle at a second time t2. KE=12mv2 ΔKE(dt)=KEt2−KEt1

[0024] The method 100 includes determining the energy output from a powertrain of the vehicle over the time period T. The energy output from the powertrain may be determined by integrating the power output from the powertrain over the time period T. The power output of the powertrain may be calculated using direct measurements of the operating parameters of the vehicle's powertrain, for example, measuring the torque and speed of an engine output shaft. Additionally or alternatively, data relating to the power output of the powertrain may be available from a data library, for example, an engine power map, stored on a controller of the vehicle. The power output may be determined at discrete time intervals by retrieving power values from the data library that correspond to the current operating parameters of the vehicle's powertrain.

[0025] In an example where the vehicle is traveling on level terrain, for example, terrain that does not have a significant uphill or downhill gradient, and neglecting any losses or external forces acting on the vehicle, the change in the vehicle's kinetic energy over the time period T is equal to the energy output from the vehicle's powertrain over the time period T.

[0026] The method 100 includes comparing the change in kinetic energy with the energy output from the powertrain.

[0027] In another example, where the vehicle is traveling uphill or downhill, and neglecting any losses or external forces acting on the vehicle, the change in the vehicle's kinetic energy over the time period T will be different from the energy output from the vehicle's powertrain over the time period T. For example, when the vehicle is traveling uphill or downhill on a mountain road, the change in the vehicle's kinetic energy is a function of the energy output from the vehicle's powertrain and the change in the vehicle's potential energy PE, as shown by Equation 3. ΔKE(dt)≈f(ΔPE(dt),fPOUTPUT(dt))

[0028] In those cases where the change in kinetic energy is not equal to the energy output from the vehicle's drivetrain, it can be concluded that the vehicle's potential energy has changed and thus the vehicle is not traveling on level terrain. More specifically, if the change in the vehicle's kinetic energy over the time period T is greater than the energy output from the vehicle's drivetrain over the time period T, as shown by Equation 4, it can be concluded that the vehicle is traveling downhill. Furthermore, the change in the vehicle's potential energy can be estimated by calculating the difference between the change in kinetic energy and the energy output from the vehicle's drivetrain over the time period T. ΔKE(dt)>fPOUTPUT(dt)

[0029] With reference to Fig.1, the method 100 includes: step 110 of determining the change in kinetic energy of the vehicle between times t1 and t2; step 120 of determining the energy output from a powertrain of the vehicle between times t1 and t2; and step 130 of comparing the change in kinetic energy of the vehicle between times t1 and t2 with the energy output from a powertrain of the vehicle between times t1 and t2. If the change in kinetic energy is greater than the energy output from the powertrain between times t1 and t2, as shown in Equation 5, the method 100 includes step 140 of performing a downshift of a transmission of the vehicle.Step 140 may only be performed if the difference between kinetic energy and the powertrain output is greater than a predetermined value, for example, only if the kinetic energy is approximately 120% of the powertrain output. (KEt2−KEt1)>∫t1t2fPOUTPUTdt

[0030] The present disclosure provides a method 100 for increasing the level of engine braking so that the driver does not need to rely as heavily on the vehicle's braking system to decelerate the vehicle during periods of downhill driving, e.g., extended downhill driving conditions. As a result, the operating temperature of the brake pads of the braking system can be maintained at a lower temperature, helping to prevent a loss of braking power to ensure adequate braking performance in an emergency situation.

[0031] In another example, the change in the vehicle's kinetic energy may be a function of the energy output from the vehicle's powertrain over the time period, the change in the vehicle's potential energy over the time period, the energy required to overcome the vehicle's rolling resistance over the time period, and / or the energy required to overcome the vehicle's aerodynamic drag over the time period, as shown by Equation 6. As such, the method 100 may include a step of determining the energy required to overcome the vehicle's rolling resistance over the time period T and / or a step of determining the energy required to overcome the vehicle's aerodynamic drag over the time period T. The energy required to overcome the vehicle's rolling resistance may be determined by integrating the amount of power used P RR, which is used to overcome the rolling resistance over the time period T. Similarly, the energy required to overcome the vehicle's air resistance can be determined by integrating the amount of power P D used in overcoming the air resistance over the time period T. ΔKE(dt)≈f(∫POUTPUT(dt),ΔPE(dt),∫PD(dt),∫PRR(dt))

[0032] The instantaneous rolling resistance force P rr can be determined using equation 7, where C RR is the dimensionless rolling resistance coefficient, N is the normal force, i.e. the force perpendicular to the surface on which a wheel of the vehicle rolls, and v is the speed of the vehicle relative to the road. The instantaneous air resistance force P D can be determined using equation 8, where ρ is the density of the air surrounding the vehicle, C Dis the dimensionless drag coefficient, A is the cross-sectional area of the vehicle and v is the speed of the vehicle relative to the air. PRR=CRRNv PD−12ρCDAv3

[0033] If the method 100 includes determining the energy required to overcome rolling resistance and / or the energy required to overcome aerodynamic drag of the vehicle, these factors may be considered when comparing the change in kinetic energy to the energy output from the powertrain between times t1 and t2, as shown in Equation 9.The method 100 may include the step of performing a downshift of a transmission of the vehicle when the sum of: the change in the kinetic energy of the vehicle between times t1 and t2; the energy required to overcome the rolling resistance of the vehicle between times t1 and t2; and the energy required to overcome the aerodynamic drag of the vehicle between times t1 and t2 is greater than the energy output from a powertrain of the vehicle between times t1 and t2. In this way, the amount of engine braking generated by the powertrain of the vehicle may be increased when it is determined that the vehicle is traveling downhill. ∑((KEt2−KEt1)+∫t1t2(CRRNv)dt+∫t1t2(12ρCDAv3)dt)>∫t1t2POUTPUTdt

[0034] The method 100 may include determining the altitude and / or inclination of the vehicle using one or more sensors. For example, the vehicle may be equipped with a GPS (Global Positioning Satellite) system configured to determine the position and / or altitude of the vehicle. The method 100 may include determining the change in potential energy of the vehicle over the time period T using altitude data derived by the GPS system. The change in potential energy of the vehicle may be calculated according to Equation 10, where m is the mass of the vehicle, g is the gravitational constant, and Δh is the change in altitude of the vehicle, for example, the altitude of the vehicle at time t1 and the altitude of the vehicle at time t2. In this way, the change in potential energy of the vehicle for the time period T may be calculated. ΔPE=mgΔh(dt)

[0035] The method may include a step of estimating the change in potential energy of the vehicle based on the determined: change in kinetic energy of the vehicle between times t1 and t2; energy required to overcome rolling resistance of the vehicle between times t1 and t2; energy required to overcome aerodynamic drag of the vehicle between times t1 and t2; and energy output from a powertrain of the vehicle between times t1 and t2. For example, the change in potential energy of the vehicle may be estimated using Equation 11. (PEt2−PEt1)≈∑(∫t1t2POUTPUTdt−∫t1t2(12ρCDAv3)dt−∫t1t2(CRRNv)dt−(KEt2−KEt1))

[0036] The method 100 may include a step of comparing the change in potential energy determined using Equation 10, i.e., by the one or more sensors, with the estimated change in potential energy determined using Equation 11. The method may include the step of confirming that the vehicle is traveling downhill using the comparison between the change in potential energy determined using Equation 10 with the estimated change in potential energy determined using Equation 11. In this way, the estimated change in potential energy using Equation 11 may be used to determine whether the GPS system is functioning properly.Furthermore, the comparison between the change in potential energy determined using Equation 10 with the estimated change in potential energy determined using Equation 11 can be used to indicate whether the rolling resistance force and / or the aerodynamic drag force of the vehicle is unexpectedly high, for example, if the change in potential energy determined using Equation 10 is less than the estimated change in potential energy determined using Equation 11.

[0037] Where the derived values for the change in potential energy determined using Equation 10 and the estimated change in potential determined using Equation 11 are different, the method 100 may include a step of canceling the downshift of the vehicle's transmission, since the discrepancy between the values may indicate a problem with one or more of the vehicle systems, such as a flat tire and / or a deployed / extended air brake / spoiler.

[0038] The method 100 may include determining the energy input to the braking system of the vehicle. For example, the method 100 may include determining the temperature of the brake pads of the braking system. The method 100 may include a step of performing a downshift of the vehicle's transmission only when the temperature of the braking system is greater than a predetermined temperature. In this way, the engine braking augmentation system may be activated only when it is detected that the operational effectiveness of the braking system is at risk, for example, during driving conditions where the driver must make heavy use of the vehicle's braking system.

[0039] It will be appreciated by those skilled in the art that, although the disclosure has been described by way of example with reference to one or more examples, it is not limited to the examples described and that alternative examples could be constructed without departing from the scope of the disclosure as defined in the appended claims.

Claims

[1] A method for boosting the engine brake of an engine for a vehicle, the method comprising: Determining the change in the kinetic energy of the vehicle over a period of time; Determining the energy output from a powertrain of the vehicle over the time period; Comparing the change in kinetic energy with the energy output; and increasing the vehicle's engine braking if the change in kinetic energy is greater than the energy output over the time period; and Determining the energy input to a braking system of the vehicle; and increasing the engine braking of the vehicle when the temperature of the braking system is greater than a predetermined temperature. [2] The method of claim 1, wherein the method comprises: Determining the energy required to overcome the rolling resistance of the vehicle over the time period; Comparing the energy output with the energy required to overcome the rolling resistance of the vehicle; and Boosting the vehicle's engine braking when the change in kinetic energy over the time period is greater than the energy output from the vehicle's powertrain less the energy required to overcome the vehicle's rolling resistance over the time period. [3] The method of claim 1, wherein the method comprises: Determining the energy required to overcome the vehicle's air resistance over the time period; Comparing the energy output with the energy required to overcome the vehicle's air resistance over the time period; and Increase the vehicle's engine braking when the change in kinetic energy over the time period is greater than the energy output from the vehicle's powertrain less the energy required to overcome the vehicle's aerodynamic drag over the time period. [4] A method according to any one of the preceding claims, wherein the method comprises determining the inclination of the vehicle using one or more sensors. [5] A method according to any one of the preceding claims, wherein the method comprises determining the altitude of the vehicle using one or more sensors. [6] A method according to claim 4 or 5, wherein the method comprises confirming that the vehicle is traveling downhill using one or more of the sensors. [7] The method of claim 6, wherein the method comprises cancelling the transmission downshift in response to a lack of confirmation that the vehicle is traveling downhill. [8] A method according to any one of the preceding claims, wherein the method further comprises providing an indication to a driver of the vehicle to perform a manual downshift of the transmission when the change in kinetic energy is greater than the energy output over the time period. [9] A method according to any one of the preceding claims, wherein the time period is greater than about 60 seconds. [10] Method according to one of the preceding claims, wherein the boosting of the engine brake is caused by the activation of an electric machine coupled to the drive train of the vehicle. [11] A method according to any one of the preceding claims, wherein the boosting of the engine brake is caused by a downshift of a transmission of the vehicle. [12] The method of claim 11, wherein the transmission is an automatic transmission. [13] A system for boosting the engine brake of an engine for a vehicle, the system comprising a controller configured to: to determine the change in the vehicle's kinetic energy over a period of time; to determine the energy output from a vehicle powertrain over the time period; to compare the change in kinetic energy with the energy release; and to cause an increase in the extent of engine braking when the change in kinetic energy is greater than the energy output over the time period; and to determine the energy supply to a braking system of the vehicle; wherein the engine brake of the vehicle is increased if the temperature of the braking system is greater than a predetermined temperature. [14] A vehicle having one or more of the systems according to claim 13.

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