Control of an automatic transmission system

Abstract

Aspects of the present invention relate to a control system (400) for controlling an automatic transmission system (204) of a vehicle (1). The automatic transmission system (204) includes at least three drive gears including a first gear having a first gear ratio, a second gear having a second gear ratio lower than the first gear ratio, and an intermediate gear having an intermediate gear ratio between the first and the second gear ratios. The control system (400) is to cause the automatic transmission system (204) to perform a double downshift to disengage the first gear and to engage the second gear, without engaging the intermediate gear. The control system (400) receives a first brake signal indicative of a first brake input to the brake input device at a first time, receives a second brake signal indicative of a second brake input to the brake input device at a second time, determines a rate of change of brake input based on the first and second brake inputs, and compares the rate of change of brake input to a brake rate threshold. A double downshift signal is output to cause the automatic transmission system (204) to perform the double downshift based on the rate of change of brake input exceeding the brake rate threshold. Aspects of the present invention also relate to a system and vehicle (1) comprising the control system (400), a method (500, 700, 800) and computer readable instructions.

Description

[0001] CONTROL OF AN AUTOMATIC TRANSMISSION SYSTEM

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to control of an automatic transmission system. Aspects of the invention relate to a control system, to a method, and to a computer readable medium for controlling an automatic transmission system of a vehicle.

[0004] BACKGROUND

[0005] Vehicles, such motor vehicles and hybrid electric vehicles comprise an internal combustion engine, which is operatively coupled to road wheels of the vehicle via a transmission system comprising a plurality of drive gears associated with a plurality of respective gear ratios.

[0006] It is known to provide an automatic transmission system and an associated control system, which controls the automatic transmission to select an appropriate gear ratio based on a plurality of vehicle operating conditions, such as an engine speed or speed of an input shaft to the automatic transmission system, and / or an accelerator pedal position.

[0007] The control system for the automatic transmission may determine when to change drive gears with reference to a shift map, which may relate desirable changes in drive gears to the vehicle operating conditions. When it is determined that a gear change to a higher or lower gear should be performed, e.g. based on the shift map, the automatic transmission system is controlled to begin a gear change by disengaging a currently engaged drive gear and engage a destination higher or lower drive gear. Disengaging the currently engaged drive gear and engaging the destination drive gear may occur over a period of time, which may be referred to as a gear shift duration.

[0008] It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

[0009] SUMMARY OF THE INVENTION

[0010] Aspects and embodiments of the invention provide a control system, a vehicle, and a method as claimed in the appended claims.

[0011] According to an aspect of the present invention there is provided a control system for controlling an automatic transmission system of a vehicle, wherein the vehicle comprises a brake system, the brake system comprising a brake input device, and the automatic transmission system including at least three drive gears, the drive gears comprising a first gear having a first gear ratio, a second gear having a second gear ratio lower than the first gear ratio, and an intermediate gear having an intermediate gear ratio between the first and the second gear ratios, wherein the control system comprises one or more processors collectively configured to: determine a rate of change of brake input; compare the rate of change of brake input to a brake rate threshold; and based on the rate of change of brake input exceeding the brake rate threshold, output a double downshift signal to cause the automatic transmission system to disengage the first gear and to engage the second gear, without engaging the intermediate gear. The one or more processors may be collectively configured to: receive a first brake signal containing information indicative of a first brake input to the brake input device at a first time; receive a second brake signal containing information indicative of a second brake input to the brake input device at a second time; and determine the rate of change of brake input based on the first and second brake inputs.

[0012] References to “engaging” a particular gear or a particular gear “being engaged by” the automatic transmissions system within the present specification may refer fully engaging the particular gear, or the particular gear being fully engaged by the automatic transmission system. References to “level of engagement" may refer to the extent to which a particular gear is engaged by the automatic transmission system.

[0013] When a vehicle comprising an automatic transmission system is decelerating, a control system for the automatic transmission system may command the automatic transmission system to perform a gear downshift in order to maintain engine speed at or above a desirable speed. Performing each downshift of the automatic transmission system takes a period of time to complete and during some driving conditions it may become desirable to perform a further gear downshift before a previously commanded gear downshift has been completed. By considering the rate of change of brake input and commanding a double downshift of the automatic transmission system if the rate of change of brake input exceeds the brake rate threshold, the control system for the automatic transmission may downshift more quickly when several downshifts are needed and may thereby control the automatic transmission to operate at speed ratios which prevent the engine speed reducing below the desirable speed, or reduce an amount by which the engine speed is reduced below the desirable speed.

[0014] The brake system may comprise a brake pressure sensor. Receiving the first and second brake signals may comprise receiving first and second brake pressure signals from the brake pressure sensor at the first and second times respectively.

[0015] The pressure of a brake system, e.g. of a brake fluid within the brake system, may be a convenient way to measure an input to the brake system. Further, brake pressure measured at an appropriate location in the brake system, such as at a brake master cylinder of the brake system, may provide an indication of brake input before an output of the brake system, such as a deceleration of the vehicle, can be measured. In this way, the double downshift can be commanded earlier.

[0016] The brake system may comprise a brake pedal position sensor, wherein receiving the first and second brake signals comprises receiving first and second brake pedal position signals from the brake pedal position sensor at the first and second times respectively.

[0017] The vehicle may comprise an internal combustion engine and may comprise an engine speed sensor arranged to determine a rotational speed of a crank shaft of the engine. The vehicle may further comprise an accelerator pedal arranged to control a power generated by the engine. The one or more processors may be further configured to: receive a shift map correlating required downshifts to engine speeds and accelerator pedal positions, receive an engine speed signal from the engine speed sensor, the engine speed signal including information indicative of a rotational speed of the crank shaft, receive an accelerator pedal position signal from the accelerator pedal, the accelerator pedal position signal including information indicative of a position of the accelerator pedal, determine whether to command a downshift based on the engine speed, the accelerator pedal position and the shift map, output a downshift signal to cause a downshift from the first gear to the intermediate gear based on the determining; and output the double downshift signal to override the downshift signal.

[0018] It may be desirable for the double downshift to be performed when the automatic transmission system would otherwise be controlled to perform a signal downshift based on a shift map for the automatic transmission system, so that the double downshift based on brake input operates in accordance with the shift map. In this way, performing a double downshift may increase the proportion of time during which the automatic transmission system operates at a speed ratio closest to a desired speed ratio, e.g. according to the shift map.

[0019] The vehicle may comprise a speed sensor configured to determine an input speed to the automatic transmission system. The one or more processors may be further configured to: receive a signal indicative of the input speed to the automatic transmission; and determine the brake rate threshold at least partially based on the signal indicative of the input speed to the automatic transmission.

[0020] The speed may be a rotational speed of a shaft providing torque to the gearbox. The input speed to the automatic transmission may provide a good indication of whether a high rate of brake input will lead to a situation in which engine speed will be significantly reduced. In this way, a double downshift may be determined at more appropriate conditions, reducing the prospect of the engine speed being reduced below a desired engine speed.

[0021] The one or more processors may be further configured to: receive a signal indicative of the gear ratio of the second gear and / or of the intermediate gear; and determine the brake rate threshold at least partially based on the gear ratio of the second gear and / or of the intermediate gear.

[0022] The brake rate threshold may be determined at least partially based on a difference in gear ratio between the first gear ratio, and the intermediate and / or second gear ratio. When a difference in gear ratio between the first, and intermediate and / or second gear ratio is relatively low, e.g. compared to the difference between the gear ratios of other gears of the automatic transmission, a lower rate of brake input may be more likely to lead to a situation in which engine speed is reduced below a desirable speed. Further, gears having relatively high gear ratios may have gear ratios which are closer to the gear ratios of adjacent gears compared to gears having relative low gear ratios Accordingly, it may be desirable for the brake rate threshold to be relatively low when the gear ratio of the second gear and / or the intermediate gear are relatively high, orwhen the difference in gear ratio between the first, and intermediate and / or second gear ratio is relatively low.

[0023] The vehicle may comprise a road gradient sensor configured to determine a gradient of the road on which the vehicle is driving. The one or more processors may be further configured to: receive a road gradient signal including information indicative of the road gradient; and determine the brake rate threshold at least partially based on the road gradient.

[0024] The greater the road gradient on which the vehicle is driving, the more torque at the wheels may be desired by the driver to accelerate following a period of braking. Hence, on a road with higher gradient it may be more desirable to perform a double downshift operation. Further, a lower rate of brake input may be more likely to lead to a situation in which the engine speed is reduced by a greater amount when road gradient is relatively high.

[0025] The vehicle may comprise a driving mode selector configured to determine a driving mode of the vehicle, wherein the one or more processors are further configured to: a driving mode selector configured to determine a driving mode of the vehicle; and determine the brake rate threshold at least partially based on the driving mode. The one or more processors may be configured to: determine a driver parameter describing a driving tendency of a driver of the vehicle, wherein the one or more processors are further configured to: receive a signal indicative of the driving parameter; and determine the brake rate threshold at least partially based on the driver parameter. The brake threshold may be between 50bar / s and 200bar / s.

[0026] The one or more processors may be configured to: monitor the rate of change of brake input over a predetermined period of time; and wherein the double downshift signal is output based on the rate of change of brake input exceeding the brake rate threshold for the predetermined period of time.

[0027] Short period of rapid changes in brake input may not lead to significant decreases engine speed. Hence, at least in some driving conditions, it may be desirable to perform a double downshift when a high rate of brake input is maintained for a period of time greater than the threshold period of time, which may indicate that a significant reduction in engine speed is likely.

[0028] The predetermined period of time may be determined based on one or more selected from: an input speed to the automatic transmission system; a destination gear of a commanded single downshift or potential double downshift; a road gradient; a driving mode, e.g. driver selectable driving mode, of the vehicle; and a parameter describing a driving tendency of a driver of the vehicle.

[0029] The vehicle may further comprise an accelerator pedal position sensor configured to determine a position of an accelerator pedal of the vehicle. The control system may have a first operating mode and a second operating mode. Outputting of the double downshift signal may be disabled in the first operating mode and enabled in the second operating mode. The one or more processors may be configured to: receive a signal indicative of the position of the accelerator pedal; and select the operating mode of the control system based on the position of the accelerator pedal.

[0030] It may be undesirable for the automatic transmission system to perform a double downshift when an accelerator pedal input is being provided by a driver. The first operating mode of the control system may be selected when the signal indicative of the position of the accelerator pedal indicates that the driver is providing an accelerator pedal input. The second operating mode of the control system may be selected when the signal indicative of the position of the accelerator pedal indicates that the driver is not providing an accelerator pedal input. The double downshift signal may be output based on the control system operating in the second operating mode. In other words, the second operating mode may be a double downshift enabled mode. The double downshift signal may not be output based on the control system operating in the first operating mode. In other words, the first operating mode may be a double downshift inhibited mode.

[0031] Additionally or alternatively, the vehicle may comprise a transmission lubricant temperature sensor configured to determine a temperature of lubricant for the automatic transmission system. The one or more processors may be configured to: receive a signal indicative of the temperature of lubricant; and select the operating mode of the control system based on the temperature of lubricant.

[0032] When the temperature of lubricant within the automatic transmission system is not sufficiently high, performance of the automatic transmission system may be reduced when performing a double downshift. Accordingly, it may be undesirable to output the double downshift signal when the temperature of lubricant is low, e.g. below a threshold temperature.

[0033] The first operating mode of the control system may be selected when the temperature of the lubricant is below the temperature threshold. The second operating mode of the control system may be selected when the temperature of the lubricant is greater than or equal to the temperature threshold.

[0034] The automatic transmission system may further comprise a shift status sensor configured to determine a status of a single downshift operation being performed by the automatic transmission system. The one or more processors may be configured to: receive the signal indicative of the status of a single downshift operation currently in progress, wherein the double downshift signal is output based on the status of the single downshift operation.

[0035] The automatic transmission system may further comprise a clutch engagement sensor configured to determine a level of engagement of a clutch for engaging the intermediate gear. The one or more processors may be configured to: receive a signal from the clutch engagement sensor indicative of a level of engagement of a clutch for engaging the intermediate gear. The double downshift signal may be output based on the level of engagement of the clutch for engaging the intermediate gear being below a threshold level of engagement.

[0036] In some driving situations, the rate of change of brake input may increase above the brake rate threshold after a single downshift of the automatic transmission system has been initiated by the automatic transmission system. It may therefore be desirable to override the single downshift to perform the double downshift instead of the single downshift. However, overriding the single downshift when a level of engagement of a clutch for engaging the intermediate gear is greater than or equal to a threshold level of engagement may reduce performance of the automatic transmission system or may not be possible based on a hardware configuration of the automatic transmission system. However, when the level of engagement of the clutch for engaging the intermediate gear is below the threshold level of engagement, the second gear may be engaged rather than the intermediate gear in order to prevent engine speed reducing below the desired engine speed.

[0037] The automatic transmission system may comprise one or more overdrive gears. An overdrive gear may be a gear with a gear ratio greater than a gear ratio of the automatic transmission system at which the vehicle is able to achieve a maximum speed. The one or more processors may be configured to: receive a signal indicative of a currently selected gear of the automatic transmission system. The double downshift signal may be output based on whether the currently selected gear is one of the one or more overdrive gears.

[0038] In driving situations in which overdrive gears are selected, there may be an increase likelihood that a driver will accelerate the vehicle following a period in which the rate of braking input is high, e.g. above the brake rate threshold. Accordingly, it may be desirable for double downshifting to be performed when the currently selected gear is an overdrive gear.

[0039] According to another aspect of the present invention, there is provided a system comprising the control system of the first-mentioned aspect and the automatic transmission system.

[0040] According to a further aspect of the invention, there is provided a vehicle comprising the system of the another aspect or the control system of the first-mentioned aspect.

[0041] According to a still further aspect of the present invention, there is provided a method for controlling an automatic transmission system of a vehicle , wherein the vehicle comprises a brake system, the brake system comprising a brake input device, and the automatic transmission system including at least three drive gears, the drive gears comprising a first gear having a first gear ratio, a second gear having a second gear ratio lower than the first gear ratio, and an intermediate gear having an intermediate gear ratio between the first and the second gear ratios, the method comprising: receiving a first brake signal containing information indicative of a first brake input to the brake input device at a first time; receiving a second brake signal containing information indicative of a second brake input to the brake input device at a second time; determining a rate of change of brake input based on the first and second brake inputs; comparing the rate of change of brake input to a brake rate threshold; and based on the rate of change of brake input exceeding the brake rate threshold, outputting a double downshift signal to cause the automatic transmission system to disengage the first gear and to engage the second gear, without engaging the intermediate gear.

[0042] According to a yet still further aspect of the present invention, there is provided computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform the a method according to the still further aspect.

[0043] Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner.

[0044] BRIEF DESCRIPTION OF THE DRAWINGS

[0045] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0046] Figure 1 shows a vehicle in accordance with an embodiment of the invention;

[0047] Figure 2 shows a schematic representation of a powertrain, a braking system, driving controls, and a control system of a vehicle in accordance with an embodiment of the invention;

[0048] Figures 3a, 3b and 3c are graphs illustrating the variation of control and sensor signals, and engine speed during a gear change;

[0049] Figure 4 shows a schematic view of a control system according to an embodiment of the invention;

[0050] Figure 5 is a flow chart illustrating a method according to the invention;

[0051] Figures 6a, 6b, 6c and 6d are graphs illustrating the variation of control and sensor signals, and engine speed during a double downshift according to the method shown in Figure 5;

[0052] Figure 7 is a flow chart illustrating another method according to the invention; and Figure 8 is a flow chart illustrating a further method according to the invention.

[0053] DETAILED DESCRIPTION

[0054] Figure 1 shows a vehicle 1 in accordance with an embodiment of the invention. In particular, the vehicle may comprise a control system 400 as described herein. In some, but not necessarily all examples, the vehicle 1 is a passenger vehicle, also referred to as a passenger car or as an automobile. In other examples, embodiments of the invention can be implemented for other applications, such as commercial vehicles.

[0055] With reference to Figure 2, the vehicle 1 may comprise a powertrain 200. The illustrated powertrain 200 comprises an internal combustion engine 202 (ICE), an automatic transmission system 204, for receiving drive torque from the ICE and providing the drive torque to a final drive system 206 to be supplied to road wheels FL, FR, RL, RR of the vehicle. In the illustrated example, the vehicle is an all-wheel drive vehicle. However, in other examples, the vehicle may be a two wheel drive vehicle, and the powertrain may be configured to provide drive torque to either the front or rear road wheels.

[0056] The illustrated powertrain 200 further comprises an electric machine 208. However, the present invention is not limited to the specific layout shown and, in some arrangements, may not comprise an electric machine and / or may comprise one or more electric machines provided at other locations within the powertrain 200.

[0057] While the vehicle 1 shown in Figures 1 and 2 is a hybrid electric vehicle (HEV). The vehicle 1 may be a plugin HEV or a mild HEV. The vehicle may have an electric-only mode of propulsion or the electric machine 208 may be configured to provide assistance such as supplementing an output torque of the ICE 202.

[0058] The electric machine 208 is powered by an electrical energy storage means 210 such as a traction battery. The automatic transmission 204, which may also be referred to as an automatic gearbox, comprises a plurality of drive gears, and may in some case comprise 8 drive gears, each gear defining a different respective gear ratio having the same polarity. The drive gears may be numbered from 1 to 8, with the gear providing the lowest gear ratio (i.e. the gear that provides the lowest output shaft rotational speed for a given input shaft rotational speed) numbered 1 and the gear providing the highest gear ratio (i.e. the highest output shaft rotational speed for a given input shaft rotational speed) labelled 8. However, it will be understood that the automatic transmission 204 may comprise as few as 3 gears and may comprise any number of gears greater than 3.

[0059] In particular the automatic transmission 204 may comprise a first (higher) gear, having first (higher) gear ratio, a second (lower) gear, having a second (lower) gear ratio, and an intermediate gear, having an intermediate gear ratio between the first and second gear ratios. The labels of first, second and intermediate gear may be applied to any series ofthree consecutive gears of the automatic transmission 204. The automatic transmission 204 may further comprise a plurality of clutches, such as friction clutches, for selectively engaging the drive gears in order to operatively connect the associated drive gear between the ICE 202 and the final drive system 206. The drive gear that is operatively connected between the ICE and final drive system 206 may be referred to as the selected gear or the engaged gear.

[0060] The vehicle 1 may further comprise a brake system 250 comprising a brake cylinder 252, which may be referred to as a brake master cylinder, and one or more wheel brake units 254, such as disc or hub brake units configured to brake wheels and / or one or more drive shafts of the vehicle based on a pressure of brake fluid within the brake system 250, as controlled by the brake master cylinder 252.

[0061] The vehicle 1 further comprises driving controls including an accelerator pedal 212 for controlling the operation of the powertrain to supply drive power to the vehicle road wheels and a brake input device, such as a brake pedal 214, for controlling the operation the brake system 250 of the vehicle. As illustrated, the vehicle may comprise an accelerator pedal position sensor 216 configured to measure a position of the accelerator pedal and output a signal indicative of the position of the accelerator pedal. The vehicle may further comprise a brake input sensor 218 configured to determine a magnitude of input to the brake system. For example, the brake input sensor 218 may be a brake pressure sensor configured to measure a pressure of brake fluid within the brake system, such as within the brake cylinder 252. Alternatively, the brake input sensor may be a brake pedal position sensor configured to measure a position of the brake pedal to determine an input to the brake system. In either case, the brake input sensor 218 may be configured to output a brake signal indicative of a brake input to the brake input device.

[0062] The vehicle or powertrain further comprises a control system 400 comprising one or more processors for controlling the operation of the powertrain 200. In particular, the control system 400 may be configured to control the operation of the automatic transmission 204 to select a desirable drive gear based on operating conditions of the vehicle and / or powertrain. In particular, the one or more processors may be configured to receive a shift map, which correlates desirable gear changes, e.g. downshift and / or upshifts, to operating parameters of the powertrain and / or vehicle. In particular, the shift map may correlate desirable gear changes with engine speed and accelerator pedal position. As illustrated, the vehicle 1 may comprise an engine speed sensor 221 configured to measure a speed, e.g. rotational speed, of the ICE, such as of a crankshaft of the ICE, and provide an engine speed signal to the one or more processors. The control system 400 may output a drive gear selection command signal to the automatic transmission 204 to control the automatic transmission to change gear to a destination gear indicated by the drive gear selection command signal.

[0063] As shown in Figure 4, the vehicle may comprise one or more sensors 220, which may be configured to output signals to the one or more processors of the control system 400, e.g. for use in the methods described above. The sensors 220 may include the accelerator pedal position sensor 216, the brake input sensor 218 and / or the engine speed sensor 221 mentioned above.

[0064] The vehicle or powertrain may further comprise a shift status sensor 222 configured to determine a status of a gear change, e.g. a single gear shift, such as single downshift operation, being performed by the automatic transmission system. The shift status sensor 222 may be configured to determine a level of engagement of the clutches of the automatic transmission system associated with the drive gears involved in the gear change. For example, the shift status sensor 222 may be configured to determine a level of engagement of a clutch engaging a destination gear of a gear change currently being performed. The shift status sensor may be referred to as a clutch engagement sensor. Alternatively, a level of clutch engagement may be determined within the control system based on an elapsed time since a gear shift signal configured to cause a gear shift has been instructed.

[0065] The vehicle may comprise a speed sensor 224 configured to determine an input speed to the automatic transmission system. The input speed to the automatic transmission system may be the speed, e.g. rotational speed, of a shaft arranged between the ICE 202 and the automatic transmission. The input speed to the automatic transmission system may be equal to the crankshaft speed of the ICE or may differ from the crankshaft speed, e.g. based on an input from the electric machine 208 being combined with a speed of the crankshaft to determine the input speed.

[0066] The vehicle may comprise a road gradient sensor 226 configured to determine gradient of a road on which the vehicle is travelling. The vehicle may comprise a transmission lubricant temperature sensor 228 configured to measure a temperature of lubricant within the automatic transmission system.

[0067] Figures 3a and 3b show signal values illustrating the operation of the control system 400, automatic transmission system 204 and brake system 250 operating to perform consecutive gear downshifts.

[0068] In Figure 3a, a first dot-dashed line 302 illustrates a drive gear selection command signal from the control system 400; a second dashed line 304 illustrates a drive gear transition signal, which indicates a drive gear which the automatic transmission system is transitioning to engage, and a third solid line 306 illustrates a currently engaged drive gear of the automatic transmission system 204. As depicted, during operation of the vehicle, the control system 400 may command the automatic transmission to perform a gear change, e.g. a downshift, from a higher drive gear, such as the first gear, to a lower drive gear, such as the intermediate gear. The drive gear selection command signal may be sent at time ti. As illustrated, the operation of the automatic transmission system to transition to select the intermediate gear may begin shortly after the automatic transmission system is commanded by the control system 400 to perform the gear change. As illustrated, the gear change may begin at time t2. The automatic transmission system may take a period of time T, e.g. the gear shift duration, to transition from the first gear to the intermediate gear, e.g. by operating a first clutch of the automatic transmission to disengage the higher gear and operating an intermediate clutch of the automatic transmission to engage the intermediate gear. The gear change may be completed at time t4.

[0069] As illustrated in Figure 3a, in some situations, it may become desirable to perform a further gear change, e.g. a further downshift, during the period of time T when the automatic transmission is performing the gear change. For example, it may become desirable, at time ta, for the automatic transmission system to change to a further lower gear, such as the second gear. However, as illustrated in Figure 3a, although the gear change may be commanded by the control system 400 during the period of time T, the automatic transmission system 204 may not begin transitioning to the second gear until the gear change to the intermediate gear is complete. As illustrated, the drive gear selection command signal may be sent at time ta and the gear change may begin at time ta. The gear change to the second gear may be completed at time te.

[0070] Figure 3b illustrates a brake input signal. For example, the brake input signal may be a brake pressure signal, e.g. from the brake pressure sensor, or a brake pedal position signal. As indicated in Figure 3b, the driving conditions in which it becomes desirable to perform a further gear change during the period of time T, e.g. at time t3, may be when a driver of the vehicle is braking.

[0071] Figure 3c illustrates an engine speed. As shown in Figure 3c, the engine speed may reduce during braking while the transmission remains in a particular gear. A downshift may therefore occur in order to maintain an engine speed above a minimum allowable engine speed 308. However, due to the delay in consecutive gearshifts shown in Figure 3a, whilst the automatic transmission system is operating with the intermediate gear selected, and prior to the gear change to the second gear being completed, the engine speed may reduce to below the minimum allowable engine speed before the second gear is engaged by the automatic transmission, e.g. may be below a minimum allowable engine speed 308. This may reduce a subsequent acceleration achievable by the vehicle.

[0072] With reference to Figure 4, in orderto reduce the risk of the engine speed reducing to an undesirably low value during braking, the vehicle 1 may comprise the control system 400, according to the present invention.

[0073] The control system 400, as illustrated in Figure 4, comprises one controller 410, although it will be appreciated that this is merely illustrative. The controller 410 comprises one or more processors 420 and may comprise one or more memories 430. The one or more processors may be configured operably execute computer- readable instructions. The one or more memories 430 may be electrically coupled to the processors 420. The one or more memories 430 may be configured to store instructions, and the one or more processors 420 may be configured to access the one or more memories and execute the instructions stored thereon. The controller 410 comprises an input means and an output means. To this end, the controller 410 may have an interface 412 comprising an electrical input 414 of the controller 410 and an electrical output means 416. The electrical input 414 may be for receiving one or more input signals relevant to the methods described herein. In particular, the controller 410 may be configured to receive one or more signals from one or more sensors 220 of the vehicle, such as the brake input sensor 218, the accelerator pedal position sensor 216, the engine speed sensor 221 , the shift status sensor 222, speed sensor 224, road gradient sensor 226 and / or the transmission lubricant temperature sensor 228. The controller 410 may be further configured to receive one or more signals from one or more further controllers or processors 450 of the control system. Additionally or alternatively, the electrical input 414 of the controller 410 may be coupled to a signal bus 452, such as a Controller Area Network (CAN) bus and may be configured to retrieve one or more inputs, e.g. from the sensors and / or further controllers / processors, via the signal bus. References in this specification to receiving a signal may correspond to retrieving the signal from the signal bus 452.

[0074] The electrical output 416 is for outputting control signals (directly or indirectly) to external actuators such as the automatic transmission system 204. In particular, the controller 410 may be configured to transmit a drive gear selection command signal to the automatic transmission signal, as described above.

[0075] Figure 5 illustrates a method 500 according to an embodiment of the invention. The method 500 is a method of controlling a powertrain of a vehicle, such as the vehicle 1 illustrated in Figure 1 . The method 500 may be performed by the system 400 illustrated in Figure 4. In particular, the memory 430 may comprise computer- readable instructions which, when executed by the processor 420, perform the method 500 according to an embodiment of the invention.

[0076] With reference to Figure 5, the control system 400 may be configured to control the operation of the automatic transmission system 204 according to a method 500. According to the method 500, the automatic transmission system may be controlled to perform a double downshift, in which the automatic transmission system is caused to disengage the first, higher gear and to engage the second, lower gear, without engaging the intermediate gear.

[0077] The method 500 comprises a first block 502, in which the controller, e.g. the one or more processors, receive a first brake signal indicative of a first brake input to the brake input device at a first time.

[0078] The method further comprises a second block 504, in which the controller, e.g. the one or more processors, receive a second brake signal containing information indicative of a second brake input to the brake input device at a second time.

[0079] The brake signals may contain information indicative of a position of a brake pedal, of a pressure in a brake cylinder, or of a force on a brake pedal. The method 500 further comprises a third block 506, in which a rate of change of brake input is determined based on the first and second brake inputs.

[0080] At a fourth block 508, the rate of change of brake input is compared to a brake rate threshold. The brake rate threshold may be a predetermined threshold or may be determined by the controller 410 according to the method 700, as described below. Where the brake signals contain information indicative of a pressure in a brake cylinder, the brake rate threshold may be between 50bar / s and 200bar / s.

[0081] The method 500 further comprises a fifth block 510, in which a double downshift signal is output to cause the automatic transmission system 204 to disengage the first gear and to engage the second gear, without engaging the intermediate gear. The double downshift signal is output based on the rate of change of brake input exceeding the brake rate threshold. The double downshift signal may be a drive gear selection command signal.

[0082] Figures 6a, 6b, 6c and 6d show signal values illustrating the operation of the control system 400, automatic transmission system 204 and brake system 250 operating according to the method 500. In Figure 6a, a first line 602 illustrates a drive gear selection command signal from the control system 400; a second line 604 illustrates a drive gear transition signal which indicates a drive gear which the automatic transmission system is transitioning to engage and a third line 606 illustrates a currently engaged drive gear of the automatic transmission system.

[0083] As illustrated, when operating according to the method 500, the control system 400 may output the drive gear selection signal, which may comprise the double downshift signal, at time ti. At time t2, the automatic transmission system may begin performing the double downshift operation to disengage the first gear and engage the second gear, without engaging the intermediate gear. The double downshift operation may be completed at time ta.

[0084] Figures 6b illustrates an example brake signal 608 during execution the method 500 and Figure 6c illustrates a rate of change of brake input. Figure 6c illustrates a rate of change of brake input 610, which may be calculated as the differential of the brake signal 608. The rate of change of brake input 610 exceeds the brake rate threshold 612 during execution of the method 500. The double downshift signal may be output immediately upon the rate of change of brake signal 610 exceeding the brake rate threshold 612 or may be output based on the rate of change of brake signal 610 exceeding the brake rate threshold 612 for a required time period. In response to the rate of change of brake signal 610 exceeding the brake rate threshold 612, the double downshift signal may be output at time ti.

[0085] As illustrated in Figure 6d, which illustrates engine speed 614, due to the performance of the double downshift operation by the automatic transmission system, the engine speed may not drop below a minimum desirable engine speed 616. With reference to Figure 7, an alternative method 700 is described. The controller 410, e.g. the one or more processors, may be configured to perform the method 700. The method 700 comprises the blocks of the method 500. In other words, the method 700 comprises the method 500.

[0086] The method 700 may further comprise a shift map receiving block 702, in which the controller, e.g. the one or more processors, receives the shift map. As described above, the shift map may correlate required downshifts to vehicle operating conditions, such as engine speeds and accelerator pedal positions. The shift map may be stored in a memory within the controller and receiving the shift map may comprise retrieving the shift map from the memory.

[0087] The method 700 may comprise an engine speed receiving block 704, in which the controller, e.g. the one or more processors, receives an engine speed signal, e.g. from the engine speed sensor 221 , and an accelerator pedal position receiving block 706, in which the controller, e.g. the one or more processors, receives an accelerator pedal position signal, e.g. from the accelerator pedal position sensor 216. It will be appreciated that the shift map receiving block 702, engine speed receiving block 704 and accelerator pedal position receiving block 706 may be performed in any order and one or more of the blocks may be performed at least partially simultaneously.

[0088] The method 700 may further comprise a downshift command determination step 708, in which the controller, e.g. the one or more processors, determines whether to command a downshift based on the engine speed, the accelerator pedal position and the shift map.

[0089] The method 700 may further comprise a downshift signal output step 710, in which a downshift signal is output to cause a downshift from the first gear to the intermediate gear. As explained above, the first gear may be any gear of the vehicle and the intermediate gear may be a gear adjacent to the first gear. The downshift signal output step 710 may be performed based on determination performed in the downshift command determination step 708.

[0090] One or more blocks of the method 500 may be performed subsequently to one or more of the shift map receiving block 702, engine speed receiving block 704, accelerator pedal position receiving block 706, downshift command determination block 708 and downshift signal output block 710. In some arrangements, one or more blocks of the method 500 may be performed based on the determination performed in the downshift command determination block 708. For example, the double downshift signal may be output in the fifth block 510 based on the determining that the downshift command should be sent. The fifth block may be performed instead of the downshift signal output block 710. In other examples, the double downshift signal may be output in the fifth block 510 to override the downshift signal, e.g. output in the downshift signal output block 710.

[0091] The method 700 may comprise a downshift status determination block 712, in which a signal indicative of the status of a downshift operation, e.g. a single downshift, currently in progress is received, e.g. from the shift status sensor 222. As mentioned above, the shift status sensor 222 may be a clutch engagement sensor and in the downshift status determination block 712, the controller, e.g. the one or more processors may receive a signal from the clutch engagement sensor indicative of a level of engagement of a clutch for engaging the intermediate gear (which may be the destination gear of the single downshift operation currently being performed). The double downshift signal may be output, e.g. in the fifth block, based on the status of the single downshift operation. In particular, the double downshift signal may be output based on the level of engagement of the clutch for engaging the intermediate gear being below a threshold level of engagement.

[0092] The method 700 may comprise a speed determination block 714, in which the controller, e.g. the one or more processors, receives a signal indicative of the input speed to the automatic transmission system. The signal indicative of the input speed to the automatic transmission system may be received from the speed sensor 224.

[0093] The method 700 may comprise a gear ratio determination block 716, in which the controller, e.g. the one or more processors, receives a signal indicative of a gear ratio of the second gear and / or of the intermediate gear. In other words, the signal may indicate the gear ratio of a destination gear of a single and / or a double downshift operation for the automatic transmission system. The signal indicative of gear ratio of the second gear and / or of the intermediate gear may be received from the automatic transmission system or may be received from one of the processors of the controller. For example, the one or more processors may determine the gear ratio of the second gear and / or of the intermediate gear based on a currently selected gear of the automatic transmission system.

[0094] The method 700 may comprise a road gradient determination block 718, in which the controller, e.g. the one or more processors, receives a road gradient signal including information indicative of the road gradient. The road gradient signal may be received from the road gradient sensor 226.

[0095] The vehicle, e.g. the control system 400, may comprise a driving mode selector configured to determine a driving mode of the vehicle. For example, the one or more processors may comprise the driving mode selector. The driving mode may be one of a default mode, an economic mode, in which the operation of the powertrain is controlled to provide improved fuel economy compared to the default mode, and a performance mode, in which the operation of the powertrain is controlled to provide improved vehicle performance, e.g. in terms of possible vehicle accelerations, compared to the default mode. The method 700 may comprise a driving mode determination block 720, in which the one or more processors receive a signal indicative of the driving mode of the vehicle. The signal indicative of the driving mode of the vehicle may be received from the driving mode selector.

[0096] The method 700 may further comprise a driving tendency determination block 722, in which the one or more processors are configured to determine a driving tendency of the driver. The driving tendency of the driver may be a parameter describing a driving style of the driver and may be based, for example, on a rate of acceleration, e.g. longitudinal and / or lateral acceleration, previously experienced by the vehicle. It will be appreciated that the speed determination block 714, the gear ratio determination block 716, the road gradient determination block 718, driving mode determination block 720 and / or the driving tendency determination block 722 may be performed in any order and that one or more of the block may be performed at least partially simultaneously.

[0097] The method 700 may further comprise a brake rate threshold determination block 724, in which the brake rate threshold is determined. The brake rate threshold may be determined based on one or more of the signals received and / or the parameters determined in the speed determination block 714, the gear ratio determination block 716, the road gradient determination block 718, driving mode determination block 720 and / or the driving tendency determination block 722. It will be appreciated that in some examples, one or more of the speed determination block 714, the gear ratio determination block 716, the road gradient determination block 718, driving mode determination block 720 and / or the driving tendency determination block 722 may be omitted and the brake rate threshold may be determined based on the signals received and / or parameters determined in the blocks included in the method. The determined brake rate threshold may be between 50bar / s and 200bar / s.

[0098] In the brake rate threshold determination block 724, the brake rate threshold may be determined at least partially based on a difference in gear ratio between the first gear ratio, and the intermediate and / or second gear ratio. For example, when a difference in gear ratio between the first, and intermediate and / or second gear ratio is relatively low, e.g. compared to the difference between the gear ratios of other gears of the automatic transmission, a lower rate of brake input may be more likely to lead to a situation in which engine speed is reduced below a desirable speed. Accordingly, when the difference in gear ratio between the first, and intermediate and / or second gear ratio is relatively low then the brake rate threshold may be determined to be relatively low, e.g. compared to when the difference in gear ratio between the first, and intermediate and / or second gear ratio is relatively high.

[0099] In the fourth block 508 of the method 700, the rate of change of brake input may be compared to the brake rate threshold determined in the brake rate threshold determination block 724.

[0100] The method 700 may comprise an accelerator pedal position determination block 726, in which a signal indicative of the position of the accelerator pedal is received. The signal indicative of the position of the accelerator pedal may be received from the accelerator pedal position sensor 216. Additionally or alternatively, the method 700 may comprise a lubricant temperature determination block 728, in which a signal indicative of the temperature of lubricant within the automatic transmission system is received. The signal indicative of the temperature of lubricant within the automatic transmission system may be received from the lubricant temperature sensor 228. The accelerator pedal position determination block 726 and / or lubricant temperature determination block 728 may be performed sequentially or may be performed at least partially simultaneously with one another and / or any of the other blocks mentioned above.

[0101] The control system 400, described above with reference to Figure 4, may have a first operating mode and a second operation mode. In the first operating mode the double downshift signal may not be output by the controller 410. In other words, when the control system is in the first operating mode, the one or more processors may be inhibited from outputting the double downshift signal. In the second operating mode, the double downshift signal may be output by the controller 410, e.g. the one or more processor. The method 700 may further comprise an operating mode determination step 730, in which the operating mode of the control system is determined. The operating mode of the control system may be determined based on the position of the accelerator pedal, e.g. as determined in the accelerator pedal position determination block 726, and / or the temperature of lubricant in the automatic transmission system, e.g. as determined in the lubricant temperature determination block 728.

[0102] In the fifth block 510 of the method 700, the double downshift signal may be output based on the operating mode of the control system, e.g. as selected in the operating mode determination step 730.

[0103] The method 700 may further comprise a current gear determination block 732, in which the controller, e.g. the one or more processors, receives a signal indicative of a currently selected gear of the automatic transmission system. For example, the one or more processors may receive the signal indicative of a currently selected gear of the automatic transmission system from the automatic transmission system.

[0104] In the fifth block 510 of the method 700, the double downshift signal may be output based on the currently selected gear of the automatic transmission system, e.g. as determined in the current gear determination block 732. For example, the automatic transmission system may comprise six or more drive gears and the double downshift signal may be output based on the currently selected gear of the automatic transmission system being one of the highest, highest two, highest three, or highest four drive gears.

[0105] In some examples, the automatic transmission system may comprise one or more overdrive gears. The double downshift signal may be output, e.g. in the fifth block 510, based on the currently selected gear being an overdrive gear.

[0106] With reference to Figure 8, a further method 800 is described. The controller 410, e.g. the one or more processors, may be configured to perform the method 800. The method 800 comprises the blocks of the method 500 and the method 700. In other words, the method 800 comprises the method 500 and the method 700.

[0107] In the fourth block 508 of the method 800, the one or more processors may monitor the rate of change of brake pressure over a brake period, which may be a period of time during which the rate of change of brake input may exceed the threshold brake rate in order to trigger the output of the double downshift signal. The brake period may be a predetermined period of time.

[0108] In the fifth block 510 of the method 800, the double downshift signal may be output based on the rate of change of brake input exceeding the brake rate threshold for the brake period. The method 800 may further comprise a brake period determination block 802, in which the brake period is determined. The brake period may be determined based on one or more of the signals received or parameters determined in the speed determination block 714, the gear ratio determination block 716, the road gradient determination block 718, driving mode determination block 720 and / or the driving tendency determination block 722, as included in the method 800.

[0109] It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

CLAIMS1 . A control system for controlling an automatic transmission system of a vehicle, wherein the vehicle comprises a brake system, the brake system comprising a brake input device, and the automatic transmission system including at least three drive gears, the drive gears comprising a first gear having a first gear ratio, a second gear having a second gear ratio lower than the first gear ratio, and an intermediate gear having an intermediate gear ratio between the first and the second gear ratios, wherein the control system comprises one or more processors collectively configured to: receive a first brake signal containing information indicative of a first brake input to the brake input device at a first time; receive a second brake signal containing information indicative of a second brake input to the brake input device at a second time; determine a rate of change of brake input based on the first and second brake inputs; compare the rate of change of brake input to a brake rate threshold; and based on the rate of change of brake input exceeding the brake rate threshold, output a double downshift signal to cause the automatic transmission system to disengage the first gear and to engage the second gear, without engaging the intermediate gear.

2. The control system of claim 1 , wherein the brake system comprises a brake pressure sensor, wherein receiving the first and second brake signals comprises receiving first and second brake pressure signals from the brake pressure sensor at the first and second times respectively.

3. The control system of claim 1 or 2, wherein the vehicle comprises an internal combustion engine and an engine speed sensor arranged to determine a rotational speed of a crank shaft of the engine, an accelerator pedal arranged to control a power generated by the engine, and wherein the one or more processors are further configured to: receive a shift map correlating required downshifts to engine speeds and accelerator pedal positions, receive an engine speed signal from the engine speed sensor, the engine speed signal including information indicative of a rotational speed of the crank shaft, receive an accelerator pedal position signal from the accelerator pedal, the accelerator pedal position signal including information indicative of a position of the accelerator pedal, determine whether to command a downshift based on the engine speed, the accelerator pedal position and the shift map, output a downshift signal to cause a downshift from the first gear to the intermediate gear based on the determining; and output the double downshift signal to override the downshift signal.

4. The control system of any one of the preceding claims, wherein the vehicle comprises a speed sensor configured to determine an input speed to the automatic transmission system, wherein the one or more processors are further configured to: receive a signal indicative of the input speed to the automatic transmission; anddetermine the brake rate threshold at least partially based on the signal indicative of the input speed to the automatic transmission.

5. The control system of any one of the preceding claims, wherein the one or more processors are further configured to: receive a signal indicative of the gear ratio of the second gear and / or of the intermediate gear; and determine the brake rate threshold at least partially based on the gear ratio of the second gear and / or of the intermediate gear.

6. The control system of any one of the preceding claims, wherein the vehicle comprises a road gradient sensor configured to determine a gradient of the road on which the vehicle is driving, wherein the one or more processor are further configured to: receive a road gradient signal including information indicative of the road gradient; and determine the brake rate threshold at least partially based on the road gradient.

7. The control system of any one of the preceding claims, wherein the one or more processors are configured to: monitor the rate of change of brake input over a predetermined period of time; and wherein the double downshift signal is output based on the rate of change of brake input exceeding the brake rate threshold for the predetermined period of time.

8. The control system of any one of the preceding claims, wherein the control system has a first operating mode and a second operating mode, wherein the vehicle further comprises an accelerator pedal position sensor configured to determine a position of an accelerator pedal of the vehicle, wherein outputting of the double downshift signal is disabled in the first operating mode and enabled in the second operating mode, and wherein the one or more processors are configured to: receive a signal indicative of the position of the accelerator pedal; select the operating mode of the control system based on the position of the accelerator pedal.

9. The control system of any one of the preceding claims, wherein the control system has a first operating mode and a second operating mode, wherein the vehicle further comprises a transmission lubricant temperature sensor configured to determine a temperature of lubricant for the automatic transmission system, wherein outputting of the double downshift signal is disabled in the first operating mode and enabled in the second operating mode, and wherein the one or more processors are configured to: receive a signal indicative of the temperature of lubricant; and select the operating mode of the control system based on the temperature of lubricant.

10. The control system of any one of the preceding claims, wherein the automatic transmission system further comprises a clutch engagement sensor configured to determine a level of engagement of a clutch for engaging the intermediate gear, wherein the one or more processors are configured to: receive a signal from the clutch engagement sensor indicative of a level of engagement of a clutch for engaging the intermediate gear, wherein the double downshift signal is output based on the level of engagement of the clutch for engaging the intermediate gear being below a threshold level of engagement.11 . The control system of any one of the preceding claims, wherein the automatic transmission system comprises one or more overdrive gears, wherein the one or more processors are configured to: receive a signal indicative of a currently selected gear of the automatic transmission system, wherein the double downshift signal is output based on whether the currently selected gear is one of the one or more overdrive gears.

12. A system comprising the control system of any preceding claim and the automatic transmission system.

13. A vehicle comprising the system of claim 12 or the control system of any one of claims 1 - 11.

14. A method for controlling an automatic transmission system of a vehicle , wherein the vehicle comprises a brake system, the brake system comprising a brake input device, and the automatic transmission system including at least three drive gears, the drive gears comprising a first gear having a first gear ratio, a second gear having a second gear ratio lower than the first gear ratio, and an intermediate gear having an intermediate gear ratio between the first and the second gear ratios, the method comprising: receiving a first brake signal containing information indicative of a first brake input to the brake input device at a first time; receiving a second brake signal containing information indicative of a second brake input to the brake input device at a second time; determining a rate of change of brake input based on the first and second brake inputs; comparing the rate of change of brake input to a brake rate threshold; and based on the rate of change of brake input exceeding the brake rate threshold, outputting a double downshift signal to cause the automatic transmission system to disengage the first gear and to engage the second gear, without engaging the intermediate gear.

15. Computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform the method according to claim 14.

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