Transmission system control

Abstract

Aspects of the present invention relate to a control system for controlling a transmission system of a vehicle, the control system comprising one or more processors collectively configured to: receive a first signal indicative of one or more vehicle conditions, wherein the first signal at least comprises a gradient signal indicative of a gradient of a surface on which the vehicle is located; determine, in dependence on the first signal, whether one or more criteria associated with the one or more vehicle conditions are met, wherein the one or more criteria at least comprise that a magnitude of a first rate of change of the gradient exceeds a rate of change threshold; and output, in dependence on a determination that the one or more criteria are met, a control signal to the transmission system to delay a change in a transmission gear for at least a first time period.

Description

[0001] TRANSMISSION SYSTEM CONTROL

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to an upshift inhibit in reaction to a road gradient change. Aspects of the invention relate to a control system, to a system, to a vehicle, to a method and to computer readable instructions.

[0004] BACKGROUND

[0005] It is known to provide an automatic transmission in a vehicle. Vehicles comprising automatic transmissions do not require input from a driver to shift gears. Gear management is instead provided by a control system to determine when a gear change should be initiated, and which gear is appropriate. Gear changes may be initiated based on changes in driving conditions, vehicle speed, road type, accelerator pedal position ora range of other factors.

[0006] It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

[0007] SUMMARY OF THE INVENTION

[0008] Aspects and embodiments of the invention provide a control system for controlling a transmission system of a vehicle, to a system, to a vehicle, to a method for controlling a transmission system of a vehicle and to computer readable instructions as claimed in the appended claims.

[0009] The disclosure provides a technique for improving the control of a transmission system of a vehicle. The technique determines whether one or more conditions of the vehicle such as the rate of change of gradient are met to thereby determine whether a delay to the change in transmission gear is needed.

[0010] According to an aspect of the present invention there is provided a control system for controlling a transmission system of a vehicle, the control system comprising one or more processors collectively configured to:

[0011] receive a first signal indicative of one or more vehicle conditions, wherein the first signal at least comprises a gradient signal indicative of a gradient of a surface on which the vehicle is located;

[0012] determine, in dependence on the first signal, whether one or more criteria associated with the one or more vehicle conditions are met, wherein the one or more criteria at least comprise that a magnitude of a first rate of change of the gradient exceeds a rate of change threshold; and

[0013] output, in dependence on a determination that the one or more criteria are met, a control signal to the transmission system to delay a change in a transmission gear for at least a first time period.

[0014] When driving on an undulating surface (such as a road), the transmission system can select an upshift as the gradient transitions from downhill to uphill or uphill to downhill. As the gradient transitions from downhill to uphill, it momentarily passes through a region of zero gradient. When passing through the zero gradient, an upshift can be commanded as the transmission system returns to the shift scheduling for flat or no gradient. This upshift is undesirable in conditions where the gradient quickly changes from downhill back to uphill. Thiscan cause an additional downshift to be actioned as the vehicle starts to climb uphill again. The control system improves the shift scheduling of a transmission system and prevents unnecessary gear changes.

[0015] The change in the transmission gear may be an upshift during the first time period and the control signal delays the upshift.

[0016] The control system comprises one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to:

[0017] receive a first signal indicative of one or more vehicle conditions, wherein the first signal at least comprises a gradient signal indicative of a gradient of a surface on which the vehicle is located;

[0018] determine, in dependence on the first signal, whether one or more criteria associated with the one or more vehicle conditions are met, wherein the one or more criteria at least comprise that a magnitude of a first rate of change of the gradient exceeds a rate of change threshold; and

[0019] output, in dependence on a determination that the one or more criteria are met, a control signal to the transmission system to delay a change in a transmission gear for at least a first time period.

[0020] Optionally, wherein the one or more processors are further collectively configured to determine the magnitude of the first rate of change of the gradient in dependence on gradient signals received at a first time and a second time respectively.

[0021] That is to say, the rate of change of the gradient may be determined by receiving a gradient signal at a first time, and a gradient signal at a second time subsequent to the first time, and determining a rate at which the gradient changes during this time period.

[0022] Optionally, wherein the one or more processors are further collectively configured to:

[0023] determine a magnitude of a second rate of change of the gradient in dependence on gradient signals received at a third time and a fourth time respectively; and

[0024] output, in dependence on a determination that the magnitude of the second rate of change of the gradient exceeds the rate of change threshold during the first time period, a control signal to the transmission system to further delay the change in the transmission gear for at least a second time period; or output, in dependence on a determination that the magnitude of the second rate of change of the gradient does not exceed the rate of change threshold during the first time period, a control signal to the transmission system to change the transmission gear.

[0025] In doing so, the rate of change is continuously monitored so as to further delay the transmission change where the road continues to be undulating or to allow the gear change to be enabled where the rate of change does not continue to exceed the threshold, that is to say, the gradient of the surface on which the vehicle is travelling is substantially constant.The second and third time may be contemporaneous. Alternatively, the third time may be subsequent to the second time.

[0026] Optionally, wherein the one or more criteria further comprise that the gradient is approaching zero.

[0027] As such, when a vehicle is approaching a flat region, this prevents a gear change in case a further uphill or downhill gradient occurs after the flat region within a certain time period. For example, under normal circumstances, a vehicle may change from a lower gear to a higher gear after going up a hill and traversing a flat region. However, this flat region may be momentary such that the vehicle will have to quickly swap gears again. By inhibiting the gear change on a flat portion, unnecessary gear changes are prevented.

[0028] Optionally, wherein the one or more criteria further comprise that a magnitude of the gradient exceeds a gradient threshold.

[0029] In doing so, this ensures that the delay to the transmission delay is only applied when the vehicle is travelling along steep enough gradients, and is not applied to relatively gentle gradients where a gear change is not necessary.

[0030] The gradient threshold may be between about -5% to about -10% and / or about 5% to about 10%.

[0031] Optionally, wherein the one or more processors are collectively configured to receive an indication of a driver mode, and wherein the one or more criteria comprise verifying that the driver mode is one of a predetermined group of driver modes.

[0032] In doing so, the transmission delay is activated when the vehicle is operating in certain driving modes, such as an offroad mode or sand mode, which are typically required when the vehicle is travelling along difficult and undulating terrain. In such modes, a lower gear may be more often required to traverse the terrain easily such that delaying a gear change in these modes is useful.

[0033] The predetermined group of driver modes may comprise one or more of offroad mode, sport mode, or sand mode.

[0034] Optionally, wherein the first signal further comprises a speed signal indicative of vehicle speed, and wherein the one or more criteria further comprise that the vehicle speed exceeds a speed threshold.

[0035] This prevents the delay being implemented where the driver is driving slowly, for example, the vehicle is travelling slowly over a speed bump. In such cases, it would be unnecessary for the delay to be applied after the speed bump. Similarly, in the case of larger gradients, if the vehicle is travelling slowly, the gear changes may still be necessary as the gradient changes.The speed threshold may be approximately 20mph.

[0036] Optionally, wherein the one or more processors are collectively configured to receive an indication of a driver demand, and wherein the one or more criteria comprise that the driver demand exceeds a demand threshold.

[0037] In doing so, the transmission delay is activated if the acceleration demanded by the user is above a certain level. A more aggressive driver demanding more acceleration from the vehicle will likely desire a lower gear in order to accelerate quickly compared to a driver applying less acceleration, and is likely to travel over any undulations more quickly, such that unnecessary changes in gear will be more noticeable to the driver. Thus, the transmission delay is responsive to the needs of the driver.

[0038] Optionally, wherein a duration of the first time period is dependent on one or more of: a vehicle speed, a driver mode, a driver demand, or a battery capacity.

[0039] For example, a vehicle travelling at a higher speed may be provided with a shorter time period. This is implemented as a vehicle will reach the next undulation quicker than someone travelling at a lower speed and therefore a shorter time period is sufficient for delaying the gear change. Different time periods can be applied dependent on the driver mode of the vehicle as such modes are representative of the road conditions and thus the form / period of undulations. Adjusting the time period dependent on driver demand is also useful as a shorter delay can be provided to a driver with lower acceleration demand and a longer time period can be provided to a more aggressive driver as it is more acceptable to maintain a lower gear when acceleration demand is higher. Vehicle performance can also be reduced if there is a fault in the vehicle battery or the battery has degraded. To counterthis, a longertime delay can be enabled to provide some ofthat performance back to the vehicle.

[0040] The driver demand can be torque demand, acceleration demand, or braking demand etc.

[0041] Optionally, wherein a duration of the second time period is dependent on one or more of: a vehicle speed, a driver mode, a driver demand, or a battery capacity.

[0042] Optionally, wherein the rate of change threshold is between about 5% per second upto about 20% per second.

[0043] This ensures that the delay is only implemented on undulating surfaces as the rate of change must be sufficiently high for the delay to be required.

[0044] According to another aspect of the invention, there is provided a system comprising the control system of any preceding statement, and a transmission system of a vehicle.

[0045] According to another aspect of the invention, there is provided a vehicle comprising the system of the preceding statement, or the control system of any preceding statement.According to another aspect of the invention, there is provided a method for controlling a transmission system of a vehicle, the method comprising:

[0046] receiving a first signal indicative of one or more vehicle conditions, wherein the first signal at least comprises a gradient signal indicative of a gradient of a surface on which the vehicle is located;

[0047] determining, in dependence on the first signal, whether one or more criteria associated with the one or more vehicle conditions are met, wherein the one or more criteria at least comprise that a magnitude of a first rate of change of the gradient exceeds a rate of change threshold; and

[0048] outputting, in dependence on a determination that the one or more criteria are met, a control signal to the transmission system to delay a change in a transmission gear for at least a first time period.

[0049] According to another aspect of the invention there is provided computer readable instructions which, when executed by a computer, are arranged to perform a method according to the preceding statement.

[0050] 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 anyway 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.

[0051] BRIEF DESCRIPTION OF THE DRAWINGS

[0052] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0053] Figure 1 shows a vehicle in accordance with an embodiment of the invention;

[0054] Figure 2 shows a schematic representation of a control system, inputs, and a powertrain;

[0055] Figure 3 shows a schematic representation of a control system;

[0056] Figure 4 shows a first flow chart showing a method for controlling a transmission system of a vehicle;

[0057] Figure 5 shows a schematic representation of an implementation of the method of Figure 4;

[0058] Figure 6 shows a schematic representation of an implementation of the method of Figure 4;

[0059] Figure 7 shows a second flow chart showing a method for controlling a transmission system of a vehicle; Figure 8 shows a schematic representation of an implementation of the method of Figure 7; and

[0060] Figure 9 shows a schematic representation of inputs to a control system.

[0061] DETAILED DESCRIPTION

[0062] Vehicles comprising automatic gearboxes do not require input from a driver to shift gears. Gear management is instead provided by a control system to determine when a gear change should be initiated and which gear is appropriate. Gear changes may be initiated based on changes in driving conditions, vehicle speed, road type, accelerator pedal position or a range of other factors.In order to determine a selected gear, a memory of the control system stores a plurality of shift maps, which relate vehicle driving conditions such as accelerator pedal position and drivetrain shaft speed to a recommended gear of the gearbox. The plurality of shift maps each relate to different operating conditions of the vehicle, such as gradients of a surface the vehicle is on, different vehicle masses and different driving styles. The control system may also interpolate between the stored shift maps to determine a further map that is most suitable for the operating conditions. The system may select or interpolate between these shift maps depending on a number of factors.

[0063] As such, the shift map may change when the vehicle is travelling on a changing gradient such as an undulating road with portions of uphill and downhill in quick succession. This may result in the system indicating that a downshift (or multiple downshifts) or an upshift (or multiple upshifts) is required. Based on the stored or determined shift map and the current gear, the control system suggests a target gear.

[0064] However, this can lead to unnecessary shifting in gears when driving on an undulating surface. For example, the control system may instruct a higher gear when transitioning from a downhill slope to an uphill slope when the vehicle travels on the flat portion between the downhill and the uphill. However, as the vehicle travels on the uphill the lower gear is required to traverse the uphill.

[0065] A shift inhibit may be used to prevent a recommended upshift or downshift. When the recommended gear for the vehicle is different from the current gear the vehicle is operating in, and the shift inhibit is enabled, the gearbox will not accept the recommended gear and the gearshift is not performed.

[0066] Having a shift inhibit ensures that unnecessary gear changes are minimised.

[0067] A vehicle 100 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 1.

[0068] With reference to Figure 1 , the vehicle 100 comprises a control system 102 as illustrated in Figures 2 and 3. The vehicle 100 also comprises a transmission system 106, and one or more input devices 104 which are arranged to provide data to the control system 102.

[0069] The control system 102 is arranged to control the transmission system 106. The vehicle 100 may be a mild hybrid electric vehicle (MHEV). An MHEV may be characterised by having no capacity to charge an electric battery using mains electricity and the electric battery may be charged by the internal combustion engine and regenerative braking only. Considered another way, the only primary energy source for an MHEV may be fossil fuels, for example petrol and diesel and the MHEV may have no electrical connection for charging the battery from an external source.

[0070] Alternatively, the vehicle 100 may be a plug-in hybrid electric vehicle (PHEV). A PHEV may be characterised by being arranged to receive electrical energy from an external source, such as via a connection to mains electricity. A PHEV may therefore comprise an external electrical connection for charging the battery.Further optionally, the vehicle 100 may have no electric machine and the only propulsion power source may be an internal combustion engine 204.

[0071] Figure 2 shows a schematic diagram 200 of the control system 102, transmission system 106 and input devices 104 of the vehicle 100. Three input devices 104 are shown for illustration purposes and the skilled person understands that one, two or more than three input devices 104 can be implemented as required.

[0072] The control system 102 is arranged to control a powertrain 202 and thus the transmission system 106 of the vehicle 100. The term powertrain is intended to mean a system comprising one or more power sources and a drivetrain 212 coupled to the one or more power sources. The powertrain 202 contains an internal combustion engine 204 and an electric machine 206. The internal combustion engine 204 and electric machine 206 may collectively be referred to as a single power source or as two power sources. Both transfer torque 208, 210 to a drivetrain 212 of the powertrain 202. The drivetrain 212 includes the transmission system 106 and may also include further components such as a torque splitter, a torque converter, and a differential. The drivetrain 212 is arranged to transfer torque to wheels 214 of the vehicle 100.

[0073] It will be understood that this represents only one possible vehicle architecture according to embodiments of the invention and that other vehicle architectures are also within the scope of the invention, such as architectures with a separate electric motor and electric generator. Further, the vehicle 100 may contain two or more separate powertrains such as fordriving the front and rear wheels of the vehicle 100 separately.

[0074] The control system 102 as illustrated in Figure 3 comprises one controller 314, although it will be appreciated that this is merely illustrative. The controller 314 comprises a processing means 302, a memory means 304, an input means 306 and an output means 308. The memory means 304 may store data about the vehicle 100, such as a plurality of shift maps and instructions for controlling the vehicle 100. The processing means 302 may be one or more electronic processing device which operably executes computer-readable instructions. The memory means 304 may be one or more memory device. The memory means 304 is electrically coupled to the processing means 302. The memory means 304 is configured to store instructions, and the processing means 302 is configured to access the memory means 304 and execute the instructions stored thereon. The input means 306 may be arranged to receive one or more input signals 310 such as from an inertial measurement unit, and the output means 308 may be arranged to output one or more output signals 312 such as a gear change command signal 228.

[0075] As shown in Figure 2, the control system 102 may provide signals 216, 218 to the internal combustion engine 204 and to the electric machine 206 to deliver a certain amount of torque or, in the case of the internal combustion engine 204, to advance or retard ignition timing or to increase or decrease a fuel / air mixture flow rate into the engine 204.The control system 102 may also receive signals 220, 222 from the internal combustion engine 204 and the electric machine 206 respectively. The signals 220, 222 may contain information indicative of rotational speed or temperature of the respective power source.

[0076] The control system 102 comprises the input means 306 and the output means 308. The input means 306 may comprise an electrical input of the control system 102. The output means 308 may comprise an electrical output of the control system 102. The input means 306 is arranged to receive input signals 310 and the output means 308 is arranged to output one or more output signals 312 such as a control signal 228 for controlling the drivetrain 212, including by instructing a gear change in the transmission system 106. The control system 102 is also configured to receive drivetrain data 229 from the drivetrain 212. The drivetrain data 229 may include information such as a target gear following an upshift, a gear change signal indicating that an upshift is about to occur and / or that a gear change has occurred, a torque converter slip value, indicating a level of slip from a torque converter of the drivetrain 212, and a predicted post-upshift gearbox input shaft speed.

[0077] The control system 102 is configured to receive a first signal 224 indicative of one or more vehicle conditions. The first signal 224 can be received by the control system 102 via input means 306 from a first input device 226. The first signal 224 comprises a gradient signal indicative of a gradient of a surface on which the vehicle 100 is located. The control system 102 is configured to determine whether one or more criteria associated with the one or more vehicle conditions are met. The determination is based on the first signal 224, and the one or more criteria comprise that a magnitude of a first rate of change of the gradient exceeds a rate of change threshold. The control system 102 may then output a control signal 228 via output means 308 to the transmission system 106 to delay a change in a transmission gear for at least a first time period based on a determination that the one or more criteria are met. Further vehicle conditions can be implemented as discussed with respect to Figure 9.

[0078] The control system 102 can additionally be configured to receive a second signal 228 from a second input device 230 and / or a third signal 232 from a third input device 234. It will be appreciated that the inclusion of three input devices 226, 230, 234 is merely illustrative. As an example, the input devices 104 can indicate the speed of the vehicle 100, a driver demand, or a driver mode.

[0079] Figure 4 illustrates a method 400 according to an embodiment of the invention. The method 400 is a method for controlling a transmission system 106 of a vehicle 100, such as the vehicle 100 illustrated in Figure 1. The method 400 may be performed by the control system 102 illustrated in Figures 2 and 3. In particular, the memory 304 may comprise computer-readable instructions which, when executed by the processor 302, perform the method 400 according to an embodiment of the invention.

[0080] As illustrated by the scenario 500 of Figure 5, when driving on an undulating surface (such as a road) represented by line 502, the transmission system 106 can select an upshift as the gradient transitions from downhill to uphill or uphill to downhill. As the gradient transitions from downhill to uphill, it momentarily passes through a region of zero gradient as can be seen by the flat portion of line 502. When passing through the zero gradient, an upshift can be commanded as the transmission system 106 returns to the shift scheduling for flator no gradient. This is represented by line 504 which shows, using existing methods, when the transmission system 106 may be instructed to change gears through an undulating road. Line 504 can be considered a ‘shift map index’. The upshift is undesirable in conditions where the gradient quickly changes from downhill back to uphill. This can cause an additional downshift to be actioned as the vehicle 100 starts to climb uphill again. This is illustrated by line 506 which shows an upshift in the gear when the vehicle 100 transitions from downhill to the flat portion of line 502 and a subsequent downshift when the vehicle 100 transitions from the flat portion to an uphill portion. The method 400 improves the shift scheduling of a transmission system and prevents unnecessary gear changes as illustrated by line 508 which shows no gear change throughout the undulating road represented by line 502. The method 400 is particularly advantageous for avoiding unnecessary upshifts.

[0081] At step 410, the control system 102 receives a first signal 224 indicative of one or more vehicle conditions. The first signal 224 at least comprises a gradient signal indicative of a gradient of a surface on which the vehicle 100 is located. In an example, the surface may be a road, a dirt track, sand etc. The gradient signal is determined using any known method to the skilled person such as using an inertial measurement unit (IMU).

[0082] The one or more vehicle conditions comprise the first signal 224 indicative of the gradient of the surface on which the vehicle 100 is travelling. However, the vehicle conditions may include additional conditions, as described below with respect to Figure 9. In some examples, the one or more vehicle conditions may comprise an indication of a driver mode of the vehicle 100. The driver mode is, for example, an offroad mode, a sport mode, a sand mode, an economy mode, a city mode, a comfort mode etc. In some examples, the first signal 224 comprises a speed signal indicative of the speed the vehicle 100 is travelling at. In some examples, the first signal 224 comprises a driver demand signal indicative of a driver demand. The driver demand is, for example, a torque demand, an acceleration demand, a braking demand etc. In other words, the driver demand is indicative of the driving style of the driver (e.g., harsh acceleration). For example, a driver may be driving aggressively (cornering quickly, braking sharply, accelerating fast) and thus may desire faster gear changes or to drive in lower gears, thereby allowing higher acceleration as opposed to optimised fuel efficiency. Any combination of these vehicle conditions can be implemented. That is to say, the first signal 224 comprises any combination of an indication of the gradient of the surface the vehicle 100 is travelling on, an indication of driver mode, a speed signal, or driver demand.

[0083] The gradient signal indicates the gradient of the surface. In particular, the gradient signal indicates a steep incline or a steep slope. For example, the gradient signal may indicate a gradient of -10%, -5%, 5%, 10% etc.

[0084] At step 420, the control system 102 determines whether one or more criteria associated with the one or more vehicle conditions are met based on the first signal 224 (including the gradient). The one or more criteria comprise that a magnitude of a first rate of change of the gradient exceeds a rate of change threshold. A threshold can be considered a quantitative point at which an action is triggered.

[0085] The magnitude of the first rate of change of the gradient is determined using at least the gradient signal received at step 410. The rate of change in the surface gradient is determined. For example, the rate of change in surface gradient could be -5% per second, +5% per second etc. The magnitude of this value is thendetermined (e.g., the magnitude of ±5% per second is 5% per second) and compared with a threshold value (i.e., a rate of change threshold). The rate of change threshold may be a predetermined threshold applied to all vehicles or may be dependent on the particular vehicle or one or more other factors.

[0086] In an example, the rate of change threshold may be any value between about 5% per second up to about 30% per second. For example, the rate of change threshold may be between about 5% per second to about 20% per second, between about 5% per second to about 10% per second, between about 10% per second to about 20% per second, between about 10% per second to about 30% per second, or between about 20% per second to about 30% per second. This ensures that the delay, discussed in relation to step 430, is only implemented on undulating surfaces as the rate of change must be sufficiently high for the delay to be required.

[0087] The magnitude of the first rate of change of the gradient can be in dependence on gradient signals received at a first time and a second time, respectively. That is to say, the rate of change of the gradient may be determined by receiving a gradient signal at a first time, and a gradient signal at a second time subsequent to the first time, and determining a rate at which the gradient changes during this time period.

[0088] If the rate of change in the surface gradient exceeds the rate of change threshold (e.g., the rate of change is 7% per second and the rate of change threshold is 5% per second), the process proceeds to step 430.

[0089] At step 430, if the one or more criteria are met (the magnitude of a first rate of change of the gradient exceeds a rate of change threshold), the control system 102 outputs a control signal 228 to the transmission system 106 to delay a change in a transmission gear for at least a first time period. This is illustrated by line 606 of Figure 6. Figure 6 shows an example scenario of a particular undulating road with corresponding shift map schedule 504 as described in relation to Figure 5. Figure 6 also shows when the delay to the transmission gear change can be applied and when the delay is active as an inhibitor as shown by line 608. As shown by line 606, when the vehicle 100 is transitioning from the downhill region to the flat region of line 502 at a first time 610, the first time period is started at the first time 610 and the delay to the change in the transmission gear is implemented. The delay is applied from the first time 610 to the second time 612 as represented by line 606. As represented by line 608, the inhibitor / delay is active from the first time 610 to the second time 612 and thus the transmission gear is not changed.

[0090] For example, the change in the transmission gear may be from a lower gear to a higher gear (i.e., an upshift). Alternatively, the change in the transmission gear may be from a higher gear to a lower gear (i.e., a downshift).

[0091] The delay is instructed for at least a first time period (e.g., from the first time 610 to the second time 612). The first time period can be changeable dependent on a number of factors. As an example, the first time period may be 5 seconds.

[0092] The delay functions as an inhibitor and causes the transmission system 106 to maintain its current gear rather than changing to a new gear instructed by the transmission system 106. For example, the transmission system 106 may instruct a higher gear when transitioning from a downhill to a flat section of road. However, the roadmay subsequently transition to an uphill in which a lower gear is typically preferred in order to maintain vehicle speed. By delaying the transmission change, the vehicle 100 is held in the lower gear and prevents an unnecessary upshift. The first time period is implemented so as to provide enough time for the undulating road to be registered whilst preventing the transmission system 106 from maintaining a gear for too long a period of time. In other words, the first time period is chosen so as not to allow the transmission system 106 to maintain a gear for too long a period where the surface gradient actually warrants a change in gear (i.e., the surface is no longer undulating).

[0093] The duration of the first time period can be dependent on one or more factors. As an example, the duration of the first time period is dependent on vehicle speed, driver mode, driver demand, or battery capacity of the vehicle 100. For example, a vehicle 100 travelling at a higher speed may be provided with a shorter time period. This is implemented as a vehicle 100 will reach the next undulation quicker than someone travelling at a lower speed and therefore a shorter time period is sufficient for delaying the gear change. Different time periods can be applied dependent on the driver mode of the vehicle 100 as such modes are representative of the road conditions and thus the form / period of undulations. Adjusting the time period dependent on driver demand is also useful as a shorter delay can be provided to a driver with lower performance demand and a longer time period can be provided to a more aggressive driver as it is more acceptable to maintain a lower gear when acceleration demand is higher. Vehicle performance can also be reduced if there is a fault in the vehicle battery or the battery has degraded. To counter this, a longer time delay can be enabled to provide some of that performance back to the vehicle 100. As such, the first time period may be varied dependent on any combination of the above factors.

[0094] Figure 7 illustrates a method 700 according to an embodiment of the invention. The method 700 is a method for controlling a transmission system 106 of a vehicle 100, such as the vehicle 100 illustrated in Figure 1. The method 700 may be performed by the control system 102 illustrated in Figures 2 and 3. In particular, the memory 304 may comprise computer-readable instructions which, when executed by the processor 302, perform the method 700 according to an embodiment of the invention.

[0095] Some of the steps performed by method 700 are the same as the steps in method 400 discussed with respect to Figure 4. In particular, step 710 corresponds to step 410, step 720 corresponds to step 420, and step 730 corresponds to step 430. Steps 740 to 760 are therefore optional steps which can be applied in addition to method 400.

[0096] At step 710, the control system 102 receives a first signal 224 indicative of one or more vehicle conditions. The first signal 224 at least comprises a gradient signal indicative of a gradient of a surface on which the vehicle 100 is located.

[0097] At step 720, the control system 102 determines whether one or more criteria associated with the one or more vehicle conditions are met based on the first signal 224. The one or more criteria comprise that a magnitude of a first rate of change of the gradient exceeds a rate of change threshold.At step 730, if the one or more criteria are met (e.g., the magnitude of a first rate of change of the gradient exceeds a rate of change threshold), the control system 102 outputs a control signal 228 to the transmission system 106 to delay a change in a transmission gear for at least a first time period (e.g., from the first time 610 to the second time 612 shown in Figures 6 and 8).

[0098] At step 740, the control system 102 determines a magnitude of a second rate of change of the gradient in dependence on gradient signals received at a third time and a fourth time respectively.

[0099] The second and third time may be contemporaneous. Alternatively, the third time may be subsequent to the second time. In other words, the second rate of change of gradient is determined after the first rate of change of gradient has been determined.

[0100] The process then proceeds to either step 750 or step 760 dependent on the determination at step 740.

[0101] If the magnitude of the second rate of change of the gradient exceeds the rate of change threshold during the first time period, the control system 102 outputs a control signal 228 to the transmission system 106 to further delay the change in the transmission gear for at least a second time period at step 750. This is represented by line 808 in Figure 8. As illustrated by Figure 8, the second time period begins at a third time which in this example is the same as the second time 612 and ends at a fourth time 814. The inhibitor is thus active from the first time 610 through to the fourth time 814 as represented by line 810.

[0102] If the magnitude of the second rate of change of the gradient does not exceed the rate of change threshold during the first time period, the control system 102 outputs a control signal 228 to the transmission system 106 to change the transmission gear at step 760.

[0103] In doing so, the rate of change is continuously monitored so as to further delay the transmission change where the road continues to be undulating or to allow the gear change to be enabled where the rate of change does not continue to exceed the threshold, that is to say, the gradient of the surface on which the vehicle 100 is travelling is substantially constant.

[0104] It is understood that whilst Figures 7 and 8 are described as comprising two time periods which cause a delay to the transmission change, the method 700 may be repeated continuously so as to implement additional time periods which cause additional delays to the transmission change. That is to say, the method 700 may return to step 740 on completion of step 750 or may return to step 710 on completion of step 760.

[0105] Similar to the duration of the first time period, the duration of the second time period can be changeable dependent on a number of factors. As an example, the duration of the second time period is dependent on vehicle speed, driver mode, driver demand, or battery capacity of the vehicle 100. For example, a vehicle 100 travelling at a higher speed may be provided with a shorter time period. This is implemented as a vehicle 100 will reach the next undulation quicker than someone travelling at a lower speed and therefore a shorter time period is sufficient for delaying the gear change. Different time periods can be applied dependent on the drivermode of the vehicle 100 as such modes are representative of the road conditions and thus the form / penod of undulations. Adjusting the time period dependent on driver demand is also useful as a shorter delay can be provided to a driver with lower acceleration demand and a longer time period can be provided to a more aggressive driver as it is more acceptable to maintain a lower gear when acceleration demand is higher. Vehicle performance can also be reduced if there is a fault in the vehicle battery or the battery has degraded. To counter this, a longer time delay can be enabled to provide some of that performance back to the vehicle 100. As such, the second time period may be varied dependent on any combination of the above factors. The first and second time period can be dependent on the same or different factors.

[0106] As an example, the second time period may be of the same duration as the first time period. Alternatively, the second time period may be of a shorter duration than the first time period. For example, the first time period may be 5 seconds and the second time period may be less than 5 seconds.

[0107] As illustrated by the input diagram 900 in Figure 9, whilst the methods 400 and 700 have been described with reference to the vehicle condition relating to the gradient of the surface the vehicle 100 is travelling on, further vehicle conditions may be received at step 410 of method 400 or step 710 of method 700 as an input to the control system 102. In otherwords, steps 410 and 710 comprise receiving a gradient signal and may comprise receiving additional inputs. The first input 902 is the gradient of the surface the vehicle 100 is travelling on. In some examples, the one or more vehicle conditions comprise an indication of a driver mode of the vehicle 100 and thus the control system 102 receives a second input 904 indicative of the driver mode at step 410 or step 710. The driver mode is, for example, an offroad mode, a sport mode, a sand mode, an economy mode, a city mode, a comfort mode etc. In some examples, the one or more vehicle conditions comprise a speed signal indicative of the speed the vehicle 100 is travelling at and thus the control system 102 receives a third input 906 indicative of the speed of the vehicle 100 at step 410 or step 710. In some examples, the one or more vehicle conditions comprise an indication of a driver demand and thus the control system 102 receives a fourth input 908 indicative of the driver demand at step 410 or step 710. The driver demand is, for example, a torque demand, an acceleration demand, a braking demand etc. In otherwords, the driverdemand is indicative of the driving style of the driver (e.g., harsh acceleration). Any combination of these vehicle conditions can be received by the control system in the methods 400 and 700. That is to say, the one or more vehicle conditions comprise any combination of the first input 902, the second input 904, the third input 906, or the fourth input 908.

[0108] If each of the vehicle conditions satisfy associated criteria as determined at step 420 of the method 400 or step 720 of the method 700, the control system 102 provides an output 912 instructing a delay to the transmission change as described with respect to steps 430 and 730 of methods 400 and 700.

[0109] The first input 902 has an associated criteria that a magnitude of a first rate of change of the gradient exceeds a rate of change threshold as discussed with respect to Figure 4. The first input 902 may additionally comprise the criteria that the gradient is approaching zero and / or that a magnitude of the gradient exceeds a gradient threshold. The gradient approaching zero can encompass gradients which are beginning to level off to zero. By including the additional criteria that the gradient is approaching zero, a gear change is prevented in case afurther uphill or downhill gradient occurs after the flat region within a certain time period. For example, under normal circumstances, a vehicle 100 may change from a lower gear to a higher gear after going up a hill and traversing a flat region. However, this flat region may be momentary such that the vehicle 100 will have to quickly swap gears again. By inhibiting the gear change on a flat portion, unnecessary gear changes are prevented. The additional criteria that a magnitude of the gradient exceeds a gradient threshold ensures that the delay to the transmission change is only applied when the vehicle 100 is travelling along steep enough gradients, and is not applied to relatively gentle gradients where a gear change is not necessary. As an example, the gradient threshold may be between about -5% to about -10% and / or about 5% to about 10%.

[0110] The second input 904 has an associated criteria that the driver mode is one of a predetermined group of driver modes. The predetermined group of driver modes may comprise one or more of offroad mode, sport mode, or sand mode. In doing so, the transmission delay is activated when the vehicle 100 is operating in certain driving modes, such as an offroad mode or sand mode, which are typically required when the vehicle 100 is travelling along difficult and undulating terrain. In such modes, a lower gear may be more often required to traverse the terrain easily such that delaying a gear change in these modes is useful.

[0111] The third input 906 is associated with a criterion that the vehicle speed exceeds a speed threshold. This prevents the delay being implemented where the driver is driving slowly, for example, the vehicle 100 is travelling slowly over a speed bump. In such cases, it would be unnecessary for the delay to be applied after the speed bump. Similarly, in the case of larger gradients, if the vehicle 100 is travelling slowly, the gear changes may still be necessary as the gradient changes. As an example, the speed threshold is approximately 20mph.

[0112] The fourth input 908 is associated with a criterion that the driver demand exceeds a demand threshold. In doing so, the transmission delay can be extended when the demand by the user is above a certain level. A more aggressive driver demanding more performance (e.g., more power and / or more torque etc) from the vehicle 100 will likely desire a lower gear in order to accelerate quickly compared to a driver applying less demand, and is likely to travel over any undulations more quickly, such that unnecessary changes in gear will be more noticeable to the driver. Thus, the transmission delay is responsive to the needs of the driver.

[0113] 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 a transmission system of a vehicle, the control system comprising one or more processors collectively configured to:receive a first signal indicative of one or more vehicle conditions, wherein the first signal at least comprises a gradient signal indicative of a gradient of a surface on which the vehicle is located;determine, in dependence on the first signal, whether one or more criteria associated with the one or more vehicle conditions are met, wherein the one or more criteria at least comprise that a magnitude of a first rate of change of the gradient exceeds a rate of change threshold; andoutput, in dependence on a determination that the one or more criteria are met, a control signal to the transmission system to delay a change in a transmission gear for at least a first time period.

2. The control system of claim 1 , wherein the one or more processors are further collectively configured to determine the magnitude of the first rate of change of the gradient in dependence on the gradient signals received at a first time and a second time respectively.

3. The control system of any preceding claim, wherein the one or more processors are further collectively configured to:determine a magnitude of a second rate of change of the gradient in dependence on gradient signals received at a third time and a fourth time respectively; andoutput, in dependence on a determination that the magnitude of the second rate of change of the gradient exceeds the rate of change threshold during the first time period, a control signal to the transmission system to further delay the change in the transmission gear for at least a second time period; or output, in dependence on a determination that the magnitude of the second rate of change of the gradient does not exceed the rate of change threshold during the first time period, a control signal to the transmission system to change the transmission gear.

4. The control system of any preceding claim, wherein the one or more criteria further comprise that the gradient is approaching zero.

5. The control system of any preceding claim, wherein the one or more criteria further comprise that a magnitude of the gradient exceeds a gradient threshold.

6. The control system of any preceding claim, wherein the one or more processors are collectively configured to receive an indication of a driver mode, and wherein the one or more criteria comprise verifying that the driver mode is one of a predetermined group of driver modes.

7. The control system of any preceding claim, wherein the first signal further comprises a speed signal indicative of vehicle speed, and wherein the one or more criteria further comprise that the vehicle speed exceeds a speed threshold.

8. The control system of any preceding claim, wherein the first signal comprises a driver demand signal indicative of a driver demand, and wherein the one or more criteria comprise that the driver demand exceeds a demand threshold .

9. The control system of any preceding claim, wherein a duration of the first time period is dependent on one or more of: a vehicle speed, a driver mode, a driver demand, or a battery capacity.

10. The control system of any of claims 4 to 9, when dependent on claim 3, wherein a duration of the second time period is dependent on one or more of: a vehicle speed, a driver mode, a driver demand, or a battery capacity.11 . The control system of any preceding claim, wherein the rate of change threshold is between about 5% per second up to about 20% per second.

12. A system comprising the control system of any preceding claim, and a transmission system of a vehicle .

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

14. A method for controlling a transmission system of a vehicle , the method comprising:receiving a first signal indicative of one or more vehicle conditions, wherein the first signal at least comprises a gradient signal indicative of a gradient of a surface on which the vehicle is located;determining, in dependence on the first signal, whether one or more criteria associated with the one or more vehicle conditions are met, wherein the one or more criteria at least comprise that a magnitude of a first rate of change of the gradient exceeds a rate of change threshold; andoutputting, in dependence on a determination that the one or more criteria are met, a control signal to the transmission system to delay a change in a transmission gear for at least a first time period.

15. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to claim 14.

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