Hybrid vehicle speed and torque control

Abstract

Aspects of the invention relate to a method and control system for controlling an electric traction motor of a vehicle, the control system comprising one or more controllers, wherein the control system is configured to: in dependence on a gap-crossing protection rate limiter, limit a rate of change of torque requested from the electric traction motor for changing the speed towards a speed target; and when the limit is removed before the speed reaches the speed target, suppress an initial increase of torque requested from the electric traction motor for changing the speed towards the speed target.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a hybrid vehicle control system and method. In particular, but not exclusively, the present disclosure relates to a hybrid vehicle control system and method for controlling vehicle creep. BACKGROUND

[0002] The vehicle creep phenomenon occurs in vehicles that include a variator in the torque path between a prime mover (torque source) such as an internal combustion engine (engine) and the wheels. Vehicle creep causes the vehicle to move with the torque path connected and the engine idling. Vehicle creep occurs due to the fluid-coupling design of the variator.

[0003] In electric traction motor to wheel torque path including vehicles but not including a variator or requiring an "idling" electric or hybrid electric vehicle, a synthetic vehicle creep function can be provided to approximate the vehicle creep desired by the driver. A synthetic vehicle creep function can also be provided in vehicles having an engine and an automatic transmission such as a dual clutch automatic transmission, where a clutch pack is provided in place of a variator.

[0004] When entering a vehicle creep state, a reversal of the torque direction can occur. For example, when entering vehicle creep from a higher vehicle speed, the torque can switch from negative torque (overrun or braking) to positive torque (to maintain a minimum idle / creep speed). If the vehicle speed increases during vehicle creep, for example due to a downhill gradient, the vehicle creep torque will become negative to maintain the idle / creep speed. If the vehicle is brought to rest by a friction brake and the friction brake is then released, the torque can switch from negative to positive.

[0005] The reversal of the torque direction associated with vehicle creep can result in a lash crossing event which can impart a jerk and a perceptible torque shock to the vehicle occupants. A lash crossing event is defined as a backlash resulting from a reversal of the torque direction. The backlash results from a reversal of the direction of rotation, which absorbs any lost motion in the mechanisms such as the powertrain providing the torque path. The lash crossing event is most perceptible when the vehicle is in gear, as the lost motion of each component in the torque path is combined. Therefore, vehicle creep is associated with a perceptible lash crossing event. SUMMARY

[0006] It is an object of the present invention to address one or more of the disadvantages associated with the prior art, to improve the comfort of the vehicle occupants, and to improve durability.

[0007] Aspects and embodiments of the invention provide a control system, a vehicle, a method and computer software as claimed in the appended claims.

[0008] According to an aspect of the invention, there is provided a control system for controlling an electric traction motor of a vehicle, the control system comprising one or more controllers, wherein the control system is configured to: limit a rate of change of torque requested from the electric traction motor to change the speed towards the speed target in dependence on a gap-crossing protection rate limiter; and suppress (i.e. reduce or avoid) an initial increase in torque requested from the electric traction motor to change the speed towards the speed target when the limit is removed before the speed reaches the speed target.

[0009] An advantage is that the comfort and durability of the vehicle is improved because the jerk is reduced during the torque reversal instructed by the speed controller. Firstly, the jerk is reduced due to the gap-crossing protection rate limiter. Secondly, the jerk is reduced because the torque is suppressed from increasing sharply when the speed controller is reinitialised after the gap-crossing protection rate limiter is removed.

[0010] The control system can be configured to suppress the initial increase in torque by controlling an integrator torque of the control method (speed controller). An advantage is that the vehicle comfort after the rate limiter is removed is further improved by compensating for the tendency of the integrator torque to wind-up significantly when the rate limiter is applied.

[0011] The control system can be configured to suppress the initial increase in torque by reducing the integrator torque to at least partially unwind the integrator torque. An advantage is that additional wind-up as an effect of the gap-crossing protection rate limiter can be unwound.

[0012] In some examples, an integrator torque of a first torque requested from the electric traction motor after the gap-crossing protection rate limiter is removed is reduced. An advantage is that the torque subsequently ramps up smoothly because the integrator torque needs to wind-up again.

[0013] In some examples, the integrator torque is controlled to reduce or eliminate a step change in the requested torque when the limit is removed. In some examples, reducing the step change comprises reducing the step change to a magnitude of less than 10 Nm.

[0014] The control system can be configured to control the torque requested from the electric traction motor to change the speed towards the speed target using a proportional torque and an integrator torque and optionally a derivative torque after the limit is removed. An advantage is that the torque ramps up smoothly and quickly because a proportional-integral-derivative (PID) speed controller or a PI speed controller regains full control of the torque once the rate limiter is removed.

[0015] The control system can be configured to enable the torque requested from the electric traction motor to increase at a rate greater than the limit rate after the limit is removed and after the initial increase is suppressed. An advantage is that the required speed target can be reached quickly.

[0016] The speed target can be a vehicle creep speed target. An advantage is smoother vehicle creep and smoother transitions to / from vehicle creep.

[0017] In some examples, the engine is operable to provide tractive torque to a first set of wheels and the electric traction motor is operable to provide tractive torque to a second set of wheels. In an example, the first set of wheels are front wheels and the second set of wheels are rear wheels. In another example, the first set of wheels are rear wheels and the second set of wheels are front wheels. An advantage is that four wheel drive vehicle creep can be achieved.

[0018] In other examples, the electric traction motor is an engine accessory drive motor generator or a crankshaft integrated motor generator.

[0019] According to another aspect of the application, there is provided a vehicle comprising a control system, an engine and an electric traction motor.

[0020] According to another aspect of the application, there is provided a method of controlling an engine and an electric traction motor of a vehicle, the method comprising: limiting a rate of change of torque requested from the electric traction motor for changing a speed towards a speed target in dependence on a hysteresis crossing protection rate limiter; and suppressing an initial increase in torque requested from the electric traction motor for changing the speed towards the speed target when the limit is removed before the speed reaches the speed target.

[0021] According to another aspect of the application, there is provided computer software which, when executed, is arranged to perform any one or more of the methods described herein.

[0022] According to yet another aspect of the application, there is provided a non-transitory computer readable medium comprising computer readable instructions which, when executed by a processor, cause any one or more of the methods described herein to be performed.

[0023] According to another aspect of the application, there is provided a control system configured to perform any one or more of the methods described herein.

[0024] One or more controllers as described herein can collectively comprise: at least one electronic processor having an electrical input for receiving information indicative of a speed and / or a speed target; and at least one electronic 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 on the at least one memory device to cause the control system to control the electric traction motor in dependence on the information.

[0025] According to another aspect of the application, there is provided a control system for controlling an electric traction motor and / or an engine of a vehicle, the control system comprising one or more controllers, wherein the control system is configured to: limit a rate of change of torque requested from the electric traction motor and / or the engine for changing a speed towards a speed target in dependence on a gap-crossing protection rate limiter; and suppress (i.e. reduce or avoid) an initial increase in torque requested from the electric traction motor for changing the speed towards the speed target when the limit is removed before the speed reaches the speed target. In examples, the speed target can be an engine idle target.

[0026] Within the scope of the present application, it is expressly intended that each aspect, embodiment, example and alternative listed in the preceding paragraphs, in the claims, and / or in the following description and drawings can be employed independently or in combination with any of the other aspects, embodiments, examples and alternatives, and that the scope of the application extends to all such combinations. In other words, each aspect, embodiment, example and alternative described herein can be employed in any combination with any other aspect, embodiment, example and alternative described herein. That is, any feature of any aspect, embodiment, example or alternative described herein can be employed with any other aspect, embodiment, example or alternative described herein. The applicant reserves the right to, and does hereby, disclaim any subject matter not described in any claim of the application. The applicant reserves the right to, and does hereby, disclaim any subject matter that is not recited in any claim of the application. BRIEF DESCRIPTION OF DRAWINGS

[0027] One or more embodiments of the application will now be described, by way of example only, with reference to the accompanying drawings in which:

[0028] Figure 1 An example of a vehicle is shown;

[0029] Figure 2 An example of a system is shown;

[0030] Figure 3A An example of a control system is shown, and Figure 3B An example of a non-transitory computer-readable storage medium is shown;

[0031] Figure 4 An example of a method is shown;

[0032] Figure 5 a block diagram of an example speed controller is shown; and

[0033] Figure 6A an example of a graph having a vehicle speed axis and a time axis is shown, and Figure 6B an example of a graph having a torque request axis and a time axis is shown. DETAILED DESCRIPTION

[0034] Figure 1 An example of a vehicle 10 in which embodiments of the application can be implemented is shown. In some, but not necessarily all, examples, the vehicle 10 is a passenger vehicle, also referred to as a passenger car or motor car. In other examples, embodiments of the application can be implemented for other applications, such as industrial vehicles.

[0035] The vehicle 10 can be a hybrid electric vehicle (HEV) having a propulsion mode of pure electric propulsion and the like. The HEV can be configured to operate as a parallel HEV. A parallel HEV includes a torque path between an engine and at least one wheel, and a torque path between an electric traction motor and at least one wheel. The torque paths can be disconnected by a torque path connector such as a clutch. A parallel HEV is different from a series HEV in that in a series HEV the purpose of the engine is to generate electrical energy and there is no torque path between the engine and the wheels.

[0036] Figure 2 A system 20 for the parallel HEV 10 is shown. The system 20 at least partially defines a powertrain of the HEV.

[0037] The system 20 includes a control system 208. The control system 208 includes one or more controllers 10. The control system 208 can include one or more of a hybrid powertrain control module, an engine control unit, a transmission control unit, a traction battery management system, and the like.

[0038] The system 20 includes an engine 202. The engine 202 is a combustion engine. The illustrated engine 202 is an internal combustion engine. The illustrated engine 202 includes three combustion chambers, however a different number of combustion chambers can be provided in other examples.

[0039] The engine 202 is operably coupled to the control system 208 to enable the control system 208 to control an output torque of the engine 202. The output torque of the engine 202 can be controlled in accordance with the type of engine 202 by controlling one or more of the following: air-fuel ratio, spark timing, lifter lift, lifter timing, throttle valve opening position, fuel pressure, turbocharger boost pressure, and the like.

[0040] The system 20 includes an optional pinion starter 206 for starting the engine 202.

[0041] The system 20 includes a vehicle transmission arrangement 204 for receiving output torque from the engine 202. The vehicle transmission arrangement 204 can include an automatic vehicle transmission or a semi-automatic vehicle transmission. The vehicle transmission arrangement 204 includes a hydrodynamic coupling torque converter 217 between the engine 202 and the gear train.

[0042] The system 20 can include a differential (not shown) for receiving output torque from the gear train. The differential can be integrated into the vehicle transmission arrangement 204 as a drive axle, or can be provided separately.

[0043] The engine 202 is mechanically connected or connectable to a first set of wheels (FL, FR) via a torque path 220. The torque path 220 extends from an output of the engine 202 to the vehicle transmission arrangement 204, then to a wheel axle / drive axle, and then to the first set of wheels (FL, FR). In the event of vehicle overspeed and / or friction braking, torque can flow from the first set of wheels (FL, FR) to the engine 202. Torque flow towards the first set of wheels (FL, FR) is positive torque, and torque flow from the first set of wheels (FL, FR) is negative torque.

[0044] The illustrated first set of wheels (FL, FR) includes front wheels, and the wheel axle is a front transaxle. Thus, the system 20 is configured to drive the front wheels by the engine 202. In another example, the first set of wheels (FL, FR) includes rear wheels. The illustrated first set of wheels (FL, FR) is a pair of wheels, however, a different number of wheels can be provided in other examples.

[0045] In the illustrated system 20, no longitudinal (central) drive axle is provided in order to make space for hybrid vehicle components. Thus, the engine 202 is not connectable to a second set of rear wheels (rear wheels RL, RR in the illustration). The engine 202 can be mounted transversely to save space. In an alternative example, the engine 202 can be configured to drive both front and rear wheels.

[0046] A torque path connector 218, such as a clutch, is provided inside and / or outside a bell housing of the vehicle transmission arrangement 204. The clutch 218 is configured to connect and disconnect the torque path 220 between the engine 202 and the first set of wheels (FL, FR). The system 20 can be configured to automatically actuate the clutch 218 without user intervention.

[0047] The system 20 includes a first electric traction motor 216. The first electric traction motor 216 can be an alternating current induction motor or a permanent magnet motor or other type of motor. The first electric traction motor 216 is located on the engine side of a clutch 218.

[0048] The first electric traction motor 216 can be mechanically coupled to the engine 202 via a belt or chain. For example, the first electric traction motor 216 can be a belt-integrated-starter generator. In the illustration, the first electric traction motor 216 is located on the accessory drive end of the engine 202, opposite the vehicle transmission end of the engine 202. In alternative examples, the first electric traction motor 216 is a crankshaft-integrated motor generator located on the vehicle transmission end of the engine 202.

[0049] The first electric traction motor 216 is configured to apply positive torque to the crankshaft of the engine 202 and is configured to apply negative torque to the crankshaft of the engine 202, for example to provide functions such as: boost the output torque of the engine 202; disable (shut off) the engine 202 while stopped or coasting; enable (start) the engine 202; and regenerative braking in regenerative mode. In hybrid electric vehicle mode, both the engine 202 and the first electric traction motor 216 are operable to supply positive torque simultaneously to boost the output torque. The first electric traction motor 216 can not be capable of sustained pure electric drive.

[0050] However, when the torque path 220 between the engine 202 and the first set of wheels (FL, FR) is disconnected, the torque path 220 between the first electric traction motor 216 and the first set of wheels (FL, FR) is also disconnected.

[0051] Figure 2 A second electric traction motor 212 is shown that is configured to enable at least electric vehicle modes including pure electric drive. In some, but not necessarily all, examples, the second electric traction motor 212 has a nominal maximum torque that is greater than the nominal maximum torque of the first electric traction motor 216.

[0052] Even when the torque path 220 between the engine 202 and the first set of wheels (FL, FR) is disconnected by the clutch 218, the vehicle 10 can be driven in electric vehicle mode because the second electric traction motor 212 is connected to at least one wheel.

[0053] The second electric traction motor 212 is configured to provide torque to the second set of wheels (RL, RR) shown. The second set of wheels (RL, RR) comprises wheels that are not from the first set of wheels (FL, FR). The second set of wheels (RL, RR) shown comprises rear wheels, and the second electric traction motor 212 is operable to provide torque to the rear wheels RL, RR via a rear axle. Thus, the vehicle 10 is rear wheel drive in electric vehicle mode. In alternative examples, the second set of wheels comprises at least one of the wheels in the first set of wheels.

[0054] The control system 208 can be configured to disconnect the torque path 220 between the engine 202 and the first set of wheels (FL, FR) in electric vehicle mode to reduce parasitic pumping energy losses. For example, the clutch 218 can be opened. In Figure 2 In examples where the first electric traction motor 216 is also connected to the first set of wheels (FL, FR), this means that the first electric traction motor 216 will also be disconnected from the first set of wheels (FL, FR).

[0055] A further benefit of the second electric traction motor 212 is that the second electric traction motor 212 can also be configured to be operable in hybrid electric vehicle mode, enabling four wheel drive operation even without a central drive shaft.

[0056] To store the electric power for the electric traction motor, the system 20 comprises a traction battery 200. The traction battery 200 provides a nominal voltage required by the power consumer, e.g. the electric traction motor. If the electric traction motor is to be operated at a different voltage, a DC-DC converter (not shown) or the like can be provided to convert the voltage.

[0057] The traction battery 200 can be a high voltage battery. A high voltage traction battery provides a nominal voltage of several hundred volts, in contrast to a traction battery for a light HEV providing a nominal voltage of tens of volts. The traction battery 200 can have a voltage and capacity to support pure electric driving for a sustained distance. The traction battery 200 can have a capacity of several kilowatt hours to maximize the range. The capacity can be tens of kilowatt hours, or even more than a hundred kilowatt hours.

[0058] Although the traction battery 200 is shown as one entity, the functionality of the traction battery 200 can be implemented using a plurality of small traction batteries in different locations on the vehicle 10.

[0059] In some examples, the first electric traction motor 216 and the second electric traction motor 212 can be configured to receive electrical energy from the same traction battery 200. By pairing the first (lightweight) electric traction motor 216 with a high-capacity battery (tens to hundreds of kilowatt-hours), the first electric traction motor 216 can be able to provide the functionality of the methods described herein over sustained periods of time, rather than brief bursts. In another example, the electric traction motors 212, 216 can be paired with different traction batteries.

[0060] Finally, the illustrated system 20 includes inverters. Two inverters 210, 214 are shown, one for each electric traction motor. In other examples, one inverter or more than two inverters can be provided.

[0061] In alternative implementations, the vehicle 10 can differ from Figure 2 the illustrated.

[0062] Figure 3A How the control system 208 is implemented is illustrated. Figure 3A The control system 208 of the illustrated vehicle 10 illustrates a controller 300. In other examples, the control system 208 can include multiple controllers on and / or outside the vehicle 10.

[0063] Figure 3A The controller 300 includes at least one electronic processor 302 and at least one electronic memory device 304 electrically coupled to the electronic processor 302 and having instructions 306 (e.g., computer programs) stored therein, the at least one electronic memory device 304 and instructions 306 being configured to, with the at least one electronic processor 302, cause performance of one or more of the methods described herein.

[0064] Figure 3B A non-transitory computer-readable storage medium 308 including the instructions 306 (computer software) is illustrated.

[0065] The control system 208 can be configured to provide a controller output to manipulate a variable (torque) toward a setpoint. An example setpoint is at least one torque target. The at least one torque target can generally be based on a torque demand, such as a driver torque demand (e.g., accelerator pedal depression, APD), an autonomous driving torque demand, or a cruise control torque demand. The at least one torque target can generally be proportional to the torque demand. The torque targets can include an engine torque target for controlling an output torque of an engine. The torque targets can include an electric traction motor torque target for controlling an output torque of an electric traction motor.

[0066] Another example setpoint is a speed target. The speed target can include an engine speed target, such as an engine idle speed target, a vehicle speed target, or an electric traction motor speed target. Torque from the engine and / or electric traction motor torque can be controlled to match the speed to the speed target used during idle, vehicle creep, cruise control, or other scenarios.

[0067] The powertrain system 20, such as Figure 2 The powertrain system 20 can operate in a variety of modes. In one mode, the engine 202 is deactivated and the torque path 220 between the engine 202 and the first set of wheels (FL, FR) is disconnected. This mode can be an electric vehicle mode. In another mode, the engine 202 is reactivated and the torque path 220 is reconnected. Other modes can be a hybrid electric vehicle mode or an engine only mode.

[0068] The vehicle 10 can be configured to creep in one or more of the above modes. In the electric vehicle mode, the second electric traction motor 212 can implement a synthetic vehicle creep function. The synthetic vehicle creep can depend on a vehicle speed target. In the hybrid electric vehicle mode, the second electric traction motor 212 and the engine 202 can together implement a four-wheel drive vehicle creep. In some examples, the first electric traction motor 216 can be used to at least partially control the engine speed. In the hybrid electric vehicle mode or the engine only mode, the torque converter 217 can enable vehicle creep when the automatic vehicle transmission is in gear. The creep speed depends at least in part on an engine idle speed target, which can be constant or variable.

[0069] Depending on which mode the vehicle 10 is in or which mode is available, the creep speed depends at least in part on some form of speed control. The speed control can correspond to an engine idle speed controller that influences the creep speed, or a vehicle creep speed controller for synthetic vehicle creep.

[0070] Figure 4 A method 400 according to aspects of the application implemented by the control system 208 is shown. In the vehicle creep case, the method 400 includes:

[0071] Depending on the gap crossing protection rate limiter, limiting a rate of change of torque requested from the electric traction motor (212 or 216) for changing the speed toward the speed target (block 406); and

[0072] When the limit is removed before the speed reaches the speed target, suppressing an initial increase of torque requested from the electric traction motor for changing the speed toward the speed target (block 408, block 410).

[0073] At block 402, the method 400 includes determining whether the vehicle 10 is in or entering a vehicle creep condition. Satisfaction of the vehicle creep condition can require at least an APD below a threshold value, such as zero APD. Satisfaction of the vehicle creep condition can require that the torque path 220 between the engine 202 and the wheels be connected (e.g., check that the vehicle transmission device 204 is in gear and / or check that the clutch 218 is closed), and / or can require that the torque path between the second electric traction motor 212 and the wheels be connected. Satisfaction of the vehicle creep condition can require a vehicle speed below a threshold value. Satisfaction of the vehicle creep condition can depend on whether the vehicle creep function is enabled by the user.

[0074] If the vehicle creep condition is not satisfied, the method 400 terminates at block 404. If the vehicle creep condition is satisfied, the control system 208 implements a vehicle creep function configured to perform the method 400 described herein.

[0075] When activated, the vehicle creep function causes the control system 208 to act as a speed controller. The control system 208 obtains a speed target (setpoint). The speed target can be an engine idle target if the engine 202 is providing vehicle creep. For a synthetic creep function using the second electric traction motor 212, the speed target can be a vehicle creep speed target. The control system 208 determines a difference between the feedback speed and the speed target (speed error). The control system 208 outputs a torque request as a function of the speed error. The function can be based on a pre-calibration.

[0076] In implementations, a PI / PID controller is used to process the speed error. A current value of the speed error is used to calculate a proportional torque. Past values of the speed error can be accumulated for use in calculating an integrator torque. A rate of change of the speed error is used to calculate a derivative torque. The final torque request can be a sum of the proportional torque, the integrator torque, and the derivative torque, where each torque can be weighted differently.

[0077] At satisfaction of the vehicle creep condition, the method 400 proceeds to block 406. Block 406 includes applying a gap-crossing protection rate limiter when a torque reversal occurs. The gap-crossing protection rate limiter limits a rate of change of the controller output (torque request), for example by saturating the torque request when needed to ensure that the rate of change of the torque request is not higher than a predetermined rate.

[0078] The gap-crossing protection rate limiter can be applied (activated) when a torque in the relevant torque path is detected or predicted to be within a predetermined range. The endpoints of the predetermined range can be a negative torque and a positive torque, such that a zero-crossing of the torque occurs between the endpoints.

[0079] The endpoints of the range should not be so wide that the speed controller slows down significantly, as the settling time will increase significantly.

[0080] At block 408, the method 400 includes removing the gap-crossing protection rate limiter once the torque is outside the range. The speed can not have reached the speed target, so the control system 208 can continue to output the torque request.

[0081] At block 410, the method 400 includes suppressing an initial increase in the torque request. This is because otherwise the first value of the torque request after the removal of the rate limiter can be significantly higher than the previous value of the torque request when the rate limiter was applied, which can create a torque shock. Figure 5 、 Figure 6A and Figure 6B The effect of block 410 according to an example PID controller implementation is illustrated.

[0082] Figure 5 is a block diagram of a PI / PID (proportional, integral, and derivative) speed controller 500 (derivative block not shown) implementing the method 400. The speed controller 500 can be the function of the above-mentioned instruction 306 of the control system 208. The above-defined speed error is input into the controller 500.

[0083] A proportional torque weighting block (Kp) 506 weights the speed error and outputs a weighted proportional torque that is proportional to the speed error.

[0084] An integrator torque weighting block (Ki) 502 weights the speed error and outputs the weighted error to an integrator block 504 that computes a weighted integrator torque based on the accumulated speed error. The weighting gains applied by the integrator torque weighting block 502 and the proportional torque weighting block 506 can be different based on calibration.

[0085] An addition block 508 computes the torque request based on the sum of the weighted proportional torque and the weighted integrator torque.

[0086] The gap-crossing protection rate limiter module 510 saturates the torque request as described above if the torque request is within a predetermined range.

[0087] A feedback block 512 implements block 410 of the method 400 and is used for the first value of the torque request corresponding to the first time step after the removal of the rate limiter block 510. The feedback block 512 receives two torque requests as described below.

[0088] First, the feedback block 512 receives the (pre-limited) torque request output by the addition block 508 for input into the rate limiter block 510.

[0089] Second, the feedback block 512 receives the limited (final) torque request output by the limiter block 510 at the previous time step, or by the limiter block 510 at the current time step if the limiter block 510 is active.

[0090] The feedback block 512 subtracts the pre-limited torque request from the limited torque request. The feedback block 512 feeds the result of the subtraction to the integrator block 504, which subtracts the result from the integrator torque.

[0091] This subtraction feedback causes the integrator torque to decrease. Depending on the implementation, the decrease is such that the final torque request equals the final torque request of the previous time step, or the decrease is such that the final torque request is at the same gradient as the final torque request of the previous time step, while the rate limiter block 510 is still active. Thus, the feedback block 512 can be summarized as suppressing (decreasing or avoiding) the initial increase in torque requested by the speed controller when removing the limit imposed by the gap-crossing protection rate limiter.

[0092] The subtraction feedback eliminates most of the windup of the integrator torque that occurs while the rate limiter module 510 is active. As previously mentioned, one of the side effects of the rate limiter is that a high integrator windup occurs, which without the subtraction feedback would result in an immediate discontinuity in the torque request once the rate limiter is removed. As a result of the subtraction feedback, the initial value of the final torque request after the rate limiter is removed starts at or near the gradient of the rate limiter, and then increases smoothly as the integrator torque winds up again.

[0093] In another implementation, the calculation of the feedback block 512 can be modified to suppress (decrease) the integrator torque to a lesser degree than described above, as long as the step / discontinuity in the final torque request is less than the step / discontinuity that would occur without the feedback block 512 (see the description of Figure 6B , 614) later). The step can be less than 10 Nm.

[0094] In the example described above, the feedback block 512 decreases the integrator torque. In another implementation, the result of the feedback block 512 can be fed to the proportional torque and / or the derivative torque, although this can have a lesser impact than the integrator torque feedback. In another variant, the feedback block 512 can be replaced with an open-loop decelerator of the final torque request.

[0095] The above example is a PI / PID controller. In other examples, the concept of suppressing the initial increase in torque can be applied to another controller architecture.

[0096] Figure 6A and Figure 6BA plot of vehicle speed and (final) torque request is shown according to comparative examples. The comparative examples include: a speed controller without a gap-crossing protection rate limiter (short dashed line 602, 612); a speed controller with a gap-crossing protection rate limiter but without feedback for reducing integrator torque (long dashed line 604, 614); and a speed controller with a gap-crossing protection rate limiter and feedback as shown (solid line 606, 616). Figure 5

[0097] Between the marker times t0 and ti, the torque request is in the range associated with torque reversal (gap crossing). Between times ti and t2, the gap-crossing protection rate limiter is not active, and the speed still increases towards the speed target. At time t2, the speed target is reached.

[0098] Figure 6A A plot of the magnitude of the manipulated variable (vehicle speed) on the y-axis versus time on the x-axis is shown. The speed target is marked with a straight dashed line 600.

[0099] The short dashed line 602 shows that, without any gap-crossing protection, the vehicle speed increases fastest to the target, but a kickback can be felt.

[0100] The long dashed line 604 shows that, with only gap-crossing protection, the vehicle speed increases slowly during the torque reversal region to ti, but when the limit is removed, the gradient suddenly increases at time ti due to the discontinuity in the torque request. The change in gradient corresponds to a jerk in the vehicle that can disturb the vehicle occupants and create a torque kick. Compared to curve 602, it takes slightly longer for the vehicle speed to reach the speed target.

[0101] The solid line 606 shows that, with a PI / PID controller with Figure 5 , the vehicle speed increases at the same rate as line 604 during torque reversal, and there is no jerk at time ti. Compared to curves 602 and 604, it can take slightly longer for the vehicle speed to reach the speed target.

[0102] Figure 6B A plot of the magnitude of the torque request on the y-axis versus time on the x-axis is shown. The time axis is aligned with Figure 6A .

[0103] The short dashed line 612 indicates the torque associated with speed line 602, and shows that, without any gap-crossing protection, the torque increases at a high rate during torque reversal, which can result in a kickback and corresponding torque kick / jerk.

[0104] ​The long dashed line 614 indicates the torque associated with the speed line 604 and shows that with gap-crossing protection only, the torque increases at a lower rate during the torque reversal. At time tl, there is a torque discontinuity due to the integral windup of the torque as the rate limiter is removed.

[0105] In the illustration, the line 614 also shows that the gap-crossing protection rate limiter includes a first, lower rate limit up to a first threshold, and a second, higher rate limit between the first threshold and a second, higher threshold. This provides a good tradeoff between controller responsiveness and gap-crossing performance. In other implementations, the gap-crossing rate limiter can include more than two rates, or can include only one rate.

[0106] The solid line 616 represents the torque associated with the speed line 606 and shows that with a PI / PID controller having Figure 5 the same rate as line 614 during the torque reversal, and there is no discontinuity at time tl. The initial rate of increase of the torque after the limit is removed is no greater than the rate of increase limited prior to time tl, and the rate of increase of the torque is allowed to subsequently increase.

[0107] For the purposes of the present disclosure, it should be understood that the controllers 300 described herein can each comprise a control unit or computing device having one or more electronic processors 302. The vehicle 10 and / or its systems can comprise a single control unit or electronic controller, or alternatively, different functions of the controller can be embodied in or hosted by different control units or controllers. A set of instructions, which when executed, cause the controller or control unit to implement the control techniques described herein, including the described methods, can be provided. The set of instructions can be embedded in the one or more electronic processors, or alternatively, the set of instructions can be provided as software to be executed by the one or more electronic processors. For example, a first controller can be implemented in software running on one or more electronic processors, and one or more other controllers can also be implemented in software running on one or more electronic processors, optionally the same one or more processors as the first controller. However, it should be understood that other arrangements are useful, and thus, the present disclosure is not intended to be limited to any particular arrangement. In any case, the set of instructions described above can be embedded in a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium), which can include any mechanism for storing information in a form readable by a machine or electronic processor / computing device, including, without limitation: a magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or electrical or other types of medium for storing such information / instructions.

[0108] It is to be understood that various alterations and modifications can be made to the application without departing from the scope thereof.

[0109] Each paragraph described as an "aspect of the invention" is a separate statement standing on its own without the need for additional features for a current or future independent claim.

[0110] Figure 4 The illustrated boxes can represent steps in a method and / or portions of code in a computer program 306. The illustration of a particular order to the boxes is not necessarily meant to imply a required or preferred order of the boxes, and the order and arrangement of the boxes can vary. Additionally, it is possible that some steps can be omitted.

[0111] While embodiments of the application have been described in the preceding paragraphs in relation to various examples, it should be appreciated that modifications can be made to the examples given without departing from the scope of the application as claimed. For example, the examples can be applied to other non-crawling speed control use cases, such as cruise control.

[0112] Features described in the preceding description can be used in combinations other than the combinations explicitly described.

[0113] Although functions have been described with reference to certain features, those functions can be performed by other features whether described or not.

[0114] Although features have been described with reference to certain implementations, those features can exist in other implementations whether described or not.

[0115] Although efforts have been made to highlight those features of the application that are considered to be most important, it should be understood that the applicant desires protection for any patentable features or combination of features referred to herein, and / or in the drawings, whether or not they are specifically stated in the foregoing description.

Claims

1. A control system for controlling an electric traction motor of a vehicle, the control system comprising one or more controllers, wherein, the control system is configured to: limit a rate of change of torque requested from the electric traction motor for changing speed towards a speed target in dependence on a gap-crossing protection rate limiter; and suppress an initial increase of torque requested from the electric traction motor for changing speed towards the speed target by controlling an integrator torque of a control method when the limit is removed before the speed reaches the speed target.

2. The control system of claim 1, wherein, the one or more controllers collectively comprise: at least one electronic processor having an electrical input for receiving information indicative of speed and / or the speed target; and at least one electronic 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 to cause the control system to control the electric traction motor in dependence on the information.

3. The control system of any preceding claim, the control system being configured to suppress the initial increase of torque by reducing the integrator torque to at least partially cancel out a wind-up of the integrator torque.

4. The control system of claim 3, wherein, An integrator torque of a first torque requested from the electric traction motor after removal of the gap-crossing protection rate limiter is reduced.

5. A control system according to any preceding claim, wherein, The integrator torque is controlled to reduce or cancel out a step change in the requested torque when the limit is removed.

6. The control system of claim 5, wherein, Reducing the step change comprises reducing the step change to a magnitude of less than 10 Nm.

7. The control system of any preceding claim, the control system being configured to control torque requested from the electric traction motor to change speed towards the speed target after removal of the limit using a proportional torque and an integrator torque and optionally a derivative torque.

8. The control system of any preceding claim, the control system being configured to enable torque requested from the electric traction motor to increase to a rate greater than the limit rate after removal of the limit and after suppressing the initial increase.

9. A control system according to any preceding claim, wherein, The speed target is a vehicle crawl speed target or an engine idle speed target associated with vehicle crawling.

10. A control system according to any preceding claim, wherein, The engine is operable to provide tractive torque to a first set of wheels and wherein the electric traction motor is operable to provide tractive torque to a second set of wheels.

11. The control system of claim 10, wherein, The first set of wheels are front wheels and the second set of wheels are rear wheels or wherein the first set of wheels are rear wheels and the second set of wheels are front wheels.

12. The control system of any one of claims 1 to 9, wherein, The electric traction motor is an engine accessory drive motor generator or a crank integrated motor generator.

13. A vehicle comprising a control system and an electric traction motor as claimed in any preceding claim.

14. A method of controlling an engine and an electric traction motor of a vehicle, the method comprising: limiting a rate of change of torque requested from the electric traction motor for changing speed towards a speed target in dependence on a gap-crossing protection rate limiter; and when the speed reaches the speed target, the initial increase in torque requested from the electric traction motor to change the speed towards the speed target is suppressed by controlling an integrator torque of a control method.

15. Computer software which, when executed, is arranged to perform the method of claim 14.

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