Engine speed stability

Abstract

Stabilization of engine speed is disclosed. A vehicle includes an engine. The vehicle includes a controller configured to: start a timer having a duration defined by a charge limit of a traction battery, and maintain engine braking and reduce a predetermined rate of change limit of engine speed during the duration. Starting the timer is responsive to depressing an accelerator pedal during engine braking. The controller is further configured to: increase the predetermined rate of change limit of the engine speed in response to expiration of the timer.

Description

Technical Field

[0001] The present disclosure relates to stabilization of engine speed. Background Art

[0002] The vehicle may employ engine braking to supplement friction braking or regenerative braking. The negative torque provided by engine braking may be related, proportional, or otherwise associated with the speed of the engine. Actuation of the accelerator pedal may cause the vehicle system controller to reduce the engine braking torque by reducing the engine speed, which may change the audible engine noise perceived by the vehicle occupants. The change in perceived noise may be distracting to the vehicle occupants, particularly when the sounds of engine braking and engine propulsion are similar. Summary of the invention

[0003] A vehicle includes an engine. The vehicle includes a controller configured to: start a timer having a duration defined by a charge limit of a traction battery, during which engine braking is maintained and a predetermined rate of change limit of engine speed is reduced. Starting the timer is responsive to depressing an accelerator pedal during engine braking. The controller is further configured to: in response to expiration of the timer, increase the predetermined rate of change limit of the engine speed.

[0004] A vehicle includes an engine. The vehicle includes a controller configured to: start a timer having a duration defined by a charge limit of a traction battery. The controller is configured to: reduce a predetermined rate of change limit of engine speed. The controller may start the timer and reduce the rate of change in response to an accelerator pedal being released during engine acceleration. The controller is further configured to: increase the predetermined rate of change of a threshold. The increase is in response to the timer expiring.

[0005] According to an embodiment of the invention, the output torque of the engine is reduced during said duration.

[0006] According to one embodiment of the invention, the output torque of the engine is offset during said duration by an electric motor associated with a driveline of the vehicle.

[0007] According to one embodiment of the present invention, the predetermined change rate threshold is negative.

[0008] A vehicle includes an engine. The vehicle includes a controller configured to: start a timer having a duration defined by a charge limit of a traction battery. The controller is configured to: maintain engine speed via wheel torque of the vehicle and a reaction force of a generator associated with the vehicle. The controller is further configured to: increase a predetermined rate of change of engine speed. The increase is responsive to expiration of the timer.

[0009] According to the present invention, a vehicle is provided, comprising: an engine; and a controller configured to: in response to pressing an accelerator pedal during engine braking, start a timer and maintain the engine speed via the vehicle's wheel torque and the reaction force of a generator associated with the vehicle, and in response to expiration of the timer, reduce the engine speed.

[0010] According to one embodiment of the invention, the duration of the timer is based on a charge limit of the traction battery.

[0011] According to one embodiment of the invention, the output torque of the engine during the duration of the timer is offset by an electric motor associated with the vehicle's driveline. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic diagram of a hybrid vehicle;

[0013] Figure 2 It is a graph including accelerator pedal depression, engine speed reduction and timer;

[0014] Figure 3 It is a graph including accelerator pedal release, engine speed reduction and timer;

[0015] Figure 4 is a graph including a duration of a timer and a charge limit of a traction battery;

[0016] Figure 5 is a flow chart of a timer used to reduce the rate of change of engine speed over a predetermined duration. DETAILED DESCRIPTION

[0017] A number of embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples and that other embodiments may take various and alternative forms. The drawings need not be drawn to scale; some features may be exaggerated or minimized to show the details of a particular component. Therefore, the specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art to apply the present invention in a variety of ways. As will be understood by those of ordinary skill in the art, the various features illustrated and described with reference to any of the accompanying drawings may be combined with the features shown in one or more of the other drawings to produce embodiments that are not explicitly shown or described. The combination of features shown provides representative embodiments for typical applications. However, various combinations and variations of features consistent with the teachings of the present disclosure may be desired for specific applications or implementations.

[0018] The internal combustion engine of a hybrid electric vehicle can be used to decelerate the vehicle through engine braking. Various types of engine braking and hybrid electric vehicles are available and can be used. Engine braking can use the inherent compression caused by the stroke of the piston and inherent friction to resist engine rotation, thereby applying negative torque to the powertrain.

[0019] The rotation of the engine can provide an auditory indication of the vehicle operation to the vehicle occupants. Meaning, the occupants can gather the vehicle acceleration characteristics from the noise generated by the engine. As discussed above, hybrid vehicles that employ engine braking may confuse the occupants because the sound caused by the engine speed is inconsistent with the torque applied to the powertrain or to accelerate and decelerate the vehicle. The timer can be implemented to reduce unstable engine speeds and reduce the confusion caused to the vehicle occupants. The timer can be based on engine braking predictions. The engine braking prediction can be based on road grade, battery charging limits, and other factors. The battery charging limit indicates the amount of regenerative braking available. As the charging limit based on the state of charge of the battery is reduced, the regenerative braking capacity decreases. As the regenerative braking capacity decreases, unstable engine speeds can be predicted because when driving down a slope with a slope that requires vehicle speed management, engine braking will be used together with the reduced regenerative braking capacity to maintain vehicle speed.

[0020] exist Figure 1 Schematically illustrated is a powertrain for a hybrid electric vehicle. The powertrain includes an internal combustion engine 20 drivably connected to a planet carrier 22, a generator 24 drivably connected to a sun gear 26, and an output shaft 28 drivably connected to a ring gear 30. Elements are drivably connected when there is a mechanical power flow path between the elements so that the rotational speeds of the elements are constrained to be approximately proportional. The planet carrier 22 supports a set of planetary gears 32 so that each planetary gear is continuously meshed with the sun gear 26 and the ring gear 30. For example, the output shaft 28 drives the wheels directly or indirectly (such as through a differential assembly).

[0021] The traction motor 34 is drivably connected to the output shaft 28. The generator 24 and the traction motor 34 are both reversible electric machines capable of converting electrical power into rotary mechanical power or converting rotary mechanical power into electrical power. The terms "generator" and "motor" should be considered as labels for convenience of description only and do not limit the function or operation of either motor. Both the generator 24 and the traction motor 34 are electrically connected to the battery 36.

[0022] The speeds of the sun gear 26, the planet carrier 22, and the ring gear 30 are linearly related, so that the speed of the planet carrier 22 is a weighted average of the speeds of the sun gear 26 and the ring gear 30. Therefore, in this arrangement, the speed of the engine 20 is not constrained to be proportional to the speed of the output shaft 28. Alternatively, by setting the generator speed, the engine speed can be selected or controlled accordingly independent of the vehicle speed. Power flows from the engine to the output shaft through a combination of mechanical power transmission and electrical power transmission. During some operating conditions, the engine 20 may produce more power than is delivered to the output shaft 28, and the difference (ignoring efficiency losses) is delivered to the battery. Under other operating conditions, the battery 36 in combination with the generator 24 and / or the traction motor 34 can supplement the power delivered by the engine 20, so that more power is delivered to the output shaft 28.

[0023] The engine 20, generator 24 and traction motor 34 are all responsive to control signals from a controller 38. These control signals determine the amount of torque produced. The controller also receives speed signals from the engine 20, generator 24 and traction motor 34 and a state of charge signal from the battery 36. The controller receives input signals from an accelerator pedal 40 and a road grade sensor 44 indicating the driver's intent.

[0024] Figure 2 A graph 100 showing the state of a vehicle accelerator pedal position 102, engine speed 110, and timer 120 is shown. The curve of the accelerator pedal position 102 indicates a step-on event 104 when the vehicle 10 is on a downward slope and speed assist is enabled. The accelerator pedal indicates that the driver may need to accelerate. The step-on event 104 may be determined based on a percentage change or rate of change of the accelerator pedal position 102 indicating a change in driver demand. In response to the change in the pedal position 102, as shown at point 116, the controller 38 may be configured to reduce the engine speed 110 under normal operation. Under normal operation, the engine speed 110 may have a rate of change 112. In response to the step-on event 104, a timer 120 having a duration 122 may be started at point 124. The rate of change 112 may be reduced within the duration 122 so that the engine speed 110 is maintained, as shown by curve 114. The engine speed 110 may have a reduced rate of change 112 so that the curve 114 is not horizontal. The curve 114 may be positive linear or negative linear. The curve 114 may be concave, convex, or a completely different function. The reduced rate of change 112 may be a function of the timer duration 122 or a function of the step-down event duration 106 , and the reduced rate of change 112 will accumulate over time.

[0025] Figure 3A graph 200 showing states of a vehicle accelerator pedal position 202, engine speed 210, and timer 220 is shown. The graph of accelerator pedal position 202 indicates a release event 204 when the vehicle 10 is on a downward slope and speed assist is enabled. The driver may have accelerated downhill and is now backing off the accelerator pedal. The release event 204 may be determined based on a percentage change or rate of change in the accelerator pedal position 202 that indicates a change in driver demand. In response to the change in pedal position 202, as shown at point 216, the controller 38 may be configured to reduce the engine speed 210 under normal operation. Under normal operation, the engine speed 210 may have a rate of change 212. In response to the release event 204, a timer 220 having a duration 222 may be started at point 224. The rate of change 212 may be reduced over the duration 222 so that the engine speed 210 is maintained, as shown by curve 214. The engine speed 210 may have a reduced rate of change 212 so that the curve 214 is not horizontal. The curve 214 may be positive linear or negative linear. The curve 214 may be concave, convex, or a completely different function. The decreasing rate of change 212 may be a function of the timer duration 222.

[0026] Figure 4 A graph 300 of a timer 304 and a charge limit 306 is shown. The timer-limit curve 302 represents the timer duration 304 as a function of the charge limit 306. The charge limit 306 may be based on the state of charge of the traction battery 36. The charge limit 306 may be based on a thermal limit. As shown, the magnitude of the charge limit 306 may be inversely proportional to the duration of the timer 304. When the charge limit 306 is a maximum charge limit or a charge limit threshold associated with the traction battery 36 (which may vary depending on the battery manufacturer and model), the duration of the timer 304 is zero.

[0027] Figure 5 A flow chart 400 is shown. The flow chart begins at start 402. In step 404, the controller 38 determines whether the engine 20 is turning. In step 406, the controller 38 determines whether the accelerator pedal 40 has been depressed or released. The determination of whether the accelerator pedal 40 has been depressed or released may depend on a percentage change in the accelerator pedal position, the absolute position of the pedal passing a threshold, or a combination thereof. If the accelerator pedal 40 has been depressed or released in step 406, the timer 304 may be started in step 408. The start of the timer may be adjusted or delayed to compensate for other environmental factors.

[0028] During the time period 302, the controller 38 may reduce the rate of change limit of the engine speed 110, 210 in step 410. Meaning, the rate of change 112, 212 of the speed of the engine 20 is limited. In other words, it may remain unchanged in a particular embodiment. For example, the engine may have a specific speed that is driven by the torque setting of the controller 38. The torque setting may be determined by the accelerator position or environmental factors. In a speed-controlled environment, the engine speed 110, 210 may change with the position of the accelerator pedal 40. For example, the engine braking torque may be based on the engine speed 110, 210. As the engine speed 110, 210 increases, the engine braking torque also increases. In this case, the depression of the accelerator pedal may cause the engine speed 110, 210 to decrease, which will reduce the negative torque provided by the engine 20. Under the condition of the low charge limit 306 (e.g., high battery state of charge), it can be predicted that engine braking will occur during downhill and suitable for enabling vehicle speed control. Thus, the engine speed 110, 210 may be maintained while the engine torque is reduced in anticipation of future engine braking. Maintaining the engine speed 110, 210 may reduce driver confusion caused when the engine speed changes while maintaining the vehicle speed, because drivers typically associate engine noise with vehicle speed. The engine speed 110, 210 may be maintained for the duration 122, 222 of the timer 304. The rate of change of the engine speed 110, 210 may be reduced for the duration 122, 222 of the timer 304. When the timer expires in step 412, the rate of change of the engine speed may be changed in step 414. The process may end or continue to run in step 416.

[0029] The words used in the specification are descriptive words rather than restrictive words, and it should be understood that, without departing from the spirit and scope of the present disclosure, various changes can be made. As described above, the features of multiple embodiments can be combined to form further embodiments of the present invention that may not be clearly described or shown. Although multiple embodiments may be described as providing advantages or being superior to other embodiments or prior art embodiments in one or more desired characteristics, it should be appreciated by those of ordinary skill in the art that, according to specific applications and embodiments, one or more features or characteristics can be compromised to achieve desired overall system properties. These properties may include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, maintainability, weight, manufacturability, ease of assembly, etc. Therefore, embodiments described as being less desirable than other embodiments or prior art embodiments in one or more characteristics are not outside the scope of the present disclosure, and can be expected to be used for specific applications.

Claims

1. A vehicle comprising: engine; The controller is configured as: In response to depressing the accelerator pedal during engine braking, starting a timer having a duration defined by a charge limit of the traction battery, during which engine braking is maintained and a predetermined rate of change limit of the engine speed is reduced; In response to expiration of the duration of the timer, the predetermined rate of change limit of the engine speed is increased.

2. The vehicle according to claim 1, wherein: The charging limit is based on the state of charge of the traction battery.

3. The vehicle according to claim 2, wherein: The magnitude of the charging limit is inversely proportional to the duration.

4. The vehicle according to claim 3, wherein: When the charge limit is greater than a charge limit threshold associated with a traction battery, the duration is zero.

5. The vehicle according to claim 1, wherein: The output torque of the engine increases during the duration.

6. The vehicle according to claim 5, wherein: The output torque of the engine during the duration is offset by an electric motor associated with a powertrain of the vehicle.

7. The vehicle according to claim 6, wherein: The electric motor accelerates the vehicle during the duration.

8. The vehicle of claim 1, wherein: The predetermined rate of change limit of the engine speed is reduced so that the engine speed is maintained during the duration.

9. The vehicle according to claim 8, wherein: The rotation speed is maintained using the vehicle's wheel torque and the reaction force of the generator.

10. The vehicle of claim 1, wherein: The predetermined rate of change limit of the engine speed is negative.

11. A vehicle comprising: engine; The controller is configured as: In response to an accelerator pedal release during engine acceleration, starting a timer having a duration defined by a charge limit of the traction battery and reducing a predetermined rate of change threshold of engine speed; In response to expiration of the duration of the timer, the predetermined rate-of-change threshold is increased.

12. The vehicle according to claim 11, wherein: The charging limit is based on the state of charge of the traction battery.

13. The vehicle according to claim 11, wherein: The magnitude of the charging limit is inversely proportional to the duration.

14. The vehicle according to claim 13, wherein: When the charge limit is a maximum charge limit associated with the traction battery, the duration is zero.

15. The vehicle of claim 11, wherein: The output torque of the engine is reduced during the duration.

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