CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

62/362,401 , filed July 14, 2016, U.S. Provisional Application No. 62/416,495, filed

November 2, 2016, U.S. Provisional Application No. 62/492,576, filed May 1 , 2017, and U.S. Provisional Application No. 62/520, 198, filed June 15, 2017, the contents of which are incorporated herein by reference thereto.

FIELD

[0002] The present disclosure relates generally to exhaust engine braking and, more particularly, to fully variable exhaust engine braking.

BACKGROUND

[0003] Compression engine brakes can be used as auxiliary brakes, in addition to wheel brakes, on relatively large vehicles, for example trucks, powered by heavy or medium duty diesel engines. A compression engine braking system is arranged, when activated, to provide an additional opening of an engine cylinder's exhaust valve when the piston in that cylinder is near a top-dead-center position of its compression stroke so that compressed air can be released through the exhaust valve. This causes the engine to function as a power consuming air compressor which slows the vehicle.

[0004] The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

SUMMARY

[0005] According to various aspects of the present disclosure, an engine braking system for an internal combustion engine having an engine valve movable between an open position and a closed position, and a cylinder having a reciprocating piston is provided. The engine braking system includes an actuator configured to selectively move the engine valve between the open position and the closed position, and a controller in signal communication with the actuator. The controller is configured to operate in at least one of: a multiple pulse high braking torque engine braking mode where (a) the engine valve is opened for a first predetermined time before the piston reaches top dead center (TDC) of a compression stroke, (b) the engine valve is subsequently closed after the first predetermined time to build up more cylinder pressure, and (c) the engine valve is opened again when the piston reaches TDC; a multiple pulse low braking torque engine braking mode where (a) the engine valve is opened for a second predetermined time before the piston reaches TDC of the compression stroke, (b) the engine valve is closed after the second predetermined time to build up more cylinder pressure, (c) the engine valve is opened for a third predetermined time when the piston is approximately mid stroke of the compression stroke, (d) the engine valve is closed after the third predetermined time to build up more cylinder pressure, and (e) the engine valve is opened again when the piston reaches TDC; a variable throttled braking torque engine braking mode where (a) the engine valve is partially opened early in the compression stroke, thereby throttling the air escaping from the cylinder past the engine valve, and (b) holding the engine valve in the partially opened position until the piston reaches TDC; an early intake valve closing (EIVC) braking torque engine braking mode where (a) the engine valve is closed earlier than a normal closing, thereby providing less than normal air during compression in the cylinder and producing a lower cylinder pressure on the compression stroke, and (b) the engine valve is opened for a third predetermined time during the compression stroke; and a late intake valve closing (LIVC) braking torque engine braking mode where (a) the engine valve is closed later than a normal closing, thereby providing less than normal air during compression in the cylinder and producing a lower cylinder pressure on the compression stroke, and (b) the engine valve is opened for a fourth predetermined time during the compression stroke.

[0006] In addition to the foregoing, the described engine braking system may include one or more of the following features: wherein the engine valve is an exhaust valve and the controller is configured to selectively operate between the multiple pulse high braking torque engine braking mode, the multiple pulse low braking torque engine braking mode, and the variable throttled braking torque engine braking mode; wherein the engine valve is an intake valve and the controller is configured to selectively operate between the EIVC braking torque engine braking mode and the LIVC braking torque engine braking mode; wherein the controller is configured to operate in the multiple pulse high braking torque engine braking mode; wherein the controller is configured to operate in the multiple pulse low braking torque engine braking mode; and wherein the controller is configured to operate in the variable throttled braking torque engine braking mode.

[0007] In addition to the foregoing, the described engine braking system may include one or more of the following features: wherein the controller is further configured to operate in at least one of (a) a high braking torque and fast bleed throttling mode, (b) a high braking torque and moderate bleed throttling mode, and (c) a high braking torque and steady state bleed throttling mode; wherein the controller is configured to selectively operate between the high braking torque and fast bleed throttling mode, the high braking torque and moderate bleed throttling mode, and the high braking torque and steady state bleed throttling mode; wherein the controller is configured to operate in the EIVC braking torque engine braking mode; and wherein the controller is configured to operate in the LIVC braking torque engine braking mode; wherein the actuator is an electrohydraulic actuator.

[0008] In addition to the foregoing, the described engine braking system may include one or more of the following features: a second actuator configured to selectively move an engine valve between an open position and a closed position, wherein the second actuator is a mechanically actuated actuator configured to be actuated by a rotating cam; a sensor in signal communication with the controller, wherein the controller is configured to selectively enable or disable exhaust engine braking based on a signal from the sensor; wherein the sensor is a GPS sensor configured to determine a location of a vehicle having the actuator; an engine braking variability switch in signal communication with the controller, the engine braking variability switch configured to enable a driver to manually select and enable operation in the multiple pulse high braking torque engine braking mode, the multiple pulse low braking torque engine braking mode, and the variable throttled braking torque engine braking mode; and wherein the controller is further configured to operate in: a maximum braking torque mode where the exhaust valve is opened at TDC of the compression stroke: a high braking torque mode where the exhaust valve is opened slightly before TDC of the compression stroke and remains open until the piston reaches TDC, and (f) a low braking torque mode where the exhaust valve is opened early in the compression stroke and remains open until the piston reaches TDC. [0009] According to various aspects of the present disclosure, an engine braking system for an internal combustion engine having an intake valve and an exhaust valve each movable between an open position and a closed position, and a cylinder having a reciprocating piston is provided. The engine braking system includes an actuator configured to selectively move the intake and exhaust valves between the open and closed positions, and a controller in signal communication with the actuator. The controller is configured to selectively operate between: a multiple pulse high braking torque engine braking mode where (a) the exhaust valve is opened for a first predetermined time before the piston reaches top dead center (TDC) of a compression stroke, (b) the exhaust valve is subsequently closed after the first predetermined time to build up more cylinder pressure, and (c) the exhaust valve is opened again when the piston reaches TDC; a multiple pulse low braking torque engine braking mode where (a) the exhaust valve is opened for a second predetermined time before the piston reaches TDC of the compression stroke, (b) the exhaust valve is closed after the second predetermined time to build up more cylinder pressure, (c) the exhaust valve is opened for a third predetermined time when the piston is approximately mid stroke of the compression stroke, (d) the exhaust valve is closed after the third predetermined time to build up more cylinder pressure, and (e) the exhaust valve is opened again when the piston reaches TDC; a variable throttled braking torque engine braking mode where (a) the exhaust valve is partially opened early in the compression stroke, thereby throttling the air escaping from the cylinder past the exhaust valve, and (b) holding the exhaust valve in the partially opened position until the piston reaches TDC; an early intake valve closing (EIVC) braking torque engine braking mode where (a) the engine valve is closed earlier than a normal closing, thereby providing less than normal air during compression in the cylinder and producing a lower cylinder pressure on the compression stroke, and (b) the engine valve is opened for a third predetermined time during the compression stroke, and a late intake valve closing (LIVC) braking torque engine braking mode where (a) the engine valve is closed later than a normal closing, thereby providing less than normal air during compression in the cylinder and producing a lower cylinder pressure on the compression stroke, and (b) the engine valve is opened for a fourth predetermined time during the compression stroke.

[0010] According to various aspects of the present disclosure, a method of engine braking for an internal combustion engine having an intake valve and an engine valve each movable between an open position and a closed position, and a cylinder having a reciprocating piston is provided. The method includes operating the exhaust valve in a normal exhaust operation where the exhaust valve is actuated to the open position when the piston is in an exhaust stroke, and the exhaust valve is actuated to the closed position when the piston is in a compression stroke, operating the intake valve in a normal intake operation where the intake valve is actuated to the open position when the piston is in an intake stroke, and the intake valve is actuated to the closed position when the piston is in a compression stroke, and operating the intake or exhaust valve in an engine braking operation comprising operating in at least one of: a multiple pulse high braking torque engine braking mode where (a) the exhaust valve is opened for a first predetermined time before the piston reaches top dead center (TDC) of a compression stroke, (b) the exhaust valve is subsequently closed after the first predetermined time to build up more cylinder pressure, and (c) the exhaust valve is opened again when the piston reaches TDC; a multiple pulse low braking torque engine braking mode where (a) the exhaust valve is opened for a second predetermined time before the piston reaches TDC of the compression stroke, (b) the exhaust valve is closed after the second predetermined time to build up more cylinder pressure, (c) the exhaust valve is opened for a third predetermined time when the piston is approximately mid stroke of the compression stroke, (d) the exhaust valve is closed after the third predetermined time to build up more cylinder pressure, and (e) the exhaust valve is opened again when the piston reaches TDC; a variable throttled braking torque engine braking mode where (a) the exhaust valve is partially opened early in the compression stroke, thereby throttling the air escaping from the cylinder past the exhaust valve, and (b) holding the exhaust valve in the partially opened position until the piston reaches TDC; an early intake valve closing (EIVC) braking torque engine braking mode where (a) the engine valve is closed earlier than a normal closing, thereby providing less than normal air during compression in the cylinder and producing a lower cylinder pressure on the compression stroke, and (b) the engine valve is opened for a third predetermined time during the compression stroke; and a late intake valve closing (LIVC) braking torque engine braking mode where (a) the engine valve is closed later than a normal closing, thereby providing less than normal air during compression in the cylinder and producing a lower cylinder pressure on the compression stroke, and (b) the engine valve is opened for a fourth predetermined time during the compression stroke.

[0011] In addition to the foregoing, the described method may include one or more of the following features: wherein operating in the engine braking operation comprises selectively operating between the multiple pulse high braking torque engine braking mode, the multiple pulse low braking torque engine braking mode, and the variable throttled braking torque engine braking mode, and wherein operating in the engine braking operation comprises selectively operate between the EIVC braking torque engine braking mode and the LIVC braking torque engine braking mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0013] FIG. 1 is a partially exploded perspective view of a valve head;

[0014] FIG. 2 is a sectional view of the valve head shown in FIG. 1 and taken along line 2-2;

[0015] FIG. 3A is a graph illustrating traditional engine valve actuation profiles compared with engine braking valve opening profiles, in accordance to one example of the present disclosure;

[0016] FIG. 3B is a graph illustrating engine braking torque of a maximum engine braking valve opening profile shown in FIG. 3A;

[0017] FIG. 3C is a graph illustrating engine braking torque of an early engine braking valve opening profile shown in FIG. 3A;

[0018] FIG. 3D is a graph illustrating engine braking of a very early engine braking valve opening profile shown in FIG. 3A;

[0019] FIG. 4A is a graph illustrating engine valve actuation profiles including a multiple pulse early engine braking valve opening profile, in accordance to one example of the present disclosure;

[0020] FIG. 4B is a graph illustrating engine braking of the multiple pulse early engine braking valve opening profile shown in FIG. 4A;

[0021] FIG. 5A is a graph illustrating engine valve actuation profiles including a multiple pulse very early engine braking valve opening profile, in accordance to one example of the present disclosure;

[0022] FIG. 5B is a graph illustrating engine braking of the multiple pulse very early engine braking valve opening profile shown in FIG. 5A; [0023] FIG. 6A is a graph illustrating engine valve actuation profiles including a variable throttle early engine braking valve opening profile, in accordance to one example of the present disclosure;

[0024] FIG. 6B is a graph illustrating engine braking of the variable throttle early engine braking valve opening profile shown in FIG. 6A;

[0025] FIG. 7A is a graph illustrating engine valve actuation profiles including an early intake valve closing engine braking valve opening profile, in accordance to one example of the present disclosure;

[0026] FIG. 7B is a graph illustrating engine braking of the early intake valve closing engine braking valve opening profile shown in FIG. 7A; and

[0027] FIG. 8 is a graph illustrating a late intake valve closing engine braking, in accordance to one example of the present disclosure.

DETAILED DESCRIPTION

[0028] The present teachings provide for variable timing of a valve profile through a variable valve actuation (WA) device configured to move the engine brake profile timing. This can be accomplished, for example, with a camless electro- hydraulic system. As such, the instant disclosure provides continuously variable engine braking utilizing cam-camless technology to meet regulatory noise compliance throughout the world. In regions having braking restrictions, the presently described technology enables activation of the engine brake further away from top dead center (TDC) to thereby provide limited braking and reduced noise. In other regions, the engine braking can be actuated closer to TDC to provide maximum braking. All levels of engine braking therebetween are contemplated. [0029] Moreover, the present disclosure provides multi-pulsed engine braking and variable throttle engine braking to provide further control and variability of engine braking torque and the noise generated thereby. In one example, multi-pulsed engine braking is performed where the exhaust valve is opened generally at mid- compression stroke for a short predetermined period of time, and quickly closed again to build up more cylinder pressure, then opened again when the piston reaches TDC, as shown in accordance with the present teachings in FIGS. 4A and 4B.

[0030] In another example, multi-pulsed engine braking is performed where the exhaust valve is opened very early in the compression stroke for a short predetermined time, quickly closed again to build up more cylinder pressure, then opened again when the piston is in mid stroke and closed again, then finally opened again when the piston reaches TDC, as shown in accordance with the present teachings in FIGS. 5A and 5B.

[0031] In yet another example, variable throttle engine braking is performed where the exhaust valve is partially opened very early in the compression stroke only slightly so that the air escaping from the cylinder is throttled pas the exhaust valve, and the valve is held open for the remainder of the compression stroke until the piston reaches TDC, as shown in accordance with the present teachings in FIGS. 6A and 6B.

[0032] In another example, early intake valve closing (EIVC) and/or late intake valve closing (LIVC) are performed to vary the amount of air drawn into the cylinder. Less air in the cylinder to compress reduces the pressure at TDC, thereby lowering the braking torque. Varying the maximum pressure available in the cylinder provides variation in the maximum braking torque, as shown in accordance with the present teachings in FIGS. 7A, 7B, and 8. [0033] With initial reference to FIG. 1 , a valve head constructed in accordance to one example of the present disclosure is shown and generally identified at reference 100. The valve head 100 may be similar to that described in commonly owned U.S. Pat. No. 9, 157,339, the contents of which are incorporated herein by reference thereto. The illustrated valve head 100 is configured to be mounted on an engine block of a diesel engine. However, the present teachings are not limited to diesel engines, and are applicable to other types of internal combustion engines.

[0034] An engine block on which the valve head 100 can be mounted can contain piston bores, and pistons can be inserted into the bores to form combustion chambers. The valve head 100 can form the top portion of the combustion chambers when mounted on the engine block. The illustrated valve head 100 is for use with six cylinders of a twelve cylinder engine, however, the present teachings are applicable to other engine configurations as well.

[0035] The valve head 100 shown in FIG. 1 includes a hybrid valve actuation system wherein both mechanical and electrohydraulic actuation mechanisms are used to open and close the engine valves of a particular cylinder. When mounted on an engine block, the valve head 100 formed part of six combustion chambers and includes twenty-four engine valves in total, four for each of the combustion chambers partially formed by the valve head 100. A feed rail 101 can be mounted at the top of valve head 100 and can include two high pressure conduits 103 that supply high pressure hydraulic fluid to electrohydraulic actuators 104, and a low pressure drain conduit 105 that allows hydraulic fluid to flow from the electrohydraulic actuators 104.

[0036] FIG. 2 illustrates a sectional view of the valve head 100 shown in FIG. 1. As seen in FIG. 2, two of the engine valves 102 corresponding to one of the cylinders are actuated by an electrohydraulic actuator 104. The other two engine valves 102 of the cylinder are mechanically actuated by a cam 1 12 and rocker arms 1 14. In one example, each engine valve 102 can be one of an intake valve and an exhaust valve. The valve head 100 includes intake ports 106 and exhaust ports 108 through which air enters and combusted gas leaves the combustion chamber, respectively, during engine operation.

[0037] The engine valves 102 actuated by the electrohydraulic 104 open and close respective passages from the combustion chamber to intake and exhaust ports 106, 108. When closed, the engine valves 102 are seated against valve seats 1 10. Thus, one of the intake ports 106 for a particular cylinder is regulated by one of the electrohydraulic actuators 104 and one of the exhaust ports 108 is also regulated by one of the electrohydraulic actuators 104. For a particular cylinder, the entry and exit of gas from the combustion chamber is regulated in part by the valves 102 that are actuated mechanically and in part by the valves 102 actuated by the electrohydraulic actuators 104.

[0038] Mechanical actuation of the engine valves 102 shown in FIGS. 1 and 2 is achieved through the rotating cam 1 12 periodically transferring motion to rocker arm 114, which in turn transfers linear motion to the engine valves 102. Such mechanical actuation illustrates one possible type of mechanical valve actuation according to the present disclosure. Other forms of mechanical actuation may also be implemented to transform the rotational motion of a cam to kinetic energy or mechanical potential energy, and ultimately to translational motion of the engine valves 102. Such mechanisms include a rotating cam placed in direct contact with an engine valve 102, or by including one or both of a lash adjuster and rocker arm between a cam and engine valve. Still other combinations of various valve train components are possible in order to achieve mechanical actuation of an engine valve. Such components include, but are not limited to, rocker arms including deactivating rocker arms and variable lift rocker arms, pushrods, hydraulic lash adjusters, and tappets.

[0039] As shown in FIG. 2, a controller 120, such as a vehicle controller or electronic control unit (ECU), can be in signal communication with the valve head 100 to control operation of the electrohydraulic actuators 104. Moreover, controller 120 can be in signal communication with an engine braking variability switch 130 and/or one or more sensors 140 to enable controller 120 to automatically control and vary the engine brake power level and thus noise emissions of the vehicle engine, as described herein in more detail. As used herein, the term controller refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.

[0040] With reference to FIGS. 3A and 3B, controller 120 is configured to perform an engine braking operation by controlling the electrohydraulic actuators 104 to open the exhaust valves 102 during a compression stroke when the piston is compressing air in the combustion chamber. Typically, the exhaust valve 102 is opened at TDC, and the compressed air is vented from the system without transferring energy to the vehicle drive train, thereby slowing the engine and thus the vehicle. The closer the piston is to TDC, the more engine braking power is produced by the engine. For example, FIG. 3B illustrates a typical engine braking at TDC that produces maximum braking torque.

[0041] However, performing engine braking at such maximum levels can lead to high noise emissions. This has led to some regions of the world regulating or prohibiting noise emissions caused by engine braking. As such, controller 120 is configured to control actuators 104 to vary engine braking timing to vary engine braking power and noise output.

[0042] In one example shown in FIG. 3C, controller 120 is configured to operate in a high braking torque mode where the exhaust valve 102 is opened early (e.g., slightly before TDC of the compression stroke) and stays open until the piston reaches TDC. Such control reduces the engine braking power and noise output compared to the maximum braking torque mode shown in FIG. 3B.

[0043] In another example shown in FIG. 3D, controller 120 is configured to operate in a low braking torque mode where the exhaust valve 102 is opened very early (earlier than shown in FIG. 3C) in the compression stroke and stays open until the piston reaches TDC. Such control reduces the engine braking power and noise output compared to the high braking torque mode shown in FIG. 3C.

[0044] In one example shown in FIGS. 4A and 4B, controller 120 is configured to operate in a multiple pulse high braking torque mode where the exhaust valve 102 is opened generally at mid-compression stroke for a short predetermined time to reduce pressure, and then closed again to build up more cylinder pressure. The exhaust valve 102 is then opened again when the piston reaches TDC. Such control provides more power dissipation than the high braking torque mode shown in FIG. 3C, without exceeding the pressure level thereof. Although FIGS. 4A and 4B illustrate the braking torque mode performing two pulses, it will be appreciated that any number of pulses may be performed. Increasing the pulses dissipates more energy through one piston stroke while minimizing the maximum pressure of each pulse, thereby enabling a higher frequency noise generation, which can be less objectionable. [0045] In another example shown in FIGS. 5A and 5B, controller 120 is configured to operate in a multiple pulse low braking torque mode where the exhaust valve 102 is opened very early in the compression stroke for a predetermined time and closed again to build up more cylinder pressure. The exhaust valve 102 is opened again when the piston is in or is approximately in mid stroke for a second predetermined time and again closed to build up more cylinder pressure. The exhaust valve 102 is then opened again when the piston reaches TDC. Such control provides more power dissipation than the lower braking torque mode shown in FIG. 3D, without exceeding the pressure level thereof. Although FIGS. 5A and 5B illustrate the braking torque mode performing three pulses, it will be appreciated that any number of pulses may be performed. Increasing the pulses dissipates more energy through one piston stroke while minimizing the maximum pressure of each pulse, thereby enabling a higher frequency noise generation, which can be less objectionable.

[0046] In one example shown in FIGS. 6A and 6B, controller 120 is configured to operate in a variable throttle mode where the exhaust valve 102 is opened very early in the compression stroke only a predetermined distance (e.g., 10- 30% of fully open) so that air escaping from the cylinder is throttled past the exhaust valve 102. The valve 102 is held open for the remainder of the compression stroke until the piston reaches TDC. Such control eliminates a pressure wave and significantly reduces noise because it is performed over a longer period of time.

[0047] Thus, the variable throttle mode affords high braking torque with variable throttling, which eliminates a pressure wave and significantly reduces noise compared to the braking torque modes shown in FIG. 3. As shown in FIG. 6B, controller 120 is configured to operate: with only high braking torque (line 150); with high braking torque and fast bleed throttling (line 152); with high braking torque and moderate bleed throttling (line 154); and with high braking torque and steady state bleed throttling (line 156).

[0048] In another example shown in FIGS. 7A and 7B, controller 120 is configured to operate in an EIVC braking torque mode where the intake valve 102 is closed early (compared to a normal intake valve closing, see FIG. 7A) while the piston is still moving downward, thereby creating a vacuum in the cylinder. As the piston moves upward in the compression stroke, there is less air to compress (since the intake valve 102 is closed early), which produces a lower maximum cylinder pressure at TDC. By varying the timing of the early closing of the intake valve 102, the EIVC braking torque mode can produce, for example, a relatively high braking torque and low braking torque, as shown in FIG. 7B.

[0049] Moreover, as shown in FIG. 8, controller 120 is configured to operate in an LIVC braking torque mode where the intake valve 102 is closed late (compared to a normal intake valve closing, see FIG. 7A). As such, the piston moves downward in the compression stroke drawing a full charge of air into the cylinder. However, as the piston begins to move upward in the compression stroke, the intake valve 102 remains open and air escapes the cylinder. Once intake valve 102 is closed, there is less air to compress, which produces a lower maximum cylinder pressure at TDC. By varying the timing of the late closing of the intake valve 102, the LIVC braking torque mode can produce, for example, a relatively high braking torque and low braking torque, as shown in FIG. 8.

[0050] As noted above, controller 120 can be in signal communication with engine braking variability switch 130 that can enable the driver to manually adjust or vary the engine braking power and noise output in real time. Switch 130 may be a physical button, soft button, user interface, or similar device for enabling the driver to manually adjust the exhaust valve activation timing to thereby vary the engine braking power and noise output. This gives the driver maximum, precise control over the power to noise output ratio of the vehicle. However, switch 130 can also allow the driver to switch to an automatic control where controller 120 automatically controls the exhaust valve activation timing, for example, based on inputs from sensor(s) 140. Moreover, switch 130 gives the driver the ability to manually enable and disable the vehicle engine braking.

[0051] Controller 120 can receive signals from sensors 140 to enable controller 120 to automatically control and vary the engine brake power level and thus noise emissions of the vehicle engine. In one example, sensor 140 is a GPS sensor configured to enable controller 120 to determine the location of the vehicle. If the vehicle enters a region known to limit or prohibit engine braking, GPS sensor 140 sends a signal to controller 120, and the controller then automatically reduces brake power level or deactivates engine braking to reduce or deactivate the engine braking. For example, if the vehicle is operating in the maximum braking torque mode and enters a geographical region that prohibits excessively loud engine braking, controller 120 can automatically transition the valve head 100 to operate in the multi-pulse low braking torque mode (FIGS. 5A and 5B) to reduce noise output from vehicle engine braking.

[0052] In another example, sensor 140 is a sensor configured to detect a grade of the road the vehicle is traveling. If controller 120 detects the vehicle is traveling on a level grade based on a signal from the grade sensor 140, controller 120 can automatically disable the vehicle from performing an engine braking operation. If controller 120 detects the vehicle is subsequently traveling on a steep downhill grade based on a signal from the grade sensor 140, controller 120 can automatically enable engine braking operation. Moreover, controller 120 can vary the engine braking mode based on the steepness of the detected grade. For example, on a slight downhill grade (e.g., 0-3%), controller 120 may operate in the multi-pulse low braking torque mode. On a steep downhill grade (e.g., 3%+) controller 120 may operate in the multi-pulse high braking torque mode.

[0053] In another example, sensor 140 is a speed sensor configured to detect a speed of the vehicle. If controller 120 detects the vehicle is traveling at a first predetermined speed based on a signal from the speed sensor 140, controller 120 can operate the vehicle in a first braking torque mode such as the multi-pulse low braking torque mode. If controller 120 detects the vehicle is traveling at a second predetermined speed based on a signal from the speed sensor 140, controller 120 can operate the vehicle in a second braking torque mode. Accordingly, controller 120 can vary braking torque based on vehicle speed.

[0054] The foregoing description of the examples has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular example are generally not limited to that particular example, but, where applicable, are interchangeable and can be used in a selected example, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.