Patent Grant
11506092
The present disclosure relates generally to a rocker arm assembly for use in a valve train assembly and more particularly to a rocker arm assembly that incorporates a dedicated rocker arm that acts on a single valve and that incorporates a biasing assembly that biases the rocker arm to a neutral position.
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.
In a typical valve train assembly used with a compression engine brake, the exhaust valve is actuated by a rocker arm which engages the exhaust valve by means of a valve bridge. The rocker arm rocks in response to a cam on a rotating cam shaft and presses down on the valve bridge which itself presses down on the exhaust valve to open it. A hydraulic lash adjuster may also be provided in the valve train assembly to remove any lash or gap that develops between the components in the valve train assembly.
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.
In an embodiment, the present invention provides a rocker arm assembly operable in a first mode and a second mode, the rocker arm assembly selectively opening first and second engine valves based on rotation of a cam shaft having a first cam lobe and a second cam lobe, the rocker arm assembly comprising: a rocker shaft; a first rocker arm assembly having a first rocker arm that receives the rocker shaft and is configured to rotate around the rocker shaft in the first mode based on engagement with the first cam lobe; a second rocker arm assembly having a second rocker arm that receives the rocker shaft and is configured to rotate around the rocker shaft and selectively act on one of the first and second engine valves in the second mode based on selective engagement with the second cam lobe; and a biasing assembly that cooperates with the second rocker arm to bias the second rocker arm to a neutral position, wherein in the neutral position, the second rocker arm is spaced from contact relative to both of the second cam lobe and the second engine valve.
The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. Other features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following:
A rocker arm assembly operable in a first mode and a second mode selectively opens first and second engine valves based on rotation of a cam shaft having a first cam lobe and a second cam lobe. The rocker arm assembly includes a rocker shaft, a first and second rocker arm assemblies and a biasing assembly. The first rocker arm assembly has a first rocker arm that receives the rocker shaft and is configured to rotate around the rocker shaft in the first mode based on engagement with the first cam lobe. The second rocker arm assembly has a second rocker arm that receives the rocker shaft and is configured to rotate around the rocker shaft and selectively act on one of the first and second engine valves in the second mode based on selective engagement with the second cam lobe. The biasing assembly cooperates with the second rocker arm to bias the second rocker arm to a neutral position. In the neutral position, the second rocker arm is spaced from contact relative to both of the second cam lobe and the second engine valve.
According to other features, the biasing assembly further includes a spring plate assembly having a first spring plate, a second spring plate and at least one biasing member. The first spring plate is fixed relative to the rocker shaft. The second spring plate is fixed for rotation with the second rocker arm. The at least one biasing member is disposed relative to the first and second spring plates and is configured to load and unload based on rotation of the second rocker arm around the rocker shaft. The spring plate assembly can define at least one window that is configured to receive the at least one biasing member. The at least one window is defined in part by a first bearing surface on the first spring plate and a second bearing surface on the second spring plate. The at least one biasing member bears against the respective first and second bearing surfaces during rotation of the second rocker arm around the rocker shaft.
In other features, the spring plate assembly comprises at least one spring retainer configured to retain the at least one biasing member within the at least one window. The first plate can define at least one slot. The second plate can define at least one aperture. A fastener extends through the at least one slot and the at least one aperture and is threadably secured into a threaded bore defined in the second rocker arm. The second spring plate rotates relative to the first spring plate while the fastener travels along the at least one slot during rotation of the second rocker arm during operation in the second mode.
According to additional features, the second rocker arm includes a capsule configured to move between a retracted position and an extended position. In the retracted position, the biasing assembly biases the second rocker arm to the neutral position. In the extended position, the second rocker arm is caused to rotate toward the second cam lobe preloading the biasing assembly.
In additional features, an orientation system can include a key extending from the rocker shaft. A keyway can be defined on the first plate. A pair of opposed stops can define a rotational limitation slot on the second plate. The key is fixed to the first plate at the keyway. Rotation of the second rocker arm is limited by engagement of the key with the opposed stops on the second plate.
In one arrangement, the first rocker arm assembly is an exhaust valve rocker arm assembly and the second rocker arm assembly is an engine brake rocker arm assembly. The exhaust valve rocker arm assembly includes an exhaust rocker arm and a valve bridge. The valve bridge has a lever pivotally coupled thereto such that during operation in the second mode, the engine brake rocker arm does not transfer motion to the valve bridge. In one configuration, the first and second engine valves are exhaust valves and one of the first and second modes includes early exhaust valve opening (EEVO). In another configuration, the first and second engine valves are intake valves and wherein one of the first and second modes includes late intake valve closing (LIVC).
A rocker arm assembly operable in a first mode and a second mode selectively opens first and second engine valves based on rotation of a cam shaft having a first cam lobe and a second cam lobe. The rocker arm assembly includes a rocker shaft, a first and second rocker arm, a capsule and a spring plate assembly. The first rocker arm is configured to rotate around the rocker shaft in the first mode based on engagement with the first cam lobe. The second rocker arm is configured to rotate around the rocker shaft and selectively act on one of the first and second engine valves in the second mode based on selective engagement with the second cam lobe. The capsule is arranged on the second engine brake rocker arm and is configured to move between an extended position and a retracted position. The spring plate assembly cooperates with the second rocker arm to bias the second rocker arm to a neutral position when the capsule is in the retracted position. In the neutral position, the second rocker arm is spaced from contact relative to both of the second cam lobe and the second engine valve. The spring plate assembly includes a first spring plate, a second spring plate and at least one biasing member. The first spring plate is fixed relative to the rocker shaft. The second spring plate is fixed for rotation with the second rocker arm. The at least one biasing member selectively biases against the first and second spring plates upon rotation of the second rocker arm.
The spring plate assembly can define at least one window that is configured to receive the at least one biasing member. The at least one window is defined in part by a first bearing surface on the first spring plate and a second bearing surface on the second spring plate. The at least one biasing member bears against the respective first and second bearing surfaces during rotation of the second rocker arm around the rocker shaft.
In other features, the spring plate assembly comprises at least one spring retainer configured to retain the at least one biasing member within the at least one window. The first plate can define at least one slot. The second plate can define at least one aperture. A fastener extends through the at least one slot and the at least one aperture and is threadably secured into a threaded bore defined in the second rocker arm. The second spring plate rotates relative to the first spring plate while the fastener travels along the at least one slot during rotation of the second rocker arm during operation in the second mode.
In additional features, in the extended position, the second rocker arm is caused to rotate toward the second cam lobe preloading the biasing assembly. An orientation system can include a key extending from the rocker shaft. A keyway can be defined on the first plate. A pair of opposed stops can define a rotational limitation slot on the second plate. The key is fixed to the first plate at the keyway. Rotation of the second rocker arm is limited by engagement of the key with the opposed stops on the second plate.
The following discussion is set forth in the context of rocker arms for opening exhaust valves configured in a compression engine braking system. The discussion focuses on a camshaft having a primary lift cam and an engine brake lift cam. It will be appreciated that the disclosure is not so limited. For example, the present disclosure can also be additionally or alternatively applicable to exhaust valves in other non-compression brake systems. Moreover, the disclosure may also be applicable to intake valves. In this regard, the camshaft can be configured with a primary lift cam and a secondary lift cam. For example, the present disclosure can also be applicable to valvetrains configured for early exhaust valve opening (EEVO), late intake valve closing (LIVC) or other variable valve actuation (VVA) configurations.
Heavy duty (HD) diesel engines with single overhead cam (SOHC) valvetrain requires high braking power, in particular at low engine speed. The present disclosure provides an added motion type de-compression engine brake. To provide high braking power without applying high load on the rest of the valvetrain (particularly the camshaft), the present disclosure provides a dedicated rocker arm for engine brake that acts on one exhaust valve. In this regard, half of the input load is experienced compared to other configurations that have two exhaust valves opening.
With initial reference to
Specifically, each cylinder includes an intake valve rocker arm assembly 220, an exhaust valve rocker arm assembly 222 and an engine brake rocker arm assembly 224. The exhaust valve rocker arm assembly 222 and the engine brake rocker arm assembly 224 cooperate to control opening of the exhaust valves and are collectively referred to as a dual exhaust valve rocker arm assembly 226. The intake valve rocker arm assembly 220 is configured to control motion of intake valves 228, 230. The exhaust valve rocker arm assembly 222 is configured to control exhaust valve motion in a drive mode. The engine brake rocker arm assembly 224 is configured to act on one of the two exhaust arms in an engine brake mode as will be described herein. A rocker shaft 234 is received by the valve train carrier 212 and supports rotation of the exhaust valve rocker arm assembly 222 and the engine brake rocker arm assembly 224.
With continued reference to
A camshaft 270 includes an exhaust main lift cam lobe 272 and an engine brake cam lobe 274. The exhaust rocker arm 240 has a first roller 276. The engine brake rocker arm 260 has a second roller 278. The first roller 276 rotatably engages the exhaust main lift cam lobe 272. As will be described in greater detail herein, the second roller 278 is configured to selectively rotatably engage the engine brake cam lobe 274. The exhaust rocker arm 240 rotates around the rocker shaft 234 based on a lift profile of the exhaust main lift cam lobe 272. The engine brake rocker arm 260 rotates around a rocker shaft 234 based on a lift profile of the engine brake cam lobe 274.
With additional reference now to
The engine brake rocker arm assembly 224 includes a biasing assembly 300 that cooperates with the engine brake rocker arm 260 to bias the engine brake rocker arm 260 to accommodate mechanical lash. As discussed herein, the biasing assembly 300 biases the engine brake rocker arm 260 to a neutral position out of contact with either the engine brake cam 274 or the valve 252. Moreover, the biasing assembly 300 can be attached to the engine brake rocker arm 260 and installed as a single assembly.
In the example embodiment, the biasing assembly 300 is a spring plate lost motion system that generally includes a spring plate assembly 302 collectively defined in part by first and second spring plates 303A, 303B. The spring plate assembly 302 defines a plurality of windows 304 collectively defined by respective first and second windows 305A, 305B. Each window 304 is configured to receive a biasing member 306 (e.g., a spring). Each of the first windows 305A are partially defined by a first spring bearing surface 307A. Each of the second windows 305B are partially defined by a second spring bearing surface 307B. A plurality of spring retainers 308 (
The first plate 303A defines slots 310. The second plate 303B defines apertures 312. Fasteners 314 are configured to pass through respective grommets 316, slots 310, and apertures 312 and threadably secure into respective threaded bores 320 defined in the engine brake rocker arm 260. The second plate 303B is fixed for rotation with the engine brake rocker arm 260. The first plate 303A is fixed to the rocker shaft 234. As will be described herein, when the engine brake rocker arm 260 is caused to rotate around the rocker shaft 234, the biasing members 306 selectively compress and retract..
With reference to
The key 422 can be coupled to the rocker shaft 234 by inserting a portion of the key 422 into a slot or opening 428 formed in the rocker shaft 234. In some examples, the key 422 is press fit into slot 428 or has a tight clearance fit with the slot 428. In the example illustration, key 422 is a generally semi-circular disc. At least a portion of the key 422 extends outwardly from the outer surface of the rocker shaft 234 when inserted therein. Engine brake rocker arm 260 is configured to receive the rocker shaft 234 such that key 422 is at least partially disposed within the keyway 424 and the rotational limitation slot 426. The key 422 can be configured differently. For example, the key 422 can take other geometrical forms such as, but not limited to, a post that can be press-fit into a complementary bore defined in the rocker shaft 234. Other mechanical features can be incorporated as part of or as a supplemental attachment to the rocker shaft 234 to couple the first spring plate 303A in a fixed orientation relative to the rocker shaft 234. The key 422 fixes the first plate 303A to the rocker shaft 234.
The rotation limitation slot 426 is defined by a pair of opposed stops 430 which are each configured to engage the key 422 to limit the rotational travel of the engine brake rocker arm 260. The rotational limitation slot 426 is defined to provide full design rotation of the engine brake rocker arm 260 without the engine brake rocker arm 260 contacting the key 422. As such, during operation, the rocker shaft 234 and key 422 remain stationary while the engine brake rocker arm 260 selectively rotates about the rocker shaft 234. The stops 430, are positioned to engage key 422 and thus limit rotation of the engine brake rocker arm 260 and facilitate maintaining the engine brake rocker arm 260 in a neutral position.
As mentioned above, the first spring plate 303A remains fixed to the rocker shaft 234. When the brake capsule 246 is “off” or collapsed, the engine brake rocker arm 260 returns to the neutral position such that the second roller 278 is held off the engine brake cam lobe 274. See
During operation, the biasing members 306 hold the engine brake rocker arm 260 in a position relative to the spring plate assembly 302. When the engine brake capsule 246 extends, such as during an engine braking event (
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.
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.
The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.
This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/US2018/063799, filed on Dec. 4, 2018, and claims benefit to U.S. Provisional Patent Application No. 62/594,147 filed on Dec. 4, 2017 and U.S. Provisional Patent Application No. 62/636,308 filed on Feb. 28, 2018. The International Application was published in English on Jun. 13, 2019 as WO 2019/113034 under PCT Article 21(2).
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