Engine Braking with Lashless Valve Trains

Engines

DEVELOPMENT Engines

Engine Braking with

Lashless Valve Trains © Hanna_photo | iStock.com / narvikk | iStock.com / shauni | iStock.com / Maksym Dragunov | iStock.com / Jacobs Vehicle Systems, Inc.

Until now, hydraulic valve lash adjusters could not be used in g Lashless valve train systems, heavy-duty diesel engines in combination with an additional utilizing technologies such as automatic or Hydraulic Lash Adjusters (HLAs), engine brake, as the engine brake causes signifcant valve lash FIGURE 1, to maintain zero-clearance during the braking process. The hydraulic compensation ele- between the mechanisms to intake ments automatically readjust to take up this play, thereby pre- and exhaust valves, have been ubiqui- tous in passenger car gasoline engines venting correct seating at the end of the cycle. Jacobs Vehicle and light-duty diesel applications for Systems has now developed systems that enable the integration decades. For applications like medium (MD) and heavy-duty (HD) diesel that of an engine brake in valve trains with hydraulic lash adjusters. require the use of dedicated engine brakes to aid in downhill control, lashless systems were simply not compatible. A conventional engine brake in operation will create an increased clearance between components of the valve train. If the HLA now readjusts, the engine components may suffer.

28 www.springerprofessional.com/automotive Engines

AUTHORS (TCO) and lower Noise, Vibration and release event into the exhaust, and pre- Harshness (NVH) emitted by the valve vents the energy from going back to the train. The adoption of lashless valve crank during the expansion stroke. This trains with HLAs can allow the OEMs to “energy absorption” helps to slow the have more fexibility in valve lift design, loaded vehicle or maintain control on a which helps in meeting more stringent downhill grade without wear and tear or emission targets. overheating the service brakes. Peter J. Jo, PMP is Engineering Development Manager for North America at COMPRESSION RELEASE LASHLESS OVERHEAD Jacobs Vehicle Systems, Inc. in ENGINE BRAKE VALVE DESIGN Bloomfeld, Connecticut (USA). A standard compression release brake Traditional MD and HD diesel engine modifes the motion of the engine valves, Overhead Valve designs require setting opening the exhaust valve at Top Dead the lash with an adjustable screw to Center (TDC) of the compression stroke account for the variations in the manu- and releasing the energy used to com- facturing tolerances of the components press the cylinder charge through the and assemblies while still allowing a gap exhaust system [1]. This is often imple- for thermal expansion during normal John Mandell is Senior Project Engineer and mented by adding two valve lift events engine operating temperatures. To allow Off-highway Valvetrain Expert for to the standard exhaust main event, for the gap, the cam must be designed the Product Development Team at FIGURE 2 (left). The Brake Gas Recircula- such that long ramps, FIGURE 2 (right), Jacobs Vehicle Systems, Inc. in Bloomfeld, Connecticut (USA). tion (BGR) event is around bottom dead are at the opening and closing of the center after the intake stroke to increase valve lifts to control the motions of the the charge in the cylinder with gas cam and prevent it from hitting against from the exhaust manifold [2]. The the rocker or the bridge, and keep the charge in the cylinder is then com- valves from hitting the seat and other pressed by the piston, which provides the parts when opening/closing. braking work released at TDC by open- Due to the engine components’ ing the exhaust valve with a compression variability, the lash is set during the Hilko Schmitt is Marketing and Business Development Manager in the On- and Off-highway valve train technology development department at Jacobs Vehicle Systems, Inc. in Guyancourt (France).

Gabriel Roberts is Engineering Director of Product Development at Jacobs Vehicle Systems, Inc. in Bloomfeld, Connecticut (USA).

Recently approved emission regulations in the EU and US are placing very

demanding CO2 and NOx limits on FIGURE 1 Hydraulic lash adjuster OEMs starting in 2027. In order to com- (© Jacobs Vehicle Systems, Inc.) ply, OEMs are evaluating technologies that have been successfully used in other applications. A new solution from Jacobs Vehicle Systems allows a conventional HLA and engine brake to work together in a modern valve train without compromise. HLAs also enable other benefts, such as reduced Total Cost of Ownership

ATZ heavyduty worldwide 01|2021 29 DEVELOPMENT Engines

FIGURE 2 Typical valve lifts (shown exaggerated for illustrative purposes) (Compression Release: CR) (© Jacobs Vehicle Systems, Inc.)

initial engine build and is then typically engine braking system were to be used FULCRUM BRIDGE adjusted and reset every 100,000 to in an overhead utilizing HLAs in the 300,000 km or 1500 to 5000 h (widely main event rockers, the bridge would Jacobs Vehicle Systems developed the dependent on OEM requirements and tilt and unload the HLA when the brake Fulcrum Bridge that makes it possible usage duties) as part of scheduled main- rocker moves to open one brake valve to utilize compression release engine tenance. As the overhead components during the compression release event, brakes with HLAs [3]. The device uses wear down, maintenance is necessary FIGURE 3. The HLA would then pump the principle of leverage and prevents the as the original set lash shifts from the out and extend to take up the increased lash adjuster from overextending during optimal operating gap. lash, thus overextending and keeping the a braking event. This is accomplished by An example of component wear can be valve from seating at the end of the com- actuating the braking valve slightly off its found in the valve seats. As the valve pression release event. This would lead centerline and diverting a proportion of head opens and closes against the seats to poor engine performance and could the braking load to the HLA via a linkage over millions of times in its operation, risk damage to the valve due to heat and mechanism. This simple, cost-effective the valve seats wear down, or recess, possible valve-to-piston contact. This device uses the braking valve tip as a resulting in the valves moving up over is the primary reason why HLAs have fulcrum point to impart an upward force time and reducing the lash or gap set not been adopted into applications that through the bridge. This upward force from the initial set point. When this lash require engine brakes. counteracts the pump-out force exerted gap is reduced beyond design limits due to wear, the engine will no longer perform optimally. At operating temperature, the valve may be hung open and leak compression which can lead to reduced engine performance, increased emissions and accelerated wear. HLAs automatically adjust to variations and wear in the overhead to maintain a zero gap between the cam, rocker and valve. This eliminates the need to perform the time-consuming task of setting the lash adjuster during the initial engine build and in service. Other benefts include a reduction in NVH by eliminating the lash that would FIGURE 3 Conventional normally result in clacking noises in the braking with HLA overhead. HLAs can be functionally sen- (© Jacobs Vehicle Systems, Inc.) sitive and factors such as component cleanliness, durability, valve train load- ing, and combustion chamber “oil can- ning” effects should be considered in the valve train design. If a conventional

30 www.springerprofessional.com/automotive Bridge may accommodate these variations, with the ability to incorporate the same mechanism into other valve train elements such as the rocker arm, push tube, fnger-follower, or cam follower. FIGURE 5 shows the Spring Bridge to be incorporated into a Single Overhead Camshaft (SOHC) engine with a dedicated cam single valve-opening rocker brake. An HLA has been incorporated into the main event exhaust rocker with Spring Bridge located between the HLA and the engine valves, allowing the HLA to function as normal during positive FIGURE 4 Braking with Fulcrum Bridge and HLA power. When in engine braking mode, (© Jacobs Vehicle Systems, Inc.) the Spring Bridge works with the main event cam design to keep the HLA loaded during bridge tilt normally asso- ciated with single-valve engine braking. The Spring Bridge operates with an internal stroke-limited piston that allows the main event lift and HLA refll portions of the cam to operate normally. When in braking mode, the main exhaust cam positions the rocker, HLA, and internal piston of the Spring Bridge in a pre- by the HLA and prevents it from overex- where the engine brake actuates the loaded condition that prevents pump- tending, FIGURE 4. The fulcrum lever braking valve changes to have the ful- out when the dedicated cam brake rocker ratio is used to design the amount of crum effect on the HLA. The same valve tilts the bridge, FIGURE 6. Either Fulcrum force proportioned back to the HLA to train cannot be used in HLA and non- Bridge or Spring Bridge can be used with maintain a balance between pump-out HLA equipped valve trains, which dedicated cam rocker brakes, overhead and collapse. Another beneft of the is one of the reasons why the Spring bolt-on brakes, bleeder brakes, and even Fulcrum Bridge is the shortened brake Bridge was developed. While the operat- lost motion rocker brakes, making it rocker ratio that reduces the required ing mechanism of the Spring Bridge is possible to adopt this system for most actuation force on the braking rocker different, the fundamental objective is engines. due to the mechanical advantage pro- the same: keep the HLA loaded during vided by the lever mechanism. This the engine brake events to prevent EMISSIONS shortened length results in less contact pump-out of the HLA, which may lead stress on the brake rocker arm and to engine damage. Several emissions improvements are camshaft. Every valve train is different and possible with a lashless valve train using has different constraints. The Fulcrum HLAs on both MD and HD engines. The Bridge may not be able to be accommo- main event is optimized, allowing the SPRING BRIDGE dated in all engine designs because rocker to follow the cam accurately, One compromise in the design of the of the valve pattern, injector location, thereby eliminating portions of the cam Fulcrum Bridge is that the position or other space constraints. The Spring design in place to handle lash variation.

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The designed ideal valve lift profle will vehicle requires up to 6 h of labor to per- signifcantly extended, or potentially be maintained during the life of the form a valve adjustment, it is easier to eliminated. In vehicles equipped with engine and will not vary signifcantly access the overhead camshaft than in special emissions equipment that is par- due to the wear of components. Using off-road applications. Engines used in ticularly susceptible to valve lift changes HLAs in the valve train to maintain the agricultural or mining equipment often over time, HLAs could greatly improve ideal valve lift should keep Diesel Partic- have complex packaging where turbo- vehicle uptime and TCO. ulate Filter (DPF) regeneration intervals chargers or exhaust aftertreatment sys- consistent. Normally-lashed engines see tems block access to the valve cover. All SUMMARY the DPF regeneration intervals decrease this must be removed to perform routine as the valve train wears, then improve service to the OHC, thereby increasing Offering HLA while ensuring compatibil- after lash adjustment. This is likely due service time and the opportunity for ity with an engine brake represents a to a change in combustion effciency as damage and incorrect reassembly. Many great opportunity for engine OEMs to the valve lift changes due to wear. times, this service needs to happen in further optimize overall internal com- the feld, creating additional environ- bustion engine effciency levels. From an mental risks. engine OEM perspective, this can help in SERVICEABILITY It is ideal for off-road applications to meeting future emission regulations over It is important to have these lashless- adopt HLAs to minimize these risks; the lifetime of the engine, while mini- enabling engine brake systems, not however, many of these engines also mizing the impact on engine complexity only to take on the challenging future require engine brakes. When Jacobs and vehicle operating safety. Solutions requirements for both on- and off-road Vehicle Systems technologies are uti- such as the Fulcrum or Spring Bridge engine performance, but also to help lized, the interval in which a technician provide fexibility during engine devel- improve serviceability. While an on-road will have to access the valve train can be opment. For the end user, the advantages of HLA and engine brake compatibility ensure an optimized TCO and driver comfort due to lowered service costs and NVH, along with increased uptime.

REFERENCES [1] Cummins, C.: Diesel Engine Brake Control. U.S. Patent No. 2,876,876, March 10, 1959 [2] Huang, S.: Method of Operating an Engine Brake. U.S. Patent No. 7,284,533 B1, October 23, 2007 [3] Jo, P.: Linkage Between an Auxiliary Motion Source and a Main Motion Load Path in an Internal Combustion Engine. U.S. Patent No. 10,626, 763 B2, April 21, 2020 [4] Ferreira, D.: Lash Adjustment in Lost Motion Engine Systems. U.S. Patent No. 10,590,810 B2, FIGURE 6 Braking with Spring Bridge and HLA (© Jacobs Vehicle Systems, Inc.) March 17, 2020

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