Dog clutch without angular backlash

Gabriela Achtenova, Michal Jasný, Jiri Pakosta, Rômulo do Nascimento Rodrigues
Center of Vehicles for Sustainable Mobility, Czech Technical University in Prague

Dog clutches are cost-effective but often suffer from angular backlash, causing discomfort. A novel, patented design has been developed to eliminate this issue using a purely mechanical blocking mechanism. This design, fully interchangeable with conventional mechanisms, requires no extra modifications but needs an external synchronization system.

Featuring innovative gearshift dogs and blocking mechanisms, it was tested with two prototypes on test benches. The results showed the design’s effectiveness, and robustness especially for hybrid and electric vehicles, addressing key shortcomings of traditional clutches.

Introduction
Greenhouse gases, CO2 regulations, alternative fuels, and vehicle electrification are critical issues driving the rapid growth of hybrid (HEV) and electric vehicles (EV) [1]. This shift demands innovative solutions in automotive engineering. This research focuses on developing a new gearshift mechanism to meet these demands. In HEVs and EVs, the electric motor can act as an external synchronization mechanism, potentially reducing costs. Parallel hybrids, requiring a wide range of gear ratios, benefit from cost-effective gearboxes like manual parallel shaft gearboxes (MT) or automated versions (AMT) [2][3]. These gearboxes commonly use synchronizers, a prevalent gearshift mechanism in passenger cars [4].

This research aims to replace the synchronizer with a new, cost-effective gearshift mechanism that eliminates the need for synchronization while maintaining or surpassing the synchronizer’s functions [5]. Typically, a dog clutch is the simplest gearshift mechanism for constant mesh gears but has been limited by driving comfort and NVH (Noise, Vibration, and Harshness) concerns. In electric powertrains, NVH issues include gear whine and gearshift mechanisms [4],[6]. Reducing angular backlash is crucial for minimizing NVH, a feature of the new mechanism, while ensuring cost-effectiveness and compactness. More compact gearboxes tend to be stiffer, further reducing NVH [7].

This research introduces a patented dog clutch design addressing angular backlash, a common issue in traditional mechanisms [7]. Using a purely mechanical blocking system, it minimizes backlash and improves shifting quality. The form of dogs enables very fast disengagement of the speed even under load. Rigorous prototype testing confirmed its functionality, durability, and comfort, making it suitable for vehicle gearboxes.

Final design of dog clutch with blockchain mechanism

The clutch assembly (Figure 1) includes a hub (1) on the gearbox shaft, a sliding gear (2) that moves axially to engage gears, a gearshift sleeve (3) for controlling movement, and a blocking ring (4) to secure the sliding gear in positions. The sliding gear is split into two halves connected by screws (5) and pins (6). One blocking ring locks the sliding gear in all three positions (engaged/neutral/engaged) and secures the gearshift sleeve in neutral. No changes to the standard MT/AMT gear selector mechanism are needed. The design’s uniqueness is confirmed by Patent No. 307443[8] and the utility model „Schaltungskupplung“ [9]. Following design optimization, prototypes of dog clutches with a blocking mechanism were produced. Two clutches for the MQ200 gearbox were made to engage 1st, 2nd, 3rd, and 4th gears, see Figure 2. The prototype production was funded and supported by ŠKODA AUTO.

Gearshift process

The blocking ring stays concentric with the hub due to its constant contact with the sliding gear or gearshift sleeve. With six contact points, the ring maintains its shape during compression. To prevent uneven deformation, which could interfere with gear movement and cause excessive wear, the ring’s ends are bent inward. Figure 3 illustrates the gearshift process, where shifting the right gear involves:
Position 1 – neutral:Black arrows show axial backlash between the sliding gear and the gearshift sleeve. The blocking ring holds both components – sliding gear (upper) and sleeve (lower) – in neutral;
Position 2 – engagement preparation:The sleeve moves right, compressing the blocking ring, while the sliding gear remains in neutral until backlash is resolved;
Position 3 – engagement in process:With backlash removed, the sleeve pushes the sliding gear right, and the blocking ring stays compressed;
Position 4 – engagement termination:The sliding gear reaches its maximum position, engaging the gearshift dogs. Both components stop moving axially, and the blocking ring is no longer compressed;
Position 5 – engaged: The blocking ring expands back to its original position, fitting into the sliding gear’s groove, preventing clutch disengagement due to torque;

Position 6 – disengagement preparation:The sleeve moves left to compress the blocking ring. Axial backlash is present, keeping the sliding gear engaged;
Position 7 – disengagement in progress:The blocking ring is fully compressed, backlash is gone. The sleeve moves the sliding gear to
Position 8 – Disengagement Termination: The sleeve reaches neutral, but the sliding gear remains slightly engaged due to kinetic energy. The decompressing blocking ring helps move the gear to neutral;
Position 9 – Neutral:The dog clutch returns to the neutral position, same as Position 1.

Prototypes of the clutch were designed for the MQ200 gearbox, where the blocking ring withstands axial forces up to 2 kN during dog engagement, transferring a maximum torque of 200 Nm. The force needed to engage and disengage the clutch via the gearshift sleeve is about 45 N, which is well within permissible limits and comparable to manual shifting forces. The sliding gear and gearshift sleeve have been optimized for powder metallurgy. For the sliding gear, only grooves for the blocking rings and threads on one half need machining, while the gearshift sleeve requires machining of the inner groove for the neutral position. The outer groove, for the gear selector fork, is for prototype compatibility and can be omitted in future designs. No additional parts are required between the sliding gear and gearshift sleeve, ensuring concentric alignment with the hub. The blocking ring is fixed securely and cannot rotate around the shaft axis due to the pin.

Verification of the dog clutch

The fulfillment of the requirements for the dog clutch with a blocking mechanism needed to be validated against the design specifications. First experiments were static to verify the shift force and unwanted disengagement. The resulting gearshift force required to compress the blocking ring was measured to be 45 N.

Further was experimentally tested that the blocking ring functions as intended, preventing unwanted disengagement of the clutch.

The dynamic tests were dedicated for verification of function and for endurance tests. The first phase of clutch prototype testing used an inertia test bench with the output shaft connected to a large inertia disc. Tests focused on smooth shift sleeve movement and proper engagement / disengagement of the dogs. No unexpected behavior was observed.

The gearbox was connected to the gearshift robot on the inertia test stand, and gearshifts were performed with various input parameters. Mismatch speed was controlled by the difference between the stationary input shaft and the rotating wheel or by gear ratios between two gears. Figure 4 shows data from a gearshift with 3rd gear engaged at a mismatch speed of 30 RPM. The gearshift process began at 0.96 s, with rising displacement and force curves. A sharp drop in force at 1.02 s indicated compression of the blocking ring, allowing the sliding gear to move. The force increased as the dogs engaged, and by 1.08 s, engagement was complete. The gearshift took about 60 ms.

To proceed with dynamic check of the blocking mechanism, the gearbox was moved to dynamometric test bench. The function for the 3rd and 4th gears were performed with positive result. Due to test bench capacity 1st and 2nd speed were not tested.

Service life (endurance) tests were conducted for the 3rd and 4th gear clutches on the inertia test bench, with each gear being shifted 180,000 times and the gearbox output set to 89 RPM. This low speed simulated a mismatch speed of around 140 RPM, optimizing the gearshift process and eliminating the need for external synchronization. Each shift took just over 2 seconds, resulting in 220 hours of continuous testing per clutch and blocking ring.

Conclusion

The new patented dog clutch with a blocking mechanism enhances efficiency and reduces costs for electric and hybrid vehicles. It offers minimal angular backlash (less than 0.1°) and can disengage under load, improving shifting comfort and torque transmission. This purely mechanical design is compatible with standard gear selectors, including sequential shifting, and requires no additional modifications. The clutch’s blocking ring withstands high axial forces, preventing unwanted disengagement. Prototypes, tested in a standard five-speed gearbox, demonstrated up to 30 mm axial space savings compared to conventional synchronizers. The design supports effective serial production using powder metallurgy and has proven durability with a service life of 700,000 cycles.

References
[1] PILLOT, Christophe. The Rechargeable Battery Market and Main Trends 2020-2030. Lyon: Avicenne Energy, 2022.
[2] HOFMANN, Peter. Hybridfahrzeuge – Ein alternatives Antriebssystem für die Zukunft. Switzerland : Springer, 2014. Second edition. ISBN: 978-3-7091-1780-4
[3] NAUNHEIMER, Harald et al. Automotive Transmissions: Fundamentals, Selection, Design and Application. Berlin : Springer-Verlag, 2011. ISBN 978-3-642-16216-8.
[4] FISCHER, Robert et al. The Automotive Transmission Book. Switzerland: Springer International Publishing, 2015. ISBN 978-3-319-05262-5.
[5] MEHRGOU, Mehdi et al. NVH Aspects of Electric Drives-Integration of Electric Machine, Gearbox and Inverter. 2018. SAE Technical Paper 2018-01-1556. doi: 10.4271/2018-011556. ISSN 0148-7191.
[6] Wu,G.,Zhang, X.,& Dong, Z. (2015). Powertrain architectures of electrified vehicles: Review, classification and comparison. Journal of the Franklin Institute, 352(2), 425–448. doi: 10.1016/j.jfranklin.2014.04.018
[7] TŮMA Jiří. Vehicle Gearbox Noise and Vibration. New Delhi: John Wiley & Sons, Ltd., 2014. ISBN 978-1-118-35941-9.
[8] ČESKÉ VYSOKÉ UČENÍ TECHNICKÉ V PRAZE, FAKULTA STROJNÍ. Řadící spojka. Inventors: JASNÝ, M., G. ACHTENOVÁ and J. PAKOSTA. File No. MPT F 16 D 11/10. Patent No. 307443. 22. August 2018. Czech Office of Industrial Property. Patent.
[9] SCHECHISCHE TECHNISCHE UNIVERSITÄT IN PRAG, FAKULTÄT FÜR MASCHINENBAU. Schaltungskupplung. Inventors: JASNÝ, M., G. ACHTENOVÁ and J. PAKOSTA. IPC-Class F16D 11/00 (2006.01). File No. DE: 20 2018 103 633.5. 26. June 2018. Deutsches Patent- und Markenamt. Utility model.

Driving sustainability – Reducing the embedded emissions of copper in electric vehicles

Bruno De Wachter, Independent Advisor, International Copper Association

Since the publication of the EU Green Deal, e-mobility OEMs and Tier 1 suppliers in Europe have been actively seeking ways to evolve towards carbon neutrality. For such a journey to be successful, open  communication across the entire value chain is essential. This article develops the case for copper, a key raw material of the EV powertrain.

Copper in EVs – There is great potential to significantly reduce embedded GHG emissions associated with copper in the years to come.

Copper has the highest electrical conductivity of all non-precious metals, a quality put to good use in the stator windings of electric motors and induction motor rotors, as well as batteries, cabling and electrical connections. As OEMs and Tier 1 automotive industry suppliers develop their decarbonization plans, reducing copper’s embedded greenhouse gas (GHG) emissions is one of the challenges. A common approach to achieving this is by setting out a series of KPIs and milestones for their copper suppliers.

The good news is that there is certainly potential for reducing the carbon emissions from copper production to net-zero over the coming 30 years, and without the need for major technological breakthroughs. But for these conditions imposed by manufacturers in the automotive industry to be effective and actually help the copper industry speed up their decarbonization process, they have to be formulated in the right way, which requires some insight into the copper production process and material flows.

The copper production process and its emissions

A whole sequence of processing steps is required to produce high purity copper. The process of extracting primary copper from ores begins, of course, with mining, followed by concentration through a flotation process, and a first stage of refining in smelters using pyrometallurgical methods. The material is then subjected to a second stage of refining through electrolysis. An alternative route for low grade ore is the hydrometallurgical process, which separates the copper from the ore through leaching and then extracts it from the remaining solution through electrowinning.

Secondary copper is produced from scrap originating from manufacturing processes or end-of-life products. High purity scrap can be remelted directly with no need for refining, while less pure scrap requires additional processing. This can take place in dedicated secondary smelters, or the material can be added to the primary production process at various stages, depending on the scrap’s purity. This means that high-quality copper metal is often produced from a combination of primary and secondary sources.

According to an analysis by the International Copper Association (ICA), copper production currently leads to a total of 97 million tonnes of GHG emissions annually, or 0.2% of total global emissions. Of these emissions, approximately 70% are generated by mining, 23% originate from smelting and refining, and the remaining 7% come from upstream and downstream transport and end-of-life treatment of products.

A major component of the GHG emissions associated with primary copper comes from electricity, from fossil fuels used in mining transport and equipment, and from fuels used in smelting furnaces at various stages of the production process. The GHG emissions of secondary copper depend on the purity of the scrap, since this determines at what stage in the refining process it is added, but they are generally lower than those from primary copper. That said, using secondary copper can never be the sole and complete solution to decarbonization, as explained later. For this reason, reducing the impact of the primary production routes should receive major focus in the decarbonization process.

The pathway to net-zero

The decarbonization of the copper production process has already started, with numerous initiatives by individual companies involved in copper mining and refining. To step up the momentum, the ICA with its members developed a path forward to bring the carbon foot print of copper production as close as possible to net zero by 2050 (’Copper – The Pathway to Net Zero’). Made public in March 2023, the Pathway sets out a pragmatic approach to decarbonizing copper production, using existing technologies. It delineates which decarbonization options can be activated, by when, and with what impact. It also outlines some enabling conditions that should be in place to achieve this.

For scope 1 and scope 2 emissions, the Pathway identifies four major types of levers. The first is equipment electrification, to include the haulage trucks used in mining. An example of good practice is demonstrated by Boliden, a Swedish mining company which introduced electric trolley assistance in its haulage trucks in 2018, saving significant amounts of diesel fuel (Boliden, 2018). At the same time, underground mining machinery is being electrified at a rapid pace, coming with the additional benefit of saving the energy and cost of ventilation. The second lever is decarbonizing the electricity supply. This includes switching from standard to green electricity, alongside the option of installing wind and solar energy farms at copper production sites. A third lever is replacing fossil fuels with biofuel, biogas, or green hydrogen, particularly in smelting furnaces. A fine example of this is at German copper producer Aurubis, which has started using hydrogen instead of natural gas for the reduction process in its anode furnaces – an innovation set to reduce GHG emissions by around 5,000 tonnes each year (Aurubis, 2023). The fourth major lever encompasses various kinds of energy efficiency improvements at various stages of the production process. In a collective commitment, ICA members declared that they will be applying these and other measures to reduce their scope 1 and 2 emissions by 30 to 40% by 2030, 70 to 80% by 2040, and 85 to 95% by 2050.

A similar approach has been followed for scope 3 emissions, subject to the proviso that the results for this category depend on all the actors in the value chain collaborating. ICA members aim to reduce these emissions as far as possible by 2050, and will do what they can to unite every stakeholder behind this goal.

Recycling and decarbonization

Copper’s infinite recyclability is a major advantage. About 80 percent of copper is used in an unalloyed form, making the recycling process more straightforward. Even for copper that is alloyed or contains other materials, recycling can still be achieved without downgrading. Unwanted elements can be efficiently removed to recover the copper in its pure state, ready to be re-used in any kind of application. Because of its high degree of recyclability, copper already in use in its various applications is not regarded as lost, but can instead be legitimately considered part of the world’s copper reserve, often referred to as society’s „urban mine”.

Its high level of recyclability, combined with the fact that copper from secondary sources produces fewer GHG emissions than primary sourced copper, could lead to the simplistic conclusion that increasing the share of secondary material would be a good strategy for reducing embedded emissions. While this solution will work at individual plant level, it does not make sense on a European or world wide scale. Due to the long average lifetime of products using copper (typically 25 to 30 years) and strong growth in copper demand (practically doubling every 30 years), the availability of end-of-life material is far too limited to meet the demand for new material. Additionally, no process is 100% efficient, and there will always be losses associated with collecting, separating, and re-processing copper scrap.

Note that a distinction should be made between fabrication scrap, which originates from the production of end-use material out of semi-finished goods, and end-of-life scrap, which originates from end-of-life products.

Globally, scrap recycling rates from end-of-life products averaged around just 15% over the period from 2000 to 2020. Estimating future recycling rates is complicated by various uncertainties, but MineSpans by McKinsey expects the end-of-life recycling input rate to increase to 23 percent over the next 30 years.

Fabrication scrap contributed to about 16% of semi-finished goods production globally, a figure expected to remain stable. Bearing this in mind, any requirement set by raw material purchasers to increase the total recycled content of new copper above 35%-40% can only result in less recycled material being used elsewhere, leading to zero net reduction in GHG emissions at global level.

Moreover, the main levers for increasing recycling rates are in the collection and separation of end-of-life material, and consequently not in the hands of copper producing companies. Design engineers at every level of the automotive industry can play their role by favouring product designs that facilitate dismantling and separation at end-of-life (“design for recycling”). In some cases, collaborations between various stakeholders and the copper industry to capture and process the cleanest scrap and create a closed loop can set a good example. Recycling rates could also benefit from incentives for end-of-life collection, from staff upskilling for end-of-life management, and from improved separation techniques for treating multi metal scrap streams. Improved systems for car registration and waste stream reporting could avoid end-of-life vehicles being exported from the EU or going under the radar in other ways.

Collaboration across the value chain

All this considered, e-mobility OEMs and Tier 1 suppliers should not be over-concerned about the feasibility of reducing the embedded GHG emissions of copper conductors. The ICA and its members have developed a decarbonization pathway for the next 30 years based on existing technologies and that will bring the carbon footprint of copper production as close as possible to net zero by 2050. But to unlock its full potential, the pathway depends on stakeholder across the value chain communicating and collaborating with each other, upstream from copper production as well as downstream.

Purchase managers from the automotive industry can work with their copper suppliers to develop a roadmap to reduce embedded emissions and offer collaboration avenues to accelerate the process.

Raw material sourcing managers responsible for purchasing copper products should be aware of the limits of using recycled content as a means of reducing embedded GHG emissions. At the same time, they could consider developing closed loop business models for copper used in the automotive industry. Design engineers can play their role in this process by facilitating dismantling and separation at end-of-life.

With this level of collaboration across the entire value chain – stake holders communicating and interacting and achieving what is within their reach – there is great potential to significantly reduce embedded GHG emissions associated with copper in the years to come, while improving the collection and recovery rates of copper in end-of-life vehicles.

Intelligent bearing monitoring with LubeSecure from HCP Sense

Nico Kratz, Test Field Manager, HCP Sense GmbH
Ansgar Thilmann, Managing Director, HCP Sense GmbH

HCP Sense is an innovative start-up from Darmstadt that develops intelligent bearing monitoring systems for industrial applications. With a focus on predictive maintenance and condition monitoring, HCP Sense offers solutions to maximize operational efficiency, minimize downtime and extend the lifespan of machines.

The LubeSecure technology utilizes the fact that a bearing under full lubrication can be viewed as a capacitor in the electrotechnical sense in which the lubricating film acts as a dielectric. By measuring the electrical impedance, it is possible to differentiate between different lubrication states. This innovative approach makes it possible to react to inadequate lubrication at an early stage, before permanent metallic contact and the associated increased wear and tear occur. With that, LubeSecure technology doesn’t detect damages when they occur, as comparable condition monitoring technologies, but detects the underlying reasons for damages before they can actually form.

The following graphic shows the Stribeck curve from an electrotechnical perspective, illustrating the relationship between the specific lubricant film thickness and the electrical behavior.

Specific applications of LubeSecure technology

LubeSecure technology offers the following applications for rolling and plain bearings, among others:

1. Lubricant film monitoring:
Over 80% of bearing damage is due to lubrication problems in the bearing. HCP Sense’s impedance-based lubricant film monitoring enables early detection of a lack of lubricant or the use of a lubricant that is unsuitable for the application in question. In addition, natural and temperature-related lubricant ageing can be reliably identified.

Furthermore, in the development of the drivetrain of electrically powered vehicles for passenger cars and commercial vehicles, energy consumption can be reduced without jeopardizing durability. This is achieved because the use of LubeScure allows the lubrication to be ideally matched to the mechanical components and the framework conditions prevailing in reality.

2. Determination of the viscosity ratio κ:
The viscosity ratio κ is the measure of the quality of lubricant film formation in bearings. This makes it possible to determine in real time when the operating condition changes from mixed to liquid friction, for example, and whether the lubricating film is sufficiently formed. The additives contained in many lubricants are also taken into account. By using machine learning, HCP Sense can determine the viscosity ratio of a wide range of lubricants in real time, thus laying the foundation for optimized and low-wear machine operation. Our machine learning algorithms are trained with customer data and test data from our in-house testbenches, making sure that we use high quality data to further improve the predictions made by LubeSecure.

3. Identification of contamination:
The technology’s high measuring frequency ensures that even the smallest particles in the bearing can be identified at an early stage. Be it metallic debris from wear in the system or non- metallic particles from your process, LubeSecure detects changes in the lubricant condition almost immediately. This allows machines to be stopped in good time and maintenance measures to be initiated before major damage occurs.

By implementing LubeSecure technology, companies can not only plan their maintenance intervals more efficiently, but also optimize the energy consumption of their machines and increase overall operational safety.

The HCP Sense technology is currently being used successfully in numerous Gearbox test benches, field tests and from 2025 as a sensor installed as standard in new machines. Customers are already benefiting from the fact that they can prevent lubrication-related bearing damage, recognize machine failures at an early stage and plan maintenance more effectively. The areas of application are diverse and range from tunnelling machines to drivetrains and household appliances.

For more information:
www.hcp-sense.com
thilmann@hcp-sense.com

„In addition to reducing the risk of failure, the optimum operating condition identified by LubeSecure also contributes to significant energy and CO2 savings.”
Ansgar Thilmann, Founder & Managing Director, Commercial Director, HCP Sense GmbH