AEI DCT WEBCAST Q&A WRAP-UP
The questions and answers listed below were taken from a recent webcast featuring Dual Clutch technology. You will find the questions and answers categorized under Lubrizol, GETRAG Ford and BorgWarner.
| GETRAG Ford | BorgWarner |
| Lubrizol | ||
|---|---|---|
| Are the clutch materials different in DCT compared to conventional manual and automatic transmissions? | The clutch materials are very similar to those in ATF torque converters and shifting clutches. Modern developments ensure that the material is durable, hard-wearing and helps to maintain friction performance. The DCT clutch materials are specifically designed to operate at high shift power for short periods, when shifting gears, and at lower shift power for longer periods under continuous slip conditions. Friction materials developed for these conditions are also found in planetary transmissions, particularly in torque converter clutches. | |
| How would do you compare the efficiency of wet and dry DCTs? | Both transmissions optimize engine efficiency by selecting the appropriate transmission ratio for any driving condition. The transmission efficiency of the dry clutch DCT is higher than that of the wet clutch DCT. Both transmissions employ an electro-hydraulic system for automatic shifting and clutch engagements. The dry clutch transmission requires a much lower volume of fluid and pressure. Hydraulic pressure is supplied by an accumulator that is charged 'in demand' by the hydraulic pump. The wet clutch transmission requires a larger hydraulic pump that continuously provides pressure and flow for clutch engagement, and flow for the clutch cooling jets. For this reason, the parasitic losses in the wet clutch DCT are four to five times higher than in the dry clutch DCT. However, it is often difficult to make a direct comparison, as the two types are found in different types of vehicles. | |
| What oil is used in both wet and dry DCTs and what is the oil change schedule recommended? | In a wet DCT with a combined sump, a dedicated DCT fluid should be used. In a wet DCT with separate sumps for gearbox and clutches, the gearbox would use a standard manual transmission fluid, whereas the clutches would be lubricated by a DCTF designed for the specific clutch material. In a dry DCT, standard MTF can be used. Oil drain intervals for wet DCTs in the marketplace today are around 40,000km. We expect dry DCTs to follow the manufacturer's MTF oil drain schedule, which is normally fill-for-life. | |
| How does DCT fuel economy compare to a manual transmission? | In theory, a manual transmission is the most fuel economical choice, however, this depends on it being driven perfectly, all the time. Due to driver error, for example during gear changing, the DCT is, in reality, more economical than a manual transmission. This applies especially to the dry clutch DCT, as, in contrast to wet clutch DCT, there are virtually no parasitic losses when shifting gear and maintaining clutch pressure. | |
| What are the unique requirements of a dry clutch DCT lubricant? | A dry clutch DCT does not need to lubricate friction materials; it needs to focus on gear performance. This can be satisfied by a manual transmission fluid. | |
| Can you make a prediction about projected annual volumes for DCTs for North America for the next few years? | A number of OEMs are marketing DCTs in their vehicles in the US: Ford, BMW and Audi, for example. In the next five years or so, we would expect to see DCT production starting in North America, perhaps for other OEMs. According to CSM Worldwide, 8% of the total transmission market in the United States will be DCTs by 2014. Go to HERE for more global predictions on DCT growth. On average, how much more expensive is a wet DCT fluid than a standard automatic fluid? Pricing varies by product, region and; distribution channel. Typically, wet DCT service fill fluids are more expensive than standard ATFs. | |
| What is the current global percentage of automatic transmissions vs. DCT's? And where do you project it will be in five years from now? | We estimate the current global percentage of DCTs to be between 1 and 2%, whereas AT is around 46%. In five years time, say 2015, data suggests DCT market share could be as much as 10%, with AT market share dropping to 37% | |
| Can you elaborate on the growth that you expect in North America? | We know that Ford has introduced Dry DCT in North America, and any of the Detroit three may introduce dry or wet DCTs in the future. DCTs used in European transplant OEMs would also take a share of the North American market. We envisage the commercial vehicle market could introduce wet DCT in the next five to ten years. | |
| Which API lube basestock type do you expect to account for the largest share of DCT fluids? | In the future, we anticipate Group III base stocks will be used in a majority of the wet DCTF applications. | |
| Can you quantify how much the Lubrizol DCT additive package can extend bearing life vs. a change in viscosity of ~2 cSt? | The statistical nature of bearing life means that it is impossible to precisely predict or quantify life for an individual bearing. However, industry bearing tests and field trials show that Lubrizol DCTF additive packages provide excellent bearing performance and durability compared to other commercial oils, even at 2 cSt lower viscosity. | |
| What are the service oil change intervals (miles) for current dry DCTs? | Oil drain intervals vary according to the OEM. In a dry DCT, we expect oil drain intervals would be fill-for-life, similar to what you find with MTF. Speaking for European OEMs, drain intervals are around- 50,000km - 80,000km, depending partly on the application and on the flexible service intervals of other components, such as engine oil. | |
| What features should DCTF have compared to other transmission fluids? | Wet DCT fluid features the combined performance of an ATF and MTF, e.g., strong friction performance like an ATF and MTF type synchronizer performance. Load carrying is also important in combined sump applications. In a DCTF, the friction is optimized for the specific friction materials used in the DCT application. | |
| Does the customer have to carry one more oil for the vehicles with DCT or is there any "backwards compatibility" of the DCT oil with previous transmission technologies? | Most OEMs have specially developed fluids for specific applications, and these should be used. Dry DCT uses MTF, so in this case, it may be possible for the oil marketer to stock one fluid. | |
| How important is fluid cleanliness to reliable, proportional control of DCTs? | Fluid cleanliness is extremely important for DCTs. In particular, the mechatronic system is very complicated, containing many ducts and bores, which must not be blocked by deposits. The clutch surfaces must remain clean for optimum friction performance. | |
| Can filters affect the additive package characteristics of the ATF? | Typical filter membrane pore size is not sufficiently small to affect the additive package. | |
| Are the lubricants used in DCT trending toward conventional oil stock or full synthetic? Advantages/disadvantages of each? | Current DCTFs in the marketplace utilize full or part-synthetic base stocks, but we predict that all-Group III mineral formulations will be used in future applications. The benefits of PAO-based materials are low temperature performance and oxidation. However, this comes at a high cost, and security of supply could be a concern. Today's Group III stocks can achieve similar levels of performance, but at lower cost, and these stocks are increasingly available globally. | |
| Are synthetic fluids required for DCTs? | First, it’s important to clarify the definition of synthetic fluids provided in the answer during the Webcast. The first generation of DCT fluids were synthetic-based i.e., requiring Group IV (PAO) base stocks. However, with the advancement of our formulating knowledge and advanced additive technology, Lubrizol has been able to optimize DCT formulations to work in both Group IV and Group III base stocks. In the future, we anticipate Group III base stocks will continue to be used in the majority of the wet DCTF applications. | |
| How do the fluid cleanliness requirements compare between a DCT and a conventional planetary transmission? | Fluid cleanliness requirements between the DCT and conventional AT are very similar in terms of the necessity to keep clutch surfaces clean. However, the mechatronic system in the DCT is more complex with ducts and bores, - which must not be blocked by deposits. The gear system is more severe in the DCT than the AT, but this does not affect fluid cleanliness requirements. | |
| In addition to formulating for durability, can the DCT fluid be formulated to positively influence fuel efficiency? | Yes, the fluid can be formulated to positively influence fuel economy. The additive must be formulated to provide maximum friction and load-carrying performance and durability, which ultimately impacts fuel efficiency. The fluid's viscosity profile can also be engineered in terms of viscosity, viscosity index, shear stability and cold temperature performance to provide the best fuel economy for the application. | |
| Is Lubrizol working with friction material suppliers to provide a "package" gearbox designer-integrator? | Most friction systems perform best when the materials, hardware, controls, and lubricants have been cooperatively designed. Lubrizol works with friction material suppliers around the world to provide additive technologies that have this synergistic benefit. | |
| Difference between DRY and WET DCT? | For a direct comparison, please go HERE. | |