Text | Whoops
If there is an Olympic number in the car circle, the last big problem is not hybrid.
Especially today, DHT hybrids, which were born for hybrids, rose overnight. When the black terms in the field of hybridization in the past, what P1, P2 all the way to P4, what several engines and several drives, what sun wheel planetary wheel, and today's DHT hybrid can not move "9 mode 11 speed", "full speed domain parallel" mix and match mix, this is a topic that can boil hair volume and brain cells until the oil is exhausted.
DHT is the next big trend of "electrification in a hybrid manner" of fuel vehicles, and our column has listed too many times in the past, and almost every self-owned brand you can call famous has either been on the DHT train or is concentrating on saving tickets. In 2021, BYD won the whole field with DM-i, and everyone saw it.
At present, the most typical ones are BYD DM-i, Great Wall Lemon DHT, Geely Thor Hi · X, Chery Kunpeng DHT. Among the joint venture brands, Toyota THS and Honda i-MMD have been waiting for a long time, and among the independent brands are GAC GMC3.0 (different from the introduction of THS), Dongfeng Mach MHD, BAIC and so on.
(From the perspective of this article, DHT takes the broad definition of "hybrid special transmission", so hybrid technologies such as THS and i-MMD, which were born before the word "DHT", are also included.) ）
Because there are patent barriers to hybrid technology (sometimes need to deliberately think of other ways to bypass), relatively more dependent on the characteristics of the car company itself (rather than Tier1), when the hybrid from the parallel-based "oil mixing" era, into today's hybrid special transmission and DHT era, you will find that these DHT structural principles are almost different. In addition to the above technology, DM-i is roughly similar to i-MMD, and the other companies are simply eight immortals across the sea.
If you can't understand the hybrid topology map released by car companies, you don't have to worry about doing a questionnaire IQ test. First, DHT hybrid is originally more than one brain-burning, second, the topology diagrams of each car company have their own drawing methods, and the third is to make the complex technology easy to understand, which requires the tacit cooperation of the technical department and the market department of the car company, which has always been rare.
Occam, razor or scythe
DM-i and the much-like i-MMD are the most familiar, simplest and easiest to understand. Both are P1+P3 dual motors/generators, single clutches. The mechanical structure is very simple, there is no more physical gear, the working mode is mainly series increased range, and the clutch is switched to oil-electricity parallel when needed.
The core components used to "mix" the two (BYD called EHS) have the same principle, and the difference is more reflected outside the DHT mechanism, such as the different engines (of course, the nonsense is different). In addition, BYD currently only uses DM-i to create PHEV plug-in hybrid models, while the Honda i-MMD has only heV hybrids, and has only recently begun to dabble in PHEV.
The main three modes of i-MMD
DM-i
Simplify and simplify the structural topology diagrams of Honda and BYD, in fact, you can get the following Occam version (the battery circuit is omitted in the figure).
The working principle of DM-i needs no further mention, in short, it is extended range hybrid plus direct drive capability. Most of the time in series increase mode to work, the internal combustion engine to maintain the work in the efficient zone; high-speed cruising itself reaches the efficient range of the internal combustion engine, the oil-electric conversion loss will also increase, so the internal combustion engine intervenes in the direct drive more competitive; when high power is required, the internal combustion engine and the motor work together, and if conditions permit, the battery can also make up for the power gap from the battery to the motor.
Very simple? The complexity is behind it.
Extended range mode is ideal, but no matter how good the internal combustion engine, its highest efficiency point will not output a lot of power. Taking byBYD's 1.5L Snapdragon engine as an example, the approximate output of the 43.04% thermal efficiency point shown in the figure is 26kW. This power is included in the "oil-electricity" power generation process loss (general efficiency of about 90%), and most working conditions other than cruise are obviously not enough.
At this time, it is necessary to increase the power generation in the internal combustion engine, and the balance between the battery supplying energy to the motor, and the ratio of the two needs to be determined in the hybrid mode. At the same time, because DM-i is a single-speed direct drive, as long as the clutch is combined with whether pure direct drive or hybrid mode, the speed of the vehicle is linked to the speed of the internal combustion engine. As the speed increases, the upper limit of the thermal efficiency of the combustion engine, the relationship between efficiency and torque (whether to increase torque efficiency or decrease torque efficiency) of the internal combustion engine are also changing.
The maximum thermal efficiency limit for increasing the speed of the vehicle has been reduced from 43% to about 37%.
This brings up a bunch of complex mathematical problems:
First of all, as long as the internal combustion engine is generating electricity, there is a conversion loss of about 90%. Secondly, the motor drive also has its own high efficiency and inefficiency zone, and the inefficiency zone can also be as low as 60-70%.
These losses may not be much for THE PHEV charged by the grid, after all, the cost of the grid is close to zero yuan, but it must be taken into account for "PHEV when it is used for HEV" or in the feed state, because the electricity in the battery is converted from fuel at this time. The efficiency of fuel power generation is at most 43%, the conversion of electrical energy needs to be multiplied by 0.9, the motor works in its inefficient area to × 0.6 ~ 0.7, and the final energy utilization efficiency will be as low as 20 ~ 30%, so it is necessary to compare with the internal combustion engine direct drive away from the efficient zone.
As long as there is a partial direct drive, the speed change must be taken into account, because the power can be "peak shaved and filled" by the motor, but the speed is not. DM-i's internal combustion engine speed and vehicle speed have a definite mathematical relationship, the speed change will inevitably lead to the change in the speed of the internal combustion engine, then is it more cost-effective to use the motor, or is it more efficient to produce by the internal combustion engine? If you choose both at the same time, how many "tasks" should each be assigned to be the most efficient overall?
Behind this is a complex calibration process, the dish is just a few, this fried can not be steamed, the raw pickle can not be fried, then how to maximize the utility requires complex calculations.
DM-i chose to plug and mix, or BYD chose such DM-i, which may also be based on this consideration: if the battery is large enough, and the electrical energy is basically from the "zero yuan purchase" grid, then it can be powered by the battery for a longer period of time to avoid the internal combustion engine deviating from the high efficiency point too much, so as to achieve ultra-low fuel consumption.
Honda has long been dominated by HEVs, and one of its optimization methods is the ultra-wide high-efficiency zone speed belt of the internal combustion engine. Since the speed of the partial direct drive cannot be solved, it is necessary to strive to make the entire speed range / the left and right directions in the figure below (rather than the torque range / up and down direction in the figure below) have a larger area of efficient zone. This allows for more use of the hybrid mode (partial direct drive) and the motor is responsible for extending the torque range.
Honda's background in developing the i-MMD and the requirements of the times at that time were completely different from today, don't forget that the i-MMD is almost ten years old.
Parallel mode run line of honda 2.0L hybrid engine: the most efficient torque point in most of the rpm range
The Great Wall added on top of the i-MMD, and the basic principle was the same as honda BYD, but the lemon DHT added a two-speed transmission to the engine's direct drive path. This is equivalent to widening the operating bandwidth of the combustion engine in direct drive and hybrid modes, freeing the combustion engine from the heavy responsibility of single-speed drive – although only one more gear.
Single gear is to use a pair of shoes to adapt to sprint sprints and marathons at the same time, the possibility of losing one or the other is higher, and still to pursue the all-round needs more soft power to squeeze their own limits; multi-gear is to separate the two to perform their duties, but need to solve the trouble of "changing shoes", and the extra cost and reliability problems.
The Lemon DHT dual gearbox uses a fork shift, which you can think of as a direct drive with an additional 2-speed manual transmission, and the added cost, weight and reliability risks are relatively limited. There is no need to worry too much about the smoothness, because the hybrid is different from the manual transmission after all, and the bug of the motor can adjust the torque and speed at both ends of the clutch to achieve a smooth combination, and the final smooth performance only depends on the calibration power of the car company.
Whether it is BYD's single gear or the Great Wall's two-speed transmission, it is the choice after weighing the resources, goals and vision at hand. DM-i's single gear is behind BYD's all-in attitude towards PHEV, which has the support of a more efficient internal combustion engine at this stage; lemon DHT is the result of the Great Wall HEV and PHEV grasping at both ends, with limited system complexity increased, in exchange for a more picky internal combustion engine choice and HEV possibility.
The magic of planetary gears
There are some things that at first glance seem unfathomable, but once you understand the principles, they are very simple— and then in a blink of an eye, they become incomprehensible admiration for such ingenious inventors.
Planetary gears are an example. Many people's understanding of planetary gear sets began with Toyota THS hybrid technology. In fact, in addition to hybridization, all AT automatic transmissions, the most basic transmission principle is the planetary gear set. Regardless of oil and electricity, planetary gear sets are actually very widely used in power and transmission systems, and it is even likely that you have more than one on your car.
Toyota's THS PSD power shunt is a planetary gear set
Although planetary gears look complex and their applications are indeed complex (I admit), the basic principles are not difficult for ordinary people to understand. This is a system that can achieve three speed couplings, when you control the speed of one of the two, you can determine the speed of the remaining one; when you change the speed of one of them, you can change the speed relationship/speed ratio of the remaining two.
The solar wheel in the center, the outer ring of gear on the periphery, and the planetary frame in between form a planetary gear set. The three can rotate freely, there is a definite speed relationship between each other, and the intermediate planetary frame may rotate at the same time as the rotation occurs, depending on the operation of the inner and outer gears, it may also be homogeneous and reversible rotation. (The torque of the three also varies, but it is not necessary to understand the hybrid.) ）
The automatic transmission makes use of this transmission principle. For a single planetary gear set, in which the sun wheel and the outer ring gear ring are used as the input and output shafts, the remaining planetary frame will set two gear ratios, that is, gears, between the input and output shafts when rotating freely and braking and locking (usually using multi-plate clutches).
Similarly, two planetary gear sets can achieve four gears (two lock-clutch, open or closed, 2×2), and three planetary gear sets can bring six gears (3 permutations). The more gears, the more planetary gear sets and multi-piece clutches are required, so the automatic transmission will be more expensive and take up more space than the manual transmission.
So AT and MT are not just "manual or automatic", so manual transmissions that can automatically shift gears will be classified as another type of AMT. The stricter term for AT should be a planetary gear set shift automatic transmission.
Toyota THS is the well-deserved spokesperson for planetary gear sets, a textbook hybrid system in which three rotating components in a planetary gear set: the sun wheel, planetary frame and outer gear ring are connected to the generator, internal combustion engine and electric motor, respectively. As shown in the figure below, the components and gears corresponding to each color are always at the same speed, so we can use the generator to adjust the speed relationship between the internal combustion engine and the wheel end.
In fact, it only needs to understand one basic principle: a system that fuses triple rotation. Controlling the rotation and stop of one of them, that is, changing the speed ratio relationship of the other two.
This lock-up clutch in THS is a one-way lock-up that prevents the internal combustion engine from reversing
The advantages and limitations of Toyota THS have been demonstrated by too many analytical articles, and they are not the focus of today's DHT topic. The reason why THS is mentioned is because Geely chose two sets of planetary gear sets and put them into the Thor Hi · X's DHT Pro hybrid transmission. Thor Hi · X Hybrid actually provides two configurations, of which "DHT" is a single gear similar to DM-i, and "DHT Pro" is Geely's housekeeping skill.
Thor Hi · X DHT Pro
To sum it up in advance, this is a crazy move to add an additional planetary gear set after i-MMD is fused with THS.
You can think of it as i-MMD based on THS, and then add a planetary gearset speed shifting mechanism, or you can think of it as THS based on i-MMD, and then add a planetary gear set to regulate speed. This new planetary gear set and the one in the THS essentially make up a 4AT (but Geely only uses three gears, so it is officially called 3 speeds).
Such a crazy move not only allows the parallel connection to have up to 3-4 gears, but also because after the internal combustion engine is completely disconnected, the two brake clutches can still affect the motor output, so that the pure electric mode also has 2 gears to choose from. And because one of the planetary gear sets is similarly arranged to THS, the Thor DHT Pro also has a power shunt mode that combines THS and i-MMD workflows. Although there is an additional set of planetary gear sets, the components of the entire system are highly reusable, creating even more amazing available modes and gears.
The purpose of all this is to achieve what Geely claims as "full-speed domain paralleling" (down to 20km/h). The full-speed domain parallel is for a more extreme comprehensive energy utilization efficiency. That is to say, for HEV or feed-in PHEV, when the electrical energy itself is converted from oil to high-cost electricity, then the inefficient area of the motor also needs to be taken into account. Whether it is expanding the available operating conditions of the direct drive or reducing the energy consumption of the motor, it has now become valuable.
From this point of view, Geely pays more attention to the fuel consumption performance of HEV than DM-i and Lemon DHT, which is possible, representing the different understandings of BYD, Great Wall and Geely for the future rhythm of pure fuel vehicle replacement (of course, this will also be based on the current electrification status of the three companies).
The advantages are obvious: even if you can't figure out how the 4-speed parallel and 2-speed pure electricity came from, you can see that the Thor DHT Pro can easily have many more transmission path options than DM-i and Lemon. More gears and more speed ratios greatly reduce the performance-energy pressure required for the combustion engine, making it easier to maintain the efficiency zone and easier to do lower energy consumption at high loads. Pure electric mode "white rubbing" a 2-stop option, power consumption can also be stained.
Of course, the disadvantages are also obvious: the cost is the easiest to understand. Dual motors are standard to today's DHT, and Thor uses two planetary gear sets, counting the planetary gear locking mechanism, up to 4 clutches. BOM aside, planetary gear sets require extremely high machining accuracy as support, more components bring volume problems, and compact design further increases the cost.
Geely specifically mentioned the new process used to process gears, intelligent heating and hardening process, which improves the accuracy of gear components from 15-20 microns to 8 microns. The double planetary gear set was stuffed into the rotor of the dual motor, and finally Geely actually made the DHT Pro into the world's most compact DHT gearbox at present, and how much resources and costs were paid for it can be imagined.
Probably Geely also knows that such a crazy DHT Pro also needs a lower cost and more reliable solution, so we see a simplified version of the single gear, that is, the Thor DHT without Pro. Geely didn't mention much about this "basic version" of Thor, but it would be an important backup and addition to the DHT Pro.
9 mode 11 speed, completely crazy?
Chery Kunpeng DHT was released very early, but has not given a specific and intuitive structure diagram, so that our column has always been holding a "no belt is not written" attitude of "no belt is not written" attitude. However, at the beginning of this year, Chery finally explained his own DHT in detail, and the result scared everyone.
If you think that the above Thor DHT Pro is enough to burn the brain, then you may wish to take a look at Kunpeng, although the official "9 modes 11 speed" is partly suspected, but it also reflects... This is almost the most complex DHT hybrid to date, and only Thor can fight. If you have the ability to understand Thor's planetary gear set, then this "almost" can be removed.
Let's first translate the above diagram:
In terms of the number of hardware, Kunpeng is not "as good as" Thor: 3 clutches, three gears. However, the relationship between the three positions of Kunpeng and the position of the motor and clutch makes its actual complexity and possibilities only a lot more.
Roughly simplifying the understanding, Kunpeng DHT can be seen as: a 3-speed dual-clutch transmission, first adding a P2.5 motor to one of the dual-clutch shafts, and then packing this "hybrid 3-speed dual-clutch" into a set of i-MMD/DM-i. Of course, it can also be understood in reverse, adding such a hybridized 3-speed dual clutch to an i-MMD.
But if you look closely, you'll see that Kunpeng is different from the previous DHTs: between the internal combustion engine and the generator, there is an extra generator/electric motor.
If we remove the motor part between the internal combustion engine and the dual-clutch transmission, and then expand the 3DCT to 7DCT, the following result is actually the hybrid system of Lynk & Co 01 HEV, the unique dual-clutch P2.5 single-motor hybrid:
With Thor DHT Pro, for Kunpeng DHT you don't have much need to cut how many gears it has, and Ben Hu has no intention of using words to tell something that his peers can't understand with video. Spring, brain cells to stay in love is not good?
In terms of (possible) advantages and disadvantages, Chery has achieved more speed ratios than Thor's two-planetary gear set with a not too high cost increase (equivalent to one more 3DCT). Although it is the same as the Lynk & Co 01 HEV as the dual-clutch structure, but because there are only three physical gears, there is only one 2-speed on the power shaft without an electric motor, and it can be combined with the generator in the P1 position, and it will not be beaten back to the fuel vehicle in the singular gear like Lynk & Co. Compared with Lynk & Co, Kunpeng has an extra P1 generator, which allows it to achieve range extended range and parallel hybrid modes, and i-MMD has it.
But it is still the same as Thor, more choices do not definitely guarantee better results. Richer ingredients may not lead to more deliciousness, not just look at the ingredients and ignore the cook, and don't ignore more ingredients for the same cook, it may become pressure rather than freedom.
The simple system is the ability to dig to the end, is to continuously tap the most accurate and ideal workflow switching mode, the most granularity. Complex systems test engineers' brain capacity and trade-offs, with countless permutations and combinations appearing, and richer choices in front of us, which does not mean that things are simpler. Not only do you need to match the various patterns and speed ratios to a variety of scenes, but also to find out what you don't need in it, so as to avoid letting the system make meaningless, low-value actions and entanglements when running.
At present, there are DHT hybrid technologies with clear and intuitive structures announced, and autonomous car companies that have been or are about to start delivering are basically these four.
It must be seriously stated that all of the above arguments are limited to theoretical derivation from structures; the "advantages and disadvantages" we speak of are also "the advantages and disadvantages of the structure" and do not point to specific technologies. This is actually very reasonable, even according to the same drawing exactly the same structure, different manufacturers can get different quality, and then there is a difference in performance.
The materials and instructions given by IKEA are the same, someone assembles the furniture quickly, nice and neat, and someone demolishes the house and the result is still twisted.
Not to mention, the advantages and disadvantages of the hybrid structure must not be directly "the advantages and disadvantages of using the structure hybrid technology". Because structure is innate, it is important, but it does not mean that the day after tomorrow is inactive. The basic capabilities of each car company are different, the ability to realize ideas is also uneven, simple structures may be stretched to the limit, and complex possibilities may be counterproductive due to lack of control.
The leg length of one meter and two is structurally suitable for running to the hurdles, but it does not mean that a guy with a height of 1.8 meters must run faster than a 1.7 meter classmate.
Not to mention that the actual performance of the hybrid system cannot be used independently as a criterion for evaluating a car. Just as the different choices of DHT structures are actually related to the foundation of the internal combustion engine, the hybrid route and pursuit, and the reliability control of the transmission system.
Hybrid efficiency is ultimately used to load the car, if a factory has the most efficient DHT, but the body-in-white lag makes the vehicle gain 200kg?
In the end, consumers buy cars, they use cars, and no one takes down the powertrain alone and uses them. The hybrid system ultimately depends on the car itself to speak, I can't give the answer, there is no shortage of reviews to recharge, and finally time will give you results.
So what's the point of studying these? Knowing the basic principles and logic, understanding the innate strengths and weaknesses, you will know which performances and details to pay attention to for the real car, and observe certain working conditions and certain performances in a targeted manner; you will know which are the natural limitations of the ceiling, and some breakthroughs are worthy of praise, which are roomless and not exhausted, whether they are deliberate or cannot be done.
Not afraid to know, not afraid to know, afraid of knowing nothing.