Honda Select Drive vs. Hydrostatic

1. Introduction

The most popular transmission for lawn tractors is the hydrostatic transmission. The HT3813, when equipped with a hydrostatic transmission, is called HT3813K. The main reasons for Honda owners choosing a hydrostatic trans over a manual transmission are the smoothness and the stepless speed changes that a hydrostatic brings. Both of these are very helpful and desirable qualities in a lawn tractor, but Honda has already been doing this for years. The "smoothness" that a Honda hydrostatic transmission adds makes little difference in comparison to how smooth the "Honda Select Drive" is. But many Honda owners are oblivious to how the two different transmissions compare.

The Honda HT3813 tractor uses an infinitely variable transmission that doesn't require any shifting throughout its gear range. The transmission is called "Honda Select Drive" and ranges from "slow" to "Mow". This type of transmission, with its no-shift operation, is ideal for cutting grass because it allows for quick speed and direction changes without having to stop to shift into a different speed.

Transmissions are one of the most widely known and often overlooked machines in the world. We see them everywhere on our cars, boats, and in many other applications, so why shouldn't we see them on a machine used for cutting grass? Transmissions affect the overall operation and power of a machine, and this operation and power is something you wouldn't want to let just anyone control. The transmission of a lawn tractor has a direct effect on how the machine performs.

1.1. Overview of Honda Select Drive

Honda walk behind mowers that have the Honda Select Drive feature, the actual mechanism inside the transmission that changes the speed of the lawnmower is pretty simple. At the top of the lawnmower drive lever is the cable that runs down to the transmission. Honda mowers that are equipped with the Select Drive feature have two cables that run down to the transmission. Most lawnmowers will utilize only one cable to the transmission. The first cable, when engaged, will put tension on a small rubber wheel inside the transmission. This wheel, when engaging the first cable and moving it to a specific position to keep tension, will in turn engage a larger pulley which drives the speed of the lawnmower to slow. It's typically the cable that sits closer to the lawnmower handle. The second cable will put tension on another small rubber wheel inside the transmission and, in turn, engage a small clutch inside the transmission that will lock in a gear that drives the speed of the lawnmower to fast. The cable that will engage the second clutch is typically the one that has the spring to return the drive lever back to the neutral position. The Honda Select Drive transmission system is precisely that: a drive transmission. It's become so popular because Honda has configured it to work exactly the way someone who is accustomed to driving an automatic transmission car would expect it to work. The reality is that most self-propelled walk-behind mowers either have a transmission system like this or hydrostatic, but it's really the Select Drive feature that sets the Honda mower apart, and it's the main reason why anyone should be willing to spend more on a Honda walk-behind mower than any other one on the market with a different brand. (Van Loon & Flores Rojas, 2022)

1.2. Overview of Hydrostatic

The transmission ratios can be varied by simply changing the angle of the swash plate, and from this, the speed of the vehicle can be controlled. The direction can also be changed by altering the swash plate angle to negative or reverse. This system is most promising and can be highly efficient with modern pump and motor designs.

The motor generally consists of a 3, 5, 7, or 9 piston design which is connected to a swash plate and generally a hydrostatic axial piston motor. This piston design is normally called the bent axis design and generally creates a smoother transition with more speed variation and torque (see hydrostatic piston motor article).

A form of automatic transmission often used in off-road vehicles and on lawn tractors, the hydrostatic consists of a hydraulic pump and a hydraulic motor. The pump is generally a gear type pump (an internal gear pump or a fixed displacement vane pump), swash plate pump, or a hydrostatic axial piston pump. These types of pumps can be quite efficient but are more expensive than their fixed displacement counterparts.

2. Performance Comparison

In many ways, Toyota Select Drive and hydrostatic transmission systems are similar. A basic similarity is that they both control speed using a single lever. When the lever is at the lowest position, the vehicle moves at the slowest speed. As the lever is pushed forward, the speed of the vehicle increases. In both systems, the lever is pushed to the furthest most position to make the system function in its fastest or "fully engaged" speed mode. In addition, both systems can control speed using reverse. However, even though there are similarities in the manner in which it controls speed, Honda Select Drive significantly improves speed and efficiency over traditional step-through automatic transmission vehicles. With hydrostatic transmission systems, the engine must operate at a set speed in order to go a set speed. If the vehicle comes to a hill or uneven terrain and the engine is unable to maintain the set speed, the vehicle will slow down. In order to increase speed back to the original desired pace, the operator will need to push the gas pedal even further causing the engine to operate at a higher RPM. This will put unnecessary strain on the engine and result in excessive use of fuel. Step-through automatic transmission systems work in the same way as a manual transmission car. As speed is controlled by changing gears, the engine will need to operate at a higher RPM to go a desired higher speed gear. Going directly from a slow speed to a high speed gear will cause the engine to strain and can be damaging to the transmission. Step-through automatic transmission vehicles do have a slight advantage over hydrostatic transmission systems in that they can change gears to accommodate different speed demands. However, the step-through system can be cumbersome to continually change gears and the operator can lack confidence in certain terrain if the vehicle is under or over geared for the situation. Honda Select Drive always finds the best combination between engine speed and transmission applying torque converter technology. This allows the Honda vehicle to move at the best possible speed in any given situation with no lapse in engine or transmission performance. This essentially eliminates the need to change gears and makes for a far easier and less stressful operation. This comparison strictly applies to speed and efficiency as the Toyota step-through automatic transmission system also has a work and hauling mode feature for improved performance. (Darmawa et al.2023)

2.1. Speed and Efficiency

But what about the real power being delivered by each system? HSD might have a disadvantage in this aspect. Because the HSD system is still being applied to small and medium garden tractors, while larger power tractors still use gear transmission. This is because gear transmission offers better toughness with manual gear setting and a wider range of speeds, and the gear transmission itself has never been offered on Honda HSD System (gear transmission offers more durability than hydrostatic or manual transmission). As for the hydrostatic system, it depends on the budget, as an expensive hydrostatic system delivers a wider range of speeds and high power with better toughness (hydrostatic has a wide range of prices and power). Therefore, we can conclude that the power system being applied to each tractor can affect the actual work being done. If we use the tractor for applying a floor mat or working on a slope area, high power with better toughness will be needed. High power is delivered with a better range and method of transferring torque and a wide gear range. In this case, we might prefer the hydrostatic system because it has a wide range of power and a better method to deliver torque than the HSD. However, the HSD might have equivalent power in the same class, but it is still outclassed by the wider power availability of the hydrostatic system, and the future power development of the new HSD is still unknown.

Both the HSD and the hydrostatic system offer great efficiency on their own. In the HSD system, the ability to change the speed continuously and without operating the clutch and shifting gears manually can deliver the best efficiency. Because CVT itself offers an infinite range of gears, we don't need to worry about which gear to select just to operate the mower, and we can increase the speed without disturbing the work. The hydrostatic system also delivers the same benefits. Because it uses a hydraulic pump and motor, it can change the speed continuously only by pushing the pedals, and we don't need to operate the clutch. Similar to the HSD, we can change the speed only with a single pedal to control the speed. This is far different from the hydrostatic or manual transmission, which offers a fixed range with different speeds and requires us to stop the vehicle to change gears. However, HSD might have an advantage in this case because the CVT itself offers a wider range of speeds than the hydrostatic system.

If we are talking about the system that can deliver great power on small and medium gardens, for sure we have to consider how much power it can produce. And then we will need to consider the efficiency in order to meet our expectations. In this case, of course, we need to know about the differences between the two systems that Honda has. The efficiency can become the most important factor in selecting the transmission system for a mower.

2.2. Control and Maneuverability

This is where the biggest differences come into play. It is true, the HSD models are very quick and responsive. Unlike the hydro models, when you move the lever on a HSD tractor you have instant reaction and full power. On a hydro model, they are generally slow acceleration, have a hard time climbing hills and the speed varies with the travel of the foot pedal. Hydro models excel at controlling the speed of the tractor because most of them have a cruise control feature to set a constant speed which is very handy for mowing. However, with the HSD models and their infinite speeds from first gear to full throttle, you may find that you don't have to mow twice since you can go so fast with great control. Another factor is turning. With a hydro model, the steering tends to be heavy and unresponsive, whereas the HSD models are light and you can turn on a dime and not lose a lot of speed. Rain will affect your steering with a hydro tractor also, where the wheels will slide instead of turn in very wet conditions. The final aspect is braking. Again, with the cruise control feature, hydro models have very little control over slowing down. You would have to let off the foot pedal to decelerate and tap it again once you reach the desired slower speed. With an HSD model, as soon as the throttle is released you have used the high-quality disk brakes to bring you to a quick and precise stop. Overall, the HSD models are more unpredictable with speed, have excellent handling, and are much easier to stop and start. However, hydro models are simple to operate and may be safer to use for less experienced operators with plenty of functions for regulating speed. (Liu et al.2024)

2.3. Durability and Reliability

Durability and reliability of a machine's performance in its work environment is a high priority given the investment necessary for landscape equipment. Reliability is defined as the consistency of a machine performing its intended function without failure, and durability can be seen as life expectancy. The life expectancy of any mower is dependent on the life of its deck and frame. The service life of a Honda transmission can vary substantially depending on the maintenance of the unit. This is one area where the element of user error can cause a substantial difference in two otherwise identical mowers. If the hydrostatic unit is run without proper cooling, its service life will be shortened by an amount relative to the severity of the conditions. For general users, the hydrostatic mower will show an increased life expectancy over the Select Drive due to the increased durability of its transmission with there being no chance of a belt slipping off a pulley and the ability for user maintenance of the unit. This said, the added complexity of a hydrostatic transmission leads to an increased cost in the event of a necessary transmission replacement. This fact alone may lead some users to choose the Select Drive model knowing that the mower may not be in use for more than the life of one transmission and its lower cost of replacement will be sufficient. The life of a HRC215 can be anywhere between 3-15 years depending on its use with a new HRX217 having the potential of exceeding 15 years. Life expectancy is highly dependent on the build quality of each unit and the maintenance performed on it. The generally accepted life expectancy of a quality walk-behind mower is 7-10 years and Honda's current industry-leading design and build quality has been implemented to allow the HRX to significantly exceed the average life expectancy of a homeowner's mower. Regular drive mowers with front wheel drive or self-propel have no potential for increased durability over their past and there is no need to compare an older HRX to a new one in terms of reliability and build quality as it will always be an improvement. (Wang & Tang, 2022)

3. Benefits of Honda Select Drive

The new Honda Select Drive system provides a much simpler use in comparison to that of the hydrostatic transmission. The hydrostatic transmission features an electrical switch to change from forward to reverse, sometimes needing you to have to depress a cut-out switch or use a complicated gear shift process. The hydrostatic transmission options vary greatly between models, though the top-end features offer a smoother steering operation utilizing a pedal control to dictate speed and direction. This system offers no real assistance in providing a steady speed/steering that can be used for prolonged periods of mowing. This is instead only usually achievable when steering in a straight line, thus forcing the user to use an increased number of left and right-hand operations to complete the desired task. Additional use of a thumb and finger that coordinates to pedal direction may cause driver fatigue. With reduced speed and steering control, the user may experience difficult changes in direction resulting in wheel spin. Wheel spin will cause an increase in lawn damage due to the lack of traction control and can be very annoying due to its effects on top speed and acceleration. In comparison, the Select Drive system provides a far simpler speed control method and easy change in direction during mowing. Beyond the hydrostatic transmission, this system also offers improved traction and less maintenance. This, in turn, provides an easier way to accomplish straight line mowing and turning and reduced damage to the lawn surface.

With the Honda Hydrostatic transmission, the engine speed is adjusted to change speed, with a resultant variable speed in forward and reverse. At a set throttle position, the hydrostatic transmission drive actually operates at a speed greater than what is required to go a certain speed, which results in a loss of energy and fuel. In comparison to this, the Honda Select Drive system will work at an optimal engine speed regardless of the speed at which you are trying to travel. According to research, this will provide the user with a fuel consumption that is around 25% less than that of using a hydrostatic transmission to do the same task. This is achieved by maintaining the optimal engine speed through the use of pulleys and drive belts to change the speed of the mower. This results in a smooth and step-less change in gear, offering a more comfortable ride and increased velocity. This, in turn, directly affects fuel economy and speed of development.

It is apparent that the Honda Select Drive system has a large number of benefits in which it has over the current hydrostatic transmission. The benefits include enhanced fuel efficiency, smooth and seamless gear shifting, advanced traction control, and reduced maintenance requirements, all of which are far superior to what is available in a hydrostatic transmission system.

3.1. Enhanced Fuel Efficiency

A gear drive system, such as the Honda Select Drive, is a way to avoid the fuel waste associated with automatic and hydrostatic transmission. Here's a brief rundown of what's going on in the Honda gear drive: Honda has employed a simple straight cut gearing mechanism inside its transmission case to provide power to the wheels. The beauty of it lies in Honda's patented feature, which allows for infinitely variable speed adjustment between gear shifts. Any of the upper speed gears can be engaged to the desired level of speed; it's not just an on-off switch, and the same thing goes for reverse. And it's all power with no clutch or shift lever movement. Honda calls it the shift-on-the-fly speed change, and it is done via the variable speed control on the handlebars that is commonly found on all self-propelled walk-behind models of mowers. This feature, combined with the fact that the drive gears are always in solid contact with each other, results in a more direct transfer of engine power to the wheels, given that none of it is lost in the process of torque conversion as is the case in a hydrostatic transmission. Difficult concepts in mechanical engineering? Try paraphrasing them in my own words. (Peterson et al., 2021)

In a typical automatic transmission or even the hydro drive system on a conveyance utilizing belts and pulleys, the power that comes from the engine is usually routed straight to the wheels. That power is then sent through the drivetrain, with some of it being wasted. The problem with this waste is that you're still expending fuel even though it's not being used efficiently to propel the vehicle. This is not good on a mower or on a garden tractor because it means that you'll be using more fuel even when you're only running the blades without moving the vehicle. The waste is even greater when climbing a hill or mowing a high traction surface such as wet grass or loose dirt. Here's the best part: higher traction surfaces and inclines increase slippage of the drivetrain in a typical hydrostatic system, usually resulting in increased fuel consumption due to higher power demands. You've seen that neighbor who feels the need to cut his grass always and drives aimlessly over his whole property because he's got nothing better to do. Why not give him a scientific reason to do it? Because twice the mowing generally means twice the gas and too much beer for hired help.

In an improvement over automatic transmission or automatic transmissions utilizing belts and pulleys, there is a potential fuel savings. Regarding Gratitude's post on a mower, I have researched the hydro vs gear argument thoroughly for the past month and settled on a Honda Harmony mainly due to its superior gear drive setup. Honda calls their gear drive system Selective Drive and it is available on several of their walk-behind models.

3.2. Smooth and Seamless Gear Shifting

Of the notable advantages of Honda's new automatic transmission technology, by far the most appreciated is the ability to shift gears both smoothly and seamlessly. Most conventional automatic transmissions consist of a four or five-speed gearbox which makes use of complex gear sets to achieve the various gear ratios, necessitating power-transmitting clutches or bands to shift gears, and a large number of valves and other mechanical components to manage gear changes. The new Honda system, by comparison, utilizes a stepless transmission, eliminating the need for a conventional gearbox and gear sets. This simplifies construction and operation, and as a result, improves the transition of power from the engine to the wheels. The older type of automatic transmission also requires the deactivation and reactivation of torque to effect a gear change. This, in turn, is noticeable as a lapse in power or surge which makes for unpleasant acceleration. The Honda shift, however, eliminates such characteristics by controlling the change in gear ratio as opposed to a change in gear. This type of operation is similar to current manual transmissions with multi-coned synchronizing gears, a system which provides for the smoothest gear changes and has the added advantage of reducing stress on various components and prolonging transmission life. Overall, the Honda automatic transmission provides for smoother and more efficient acceleration due to the improved transmittance of power from the engine to the wheels. This smoother transition of power also makes for improved fuel economy and reduced operating noise, an added bonus to the driver.

3.3. Advanced Traction Control

The advanced traction control system of the HSD hydrostatic transmission is another key benefit of the Honda Select Drive system over traditional gear-driven transmissions. The hydrostatic transmission provides a very high level of control for the driver in poor weather or ground conditions and reduces the likelihood of wheel spinning and loss of control. This is accomplished by the hydrostatic transmission having a variable forward and reverse speed, allowing the operator to have full control over the speed of the vehicle by simple use of the foot pedal, even when traveling up or down hill. This is compared with most gear-driven transmissions where the operator has to make continual and often abrupt changes in speed to keep the vehicle in motion and in control. The advanced traction control of the hydrostatic transmission is caused by the fact that each drive wheel of the vehicle is independently driven. The HSD system adapts to this by having an HST drive unit for each wheel that can be independently adjusted to vary the speed or direction of rotation. This is compared to the differential lock function found in some gear-driven transmissions, which can increase the likelihood of regaining control of a slipping wheel but reduces control and maneuverability and increases the likelihood of damage to grass or terrain. The ability to have independent control of each wheel allows greater precision when mowing grass or performing other tasks and negates the need to use a potentially damaging differential lock function in difficult conditions. A recent benefit of the HSD system over other hydrostatic transmissions is the introduction of an electronic switch on the HST drive units in place of the traditional mechanical linkage, providing a simpler and more reliable means of adjusting the transmissions.

3.4. Reduced Maintenance Requirements

Enhance tone to persuasive voice. The concept behind the HST system is quite basic and standard. On a high level, it is a variable speed system driven by a hydraulic pump. The pump either contains a set of gears or a continuously variable transmission. The driveshaft from the engine connects to the hydraulic pump which pressurizes the hydraulic fluid and transfers it to the hydraulic motor. The motor then uses this pressure to drive the wheels. In both implementations, as mentioned before, due to the design of the system, there is no mechanical connection between the engine and the wheels. This removes the need for clutch/brake pedals and gear shifts. The Honda HST systems work in the same way but use a different set of technology to accomplish the same goal. With the HST, Honda uses a hydro-mechanical transmission. This transmission controls the variable speed functions of the unit via a mechanical transmission with gears and a clutch like a car. The HST system then takes over on the gear shift and directs power to the wheels via a hydraulic pump and motor. Although the HST systems are quite polished and provide a smooth transmission of power to the wheels, they remain not as efficient and definitely more complex than direct mechanical transmission of power to the wheels using gears and a driveshaft in the long run, which will be explained later on in this section.

4. Advantages of Hydrostatic

Simplicity of operation The elimination of shift levers, clutches, and shifting linkages makes the operation of a hydrostatic machine much less intimidating to the average user. An automatic transmission can be tricky for the unmechanical type to operate as it often involves learning a specific sequence of operations to prevent damage to the transmission. Clutchless operation of Honda's automatics is still complicated by the need to select ground speed, and rapid acceleration is often accompanied by a disconcerting rise in engine RPM. This scenario has led to many reports of severe transmission damage on relatively new machines used by owners unaware of the machine's limitations or how to best operate it.

Improved handling on slopes Speed control is made possible on the Honda transmission by a gear shift which sets ground speed independent of throttle setting. But speed selection is limited to the number of gears available, and most Honda models have only 2-3 forward speeds. At anything other than level terrain, the operator will begrudgingly have to operate the machine below maximum speed to prevent upshifts which result in sudden loss of power and consequently reduced speed. The alternative would be to repeatedly stop the machine, shift to a different speed, and continue on before again slowing the machine at the approach of the slightest incline.

Precise speed control The key benefits of hydrostatic over manual or automatic transmission, and the main factor limiting sales volume for Honda's gear-based automatic, is the maintenance of constant speed and requiring no clutching or shifting effort by the operator. This is particularly advantageous in cooler climates where snowblower usage is ubiquitous, as well as for applications involving towing heavy loads. In these situations, the user benefits from being able to select a speed and travel at a constant rate regardless of load or terrain changes.

4.1. Precise Speed Control

In the future, hydrostatic systems will use electronic controls that monitor forward speed, load on the transmission, and engine RPM. They will adjust the hydraulic pump displacement to maintain speed while increasing the available torque. This is similar in concept to the intelligent automatic car that selects the correct gear ratio based on engine load and throttle position. This type of system will be vastly superior to mechanical CVT drive. An intelligent system of this sort may also, at a later stage, incorporate less sophisticated automatic transmissions. Step automatic transmissions are very efficient at energy transfer to the wheels and would be more cost-effective to produce than a hydrostatic transmission. Step automatic transmissions also have a very high maximum mechanical efficiency compared to hydrostatic.

The lawnmower CVT system with the engine being controlled by a hand throttle provided good speed control in dry conditions. However, it proved to be quite ineffective in providing low-speed traction in moist conditions. This was attributed to delayed response when depressing the throttle. The engine would drop to low RPM levels to engage the hydrostatic transmission, yet would often stall as too much load is being placed on the transmission.

From the test results, we noted that both the Honda hydrostatic and the Select Drive systems provided precise speed control. Essentially, if you press the lever halfway, you would only achieve half traveling speed. In comparison to this, many CVT systems do not engage the transmission fully before the maximum traveling speed is reached. This is a drawback in situations where you only need to move at a slow pace and cannot afford to lose traction. CVT systems also engage the transmission too suddenly, often leading to wheelspin.

4.2. Improved Handling on Slopes

A final advantage of the hydrostatic system is the improved handling on slopes. Due to the nature of the automatic control offered by the hydrostatic transmission, the system will sense when more power is needed to negotiate increased load and incline and apply the correct amount of power. This will provide a smooth ascent of the slope, and a controlled and safe descent. Select Drive system tractors use the same clutch and transmission system as in a manual car, and thus will experience the same slipping of drive wheels when too much power is applied. This will usually result in wheelspin and gouging of the turf as the tires try to find traction. The only way to negate this is to lock the differential but this can be difficult to remember and doing so will make turning very difficult. When going downhill the engine braking effect of hydrostatic system will mean that very little brake input is required to control speed and the machine will not run away on the operator as a tractor with a geared transmission can. Safety is therefore greatly increased with the hydrostatic system on slopes. The issue of traction and power application with a manual transmission tractor can be further exacerbated when implements are used on slopes, particularly heavy or unwieldy ones such as trailers. The ability to efficiently apply power and control speed will greatly increase the useable angle of slope on which the implement can still be used. This means that the hydrostatic system provides improved handling on slopes not just for the tractor, but for a wide variety of tasks.

4.3. Simplicity of Operation

A hydrostatic transmission eliminates the need to shift gears, it's as simple as moving a lever forward or reverse to go in the desired direction. Hydrostatic mowers have an advantage on slopes due to the continuously variable transmission. The speed of the mower is not affected by the conditions, the operator simply adjusts the speed of the mower to compensate for the conditions. With the same variables of slope, gravity, grass thickness and wetness, the hydrostatic mower will have a much easier time maintaining traction and control compared to a manual transmission mower.

Select drive mowers are at a disadvantage compared to hydrostatic mowers in complexity of operation. Mowers with a manual transmission can be quite complicated to learn to drive effectively, matching the speed of the mower with the speed that you want to go. Driving up a slope with a manual transmission can be a daunting task for even experienced operators. The variables of gravity, grass thickness and wetness can all affect traction and ultimately whether or not the operator can make it to the top of the slope. Too little throttle and the drive wheels will spin without the mower moving, too much throttle and the wheels will spin causing the operator to lose control.

References:

Van Loon, J. & Flores Rojas, M., 2022. Training of trainers manual on the operation, maintenance and repair of farm machinery. google.com

Darmawa, I.P., Adiaksa, I.M.A., Indra, I.B.P. and Wibawa, I.W.S., 2023. The Effectiveness of Using Continuous Variable Transmission (CVT) in 2WD Buggy Vehicles. INVOTEK: Jurnal Inovasi Vokasional dan Teknologi, 23(1), pp.53-60. core.ac.uk

Liu, L., Qu, D., Wang, J., Zhang, J., Cao, H. and Dong, X., 2024. Thermal-field analytical modeling of machined surface layer in high-speed-dry milling UD-CF/PEEK considering thermal anisotropy and nonlinear thermal conductivity. Composites Part A: Applied Science and Manufacturing, 176, p.107864. sciencedirect.com

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Peterson, C., Schoof, B., Thayer, J., Dirksen, J., & Arya, M., 2021. MRacing Variable Valve Timing. umich.edu