Technical Trend of the Power Shift Transmission (PST) of Agricultural Tractor

1. 기술해설
68 Journal of Drive and Control 2020. 3
Technical Trend of the Power Shift Transmission (PST) of
Agricultural Tractor
Md Abu Ayub Siddique, Taek-Jin Kim, and Yong-Joo Kim
1. Introduction
Agricultural tractors are being automation and
intelligence due to enhance working efficiency,
minimize driving effort, and adjust precision agriculture.
Tractors are designed to deliver high traction forces at
low speed. It is important for a powertrain to supply
continuous power to the driving axles during operations.
That is why several researchers and manufacturers
developed various power transmission systems.
There are two types of transmissions for tractor such
as manual transmission (MT), automatic transmission
(AT). The AT is called auto or self-shifting
transmission or n-speed transmission, which changes
gear ratios at various steps or automatically. The AT of
the tractor is also two types, which are step and
stepless transmission. On the basis of variable
transmissions, the speeds may be variable in discrete
steps or continuously variable within a range. The
step-variable transmissions usually employ either gears
or chains and provide fixed speed ratios with no-slip
(Xu et al. 2018). The step-variable transmission includes
the two types of power-shift transmission (PST) and
dual-clutch transmission (DCT). According to
Blagonravov et al., (2016), the stepless transmissions
use either belts, chains, or rolling-contact bodies. It is
classified as the hydro-mechanical transmission (HMT)
and hydrostatic transmission (HST). This study deals
with the power-shift transmission (PST).
The PST is the technology that allows the changing
gears on the run under loads conditions of the vehicles.
Li et al., (2018) reported that the PST is one of the
key technologies of a tractor for an engaging clutch by
an electric control system to improve the power,
economy, and driving comfort. In addition, the PST is
the most popular advanced technology for power
transmission due to be comparatively easier and
convenient to control and maintain on-farm for a driver
(Liang et al., 2018). There are two types of PST such
as the partial and full PST. The partial PST deals two
or more speeds without a clutch, although it must have
clutched to shift gears, and a full PST means the users
can shift all gears without clutching.
The ZF and CARRARO are specialist companies of
transmission, who lead the design, manufacture, and
supply of power-shift transmission for a medium and
large industrial vehicle, construction machinery, and
tractors. They are continuously developing new
technologies to improve efficiency, reduce fuel
consumption, and improve reliability by implementing
the advanced control techniques of their products.
According to Liang et al. (2018), MT efficiency is
almost 96%, which is the highest. AT is around 86%
with high torque like MT. In the case of HMT, the
overall efficiency is approximately 85% (Zhou et al.,
2014), and can transmit power smoothly. However, the
HMT is applicable to high-power vehicles. According to
John Deere, the HMT is around 5% better in fuel
consumption than the e23 power-shift transmission, but
the PST has a high performance of shifting, and quick
response (Panzani et al., 2010). Tseng and Yu (2015)
reported that the PST can remove the clutch friction in
the vehicle without losses of the dynamic performance.
Nievelstein (2005) mentioned several factors that
influence fuel consumption such as weight, design, speed,
and driver of the PST vehicle. Nievelstein observed that
the PST can save almost 1.9~4.7% of fuel effectively.
Tanelli et al., (2011) reported that the PST is a very
popular technology for power transmission to ensure the
maximum flexibility of use at each speed and to exploit
the maximum engine power available in all working
conditions. Yang et al., (2018) also reported that the
most important reason for getting popularity of the PST
is the wide range of applications (from low to high

2. 기술해설
드라이브 · 컨트롤 2020. 3 69
power vehicles) than the HMT. Considering drivers’
comfort, flexibility, smooth shifting power, fuel
economy, and especially wide range of applications, the
technical trend of the PST technology for agricultural
tractors was reviewed, but the limitation of this
technical review is that this paper is emphasized on the
commercialization of PST technology only. Therefore,
the objective of this technical review is to introduce the
technical trend of the PST for agricultural tractors.
2. Commercialized PST for agricultural
tractors
The tractor manufacturing companies such as John
Deere, New Holland, Kubota, DEUTZ FAHR, Case IH,
and STEYR who are commercially customized their
machinery using the partial and full PST technologies
and selling globally. It was found that the tractor
manufacturing companies have commercialized both
partial and full PST. It was noticed that most of the
companies customized their low horsepower machinery
with partial PST and high horsepower machinery with
full PST. New Holland uses partial PST up to T7.210
model tractors, and full PST was applied from T7.170
to the T7.260 model of tractors. In the case of Kubota,
it was observed that they manufactured the M8 series
(210 hp) tractor with the partial PST. The status of the
commercialized PST is in Fig. 1.
In this study, the leading agricultural company John
Deere, New Holland, Kubota, as well as Korean
company will be investigated for products and patents.
The customized PST technology is discussed two of
them in detail.
Fig. 1 The status of the commercialized PST
John Deere (USA) customized the full power-shift
e23 transmission for its 7R, 8R, and 8RT Series
tractors. The e23 power-shift e23 transmission is shown
in Fig. 2. All transmissions use hydraulic wet
multi-plate clutches. It is a reliable 23 speeds PST. The
e23 has featured 23 forward gears and 11 reverse gears.
The engine power is transmitted to the output shaft
through input shaft by operating the gears. The forward
and reverse gears were spaced around 15 and 30%
apart, respectively in order to provide smooth shifting
between gears, even gears spaced increases the
efficiency, smooth shifting, and automated shifting when
utilize the efficiency Manager. The maximum ground
speed of the e23 can reach in gear F20. As a result,
the gears F21 and F23 maintains the engine revolution
speed to save fuel. The e23 can control either right
hand (Forward and reverse direction, neutral position,
and electric park lock) or left hand (Forward and
reverse direction, neutral position, and electric park
lock) reverser.
The right-hand reverser has three main controls,
namely foot brake with integrated AutoClutch, set speed
adjuster, and gear selector control lever with integrated
reverser, whereas the left-hand reverser has four main
controls. The multi-function left-hand reverser is the
additional main control of the left-hand reverser.
However, both reversers provide the full power-shifts on
driving mode; no need to stop or clutch.
The mechanical front-wheel drive (MFWD) provides
four by four capacities to tractors with different sized
wheels (front and rear) as front wheels of tractors turn
Fig. 2 The e23 power-shift transmission of John
Deere

3. 기술해설
70 Journal of Drive and Control 2020. 3
faster than the rear wheels. The e23 has a spring-
engaged or hydraulically-disengaged park brake. The
feature control of park brake prevents the accidental
braking when the tractor is at high speed, and the air
brake system automatically activates. As a result, the
e23 PST is easier to operate for all levels of operators.
The new dynamic command transmission system is
shown in Fig. 3. A dynamic command transmission is
developed by New Holland (USA) as a partial
power-shift transmission up to T7.210 series tractor, and
from T7.170 to T7.260, New Holland customized Range
Command and Power Command as a full power-shift
transmission. The 8 steps partial power-shift
transmission is a dual-clutch concept, similar to that
which operates the seamless range shifting within the
Auto Command transmission.
The dynamic command transmission consists of 3
ranges (A, B, and C) which help to perform various
agricultural works (heavy and light draft, bailing, and
haulage). This can deliver either 40 km/h at a reduced
engine speed for the economy or a high 50 km/h
transport speed. It can set more working speeds,
provides programming options that simplify the work. It
is an automatic shifting rival to the smoothness of
premium automobiles.
It has an additional clutch pack and reduction gears,
which provide an additional 16 gears below the
standard to deliver a total of 32×32 gears. The engine
power is transmitted through the input shaft by the
clutch (Even and Odd) and gears (4 Even and 4 Odd)
to the output shaft.
Fig. 3 The dynamic command transmission system
of New Holland
The 4 odd gears, and reverse and odd clutch are
installed on one shaft. The forward and even clutch,
and 4 even gears are set on the second shaft. The
power is modulated between the two clutches because
the odd gear is disengaged with the odd clutch, and the
even clutch is engaged in the even gear ratio.
Consequently, the forward and reverse clutches maintain
the power shuttle, even on steep gradients while the
range shifting is all robotized.
3. Patents on the PST technology
The patents related to PST technology were selected
to know the development technique, function, and
nobility of the PST for being popular technology for
power transmission. The patents are listed in Table 1.
The selected patents are discussed in details as follow:
John Deere mentioned the design and arrangement of
the gear pairings of the planetary transmission in
different operation modes. In the first shifting operation,
a clutch is connected to an input shaft that is connected
to the output shaft for operating in the fixed drive
mode, wherein the planetary transmission runs as a
flywheel. In a second shifting, the clutch is released so
that the planet carrier is driven by the planetary set.
This arrangement of the planetary set can be operated
in the gear reduction or in the reverse mode.
The diagram of John Deere PST is shown in Fig. 4.
The power shift transmission (10) comprises an input
shaft (18) and a first output shaft (20), which can be
brought into a drive connection by means of a
planetary transmission (22) as well as by means of a
first shift element (24) and a second shift element (26),
which are both shown herein as clutches. The planetary
transmission (22) has a planet gear carrier (28), on
which a dual-stage planetary gear set (30) is rotatably
mounted. The dual-stage planetary gear set (30)
comprises an input-side planet gear (32) as well as an
output-side planet gear 34.
Fig. 5 shows the schematic diagram of the PST
developed by New Holland (10). This patent deals with
a large number of forward ratios and smooth shifting
between gear ratios. In this invention, the PST requires
only a single clutch swap for most changeovers

4. 기술해설
드라이브 · 컨트롤 2020. 3 71
Title of patents Nobility Company, Year
Power shift transmission
To reduce the production cost, and no
need additional operation mode like a
two-stage PST
Deere and Company,
2015
Smoothly shifting multispeed
transmission
To reduce jerky shifting, and ensure
smoothness and accuracy
New Holland, 2005
Transmission for a tractor
To transmit a forward or reverse driving
force into traveling speed at a low cost,
and to enhance the transmission efficiency.
Kubota, 1999
Power shift transmission for
vehicle
To provide a speed reducer by using two
selectable clutches and synchronizers
LS Mtron, 2015
Table 1 The list of the patents on the PST technology
Fig. 4 The diagram of the PST technology of John
Deere
Fig. 5 The schematic diagram of the PST
developed by New Holland
between adjacent ratios and uses double swaps for only
a few changeovers. Three close-ratio forward speeds
and one reverse along with a second output that is an
11 speed, wide ratio, and transmission. The two
transmissions are arranged in series resulting in 33
forward ratios and 11 reverse ratios. Although some of
the ratios produced are nearly duplicates of others,
skipping these duplicate ratios still yields at least 28
usable forward speeds.
The gear selection 1 produces for clutches C1, C4,
and C6 are engaged. The clutch C1 is connected to
gear G1 that is attached to input shaft I and that is
why the gear G1 is constantly rotating. If the C1 clutch
engaged, the G2 rotates, and G2 drives G3. The G3 is
connected to the shaft C, and shaft C drives shaft A by
G4 and G5. In case, gears G4 and G5 drive shaft A by
shaft C so that speed of shaft A is determined by the
selection of clutch either C1, C2, C3 or C10 (reverse)
that is interconnected shaft I to shaft C with different
size gears. This patent is able to reduce jerky shifting
and ensure smoothness and accuracy.
The Kubota has developed the Glide Shift
Transmission (GST) which employs a power synchro
shift and single clutch pack system resulting in
improved maneuverability and workability while
obtaining a power efficiency equivalent to that of
manual gear type transmissions. The main benefit of the
Kubota Glide Shift transmission is that you never have
to use the clutch. You can shift up through all 12
forward gears without ever needing to touch your
clutch. Like the hydraulic shuttle shift, you can also
shift from forward to reverse or vice versa without the
clutch. The nobility is to transmit a forward or reverse
driving force into traveling speed at a low cost, and to
enhance the transmission efficiency.
LS Mtron invented a PST to reduce power loss and
improve power efficiency. The PST consists of a
driving shaft operated by the received power from an
engine of a vehicle. A first clutch provided to the
driving shaft, and a first and a second gear selectively

5. 기술해설
72 Journal of Drive and Control 2020. 3
Title of papers Keywords Journal, Vol., Year
Coordinated control of gear shifting
process with multiple clutches for
power-shift transmission
Transmission efficiency, and high fuel
economy
Mechanism and Machine
Theory, 140, 2019
Analysis of shifting performance of
power shuttle transmission
Performance, accuracy, and stability
Journal of Terramechanics,
44, 2007
Automatic starting control of tractor
with a novel power-shift
transmission
Driving comfort, safety, and service life
of a tractor powertrain
Mechanism and Machine
Theory, 131, 2019
Analytical study to estimate the
performance of the power shift
drive (PSD) axle for a forklift
Accuracy, efficiency, and economy
International Journal of
Automotive Technology,
11, 2010
Table 2 The list of the published articles on the PST
receiving power by the first clutch. The nobility is to
provide a speed reducer by using two selectable
clutches and synchronizers.
It is observed that the patents on the PST are
executed to manufacture commercially. Interestingly, it
is noticed that the objectives of all studied inventions
were to reduce the production cost, convenience to the
users, economically efficient, and high accuracy.
Therefore, it is clear that PST technology can fulfill the
demand of consumers.
4. Papers published on the PST
There are lots of published articles on PST
technology. In this study, 6 published articles were
selected from thousands of articles because those articles
are published in highly reputed Elsevier and Science
direct journals which have an impact factor (IF) over 2.
Also, those articles were conducted based on the
keywords of design, performance, failure detection, and
control methods of the PST for improving transmission
efficiency that suits the interest of this technical review.
The published articles are listed in Table 2.
Li et al. (2019a) were conducted an experiment on
the control gear shifting process of the PST. They
developed a dynamic model of novel PST and analyzed
the upshift and downshift processes. The control
strategies were also developed to ensure gear shifting
quality and continuous power flow for tractor field
operations. The structure of the developed powertrain in
this study is shown in Fig. 6.
Fig. 6 The structure of the powertrain (Li et al.,
2019a)
This novel PST was designed considering some
functions: i) Four-speed PST gearbox: the four gears (I,
II, III, IV) in the PST gearbox can be shifted by
engaging friction clutch C1, C2, C3, and C4, respectively.
ii) Motion inverter: the motion inverter consists of a
clutch (CF), brake (B), and 2K-H planetary gear train
with the dual planet. iii) Four-speed partial PST
gearbox: two of the gears are shifted by controlling the
clutches CM1 and CM2, respectively. The other two
gears are shifted by synchronizers which can be
controlled manually or electronically.
It was found that the work speed was ∼9 km/h at
70% throttle opening of the gear and the upshift
command was issued at 0.2 s. The jerk of the vehicle
is less than 15 m/s3
during the downshift process
(within 1 s), which ensures the excellent power
continuity, smoothness, and responsiveness for the gear
shifts of transmission with multiple clutches.

6. 기술해설
드라이브 · 컨트롤 2020. 3 73
Another research was conducted by Kim et al.,
(2007) collaborated with Tongyang Moolsan Co., Ltd.,
Korea and Seoul National University for shifting
performance. They developed the EASY 5 models of
the hydraulic control system and power shuttle
transmission. The models for the hydraulic control
system and power shuttle transmission were verified by
an experimental powertrain constructed for the
validation purpose, which is shown in Fig. 7 (a). The
powertrain comprises a variable speed motor (7.5 kW),
a power shuttle transmission, an inertia mass, and a
direct current (DC) dynamometer. The power driveline
was designed using flexible couplings. The experimental
powertrain is shown in Fig. 7 (b).
Fig. 7 The experimental powertrain (a) schematic
of powertrain, and (b) input and output
shaft of power shuttle transmission
It is observed that the modulating pressure and time
in the clutch were significantly affected the shifting
quality. The peak torques of the input shaft and clutch
were increased with the increase of tractor speed and
reverse gear ratio. Kim suggested that for a better
shifting performance, the reverse speed should be 20%
faster than the forward speed. The weight of the tractor
also increases the axle torques but has no effect on the
power transmission. The damper did not affect the peak
input shaft torque but eliminated the torque fluctuations.
Kim also mentioned that a proper hydraulic control
system is important to develop the power shuttle
transmission for agricultural tractors.
Li et al., (2019b) also conducted a study, which
deals with the hydro-viscous drive (HVD) technology to
improve starting comfort without affecting the drivetrain
service life of a novel PST of a tractor. This control
system obtains the real-time target angular acceleration
of clutch driven disk according to the target angular
acceleration database and the real-time angular velocity
difference between driving and driven disks of the
clutch.
Park et al., (2010) conducted an experiment at Ajou
University, Korea on the power-shift drive (PSD). In
this study, the dynamic simulation model was developed
and analyzed the movement. The simulation model is
composed of a torque converter, a gearbox, a
differential, hub reduction and an engine, which the
power source of the 1st
forward and reverse PSD axle.
When the transmission is connected to the forward
clutch, the power is delivered through the forward
coupling, which is linked to the differential box. The
power is delivered from the reverse coupling to the
wheel through the reverse gear driveline when the
reverse signal is turned on.
Other studies were also conducted to improve the
transmission efficiency considering shaft torque,
acceleration and vehicle jerk. They also considered the
comfort of users, the shifting performance, accuracy,
fault detection, and failure of the shifting. In these
studies, they had developed and applied several
algorithms to enhance PST performance.
Finally, the overview stands by that there are several
types of research on PST, which have been conducted.
Recently, most of the researcher belonged to the leading
countries of agricultural machinery production are trying
to detect a fault or enhance the performance by
applying various new technique and algorithm. Results
indicate that the PST is able to ensure high accuracy
and comfort for the users. Also, the continuity and

7. 기술해설
74 Journal of Drive and Control 2020. 3
smoothness of power transmission ensure the service
life of a tractor transmission with a guarantee.
5. Conclusion
In this technical review, the research trend such as
products, patents, and published papers (3P) of the
power-shift transmission (PST) was discussed and analyzed.
In Korea, the PST is not yet commercialized. Though
the research on the PST is ongoing, more research and
development are needed to customize the PST technology.
Most of the leading companies have already developed
PST technology and are extending the coverage of the
technology less than 100 hp. It is necessary to secure
economic feasibility to apply this technology to small
horsepower tractors.
The Korean company is also developing this
technology and plans to commercialize it soon.
However, Korean PST should also have the same level
of performance and economic feasibility as leading
companies. Also, patent avoidance and registration
strategy are needed.
Reference
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8. 기술해설
드라이브 · 컨트롤 2020. 3 75
[저자 소개]
Md Abu Ayub Siddique
E-mail : engg.ayub64@gmail.com
Tel: 042-821-7870
2016: B.Sc. in Agricultural Engineering,
Hajee Mohammad Danesh Science and
Technology University, Dinajpur,
Bangladesh.
2019: M.Sc. in Agricultural Machinery Engineering,
Chungnam National University, Korea. Mr. Ayub is doing
a Ph.D. in the same department and same university. His
research interest is the hydraulic system modeling and
analysis.
Taek-Jin Kim
E-mail : taekjin79@nate.com
Tel: 042-821-7870
Graduated from Chungnam National
University in 2019. 2008-2018: Senior
Research Fellow, Kukje Machinery
Co., Ltd., Korea. Recently, Mr. Kim
is doing a Ph.D. in Agricultural Machinery Engineering,
Chungnam National University, Korea.
Professor Yong-Joo Kim
E-mail : babina@cnu.ac.kr
Tel: 042-821-6716
2008: Ph.D. in Bio-Mechatronics
Engineering, Sungkyunkwan University,
Korea. 2008～2014: Head of the power
machinery technology group, LS Mtron
Central Research Institute, Korea.
2014～Present: Associate professor, Department of
Biosystems Machinery Engineering, Chungnam National
University, Korea. Prof. Kim is the associate member of
KSAM, KSPA, KSFC, and so on. His research interest in
design and analysis of agricultural power machinery.