Development of Vane Pump for Medium Passenger Vehicle CVTProductIntroduction

Development of Vane Pump for Medium Passenger Vehicle CVTHAGIWARA Takahiro, OOTAKI Masashi, KONDO Hirotoshi, SHINDO Shota

1Introduction

3This report introduces a vane pump for medium passenger vehicle CVT Note 1). This vane pump will bemounted, as a hydraulic power source, to the transmission
mechanism for medium passenger vehicles developed byJATCO Ltd. as the successor of existing CVT unit thathas already been in mass production and rolled out globally.
Production of this product was started at KYB
Kanayama in October 2020.
Note 1) An acronym for Continuously Variable Transmission.

2

Newly Developed CVT Unit

Compared with the existing type, the new CVT unit thathas just been developed by JATCO Ltd. has the following
features:① Lower fuel consumption due to lower friction② Superior operation feeling③ Lower NVH Note 2)
The new CVT unit has been developed on the assumption that it will mainly be combined with an environmentally friendly downsized turbo engine.
The product is backed up by a global supply chain withproduction sites including Japan, China, and Mexico.

Newly Developed Vane Pump

Partly because it was to be mounted as the successor of
the existing CVT, the new vane pump needed to be rolled
out globally including Japan, China, and Mexico in thesame manner as for the existing vane pump. So, it was
mandatory to achieve a sophisticated design quality
during the development stage.
Based on the existing vane pump, we promoted thedevelopment of a new model with a focus on the discharge
performance and durability being equivalent to or superior to that of the existing model as well as lower friction.
As a trade-off for lower friction with equivalent discharge
performance, a vane pump will inevitably be less durable.
Still, we obtained an optimal design satisfying the specification requirements.
Furthermore, we strove to reduce the pump weight forenvironmental conservation and lower the production costthat was also demanded by end-users.
Photo 2 shows the appearance of the newly developed
vane pump. Table 1 shows the detailed specifications andTable 2 the major improvements.

Note 2) An acronym for Noise, Vibration, and Harshness.

Photo 1 Appearance of new CVT unit
(Extracted from JATCO Ltd.’s website)― 26 ―

Photo 2Appearance of new vane pump

Table 1

Specifications of new vane pump

TypeBalanced vane pump

Basic discharge

11.3 cm3/rev

Pump revolutions

Up to 7300 rpm

Discharge pressure

Up to 6 MPa

Oil temperature-40°C - 140°C

Production site

Japan, China, Mexico

KAYABA TECHNICAL REVIEW No. 65 OCT. 2022
Table 2

Performance improvements

ments, achieving the lower driving torque as aimed for.
Note 3) PV factor = P (surface pressure) × V (velocity); One of・A notch in the cam ring
Improvements ・Aluminum cover instead of iron cover・Ports of an optimal shape

Excessiveflow

Performance Improvements

Spool

Discharge port

Suction port

Suctionpressure UP

Discharge

SuctionSuction port
Orifice

Discharge
port

Fig. 1 Oil circulation in vane pumpComparison of internal circulation between pumps
Difference ininternal circulation:
About 10%

Flow rate [L/min.]

4.1 Optimally Designed Cam Ring Notch
To ensure that the CVT unit can deliver lower friction
for lower fuel consumption, the driving torque of the vanepump must be reduced.
The driving torque equation for vane pumps can be
expressed as (Basic discharge × Pressure) / 2π. Since there
is no change in service pressure between the existing andnew models, the basic discharge was reduced for lower
driving torque. However, a precondition was that the newmodel must meet the performance specifications equivalent to those of the existing one.
The new vane pump is of a type with an integral flow
control valve (spool). It should be designed to internally
maintain a flow rate that can well cover the required discharge characteristics according to the pump speed.
A vane pump with an internal flow control valve canmake use of the power of any excessive internal circulating flow to enhance the suction capability (Fig. 1).
In designing the new pump, the basic discharge wasreduced, resulting in about 10% lower internal circulating
flow. This led to lower suction capability, making thepump likely to suffer cavitation (Fig. 2).
Cavitation is a phenomenon in which the air dissolvedin the hydraulic fluid forms bubbles. Repetitive formationand collapse of such bubbles wears and damages thepump components. This is because we expected the newvane pump to be unable to satisfy the requirements fordurability testing merely by reducing the basic discharge
while keeping the other specification items unchanged
from the existing ones.
Several countermeasures could be considered. From theviewpoint of cost-effectiveness, we introduced a "notch"
in the suction part of the cam ring that serves as a suction
oil path. The notch expanded the suction oil path to reduce
the pressure loss, raising the suction capability (Fig. 3).
In response to the introduction of the notch, the surfacepressure on the cam ring applied by the sliding vanes
increased, resulting in a higher PV factor Note 3). Thisresulted in various durability disadvantages including
abnormal wear of the cam ring.
Then, in order to determine the balance between thenotch depth and the PV factor, in other words, the point at
which performance and durability can go hand in hand,the new vane pump was subjected to a durability test to
identify the critical point. We finally determined theoptimal size of the notch (Fig. 4).
Through these development efforts, the new vane pumpsatisfied both the durability and performance require-Internal circulationof existing pump
Internal circulationof new pump
Discharge ofexisting pump
Internal circulationof existing pump
Discharge of newpump
Internal circulationof new pump

Pump speed [rpm]Fig. 2― 27 ―

Comparison of internal circulation between pumps

Existing modelFig. 3New model

Comparison of cam ring specifications
PV factor critical line graph

P: Surface pressure [N/mm2]

4

the wear factors

Large Notch

Development
Model
PV factor

NG Area

Small Notch

Current Model
V: Velocity [m/sec]

Fig. 4

PV factor critical line graph

PV factor

OK AreaDevelopment of Vane Pump for Medium Passenger Vehicle CVT

4.2 Aluminum Cover Instead of Iron Cover(Weight and Cost Reduction)
The existing vane pump for medium passenger vehicle
CVT used a core oil path cover made of cast iron (Figs. 5and 6). The new product has been designed to have analuminum diecast cover. With this design, the weight ofthe cover alone has been reduced by 350 g, which is anapproximately 30% reduction in the total weight of thevane pump, contributing to substantial weight reduction,and consequently lower fuel consumption.
Furthermore, the manufacturing method has beenchanged from the cast iron system to an aluminum diecastsystem. This has helped improve the productivity andreduce the manufacturing cost.
Along with the introduction of the aluminum diecast
cover, however, the geometry of the oil path inside thecover changed in such a manner that the oil was unlikely
to flow smoothly. We noticed that the new oil path geometry worsened the pump's NVH (Figs. 7 and 8).

4.3 Ports of Optimal ShapeIt was mandatory to improve the pump's NVH in orderto satisfy the requirement that the NVH of the new pump
be equivalent or superior to that of the existing model.
However, the oil path of the new cover, which was a factor
that deteriorated NVH, could not be improved from theviewpoint of manufacturing method. It was impossible todesign an oil path for the diecast cover that is similar tothat of the cast iron cover.

Optimized port shape

Existing (cast iron)

New (aluminum diecast)Time [msec]

Comparison of appearance of cover
Discharge pressure[MPa]Fig. 5

Ports of side plate

Vibration [m/sec2]

Fig. 9Time [msec]

Existing (core oil path)

Fig. 10Comparison of oil path

Pump discharge pressure and vibration before
improvement

Vibration [m/sec2]Fig. 6

New (diecast oil path)

Fig. 7

Time [msec]

New (diecast oil path)Comparison of flow in oil path
HighPressureloss
Low

Existing (core oil path)
Fig. 8Discharge pressure[MPa]

Existing (core oil path)

Time [msec]

New (diecast oil path)
Fig. 11

Visual comparison of pressure loss in oil path― 28 ―

Pump discharge pressure and vibration afterimprovement

KAYABA TECHNICAL REVIEW No. 65 OCT. 2022

Then, we decided to pursue an optimal shape of theports of the side plate for the aluminum cover. With theoptimal port design, the discharge pulsation was reduced
to suppress the vibration, satisfying the NVH requirement(Figs. 9, 10 and 11).

5Evaluation

This development project was highly rated by JATCO
Ltd. and won the FY2020 JATCO QCDS Best Performance Award.
This prize is awarded only to the one company globallyrated as overall No.1 in development, quality, cost anddelivery. We were only able to win this prize with thecooperation from those concerned not only in Development but also in other departments. We would like to takethis opportunity to deeply thank all those concerned.
As a quality-specific prize, we also won the JATCO
Regional Special Award at the same time.
Furthermore, KIMZ (KYB Industrial Machinery (Zhenjiang)), which launched production in March 2021 after
KYB Kanayama was established, won the QCDS A-rankAward. KYB has been highly evaluated both at home andabroad.

Photo 3

6Compared with the existing model, this newly developed product has achieved the following:① About 10% lower pump driving torque② About 30% lighter pump③
Simultaneous achievement of durability and lowdriving torque④ Lower noise⑤ Lower costThe considerations discussed in this development
project are shown in the inclined developed views of theexisting and new products (Fig. 12).

7In Closing

We sincerely appreciate the cooperation of all thoseengaged in program development from JATCO Ltd. andall other partner companies and all those concerned in
relevant KYB departments.

QCDS Best Performance Award (right), Regional
Special Award (left)

Photo 4Conclusions

QCDS A-rank Award (China)― 29 ―

Development of Vane Pump for Medium Passenger Vehicle CVT

Existing productCast iron

New product
Aluminum diecast

Optimized port shape
Notch addedFig. 12Inclined developed views of existing and new products― 30 ―KAYABA TECHNICAL REVIEW No. 65 OCT. 2022

Author 
HAGIWARA Takahiro

OOTAKI Masashi

Joined the company in 2010.
Pump Engineering Dept., Steering
Business Dept., Automotive
Components Operations
Engaged in design of vane pumps.

Joined the company in 2012.
Pump Engineering Dept., Steering
Business Dept., Automotive
Components Operations
Engaged in design of vane pumps.

KONDO Hirotoshi

SHINDO Shota

Joined the company in 2013.
Gifu Local Office, Basic Technology
R&D Center, Engineering Div.
Engaged in design of vane pumps.

Joined the company in 2014.
Pump Engineering Dept., Steering
Business Dept., Automotive
Components Operations
Engaged in design of vane pumps.

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