Development of Vane Pump for AT

ProductIntroduction

Development of Vane Pump for AT
GOMI Hiroki

1

Table 1Introduction

The vane pump for AT Note 1) introduced in this paper isto be used as a hydraulic source of the new AT mounted
on the new SUV Note 2) that has been developed by Mazda
Motor Corporation. Manufacturing of this product waslaunched in December 2021.
Note 1) Automatic Transmission.
Note 2) Sport Utility Vehicle.

2

The AT unit (Photo 1) on which the newly developed
vane pump will be mounted is a step-type automatictransmission (hereinafter “the AT"). The AT uses a powertransmission system that is different from that used inCVT Note 3) for which KYB has developed and produced
vane pumps so far. The pump used for the AT is required
to deliver a discharge pressure diﬀerent from that of thepump used for CVT. KYB is preparing its first vanepump product lineup for the AT. Table 1 compares thespeciﬁcations of these two types of transmission.
Note 3) Continuously Variable Transmission.

TypeATCVT

Speed change byGearset

Belt

Hydraulic pressure
requirement

Up to 2.1 MPa

Up to 6.0 MPa

3About AT Unit

Comparison of speciﬁcations of AT and CVT

Newly Developed Vane Pump

The newly developed vane pump is based on the existing product for CVT. Since the pump speciﬁcations for
the AT are different from those for CVT as describedabove, we reviewed all the speciﬁcations of the existingvane pump for CVT to set up optimal speciﬁcations for
the AT during the development stage.
The first point to be considered in the development
stage was that the vane pump for the AT is only required
to deliver a low discharge pressure. Then, we reduced thefriction of the existing product as far as possible while
maintaining the required durability, contributing to improved fuel eﬃciency of the vehicle.
We also improved NVH Note 4) which is essential for thepump start-up characteristics and the vehicle ride comfort, achieving an optimal design to satisfy the required
speciﬁcations.
Photo 2 and Table 2 show the appearance and detailed
speciﬁcations of the new vane pump respectively.

Photo 1 Appearance of transmission unit ** The use of the photo has been approved by Mazda
Motor Corporation. All rights reserved.

Photo 2 Appearance of new vane pump― 32 ―

KAYABA TECHNICAL REVIEW No. 66 APR. 2023

Table 2

Speciﬁcations of new vane pump

TypeBalanced vane pump

Basic discharge

15.9cm3/rev

Pump revolutions

Max. 7,420 rpm

Discharge pressure

Max. 2.1 MPa

Oil temperature range-40˚C to 165˚C

Production siteJapanNote 4) Noise, Vibration, and Harshness.

4

Performance Improvements

4. 1 Improvement of Volume Efﬁciency
In the newly developed vane pump, the clearances ofthe sliding parts have been optimized, specifically reduced, to match the discharge pressure. The smallerclearances lead to less leakage or lower ﬂow loss in thepump, resulting in higher volume efficiency but lower
durability, such as seizure of the sliding parts, is unavoidable. Still, a deformation study through FEM analysis(Fig. 1) and a critical durability test helped us set an optimal clearance. As a result, the volume eﬃciency has been
improved while the required durability is maintained.
Deformation
HighFor item [1], lowering the working pressure of theﬂow control valve can reduce the loss torque due to pressure loss. This causes the ﬂow control valve to internallycirculate excess ﬂow, thereby enabling the pump to leverage the flow to improve the suction capability (Fig. 2).
However, the reduced working pressure naturally lowers
the hydraulic pressure in the internal circuit, resulting in
the disadvantage of lower resistance to cavitation. Cavitation is a phenomenon in which the air dissolved in thehydraulic fluid is released as air bubbles. Repeated release and dissipation of such air bubbles causes wear ordamage to the pump components.
To resolve the problem, the suction part of the camring was machined to have notches, expanding the suction oil path. This reduced the pressure loss to improve
the suction capability (Fig. 3).
For item [2], the cam ring bore, which decides the basic discharge, has been enlarged in some parts from thatof the existing product. With this design change, thewidth of the cam ring has been reduced by 24% (Fig. 4).
This reduced the area of vanes to which pressure is applied, resulting in a lower sliding torque.
For item [3], KYB introduced its thinnest vanes (29%thinner than the existing vanes) for the ﬁrst time to further reduce the area to which pressure is applied and thesliding area (Fig. 5).
These improvements reduced the loss torque by about
20% from the existing product that performs equivalentwork, successfully improving the mechanical eﬃciency.
Excess flow

Spool

Suction port

Discharge port

Increase in suction
pressure

Low
Suction port
Discharge

Fig. 1

SuctionExisting productNew productOrifice

Discharge
port

Example of FEM analysis

4. 2 Improvement of Mechanical Efﬁciency
The driving torque of a vane pump is the sum of thetheoretical torque and the loss torque (friction). To improve the mechanical eﬃciency, it is primarily necessary
to reduce the loss torque. Major components of the loss
torque include the torque consumed for pressure loss inoperating the flow control valve Note 5) and the sliding
torque for the vanes to maintain contact with the walls of
the cam ring. To reduce these two kinds of loss torque,the following improvements were made.

Working pressure of flow control
valve -> Pressure difference
between P1 and P2

Fig. 2

Oil circuit in vane pumpNote 5) When the pump has an integrated ﬂow control valve.

Existing product[1] Lowering the working pressure of the ﬂow controlvalve[2] Using a thinner cam ring
[3] Using thinner vanes― 33 ―

New productFig. 3 Comparison of cam ring speciﬁcations

Development of Vane Pump for ATShoulder
Existing productNew product24% thinner

Existing productFig. 6

Existing productNew productRotor geometry

New product

Oil seal

Illustration of thinning of cam ring

Fig. 4

View from the direction of the arrow
24% shorter

Direction to view

Existing product(With equivalent basic
discharge rate)

29% thinner
New productFig. 5Thinning of vanes

Fig. 7

4. 3 Improvement of Start-up Characteristics
As described above, reduction of the loss torque wasachieved by thinning the vanes to deliver a lower contactpressure against the walls. The trade-oﬀ was lower startup capability. As the transmission pump has recently
been required to deliver rapid start-up from the viewpointof improvement of automobile functionality, the start-up
characteristics needed to be improved.
Then, we changed the rotor design to eliminate the"shoulders", reducing the sliding resistance of the sticking-out vanes (Fig. 6). We also optimized the back pressure for pushing the vanes out and the clearance of thesliding parts of the vanes to improve the start-up capability at low temperatures, successfully achieving start-up
characteristics that were superior to those of the existingproduct. Furthermore, the pump cover has been fittedwith an oil seal to attain improved airtightness, preventing oil release from the pump during halts and reducing
the time needed to suck the fluid again during restart.
These measures contribute to further improved start-up
characteristics (Fig. 7).
4. 4 Improvement of NVH
As automobiles have recently become quieter year after year, the demand for quieter transmissions has been
rising. It is also a must for pumps to have improved NVH
characteristics.
In the newly developed vane pump, the port proﬁle inthe side plate was optimized to suit the environment
where the transmission unit is used (Fig. 8). The optimized port helped reduce the discharge pulsation, sup-Oil sealpressing vibration. The notches in the side plate, whichconnect the vane chamber with the port and help build apressure in the vane chamber, were tuned through simulation (Fig. 9). This improved the quietness of the pumpduring both normal and high-speed rotations.
While the existing product had these notches only inside plate A, the new product has the notches in both sideplates A and B. This design change increased the supplyof high-pressure ﬂuid to the vane chambers to alleviate
the delay in pressure rise during high-speed rotation or
during the use of ﬂuid with much entrained air, serving
as measures for cavitation (Fig. 10).

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Optimized port
& notch profile

Fig. 8

Ports and notches of side plate

KAYABA TECHNICAL REVIEW No. 66 APR. 2023

Pump internal pressure [MPa]The rate of change in pump internalpressure (pressure in the vanechamber) was estimated throughsimulation before tuning.

6The vane pump for the AT was developed according tospecifications that KYB has never experienced in its
product development history. Mass production of thevane pump has been achieved through great cooperationof all those who were involved in the development project.
I would like to take this opportunity to deeply thank allpartners including those involved in the program from
Mazda Motor Corporation as well as all personnel in therelated functions of KYB.

ExistingproductProposed
improvement 1
Proposed
improvement 2

Rotation angle [deg]Fig. 9

Example of simulation of pressure in vane chambers

Notch added

Existing productFig. 105In Closing

New productNotches added

Conclusions

We have developed KYB's ﬁrst vane pump for the AT
and achieved the following:[1] Development of a vane pump optimized for the AT[2] About 20% lower loss torque than existing product[3] Achievement of both durability and low driving
torque[4] Improved start-up characteristics[5] Lower noise
The improvements discussed in this development project are shown in the inclined development views of theexisting and new products (Fig. 11).

― 35 ―

Development of Vane Pump for AT

Existing
既存品
productNewproduct
Oil seal added
Lower profile
Lower profile
Geometry changed

Optimized clearance

Optimized backpressure
Additional notch
Optimized ports
and notches□：Improved efficiency
start-up□：Improved
characteristics□：Improved NVH

Fig. 11Lower working pressure offlow control valve

Inclined development views of existing and new products― 36 ―KAYABA TECHNICAL REVIEW No. 66 APR. 2023

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

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