Truck & Off-Highway Engineering – June 2019

8 June 2019 TRUCK & OFF-HIGHWAY ENGINEERING

Engine Control
Module (ECM) Diesel Engine

Variable Pump

(Series 45)

Reservoir Filter

Microcontroller

(PLUS+1™)

Temperature

Sensors T

T

ReverseDisplacement T

Motor (RDM)

ALL IMAGES: DANFOSS POWER SOLUTIONS

typical time period needed during the duty-cycle peak power

demand, which is usually around 5 to 10 seconds per instance.

When the machine returns to a situation with less-demand-

ing engine power requirements, the liquids can then be over-

cooled to reduce the fluids’ temperature if necessary.

Preventing engine overspeed

Hydrostatic and hydromechanical (CVT) transmissions offer an

advantage with dynamic braking behavior—reducing the need

for service brake use. During the dynamic braking event, machine

energy is dissipated by resistance and losses in the driveline sys-

tem as well as the available braking torque from the engine.

When wheel loaders experience dynamic braking, engine

overspeed can become a concern due to the high travel

speed and operating weight of the vehicle. There are already

various control system architectures in place that can help

avoid an overspeed condition. However, a typical approach is

to dissipate the energy into non-usable heat energy within

the hydraulic system, which then needs to be cooled. This

increases risk of excess heat in the system while reducing

overall efficiency due to the additional cooling required.

One method to reduce this waste is by commanding the

hydraulic fan drive to run at full speed when dynamic braking.

This reduces the amount of torque the engine has to dissi-

pate, as it’s being reallocated to run the fan drive at full

speed—subsequently reducing the overspeed behavior.

Enabling better engine performance in cold

environments

For construction equipment operating in cold ambient condi-

tions, maintaining acceptable engine operating temperatures

can become problematic. In these situations, reducing the mini-

mum fan speed (potentially even zero rpm) can be of signifi-

cant value. Even if the fan drive is running at a low speed

(around 30% of maximum), it can be difficult to get enough

27"

100%

"

50"

30"

30"

16"

16"

<90% <10%

120

100

80

60

40

20

0

Engine Load (

%)

0 5 10 15 20 25 30 35

Time (sec)

Engine Load

heat into the engine in order to achieve optimal performance.

By reducing the fan speed in these conditions, machine

uptime can be enhanced as it may no longer be required to

install radiator grille covers or other restriction devices used

to maintain engine temperatures.

Minimum fan speed can be challenging for larger fan drives

that use a piston pump due to minimum margin pressure—or

low-pressure standby. This pressure is directly associated with

minimum fan speed. Therefore, the ability to achieve a lower

operating pressure will result in a lower minimum fan speed,

which contributes to better engine performance.

Other fan drive configurations offer additional options and

flexibility. Closed-loop fan drive systems, and similar types, cou-

pled with a closed loop control make it possible to manipulate

the control input to create a zero-stand speed condition for the

fan drive. This basically puts the fan motor on standby, achieving

the lowest fan drive operation possible. Implementing new tech-

nologies can directly increase wheel loader operability in cli-

mates affected by cold operating temperatures.

When engineering teams look for new ways to streamline

power management and boost engine performance, they

should examine how the thermal management system is be-

ing applied. Considering the wheel loader as a complete, co-

hesive system (rather than a combination of autonomous sys-

tems) can result in unexpected improvements in efficiency.

Aaron Becker, market development manager at Danfoss Power

Solutions, wrote this article for Truck & Off-Highway Engineering.

Becker has a diverse background in product engineering,

manufacturing engineering, quality and sales in both ISO

(APQP framework) and AS9100 manufacturing environments.

A typical fan drive system operates the charge air cooler (CAC), the

radiator, and the oil cooler. Separating the two into one larger system and

a smaller system offers power management efficiencies, as the CAC only

requires about 10% of the total power demand.

This chart shows the engine load during the bucket fill cycle. The engine

reaches peak engine load near the beginning of the cycle.

An open circuit piston pump thermal management configuration with a reverse

displacement motor. This system is built with a variety of Danfoss components.

TECHNICAL INNOVATIONS