color=blue>Help for Webmasters « back to results for ""
Below is a cache of http://delphi.com/pdf/techpapers/2004-01-1375.pdf. It's a snapshot of the page taken as our search engine crawled the Web.
The web site itself may have changed. You can check the current page or check for previous versions at the Internet Archive. Yahoo! is not affiliated with the authors of this page or responsible for its content.
2004-01-1375 Ultrasonic Air Temperature Sensing for Automatic Climate Control Vehicle Test 400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-5760 Web: www.sae.org
SAE TECHNICAL
PAPER SERIES
2004-01-1375
Ultrasonic Air Temperature Sensing for
Automatic Climate Control Vehicle Test
Taeyoung Han, David K. Lambert,
Dale L. Partin and Michel F. Sultan
Delphi Research Labs
Reprinted From: Developments in Automotive Climate Control Technology
(SP-1859)
2004 SAE World Congress
Detroit, Michigan
March 8-11, 2004 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or
transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise,
without the prior written permission of SAE.
For permission and licensing requests contact:
SAE Permissions
400 Commonwealth Drive
Warrendale, PA 15096-0001-USA
Email: permissions@sae.org
Fax: 724-772-4891
Tel: 724-772-4028
For multiple print copies contact:
SAE Customer Service
Tel:
877-606-7323 (inside USA and Canada)
Tel:
724-776-4970 (outside USA)
Fax: 724-776-1615
Email: CustomerService@sae.org
ISBN 0-7680-1319-4
Copyright © 2004 SAE International
Positions and opinions advanced in this paper are those of the author(s) and not necessarily those of SAE.
The author is solely responsible for the content of the paper. A process is available by which discussions
will be printed with the paper if it is published in SAE Transactions.
Persons wishing to submit papers to be considered for presentation or publication by SAE should send the
manuscript or a 300 word abstract of a proposed manuscript to: Secretary, Engineering Meetings Board, SAE.
Printed in USA
ABSTRACT
An ultrasonic air temperature sensor, intended to
help improve automatic climate control (ACC), has been
demonstrated in a vehicle. Ideally, ACC should be
based on inputs correlated with thermal comfort.

Current ACC systems do not measure the air
temperature best correlated to thermal comfort at
breath level in front of an occupant. This limits the
thermal comfort that ACC can provide under transient
conditions. An ultrasonic sensor measures the bulk air
temperature, is transparent to the driver, and can use
commercially available components. In a proof-of-
concept test, we monitored the thermal transients in a
vehicle during cool-down after a hot soak and also
during warm-up after a cold soak. The ultrasonic path
was along the roof console. The ultrasonic temperature
always agreed to ±1 ºC with the air temperature
measured by a thermocouple at the midpoint of the
ultrasonic path. Compared to breath-level temperature,
there was good agreement for the winter test but, for the
summer test there was a 5 ºC constant shift.

Thermocouple data taken at the two locations showed
the same effect. The ultrasonic sensor is rapid and
precise, and it is a good candidate for improving ACC.



INTRODUCTION


We recently showed that thermal comfort could be
improved by basing control on the air temperature at
breath level [1]. We also proposed an unobtrusive
ultrasonic method to measure bulk air temperature in
vehicles, shown in Figure 1, and showed that it had
accuracy of ±0.5 ºC. Ultrasonic pulses, above the range
of human hearing, are timed as they move from the
source to the detector [2]. The measured delay gives an
indication of the average temperature of the air along the
path. In this paper we demonstrate an unobtrusive
ultrasonic air temperature sensor in a vehicle. To
evaluate its performance, two tests were performed: cool
down from a hot soak (summer test) and warm up from a
cold soak (winter test). The air temperature measured
by the ultrasonic sensor is compared to the
temperatures measured at various locations in the
vehicle by conventional thermocouples.


Most production ACC systems utilize cabin
temperature as one input to help control interior
temperature. Other commonly used inputs are outside
ambient temperature and solar load. Two types of cabin
temperature sensors are conventionally used: fan-
aspirated in-car sensors intended to measure air
temperature, and infrared (IR) sensors intended to
respond to average temperature of the surfaces in the
field of view. Even the best implementations of fan-
aspirated in-car temperature sensors for ACC in vehicles
suffer from tracking error, time-lag, and drift problems.
The in-car temperature sensor is usually located in the
instrument panel, behind a small grille. This sensor
picks up air temperature trends, but absolute accuracy is
degraded by air stratification, heat storage in the
instrument panel, and discharge from nearby heater
vents. In vehicle tests, the temperature indicated by the
in-car sensor sometimes is as much as 10 ºC different
from the air temperature at breath level. The system is
sometimes even driven away from desirable conditions.
Another problem with the in-car sensor is its response
time. The error between the temperature sensor and
true breath-level temperature depends on the initial
ambient conditions. The in-car temperature sensor
tends to overestimate the interior temperature during a
cool-down, and underestimate the temperature during a
warm-up. This can cause overshoot past the desired
control point and uncomfortable conditions.
Delphi supplies an IR system for ACC. It was first
used on the 1999 Jeep Grand Cherokee. One or more
IR detectors in the instrument panel view the driver, the
front seat passenger, or both. The IR system is intended
to provide the average surface temperature of the
objects within its field of view. However, the temperature
of a solid surface in a vehicles interior changes slowly in
response to a change in air temperature. During a fast
transient, a special algorithm is needed to compensate
for the sensor output lag compared to the breath-level air
temperature.
Thermal comfort is affected by factors besides air
temperature. People differ in their individual
preferences. Radiant heat exchange and the distribution
of air velocity around the occupant [3] are important.
Other variables that influence thermal comfort are the
solar load, the occupants clothing, and the humidity in
the passenger compartment. The importance of breath-
level air temperature was shown in [1]. Subjective
2004-01-1375
Ultrasonic Air Temperature Sensing for Automatic Climate
Control Vehicle Test
Taeyoung Han, David K. Lambert, Dale L. Partin and Michel F. Sultan
Delphi Research Labs
Copyright © 2004 SAE International
1 thermal comfort votes from occupants were compared
with temperatures from the in-car sensor and from a
thermocouple at breath level. In Figs. 2a and 2b, we plot
the measured temperatures as a function of comfort
votes. To quantify the correlation of the sensor outputs
to thermal comfort we use the linear correlation
coefficient, r. There is scatter in the comfort votes due to
the subjective evaluation of thermal comfort. Despite
this, the correlation of comfort votes to breath-level
temperature (r = 0.71) is much better than it is to the
temperature measured by the in-car sensor (r = 0.28).
The data show that perceived thermal comfort could be
significantly improved if the input to the ACC control
system from the in-car sensor were replaced by input
from a sensor that measures the bulk air temperature in
front of the occupant
In the following, Section II provides background
information about ultrasonic temperature measurement
and its use in a vehicle. Section III compares ultrasonic
measurements of bulk air temperature in a vehicle with
thermocouple temperature measurements under various
HVAC operating conditions. Finally, Section IV
discusses implementation of ultrasonic temperature
measurement in a vehicle.

BACKGROUND
The ultrasonic sensor determines bulk air
temperature, T, from a measurement of the speed of
sound, c, in the air. Our application is new, but the use
of the speed of sound to measure T is well established
[4].
From theory, sound propagates at velocity c that
can be expressed in terms of other known quantities [5-
7] as
µ T
R
c
=
.
(1)
Here R is the universal gas constant, T is the
absolute temperature (in K),
µ is the average molecular
weight of the gas m