Slope sensor for a vehicle

First and second sample-hold circuits sample and hold the atmospheric pressure alternately every time when a vehicle travels a predetermined distance. A signal representing a difference between the holding values of the first and second sample-hold circuits, that is, a signal representing a slope of the road on which the vehicle is travelling is displayed through a latch circuit.

BACKGROUND OF THE INVENTION 
This invention relates to a slope sensor for a vehicle which detects the 
slope of a road on which the vehicle is travelling. 
A publicly known slope sensor has such a mechanical structure that the 
slope of a vehicle is detected with a vertical line indicated by weight as 
a reference. So, because of vibrations, deceleration and/or acceleration 
it can not accurately measure a slope of a road while the vehicle is 
travelling. This has been also the case with a vehicle when it is inclined 
by the weight of a load and occupants. 
SUMMARY OF THE INVENTION 
The object of this invention is to provide a slope sensor which can display 
the value of a slope accurately while the vehicle is running. 
The invention is based on the fact that the atmospheric pressure decreases 
by about 1.2 millibars with an increase of altitude of 10 m. The above 
object is attained by determining the slope from a travel distance and an 
atmospheric pressure difference.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of this invention will be explained hereinafter. In FIG. 1 
showing a whole rough construction of the embodiment, the reference 
numeral 1 denotes a distance sensor for sensing a travel distance of a 
vehicle, 2 an atmospheric pressure sensor for sensing a momentarily 
varying atmospheric pressure, 31 and 32 first and second sample-hold 
circuits for sampling and holding a pressure signal from the atmospheric 
pressure sensor 2 alternately by a travel distance signal at each 
predetermined travel distance. The reference numeral 4 denotes a pressure 
difference sensing circuit which detects a difference between the outputs 
of the first sample-hold circuit 31 and the second sample-hold circuit 32. 
Numeral 5 denotes a slope display circuit which converts the output of the 
pressure difference sensing circuit 4 into a slope value and displays it. 
The slope sensor constituted by the above elements is formed in an 
integral body and placed on a dashboard or a meter panel. 
The operation of the above slope sensor will be explained next with 
reference to FIGS. 2 and 3, which demonstrate detailed electric connection 
diagrams of FIG. 1. The numeral 10 denotes a distance sensor having a reed 
switch 10b which generates four pulses at one revolution of magnets 10a 
connected to a publicly known speedometer cable shaft. In the present 
embodiment, the distance sensor 10 generates one pulse signal at a travel 
distance of about 0.4 m. Numeral 11 is a waveshaper circuit which shapes 
the waveform of the signal from the distance sensor 10 and is constituted 
by a capacitor 111, a waveshaping transistor 112, a noise filter circuit 
113 and a NAND gate 114 having a hysteresis characteristic. Numeral 12 is 
a counter circuit which counts the pulse signal from the waveshaper 11. 
The counter 12 is constructed for example by a publicly known integrated 
circuit CD4024 of RCA and generates a reset signal for a later-mentioned 
control signal generating circuit 130 at every 64th pulse at its sixth 
output stage Q.sub.6 and generates a gate signal for a later-mentioned 
sample-hold circuits 31 and 32 and a switching circuit 43 at every 128th 
pulse at its seventh output stage Q.sub.7. Numeral 121 denotes a circuit 
for generating a reset pulse at switch-on time of a power supply (+V). 
Numeral 122 denotes a NAND gate for giving a reset pulse to the control 
signal generating circuit 130. A clock signal is generated by a clock 
signal generating circuit 131, shaped by a waveform shaping circuit 131a 
and applied to the control signal generating part 130. A frequency 
dividing circuit 132 in the control signal generating part 130, which is 
constructed for example by an integrated circuit CD4024 of RCA, 
frequency-divides the clock signals and generates a signal of about 100 Hz 
at a fifth output stage Q.sub.5. This signal is applied to a frequency 
dividing circuit 133 constructed for example by a publicly known 
integrated circuit CD4017 of RCA. The frequency dividing circuit 133 is 
reset by the counter circuit 12 and, in response to first, third, fifth 
and seventh pulses of the frequency dividing circuit 132, and it generates 
a sample-hold signal Q.sub.1, .+-.20% sensing signal Q.sub.3, a latch 
signal Q.sub.5 and a clock inhibiting signal Q.sub.CE at its first, third, 
fifth and seventh output stages [1], [3], [5] and [7], respectively. In 
the gate circuit 134, AND gates 134a and 134b are opened alternately by a 
gate signal Q.sub.7 of the frequency dividing circiut 132 at each 64th 
distance pulse signal, i.e., every vehicle travelling distance of 25.6 m 
(=0.4 m.times.64), thereby to make analog switches in the sample-hold 
circuits 31 and 32 alternately conductive. 
In the atmospheric pressure sensor 20 using a publicly known diaphragm type 
semiconductor pressure sensor, an air-tightly formed chamber is separated 
by a diaphragm from the atmosphere (e.g., in an engine compartment or 
vehicle cabin), and a displacement of the diaphragm is detected by a 
bridged pressure-resistance transducer element. A voltage proportional to 
the atmospheric pressure is generated across output terminals 20a and 20b. 
It is publicly known that the diaphragm surface is made to contact with 
the atmosphere through a filter or an orifice having a ventilation 
resistance in order not to respond to a casual pressure variation. A small 
output voltage is amplified by an amplifying circuit 21 formed by a 
publicly known integrated circuit, e.g., .mu.A725 of Fairchild Inc. The 
amplified voltage is applied to first or second sample-hold circuit 31 or 
32 constructed by an analog switch using an integrated circuit such as 
CD4066 of RCA, a capacitor and an integrated circuit CA3130 (operational 
amplifier) of RCA. These sample-hold circuits 31 and 32 hold the 
atmospheric pressure signal alternately, in response to the alternative 
turning-on of the analog switches, by the sample-hold signal Q.sub.1 at 
each 25.6 m travel of vehicle. The atmospheric pressure signals held by 
the capacitors of the first and second sample-hold circuits 31 and 32 are 
applied to an inverted input terminal (-) and a non-inverted input 
terminal (+) of an operational amplifier circuit 41 formed by an 
integrated circuit, e.g., .mu.A725 of Fairchild Inc., which generates an 
amplified difference signal. The signal is phase-inverted by an inverter 
circuit 42 formed by an integrated circuit, e.g., .mu.A741 of Fairchild 
Inc. The outputs of the inventer 42 and the operational amplifier 41 
appear alternately at a terminal 4a as an output signal of an atmospheric 
pressure difference sensor circuit 4 through a switching circuit 43 formed 
by an analog switch of a publicly known integrated circuit e.g., CD4066 of 
RCA. In FIG. 4 for explanating the role of the inverter circuit 42, 
accordingly as the travel distance increases from a to e as shown by (A) 
in FIG. 4, in increasing atmospheric pressure signal is applied to the 
first and second sample-hold circuits 31 and 32. Then, the output of the 
differential amplifier 41 changes its phase alternately as shown by (B) in 
FIG. 4. In order to avoid this unfavorable situation, the phase is 
inverted by the inverter circuit 42 such that the result of subtraction of 
a previous sample-hold value from a present sample-hold value appears at 
the terminal 4a. 
When the output signal of the atmospheric pressure difference sensing 
circuit 4 is applied to a slope display circuit 5 in FIG. 3, it is 
compared with reference voltages V.sub.1 ;V.sub.1 ', V.sub.2 ;V.sub.2 ', 
V.sub.3 ;V.sub.3 ' and V.sub.4 ;V.sub.4 ' corresponding to slopes 
.+-.2.5%, .+-.5%, .+-.10% and .+-.20% by comparators 511 to 518 of a 
comparator circuit 51, which are formed by a publicly known integrated 
circuit MC3302 of Motorola Inc. Depending on the signal value, a digital 
signal "1" or "0" appears at the output of each comparator. In this 
embodiment, it is so arranged that in the case of an ascendingly slope the 
output of each comparator becomes "1" or "0" according as the input signal 
is higher or lower than the respective reference voltage V.sub.1, V.sub.2, 
V.sub.3, or V.sub.4, while in the case of a descending slope the output of 
each comparator becomes " 0" or "1" according as the signal is higher or 
lower than the respective reference voltage V.sub.1 ', V.sub.2 ', V.sub.3 
' or V.sub.4 '. Numerals 519a, 519b and 519c denote noise absorbing 
capacitors. These "1" or "0" signals are applied to a latch circuit 52 
formed for example by a publicly known integrated circuit RCA CD4035, and 
they are latched at a time when the latch signal Q.sub.3 is inputted. The 
latched signals are applied through output buffers of publicly known 
integrated circuit, for example, CD450107 of RCA to light emitting diodes 
531 to 537 forming a bar graph display circuit 53. The light emitting 
diode 534 is always "on". When only this diode 534 is "on", it means that 
the slope is within .+-.2.5%. When the slope exceeds .+-.2.5%, at least 
one of the light emitting diodes 531 to 533 or at least one of the light 
emitting diodes 535 to 537 becomes "on" depending on the sign and the 
absolute value of the slope. When the atmospheric pressure varies to such 
an extent that the slope exceeds 20%, that is to say, when the output of 
the comparator 511 or 518 corresponding to one of .+-.20% slopes become 
"1" in the comparator circuit 51, a sensor circuit 54 for detecting a 
slope of more than .+-.20%, which is formed by a publicly known integrated 
circuit CD4013 of RCA (used as two D-type flip-flops) and an OR gate, 
detects the "1" level signal from one of the comparators 511 and 518 in 
response to the signal Q.sub.3 to generate a "1" level signal at the 
output of an OR gate. The "1" level signal is then applied to the clock 
inhibiting terminal CE of the frequency dividing circuit 133 to prevent 
any subsequent counting operation of the circuit 133. So, the signal is no 
longer displayed. In the figure, it is noted that a stabilized power 
supply voltage +V is applied to the elements in the integrated circuit 
blocks, and a voltage +V.sub.1 is also applied to the atmospheric pressure 
sensor 20. The voltages +V, +V.sub.1 and +V/2 V may be generated by a 
stabilized power supply circuit (not shown) connected through a key switch 
to a car battery. 
Although in the above embodiment a bar graph display using light emitting 
diodes is used, other displays such as a picture display and a lamp 
display, etc. may be used, or the output of the sensor circuit may be A-D 
converted for a numerical display. Furthermore, besides as a visible 
display, the thus detected slope value may be introduced into a system for 
controlling the travel of the vehicle as information data showing a load 
state of the vehicle. Although in the above embodiment, the hold value of 
an electric signal showing a slope value has operated two sample-hold 
circuits alternately, these circuits may be connected in cascade such that 
a signal held by the first sample-hold circuit be held by the second 
sample-hold circuit by a timing signal generated at each travel distance 
and immediately thereafter held again by the first sample-hold circuit. In 
such a case, the phase inversion as shown in FIG. 2 will not be necessary.