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H-Point Measurement Methodology & Techniques: HPM and HPD

Advanced Structures India Pvt Ltd is an independent automotive product development company based out of Bangalore, India with operations in India, China and US. Below is blog entry from our engineers about H-Point Measurement Methods. We can be contacted on business@advancedstructures.in for business enquiries and careers@advancedstructures.in for open positions.


Vehicle development starts with inputs from many domains such as designing, manufacturing, marketing, ergonomics, electronics, etc. Market researchers study the market of a particular country and then focus on the target population for which the vehicle must be developed. Once the target population is identified, the next step is to set the percentile of population for which the vehicle needs to be designed. This is done by the anthropometric survey of the target population. Subject majority (~greater than 80%) decides the actual percentile population for which the vehicle must be produced. This data provides the critical input to set a single point around which vehicle ergonomics and interiors are designed for further vehicle development.

This key point is used at two vehicle development stages –

  • To design the complete interiors, to decide the occupants interior packaging and to understand overall occupant shell which assist in the external design of the vehicle.
  • Auditing or benchmarking of any produced/ competitor vehicle, as this is the key point from where other dimensions can be measured or checked as per requirement.

All vehicles have unique interior packaging & spacing which makes them different from one another in terms of comfort & accessibility. Designing for these parameters starts from the reference point known as “Hip Point”, popularly known as “H-Point”.

H-Point: Understanding and Explanation

H-Point is a pivot point or centre point between the torso line & upper leg line of a human body and is used to specify the occupant’s hip location.

H Point location side view
          H Point location on human body

A non-adjustable seat has only one H-point location, whereas an adjustable seat (e.g., the driver’s) has a number of H-point locations. The extremes of these can be mapped and described as the seat movement envelope for H-Point. In order to have one point of reference for occupant packaging, the manufacturer will select a unique design H-point known as the Seating Reference Point (SgRP or R-Point), which forms reference for all other design needs.

 

Ergonomics Parameters affected by H Point

H-Point Location on a Seat or Vehicle

H-point is measured with respect to a defined set of procedures as specified by the SAE body. The standards followed are SAE J4002, SAE J4003, SAE J4004 & AIS 097 and the measurement of H-Point is termed as “H-point Measurement”. Many other key dimensions & points are also identified during the H-point measurement process. Following are the key measurement techniques:

 

How to measure H PointH-Point Machine is a manikin having different percentile adjustments. The construction & various specifications of the manikin are specified in the SAE standards. H-Point machine gives us freedom to physically locate the H-Point location for any specified seat.

The first H-Point machine was HPM-I as defined in SAE J826 standard. HPM-I had some challenges while measuring the H-Point & other key points, hence for the ease of measurement a modified H-point machine was suggested by the SAE body named HPM-II as described in SAE J4002 standard. This resulted in greater ease of use, additional features & measurement capabilities. 

H-Point Design(HPD) tool is a simplified CAD representation of the H-Point Machine. This can be used in any CAD software in association with the physical H-Point Machine for vehicle designing, auditing & benchmarking purposes. SgRP is used to position the HPD in CAD environment.

Both the H-Point Machine & HPD can be used together as well as independently with some prior parameter information for various customer requirements.

Basic differences between HPM & HPD

HPM Vs HPD Comparison for cost, usage,pre-requirements and time.

Difference between HPM and HPD H Point Machine

Utlization of HPM

use of H Point for vehicle development

The use of HPM/HPD during vehicle designing & auditing are mostly done by the manufacturers for the vehicle development. 

Use of H-point Measurement in New Product Development(NPD)H Point reverse engineering for new vehicleSince all the vehicles have distinctive dimensions, vehicle benchmarking becomes a very important tool for comparing different competitor vehicles. H-Point plays a major role in benchmarking as it gives a single point of reference for all vehicles. From H-Point we can measure different internal & external dimensions to compare different vehicles on dimensions, ergonomics, interior space availability, etc.

Dimensional measurement using H-point gives various important comparison parameters for vehicles, such as-

  • Comfort which is felt & experienced while using different vehicles in terms of space provided inside a vehicle.
  • Ease of accessibility which a person gets while using internal controls inside a vehicle.
  • Ease with which different percentile population can drive a particular vehicle.

HPM Role in User Comfort Measurement

H-point Measurement also plays a very important & key role in comparing the seat comfort of competitor vehicles for different category & class of vehicles. A seat can be easily benchmarked for a range of percentile population depending upon various features provided in the seat, such as seat travel, height adjustment, lumbar support, etc. Many important vehicle dimensions (more than 100) are listed in SAE j1100 standard which can be obtained from the H-Point location. All these dimensions, from the H-Point location to specified interior & exterior points, helps to benchmark various vehicles with same point of reference.

H Point Machine on Indian car
HPM on vehicle seat

Below are few important HPM outputs

Output of H Point Measurement ProcessH Point

It effects all other major internal & external dimensions. Higher H-Point generally provides more legroom for both driver & passenger seats. Buses, SUVs, Minivans, etc type of vehicles have generally higher H-Points. Sedans have generally lower H Point for comfortable riding posture.

Seat Height

Represented as H30 as per SAE J1100. Defines driver’s seated posture. Sports cars & sedans have generally low H30 (about 150-250mm) whereas heavy commercial trucks have high H30(more than 405mm). Adjustable seats provide a better occupancy for larger range of occupants.

H Point Travel

Seat travel decides the adaptability of the seat for a range of population. More seat travel is always preferred as it can accommodate more percentile users & also provides much room for any occupant. This also defines the seat track length. As per SAE, a seat track length of more than 240mm is sufficient to accommodate 95% of drivers in passenger cars. 

Head Room

This is the space provided for sufficient movement of the upper body & head region of the occupant.

Leg Room

Higher the legroom more is the comfort in the occupant area. Hence, sufficient legroom must be provided for a comfortable driving posture. Sedans generally have higher legroom for long & comfortable driving conditions. 

Seat Cushion Angle

A cushion angle of about 5 to 25 degrees is preferred. This permits the user to take best comfortable position by transferring the torso weight on to the seatback. In passenger & sports cars, seatback angle will be more reclined i.e. about 20 to 28 degrees, whereas in heavy commercial vehicles the driver sits more erect with a preferred seatback angle of 12 to 18 degrees.

Lumbar Support

It is one of the most important characteristics of the seat as it defines the shape of occupant’s spinal column in the lumbar area of the seat. The lumbar area must maintain the natural curvature of the spinal column for avoiding any back problems. An adjustable lumbar support will always be helpful for accommodating the seat by more occupants maintaining their natural curvature.

Accelerator Heal Point(AHP)

It specifies the position of the heel of the driver on the depressed floor covering. It is a very important point from design point of view as it defines the seat height.

Challenges of H-point Measurements 

  • Accuracy – As all points are located in open space inside vehicle, it is important to have good accuracy for 3D measurement. We use highly precise CMM instruments having high accuracy (0.01 microns) to get accurate measured values. This removes chance of any error due to manual measurement.
  • Setting up of H-Point Tool – Physically setting up H-Point manikin over the vehicle seat requires high precision. The manikin must be set up strictly following the AIS & SAE standards. We utilise our experience of using H-Point Manikin on Indian as well as international vehicles (for different percentile population) to compare vehicles, with accurate and precise measurements.
  • Time – Setting up H-Point tool is time consuming as it requires strict adherence to process as per standards. Manually measuring is again a tedious work and thus at ASI, we use CMM for taking accurate, easy & rapid measurement once the manikin is set. CAD output data from CMM is further helpful in obtaining other vehicle dimensions which can directly be used in complete vehicle CAD model.

Ashish Kumar